Biolayer Interferometry Assay for Cyclin-Dependent Kinase-Cyclin Association Reveals Diverse Effects of Cdk2 Inhibitors on Cyclin Binding Kinetics.

Cyclin-dependent kinases (CDKs) are key mediators of cell proliferation and have been a subject of oncology drug discovery efforts for over two decades. Several CDK and activator cyclin family members have been implicated in regulating the cell division cycle. While it is thought that there are canonical CDK-cyclin pairing preferences, the extent of selectivity is unclear, and increasing evidence suggests that the cell-cycle CDKs can be activated by a pool of available cyclins. The molecular details of CDK-cyclin specificity are not completely understood despite their importance for understanding cancer cell cycles and for pharmacological inhibition of cancer proliferation. We report here a biolayer interferometry assay that allows for facile quantification of CDK binding interactions with their cyclin activators. We applied this assay to measure the impact of Cdk2 inhibitors on Cyclin A (CycA) association and dissociation kinetics. We found that Type I inhibitors increase the affinity between Cdk2 and CycA by virtue of a slowed cyclin dissociation rate. In contrast, Type II inhibitors and other small-molecule Cdk2 binders have distinct effects on the CycA association and dissociation processes to decrease affinity. We propose that the differential impact of small molecules on the cyclin binding kinetics arises from the plasticity of the Cdk2 active site as the kinase transitions between active, intermediate, and inactive states.

Race-based disparities in access to surgical palliation for hypoplastic left heart syndrome.

BACKGROUND: Racial disparities in outcomes have been shown to persist in many operative specialties, including the management of congenital heart disease. Using a demographic-adjusted methodology, we examined whether patient race influenced access to high-performing centers for the operative management of hypoplastic left heart syndrome. METHODS: The 2005-2017 National Inpatient Sample was queried to identify all pediatric (≤5 years) hospitalizations with an operation for hypoplastic left heart syndrome. A racial disparity index was generated for each hospital and defined as the proportion of White patients receiving operative management for hypoplastic left heart syndrome divided by the proportion of White patients admitted for respiratory failure. This methodology quantified hospital-level racial variation while adjusting for the local racial makeup of each center. RESULTS: Of the 17,275 patients who met inclusion criteria, 64.1% were managed at high-volume centers. Patients at high-volume centers had a similar distribution of operative type, age, and burden of comorbidities. The mean racial disparity index steadily grew from 1.06 at the lowest volume decile of operative volume to 1.51 at the highest, indicating an increasing proportion of White patients as volume increased. Using risk-adjusted analysis, each decile increase in hospital volume was associated with a 14% relative reduction in odds of mortality and a 0.06 increase in predicted racial disparity index. Increasing volume was further associated with reduced odds of non-home discharge but did not alter resource utilization. CONCLUSION: We demonstrate that high-volume centers disproportionally serve White patients and have superior clinical outcomes compared to low-volume centers. This study highlights the critical importance of equitable access to expert care for high-risk conditions such as hypoplastic left heart syndrome.

Disruptin, a cell-penetrating peptide degrader of EGFR: Cell-Penetrating Peptide in Cancer Therapy.

Disruptin is a cell-permeable decoy peptide designed to destabilize activated EGFR, both by inhibiting Hsp90 chaperoning and dissociating the active asymmetric EGFR dimer, which leads to an increase in engagement of activated EGFR with the proteolytic degradation machinery and subsequent loss from the cells. Disruptin is an N-terminally biotinylated nonadecapeptide, with 8 amino acids from the αC-helix-ß4 sheet loop of EGFR (S767-C774) fused to a TAT undecapeptide. The S767-R775 loop is at the interface with juxtamembrane domains in the active EGFR dimers and is a binding site for Hsp90. Cellular studies in EGFR-activated tumor cells demonstrated that Disruptin causes the disappearance of EGFR protein from cells over a few hours, a growth inhibitory effect, similar but more effective than the EGFR kinase inhibition. Interestingly, cells without activated EGFR remained unaffected. In vivo studies showed that Disruptin slowed the growth of small tumors. Larger tumors responded to intratumoral injections but did not respond to systemic administration at tolerated doses. Investigation of these results revealed that systemic administration of Disruptin has acute toxicities, mainly related to its TAT peptide moiety. Therefore, we conclude that although the efficacy of both in vitro and in vivo intratumoral injection of Disruptin supports the therapeutic strategy of blocking activated EGFR dimerization, Disruptin is not suitable for further development. These studies also highlight the importance of the chosen models and drug-delivery methods for such investigations.

