Durable pharmacological responses from the peptide drug ShK-186, a specific Kv1.3
channel inhibitor that suppresses T cell mediators of autoimmune disease.
Eric J. Tarcha, Victor Chi, Ernesto J. Muñoz-Elias, David Bailey, Luz M. Londono, Sanjeev K.
Upadhyay, Kayla Norton, Amy Banks, Indra Tjong, Hai Nguyen, Xueyou Hu, Greg W. Rupert,
Scott E. Boley, Richard Slauter, James Sams, Brian Knapp, Dustin Kentala, Zachary Hansen,
Michael W. Pennington, Christine Beeton, K. George Chandy, and Shawn P. Iadonato
Kineta Inc., 219 Terry Ave N, Suite 300, Seattle, WA 98109-5208 (E.J.T, E.J.M., L.L., A.B.,
K.N., S.P.I.), Department of Physiology and Biophysics and the Department of Surgery, UC
Irvine, Irvine, CA 92697 (V.C., S.K.U., K.G.C.), MPI Research, 54943 North Main Street,
Mattawan, MI 49071-9399 (G.W.R., S.E.B., R.S., J.S., B.K., D.K., Z.H.), Peptides International,
11621 Electron Drive, Louisville, KY 40299 (M.W.P.), and Department of Molecular Physiology
and Biophysics, Baylor College of Medicine, Houston, TX 77030 (X.H., C.B.)
RUNNING TITLE PAGE
a) Durable pharmacological responses from ShK-186
b) Corresponding author: Eric J. Tarcha, 219 Terry Ave N., Suite 300, Seattle, WA 98109-5208;
Tel: 206-378-0400; Fax: 206-378-0408; Email: firstname.lastname@example.org
c) Text pages: 27
d) Abbreviations: ACN, acetonitrile; ADME, absorption, distribution, metabolism, excretion;
ANOVA, analysis of variance; AT-EAE, adoptive transfer experimental autoimmune
encephalomyelitis; AUC0-inf, area under the concentration-time curve from 0 to infinity; CFA,
complete Freund’s adjuvant; Cmax, maximum plasma concentration; CT, computed tomography;
DA, Dark Agouti; DMF, dimethylformamide; DOTA, 1,4,7,10-tetraazacyclododecane-1,4,7,10-
tetraacetic acid; DTH, delayed-type hypersensitivity reaction; CR-EAE, chronic-relapsing
experimental autoimmune encephalomyelitis; EDTA, ethylene diamine tetraacetic acide; ELISA,
enzyme-linked immunosorbent assay; Fmoc, Fluorenylmethyloxycarbonyl; HOBt, N-
Hydroxybenzotriazole; HPLC, high pressure liquid chromatography; IACUC, institutional animal
care and use committee; LOQ, limit of quantitation; MS, mass spectrometry; OVA, ovalbumin;
PBMC, peripheral blood mononuclear cell; PD, pharmacodynamic; PIA, pristane-induced
arthritis; PK, pharmacokinetic; RA, rheumatoid arthritis; SD, Sprague Dawley; SPECT, single-
photon emission computed tomography; t-bu, tertiary butyl; TCA, trichloroacetic acid; TFA,
e) Drug Discovery and Translational Medicine
The Kv1.3 channel is a recognized target for pharmaceutical development to treat autoimmune
diseases and organ rejection. ShK-186, a specific peptide inhibitor of Kv1.3, has shown promise
in animal models of multiple sclerosis and rheumatoid arthritis. Here, we describe the
development of tools and methods to establish a pharmacokinetic (PK) - pharmacodynamic
(PD) relationship for ShK-186, and test the hypothesis that the drug can provide a sustained PD
effect in disease models. The PK of ShK-186 was evaluated in rats and cynomolgus monkeys
using a validated HPLC-MS/MS method, ELISA, and patch-clamp to measure the free fraction
in plasma. These results were compared with SPECT/CT data collected with an 111In-DOTA-
conjugate of ShK to assess whole blood PK parameters as well as the drug’s absorption,
distribution and excretion. Analysis of these data support a model wherein ShK-186 is absorbed
slowly from the injection site resulting in blood concentrations above the Kv1.3 channel-blocking
Kd for up to 7 days in monkey. PD studies on human peripheral blood mononuclear cells
showed that transient ShK-186 treatment resulted in a sustained suppression of cytokine
responses and may contribute to prolonged drug effects. In rat delayed-type hypersensitivity
and chronic relapsing-remitting experimental autoimmune encephalomyelitis models, a single
dose of drug every 3 – 5 days was as effective as daily administration. These data support a
model whereby the PD effects of ShK-186 are governed primarily by its slow distribution from
peripheral tissues and its long residence time on the Kv1.3 channel.
The Kv1.3 channel has been an active target of pharmaceutical development for more than 15
years (recently reviewed in Chi et al., 2011). The interest in this channel derives from its
important function in activated effector-memory T cells, which are major mediators of
autoimmune disease (Beeton et al., 2006; Wulff et al., 2003). Engagement of the T cell receptor
by antigen presenting cells results in an influx of calcium into the cytoplasm, initially from the
endoplasmic reticulum but subsequently from the extracellular space via the CRAC channel
(reviewed in Cahalan and Chandy 2009). The opening of the voltage-gated Kv1.3 and calcium-
activated KCa3.1 potassium channels in the T cell membrane and the efflux of potassium ions
promotes calcium entry and sustains intracellular calcium at concentrations necessary for T cell
activation (reviewed in Cahalan and Chandy 2009). Resting T cells express a mixture of both K+
channels. However, upon activation, naïve and central-memory T (TCM) cells increase
expression of the KCa3.1 channel, while effector-memory T (TEM) cells upregulate Kv1.3
channel expression (Wulff et al., 2003). In the latter cell population, the degree of Kv1.3
expression is a measure of cell activation, and the channel is required for the maintenance of
the effector memory cell-phenotype (Hu et al., 2007; Hu et al., 2012).
We and others have previously shown that Kv1.3HIGH CCR7- activated TEM cells are present at
sites of inflammation in autoimmune disease, and auto-reactive T cells from subjects with
multiple sclerosis, type 1 diabetes, and rheumatoid arthritis express the Kv1.3HIGH phenotype of
activated TEM cells (Rus et al., 2005; Beeton et al., 2006). In addition, specific Kv1.3-inhibitors
have been found to be effective in numerous animal models of inflammation including adoptive
and chronic relapse-remitting experimental autoimmune encephalomyelitis (AT-EAE, CR-EAE)
(Beeton et al., 2005; Beeton et al., 2006), pristane-induced arthritis (PIA) (Beeton et al., 2006),
the delayed-type hypersensitivity (DTH) reaction (Koo et al., 1997; Beeton et al., 2005; Matheu
et al., 2008), allergic contact dermatitis (Azam et al., 2007), allogeneic kidney transplant (Grgic
et al., 2009), spontaneous autoimmune diabetes (Beeton et al., 2006), vascular neointima
hyperplasia (Choeng et al., 2011), anti-glomerular basement membrane glomerulonephritis
(Hyodo et al., 2010), and psoriasis (Gilhar et al., 2010). For these reasons, numerous groups
have focused on developing specific and potent inhibitors of the Kv1.3 channel for the treatment
of inflammation and autoimmune disease (reviewed in Cahalan and Chandy 2009, Rangaraju et
al., 2009). Much of this effort has focused on developing small molecule inhibitors of Kv1.3, but
identifying compounds that are adequately specific has proved challenging, and to date, no drug
specifically targeting Kv1.3 has entered clinical trials.
