Nicola M. Heron

PURPOSE: In the current study, we examined the in vivo effects of AZD1152, a novel and specific inhibitor of Aurora kinase activity (with selectivity for Aurora B). EXPERIMENTAL DESIGN: The pharmacodynamic effects and efficacy of AZD1152 were determined in a panel of human tumor xenograft models. AZD1152 was dosed via several parenteral (s.c. osmotic mini-pump, i.p., and i.v.) routes. RESULTS: AZD1152 potently inhibited the growth of human colon, lung, and hematologic tumor xenografts (mean tumor growth inhibition range, 55% to > or =100%; P < 0.05) in immunodeficient mice. Detailed pharmacodynamic analysis in colorectal SW620 tumor-bearing athymic rats treated i.v. with AZD1152 revealed a temporal sequence of phenotypic events in tumors: transient suppression of histone H3 phosphorylation followed by accumulation of 4N DNA in cells (2.4-fold higher compared with controls) and then an increased proportion of polyploid cells (>4N DNA, 2.3-fold higher compared with controls). Histologic analysis showed aberrant cell division that was concurrent with an increase in apoptosis in AZD1152-treated tumors. Bone marrow analyses revealed transient myelosuppression with the drug that was fully reversible following cessation of AZD1152 treatment. CONCLUSIONS: These data suggest that selective targeting of Aurora B kinase may be a promising therapeutic approach for the treatment of a range of malignancies. In addition to the suppression of histone H3 phosphorylation, determination of tumor cell polyploidy and apoptosis may be useful biomarkers for this class of therapeutic agent. AZD1152 is currently in phase I trials.

The Aurora kinases have been the subject of considerable interest as targets for the development of new anticancer agents. While evidence suggests inhibition of Aurora B kinase gives rise to the more pronounced antiproliferative phenotype, the most clinically advanced agents reported to date typically inhibit both Aurora A and B. We have discovered a series of pyrazoloquinazolines, some of which show greater than 1000-fold selectivity for Aurora B over Aurora A kinase activity, in recombinant enzyme assays. These compounds have been designed for parenteral administration and achieve high levels of solubility by virtue of their ability to be delivered as readily activated phosphate derivatives. The prodrugs are comprehensively converted to the des-phosphate form in vivo, and the active species have advantageous pharmacokinetic properties and safety pharmacology profiles. The compounds display striking in vivo activity, and compound 5 (AZD1152) has been selected for clinical evaluation and is currently in phase 1 clinical trials.

A variety of medium-ring heterocycles, prepared efficiently by the Ru-catalyzed diene metathesis method, undergo asymmetric catalytic ethylmagnesation to afford nonracemic unsaturated alcohols and amides in excellent enantiomeric purity (>98% ee). Noteworthy features of these studies are as follows: (i) Eight-membered unsaturated tosyl amides are readily prepared by transition-metal-catalyzed metathesis. (ii) With six-, seven-, and eight-membered N-containing substrates the presence of an electron-withdrawing Ts unit is required for efficient carbomagnesation (corresponding alkylamines are inert). Chiral medium-ring heterocycles are resolved by the Zr-catalyzed C−C bond-forming reaction to afford recovered starting materials in up to >99% ee. The kinetic resolution data indicate that simple steric models can reliably predict the sense of the asymmetric induction in the asymmetric carbomagnesation or kinetic resolution. However, experimental results presented herein also illustrate that the observed levels of enantioselectivity cannot be predicted on the basis of such paradigms.

The synthesis of a novel series of quinazolines substituted at C4 by five-membered ring aminoheterocycles is reported. Their in vitro structure-activity relationships versus Aurora A and B serine-threonine kinases is discussed. Our results demonstrate that quinazolines with a substituted aminothiazole at C4 possess potent Aurora A and B inhibitory activity and excellent selectivity against a panel of various serine-threonine and tyrosine kinases, as exemplified by compound 46. We found also that the position and nature of the substituent on the thiazole play key roles in cellular potency. Compounds with an acetanilide substituent at C5' have the greatest cellular activity. The importance of the C5' position for substitution has been rationalized by ab initio molecular orbital calculations. Results show that the planar conformation with the sulfur of the thiazole next to the quinazoline N-3 is strongly favored over the other possible planar conformation. Compound 46 is a potent suppressor of the expression of phospho-histone H3 in tumor cells in vitro as well as in vivo, where 46, administered as its phosphate prodrug 54, suppresses the expression of phospho-histone H3 in subcutaneously implanted tumors in nude mice.