Plexin D1 emerges as a novel target in the development of neural lineage plasticity in treatment-resistant prostate cancer

Treatment-induced neuroendocrine prostate cancer (t-NEPC) often arises from adenocarcinoma via lineage plasticity in response to androgen receptor signaling inhibitors, such as enzalutamide. However, the specific regulators and targets involved in the transition to NEPC are not well understood. Plexin D1 (PLXND1) is a cellular receptor of the semaphorin (SEMA) family that plays important roles in modulating the cytoskeleton and cell adhesion. Here, we found that PLXND1 is highly expressed and positively correlated with neuroendocrine markers in patients with NEPC. High PLXND1 expression is associated with poorer prognosis in prostate cancer patients. Additionally, PLXND1 was upregulated and negatively regulated by androgen receptor signaling in enzalutamide-resistant cells. Knockdown or knockout of PLXND1 inhibit neural lineage pathways, suppressing NEPC cell proliferation, PDX tumor organoid viability, and xenograft tumor growth. Mechanistically, the chaperone protein HSP70 regulates PLXND1 protein stability through degradation, and inhibition of HSP70 decreases PLXND1 expression and NEPC organoid growth. In summary, our findings suggest that PLXND1 could be a new therapeutic target and molecular indicator for NEPC.

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.

Stromal-derived MAOB promotes prostate cancer growth and progression

Prostate cancer (PC) develops in a microenvironment where the stromal cells modulate adjacent tumor growth and progression. Here, we demonstrated elevated levels of monoamine oxidase B (MAOB), a mitochondrial enzyme that degrades biogenic and dietary monoamines, in human PC stroma, which was associated with poor clinical outcomes of PC patients. Knockdown or overexpression of MAOB in human prostate stromal fibroblasts indicated that MAOB promotes cocultured PC cell proliferation, migration, and invasion and co-inoculated prostate tumor growth in mice. Mechanistically, MAOB induces a reactive stroma with activated marker expression, increased extracellular matrix remodeling, and acquisition of a protumorigenic phenotype through enhanced production of reactive oxygen species. Moreover, MAOB transcriptionally activates CXCL12 through Twist1 synergizing with TGFβ1-dependent Smads in prostate stroma, which stimulates tumor-expressed CXCR4-Src/JNK signaling in a paracrine manner. Pharmacological inhibition of stromal MAOB restricted PC xenograft growth in mice. Collectively, these findings characterize the contribution of MAOB to PC and suggest MAOB as a potential stroma-based therapeutic target.

Genomic and Evolutionary Characterization of Concurrent Intraductal Carcinoma and Adenocarcinoma of the Prostate

Intraductal carcinoma of the prostate (IDC-P) is a lethal prostate cancer subtype that generally coexists with invasive high-grade prostate acinar adenocarcinoma (PAC) but exhibits distinct biological features compared with concomitant adenocarcinoma. In this study, we performed whole-exome, RNA, and DNA-methylation sequencing of IDC-P, concurrent invasive high-grade PAC lesions, and adjacent normal prostate tissues isolated from 22 radical prostatectomy specimens. Three evolutionary patterns of concurrent IDC-P and PAC were identified: early divergent, late divergent, and clonally distant. In contrast to those with a late divergent evolutionary pattern, tumors with clonally distant and early divergent evolutionary patterns showed higher genomic, epigenomic, transcriptional, and pathologic heterogeneity between IDC-P and PAC. Compared with coexisting PAC, IDC-P displayed increased expression of adverse prognosis-associated genes. Survival analysis based on an independent cohort of 505 patients with metastatic prostate cancer revealed that IDC-P carriers with lower risk International Society of Urological Pathology (ISUP) grade 1-4 adenocarcinoma displayed a castration-resistant free survival as poor as those with the highest risk ISUP grade 5 tumors that lacked concurrent IDC-P. Furthermore, IDC-P exhibited robust cell-cycle progression and androgen receptor activities, characterized by an enrichment of cellular proliferation-associated master regulators and genes involved in intratumoral androgen biosynthesis. Overall, this study provides a molecular groundwork for the aggressive behavior of IDC-P and could help identify potential strategies to improve treatment of IDC-P.

SIGNIFICANCE

The genomic, transcriptomic, and epigenomic characterization of concurrent intraductal carcinoma and adenocarcinoma of the prostate deepens the biological understanding of this lethal disease and provides a genetic basis for developing targeted therapies.

Therapeutic Resistance Models and Treatment Sequencing in Advanced Prostate Cancer

Current common treatments for castration-resistant prostate cancer (CRPC) typically belong to one of three major categories: next-generation anti-androgen therapies (NGAT) including enzalutamide, abiraterone acetate, apalutamide, and darolutamide; taxane therapy represented by docetaxel; and PARP inhibitors (PARPi) like olaparib. Although these treatments have shown efficacy and have improved outcomes for many patients, some do not survive due to the emergence of therapeutic resistance. The clinical landscape is further complicated by limited knowledge about how the sequence of treatments impacts the development of therapeutic cross-resistance in CRPC. We have developed multiple CRPC models of acquired therapeutic resistance cell sublines from C4-2B cells. These include C4-2B MDVR, C4-2B AbiR, C4-2B ApaR, C4-2B DaroR, TaxR, and 2B-olapR, which are resistant to enzalutamide, abiraterone, apalutamide, darolutamide, docetaxel, and olaparib, respectively. These models are instrumental for analyzing gene expression and assessing responses to various treatments. Our findings reveal distinct cross-resistance characteristics among NGAT-resistant cell sublines. Specifically, resistance to enzalutamide induces resistance to abiraterone and vice versa, while maintaining sensitivity to taxanes and olaparib. Conversely, cells with acquired resistance to docetaxel exhibit cross-resistance to both cabazitaxel and olaparib but retain sensitivity to NGATs like enzalutamide and abiraterone. OlapR cells, significantly resistant to olaparib compared to parental cells, are still responsive to NGATs and docetaxel. Moreover, OlapR models display cross-resistance to other clinically relevant PARP inhibitors, including rucaparib, niraparib, and talazoparib. RNA-sequencing analyses have revealed a complex network of altered gene expressions that influence signaling pathways, energy metabolism, and apoptotic signaling, pivotal to cancer's evolution and progression. The data indicate that resistance mechanisms are distinct among different drug classes. Notably, NGAT-resistant sublines exhibited a significant downregulation of androgen-regulated genes, contrasting to the stable expression noted in olaparib and docetaxel-resistant sublines. These results may have clinical implications by showing that treatments of one class can be sequenced with those from another class, but caution should be taken when sequencing drugs of the same class.

Allosteric inhibition of HSP70 in collaboration with STUB1 augments enzalutamide efficacy in antiandrogen resistant prostate tumor and patient-derived models

Ubiquitin proteasome activity is suppressed in enzalutamide resistant prostate cancer cells, and the heat shock protein 70/STIP1 homology and U-box-containing protein 1 (HSP70/STUB1) machinery are involved in androgen receptor (AR) and AR variant protein stabilization. Targeting HSP70 could be a viable strategy to overcome resistance to androgen receptor signaling inhibitor (ARSI) in advanced prostate cancer. Here, we showed that a novel HSP70 allosteric inhibitor, JG98, significantly suppressed drug-resistant C4-2B MDVR and CWR22Rv1 cell growth, and enhanced enzalutamide treatment. JG98 also suppressed cell growth in conditional reprogramed cell cultures (CRCs) and organoids derived from advanced prostate cancer patient samples. Mechanistically, JG98 degraded AR/AR-V7 expression in resistant cells and promoted STUB1 nuclear translocation to bind AR-V7. Knockdown of the E3 ligase STUB1 significantly diminished the anticancer effects and partially restored AR-V7 inhibitory effects of JG98. JG231, a more potent analog developed from JG98, effectively suppressed the growth of the drug-resistant prostate cancer cells, CRCs, and organoids. Notably, the combination of JG231 and enzalutamide synergistically inhibited AR/AR-V7 expression and suppressed CWR22Rv1 xenograft tumor growth. Inhibition of HSP70 using novel small-molecule inhibitors coordinates with STUB1 to regulate AR/AR-V7 protein stabilization and ARSI resistance.