Our group is developing ShK-186 as a specific 39 amino acid peptide inhibitor of Kv1.3. To
date, the FDA has approved more than 55 peptide drugs in roughly 33 mechanistic classes,
making peptides one of the most active areas of biologics drug research. However, the peptide
field has suffered from a perception that frequent dosing is required for sustained
pharmacodynamic (PD) activity and that patients have a poor acceptance of parenteral
therapies. Therefore, careful attention to dose frequency and dose presentation are important to
the development of a commercially viable peptide drug. Here, we report on the optimization of
ShK-186 dose and dose frequency in animal models of disease as part of our recently
completed nonclinical program for the drug.
Previous studies from our group have characterized the level of Kv1.3 channel blocking activity
in the serum of Lewis rats following a single subcutaneous administration of ShK-186 in an
experimental formulation (Beeton et al., 2005). Peak serum drug activity occurred 30 min
following injection and returned to baseline by 7 h post-dose suggesting that at least daily
administration of the drug was required for efficacy. For this reason, previous animal studies
that investigated ShK peptides were performed using a daily or greater than daily dose
frequency. During the course of preclinical development of ShK-186, anecdotal evidence
suggested a prolonged PD effect of the drug following single or repeated administrations. We
therefore hypothesized that the peptide could display a durable therapeutic effect beyond its
residence time in the central compartment, and this could enable less frequent and more flexible
therapeutic administration of the compound.
In the current study, we describe the development of analytical tools and methods to accurately
measure the pharmacokinetics (PK) and biodistribution of ShK-186 following administration to
rats and monkeys using the intended clinical route of administration and formulation. We
compare PK data from ELISA, HPLC-MS, functional patch-clamp, and radiolabeling studies to
estimate free and bound drug fractions and terminal elimination kinetics over a range of
concentrations around the Kd of the drug. Finally, we use animal models of autoimmune disease
(DTH, CR-EAE, PIA) to demonstrate that infrequent drug administration (once every 3 – 5 days)
is adequate for therapeutic effect, and we describe a general mechanism by which highly
charged peptide toxins can exert durable pharmacological effects over an extended period.
Animals. DA and Lewis rats, 8-10 weeks old, were purchased from Harlan Laboratories
(Indianapolis, IN, USA) and housed under pathogen-free conditions with food and water ad
libitum. DTH trials were approved by the Baylor College of Medicine and Infectious Disease
Research Institute (IDRI) Institutional Animal Use and Care Committees (IACUC). EAE trials
were approved by the University of California at Irvine and the IDRI IACUCs. PIA and DTH trials
were approved by Baylor College of Medicine at Houston.
Sprague Dawley [Crl:CD®SD] rats (6 – 9 weeks old) were purchased from Charles River
Laboratories (Willmington, MA, USA) and housed in a temperature (64-79°C) and humidity (30-
70%) controlled facility. Food and water were ad libitum. PK studies in SD rats were approved
by either the MPI Research or IDRI IACUCs.
Non-naïve cynomolgus (Macaca fascicularis) and squirrel monkeys (Saimiri boliviensis) were
between 2 and 5 years of age and were transferred from the MPI Research (Mattawan, MI,
USA) stock colony. All cynomolgus monkeys were of Chinese origin. The squirrel monkey was
of Bolivian origin and provided by the University of Texas MD Anderson Cancer Center
(Houston, TX USA). Animals were housed individually in stainless steel cages in an
environmentally controlled room. The monkeys were provided environmental enrichment;
fluorescent lighting was provided 12 hours per day. Temperature was maintained between 64
and 84°C; humidity was 30-70%. Animals were provided Certified Primate Diet (PMI Nutrition
International, Inc., St. Louis, MO, USA) twice daily. Primatreats® and other enrichment foods
were provided on a regular basis. Water was available ad libitum. Primate studies were
approved by the MPI Research IACUC.
Drugs. ShK-186 and ShK-198 were manufactured using an Fmoc-tBu solid-phase strategy on
an amide resin. All of the coupling steps were mediated with 6-Cl-HOBT in the presence of
diisopropyl carbodiimide. Fmoc removal was facilitated with 20% piperidine in DMF containing
0.1 M HOBt to buffer the piperidine and minimize potential racemization at the 6 Cys residues.
Following assembly, the peptide was cleaved from the resin and simultaneously deprotected
using a TFA cleavage cocktail (Reagent K) containing aromatic cationic scavengers for 2hr at
room temperature. The crude peptide was filtered from the spent resin and subsequently
isolated by precipitation into ice cold diethyl ether. The crude peptide was dissolved in 50%
acetic acid and subsequently diluted into 3 L of H2O. The pH of this peptide solution was
adjusted to 8.0 with NH4OH and allowed to slowly stir overnight. Disulfide bond formation was
mediated by air oxidation or through the addition of a glutathione exchange system. ShK and its
derivatives spontaneously fold to a major thermodynamically favored isomer which is the
biologically active form of the peptides. The folded peptide was loaded onto a preparative RP-
HPLC column and purified using a gradient of ACN versus H2O containing 0.05% TFA. The
fractions containing the desired peptide purity were pooled together and lyophilized to produce
an acetate salt. Drug was formulated at 0.5 – 25 mg/mL in 10mM sodium phosphate, 0.8%
NaCl, 0.05% polysorbate 20, pH 6.0.
Serum and plasma stability studies. Shk-186 peptide was solubilized at a concentration of 10
mg/mL in formulation buffer. 25 µl of the stock peptide solution was spiked into 475 µl of a 1:1
dilution of serum, plasma, or whole blood with RPMI to a final concentration of 0.5 mg/ml and
incubated at 37°C for the indicated period. 50 µl of the sample was then mixed with 50 µl 4%
trichloro-acetic acid (TCA), and the sample was vortexed for 30 sec and placed at 4°C for 15
min. The TCA mixture was centrifuged at 12,000 RPM for 5 minutes to pellet the precipitated
proteins, and the supernatant was analyzed on an Agilent 1100 HPLC system fitted with a
Grace Vydac C18, 5.0 μm, 300 Å, 4.6 x 250 mm column (Grace, Deerfield, IL, USA). Mobile
phase A was composed of 0.1%TFA in 95% water/5% ACN, and mobile phase B was
composed of 0.1% TFA in 5% Water/95% ACN. The system flow rate was 1 mL/min.
HPLC-MS/MS method for measuring ShK-186 and metabolites in plasma. Whole-blood
samples were collected into K2EDTA-containing tubes and processed by centrifugation to
plasma. Plasma was supplemented 20:1 (v/v) with HALT® Phosphatase Inhibitor Cocktail
(Thermo Scientific, Rockford IL, USA) and stored frozen at -70°C until analysis. 50 µL of an
internal standard (2mg/mL ShK in 90:10 H2O:ACN v/v; Bachem AG, Bubendorf, Switzerland)
were added to 100 µL of plasma. The combined sample was diluted with 300 µL H2O and
purified using a Waters Sep-Pak® tC18, 25mg, 96-well SPE plate (Millford, MA, USA). Samples
were eluted in 500µL TFA/H2O/ACN (1:70:30, v/v) and evaporated under N2. The residue was
reconstituted in 200 µL TFA/H2O/ACN (0.02:90:10, v/v/v) and analyzed by HPLC-MS/MS. HPLC
was performed on an Agilent 1200 series instrument fitted with an ACE 5 C18-PFP 50 x 2.1
mm, 5 µm column (Advanced Chromatography Technologies, Aberdeen, UK). Mobile phase A
was formic Acid/H2O (2:1000, v/v), and mobile phase B was formic acid/H2O/ACN (2:500:500,
v/v/v). The flow rate was 300 µL/min. Mass spectrometry was performed on a SCIEX API 5000
instrument (Applied Biosystems, Carlsbad, CA, USA) using turbo ion spray in the positive mode.
