Inhibitors In Prostate Cancer Research Articles

Role of antihypertensive medicines in prostate cancer: a systematic review

BackgroundHypertension is associated with the risk of prostate cancer (PCa) and its progression, however, it remains unclear whether antihypertensive medicines alter PCa risk or prognosis. This systematic review evaluated the role of calcium channel blockers (CCBs) and renin-angiotensin system (RAS) inhibitors in the risk and prognosis of PCa. This review was performed in line with PRISMA 2020 guidelines.MethodsEligible studies comprised peer-reviewed observational studies which reported the role of CCBs and RAS inhibitors in PCa, had accessible full texts, and were written in English. Using a combination of keywords, 5 electronic bibliographic databases which included Web of Science, EMBASE, PubMed, Google Scholar and Scopus were searched.ResultsA total of 1,346 studies were retrieved and 18 met the inclusion criteria. Thirteen studies reported reduced or no associated risk, improved prognosis, and survival with the use of RAS inhibitors. Studies on CCBs showed evidence of associated risk of PCa. Data extraction from retrieved studies focused on included study characteristics, setting, authors, year, outcomes of interest, and risk ratios. The quality assessment of included studies by the National Heart, Lung, and Blood Institute study assessment tools, showed that all studies had good quality.ConclusionsThe use of RAS inhibitors was mostly associated with lower risks or improved prognosis of PCa. CCBs may also be associated with risks of PCa. This suggests that high-risk patients managed with CCBs should be actively monitored for PCa. However, there is need for further evidence from large-scale prospective, controlled cohort studies to determine any influence of CCBs on PCa.

Reciprocal negative feedback regulation of ATF6α and PTEN promotes prostate cancer progression.

Phosphatase and tensin homolog (PTEN) loss tightly correlates with prostate cancer (PCa) progression and metastasis. Inactivation of PTEN leads to abnormal activation of PI3K/AKT pathway. However, results from clinical trials with AKT inhibitors in PCa have been largely disappointing. Identification of novel regulators of PTEN in PTEN-dysfunctional PCa is urgently needed. Here we demonstrated that the expression level of PTEN is inversely correlated with the signature score of unfolded protein response (UPR) in PCa. Importantly, PTEN suppresses the activity of ATF6α, via interacting to de-phosphorylate ATF6α and consequently inhibiting its nuclear translocation. Conversely, ATF6α promotes the ubiquitination and degradation of PTEN by inducing CHIP expression. Thus, ATF6α and PTEN forms a negative feedback loop during PCa progression. Combination of ATF6α inhibitor with AKT inhibitor suppresses tumor cell proliferation and xenograft growth. Importantly, this study highlighted ATF6α as a therapeutic vulnerability in PTEN dysfunctional PCa.

Triggering pyroptosis enhances the antitumor efficacy of PARP inhibitors in prostate cancer.

PARP inhibitors have revolutionized the treatment landscape for advanced prostate cancer (PCa) patients who harboring mutations in homologous recombination repair (HRR) genes. However, the molecular mechanisms underlying PARP inhibitors function beyond DNA damage repair pathways remain elusive, and identifying novel predictive targets that favorably respond to PARP inhibitors in PCa is an active area of research. The expression of GSDME in PCa cell lines and human PCa samples was determined by western blotting. Targeted bisulfite sequencing, gene enrichment analysis (GSEA), clone formation, construction of the stably transfected cell lines, lactate dehydrogenase (LDH) assay, western blotting as well as a mouse model of subcutaneous xenografts were used to investigate the role of GSDME in PCa. The combinational therapeutic effect of olaparib and decitabine was determined using both in vitro and in vivo experiments. We have found low expression of GSDME in PCa. Interestingly, we demonstrated that GSDME activity is robustly induced in olaparib-treated cells undergoing pyroptosis, and that high methylation of the GSDME promoter dampens its activity in PCa cells. Intriguingly, genetically overexpressing GSDME does not inhibit tumor cell proliferation but instead confers sensitivity to olaparib. Furthermore, pharmacological treatment with the combination of olaparib and decitabine synergistically induces GSDME expression and cleavage through caspase-3 activation, thus promoting pyroptosis and enhancing anti-tumor response, ultimately resulting in tumor remission. Our findings highlight a novel therapeutic strategy for enhancing the long-term response to olaparib beyond HRR-deficient tumors in PCa, underscoring the critical role of GSDME in regulating tumorigenesis.

