Tiancheng Liu

Washington State University, Pullman, Washington, United States

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Publications (21)70.89 Total impact

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    ABSTRACT: Prostate-specific membrane antigen (PSMA) remains an important target for diagnostic and therapeutic application for human prostate cancer. Model cell lines have been recently developed to study canine prostate cancer but their PSMA expression and enzymatic activity have not been elucidated. The present study was focused on determining PSMA expression in these model canine cell lines and the use of fluorescent small-molecule enzyme inhibitors to detect canine PSMA expression by flow cytometry. Western blot and RT-PCR were used to determine the transcriptional and translational expression of PSMA on the canine cell lines Leo and Ace-1. An endpoint HPLC-based assay was used to monitor the enzymatic activity of canine PSMA and the potency of enzyme inhibitors. Flow cytometry was used to detect the PSMA expressed on Leo and Ace-1 cells using a fluorescently tagged PSMA enzyme inhibitor. Canine PSMA expression on the Leo cell line was confirmed by Western blot and RT-PCR, the enzyme activity, and flow cytometry. Kinetic parameters Km and Vmax of PSMA enzymatic activity for the synthetic substrate (PABGγG) were determined to be 393 nM and 220 pmol min(-1) mg protein(-1) , respectively. The inhibitor core 1 and fluorescent inhibitor 2 were found to be potent reversible inhibitors (IC50 = 13.2 and 1.6 nM, respectively) of PSMA expressed on the Leo cell line. Fluorescent labeling of Leo cells demonstrated that the fluorescent PSMA inhibitor 2 can be used for the detection of PSMA-positive canine prostate tumor cells. Expression of PSMA on Ace-1 was low and not detectable by flow cytometry. The results described herein have demonstrated that PSMA is expressed on canine prostate tumor cells and exhibits similar enzymatic characteristics as human PSMA. The findings show that the small molecule enzyme inhibitors currently being studied for use in diagnosis and therapy of human prostate cancer can also be extended to include canine prostate cancer. Importantly, the findings demonstrate that the potential of the inhibitors for use in diagnosis and therapy can be evaluated in an immunocompetent animal model that naturally develops prostate cancer before use in humans. Prostate. © 2014 Wiley Periodicals, Inc.
    The Prostate 01/2014; · 3.84 Impact Factor
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    ABSTRACT: Developing simple and effective approaches to detect tumor markers will be critical for early diagnosis or prognostic evaluation of prostate cancer treatment. Prostate‑specific membrane antigen (PSMA) has been validated as an important tumor marker for prostate cancer progression including angiogenesis and metastasis. As a type II membrane protein, PSMA can be constitutively internalized from the cell surface into endosomes. Early endosomes can fuse with multivesicular bodies (MVB) to form and secrete exosomes (40-100 nm) into the extracellular environment. Herein, we tested whether some of the endosomal PSMA could be transferred to exosomes as an extracellular resource for PSMA. Using PSMA-positive LNCaP cells, the secreted exosomes were collected and isolated from the cultured media. The vesicular structures of exosomes were identified by electron microscopy, and exosomal marker protein CD9 and tumor susceptibility gene (TSG 101) were confirmed by western blot analysis. Our present data demonstrate that PSMA can be enriched in exosomes, exhibiting a higher content of glycosylation and partial proteolysis in comparison to cellular PSMA. An in vitro enzyme assay further confirmed that exosomal PSMA retains functional enzymatic activity. Therefore, our data may suggest a new role for PSMA in prostate cancer progression, and provide opportunities for developing non-invasive approaches for diagnosis or prognosis of prostate cancer.
    International Journal of Oncology 01/2014; · 2.66 Impact Factor
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    ABSTRACT: Understanding the molecular mechanism of prostate cancer progression from androgen dependence to independence may lead to developing more effective treatments against prostate cancer. Herein, our previous in vitro model was employed to assess the effects of continuous androgen-deprivation on developing the metastatic phenotype from androgen-dependent prostate cancer cells (LNCaP). The results indicated that long-term androgen deprivation resulted in overexpression of calpain 2 and increased expression of filamin A (FlnA), but not for calpain 1. The enhanced activity of calpain 2 was confirmed by the accumulation of cleaved FlnA fragments, which could be effectively blocked by calpeptin (an inhibitor of calpain 2). Therefore, the combination of calpain 2 inhibitor and androgen deprivation may provide new therapeutic strategy for patients to prevent or postpone prostate cancer progression.
