ABSTRACT
The RAS-RAF-MEK-MAPK cascade is an essential signaling pathway, with activation typically mediated through cell surface receptors. The kinase inhibitors vemurafenib and dabrafenib, which target oncogenic BRAF V600E, have shown significant clinical efficacy in melanoma patients harboring this mutation. Because of paradoxical pathway activation, both agents were demonstrated to promote growth and metastasis of tumor cells with RAS mutations in preclinical models and are contraindicated for treatment of cancer patients with BRAF WT background, including patients with KRAS or NRAS mutations. In order to eliminate the issues associated with paradoxical MAPK pathway activation and to provide therapeutic benefit to patients with RAS mutant cancers, we sought to identify a compound not only active against BRAF V600E but also wild type BRAF and CRAF. On the basis of its superior in vitro and in vivo profile, compound 13 was selected for further development and is currently being evaluated in phase I clinical studies.
Subject(s)
Antineoplastic Agents/chemistry , Antineoplastic Agents/pharmacology , Phenylurea Compounds/chemistry , Phenylurea Compounds/pharmacology , Proto-Oncogene Proteins B-raf/genetics , Pyrimidines/chemistry , Pyrimidines/pharmacology , ras Proteins/metabolism , Animals , Antineoplastic Agents/chemical synthesis , Antineoplastic Agents/pharmacokinetics , Biological Availability , Cell Line, Tumor/drug effects , Chemistry Techniques, Synthetic , Dogs , Female , Half-Life , Humans , Male , Mice, Nude , Molecular Targeted Therapy , Mutation , Phenylurea Compounds/chemical synthesis , Phenylurea Compounds/pharmacokinetics , Proto-Oncogene Proteins B-raf/antagonists & inhibitors , Proto-Oncogene Proteins B-raf/metabolism , Proto-Oncogene Proteins c-raf/metabolism , Pyrimidines/chemical synthesis , Pyrimidines/pharmacokinetics , Rats, Sprague-Dawley , Structure-Activity Relationship , Xenograft Model Antitumor Assays , ras Proteins/geneticsABSTRACT
Structure-activity relationship (SAR) studies on the tricyclic isoxazole series of MRP1 modulators have resulted in the identification of potent and selective inhibitors containing cyclohexyl-based linkers. These studies ultimately identified compound 21b, which reverses drug resistance to MRP1 substrates, such as doxorubicin, in HeLa-T5 cells (EC(50)=0.093microM), while showing no inherent cytotoxicity. Additionally, 21b inhibits ATP-dependent, MRP1-mediated LTC(4) uptake into membrane vesicles prepared from the MRP1-overexpressing HeLa-T5 cells (EC(50)=0.064microM) and shows selectivity (1115-fold) against the related transporter, P-glycoprotein, in HL60/Adr and HL60/Vinc cells. Finally, when dosed in combination with the oncolytic MRP1 substrate vincristine, 21b showed tumor regression and growth delay in MRP1-overexpressing tumors in vivo.