Novel inhibition of AKR1C3 and androgen receptor axis by PTUPB synergizes enzalutamide treatment in advanced prostate cancer

Castration-resistant prostate cancer (CRPC) is the main driving force of mortality in prostate cancer patients. Among the parameters contributing to the progression of CRPC and treatment failure, elevation of the steroidogenic enzyme AKR1C3 and androgen receptor variant 7 (AR-V7) are frequently reported. The AKR1C3/AR-V7 complex has been recognized as a major driver for drug resistance in advanced prostate cancer. Herein we report that the level of AKR1C3 is reciprocally regulated by the full-length androgen receptor (AR-FL) through binding to the distal enhancer region of the AKR1C3 gene. A novel function of PTUPB in AKR1C3 inhibition was discovered and PTUPB showed more effectiveness than indomethacin and celecoxib in suppressing AKR1C3 activity and CRPC cell growth. PTUPB synergizes with enzalutamide treatment in tumor suppression and gene signature regulation. Combination treatments with PTUPB and enzalutamide provide benefits by blocking AR/AR-V7 signaling, which inhibits the growth of castration relapsed VCaP xenograft tumors and patient-derived xenograft organoids. Targeting of the ARK1C3/AR/AR-V7 axis with PTUPB and enzalutamide may overcome drug resistance to AR signaling inhibitors in advanced prostate cancer.

Wntless expression promotes lineage plasticity and is associated with neuroendocrine prostate cancer

Resistance to androgen receptor (AR) targeted therapies remains as the main reason for most prostate cancer related deaths. Lineage plasticity resulting in altered, treatment insensitive prostate tumor cell phenotypes such neuroendocrine differentiated prostate cancer is a common manifestation within resistant tumors upon AR-targeted therapies. The mechanisms responsible for lineage plasticity in prostate cancer remain incompletely understood. Here we demonstrate that the enzalutamide resistant MDVR cell line possesses lineage plastic characteristics associated with overexpression of the Wnt transporter Wntless (WLS). Furthermore, we present evidence that overexpression of WLS is common in varying cell line models of lineage plastic prostate cancer, is higher in neuroendocrine patient samples, and positively correlates with the neuroendocrine marker SYP in clinical data. Targeting WLS in lineage plastic cellular models reduces viability and represses lineage plasticity associated gene expression. Our study provides insight into the importance of WLS to the development of lethal resistant prostate cancer and provides a potential target for the treatment of advanced disease.

Bioengineered BERA-Wnt5a siRNA Targeting Wnt5a/FZD2 Signaling Suppresses Advanced Prostate Cancer Tumor Growth and Enhances Enzalutamide Treatment

The next-generation antiandrogen drugs such as enzalutamide and abiraterone extend survival times and improve quality of life in patients with advanced prostate cancer. However, resistance to both drugs occurs frequently through mechanisms that are incompletely understood. Wnt signaling, particularly through Wnt5a, plays vital roles in promoting prostate cancer progression and induction of resistance to enzalutamide and abiraterone. Development of novel strategies targeting Wnt5a to overcome resistance is an urgent need. In this study, we demonstrated that Wnt5a/FZD2-mediated noncanonical Wnt pathway is overexpressed in enzalutamide-resistant prostate cancer. In patient databases, both the levels of Wnt5a and FZD2 expression are upregulated upon the development of enzalutamide resistance and correlate with higher Gleason score, biochemical recurrence, and metastatic status, and with shortened disease-free survival duration. Blocking Wnt5a/FZD2 signal transduction not only diminished the activation of noncanonical Wnt signaling pathway, but also suppressed the constitutively activated androgen receptor (AR) and AR variants. Furthermore, we developed a novel bioengineered BERA-Wnt5a siRNA construct and demonstrated that inhibition of Wnt5a expression by the BERA-Wnt5a siRNA significantly suppressed tumor growth and enhanced enzalutamide treatment in vivo. These results indicate that Wnt5a/FZD2 signal pathway plays a critical role in promoting enzalutamide resistance, and targeting this pathway by BERA-Wnt5a siRNA can be developed as a potential therapy to treat advanced prostate cancer.

Activation of neural lineage networks and ARHGEF2 in enzalutamide-resistant and neuroendocrine prostate cancer and association with patient outcomes

Background

Treatment-emergent neuroendocrine prostate cancer (NEPC) after androgen receptor (AR) targeted therapies is an aggressive variant of prostate cancer with an unfavorable prognosis. The underlying mechanisms for early neuroendocrine differentiation are poorly defined and diagnostic and prognostic biomarkers are needed.

Methods

We performed transcriptomic analysis on the enzalutamide-resistant prostate cancer cell line C4-2B MDVR and NEPC patient databases to identify neural lineage signature (NLS) genes. Correlation of NLS genes with clinicopathologic features was determined. Cell viability was determined in C4-2B MDVR and H660 cells after knocking down ARHGEF2 using siRNA. Organoid viability of patient-derived xenografts was measured after knocking down ARHGEF2.

Results

We identify a 95-gene NLS representing the molecular landscape of neural precursor cell proliferation, embryonic stem cell pluripotency, and neural stem cell differentiation, which may indicate an early or intermediate stage of neuroendocrine differentiation. These NLS genes positively correlate with conventional neuroendocrine markers such as chromogranin and synaptophysin, and negatively correlate with AR and AR target genes in advanced prostate cancer. Differentially expressed NLS genes stratify small-cell NEPC from prostate adenocarcinoma, which are closely associated with clinicopathologic features such as Gleason Score and metastasis status. Higher ARGHEF2, LHX2, and EPHB2 levels among the 95 NLS genes correlate with a shortened survival time in NEPC patients. Furthermore, downregulation of ARHGEF2 gene expression suppresses cell viability and markers of neuroendocrine differentiation in enzalutamide-resistant and neuroendocrine cells.

Conclusions

The 95 neural lineage gene signatures capture an early molecular shift toward neuroendocrine differentiation, which could stratify advanced prostate cancer patients to optimize clinical treatment and serve as a source of potential therapeutic targets in advanced prostate cancer.

Abstract 1850: Characterizing senescence response to PARP inhibition may provide opportunities for enhanced efficacy through combinations with senolytic agents

Background: Inhibition of poly (ADP-ribose) polymerase (PARP) is an exciting treatment strategy recently approved for prostate cancer patients with homologous recombination repair defects. Despite this advance in the field, it remains unclear how PARP inhibitor (PARPi) sensitive cells respond to treatment. We previously demonstrated that treatment with the PARPi olaparib induces not only cell death, but also G2/M arrested senescence characterized by activation of the p53 signaling pathway. We hypothesize that targeting PARPi induced senescence may provide a means to enhance the efficacy of PARPi treatment. In our current work, we sought to 1) understand whether senescence induction is a generalized response to all PARPi’s and 2) characterize senescence induction to guide the development of novel treatment strategies combining a PARPi with a senolytic drug.