    International Journal of Oncology 11/2013; · 2.66 Impact Factor
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    ABSTRACT: Elucidating the role of androgen deprivation in the transition from androgen-dependence to independence may enable the development of more specific therapeutic strategies against prostate cancer. Our previous in vitro model was employed to further assess the effects of continuous androgen‑deprivation on prostate cancer cells (LNCaP) with respect to both androgen receptor (AR) and c-Met expression. The results indicated that long-term androgen deprivation resulted in a signaling pathway switch from AR to c-Met in androgen-sensitive cells, which was confirmed by immunofluorescence imaging and western blot analysis. This signaling pathway switch may be predictive of a more aggressive disease state following androgen deprivation therapy.
    International Journal of Oncology 07/2013; · 2.66 Impact Factor
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    ABSTRACT: Prostate-specific membrane antigen (PSMA) is a notable biomarker for diagnostic and therapeutic applications in prostate cancer. Gold nanoparticles (AuNPs) provide an attractive nanomaterial platform for combining a variety of targeting, imaging, and cytotoxic agents into a unified device for biomedical research. In this study, we present the generation and evaluation of the first AuNP system functionalized with a small molecule phosphoramidate peptidomimetic inhibitor for the targeted delivery to PSMA-expressing prostate cancer cells. The general approach involved the conjugation of streptavidin-coated AuNPs with a biotin-linked PSMA inhibitor (CTT54) to generate PSMA-targeted AuNPs. In vitro evaluations of these targeted AuNPs were conducted to determine PSMA-mediated and time-dependent binding to PSMA-positive LNCaP cells. The PSMA-targeted AuNPs exhibited significantly higher and selective binding to LNCaP cells compared to control non-targeted AuNPs, thus demonstrating the feasibility of this approach.
    Bioorganic & medicinal chemistry letters 11/2012; · 2.65 Impact Factor
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    ABSTRACT: Emergence of androgen-independent cancer cells during androgen deprivation therapy presents a significant challenge to successful treatment outcomes in prostate cancer. Elucidating the role of androgen deprivation in the transition from an androgen-dependent to an androgen-independent state may enable the development of more effective therapeutic strategies against prostate cancer. Herein, we describe an in vitro model for assessing the effects of continuous androgen-deprivation on prostate cancer cells (LNCaP) with respect to the expression of two prostate-specific markers: the androgen receptor (AR) and prostate-specific membrane antigen (PSMA). Compared with androgen-containing normal growth medium, androgen-deprived medium apparently induced the concomitant downregulation of AR and PSMA over time. Decreased protein levels were confirmed by fluorescence imaging, western blotting and enzymatic activity studies. In contrast to the current understanding of AR and PSMA in prostate cancer progression, our data demonstrated that androgen-deprivation induced a decrease in AR and PSMA levels in androgen-sensitive LNCaP cells, which may be associated with the development of more aggressive disease-state following androgen deprivation therapy.
    International Journal of Oncology 10/2012; · 2.66 Impact Factor
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    ABSTRACT: Prostate-specific membrane antigen (PSMA) remains an active target for imaging and therapeutic applications for prostate cancer. In the present study, an irreversible phosphoramidate inhibitor, CTT-54 (IC50 = 14 nM), has been modified to deliver 99mTc-(CO)3-DTPA as a SPECT imaging payload to PSMA+ cells in vivo and in vitro. Percent uptake, competitive binding, and internalization will evaluate the imaging agent in vitro. Preliminary biodistribution and imaging will be utilized for in vivo evaluation. In vitro studies demonstrate that the radiotracer 99mTc-(CO)3-DTPA-CTT-54 exhibits increasing cellular uptake in the PSMA+ LNCaP cells over time. More importantly, it was found that 99mTc-(CO)3-DTPA-CTT-54 is rapidly internalized into LNCaP cells, presumably through the PSMA enzyme-inhibitor complex. In a pilot biodistribution study, increasing accumulation of the radiotracer in LNCaP xenografts was observed from 2 to 4 hr and significant clearance from non-target tissues. While DTPA may not represent the ideal chelate structure for 99mTc(CO)3, the data provides proof-of-concept support for the development of a next-generation phosphoramidate-based PSMA inhibitor-conjugates for use as SPECT imaging agents.
