Targeting bladder cancer-macrophage interactions by SPARC peptides

Bladder cancer is one of the privileged cancers treated with two modalities of immune therapeutics: intravesical Bacille Calmette-Guérin (BCG) for non-muscle invasive disease and immune checkpoint inhibitors for advanced metastatic muscle invasive disease. However, recurrence, intolerance and adverse events are encountered in both modalities with limited second and third line treatment options. Clinical data indicated that pretreatment infiltration of bladder tumors with tumor associated macrophages (TAMs) is associated with BCG failure, resistance to standard of care chemo- and immune-therapy and poor disease outcome. Preclinical studies indicated that macrophage infiltration is the forerunner of carcinogen-induced preneoplastic bladder lesions and progresses throughout overt neoplastic and metastatic disease. Thus, TAMs represent a plausible therapeutic target for bladder cancer. Capitalizing on our earlier report that SPARC, as tumor suppressor of BCa, we developed peptides mapping the biologically active domains of SPARC and investigated their direct effect on tumor cell malignant phenotype. In tandem, we determined the effect of SPARC-peptides on macrophage differentiation, polarization, and anti-tumor effects. We identified a potent inhibitory effect of our peptides on a panel of bladder cancer cell survival and invasiveness in 2D and 3D cultures. Using macrophage cell lines as well as bone marrow-derived myeloid cells, we found these peptides induced an M1 phenotype in response to cytokine stimulation, with enhanced phagocytic activity and macrophage-induced tumor cell killing in vitro. Moreover, SPARC-peptides inhibited macrophage polarization to M2 phenotype. Our data strongly suggest that SPARC-peptides are promising therapeutic candidates for bladder cancer.