Antagonists of inhibitor of apoptosis proteins based on thiazole amide isosteres

Discovery of new imidazotetrazinones with potential to overcome tumor resistance

We describe the design, organic synthesis, and characterization, including X-ray crystallography, of a series of novel analogues of the clinically used antitumor agent temozolomide, together with their in vitro biological evaluation. The work has resulted in the discovery of a new series of anticancer imidazotetrazines that offer the potential to overcome the resistance mounted by tumors against temozolomide. The rationally designed compounds that incorporate a propargyl alkylating moiety and a thiazole ring as isosteric replacement for a carboxamide, are readily synthesized (gram-scale), exhibit defined solid-state structures, and enhanced growth-inhibitory activity against human tumor cell lines, including MGMT-expressing and MMR-deficient lines, molecular features that confer tumor resistance. The cell proliferation data were confirmed by clonogenic cell survival assays, and DNA flow cytometry analysis was undertaken to determine the effects of new analogues on cell cycle progression. Detailed 1H NMR spectroscopic studies showed that the new agents are stable in solution, and confirmed their mechanism of action. The propargyl and thiazole substituents significantly improve potency and physicochemical, drug metabolism and permeability properties, suggesting that the thiazole 13 should be prioritized for further preclinical evaluation.

A rational in silico approach to identify inhibitors of Batroxrhagin from Bothrops atrox

Bothrops atrox venom comprises several types of bioactive molecules, enzymatic and non-enzymatic, among those, Batroxrhagin is the most predominant SVMP P-III enzyme, which are responsible for induction of local and systemic hemorrhage and muscle fibers damage, impairing regeneration. Due to great difficulties in establishing an antibothropic drug, new strategies must be addressed to achieve a more effective and efficient treatment. There are no studies of specific catalytic inhibitors of Batroxrhagin. However, there are in vitro studies that have described similar metalloprotease inhibitors. The inhibitor batimastat was used as a leading compound for the search and selection of similar candidates. This molecule is widely cited as a metalloprotease inhibitor and as an antimetastatic. In addition to batimastat-like molecules, four other reported metalloprotease inhibitors were included to compose the study's positive control group. Hence, 580 molecules were tested. The three-dimensional structure of B. atrox Batroxrhagin was predicted based on homologous structures using Modeller 9.20. Molecular docking calculation was performed using Autodock 4.2 and molecular surfaces and interactions were analyzed using Biovia/Discovery Studio 2017. Among 576 molecules, 42 similar to batismast resulted in a better energy of interaction than all positive controls, including batimastat itself. The batimastat-like molecules with lowest energy and positive controls were subjected to molecular dynamics for 30 ns in Gromacs 2019.4. This batimastat-like molecule produced better stability among all the Batroxrhagin-ligand complexes analyzed. Overall, the proposed compounds present justifiable evidence for future in vitro tests aiming to inhibit Batroxrhagin. Communicated by Ramaswamy H. Sarma.

Estrogen Receptor-α Targeting: PROTACs, SNIPERs, Peptide-PROTACs, Antibody Conjugated PROTACs and SNIPERs

Targeting selective estrogen subtype receptors through typical medicinal chemistry approaches is based on occupancy-driven pharmacology. In occupancy-driven pharmacology, molecules are developed in order to inhibit the protein of interest (POI), and their popularity is based on their virtue of faster kinetics. However, such approaches have intrinsic flaws, such as pico-to-nanomolar range binding affinity and continuous dosage after a time interval for sustained inhibition of POI. These shortcomings were addressed by event-driven pharmacology-based approaches, which degrade the POI rather than inhibit it. One such example is PROTACs (Proteolysis targeting chimeras), which has become one of the highly successful strategies of event-driven pharmacology (pharmacology that does the degradation of POI and diminishes its functions). The selective targeting of estrogen receptor subtypes is always challenging for chemical biologists and medicinal chemists. Specifically, estrogen receptor α (ER-α) is expressed in nearly 70% of breast cancer and commonly overexpressed in ovarian, prostate, colon, and endometrial cancer. Therefore, conventional hormonal therapies are most prescribed to patients with ER + cancers. However, on prolonged use, resistance commonly developed against these therapies, which led to selective estrogen receptor degrader (SERD) becoming the first-line drug for metastatic ER + breast cancer. The SERD success shows that removing cellular ER-α is a promising approach to overcoming endocrine resistance. Depending on the mechanism of degradation of ER-α, various types of strategies of developed.

