Monday, August 21, 2017

Covalent inhibitors for eradication of drug-resistant HIV-1 reverse transcriptase: From design to protein crystallography

Albert H. Chan, Won-Gil Lee, Krasimir A. Spasov, José A. Cisneros, Shalley N. Kudalkar, Zaritza O. Petrova, Amanda B. Buckingham, Karen S. Anderson, and William L. Jorgensen

PNAS 2017

doi: 10.1073/pnas.1711463114 

Development of resistance remains a major challenge for drugs to treat HIV-1 infections, including those targeting the essential viral polymerase, HIV-1 reverse transcriptase (RT). Resistance associated with the Tyr181Cys mutation in HIV-1 RT has been a key roadblock in the discovery of nonnucleoside RT inhibitors (NNRTIs). It is the principal point mutation that arises from treatment of HIV-infected patients with nevirapine, the first-in-class drug still widely used, especially in developing countries. We report covalent inhibitors of Tyr181Cys RT (CRTIs) that can completely knock out activity of the resistant mutant and of the particularly challenging Lys103Asn/Tyr181Cys variant. Conclusive evidence for the covalent modification of Cys181 is provided from enzyme inhibition kinetics, mass spectrometry, protein crystallography, and antiviral activity in infected human T-cell assays. The CRTIs are also shown to be selective for Cys181 and have lower cytotoxicity than the approved NNRTI drugs efavirenz and rilpivirine.

Saturday, August 19, 2017

Road Map for the Structure-Based Design of Selective Covalent HCV NS3/4A Protease Inhibitors

Letitia Shunmugam, Pritika Ramharack, Mahmoud E. S. Soliman

The Protein Journal

Over the last 2 decades, covalent inhibitors have gained much popularity and is living up to its reputation as a powerful tool in drug discovery. Covalent inhibitors possess many significant advantages including increased biochemical efficiency, prolonged duration and the ability to target shallow, solvent exposed substrate-binding domains. However, rapidly mounting concerns over the potential toxicity, highly reactive nature and general lack of selectivity have negatively impacted covalent inhibitor development. Recently, a great deal of emphasis by the pharmaceutical industry has been placed toward the development of novel approaches to alleviate the major challenges experienced through covalent inhibition. This has unexpectedly led to the emergence of “selective” covalent inhibitors. The purpose of this review is not only to provide an overview from literature but to introduce a technical guidance as to how to initiate a systematic “road map” for the design of selective covalent inhibitors which we believe may assist in the design and development of optimized potential selective covalent HCV NS3/4A viral protease inhibitors.

Friday, August 18, 2017

Covalent Enzyme Inhibition through Fluorosulfate Modification of a Noncatalytic Serine Residue

Olugbeminiyi O. Fadeyi , Lise R. Hoth, Chulho Choi, Xidong Feng, Ariamala Gopalsamy, Erik C. Hett†∥, Robert E. Kyne Jr., Ralph P. Robinson, and Lyn H. Jones

ACS Chem. Biol., 2017, 12 (8), 2015–2020
DOI: 10.1021/acschembio.7b00403

Irreversible enzyme inhibitors and covalent chemical biology probes often utilize the reaction of a protein cysteine residue with an appropriately positioned electrophile (e.g., acrylamide) on the ligand template. However, cysteine residues are not always available for site-specific protein labeling, and therefore new approaches are needed to expand the toolkit of appropriate electrophiles (“warheads”) that target alternative amino acids. We previously described the rational targeting of tyrosine residues in the active site of a protein (the mRNA decapping scavenger enzyme, DcpS) using inhibitors armed with a sulfonyl fluoride electrophile. These inhibitors subsequently enabled the development of clickable probe technology to measure drug-target occupancy in live cells. Here we describe a fluorosulfate-containing inhibitor (aryl fluorosulfate probe (FS-p1)) with excellent chemical and metabolic stability that reacts selectively with a noncatalytic serine residue in the same active site of DcpS as confirmed by peptide mapping experiments. Our results suggest that noncatalytic serine targeting using fluorosulfate electrophilic warheads could be a suitable strategy for the development of covalent inhibitor drugs and chemical probes.

