Natulan (Procarbazine) is a methylhydrazine derivative which in animal experiments inhibits a series of transplantable tumours. The Walker carcinoma is markedly affected. Even well established Walker tumours disappear completely under Natulan treatment. Tumour tissue is replaced by fibrous tissue. Natulan does not act selectively on neoplastic tissue, it also depresses the growth of other rapidly proliferating tissues such as the bone marrow. As regards the mechanism of action the following data are known: Natulan lowers the mitotic index by prolonging the interphase and hindering the cell from entering into mitosis. In Ehrlich ascites tumour cells chromatid breaks were observed. Natulan depolymerizes deoxyribonucleic acid (DNA) in vitro. In vivo the synthesis of DNA is inhibited. Furthermore alkylation of purine bases has been demonstrated. All these mechanisms may be responsible for the cytotoxic effect of methylhydrazine derivatives. Natulan does not possess cross-resistance towards other cytotoxic agents. This phenomenon is a further proof of its particular mechanism of actio