    The Prostate 06/2012; 72(8):904-12. · 3.84 Impact Factor
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    ABSTRACT: Prostate-specific membrane antigen (PSMA), a type II membrane glycoprotein, its high expression is associated with prostate cancer progression, and has been becoming an active target for imaging or therapeutic applications for prostate cancer. On the other hand, streptavidin-biotin system has been successfully employed in pretargeting therapy towards multiple cancers. Herein, we describe the synthesis of bifunctional ligands (biotin-CTT54, biotin-PEG(4)-CTT54, and biotin-PEG(12)-CTT54) possessing two functional motifs separated by a length-varied polyethylene glycol (PEG) spacer: one (CTT54) binds tumor-marker PSMA and the other (biotin) binds streptavidin or avidin. All three compounds exhibited high potencies (IC(50) values: 1.21, 2.53, and 10nM, respectively) and irreversibility; but only biotin-PEG(12)-CTT54 demonstrated specifically labeling PSMA-positive prostate cancer cells in a two-step pretargeting procedure. Additionally, the pre-formulated complex between biotin-PEG(12)-CTT54 and Cy5-streptavidin displayed the improved inhibitory potency (IC(50)=1.86 nM) and irreversibility against PSMA and rapid uptake of streptavidin conjugate into PSMA-positive prostate cancer cells through PSMA-associated internalization. Together, all these results supported a proof-concept that combination of streptavidin and PSMA's biotinylated inhibitor may lead to development of a novel strategy of tumor-targeting imaging or drug delivery towards prostate cancer.
    Bioorganic & medicinal chemistry letters 04/2012; 22(12):3931-4. · 2.65 Impact Factor
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    ABSTRACT: BACKROUND: Prostate circulating tumor cells (PCTCs) in circulation are shed from either a primary tumor or metastases, which are directly responsible for most prostate cancer deaths. Quantifying exfoliated PCTCs may serve as an indicator for the clinical management of prostate cancer, isolating and removing of PCTCs could potentially reduce prostate cancer metastasis, and culturing and characterizing captured PCTCs could facilitate the development of personalized treatment options. Prostate-specific membrane antigen (PSMA) is an established biomarker for prostate cancer being strongly expressed on prostate tumor cells associated with high-grade primary, androgen independent, and metastatic tumors. Suspensions of PSMA+ (LNCaP) cells were pre-targeted with the irreversible PSMA inhibitor biotin-PEG(12)-CTT-54 to serve as a bait to capture PSMA+ cells using streptavidin-coated magnetic beads. Decreasing numbers of LNCaP cells were spiked into blood to determine the cell captured efficiency, recovery and viability. High selectivity, recovery, and viability were achieved for the capture of PSMA+ cells in both model experiments with mixtures of LNCaP cells and WBCs as well as blood samples spiked with LNCaP cells. As low as 10 cells were captured from 1 ml of blood with nearly 90% viability. More importantly, captured cells could be subsequently propagated in vitro. This methodology for the detection, isolation, and culture of PCTCs from peripheral blood can serve as an effective tool for the detection of metastatic prostate cancer, treatment monitoring, and the development of personalized therapy based on the responsiveness of PCTCs to chemotherapeutic strategies.
