(P 99) ACQUIRED NF2 MUTATION CONFERS RESISTANCE TO TRK INHIBITION IN AN EX VIVO LMNA::NTRK1-REARRANGED SOFT TISSUE SARCOMA CELL MODEL

Objective: The neurotrophic receptor tyrosine kinase genes (NTRK1,NTRK2, and NTRK3) belong to a family of nerve growth factor receptor genes encoding a single transmembrane receptor tyrosine kinase (RTK) protein (also called as Trk A, B, and C). Genomic rearrangement is the most common mechanism of oncogenic activation for this family of receptors, resulting in sustained cancer cell proliferation through the activation of MAPK and AKT downstream pathways. Several targeted therapies have been approved for tumors harboring NTRK fusions. Secondary mutations in NTRK1 (G595R and G667C) and for example reactivation of RAF>MEK>ERK signaling through point mutations in key members of the pathway have been well described and mechanism to overcome resistance have been investigated and a new generation TRK-inhibitors have been developed.
A patient derived ex vivo cell model was established from a LMNA::NTRK1 rearranged soft tissue tumor and used to model and investigate acquired resistance ex vivo to targeted TRK inhibition in order to eventually guide further patient care.

Methods: Patient derived LMNA::NTRK1 rearranged soft tissue tumor cells were continuously exposed to targeted therapy with a TRK inhibitor with ascending dosages, starting at the IC50. 6.5 months after continuous drug exposure, individual resistant clones grew out and were molecularly characterized. Parental and resistant cell models were functionally tested in a medium throughput drug screen using several targeted therapies and chemotherapies in six-point dose response curves.

Results: A molecularly characterized patient derived LMNA::NTRK1 rearranged soft tissue TRK inhibitor resistant ex vivo tumor cell model was established. Parental cells showed continuous sensitivity to TRK targeted treatment while the resistant clones lost their sensitivity. Molecular profiling of the resistant clones revealed an acquired NF2 loss of function mutation compared to the parental cells. RNASeq showed upregulation of the mTORC1 and MAPK pathways in resistant cells. Drug screening revealed new drug sensitivities in resistant cells and synergistic drug combination using TRK inhibition together with MEK and mTOR inhibition were identified.

Conclusion: We developed a comprehensive ex vivo model of acquired drug resistance to targeted TRK therapy with in a LMNA::NTRK1 rearranged soft tissue tumor and discovered a new NF2 loss of function resistant mutation. Functional drug screening allows to unravel new drug sensitivities and showed increased sensitivity to mTOR inhibitors and allows to further guide patient care in a functional precision oncology setting.