TABLE 1

Properties of Pgp probe substrates and inhibitor

Probe	mol. wt.^a	Apparent Permeability (P_app B→A)^b	Postulated Binding Site^c	Comment	Reference
		nm/s
Calcein-AM	995	N.D.	R,P	High throughput screening probe	Tiberghien and Loor, 1996; Polli et al., 2001; Schwab et al., 2003
Colchicine	399	53	H	Single binding site in Pgp	Shapiro and Ling, 1997; Martin et al., 2000
Digoxin	781	16	R	Clinically important probe	Englund et al., 2004; Keogh and Kunta, 2006
Prazosin	382	283	P	Historical probe for Pgp binding studies	Shapiro et al., 1999; Isenberg et al., 2001
Vinblastine	811	97	R	Historical probe for multidrug resistance	Doppenschmitt et al., 1999
GF120918	564	N.D.	M	Clinically significant inhibitor and research tool	Polli et al., 2001; Tang et al., 2002

N.D., not determined; R, rhodamine 123/anthracycline site; P, progesterone/prazosin site; H, Hoechst 33342 site; M, central modulation site.
↵ a Molecular weight of the free form.
↵ b Apparent permeability in the presence of the Pgp inhibitor GF120918 (5 μM).
↵ c Shapiro and Ling, 1997; Martin et al., 2000; Lugo and Sharom, 2005.