Solid cancer cells commonly enter the blood and disseminate systemically but are highly inefficient at forming distant metastases for poorly understood reasons.,We studied human melanomas that differed in their metastasis histories in patients and in their capacity to metastasize in NSG mice.,All melanomas had high frequencies of cells that formed subcutaneous tumours, but much lower percentages of cells that formed tumours after intravenous or intrasplenic transplantation, particularly among inefficient metastasizers.,Melanoma cells in the blood and visceral organs experienced oxidative stress not observed in established subcutaneous tumours.,Successfully metastasizing melanomas underwent reversible metabolic changes during metastasis that increased their capacity to withstand oxidative stress, including increased dependence upon NADPH-generating enzymes in the folate pathway.,Anti-oxidants promoted distant metastasis in NSG mice.,Folate pathway inhibition using low-dose methotrexate, ALDH1L2 knockdown, or MTHFD1 knockdown inhibited distant metastasis without significantly affecting the growth of subcutaneous tumors in the same mice.,Oxidative stress thus limits distant metastasis by melanoma cells in vivo.
Melanoma is highly resistant to current modalities of therapy, with the extent of pigmentation playing an important role in therapeutic resistance.,Nuclear factor-κB (NF-κB) is constitutively activated in melanoma and can serve as a molecular target for cancer therapy and steroid/secosteroid action.,Cultured melanoma cells were used for mechanistic studies on NF-κB activity, utilising immunofluorescence, western blotting, EMSA, ELISA, gene reporter, and estimated DNA synthesis assays.,Formalin-fixed, paraffin-embedded specimens from melanoma patients were used for immunocytochemical analysis of NF-κB activity in situ.,Novel 20-hydroxyvitamin (20(OH)D3) and classical 1α,25-dihydroxyvitamin D3 (1,25(OH)2D3) secosteroids inhibited melanoma cell proliferation.,Active forms of vitamin D were found to inhibit NF-κB activity in nonpigmented cells, while having no effect on pigmented cells.,Treatment of nonpigmented cells with vitamin D3 derivatives inhibited NF-κB DNA binding and NF-κB-dependent reporter assays, as well as inhibited the nuclear translocation of the p65 NF-κB subunit and its accumulation in the cytoplasm.,Moreover, analysis of biopsies of melanoma patients showed that nonpigmented and slightly pigmented melanomas displayed higher nuclear NF-κB p65 expression than highly pigmented melanomas.,Classical 1,25(OH)2D3 and novel 20(OH)D3 hydroxyderivatives of vitamin D3 can target NF-κB and regulate melanoma progression in nonpigmented melanoma cells.,Melanin pigmentation is associated with the resistance of melanomas to 20(OH)D3 and 1,25(OH)2D3 treatment.