Circulating tumour DNA reveals genetic traits of patients with intraductal carcinoma of the prostate.

OBJECTIVES: To investigate the genetic alterations of patients with prostate cancer (PCa) with and without intraductal carcinoma of the prostate (IDC-P). PATIENTS AND METHODS: We performed targeted sequencing of plasma cell-free DNA on 161 patients with prostate adenocarcinoma (PAC) with IDC-P and 84 without IDC-P. Genomic alterations were compared between these two groups. The association between genetic alterations and patients' survival outcomes was also explored. RESULTS: We identified that 29.8% (48/161) and 21.4% (18/84) of patients with and without IDC-P harboured genomic alterations in DNA repair pathways, respectively (P = 0.210). Pathogenic germline DNA repair alterations were frequently detected in IDC-P carriers compared to IDC-P non-carriers (11.8% [19/161] vs 2.4% [two of 84], P = 0.024). Germline BReast CAncer type 2 susceptibility protein (BRCA2) and somatic cyclin-dependent kinase 12 (CDK12) defects were specifically identified in IDC-P carriers relative to PAC (BRCA2: 8.7% [14/161] vs 0% and CDK12: 6.8% [11/161] vs 1.2% [one of 84]). Patients with IDC-P had a distinct androgen receptor (AR) pathway alteration, characterised by an enrichment of nuclear receptor corepressor 2 (NCOR2) mutations compared with patients with pure PAC (21.1% [34/161] vs 6.0% [five of 84], P = 0.004). Increased AR alterations were detected in patients harbouring tumours with an IDC-P proportion of ≥10% vs those with an IDC-P proportion of <10% (6.4% [five of 78] vs 18.1% [15/83], P = 0.045). For IDC-P carriers, tumour protein p53 (TP53) mutation was associated with shorter castration-resistant-free survival (median 10.9 vs 28.9 months, P = 0.026), and BRCA2 alteration was related to rapid prostate-specific antigen progression for those receiving abiraterone treatment (median 9.1 vs 11.9 months, P = 0.036). CONCLUSION: Our findings provide genomic evidence explaining the aggressive phenotype of tumours with IDC-P, highlighting the potential therapeutic strategies for this patient population.

AKR1C3 expression in primary lesion rebiopsy at the time of metastatic castration-resistant prostate cancer is strongly associated with poor efficacy of abiraterone as a first-line therapy.

BACKGROUND: Previous studies had demonstrated that aldo-keto reductase family 1 member C3 (AKR1C3), a crucial enzyme in the steroidogenic pathway, played an important role in abiraterone (ABI)-resistance in metastatic castration-resistant prostate cancer (mCRPC) by increasing intratumoral androgen synthesis. However, its value in predicting treatment response in patients with mCRPC is unknown. METHOD AND MATERIALS: Data of 163 patients with metastatic prostate cancer between 2016 and 2018 were retrospectively analyzed. All patients received androgen deprivation therapy plus bicalutamide after initial diagnosis. After mCRPC, either ABI or docetaxel (DOC) treatment was used. No patient had the experience of therapy to the primary tumor. AKR1C3 protein was detected by immunohistochemical staining from rebiopsy (re-Bx) of primary prostate lesions at mCRPC. Kaplan-Meier curves and Cox regression were used to analyze the association between AKR1C3 and treatment outcomes. RESULTS: AKR1C3 was positive in 58 of 163 (35.6%) cases. AKR1C3 was associated with significantly shorter median prostate-specific antigen progression-free survival (mPSA-PFS, 5.6 mo vs 10.7 mo; P < .001), median radiographic progression-free survival (mrPFS, 11.1 mo vs 18.0 mo; P = .018), and numerically shorter median overall survival (mOS, 20.4 mo vs 26.4 mo; P = .157). Notably, AKR1C3-positive patients treated with ABI, but not DOC, had shorter mPSA-PFS and mrPFS compared with AKR1C3-negative men, (mPSA-PFS, 5.7 mo vs. 11.2 mo; P < .001; mrPFS, 12.4 mo vs 23.3 mo; P = .048). However, AKR1C3 expression had no correlation to PSA response or OS. Multivariate Cox regression indicated that AKR1C3 was independently accompanied with rapid PSA progression (hazard ratio [HR], 3.64; 95% confidence interval [CI], 2.10-6.31; P < 0.001) and radiological progression (HR, 2.08; 95% CI, 1.05-4.11; P = .036) in the ABI-treated subgroup. CONCLUSION: This study demonstrated that AKR1C3 detection in tissues from prostate re-Bx at mCRPC was associated with early resistance to ABI but not DOC. These results will help to make optimal personalized treatment decisions for patients with mCRPC, facilitate physicians predicting the effectiveness of ABI.

