Design of BET Inhibitor Bottlebrush Prodrugs with Superior Efficacy and Devoid of Systemic Toxicities.

Prodrugs engineered for preferential activation in diseased versus normal tissues offer immense potential to improve the therapeutic indexes (TIs) of preclinical and clinical-stage active pharmaceutical ingredients that either cannot be developed otherwise or whose efficacy or tolerability it is highly desirable to improve. Such approaches, however, often suffer from trial-and-error design, precluding predictive synthesis and optimization. Here, using bromodomain and extra-terminal (BET) protein inhibitors (BETi)-a class of epigenetic regulators with proven anticancer potential but clinical development hindered in large part by narrow TIs-we introduce a macromolecular prodrug platform that overcomes these challenges. Through tuning of traceless linkers appended to a "bottlebrush prodrug" scaffold, we demonstrate correlation of in vitro prodrug activation kinetics with in vivo tumor pharmacokinetics, enabling the predictive design of novel BETi prodrugs with enhanced antitumor efficacies and devoid of dose-limiting toxicities in a syngeneic triple-negative breast cancer murine model. This work may have immediate clinical implications, introducing a platform for predictive prodrug design and potentially overcoming hurdles in drug development.

Thrombopoietin receptor activation: transmembrane helix dimerization, rotation, and allosteric modulation.

We report how rotational variations in transmembrane (TM) helix interactions participate in the activity states of the thrombopoietin receptor (TpoR), a type 1 cytokine receptor that controls the production of blood platelets. We also explore the mechanism of small-molecule agonists that do not mimic the natural ligand. We show, by a combination of cysteine cross-linking, alanine-scanning mutagenesis, and computational simulations, that the TpoR TM dimerizes strongly and can adopt 3 different stable, rotationally related conformations, which may correspond to specific states of the full-length receptor (active, inactive, and partially active). Thus, our data suggest that signaling and inactive states of the receptor are related by receptor subunit rotations, rather than a simple monomer-dimer transition. Moreover, results from experiments with and without agonists in vitro and in cells allow us to propose a novel allosteric mechanism of action for a class of small molecules, in which they activate TpoR by binding to the TM region and by exploiting the rotational states of the dimeric receptor. Overall, our results support the emerging view of the participation of mutual rotations of the TM domains in cytokine receptor activation.

Structure-activity relationships and hepatic safety risks of thiazole agonists of the thrombopoietin receptor.

5-F substitution of an aminothiazole moiety within a series of thrombopoietin receptor agonists leads to potent agents with an improved hepatic safety profile in rodent toxicology studies.

The identification of orally bioavailable thrombopoietin agonists.

Recently, we disclosed a series of potent pyrimidine benzamide-based thrombopoietin receptor agonists. Unfortunately, the structural features required for the desired activity conferred physicochemical properties that were not favorable for the development of an oral agent. The physical properties of the series were improved by replacing the aminopyrimidinyl group with a piperidine-4-carboxylic acid moiety. The resulting compounds possessed favorable in vivo pharmacokinetic properties, including good bioavailability.

Molecular features crucial to the activity of pyrimidine benzamide-based thrombopoietin receptor agonists.

The identification of small molecule modulators of biological processes mediated via protein-protein interactions has generally proved to be a challenging endeavor. In the case of the thrombopoietin receptor (TPOr), however, a number of small molecule types have been reported to display biological activity similar to that of the agonist protein TPO. Through a detailed analysis of structure-activity relationships, X-ray crystal structures, NMR coupling constants, nuclear Overhauser effects, and computational data, we have determined the agonism-inducing conformation of one series of small molecule TPOr agonists. The relationship of this agonism-inducing conformation to that of other series of TPO receptor agonists is discussed.

Publisher Correction: Reduction of liver fibrosis by rationally designed macromolecular telmisartan prodrugs.

In the version of this Article originally published, the author Peter Blume-Jensen was not denoted as a corresponding author; this has now been amended and the author's email address has been added. The 'Correspondence and requests for materials' statement was similarly affected and has now been updated with the author's initials 'P.B-J.'

Reduction of liver fibrosis by rationally designed macromolecular telmisartan prodrugs.

At present there are no drugs for the treatment of chronic liver fibrosis that have been approved by the Food and Drug administration of the United States. Telmisartan, a small-molecule antihypertensive drug, displays antifibrotic activity, but its clinical use is limited because it causes systemic hypotension. Here, we report the scalable and convergent synthesis of macromolecular telmisartan prodrugs optimized for preferential release in diseased liver tissue. We optimized the release of active telmisartan in fibrotic liver to be depot-like (that is, a constant therapeutic concentration) through the molecular design of telmisartan brush-arm star polymers, and show that these lead to improved efficacy and to the avoidance of dose-limiting hypotension in both metabolically and chemically induced mouse models of hepatic fibrosis, as determined by histopathology, enzyme levels in the liver, intact-tissue protein markers, hepatocyte necrosis protection, and gene-expression analyses. In rats and dogs, the prodrugs are retained long-term in liver tissue and have a well-tolerated safety profile. Our findings support the further development of telmisartan prodrugs that enable infrequent dosing in the treatment of liver fibrosis.

