EFFICIENTLY TARGETING DRUG EFFLUX THROUGH MODULATION OF P-GLYCOPROTEIN ACTIVITY BY SMALL MOLECULES: DESIGN, BIOLOGICAL AND COMPUTATIONAL STUDY.

One of the most studied mechanisms of chemoresistance in cancer cells is the overexpression of ATP-Binding Cassette (ABC) transporters, which are actively involved in the efflux of chemotherapeutic agents. Among these, ABCB1/P-glycoprotein (P-gp) represents a main concern due to its ample spectrum of substrates and to its overexpression in Cancer Stem Cells (CSCs) [1], a small population with great tumorigenicity, self-renewal ability and resistance to cancer therapy. In this setting our efforts aimed at the development of a library of P-gp ligands starting from an already studied inhibitor, MC70 ([4’-(6,7-dimethoxy-3,4-dihydro-1H-isoquinolin-2-ylmethyl)biphenyl-4-ol], EC50 = 690 nM) [2]. The structural modification carried out in the past years focused on several aspects: i) we developed a first series of compounds through the functionalization of the phenolic group of MC70 with alkyl and oxyalkyl chains; by tuning the length of the substituent we reached an EC50 of 5.4 nM [3]; ii) through the introduction of more complex moieties containing variously substituted furazan (1,2,5-oxadiazole) ring, we obtained several compounds with EC50 between 0.5 and 1 nM [4]; three of these proved able to induce doxorubicin accumulation in glioblastoma multiforme cells even in presence of blood brain barrier [5]; iii) the “decoration” of the biphenyl core of MC70 lead to compounds with comparable activity, but in this case we found that one of them was particularly efficient in restoring doxorubicin activity in co-administration assay [6]. In the last work we fulfilled a more “drastic” modification of the phenolic group introducing a variety of structural features which are determinants for properties of key impact on molecular recognition, such as hydrogen bond acceptor and donor capability, steric bulkiness, polarity and hydrophobicity [7]. Along this series, we obtained a ligand with an EC50 of 15 nM which reversed the chemoresistance mediated by P-gp in CSCs, the hardest tumour component to be eradicated, coming from glioblatoma multiforme and pleuric mesothelioma. Its activity on P-gp was rationalized through an in-depth molecular dynamics study encompassing well-tempered molecular dynamics [8] and unbiased molecular dynamics: the putative binding modes of the compound have been envisaged, taking into account the two possible ionization states of the ligand, and some relevant dynamical properties of the complexes have been studied, revealing a “promiscuous” mechanism of interaction with P-gp.