Novel nomograms for castration-resistant prostate cancer and survival outcome in patients with de novo bone metastatic prostate cancer.

OBJECTIVES: To develop nomograms predicting the incidence of castration-resistant prostate cancer (CRPC) and overall survival (OS) for de novo metastatic prostate cancer (PCa). PATIENTS AND METHODS: Data from 449 patients with de novo metastatic PCa were retrospectively analysed. Patients were randomly divided into a training (n = 314, 70%) and a validation cohort (n = 135, 30%). Predictive factors were selected using a Cox proportional hazards model and were further used for building predictive models. The outcomes were incidence of CRPC and OS. RESULTS: Predictive factors included: Gleason score (GS), intraductal carcinoma of the prostate (IDC-P), Eastern Cooperative Oncology Group status, and alkaline phosphatase, haemoglobin and prostate-specific antigen levels. IDC-P and GS were the strongest prognosticators for both the incidence of CRPC and OS. Nomograms for predicting CRPC and OS had an internal validated concordance index of 0.762 and 0.723, respectively. Based on the ß coefficients of the final model, risk classification systems were constructed. For those with favourable, intermediate and poor prognosis, the median time to CRPC was 62.6, 28.0 and 13.0 months (P < 0.001), respectively; and the median OS was not reached, 55.0 and 33.0 months, respectively (P < 0.001). CONCLUSIONS: We developed two novel nomograms to predict the incidence of CRPC and OS for patients with de novo metastatic PCa. These tools may assist in physician decision-making and the designing of clinical trials.

MicroRNA-181a promotes docetaxel resistance in prostate cancer cells.

BACKGROUND: Docetaxel is one of the primary drugs used for treating castration resistant prostate cancer (CRPC). Unfortunately, over time patients invariably develop resistance to docetaxel therapy and their disease will continue to progress. The mechanisms by which resistance develops are still incompletely understood. This study seeks to determine the involvement of miRNAs, specifically miR-181a, in docetaxel resistance in CRPC. METHODS: Real-time PCR was used to measure miR-181a expression in parental and docetaxel resistant C4-2B and DU145 cells (TaxR and DU145-DTXR). miR-181a expression was modulated in parental or docetaxel resistant cells by transfecting them with miR-181a mimics or antisense, respectively. Following transfection, cell number was determined after 48 h with or without docetaxel. Cross resistance to cabazitaxel induced by miR-181a was also determined. Western blots were used to determine ABCB1 protein expression and rhodamine assays used to assess activity. Phospho-p53 expression was assessed by Western blot and apoptosis was measured by ELISA in C4-2B TaxR and PC3 cells with inhibited or overexpressed miR-181a expression with or without docetaxel. RESULTS: miR-181a is significantly overexpressed in TaxR and DU145-DTXR cells compared to parental cells. Overexpression of miR-181a in parental cells confers docetaxel and cabazitaxel resistance and knockdown of miR-181a in TaxR cells re-sensitizes them to treatment with both docetaxel and cabazitaxel. miR-181a was not observed to impact ABCB1 expression or activity, a protein which was previously demonstrated to be highly involved in docetaxel resistance. Knockdown of miR-181a in TaxR cells induced phospho-p53 expression. Furthermore, miR-181a knockdown alone induced apoptosis in TaxR cells which could be further enhanced by the addition of DTX. CONCLUSIONS: Overexpression of mir-181a in prostate cancer cells contributes to their resistance to docetaxel and cabazitaxel and inhibition of mir-181a expression can restore treatment response. This is due, in part, to modulation of p53 phosphorylation and apoptosis.

