Exploring the chemosensitising effects of novel 2-amino (substituted)-1,3-benz- or napth-oxazines

Chemotherapy of cancer often employs compounds which cause double-stranded DNA breaks (DSBs). Such damage is particular difficult for the cell to repair and ideally leads to cell death by apoptosis following cell cycle arrest and unsuccessful repair. Consequently, any inhibition of the repair pathways involved in DSB repair should increase the effectiveness of these therapies and there is much interest in finding effective inhibitors. This study investigates a family of novel benz- or napth-oxazines for their ability to inhibit the PI3K family of enzymes including the related DNA-PK, a key enzyme involved in DSB break repair. Earlier studies by other groups with the related chromones such as LY294002 produced promising results as radio- and chemosensitisers. While three of our four compounds investigated showed some inhibitory activity against DNA-PK they showed little sensitising effect in combination with etoposide, doxorubicin, daunorubicin and bleomycin, all known to cause DSBs. Paradoxically, the compound with the least DNA-PK inhibitory activity, 2-((3-methoxybut-3en-2-yl)amino)-8methyl-4Hbenzo[1,3]oxazin-4-one (LTUSI54), had a marked sensitising effect when used in combination with these drugs. Similar sensitisation was noted in the treatment of both HCT116 and HeLa cells. Results obtained revealed that the inhibition of tumour growth was neither due to increased cell death nor the inhibition of etoposide-induced DSB repair. Cell cycle analysis of Hela cells treated with both etoposide and LTUSI54 identified cell cycle arrest in S and G2 phases of the cycle. Hence, this thesis identifies a compound which sensitises tumour cells to the effects of etoposide through a novel mechanism.

Submission note: A thesis submitted in total fulfilment of the requirements for the degree of Doctor of Philosophy to the Institute of Molecular Science, Faculty of Science, Technology and Engineering, La Trobe University, Bendigo.