Identification of RP-6685, an Orally Bioavailable Compound that Inhibits the DNA Polymerase Activity of Polθ.

DNA polymerase theta (Polθ) is an attractive synthetic lethal target for drug discovery, predicted to be efficacious against breast and ovarian cancers harboring BRCA-mutant alleles. Here, we describe our hit-to-lead efforts in search of a selective inhibitor of human Polθ (encoded by POLQ). A high-throughput screening campaign of 350,000 compounds identified an 11 micromolar hit, giving rise to the N2-substituted fused pyrazolo series, which was validated by biophysical methods. Structure-based drug design efforts along with optimization of cellular potency and ADME ultimately led to the identification of RP-6685: a potent, selective, and orally bioavailable Polθ inhibitor that showed in vivo efficacy in an HCT116 BRCA2-/- mouse tumor xenograft model.

A strategy to reduce biliary clearance in early drug discovery.

INTRODUCTION: Biliary excretion can modulate the pharmacokinetic profile of drug candidates, and may represent a liability for drug-drug interactions. This study proposes a strategy to reduce biliary clearance using the efflux ratio in Caco-2 cells in parallel to an abbreviated pharmacokinetic study in bile duct-cannulated rats (BDC). METHODS: Apical to basolateral (A to B) and basolateral to apical (B to A) permeability of 20 new chemical entities (NCEs) were determined in a 24-well permeability assay. In parallel, biliary excretion was determined in an abbreviated format in BDC rats. Test compounds were administered via an intravenous dose of 1 mg/kg and the percentage (%) of parent compound excreted in the bile in the first 3 hours after dosing was determined by LC-MS/MS analysis. RESULTS: A reasonably good correlation (r(2)=0.635) between the in vitro efflux ratio from the Caco-2 assay and in vivo biliary excretion of parent compound in BDC rats was observed. All seven compounds with an efflux ratio of <5 had less than 25% of the parent excreted in rat bile. In contrast, 3 out of the 13 compounds with an efflux ratio >5 had less than 25% of the dose excreted in rat bile. DISCUSSION: This suggests that a compound with an efflux ratio of <5 is at lower risk of having significant biliary clearance and that Caco-2 efflux ratio obtained from a high throughput screening assay may be used as an early indicator of biliary excretion. Although, we propose to reduce the occurrence of false positive prediction for biliary clearance (23%) by performing abbreviated PK in BDC rats for compounds with high efflux ratio.

A membrane vesicle-based assay to enable prediction of human biliary excretion.

1. Prediction of biliary excretion is a challenge due to the lack of in vitro assays. Our laboratory previously demonstrated a highly significant correlation between in vitro IC50 values against mrp2 using rat canalicular liver plasma membrane vesicles and in vivo biliary excretion (Colombo et al., 2012). This study explores the possibility of predicting in vivo biliary excretion in human using membrane vesicles prepared from MDCKII cells transfected with human ABCC2. 2. In vitro MRP2 activity was determined by measuring the ATP-dependent uptake of 5(6)-carboxy-2',7'-dichlorofluorescein (CDCF) in inside-out membrane vesicles isolated from MDCK-ABCC2 cells. CDCF uptake was time- and concentration-dependent (Km of 4.0 ± 1.2 µM and a Vmax of 7.8 ± 0.9 pmol/mg/min) and inhibited by benzbromarone and MK-571 with IC50 values of 1.2 and 7.6 µM, respectively. 3. A significant linear correlation (r(2 )= 0.790) between the in vitro IC50 values from the described MRP2 assay and in vivo biliary excretion in humans was observed using 11 well-documented drugs covering low to high biliary excretions. 4. This study demonstrates, for the first time, that inhibition of CDCF uptake in MDCKII-ABCC2 vesicles not only provides a screening assay to assess MRP2 drug-drug interaction potential, but is also predictive of human MRP2-mediated biliary excretion.

Mercury and flooding cycles in the Tapajós River basin, Brazilian Amazon: the role of periphyton of a floating macrophyte (Paspalum repens).