Abstract 154: Novel AKT isoform-preferred substrates as potentially targetable drivers of metastatic prostate cancer

Abstract PI3K/AKT pathway activating mutations are the most prevalent in all of human cancers, and yet drugs that target the PI3K lipid kinase or AKT serine/threonine kinase families have performed poorly in clinical trials on solid cancers. PTEN loss, one of the most frequent mutations in prostate cancer (PC), results in AKT activation, an assumed driver of aggressive metastatic disease (mPC). The poor efficacy of PI3K/AKT inhibitors in PC likely relate to multiple PI3K and AKT isoforms which have compensatory or even oppositional roles. Whereas PI3K-p110 isoform-specific inhibitors are being used in clinical trials, no clinical AKT isoform-specific inhibitors exist. Data from our lab and others indicate that progression to aggressive mPC is dependent on AKT2-, and possibly AKT3-specific pathways. However, previous screens could not distinguish between direct vs. indirect AKT isoform-preferred substrates, and they only focused on substrates with canonical phosphorylation motifs (RxRxxS*/T*). We addressed this gap using a novel phosphoproteomics analysis that identifies direct AKT isoform substrates from PC lysates in which substrates are in endogenous protein-protein complexes. Scores of novel and previously known substrates were identified that are preferred by individual or combinations of AKT isoforms, conforming to both the canonical and four novel non-canonical motifs; >95% of these sites exist in phosphoproteome databases. By comparing data from PC cell lines isogenic for PTEN loss or expression, we identified PTEN-influenced substrate phosphorylation or AKT isoform preference. However, most of these cases did not correlate with changes in substrate abundance, suggesting novel roles for PTEN in regulating substrate modifications or cellular compartmentalization. We hypothesize that AKT2 and AKT3 substrate phosphorylation drives parameters of in vitro and in vivo mPC progression, suggesting that these AKT isoforms may be therapeutic targets if specific inhibitors can be produced. Data will be shown i) confirming AKT isoform preference of specific substrates, ii) identifying novel mechanisms by which PTEN influences substrate usage or isoform preference via altering cellular compartmentalization or post-translational modification, and iii) validating our identified non-canonical AKT isoform-specific phosphorylation sites. We also show that the phosphorylation of AKT2/3-preferred substrates drives metastatic progression in vitro and in vivo. Our data identify a much broader array of AKT isoform-specific, -preferred and -shared substrates, including those encoding previously unidentified non-canonical phosphorylation motifs. We also show novel function for PTEN, namely, to influence AKT isoform substrate usage and preference. These data will allow us to develop AKT isoform-specific inhibitors that could be used to suppress mPC progression. Citation Format: Seamus Degan, Renae Holtz, Henry G. Withers, Jun Qu, Sailee Suryakant Rasam, Irwin H. Gelman. Novel AKT isoform-preferred substrates as potentially targetable drivers of metastatic prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 154.

What Do We Have to Know about PD-L1 Expression in Prostate Cancer? A Systematic Literature Review (Part 6): Correlation of PD-L1 Expression with the Status of Mismatch Repair System, BRCA, PTEN, and Other Genes.

Pembrolizumab (anti-PD-1) is allowed in selected metastatic castration-resistant prostate cancer (PC) patients showing microsatellite instability/mismatch repair system deficiency (MSI-H/dMMR). BRCA1/2 loss-of-function is linked to hereditary PCs and homologous recombination DNA-repair system deficiency: poly-ADP-ribose-polymerase inhibitors can be administered to BRCA-mutated PC patients. Recently, docetaxel-refractory metastatic castration-resistant PC patients with BRCA1/2 or ATM somatic mutations had higher response rates to pembrolizumab. PTEN regulates cell cycle/proliferation/apoptosis through pathways including the AKT/mTOR, which upregulates PD-L1 expression in PC. Our systematic literature review (PRISMA guidelines) investigated the potential correlations between PD-L1 and MMR/MSI/BRCA/PTEN statuses in PC, discussing few other relevant genes. Excluding selection biases, 74/677 (11%) PCs showed dMMR/MSI; 8/67 (12%) of dMMR/MSI cases were PD-L1+. dMMR-PCs included ductal (3%) and acinar (14%) PCs (all cases tested for MSI were acinar-PCs). In total, 15/39 (39%) PCs harbored BRCA1/2 aberrations: limited data are available for PD-L1 expression in these patients. 13/137 (10%) PTEN- PCs were PD-L1+; 10/29 (35%) PD-L1+ PCs showed PTEN negativity. SPOP mutations may increase PD-L1 levels, while the potential correlation between PD-L1 and ERG expression in PC should be clarified. Further research should verify how the efficacy of PD-1 inhibitors in metastatic castration-resistant PCs is related to dMMR/MSI, DNA-damage repair genes defects, or PD-L1 expression.