Methods: PARPi sensitive LNCaP and C4-2B prostate tumor cells were treated with olaparib, rucaparib, niraparib, or talazoparib for 5 days to induce senescence. Both vehicle treated and quiescent cells (LNCaP and C4-2B cultured in FBS-low (0.2%) conditions) were used as controls. Cell viability, flow cytometry, and beta-galactosidase activity assays tested response to PARPi’s. Western blot was used to detect PARP activity, apoptosis, and DNA damage response. RNA-sequencing was performed to characterize senescence induced signaling alterations.

Results: We found that exposure to rucaparib, niraparib, and talazoparib all induce a robust G2/M arrested senescence response in LNCaP and C4-2B cells, suggesting that senescence induction is a class effect of PARPi’s. PARPi induced senescence is characterized by activation of the p53 signaling pathway and significantly increased expression of the cyclin-dependent kinase inhibitor p21. Furthermore, PARPi induced senescence is distinct from quiescence, suggesting that response to PARP inhibition is phenotypically different from a more general growth arrest. RNA-sequencing revealed several signaling changes associated with senescence which may provide novel treatment opportunities.

Conclusions: Senolytics are a class of drugs thought to specifically target senescent cells. Our results demonstrate that PARPi’s induce senescence. Future work will be directed at further characterizing PARPi induced senescence, leading to rationally selected senolytic drug combinations which may enhance the efficacy of PARPi therapy.

Citation Format: Alan P. Lombard, Wei Lou, Christopher P. Evans, Allen C. Gao. Characterizing senescence response to PARP inhibition may provide opportunities for enhanced efficacy through combinations with senolytic agents [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 1850.

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.

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.

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 promotes cellular viability and resistance to docetaxel and cabazitaxel in castration-resistant prostate cancer

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've 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 anti-androgens. 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.

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.

Bidirectional Cross-talk between MAOA and AR Promotes Hormone-Dependent and Castration-Resistant Prostate Cancer

Androgen receptor (AR) is the primary oncogenic driver of prostate cancer, including aggressive castration-resistant prostate cancer (CRPC). The molecular mechanisms controlling AR activation in general and AR reactivation in CRPC remain elusive. Here we report that monoamine oxidase A (MAOA), a mitochondrial enzyme that degrades monoamine neurotransmitters and dietary amines, reciprocally interacts with AR in prostate cancer. MAOA was induced by androgens through direct AR binding to a novel intronic androgen response element of the MAOA gene, which in turn promoted AR transcriptional activity via upregulation of Shh/Gli-YAP1 signaling to enhance nuclear YAP1-AR interactions. Silencing MAOA suppressed AR-mediated prostate cancer development and growth, including CRPC, in mice. MAOA expression was elevated and positively associated with AR and YAP1 in human CRPC. Finally, genetic or pharmacologic targeting of MAOA enhanced the growth-inhibition efficacy of enzalutamide, darolutamide, and apalutamide in both androgen-dependent and CRPC cells. Collectively, these findings identify and characterize an MAOA-AR reciprocal regulatory circuit with coamplified effects in prostate cancer. Moreover, they suggest that cotargeting this complex may be a viable therapeutic strategy to treat prostate cancer and CRPC. SIGNIFICANCE: MAOA and AR comprise a positive feedback loop in androgen-dependent and CRPC, providing a mechanistic rationale for combining MAOA inhibition with AR-targeted therapies for prostate cancer treatment.

WLS-Wnt signaling promotes neuroendocrine prostate cancer

Neuroendocrine prostate cancer (NEPC) is a lethal prostate cancer subtype arising as a consequence of more potent androgen receptor (AR) targeting in castration-resistant prostate cancer (CRPC). Its molecular pathogenesis remains elusive. Here, we report that the Wnt secretion mediator Wntless (WLS) is a major driver of NEPC and aggressive tumor growth in vitro and in vivo. Mechanistic studies showed that WLS is a transcriptional target suppressed by AR that activates the ROR2/PKCδ/ERK signaling pathway to support the neuroendocrine (NE) traits and proliferative capacity of NEPC cells. Analysis of clinical samples and datasets revealed that WLS was highly expressed in CRPC and NEPC tumors. Finally, treatment with the Wnt secretion inhibitor LGK974 restricted NE prostate tumor xenograft growth in mice. These findings collectively characterize the contribution of WLS to NEPC pathogenesis and suggest that WLS is a potential therapeutic target in NEPC.

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WLS is highly expressed in neuroendocrine prostate cancer clinical samples

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WLS is a transcriptional target suppressed by androgen receptor

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WLS drives neuroendocrine prostate cancer through the ROR2/PKCδ/ERK pathway

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Wnt secretion inhibitor treatment limits neuroendocrine prostate tumor growth in mice

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.

Targeting cellular heterogeneity with CXCR2 blockade for the treatment of therapy-resistant prostate cancer

Hormonal therapy targeting androgen receptor (AR) is initially effective to treat prostate cancer (PCa), but it eventually fails. It has been hypothesized that cellular heterogeneity of PCa, consisting of AR⁺ luminal tumor cells and AR^- neuroendocrine (NE) tumor cells, may contribute to therapy failure. Here, we describe the successful purification of NE cells from primary fresh human prostate adenocarcinoma based on the cell surface receptor C-X-C motif chemokine receptor 2 (CXCR2). Functional studies revealed CXCR2 to be a driver of the NE phenotype, including loss of AR expression, lineage plasticity, and resistance to hormonal therapy. CXCR2-driven NE cells were critical for the tumor microenvironment by providing a survival niche for the AR⁺ luminal cells. We demonstrate that the combination of CXCR2 inhibition and AR targeting is an effective treatment strategy in mouse xenograft models. Such a strategy has the potential to overcome therapy resistance caused by tumor cell heterogeneity.

Abstract 5681: Design, synthesis and study of small molecules with both AR degradation and AKR1C3 inhibitory activities

Prostate cancer is the most common cancer in men and it is estimated that 32,000 men in the US alone will die of this cancer in 2019. Androgen deprivation therapy (ADT) has been the mainstay of prostate cancer therapy. However, most of the patients will progress to castration resistance prostate cancer (CRPC) after several years of treatment. The current treatment of CRPC includes chemotherapeutic agents (docetaxel) and agents that target androgen signaling (abiraterone, enzalutamide and apalutamide). Ultimately, however, most patients develop resistance to the treatments. Two of the mechanisms of resistance involve the expression of constitutively active androgen receptor variant (AR-V7) and the increase in intra-tumoral biosynthesis of androgens. Several treatment strategies targeting AR-V7 have been reported. For the intra-tumoral biosynthesis of androgens, one of the enzymes, AKR1C3, plays a critical role in the development of CRPC and has been reported to be consistently elevated in CRPC patients who are resistant to abiraterone and enzalutamide.

We have been involved in the development of agents to treat CRPC and overcome drug resistance of CRPC patients. We reported that niclosamide, an FDA-approved anthelminthic agent, could degrade AR-V7. We also reported that niclosamide, as well as an AKR1C3 inhibitor, indomethacin, were able to overcome enzalutamide and abiraterone resistance in several prostate cancer cell lines, suggesting that niclosamide is also an AKR1C3 inhibitor. By examining the reported structures of AKR1C3 inhibitors, niclosamide was found to contain the core scaffold of 4-Hydroxy-1-(4-methoxybenzyl)-N-(3-(trifluoromethyl) phenyl)-1H-1,2,3-triazole-5-carboxamide. Using this knowledge, we designed a series compounds with dual AR degrading and AKR1C3 inhibitory activities. Preliminary studies showed the compounds caused AR-V7 degradation and to a lesser extent AR full length degradation. The compounds also inhibited AKR1C3 and caused a dose dependent growth inhibition of several prostate cancer cell lines.

