Phase 1b/2, open label, multicenter, study of the combination of SD-101 and pembrolizumab in patients with advanced/metastatic melanoma resistant to anti-PD-1/PD-L1 therapy.

Abstract

9555 Background: SD-101 is a synthetic CpG-ODN agonist of TLR9 that stimulates dendritic cells to release IFN-alpha and mature into antigen presenting cells - activating T cell anti-tumor responses. Pembrolizumab has demonstrated activity in melanoma. SYNERGY-001/KEYNOTE-184 study assesses the safety and preliminary efficacy of the combination of intratumoral SD-101 and intravenous pembrolizumab in PD1/PDL 1 resistant unresectable stage IIIC- IV melanoma. A prior phase 2 study with SD-101 at 8 mg per injection resulted in a 21.4% ORR in this population (Abstract 3781, ESMO 2018). We report preliminary data in this ongoing phase 2 trial evaluating efficacy at a lower SD-101 dose of 2 mg per injection. Methods: PD1/PDL 1 resistant melanoma patients received 2 mg of SD-101 intratumorally per lesion in 1-4 lesions (weekly x 4 doses followed by Q3W x 7). Pembrolizumab was administered at a dose of 200 mg intravenously Q3W. Scans were performed Q9W. Responses were assessed per RECIST v1.1. Results: 23 patients have been enrolled with baseline characteristics: median age 65 years; male: 77%; stage at screening: IIIC = 26%; IV = 57%, unknown = 17%; LDH > ULN: 36%. Lines of prior therapy: 1: 52%; 2: 22%; > 2: 26%. Prior anti CTL-A4 therapy: 39%. Best overall response on prior antiPD-1/PD-L1: PD: 88%, PR/CR: 8%, SD: 4%. Safety: Grade ≥3 treatment-related AEs: pneumonia and constipation (8%). No immune-related AEs reported. 2 non-treatment related SAEs reported from 2 patients: pneumonia and intussusception. 4 patients discontinued treatment early: 1 post SAE, per patient’s request, 3 due to PD. 1 patient died due to malignant pleural effusion after 1 dose of SD 101 and Pembrolizumab. No treatment related deaths. Efficacy: Mean duration on treatment: 39 days (1 - 169). mITT population: six patients at time of first CT scan at day 64: PR: 1, SD: 1, PD:3; non-evaluable: 1. 17 patients on study have not yet had first CT scan. Conclusions: The TLR9 innate immune stimulant, SD-101, in combination with pembrolizumab is well tolerated. Mature efficacy data, with additional first and second follow-up CT scans, will be presented at the meeting. Clinical trial information: NCT02521870.