| Summary: | 碩士 === 國立陽明大學 === 生物藥學研究所 === 101 === A series of indolizino[6,7-b]indole derivatives were designed and synthesized as hybrid molecules of β-carboline, a moiety with topoisomerase inhibitory activity, and bis(hydroxymethyl)pyrrole, a DNA cross-linking moiety. The antitumor activities of these compounds were preliminarily evaluated, and they exhibited significant cytotoxicity against a variety of human tumor cells in in vitro and in vivo models. Besides, these compounds were subjected to be evaluated for their antitumor activity against multiple drug resistant (MDR) cancer cells, and a couple of these compounds were demonstrated to have antitumor activity against MDR cancer cells as compared to their parental cells. Hence, this study aimed to screen indolizino[6,7-b]indole derivatives with selective cytotoxicity to chemoresistant cancer cells and further unravel the mechanism underlying the selective cytotoxicity. Two of indolizino[6,7-b]indole derivatives, BO-1922 and BO-1978, were selected because they were more toxic against KBvin10 and CEM/VBL (MDR cells) than their parental cell lines, KB and CCRF-CEM, respectively. In order to understand the selective toxic mechanism of indolizino[6,7-b]indoles against MDR cancer cells, KB and KBvin10 cells were used for comparative study. BO-1922 and BO-1978 were shown to cause G1 delay and G2/M arrest in KB and KBvin10 cells. The induction of cleaved-caspase-3 has been found in both cell lines after they were treated with BO-1922, indicating that BO-1922 could evoke apoptosis. Moreover, BO-1922 induced DNA double-strand breaks in both KB and KBvin10 cells in a dose-dependent manner. Intriguingly, as compared to KB cells, the attenuated Src activation was observed in KBvin10 cells under BO-1922 or BO-1978 treatment. In addition, the in vivo toxicity of BO-1922 and BO-1978 were also evaluated in ICR mice. The half lethal doses of BO-1922 and BO-1978 to ICR mice are 77.4 mg/kg and 93.7 mg/kg, respectively. The toxicity was further evaluated according to the complete blood count, blood chemistry test and histopathological examination of main organs after receiving these compounds for 48 h and 14 days, respectively. No obvious abnormality was found according to the histopathological examination and blood test results, indicating that both compounds have potential for future therapeutic application. To sum up, the in vitro screening of indolizino[6,7-b]indoles antitumor efficacy have revealed positive result. The bioactivity tests have shown that BO-1922 and BO-1978 cause cell cycle disturbance; moreover, these compounds have been found to induce the apoptosis of cancer cells, and the effect is obvious under BO-1922 treatment. The attenuated Src activation has been confirmed in KBvin10 cells, which could inspire future exploration on the role of MDR characteristic in DNA repair. The toxicity of BO-1922 and BO-1978 has been evaluated using in vivo model, although the LD50 values are restricted, BO-1922 and BO-1978 are still potential candidates for further pharmaceutical antitumor development since there is no sign of acute toxicity based on results from the present study.
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