Phase 1a/1b study design of the novel STING agonist, immune-stimulating antibody-conjugate (ISAC) TAK-500, with or without pembrolizumab in patients with advanced solid tumors.

TPS2690 Background: Tumor resistance to immune checkpoint inhibitors (CPIs), including pembrolizumab, is common. Suggested mechanisms of resistance include reduced interferon (IFN) signaling, immune escape, and immunosuppressive tumor phenotypes. Innate immune cell stimulation in the tumor microenvironment may be a potential pathway to overcome this resistance. Stimulator of interferon genes (STING) is a cytosolic protein critical for initiation of type-1 IFN-dependent innate immunity. TAK-500 is a novel ISAC comprising a STING agonist (based on TAK-676, which is currently in phase 1 clinical trials [NCT04420884, NCT04879849]), an IgG1 anti-cysteine-cysteine chemokine receptor 2 (CCR2) antibody, and a self-immolating maleimide-containing protease-cleavable peptide linker. CCR2-expressing myeloid cells, including tumor associated macrophages (TAMs), promote immune evasion in part by reducing infiltration of CD8+ T cells into the tumor microenvironment. As such, TAK-500 has the potential to mitigate CPI resistance in solid tumors via targeted STING activation of tumor-infiltrating CCR2-expressing myeloid cells, thus leading to stimulation of innate and adaptive immunity within the tumor microenvironment through three potential mechanisms of action: activation of IFN signaling, reprogramming of CCR2-expressing myeloid cells to an inflammatory phenotype, and blockade of suppressive TAM recruitment. Methods: Adult patients with a diagnosis of locally advanced or metastatic gastroesophageal adenocarcinoma, pancreatic adenocarcinoma, hepatocellular carcinoma, non-squamous non-small cell lung cancer, squamous cell carcinoma of the head and neck, mesothelioma or triple-negative breast cancer are eligible. All patients must have progressive disease while on, or be intolerant to, all current standard therapies. Approximately 106 patients in total will be enrolled to the dose escalation and expansion cohorts. In the dose escalation phase, intravenous (IV) TAK-500 will be administered over the range 8–480 µg/kg on day 1 of every 21-day cycle (Q3W) to establish the pharmacologically active dose (PAD) range. An additional escalation cohort of patients will receive TAK-500 + IV pembrolizumab 200 mg Q3W, starting at a dose of TAK-500 that is 1–2 dose levels below the lowest PAD range established in the single agent cohort. Dose escalation in both cohorts will be guided by Bayesian Optimal Interval design. In the dose expansion phase, only the combination of TAK-500 + pembrolizumab will be evaluated. Primary objectives of this study are safety and tolerability; secondary objectives include determination of the PAD range, the recommended phase 2 dose, pharmacokinetics, pharmacodynamics, and antitumor activity of TAK-500 as a single agent and in combination with pembrolizumab. Clinical trial information: NCT05070247.