Microtubules are a proven target for anticancer drug development because they are critical for mitotic spindle formation and the separation of chromosomes at mitosis. Quinazolinone alkaloids are the active components contained in the plants of Rutaceae. Many investigators have indicated that quinazolinones have anti-tumor activity. However, the reasons why the molecular mechanisms of quinazolinones produced their biological effects remain unknown. In our study, the screening test for anti-tumor activity of quinazolinone derivatives has demonstrated that HL66 displayed anti-proliferation in several cancer cell types, especially for skin cancer M21 cells. We here report a novel synthetic anti-microtubule agent 2-(naphthalene-1-yl)-6-pyrrolidinyl-4-quinazolinone (HL66), a quinazolinone analog. The data presented in this report show that the HL66-induced cell death in M21 cells that was resistant to apoptosis, we identified mitotic catastrophe with characteristics of abnormal chromosome segregation, irregular nuclei and large cells with multiple micronuclei. We also demonstrate that HL66 is a tubulin-destabilizing agent and causes cell cycle arrest at S and G2/M phase. In addition, HL66-induced M21 cell mitotic catastrophe was caspase-independent and accompanied by the phosphorylation of Bcl-2 and translocation of cyclin B1 to nucleus. Results demonstrated that HL66 inhibits the dephosphorylation on Thr14 or Tyr15 of Cdk1 and the formation of Cdk1/cyclin B1 complex, leading to the failure of the progression of cell cycle from prophase to metaphase. Furthermore, our data show that the aberrant expression of the cell cycle regulatory molecules of G1/S (cyclin D1/Cdk4; cyclin A or E/Cdk2) and G2/M (Cdk1/cyclin B1) phase may lead to abnormal cell cycle during HL66-induced M21 cell mitotic catastrophe. Taken together, these results describe a novel pharmacological property of HL66 as a microtubule inhibitor, which may make it an attractive new agent for treatment of cancer.