Estradiol Has Differential Effects on Acute Colonic Inflammation in the Presence and Absence of Estrogen Receptor ß Expression.

BACKGROUND: Inflammatory bowel disease (IBD) increases the risk of developing colon cancer. This risk is higher in men compared to women, implicating a role for female hormones in the protection against this disease. Studies from our laboratory demonstrated that estradiol (E2) protects against inflammation-associated colon tumor formation when administered following chemical carcinogen and induction of chronic colitis. AIM: This study seeks to better understand the effect of E2 on acute colitis in the presence and absence of estrogen receptor ß (ERß). METHODS: Inflammation was induced by 2,4,6-trinitrobenzenesulfonic acid in wild-type (WT) and ERß knockout (ERßKO) mice implanted with a control or E2-containing pellet and killed 5 days later. Inflammation and injury were scored by a pathologist. Apoptosis and proliferation were assessed by immunohistochemistry. Cytokines were measured by multiplex analysis. RESULTS: E2 treatment reduced inflammation in the middle colon in WT mice and the distal colon in ERßKO mice compared to control mice. WT mice had reduced IL-6, IL-12, IL-17, GM-CSF, IFN-γ, MCP-1, MIP-1α, and TNF-α, and ERßKO had reduced IL-6 and IFN-γ expression in response to E2. Injury scores were lower in E2-treated ERßKO mice compared to control ERßKO mice. ERßKO mice had increased proliferation in the basal third of crypts in the distal colon and decreased apoptosis in the proximal colon. CONCLUSIONS: These data suggest that E2 has differential protective effects against acute colitis in the presence or absence of ERß and provide insight into how E2 may protect against IBD.

IGFBP3 promotes resistance to Olaparib via modulating EGFR signaling in advanced prostate cancer.

Olaparib is a pioneering PARP inhibitor (PARPi) approved for treating castration-resistant prostate cancer (CRPC) tumors harboring DNA repair defects, but clinical resistance has been documented. To study acquired resistance, we developed Olaparib-resistant (OlapR) cell lines through chronic Olaparib treatment of LNCaP and C4-2B cell lines. Here, we found that IGFBP3 is highly expressed in acquired (OlapR) and intrinsic (Rv1) models of Olaparib resistance. We show that IGFBP3 expression promotes Olaparib resistance by enhancing DNA repair capacity through activation of EGFR and DNA-PKcs. IGFBP3 depletion enhances efficacy of Olaparib by promoting DNA damage accumulation and subsequently, cell death in resistant models. Mechanistically, we show that silencing IGFBP3 or EGFR expression reduces cell viability and resensitizes OlapR cells to Olaparib treatment. Inhibition of EGFR by Gefitinib suppressed growth of OlapR cells and improved Olaparib sensitivity, thereby phenocopying IGFBP3 inhibition. Collectively, our results highlight IGFBP3 and EGFR as critical mediators of Olaparib resistance.

Olaparib-Induced Senescence Is Bypassed through G2-M Checkpoint Override in Olaparib-Resistant Prostate Cancer.

PARP inhibition represents the dawn of precision medicine for treating prostate cancer. Despite this advance, questions remain regarding the use of PARP inhibitors (PARPi) for the treatment of this disease, including (i) how specifically do PARPi-sensitive tumor cells respond to treatment, and (ii) how does PARPi resistance develop? To address these questions, we characterized response to olaparib in sensitive LNCaP and C4-2B cells and developed two olaparib-resistant derivative cell line models from each, termed LN-OlapR and 2B-OlapR, respectively. OlapR cells possess distinct morphology from parental cells and display robust resistance to olaparib and other clinically relevant PARPis, including rucaparib, niraparib, and talazoparib. In LNCaP and C4-2B cells, we found that olaparib induces massive DNA damage, leading to activation of the G2-M checkpoint, activation of p53, and cell-cycle arrest. Furthermore, our data suggest that G2-M checkpoint activation leads to both cell death and senescence associated with p21 activity. In contrast, both LN-OlapR and 2B-OlapR cells do not arrest at G2-M and display a markedly blunted response to olaparib treatment. Interestingly, both OlapR cell lines harbor increased DNA damage relative to parental cells, suggesting that OlapR cells accumulate and manage persistent DNA damage during acquisition of resistance, likely through augmenting DNA repair capacity. Further impairing DNA repair through CDK1 inhibition enhances DNA damage, induces cell death, and sensitizes OlapR cells to olaparib treatment. Our data together further our understanding of PARPi treatment and provide a cellular platform system for the study of response and resistance to PARP inhibition.