Differential protein stability of EGFR mutants determines responsiveness to tyrosine kinase inhibitors.

Non-small cell lung cancer (NSCLC) patients carrying specific EGFR kinase activating mutations (L858R, delE746-A750) respond well to tyrosine kinase inhibitors (TKIs). However, drug resistance develops within a year. In about 50% of such patients, acquired drug resistance is attributed to the enrichment of a constitutively active point mutation within the EGFR kinase domain (T790M). To date, differential drug-binding and altered ATP affinities by EGFR mutants have been shown to be responsible for differential TKI response. As it has been reported that EGFR stability plays a role in the survival of EGFR driven cancers, we hypothesized that differential TKI-induced receptor degradation between the sensitive L858R and delE746-A750 and the resistant T790M may also play a role in drug responsiveness. To explore this, we have utilized an EGFR-null CHO overexpression system as well as NSCLC cell lines expressing various EGFR mutants and determined the effects of erlotinib treatment. We found that erlotinib inhibits EGFR phosphorylation in both TKI sensitive and resistant cells, but the protein half-lives of L858R and delE746-A750 were significantly shorter than L858R/T790M. Third generation EGFR kinase inhibitor (AZD9291) inhibits the growth of L858R/T790M-EGFR driven cells and also induces EGFR degradation. Erlotinib treatment induced polyubiquitination and proteasomal degradation, primarily in a c-CBL-independent manner, in TKI sensitive L858R and delE746-A750 mutants when compared to the L858R/T790M mutant, which correlated with drug sensitivity. These data suggest an additional mechanism of TKI resistance, and we postulate that agents that degrade L858R/T790M-EGFR protein may overcome TKI resistance.

Tyrosine Kinase Inhibitors. 20. Optimization of Substituted Quinazoline and Pyrido[3,4-d]pyrimidine Derivatives as Orally Active, Irreversible Inhibitors of the Epidermal Growth Factor Receptor Family.

Structure-activity relationships for inhibition of erbB1, erbB2, and erbB4 were determined for a series of quinazoline- and pyrido[3,4-d]pyrimidine-based analogues of the irreversible pan-erbB inhibitor, canertinib. Cyclic amine bearing crotonamides were determined to provide rapid inhibition of cellular erbB1 autophosphorylation and good metabolic stability in liver microsome and hepatocyte assays. The influence of 4-anilino substitution on pan-erbB inhibitory potency was investigated. Several anilines were identified as providing potent, reversible pan-erbB inhibition. Optimum 4- and 6-substituents with known 7-substituents provided preferred irreversible inhibitors for pharmacodynamic testing in vivo. Quinazoline 54 and pyrido[3,4-d]pyrimidine 71 were identified as clearly superior to canertinib. Both compounds possess a piperidinyl crotonamide Michael acceptor and a 3-chloro-4-fluoroaniline, indicating these as optimized 6- and 4-substituents, respectively. Pharmacokinetic comparison of compounds 54 and 71 across three species selected compound 54 as the preferred candidate. Compound 54 (PF-00299804) has been assigned the nomenclature of dacomitinib and is currently under clinical evaluation.

2-Alkylamino- and alkoxy-substituted 2-amino-1,3,4-oxadiazoles-O-Alkyl benzohydroxamate esters replacements retain the desired inhibition and selectivity against MEK (MAP ERK kinase).

