BI2536 has been developed as a potential therapeutic agent for various
cancers but not in
oral cancer cells. Since
BI2536 exhibits mitosis-regulating activity which are the most radiosensitive, we hypothesized that
BI2536 might modulate the radiosensitivity of
oral cancer cells. Human normal fibroblasts,
oral cancer SAS, and OECM1 cells were treated with
BI2536 (0-50 nM) and/or radiation (0-4 Gy). MTT assay, Liu's staining, flow cytometry, clonogenic assay,
Annexin V/
propidium iodide (PI) staining, western blot analysis, and
small interfering RNA knockdown experiments were used to assess cell viability, morphology, cell cycle progression, radiation survival, and expression of regulatory
proteins in vitro. Male BALB/c nude mice implanted with SAS cells were used to examine the effects of
BI2536 in vivo. Treatment with
BI2536 preferentially inhibited the viability of SAS and OECM1 cells, but not the normal fibroblasts. Morphological examination and
Annexin V/PI staining of BI2536-treated
oral cancer cells showed mitotic catastrophe and apoptosis.
A DNA histogram revealed
BI2536 induced G2/M and upregulation of phosphorylated H3 indicating accumulation in the M phase.
BI2536 modulated the expression of PLK1, cell division control
protein (Cdc)2, Cdc20, Cdc25c,
adenomatous polyposis coli 3, and
cyclin B1.
At 10 nM,
BI2536 exhibited low cytotoxicity, effectively induced mitotic catastrophe, and more importantly, sensitized
oral cancer cells to
radiotherapy. The animal study showed that
BI2536 (10 mg/kg) + radiation (2 Gy) resulted in stronger
tumor inhibition than that associated with radiation alone. Our findings showed that
BI2536 could be an effective radiosensitizer both in vitro and in vivo.