Dietary fish oil reduces DNA adduct formation while estradiol upregulates apoptosis in response to DNA damage in the rat colon.

BACKGROUND: Dietary fish oil is associated with a decrease in colon cancer incidence: in part through a reduction in DNA adduct formation and an induction of colonocyte apoptosis. Estradiol (E(2)) has also been demonstrated to be protective against colon cancer incidence. Studies evaluating fish oil diets and DNA adduct formation in the colon have been conducted in male models without regard to possible interactions with E(2). AIMS: The aim of this study was to evaluate the effects of E(2) and fish oil both together and separately in female rats at the point of DNA damage. METHODS: Ovariectomized female Sprague-Dawley rats were fed either a corn oil or fish oil diet in the presence or absence of E(2) for two weeks prior to being sacrificed at four time points following injection with azoxymethane. O(6)-methyldeoxyguanosine (O(6)-MedG) DNA adducts and apoptosis were examined using immunohistochemistry. RESULTS: Dietary fish oil reduced DNA adduct formation independent of the presence of E(2) at both 9 and 12 h post carcinogen. E(2) itself did not suppress adduct formation. E(2) significantly induced apoptosis 12 h after carcinogen independent of diet, primarily in the luminal third of the crypts. Fish oil was not associated with increased colonocyte apoptosis. CONCLUSIONS: These data demonstrate that fish oil is protective against DNA damage in the colon regardless of gender through reduction of O(6)-MedG adduct formation. Additionally, E(2) is capable of inducing apoptosis directly at the point of DNA damage.

Dysregulated androgen synthesis and anti-androgen resistance in advanced prostate cancer.

Current therapies for treating castration resistant prostate cancer (CRPC) include abiraterone and enzalutamide which function by inhibiting androgen signaling by targeting androgen synthesis and antagonizing the androgen receptor (AR) respectively. While these therapies are initially beneficial, resistance inevitably develops. A number of pathways have been identified to contribute to CRPC progression and drug resistance. Among these is aberrant androgen signaling perpetuated by increased expression and activity of androgenic enzymes. While abiraterone inhibits the androgenic enzyme, CYP17A1, androgen synthesis inhibition by abiraterone is incomplete and sustained androgenesis persists, in part due to increased levels of AKR1C3 and steroid sulfatase (STS). Expression of both of these enzymes is increased in CRPC and is associated with resistance to anti-androgens. A number of studies have identified methods for targeting these enzymes. Indomethacin, a non-steroidal anti-inflammatory drug commonly used to treat inflammatory arthritis has been well established as an inhibitor of AKR1C3. Treatment of CRPC cells with indomethacin reduces cell growth and improves the response to enzalutamide and abiraterone. Similarly, STS inhibitors have been shown to reduce intracrine androgens and also reduce CRPC growth and enhance anti-androgen treatment. In this review, we provide an overview of androgen synthesis in CRPC and strategies aimed at inhibiting intracrine androgens.

Activation of the ABCB1 Amplicon in Docetaxel- and Cabazitaxel-Resistant Prostate Cancer Cells.

