Induction of autophagy by dual mTORC1-mTORC2 inhibition in BCR-ABL-expressing leukemic cells

Over recent years, there have been substantial research advances on the mechanisms by which BCR-ABL transforms hematopoietic cells and promotes leukemic cell growth and survival. Among the diverse signaling cascades activated by BCR-ABL, the mTOR pathway plays a critical role in mRNA translation of genes that promote leukemogenesis and mitogenic responses. We have recently shown that dual targeting of mTORC1 and mTORC2 complexes using a catalytic mTOR inhibitor, OSI-027, results in generation of potent antileukemic effects against BCR-ABL transformed cells. Such effects were also seen in cells expressing the T315I mutation, which is resistant to all currently approved BCR-ABL kinase inhibitors. Our studies also demonstrate that such dual catalytic inhibition of mTORC2 and mTORC1 complexes in BCR-ABL-expressing K562 cells results in induction of autophagy, and that inhibition of the autophagic process using chloroquine promotes apoptosis of these cells. Altogether, our studies suggest that autophagy may be a limiting factor for the induction of apoptosis during dual mTORC2-mTORC1 targeting, in at least some types of BCR-ABL-expressing cells and have raised the potential of combinations of catalytic inhibitors of mTOR with autophagy inhibitors for the treatment of refractory Ph+ leukemias.