    The Prostate 04/2012; 72(14):1532-41. · 3.84 Impact Factor
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    ABSTRACT: Prostate-specific membrane antigen (PSMA), a type II transmembrane protein, has been becoming an active target for imaging and therapeutic applications for prostate cancer. Recently, the development of its various chemical inhibitor scaffolds has been explored to serve as carriers for therapeutic or diagnostic payloads targeted to PSMA-positive tumor cells. However, there have been few efforts to definitively determine the optimal length of linker between PSMA inhibitor cores and their payload molecules with regard to the affinity to PSMA and in vitro performance. In our present model study, three spacer-length varied fluorescent inhibitors (FAM-CTT-54, FAM-X-CTT-54 and FAM-PEG(8)-CTT-54) were synthesized, and further enzymatic inhibition studies displayed linker length-dependent changes in: inhibitory potency (IC(50)=0.41 nM, 0.35 nM, 1.93 nM), modes of binding (reversible, slowly reversible, irreversible), respectively. Furthermore, cell-labeling imaging revealed the spacer length-related change of fluorescence intensity (FAM-X-CTT-54>FAM-PEG(8)-CTT-54>FAM-CTT-54). These results suggest that selection of linkers and their lengths will be important considerations in the development of next-generation prostate tumor-targeted imaging probes and therapeutic agents that specifically home to PSMA on tumor cells.
    Bioorganic & medicinal chemistry letters 12/2011; 21(23):7013-6. · 2.65 Impact Factor
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    ABSTRACT: The proof of principle for high-resolution analysis of intact singly charged proteins of any size is presented. Singly charged protein ions were produced by electrospray ionization followed by surface-induced charge reduction at atmospheric pressure. The inlet and trapping system "stops" the forward momentum of the protein ions over a very broad range to be captured by the digitally produced electric fields of a large radius linear ion trap whereupon they are moved into a smaller radius linear ion trap and collected and concentrated in front of its exit end-cap electrode using digital waveform manipulation. The protein ions are then ejected on demand from the end of the small radius linear quadrupole in a tightly collimated ion beam with an instrumentally defined kinetic energy into the acceleration region of an orthogonal acceleration reflectron time-of-flight mass analyzer where their flight times were measured and detected with a Photonis BiPolar TOF detector. We present results that clearly prove that massive singly charged ions can yield high-resolution mass spectra with very low chemical noise and without loss of sensitivity with increasing mass across the entire spectrum. Analysis of noncovalently bound protein complexes was demonstrated with streptavidin-Cy5 bound with a biotinylated peptide mimic. Our results suggest proteins across the entire range can be directly quantified using our mass analysis technique. We present evidence that solvent molecules noncovalently adduct onto the proteins while yielding consistent flight time distributions. Finally, we provide a look into future that will result from the ability to rapidly measure and quantify protein distributions.
    Analytical Chemistry 11/2011; 83(24):9406-12. · 5.70 Impact Factor
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    ABSTRACT: Prostate-specific membrane antigen (PSMA), a well-known biomarker of prostate cancer, has also been found to be highly expressed in the neovasculature of multiple non-prostatic solid tumors. As a consequence, it has the potential to become a biomarker for tumor-associated vasculature. Herein, we describe an in vitro model for assessing PSMA expression associated with tube formation by primary human umbilical vein endothelial cells (HUVECs) cultured in Matrigel and induced by tumor-conditioned medium (TCM) derived from human breast cancer cells (MDA-MB-231). In contrast to vascular endothelial growth factor (VEGF)-containing endothelial cell medium, TCM induced higher expression of PSMA in HUVECs. The vessel-like tubes were detected by imaging with fluorescent PSMA inhibitors. Consequently, this in vitro model is expected to enable subsequent studies aimed at determining the role of PSMA in angiogenesis and factors that induce it.