Citation Format: Enming Xing, Xiaotian Kong, Wei Lou, Ruihua Shi, Xiaolin Cheng, Allen C. Gao, Pui Kai Li. Design, synthesis and study of small molecules with both AR degradation and AKR1C3 inhibitory activities [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5681.

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.

Germline and somatic DNA repair gene alterations in prostate cancer

BACKGROUND

Emerging evidence has suggested that DNA repair gene alterations may be important in prostate cancer pathogenesis. In the current study, the authors sought to characterize alterations in DNA repair pathway genes in both primary and metastatic prostate tumors with attention to tissue distribution as well as specific genomic alterations.

METHODS

The authors studied the distribution and type of alterations in 24 genes that are considered important for DNA repair in 944 prostate cancers harvested from localized and metastatic tumors. Tumor DNA underwent hybrid capture for all coding exons of 287 or 395 cancer-related genes plus select introns from 19 or 31 genes frequently rearranged in cancer. Captured libraries were sequenced to a median exon coverage depth of >×500. Specific genomic alterations were characterized and the frequencies of mutations by tissue site (prostate vs metastases) were compared using logistic regression.

RESULTS

A total of 152 patients from the cohort of 944 men (16%) harbored a germline or somatic mutation in ≥1 DNA repair genes. The most frequently mutated genes were BRCA2 (11.4%) and ATM (5.8%), followed by MSH6 (2.5%) and MSH2 (2.1%). Mutations were identified in approximately 20.1% of primary prostate tumors compared with 18.8% of bone metastases. When stratified by tissue site, the highest rates of DNA repair mutations were found in solid organ metastases, including brain and visceral metastases, compared with prostate.

CONCLUSIONS

DNA repair gene mutations are more common in metastatic than localized prostate tumors. Visceral and other solid organ metastases appear enriched for these mutations compared with localized tumors or bone and lymph node metastases.

Resistance Mechanisms to Taxanes and PARP Inhibitors in Advanced Prostate Cancer

The clinical landscape concerning advanced prostate cancer is rapidly changing and reaching beyond androgen deprivation therapy and androgen receptor targeted therapies. Taxane chemotherapy is a critical tool in the management of advanced prostate cancer. Additionally, novel drug classes such as PARP inhibitors are being investigated. Despite tremendous progress, resistance to therapy remains as a major impediment to further improvement. Resistance mechanisms appear diverse and are not fully known or understood. This review will highlight recent advances in research regarding mechanisms of resistance to both taxanes (such as increased drug efflux capacity) and PARP inhibitors (such as reversion mutations which restore DNA-repair proficiency). Understanding resistance to therapy promises to remove barriers blocking progress toward improved patient outcomes.

Therapeutic Targeting of MDR1 Expression by RORγ Antagonists Resensitizes Cross-Resistant CRPC to Taxane via Coordinated Induction of Cell Death Programs

Overexpression of ATP-binding cassette subfamily B member 1 (ABCB1)-encoded multidrug resistance protein 1 (MDR1) constitutes a major mechanism of cancer drug resistance including docetaxel (DTX) and cabazitaxel (CTX) resistance in castration-resistant prostate cancer (CRPC). However, no therapeutics that targets MDR1 is available at clinic for taxane sensitization. We report here that retinoic acid receptor-related orphan receptor γ (RORγ), a nuclear receptor family member, unexpectedly mediates MDR1/ABCB1 overexpression. RORγ plays an important role in controlling the functions of subsets of immune cells and has been an attractive target for autoimmune diseases. We found that its small-molecule antagonists are efficacious in resensitizing DTX and CTX cross-resistant CRPC cells and tumors to taxanes in both androgen receptor-positive and -negative models. Our mechanistic analyses revealed that combined treatment with RORγ antagonists and taxane elicited a robust synergy in killing the resistant cells, which involves a coordinated alteration of p53, Myc, and E2F-controlled programs critical for both intrinsic and extrinsic apoptosis, survival, and cell growth. Our results suggest that targeting RORγ with small-molecule inhibitors is a novel strategy for chemotherapy resensitization in tumors with MDR1 overexpression.

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.

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.

Abstract 1823: SNORD78 promotes prostate cancer progression and regulates AR expression and signaling

While small nucleolar RNAs (snoRNAs) have long been thought of as housekeeping genes, emerging evidence now suggests that snoRNAs are involved in more than previously thought and also in the development of disease. In cancer, it is understood that snoRNA expression and function can be altered, but little is known regarding the role of snoRNAs in these diseases. SNORD78 is a C/D box snoRNA which has been shown to be overexpressed in prostate cancer and associated with disease progression. However, there are no studies functionally characterizing SNORD78 in prostate cancer. In this study we sought to understand the functional contribution of SNORD78 in prostate cancer progression. Oncomine was used to assess SNORD78 expression in clinical prostate cancer samples. LNCaP and C4-2B prostate cancer cell lines were used. We used siRNAs to inhibit SNORD78 expression and cell viability assays to assess cell growth. ELISAs were used to assess PSA secretion and cell death. Western blots and quantitative PCR were used to assess cell death (PARP-cleavage) and AR expression and signaling. We found that SNORD78 expression was up-regulated in prostate tumors and associated with metastatic progression. Cell viability assays demonstrated that inhibition of SNORD78 expression resulted in a drastic reduction in prostate cancer cell growth and lower secretion of PSA into the media. Cell death ELISAs and western blots for cleaved-PARP showed that SNORD78 inhibition induced robust apoptosis in both LNCaP and C4-2B cells. As the androgen receptor (AR) is the primary target for prostate cancer therapy, we tested whether SNORD78 regulated AR expression and signaling. Inhibition of SNORD78 in both LNCaP and C4-2B cells resulted in reduced AR mRNA and protein levels. We also found that SNORD78 knockdown led to decreased levels of PSA and NKX3.1, suggesting that AR downstream signaling was inhibited. Our findings suggest that SNORD78 promotes prostate cancer cell viability and disease progression. We also demonstrate that SNORD78 regulates the AR and may be involved in promoting AR signaling needed for prostate cancer cell survival. Collectively, these data suggest that SNORD78 plays a critical role in prostate cancer progression and may represent a novel therapeutic target.

Citation Format: Alan P. Lombard, Chengfei Liu, Cameron M. Armstrong, Leandro S. D'Abronzo, Wei Lou, Christopher P. Evans, Allen C. Gao. SNORD78 promotes prostate cancer progression and regulates AR expression and signaling [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1823.

Abstract 3030: HSD3B1 mediated anti-androgen resistance in prostate cancer requires specific androgen precursors

Resistance to anti-androgens, such as enzalutamide (Enza) or abiraterone (Abi), develops within 24 months of initial exposure in most prostate cancer (PCa) patients. Commonly, dysregulated androgen signaling is a key feature of resistant disease. Previous studies demonstrate that androgen synthesis is upregulated in Enza and Abi resistance. HSD3B1 is steroidogenic enzyme which contributes to androgen synthesis and is associated with PCa progression. This study aims to determine the role of HSD3B1 in promoting Enza and Abi resistance in PCa.