Mass detection was performed using multiple reaction monitoring (ShK-186 m/z 741.5→841.0,
ShK-198 m/z 728→840.6, internal standard m/z 676.8→769.0). The dwell times for the internal
standard, ShK-186, and ShK-198 were each 500 ms.
ELISA methods for measuring ShK-186 in plasma. Whole-blood samples were collected in
K2EDTA-containing tubes and processed by centrifugation to plasma. Plasma samples were
stored at -70°C, and thawed immediately prior to analysis. For the competition ELISA (cELISA),
BD ELISA plates (BD, Franklin Lakes, NJ, USA) were coated with 100µL of a 10µg/mL ShK-198
solution overnight at room temperature and blocked for 2h with 5% BSA (Sigma-Aldrich Corp,
St. Louis, MO) in PBS the following day. Plasma samples were spiked with 1µg/mL of anti-ShK-
186 IgG1 antibody P2F12 (Kineta Inc., Seattle, WA, USA) and incubated at room temperature
for 15 min prior to addition onto the ELISA plate. Each sample was run in triplicate, with 50µL
added to each well and incubated for 1 h at room temperature. Samples are washed 6x’s with
PBS and 0.1% Tween-20 (PBT). HRP-conjugated goat anti-mouse IgG antibody (BioLegend,
San Diego, CA, USA) was used as a secondary (1:10,000 in PBT), and the ELISA was
developed with Pierce Ultra TMB substrate solution (Thermo Fisher Scientific, Waltham, MA,
USA). Samples were read on a Multiskan Spectrum (Thermo Scientific, Franklin, MA, USA) @
450 nM. Standard curves were generated with known concentrations of ShK-198 spiked into
K2EDTA isolated SD plasma (Bioreclamation LLC, Liverpool, NY, USA). For the sandwich
ELISA, BD ELISA plates (BD, Franklin Lakes, NJ, USA) were coated with 50µL of a 5µg/mL
anti-ShK-186 IgG2B capture antibody (P3B3, Kineta Inc., Seattle, WA, USA) solution for 1h at
37 °C and blocked for 2h with 5% BSA (Sigma-Aldrich Corp, St. Louis, MO) in PBS for 1 hour at
room temperature. Plasma samples or controls were diluted either 1:5 or 1:10 in PBS and
added to the plate. Each sample was run in triplicate, with 100µL added to each well and
incubated for 2 h at room temperature. Samples are washed 6x’s with PBT. A biotinylated anti-
ShK-186 IgG1 detection antibody (P2F12, Kineta Inc., Seattle, WA, USA) along with an HRP-
conjugated streptavidin (Thermo Fisher Scientific, Waltham, MA, USA) was used as secondary
detection reagents (1:10,000 in PBT), and the ELISA was developed with Pierce Ultra TMB
substrate solution (Thermo Fisher Scientific, Waltham, MA, USA). Samples were read on a
Biotek ELx808 (BioTek, Winooski, VT, USA) @ 450 nM. Standard curves were generated with
known concentrations of ShK-186 spiked into K2EDTA isolated SD plasma (Bioreclamation LLC,
Liverpool, NY, USA).
Measurement of channel blocking activity in plasma. Whole blood samples were collected
into heparin containing tubes and processed to plasma by centrifugation. Plasma samples were
stored at -70°C until analysis. Electrophysiological recordings were carried out in the whole-cell
configuration of the patch-clamp technique as described (Beeton et al., 2005), using Kv1.3-
transfected cell lines. The external solution was sodium Ringer’s and the pipette solution was
KF (300mOsm). Kv1.3 currents were elicited by 200-ms depolarizing pulses from a holding
potential of -80 to +40 mV. All recordings were done using PULSE software and a HEKA EPC-9
amplifier (HEKA Elektronik, Lambrecht, Germany). To generate a standard curve for the
assessment of levels of ShK-186 in plasma, a known amount of ShK-186 was added to rat
plasma (Heparin plasma, Bioreclamation LLC, Liverpool, NY, USA) and incubated at 37 °C for 1
h. These spiked plasma standard solutions were then appropriately diluted in Na+ ringer’s
solution before applying to cells. The reduction in peak current at +40 mV for each
concentration was used to generate a dose-response curve using Origin software (OriginLab
Corp., Northampton, MA). A similar reduction in peak current at +40mV after application of
plasma samples from treated animals (sometimes diluted in Na+ Ringer, as needed) was used
to determine the amount of ShK-186 in blood at each time point following injection.
SPECT/CT scanning of radiolabeled ShK-221. ShK-221 (100µg) was radiolabelled with 2 mCi
111Indium chloride (GE Healthcare, Arlington Heights, IL USA) in a 300µL reaction containing
50mM sodium acetate, pH5.0 for 30 min at 95°C. The reaction was quenched by the addition of
EDTA to a final concentration of 50 mM, and the radiolabeling efficiency was assessed by
reverse-phase HPLC (Luna 5µ C18(2) 100A 250 x 4.6 mm column, Phenomenex, Torrance, CA
USA) on an Agilent 1100 system using an IN/US Systems Gamma RAM Model 4 radio-HPLC
detector (LabLogic Systems, Brandon, FL USA). The labeling efficiency varied from 89-98% by
this method. SPECT/CT scanning (NanoSPECT/CT Preclinical Imager, Mediso, Budapest,
Hungary) was carried out on anesthetized animals in four 15 min scans during the first hour and
one scan each at 4, 8, and 24, 48, 72, 120 and 160 h post dose. The individual projection frame
time for each helical SPECT was set such that the duration of each scan would last for
approximately 15 to 45 minutes (varying by time-point to account for isotope decay) and allow
for significant collection of statistics within each frame. The characteristic peaks detected from
the spectra for 111In were 245 and 171 keV (primary and secondary, respectively). The resulting
projection data were reconstructed after each scan using an iterative model that takes
advantage of the pinhole geometry to achieve a resolution of approximately 2 mm.
Approximately 10 µL blood samples were collected after each scan and the amount of
radioactivity in the sample was measured using a Wallac Wizard 1470 scintillation counter
(Perkin Elmer, Waltham, MA USA). Drug concentrations were computed by taking account of
the specific activity of the administered dose, the half-life of 111In (67.3 h) and the counting
efficiency of the instrument.
Suppression of cytokine responses in PBMCs. Peripheral blood mononuclear cells (PBMCs)
were isolated from human whole blood using CPT® Vacutainers (Beckton, Dickinson, Franklin
Lakes, New Jersey, USA) and dispersed into RPMI media. 100 µL of media containing 2 X 105
PBMCs were added to each well of a 96-well dish and treated with the addition of 50 µL ShK-
186 in media at varying concentrations for 1 h at 37°C, 5% CO2. Cells were washed twice with
RPMI, resuspended in 200 µL fresh media supplemented with 40 µM thapsigargin, and
stimulated for 48 h at 37°C, 5% CO2. Cytokine production was measured in the overlying media
using a Luminex Assay (Millipore, Bellerica, MA, USA) specific for IL-2, IFNγ, IL-17, or IL-4.
