Strong single-agent and PD-1/PD-L1 combination antitumor activity of antisense oligonucleotides suppressing Neuropilin 1 expression.

e14592 Background: While the introduction of immune checkpoint inhibitors (ICIs) is considered as a breakthrough in cancer therapy, large proportions of patients still do not respond or develop resistance, indicating a need for new targets and therapies to provide long-term therapeutic benefits. Neuropilin-1 (NRP1) is a membrane-bound multi domain protein expressed by different cell types in the tumor microenvironment. NRP1 promotes cell migration, survival, and angiogenesis via distinct domains. Moreover, it mediates immunosuppression by stabilization of regulatory T cells, attraction of immunosuppressive myeloid cells into the tumor microenvironment, and exhaustion of effector T cells. Therapeutic benefit is expected to be superior by simultaneous suppression of all functions and consequently all domains, which can be optimally achieved by suppression of its expression, for example mediated by antisense oligonucleotides (ASOs), instead of e.g. domain specific antibodies. Methods: Using our in-house bioinformatics and screening systems, we have identified potent and specific locked nucleic acid (LNA) modified ASOs specifically targeting NRP1. Mice bearing established syngeneic MC38 or EMT6 tumors were treated by intraperitoneal injection of unformulated ASO either as monotherapy or in combination with ICIs. Tumor growth and survival were determined as well as target engagement. Results: After systemic administration of different NRP1-specific ASOs we observed a potent downregulation of NRP1 expression in different cell types in tumors, including myeloid cells, T cells and non-immune cells as well as a strong reduction of soluble NRP1 plasma levels. Suppression of NRP1 correlated with both a delayed tumor growth or even complete tumor regression and prolonged survival as a monotherapy which was further improved in combination with ICIs. Particularly in an EMT6 breast cancer model, combination of NRP1 ASOs with PD-1 antibody resulted in tumor rejection and long-term survival in most animals. Rechallenge of long-term surviving mice with EMT6 tumor cells did not result in tumor growth. Conclusions: We could show that ASO-mediated suppression of NRP1 expression has strong potential as a novel therapeutic strategy, especially in combination with ICIs. Additional studies to further elucidate the mechanisms underlying the observed anti-tumor efficacy as well as IND-enabling activities are underway to progress the program towards clinical testing.