Preclinical evaluation of the third-generation, bi-steric mTORC1-selective inhibitor RMC-6272 in NF2-deficient models

Abstract

NF2-associated meningiomas are progressive, highly morbid and are non-responsive to chemotherapies, highlighting the need for improved treatments. We have established aberrant activation of mechanistic target of rapamycin (mTOR) signaling in NF2-deficient tumors, leading to clinical trials with first- and second-generation mTOR inhibitors. However, results have been mixed, showing stabilized tumor growth without shrinkage offset by adverse side-effects. To address these limitations, here we explored the potential of third-generation, bi-steric mTORC1 inhibitors using the preclinical tool compound RMC-6272. Employing human NF2-deficient meningioma lines, we compared mTOR inhibitors rapamycin (first-generation), INK128 (second-generation) and RMC-6272 (third-generation) using in vitro dose-response testing, cell-cycle analysis and immunoblotting. Furthermore, the efficacy of RMC-6272 was assessed in NF2-null 3D-spheroid meningioma models, and its in vivo potential was evaluated in two orthotopic meningioma mouse models. Treatment of meningioma cells revealed that, unlike rapamycin, RMC-6272 demonstrated superior growth inhibitory effects, cell cycle arrest, and complete inhibition of phosphorylated 4E-BP1 (mTORC1 readout). Moreover, RMC-6272 had a longer retention time than INK128 and inhibited expression of several eIF4E-sensitive targets on the protein level. RMC-6272 treatment of NF2 spheroids showed significant shrinkage in size as well as reduced proliferation. Further, in vivo studies in mice revealed effective blockage of meningioma growth by RMC-6272, compared with vehicle controls. Our study in preclinical models of NF2 supports possible future clinical evaluation of third-generation, investigational mTORC1 inhibitors, such as RMC-5552, as a potential treatment strategy for NF2.