DTH model in rat. Active DTH was induced and monitored as described (Beeton and Chandy
2007). Briefly, Lewis rats were immunized in the flanks with ovalbumin (OVA) (200 µg/rat)
emulsified in complete Freund’s adjuvant (CFA) (Sigma, St Louis, MO, USA). Seven to nine
days later, animals were challenged under isoflurane anesthesia in the pinna of one ear with 20
µg OVA dissolved in saline and in the other ear with saline. Animals received one or two
subcutaneous injection(s) of either ShK-186 or vehicle at the time of challenge or on the four
days preceding challenge. Thickness of both ears was measured 24 hours after challenge with
a spring-loaded micrometer (Mitutoyo America Corporation, Aurora, IL, USA).
CR-EAE model in rat. The CR-EAE model in DA rats (Lorentzen et al., 1995) was used with
minor modifications. Briefly, animals were immunized on day 0 by subcutaneous injection at the
base of the tail with 0.2 ml of a 1:1 emulsion of homogenized SD rat spinal cord (Bioreclamation
LLC) in CFA supplemented to 4 mg/ml of M. tuberculosis H37Ra (Sigma, St Louis, MO, USA)
under isoflurane anesthesia. Each rat received ~80 mg of spinal cord and 400 µg of H37Ra.
Either ShK-186 or placebo was administered subcutaneously on alternate flanks as appropriate.
Animals were observed daily by measuring their body weight and assessing clinical signs of
disease. Animals were included in the study and randomized into experimental groups
sequentially as they reached a clinical score of 1. Scores were assigned as follows: 0, no
illness; 0.5, no tail coil; 1, no tail coil and flaccid tail (tail dropped straight down 5 consecutive
times); 2 mild paraparesis, wobbling; 3, moderate to severe paraparesis, falling on its side,
unable to stand on hind legs; 3.5, 1 limb paralysis; 4, 2 limb paralysis; 5, 2 limb paralysis with
incontinence; 6, death. A cumulative clinical score was calculated for each rat by adding the
daily scores from the day of disease onset (CS =>1) until the end of treatment and averaged to
obtain a mean cumulative clinical score. Disease prevalence was calculated as the number of
animals with CS > 0.5 divided by the number of living animals per day and expressed as a
percentage. During the chronic phase, an animal was considered to have a relapse if its clinical
score was greater than 1.
Statistical and computational analysis. Statistical analysis was carried out using the one-way
ANOVA (EAE model and cytokine expression studies), the two-tailed, Mann-Whitney U test
(DTH model) or the paired t-test (pharmacokinetic studies). Goodness of model fit was
determined using the R2 statistic. Pharmacokinetic calculations were as follows: Cmax and Tmax
were as observed in the dataset. AUC was computed using a linear trapezoidal method. The
terminal elimination half-life was computed from the slope of the regression with the best
adjusted R2 value. AUCt-∞ was calculated by dividing the last observed drug concentration by
the terminal elimination slope.
Pharmacokinetic properties of ShK-186 in representative species. As a precursor to PK
studies of ShK-186 in nonclinical species, we evaluated the stability of the peptide in serum,
plasma, and whole blood from Sprague Dawley rat, cynomolgus monkey (Macaca fascicularis)
and human. Preliminary spiking-in studies identified a single metabolite in the serum from all
three species that was characterized by mass spectrometry as the dephosphorylated form of
ShK-186 (referred to as ShK-198, Suppl. Fig. 1A-C). Conversion of ShK-186 to its metabolite
occurred most readily in serum and in plasma samples treated with citrate or heparin as the
anticoagulant. The peptide is most stable in plasma containing K2EDTA or specific phosphatase
inhibitors (sodium fluoride, sodium orthovanadate, sodium pyrophosphate and beta-
glycerophosphate), suggesting that endogenous phosphatases are responsible for its
conversion. The metabolite was synthesized and evaluated for its channel blocking activity
against the cloned Kv1.3 channel. ShK-198 is an active inhibitor of Kv1.3 currents with a
Kd=4.3±1.8pM (Suppl. Fig. 1D).
In order to measure the PK properties of both the parent and metabolite in nonclinical species,
we developed an HPLC-MS/MS method to assess drug concentrations in plasma. The method
was validated for both rat and cynomolgus monkey K2EDTA plasma with a lower limit of
quantitation (LOQ) of 2 ng/mL (450 pM). Using this method, we measured the in vivo
pharmacokinetic properties of ShK-186 following a single subcutaneous administration (the
intended clinical route of administration) to rat and monkey. Both rat and monkey have effector
memory T cells that express large numbers of the Kv1.3 channel after activation and are
therefore relevant nonclinical species for testing ShK-186 (Chi et al., 2011).
The PK profile of ShK-186 is characterized by a short residence time in the central compartment
of rat and monkey species. In rat, following a single administration, ShK-186 reaches a
maximum plasma concentration between 1 and 5 min, whereas its metabolite reaches its Cmax
between 1 and 15 min (Fig. 1A and B and Table 1 and 2). While the Cmax and AUC for both the
parent and metabolite increase with dose in rat, the relationship between Cmax and dose was
largely non-linear (R2=0.8), whereas the relationship between AUC and dose was roughly linear
through the 500µg/kg dose (R2=0.97, Fig. 1E). The half-life in rat ranged from 4.4 to 9.2 min for
ShK-186 and from 6.1 to 16.4 min for ShK-198 (Table 1 and 2). Clearance values for ShK-186
and ShK-198 in rat were not statistically different (paired t-test, t(4)=2.2, p=0.1) and ranged from
441.4 to 1453.3 mL/kg*min.
The PK of ShK-186 (Fig. 1C) and ShK-198 (Fig. 1D) following a single subcutaneous
administration to monkey demonstrated a linear relationship between dose and both AUC and
Cmax (slope=1.02 – 1.27, R2=0.97, Fig. 1F) through the entire range of doses from 35 to 1000
µg/kg. The monkey half-life ranged from 8.8 – 23.8 min for ShK-186 and from 16.7 – 73.5 min
for ShK-198. Clearance rates in the monkey were generally lower for ShK-198 than ShK-186
and ranged from 18.7 to 141.3 mL/kg*min (Table 1 and 2).
In order to bolster data from the HPLC-MS method, the quantity of drug in plasma following a
single 500 µg/kg subcutaneous dose to rat was measured using two ELISA formats (competition
and sandwich) as well as patch-clamp analysis to measure the level of channel-blocking activity.
Since neither ELISA nor patch-clamp can distinguish between the parent and metabolite (both
are active and share the same peptide epitopes), the results of these studies were compared to
the sum of ShK-186 and ShK-198 as independently determined by HPLC-MS. Both the
competition and sandwich ELISA methods yielded drug concentrations that were moderately but
significantly higher than those determined by HPLC-MS for time points between 15 and 120 min
(Fig. 2 and Suppl. Table 1). Analysis of these data results in a longer computed half-life (~80
min) of the drug by ELISA and a lower overall clearance rate (~65 mL/kg*min) when compared
to HPLC-MS. The LOQ of each of the ELISA methods was approximately 1 ng/mL (225pM).
The functional drug concentration at each time point was also assessed by measuring the Kv1.3
channel-blocking activity of diluted plasma from animals administered ShK-186. Drug
concentrations were derived using a standard curve composed of ShK-186 in naïve rat plasma.
