Effects of N1, $N^{13}\text{-}\text{Diethylnorspermine}$ (DENSPM) and X-Radiation Treatment on Human Colorectal Tumor Clones with Varying X-Radiation and Drug Responses

This study was designed to examine the effects of treatment with N1, $N^{13}\text{-}\text{diethylnorspermine}$ (DENSPM), a spermine analog, and X radiation on survival and on the polyamine and spermidine/spermine $N^{1}\text{-}\text{acetyltransferase}$ (SSAT) levels in closely related human colorectal tumor (HCT116) clones exhibiting a wide range of X-radiation and drug responses. After treatment with DENSPM and X radiation, clonogenic cell survival was measured. SSAT protein levels were measured by Western blot analysis and SSAT enzymatic activities by the conversion of $[1\text{-}{}^{14}{\rm C}]\text{acetyl}\text{-}{\rm CoA}$ into $[1\text{-}{}^{14}{\rm C}]\text{acetylspermidine}$. Polyamine [i.e. putrescine (PUT), spermine (SPM) and spermidine (SPD)] levels were measured with high-performance liquid chromatography. DENSPM enhanced the efficacy of radiation treatment in HCT116, HCT116-Clone2 (a radiation-resistant clone) and HCT116-Clone10 (a clone with similar X-radiation response as the parental HCT116 cells) but not in HCT116-CloneK (an X-radiation-sensitive but relatively drug-resistant clone). Treatment with DENSPM without X radiation caused the most significant increase in SSAT activity (∼22-fold) and an almost complete depletion of SPD levels in HCT116-CloneK. Our results suggest that (a) the lack of sensitization of X-radiation treatment by DENSPM in HCT116-CloneK was likely due to the prior depletion of SPD levels by DENSPM alone, (b) natural polyamine contents and/or inducibility of SSAT may be important factors influencing cellular response to combined X-radiation and DENSPM treatments, and (c) more importantly, there may be a potentially novel role for combining polyamine analogs such as DENSPM with X rays.