Modulation of the tumor immune microenvironment by targeting STAT3 and CD47-SIRPa axis for the treatment of osteosarcoma-lung metastasis.

Despite the multimodal treatment approach with aggressive chemotherapy and surgery, 30-35% of Osteosarcoma (OS) patients develop lung metastases and the survival rate for these patients is <20%. Novel therapeutic strategies are urgently needed, and immunotherapy is of significant interest. Unfortunately, the response rate to several different immunotherapies has been disappointing. The lack of response may be secondary to tumor immune microenvironment (TME) highly infiltrated by immune suppressive cells. Immune suppressive cells blunt anti-tumor effector response. The outcome for patients with metastatic OS has been shown to correlate with the phenotype of macrophages (anti-tumor M1 vs pro-tumor M2). We have demonstrated that targeting the immune checkpoint PD1-PDL1 pathway reduced lung metastases and altered TME. This was associated with the phenotypic change in macrophages from M2 to M1 and a decrease in activated STAT3. STAT3 is an oncogene that regulates TME. These observations suggest that strategies targeting STAT3 and tumor-associated immune suppressive cells may be of significant therapeutic benefit. In our preliminary studies, we observed that inhibition of STAT3 activation by orally bioavailable small molecule WP1066 executed cytotoxic effect on OS cells as well as immune suppressive cells. Moreover, WP1066 treated OS cells were efficiently phagocytosed by alveolar macrophages. Importantly, in vivo WP1066 treatment of animals infused with OS cells significantly prolonged the survival and altered TME. Multiple studies along with our observation suggest that OS cells constitutively express CD47, a “don’t eat me” surface protein that suppresses activation of innate immune cells (macrophage, dendritic cells, and NK cells). The anti-CD47 antibody has been shown to enhance anti-tumor immunity and eradicate tumors. In the study, we propose to investigate the synergistic therapeutic efficacy of WP1066, a STAT3 inhibitor, and anti-CD47 antibody against metastatic OS. We anticipate that the combination therapy will modulate the TME from a tumor-permissive to anti-tumor phenotype by blocking STAT3 activation and promoting M1 macrophages, which in turn will induce the regression of the lung metastases. We will determine the therapeutic benefit by using our well-established syngeneic experimental metastasis model. In addition, we will also perform immune landscape profiling of lungs after the treatment. Most importantly, we will determine the therapeutic efficacy in clinically relevant orthotopic metastasis model using syngeneic and humanized xenogeneic settings. The proposed study is of significant interest with clinical translational implications. Successful completion of the study will establish a “proof of concept” of a novel immune therapeutic strategy to successfully alter TME and enhance anti-tumor immunity with survival benefit. This approach is likely to be applicable for a wide range of sarcomas which also metastasize to the lungs.