Docetaxel and cabazitaxel-based taxane chemotherapy are critical components in the management of advanced prostate cancer. However, their efficacy is hindered due to de novo presentation with or the development of resistance. Characterizing models of taxane-resistant prostate cancer will lead to creation of strategies to overcome insensitivity. We have previously characterized docetaxel-resistant C4-2B and DU145 cell line derivatives, TaxR and DU145-DTXR, respectively. In the present study, we characterize cabazitaxel-resistant derivative cell lines created from chronic cabazitaxel exposure of TaxR and DU145-DTXR cells, CabR and CTXR, respectively. We show that CabR and CTXR cells are robustly resistant to both taxanes but retain sensitivity to antiandrogens. Both CabR and CTXR cells possess increased expression of ABCB1, which is shown to mediate resistance to treatment. Interestingly, we also present evidence for coordinated overexpression of additional genes present within the 7q21.12 gene locus where ABCB1 resides. This locus, known as the ABCB1 amplicon, has been demonstrated to be amplified in multidrug-resistant tumor cells, but little is known regarding its role in prostate cancer. We show that two ABCB1-amplicon genes other than ABCB1, RUNDC3B and DBF4, promote cellular viability and treatment resistance in taxane-resistant prostate cancer models. We present evidence that coordinated amplification of ABCB1-amplicon genes is common in a subset of prostate cancer patients. These data together suggest that ABCB1-amplicon activation plays a critical role in taxane resistance.

ARVib suppresses growth of advanced prostate cancer via inhibition of androgen receptor signaling.

Targeting androgen signaling with the second-generation anti-androgen drugs, such as enzalutamide (Enza), abiraterone (Abi), apalutamide (Apal), and darolutamide (Daro), is the mainstay for the treatment of castration-resistant prostate cancer (CRPC). While these treatments are effective initially, resistance occurs frequently. Continued expression of androgen receptor (AR) and its variants such as AR-V7 despite AR-targeted therapy contributes to treatment resistance and cancer progression in advanced CRPC patients. This highlights the need for new strategies blocking continued AR signaling. Here, we identify a novel AR/AR-V7 degrader (ARVib) and found that ARVib effectively degrades AR/AR-V7 protein and attenuates AR/AR-V7 downstream target gene expression in prostate cancer cells. Mechanistically, ARVib degrades AR/AR-V7 protein through the ubiquitin-proteasome pathway mediated by HSP70/STUB1 machinery modulation. ARVib suppresses HSP70 expression and promotes STUB1 nuclear translocation, where STUB1 binds to AR/AR-V7 and promotes its ubiquitination and degradation. ARVib significantly inhibits resistant prostate tumor growth and improves enzalutamide treatment in vitro and in vivo. These data suggest that ARVib has potential for development as an AR/AR-V7 degrader to treat resistant CRPC.

Integrated exome and RNA sequencing of TFE3-translocation renal cell carcinoma.

TFE3-translocation renal cell carcinoma (TFE3-tRCC) is a rare and heterogeneous subtype of kidney cancer with no standard treatment for advanced disease. We describe comprehensive molecular characteristics of 63 untreated primary TFE3-tRCCs based on whole-exome and RNA sequencing. TFE3-tRCC is highly heterogeneous, both clinicopathologically and genotypically. ASPSCR1-TFE3 fusion and several somatic copy number alterations, including the loss of 22q, are associated with aggressive features and poor outcomes. Apart from tumors with MED15-TFE3 fusion, most TFE3-tRCCs exhibit low PD-L1 expression and low T-cell infiltration. Unsupervised transcriptomic analysis reveals five molecular clusters with distinct angiogenesis, stroma, proliferation and KRAS down signatures, which show association with fusion patterns and prognosis. In line with the aggressive nature, the high angiogenesis/stroma/proliferation cluster exclusively consists of tumors with ASPSCR1-TFE3 fusion. Here, we describe the genomic and transcriptomic features of TFE3-tRCC and provide insights into precision medicine for this disease.

Integrated Molecular Characterization of Fumarate Hydratase-deficient Renal Cell Carcinoma.

