Kshitij A Patkar

Torrey Pines Institute for Molecular Studies, Port St. Lucie, Florida, United States

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Publications (8)41.19 Total impact

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    ABSTRACT: In the mouse 55°C warm-water tail-withdrawal assay, a single administration of nor-BNI (10 mg/kg, i.p.) antagonized kappa opioid receptor (KOR) agonist-induced antinociception up to 14 days, whereas naloxone (10 mg/kg, i.p.) mediated antagonism lasted less than a day. In saturation binding experiments, mouse brain membranes isolated and washed 1 or 7, but not 14 days after nor-BNI administration demonstrated a significant time dependent decrease in maximal KOR agonist [(3)H]U69,593 binding. To determine whether brain concentrations of nor-BNI were sufficient to explain the antagonism of KOR-mediated antinociception, mouse blood and perfused brain were harvested at time points ranging from 30 min to 21 days after a single administration and analyzed for the presence of nor-BNI using LC-MS/MS. Nor-BNI was detected in the perfused brain homogenate up to 21 days after administration (30 nmol, i.c.v. or 10 mg/kg, i.p.). Subsequent experiments in which nor-BNI was administered at doses estimated from the amounts detected in the brain homogenates isolated from pretreated mice over time demonstrated significant antagonism of U50,488 antinociception in a manner consistent with the magnitude of observed KOR antagonism. The dose (1.4 nmol) approximating the lowest amount of nor-BNI detected in brain on day 14 did not antagonize U50,488-induced antinociception, consistent with the absence of U50,488 antagonism observed in vivo at this time point after pre-treatment. Overall, the physical presence of nor-BNI in the mouse brain paralleled its in vivo pharmacological profile, suggesting physico-chemical and pharmacokinetic properties of nor-BNI may contribute to the prolonged KOR antagonism.
    Journal of Pharmacology and Experimental Therapeutics 07/2013; · 3.89 Impact Factor
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    ABSTRACT: BACKGROUND: Currently available therapies for Alzheimer's disease (AD) do not treat the underlying cause of AD. Anecdotal observations in nursing homes from multiple studies strongly suggest an inverse relationship between cancer and AD. Therefore, we reasoned that oncology drugs may be effective against AD. METHODS: We screened a library of all the FDA-approved oncology drugs and identified bis-chloroethylnitrosourea (BCNU or carmustine) as an effective amyloid beta (Abeta) reducing compound. To quantify Abeta levels, Chinese hamster ovary (CHO) cells stably expressing amyloid precursor protein 751WT (APP751WT) called 7WD10 cells were exposed to different concentrations of BCNU for 48 hours and the conditioned media were collected. To detect Abeta the conditioned media were immunoprecipitated with Ab9 antibody and subjected to immunoblot detection. Amyloid plaques were quantified in the brains of a mouse model of AD after chronic exposure to BCNU by thoflavin S staining. RESULTS: BCNU decreased normalized levels of Abeta starting from 5 microM by 39% (P <0.05), 10 microM by 51% (P <0.01) and 20 microM by 63% (P <0.01) in CHO cells compared to a control group treated with butyl amine, a structural derivative of BCNU. Interestingly, soluble amyloid precursor protein alpha (sAPPalpha) levels were increased to 167% (P <0.01) at 0.5 microM, 186% (P <0.05) at 1 microM, 204% (P <0.01) at 5 microM and 152% (P <0.05) at 10 microM compared to untreated cells. We also tested the effects of 12 structural derivatives of BCNU on Abeta levels, but none of them were as potent as BCNU. BCNU treatment at 5 microM led to an accumulation of immature APP at the cell surface resulting in an increased ratio of surface to total APP by 184% for immature APP, but no change in mature APP. It is also remarkable that BCNU reduced Abeta generation independent of secretases which were not altered up to 40microM. Interestingly, levels of transforming growth factor beta (TGFbeta) were increased at 5 microM (43%, P <0.05), 10 microM (73%, P <0.01) and 20 microM (92%, P <0.001). Most significantly, cell culture results were confirmed in vivo after chronic administration of BCNU at 0.5 mg/kg which led to the reduction of Abeta 40 by 75% and amyloid plaque burden by 81%. Conversely, the levels of sAPPalpha were increased by 45%. CONCLUSIONS: BCNU reduces Abeta generation and plaque burden at non-toxic concentrations possibly through altered intracellular trafficking and processing of APP. Taken together these data provided unequivocal evidence that BCNU is a potent secretase-sparing anti-Abeta drug. See related commentary article here http://www.biomedcentral.com/1741-7015/11/82.
