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 >3 muM 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.