Abstract 653: Molecular pathology of metastatic prostatic adenocarcinoma treated with bipolar androgen therapy (BAT) reveals a correlation between MYC mRNA and protein

Abstract Molecular analysis of tissue samples from metastatic cancer lesions can improve our understanding of drug response and resistance. Since prostate cancer cells initially require androgen signaling through the androgen receptor (AR) for proliferation, the treatment of metastatic prostate cancer involves surgical or chemical castration. While most patients respond initially, nearly all develop acquired resistance to combined androgen blockade using both first and second line agents. This resistance is often related to overexpression of AR, which is frequently driven by AR gene amplification. In some patients, this increased AR appears to render tumor cells sensitive to high dose androgens in a manner that paradoxically inhibits their growth. Bipolar Androgen Therapy (BAT) was introduced several years ago at our institution in which patients with castration resistant prostate cancer (CRPC) are treated intermittently with high dose testosterone. Prior clinical trials have shown that BAT can produce biochemical and objective responses, and may re-sensitize prostate cancer to subsequent second generation AR inhibitors. To define the mechanism(s) by which BAT results in tumor regression, we performed a clinical trial (NCT03554317) for patients with CRPC that included biopsies of soft tissue metastases before BAT and after 3 cycles of BAT (C4D1). Up to four tissue cores were taken per biopsy with two cores for formalin fixation and paraffin embedding (FFPE) and the others snap frozen. Histologically viable tumor cells were present for both the pretreatment and C4D1 time points for 24 of the 42 enrolled patients. The FFPE samples were stained for H&E and by IHC for AR, MYC and Ki67. MYC and Ki67 IHC stained slides were subjected to quantitative image analysis using HALO software (Indica Labs). Adequate frozen tumor tissue was available for laser capture microdissection and adequate amounts of RNA were obtained from 15 patients with paired pretreatment and C4D1 biopsies. RNAseq libraries were prepared using the NuGEN Ovation RNA-Seq System V2 and barcoded libraries were sequenced to an average depth of > 100 million reads per sample on an Illumina NovaSeq. Gene expression values were obtained with RSEM using Star aligner with GRCh38 (human). When comparing the C4D1 samples to the pretreatment samples, there were marked decreases in tumor MYC protein levels in approximately half of the treated patients, which was associated with decreased Ki67, decreased tumor volume, and prolonged progression-free survival on BAT. Using an image analysis computed H-SCORE for MYC, there was a strong correlation between MYC protein levels and MYC mRNA using RNAseq (r=0.81, p = 2.3 x 10-7). This indicates that MYC protein levels correlate with MYC mRNA and that reductions of MYC protein by BAT are likely related to reductions of MYC mRNA in clinical metastatic tissue samples. Citation Format: Carolina Gomes Alexandre, Tracy Jones, Jessica L. Hicks, John T. Isaacs, Anuj Gupta, Alyza Skaist, Laura Sena, Jennifer Meyers, Emmanuel Antonarakis, Mark Markowski, Samuel Denmeade, Srinivasan Yegnasubramanian, Angelo Michael De Marzo. Molecular pathology of metastatic prostatic adenocarcinoma treated with bipolar androgen therapy (BAT) reveals a correlation between MYC mRNA and protein [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 653.