    International Journal of Oncology 02/2011; 38(5):1349-55. · 2.66 Impact Factor
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    ABSTRACT: The enzyme-biomarker prostate-specific membrane antigen (PSMA) is an emerging target for imaging and therapeutic applications for prostate cancer. However, the use of PSMA for detecting circulating prostate tumor cells remains under-explored. The present study focuses on the specific labeling of PSMA+ prostate cancer cells with a fluorescent PSMA inhibitor and the quantitation of PSMA+ cells in blood by flow cytometry (FC) using a gating strategy to separate labeled PSMA+ cells from peripheral blood mononuclear cells. Suspensions of PSMA+ (LNCaP) and PSMA- (DU145) cells were incubated with the fluorescent PSMA inhibitor FAMX-CTT-54. Incubation parameters (time, temperature, and label concentration) were varied to optimize cell labeling. A gating protocol based on double fluorescent labeling of CD45 and PSMA was developed for the quantitiation of LNCaP cells in the presence of white blood cells from bovine blood. Nonfluorescent beads were added to the labeled cell mixture and served as internal standard for precise cellular quantification of LNCaP cells by flow cytometry. The fluorescent PSMA inhibitor FAMX-CTT-54 was specific for PSMA+ cells. The minimum time and concentration of FAMX-CTT-54 for effective labeling of PSMA+ cell suspensions at 37°C was 7.5 min and 35 nM, respectively; no labeling was observed on PSMA- cells. Co-incubation or pre-incubation of PSMA+ cells with the unlabeled PSMA inhibitor CTT-54 resulted in a concentration-dependent reduction in fluorescent labeling with FAMX-CTT-54 thereby confirming that the labeling was specific for PSMA. In blood samples in which LNCaP cells were added, an average of five cells were detected in a 115 µl sample of the most dilute sample examined (29 cells/ml); three cells were expected theoretically. The greater loss of labeling of PSMA+ cells with FAMX-CTT-54 when pre-incubated with CTT-54 is consistent with the irreversible mode of binding of CTT-54 to PSMA and subsequent internalization of the PSMA-inhibitor complex. The results suggest that fluorescent PSMA inhibitors can be utilized to effectively detect and quantify PSMA+ cells by FC. These results support the use of such compounds in the application of FC to detect, quantify, and characterize circulating prostate tumor cells.
    The Prostate 01/2011; 71(1):52-61. · 3.84 Impact Factor
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    ABSTRACT: Prostate-specific membrane antigen (PSMA) remains an active target for imaging and therapeutic applications for prostate cancer. Although radionuclide-based imaging is generally more sensitive and also has been deeply explored, near-infrared fluorescence imaging agents are simple to prepare and compatible with long-term storage conditions. In the present study, a near-infrared fluorescent imaging probe (Cy5.5-CTT-54.2) has been developed by chemical conjugation of Cy5.5N-hydroxysuccinimide ester (Cy5.5-NHS) with a potent PSMA inhibitor CTT-54.2 (IC(50)=144 nM). The probe displays a highly potency (IC(50)=0.55 nM) against PSMA and has demonstrated successful application for specifically labeling PSMA-positive prostate cancer cells in both two and three-dimensional cell culture conditions. These results suggest that the potent, near-infrared Cy5.5-PSMA inhibitor conjugate may be useful for the detection of prostate tumor cells by optical in vivo imaging.
    Bioorganic & medicinal chemistry letters 09/2010; 20(23):7124-6. · 2.65 Impact Factor
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    Tiancheng Liu, Lisa Y Wu, Clifford E Berkman
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    ABSTRACT: Prostate-specific membrane antigen (PSMA), an established enzyme-biomarker for prostate cancer, has attracted considerable attention as a target for imaging and therapeutic applications. We aimed to determine the effects of PSMA-targeted photodynamic therapy (PDT) on cytoskeletal networks in prostate cancer cells. PSMA-targeted PDT resulted in rapid disruption of microtubules (alpha-/beta-tubulin), microfilaments (actin), and intermediate filaments (cytokeratin 8/18) in the cytoplasm of LNCaP cells. The collapse of cytoplasmic microtubules and the later nuclear translocation of alpha-/beta-tubulin were the most dramatic alternation. It is likely that these early changes of cytoskeletal networks are partly involved in the initiation of cell death.
