Induction of micronuclei in a transplantable murine tumor after multimodality treatment with cis-platin, radiation and hyperthermia

Background: Tumor response after multimodality treatment using combination of radiation, chemotherapeutic drugs and hyperthermia usually assessed by parameters such as tumor growth delay, volume doubling time and regression response. The study herein was conducted to investigate the usefulness of micronucleus assay for assessing the multimodality treatment. Materials and Methods: The induction of micronuclei (MN) in a transplantable solid tumor grown in inbred Balb/c mice was analyzed after treating the tumors with cis-platin (cDDP), radiation (RT) and hyperthermia (HT). Results: The MN frequency in tumor was measured at 1, 3, 5 and 7 days of post-treatment. On day 1, all the cDDP and RT groups, except HT treatment produced significantly higher MN counts from that of the untreated tumors. Cis-platin treatment resulted in a dose-dependent linear increase in the frequency of MN induction on day one. Combination of radiation with cDDP or HT, as bimodality treatment further increased the MN counts. In the tri-modality group (cDDP+RT+HT) the MN counts were not significantly higher than the bi -modality treatments, however there was an immediate tumor shrinkage indicating the contribution of other forms of cell death. Although, MN counts were declined after day five post-treatment, remained significantly higher than the control on day seven-post treatment in hyperthermia alone or its combination with RT and RT+ cDDP groups. Conclusion: Micronucleus assay may be useful for assessing the post-treatment regression response of resistant tumors, while monitoring the response of sensitive tumors the parameters such as apoptosis and necrosis may also contribute considerably to tumor cell loss contributing immediate tumor regression. Iran. J. Radiat. Res., 2009 7 (3): 119-125