As we move into the era of precision medicine, the growing relevance of genetic alterations to prostate cancer (PCa) development and treatment demonstrates the importance of characterizing preclinical models at the genomic level. Our study investigated the genomic characterization of eight PCa cell lines to understand which models are clinically relevant. We designed a custom AmpliSeq DNA gene panel that encompassed key molecular pathways targeting AR signaling, apoptosis, DNA damage repair, and PI3K/AKT/PTEN, in addition to tumor suppressor genes. We examined the relationship between cell line genomic alterations and therapeutic response. In addition, using DepMap’s Celligner tool, we identified which preclinical models are most representative of specific prostate cancer patient populations on cBioPortal. These data will help investigators understand the genetic differences in preclinical models of PCa and determine which ones are relevant for use in their translational research.

Extracellular vesicles (EVs) provide a minimally invasive liquid biopsy source of tumor-specific markers for patients who have already undergone prostatectomies.Our laboratory has previously demonstrated enrichment of the cancer-type solute carrier organic anion transporter family 1B3 (ct-SLCO1B3) and the ATP Binding Cassette Subfamily Member C (ABCC3) in castration-resistant cell lines (CRPC).However, their expression in EVs has yet to be explored.Our study demonstrated that ct-SLCO1B3 and ABCC3 are highly detectable in CRPC cell line-derived EVs.We also showed that ct-SLCO1B3 and ABCC3 were detectable in a CRPC xenograft mouse model, both intratumorally and in plasma-derived EVs.Our results provide evidence for EV-contained ct-SLCO1B3 and ABCC3 as novel, EV-based tumor markers for prostate cancer progression.

Background/Aim: Gonadotropin-releasing hormone 2 (GNRH2) is a poorly-studied peptide hormone that is widely distributed in the central nervous system and expressed in peripheral tissues of mammals. The non-synonymous rs6051545 variant in GNRH2 (A16V) has been linked to higher serum testosterone concentrations. This study investigated whether the A16V variant is associated with altered androgen-deprivation therapy (ADT) progression-free survival (PFS) and overall survival (OS). Patients and Methods: We examined the expression of GNRH2 in prostate tissue microarrays comprising normal tissue, prostatic hyperplasia, and prostate cancer using immunofluorescence. We also evaluated the GNRH2 genotype in 131 patients with prostate cancer who received ADT and compared PFS and OS between the variant and wild-type genotypes. Results: GNRH2 was detected in all prostate tissues, although expression did not vary with Gleason grade or disease stage (p=0.71). The GNRH2 A16V genotype was not associated with PFS or OS; however, univariate and multivariate analyses revealed Gleason score and definitive local therapy were each associated with PFS (p≤0.0074), whereas age and Gleason score were associated with OS (p≤0.0046). Conclusion: GNRH2 is expressed in normal, hyperplastic, and neoplastic prostate tissues; the A16V variant is not related to treatment outcome or survival.

Therapeutic agents that overcome acquired resistance to current androgen receptor (AR) pathway targeted therapies in patients with castration-resistant prostate cancer (CRPC) remain an unmet clinical need. A multitude of pathways are implicated in acquired treatment resistance, including the PI3K/mTOR/AKT, WNT/β-catenin, and DNA damage repair pathways. Notably, the androgen receptor splice variant 7 (AR-V7) activates the AR pathway in the absence of androgens, playing a crucial role in CRPC progression. An unbiased high throughput drug screen evaluating an array of inhibitors targeting diverse signaling pathways revealed highly synergistic activity of BH3 mimetics in AR-V7 expressing CRPC cell lines (e.g. LNCaP95, 22Rv1, VCaP-CR). Combinations targeting MCL-1 and BCL-xL (S63845 with A-1331852 or Navitoclax) displayed increased antitumor activity compared to those targeting MCL-1 and BCL-2 (S63845 with Venetoclax). Synergy among BCL-xL and MCL-1 targeted combinations was demonstrated using 2D and 3D CellTiter-Glo viability assays. Combination treatments in 3D spheroid cultures of 22RV1 and LNCaP95 cells confirmed the synergy observed in 2D assays. Furthermore, combined BCL-xL and MCL-1 inhibition altered AR-V7 expression and activated c-PARP cleavage. Drug combinations synergistically targeting BCL-xL and MCL-1 should be further explored for the treatment of therapy-resistant CRPC. Citation Format: Giulia C. Napoli, Andres F. Leon, Erica L. Beatson, Keith T. Schmidt, Emily N. Risdon, Cindy H. Chau, Douglas K. Price, William D. Figg. Treatment combinations targeting MCL-1 and BCL-xL exert synergistic anti-tumor effects in AR-V7 expressing CRPC cell lines [abstract]. In: Proceedings of the AACR Special Conference: Advances in Prostate Cancer Research; 2023 Mar 15-18; Denver, Colorado. Philadelphia (PA): AACR; Cancer Res 2023;83(11 Suppl):Abstract nr B068.