    BMC Medicine 03/2013; 11(1):81. · 7.28 Impact Factor
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    ABSTRACT: BACKGROUND AND PURPOSE: Cyclic peptides are resistant to proteolytic cleavage, therefore potentially exhibiting activity after systemic administration. We hypothesized that the macrocyclic κ opioid receptor (KOR)-selective antagonist [D-Trp]CJ-15,208 would demonstrate antagonist activity after systemic, i.e., subcutaneous (s.c.) and oral (per os, p.o.), administration. EXPERIMENTAL APPROACH: C57BL/6J mice were pretreated with [D-Trp]CJ-15,208 s.c. or p.o. before administration of the KOR-selective agonist U50,488 and the determination of antinociception in the warm-water tail withdrawal assay. The locomotor activity of mice treated with [D-Trp]CJ-15,208 was determined by rotorod testing. Additional mice demonstrating cocaine-conditioned place preference (CPP) and subsequent extinction were pretreated daily with vehicle or [D-Trp]CJ-15,208 and then exposed to repeated forced-swim stress or a single additional session of cocaine place conditioning before re-determining place preference. KEY RESULTS: Pretreatment with [D-Trp]CJ-15,208 administered s.c. or p.o. dose-dependently antagonized the antinociception induced by intraperitoneal administration of U50,488 in mice tested in the warm water tail withdrawal assay for less than 12 and 6 h, respectively. [D-Trp]CJ-15,208 also produced modest (<25%), short duration antinociception mediated through KOR agonism. Orally administered [D-Trp]CJ-15,208 dose-dependently antagonized centrally administered U50,488-induced antinociception, and prevented stress-, but not cocaine-induced, reinstatement of extinguished cocaine-seeking behavior, consistent with its KOR antagonist activity, without affecting locomotor activity. CONCLUSIONS AND IMPLICATIONS: The macrocyclic tetrapeptide [D-Trp]CJ-15,208 is a short-duration κ opioid receptor antagonist with weak KOR agonist activity that is active after oral administration and demonstrates blood-brain barrier permeability. These data validate the use of systemically active peptides such as [D-Trp]CJ-15,208 as potentially useful therapeutics.
    British Journal of Pharmacology 02/2013; · 5.07 Impact Factor
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    Kshitij A Patkar, Thomas F Murray, Jane V Aldrich
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    ABSTRACT: Structural modifications affecting the efficacy of analogues of the endogenous opioid peptide dynorphin (Dyn) A have focused on the N-terminal "message" sequence based on the "message-address" concept. To test the hypothesis that changes in the C-terminal "address" domain could affect efficacy, modified amino acids and cyclic constraints were incorporated into this region of the partial agonist [N-benzylTyr(1)]Dyn A-(1-11). Modifications in the C-terminal domain of [N-benzylTyr(1)]Dyn A-(1-11)NH(2) resulted in increased kappa opioid receptor (KOR) affinity for all of the linear analogues but did not affect the efficacy of these peptides at KOR. Cyclization between positions 5 and 8 yielded [N-benzylTyr(1),cyclo(d-Asp(5),Dap(8))]Dyn A-(1-11)NH(2) (zyklophin, 13) ( J. Med. Chem. 2005 , 48 , 4500 - 4503 ) with high selectivity for KOR. In contrast to the linear peptides, this peptide exhibits negligible efficacy in the adenylyl cyclase (AC) assay and is a KOR antagonist. These data are consistent with our hypothesis that appropriate modifications in the "address" domain of Dyn A analogues may affect efficacy.
