The non-receptor protein tyrosine phosphatase SHP2, encoded by PTPN11, has an important role in signal transduction downstream of growth factor receptor signalling and was the first reported oncogenic tyrosine phosphatase. Activating mutations of SHP2 have been associated with developmental pathologies such as Noonan syndrome and are found in multiple cancer types, including leukaemia, lung and breast cancer and neuroblastoma. SHP2 is ubiquitously expressed and regulates cell survival and proliferation primarily through activation of the RAS–ERK signalling pathway. It is also a key mediator of the programmed cell death 1 (PD-1) and B- and T-lymphocyte attenuator (BTLA) immune checkpoint pathways. Reduction of SHP2 activity suppresses tumour cell growth and is a potential target of cancer therapy. Here we report the discovery of a highly potent (IC50 = 0.071 μM), selective and orally bioavailable small-molecule SHP2 inhibitor, SHP099, that stabilizes SHP2 in an auto-inhibited conformation. SHP099 concurrently binds to the interface of the N-terminal SH2, C-terminal SH2, and protein tyrosine phosphatase domains, thus inhibiting SHP2 activity through an allosteric mechanism. SHP099 suppresses RAS–ERK signalling to inhibit the proliferation of receptor-tyrosine-kinase-driven human cancer cells in vitro and is efficacious in mouse tumour xenograft models. Together, these data demonstrate that pharmacological inhibition of SHP2 is a valid therapeutic approach for the treatment of cancers.

The causative agent of severe acute respiratory syndrome (SARS) has been identified as a novel coronavirus, SARS-CoV. The main proteinase of SARS-CoV, 3CLpro, is an attractive target for therapeutics against SARS owing to its fundamental role in viral replication. We sought to identify novel inhibitors of 3CLpro to advance the development of appropriate therapies in the treatment of SARS. 3CLpro was cloned, expressed, and purified from the Tor2 isolate. A quenched fluorescence resonance energy transfer assay was developed for 3CLpro to screen the proteinase against 50,000 drug-like small molecules on a fully automated system. The primary screen identified 572 hits; through a series of virtual and experimental filters, this number was reduced to five novel small molecules that show potent inhibitory activity (IC50 = 0.5-7 microM) toward SARS-CoV 3CLpro.

SHP2 is a nonreceptor protein tyrosine phosphatase (PTP) encoded by the PTPN11 gene involved in cell growth and differentiation via the MAPK signaling pathway. SHP2 also purportedly plays an important role in the programmed cell death pathway (PD-1/PD-L1). Because it is an oncoprotein associated with multiple cancer-related diseases, as well as a potential immunomodulator, controlling SHP2 activity is of significant therapeutic interest. Recently in our laboratories, a small molecule inhibitor of SHP2 was identified as an allosteric modulator that stabilizes the autoinhibited conformation of SHP2. A high throughput screen was performed to identify progressable chemical matter, and X-ray crystallography revealed the location of binding in a previously undisclosed allosteric binding pocket. Structure-based drug design was employed to optimize for SHP2 inhibition, and several new protein-ligand interactions were characterized. These studies culminated in the discovery of 6-(4-amino-4-methylpiperidin-1-yl)-3-(2,3-dichlorophenyl)pyrazin-2-amine (SHP099, 1), a potent, selective, orally bioavailable, and efficacious SHP2 inhibitor.

