Discovery of Novel Tubulin Polymerization Inhibitors and Survivin Inhibitors as Potential Anticancer Agents.

摘要

Melanoma is the most dangerous form of skin cancer and accounts for the majority of skin cancer death. Although considerable advances have been made in melanoma treatment in recent years, there are many problems associated with current therapies. Drug resistance to targeted therapies is almost inevitable after short term treatment. Immunotherapies generally have low response rate and the effects vary among patients. Therefore, the need to develop new and more effective treatment for melanoma is high.;The work presented here focuses on discovery of novel anticancer agents for melanoma by targeting two important cancer targets: tubulin and survivin. Microtubules play important role in mitosis and cell division. Cancer cells divide more rapidly than normal cells, and thus are more sensitive to tubulin targeting agents which disrupt mitosis. Targeting tubulin for anticancer treatment has been very successful. Chapter 3 describes our discovery process of a series of novel tubulin polymerization inhibitors. Our lab previously reported a set of 2-aryl-4-benzoyl-imidazoles (ABI) derivatives with potent anti-proliferative activity against melanoma cells and xenografts. A new series of 4-aryl-2-benzoyl-imidazoles were designed and synthesized after further optimization of the ABI series. The new scaffold reversed the position of the aryl group and benzoyl group on the imidazole ring of ABI structure and thus was named RABI. Those newly synthesized compounds were tested against eight different cancer cells, including multidrug-resistant cancer cell lines. The in vitro results showed that several compounds in this series had excellent anti-proliferative activities. The best compound displayed IC50 value in single-digit nano-molar against several tumor cell lines. In addition, RABI compounds showed advantages in overcoming multiple drug resistance, compared with existing tubulin targeting agents, paclitaxel, colchicine, and vinblastine. Mechanism of action for the RABI compounds was investigated using cell cycle analysis, tubulin polymerization assay, competitive mass spectrometry binding assay, and molecular docking studies. These studies suggested that RABI compounds exerted their anticancer effects by inhibiting tubulin polymerization at the colchicine binding site. The RABI compounds represent promising cancer drug candidates for further development.;Another attractive target for anticancer treatment is survivin. The differential expression of survivin between normal differentiated cells and tumor cells and the essential role of survivin in tumor make it an ideal target for cancer. Although survivin is an attractive cancer drug target, the pool of existing survivin inhibitors is quite limited. Thus, it is highly significant to develop new survivin inhibitors. Our attempts to search for new survivin inhibitors were initiated by the identification of UC-112 which turned out to be a potent and selective survivin inhibitor. UC-112 was discovered through virtual screening from a library of compounds. It showed good potency both in vitro and in vivo. Structural modifications of the UC-112 oxyquinoline template generated a number of UC-112 analogs. The new analogs were tested on a panel of cancer cell lines. The results suggested that the new derivatives had strong anticancer activity. Several compounds showed IC 50 value in the nano-molar range. The structure-activity relationships were also elucidated through the structural modifications. Our best compounds along with UC-112 were submitted for NCI-60 cancer cell line screening. The results from the screening indicated the best compound in this series improved potency in terms of GI50. The most potent compound also showed good drug-like properties. Mechanism of action for the UC-112 analogs was investigated using Western blot and drug affinity responsive target stability (DARTS) assay. This set of compounds selectively inhibited the expression of survivin over other IAP proteins and also protected survivin from digestion by pronase in the DARTS assay. The most potent compound from the in vitro assay effectively suppressed tumor growth in melanoma xenograft. This novel scaffold represents a new structure template for survivin inhibitors and can be further developed as potential anticancer agents.