Equivalent benefit of rapamycin and a potent mTOR ATP-competitive inhibitor, MLN0128 (INK128), in a mouse model of tuberous sclerosis.

Tuberous sclerosis complex (TSC) is a hamartoma syndrome in which brain, renal, and lung tumors develop and cause both morbidity and death. Loss of either TSC1 or TSC2 in TSC hamartomas leads to activation of mTORC1. Rapamycin and related drugs have been shown to have clinical benefit for these tumors in patients with TSC and those with sporadic forms of TSC-related neoplasms. However, lifelong therapy seems to be required, as tumors are not eliminated by this treatment. We examined the potential benefit of MLN0128, a novel potent mTOR ATP-competitive inhibitor, as a therapeutic strategy for renal cystadenomas that develop in A/J Tsc2(+/-) mice. Rapamycin given by intraperitoneal injection at 3 mg/kg 3 times per week, and MLN0128 given by gavage at 0.75 mg/kg 5 times per week had equivalent effects in suppressing tumor development during a 4-week treatment period, with an approximate 99% reduction in microscopic tumor cell volume. Marked reduction in activation of mTOR complex (mTORC)1 and blockade of cell growth was seen with both drugs, whereas only MLN0128 treatment had effects in blocking mTORC2 and 4EBP1 phosphorylation. However, when either drug was discontinued and mice were observed for two additional months, there was dramatic recovery of tumor growth, with extensive proliferation. Hence, longlasting tumor growth control is not achieved with transient treatment with either drug, and MLN0128 and rapamycin have equivalent therapeutic benefit in this mouse model. Differences in side-effect profiles might make MLN0128 more attractive for treatment of patients with TSC-related tumors, but will require additional study in humans. ©2013 AACR.