The steady-state cleavage of catechols by 2,3-dihydroxybiphenyl 1,2-dioxygenase (DHBD), the extradiol dioxygenase of the biphenyl biodegradation pathway, was investigated using a highly active, anaerobically purified preparation of enzyme. The kinetic data obtained using 2,3-dihydroxybiphenyl (DHB) fit a compulsory order ternary complex mechanism in which substrate inhibition occurs. The K m for dioxygen was 1280 ؎ 70 M, which is at least 2 orders of magnitude higher than that reported for catechol 2,3-dioxygenases. K m and K d for DHB were 22 ؎ 2 and 8 ؎ 1 M, respectively. DHBD was subject to reversible substrate inhibition and mechanism-based inactivation. In air-saturated buffer, the partition ratios of catecholic substrates substituted at C-3 were inversely related to their apparent specificity constants. Small organic molecules that stabilized DHBD most effectively also inhibited the cleavage reaction most strongly. The steady-state kinetic data and crystallographic results suggest that the stabilization and inhibition are due to specific interactions between the organic molecule and the active site of the enzyme. t-Butanol stabilized the enzyme and inhibited the cleavage of DHB in a mixed fashion, consistent with the distinct binding sites occupied by t-butanol in the crystal structures of the substrate-free form of the enzyme and the enzyme-DHB complex. In contrast, crystal structures of complexes with catechol and 3-methylcatechol revealed relationships between the binding of these smaller substrates and t-butanol that are consistent with the observed competitive inhibition.The microbial degradation of aromatic compounds constitutes an essential link in the global carbon cycle. The aerobic degradation of aromatic compounds such as toluene, naphthalene, and biphenyl generally proceeds via a catecholic catabolite with hydroxyl substituents on two adjacent carbon atoms. This catecholic compound is cleaved by a dioxygenase from one of two very different classes. Intradiol dioxygenases utilize non-heme ferric iron to cleave the aromatic nucleus ortho to (between) the hydroxyl substituents whereas extradiol dioxygenases utilize non-heme ferrous iron to cleave the aromatic nucleus meta (adjacent) to the hydroxyl substituents. The mechanism of intradiol dioxygenases is better understood due to their greater stability, favorable properties for spectroscopic examination, and the accessibility of catalytic intermediates (1, 2). Interest in extradiol dioxygenases is nonetheless considerable, not only because of their general metabolic significance and catalytic properties, but also because of the potential exploitation of these enzymes in the degradation of environmental pollutants such as polychlorinated biphenyls.2,3-Dihydroxybiphenyl 1,2-dioxygenase (DHBD) 1 is a component of the aerobic biphenyl degradation pathway of a number of microorganisms and cleaves 2,3-dihydroxybiphenyl (DHB) in an extradiol fashion as shown in Scheme 1. Crystallographic studies of DHBD from Burkholderia cepacia LB400 (3) and Pseudomonas...

2,3-Dihydroxybiphenyl 1,2-dioxygenase (EC 1.13.11.39), the extradiol dioxygenase of the biphenyl biodegradation pathway, is subject to inactivation during the steadystate cleavage of catechols. Detailed analysis revealed that this inactivation was similar to the O 2 -dependent inactivation of the enzyme in the absence of catecholic substrate, resulting in oxidation of the active site Fe(II) to Fe(III). Interestingly, the catecholic substrate not only increased the reactivity of the enzyme with O 2 to promote ring cleavage but also increased the rate of O 2 -dependent inactivation. Thus, in air-saturated buffer, the apparent rate constant of inactivation of the free enzyme was (0.7 ؎ 0.1) ؋ 10 ؊3 s ؊1 versus (3.7 ؎ 0.4) ؋ 10 ؊3 s ؊1 for 2,3-dihydroxybiphenyl, the preferred catecholic substrate of the enzyme, and (501 ؎ 19) ؋ 10 ؊3 s ؊1 for 3-chlorocatechol, a potent inactivator of 2,3-dihydroxybiphenyl 1,2-dioxygenase (partition coefficient ‫؍‬ 8 ؎ 2, K m app ‫؍‬ 4.8 ؎ 0.7 M). The 2,3-dihydroxybiphenyl 1,2-dioxygenase-catalyzed cleavage of 3-chlorocatechol yielded predominantly 2-pyrone-6-carboxylic acid and 2-hydroxymuconic acid, consistent with the transient formation of an acyl chloride. However, the enzyme was not covalently modified by this acyl chloride in vitro or in vivo. The study suggests a general mechanism for the inactivation of extradiol dioxygenases during catalytic turnover involving the dissociation of superoxide from the enzyme-catecholic-dioxygen ternary complex and is consistent with the catalytic mechanism.