Inhibition of Polyamine Synthesis Suppresses Growth and γ-Ray-Induced Sublethal and Potentially Lethal Damage Recovery in Human Tumor Cells in Culture

Polyamines are ubiquitous polycations that interact with negatively charged macromolecules, including DNA. Since DNA is a target for radiation damage, we tested the hypothesis that radiation survival responses are polyamine‐dependent in cells derived from human tumors arising at different sites (lung [A549], cervix [HeLa], and brain [D54 and U251]). Untreated cultures displayed different growth rates (HeLa ≈ A549 > D54 > U251). Treatment with the specific ornithine decarboxylase inhibitor α‐difluoro‐methylornithine (DFMO) for 2 days or more suppressed putrescine and spermidine contents in all four cell lines. DFMO inhibited growth of each line, but to varying degrees (U251 > HeLa ≈ A549 > D54). Polyamine depletion generally suppressed γ‐ray‐induced sublethal and potentially lethal damage recovery. The degree of suppression of these recovery processes varied among cell lines (D54 > A549 ≈ HeLa > U251), which correlated inversely with the ability of DFMO to suppress cell growth. These data suggest that agents such as DFMO, which suppress polyamine contents, may be useful adjuvants to radiation therapy by inhibiting either radiation recovery processes or cell proliferation, or both, during fractionated radiotherapy schedules. © 1993 Wiley‐Liss, Inc.