Integrin involvement in freeze resistance of androgen-insensitive prostate cancer.

Cryoablation has emerged as a primary therapy to treat prostate cancer. Although 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 treatment resistance to many therapies. As this resistance has been linked with alpha6beta4 integrin overexpression as a result of androgen receptor (AR) loss, we investigated whether alpha6beta4 integrin expression, as a result AR loss, contributes to the reported increased freeze tolerance of AI prostate cancer. A series of studies using 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. Investigation into alpha6beta4 integrin expression revealed that AI cell lines overexpressed this protein, thereby altering morphological characteristics and increasing adhesion characteristics. Molecular investigations revealed a significant decrease in caspases-8, -9, and -3 levels in AI cells after freezing. Inhibition of alpha6beta4 integrin resulted in increased caspase activity after freezing (similar to AS cells) and enhanced cell death. These data show that AI cells show an increase in post-freeze susceptibility after inhibition of alpha6beta4 integrin function. Further understanding the role of androgen receptor-related alpha6beta4 integrin expression in prostate cancer cells responses to freezing might lead to novel options for neo-adjunctive treatments targeting the AR signaling pathway.