The identification of BRAF as the driver mutation in melanoma enabled the development of targeted inhibitors that revolutionized the treatment of melanoma patients. In addition to immunotherapy, for patients harboring the BRAF p.V600E mutation the combined BRAF/MEK targeted therapy is a common therapeutic approach. However, the majority of patients develop resistance whose underlying molecular mechanisms are still not completely understood and, thus, remain a major challenge for melanoma treatment. In the proposed study, we plan to establish biopsy-derived melanoma cell lines resistant to BRAF/MEK inhibitors and to investigate the mechanisms of resistance. The data obtained from cBioPortal database indicate that the importance of mutated p53 family members (mutations in TP53 and/or TP63 occur in approximately 40% of melanoma samples) should be considered in BRAF mutated tumors where mutations in TP53 and TP63 occur in 21.6% and 14.7% cases, respectively. In addition, according to the previous studies by us and others, the altered expression and dysregulation of p53 family isoforms could promote the development of resistance to BRAF/MEK inhibitor therapy in metastatic melanoma. After acquiring the mutational status, expression profile and subcellular localization of isoforms as well as their mutual interactions, we will determine the functional relationship between the p53 family members. By knocking down specific group of p53 family isoforms and performing different bioassays we aim to determine their roles in BRAF/MEK inhibitor resistant melanoma. We are confident that the proposed research will decipher the molecular mechanisms of p53-driven resistance of melanoma cells to BRAF/MEK inhibitors, establish the specific signature of p53 family isoform expression that could indicate targeted therapy effectiveness and identify potential therapeutic targets.