Membrane-Fusing Vehicles for Re-Sensitizing Transporter-Mediated Multiple-Drug Resistance in Cancer.

Reversing the multiple drug resistance (MDR) arising from the overexpression of the efflux transporters often fails mainly due to the high toxicity or the poor water solubility of the inhibitors of these transporters. Here, we demonstrate the delivery of an inhibitor targeting three ABC transporters (ABCB1, ABCC1 and ABCG2) directly to the cell membrane using membrane-fusing vehicles (MFVs). Three different transfected MDCK II cell lines, along with parental cells, were used to investigate the inhibitory effect of cyclosporine A (CsA) in solution versus direct delivery to the cell membrane. CsA-loaded MFVs successfully reversed MDR for all three investigated efflux transporters at significantly lower concentrations compared with CsA in solution. Results showed a 15-fold decrease in the IC50 value for ABCB1, a 7-fold decrease for ABCC1 and an 11-fold decrease for ABCG2. We observed binding site specificity for ABCB1 and ABCG2 transporters. Lower concentrations of empty MFVs along with CsA contribute to the inhibition of Hoechst 33342 efflux. However, higher concentrations of CsA along with the high amount of MFVs activated transport via the H-binding site. This supports the conclusion that MFVs can be useful beyond their role as delivery systems and also help to elucidate differences between these transporters and their binding sites.

In Vitro-In Vivo Relationship in Mini-Scale-Enabling Formulations of Corallopyronin A.

In vivo studies in mice provide a valuable model to test novel active pharmaceutical ingredients due to their low material need and the fact that mice are frequently used as a species for early efficacy models. However, preclinical in vitro evaluations of formulation principles in mice are still lacking. The development of novel in vitro and in silico models supported the preclinical formulation evaluation for the anti-infective corallopyronin A (CorA). To this end, CorA and solubility-enhanced amorphous solid dispersion formulations, comprising povidone or copovidone, were evaluated regarding biorelevant solubilities and dissolution in mouse-specific media. As an acidic compound, CorA and CorA-ASD formulations showed decreased solubilities in mice when compared with human-specific media. In biorelevant biphasic dissolution experiments CorA-povidone showed a three-fold higher fraction partitioned into the organic phase of the biphasic dissolution, when compared with CorA-copovidone. Bioavailabilities determined by pharmacokinetic studies in BALB/c mice correlated with the biphasic dissolution prediction and resulted in a Level C in vitro-in vivo correlation. In vitro cell experiments excluded intestinal efflux by P-glycoprotein or breast cancer resistance protein. By incorporating in vitro results into a physiologically based pharmacokinetic model, the plasma concentrations of CorA-ASD formulations were predicted and identified dissolution as the limiting factor for bioavailability.

Synthesis and biological assessment of new pyrimidopyrimidines as inhibitors of breast cancer resistance protein (ABCG2).

Multidrug resistance constitutes a serious obstacle of the treatment success of cancer by chemotherapy. Mostly it is driven by expression of ABC transport proteins that actively efflux the anticancer agents out of the cell. This work describes the design and synthesis of 12 new pyrimidopyrimidines, as well as their inhibition of ABCG2 a transporter referred also to as breast cancer resistance protein, the selectivity versus ABCB1 (P-glycoprotein/P-gp) and ABCC1 as well as the investigation of their accumulation in single cells. From these results, N-(3,5-dimethoxyphenyl)-2-methyl-7-phenyl-5-(p-tolyl)pyrimido[4,5-d]pyrimidin-4-amine 7 h was identified as promising hit that deserves further investigation showing a selective and effective inhibition of ABCG2 with IC50 equal to 0.493 µM only 2-fold less active than Ko143.

Halogenation-Guided Chemical Screening Provides Insight into Tjipanazole Biosynthesis by the Cyanobacterium Fischerella ambigua.

Halogenated natural products (HNPs) show a wide range of interesting biological activities. Chemistry-guided screening with a software tool dedicated to identifying halogenated compounds in HPLC-MS data indicated the presence of several uncharacterised HNPs in an extract of the cyanobacterium Fischerella ambigua (Näg.) Gomont 108b. Three new natural products, tjipanazoles K, L, and M, were isolated from this strain together with the known tjipanazoles D and I. Taking into account the structures of all tjipanazole derivatives detected in this strain, reanalysis of the tjipanazole biosynthetic gene cluster allowed us to propose a biosynthetic pathway for the tjipanazoles. As the isolated tjipanazoles show structural similarity to arcyriaflavin A, an inhibitor of the clinically relevant multidrug-transporter ABCG2 overexpressed by different cancer cell lines, the isolated compounds were tested for ABCG2 inhibitory activity. Only tjipanazole K showed appreciable transporter inhibition, whereas the compounds lacking the pyrrolo[3,4-c] ring or featuring additional chloro substituents were found to be much less active.

New Inhibitors of Breast Cancer Resistance Protein (ABCG2) Containing a 2,4-Disubstituted Pyridopyrimidine Scaffold.

Multidrug resistance (MDR) occurring during cancer chemotherapy is a major obstacle for effectiveness and response to therapy and is often caused by ATP-binding cassette (ABC) efflux transporters. Belonging to the family of ABC transporters, breast cancer resistance protein is getting more and more in the spotlight of research. As a strategy to overcome MDR, inhibitors of ABC transporters were synthesized, which could be applied in combination with cytostatic drugs. For this purpose, 2,4-disubstituted pyridopyrimidine derivatives were synthesized. The investigations confirmed three key characteristics of good inhibitors: a low intrinsic cytotoxicity and a high potency and selectivity toward ABCG2. For selected compounds the interaction with ABCG2 was elucidated and their effect on ATPase activity and conformation sensitive 5D3 antibody binding was investigated. Their ability to reverse MDR in coadministration with the active metabolite of irinotecan and mitoxantron was confirmed.

Structure activity relationships, multidrug resistance reversal and selectivity of heteroarylphenyl ABCG2 inhibitors.

An overexpression of the transmembrane ATP-binding cassette transporter G2 (ABCG2, BCRP) in cancer tissues is supposed to play a role in the multidrug resistance (MDR) of tumors resulting in an inefficient chemotherapy. Therefore, co-administration of selective and non-toxic ABCG2 inhibitors is a promising strategy for improving the efficacy of chemotherapy by blocking ABCG2-mediated export of the cytostatic drugs. In the present study, we designed a small library of 38 novel compounds containing a heteroaryl-phenyl scaffold possessing several (bioisosteric) moieties, and twelve new precursors. We investigated the library for ABCG2 inhibition, for the selectivity against MDR-involved efflux pump ABCB1 (P-gp) and for toxicity. Structure activity relationship (SAR) studies revealed that, at least a phenylheteroaryl-phenylamide scaffold is necessary for observing an ABCG2 inhibition. 4-Methoxy-N-(2-(2-(6-methoxypyridin-3-yl)-2H-tetrazol-5-yl)phenyl)benzamide (43) exhibited a high potency (IC50 = 61 nM)), selectivity, low intrinsic toxicity and reversed the ABCG2-mediated drug resistance in presence of only 0.1 µM.