Studies on propafenone-type modulators of multidrug-resistance IV1): synthesis and pharmacological activity of 5-hydroxy and 5-benzyloxy derivatives

From phenothiazine to 3-phenyl-1,4-benzothiazine derivatives as inhibitors of the Staphylococcus aureus NorA multidrug efflux pump

Overexpression of efflux pumps is an important mechanism by which bacteria evade effects of substrate antimicrobial agents and inhibition of such pumps is a promising strategy to circumvent this resistance mechanism. NorA is a Staphylococcus aureus multidrug efflux pump, the activity of which confers decreased susceptibility to many structurally unrelated agents, including fluoroquinolones, resulting in a multidrug resistant (MDR) phenotype. In this work, a series of 1,4-benzothiazine derivatives were designed and synthesized as a minimized structural template of phenothiazine MDR efflux pump inhibitors (EPIs) in an effort to identify more potent S. aureus NorA EPIs. Almost all derivatives evaluated showed good activity in combination with ciprofloxacin against S. aureus ATCC 25923; some were capable of completely restoring ciprofloxacin activity in a norA-overexpressing strain (SA-K2378). Compounds 6k and 7j displayed good activity against SA-1199B, a strain that also overexpresses norA, in an ethidium bromide (EtBr) efflux inhibition assay.

Diphenylcyclohexylamine derivatives as new potent multidrug resistance (MDR) modulators

A series of compounds with a diphenylmethyl cyclohexyl skeleton, loosely related to verapamil, has been synthesized and tested as MDR modulators on anthracycline-resistant erythroleukemia K 562 cells. Their residual cardiovascular action (negative inotropic and chronotropic activity as well as vasorelaxant activity) was evaluated on guinea-pig isolated atria preparations and on guinea-pig aortic strip preparations. Most compounds of the series possess a good MDR-reverting activity together with a low cardiovascular action. Among them, compounds 3a1, 7a, and 8a are more potent than verapamil as MDR reverters and lack any cardiovascular action; they can represent useful leads for the development of new safe MDR reversing drugs.

MCASE study of the multidrug resistance reversal activity of propafenone analogs

A database containing 130 propafenone type chemicals which have been tested for their multidrug resistance (MDR) reversal activity was compiled. Using the Multiple Computer-Automated Structure Evaluation (MCASE) program to analyze this database, an underlying relationship between MDR reversal activity and octanol/water partition coefficient was found. An MDR reversal model was created based on this database by the baseline activity identification algorithm (BAIA) of the MCASE program. The main phamacophores relevant to MDR reversal activity were identified.

Three-Dimensional Quantitative Structure−Activity Relationship Analysis of Propafenone-Type Multidrug Resistance Modulators: Influence of Variable Selection on Test Set Predictivity

An extended set of multidrug-resistance modulators of the propafenone type were investigated using CoMFA and CoMSIA. A number of 3D-QSAR models were derived from steric, electrostatic, and hydrophobic fields and their combinations. The hydrophobic fields alone and in combination with the steric and both (steric and electrostatic) fields yielded the models with the highest cross-validated predictivity, in agreement with a previous analysis of a smaller data set of propafenone-type multidrug-resistance (MDR) modulators. Inclusion of lipophilicity did not lead to an improvement of the models. The results point to the importance of hydrophobicity as a space-directed molecular property for MDR-modulating activity. The influence of variable selection applying the GOLPE procedure was investigated with an external test set. Variable-selection procedure was repetitively applied, keeping at each stage variables with uncertain contribution to the models. For the CoMFA-based 3D-QSAR models, an increase in external prediction quality was found. In contrast, the CoMSIA-based 3D-QSAR models were not improved by the GOLPE variable-selection procedure.

The medicinal chemistry of multidrug resistance (MDR) reversing drugs

Multidrug resistance (MDR) is a kind of resistance of cancer cells to multiple classes of chemotherapic drugs that can be structurally and mechanistically unrelated. Classical MDR regards altered membrane transport that results in lower cell concentrations of cytotoxic drug and is related to the over expression of a variety of proteins that act as ATP-dependent extrusion pumps. P-glycoprotein (Pgp) and multidrug resistance protein (MRP1) are the most important and widely studied members of the family that belongs to the ABC superfamily of transporters. It is apparent that, besides their role in cancer cell resistance, these proteins have multiple physiological functions as well, since they are expressed also in many important non-tumoural tissues and are largely present in prokaryotic organisms. A number of drugs have been identified which are able to reverse the effects of Pgp, MRPI and sister proteins, on multidrug resistance. The first MDR modulators discovered and studied in clinical trials were endowed with definite pharmacological actions so that the doses required to overcome MDR were associated with unacceptably high side effects. As a consequence, much attention has been focused on developing more potent and selective modulators with proper potency, selectivity and pharmacokinetics that can be used at lower doses. Several novel MDR reversing agents (also known as chemosensitisers) are currently undergoing clinical evaluation for the treatment of resistant tumours. This review is concerned with the medicinal chemistry of MDR reversers, with particular attention to the drugs that are presently in development.

Structure-activity relationship of P-glycoprotein substrates and modifiers

The air-water partition coefficients, K(aw), highly correlated with the corresponding lipid-water partition coefficients, K(lw), and the critical micelle concentrations, CMC, were measured for 11 compounds for which the kinetic parameters of P-glycoprotein ATPase activation (Michaelis-Menten constant, K(m), and maximal velocity, V(max)) had been determined previously in inside-out vesicles of CR1R12 Chinese hamster ovary cells. In addition, the hydrogen bond donor patterns (type I and type II) relevant for substrate recognition by P-glycoprotein were determined from the energy-minimized three-dimensional structure of these compounds. A linear relation between the air-water partition coefficient, K(aw), and the inverse of the Michaelis-Menten constant, K(m), was observed such that K(m) x K(aw) approximately = 1. The maximal velocity, V(max), was shown to decrease with the number and strength of electron donor (hydrogen bond acceptor) groups in recognition patterns. If two substrates are applied simultaneously to P-glycoprotein the compound with the higher potential to form hydrogen bonds generally acts as an inhibitor. We conclude that partitioning into the lipid membrane is the rate-limiting step for the interaction of a substrate with P-glycoprotein and that dissociation of the P-glycoprotein-substrate complex is determined by the number and strength of the hydrogen bonds formed between the substrate and the transporter.

Design, synthesis, and in vitro activity of catamphiphilic reverters of multidrug resistance: discovery of a selective, highly efficacious chemosensitizer with potency in the nanomolar range

On the basis of the results obtained in previous research, three series of compounds (A-C), derived from verapamil, were designed and synthesized to obtain drugs able to revert multidrug resistance (MDR), an acquired resistance that frequently impairs cancer chemotherapy. The ability of the obtained compounds to revert MDR was evaluated on anthracycline-resistant erythroleukemia K 562 cells, measuring the uptake of THP-adriamycin (pirarubicin) by continuous spectrofluorometric monitoring of the decrease of the fluorescence signal of the anthracycline at 590 nm (lambdaex = 480 nm), after incubation with cells. Cardiovascular activity, which is responsible for unwanted side effects, was also evaluated. The results obtained show that many of the compounds studied are potent reverters of MDR and are endowed with reduced cardiovascular activity. One of the compounds (7, MM36) presents a pharmacological profile (unprecedented nanomolar potency, high reversal of MDR, low cardiovascular activity) that makes it a promising drug candidate to treat MDR and a useful tool for studying P-glycoprotein.