Characterization of Novel Diaryl Oxazole-Based Compounds as Potential Agents to Treat Pancreatic Cancer

Abstract

A series of diaryl-and fluorenone-based analogs of the lead compound UA-62784 [4-(5-(4-methoxyphenyl)oxazol-2-yl)-9H-fluoren-9-one] was synthesized with the intention of improving upon the selective cytotoxicity of UA-62784 against human pancreatic cancer cell lines with a deletion of the tumor suppressor gene deleted in pancreas cancer locus 4 (DPC-4, SMAD-4). Over 80 analogs were synthesized and tested for antitumor activity against pancreatic cancer (PC) cell lines (the PC series). Despite a structural relationship to UA-62784, which inhibits the mitotic kinesin centromere protein E (CENP-E), none of the analogs was selective for DPC-4-deleted pancreatic cancer cell lines. Furthermore, none of the analogs was a potent or selective inhibitor of four different mitotic kinesins (mitotic kinesin-5, CENP-E, mitotic kinesin-like protein-1, and mitotic centromere-associated kinesin). Therefore, other potential mechanisms of action were evaluated. A diaryl oxazole lead analog from this series, PC-046 [5-(4-methoxyphenyl)-2-(3-(3-methoxyphenyl)pyridin-4-yl) oxazole], was shown to potently inhibit several protein kinases that are overexpressed in human pancreatic cancers, including tyrosine receptor kinase B, interleukin-1 receptor-associated kinase-4, and proto-oncogene Pim-1. Cells exposed to PC-046 exhibit a cell cycle block in the S-phase followed by apoptotic death and necrosis. PC-046 effectively reduced MiaPaca-2 tumor growth in severe combined immunodeficiency mice by 80% compared with untreated controls. The plasma half-life was 7.5 h, and cytotoxic drug concentrations of Ͼ3 M were achieved in vivo in mice. The diaryl oxazole series of compounds represent a new chemical class of anticancer agents that inhibit several types of cancer-relevant protein kinases.Pancreatic cancer is the fourth leading cause of death from cancer in North America (Jemal et al., 2008). There are two agents approved in the United States for the treatment of metastatic pancreas cancer: 1) the cytidine analog gemcitabine and 2) the epidermal growth factor receptor inhibitor erlotinib (Tarceva) (Burris and Rocha-Lima, 2008). Neither drug alone or in combination is curative, and only incremental improvements in survival are produced by these agents (Burris and Rocha-Lima, 2008). Whereas many other anticancer agents have been explored in the treatment of metastatic pancreatic cancer, none has yet proven to be effective. Thus, new agents with novel mechanisms of action are needed to treat metastatic pancreatic adenocarcinoma, which is the most commonly diagnosed stage of this disease.The original intent of the chemistry campaign in this project was to develop analogs of a lead molecule UA-62784 that had showed modest selectivity for human pancreatic cancer cells with the deleted in pancreas cancer locus 4 (DPC-4) gene deletion (Henderson et al., 2009). The DPC-4 deletion interrupts tumor suppression mediated by transforming growth factor-␤ signaling (Jones et al., 2008), and more than half of pancreatic cancers have DPC-4 deletions (...

Mechanisms of Chromosome Congression during Mitosis

“…However, a subsequent study demonstrated that this compound does not exert its cellular activity by inhibiting CENP-E and rather binds microtubules tightly [461,462]. Another study that tested the antitumor activity of UA62784 and 80 analogs against pancreatic cancer cell lines revealed that these compounds potently inhibit several protein kinases that are overexpressed in these cancer cells, but not mitotic Kinesins (Kinesin-5, CENP-E, MKLP-1, and MCAK) [463]. Another compound, Syntelin, was also reported to be a highly selective CENP-E inhibitor [464].…”

The diaryl oxazole PC-046 is a tubulin-binding agent with experimental anti-tumor efficacy in hematologic cancers

“…The synthesis of PC-046 is reported elsewhere [3]. For in vitro studies, PC-046 stock is prepared in DMSO and subsequently diluted into aqueous media at a final working concentration of less than 0.1% DMSO.…”

“…Pharmacokinetics of a single 100 mg/kg dose of PC-046 in non-tumor bearing SCID mice was analyzed by reversed phase chromatography and tandem mass spectrometry [3]. PC-046 was administered intravenously (IV), intraperitoneally (IP) or orally (PO) to compare bioavailability of different routes of administration.…”

“…This analog was quite potent in vitro but produced only a 1.7-fold selectivity for inhibiting growth of the DPC4 (-/-) BxPC3 pancreatic cancer cell line compared to the DPC4 (+/+) isogenic cell line. PC-046 was active in SCID mice bearing flank tumor xenografts of the human MiaPaCa-2 pancreatic cancer cell line [3]. Mechanistically, PC-046 was shown to inhibit several cancer-relevant kinases in vitro , including TRK-B, PDGF-alpha and -beta, and FLT-1 at pharmacologically-achievable concentrations.…”

Recent Advances of Kinesin Motor Inhibitors and their Clinical Progress

“…AS-2 is a nonspecific kinesin inhibitor targeting several superfamily members including KHC, MPP1, MKLP1, RabK6, KIFC1, KIFC3, CENP-E, and Eg5 [64]. UA62784 has been reported to induce mitotic arrest and apoptosis in pancreatic carcinoma cell lines with high potency [65]. Initially, Henderson and co-workers described that UA62784, a fluorenone small molecule inhibits directly CENP-E microtubule-associated ATPase activity.…”