Phase II Clinical Trial and Preclinical Evaluation of a Novel CD47 Blockade Combination in Refractory Microsatellite-Stable Metastatic Colorectal Cancer.

[PURPOSE] In this preclinical human immune system patient-derived xenograft (HIS-PDX) model and phase II clinical trial, we assessed evorpacept (anti-CD47 engineered fusion protein with inactive Fc), cetuximab, and pembrolizumab (triple therapy) in microsatellite-stable (MSS) colorectal cancer.

[PATIENTS AND METHODS] HIS BALB/c-Rag2nullIl2rγnullSirpαNOD mice with PDXs were treated with triple therapy or its components. Patients with refractory MSS colorectal cancer were treated with triple therapy in a safety run-in (stage 1) followed by expansion (stage 2, planned N = 42). The co-primary objectives were to determine the recommended dose of evorpacept and objective response rate (vs. historic control).

[RESULTS] In HIS-PDX mice, triple therapy decreased the growth of MSS colorectal cancer tumors and increased tumor-infiltrating CD8+ T cells. Sixteen patients were treated on the clinical trial across two evorpacept dose levels: N = 12 in stage 1 and N = 4 in stage 2. Trial enrollment was terminated early because of safety concerns (one treatment-related grade 5 event each of hemophagocytic lymphohistiocytosis and cytokine release syndrome). Otherwise, the adverse event profile was as expected. Among all patients, the objective response rate was 6.3%; formal hypothesis testing was not performed. The disease control rate was 12.5%, the median progression-free survival was 2.3 months, and the median overall survival was 10.9 months. Blood- and tumor-based clinical trial correlative analyses identified innate and adaptive immune system activation.

[CONCLUSIONS] Whereas triple therapy demonstrated evidence of efficacy in refractory MSS colorectal cancer, safety concerns halted enrollment. Further investigation is necessary to determine the optimal use of CD47-targeted therapies in MSS colorectal cancer.

[SIGNIFICANCE] Evorpacept, cetuximab, and pembrolizumab demonstrated antitumor activity in a preclinical HIS-PDX model and clinical trial in refractory MSS colorectal cancer; however, immune-related adverse events prompted early termination of study enrollment. Evidence of innate and adaptive antitumor immune activation was identified. The role of SIRPα/CD47 blockade in the treatment of MSS colorectal cancer needs to be further elucidated in future trials.