Abstract:
Increasing burden of breast cancer in Pakistan demands population based therapeutic
research. For basic cancer research, cancer cell lines are used as model system all over the world.
We developed four Primary cell lines of Pakistani origin; derived from invasive ductal
carcinomas. The cell lines differ with respect to expression of K-RAS and status of DNA
damage. We targeted two key players of non-homologous end joining pathway (NHEJP); DNA
PKcs and artemis to evaluate their role in radiotherapy of breast cancers. We propose that repair
mechanism is activated at a higher dose of radiations hence lower dose of radiation, that did not
trigger the repair mechanism is more lethal for cancer cells. Our results clearly indicate that the
ionizing radiation induced DNA damage is repaired mainly by NHEJP as inhibition of key
regulator of NHEJP makes the cell deficient of DNA damage repair and resulted in accumulation
of DNA damage following IR. We recommend the development of radiosensitizers from
inhibitors of artemis and DNA PKcs as these inhibitors increase the cancer cell lethality when
coupled with IR. DNAPKcs inhibitor (NU7026) lowers cell viability by up to 50% at 4Gy of
radiation dose and 10μM concentration. We used 2-hydroxy-5-methoxybenzaldehyde 4-anilino 6-(3,5-dimethyl-H-pyrazol--yl)-,3,5-triazin-2-ylhydrazone for inhibition of artemis and our
findings suggest the role of artemis in cell cycle arrest/apoptosis that is independent of DNA
damage repair following IR. DNAPKcs inhibition resulted in defects in repair pathway while the
novel artemis inhibitor does not show such effect while inhibition of artemis followed by IR
caused increased cell killing at low dose of radiation as compared to DNA PKcs. To minimize
the side effects of radiotherapy and achieve better therapeutic ratio such radiosensitizers are a
need of the hour that target cell cycle check points instead of DNA damage repair pathways of
the cells when used as chemotherapeutic drugs.
