Development of small-molecule P-gp inhibitors of the N-benzyl 1,4-dihydropyridine type: novel aspects in SAR and bioanalytical evaluation of multidrug resistance (MDR) reversal properties.

Novel series of N-benzyl 1,4-dihydropyridines have been prepared by facile syntheses. All relevant substituents of the molecular scaffold have been varied. The resulting compounds were biologically evaluated as P-glycoprotein (P-gp) inhibitors. Substitutions of the N-benzyl residue favour biological activity beside respective 3-ester functions. Most active compounds were further evaluated as multidrug resistance (MDR) modulators to restore the cytotoxic properties of varying daunorubicin applications.

Discovery of a novel class of small-molecule antibacterial agents against Staphylococcus aureus.

Background: With constantly increasing resistance against the known antibiotics, the search for novel antibacterial compounds is a challenge. The number of synthetic antibacterial agents is limited. Materials & methods: We discovered novel small-molecule antibacterial agents that are accessible via a simple two-step procedure. The evaluation against Staphylococcus aureus showed antibacterial effects depending on the substituent positioning at the residues of the molecular scaffold. Additionally, we investigated the potential of the compounds to increase the antibacterial activity of tetracycline. Results: The most effective antibacterial compounds possessed a 3-methoxy function at an aromatic residue. In combination with tetracycline, we found a strong effect for a few compounds in boosting the antibacterial activity, so the first promising lead compounds with dual activities could be identified.

Discovery of pyridine-2-ones as novel class of multidrug resistance (MDR) modulators: first structure-activity relationships.

A novel facile synthesis led to pyridine-2-one target structures of which first series with varying substituents have been yielded and biologically characterized as novel multidrug resistance (MDR) modulators inhibiting P-glycoprotein (P-gp). Structure-activity relationships prove a dependency of the MDR-modulating properties from the kind and positioning of hydrogen bond acceptor functions within the molecular skeleton. Cyano functions turned out as biologically effective substituents for a potential hydrogen bonding to the protein target structure.

Novel structure-activity relationships and selectivity profiling of cage dimeric 1,4-dihydropyridines as multidrug resistance (MDR) modulators.

Synthesized series of cage dimeric 1,4-dihydropyridines have been systematically evaluated as MDR modulators in in vitro assays to investigate structure-dependent selectivity properties of inhibiting most cancer-relevant efflux pump proteins. Structure-activity relationships of each P-glycoprotein (P-gp) and multidrug resistance associated protein (MRP) 1 and MRP2 inhibition are discussed and prove to be mainly determined by certain aromatic substitution patterns. The characterization of breast cancer resistance protein (BCRP) inhibition results in the discovery of benzyloxy substituted derivatives as selective P-gp inhibitors.

Characteristic CT features of pheochromocytomas - probability model calculation tool based on a multicentric study.

OBJECTIVES: The aim of the study was to evaluate the CT features of adrenal tumors in an effort to identify features specific to pheochromocytomas and second, to define a feasible probability calculation model. METHODS: This multicentric retrospective study included patients from the period 2003 to 2017 with an appropriate CT examination and a histological diagnosis of an adrenal adenoma, pheochromocytoma, adrenocortical carcinoma, or metastasis. In total, 346 patients were suitable for the CT image analysis, which included evaluation of the largest diameter, the shape of the lesion, the presence of central necrosis and its margins, and the presence of an enhancing peripheral rim ("ring sign"). RESULTS: Pheochromocytomas have a significantly more spherical shape (P<0.001), whereas an elliptical shape significantly reduces the probability of a pheochromocytoma (odds ratio = 0.015), as does another shape (odds ratio = 0.006). A "ring sign" is also more frequent in pheochromocytomas compared to other adrenal tumors (P=0.001, odds ratio = 6.49). A sharp necrosis also increases the probability of a pheochromocytoma more than unsharp necrosis (odds ratio 231.6 vs. 20.2). The probability calculation model created on the basis of the results confirms a high sensitivity and specificity (80% and 95%). CONCLUSION: This study confirms the value of anatomical features in the assessment of adrenal masses with the ability to significantly improve the identification of pheochromocytomas. Advanced assessment of the tumor shape was defined and a original comprehensive calculating tool of the pheochromocytoma probability was created on the basis of the results presented here and could be used in clinical routine.

Biological evaluation of bishydroxymethyl-substituted cage dimeric 1,4-dihydropyridines as a novel class of p-glycoprotein modulating agents in cancer cells.

A series of N-substituted cage dimeric 1,4-dihydropyridines 3a-e was evaluated as inhibitors of membrane efflux pump P-glycoprotein (P-gp) in multidrug resistant (mdr) cancer cells. Structure-activity relationships (SAR) and cytotoxic properties are discussed. Effective concentrations for overcoming mdr have been demonstrated in competition studies with the P-gp substrate epirubicin.

