Aromatic 2-(thio)ureidocarboxylic acids as a new family of modulators of multidrug resistance-associated protein 1: synthesis, biological evaluation, and structure-activity relationships.

Four series of aromatic carboxylic acids were prepared with a urea or thiourea moiety at the neighboring position to the carboxyl group and benzene or thiophene as aromatic scaffold. Using a calcein AM assay, these compounds were evaluated as inhibitors of multidrug resistance-associated protein 1 (MRP1) and selected compounds were examined toward P-glycoprotein (P-gp) as well as breast cancer resistance protein (BCRP) to assess selectivity for MRP1. Two 2-thioureidobenzo[b]thiophene-3-carboxylic acids (48, 49) were identified as particularly potent inhibitors of MRP1, with IC50 values of around 1 microM. The structural features of this new family of nontoxic MRP1 inhibitors include a (thio)urea disubstituted with preferentially two alkyl groups at the terminal nitrogen and an additional fused aromatic ring.

Phenylnannolones A-C: biosynthesis of new secondary metabolites from the myxobacterium Nannocystis exedens.

Myxobacteria are gliding bacteria that belong to the delta-Proteobacteria and are known for their unique biosynthetic capabilities. Among myxobacteria, Nannocystis spp. are most closely related to marine myxobacteria and their secondary metabolism has hardly been investigated. Phenylnannolones A (1), B (2) and C (3) were obtained from a culture of Nannocystis exedens that was isolated from the intertidal region of Crete. Compound 1 had inhibitory activity toward the ABCB1 gene product P-glycoprotein and reversed daunorubicin resistance in cultured cancer cells. Phenylnannolone A has an unusual structural architecture; it is composed of an ethyl-substituted polyene chain linked to a pyrone moiety on one side and to a phenyl ring on the other. The investigation of the biosynthesis with labelled precursors revealed acetate, butyrate and phenylalanine as building blocks for 1. The labelling pattern suggested novel biochemical reactions for the biosynthesis of the starter unit.

A 4-aminobenzoic acid derivative as novel lead for selective inhibitors of multidrug resistance-associated proteins.

We present a novel lead for inhibitors of multidrug resistance-associated proteins (MRPs). Compound 1 (4-[(5,6,7,8-tetrahydro-4-oxo-4H-[1]benzothieno[2,3-d][1,3]thiazin-2-yl)amino]benzoic acid) was about six times more potent than the known inhibitor MK571 at MRP1, while at MRP2 its effect was similar to that of MK571. Structural analogs were also evaluated. Among them, compound 2, sharing the 4-aminobenzoic acid substructure with 1, also inhibited MRP1. Both derivatives were inactive against P-gp. It can be concluded that their carboxyl group is needed for inhibition of MRPs and accounts for the selectivity of these compounds.

Relevance of drug uptake and efflux for cisplatin sensitivity of tumor cells.

Platinum sensitivity and platinum resistance may involve altered activity of transport proteins. In order to assess the role of drug uptake and efflux in this phenomenon, we compared the expression of three copper transporters, intracellular platinum accumulation, DNA platination and cytotoxicity of cisplatin in two cisplatin-sensitive and -resistant tumor cell line pairs (ovarian A2780/A2780cis and cervical HeLa/HeLaCK cells). Gene expression of importer CTR1, and ATP7A and ATP7B efflux transporters (with and without cisplatin treatment) was investigated using quantitative real-time PCR and platinum concentrations were determined by flameless atomic absorption spectrometry. After incubation with cisplatin, DNA platination was significantly lower in the resistant variants compared to the respective sensitive cell lines, whereas no obvious difference in DNA repair was found. Accordingly, the resistant variants exhibited lower intracellular platinum concentrations than their respective parental cells (2.5- and 2.9-fold lower in A2780cis and HeLaCK cells, respectively). No differences in efflux were observed. Resistant cells expressed lower levels of CTR1 (1.5-1.8-fold) than their sensitive counterparts. Expression differences of ATP7A and ATP7B between resistant and sensitive cells were cell type-specific. The results highlight the relevance of CTR1 for cisplatin sensitivity as there is a clear relationship between lower CTR1 expression, intracellular concentration, DNA platination and cytotoxicity of cisplatin in both resistant cell lines. Our data provide the basis for a quantitative understanding of alterations in uptake and efflux processes leading to cisplatin resistance and might hence facilitate the development of ex vivo assays that can predict cisplatin sensitivity in tumor specimens of patients.