Abstract 610: Blockade of tumor expression of PD-1 promotes lung cancer growth in a murine model

Abstract

Abstract Lung cancer remains one of the most prevalent and fatal malignancies worldwide. There are substantial evidences that immunotherapies offer significant benefits among lung cancer patients. Pembrolizumab, a humanized programmed death receptor-1(anti-PD-1) antibody is now approved by FDA as a first-line treatment of patients with metastatic non-small cell lung cancer (NSCLC). Recent data demonstrate that PD-1 is not only expressed by immune cells, but also by human melanoma cells. However, little is known about the biological significance of PD-1 pathway in cancer including NSCLC. Thus, we examined PD-1 expression in a series of established murine lung cancer cell lines. RT-PCR amplification and sequencing of the full coding sequence of the murine PD-1 (PDCD1) gene revealed the presence of PDCD1 mRNA in the M109 lung cancer cells. Flow cytometry and immunofluorescence analysis demonstrated PD-1 protein expression in these murine lung cancer cells. To determine the molecular function of tumor PD-1 in lung cancer survival, we treated M109 cells in culture with either anti- mouse PD-1(100ug/ml) or isotype control antibody and found that PD-1 inhibition significantly enhanced cancer cell viability as measured by MTT and clonogenic assay. Alternative PD1 inhibition by either knockdown of PDCD1 via siRNA or knockout of PDCD1 by CRISPR-Cas9 all lead to increased survival of M109 cells. Furthermore, PDCD1-knockout M109 cells had no survival difference in the presence of anti-PD1 compared to its PD1-expressing parental cells. Conversely, treatment with recombinant PD-L1 fusion protein exhibited significantly increased apoptotic rates (7.5±3.2% vs 2.1±1.2%) suppressing the tumor cell growth in the wild-type M109 in culture. To validate these results in in vivo models, NSG mice were used to determine the direct impact of anti-PD1 on M109 xenografts without the interplay of host immune system. M109 xenografts treated with antiPD-1 (10mg/kg i.p.) antibodies showed accelerated growth compared to those treated by IgG control (2487±473 vs 1499±292mm3 at days 21 after tumor inoculation, p=0.013). M109 subcutaneous tumors in the PD-1 knockout mice also manifested more rapid growth than the same tumors implanted in wild-type mice. Taken together, our results uncover a novel function of PD-1/PD-L1 axis in lung cancer survival and implicate possible tumor-promoting effects from anti-PD-1 therapy upon PD1-expressing lung cancer in the absence of effective immune response. We plan to interrogate bio-specimens collected through NRG trials to establish the translational potential of these findings. Citation Format: Shisuo Du, Qing Guan, Adam P. Dicker, Bo LU. Blockade of tumor expression of PD-1 promotes lung cancer growth in a murine model [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 610. doi:10.1158/1538-7445.AM2017-610