Abstract 2085: Treatment of human melanoma cells with dasatinib requires inactivation of both mTOR and MAPK pathways to achieve high cell eradication efficacy

Abstract

Abstract Advanced stages of melanoma are resilient to therapy and new strategies for the treatment are required. About 60% of melanomas harbor the mutated BRAF oncogene, which activate the MAPK pathway. This BRAF driver mutation can be targeted by a small molecule drug vemurafenib. However, most of patients develop resistance during treatment and even drug addiction is acquired. The nonreceptor SRC tyrosine kinase is highly expressed and deregulated in melanoma and can be efficiently inhibited by the inhibitor dasatinib, an anticancer drug which is already used for the treatment of some tumor types. SRC does not have its own canonical pathway but is capable of activating and augmenting different signaling routes in cancer cells. We found that melanoma tumor cell lines analysed were generally resistant to dasatinib irrespective of BRAF or NRAS mutational status. The exception was the cell line Hbl which was very sensitive even to low dasatinib doses and Hbl cells were completely eradicated by 10 nM of dasatinib in several days. The sensitivity of Hbl to dasatinib was dependent on the drug ability to inhibit completely both the MAPK and AKT/mTOR signaling pathways. Dasatinib was capable of inhibiting SRC activation resulting in the repression of AKT activation in Hbl cells. AKT phosphorylation at Ser473 was fully abolished and Thr308 was severely attenuated through inhibiting SRC by dasatinib in Hbl cells. These two phosphorylations are required for AKT activity. MAPK pathway (ERK1/2 phosphorylation) was also inhibited in Hbl cells. Dasatinib also inhibited the phosphorylation of SRC at Tyr416 (a hallmark of SRC activity) in Hbl cells and, surprisingly, also in other dasatinib-resistant melanoma cells. Importantly, although SRC was dephosphorylated at Tyr416, dasatinib was unable to inactivate AKT and MAPK pathway (ERK1/2) in all other melanoma cells. Molecular changes closely correlated with proliferation assays. Our data indicate that the combination therapy of melanoma with dasatinib would bring benefit to patients only by blocking both MAPK and AKT signaling pathways in melanoma cells. Altogether, more molecular knowledge of the effects of the powerful anticancer drug dasatinib is required in order to be used for the treatment of melanoma. This work was supported by the Institutional research project PROGRESQ25 from Charles University Prague. Citation Format: Jiri Vachtenheim, Jiri Réda, Kateřina Vlčková, Lubica Ondrušová. Treatment of human melanoma cells with dasatinib requires inactivation of both mTOR and MAPK pathways to achieve high cell eradication efficacy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2085.