Introduction

The pharmaceutical industry is always in hot pursuit of new therapies to combat diseases and other ailments. Generally, the route is difficult and costly involving the identification of novel disease targets and the design of novel compounds for these targets. An alternative option is that new drugs can be designed from modification of currently existing molecules to achieve compounds with an overall superior therapeutic profile. However, sometimes a class of a drug, designed for a specific indication, can be fortuitously shown to have therapeutic effects in a completely different disease state. In most of these cases, it is the mode of action of the drug and not necessarily similarities in the disease mechanisms per se that make these compounds useful across a spectrum of diseases. This is the case for potassium channel openers (KCOs), compounds originally developed as anti-hypertensive agents as they are able to relax vascular smooth muscle. They act by opening potassium channels in cell membranes resulting in membrane hyperpolarization and consequently relaxation of the muscle cells. Cromakalim is one of the earliest used KCOs and is a benzopyran prototype. In addition to its ability to relax vascular smooth muscle cromakalim was shown to also relax airway smooth muscle (ASM). Because of this property, this class of drugs has been receiving increasing attention due to their potential use in respiratory diseases and many studies have been undertaken to investigate this.