Tetrahydrouridine-decitabine for non-cytotoxic epigenetic therapy of NSCLC to enhance immunotherapeutic effect of anti-PD1 in vivo.

Abstract

11552 Background: NSCLC response to anti-PD1 therapy is ~20%, largely because most NSCLC avoids immune-recognition in the 1stplace, e.g., by epigenetics to suppress neo-antigen expression. DNA methyltransferase (DNMT1) mediates this repression and is depleted by decitabine (Dec). Unfortunately Dec has trivial distribution into solid cancer tissues because of rapid deamination by cytidine deaminase (CDA). Therefore, to improve tissue-distribution of Dec with the low Cmax/long Tmax profile needed for DNMT1-depletion without cytotoxicity, we combined Dec with a CDA inhibitor tetrahydrouridine (THU). Methods: C57/BL6 mice were inoculated with LL3-luc cells via tail vein. After documentation of lung invasion by live-imaging, mice (n = 5/group) were randomized to PBS, THU-Dec (10/0.1 mg/kg sc 3×/wk), anti-PD1 (5 mg/kg ip q5d, DX400 from Merck) or THU-Dec/anti-PD1 combination. Antigen presentation, PD, MDSCs, and T-cells were measured in blood and tumor. Results: THU-Dec or anti-PD1 alone decreased tumor by imaging and increased survival, however, THU-Dec/anti-PD1 combination extended median survival the most and completely regressed tumor in 2/5 mice (median survival days PBS 37, THU-Dec 56, anti-PD1 62, THU-Dec/anti-PD1 77). Rechallenge of cured mice with LL2-luc confirmed immune-memory effect, with no engraftment vs expected engraftment in controls. Consistent with the pharmacologic rationale, THU-Dec produced > 2-fold more DNMT1-depletion in tumor vs PBS. Consistent with non-cytotoxic effect, absolute lymphocyte counts were preserved with THU-Dec, while numbers of G-MDSC decreased (2.9 k/µL PBS vs 0.3 k/µL THU-Dec/anti-PD1, p < 0.01). Expression of neoantigens MAGE-A1 and MAGE-A3 increased > 4-fold with THU-Dec vs PBS (p < 0.01). THU-Dec/anti-PD1 increased tumor infiltrating lymphocytes 6-fold vs PBS (p < 0.01) and decreased regulatory T-cells 2.5-fold vs PBS (p < 0.01). IFNγ expression in tumor increased 2.4-fold with THU-Dec/anti-PD1 vs PBS (p < 0.01). Conclusions: THU-Dec/anti-PD1 produced marked survival improvements and cures in tumor-bearing mice, scientific validation of our clinical trial NCT02664181 combining THU-Dec/nivolumab in 2nd line for NSCLC.