Gemcitabine (dFdC, 2,2-difluorodeoxycytidine) is a deoxycytidine nucleoside analogue of deoxycytidine in which two fluorine atoms have been inserted into the deoxyribose ring. Like other nucleoside analogues, gemcitabine is a prodrug. It is inactive in its original form, and depends on the intracellular machinery to gain pharmacological activity. What makes gemcitabine different from other nucleoside analogues is that it is actively transported across the cell membrane, it is phosphorylated more efficiently and it is eliminated at a slower rate. These differences, together with self-potentiation mechanisms, masked DNA chain termination and extensive inhibitory efficiency against several enzymes, are the source of gemcitabines cytotoxic activity against a wide variety of tumors. This unique combination of metabolic properties and mechanistic characteristics is only found in very few other anticancer drugs, and both the FDA and the EMEA have already approved its use for clinical purposes, for the treatment of several types of tumors. In spite of the promising results associated with gemcitabine, the knowledge of its mode of action and of the enzymes it interacts with is still not fully documented. In this article we propose to review all these aspects and summarize the path of gemcitabine inside the cell.

This review provides an updated atomic-level perspective regarding the enzyme 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoAR), linking the more recent data on this enzyme with a structure/function interpretation. This enzyme catalyzes one of the most important steps in cholesterol biosynthesis and is regarded as one of the most important drug targets in the treatment of hypercholesterolemia. Taking this into consideration, we review in the present article several aspects of this enzyme, including its structure and biochemistry, its catalytic mechanism and different reported and proposed approaches for inhibiting this enzyme, including the commercially available statins or the possibility of using dimerization inhibitors.