A novel CRISPR-engineered prostate cancer cell line defines the AR-V transcriptome and identifies PARP inhibitor sensitivities.

Resistance to androgen receptor (AR)-targeted therapies in prostate cancer (PC) is a major clinical problem. A key mechanism of treatment resistance in advanced PC is the generation of alternatively spliced forms of the AR termed AR variants (AR-Vs) that are refractory to targeted agents and drive tumour progression. Our understanding of how AR-Vs function is limited due to difficulties in distinguishing their discriminate activities from full-length AR (FL-AR). Here we report the development of a novel CRISPR-derived cell line which is a derivative of CWR22Rv1 cells, called CWR22Rv1-AR-EK, that has lost expression of FL-AR, but retains all endogenous AR-Vs. From this, we show that AR-Vs act unhindered by loss of FL-AR to drive cell growth and expression of androgenic genes. Global transcriptomics demonstrate that AR-Vs drive expression of a cohort of DNA damage response genes and depletion of AR-Vs sensitises cells to ionising radiation. Moreover, we demonstrate that AR-Vs interact with PARP1 and PARP2 and are dependent upon their catalytic function for transcriptional activation. Importantly, PARP blockade compromises expression of AR-V-target genes and reduces growth of CRPC cell lines suggesting a synthetic lethality relationship between AR-Vs and PARP, advocating the use of PARP inhibitors in AR-V positive PC.

MiR-492 exerts tumor-promoting function in prostate cancer through repressing SOCS2 expression.

MiRNAs have been verified to play a role in the development and progression of prostate cancer (PCa). However, the role of miR-492 in PCa has not been mentioned. We aim to detect the expression of miR-492 in PCa and explore its underlying mechanism. The relative expression of miR-492 in PCa tissue samples to normal prostate tissues was detected using quantitative Real Time-Polymerase Chain Reaction (qRT-PCR). The level of miR-492 in PCa-derived cell lines compared with the normal prostate cell line was also measured. Cell counting kit-8 (CCK-8) and colony formation assays were employed to investigate the cell proliferation ability. Transwell assay and wound-healing assays were utilized to explore the cell invasion and migration abilities. Luciferase assay and Western blot were utilized to explore the underlying mechanism of miR-492 in PCa cells. MiR-492 expressed significantly higher in PCa tissues than that in the normal tissues. Its expression level was also over-expressed in PCa cells compared with that in the normal cells. The up-regulation of miR-492 promoted the growth, invasion, and migration of the cells, while down-regulation had the opposite effects. SOCS2 was identified as a potential target for miR-492 in PCa. Silencing of SOCS2 could neutralize the inhibitory function of miR-492 inhibitor in PCa cells. This study demonstrated that miR-492 was over-expressed in PCa and exerted tumor-promoting function in PCa cells via repressing SOCS2 expression. This might provide a new sight for future accurate therapy for PCa.

Integrin Inhibitors in Prostate Cancer.

Prostate cancer (PCa) is the most frequently diagnosed cancer and the third highest cause of cancer-related deaths in men in the U.S. The development of chemotherapeutic agents that can bind PCa tumor cells with high specificity is critical in order to increase treatment effectiveness. Integrin receptors and their corresponding ligands have different expression patterns in PCa cells. They have been identified as promising targets to inhibit pathways involved in PCa progression. Currently, several compounds have proven to target specific integrins and their subunits in PCa cells. In this article, we review the role of integrins inhibitors in PCa and their potential as therapeutic targets for PCa treatments. We have discussed the following: natural compounds, monoclonal antibodies, statins, campothecins analog, aptamers, d-aminoacid, and snake venom. Recent studies have shown that their mechanisms of action result in decrease cell migration, cell invasion, cell proliferation, and metastasis of PCa cells.

Immune Checkpoint Inhibitors and Prostate Cancer: A New Frontier?

Despite recent advances in the treatment of metastatic castration-resistant prostate cancer (mCRPC), agents that provide durable disease control and long-term survival are still needed. It is a fact that a tumor-induced immunosuppressive status (mediated by aberrant activation of inhibitory immune checkpoint pathways as a mechanism to evade host immune surveillance) plays a crucial role in the pathogenesis of cancer, including prostate cancer (PC), making CRPC patients suitable candidates for immunotherapy. Therefore, growing interest of anticancer research aims at blocking immune checkpoints (mainly targeting CTLA-4 and PD1/PD-L1 pathways) to restore and enhance cellular-mediated antitumor immunity and achieve durable tumor regression. In this review, we describe the current knowledge regarding the role of immune checkpoints in mediating PC progression, focusing on CTLA-4 and PD1 pathways. We also provide current clinical data available, an update on ongoing trials of immune checkpoint inhibitors in PC. Finally, we discuss the necessity to identify prognostic and predictive biomarkers of immune activity, and we analyze new immune checkpoints with a role as promising targets for PC therapy.