This paper reports a second generation MEK inhibitor. The previously reported potent and efficacious MEK inhibitor, PD-184352 (CI-1040), contains an integral hydroxamate moiety. This compound suffered from less than ideal solubility and metabolic stability. An oxadiazole moiety behaves as a bioisostere for the hydroxamate group, leading to a more metabolically stable and efficacious MEK inhibitor.

The discovery of the benzhydroxamate MEK inhibitors CI-1040 and PD 0325901.

A novel series of benzhydroxamate esters derived from their precursor anthranilic acids have been prepared and have been identified as potent MEK inhibitors. 2-(2-Chloro-4-iodo-phenylamino)-N-cyclopropylmethoxy-3,4-difluoro-benzamide, CI-1040, was the first MEK inhibitor to demonstrate in vivo activity in preclinical animal models and subsequently became the first MEK inhibitor to enter clinical trial. CI-1040 suffered however from poor exposure due to its poor solubility and rapid clearance, and as a result, development of the compound was terminated. Optimization of the diphenylamine core and modification of the hydroxamate side chain for cell potency, solubility, and exposure with oral delivery resulted in the discovery of the clinical candidate N-(2,3-dihydroxy-propoxy)-3,4-difluoro-2-(2-fluoro-4-iodo-phenylamino)-benzamide PD 0325901.

Synthesis and structure-activity relationships of N-6 substituted analogues of 9-hydroxy-4-phenylpyrrolo[3,4-c]carbazole-1,3(2H,6H)-diones as inhibitors of Wee1 and Chk1 checkpoint kinases.

A series of N-6 substituted 9-hydroxy-4-phenylpyrrolo[3,4-c]carbazole-1,3(2H,6H)-diones were prepared from N-substituted (5-methoxyphenyl)ethenylindoles. The target compounds were tested for their ability to inhibit the G2/M cell cycle checkpoint kinases, Wee1 and Chk1. Analogues with neutral or cationic N-6 side chains were potent dual inhibitors. Acidic side chains provided potent (average IC(50) 0.057 microM) and selective (average ratio 223-fold) Wee1 inhibition. Co-crystal structures of inhibitors bound to Wee1 show that the pyrrolo[3,4-c]carbazole scaffold binds in the ATP-binding site, with N-6 substituents involved in H-bonding to conserved water molecules. HT-29 cells treated with doxorubicin and then target compounds demonstrate an active Cdc2/cyclin B complex, inhibition of the doxorubicin-induced phosphorylation of tyrosine 15 of Cdc2 and abrogation of the G2 checkpoint.

Amyloid-beta(1-42) rapidly forms protofibrils and oligomers by distinct pathways in low concentrations of sodium dodecylsulfate.

Alzheimer's disease (AD) is characterized by large numbers of senile plaques in the brain that consist of fibrillar aggregates of 40- and 42-residue amyloid-beta (Abeta) peptides. However, the degree of dementia in AD correlates better with the concentration of soluble Abeta species assayed biochemically than with histologically determined plaque counts, and several investigators now propose that soluble aggregates of Abeta are the neurotoxic agents that cause memory deficits and neuronal loss. These endogenous aggregates are minor components in brain extracts from AD patients and transgenic mice that express human Abeta, but several species have been detected by gel electrophoresis in sodium dodecylsulfate (SDS) and isolated by size exclusion chromatography (SEC). Endogenous Abeta aggregation is stimulated at cellular interfaces rich in lipid rafts, and anionic micelles that promote Abeta aggregation in vitro may be good models of these interfaces. We previously found that micelles formed in dilute SDS (2 mM) promote Abeta(1-40) fiber formation by supporting peptide interaction on the surface of a single micelle complex. In contrast, here we report that monomeric Abeta(1-42) undergoes an immediate conversion to a predominant beta-structured conformation in 2 mM SDS which does not proceed to amyloid fibrils. The conformational change is instead rapidly followed by the near quantitative conversion of the 4 kDa monomer SDS gel band to 8-14 kDa bands consistent with dimers through tetramers. Removal of SDS by dialysis gave a shift in the predominant SDS gel bands to 30-60 kDa. While these oligomers resemble the endogenous aggregates, they are less stable. In particular, they do not elute as discrete species on SEC, and they are completed disaggregated by boiling in 1% SDS. It appears that endogenous oligomeric Abeta aggregates are stabilized by undefined processes that have not yet been incorporated into in vitro Abeta aggregation procedures.

