Studies on the effect of ErbB tyrosine kinase inhibitors on malignant melanoma growth and survival in vitro

• Malignant melanoma has one of the fastest increasing incidences among the different types of cancerin the Western world. This raise can partly be ascribed to the change in sun habits that has takenplace during the last decades, since the major external risk factor for melanoma is exposure toultraviolet radiation. Patients with early stages of melanoma can often be cured by surgery, howeverfor patients suffering from metastatic melanoma there are only a few treatment options available.Unfortunately malignant melanoma is often resistant to radio-, bio- and chemotherapy and treatmentwith the currently most frequently used agent, dacarbazine, is characterized by a very low clinicalresponse rate. Therefore, there is an urgent need for new treatment strategies which can increase theoverall survival and cause less severe side effects.The aim of this thesis was to investigate the anti-tumor effect of two different tyrosine kinaseinhibitors (TKIs), gefitinib and canertinib, on two different human malignant melanoma (RaH3 andRaH5) cell lines. We investigate the effect of these two drugs on cell proliferation and survival andstudied the effect of gefitinib and canertinib on ErbB1-4 receptor phosphorylation, as well as Akt,Erk1/2 and Stat3 activity.Our results showed that phosphorylation of ErbB1, ErbB2 and ErbB3 decreased followingtreatment with both gefitinib and canertinib and that the subsequent downstream signaling via Akt,Erk1/2 and Stat3 was inhibited after TKI treatment. However, it was noted that the gefitinibinducedinhibition of Akt, and particularly Erk1/2, was transient and only a weak inhibition of Stat3phosphorylation was seen. Gefitinib treatment of the RaH3 and RaH5 cells resulted in anaccumulation of the cells in the G1 phase of the cell cycle without any induction of apoptosis.Canertinib caused a more pronounced inhibition of Akt, Erk1/2, and Stat3 phosphorylation thangefitinib. This might be one explanation to why canertinib induced apoptosis in RaH3 and RaH5cells whereas gefitinib only caused cell cycle arrest. In conclusion, gefitinib and canertinib displaypromising anti-tumor effects on ErbB expressing malignant melanoma and might be used in futurestudies in combination with conventional chemotherapy or other targeted therapies in the treatmentof malignant melanoma.

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