Derivatization of inhibitor of apoptosis protein (IAP) ligands yields improved inducers of estrogen receptor α degradation

Aberrant expression of proteins often underlies many diseases, including cancer. A recently developed approach in drug development is small molecule-mediated, selective degradation of dysregulated proteins. We have devised a protein-knockdown system that utilizes chimeric molecules termed specific and nongenetic IAP-dependent protein erasers (SNIPERs) to induce ubiquitylation and proteasomal degradation of various target proteins. SNIPER(ER)-87 consists of an inhibitor of apoptosis protein (IAP) ligand LCL161 derivative that is conjugated to the estrogen receptor α (ERα) ligand 4-hydroxytamoxifen by a PEG linker, and we have previously reported that this SNIPER efficiently degrades the ERα protein. Here, we report that derivatization of the IAP ligand module yields SNIPER(ER)s with superior protein-knockdown activity. These improved SNIPER(ER)s exhibited higher binding affinities to IAPs and induced more potent degradation of ERα than does SNIPER(ER)-87. Further, they induced simultaneous degradation of cellular inhibitor of apoptosis protein 1 (cIAP1) and delayed degradation of X-linked IAP (XIAP). Notably, these reengineered SNIPER(ER)s efficiently induced apoptosis in MCF-7 human breast cancer cells that require IAPs for continued cellular survival. We found that one of these molecules, SNIPER(ER)-110, inhibits the growth of MCF-7 tumor xenografts in mice more potently than the previously characterized SNIPER(ER)-87. Mechanistic analysis revealed that our novel SNIPER(ER)s preferentially recruit XIAP, rather than cIAP1, to degrade ERα. Our results suggest that derivatized IAP ligands could facilitate further development of SNIPERs with potent protein-knockdown and cytocidal activities against cancer cells requiring IAPs for survival.

Pharmacological Potential and Synthetic Approaches of Imidazo[4,5-b]pyridine and Imidazo[4,5-c]pyridine Derivatives

The structural resemblance between the fused imidazopyridine heterocyclic ring system and purines has prompted biological investigations to assess their potential therapeutic significance. They are known to play a crucial role in numerous disease conditions. The discovery of their first bioactivity as GABA_A receptor positive allosteric modulators divulged their medicinal potential. Proton pump inhibitors, aromatase inhibitors, and NSAIDs were also found in this chemical group. Imidazopyridines have the ability to influence many cellular pathways necessary for the proper functioning of cancerous cells, pathogens, components of the immune system, enzymes involved in carbohydrate metabolism, etc. The collective results of biochemical and biophysical properties foregrounded their medicinal significance in central nervous system, digestive system, cancer, inflammation, etc. In recent years, new preparative methods for the synthesis of imidazopyridines using various catalysts have been described. The present manuscript to the best of our knowledge is the complete compilation on the synthesis and medicinal aspects of imidazo[4,5-b]pyridines and imidazo[4,5-c]pyridines reported from the year 2000 to date, including structure–activity relationships.

Pyrazoles as non-classical bioisosteres in prolylcarboxypeptidase (PrCP) inhibitors

Bioisosteres are integral components of modern pharmaceutical research that allow structural optimization to maximize in vivo efficacy and minimize adverse effects by selectively modifying pharmacodynamic, pharmacokinetic and physicochemical properties. A recent medicinal chemistry campaign focused on identifying small molecule inhibitors of prolylcarboxypeptidase (PrCP) initiated an investigation into the use of pyrazoles as bioisosteres for amides. The results indicate that pyrazoles are suitable bioisosteric replacements of amide functional groups. The study is an example of managing bioisosteric replacement by incorporating subsequent structural modifications to maintain potency against the selected target. A heuristic model for an embedded pharmacophore is also described.

Targeting protein-protein interaction by small molecules

Protein-protein interactions (PPIs) are critical regulatory events in physiology and pathology, and they represent an important target space for pharmacological intervention. However, targeting PPIs with small molecules is challenging owing to the large surface area involved in protein-protein binding and the lack of obvious small-molecule-binding pockets at many protein-protein interfaces. Nonetheless, successful examples of small-molecule modulators of PPIs have been growing in recent years. This article reviews some of the recent advances in the discovery of small-molecule regulators of PPIs that involve key oncogenic proteins. Our discussion focuses on the three key modes of action for these small-molecule modulators: orthosteric inhibition, allosteric regulation, and interfacial binding/stabilization. Understanding the opportunities and challenges of these diverse mechanisms will help guide future efforts in developing small-molecule modulators against PPIs.