Enza resistant (C4-2B MDVR) and Abi resistant (C4-2B AbiR) C4-2B PCa cells were generated by chronically exposing parental C4-2B cells to increasing Enza or Abi concentrations for &gt;12 months. Cells were maintained in 20 µM Enza or 10 µM Abi thereafter. Microarray, RNA-seq, and rtPCR were used to determine differences in gene expression between parental and anti-androgen resistant cells and confirmed by Western blot. HSD3B1 expression was knocked down in C4-2B MDVR and C4-2B AbiR cells using shRNA and cell number was determined in media containing FBS, charcoal dextran stripped FBS (CDFBS), or CDFBS supplemented with 100 nM pregnenolone (P5), 100 nM DHEA, or 10 nM DHT in the presence and absence of 20 µM Enza or 10 µM Abi. PSA secretion was determined by ELISA and PSA-luciferase activity was measured by reporter assay.

C4-2B MDVR and C4-2B AbiR cells have increased HSD3B1 expression compared to parental C4-2B cells. This correlates to an increase in intracrine androgens in C4-2B MDVR cells as determined by LC-MS. Knockdown of HSD3B1 in C4-2B MDVR resensitized cells to Enza in FBS, CDFBS+DHT and CDFBS+P5 conditions as determined by a reduction in cell number and PSA secretion and/or PSA-luciferase activity in response to Enza. In the C4-2B AbiR cells, inhibition of HSD3B1 re-sensitized cells to treatment with Abi in FBS, CDFBS, and CDFBS+P5 conditions with the greatest effects seen in the FBS and CDFBS+P5 conditions. Supplementation with P5, but not DHEA, was able to induce PSA-luciferase activity and cell growth in C4-2B MDVR and C4-2B AbiR cells and this could be blocked by knockdown of HSD3B1.

HSD3B1 overexpression in C4-2B MDVR and C4-2B AbiR cells contributes to Enza and Abi resistance and targeting this enzyme could be a viable strategy to improve anti-androgen response in PCa cells. HSD3B1 activity is reliant on select androgen precursors, such as pregnenolone, indicating preference towards a specific androgen synthesis pathway by HSD3B1 in mediating anti-androgen resistance.

Citation Format: Cameron M. Armstrong, Chengfei Liu, Wei Lou, Alan P. Lombard, Christopher Evans, Allen C. Gao. HSD3B1 mediated anti-androgen resistance in prostate cancer requires specific androgen precursors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3030.

Abstract 4842: Overcoming EGFR and ERK-mediated resistance to enzalutamide in castration-resistant prostate cancer

The present project was undertaken to determine whether the activation of the EGFR family (EGFR/ErbB2/ErbB3/ErbB4) and its downstream signaling effector ERK1/2 plays a role in enzalutamide resistance and whether treatment with ErbB or ERK inhibitors overcome this resistance. C4-2B (enzalutamide sensitive) and 22Rv1 (partially enzalutamide resistant) cell lines cultured for prolonged periods in enzalutamide, developed resistance to this drug (C4-2B/MDVR and 22Rv1/MDVR, respectively). Whole genome comparison of enza-resistant to parental lines demonstrated that the ErbB signaling network was significantly upregulated in the enza-resistant lines. Comparison of various enza-sensitive and resistant lines demonstrated a strong correlation between phosphorylation at EGFR(Y1068) and enza resistance. Inhibition of EGFR, but not that of ErbB2 or ErbB3 prevented cell viability. The EGFR inhibitors erlotinib and dacomitinib, but not the ErbB2 inhibitor lapatinib, suppressed viability in combination with enzalutamide. We hypothesized that enza-resistant tumors expressing higher levels of EGFR would be more responsive to erlotinib. To test this hypothesis, we compared the effects of erlotinib and enzalutamide, individually or in combination, in organelles from PDX tumors expressing high or low EGFR levels. Significantly, tumors expressing high EGFR, but not those expressing low EGFR, were responsive to the combination. Finally, we investigated the cause for greater efficacy with erlotinib compared to lapatinib in PCa. Comparison of the effects of different ligands revealed that while both lapatinib and erlotinib inhibited EGFR phosphorylation, only erlotinib but not lapatinib was able to inhibit EGF-induced ERK phosphorylation. This indicated an important role for ERK in the mediation of EGFR ligand induced enzalutamide resistance. Continuous culture of enza-sensitive C4 cells in enzalutamide resulted in the development of ERK phosphorylation in these PTEN-null cells that normally do not express phosphorylated ERK, and the newly ERK phosphorylated cells also were more susceptible to erlotinib as well. In support of a role for ERK in mediating the effects of EGFR activation in enza-resistant cells, inhibition of EGFR but not ErbB2 or ErbB3 inhibited ERK phosphorylation, and the ERK inhibitor ulitertinib inhibited viability of enza-resistant lines. We conclude that enzalutamide treatment causes an increase in EGFR ligands that result in the phosphorylation of EGFR at Y1068, which further resulted in phosphorylation of ERK. EGFR inhibitors that prevent ERK phosphorylation were effective in suppressing viability of enza-resistant CRPC cells, whereas ErbB2 inhibitors that did not affect ERK phosphorylation were unable to affect cell viability. These results demonstrate why certain ErbB inhibitors failed to affect enza-resistant CRPC tumors but provide encouragement for others.

Citation Format: Thomas M. Steele, Maitreyee K. Jathal, Salma Siddiqui, Sisi Qin, Clifford G. Tepper, Ralph W. deVere White, Manish Kohli, Liewei Wang, Allen C. Gao, Paramita M. Ghosh. Overcoming EGFR and ERK-mediated resistance to enzalutamide in castration-resistant prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4842.

Abstract 1018: GnRH antagonists have direct inhibitory effects on castration-resistant prostate cancer via intracrine androgen and AR-V7 expression

Hormone therapy is currently the mainstay in the management of locally advanced and metastatic prostate cancer (PCa). Degarelix (Firmagon, Deg), a GnRH receptor antagonist demonstrated some advantages over the LHRH agonist Leuprolide (Leup) by avoiding “testosterone flare” and lower FSH levels. We compared the effect of Deg and Leup on prostate cancer (PC) cell progression in vitro and in vivo. GnRHR2 was readily detectable in PC cells. AR transcriptional activity reported by PSA-Luc assay was modulated by both Leup and Deg. In LNCaP and C4-2B MDVR cells, 20µM Deg significantly reduced the cell viability (p&lt;0.01). GnRH-antagonist (alone or in combination with AA or Enza) counteracted the transactivation activity of AR by reducing AR-FL and AR variants at the protein level. In C4-2BMDVR cells, Deg reduced AR-V7 protein expression by 26 to 40% alone or combined with AA and Enza compared to control. Leup, however, enhanced variant expression. Deg reduced AR-variant levels from 17 to 41% in monotherapy or combinations compared to control. In mice, Leup slightly suppressed tumor growth compared to controls (p&gt;0.05). However, tumors in Deg-treated group were 1.5-fold smaller than Leup-treated group but 1.7-fold bigger than surgical castration-group. Ki67 IHC staining confirmed the difference in tumor proliferation among groups. Measurements of intratumoral steroids by LC-MS from tumors, serum samples or cell pellets confirmed that Deg decreased the levels of testosterone and steroidogenesis pathway intermediates, comparable to surgical castration; while Leup had no inhibitory effect. Our results suggest a selective mechanism of action of Deg against AR-variants. The present study provides additional molecular insights regarding the mechanism of Deg compared to GnRH agonist therapy which may have clinical implications.

Citation Format: Vito Cucchiara, Joy C. Yang, Chengfei Liu, Hans Adomat, Emma Guns, Martin E. Gleave, Allen C. Gao, Christopher P. Evans. GnRH antagonists have direct inhibitory effects on castration-resistant prostate cancer via intracrine androgen and AR-V7 expression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1018.