Abstract 3385: Increased eIF4E phosphorylation prevents response of prostate cancer cells to mTOR inhibitors.

Abstract Inhibitors of the mammalian target of rapamycin (mTOR) had been used in various clinical trials, but with limited efficacy. The overall goal of the present studies was to identify predictive markers of response to mTOR inhibitors in prostate cancer (PCa) cells. We previously showed that the mTOR pathway is activated in castration resistant PCa (CRPC), while its inhibition upregulates androgen receptor (AR) signaling, resulting in resistance to mTOR inhibitors (Wang et al, Oncogene, 2008). mTOR forms two complexes, mTORC1 and mTORC2: in this study we compared the effects of RAD001, an mTORC1 inhibitor, BEZ235, a dual mTOR/PI3K inhibitor, and Torin1, which inhibits both mTORC1 and mTORC2. Comparison of the effects of RAD001, alone, or in combination with the AR inhibitor bicalutamide in various CRPC cell lines showed that although C4-2 cells responded well to the combination, other cell lines, such as LNCaP-AI, PC-346C and CWR-R1, did not. The resistance of LNCaP-AI and CWR-R1 was partially overcome by treatment with BEZ-235 or Torin1, alone or in combination with bicalutamide; however, PC-346C cells were resistant to all three drugs. In an effort to identify the mechanism of resistance to mTOR inhibitors, therefore, the molecular effects of the drugs in downstream targets p70S6 kinase, 4E-BP1, eIF4G, Akt and eIF4E were compared in C4-2 (least resistant) and PC-346C (most resistant) cell lines. Western blots revealed that p70S6 kinase was downregulated by all the drugs whereas 4E-BP1 phosphorylation was effectively downregulated by BEZ235, but not Torin1, or RAD001. Phosphorylation of both p70S6K and 4E-BP1 results in activation of the translation initiation complex: a complex of eIF4E and eIF4G, therefore, inactivation of the translation initiation complex requires inhibition of eIF4E phosphorylation, which is independent of mTOR activation. In C4-2 cells, eIF4E phosphorylation was increased by RAD001 but suppressed by the other two drugs. However, in PC-346C cells, despite inhibition of 4E-BP1 phosphorylation, eIF4E phosphorylation was increased by all 3 drugs. Our data indicate eIF4E phosphorylation as a likely cause of resistance to mTOR inhibitors in PCa. Citation Format: Leandro S. D'Abronzo, Ryan Beggs, Swagata Bose, Paramita Ghosh. Increased eIF4E phosphorylation prevents response of prostate cancer cells to mTOR inhibitors. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3385. doi:10.1158/1538-7445.AM2013-3385

Androgen-independent prostate cancer cells circumvent EGFR inhibition by overexpression of alternative HER receptors and ligands

The deregulation of the epidermal growth factor receptor (EGFR) pathway plays a major role in the pathogenesis of prostate cancer (PCa). However, therapies targeting EGFR have demonstrated limited effectiveness in PCa. A potential mechanism to overcome EGFR blockade in cancer cells is the autocrine activation of alternative receptors of the human EGFR (HER) family through the overexpression of the HER receptors and ligands. In the present study, we were interested in analyzing if this intrinsic resistance mechanism might contribute to the inefficacy of EGFR inhibitors in PCa. To this end, we selected two androgen-independent human prostate carcinoma cell lines (DU145 and PC3) and established DU145 erlotinib-resistant cells (DUErR). Cells were treated with three EGFR inhibitors (cetuximab, gefinitib and erlotinib) and the sensitivity to each treatment was assessed. The gene expression of the four EGFR/HER receptors and seven ligands of the HER family was analyzed by real-time PCR prior to and after each treatment. The receptors expression and activation were further characterized by flow cytometry and western blot analysis. EGFR inhibition rapidly induced enhanced gene expression of the EGF, betacellulin and neuregulin-1 ligands along with HER2, HER3 and HER4 receptors in the DU145 cells. In contrast, slight changes were observed in the PC3 cells, which are defective in the phosphatase and tensin homolog (PTEN) tumor suppressor gene. In the erlotinib-resistant DUErR cells, the expression of HER2 and HER3 was increased at mRNA and protein levels together with neuregulin-1, leading to enhanced HER3 phosphorylation and the activation of the downstream PI3K/Akt survival pathway. HER3 blockage by a monoclonal antibody restored the cytostatic activity of erlotinib in DUErR cells. Our results confirm that the overexpression and autocrine activation of HER3 play a key role in mediating the resistance to EGFR inhibitors in androgen-independent PCa cells.

