Stephen T Pisle

Epidithiodiketopiperazines (ETPs) exhibit in vitro antiangiogenic and in vivo antitumor activity by disrupting the HIF-1α/p300 complex in a preclinical model of prostate cancer

The downstream targets of hypoxia inducible factor-1 alpha (HIF-1α) play an important role in tumor progression and angiogenesis. Therefore, inhibition of HIF-mediated transcription has potential in the treatment of cancer. One attractive strategy for inhibiting HIF activity is the disruption of the HIF-1α/p300 complex, as p300 is a crucial coactivator of hypoxia-inducible transcription. Several members of the epidithiodiketopiperazine (ETP) family of natural products have been shown to disrupt the HIF-1α/p300 complex in vitro; namely, gliotoxin, chaetocin, and chetomin. Here, we further characterized the molecular mechanisms underlying the antiangiogenic and antitumor effects of these ETPs using a preclinical model of prostate cancer. In the rat aortic ring angiogenesis assay, gliotoxin, chaetocin, and chetomin significantly inhibited microvessel outgrowth at a GI50 of 151, 8, and 20 nM, respectively. In vitro co-immunoprecipitation studies in prostate cancer cell extracts demonstrated that these compounds disrupted the HIF-1α/p300 complex. The downstream effects of inhibiting the HIF-1α/p300 interaction were evaluated by determining HIF-1α target gene expression at the mRNA and protein levels. Dose-dependent decreases in levels of secreted VEGF were detected by ELISA in the culture media of treated cells, and the subsequent downregulation of VEGFA, LDHA, and ENO1 HIF-1α target genes were confirmed by semi-quantitative real-time PCR. Finally, treatment with ETPs in mice bearing prostate tumor xenografts resulted in significant inhibition of tumor growth. These results suggest that directly targeting the HIF-1α/p300 complex with ETPs may be an effective approach for inhibiting angiogenesis and tumor growth.

Bioluminescent imaging study: FAK inhibitor, PF-562,271, preclinical study in PC3M-luc-C6 local implant and metastasis xenograft models

Focal adhesion kinase (FAK) is essential in regulating integrin signaling pathways responsible for cell survival and proliferation, as well as motility, making FAK a distinctive target in the field of anticancer drug development, especially with regards to metastatic disease.1 Our objective was to demonstrate tumor growth inhibition by PF-562,271, a selective inhibitor of FAK and FAK2, or Pyk2,2 in mouse xenograft models, both subcutaneous and metastatic, employing the human prostate cancer cell line PC3M-luc-C6, a modified PC3M cell line that expresses luciferase. After two weeks of treatment with PF-562,271, 25 mg/kg PO BID 5x/wk, the subcutaneous model showed a 62 % tumor growth inhibition compared to control based on tumor measurements (p < 0.05), with a 88% vs. a 490% increase in bioluminescent signal for treatment and control respectively (p < 0.05). In the metastasis model, the percent change from baseline, after 18 days of treatment, of the treatment group was 2,854% vs. 14,190% for the vehicle (p < 0.01). These results show that PF-562,271 has a potent effect on metastatic prostate cancer growth in vivo.

Activity of VT-464, a selective CYP17 lyase inhibitor, in the LNCaP prostate cancer xenograft model.

64 Background: With the recent FDA approval of abiraterone acetate, CYP17 (17α hydroxylase/C17, 20-lyase) has become a proven target for the treatment of castration- resistant prostate cancer. Inhibition of CYP17-lyase causes a decrease in circulating androgens, severely hampering activation of the androgen receptor signaling pathway that prostate cancer relies on for proliferation. However, inhibition of CYP17-hydroxylase, a second enzymatic activity of CYP17, leads to an increase in upstream steroids that can cause mineralocorticoid excess syndrome as well as a decrease in cortisol production. VT-464 is a novel, selective CYP17 lyase inhibitor with decreased activity against CYP17 hydroxylase. The study objectives were to observe the effects of VT-464 in a prostate cancer xenograft model and to compare its activity to abiraterone acetate and surgical castration. METHODS SCID mice were implanted subcutaneously with LNCaP cells. When tumors reached 100mm3, mice were randomized to receive vehicle (0.5% CMC in saline, 5ml/kg), or VT-464 at 15, 50, or 100mg/kg p.o. bid. A second cohort of LNCaP tumor-bearing mice received vehicle, surgical castration, or VT-464 or abiraterone acetate at 100mg/kg p.o. bid for 28 days. RESULTS In the LNCaP xenograft model, percent growth inhibition (± S.E.) of 9.6 (±15.6), 38.5(±12.4), and 73.9 (±13.2) was observed on day 21 of treatment for the VT-464 doses of 15, 50, and 100 mg/kg, respectively. VT-464 -treated (100mg/kg) mice had a significantly reduced tumor volume ratio (V/V0) on day 28 compared to control and abiraterone acetate (p<0.05, p<0.01, respectively). Reduction in tumor volume ratios were similar between VT-464-treated (100 mg/kg) and castrate animals. CONCLUSIONS VT-464 exhibited dose-dependent growth inhibition with significantly reduced tumor growth at the highest dose compared to abiraterone acetate. The reduction in tumor growth in VT-464-treated animals was similar to that of castrate animals. These preclinical results show promising activity of VT-464 in the treatment of prostate cancer.