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.

A Circulating Tumor Cell-RNA Assay for Assessment of Androgen Receptor Signaling Inhibitor Sensitivity in Metastatic Castration-Resistant Prostate Cancer

Rationale: Our objective was to develop a circulating tumor cell (CTC)-RNA assay for characterizing clinically relevant RNA signatures for the assessment of androgen receptor signaling inhibitor (ARSI) sensitivity in metastatic castration-resistant prostate cancer (mCRPC) patients. Methods: We developed the NanoVelcro CTC-RNA assay by combining the Thermoresponsive (TR)-NanoVelcro CTC purification system with the NanoString nCounter platform for cellular purification and RNA analysis. Based on the well-validated, tissue-based Prostate Cancer Classification System (PCS), we focus on the most aggressive and ARSI-resistant PCS subtype, i.e., PCS1, for CTC analysis. We applied a rigorous bioinformatic process to develop the CTC-PCS1 panel that consists of prostate cancer (PCa) CTC-specific RNA signature with minimal expression in background white blood cells (WBCs). We validated the NanoVelcro CTC-RNA assay and the CTC-PCS1 panel with well-characterized PCa cell lines to demonstrate the sensitivity and dynamic range of the assay, as well as the specificity of the PCS1 Z score (the likelihood estimate of the PCS1 subtype) for identifying PCS1 subtype and ARSI resistance. We then selected 31 blood samples from 23 PCa patients receiving ARSIs to test in our assay. The PCS1 Z scores of each sample were computed and compared with ARSI treatment sensitivity. Results: The validation studies using PCa cell line samples showed that the NanoVelcro CTC-RNA assay can detect the RNA transcripts in the CTC-PCS1 panel with high sensitivity and linearity in the dynamic range of 5-100 cells. We also showed that the genes in CTC-PCS1 panel are highly expressed in PCa cell lines and lowly expressed in background WBCs. Using the artificial CTC samples simulating the blood sample conditions, we further demonstrated that the CTC-PCS1 panel is highly specific in identifying PCS1-like samples, and the high PCS1 Z score is associated with ARSI resistance samples. In patient bloods, ARSI-resistant samples (ARSI-R, n=14) had significantly higher PCS1 Z scores as compared with ARSI-sensitive samples (ARSI-S, n=17) (Rank-sum test, P=0.003). In the analysis of 8 patients who were initially sensitive to ARSI (ARSI-S) and later developed resistance (ARSI-R), we found that the PCS1 Z score increased from the time of ARSI-S to the time of ARSI-R (Pairwise T-test, P=0.016). Conclusions: Using our new methodology, we developed a first-in-class CTC-RNA assay and demonstrated the feasibility of transforming clinically-relevant tissue-based RNA profiling such as PCS into CTC tests. This approach allows for detecting RNA expression relevant to clinical drug resistance in a non-invasive fashion, which can facilitate patient-specific treatment selection and early detection of drug resistance, a goal in precision oncology.

KDM8/JMJD5 as a dual coactivator of AR and PKM2 integrates AR/EZH2 network and tumor metabolism in CRPC

During the evolution into castration or therapy resistance, prostate cancer cells reprogram the androgen responses to cope with the diminishing level of androgens, and undergo metabolic adaption to the nutritionally deprived and hypoxia conditions. AR (androgen receptor) and PKM2 (pyruvate kinase M2) have key roles in these processes. We report in this study, KDM8/JMJD5, a histone lysine demethylase/dioxygnase, exhibits a novel property as a dual coactivator of AR and PKM2 and as such, it is a potent inducer of castration and therapy resistance. Previously, we showed that KDM8 is involved in the regulation of cell cycle and tumor metabolism in breast cancer cells. Its role in prostate cancer has not been explored. Here, we show that KDM8's oncogenic properties in prostate cancer come from its direct interaction (1) with AR to affect androgen response and (2) with PKM2 to regulate tumor metabolism. The interaction with AR leads to the elevated expression of androgen response genes in androgen-deprived conditions. They include ANCCA/ATAD2 and EZH2, which are directly targeted by KDM8 and involved in sustaining the survival of the cells under hormone-deprived conditions. Notably, in enzalutamide-resistant cells, the expressions of both KDM8 and EZH2 are further elevated, so are neuroendocrine markers. Consequently, EZH2 inhibitors or KDM8 knockdown both resensitize the cells toward enzalutamide. In the cytosol, KDM8 associates with PKM2, the gatekeeper of pyruvate flux and translocates PKM2 into the nucleus, where the KDM8/PKM2 complex serves as a coactivator of HIF-1α to upregulate glycolytic genes. Using shRNA knockdown, we validate KDM8's functions as a regulator for both androgen-responsive and metabolic genes. KDM8 thus presents itself as an ideal therapeutic target for metabolic adaptation and castration-resistance of prostate cancer cells.

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.

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.

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 β 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.

The N-terminal kinase suppressor of Ras complex has a weak nucleoside diphosphate kinase activity

INTRODUCTION

An increasing number of studies have proven that the kinase suppressor of Ras (KSR1) functions as a scaffolding protein that coordinates the assembly of a multiprotein complex containing mitogen-activated protein kinase and its upstream regulators. However, a few studies have reported that KSR1 can activate c-Raf-1. Therefore, whether KSR1 possesses a kinase activity has been an unresolved issue until now.

MATERIALS AND METHODS

pCMV-Tag2b-KSR plasmids were transfected into 293T cells. In vitro autophosphorylation was assayed by autoradiography and in vitro kinase was assayed by reversed-phase high performance liquid chromatography.

RESULTS

We observed that wild-type KSR1 (WT-KSR) and N-terminal KSR1 (N-KSR) were phosphorylated, but the C-terminal KSR1 (C-KSR) and vector proteins were not. The high performance liquid chromatography profile showed not only the adenosine diphosphate peak but also the uridine triphosphate peak in the WT-KSR and N-KSR groups; both peaks were considerably more significant in these groups than in the others. The WT-KSR and N-KSR groups exhibited transphosphorylation and autophosphorylation activities, while the other groups revealed almost no activity.

DISCUSSION

Here, we demonstrate the nucleoside diphosphate kinase activity of the KSR1 complex and that this activity can be independent of the C-terminus of KSR1. Additionally, we found the autophosphorylation activity of the KSR1 complex to be extremely weak, suggesting that the KSR1 complex possesses an extremely weak kinase activity irrespective of whether it is nucleoside diphosphate kinase activity or serine/threonine protein kinase activity. These data suggest that the kinase activity of the KSR1 complex is derived from its associated proteins.

A proteomic approach to elucidate the multiple targets of selenium-induced cell-growth inhibition in human lung cancer

BACKGROUND

  Methylseleninic acid (MSA) has been implicated as a promising anticancer agent for lung cancer. However, the underlying molecular mechanism(s) responsible for MSA's action is not well understood. Our study aimed to examine the cellular effects of MSA on L9981 human high-metastatic large cell lung cancer cells and gain insights into its possible molecular mechanism(s) through a proteomic approach.

METHODS

  L9981 cells were exposed to MSA at different concentrations and time points. The effects of MSA on cell proliferation and apoptosis were detected by cell viability analyzer Vi-CELL and flow cytometric analysis, respectively. We analyzed the alterations in the proteome profile of L9981 cells induced by MSA using the 2-D difference in gel electrophoresis (2-D DIGE) and identified the differentially expressed proteins using a liquid chromatography system followed by tandem mass spectrometry (LC-MS/MS).

