Investigating the role of stereochemistry in the activity of anticancer acylfulvenes: Synthesis, reductase-mediated bioactivation, and cellular toxicity

Acylfulvenes comprise a family of semisynthetic natural product derivatives with potent antitumor activities. Previous studies indicated that acylfulvenes are bioactivated by NADPH-dependent alkenal/one reductase (AOR), presumably generating intermediates with the capacity to alkylate cellular targets, such as DNA, proteins, and glutathione. This process is thought to induce apoptosis, and the chemical and biochemical pathways involved are topics of current investigation. In this study, four acylfulvene analogues were synthesized: (-)-acylfulvene, (+)-acylfulvene, (-)-(hydroxymethyl)acylfulvene, and (+)-(hydroxyrnethyl)-acylfulvene. These compounds were synthesized by a chiral-resolution method, described for the first time in this report, and by asymmetric synthesis using a method formally demonstrated previously. Cell toxicity studies indicate a positive con-elation between AOR level and acylfulvene sensitivity. The absolute configuration of acylfulvene analogues has a significant influence on cytotoxicity. (-)-(Hydroxymethyl)acylfulvene is 25 times more potent than (+)-(hydroxymethyl)acylfulvene in cells transfected with an AOR overexpression vector. Based on kinetic parameters, the rates of AOR-mediated activation are more strongly dependent on acylfulvene substitution than on absolute stereochemistry. These data support the role of AOR-mediated metabolism and indicate the involvement of other stereochemically dictated pathways, such as transport and biomolecule binding, in contributing to the cytotoxicity of acylfulvenes.