Tyrosine kinase inhibitors. 19. 6-Alkynamides of 4-anilinoquinazolines and 4-anilinopyrido[3,4-d]pyrimidines as irreversible inhibitors of the erbB family of tyrosine kinase receptors.

Structure-activity relationships for inhibition of erbB1, erbB2, and erbB4 were determined for a series of alkynamide analogues of quinazoline- and pyrido[3,4-d]pyrimidine-based compounds. The compounds were prepared by coupling the appropriate 6-aminoquinazolines or 6-aminopyrido[3,4-d]pyrimidines with alkynoic acids, using EDCI.HCl in pyridine. The compounds showed pan-erbB enzyme inhibition but were on average about 10-fold more potent against erbB1 than against erbB2 and erbB4. For cellular inhibition, the nature of the alkylating side chains was an important determinant, with 5-dialkylamino-2-pentynamide type Michael acceptors providing the highest potency. This is suggested to be due to an improved ability of the amine to participate in an autocatalysis of the Michael reaction with enzyme cysteine residues. Pyrido[3,4-d]pyrimidine analogue 39 was selected for in vivo evaluation and achieved tumor regressions at 10 mg/kg in the A431 human epidermoid carcinoma and at 40 mg/kg for the SF767 human glioblastoma and the SKOV3 human ovarian carcinoma. Complete stasis was observed at 40 mg/kg in the BXPC3 human pancreatic carcinoma as well as in the H125 human non-small-cell lung carcinoma.

Metabolic activation of troglitazone: identification of a reactive metabolite and mechanisms involved.

Troglitazone (TGZ), the first glitazone used for the treatment of type II diabetes mellitus and removed from the market for liver toxicity, was shown to bind covalently to microsomal protein and glutathione (GSH) following activation by cytochrome P450 (P450). The covalent binding of (14)C-TGZ in dexamethasone-induced rat liver microsomes was NADPH-dependent and required the active form of P450; it was completely inhibited by ketoconazole (10 microM) and GSH (4 mM). The covalent binding in P450 3A4 Supersomes (9.2 nmol of TGZ Eq/nmol P450) was greater than that with P450 1A2 (0.7), 2C8 (3.7), 2C19 (1.4), 2E1 (0.6), and 2D6 (1.1) and 3A5 (3.0). The covalent binding in liver microsomes from rats pretreated with dexamethasone (5.3 nmol of TGZ Eq bound/nmol P450) was greater than that from rats pretreated with vehicle (3.5), beta-naphthoflavone (0.4), phenobarbital (1.1), or pyridine (2.5). A TGZ-GSH adduct was detected by liquid chromatography-tandem mass spectrometry and radioactivity detection with a deprotonated quasi-molecular ion [M-H](-) at m/z 745, with fragment ions at m/z 438 (deprotonated TGZ moiety), and at m/z 306 (deprotonated GSH moiety). The TGZ-GSH adduct was determined to be 5-glutathionyl-5-[4-(6-hydroxy-2,5,7,8-tetramethylchroman-2-ylmethoxy)benzyl]-thiazolidine-2,4-dione based on collision-induced dissociation fragmentation, and one- and two-dimensional NMR analysis of the isolated adduct. The synthetic 5-hydroxy TGZ and the benzylidene derivative of TGZ did not react with GSH or GSH ethyl ester. The mechanisms for metabolic activation of TGZ may involve an ultimate reactive sulfonium ion which could be formed from an initial sulfoxide followed by a formal Pummerer rearrangement, or a C5 thiazolidinedione radical or a sulfur cation radical.