Abstract 589: Hedgehog signaling augments PDL-1 expression in cancer cells under hypoxic condition to inhibit antitumor effects by activated lymphocytes

[Background] Hedgehog (Hh) signaling is activated under hypoxic condition in cancerous tissue. This is thought to be one of the mechanisms of the induction of malignant phenotype of cancers. We have shown that Hh inhibitor decreases proliferation, invasiveness, and tumorigenesis. We have also revealed that Hh signaling plays pivotal roles for the maintenance of function in activated lymphocytes and dendritic cells under hypoxia. Recently, immune checkpoint inhibitor takes much attention, however, response rate is still limited. The mechanisms regulating PDL-1 expression also remains unclear. In this study, to increase reponse rate of immune checkpoint inhibitor, we investigated whether hypoxia-induced activation of Hh signaling contributes to PDL-1 expression in cancer and whether it affects the antitumor function of activated lymphocytes. [Materials and Methods] Pancreatic cancer cell line, Panc-1, gallbladder cancer cell line, NOZ and GBd, and lung small cell cancer cell line, SBC-5 were used as target cancer cells. Human lymphocytes derived from PBMC were activated by using anti CD3 mAb and IL-2, and were used as effector cells. For normoxic conditions, cells were cultured in 5% CO2 and 95% air. For hypoxic conditions, cells were cultured in 1% O2, 5% CO2, and 94% N2 using a multigas incubator. For Hh signaling inhibition, cyclopamine, polysaccharide-K (PSK), and small interfering RNA targeting Gli1, Smo, MAML3, and RBPJ were used. Cell numbers were counted by light microscope. Expression of cell surface molecules was estimated by FACS. [Results] 1) Hypoxia augmented PDL-1 expression in all 4 cancer cell lines. 2) Inhibition of Hh signaling using MAML3 siRNA, cyclopamine and PSK reduced PDL-1 expression under hypoxia in all 4 cancer cell lines. 3) When activated lymphocytes were cocultured with cancers treated with a Hh inhibitor, activated lymphocyte cell numbers significantly increased under hypoxia. 4) In contrast, this increase was abrogated when cancer cells were treated with a PDL-1 neutralizing antibody. 5) When activated lymphocytes were cocultured with cancers treated with a Hh inhibitor and/or anti-PDL-1 Ab, the percent of CD8+ lymphocytes decreased in both the cyclopamine- and anti-PDL-1-treated groups under hypoxic conditions, while there was no significant change in CD3 expression. 6) NKG2D expression increased on activated lymphocytes in anti PDL-1Ab-treated group. [Conclusion] These results suggest that Hh signaling is one of regulatory pathways of PDL-1 expression under hypoxia and that inhibiting Hh signaling may induce lymphocyte antitumor activity. Therefore, Hh inhibition could be a promising drug target, not only as a direct tumor suppressor agent, but also as a PDL-1 inhibitor. Citation Format: Hideya Onishi, Akiko Fujimura, Yasuhiro Oyama, Makoto Kawamoto, Akio Yamasaki, Takashi Morisaki. Hedgehog signaling augments PDL-1 expression in cancer cells under hypoxic condition to inhibit antitumor effects by activated lymphocytes [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 589. doi:10.1158/1538-7445.AM2017-589