Methyl hydrazine (MH) is a reducing agent and electron donor previously found to radiosensitize anoxic bacterial cells. This compound has now been shown also to radiosensitize Ehrlich ascites tumor cells in vivo (dose modifying factor of 2) at concentrations non-lethal to cells or the host mouse. When MH-treated Ehrlich ascites cells are layered upon an alkaline sucrose density gradient the resulting DNA profile resembles that of cells receiving a large dose of x-radiation, i.e., a shift toward the top of the gradient, suggesting the production of a great many single-strand breaks. This effect is also observed with nucleoprotein isolated from Ehrlich ascites cells. Incubation of MH-treated cells in saline in the absence of MH allows partial rejoining of single-strand breaks. The normal strand break repair period following radiation injury may be less effective for cells in the presence of MH, possibly explaining the observed radiosensitization effect.

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