    Cancer letters 05/2010; 296(1):106-12. · 5.02 Impact Factor
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    ABSTRACT: The limitation of specific delivery of photosensitizers to tumor sites, represents a significant shortcoming of photodynamic therapy (PDT) application at present. Prostate-specific membrane antigen (PSMA), a validated biomarker for prostate cancer, has attracted considerable attention as a target for imaging and therapeutic applications for prostate cancer. The present study focuses on the investigation of a PSMA inhibitor-conjugate of pyropheophorbide-a (Ppa-conjugate 2.1) for a targeted PDT application and the mechanism of its mediated-cell death in prostate cancer cells. Multiple fluorescence labeling methods were employed to monitor PDT-treated prostate cancer cells by confocal laser scanning microscopy. Our results demonstrate that Ppa-conjugate 2.1 mediated apoptosis is specific to PSMA+ (positive) LNCaP cells, but not PSMA- (negative) PC-3 cells. Furthermore, these results indicate that following PDT, the activation of caspase-8, -3, -9, cleavage of poly(ADP-ribose) polymerase (PARP) and DNA fragmentation is sequential. The appearance of cleaved beta-actin further supported involvement of caspase-3. Specific caspase inhibitor blocking studies reveal that the caspase-8/-3 cascade pathway plays a key role in apoptosis of LNCaP cells induced by Ppa-conjugate 2.1. The demonstrated selective targeting and efficacy of this agent suggests that targeted PDT could serve as an alternative treatment option for prostate cancer.
    International Journal of Oncology 04/2010; 36(4):777-84. · 2.66 Impact Factor
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    ABSTRACT: Prostate-specific membrane antigen (PSMA) is a transmembrane protein commonly found on the surface of late-stage and metastatic prostate cancer and a well-known imaging biomarker for staging and monitoring therapy. Although (111)In-labeled capropmab pendetide is the only approved agent available for PSMA imaging, its clinical use is limited because of its slow distribution and clearance that leads to challenging image interpretation. A small-molecule approach using radiolabeled urea-based PSMA inhibitors as imaging agents has shown promise for prostate cancer imaging. The motivation of this work is to explore phosphoramidates as a new class of potent PSMA inhibitors to develop more effective prostate cancer imaging agents with improved specificity and clearance properties. N-succinimidyl-4-(18)F-fluorobenzoate ((18)F-SFB) was conjugated to S-2-((2-(S-4-amino-4-carboxybutanamido)-S-2-carboxyethoxy)hydroxyphosphorylamino)-pentanedioic acid (Phosphoramidate (1)), yielding S-2-((2-(S-4-(4-(18)F-fluorobenzamido)-4-carboxybutanamido)-S-2-carboxyethoxy)hydroxyphosphorylamino)-pentanedioic acid (3). In vivo studies were conducted in mice bearing either LNCaP (PSMA-positive) or PC-3 (PSMA-negative) tumors. PET images were acquired at 1 and 2 h with or without a preinjection of a nonradioactive version of the fluorophosphoramidate. Tissue distribution studies were performed at the end of the 2 h imaging sessions. Phosphoramidate (1) and its fluorobenzamido conjugate (2) were potent inhibitors of PSMA (inhibitory concentration of 50% [IC(50)], 14 and 0.68 nM, respectively). PSMA-mediated tumor accumulation was noted in the LNCaP versus the PC-3 tumor xenografts. The LNCaP tumor uptake was also blocked by the administration of nonradioactive (2) prior to imaging studies. With the exception of the kidneys, tumor-to-tissue and tumor-to-blood ratios were greater than 5:1 at 2 h. The strong kidney uptake may be due to the known PSMA expression in the mouse kidney, because significant reduction (>6-fold) in kidney activity was seen in mice injected with (2). (18)F-labeled phosphoramidate (3) is a representative of a new class of PSMA targeting peptidomimetic molecules that shows great promise as imaging agents for detecting PSMA+ prostate tumors.