Expedient synthesis of highly potent antagonists of inhibitor of apoptosis proteins (IAPs) with unique selectivity for ML-IAP

A series of novel, potent antagonists of the inhibitor of apoptosis proteins (IAPs) were synthesized in a highly convergent and rapid fashion (≤6 steps) using the Ugi four-component reaction as the key step, thus enabling rapid optimization of binding potency. These IAP antagonists compete with caspases 3, 7, and 9 for inhibition by X chromosome-linked IAP (XIAP) and bind strongly (nanomolar binding constants) to several crucial members of the IAP family of cancer pro-survival proteins to promote apoptosis, with a particularly unique selectivity for melanoma IAP (ML-IAP). Experiments in cell culture revealed powerful cancer cell growth inhibitory activity in multiple (breast, ovarian, and prostate) cell lines with single agent toxicity at low nanomolar levels against SKOV-3 human ovarian carcinoma cells. Administration of the compounds to human foreskin fibroblast cells revealed no general toxicity to normal cells. Furthermore, computational modeling was performed, revealing key contacts between the IAP proteins and antagonists, suggesting a structural basis for the observed potency.

Discovery of a potent small-molecule antagonist of inhibitor of apoptosis (IAP) proteins and clinical candidate for the treatment of cancer (GDC-0152)

A series of compounds were designed and synthesized as antagonists of cIAP1/2, ML-IAP, and XIAP based on the N-terminus, AVPI, of mature Smac. Compound 1 (GDC-0152) has the best profile of these compounds; it binds to the XIAP BIR3 domain, the BIR domain of ML-IAP, and the BIR3 domains of cIAP1 and cIAP2 with K(i) values of 28, 14, 17, and 43 nM, respectively. These compounds promote degradation of cIAP1, induce activation of caspase-3/7, and lead to decreased viability of breast cancer cells without affecting normal mammary epithelial cells. Compound 1 inhibits tumor growth when dosed orally in the MDA-MB-231 breast cancer xenograft model. Compound 1 was advanced to human clinical trials, and it exhibited linear pharmacokinetics over the dose range (0.049 to 1.48 mg/kg) tested. Mean plasma clearance in humans was 9 ± 3 mL/min/kg, and the volume of distribution was 0.6 ± 0.2 L/kg.

Synthesis of sansalvamide A peptidomimetics: triazole, oxazole, thiazole, and pseudoproline containing compounds

Peptidomimetic-based macrocycles typically have improved pharmacokinetic properties over those observed with peptide analogs. Described are the syntheses of 13 peptidomimetic derivatives that are based on active Sansalvamide A structures, where these analogs incorporate heterocycles (triazoles, oxazoles, thiazoles, or pseudoprolines) along the macrocyclic backbone. The syntheses of these derivatives employ several approaches that can be applied to convert a macrocyclic peptide into its peptidomimetic counterpart. These approaches include peptide modifications to generate the alkyne and azide for click chemistry, a serine conversion into an oxazole, a Hantzsch reaction to generate the thiazole, and protected threonine to generate the pseudoproline derivatives. Furthermore, we show that two different peptidomimetic moieties, triazoles and thiazoles, can be incorporated into the macrocyclic backbone without reducing cytotoxicity: triazole and thiazole.

Recognition of Smac-mimetic compounds by the BIR domain of cIAP1

Inhibitor of apoptosis proteins (IAPs) are negative regulators of apoptosis. As IAPs are overexpressed in many tumors, where they confer chemoresistance, small molecules inactivating IAPs have been proposed as anticancer agents. Accordingly, a number of IAP-binding pro-apoptotic compounds that mimic the sequence corresponding to the N-terminal tetrapeptide of Smac/DIABLO, the natural endogenous IAPs inhibitor, have been developed. Here, we report the crystal structures of the BIR3 domain of cIAP1 in complex with Smac037, a Smac-mimetic known to bind potently to the XIAP-BIR3 domain and to induce degradation of cIAP1, and in complex with the novel Smac-mimetic compound Smac066. Thermal stability and fluorescence polarization assays show the stabilizing effect and the high affinity of both Smac037 and Smac066 for cIAP1- and cIAP2-BIR3 domains.

2-(4-Bromo-phen-yl)-5-dodec-yloxy-1,3-thia-zole

In the structure of the title compound, C₂₁H₃₀BrNOS, an important inter­mediate for the preparation of liquid crystal compounds, the saturated C₁₂ chain shows a linear conformation while the benzene and thia­zole rings are essentially coplanar [dihedral angle = 4.5 (4)°]. The crystal packing shows no significant inter­molecular inter­actions.

Design of a series of bicyclic HIV-1 integrase inhibitors. Part 2: azoles: effective metal chelators

Synthesis of a diverse set of azoles and their utilizations as an amide isostere in the design of HIV integrase inhibitors is described. The Letter identified thiazole, oxazole, and imidazole as the most promising heterocycles. Initial SAR studies indicated that these novel series of integrase inhibitors are amenable to lead optimization. Several compounds with low nanomolar inhibitory potency are reported.