(P 274) TYK2 AND MEK COMBINATION THERAPY IN MALIGNANT PERIPHERAL NERVE SHEATH TUMORS AND OTHER SOFT TISSUE SARCOMAS

Objective: Malignant peripheral nerve sheath tumors (MPNST) are aggressive sarcomas that occur sporadically, secondary to radiation therapy, or from malignant transformation of benign plexiform neurofibromas in individuals with the Neurofibromatosis Type 1 (NF1) cancer predisposition syndrome. MPNST are often refractory to radiation and chemotherapy with high rates of recurrence and progression to metastatic disease. Our lab previously found that TYK2 was highly expressed in the majority of MPNST and showed that Tyk2/TYK2 knockdown in murine and human MPNST cells significantly increased cell death. Furthermore, these Tyk2 knockdown cells demonstrated decreased growth capacity in subcutaneous and metastasis models. In this study, our objectives were to evaluate TYK2 expression in other soft tissue sarcomas and to determine the therapeutic potential of TYK2 inhibition alone or in combination in MPNST and other soft tissue sarcomas.

Methods: Immunohistochemistry (IHC) for TYK2 was performed on a cohort of MPNST as well as a tissue microarray composed of soft tissue sarcomas (5 MPNST, 13 leiomyosarcoma (LMS), 3 chondrosarcoma, 3 Ewing's sarcoma, 2 myxoid chondrosarcoma, and 5 angiosarcoma). MPNST and sarcoma cell lines, including LMS, angiosarcoma and synovial sarcoma, were treated with the TYK2 inhibitor deucravacitinib, alone or in combination with a MEK inhibitor (mirdametinib) in IncuCyte live cell imaging assays for cell confluence and apoptosis. IC50 values were calculated and synergy was analyzed by SynergyFinder 2.0 software. Downstream signaling consequences of TYK2 inhibition were assessed by RNA-seq, qPCR pathway array and the automated Simple Western WES system. Mirdametinib and deucravacitinib combination therapy was evaluated in multiple mouse models of MPNST in vivo.

Results: IHC revealed elevated TYK2 protein levels in 56% of MPNST, 89% of synovial sarcoma, 60% of fibrosarcoma, 54% of undifferentiated pleomorphic sarcoma and 38% of leiomyosarcoma. Following TYK2 inhibition in MPNST cells, RNA-seq and qPCR array showed upregulation of the MEK/ERK pathway and diminished expression of genes involved in the cell cycle, mitotic, and glycolysis pathways. MEK inhibitors synergized with TYK2 inhibitors to increase MPNST apoptosis and decrease cell proliferation. Interestingly, mirdametinib and deucravacitinib were also synergistically cytotoxic in other sarcoma subtypes, including SKLMS1 (non-uterine leiomyosarcoma), SKUT1 (uterine leiomyosarcoma), PCB-011 (angiosarcoma), and FUJI (synovial sarcoma) cell lines. Finally, the combination of mirdametinib and deucravacitinib dramatically reduced tumor growth in several MPNST mouse models.

Conclusion: TYK2 inhibitors decrease proliferation of MPNST cells while upregulating MEK/ERK pathway signaling in an apparent compensatory mechanism. Combining TYK2 and MEK inhibitors synergistically blocks MPNST growth in vitro and in vivo as well as other soft tissue sarcomas in vitro. These findings support the development of a combination deucravacitinib and mirdametinib phase 1/2 clinical trial in soft tissue sarcomas with an emphasis on MPNST.