Androgen receptor and HIF-1α interaction in prostate cancer.

197 Background: Prostate cancer is the most common noncutaneous cancer among men in the United States, and its progression is largely controlled by the androgen receptor (AR). Androgen deprivation therapy (ADT) is an initially effective treatment for prostate cancer, but most tumors eventually become castrate resistant. Tumor hypoxia also appears to be associated with a poor prognosis in prostate cancer. HIF-1a regulates the transcription of genes that allow tumor survival and growth in low oxygen conditions. Our laboratory has data showing that in response to castration and anti-androgen therapy in mice, there was a strong transcriptional relationship between HIF-1a and AR, as measured by quantitative RT-PCR, suggesting an interaction between the two proteins. Thus, the purpose of this study was to determine if there is a molecular interaction between HIF-1a and AR in prostate cancer cells. METHODS We used Western blot analysis to examine the expression levels of HIF-1a and AR in LNCaP prostate cancer cells to determine if they are upregulated together at the protein level. Four experimental conditions were tested: control (no treatment), DHT for induction of AR expression, CoCl2 for induction of HIF-1a, and a combination treatment of DHT and CoCl2. Immunoprecipitation experiments were carried out to determine if there is an association between HIF-1a and AR. In addition, cells were fractionated into nuclear and cellular cells extracts, followed by Western blot analysis to determine where in the cells this interaction occurs. RESULTS Western blot analysis of cell lysates showed synergistic upregulation of both HIF-1a and AR expression only under combined CoCl2 and DHT treatment conditions. In addition, immunoprecipitation experiments showed that HIF-1a and AR exist in a complex with one another, and fractionation experiments indicated this complex occurs in the nucleus. CONCLUSIONS Our results demonstrate that HIF-1a and AR associate with one another in cells. Binding assays are in progress to determine the nature of this interaction. In addition, we are examining the cellular consequences of this protein interaction, as it is possible that upregulation of HIF-1a in response to low androgen contributes to the development of tumor resistance to ADT.

Abstract 2331: Select epidithiodiketopiperazine (ETP) compounds disrupt the HIF-1α/p300 interaction and HIF-mediated transcription

As solid tumors grow, regions in the tumor become hypoxic because of increased metabolism, heterogeneous and abnormal vasculature delivering oxygen within the tumor, and greater size. In order for the tumor to continue to grow, it depends on survival mechanisms to overcome this hypoxic state, including up-regulation in glycolysis, invasion and metastasis, and angiogenesis, or the growth of new blood vessels. The hypoxia-inducible factor (HIF) transcription factor complex is a major mediator of the cell9s response to a hypoxic state and a tumor9s survival mechanism under hypoxia. The complex is composed of the hypoxia-dependent HIF-1α subunit and a constitutively expressed HIF-1α subunit, and it requires the co-activator protein p300 to function. In the presence of oxygen, HIF-1α is rapidly degraded. Under hypoxia, HIF-1α forms a complex with HIF-1α and p300 in the nucleus to up-regulate transcription of pro-survival and angiogenic genes. Targeting this transcription factor complex in tumors could circumvent the tumor9s hypoxia survival mechanism and lead to growth arrest and cell death. The compounds chetomin, chaetocin, and gliotoxin, members of the epidithiodiketopiperazine (ETP) family of fungal metabolites, have been shown to disrupt the HIF-1α/p300 interaction in an over-expression system. In the following experiments, we sought to validate the disruption of the HIF-1α /p300 transcription factor complex in cells, and to determine the associated downstream cellular effects. By co-immunoprecipitation of the complex from prostate cancer cells, we were able to show that treatment with those select ETPs under hypoxic conditions disrupted the HIF-1α/p300 complex. We performed an enzyme-linked immunosorbent assay (ELISA) to determine the effect of ETPs on levels of secreted vascular endothelial growth factor (VEGF), a major target of HIF transcription. We observed a decrease in VEGF concentration that correlated with ETP treatment under hypoxia. Quantitative real-time polymerase chain reaction (qRT-PCR) was performed to examine the transcription levels of other HIF target genes to validate that disruption of the HIF-1α/p300 complex by select ETP treatments indeed affects HIF-mediated transcription. In order to determine the antiangiogenic effects of these agents in vivo, ongoing animal studies in our lab are testing the efficacy of these ETPs in reducing tumor growth and determining feasibility of pre-clinical development. Targeting the HIF complex could circumvent a tumor9s survival mechanism under hypoxia, and would be a new treatment strategy in solid tumors. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2331. doi:1538-7445.AM2012-2331

Abstract B28: Organic anion transporting polypeptide 1B3 as a novel biomarker for hypoxia in prostate cancer.

