Immunotherapy of metastases in a mouse model of pancreatic adenocarcinoma

Metastatic pancreatic adenocarcinoma remains one of the most treatment-refractory malignancies. Although MBTA immunotherapy, consisting of mannan-BAM, Toll-like receptor ligands, and an agonistic anti-CD40 antibody, effectively eradicates primary tumors and induces systemic antitumor immunity, its efficacy against large established metastatic lesions remains limited. We hypothesized that therapeutic outcomes could be improved by combining MBTA with interventions targeting biological vulnerabilities of metastatic tumors. A bilateral Panc02 pancreatic adenocarcinoma model was employed to mimic primary tumors and established distant lesions. MBTA was administered intratumorally into primary tumors, while metastatic lesions were targeted using systemic or local interventions affecting glutamine metabolism, apoptosis, or tumor-cell membrane integrity. Combinations with immune checkpoint inhibitors and anti-TGF-β antibody were evaluated in a bilateral MC38 colorectal adenocarcinoma model. Treatment of primary tumors with MBTA generated a systemic antitumor response that significantly delayed the growth of distant tumors and prolonged survival but rarely induced complete responses. Therapeutic efficacy was enhanced by combining MBTA with the glutamine antagonist prodrug LTP607, the Smac mimetic LCL161, or intratumoral administration of the membrane-disruptive peptide LTX-315, each producing durable complete responses in a subset of animals. Direct treatment of both primary and distant tumors with MBTA further improved cure rates, which were additionally increased by blockade of the CD47-SIRPα axis. In contrast, immune checkpoint inhibitors and anti-TGF-β antibody provided minimal additional benefit when combined with MBTA. These findings suggest that MBTA-induced systemic immunity alone may be insufficient for eradication of large established metastatic lesions. However, therapeutic strategies targeting intrinsic vulnerabilities of metastatic tumors substantially enhance antitumor efficacy. Collectively, the results support the development of MBTA-based combination therapies for advanced metastatic cancer.