The use of 1,25α dihydroxyvitamin D3 as a cryosensitizing agent in a murine prostate cancer model

Cryotherapy has emerged as a primary treatment option for prostate cancer(CaP); however, incomplete ablation in the periphery of the cryogenic lesion can lead to recurrence. Accordingly, we investigated the use of a nontoxic adjunctive agent, Vitamin D(3), with cryotherapy to sensitize CaP to low temperature induced, non-ice rupture related cell death. Vitamin D(3) (calcitriol) has been identified as a possible adjunct in the treatment of cancer due to its anti-proliferative and anti-tumorigenic properties. This study aimed to identify the cellular responses and molecular pathways activated when vitamin D(3) (calcitriol) is combined with cryotherapy in a murine prostate cancer model. Single freeze-thaw events above −15°C had little effect on cancer cell viability; however, pre-treatment with calcitriol in conjunction with cryo significantly increased cell death. The −15°C calcitriol combination increased cell death to 55% following a single freeze, compared to negligible cell loss by freezing or calcitriol alone. Repeat cryo-combination yielded90% cell death, compared to 65% in dual freeze-only cycles. Western blot analysis following calcitriol cryosensitization regimes confirmed the activation of apoptosis. Specifically, pro-apoptotic Bid and pro-caspase–3 were found to decrease at 1h following combination treatment, indicating cleavage to the active forms. A parallel in vivo study confirmed the increased cell death when combining cryotherapy with calcitriol pre-treatment. The development of an adjunctive therapy combining calcitriol and cryotherapy represents a potentially highly effective, less toxic, minimally invasive treatment option. These results suggest a role for calcitriol and cryo as a combinatorial treatment for CaP with the potential for clinical translation.