Abstract 1720: IGFBP3 signaling promotes resistance to next-generation antiandrogens therapeutics in advanced prostate cancer

Abstract Background: Next-generation antiandrogen therapeutics (NGATs) have irrefutably improved the survival of prostate cancer patients. However, treatment resistance to NGATs remains a clinical challenge for men with castration-resistant prostate cancer (CRPC). The molecular mechanisms underlying resistance to NGAT remain confounding. Insulin growth factor binding protein 3 (IGFBP3) is associated with prostate cancer tumorigenesis and progression. It is known that IGFBP3 induces sphingosine kinase (SphK1) activation subsequently inducing sphingosine-1-phosphate (S1P) production. Previously, we found that IGFBP3 is necessary for PARP inhibitor resistance in acquired resistant models (OlapR cells). We hypothesize that IGFBP3 is required for acquired and intrinsic NGAT resistance. Methods: Enzalutamide-resistant (MDVR), Abiraterone-resistant (AbiR), Apalutamide-resistant (ApalR), and Darolutamide-resistant (DaroR) C4-2B subline cells exhibit stout NGAT resistance compared to C4-2B parental cells. In addition, this study also utilized 22Rv1 cells that display intrinsic resistance to Enzalutamide. We performed transcriptomic analysis on enzalutamide-treated patients’ cohorts and the enzalutamide-resistant prostate cancer cell lines. RNAseq, real time qPCR, immunoblot, and ELISA were used to determine IGFBP3 expression and secretion levels. Cell viability was determined in resistant cell lines after silencing IGFBP3 and SphK1 using siRNA or inhibiting SphK1 using SphK1 inhibitor, SKI-II. Results: This study found that IGFBP3 was upregulated in NGAT resistant models (MDVR, AbiR, ApalR, DaroR, and 22Rv1 cells) using transcriptomics. We found that NGAT resistant models highly express IGFBP3 and SphK1 using RNA-seq, qPCR, and immunoblot. SphK1 is a lipid kinase that phosphorylates sphingosine to form S1P metabolite which promotes tumor survival, proliferation, and resistance. We discovered high levels of IGFBP3 and S1P secretion in the resistant models. We found that inhibition of IGFBP3/SphK1 decreased both SphK1 expression and S1P secretion. Mechanistically, IGFBP3 activated the Sphingolipids pathway to promote cell survival and subsequently enforce the growth factor signaling to enhance cell proliferation. Ablating the expression of IGFBP3 promotes the formation of ceramide which induces the apoptotic cascade. Conclusion: We demonstrated that increased IGFBP3 expression by NGAT treatment leads to increased sphingolipid metabolism by simultaneously demoting ceramide-induced apoptosis and fostering S1P production through SphK1 activation. Thus, IGFBP3 induces the activation of SphK1 to hijack the sphingosine metabolism to fuel NGAT resistance. Our findings demonstrate that targeting the IGFBP3/SphK1 signaling axis enhances our ability to resensitizes resistant CRPC to NGAT therapeutics. Citation Format: Amy Rose Leslie, Shu Ning, Masuda Sharifi, Zachary A. Schaaf, James P. Maine, Wei Lou, Chengfei Liu, Alan P. Lombard, Allen C. Gao. IGFBP3 signaling promotes resistance to next-generation antiandrogens therapeutics in advanced prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 1720.