43. Targeted modulation of integrin expression increases freeze sensitivity of androgen-insensitive prostate cancer

Abstract

Cryoablation has emerged as a primary therapy to treat prostate cancer. While effective, the assumption that freezing serves as a ubiquitous lethal stress is challenged by clinical experience and experimental evidence demonstrating time temperature related cell death dependence. The age-related transformation from an androgen-sensitive (AS) to an androgen-insensitive (AI) phenotype is a major challenge in the management of prostate cancer. AI cells exhibit morphological changes and resistance to many treatment therapies. This resistance has been linked with α 6 β 4 integrin overexpression as a result of androgen receptor (AR) loss. As such, we investigated the influence of increased α 6 β 4 integrin expression as a result of AR loss, on the reported increased freeze tolerance of AI prostate cancer. Further, we evaluated the targeted modulation of integrin expression in combination with cryoablation on human prostate cancer cell death. A series of studies using established AS (LNCaP LP and PC-3 AR) and AI (LNCaP HP and PC-3) cell lines were designed to investigate the cellular mechanisms contributing to variations in freezing response. Samples were frozen, thawed, and temporally assessed using fluorescence microscopy, flow cytometry and immunoblotting. Investigation into α 6 β 4 integrin expression confirmed that AI cell lines overexpressed this protein, thereby altering cellular morphology and increasing adhesion characteristics. For instance, following freezing to −15 °C, AI cells were found to exhibit increased resistance to freezing injury compared to AS cells (55% vs. 18%, respectively). Molecular investigations revealed a significant decrease in caspase 8, 9, and 3 levels in AI cells following freezing. Inhibition of α 6 β 4 integrin in AI samples resulted in increased caspase activity and enhanced cell death. These studies demonstrate that integrin expression significantly influences cell tolerance to cryoablation. The data show that the inhibition of α 6 β 4 integrin function results in a significant increase in freeze sensitivity of AI prostate cancer cells. Given these results, understanding the role of androgen-receptor related integrin expression in cell response to freezing may lead to novel options for neo-adjunctive approaches to treat prostate cancer.