IN-VIVO TUMOR MEASUREMENT OF DNA-DAMAGE, DNA-REPAIR AND NAD POOLS AS INDICATORS OF RADIOSENSITIZATION BY METOCLOPRAMIDE

Metoclopramide (MCA), a N-substituted benzamide, causes DNA strand bre aks and inhibits DNA repair in vitro and sensitizes radiation and chem otherapeutic drugs in human squamous cell carcinomas when xenographed into nude mice or in a rat glioma model, Here we report on the evaluat ion of the mechanism behind the radiosensitizing effects of MCA, DNA d amage was measured in vivo in a CBA-mouse tumor line (A12B3, sarcoma t umor) by using both alkaline elution and nucleoid sedimentation analys is of cell suspensions prepared from either resected tumor, spleen tis sues or whole blood samples, The amount of DNA damage caused by radiat ion alone, measured 30 min after the irradiation was started, was dose dependent up to 18 Gy in all tissues, The radiation-induced DNA damag e in tumor tissue was elevated compared to radiation alone in the pres ence of MCA, but the level was not higher at 18 Gy compared to 6 Gy. T he DNA repair was delayed after irradiation of 18 Gy in the presence o f MCA, and it was still not fully repaired 12 h after irradiation, HPL C analysis of the NAD pools in tumor tissue after DNA damage induction showed a delay in the recovery of the NAD pools (presumably due to th e presence of still unrepaired DNA) after exposure to MCA (2 mg/kg) radiation (6 Gy) compared to tumors exposed to radiation (6 Gy) only, which were fully restored after 48 h, These data confirm earlier-publi shed in vitro data on MCA as an inducer of DNA damage and an effector of DNA repair, In addition, the in vivo measurement of radiation-induc ed DNA damage and DNA repair using the nucleoid sedimentation and alka line elution assays together with NAD pool determinations may prove to be effective intermediate endpoints in the evaluation of drugs as pot ential radiosensitizers.