Abstract 255: Dual targeting of Delta-like ligand 4 (DLL4) and programmed death 1(PD1) inhibits tumor growth and generates enhanced long-term immunological memory

Blocking DLL4, a Notch ligand, effectively inhibits tumor growth by increasing non-functional angiogenesis and decreasing the cancer stem cells (CSC) population. We are currently testing an anti-DLL4 antibody, demcizumab, in Phase1B trials in NSCLC, pancreatic, and ovarian cancer. DLL4 is also known to modulate immune responses. In the current study we examine the impact of anti-DLL4 on anti-tumor immune responses as a single agent and in combination with the key immune checkpoint inhibitor Programmed Cell Death Protein 1 (PD1). While the recent clinical success of PD1 inhibitors represents a new and promising cancer immunotherapeutic approach, high initial response rates are often associated by a lack of long-term, durable effects in a significant number of patients. Therefore, we hypothesized that dual blockade of DLL4 and PD1 might further impact tumor growth by further enhancing anti-tumor immune immunity. Our data demonstrates that dual blockade of DLL4 and PD1 using antibodies not only reduces tumor growth, but also led to tumor rejection in ∼50% in CT26WT tumor-bearing mice, similar to those treated with anti-PD1 alone (no tumor rejection was observed with anti-DLL4 alone). Anti-PD1 increased specific CD8+ T cell-mediated IFN-γ production while decreasing IL6. Anti-DLL4 treatment reduced IL17 production. Interestingly, only the dual blockage led to increased production of IL2 by splenocytes. Since IL2 is required for secondary population expansion of CD8+ memory T cells, increased IL2 in the combination group suggests potential for increased T cell activation, maintenance and memory T cell function, as compared to single agent anti-DLL4 and anti-PD1. While anti-PD1 reduced inhibition of CD4+ T cell proliferation by Tregs, the dual blockade significantly reduced Treg-mediated CD8+ T cell suppression. Furthermore, both effector and memory CD8+ T cell frequencies were increased within the total CD8+ T cell population. Interestingly, anti-PD1 decreased granulocytic MDSCs, while anti-DLL4 reduced monocytic MDSCs. Mice cured with single-agent anti-PD1 and anti-DLL4/anti-PD1 combination treatments were protected from series of re-challenge with tumor cells, suggesting the existence of immunologic memory. Interestingly, more mice were protected from tumor re-challenge when both DLL4 and PD1 were blocked, as compared to PD1 alone. Surprisingly, mice previously treated with the anti-DLL4/anti-PD1 combination produced more IL2, clearly indicating the role of DLL4 blockade in enhancing anti-tumor immunity. Therefore, these results show that dual targeting of DLL4 and PD1 may be an effective and durable cancer therapy by increasing anti-tumor immune response and promoting long-term immunological memory. Citation Format: Minu Srivastava, Christopher L. Murriel, Julie Roda, Hyun-Bae Jie, Fumiko Axelrod, Ming-Hong Xie, Rui Yun, Erin Mayes, Trevor Bentley, Belinda Cancilla, Raymond Tam, Tracy Tang, Ann Kapoun, John Lewicki, Tim Hoey, Austin Gurney, Angie Inkyung Park. Dual targeting of Delta-like ligand 4 (DLL4) and programmed death 1(PD1) inhibits tumor growth and generates enhanced long-term immunological memory. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 255. doi:10.1158/1538-7445.AM2015-255