Similarly to the ELISA methods, the patch clamp bioassay is unable to discriminate between
ShK-186 and ShK-198 and therefore, the results were compared to the sum of ShK-186 and
ShK-198 as measured by HPLC-MS. The detectable concentration by patch analysis is on par
with the ELISA methods, but higher than the HPLC-MS method, indicating a low steady
channel-blocking concentration of peptide during the elimination phase. The apparent half-life is
~54 min, resulting in a slow clearance of 41 mL/kg*min.
These data taken together indicate that ShK-186 and its metabolite ShK-198 reach a maximum
concentration in plasma 1 to 15 min following a single subcutaneous injection of drug in both
species. The parent and metabolite display rapid clearance from the central compartment as
measured using three distinct analytical methods. The LOQ of the HPLC-MS and ELISA
methods are above the Kd of ShK-186 on the cloned Kv1.3 channel (58.2±9 pM) and so lack the
sensitivity to estimate the terminal elimination phase at low but potentially therapeutic drug
concentrations. The patch-clamp method displays greater sensitivity, but lacks the robustness
and reproducibility of the other methods when assessing biological samples. A potential
shortcoming of all three methods is that they likely only measure the unbound drug fraction in
ADME studies with a radiolabeled analog of ShK-186. One mechanism by which ShK-186
could exert a prolonged pharmacodynamic effect is by distributing to extravascular
compartments where the drug half-life is significantly longer than in the central compartment or
by displaying a long terminal elimination phase that is above its Kd but below the LOQ of
available analytical methods. In order to enhance the sensitivity of our in vivo studies, measure
the biodistribution of ShK-186 and evaluate the total (bound plus unbound) drug concentration
in whole blood, we developed a radiolabeled analog of the compound.
ShK-186 contains a single iodinatable tyrosine at position 23. However, iodine incorporation into
the ring, which is predicted to interact within the pore region of the Kv1.3 channel (Pennington et
al., 1996), results in disruption of the channel binding properties of the drug. We therefore
modified the amino terminus of ShK-198 with a six-carbon linker attached via a peptide bond to
one of the carboxylic acids of a DOTA chelate (Suppl. Fig. 2A). The DOTA-conjugate,
designated ShK-221, was readily coordinated with indium or gadolinium (Suppl. Fig. 2B-C) and
retained the full activity of the parent molecule (Suppl. Fig. 3). We prepared and administered
111In-labeled ShK-221 by subcutaneous injection to Sprague Dawley rat (1.0 mCi, 100 µg/kg)
and squirrel monkey (0.83 mCi, 35 µg/kg). The radiolabeling efficiency ranged from 89-98%
over the series of experiments as determined by HPLC. Biodistribution of radiolabeled ShK-221
was evaluated by SPECT imaging continuously for the first hour post-dose, and then at 4, 8, 24,
48, 72, 120, and 160 h. Background levels in the detection system was approximately 0.1µCi/m3
(~5 ng/m3 of ShK-221 at the initial time point and 26 ng/m3 at the last time point). Blood samples
were collected following each scan, and total radioactivity in whole blood was measured by
scintillation counting. Computed tomography was performed at each time point to enable
colocalization of the radiolabel with key anatomical structures.
Biodistribution of 111In-ShK-221 in the squirrel monkey was characterized principally by slow
absorption from the injection site over the entire 160 h period (Fig. 3A and E). The quantity of
drug present at the injection site followed a biphasic exponential decay (R2=0.95) with an initial
half-life of approximately 1-1.5 h and a terminal half-life of >48 h (Fig. 3E). During the first hour,
significant radioactivity could be observed in the kidney, increasing in intensity through 1 hour
(~1% injected dose(ID)/g, Suppl. Table 2) and slowly declining to approximately baseline by 48
hours. Radioactivity in the monkey kidney was primarily observed in the cortical and medullary
regions during all time points and was comparatively absent in the renal pelvis except for the
first hour (Fig 3B). Significant bladder associated radioactivity (Tmax=0.75 – 1 h, 0.34 %ID/g) was
only observed during the first four hours, after which relatively little radiolabel was detected in
bladder. No other organ showed significant levels of radioactivity except for liver, which peaked
at 0.75 - 1 h post dose administration (0.166 %ID/g). Muscle, heart and brain all had <0.1 %ID/g
at all time points (Suppl. Table 2).
Biodistribution of 111In-ShK-221 in the rat was similar to monkey and characterized by slightly
faster absorption from the injection site and excretion through the urine over the first 24 h (Fig
3C and E). Significant radioactive label was observed in rat bladder (9.4 %ID/g), kidney (2.9
%ID/g) and liver (0.4 %ID/g) during the first hour (Fig. 3C). While little label was identified in the
bladder at later time points, the amount of drug in liver and kidney was relatively constant
through the first 24 h. Cross-sectional views of the rat kidney showed that, with the exception of
the first hour, radioactivity was concentrated primarily in the cortical regions similar to the
monkey (Fig. 3D).
Evaluation of blood-associated radioactivity in monkey at each time point also demonstrated a
biphasic exponential decay (R2=0.99) with an initial half-life of approximately 1 h and a terminal
half-life of >64 h (Fig.3F). In monkey much of the terminal elimination phase was reflected by
blood concentrations below the LOQ of previous methods but well above the Kd for ShK-186.
80% of the Kv1.3 channels in whole blood would be expected to be bound by drug through
approximately 5 days post-dose, and concentrations remain above the Kd for the entire 160 h
The whole blood-associated radioactivity the rat also showed a biphasic exponential decay
(R2=0.99) with an initial half-life of approximately 1.7 h and a terminal half-life of >72 h (Fig.3F).
The drug concentrations, like the monkey, were well above the Kd for ShK-186 until 5 days post
dose. 80% of the Kv1.3 channels in whole blood would be expected to be bound by drug
approximately 3-5 days post-dose.
In summary, the biodistribution of radiolabeled ShK-221 in rat and squirrel monkey is
characterized by a very slow distribution from the injection site, significant concentrations of
drug peripherally in the injection site, kidney, and liver and a long terminal elimination phase in
whole blood. Drug levels remain above ~200 pM in blood for approximately 7 days in the
monkey and 3 days in the rat.
Suppression of cytokine responses in human PBMCs. Another way that ShK-186 could
exert a durable PD effect is through a sustained interaction with the Kv1.3 channel on
lymphocytes. We therefore assessed the duration of lymphocyte suppression following
exposure to ShK-186. We have previously shown that ShK-186 suppresses thapsigargin-
induced expression of IL-2, IL-17, IFNγ, and IL-4 in freshly isolated human PBMCs (Chi et al.,
2011). In the current series, we exposed PBMCs to the drug either continuously during a 48 h
period of thapsigargin stimulation, for 1 h prior to 48 h of stimulation, or for 1 h up to 16 h prior to
stimulation, and measured the IL-2 responses by ELISA (Fig. 4). In cases of transient exposure,
the cells were thoroughly washed with media prior to thapsigargin treatment. There was no
statistically significant difference (one-way ANOVA, F(3,12)=0.40, p=0.76) between continuous
drug treatment versus transient drug exposure up to 16 h prior to thapsigargin stimulation.
These data are consistent with a model where ShK-186 rapidly associates with but slowly
dissociates from the Kv1.3 channel of lymphocytes.
Suppression of the DTH response in vivo; dose frequency and dose-response studies.