RESULTS

  We found that MSA inhibited cell proliferation in a dose-dependent manner and significantly induced early apoptosis in L9981 cells. 2-D DIGE showed that MSA induced significant changes (>1.29 fold) in the expression levels of 42 protein spots compared to the untreated control (P < 0.05). As identified by LC-MS/MS, proteins that underwent changes in response to MSA were related to various biological functions, including: (i) endoplasmic reticulum stress (upregulation of molecular chaperones like heat shock protein A5, protein disulfide-isomerase precursor, and calreticulin precursor); (ii) oxidative stress response/ thioredoxin system (decreased thioredoxin-like protein 1 and increased thioredoxin reductase 1); (iii) translation regulation (downregulation of translation factors like elongation factor 1-beta and eukaryotic translation initiation factor 6); (iv) mitochondrial bioenergetic function (upregulation of adenosine triphosphate synthase subunit beta and mitochondria); and (v) cell signal transduction regulation (decreased peptidyl-prolyl cis-trans isomerase A and 14-3-3 protein gamma). The protein and gene expression levels of those proteins of interest were further confirmed by Western blot and/or real-time reverse transcription polymerase chain reaction.

CONCLUSION

  Our results suggest that MSA may inhibit cell proliferation and induce apoptosis in lung cancer by modulating multiple targets involved in various crucial cellular processes.

Role of Androgen Receptor Variants in Prostate Cancer: Report from the 2017 Mission Androgen Receptor Variants Meeting

CONTEXT

Although a number of studies have demonstrated the importance of constitutively active androgen receptor variants (AR-Vs) in prostate cancer, questions still remain about the precise role of AR-Vs in the progression of castration-resistant prostate cancer (CRPC).

OBJECTIVE

Key stakeholders and opinion leaders in prostate cancer convened on May 11, 2017 in Boston to establish the current state of the field of AR-Vs.

EVIDENCE ACQUISITION

The meeting "Mission Androgen Receptor Variants" was the second of its kind sponsored by the Prostate Cancer Foundation (PCF). This invitation-only event was attended by international leaders in the field and representatives from sponsoring organizations (PCF and industry sponsors). Eighteen faculty members gave short presentations, which were followed by in-depth discussions. Discussions focused on three thematic topics: (1) potential of AR-Vs as biomarkers of therapeutic resistance; (2) role of AR-Vs as functionally active CRPC progression drivers; and (3) utility of AR-Vs as therapeutic targets in CRPC.

EVIDENCE SYNTHESIS

The three meeting organizers synthesized this meeting report, which is intended to summarize major data discussed at the meeting and identify key questions as well as strategies for addressing these questions. There was a critical consensus that further study of the AR-Vs is an important research focus in CRPC. Contrasting views and emphasis, each supported by data, were presented at the meeting, discussed among the participants, and synthesized in this report.

CONCLUSIONS

This article highlights the state of knowledge and outlines the most pressing questions that need to be addressed to advance the AR-V field.

PATIENT SUMMARY

Although further investigation is needed to delineate the role of androgen receptor (AR) variants in metastatic castration-resistant prostate cancer, advances in measurement science have enabled development of blood-based tests for treatment selection. Detection of AR variants (eg, AR-V7) identified a patient population with poor outcomes to existing AR-targeting therapies, highlighting the need for novel therapeutic agents currently under development.

Concordance of Circulating Tumor DNA and Matched Metastatic Tissue Biopsy in Prostate Cancer

Background

Real-time knowledge of the somatic genome can influence management of patients with metastatic castration-resistant prostate cancer (mCRPC). While routine metastatic tissue biopsy is challenging in mCRPC, plasma circulating tumor DNA (ctDNA) has emerged as a minimally invasive tool to sample the tumor genome. However, no systematic comparisons of matched "liquid" and "solid" biopsies have been performed that would enable ctDNA profiling to replace the need for direct tissue sampling.

Methods

We performed targeted sequencing across 72 clinically relevant genes in 45 plasma cell-free DNA (cfDNA) samples collected at time of metastatic tissue biopsy. We compared ctDNA alterations with exome sequencing data generated from matched tissue and quantified the concordance of mutations and copy number alterations using the Fisher exact test and Pearson correlations.

Results

Seventy-five point six percent of cfDNA samples had a ctDNA proportion greater than 2% of total cfDNA. In these patients, all somatic mutations identified in matched metastatic tissue biopsies were concurrently present in ctDNA. Furthermore, the hierarchy of variant allele fractions for shared mutations was remarkably similar between ctDNA and tissue. Copy number profiles between matched liquid and solid biopsy were highly correlated, and individual copy number calls in clinically actionable genes were 88.9% concordant. Detected alterations included AR amplifications in 22 (64.7%) samples, SPOP mutations in three (8.8%) samples, and inactivating alterations in tumor suppressors TP53 , PTEN , RB1 , APC , CDKN1B , BRCA2 , and PIK3R1 . In several patients, ctDNA sequencing revealed robust changes not present in paired solid biopsy, including clinically relevant alterations in the AR, WNT, and PI3K pathways.

Conclusions

Our study shows that, in the majority of patients, a ctDNA assay is sufficient to identify all driver DNA alterations present in matched metastatic tissue and supports development of DNA biomarkers to guide mCRPC patient management based on ctDNA alone.

Quercetin Targets hnRNPA1 to Overcome Enzalutamide Resistance in Prostate Cancer Cells

Prostate cancer remains dependent on androgen receptor signaling even after castration. Aberrant androgen receptor signaling in castration-resistant prostate cancer is mediated by mechanisms such as alterations in the androgen receptor and activation of interacting signaling pathways. Clinical evidence confirms that resistance to the next-generation antiandrogen, enzalutamide, may be mediated to a large extent by alternative splicing of the androgen receptor to generate constitutively active splice variants such as AR-V7. The splice variants AR-V7 and AR^v567es have been implicated in the resistance to not only enzalutamide, but also to abiraterone and other conventional therapeutics such as taxanes. Numerous studies, including ours, suggest that splicing factors such as hnRNPA1 promote the generation of AR-V7, thus contributing to enzalutamide resistance in prostate cancer cells. In the present study, we discovered that quercetin, a naturally occurring polyphenolic compound, reduces the expression of hnRNPA1, and consequently, that of AR-V7. The suppression of AR-V7 by quercetin resensitizes enzalutamide-resistant prostate cancer cells to treatment with enzalutamide. Our results indicate that quercetin downregulates hnRNPA1 expression, downregulates the expression of AR-V7, antagonizes androgen receptor signaling, and resensitizes enzalutamide-resistant prostate cancer cells to enzalutamide treatment in vivo in mouse xenografts. These findings demonstrate that suppressing the alternative splicing of the androgen receptor may have important implications in overcoming the resistance to next-generation antiandrogen therapy. Mol Cancer Ther; 16(12); 2770-9. ©2017 AACR.

