Author ORCID Identifier
Date of Graduation
Doctor of Philosophy (PhD)
We previously showed that the hypoxia-activated prodrug TH-302 (Evofosfamide) reduces intratumoral hypoxia through a tissue remodeling process, initiates tumor vasculature reorganization, and sensitizes aggressive, spontaneous murine models of prostate cancer to immune checkpoint blockade (ICB). In a clinical trial testing the combination of TH-302 with cytotoxic T-lymphocyte-associated protein (CTLA-4) blockade (NCT03098160) a subset of metastatic, ICB refractory patients showed prolonged progression free survival. While these studies highlight hypoxia as therapeutically tractable, we lack a complete understanding of the contribution of the tumor vasculature to hypoxia reduction therapy, as well as the downstream consequences of hypoxia reduction on the cellular composition of the tumor microenvironment and the responsiveness to immunotherapy. Here, we used a Kras+/G12DTP53+/R172HPdx1-Cre (KPC) derived model of pancreatic adenocarcinoma (PDAC) to examine the tumor response to and adaptive resistance mechanisms engaged by therapy with two established methods of hypoxia-reducing therapy: the hypoxia-activated prodrug TH-302 and vascular endothelial growth factor receptor 2 (VEGFR-2) blockade. The combination of both modalities normalized tumor vasculature and led to an accumulation of DNA damage yielding a significant delay in tumor growth. In contrast to prior observations in other cancers, the combination did
not, however, significantly alleviate overall tissue hypoxia or sensitize tumors to ICB therapy despite qualitative improvements to the CD8 T cell response. Whole tumor RNA sequencing suggested an increased influx of granulocytic myeloid derived suppressor cells (G-MDSC) into treated tumors potentially responding to increased tumor-intrinsic release of the chemokine CCL9. Blockade of the CCL9 cognate receptor, CCR1, was found inhibit G-MDSC migration towards TH-302 and VEGFR-2 blockade treated tumor supernatants, and G-MDSC depletion was found to increase sensitivity to ICB in combination treated animals. These data suggest that pancreatic tumors modulate G-MDSC migration as an adaptive response to vascular normalization with both a hypoxia-activated prodrug and anti-angiogenic therapy, and that these immunosuppressive myeloid cells act in a setting of persistent hypoxia to maintain adaptive immune resistance.
Hypoxia, Angiogenesis, MDSC, Tumor immune microenvironment
Available for download on Thursday, April 25, 2024