Structure–Activity Relationship Studies on Tetrahydroisoquinoline Derivatives: [4′-(6,7-Dimethoxy-3,4-dihydro-1H-isoquinolin-2-ylmethyl)biphenyl-4-ol] (MC70) Conjugated through Flexible Alkyl Chains with Furazan Moieties Gives Rise to Potent and Selective Ligands of P-glycoprotein

Abstract

P-glycoprotein (P-gp) is a well-known membrane transporter expressed in a number of strategic biological barriers, where it exerts a protective effect of paramount importance. Conversely it is one of the main causes of multidrug resistance (MDR), being capable of effluxing many chemotherapeutics. In a development of previous research, a small library of compounds was created conjugating diversely substituted furazan rings with MC70, a well-known P-gp inhibitor. These compounds were assessed for their potency against P-gp and another transporter (MRP1), for their apparent permeability (Papp) and for their ability to induce ATPase activity, thus delineating a complete functional profile. They displayed a substrate mechanism of action and high selectivity toward P-gp, unlike the lead compound. Data relating to their activity range from low micromolar to sub-nanomolar EC50, the most interesting compounds being 15 (0.97 nM), 19 (1.3 nM), 25 (0.60 nM), and 27 (0.90 nM).

New Tetrahydroisoquinoline Derivatives Overcome Pgp Activity in Brain-Blood Barrier and Glioblastoma Multiforme in Vitro

“…Compounds 1 – 5 [ 18 ] and 6 [ 19 ] were synthesized from MC70 , which was prepared according to the straightforward metal-free synthetic route reported in Scheme 1 .…”

“…Our research group has recently developed a library of Pgp ligands, based on the tetrahydroisoquinoline scaffold, a substructure characterizing several Pgp ligands [ 18 , 19 ]. The compounds were designed by functionalizing the phenolic group of MC70 , an already known Pgp inhibitor [ 20 ] with two types of substituents: 1,2,5-oxadiazole (furazan) moiety linked through alkyl spacers [ 18 ], and flexible alkyl chains of different length [ 19 ]. From this library, we selected 6 compounds with an EC 50 for Pgp ranging from 0.60 nM to 54 nM ( Table 1 ), i.e., superimposable with the last-generation of Pgp inhibitors [ 21 ].…”

Structure–Activity Relationship Studies on 6,7‐Dimethoxy‐2‐phenethyl‐1,2,3,4‐tetrahydroisoquinoline Derivatives as Multidrug Resistance Reversers

“…Calcein‐AM experiment : These experiments were performed as described by Guglielmo et al. with minor modifications . Each cell line (30 000 cells per well) was seeded into a black CulturePlate 96‐well plate with medium (100 μL), and the cells were allowed to become confluent overnight.…”

“…ATPlite assay : The MDCK‐MDR1 cells were seeded into a 96‐well microplate in complete medium (100 μL) at a density 2×10 4 cells per well . The plate was incubated overnight in a humidified atmosphere with 5 % CO 2 at 37 °C.…”

“…The culture medium was replaced every 48 h, and the cells were kept for 21 days in culture. The trans epithelial electrical resistance (TEER) of the monolayers was measured daily, before and after the experiment, by using an epithelial voltohmmeter (Millicell‐ERS) . Generally, TEER values greater than 1000 Ω for a 21 day culture are considered optimal.…”