Potent, selective spiropyrrolidine pyrimidinetrione inhibitors of MMP-13.

Explorations in the pyrimidinetrione series of MMP-13 inhibitors led to the discovery of a series of spiro-fused compounds that are potent and selective inhibitors of MMP-13. While other spiro-fused motifs are hydrolytically unstable, presumably due to electronic destabilization of the pyrimidinetrione ring, the spiropyrrolidine series does not share this liability. Greater than 100-fold selectivity versus other MMP family members was achieved by incorporation of an extended aryl-heteroaryl P1'group. When dosed as the sodium salt, these compounds displayed excellent oral absorption and pharmacokinetic properties. Despite the selectivity, a representative of this series produced fibroplasia in a 14 day rat study.

Structure and Property Guided Design in the Identification of PRMT5 Tool Compound EPZ015666.

The recent publication of a potent and selective inhibitor of protein methyltransferase 5 (PRMT5) provides the scientific community with in vivo-active tool compound EPZ015666 (GSK3235025) to probe the underlying pharmacology of this key enzyme. Herein, we report the design and optimization strategies employed on an initial hit compound with poor in vitro clearance to yield in vivo tool compound EPZ015666 and an additional potent in vitro tool molecule EPZ015866 (GSK3203591).

Amide-Assisted Hydrolysis of beta-Carboxamido-Substituted Phosphinic Acid Esters.

Phosphinic acids are of interest due to their ability to inhibit metalloproteases. The hydrolysis of a phosphinic acid ester is typically one of the final steps in the synthesis of such inhibitors. We have found that the acid-catalyzed hydrolysis of a phosphinic acid ester containing a beta-carboxamido group is facilitated by the presence of the amide. The promotion of the hydrolysis is dependent on the electron density of the amide suggesting the intermediacy of a cyclic imidate structure (C). The hydrolysis of phosphinic acid esters containing a beta-carboxamido group is conveniently and quantitatively effected by treating the ester with 10:90 H(2)O:TFA.

An MMP13-selective inhibitor delays primary tumor growth and the onset of tumor-associated osteolytic lesions in experimental models of breast cancer.

We investigated the effects of the matrix metalloproteinase 13 (MMP13)-selective inhibitor, 5-(4-{4-[4-(4-fluorophenyl)-1,3-oxazol-2-yl]phenoxy}phenoxy)-5-(2-methoxyethyl) pyrimidine-2,4,6(1H,3H,5H)-trione (Cmpd-1), on the primary tumor growth and breast cancer-associated bone remodeling using xenograft and syngeneic mouse models. We used human breast cancer MDA-MB-231 cells inoculated into the mammary fat pad and left ventricle of BALB/c Nu/Nu mice, respectively, and spontaneously metastasizing 4T1.2-Luc mouse mammary cells inoculated into mammary fat pad of BALB/c mice. In a prevention setting, treatment with Cmpd-1 markedly delayed the growth of primary tumors in both models, and reduced the onset and severity of osteolytic lesions in the MDA-MB-231 intracardiac model. Intervention treatment with Cmpd-1 on established MDA-MB-231 primary tumors also significantly inhibited subsequent growth. In contrast, no effects of Cmpd-1 were observed on soft organ metastatic burden following intracardiac or mammary fat pad inoculations of MDA-MB-231 and 4T1.2-Luc cells respectively. MMP13 immunostaining of clinical primary breast tumors and experimental mice tumors revealed intra-tumoral and stromal expression in most tumors, and vasculature expression in all. MMP13 was also detected in osteoblasts in clinical samples of breast-to-bone metastases. The data suggest that MMP13-selective inhibitors, which lack musculoskeletal side effects, may have therapeutic potential both in primary breast cancer and cancer-induced bone osteolysis.

A rational chemical intervention strategy to circumvent bioactivation liabilities associated with a nonpeptidyl thrombopoietin receptor agonist containing a 2-amino-4-arylthiazole motif.