Correlation of calculated molecular orbital energies of some phenothiazine compounds with MDR reversal properties.

Molecular orbital energies of energetically minimized series of extended aromatic and aminoalkyl side chain substituted phenothiazine compounds have been considered with respect to charge transfer (CT) binding properties to P-glycoprotein (P-gp) amino acids of the first P-gp loop. A dependency of decreasing energies of lowest unoccupied orbitals (E(lumo)) with reduced CT binding properties to an increasing P-gp mediated multidrug resistance (MDR) has been found for the extended aromatic compounds.

Discovery of 9,10-Dihydroacridines as Novel Class of ABCB1 Inhibitors.

Nonplanar 9,10-dihydroacridines were synthesized as promising C2 symmetric molecular scaffolds as inhibitors of the transmembrane efflux pump ABCB1. Within the series structure-activity relationships are discussed revealing the importance of hydrogen bond acceptor functions. A selectivity of ABCB1 inhibition is demonstrated for selected candidates and a bioanalytical study proved nontoxicity as well as missing ABCB1 substrate properties. The results encourage to further develop the promising class of ABCB1 inhibitors.

Evaluation of the first cytostatically active 1-aza-9-oxafluorenes as novel selective CDK1 inhibitors with P-glycoprotein modulating properties.

The first series of synthetic 1-aza-9-oxafluorenes with cytostatic activities in the micromolar range was evaluated as cyclin-dependent kinase (CDK1) inhibitors. Activity was found to be selective in comparison to the inhibition of other kinases within the CDK family. Compounds were shown to inhibit the membrane-efflux pump P-glycoprotein responsible for multidrug resistance in cancer cells. First structure-activity relationships are discussed.

Novel structurally varied N-alkyl 1,4-dihydropyridines as ABCB1 inhibitors: structure-activity relationships, biological activity and first bioanalytical evaluation.

Series of structurally varied N-alkyl 1,4-dihydropyridines and novel benzo-annelated derivatives as 1,4- dihydroquinolines have been characterized as ABCB1 inhibitors. Structure-activity relationships (SARs) are discussed. Cytotoxic activities of selected compounds have been determined. A first bioanalysis of ABCB1 substrate properties has been carried out in a cell-based model. Compounds with highest ABCB1 inhibiting activities were no substrates of ABCB1 and not transported by the efflux pump, thus profiling the new ABCB1 inhibitors.

Multidrug resistance reversal properties and cytotoxic evaluation of representatives of a novel class of HIV-1 protease inhibitors.

OBJECTIVES: P-Glycoprotein (P-gp) plays a central role in the development of resistance against cytostatics in anticancer therapy and against human immunodeficiency virus (HIV) therapeutics of the HIV-1 protease inhibitor type. An approach to reverse the so-called multidrug resistance (MDR) phenomenon by the use of P-gp inhibiting agents is a challenge in the therapy of cancer and AIDS. Effective in-vitro inhibitors have P-gp substrate properties so that the expected in-vivo effects have been disappointing so far. Consequent higher dosages cause toxic effects. METHODS: Novel HIV-1 protease inhibitors (H17, JW41, JW33 and JW46) have been evaluated in comparison with ritonavir as P-gp inhibiting agents, in the exclusively P-gp overexpressing model cell line mouse T lymphoma using flow cytometry. The cytotoxic properties against various cell lines were characterized in the MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) assay to estimate potential toxic effects in therapeutically relevant concentrations in metabolically active HepG2 cells, drug-sensitive Jurkat cells and in gastric carcinoma cells. KEY FINDINGS: Concentration-dependent effective reversal properties have been discussed in context and proved to be mainly influenced by the number of potential hydrogen bond acceptor functions. The compounds showed no cytotoxic properties in P-gp inhibiting concentration ranges. Ritonavir, a known P-gp substrate, proved to be less toxic in the P-gp expressing cell line than in the nonexpressing cell line at the cell-exposed concentrations and thus showed P-gp substrate properties. Two compounds, H17 and JW41, showed no P-gp substrate properties, with higher toxicity in the P-gp expressing cell line compared with the nonexpressing cell line. CONCLUSIONS: The novel compounds have been shown to be prospective AIDS therapeutics, acting as effective and nontoxic P-gp inhibitors compared with ritonavir, which is a known P-gp inhibitor with unfavourable toxic and P-gp substrate properties.

First biological evaluation of developed 3-benzyloxyfluorenes as novel class of MDR modulators.

A series of 3-benzyloxy-1-aza-9-oxafluorenes has been synthesized and biologically evaluated as novel MDR modulators. The concentration dependent inhibition of the efflux pump ABCB1 (P-glycoprotein) has been characterized and is discussed in relation to calculated lipophilicity data. Instead of the molecular lipophilicity the exact positioning of functional groups was found decisive for the biological activities.

Impact of novel MDR modulators on human cancer cells: reversal activities and induction studies.

