Targeting PI3K/mTOR signaling exerts potent antitumor activity in pheochromocytoma in vivo

Transcriptomic analyses of tumors from rats treated with BEZ235 or placebo identified potential mediators of therapy response. Slc6a2, encoding the norepinephrine transporter (NET), was downregulated in a dose-dependent manner by BEZ235 in rat PCCs. Moreover, BEZ235 reduced Slc6a2/NET expression also in PCC cell lines (PC12, MPC, MTT). Studies of a BEZ235-resistant derivative of the MPC cell line (MPCR) confirmed that the reduction of NET expression associates with the response to the drug. Reduction of NET expression following BEZ235 treatment in vivo could be monitored by Positron Emission Tomography (PET) using a tracer targeting NET. Altogether, we demonstrate the efficacy of BEZ235 against PCC in vivo, and show that functional imaging can be employed to monitor the response of PCC to PI3K/mTOR inhibition therapy.