The effects of N-methylformamide on artificial and spontaneous metastases from a murine hepatocarcinoma.

The effects of the differentiation-inducing polar solvent N-methylformamide (NMF) on artificially induced and spontaneous metastases from a murine hepatocarcinoma (HCA-1) in C3Hf/Kam mice were investigated. Exposure of HCA-1 cells in vitro for 6 days to 1.0% or 1.25% NMF resulted in an increase in the number of lung nodules formed in mice when these cells were injected into their tail veins. This in vitro NMF exposure increased cell volume and induced only a slight amount of cytotoxicity. Administration of NMF to mice 1 day before i.v. tumour cell inoculation resulted in a dose-dependent increase in the number of lung nodules formed, beginning at an NMF dose of 600 mg kg-1. NMF caused a similar magnitude of metastasis enhancement in immunosuppressed mice. However, when the maximum dose tested (1,800 mg kg-1) was administered as 6 daily fractions of 300 mg kg-1 each, no increase in artificial metastases was detected. Administration of NMF to mice one day after i.v. tumour cell injection resulted in a dose-dependent decrease in the number of lung nodules. In mice bearing 5-6 mm HCA-1 leg tumours, treatment with 6 daily fractions of NMF (300 mg kg-1 each) significantly reduced the number of spontaneous pulmonary metastases, yet had very little effect on the growth of the primary tumour. These data suggest that, in a clinically relevant treatment setting, NMF can reduce metastasis formation.