Our ADME studies suggested that a low but therapeutically relevant drug concentration
persisted in the blood for several days following a single administration of ShK-186. We
therefore evaluated the relationship between dose frequency and therapeutic efficacy in animal
models of effector-memory T cell-mediated disease. The simplest model for assessing drug
effects is the DTH reaction, an immune response largely mediated by skin-homing effector-
memory CD4+ T cells (Soler et al., 2003; Matheu et al., 2008). We immunized groups of 5 – 8
Lewis rats with OVA in complete Freund’s adjuvant (CFA) followed 7 – 9 days later by elicitation
of the DTH response in the ears of immunized animals. Ear swelling was measured 24 h post-
elicitation. The durability of drug effect was assessed by treating animals with ShK-186 at
varying times prior to or coincident with the elicitation phase. The day of ear challenge is
referred to as Day 0 for reference.
Animals that were treated with two doses of 10 or 100 µg/kg ShK-186 on Day 0 and Day 1 (the
standard regimen) were compared with single 100 µg/kg doses administered on Days 0, -1, -2, -
3, or -4. Two doses administered on Day 0 and 1 and single doses administered on Days -1
through -4 yielded statistically significant reductions in ear swelling relative to placebo-treated
animals (two-tailed Mann-Whitney test, Fig. 5A). Single doses administered prior to Day -4 did
not result in a significant reduction in ear swelling relative to the control group (data not shown).
We conclude that a single subcutaneous injection of ShK-186 is sufficient to suppress the DTH
response in rat for a period of 5 days.
In order to establish a relationship between dose-level and the time of dosing, we evaluated the
suppressive effect of a single ascending dose (0.1 - 100 µg/kg) of ShK-186 administered 2 days
prior to ear challenge. A dose-dependent reduction in ear swelling was observed over the 3-log
dose range, with doses ≥1 µg/kg achieving statistical significance relative to vehicle-treated
animals (Fig. 5B). These data are consistent with the ADME data above that show a single dose
of ShK-186 can support therapeutic drug concentrations in rat whole blood for up to 5 days.
Treatment strategies in the CR-EAE and PIA models. CR-EAE is widely used as a model of
multiple sclerosis. This model was extensively characterized in guinea pigs (Raine et al., 1977;
Keith et al., 1979) and more recently in DA rats (Feurer et al., 1985; Lorentzen et al., 1995) and
unlike the acute EAE models includes relapses and some degree of demyelination (Lassman
and Wisniewsky, 1979; Lorentzen et al., 1995; Matheu et al., 2008). Moreover, due to its
protracted nature, it is an adequate model for testing dosing schedules. The initial wave of
disease is largely adjuvant mediated and composed primarily of central memory T cells,
whereas subsequent waves of disease are principally effector-memory T cell mediated and
therefore Kv1.3-dependent (Matheu et al., 2008). We have previously shown ShK-186 to be
effective in the CR-EAE model using daily dosing at 100 µg/kg (Matheu et al., 2008). In the
present study, we explored the effect of less frequent dose administration on drug efficacy in
Two study designs were explored. In the first, a lead-in period with daily drug administration was
initiated at the time of disease induction and continued throughout the first wave of disease.
Seven days following disease onset, animals were randomized to receive 100 µg/kg ShK-186
every 2 or 3 days through the remainder of the study. Daily drug treatment caused a statistically
significant reduction in mean clinical score compared to placebo treated animals during the first
wave of disease (Fig. 6A). Following lead-in, drug administration every 2 or 3 days resulted in
continued significantly lower mean daily clinical score in treated relative to control animals. The
average cumulative clinical score was 161.1±162.3, 72.5±98.1, and 71.3±103.3 for the placebo,
every-2-day, and every-3-day dosing groups, respectively. Animals were scored twice daily.
In a second series of experiments, we evaluated the effect of reduced dose frequency on EAE
without the drug lead-in period. In this study, groups of DA rats were randomized to receive
placebo, daily ShK-186, or ShK-186 every three days beginning at a clinical score ≥1. Both
drug-treated groups exhibited a significantly lower mean daily clinical score than placebo-
treated animals (Fig. 6B). However, there was no statistically significant difference between
daily and every-third-day dose administration. Mean cumulative clinical scores were 49.7±26.7,
36.9±20.6, and 30±19.3 for the placebo, daily, and every third day dosing groups respectively.
The percentage of rats with one or more relapses was 70% (9/13), 21% (3/14) and 21% (3/14),
and the total number of relapses observed during the chronic phase were 15, 6 and 5 for the
placebo treated, ShK186 daily, every three day treated groups, respectively. Animals were
scored once daily.
Finally, we wished to evaluate the durability of disease suppression in the CR-EAE model
following cessation of drug administration. Disease was elicited in groups of DA rats and the
animals were allowed to develop a relapsing disease. On day 10 following disease onset
(clinical score ≥1), animals were randomized to receive daily placebo or 100 µg/kg ShK-186 for
a period of 14 days. Drug treatment was discontinued on Day 24, and the animals were
monitored for an additional 15 days. There was no difference between the placebo and drug-
treated groups prior to drug treatment (Fig. 6C). During the 14 days of daily drug administration,
there was a statistically significant reduction in mean clinical score in drug treated versus control
animals. Once treatment was withdrawn, the mean clinical score in the drug treated group
slowly returned to the level of placebo over a period of approximately 5 days (Suppl. Table 2).
However, there was no rebound effect observed in the previously-treated animals.
As a final test of the effectiveness of less than daily dosing, we evaluated ShK-186
administration every other day in the PIA model of rheumatoid arthritis (Beeton et al., 2006).
ShK-186 administered once daily (100ug/kg) has been previously reported to reduce the
number of joints affected and the severity of joint swelling in the PIA model in DA rats (Beeton et
al., 2006). Here, we demonstrate that ShK-186 administered on alternate days (100 ug/kg) also
ameliorates the disease (Suppl. Fig. 4).
The data from these four studies are consistent with a model of durable drug effects following a
single subcutaneous dose of ShK-186 and are consistent with observations made using the
In the current study, we tested the hypothesis that a single dose of ShK-186 could exert
therapeutic effects for a period of time after the bulk of the administered dose has disappeared
from the central compartment.
PK studies were performed using HPLC-MS, ELISA, and patch-clamp to measure the unbound
drug fraction in plasma, and a radiolabeled analog of ShK was used to measure the total drug
concentration (unbound plus bound) in whole blood. The Cmax of both ShK-186 and ShK-198 are
rapidly reached following subcutaneous injection to rat and monkey. Both parent and metabolite
have a short apparent half-life in the central compartment with >90% of the Cmax eliminated by 2
h in both species at all the tested doses. The half-life is shorter and the apparent clearance
greater for ShK-186 than ShK-198, likely reflecting the independent action of endogenous
phosphatases on the conversion of ShK-186 to its metabolite.
Previous studies suggest that only 10% of the drug is available unbound in plasma (Chi et al.,
2011). This is consistent with the observation that at 1 h following administration of a 35 µg/kg
dose to cynomolgus monkey, approximately 1 nM of ShK-186/198 is observed in plasma by
HPLC-MS, whereas after administration of the same dose of radiolabeled ShK-221 to squirrel
monkey, approximately 15 nM of drug is measured in whole blood, suggesting an unbound
fraction of ~7% by this method. The free fraction of the drug may actually be lower in the rat
compared to non-human primates. At 1 h post dose of 100 µg/kg, approximately 0.1 nM of
ShK-186/198 is observed in rat plasma by HPLC-MS compared to 14 nM of ShK-221 in whole
blood. This may be due to the drug binding to other blood constituents such as platelets, which
express Kv1.3 on their surface and have been found to be present in exceedingly high numbers
in rat whole blood (5-10 x Human) (McCloskey et al., 2010; Trowbridge et al., 1984). The effect
of ShK-186 on platelet expressed Kv1.3 has not been explored.