The organic anion transporting polypeptide 1B3 (OATP1B3) is aberrantly expressed in prostate cancer. We showed that OATP1B3 expression correlated to Gleason score in primary prostate cancer samples. As a transporter, OATP1B3 functions to influx both endogenous small molecules and xenobiotics. We also demonstrated that decreased survival and decreased progression in patients with prostate cancer was associated with a polymorphism in SLCO1B3, the gene encoding OATP1B3. However, OATP1B3 has not been validated as a clinical biomarker and the cause of expression in cancer is unknown. The purpose of this study was to identify a molecular regulation that explains OATP1B3 expression in cancer. In this study, we show that hypoxia increases the transcriptional and translational expression of OATP1B3 in cancer, that hypoxia-inducible factor 1-alpha (HIF1-alpha) binds putative hypoxia response elements in the SLCO1B3 promoter region by chromatin immunoprecipitation, and show co-localization of hypoxia and OATP1B3 by immunohistochemistry in clinical tissue samples. Additionally, cooperation between androgen- and hypoxia-signaling pathways explains the increased expression of OATP1B3 in prostate cancer xenografts under castration conditions. These data provide a foundation for the use of OATP1B3 as a biomarker of cancerous disease. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr B28.

Abstract 3095: The molecular, cellular, and physiological consequences of disrupting the HIF-1α interaction

Many cancers contain regions of hypoxia due to rapid cell proliferation and the presence of blood vessels within the tumor that are structurally and functionally abnormal, resulting in the heterogeneity of blood flow. This state of hypoxia is associated with increased risk of treatment failure, metastasis and patient mortality. A principal mechanism by which cancer cells adapt to the hypoxic microenvironment is through the activity of hypoxia-inducible factor 1 (HIF-1), a heterodimeric transcription factor composed of an O2-regulated HIF-1α subunit that dimerizes with a constitutively expressed HIF-1β subunit. HIF-1α expression under hypoxic conditions regulates hundreds of genes including those that play key roles in invasion/metastasis, angiogenesis, tumor cell immortalization, and resistance to chemotherapy and radiation. Therefore, the inhibition of transcription driven by HIF has the potential for cancer treatment. One way to reduce the activity of this protein is by disrupting the complex that HIF forms with p300, an essential transcriptional coactivator. Previous data from our laboratory showed that several members of the epidithiodiketopiperazine (ETP) family of natural products are able to block the interaction between HIF-1α and p300. Here, we extend these studies by examining the comprehensive effect that select ETPs have on the disruption of the HIF/p300 complex at the molecular, cellular, and physiological levels. We began our studies by performing a series of rat aortic ring assays to determine the antiangiogenic effect of selected ETPs, namely chetomin, chaetocin, and gliotoxin. Chetomin and chaetocin concentrations of 50 nM inhibited approximately 90% of outgrowth, while 500 nM of gliotoxin was needed to achieve a similar effect; these compounds had GI50 of 22, 11, and 175 nM, respectively. In ongoing work, we hope to determine if the antiangiogenic effects that were observed in our rat aortic ring assays, are due to disruption of the HIF/p300 complex. To this end we are immunoprecipitating the complex from cells in the absence or presence of the aforementioned ETPs. The molecular consequences of blocking the HIF/p300 interaction will be assayed by qRT-PCR for hypoxia-regulated genes such as VEGF and GLUT1; cell proliferation and migration assays will also be performed to monitor cellular effects. Together, these results will be key in determining the feasibility of targeting this interaction for cancer therapeutics. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3095. doi:10.1158/1538-7445.AM2011-3095

Antiandrogens in the 21st century.

Prostate cancer (PCa) is the second most common cause of cancer-related death among men, with around 218,000 new cases annually and 27,000 deaths. Most prostate cancer is hormone dependent and is treated with androgen deprivation therapy (ADT). When combined with an antiandrogen this combination results in complete androgen blockade (CAB). If the disease progresses to castration-resistant prostate cancer (CRPC) CAB is no longer effective; this failure of therapy is commonly associated with increased levels of AR expression, through various mechanisms, which have been shown in mouse xenograft models to be necessary and sufficient to confer resistance to antiandrogen therapy. Tran and Ouk et al. have recently published a paper characterizing two novel antiandrogens, RD162 and MDV3100, which retain activity even under increased androgen expression that is seen in most CRPC. RD162 and MDV3100 suppress growth of PCa cell lines in vitro and in vivo, with a decrease in tumor volume compared to bicalutamide in an AR overexpressing cell line. A benefit was also seen with an increase in median times to progression of 151 days for RD162 compared to bicalutamide. In an in vitro experiment employing the LNCaP/AR cell line, induction of PSA and TMPRSS2 was only seen with bicalutamide treatment.