These data provide evidence that irradiated hEPCs can induce strong bystander killing in A549 and MIA PaCa-2 cancer cells that is mediated by TNF-α and TGF-β.
William T. Turchan, BS, Ronald H. Shapiro, MD, Garret V. Sevigny, BS, Helen Chin-Sinex, BS, Benjamin Pruden, MD, Marc S. Mendonca, PhD; Indiana University School of Medicine
BACKGROUND: Using A549 tumor xenographs, we found that coinjection of CBM3 human endothelial progenitor cells (hEPCs) with A549 non–small-cell lung cancer (NSCLC) cells significantly increased the tumor growth rate compared with A549 cells alone but, paradoxically, also increased A549 tumor cure after a single 5-Gy dose of x-rays (P < .05). We hypothesized that irradiated hEPCs may be inducing bystander killing in A549 cancer cells in tumor xenographs, thus improving tumor cure.
METHODS: Using dual-chamber Transwell dishes, we tested whether medium from irradiated CBM3 and CBM4 hEPCs would induce bystander cell killing in A549 NSCLC cells and, as an additional control, in MIA PaCa-2 human pancreatic cancer cells. The CBM3 and CBM4 hEPCs were plated into the upper Transwell chamber, and the A549 or MIA PaCa-2 cells were plated in the lower Transwell chamber. The top inserts with the CBM3 or CBM4 hEPCs were subsequently removed, irradiated, and then placed back into the Transwell dish for 3 hours to allow for diffusion of any potential bystander factors from the irradiated hEPCs in the upper chamber through the permeable membrane to the unirradiated cancer cells in the lower chamber. After the 3-hour incubation, the cancer cells were replated for clonogenic survival.
RESULTS: The data clearly showed that exposure to the medium from irradiated CBM3 and CBM4 hEPCs induced significant bystander killing and decreased the surviving fraction of A549 and MIA PaCa-2 cells to 0.46 (46%) ± 0.22 and 0.74 ± 0.07 (74%), respectively (P < .005 and P < .0001). Moreover, antibody depletion studies demonstrated that the bystander killing that was induced in both A549 and MIA PaCa-2 cells was mediated by the cytokines TNF-Î± and TGF-Î² (P < .05).
CONCLUSION: These data provide evidence that irradiated hEPCs can induce strong bystander killing in A549 and MIA PaCa-2 cancer cells that is mediated by TNF-Î± and TGF-Î².
Proceedings of the 98th Annual Meeting of the American Radium Society -americanradiumsociety.org