Canertinib-induced leukemia cell death signaling : effects of a pan-ERBB inhibitor

Abstract: Acute myelogenous leukemia (AML) is the most common acute leukemia affecting adults, the second most frequent leukemia in children, and remains one of the most difficult to cure. Despite a substantial progress in understanding the pathogenesis of AML, general and rather unspecific cytostatic drugs such as cytarabine and anthracyclins still make up the cornerstones of therapy. Problems with these protocols include toxicity and the occurrence of resistance to the drugs in many patients. In order to extend the treatment options and ultimately improve survival for patients with leukemia it is imperative to increase the therapeutic arsenal with effective targeted therapies, preferentially with different mechanisms of action. AML due to a substantial heterogeneity between patients and within the clones in the same patient, as well as T-cell malignancies, are particularly difficult to treat since it is almost impossible to eradicate all leukemic stem cells using chemotherapy, thus there is a need to find more specific and effective treatments. Canertinib is a novel tyrosine kinase inhibitor developed for the treatment of certain solid cancers and has been designed to specifically inhibit all member of the ERBB-receptor family (ERBB1, ERBB2, ERBB3 and ERBB4). However, there are indications that canertinib has a broader specificity and it has not been tested on patients with leukemia.The aim of this thesis was to investigate the anti-proliferative and pro-apoptotic effects and mechanisms of canertinib in human leukemia cells, and more specifically to clarify the cell death pathway and potential targets for the drug in these cells.Canertinib treatment of leukemia cell lines resulted in an ERBB-independent induction of the intrinsic apoptotic pathway and activation of caspase-10, -9, and -8 as a consequence of Akt and Erk inhibition. In the human T-cell leukemia cell line Jurkat, the effects were associated to dephosphorylation of the lymphocyte-specific proteins, Lck and Zap-70. However, as full-length ERBB receptors were absent in leukemic cell lines other possible targets for canertinib were investigated. The FLT3 receptor, frequently mutated in AML, was discovered as a target since canertinib inhibited FLT3 autophosphorylation and kinase activity as well as downstream targets. The search for other possible proteins that might account for the effect exerted by canertinib, lead to the discovery of a truncated form of ERBB2 in human leukemic cells.In conclusion, canertinib display promising anti-tumor effects on malignant hematopoietic cells and might be used in future studies in combination with conventional chemotherapy or other targeted therapies in the treatment of leukemia.