ABCB1 Mediates Cabazitaxel-Docetaxel Cross-Resistance in Advanced Prostate Cancer

Advancements in research have added several new therapies for castration-resistant prostate cancer (CRPC), greatly augmenting our ability to treat patients. However, CRPC remains an incurable disease due to the development of therapeutic resistance and the existence of cross-resistance between available therapies. Understanding the interplay between different treatments will lead to improved sequencing and the creation of combinations that overcome resistance and prolong survival. Whether there exists cross-resistance between docetaxel and the next-generation taxane cabazitaxel is poorly understood. In this study, we use C4-2B and DU145 derived docetaxel-resistant cell lines to test response to cabazitaxel. Our results demonstrate that docetaxel resistance confers cross-resistance to cabazitaxel. We show that increased ABCB1 expression is responsible for cross-resistance to cabazitaxel and that inhibition of ABCB1 function through the small-molecule inhibitor elacridar resensitizes taxane-resistant cells to treatment. In addition, the antiandrogens bicalutamide and enzalutamide, previously demonstrated to be able to resensitize taxane-resistant cells to docetaxel through inhibition of ABCB1 ATPase activity, are also able to resensitize resistant cells to cabazitaxel treatment. Finally, we show that resensitization using an antiandrogen is far more effective in combination with cabazitaxel than docetaxel. Collectively, these results address key concerns in the field, including that of cross-resistance between taxanes and highlighting a mechanism of cabazitaxel resistance involving ABCB1. Furthermore, these preclinical studies suggest the potential in using combinations of antiandrogens with cabazitaxel for increased effect in treating advanced CRPC. Mol Cancer Ther; 16(10); 2257-66. ©2017 AACR.

Abstract 3186: Taxane resistance in prostate cancer: A role for miRNA 181a

Introduction: Docetaxel (DTX) is one of the primary drugs used for treating castration resistant prostate cancer (CRPC). Unfortunately, over time patients invariably develop resistance to DTX 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 DTX resistance in CRPC.

Methods: Total RNA from parental C4-2B prostate cancer cells and DTX resistant C4-2B cells (C4-2B TaxR) was submitted for small RNA deep sequencing. Data was analyzed to ascertain which miRNAs expressions were most altered in C4-2B TaxR cells compared to parental cells. Having identified an increase in miR-181a in resistant cells, its expression was modulated in C4-2B and C4-2B TaxR cells by transfecting them with miR-181a mimics or antisense, respectively. Following transfection, cell number was determined after 48 h with or without DTX. 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 cells with inhibited miR-181a expression with or without DTX.

Results: miR-181a is significantly upregulated in C4-2B TaxR cells compared to parental C4-2B cells as analyzed by small RNA sequencing. Overexpression of miR-181a in C4-2B cells confers DTX and cabazitaxel resistance. Knockdown of miR-181a in C4-2B TaxR cells re-sensitizes them to treatment with both DTX and cabazitaxel. miR-181a knockdown alone induced apoptosis in C4-2B TaxR cells which is further enhanced by DTX. We next assessed if miR-181a altered expression or activity of ABCB1, which is overexpressed/active in C4-2B TaxR cells and promotes resistance to DTX by pumping the drug out of cells. We found that miR-181a does not impact ABCB1 expression or activity. Since we previously demonstrated that phospho-p53 can modulate DTX sensitivity, we determined if miR-181a can alter p53 expression in C4-2B TaxR cells. Knockdown of miR-181a in C4-2B TaxR cells induced phospho-p53 expression, suggesting that miR-181a induced resistance to DTX is mediated by inhibition of phospho-p53 expression.

Conclusions: Overexpression of miR-181a in C4-2B TaxR cells contributes to their resistance to DTX and inhibition of miR-181a expression can restore treatment response. This is due, in part, to modulation of p53 phosphorylation and induction of apoptosis.

Note: This abstract was not presented at the meeting.

Citation Format: Cameron M. Armstrong, Chengfei Liu, Wei Lou, Allen C. Gao. Taxane resistance in prostate cancer: A role for miRNA 181a [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3186. doi:10.1158/1538-7445.AM2017-3186

Androgen Receptor Regulation of Local Growth Hormone in Prostate Cancer Cells

Prostate cancer (PCa) growth is mainly driven by androgen receptor (AR), and tumors that initially respond to androgen deprivation therapy (ADT) or AR inhibition usually relapse into a more aggressive, castration-resistant PCa (CRPC) stage. Circulating growth hormone (GH) has a permissive role in PCa development in animal models and in human PCa xenograft growth. As GH and GH receptor (GHR) are both expressed in PCa cells, we assessed whether prostatic GH production is linked to AR activity and whether GH contributes to the castration-resistant phenotype. Using online datasets, we found that GH is highly expressed in human CRPC. We observed increased GH expression in castration-resistant C4-2 compared with castration-sensitive LNCaP cells as well as in enzalutamide (MDV3100)-resistant (MDVR) C4-2B (C4-2B MDVR) cells compared with parental C4-2B. We describe a negative regulation of locally produced GH by androgens/AR in PCa cells following treatment with AR agonists (R1881) and antagonists (enzalutamide, bicalutamide). We also show that GH enhances invasive behavior of CRPC 22Rv1 cells, as reflected by increased migration, invasion, and anchorage-independent growth, as well as expression of matrix metalloproteases. Moreover, GH induces expression of the AR splice variant 7, which correlates with antiandrogen resistance, and also induces insulinlike growth factor 1, which is implicated in PCa progression and ligand-independent AR activation. In contrast, blockade of GH action with the GHR antagonist pegvisomant reverses these effects both in vitro and in vivo. GH induction following ADT or AR inhibition may contribute to CRPC progression by bypassing androgen growth requirements.

Abstract 5638: Combination use of EF2K and VPS34 inhibitors with anti-androgen against drug-resistant castration resistant prostate cancer

INTRODUCTION AND OBJECTIVES:

Modulating the activity of eukaryotic elongation factor 2 kinase (eEF2K) has been suggested to regulate protein elongation to block autophagy in the tumor microenvironment. Among inhibitors of eEF2K, one would also inhibit VPS34, a class III phosphatidylinositol-3 kinase, and abrogate autophage flux to impair the survival escape mechanism. We tested the eEF2K and VPS 34 inhibitors from Janssen alone or in combination with anti-androgens for their effects on proliferation of prostate cancer cell lines, especially some castration resistant PC (CRPC) lines.

MATERIALS AND METHODS:

Cell proliferation was assessed with various concentrations of the EF2K or VPS34 inhibitor on CRPC lines using WST-1 viability assay. Effect of combinations of EF2K or VPS34 inhibitor with anti-androgens abiraterone (Abi) or enzalutamide (Enza) on drug-resistant CRPC cells was further explored. Western blot analysis was performed to examine the response of key autophagic molecules, androgen receptor (AR) and variant. Real time RT-PCR (RT-qPCR) was used to elucidate the effect of EF2K or VPS34 inhibitor alone or together with anti-androgens on AR, AR variant and their downstream molecules.

RESULTS:

EF2K and VPS34 inhibitors suppressed CRPC cell growth in a dose-response manner with IC50 ranging from 1 to 5 µM. These inhibitors displayed synergy with Abi and Enza against drug-resistant CRPC cells; especially on the pair of enza + EF2K inhibitor with p = 0.02 for significant difference when compared to enza or EF2K inhibitor alone. To our surprise, no significant autophagy was induced by these two inhibitors according to the autophagy markers detected by Western blots. VPS34 inhibitor alone and when combined with Abi and Enza showed AR/variant degrading ability. This downregulation was at the expression level with significant change of AR and V7, together with their transactivation markers PSA, TMPRS2, NKx3.1 and FKBP5 detected by RT-qPCR.

CONCLUSION:

EF2K and VPS34 inhibitors when combined with anti-androgens may solicit profound inhibitory effect on drug-resistant CRPC cells. Molecular delineation demonstrated the direct target might be AR and its variants. These combinations offered a new therapeutic option for advanced PC treatments.

Citation Format: Joy C. Yang, Vito Cucchiara, Allen C. Gao, Christopher P. Evans. Combination use of EF2K and VPS34 inhibitors with anti-androgen against drug-resistant castration resistant prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5638. doi:10.1158/1538-7445.AM2017-5638

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.