A Phase I, First-in-Human, Dose-Escalation, Expansion Trial of Cytokine-Encoding Synthetic mRNA Mixture Alone or with Cemiplimab in Advanced Solid Tumors

We investigated SAR441000 (mixture of four mRNAs encoding IL-12, single-chain IFN-α-2b, GM-CSF, and IL-15 sushi domain) alone or in combination with cemiplimab in patients with advanced solid tumors.

SAR441000 was intratumorally administered weekly in a 4-week cycle in monotherapy and in a 3-week cycle at a predefined dose level with 350 mg cemiplimab (intravenously) every 3 weeks in combination therapy. The primary objective was to determine MTD or maximum administered dose, overall safety, tolerability, and objective response rate of SAR441000.

We enrolled 77 patients previously treated with anticancer therapies [escalation monotherapy: N = 21; escalation combination: N = 15; and expansion combination (PD-1–refractory melanoma): N = 41]. The maximum administered dose at dose level 8 was 4,000 µg. The most common grade ≥3 treatment–related adverse events was fatigue in the escalation phase (monotherapy: 28.6% and combination therapy: 66.7%) and injection-site pain (31.7%) in the expansion phase. In combination therapy, one patient in the escalation phase and two patients in the expansion phase achieved partial responses. At 4,000 μg (highest dose) across all cohorts, the maximum fold change in plasma cytokine concentration was the highest and lowest for IFN-α-2 (74.9-fold) and IL-15 (1.96-fold), respectively. Increased blood IFN-γ and inducible protein-10 levels were observed for most patients.

Intratumoral administration of SAR441000 in combination with cemiplimab was generally well tolerated with antitumor activity in the locoregional disease setting. Anecdotal evidence of pharmacodynamic immunomodulatory effect and distant noninjected lesion antitumor response was observed, without significant effects in patients with advanced solid tumors previously treated with anti–PD-1 therapies.