Cyclophosphamide: Old Drug with Great Future

This paper does not describe the results of a systematic search for the mechanism of action of cyclophosphamide and the consequences and possible indications arising from this mechanism. Rather, it describes a puzzle in which our own results, with some of them being very old, were re-evaluated with the latest biochemical knowledge and supplemented by results from the scientific literature. The mechanism of action of cyclophosphamide, which has been indispensable in clinical practice for 60 years, was unknown until recently simply because biochemical knowledge was lacking and because results from in vitro experiments were uncritically extrapolated to in vivo conditions. In vitro, the DNA alkylating metabolite phosphoramide mustard (PAM) is formed from the CP metabolite aldophosphamide (ALD) by phosphate and bicarbonate ion-catalyzed β-elimination of acrolein; in vivo, however, ALD is cleaved by phosphoesterases or DNA polymerase δ and ε, which are associated with 3′-5′ exonucleases, into the complementary metabolites PAM and 3-hydroxypropanal (HPA). The following describes the mechanism of action of CP, namely the complementary interaction of alkylating PAM and apoptosis-enhancing HPA, and it is shown that by optimizing the complementary effects of PAM and HPA, the antitumor efficacy in the P388 mouse tumor model can be increased by more than ten thousand-fold. Further experiments show that by optimizing the interaction of DNA alkylation and enhancing the resulting apoptosis by HPA, the formation of resistant metastases can be prevented and low-toxicity chemotherapy can be achieved.