Technetium 99m Sestamibi: Mechanism of Action Essay

Technetium 99m sestamibi is a radiopharmaceutical that has been approved by the FDA as an agent for myocardial perfusion imaging used for visualizing how the blood circulates through the heart. Sestamibi has the following characteristics: it is cationic and lipophilic and serves as a substrate for P-glycoprotein and the MRP1. The organism moves to tissues containing large quantities of mitochondria and having negative membrane potentials. Particularly, the blood circulation in the region, the mitochondrial volume and the membrane potential determine the delivery of the radiopharmaceutical into the myocardium. When the transmembrane potential is negative, sestamibi is able to diffuse into the mitochondria. Due to the described characteristics of this radiopharmaceutical, its absorption and accumulation occur in the tissues in which the flow is adequate and metabolic activity is high. At the same time, if a lack of absorption is detected, it would point to a loss of perfusion and the absence of mitochondrial activity, like in myocardial infarction. Another reason for lacking sestamibi uptake is efflux mechanisms, like in cancer drug resistance with overexpressed P-glycoprotein and MRP1.