Targeted therapies and autophagy: new insights from chronic myeloid leukemia.

Patients who develop chronic myeloid leukemia (CML) are currently treated with tyrosine kinase inhibitors (TKIs), which inhibit the function of the oncogene BCR/Abl. Most CML cells undergo apoptosis when BCR/Abl tyrosine kinase activity is suppressed by TKIs. Cells surviving drug treatment are either stem cells (CML in early phase) or cells with BCR/Abl-dependent or -independent mechanisms of drug resistance (CML in advanced phase). Since survival of these cells is thought to be responsible for disease recurrence, it is critical to find ways to fully eradicate CML stem cells. We have recently shown that when CML cells, including stem cells, are exposed to TKI they activate an autophagic program, which relies on intracellular calcium and is not inhibited by Bcl-2. Pharmacological or RNAi-mediated inhibition of autophagy potentiates the effect of TKI in inducing death of CML cells, including the stem cells. These data strongly suggest that inhibition of autophagy may improve the therapeutic effects of TKIs in the treatment of CML. In addition, they give credence to the idea that in cancer cells autophagy is part of a stereotypic response to stress and specifically to abrogation of their main oncogenic signal(s).