No abstract

Background: Cis-but not carbo-based chemo leads to durable disease control in a subset of pts with mUC, but the underlying mechanisms remain elusive. Exploratory data from the randomised Ph III IMvigor130 study suggested improved OS with the addition of atezo to cis-but not carbo-based chemo (Galsky AACR 2021). Here we tested the hypothesis that cis may induce immunomodulatory effects.

5145 Background: Increased AR level, characteristic of advanced PC, has been linked to AI growth while its down-regulation to restored androgen-dependence (AD). However, the mechanisms of AR overexpression remain in dispute. The objectives were to study the proteins comprising a novel ARS that binds to 5’-UTR of AR gene, which is partially lost in AI LNCaP cells; the status of ARS proteins in AD and AI human specimens and therapeutic modulation of ARS proteins. Methods: Parental AD LNCaP cells and its AI- derivative expressing 4 fold more AR-mRNA and protein than parental AD LNCaP were used to isolate, in vitro/in vivo characterize and therapeutically modulate ARS proteins and cell growth. NYU Tissue Bank provided human samples. Assays: column chromatography, SDS-PAGE, mass spectrometry, EMSA, Southwersten-Western, ChIP, cDNA array, real time PCR, si-RNA, immunohistochemistry. Results: Pur alpha (Pura) and hnRNP-K are part of ARS complex that binds in vitro and in vivo to a defined DNA sequence in 5’UTR of AR gene. AI cells with high AR had 3 times less Pura: its forced expression lowered AR levels. Pura knockdown in AD cells yielded higher AR levels and AI growth. Hormone-naive human PC specimens had significantly increased AR (0.0317) and lower Pura-RNA (0.0317) than hormone resistant PCs. In-vivo binding of Pura (ChIP) to 5’UTR was also reduced (p=0.0028). Histone deactetylase inibitors (HDACI) increased binding of Pura to 5’UTR, decreased AR levels and inhibited AI-growth of LNCaP cells. Conclusions: We show that AR over-expression and AI-growth of a hormone resistant PC cell line are affected by a loss of a repressor complex that binds to 5’-UTR of AR gene. Pura is a crucial part of this complex. We have convincing evidence obtained in hormone naive and resistant human samples to indicate that similar mechanism might be responsible for human PC progression. We determined HDACI can restore Pura levels and androgen-dependence. No significant financial relationships to disclose.