PURPOSE: Fumarate hydratase-deficient renal cell carcinoma (FH-deficient RCC) is a rare but lethal subtype of RCC. Little is known about the genomic profile of FH-deficient RCC, and the therapeutic options for advanced disease are limited. To this end, we performed a comprehensive genomics study to characterize the genomic and epigenomic features of FH-deficient RCC. EXPERIMENTAL DESIGN: Integrated genomic, epigenomic, and molecular analyses were performed on 25 untreated primary FH-deficient RCCs. Complete clinicopathologic and follow-up data of these patients were recorded. RESULTS: We identified that FH-deficient RCC manifested low somatic mutation burden (median 0.58 mutations per megabase), but with frequent somatic copy-number alterations. The majority of FH-deficient RCCs were characterized by a CpG sites island methylator phenotype, displaying concerted hypermethylation at numerous CpG sites in genes of transcription factors, tumor suppressors, and tumor hallmark pathways. However, a few cases (20%) with low metastatic potential showed relatively low DNA methylation levels, indicating the heterogeneity of methylation pattern in FH-deficient RCC. Moreover, FH-deficient RCC is potentially highly immunogenic, characterized by increased tumor T-cell infiltration but high expression of immune checkpoint molecules in tumors. Clinical data further demonstrated that patients receiving immune checkpoint blockade-based treatment achieved improved progression-free survival over those treated with antiangiogenic monotherapy (median, 13.3 vs. 5.1 months; P = 0.03). CONCLUSIONS: These results reveal the genomic features and provide new insight into potential therapeutic strategies for FH-deficient RCC.

Cross-Resistance Among Next-Generation Antiandrogen Drugs Through the AKR1C3/AR-V7 Axis in Advanced Prostate Cancer.

The next-generation antiandrogen drugs, XTANDI (enzalutamide), ZYTIGA (abiraterone acetate), ERLEADA (apalutamide) and NUBEQA (darolutamide) extend survival times and improve quality of life in patients with advanced prostate cancer. Despite these advances, resistance occurs frequently and there is currently no definitive cure for castration-resistant prostate cancer. Our previous studies identified that similar mechanisms of resistance to enzalutamide or abiraterone occur following treatment and cross-resistance exists between these therapies in advanced prostate cancer. Here, we show that enzalutamide- and abiraterone-resistant prostate cancer cells are further cross-resistant to apalutamide and darolutamide. Mechanistically, we have determined that the AKR1C3/AR-V7 axis confers this cross-resistance. Knockdown of AR-V7 in enzalutamide-resistant cells resensitize cells to apalutamide and darolutamide treatment. Furthermore, targeting AKR1C3 resensitizes resistant cells to apalutamide and darolutamide treatment through AR-V7 inhibition. Chronic apalutamide treatment in C4-2B cells activates the steroid hormone biosynthesis pathway and increases AKR1C3 expression, which confers resistance to enzalutamide, abiraterone, and darolutamide. In conclusion, our results suggest that apalutamide and darolutamide share similar resistant mechanisms with enzalutamide and abiraterone. The AKR1C3/AR-V7 complex confers cross-resistance to second-generation androgen receptor-targeted therapies in advanced prostate cancer.

Steroid Sulfatase Stimulates Intracrine Androgen Synthesis and is a Therapeutic Target for Advanced Prostate Cancer.

PURPOSE: Most patients with prostate cancer receiving enzalutamide or abiraterone develop resistance. Clinical evidence indicates that serum levels of dehydroepiandrosterone sulfate (DHEAS) and biologically active DHEA remain in the high range despite antiandrogen treatment. The conversion of DHEAS into DHEA by steroid sulfatase (STS) may contribute to sustained intracrine androgen synthesis. Here, we determine the contribution of STS to treatment resistance and explore the potential of targeting STS to overcome resistance in prostate cancer. EXPERIMENTAL DESIGN: STS expression was examined in patients and cell lines. In vitro, STS activity and expression were modulated using STS-specific siRNA or novel STS inhibitors (STSi). Cell growth, colony formation, androgen production, and gene expression were examined. RNA-sequencing analysis was conducted on VCaP cells treated with STSi. Mice were treated with STSis with or without enzalutamide to determine their effects in vivo. RESULTS: STS is overexpressed in patients with castration-resistant prostate cancer (CRPC) and resistant cells. STS overexpression increases intracrine androgen synthesis, cell proliferation, and confers resistance to enzalutamide and abiraterone. Inhibition of STS using siRNA suppresses prostate cancer cell growth. Targeting STS activity using STSi inhibits STS activity, suppresses androgen receptor transcriptional activity, and reduces the growth of resistant C4-2B and VCaP prostate cancer cells. STSis significantly suppress resistant VCaP tumor growth, decrease serum PSA levels, and enhance enzalutamide treatment in vitro and in vivo. CONCLUSIONS: These studies suggest that STS drives intracrine androgen synthesis and prostate cancer proliferation. Targeting STS represents a therapeutic strategy to treat CRPC and improve second-generation antiandrogen therapy.

