Kelie M. Reece

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.

The ERCC1 N118N polymorphism does not change cellular ERCC1 protein expression or platinum sensitivity

Genetic polymorphisms in ERCC1 are thought to contribute to altered sensitivity to platinum-based chemotherapy. Although ERCC1 N118N (500 C>T, rs11615) is the most studied polymorphism, the impact of this polymorphism on platinum-based chemotherapy remains unclear. This is the first study in which the functional impact of ERCC1 N118N on gene expression and platinum sensitivity was explored. The aim of this study is to investigate if the reduced codon usage frequency of AAT, which contains the variant allele of the silent mutation, has functional impact on ERCC1 in a well-controlled biological system. Specifically, the ERCC1 cDNA clone with either the C or T allele was introduced into an ERCC1 deficient cell line, UV20, and assayed for the effect of the two alleles on ERCC1 transcription, translation and platinum sensitivity. Both ERCC1 mRNA and protein expression levels increased upon cisplatin treatment, peaking at 4h post-treatment, however there were no differences between the two alleles (p>0.05). Cells complemented with ERCC1 showed significantly higher survival proportion than the parental cell line following platinum exposure (p<0.0001), although no differences were observed between the cells transfected with the wild type or the polymorphic allele. These data suggest that N118N itself is not related to the phenotypic differences in ERCC1 expression or function, but rather this polymorphism may be linked to other causative variants or haplotypes.

Dual Targeting of the Androgen Receptor and Hypoxia-Inducible Factor 1α Pathways Synergistically Inhibits Castration-Resistant Prostate Cancer Cells

Enzalutamide is a potent second-generation androgen receptor (AR) antagonist with activity in metastatic castrate-resistant prostate cancer (CRPC). Although enzalutamide is initially effective, disease progression inevitably ensues with the emergence of resistance. Intratumoral hypoxia is also associated with CRPC progression and treatment resistance. Given that both AR and hypoxia inducible factor-1 α (HIF-1α) are key regulators of these processes, dual targeting of both signaling axes represents an attractive therapeutic approach. Crosstalk of the AR and HIF-1α signaling pathways were examined in prostate cancer cell lines (LNCaP, 22Rv1) with assays measuring the effect of androgen and hypoxia on AR-dependent and hypoxia-inducible gene transcription, protein expression, cell proliferation, and apoptosis. HIF-1α inhibition was achieved by siRNA silencing HIF-1α or via chetomin, a disruptor of HIF-1α-p300 interactions. In prostate cancer cells, the gene expression of AR targets (KLK3, FKBP5, TMPRSS2) was repressed by HIF-signaling; conversely, specific HIF-1α target expression was induced by dihydrotestosterone-mediated AR signaling. Treatment of CRPC cells with enzalutamide or HIF-1α inhibition attenuated AR-regulated and HIF-1α–mediated gene transcription. The combination of enzalutamide and HIF-1α inhibition was more effective than either treatment alone. Similarly, the combination also reduced vascular endothelial growth factor protein levels. HIF-1α siRNA synergistically enhanced the inhibitory effect of enzalutamide on cell growth in LNCaP and enzalutamide-resistant 22Rv1 cells via increased enzalutamide-induced apoptosis. In conclusion, the combination of enzalutamide with HIF-1α inhibition resulted in synergistic inhibition of AR-dependent and gene-specific HIF-dependent expression and prostate cancer cell growth.

Inhibition of the HIF1α-p300 interaction by quinone- and indandione-mediated ejection of structural Zn(II).

Protein-protein interactions between the hypoxia inducible factor (HIF) and the transcriptional coactivators p300/CBP are potential cancer targets due to their role in the hypoxic response. A natural product based screen led to the identification of indandione and benzoquinone derivatives that reduce the tight interaction between a HIF-1α fragment and the CH1 domain of p300. The indandione derivatives were shown to fragment to give ninhydrin, which was identified as the active species. Both the naphthoquinones and ninhydrin were observed to induce Zn(II) ejection from p300 and the catalytic domain of the histone demethylase KDM4A. Together with previous reports on the effects of related compounds on HIF-1α and other systems, the results suggest that care should be taken in interpreting biological results obtained with highly electrophilic/thiol modifying compounds.

Contribution of the OATP1B Subfamily to Cancer Biology and Treatment

The organic anion transporter 1B (OATP1B) subfamily consists of OATP1B1 and OATP1B3. 1 These transporters have generally been considered liver‐specific; however, recent evidence demonstrates that they are also expressed in extrahepatic tissues and in some tumors. This review discusses the potential influence of extrahepatic OATP1B expression on homeostasis and pathophysiology and its implications for pharmacotherapy in general.

A novel regulator (USP10) of p53: Implications for tumor suppression and therapeutic targeting

p53 is a tumor suppressor protein that plays a central role in oncogenesis by regulating cell fate after cellular stress and repressing the proliferation of damaged cells.1 The importance of p53 in preventing tumor development is highlighted by the fact that the p53 pathway is mutated in most types of human cancers, thus making it a desirable target for cancer therapeutics.2,3 p53 promotes tumor suppression through its ability to function as a sequence-specific transcription factor that induces the expression of genes involved in a variety of cellular functions including cell growth arrest, apoptosis, DNA repair, and cell senescence.4,2,1

Are race-specific ERCC1 haplotypes in melanoma cases versus controls related to the predictive and prognostic value of ERCC1 N118N?