    Journal of Medicinal Chemistry 10/2009; 52(21):6814-21. · 5.61 Impact Factor
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    Jane V Aldrich, Kshitij A Patkar, Jay P McLaughlin
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    ABSTRACT: The cyclic peptide zyklophin {[N-benzylTyr(1),cyclo(D-Asp(5),Dap(8))-dynorphin A-(1-11)NH(2), Patkar KA, et al. (2005) J Med Chem 48: 4500-4503} is a selective peptide kappa opioid receptor (KOR) antagonist that shows activity following systemic administration. Systemic (1-3 mg/kg s.c.) as well as central (0.3-3 nmol intracerebroventricular, i.c.v.) administration of this peptide dose-dependently antagonizes the antinociception induced by the selective KOR agonist U50,488 in C57BL/6J mice tested in the 55 degrees C warm water tail withdrawal assay. Zyklophin administration had no effect on morphine- or SNC-80-mediated antinociception, suggesting that zyklophin selectively antagonizes KOR in vivo. Additionally, the antagonism of antinociception induced by centrally (i.c.v.) administered U50,488 following peripheral administration of zyklophin strongly suggests that the peptide crosses the blood-brain barrier to antagonize KOR in the CNS. Most importantly, the antagonist activity of zyklophin (3 mg/kg s.c.) lasts less than 12 h, which contrasts sharply with the exceptionally long duration of antagonism reported for the established small-molecule selective KOR antagonists such as nor-binaltorphimine (nor-BNI) that last weeks after a single administration. Systemically administered zyklophin (3 mg/kg s.c.) also prevented stress-induced reinstatement of cocaine-seeking behavior in a conditioned place preference assay. In conclusion, the peptide zyklophin is a KOR-selective antagonist that exhibits the desired shorter duration of action, and represents a significant advance in the development of KOR-selective antagonists.
    Proceedings of the National Academy of Sciences 10/2009; 106(43):18396-401. · 9.81 Impact Factor
  • Kshitij A Patkar, W Edward Highsmith, Jane V Aldrich
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    ABSTRACT: Herein, we describe a general strategy for the facile synthesis of a multifunctional amino acid derivative bearing both fluorescent and photolabile groups such as the lysine derivative NvocLys(CO(CH2)5NH-NBD)OCH2CN (1) that can be used as a biophysical tool for studying protein structure. The synthetic strategy involves functionalization of the amine groups while the amino acid is attached to a solid support, followed by esterification of the carboxylic acid in solution. The solid support protects the caboxylic acid, preventing a side reaction associated with the synthesis in solution and obviating the need for chromatographic purification of several intermediates. This synthetic strategy can be used for the preparation of a variety of amino acid derivatives with unusual alpha-amine and side chain functionalities.
    Amino Acids 04/2008; 36(2):203-7. · 3.91 Impact Factor
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    ABSTRACT: The cyclic dynorphin A analogue [N(alpha)-benzylTyr(1),cyclo(D-Asp(5),Dap(8))]dynorphin A-(1-11)NH(2) (Dap = 2,3-diaminopropionic acid) exhibits nanomolar affinity (30 nM) and high selectivity (K(i) ratio (kappa/mu/delta) = 1/194/330) for kappa-opioid receptors. This analogue antagonizes dynorphin A-(1-13)NH(2) at kappa-opioid receptors in the adenylyl cyclase assay (K(B) = 84 nM). This is the first dynorphin A-based antagonist with modifications in the C-terminal "address" domain that alter efficacy and thus represents a novel selective kappa-opioid receptor antagonist.
    Journal of Medicinal Chemistry 08/2005; 48(14):4500-3. · 5.61 Impact Factor
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Publication Stats

55 Citations
41.19 Total Impact Points

Institutions

  • 2013
    • Torrey Pines Institute for Molecular Studies
      Port St. Lucie, Florida, United States
  • 2008–2009
    • University of Kansas
      • Department of Medicinal Chemistry
      Lawrence, KS, United States
  • 2005
    • University of Maryland, Baltimore
      • Department of Pharmaceutical Sciences (PSC)
      Baltimore, MD, United States