A Novel Polyamine-Targeted Therapy for BRAF Mutant Melanoma Tumors

Abstract

Mutant serine/threonine protein kinase B-Raf (BRAF) protein is expressed in over half of all melanoma tumors. Although BRAF inhibitors (BRAFi) elicit rapid anti-tumor responses in the majority of patients with mutant BRAF melanoma, the tumors inevitably relapse after a short time. We hypothesized that polyamines are essential for tumor survival in mutant BRAF melanomas. These tumors rely on both polyamine biosynthesis and an upregulated polyamine transport system (PTS) to maintain their high intracellular polyamine levels. We evaluated the effect of a novel arylpolyamine (AP) compound that is cytotoxic upon cellular entry via the increased PTS activity of melanoma cells with different BRAF mutational status. Mutant BRAF melanoma cells demonstrated greater PTS activity and increased sensitivity to AP compared to wild type BRAF (BRAFWT) melanoma cells. Treatment with an inhibitor of polyamine biosynthesis, α-difluoromethylornithine (DFMO), further upregulated PTS activity in mutant BRAF cells and increased their sensitivity to AP. Furthermore, viability assays of 3D spheroid cultures of mutant BRAF melanoma cells demonstrated greater resistance to the BRAFi, PLX4720, compared to 2D monolayer cultures. However, co-treatment with AP restored the sensitivity of melanoma spheroids to PLX4720. These data indicate that mutant BRAF melanoma cells are more dependent on the PTS compared to BRAFWT melanoma cells, resulting in greater sensitivity to the PTS-targeted cytotoxic AP compound.

Polyamine metabolism and cancer: treatments, challenges and opportunities

“…Although BRAF-mutant tumours initially respond to BRAF inhibitors, resistance to these inhibitors develops rapidly 41 . Interestingly, BRAF-mutant melanoma cells possess greater polyamine transport activity than their normal BRAF counterparts 42 . Furthermore, in vitro studies demonstrated that, when exposed to naphthalene conjugates that could enter the cell via only the polyamine transport system, there was selective killing of BRAF-mutant melanoma cells, whereas wild-type melanoma cells were resistant, indicating that BRAF-mutant melanoma cells can be more susceptible to certain drugs owing to the increase in polyamine transport activity.…”

“…Furthermore, in vitro studies demonstrated that, when exposed to naphthalene conjugates that could enter the cell via only the polyamine transport system, there was selective killing of BRAF-mutant melanoma cells, whereas wild-type melanoma cells were resistant, indicating that BRAF-mutant melanoma cells can be more susceptible to certain drugs owing to the increase in polyamine transport activity. Additionally, treatment with a polyamine analogue may reduce the incidence of developed resistance to BRAF inhibitors 42 .…”

Oncology Therapeutics Targeting the Metabolism of Amino Acids

“…mTORC1 induces AMD1 expression, stabilizing the AMD1 proenzyme by phosphorylating Ser298 [240]. Increased polyamine transport activity has been reported to be linked to BRAF inhibitor resistance in BRAF-mutated melanomas [241]. Elevated polyamine levels and those of related metabolites (e.g., N-acetylputrescine, cadaverine, and 1,3-diaminopropane) can be used as a biomarker for cancer.…”

5'-Methylthioadenosine and Cancer: old molecules, new understanding

“…Increases in polyamine biosynthesis and intracellular polyamine content levels are of the most consistent biochemical alterations observed in cancer cells of all types, denoting their importance for tumorigenesis. A recent study highlights the dependence of melanoma cells not only on higher levels of polyamine biosynthesis but also on upregulated polyamine transport systems 88. They are also involved in carcinogenesis and tumor biology properties such as those of breast cancer 89 and lung adenocarcinoma invasiveness and metastasis 90.…”