Scott A. Watkins

Novel, potent and selective cyclin D1/CDK4 inhibitors: indolo[6,7-a]pyrrolo[3,4-c]carbazoles.

The synthesis and CDK inhibitory properties of a series of indolo[6,7-a]pyrrolo[3,4-c]carbazoles is reported. In addition to their potent CDK activity, the compounds display antiproliferative activity against two human cancer cell lines. These inhibitors also effect strong G1 arrest in these cell lines and inhibit Rb phosphorylation at Ser780 consistent with inhibition of cyclin D1/CDK4.

Aryl[a]pyrrolo[3,4-c]carbazoles as selective cyclin D1-CDK4 inhibitors

The synthesis of new analogues of Arcyriaflavin A in which one indole ring is replaced by an aryl or heteroaryl ring is described. These new series of aryl[a]pyrrolo[3,4-c]carbazoles were evaluated as inhibitors of Cyclin D1-CDK4. A potent and selective D1-CDK4 inhibitor, 7a (D1-CDK4 IC(50)=45 nM), has been identified. The potency, selectivity profile against other kinases, and structure-activity relationship (SAR) trends of this class of compounds are discussed.

Synthesis of quinolinyl/isoquinolinyl[a]pyrrolo [3,4-c] carbazoles as cyclin D1/CDK4 inhibitors.

A novel series of pyrrolo[3,4-c] carbazoles fused with a quinolinyl/isoquinolinyl moiety were synthesized and their D1/CDK4 inhibitory and antiproliferative activity were evaluated. Compound 8H, 14H-isoquinolinyl[6,5-a]-pyrrolo[3,4-c]carbazole-7,9-dione (1d) was found to be a highly potent D1/CDK4 inhibitor with an IC(50) of 69 nM. Compound 1d also inhibited tumor cell growth, arrested tumor cells in G1 phase and inhibited pRb phosphorylation.

Studies on cyclin-dependent kinase inhibitors: indolo-[2,3-a]pyrrolo[3,4-c]carbazoles versus bis-indolylmaleimides

A series of indolo[2,3-a]pyrrolo[3,4-c]carbazoles and their bis-indolylmaleimides precursors have been prepared in order to compare their activity as D1-CDK4 inhibitors. Both enzymatic and antiproliferative assays have shown that the structurally more constrained indolo[2,3-a]pyrrolo[3,4-c]carbazoles are consistently more active (8-42-fold) in head-to-head comparison with their bis-indolylmaleimides counterparts. Cell-cycle analysis using flow cytometry have also shown that the indolocarbazoles are selective G1 blockers while the bis-indolylmaleimides arrest cells in the G2/M phase.

Conditional transformation of rat embryo fibroblast cells by a cyclin D1-cdk4 fusion gene.

Cyclin D1 gene overexpression is a frequent event in a number of human cancers. These observations have led to the suggestion that cyclin D1 alterations might play a role in the etiology of cancer. This possibility is supported by the finding that transfection of mammalian cells with cyclin D1 can accelerate progression through the G1 phase of the cell cycle. Moreover, cyclin D1 can function as an oncogene by cooperating with activated Ha-ras to transform primary rat embryo fibroblasts (REFs). In addition, cyclin D1 transgenics develop hyperplasia and neoplasia of the thymus and mammary gland. We have constructed a novel fusion gene consisting of full-length human cyclin D1 and cdk4 genes. This fusion gene was expressed in insect cells and the fusion protein was shown to be enzymatically active. The fusion gene was expressed in mammalian cells under the control of tet-repressor. This fusion gene immortalized primary REFs, and cooperated with activated Ha-ras to transform primary REFs, in terms of anchorage-independent growth in vitro and formation of tumors in vivo. Utilizing a tet-regulated gene expression system, we have shown that proliferation of stably transfected primary REFs in vitro and in vivo is dependent on the continued expression of the cyclin D1-cdk4 fusion gene. These cell lines could be useful in the discovery of novel cancer therapeutics to modulate cyclin D1.cdk4 activity.

Abstract B235: Characterization of LY2228820 dimesylate, a potent and selective inhibitor of p38 MAPK with antitumor activity.

p38α mitogen-activated protein kinase (MAPK) is activated by cancer cells in response to environmental factors, such as oncogenic stress, radiation, and chemotherapy. p38α MAPK phosphorylates a number of substrates, including MAPKAP-K2 (MK2), and regulates the production/message stability of cytokines produced in the tumor microenvironment, such as TNFα, IL1 β, IL-6 and IL-8. p38α MAPK is activated and highly expressed in human cancers and may play a role in tumor growth, invasion and metastasis. LY2228820 dimesylate is a tri-substituted imidazole derivative that is a potent and ATP-competitive inhibitor of the α and β isoforms of p38 MAPK in vitro (IC50 = 5.3 nM and 3.2 nM, respectively). This compound displays > 1000-fold selectivity for p38α MAPK versus 179 other kinases tested (including p38δ and γ isoforms). In cell-based assays, LY2228820 dimesylate also potently and selectively inhibits phosphorylation of MK2 (Thr334) in TNFα-stimulated HeLa cells (IC50 = 8.1 nM) and anisomycin-induced mouse RAW264.7 macrophages (IC50 = 35.3 nM) with no changes in phosphorylation of p38α MAPK, JNK, ERK1/2, c-jun, ATF2 or cMyc at concentrations up to 10μM. LY2228820 dimesylate also reduces TNFα secretion by LPS/IFNγ-stimulated macrophages (IC50 = 6.3 nM). In mice transplanted with B16-F10 melanomas, phospho-MK2 was effectively inhibited by LY2228820 dimesylate in tumors in a dose-dependent manner (TMED70 = 19.4 mg/kg). Significant target inhibition (>40% inhibition of phospho-MK2) was maintained for approx. 4–8hrs following a single 10mg/kg oral dose. In a broad range of xenograft models (A-549 NSCLC, SK-OV-3 Ovarian, U-87MG Glioma, MDA-MB-468 Breast), LY2228820 dimesylate demonstrates significant tumor growth delay. In summary, LY2228820 dimesylate is a novel, potent and selective inhibitor of p38 MAPK with anti-tumor activity. Further studies are ongoing to determine its molecular mechanism(s) of action, potential for combination with standard-of-care agents, and potential clinical activity. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr B235.