The Aurora kinase inhibitor SNS-314 shows broad therapeutic potential with chemotherapeutics and synergy with microtubule-targeted agents in a colon carcinoma model.

Aurora kinases play key roles in regulating centrosome maturation, mitotic spindle formation, and cytokinesis during cell division, and are considered promising drug targets due to their frequent overexpression in a variety of human cancers. SNS-314 is a selective and potent pan Aurora inhibitor currently in a dose escalation phase 1 clinical trial for the treatment of patients with advanced solid tumors. Here, we report the antiproliferative effects of SNS-314 in combination with common chemotherapeutics in cell culture and xenograft models. The HCT116 colorectal carcinoma cell line, with intact or depleted p53 protein levels, was treated with SNS-314 and a cytotoxic chemotherapeutic from a panel comprised of gemcitabine, 5-fluorouracil (5-FU), carboplatin, daunomycin, SN-38 (the active metabolite of irinotecan), docetaxel, and vincristine. Combinations were administered under either concurrent or sequential schedules. SNS-314 has predominantly additive effects when administered concurrently with commonly used anticancer agents. Sequential administration of SNS-314 with chemotherapeutic compounds showed additive antiproliferative effects with carboplatin, gemcitabine, 5-FU, daunomycin, and SN-38, and synergy was observed in combination with gemcitabine, docetaxel, or vincristine. The most profound antiproliferative effects were observed with sequential administration of SNS-314 followed by docetaxel or vincristine. In vivo, SNS-314 potentiated the antitumor activity of docetaxel in xenografts. Both the in vitro synergies observed between SNS-314 and agents that target the mitotic spindle and the potentiation seen with docetaxel in vivo are consistent with a mechanism of action in which Aurora inhibition bypasses the mitotic spindle assembly checkpoint and prevents cytokinesis, augmenting subsequent spindle toxin-mediated mitotic catastrophe and cell death.

Fragment-based discovery of nonpeptidic BACE-1 inhibitors using tethering.

BACE-1 (beta-site amyloid precursor protein cleaving enzyme), a prominent target in Alzheimer's disease drug discovery efforts, was surveyed using Tethering technology to discover small molecule fragment ligands that bind to the enzyme active site. Screens of a library of >15000 thiol-containing fragments versus a panel of BACE-1 active site cysteine mutants under redox-controlled conditions revealed several novel amine-containing fragments that could be selectively captured by subsets of the tethering sites. For one such hit class, defined by a central aminobenzylpiperidine (ABP) moiety, X-ray crystal structures of BACE mutant-disulfide conjugates revealed that the fragment bound by engaging both catalytic aspartates with hydrogen bonds. The affinities of ABP fragments were improved by structure-guided chemistry, first for conjugation as thiol-containing fragments and then for stand-alone, noncovalent inhibition of wild-type (WT) BACE-1 activity. Crystallography confirmed that the inhibitors bound in exactly the same mode as the disulfide-conjugated fragments that were originally selected from the screen. The ABP ligands represent a new type of nonpeptidic BACE-1 inhibitor motif that has not been described in the aspartyl protease literature and may serve as a starting point for the development of BACE-1-directed Alzheimer's disease therapeutics.

Aminoethylenes: a tetrahedral intermediate isostere yielding potent inhibitors of the aspartyl protease BACE-1.

A series of novel beta-site amyloid precursor protein cleaving enzyme (BACE-1) inhibitors containing an aminoethylene (AE) tetrahedral intermediate isostere were synthesized and evaluated in comparison to corresponding hydroxyethylene (HE) compounds. Enzymatic inhibitory values were similar for both isosteres, as were structure-activity relationships with respect to stereochemical preference and substituent variation (P2/P3, P1, and P2'); however, the AE compounds were markedly more potent in a cell-based assay for reduction of beta-secretase activity. The incorporation of preferred P2/P3, P1, and P2' substituents into the AE pharmacophore yielded compound 7, which possessed enzymatic and cell assay IC(50)s of 26 nM and 180 nM, respectively. A three-dimensional crystal structure of 7 in complex with BACE-1 revealed that the amino group of the inhibitor core engages the catalytic aspartates in a manner analogous to hydroxyl groups in HE inhibitors. The AE isostere class represents a promising advance in the development of BACE-1 inhibitors.