Melanoma is the deadliest form of skin cancer, leading to around 55,000 deaths a year. Worryingly, melanoma rates are increasing in the U.K. and worldwide. BRAF mutant melanoma accounts for around 50% of melanoma skin cancer; these patients have an activating mutation in the BRAF protein leading to hyperactivation of the MAPK pathway. BRAF mutant patients can be treated with a combination of BRAF and MEK targeting agents, which work synergistically, showing that synergistic drug combinations are effective in this clinical context. However, resistance still occurs in these patients leading to eventual death, showing there is a need for other therapeutic options. This study aimed to investigate other synergistic drug combinations for the treatment of melanoma using the in silico model SynFinder17, which was generated to predict synergistic drug combinations. Firstly, different synergy equations (Combination Index, Highest Single Agent, Bliss and Loewe) were compared in BRAF mutant melanoma using a BRAF and MEK inhibitor combination as a positive control and a sham combination, a drug combined with itself, of one of these inhibitors. The Loewe equation was the only equation that produced a strong positive synergy score in the synergistic control and produce an additive value for the sham combination. Therefore, the Loewe equation was used for further comparison in the study. Using the Loewe equation, a BRAF and Wnt/beta-catenin inhibitor combination was investigated and was found to be synergistic in 40% of the cell line models used. Further investigation revealed this was not linked to MAPK or Wnt/beta-catenin signalling. However, mTORC1 signalling was differentially affected by the drug combination in the models that responded synergistically and non-synergistically, and it was possible to re-sensitise the A375 cell line to synergy using an mTOR inhibitor. Lastly, the relationship with MITF, an important transcription factor in melanoma, was investigated. The cells that responded synergistically to the drug combination had higher basal levels of MITF which further increased when treated with the BRAF and Wnt/beta-catenin inhibitor combination. This rise was coupled with an increase in the expression of genes linked to differentiation. This correlates with the rheostat model of MITF levels in melanoma which predicts that high levels of MITF are linked to differentiation and reduced proliferation. Although these findings require further validation in more clinically relevant melanoma models, they highlight that a BRAF and Wnt/beta-catenin inhibitor combination could be used to treat a subset of melanoma patients expressing high levels of MITF.
Date of Award | 1 Aug 2022 |
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Original language | English |
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Awarding Institution | - The University of Manchester
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Supervisor | Bruno M Simões (Supervisor) & Paul Townsend (Supervisor) |
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Prediction and Validation of Novel Drug Synergy
Criscuolo, C. (Author). 1 Aug 2022
Student thesis: Phd