Methylmercury (MeHg) increases mercury (Hg) toxicity and is biomagnified in the trophic chain contaminating riverine Amazon populations. Freshwater macrophyte roots are a main site of Hg methylation in different Brazilian environments. Paspalum repens periphyton was sampled in four floodplain lakes during the dry, rainy and wet seasons for measurement of total Hg (THg), MeHg, Hg methylation potentials, %C, %N, δ(13)C, δ(15)N and bacterial heterotrophic production as (3)H-leucine incorporation rate. THg concentration varied from 67 to 198 ng/g and the potential of Me(203)Hg formation was expressive (1-23%) showing that periphyton is an important matrix both in the accumulation of Hg and in MeHg production. The concentration of MeHg varied from 1 to 6 ng/g DW and was positively correlated with Me(203)Hg formation. Though methylmercury formation is mainly a bacterial process, no significant correlation was observed between the methylation potentials and bacterial production. The multiple regressions analyses suggested a negative correlation between THg and %C and %N and between methylation potential and δ(13)C. The discriminant analysis showed a significant difference in periphyton δ(15)N, δ(13)C and THg between seasons, where the rainy season presented higher δ(15)N and the wet period lighter δ(13)C, lower THg values and higher Me(203)Hg formation. This exploratory study indicates that the flooding cycle could influence the periphyton composition, mercury accumulation and methylmercury production.

Biarylimidazoles as inhibitors of microsomal prostaglandin E2 synthase-1.

Microsomal prostaglandin E(2) synthase (mPGES-1) represents a potential target for novel analgesic and anti-inflammatory agents. High-throughput screening identified several leads of mPGES-1 inhibitors which were further optimized for potency and selectivity. A series of inhibitors bearing a biaryl imidazole scaffold exhibits excellent inhibition of PGE(2) production in enzymatic and cell-based assays. The synthesis of these molecules and their activities will be discussed.

Linking bisphosphonates to the free amino groups in fluoroquinolones: preparation of osteotropic prodrugs for the prevention of osteomyelitis.

Osteomyelitis is an infection located in bone and a notoriously difficult disease to manage, requiring frequent and heavy doses of systemically administered antibiotics. Targeting antibiotics to the bone after systemic administration may provide both greater efficacy of treatment and less frequent administration. By taking advantage of the affinity of the bisphosphonate group for bone mineral, we have prepared a set of 13 bisphosphonated antibacterial prodrugs based on eight different linkers tethered to the free amino functionality on fluoroquinolone antibiotics. While all but one of the prodrugs were shown in vitro to be effective and rapid bone binders (over 90% in 1 h), only eight of them demonstrated the capacity to significantly regenerate the parent drug. In a rat model of the disease, a selected group of agents demonstrated their ability to prevent osteomyelitis when used in circumstances under which the parent drug had already been cleared and is thus inactive.

Bisphosphonated fluoroquinolone esters as osteotropic prodrugs for the prevention of osteomyelitis.

Osteomyelitis is a difficult to treat bacterial infection of the bone. Delivering antibacterial agents to the bone may overcome the difficulties in treating this illness by effectively concentrating the antibiotic at the site of infection and by limiting the toxicity that may result from systemic exposure to the large doses conventionally used. Using bisphosphonates as osteophilic functional groups, different forms of fluoroquinolone esters were synthesized and evaluated for their ability to bind bone and to release the parent antibacterial agent. Bisphosphonated glycolamide fluoroquinolone esters were found to present a profile consistent with effective and rapid bone binding and efficient release of the active drug moiety. They were assessed for their ability to prevent bone infection in vivo and were found to be effective when the free fluoroquinolones were not.

MF498 [N-{[4-(5,9-Diethoxy-6-oxo-6,8-dihydro-7H-pyrrolo[3,4-g]quinolin-7-yl)-3-methylbenzyl]sulfonyl}-2-(2-methoxyphenyl)acetamide], a selective E prostanoid receptor 4 antagonist, relieves joint inflammation and pain in rodent models of rheumatoid and osteoarthritis.

