COMPARISON OF THE CCNU AND BCNU MODIFICATION OF THE INVITRO RADIATION RESPONSE IN 9L BRAIN-TUMOR CELLS OF RATS

Rat brain tumor cells (9L) were exposed for 1 hr to combinations of 1,3-bis(2-chloroethyl)-l-nitrosourea (BCNU, 3 μg/ml) or 1-(2-chloroethyl)-3-cyclohexyl-l-nitrosourea (CCNU, 3 μg/ml) and graded doses of radiation (0-20 Gy). BCNU significantly modified the shoulder of the X-ray survival curve, especially when given 15 hr before irradiation. CCNU modified the shoulder of the X-ray curve to a lesser extent than an equivalent concentration of BCNU. Dose enhancement ratios (DER's) in the shoulder region for time intervals from 5-23 hr were larger for the BCNU-radiation combination than for the CCNU-radiation combination. At all other time intervals studied, DER's in the shoulder region for the BCNU-radiation combination were at least as large as those obtained for the CCNU-radiation combination. These results suggest that BCNU-radiation protocols may elicit a better clinical response than CCNU-radiation protocols. © 1979.