Aim: Cisplatin is the first platinum drug that shows promising anti-tumor effect clinically. Oxaliplatin, a third-generation platinum drug that incorporates a diaminocyclohexane (DACH) structural entity, can overcome cisplatin resistance. R,R-5, a novel platinum compound that integrates the DACH entity with a demethylcantharidin (DMC) component that is derived from a traditional Chinese medicine (TCM) , can also overcome cisplatin resistance. The principal objectives of this study was to investigate in detail, the effect of these compounds at the antephase and G2 checkpoints of the cell cycle, and to establish the relationship (if any) between different structural entities with checkpoint activation. The ultimate aim of the study was to ascertain the potential for the development of novel checkpoint abrogators as anti-tumor agents. / Background: A common procedure in current cancer chemotherapy is to induce genomic stress in cancer cells, leading to irreparable DNA damage and eventually cell death. However, there are several DNA repair mechanisms in cancer cells to maintain genomic stability, which require cell cycle checkpoints to stop cell proliferation for DNA damage repair, thereby avoiding errors in cellular events like DNA replication, transcription and mitosis. Among these cell cycle checkpoints, antephase and G2 checkpoints are two gate checkpoints for mitosis. Abrogation of G2 checkpoint has been reported to give rise to synergistic cytotoxic effect with DNA damaging agents, representing a means of circumventing drug resistance in chemotherapy. / Conclusions: Acute stress to cisplatin can activate the MMR/c-Abl/MEKK1/p38MAPK pathway, leading to the activation of antephase checkpoint, and stop cells from entering mitosis immediately. DACH-containing platinum compound oxaliplatin fails to activate this antephase checkpoint. However, both cisplatin and oxaliplatin can activate the G2 checkpoint, which can be abrogated by DMC. In contrast, RR-5 can bypass both the antephase and G2 checkpoints. In summary, novel TCM-platinum compound R,R-5 can bypass mitotic DNA damage checkpoints in cancer cells and thus has the potential for further development as an anti-cancer drug. / Methods: Microarray analysis was used to detect gene transcription profiles after drug treatments. The activation of mitotic checkpoints was inspected by counting mitotic cells and utilizing flow cytometry. Using Western blotting, the activation of certain key players in the antephase and G2 checkpoint was revealed. MTT assays were performed to show the outcome of checkpoint activation. / Results: In HCT116 cells, 35 genes that facilitate G2/M transition were found to be up-regulated after R,R-5 treatment compared with oxaliplatin in the microarray analysis, implying the bypass of mitotic checkpoints by R,R-5 rather than oxaliplatin. Acute stress (2 hour) of cisplatin activated the antephase checkpoint, resulting in a rapid decrease in mitotic index and phosphorylation of histone H1, which avoided mitotic catastrophe and promoted cell survival in HeLa cells. Further experiments demonstrated that this antephase checkpoint could be abrogated by c-Abl and p38MAPK inhibitors, or siRNAs against c-Abl or MEKK1, suggesting that this checkpoint may be controlled by an MMR/c-Abl/MEKK1/p38MAPK pathway. In contrast, oxaliplatin and R,R-5 did not activate this antephase checkpoint. Moreover, after 24 hour oxaliplatin treatment in HeLa cells, the mitotic index and CDK1 activity were decreased, which could be restored by concomitant treatment with ATM/ATR inhibitor and DMC. This indicated the activation of G2 checkpoint by oxaliplatin and implied that DMC can abrogate oxaliplatin-activated G2 checkpoint by restoring CDK1 activity. Cisplatin could also activate G2 checkpoint, whereas R,R-5 apparently bypassed this G2 checkpoint. / Guan, Huaji. / Adviser: Vincent Hon Leung Lee. / Source: Dissertation Abstracts International, Volume: 72-04, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references (leaves 212-249). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. Ann Arbor, MI : ProQuest Information and Learning Company, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. Ann Arbor, MI : ProQuest Information and Learning Company, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.