Discovery and Characterization of 2-Anilino-4- (Thiazol-5-yl)Pyrimidine Transcriptional CDK Inhibitors as Anticancer Agents

The main difficulty in the development of ATP antagonist kinase inhibitors is target specificity, since the ATP-binding motif is present in many proteins. We introduce a strategy that has allowed us to identify compounds from a kinase inhibitor library that block the cyclin-dependent kinases responsible for regulating transcription, i.e., CDK7 and especially CDK9. The screening cascade employs cellular phenotypic assays based on mitotic index and nuclear p53 protein accumulation. This permitted us to classify compounds into transcriptional, cell cycle, and mitotic inhibitor groups. We describe the characterization of the transcriptional inhibitor class in terms of kinase inhibition profile, cellular mode of action, and selectivity for transformed cells. A structural selectivity rationale was used to optimize potency and biopharmaceutical properties and led to the development of a transcriptional inhibitor, 3,4-dimethyl-5-[2-(4-piperazin-1-yl-phenylamino)-pyrimidin-4-yl]-3H-thiazol-2-one, with anticancer activity in animal models

Diene-derived N-(3,4-Dihydro-4-oxoquinazolin-3-yl)aziridines : preparation and reactivity

The reaction of naphthalene with 3-acetoxyamino-2-alkylquinazolinones (QNHOAc) in the presence of hexamethyldisilazane (HMDS) gave a mixture of mono- and bis-aziridines in a ratio which depends upon the bulk of the (Q)2-substitutent. By following the aziridination by NMR spectroscopy it was concluded that the first formed aziridine was the endo-N-invertomer and that bis-aziridination occurred only after N-inversion to the exo-N-invertomer. In the absence of HMDS the corresponding bis-aziridine is the major product. O6NHOAc [Q6 = 2 (S)-(2,2-dimethyl-1-hydroxypropyl)quinazolin-4(3H)-one] was found to convert cyclopentadiene, 1,3- and 1,4-cyclohexadiene and cycloheptadiene into the corresponding N-(Q6)-aziridines in the presence of titanium(IV) tert-butoxide with complete or high diastereoselectivity. Accompanying these aziridines in the case of 1,3- and 1,4-cyclohexadiene were N-(Q6)-substituted dienylamines formed with complete diastereoselectivity by formal insertion into the (bis)allylic carbon hydrogen bonds. In ring-opening of the 1,3-cyclohexadiene-derived aziridine above (two diastereoisomers) by mild acid, formation of the alcohol product involves participation by the Q6-carbonyl oxygen. Cyclisation of each of these alcohols with carbonyl diimidazole and N-Q6 bond reduction using samarium(II) iodide gave the corresponding oxazolidinones in enantiopurified form.;The electron-withdrawing effect of the quinazolinone ring activates N-(Q)-aziridines towards attack by nucleophiles including thiolate and selenolate in the absence of acid. Several factors were found to influence regioselectivity in ring-opening of N-(Q)-aziridine-2-carboxylic esters at C2 including co-ordination of the aziridine to samarium(III) ion and overlap of the C-N sigma anti-bonding orbital with the carbonyl pi anti-bonding orbital. (Q)2-Trifluoromethyl-substituted aziridines undergo ring-opening at a faster rate due to increased stabilisation of the nitrogen anion intermediate

Inhibitors of Polo-like kinase reveal roles in spindle-pole maintenance

Polo-like kinases (Plks) have several functions in mitotic progression and are upregulated in many tumor types. Small-molecule Plk inhibitors would be valuable as tools for studying Plk biology and for developing antitumor agents. Guided by homology modeling of the Plk1 kinase domain, we have discovered a chemical series that shows potent and selective Plk1 inhibition. The effects of one such optimized benzthiazole N-oxide, cyclapolin 1 (1), on purified centrosomes indicate that Plks are required to generate MPM2 epitopes, recruit gamma-tubulin and enable nucleation of microtubules. The compound can also promote loss of centrosome integrity and microtubule nucleating ability apparently through increased accessibility of protein phosphatases. We show that treatment of living S2 cells with cyclapolin 1 leads to collapsed spindles, in contrast to the metaphase-arrested bipolar spindles observed after RNAi. This different response to protein depletion and protein inhibition may have significance in the development of antitumor agents

Synthesis and biological activity of 2-anilino-4-(1H-pyrrol-3-yl) pyrimidine CDK inhibitors

A series of 2-anilino-4-(1H-pyrrol-3-yl)pyrimidines were prepared and evaluated for their ability to inhibit cyclin-dependent kinases (CDKs). A number of analogues were found to be potent CDK2 and CDK4 inhibitors and to exhibit anti-proliferative activity against human tumour cell lines. Structure-activity relationships and biochemical characterization are presented