The two distinct ELISA methods, as well as the functional Kv1.3 patchclamp method,
consistently measure significantly more drug in plasma than HPLC-MS. This may represent an
intermediate value between free and total drug concentration in blood. Whereas the HPLC-MS
method utilizes a solid-phase extraction of plasma samples that likely removes all bound drug at
the initial processing step, ELISA studies are conducted with neat plasma samples. As such,
interaction of ShK with the antibody in the ELISA system may shift the equilibrium between
bound and unbound drug fractions. Similar and corroborative results were observed using the
functional patchclamp assay which may be a result of a portion of the bound drug being
released due to dilution and infusion of the plasma into the patch chamber.
The more sensitive radiolabeling method allows the detection of a biphasic terminal elimination
profile for ShK in both species characterized by a rapid initial phase and a very long terminal
phase. The terminal half-life computed using 111In-ShK-221 was >64 h in monkey with sustained
blood levels above the Kd for 7 days. The blood concentrations mimic a biphasic (fast then slow)
absorption from the injection site. The parent peptide of ShK-186 was originally isolated from
the venom of Stichodactyla helianthus (Castenada et al., 1995) and ShK-186 may share some
of the in vivo characteristics of the complex peptide mixtures found in animal venom. Rate-
limiting absorption resulting in prolonged plasma exposure has been described for whole animal
venoms (Audebert et al., 1994; Barral-Netto et al., 1990). The long absorption phase has been
used to explain the frequent relapse in envenomation patients long after exposure and/or
treatment with antivenom (Dart et al., 2001; Guittierrez et al., 2003, Seifert and Boyer, 2001),
and venoms are often described as having a depot effect. Venom and toxin pharmacokinetics
are also characterized by large apparent volumes of distribution and slow elimination from deep
and shallow peripheral compartments (Ismail et al., 1996). The apparent volume of distribution
for ShK-186 is large in both rat (2743 – 16458 mL/kg) and monkey (1729 – 2664 mL/kg),
consistent with that reported for other animal venoms. Slow elimination of venom from
peripheral compartments can further amplify the duration of their effects and contribute to the
slow recovery of envenomation patients.
A further contributing factor to the long PD effect of ShK-186 could be explained by its slow
dissociation from the Kv1.3 channel. Studies with PBMCs show that there is essentially no
difference between continuous drug treatment during stimulation and drug treatment up to 16 h
prior to stimulation. While we did not formally measure an off-rate of the drug on the Kv1.3
channel using traditional methods, we did show that its pharmacodynamic effect can persist for
many hours after exposure to the cells. The receptor dissociation half-life of some animal toxins
has been reported to be as long as one week (Berg and Hall 1975, Chang and Huang 1975).
Significant amounts of radioactivity were observed in the bladder of both rat (~17 % injected
dose) and monkey (~1% injected dose) at the earliest time points following administration of
111In-ShK-221, suggesting that glomerular filtration is the principal elimination pathway for the
peptide shortly after injection. The large amount of drug excreted by the rat in the first hour is
most likely a reflection of the increased metabolism of the rat compared to the monkey.
Following 1 h in rat and approximately 4 h in monkey, little radioactivity is observed in bladder
whereas significant amounts of radioactivity can still be observed in the kidney cortex. Cortical
concentration has been reported for numerous radiolabeled versions of peptide drugs including
octreotide, bombesin, exendin, and gastrin (Gotthardt et al., 2007). The mechanism of cortical
retention has been most thoroughly described for octreotide. Tubular reabsorption of the
cationic octapeptide is mediated by megalin, a scavenger receptor expressed in the proximal
kidney tubule (de Jong et al., 2005). Mice with a kidney-specific disruption of the receptor lack
the cortical retention of radiolabeled octreotide seen in wild-type mice. Renal uptake of
octreotide is partially mediated by charge and can be disrupted by co-infusion of the positively
charged amino acids L-lysine and L-arginine (Bodei et al., 2003). ShK-186 carries a net +6
charge at physiological pH, and so its cortical retention may be mediated by a similar
ADME studies with radiolabeled ShK suggest that a single dose of drug can provide
therapeutically meaningful blood concentrations for up to 5 days in rat and 7 days in monkey.
These data are consistent with the data collected from the rat DTH model where a single
administered dose provides a statistically significant reduction in ear swelling for up to five days.
Likewise, dose administration every 3 days in the CR-EAE model provided statistically
indistinguishable reductions in clinical score compared to daily drug administration. These
observations are relevant to the future clinical development of ShK-186, since an optimized
dose frequency will ensure therapeutic efficacy, improve patient compliance, and reduce the
potential for drug accumulation during chronic administration.
Participated in research design: Bailey, Beeton, Boley, Chandy, Chi, Iadonato, Knapp, Munoz,
Pennington, Slauter, Tarcha, Rupert
Conducted experiments: Bailey, Beeton, Chi, Hansen, Hu, Iadonato, Kentala, Munoz, Nguyen,
Norton, Banks, Tarcha, Tjong, Upadhyay
Contributed new reagents or analytical tools: Bailey, Pennington, Tarcha
Performed data analysis: Bailey, Beeton, Chandy, Chi, Iadonato, Knapp, Munoz, Nguyen,
Wrote or contributed to the writing of the manuscript: Iadonato; Tarcha, Munoz, Chi (sections
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This work was supported by the National Institutes of Health National Institute of Allergy and
Infectious Diseases Grant R43AI085691 (SI) and NIH R01NS48252 (KGC).
FIGURE 1. Pharmacokinetic profiles of ShK-186 and ShK-198 in plasma following a single
dose to rat and monkey. ShK-186 was administered by subcutaneous injection to Sprague
Dawley rats (A and B, n=3-9 animals/dose/time point) and cynomolgus monkeys (C and D, n=2-
16 animals/dose/time point) and plasma samples were collected at time intervals ranging from 1
minute to 24 hours. Samples were analyzed using a validated HPLC-MS/MS method that can
resolve both the parent compound (ShK-186, A and C) and its metabolite (ShK-198, B and D).
The Cmax and AUC0-inf were computed for rat (E) and monkey (F) at each dose level using non-
compartmental analysis and the linear trapezoidal method.
FIGURE 2. A comparison of three methods for detecting ShK-186 in pharmacokinetic
studies. HPLC-MS measurements of plasma drug concentrations following a 500 µg/kg ShK-
186 subcutaneous injection to rat were compared to PK measurements obtained using a
functional assay (patch clamp) and both a competition and sandwich ELISA. Since neither the
functional assay nor the ELISA methods can distinguish drug from metabolite, HPLC-MS data
from both compounds were summed for comparison. Patch clamp analysis was performed on
the cloned Kv1.3 channel stably expressed in L929 cells. HPLC-MS data are from historical
studies involving a total of n=9 animals; patch clamp and ELISA data were collected from n=3
FIGURE 3. Biodistribution studies with radiolabeled ShK in rat and squirrel monkey. 111In-
labelled ShK-221 was administered to Sprague Dawley rat (100µg/kg; 1.0mCi) and squirrel
monkey (35µg/kg; 0.84mCi) as a single subcutaneous injection to the scapular region of each
animal. SPECT and CT scans were collected continuously during the first hour (4 x 15 m
intervals) and at 4, 8, 24, 48, 72, 120, and 160 h post-dose. Flattened 2D images of the 3D
reconstructions are shown for the 4, 24, 72 and 160 h time points for monkey (A) and the 1, 8
and 24 h time points for rat (C). Both animals show slow absorption of drug from the injection
site and significant early and sustained distribution to kidney and to a lesser extent liver. Kidney
associated radioactivity in both species was principally identified in the cortex (B and D).
