Introduction: Men are 3-4 times more likely to be diagnosed with bladder cancer (BCa) than women, who often have more aggressive tumors. Intravesical instillation of BCG is one of the first immunotherapies in widespread use and is given to patients with non-muscle invasive bladder cancer (NMIBC). Newer PD-1/PD-L1 checkpoint inhibitors now also have proven efficacy against BCa. Nonetheless, approximately 35% of patients fail to respond to BCG, with response rates to checkpoint immunotherapy much lower. Based on prior work suggesting the importance of the androgen receptor (AR) in BCa, we investigated AR-targeting as a novel strategy to improve the response to BCa immunotherapy in the MBT-2 murine BCa model.
Methods: Subcutaneous injection of 106 MBT-2 cells into male and female C3H mice was performed, with tumors harvested at tumor size limits. The AR antagonist enzalutamide (ENZ) was given in alone or combination with anti-PD-1 or intra-tumoral BCG treatments as previously described. Selected human NMIBC were collected following transurethral resection. After digestion of fresh human and murine tumors, flow cytometry analyses characterized the immune cells present. The anti-proliferative effect of AR antagonists against human and murine BCa cell lines was tested in vitro.
Results: The CD45+/CD45- ratio, extent of tumor infiltrating lymphocytes, and expression of immune checkpoint markers from the MBT-2 model is comparable to the immune composition of NMIBC tumors resected from patients. Moreover, the model also recapitulates previously observed human tumor immune cell gender differences. AR antagonist ENZ demonstrated anti-proliferative effects in lower grade human and murine BCa cell lines, while limited differences were seen in human high grade BCa cell lines. While ENZ alone had no effect in vivo, its use in combination with either anti-PD-1 or BCG treatment in male mice synergized to improve response rates. Complete response was confirmed by re-challenge of mice, demonstrating immune memory. Notably, the proportion of complete responses in male mice treated with the combination treatment is similar to that observed in female mice with either immunotherapy alone. Flow cytometry analyses showed that these therapeutic benefits in male mice are related to an increase in pro-inflammatory tumor infiltrating dendritic cells as well as a decrease in anti-inflammatory tumor infiltrating dendritic cells and myeloid-derived suppressor cells.
Conclusions: Our results suggest that combining AR antagonism with immunotherapy in male BCa patients may potentiate the antitumor immune response and increase response rates. Accordingly, a Phase II trial to evaluate the efficacy of AR antagonism in combination with BCG to decrease NMIBC tumor recurrences in men is planned. Further, the MBT-2 murine model appears relevant to investigate immunologic BCa sex differences.
Source of Funding: Cancer Research Society (Upcycle Grant)
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