Structural Determinants of CDK4 Inhibition and Design of Selective ATP Competitive Inhibitors

AbstractA number of selective inhibitors of the CDK4/cyclin D1 complex have been reported recently. Due to the absence of an experimental CDK4 structure, the ligand and protein determinants contributing to CDK4 selectivity are poorly understood at present. Here, we report the use of computational methods to elucidate the characteristics of selectivity and to derive the structural basis for specific, high-affinity binding of inhibitors to the CDK4 active site. From these data, the hypothesis emerged that appropriate incorporation of an ionizable function into a CDK2 inhibitor results in more favorable binding to CDK4. This knowledge was applied to the design of compounds in the otherwise CDK2-selective 2-anilino-4-(thiazol-5-yl)pyrimidine pharmacophore that are potent and highly selective ATP antagonists of CDK4/cyclin D1. The findings of this study also have significant implications in the design of CDK4 mimic structures based on CDK2

The limits to dividend arbitrage: Implications for cross-border investment, Working paper

ABSTRACT The economic significance of the tax on cross-border dividends depends on the limits to dividend arbitrage. In the case of Canadian payments to the U.S. we observe these limits exactly because we see the actual pricing of the dividend-arbitrage transactions. These transactions recover only some withholding, so that Canadian and non-tax U.S. accounts perceive different expected returns from Canadian stocks, where the difference increases with dividend yield. The resulting difference in expected utility of wealth is small but the difference in efficient portfolio weights is potentially large and increasing in yield, and the actual difference between Canadian and U.S. holdings of Canadian stocks is large and increasing in yield. Governments may thus take advantage of robust financial markets to boost domestic governance of domestic firms at a low utility cost, though this may be more preferable for zero-dividend firms, whose governance moves abroad. 1 How do cross-border dividend taxes affect cross-border investment? We focus on investment across the U.S./Canada border and address this question, which is really two: what tax remains net of dividend arbitrage, and how does this net tax affect cross-border investment? Identifying the net tax presents a major empirical challenge, because the usual spot-market data cannot show it. Bid/ask spreads are too large, relative to the potential gains from trade, for such data to show what, if anything, is gained by selling shares cum-dividend and later buying them back. We turn instead to the lending market, for which our data show directly the actual pricing of dividend-arbitrage transactions by U.S. investors. We find that arbitrage recovers only some of the tax, which implies a large volume of tax-disadvantaged investment that includes all U.S. retirement money in international-equity mutual funds. How does this net tax affect U.S. investment in Canada? The net tax is small so it might seem that the effect should be small too, but the robustness of our financial markets suggests otherwise. It is well-known (e.g. 1 Because the magnification is an emergent property of wide choices, the usual optimizations over country indices do not capture it. We can see some of it if we disaggregate these indices, though for two reasons it is not feasible to see the full effect. We cannot optimize over all assets we observe because their sample covariance matrix will not invert, and even if we had their true covariance matrix, the absence of the assets we do not observe is likely to understate the effect. That is, the effect of taxing an asset is likely to grow as substitution into other assets grows easier, but removing assets from the problem makes substitution harder. What we can do is gauge how the sensitivity grows as we move toward the true problem by enlarging the investible universe a little. When we move from optimizing over a U.S. and a Canadian market index to optimizing over 53 sub-portfolios of these stocks, we find that the effect of the tax on U.S. investment in Canadian stocks grows fivefold. Does this sensitivity of efficient weights translate to sensitivity of actual weights? We take this question to the portfolio weights of Canadian and U.S. institutions. In both the 13f disclosures by major institutions and also the statutory disclosures by mutual funds we find that U.S. weights on Canadian shares decline significantly as dividend yield increases. We do not find this sensitivity in Canadian weights on U.S. shares, which is consistent with the very different structure of retirement investing in Canada. A potentially useful perspective on these results is that the large effect on holdings of the small tax on dividends could be a policy goal. The withholding tax repatriates governance of domestic firms at the cost of a small reduction of expected utility of wealth. This could be attractive to domestic authorities, though the relation to 2 yield may be unfortunate since zero-dividend firms may be the ones whose voters should be closer. The rest of the paper is in six sections: Section I covers the relevant background, Section II describes the data, Section III covers dividend arbitrage, Section IV infers portfolio-weight sensitivity from portfolio theory, Section V relates actual portfolio weights to yields, and Section VI summarizes and concludes. I. Background This section covers the legislation, literature and theory relevant to our analysis. Because our data cover stocks from Canada and the U.S., we focus primarily on the background relevant to investing across their border