Sunday, August 6, 2017

Development of Novel Peptide-based Michael Acceptors Targeting Rhodesain and Falcipain-2 for the Treatment of Neglected Tropical Diseases (NTDs)

Santo Preveti, Roberta Ettari, Sandro Cosconati, Giorgio Amendola, Khawla Chouchene, Annika Wagner, Ute A. Hellmich, Kathrin Ulrich, R. Luise Krauth-Siegel, Peter R. Wich, Ira Schmid, Tanja Schirmeister, Jiri Gut, Philip J. Rosenthal, Silvana Grasso, and Maria Zappalà

J. Med. Chem. 2017

DOI: 10.1021/acs.jmedchem.7b00405

This paper describes the development of a class of peptide-based inhibitors as novel antitrypanosomal and antimalarial agents. The inhibitors are based on a characteristic peptide-sequence for the inhibition of the cysteine proteases rhodesain of T. b. rhodesiense and falcipain-2 of P. falciparum. We exploited the reactivity of novel unsaturated electrophilic functions such as vinyl-sulfones, -ketones, -esters and –nitriles. The Michael acceptors inhibited both rhodesain and falcipain-2, at nanomolar and micromolar level, respectively. In particular, the vinyl ketone 3b has emerged as a potent rhodesain inhibitor (k2nd= 67•106 M-1 min-1), endowed with a picomolar binding affinity (Ki = 38 pM), coupled with a single-digit micromolar activity against T. b. brucei (EC50 = 2.97 µM), thus being considered as a novel lead compound for the discovery of novel effective antitrypanosomal agents.

Saturday, August 5, 2017

Recent Developments in JAK3 Inhibition: Isoform Selectivity by Covalent Targeting of Cys909

Michael Forster, Matthias Gehringer,  Stefan A. Laufer
doi: 10.1016/j.bmcl.2017.07.079

Janus kinases (JAKs) are a family of four cytosolic protein kinases with a high degree of structural similarity. Due to its very restricted role in immune regulation, JAK3 was promoted as an excellent target for immunosuppression for more than a decade, but clinical validation of this concept is still elusive. During the last years, speculation arose that kinase activity of JAK1, which cooperates with JAK3 in cytokine receptor signaling, may have a dominant role over the one of JAK3. Until recently, however, this issue could not be appropriately addressed due a lack of highly isoform-selective tool compounds. With the recent resurgence of covalent drugs, targeting of a specific cysteine that distinguishes JAK3 from the other JAK family members became an attractive design option. By applying this strategy, a set of JAK3 inhibitors with excellent selectivity against other JAK isoforms and the kinome was developed within the last three years and used to decipher JAK3-dependent signaling. The data obtained with these tool compounds demonstrates that selective JAK3 inhibition is sufficient to block downstream signaling. Since one of these inhibitors is currently under evaluation in phase II clinical studies against several inflammatory disorders, it will soon become apparent whether selective JAK3 inhibition translates into clinical efficacy.

Tuesday, August 1, 2017

Electrophilic Triterpenoid Enones: A Comparative Thiol-Trapping and Bioactivity Study

Danilo Del Prete, Orazio Taglialatela-Scafati, Alberto Minassi, Carmina Sirignano, Cristina Cruz, Maria L. Bellido, Eduardo Muñoz, and Giovanni Appendino

J. Nat. Prod., Article ASAP
DOI: 10.1021/acs.jnatprod.7b00271
Publication Date (Web): July 28, 2017

Bardoxolone methyl (1) is the quintessential member of triterpenoid cyanoacrylates, an emerging class of bioactive compounds capable of transient covalent binding to thiols. The mechanistic basis for this unusual “pulsed reactivity” profile and the mode of its biological translation are unknown. To provide clues on these issues, a series of Δ1-dehydrooleanolates bearing an electron-withdrawing group at C-2 (7a–m) were prepared from oleanolic acid (3a) and comparatively investigated in terms of reactivity with thiols and bioactivity against a series of electrophile-sensitive transcription factors (Nrf2, NF-κB, STAT3). The emerging picture suggests that the triterpenoid scaffold sharply decreases the reactivity of the enone system by steric encumbrance and that only strongly electrophilic and sterically undemanding substituents such as a cyanide or a carboxylate group can re-establish Michael reactivity, albeit in a transient way for the cyanide group. In general, a substantial dissection between the thiol-trapping ability and the modulation of biological end-points sensitive to thiol alkylation was observed, highlighting the role of shape complementarity for the activity of triterpenoid thia-Michael acceptors.

Thiol Reactivity of N-Aryl α-Methylene-γ-lactams: Influence of the Guaianolide Structure [@KayBrummond]

 Daniel P. Dempe, Chong-Lei Ji, Peng Liu, and Kay M. Brummond The Journal of Organic Chemistry, 2020 DOI: 10.1021/acs.joc.2c01530 The α-meth...