The current study examined the bioactivation potential of a nonpeptidyl thrombopoietin receptor agonist, 1-(3-chloro-5-((4-(4-fluoro-3-(trifluoromethyl)phenyl)thiazol-2-yl)carbamoyl)pyridine-2-yl)piperidine-4-carboxylic acid (1), containing a 2-carboxamido-4-arylthiazole moiety in the core structure. Toxicological risks arising from P450-catalyzed C4-C5 thiazole ring opening in 1 via the epoxidation-->diol sequence were alleviated, since mass spectrometric analysis of human liver microsome and/or hepatocyte incubations of 1 did not reveal the formation of reactive acylthiourea and/or glyoxal metabolites, which are prototypic products derived from thiazole ring scission. However, 4-(4-fluoro-3-(trifluoromethyl)phenyl)thiazol-2-amine (2), the product of hydrolysis of 1 in human liver microsomes, hepatocytes, and plasma, underwent oxidative bioactivation in human liver microsomes, since trapping studies with glutathione led to the formation of two conjugates derived from the addition of the thiol nucleophile to 2 and a thiazole- S-oxide metabolite of 2. Mass spectral fragmentation and NMR analysis indicated that the site of attachment of the glutathionyl moiety in both conjugates was the C5 position in the thiazole ring. Based on the structures of the glutathione conjugates, two bioactivation pathways are proposed, one involving beta-elimination of an initially formed hydroxylamine metabolite and the other involving direct two-electron oxidation of the electron-rich 2-aminothiazole system to electrophilic intermediates. This mechanistic insight into the bioactivation process allowed the development of a rational chemical intervention strategy that involved blocking the C5 position with a fluorine atom or replacing the thiazole ring with a 1,2,4-thiadiazole group. These structural changes not only abrogated the bioactivation liability associated with 1 but also resulted in compounds that retained the attractive pharmacological and pharmacokinetic attributes of the prototype agent.

Pyrimidine benzamide-based thrombopoietin receptor agonists.

A series of pyrimidine benzamide-based thrombopoietin receptor agonists is described. The lead molecule contains a 2-amino-5-unsubstituted thiazole, a group that has been associated with idiosyncratic toxicity. The potential for metabolic oxidation at C-5 of the thiazole, the likely source of toxic metabolites, was removed by substitution at C-5 or by replacing the thiazole with a thiadiazole. Potency in the series was improved by modifying the substituents on the pyrimidine and/or on the thiazole or thiadiazole pendant aryl ring. In vivo examination revealed that compounds from the series are not highly bioavailable. This is attributed to low solubility and poor permeability.

Potent, selective pyrimidinetrione-based inhibitors of MMP-13.

Using SAR from two related series of pyrimidinetrione-based inhibitors, compounds with potent MMP-13 inhibition and >100-fold selectivity against other MMPs have been identified. Despite high molecular weights, clogPs, and polar surface areas, the compounds are generally well absorbed and have excellent pharmacokinetic (PK) properties when dosed as sodium salts. In a rat fibrosis model, a compound from the series displayed no fibrosis at exposures many fold greater than its MMP-13 IC50.

Potent pyrimidinetrione-based inhibitors of MMP-13 with enhanced selectivity over MMP-14.

Through the use of computational modeling, a series of pyrimidinetrione-based inhibitors of MMP-13 was designed based on a lead inhibitor identified through file screening. Incorporation of a biaryl ether moiety at the C-5 position of the pyrimidinetrione ring resulted in a dramatic enhancement of MMP-13 potency. Protein crystallography revealed that this moiety binds in the S(1)(') pocket of the enzyme. Optimization of the C-4 substituent of the terminal aromatic ring led to incorporation of selectivity versus MMP-14 (MT-1 MMP). Structure activity relationships of the biaryl ether substituent are presented as is pharmacokinetic data for a compound that meets our in vitro potency and selectivity goals.

Phosphinic acid-based MMP-13 inhibitors that spare MMP-1 and MMP-3.

Phosphinic acid-based inhibitors of MMP-13 have been investigated with the aim of identifying potent inhibitors with high selectivity versus MMP-1. Independent variation of the substituents on a P(1)' phenethyl group and a P(2) benzyl group improved potencies in both cases around 3-fold over the unsubstituted parent. Combining improved P(1)' and P(2) groups into a single molecule gave an inhibitor with a 4.5 nM IC(50) against MMP-13 and which is 270-fold selective over MMP-1.

Pyran-containing sulfonamide hydroxamic acids: potent MMP inhibitors that spare MMP-1.

The SAR of a series of sterically hindered sulfonamide hydroxamic acids with relatively large P1' groups is described. The compounds typically spare MMP-1 while being potent inhibitors of MMP-13. The metabolically more stable compounds in the series contain either a monocyclic or bicyclic pyran ring adjacent to the hydroxamate group. Despite the sparing of MMP-1, pre-clinical and clinical studies revealed that fibrosis in rats and MSS in humans is still produced.