Vitamin D ₃ cryosensitization increases prostate cancer susceptibility to cryoablation via mitochondrial‐mediated apoptosis and necrosis

Abstract

What's known on the subject? and What does the study add? Cryoblation is a highly effective treatment for prostate cancer yet concerns of recurrance remain due to cell survival in the periphery of the frozen volume of tissue where lethal temperatures may not be achieved. To improve efficiency research has focused on the use of low dose adjunctive agents, including vitamin D 3 to senstitise cells to mild freezing thereby increasing cancer destruction. This study describes a molecular basis of Vitamin D 3 cryosensitization including the response and efficacy of the combination in both androgen‐sensitive and insensitive prostate cancer. The data support a putative role for Vitamin D 3 cryosensitization in enhancing prostate cancer sensitivity to mild freezing temperatures providing insight for further optimization and application of this therapeutic option. OBJECTIVES To investigate the effect and molecular mechanisms of action of Vitamin D 3 (VD 3 ) as a neo‐adjunctive agent before cryosurgery in an effort to increase treatment efficacy for prostate cancer (CaP). To eliminate the potential for disease recurrence that exists at the periphery of the freeze lesion, where temperatures may be insufficient to destroy both androgen‐sensitive (AS) and androgen‐insensitive (AI) CaP. METHODS Human CaP cells, LNCaP, were each genetically altered to express the AS and AI phenotypes and subjected to VD 3 treatment and freezing in an in vitro and tissue‐engineered model. Cell viability, caspase inhibitor and western blot studies were used to determine the basis of the different responses of AI and AS cells to VD 3 cryosensitization. RESULTS VD 3 was found to be a highly effective cryosensitizer, resulting in a >50% overall increase in cell death after −15 °C freezing. Fluorescence microscopy, western blot analysis and caspase protease assays confirmed that the increased activation of apoptosis was modulated through a mitochondrial‐mediated pathway. Caspase inhibition studies showed that apoptosis played an integral role in cell death, with VD 3 cryosensitivation‐induced apoptotic events responsible for >30% of the overall cell death after −15 °C freezing. CONCLUSIONS The present study suggests that the use of VD 3 as a cryosensitizer increases cryoablation efficacy through the increased activity of apoptosis as well as through necrosis. The data show that through VD 3 treatment the overall level of AI CaP cell tolerance to freezing is reduced to a level similar to that of AS CaP. VD 3 pre‐treatment in conjunction with cryoablation may increase treatment efficacy and reduce disease recurrence for CaP patients.