Abstract 3353: The emerging role of extracellular HSP90 in prostate cancer progression to a metastatic phenotype

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Abstract Background: Metastasis is the central cause of lethal prostate cancer (PCa). Mechanisms regulating metastasis represent high-potential therapeutic targets for preventing development of lethal PCa. Inhibitors of extracellular heat shock protein 90 (eHSP90) have been shown to inhibit prostate cell motility. In contrast to the intracellular HSP90 (iHSP90), whose biology has been extensively studied, and whose therapeutic targeting is associated with systemic toxicity, the biology of extracellular HSP90 is not well understood. We undertook a series of investigations to better understand eHSP90 biology in PCa. Methods: Human PCa cells were subjected to cellular stress by heat shock combined with serum starvation. Resultant conditioned media was probed for matrix metalloproteinase 2 (MMP-2) by zymography and subject to scratch-wound and Boyden chamber invasion assays. Expression of HSP90 and CDC37 was measured by Western blot. Plasma from patients with PCa and healthy controls was probed for eHSP90 by ELISA. Results: We have examined expression of iHSP90 and eHSP90 after cellular stress, induced by heat shock and serum starvation, in human PC3, LNCaP, C4-2B, 1532NPTX and 1532CPTX PCa cell lines. Cell stress induces increased eHSP90 in all PCa cell lines examined. This is associated with a decrease in MMP-2 activity in conditioned media. Conditioned media from stressed cells was also shown to decrease invasion of PC3 cells, consistent with changes in MMP-2. Of high interest, the addition of protease inhibitors to conditioned media led to a complete reversal of the MMP-2 response: its activity increased with cellular stress. When measuring HSP90α in plasma from healthy controls (N = 20) and patients with PCa (N = 40, 20 localized and 20 metastatic), we demonstrated a significant (p=.001) >2 fold increase in PCa compared to control. Further, a significant increase in HSP90α was observed when low versus high T stage lesions were compared. There was no statistically significant difference in HSP90α for those with metastasis to regional lymph nodes, non-regional lymph nodes, bone, or liver. Conclusion: We demonstrate that increased eHSP90 due to cellular stress is a response observed across all PCa cell lines examined and should be considered typical. Its association with extracellular MMP-2 activity is dependent on the presence of other proteases and indicates a complex regulatory mechanism. Examination of eHSP90 in humans supports its association with aggressive disease. These factors support further investigation of underlying biology and therapeutic opportunities. Citation Format: Katelyn O'Neill, Johnny Zigmond, Raymond Bergan. The emerging role of extracellular HSP90 in prostate cancer progression to a metastatic phenotype [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3353.