Previous evidence has implicated E prostanoid receptor 4 (EP4) in mechanical hyperalgesia induced by subplantar inflammation. However, its role in chronic arthritis remains to be further defined because previous attempts have generated two conflicting lines of evidence, with one showing a marked reduction of arthritis induced by a collagen antibody in mice lacking EP4, but not EP1-EP3, and the other showing no impact of EP4 antagonism on arthritis induced by collagen. Here, we assessed the effect of a novel and selective EP4 antagonist MF498 [N-{[4-(5,9-diethoxy-6-oxo-6,8-dihydro-7H-pyrrolo[3,4-g]quinolin-7-yl)-3-methylbenzyl]sulfonyl}-2-(2-methoxyphenyl)acetamide] on inflammation in adjuvant-induced arthritis (AIA), a rat model for rheumatoid arthritis (RA), and joint pain in a guinea pig model of iodoacetate-induced osteoarthritis (OA). In the AIA model, MF498, but not the antagonist for EP1, MF266-1 [1-(5-{3-[2-(benzyloxy)-5-chlorophenyl]-2-thienyl}pyridin-3-yl)-2,2,2-trifluoroethane-1,1-diol] or EP3 MF266-3 [(2E)-N-[(5-bromo-2-methoxyphenyl)sulfonyl]-3-[5-chloro-2-(2-naphthylmethyl)phenyl]acrylamide], inhibited inflammation, with a similar efficacy as a selective cyclooxygenase 2 (COX-2) inhibitor MF-tricyclic. In addition, MF498 was as effective as an nonsteroidal anti-inflammatory drug, diclofenac, or a selective microsomal prostaglandin E synthase-1 inhibitor, MF63 [2-(6-chloro-1H-phenanthro[9,10-d]imidazol-2-yl)isophthalonitrile], in relieving OA-like pain in guinea pigs. When tested in rat models of gastrointestinal toxicity, the EP4 antagonist was well tolerated, causing no mucosal leakage or erosions. Lastly, we evaluated the renal effect of MF498 in a furosemide-induced diuresis model and demonstrated that the compound displayed a similar renal effect as MF-tricyclic [3-(3,4-difluorophenyl)-4-(4-(methylsulfonyl)phenyl)-2-(5H)-furanone], reducing furosemide-induced natriuresis by approximately 50%. These results not only suggest that EP4 is the major EP receptor in both RA and OA but also provide a proof of principle to the concept that antagonism of EP4 may be useful for treatment of arthritis.

Novel non-nucleobase inhibitors of Staphylococcus aureus DNA polymerase IIIC.

The preparation and biological evaluation of 5-substituted-6-hydroxy-2-(anilino)pyrimidinones as a new class of DNA polymerase IIIC inhibitors, required for the replication of chromosomal DNA in Gram-positive bacteria, are described. These new dGTP competitive inhibitors displayed good levels of in vitro inhibition and antibacterial activity against Staphylococcus aureus. A new class of dATP competitive inhibitors, 6-substituted-2-amino-5-alkyl-pyrimidin-4-ones, whose antibacterial activity was unaffected by serum, were identified.

Allotopic antagonism of the non-peptide atrial natriuretic peptide (ANP) antagonist HS-142-1 on natriuretic peptide receptor NPR-A.

The microbial polysaccharide HS-142-1 has been documented as an antagonist of natriuretic peptides. It inhibits activation and peptide binding to both guanylate receptors natriuretic peptide receptor (NPR)-A and NPR-B, but has no effect on the non-cyclase receptor NPR-C. At first sight the effect of HS-142-1 on peptide binding appears to be surmountable, suggesting that it might be competitive despite its chemically divergent nature. We explored its mode of action on wild-type NPR-A (WT), on a disulphide-bridged constitutively active mutant (C423S) and on truncated mutants lacking either their cytoplasmic domain (DeltaKC) or both the cytoplasmic and the transmembrane domains (ECD). On the WT, HS-142-1 inhibited atrial natriuretic peptide (ANP) binding with a pK value of 6.51 +/- 0.07 (K(d)=0.31 microM). It displayed a similar effect on the C423S mutant (pK=6.31 +/- 0.11), indicating that its action might not be due to interference with receptor dimerization. HS-142-1 also inhibited ANP binding to DeltaKC with a pK of 7.05 +/- 0.05 (K(d)=0.089 microM), but it was inactive on ANP binding to ECD at a concentration of 10(-4) M, suggesting that the antagonism was not competitive at the peptide-binding site located on the ECD and that the transmembrane domain might be required. HS-142-1 also enhanced dissociation of NPR-A-bound (125)I-ANP in the presence of excess unlabelled ANP, implying an allotopic (allosteric) mode of action for the antagonist.