The benzoaxines have been developed from structurally similar
chromones as specific inhibitors of the PI3K family to sensitize
cancer cells to the effects of chemotherapeutic agents; most have been shown to do this through specific inhibition of
DNA-PK and DNA repair mechanisms. In this study we examined the
benzoxazine, 2-((3-methoxybut-3en-2-yl)amino)-8methyl-4H-benzo[1,3]oxazin-4one (
LTUSI54). This compound had no
DNA-PK or PI3K inhibitory activity but still sensitized HeLa cells to the effects of
Etoposide.
LTUSI54 works synergistically with
Etoposide to inhibit growth of HeLa cells and sub G1 analysis indicates that this is not due to an increase in apoptosis.
LTUSI54 neither enhances
DSB formation due to
Etoposide nor does it delay the repair of such damage. Cell cycle analysis shows a clear G2 block with
Etoposide alone while, in combination with
LTUSI54 there is an additional S phase arrest. Phospho-
kinase analysis indicated that
LTUSI54 engages key regulators of cell cycle progression, specifically p38α, p53 and ERK 1/2. From our results we hypothesize that
LTUSI54 is promoting the cell cycle arrest through activation of p38α pathways, independent of p53 mechanisms. This results in a decrease in p53 phosphorylation and hence, restricted apoptosis. Changes in cell number appear to be the result of p38α pathways disrupting cell cycle progression, at the S and G2 checkpoints. Further investigation into the finer mechanisms by which
LTUSI54 effects cell cycle progression would be of great interest in assessing this compound as a chemosensitising agent.