Background: Methylation is reported to support cancer immune tolerance. We conducted a phase 1 dose-escalation trial [NCT02998567] of combination guadecitabine (G; DNA hypomethylating agent) and pembrolizumab (P) in patients (pts) with advanced cancers. We hypothesized that G can normalize the expression of epigenetically suppressed immune genes, increase interferon producing tumor-infiltrating lymphocytes (TILs), and enhance the anticancer activity of P. Methods: In dose escalation (Es), pts received G (45 mg/m2 or 30 mg/m2, administered SC on days 1-4) with P (200 mg, administered IV starting from cycle 2 onwards) as outpatient Q3W; in expansion (Ex), the RP2D of G (30 mg/m2) with P (200 mg) Q3W was administered. Pre-treatment and on-treatment tumor biopsies were evaluated for PD-L1 expression, tumor infiltrating lymphocytes, gene expression by RNAseq and methylome studies. Longitudinal analyses of peripheral blood CD3, CD4 and CD8 lymphocytes by flow cytometry were performed. Results: Overall, 34 pts (Es, n = 14; Ex, n = 20) were evaluable for safety. The most common treatment-related adverse events (TRAEs) were neutropenia (n = 21), fatigue (n = 6) and thrombocytopenia (n = 3), diarrhea (n = 2). G3+ TRAEs were neutropenia (n = 14), febrile neutropenia (n = 4), raised ALP (n = 1), raised AST (n=1), colitis (n = 1), diarrhoea (n = 1) and lung infection (n = 1). Two DLTs (neutropenia, febrile neutropenia) were reported at G 45mg/m2 with none reported at G 30mg/m2. There were no treatment-related deaths. In total, 28 pts (Es, n = 12; Ex, n = 16) were evaluable for antitumor activity studies (≥2 scans); ORR (CR+PR) and DCR (CR+PR+SD) were 3% and 57%; 10/15 pts with non-small cell lung cancer (13 pts resistant/refractory to PD-1/PD-L1 targeting agents) were evaluable, with a DCR of 80% and 5 pts having DCR > 6 months with 8 pts remaining on study treatment. Overall, 25 paired biopsies were obtained. Using LINE1 sequences to study global methylation, both tumor biopsies and peripheral blood showed reduced methylation post-G treatment. Preliminary data on tumor-infiltrating lymphocytes assessed by multicolor immunofluorescence in 9 paired biopsies showed a numerical increase in median values of T-helper (CD4+FOXP3-) (10.20 to 19.70, p = 0.5469), T-regulatory (CD4+FOXP3+) (5.1 to 6.7, p=0.8438), and T-cytotoxic (CD8+) cell densities (2.7 to 7.4, p=0.6523) . Comparing with matched pre-treatment, on treatment tumor had numerical increases in interferon alpha and gamma response pathway activation in serial biopsy RNAseq analyses but did not reach significance. Conclusions: G plus P resulted in no unexpected toxicities with evidence suggestive of biological and anti-cancer activity.

Citation Format: Dionysis Papadatos-Pastos, Abhijit Pal, Melek Akay, Malaka Ameratunga, Sanjena Mithra, Joo-Ern Ang, Sofia Levva, Reece Caldwell, Ruth Riisnaes, Mateus Crespo, Wei Yuan, George Seed, Bora Gurel, Ines Figueiredo, Rita Pereira, Susana Miranda, Anna Ferreira, Suzanne Carreira, Claudia Bertan, Chloe Baker, Ricardo Morilla, Robert Brown, Nahal Masrour, Toby Prout, Anna Zachariou, Alison Turner, Mona Parmar, Mark Van de Velde, Ben Jenkins, Christina Yap, Nina Tunariu, Udai Banerji, Juanita Lopez, Anna Minchom, Johann De Bono. HyPeR: A phase 1, dose escalation and expansion trial of guadecitabine (SGI-110), a second-generation hypomethylating agent in combination with pembrolizumab (MK3475) in patients with refractory solid tumors [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr CT129.