Resistance to receptor tyrosine kinase inhibitors in solid tumors: can we improve the cancer fighting strategy by blocking autophagy?

A growing field of evidence suggests the involvement of oncogenic receptor tyrosine kinases (RTKs) in the transformation of malignant cells. Constitutive and abnormal activation of RTKs may occur in tumors either through hyperactivation of mutated RTKs or via functional upregulation by RTK-coding gene amplification. In several types of cancer prognosis and therapeutic responses were found to be associated with deregulated activation of one or more RTKs. Therefore, targeting various RTKs remains a significant challenge in the treatment of patients with diverse malignancies. However, a frequent issue with the use of RTK inhibitors is drug resistance. Autophagy activation during treatment with RTK inhibitors has been commonly observed as an obstacle to more efficacious therapy and has been associated with the limited efficacy of RTK inhibitors. In the present review, we discuss autophagy activation after the administration of RTK inhibitors and summarize the achievements of combination RTK/autophagy inhibitor therapy in overcoming the reported resistance to RTK inhibitors in a growing number of cancers.