    Journal of Nuclear Medicine 11/2009; 50(12):2042-8. · 5.77 Impact Factor
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    ABSTRACT: The lack of specific delivery of photosensitizers (PSs), represents a significant limitation of photodynamic therapy (PDT) of cancer. The biomarker prostate-specific membrane antigen (PSMA) has attracted considerable attention as a target for imaging and therapeutic applications for prostate cancer. Although recent efforts have been made to conjugate inhibitors of PSMA with imaging agents, there have been no reports on PS-conjugated PSMA inhibitors for targeted PDT of prostate cancer. The present study focuses on the use of a PSMA inhibitor-conjugate of pyropheophorbide-a (Ppa-conjugate 2) for targeted PDT to achieve apoptosis in PSMA+ LNCaP cells. Confocal laser scanning microscopy with a combination of nuclear staining and immunofluorescence methods were employed to monitor the specific imaging and PDT-mediated apoptotic effects on PSMA-positive LNCaP and PSMA-negative (PC-3) cells. Our results demonstrated that PDT-mediated effects by Ppa-conjugate 2 were specific to LNCaP cells, but not PC-3 cells. Cell permeability was detected as early as 2 hr by HOE33342/PI double staining, becoming more intense by 4 hr. Evidence for the apoptotic caspase cascade being activated was based on the appearance of poly-ADP-ribose polymerase (PARP) p85 fragment. Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay detected DNA fragmentation 16 hr post-PDT, confirming apoptotic events. Cell permeability by HOE33342/PI double staining as well as PARP p85 fragment and TUNEL assays confirm cellular apoptosis in PSMA+ cells when treated with PS-inhibitor conjugate 2 and subsequently irradiated. It is expected that the PSMA targeting small-molecule of this conjugate can serve as a delivery vehicle for PDT and other therapeutic applications for prostate cancer.
    The Prostate 02/2009; 69(6):585-94. · 3.84 Impact Factor
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    ABSTRACT: The mode of inhibition for phosphoramidate peptidomimetic inhibitors of prostate-specific membrane antigen was determined by inhibition reversibility experiments. The results revealed that these inhibitors can be classified into three types: pseudoirreversible (compounds 1-3), moderately reversible (compounds 4-9), and rapidly reversible inhibitors (compounds 10 and 11). Representative compounds from each class were further evaluated for their ability to induce cellular internalization of PSMA. Results from these experiments revealed that the pseudoirreversible inhibitor 1 induced the greatest PSMA internalization. The discovery of pseudoirreversible PSMA inhibitors is expected to provide a new avenue of investigation and therapeutic applications for prostate cancer and neurological disorders.
    Biochemistry 12/2008; 47(48):12658-60. · 3.38 Impact Factor
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    ABSTRACT: [corrected] Prostate-specific membrane antigen (PSMA) remains an attractive target for imaging and therapeutic applications for prostate cancer. Recent efforts have been made to conjugate inhibitors of PSMA with imaging agents. Compared to antibodies, small-molecule inhibitors of PSMA possess apparent advantages for in vivo applications. To date, there are no reports on the cellular fate of such constructs once bound the extracellular domain of PSMA. The present study was focused on precisely defining the binding specificity, time-dependent internalization, cellular localization, and retention of inhibitor conjugates targeted to PSMA on LNCaP cells. A novel fluorescent inhibitor was prepared as a model to examine these processes. Fluorescence microscopy of LNCaP and PC-3 cell lines was used to monitor the specificity, time-dependent internalization, cellular localization, and retention of a fluorescent PSMA inhibitor. Fluorescent inhibitor 2 was found to be a potent inhibitor (IC50 = 0.35 nM) of purified PSMA. Its high affinity for PSMA on living cells was confirmed by antibody blocking and competitive binding experiments. Specificity for LNCaP cells was demonstrated as no labeling by 2 was observed for negative control PC-3 cells. Internalization of 2 by viable LNCaP cells was detected after 30 min incubation at 37 degrees C, followed by accumulation in the perinuclear endosomes. It was noted that internalized fluorescent inhibitor can be retained within endosomes for up to 150 min without loss of signal. Our results suggest that potent, small-molecule inhibitors of PSMA can be utilized as carriers for targeted delivery for prostate cancer for future imaging and therapeutic applications.
    The Prostate 07/2008; 68(9):955-64. · 3.84 Impact Factor

Publication Stats

208 Citations
70.89 Total Impact Points

Institutions

  • 2008–2014
    • Washington State University
      • Department of Chemistry
      Pullman, Washington, United States
  • 2006
    • San Francisco State University
      • Department of Chemistry and Biochemistry
      San Francisco, CA, United States