Current strategies for targeting the activity of androgen receptor variants.

Current therapies for advanced prostate cancer, such as enzalutamide and abiraterone, focus on inhibiting androgen receptor (AR) activity and reducing downstream signaling pathways to inhibit tumor growth. Unfortunately, cancer cells are very adaptable and, over time, these cells develop mechanisms by which they can circumvent therapeutics. One of the many mechanisms that have been discovered is the generation of AR variants. These variants are generated through alternative splicing of the full length AR and often lack the ligand binding domain. This leads to forms of the AR that are constitutively active that continue to promote prostate cancer cell growth even in the absence of ligand. The high prevalence of AR variants and their role in disease progression have prompted a number of studies investigating ways to inhibited AR variant expression and activity. Among these are the anti-helminthic drug, niclosamide, which selectively promotes degradation of AR variants over full length AR and re-sensitizes anti-androgen resistant prostate cancer cells to treatment with enzalutamide and abiraterone. Other AR variant targeting mechanisms include interfering with AR variant co-activators and the development of drugs that bind to the DNA or N-terminal AR domains, which are retained in most AR variants. The clinical efficacy of treating prostate cancer by targeting AR variants is under investigation in several clinical trials. In this review, we provide an overview of the most relevant AR variants and discuss current AR variant targeting strategies.

Wntless promotes cellular viability and resistance to enzalutamide in castration-resistant prostate cancer cells.

BACKGROUND: De-regulation of Wnt signaling pathways has been shown to be associated with progression of castration-resistant prostate cancer and more recently, studies indicate that both canonical and non-canonical Wnt pathways may mediate resistance to anti-androgen therapies such as enzalutamide. However, the mechanisms by which Wnt signaling is altered in prostate cancer remain poorly understood. Wnt pathway function begins with Wnt biogenesis and secretion from Wnt signal sending cells. While previous studies have investigated downstream mechanisms of Wnt pathway alterations in prostate cancer, little is known on the role of Wnt secretion mediating proteins. Wntless (WLS) is thought to be essential for the secretion of all Wnts. In this study, we sought to understand the role of WLS in prostate cancer. METHODS: RNA-seq and gene set enrichment analysis were used to understand expression profile changes in enzalutamide-resistant C4-2B-MDVR (MDVR) cells versus parental C4-2B cells. Quantitative-PCR and western blot were used to confirm RNA-seq data and to assess expression changes of gene targets of interest. Rv1 cells were used as a separate model of enzalutamide-resistant prostate cancer. RNAi was used to inhibit WLS expression. Cell viability, colony formation, and PSA ELISA assays were used to assess cell growth and survival. RESULTS: Transcriptomic profiling revealed enriched Wnt pathway signatures in MDVR versus parental C4-2B cells. We further show that MDVR cells upregulate Wnt signaling and overexpress WLS. Inhibition of WLS decreases Wnt signaling, markedly attenuates prostate cancer cell viability, induces apoptosis, and re-sensitizes enzalutamide-resistant cells to enzalutamide treatment. Lastly, we show that inhibition of WLS reduces AR and AR-variants expression and downstream signaling. CONCLUSIONS: Our findings support a role for WLS in the progression of prostate cancer to a treatment-resistant state. Further efforts to understand Wnt signaling pathway alterations in this disease may lead to the development of novel treatments.

AKR1C3 Promotes AR-V7 Protein Stabilization and Confers Resistance to AR-Targeted Therapies in Advanced Prostate Cancer.

