Editorial [Hot Topic: Active Drug Transport in Drug Discovery and Medicinal Chemistry(Guest Editor: Nicola A. Colabufo)]

Drug bioavailability depends on several pharmacokinetic aspects such as passive diffusion and active transport through several physiological barriers, in particular membranes of the gastrointestinal tract and the blood brain barrier. These two barriers represent the first line of defense of the organism through which the passive and active transports as well as the metabolism modulate drug absorption and disposition. Several pharmacokinetic parameters such as LogP, LogD and Ka address the passive diffusion of xenobiotics but these three features alone can not explain the physiological absorption and transport of drugs. Drug delivery is a combination with other factors such as metabolism and active transport. In this issue, the roles of the most studied proteins involved in the active transport, such as ATP Binding Cassette (ABC) transporters, have been deepened. The physiological involvement of ABC transporters in Blood Brain Barrier (BBB) and in GastroIntestinal (GI) tract has been illustrated focusing in particular on the role of these transporters in drugs influx and efflux (Colabufo et al.; Dobson et al.; Nicolazzo et al.). The methodologies to overcome the restrictive and selective physiological lines of defense of the organism (BBB and GI) have been outlined and the recent technological progresses in this field have been reported (Hammarlund-Udenaes et al.; Trapani et al.). Since ABC transporters are also implicated in MultiDrug Resistance (MDR), the involvement of some pumps, such as P-gp, BCRP and MRPs in chemotherapeutic agents active transport has been reported (Tucci et al.). In addition, it has been recently demonstrated that ABC transporters are involved in genetic pathologies such as cystic fibrosis, in neurodegenerative diseases such as Alzheimer's and Parkinson's diseases and in pathologies related to the trafficking of endogenous proteins, lipids, aminoacids etc (Rapposelli et al.; Azzariti et al.). Many thanks to all the authors for the prompt submission of their manuscripts and for their comprehensive contributions.