Enzymatic depletion of L-Met using an engineered human enzyme as a novel therapeutic strategy for melanoma
Metastatic melanoma is an aggressive form of cancer responsible for the majority of skin cancer related deaths. While treatment for metastatic melanoma has improved in recent years with the introduction of targeted therapies and immunotherapies, the five year survival rate for stage IV melanoma remains only 15-20%. To address the need for alternative options for melanoma treatment, we have evaluated the use of an engineered human enzyme called methionine-ɣ-lyase (hMGL). Many cancers including melanoma, have a high requirement for L-methionine (L-Met) in comparison with non-cancerous cells. The hMGL enzyme exploits this metabolic vulnerability by degrading extracellular L-Met resulting in cancer cell starvation. The goal of this project was to assess the efficacy and identify mechanisms of action of the hMGL enzyme in melanoma models. In vitro and in vivo methods were used to evaluate the efficacy of L-Met depletion using hMGL on melanoma skin cancer. Four melanoma cancer cell lines were used, three were derived from human melanomas while one was a commonly utilized mouse melanoma line. Cell viability, cell cycle, and cell death parameters were evaluated first to establish that melanoma is sensitive to hMGL treatment. Global omics data sets including RNA-seq and metabolomics were generated from in vitro samples to give some insight into potential mechanisms of action to be investigated further. Since L-Met is involved in many cellular processes, it is not surprising that multiple mechanisms were found to be perturbed with hMGL treatment. Upregulation of the uncharged tRNA amino acid sensing pathway and an increase in DNA replication stress and ROS were observed with hMGL treatment. Drugs to be used in combination with hMGL were identified based on mechanistic relevance and screened in vitro. Treatment with hMGL inhibited tumor growth in both human xenograft and mouse allograft orthotopic melanoma models. The results of this study provide rationale for further mechanistic evaluation and clinical development of hMGL for the treatment of melanoma skin cancer.