Abstract A21: Dual-kinase inhibition of EGFR/ERBB2 as a therapeutic strategy in prostate cancer

Abstract Androgen withdrawal therapy (AWT) remains the cornerstone of advanced prostate cancer (PCa) therapy; however, patients on this therapy eventually relapse, caused by the advent of castration-resistant PCa. This stimulates investigation into additional therapeutic targets that may delay or impede the development of CRPC. The EGFR family of receptor tyrosine kinases is intimately involved in prostate cancer (PCa) development. EGFR/ErbB1 and HER2/ErbB2 have been clinical targets in androgen-dependent PCa but targeting each individually encourages compensatory signaling by a third member, HER3/ErbB3. Activated HER3/ErbB3 contributes to the onset of castrate-resistant PCa (CRPC), presently an incurable condition. We previously showed that dual EGFR/HER2 inhibition sensitizes PCa cells to androgen withdrawal by suppressing ErbB3 (Clin Cancer Res. 2011 Oct 1;17(19):6218–28). Based on these results, we hypothesized that the dual EGFR/HER2 inhibitor lapatinib (‘Tykerb’, Lap) may sensitize PCa cells to AWT. Athymic nu/nu mice were subcutaneously implanted with CWR22 (androgen-dependent) or CWR22Rv1 (CRPC) tumors derived from human prostate tumors. Tumor-bearing mice were either castrated or left intact, and were treated with the FDA-approved, reversible, dual-kinase, small-molecule inhibitor lapatinib or vehicle alone. Castration prevented tumor growth in CWR22 tumor-bearing mice, both those treated with lapatinib or vehicle, but in intact mice, lapatinib actually stimulated tumor growth. In CWR22Rv1 tumor-bearing mice, lapatinib was ineffective, both in intact or castrated animals. Therefore we further investigated the effect of dual EGFR/ErbB2 inhibitors in PCa. Comparison of various cells showed that lapatinib was effective in LNCaP cells and its CRPC derivatives, but was ineffective in other lines, including PC-346C cells which express a wild-type androgen receptor (AR), whereas LNCaP cells and its derivatives express a mutant AR (T877A). In the latter cell line, lapatinib increased cell growth similar to that seen in CWR22 tumors. Hence, we investigated the effect of other dual EGFR/HER2 inhibitors in PCa cells. In contrast to lapatinib, dacomitinib (PF00299804, Pfizer, PF), an irreversible, small-molecule, dual-kinase inhibitor currently in several clinical trials for a variety of tumors, was more effective and completely inhibited cell growth in the majority of cell lines. When combined, PF and Lap decreased tumor cell viability, increased cell cycle arrest, increased apoptosis, and downregulated ErbB3 protein. These preclinical data support the hypothesis that dual-kinase inhibition may be a viable therapeutic strategy. They also indicate that prostate cancer patients must be carefully preselected, based on their tumor type, and offered personalized therapeutic regimens in order to ensure maximum efficacy of dual-kinase inhibitory treatment.

Akt down‐modulation induces apoptosis of human prostate cancer cells and synergizes with EGFR tyrosine kinase inhibitors

PTEN is a well-characterized tumor suppressor that negatively regulates cell growth and survival through the modulation of PI3K/Akt pathway. In this paper, we investigated the effects of an PI3K/Akt inhibitor, perifosine, in human prostate cancer (PCa) cells analyzing cell proliferation, apoptosis, and the synergy with EGFR inhibitors. Clinically achievable concentrations of perifosine, as well as Akt gene knockdown, induced a G0/G1 arrest and apoptosis in PTEN defective PCa cells. Although PTEN introduction was able to restore the control of Akt activity and to reduce cell proliferation, the manipulation of PTEN gene was not able alone to influence apoptosis. Perifosine induced apoptotic program also in PTEN positive cells when Akt activity was augmented by EGF suggesting the possibility that this drug could be used in combination with EGFR inhibitors. The combination treatment between erlotinib and pharmacological or molecular Akt knockdown, indeed, showed synergistic effects. This is the first demonstration that a pharmacological compound against Akt activity can restore the efficacy against EGFR inhibitors in PCa and has important therapeutic fallout since EGFR inhibitors have demonstrated very low effectiveness in PCa patients. Taken together our data have an important clinical relevance in the treatment of advanced prostate tumors. However, further studies in the setting of combination therapies in advanced PCas are necessary.