PURPOSE: Novel multidrug resistance (mdr) modulators have been proved as inhibitors of P-glycoprotein (P-gp). We first investigated the in vitro effects of selected compounds in human cancer cells on multidrug resistance reversal effects compared to drug standards and on P-gp induction to characterize the potential of the compounds as clinical candidates. METHODS: The uptake of daunorubicin into a parental cancer cell line and P-gp expressing subcell line in presence of the modulators was characterized by flow cytometry. Induction of P-gp was investigated in P-gp expressing and non-expressing cancer cell lines on the RNA level by real-time quantitative polymerase chain reaction (RTQ-PCR) and protein quantification. Results were additionally confirmed by northern blot techniques and functionality assays in selected cell lines. RESULTS: The novel modulators showed activities as mdr reversers in a P-gp specific human cancer cell model with mainly increased uptake rates of daunorubicin into the drug-resistant cell line. H17 proved to be more active than cyclosporine A as a known strong mdr modulator. The induction studies revealed practically no induction potential of the compounds in usual short-time drug application regimes in all cell lines. Furthermore, the novel modulators did not increase the efflux of a P-gp model substrate in the functionality model assay. This confirmed the results of non-P-gp induction which was observed on both the RNA and the protein levels. CONCLUSIONS: The novel mdr modulators proved as perspective candidates for further clinical studies because they turned out to be highly active in human cancer cell models. Furthermore, they showed no potential to induce the transmembrane efflux pump P-gp. This is a significant advantage compared to modulators which failed in clinical trials because of induction-effects that increase cellular resistances and, moreover, side effects in normal cells.

Novel insight in structure-activity relationship and bioanalysis of P-glycoprotein targeting highly potent tetrakishydroxymethyl substituted 3,9-diazatetraasteranes.

Novel 3,9-diazatetraasteranes have been synthesized with varied aromatic substitution patterns and evaluated as P-glycoprotein (P-gp) inhibitors. Structure-activity relationships (SAR) are discussed in relation to determined physicochemical properties. The potential to induce P-gp expression has been evaluated in cancer cell lines. The bioanalytical results indicate favorable noninducing properties compared to P-gp inducing drug standard.

P-glycoprotein effects of cyclic urea HIV protease inhibitor DMP 323 in competitional absorption studies.

Cyclic ureas form a perspective class of non-peptidic HIV-1 protease inhibitors with major bioavailability problems. Low absorption rates of DMP 323 as one of the first representatives led to investigations whether transport efflux pump P-glycoprotein (P-gp) within the intestine may be partly responsible for the low absorption rates. DMP 323 proved to be a P-gp substrate in competition studies with P-gp inhibitor ritonavir and H17 as a representative of another class of non-peptidic HIV-1 protease inhibitors. Intestinal DMP 323 absorption was mainly increased under co-application of both ritonavir and H17. DMP 323 used as a membrane efflux pump inhibitor itself showed little affinities to P-gp compared to H17 as strong P-gp inhibitor. So P-gp proved to play a decisive role in the low intestinal absorption of the cyclic urea representative DMP 323.

Comparative effects on intestinal absorption in situ by P-glycoprotein-modifying HIV protease inhibitors.

PURPOSE: P-glycoprotein (P-gp) is made responsible for the limited oral bioavailability of P-gp substrates like peptidic HIV protease inhibitors (PIs). With respect to combined application of two PIs in antiretroviral regimes, we first investigated the influences on intestinal saquinavir uptake using different PIs in in situ perfusion studies. METHODS: Perfusion experiments were carried out in three intestinal segments with P-gp substrates talinolol and saquinavir using fixed concentrations of PIs and with each varying concentrations in the jejunum and ileum. Furthermore, cellular uptake of fluorescent P-gp substrate rhodamine-123 and MRP-substrate carboxyfluorescein has each been quantified in P-gp and MRP-expressing cells by flow cytometry under co-administration of PIs. RESULTS: Increase of calculated permeabilities of P-gp-specific substrate talinolol was found under co-administration of both PIs, ritonavir and H17, with highest absorption rates in the ileal and colon segment. H17 proved to be a better P-gp inhibitor than ritonavir by resulting IC50 values and also in the cellular uptake of rhodamine. Similar increases of permeabilities in ileum and colon have also been found for saquinavir as P-gp as well as MRP-substrate with differences in the jejunal uptake, which was found higher for H17. Additional MRP-inhibitory activities of H17 were proved by increasing cellular uptake rates of carboxyfluorescein in MRP-expressing cells. CONCLUSIONS: The investigated PIs were characterized as effective P-gp inhibitors in the intestinal absorption of P-gp substrates. H17 showed MRP-inhibitory effects that also favor intestinal drug absorption of corresponding substrates. With respect to combined therapeutic application of PIs, compounds like H17 raise hopes for improved bioavailability of poorly absorbed compounds.