Mechanism-of-Action-Based Development of New Cyclophosphamides

Abstract

Even more than 60 years after its introduction into the clinic, cyclophosphamide (CP), which belongs to the group of alkylating cytostatics, is indispensable for the treatment of cancer. This is despite the fact that its exact mechanism of action was unknown until a few years ago, and therefore, all attempts to improve the effectiveness of CP failed. The reason for not knowing the mechanism of action was the uncritical transfer of the chemical processes that lead to the formation of the actual alkylating CP metabolite phosphoreamide mustard (PAM) in vitro to in vivo conditions. In vitro—e.g., in cell culture experiments—PAM is formed by β-elimination of acrolein from the pharmacologically active CP metabolite aldophosphamide (ALD). In vivo, on the other hand, it is formed by enzymatic cleavage of ALD by phosphodiesterases (PDE) with the formation of 3-hydroxypropanal (HPA). The discovery of HPA as a cyclophosphamide metabolite, together with the discovery that HPA is a proapoptotic aldehyde and the discovery that the cell death event in therapy with CP is DNA-alkylation-initiated p53-controlled apoptosis, led to the formulation of a mechanism of action of CP and other oxazaphosphorine cytostatics (OX). This mechanism of action is presented here and is confirmed by newly developed CP-like compounds with lower toxicity and an order of magnitude better effectiveness.