Objectives Although it does not alter the ERCC1 phenotype, the ERCC1 500C>T (rs11615) polymorphism has undergone a myriad of investigations into its role as a marker for nucleotide excision repair (NER) function in different races, diseases and treatment outcomes. The goal of our study was to test the hypothesis that 500C>T is in linkage disequilibrium (LD) with causative alleles, and that these haplotypes are more frequent in Caucasians with melanoma than in healthy Caucasians or African Americans. Design In this case–control study, we selected race-specific ERCC1 single-nucleotide polymorphism (SNPs), conducted LD analysis with ERCC1 500C>T and compared the frequency of ERCC1 diplotypes in Caucasians with melanoma (n=165), healthy Caucasians (n=150) and healthy African Americans (n=159). The haplotype was further studied using a fusion gene containing multiple ERCC1 SNPs. Setting Large cancer institute in the USA. Participants A total of 165 Caucasian melanoma patients, 159 healthy Caucasian controls and 159 African American healthy controls. Men and women were enrolled in the clinical trial; however, since the screening trial included prostate cancer screening in addition to screening for other cancers, only male controls were available. Outcome measures The outcome measures were melanoma risk in Caucasians, and LD between ERCC1 SNP, N118N and other race-specific allelic variants. Results When compared to ERCC1 500C>T alone, a race-specific three-SNP variant haplotype in ERCC1 (comprised of rs11615, rs3212950 and rs3212948) was even more frequent in Caucasians with melanoma than in healthy Caucasians (p=0.0034) or African Americans (p<0.0001). A plasmid containing the variant haplotype was not differentially expressed. Conclusions We demonstrate that ERCC1 500C>T participates in a previously characterised cancer-risk haplotype found more frequently in Caucasians, while LD is weak in African Americans; this haplotype appears to also be related to melanoma. It is therefore likely that ERCC1 500C>T is only a valid NER, disease or treatment outcome marker in Caucasians.

Differential Expression of OATP1B3 Mediates Unconjugated Testosterone Influx

Castration-resistant prostate cancer (CRPC) has greater intratumoral testosterone concentrations than similar tumors from eugonadal men; simple diffusion does not account for this observation. This study was undertaken to ascertain the androgen uptake kinetics, functional, and clinical relevance of de novo expression of the steroid hormone transporter OATP1B3 (SLCO1B3). Experiments testing the cellular uptake of androgens suggest that testosterone is an excellent substrate of OATP1B3 (Km = 23.2 μmol/L; Vmax = 321.6 pmol/mg/minute), and cells expressing a doxycycline-inducible SLCO1B3 construct had greater uptake of a clinically relevant concentration of 3H-testosterone (50 nmol/L; 1.6-fold, P = 0.0027). When compared with Slco1b2 (−/−) mice, Slco1b2 (−/−)/hSLCO1B3 knockins had greater hepatic uptake (15% greater AUC, P = 0.0040) and lower plasma exposure to 3H-testosterone (17% lower AUC, P = 0.0030). Of 82 transporters genes, SLCO1B3 is the second-most differentially expressed transporter in CRPC cell lines (116-fold vs. androgen-sensitive cells), with a differentially spliced cancer-type ct-SLCO1B3 making up the majority of SLCO1B3 expression. Overexpression of SLCO1B3 in androgen-responsive cells results in 1.5- to 2-fold greater testosterone uptake, whereas siRNA knockdown of SLCO1B3 in CRPC cells did not change intracellular testosterone concentration. Primary human prostate tumors express SLCO1B3 to a greater extent than ct-SLCO1B3 (26% of total SLCO1B3 expression vs. 0.08%), suggesting that androgen uptake in these tumor cells also is greater. Non-liver tumors do not differentially express SLCO1B3. Implications: This study suggests that de novo OATP1B3 expression in prostate cancer drives greater androgen uptake and is consistent with previous observations that greater OATP1B3 activity results in the development of androgen deprivation therapy resistance and shorter overall survival. Mol Cancer Res; 15(8); 1096–105. ©2017 AACR.

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.

Dual targeting of the androgen receptor and hypoxia-inducible factor-1α pathways to synergistically inhibit castrate-resistant prostate cancer.

270 Background: Enzalutamide is a potent second-generation androgen receptor (AR) antagonist with activity in metastatic castrate-resistant prostate cancer (CRPC). While enzalutamide is initially effective, disease progression inevitably ensues with the emergence of resistance. Intratumoral hypoxia is also associated with CRPC progression and treatment resistance. Given that both AR and HIF-1α are key regulators of these processes, dual targeting of both signaling axis represents an attractive therapeutic approach. Methods: Crosstalk of the AR and HIF-1α signaling pathways were examined in prostate cancer cell lines (LNCaP, 22Rv1) with assays measuring the effect of androgen and hypoxia on AR-dependent and hypoxia-inducible gene transcription, protein expression, cell proliferation, and apoptosis. Cells were stimulated with dihydrotestosterone (DHT) or the hypoxia mimetic cobalt chloride. HIF-1α inhibition was achieved by siRNA silencing HIF-1α or via chetomin, a disruptor of HIF-1α-p300 interactions. Res...