BMET-14STAT3 INHIBITION ENHANCES THERAPEUTIC EFFICACY OF RADIATION TREATMENT AGAINST ESTABLISHED BRAIN METASTASIS IN MURINE MELANOMA MODEL

Abstract

INTRODUCTION: Melanoma patients that develop brain metastasis have a median survival of 6 months. Radiation, a standard of care for local control of melanoma, has been reported to have immune stimulatory capacities. Therefore, we investigated the combinatorial effect of inhibitors of the signal transducer and activator of transcript 3 (STAT3) pathway, a potent mediator of immune suppression, and whole-brain radiation in a murine brain metastasis model. METHODS: C57BL/6 mice were intracerebrally implanted with B16 melanoma, irradiated with 7.5 Gy, and treated with an advanced lipid nanoparticle system that contained miR-124 (LNP-124) that inhibits the STAT3 pathway, or WP1066, a small molecule inhibitor of STAT3. Mice surviving 130+ days after tumor implantation were subcutaneously rechallenged with tumor. RESULTS: Monotherapy (LNP-124, WP1066, or radiation alone) demonstrated longer survival relative to untreated control mice; combination therapies further extended survival compared to single treatment agents. Median survival for mice receiving radiation combined with LNP124 or WP1066 was 65 days and 45.5 days, respectively, compared to 15 days for untreated mice and 19 - 40 days for monotherapy. While no untreated mice (control) survived over 20 days, the survival rate at day 130 for mice receiving combination therapy was almost 40%. Flow cytometry analysis showed higher IL-2 production in T cells from tumor-draining lymph nodes in mice treated with radiation plus STAT3 inhibitor. SUMMARY: These results indicate the combination of STAT3 inhibition and radiation enhances the therapeutic effect against established murine brain metastasis. The implications for this combination on antitumor immunity, immunologic memory and protection from recurrence will also be discussed.