Quantification of 111In-ShK-221 at the injection site in monkey (top) and rat (bottom) revealed a
biphasic decay with an initial half-life of approximately 0.5 -1.5 h and a terminal half-life of >48 h
(E). Drug concentrations in monkey (top) and rat (bottom) whole blood followed a similar
biphasic decay with an initial half-life of approximately 1.5 h and a terminal half-life of >64 h (F).
Blood concentrations remained above the Kd for Kv1.3 throughout the entire study period and
above the 80% saturation concentration (233pM) through the first 120 h consistent with a slow,
continuous distribution from the injection site throughout the study period.
FIGURE 4. Durable effect of drug treatment on human PBMCs. Time of treatment studies
were conducted in human PBMCs where the effect of drug treatment timing and duration on
thapsigargin-stimulated IL-2 responses was measured. Continuous drug treatment during the 48
h stimulation period (A, black bar) was compared with drug pretreatment for 1 h followed by a
brief washout and stimulation for 48 h (B, open bar) or drug pretreatment (1 h) followed by
washout, media incubation (16 h) and thapsigargin stimulation (48 h) (C, hatched bar). Drug
treatment for a 1 h period up to 16 h prior to stimulation was statistically indistinguishable from
continuous drug treatment. None of the treatment times and durations were significantly
different (one-way ANOVA, F(3,12)=0.40, p=0.76).
FIGURE 5. Time of administration and dose-dependent suppression of the DTH response.
Lewis rats were immunized with ovalbumin in CFA and challenged 7 – 9 days later by injection
of ovalbumin to the ear pinna. The day of challenge is represented as Day 0. The DTH reaction
was measured 24 h post-challenge (Day 1). ShK-186 administered at 10 or 100 µg/kg in two
doses on Day 0 and Day 1 or as a single 100 µg/kg dose on Day -1, -2, -3, and -4 resulted in a
significant reduction in ear swelling relative to placebo-treated animals when measured on Day
1 post-challenge (A; two-tailed Mann-Whitney; * p<0.05, ** p<0.01). These data indicate that a
single ShK-186 dose can suppress the DTH response for a period of up to 5 days. Using the
DTH model, a dose-response study was conducted with a single dose of ShK-186 administered
on Day -2 (B). Doses between 0.1 and 100 µg/kg show a clear dose-response relationship, with
all but 0.1 µg/kg achieving statistical significance relative to placebo.
FIGURE 6. Alternate dosing schedules are effective in chronic EAE model. An initial study
evaluated lead-in dosing followed by less than daily drug administration (A). Male DA rats were
immunized with spinal cord homogenate in CFA and administered ShK-186 (100 µg/kg/day,
n=25) or vehicle (n=12) during the prodromal period and for 7 days following onset of EAE, after
which drug treated animals were randomized to receive a maintenance dose of 100 µg/kg ShK-
186 every 2 (n=12) or 3 (n=13) days. ShK-186 significantly reduced (p<0.001) the severity of
the initial episode of disease. Maintenance therapy administered at 48 or 72 h intervals
significantly (p<0.001, one-way repeated measures ANOVA) reduced the severity of CR-EAE. A
second study measured the effect of infrequent drug administration beginning at disease onset
(B). Female DA rats (n=13/group) were immunized with spinal cord homogenate in CFA to elicit
a chronic, relapsing EAE. Following onset of symptoms (clinical score >1), animals were
randomized to receive daily placebo, daily ShK-186 or ShK-186 every 2 or 3 days. Drug
treatment resulted in significantly lower clinical scores and a lower frequency of disease
incidence (inset) during the chronic phase in the daily and every-third-day treated groups
compared with placebo (repeated measures ANOVA, F(2,60)=39.4, p<0.0001). Mean clinical
scores were not lower relative to placebo in the group treated on alternate days in this study
(data not shown). A final study measured the durability of response of a period of drug therapy
(C). Female DA rats (n=23) were immunized and allowed to proceed to CR-EAE. 10 days
following the onset of symptoms, animals were randomized to receive daily placebo (n=10) or
ShK-186 100 µg/kg (n=13) for 14 days. Therapy was discontinued on day 24 and the time
required for treated animals to return to baseline disease was evaluated. The previously-treated
group had mean clinical scores significantly lower than placebo controls on days 24, 25, 26, and
28 (Suppl. Table 2) consistent with a 5 day window for disease recurrence.
Table 1: ShK-186 pharmacokinetic parameters in Sprague Dawley rat and cynomolgus monkey
t½ Cmax AUC0-inf_obs Cl
5 8.8 12.8 247.6 141.3
5 14.5 33.6 823.1 121.8
5 23.8 69.8 1935.9 78.5
5 11.3 106.6 2220.9 112.2
5 14.0 173.8 3496.4 86.0
5 15.8 192.5 4734.0 105.6
5 13.0 358.0 9552.7 104.6
1 4.4 26.2 115.9 441.4
1 9.2 27.0 249.5 640.9
5 4.7 29.7 282.9 886.3
1 5.2 42.7 587.5 847.2
5 7.9 48.0 690.6 1453.3
Table 2: ShK-198 pharmacokinetic parameters in Sprague Dawley rat and cynomolgus monkey
t½ Cmax AUC0-inf_obs Cl
5 22.7 23.0 771.9 46.0
5 24.5 55.6 2298.4 43.6
5 16.7 94.2 2555.9 58.7
15 22.8 117.0 5943.2 42.1
5 73.5 168.0 8588.5 35.1
15 30.8 321.0 17750.6 28.2
15 25.4 852.5 53389.9 18.7
1 6.1 11.8 102.5 486.6
5 10.4 11.6 243.9 617.9
5 7.5 36.4 480.5 522.1
15 16.4 33.9 1039.6 488.5
5 8.7 53.9 1219.2 819.9
030 60 90 120
35 μ μg/kg
100 μ μg/kg
150 μ μg/kg
250 μ μg/kg
300 μ μg/kg
500 μ μg/kg
1000 μ μg/kg
0 60120 180240
0 1020 30 40
50 μ μg/kg
150 μ μg/kg
250 μ μg/kg
500 μ μg/kg
1000 μ μg/kg
0 20 40 60
Rat PK-Dose Relationship
Dose Log[μ μg/kg]
Cyno PK-Dose Relationship
Dose Log[μ μg/kg]
0 100 200 300
4 Hr24 Hr 72 Hr160 Hr
1 Hr 8 Hr24 Hr
0 50 100
% Injected Dose
0 50 100
% Injected Dose
ShK + Thapsigargin (48 h)
Thapsigargin (48 h)ShK (1h)
Thapsigargin (48 h) ShK (1h)Media (16 h)
μ μg/kg ShK-186
1 10 100
Dose: PL 10100 100 100 100 100 100
0/10/1 0/10 -1-2-3 -4
-10 -50510 15 20 2530 35 Download full-text
Every 2 days (100μg/kg)Every 3 days (100μg/kg)
day post onset
Daily 100 µg/kg
E2D 100 µg/kg
E3D 100 µg/kg