Abstract
The application of cold injury to cells for the treatment of cancer is not a new concept. Prostate cryotherapy has developed rapidly over the last decade thanks to significant advances in cryoprobe technology. The ideal temperature for tissue destruction was identified to be < -40°C which is technically difficult to achieve, and would pose significant damage to neighbouring organs if applied. As a result, local and systemic failure is frequently observed. To date, the strategies for modifications of the techniques and delivery mechanisms have been associated with improved outcome and reduce complications. During freezing, tissues within the ice ball are exposed to various damaging stresses which may actually be insufficient to ensure complete tissue ablation especially in the peripheral zone. With better understanding of the molecular mechanisms involved in cryogenic injury, it may be possible to identify and use candidate adjunctive therapies, either as sensitisers pre- or concomitantly with cryotherapy, to enhance the efficacy of the procedure. This study has sought to advance understanding on the effects of cryoinjury on human prostate cancer cell biology. We developed a robust and reproducible in vitro model of prostate cryoinjury, which was then used to identify key transcriptional changes in cells by microarray analysis. Specifically, we found specific changes in gene expression of TNF-α receptor superfamily, caspase 3 and caspase 8 which suggested potential synergy between TRAIL treatment and cryotherapy. This synergy was confirmed using our in vitro model; the mode of death was mainly by necrosis. Local tumour cell kill by necrosis is associated with an infiltration of antigen presenting cells (dendritic cells), uptake of released antigen, trafficking of these cells to regional lymph nodes to prime antitumour T cells responses. We evaluated the immunological effect of cryotherapy-treated prostate cancer cells on monocyte derived DC as this exact scenario may potentially occur during prostate destruction in vivo by cryotherapy. We demonstrated that cryotreated tumour cells are overall stimulatory to DC phenotypically and in terms of functionally. In this way, 'cryoimmunotherapy' may be a credible means of generating antigen specific T cell responses to target micrometastases and remote sites of tumour spread. We evaluated of the role of the AQPs expression in prostate cancer cells. AQPs are membrane proteins that facilitate selective water and small solute movement across the plasma membrane. AQP3 expression was increased upon exposure to freezing injury. Inhibition of AQP3 was successful in increasing the sensitivity of prostate cancer cells to cryoinjury and a significant increase in cell death was attained at -10°C freezing temperature. The observed effect was possibly due to increased intracellular ice formation at higher freezing temperatures. Overall, new insights into the molecular and immunological aspects of cryotherapy may lead to the logical design of new clinical strategies to improve the overall efficacy of cryotherapy. Most likely, sensitisation of prostate cancer by local or systemic delivery of agents designed to accentuate direct or indirect cell injury followed by cryotherapy will form the next generation of clinical trials for a clinical scenario for which there remains no standard of care.