First published September 6, 2018 - More info
Despite the success of T cell checkpoint blockade against melanoma, many “cold” tumors such as prostate cancer remain unresponsive. We find that hypoxic zones are prevalent across pre-clinical prostate cancer and resist T cell infiltration even in the context of CTLA-4 and PD-1 blockade. We show that the hypoxia-activated prodrug TH-302 reduces or eliminates hypoxia in these tumors. Combination therapy with this hypoxia-prodrug and checkpoint blockade cooperate to cure more than 80% of TRAMP-C2 prostate tumors. Immunofluorescence imaging shows that TH-302 drives an influx of T cells into hypoxic zones, which are then amplified by checkpoint blockade. Further, combination therapy reduces myeloid-derived suppressor cell density by more than 50%, and causes a persistent defect in the capacity of the tumor to replenish the granulocytic subset. Spontaneous prostate tumors in TRAMP transgenic mice, which are completely resistant to checkpoint blockade, show minimal adenocarcinoma tumor burden at 36 weeks of age and no evidence of neuroendocrine tumors. Survival of Pb-Cre4, Ptenpc−/−Smad4pc−/− mice with highly aggressive prostate adenocarcinoma is also significantly extended by the combination of hypoxia-prodrug and checkpoint blockade. This combination of hypoxia disruption and T cell checkpoint blockade may render some of the most therapeutically resistant cancers sensitive to immunotherapy.