The mechanisms resulting in resistance to next-generation antiandrogens in castration-resistant prostate cancer are incompletely understood. Numerous studies have determined that constitutively active androgen receptor (AR) signaling or full-length AR bypass mechanisms may contribute to the resistance. Previous studies established that AKR1C3 and AR-V7 play important roles in enzalutamide and abiraterone resistance. In the present study, we found that AKR1C3 increases AR-V7 expression in resistant prostate cancer cells through enhancing protein stability via activation of the ubiquitin-mediated proteasome pathway. AKR1C3 reprograms AR signaling in enzalutamide-resistant prostate cancer cells. In addition, bioinformatical analysis of indomethacin-treated resistant cells revealed that indomethacin significantly activates the unfolded protein response, p53, and apoptosis pathways, and suppresses cell-cycle, Myc, and AR/ARV7 pathways. Targeting AKR1C3 with indomethacin significantly decreases AR/AR-V7 protein expression in vitro and in vivo through activation of the ubiquitin-mediated proteasome pathway. Our results suggest that the AKR1C3/AR-V7 complex collaboratively confers resistance to AR-targeted therapies in advanced prostate cancer.

Overexpressed ABCB1 Induces Olaparib-Taxane Cross-Resistance in Advanced Prostate Cancer.

Castration-resistant prostate cancer remains as an incurable disease. Exploiting DNA damage repair defects via inhibition of poly (ADP-ribose) polymerase (PARP) is becoming an attractive therapeutic option. The TOPARP-A clinical trial demonstrated that the PARP inhibitor olaparib may be an effective strategy for treating prostate cancer. However, several unanswered questions regarding the use of olaparib remain: 1) How do we best stratify patients for olaparib treatment? 2) Where do we place olaparib in the treatment sequence paradigm? 3) Is there cross-resistance between olaparib and currently used therapies? Here, we tested putative cross-resistance between current therapies and olaparib in treatment-resistant castration-resistant prostate cancer models. Docetaxel-resistant cells exhibited robust resistance to olaparib which could be attributed to blunted PARP trapping in response to olaparib treatment. Upregulated ABCB1 mediates cross-resistance between taxanes and olaparib, which can be overcome through decreasing ABCB1 expression or inhibiting ABCB1 using elacridar or enzalutamide. We also show that combining olaparib with enzalutamide is more effective in olaparib-sensitive cells than either single agent. Our results demonstrate that cross-resistance between olaparib and other therapies could blunt response to treatment and highlight the need to develop strategies to maximize olaparib efficacy.

Intra versus Inter Cross-resistance Determines Treatment Sequence between Taxane and AR-Targeting Therapies in Advanced Prostate Cancer.

Current treatments for castration resistant prostate cancer (CRPC) largely fall into two classes: androgen receptor (AR)-targeted therapies such as the next-generation antiandrogen therapies (NGAT), enzalutamide and abiraterone, and taxanes such as docetaxel and cabazitaxel. Despite improvements in outcomes, patients still succumb to the disease due to the development of resistance. Further complicating the situation is lack of a well-defined treatment sequence and potential for cross-resistance between therapies. We have developed several models representing CRPC with acquired therapeutic resistance. Here, we utilized these models to assess putative cross-resistance between treatments. We find that resistance to enzalutamide induces resistance to abiraterone and vice versa, but resistance to neither alters sensitivity to taxanes. Acquired resistance to docetaxel induces cross-resistance to cabazitaxel but not to enzalutamide or abiraterone. Correlating responses with known mechanisms of resistance indicates that AR variants are associated with resistance to NGATs, whereas the membrane efflux protein ABCB1 is associated with taxane resistance. Mechanistic studies show that AR variant-7 (AR-v7) is involved in NGAT resistance but not resistance to taxanes. Our findings suggest the existence of intra cross-resistance within a drug class (i.e., within NGATs or within taxanes), whereas inter cross-resistance between drug classes does not develop. Furthermore, our data suggest that resistance mechanisms differ between drug classes. These results may have clinical implications by showing that treatments of one class can be sequenced with those of another, but caution should be taken when sequencing similar classed drugs. In addition, the development and use of biomarkers indicating resistance will improve patient stratification for treatment. Mol Cancer Ther; 17(10); 2197-205. ©2018 AACR.