1253P Safety and efficacy of Wnt inhibition with a DKK1 inhibitor, DKN-01, in combination with atezolizumab in patients with advanced oesophagogastric adenocarcinoma: Phase IIa results of the WAKING trial

Immune checkpoint inhibitor (ICI) monotherapy has limited efficacy in patients (pts) with mismatch repair proficient (MMRp) oesophagogastric adenocarcinoma (OGA). Dickkopf-1 (DKK1) modulates Wnt/β-Catenin signaling and promotes a T-cell excluded or ‘immune desert’ tumour microenvironment (TME). DKN-01, a DKK1 neutralising antibody, can favourably reprogram the TME by reducing levels of myeloid-derived suppressor cells (MDSCs) and increasing entry of effector T-cells and may improve responses when added to ICI monotherapy. This phase IIa study (3+3 design) evaluated the safety and efficacy of DKN-01 (300mg/600mg) and atezolizumab (840mg) given intravenously q2W in pts with pre-treated, anti PD1/PDL1 naïve, MMRp advanced OGA. The primary endpoint was to establish the safety, tolerability, and recommended phase II dose (RP2D) for the efficacy phase. Safety, efficacy, and translational analyses (including intratumoural DKK1/PD-L1, peripheral MDSC and NK cell populations, TCR diversity analysis, tumour genomics and stool microbiome) are ongoing. Eleven pts were treated on study (5 pts at DKN-01 300mg, 6 at 600mg). Eight pts completed the DLT period (3 at 300mg, 5 at 600mg) and were therefore evaluated for the safety endpoint. No dose limiting toxicities were observed. Of the 11 treated pts, 10 (90.9%) experienced at least one treatment-related AE (TRAE). The most common TRAEs (experienced by ≥ 2 pts) were fatigue (36%), anaemia (18%), hypothyroidism (18%), diarrhoea (18%) and pain (18%). One pt experienced G3 urticaria and 1 experienced an SAE of G2 pneumonitis, both were treatment related. Of the 8 pts evaluated for the safety endpoint, 1 pt (12.5%) had PR and 4 pts (50%) had SD as their best response. No clear trend between peripheral MDSC levels at baseline and during treatment have yet been observed. Additional biomarker work is ongoing. DKN-01 plus atezolizumab has a manageable safety profile with no new safety signals in pts with advanced OGA. DKN-01 600mg plus atezolizumab 840mg q2W was the RP2D taken through to the ongoing expansion phase to confirm efficacy.