Extracellular vesicles (EVs) provide a minimally invasive source of tumor-specific markers for liquid biopsy that can be utilized for cancer detection, diagnosis, or monitoring progression. Our laboratory has previously demonstrated the endogenous expression of all transporter systems in the common prostate cancer cell lines (LNCaP, 22Rv1, PC3, DU-145) using a medium throughput TaqMan-based qRT-PCR assay. We identified the two most differentially expressed transporter genes in castration-resistant prostate cancer cells (CRPC) as the cancer-type solute carrier organic anion transporter family 1B3 (ct-SLCO1B3) and the ATP Binding Cassette Subfamily Member C (ABBC3). Both transporters have been investigated as EV-derived tumor markers; however, their detection in prostate cancer-derived EVs remains to be determined. This study aims to investigate whether ct-SLCO1B31B3 and ABCC3 mRNA exists in prostate cancer-derived EVs and can be further detected using plasma specimens. We isolated EVs from prostate cancer (LNCaP, 22Rv1, PC3, DU-145) cell line supernatant and extracted exosomal RNA for qPCR analyses. Both ct-SLCO1B3 and ABBC3 transcripts were only detected in CRPC-derived EV cells vs androgen-responsive prostate cancer cells. To explore the possibility that both transcripts in CRPC-derived EVs can be detected in plasma, we isolated plasma EVs derived from human prostate cancer xenograft mice, and then performed digital droplet PCR analysis. We demonstrated that ct-SLCO1B3 and ABBC3 are detectable in the DU-145 xenograft mouse model, both in tissues and in plasma-derived EVs. Our results provide evidence that ct-SLCO1B3 and ABCC3 exist in EVs and can be detected (at least) in mouse plasma, potentially supporting their roles as novel, plasma-based biomarkers for monitoring prostate cancer progression. Citation Format: Erica L. Beatson, Kristi Y. Lee, Martina A. Knechel, Elijah R. Sommer, Roger Depaz, Emily N. Risdon, Andres F. Leon, Jonathan D. Strope, Douglas K. Price, Cindy H. Chau, William D. Figg. Exosomal cancer-type SLCO1B3 and ABCC3 as potential biomarkers of castration resistant prostate cancer [abstract]. In: Proceedings of the AACR Special Conference: Advances in Prostate Cancer Research; 2023 Mar 15-18; Denver, Colorado. Philadelphia (PA): AACR; Cancer Res 2023;83(11 Suppl):Abstract nr B044.

Understanding mechanisms of resistance to abiraterone, one of the primary drugs approved for the treatment of castration resistant prostate cancer, remains a priority. The organic anion polypeptide 1B3 (OATP1B3, encoded by SLCO1B3 ) transporter has been shown to transport androgens into prostate cancer cells. In this study we observed and investigated the mechanism of induction of SLCO1B3 by abiraterone. Prostate cancer cells (22Rv1, LNCaP, and VCAP) were treated with anti-androgens and assessed for SLCO1B3 expression by qPCR analysis. Abiraterone treatment increased SLCO1B3 expression in 22Rv1 cells in vitro and in the 22Rv1 xenograft model in vivo. MicroRNA profiling of abiraterone-treated 22Rv1 cells was performed using a NanoString nCounter miRNA panel followed by miRNA target prediction. TargetScan and miRanda prediction tools identified hsa-miR-579-3p as binding to the 3′-untranslated region (3′UTR) of the SLCO1B3 . Using dual luciferase reporter assays, we verified that hsa-miR-579-3p indeed binds to the SLCO1B3 3′UTR and significantly inhibited SLCO1B3 reporter activity. Treatment with abiraterone significantly downregulated hsa-miR-579-3p, indicating its potential role in upregulating SLCO1B3 expression. In this study, we demonstrated a novel miRNA-mediated mechanism of abiraterone-induced SLCO1B3 expression, a transporter that is also responsible for driving androgen deprivation therapy resistance. Understanding mechanisms of abiraterone resistance mediated via differential miRNA expression will assist in the identification of potential miRNA biomarkers of treatment resistance and the development of future therapeutics.

The U.S. Food and Drug Administration recently approved two poly-adenosine diphosphate-ribose polymerase (PARP) inhibitors, olaparib and rucaparib, for treatment of biomarker-positive metastatic castrate resistant prostate cancer. The benefits of PARP inhibition have been well characterized in patients who haveBRCA1andBRCA2mutations in several forms of cancer.BRCA1andBRCA2occupy key roles in DNA damage repair, which is comprised of several different pathways with numerous participants. Patients with mutations in other key genes within the DNA damage repair pathway may also respond to treatment with PARP inhibitors, and identification of these alterations could significantly increase the percentage of patients that may benefit from PARP inhibition. This review focuses on the potential for synthetically lethal interactions between PARP inhibitors and non-BRCADNA damage repair genes. Implications for Practice The treatment potential of PARP inhibition has been well characterized in patients withBRCA1andBRCA2mutations, but there is compelling evidence for expanding the use of PARP inhibitors to mutations of other non-BRCADNA damage repair (DDR) genes. This could increase the percentage of patients that may benefit from treatment with PARP inhibitors alone or in combination with other therapies. Understanding the significance of PARP inhibitor-sensitizing alterations in other common non-BRCADDR genes will help guide clinical decisions to provide targeted treatment options to a wider population of patients.