DIFFERENTIAL RESPONSES TO X-IRRADIATION OF SUB-POPULATIONS OF 2 HETEROGENEOUS HUMAN CARCINOMAS INVITRO

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  • 1 January 1982
    • journal article
    • research article
    • Vol. 42  (7) , 2556-2561
Abstract
The responses of 2 heterogeneous human cancer cell lines and their derivative clones to graded single doses of X-rays were examined in vitro. One system consisted of the human colon carcinoma line DLD-1 and 2 subpopulations (clones A and D). The 2nd system consisted of the human lung carcinoma line (LX1) and 4 subpopulations (LX1-1, LX1-2, LX1-3 and LX1-9). These subpopulations are markedly heterogeneous in karyotype, morphology, drug sensitivity, tumorigenicity and expression of membrane glycoproteins (such as carcinoembryonic antigen and tumor colonic mucoprotein antigen). Exponentially growing cultures were irradiated with graded single doses of 100-kVp X-rays. Survival was assessed using colony formation as the end point, and responses from multiple experiments were fitted to the single-hit, multitarget equation of cell survival. Values for the mean lethal dose (Do, grays), quasithreshold dose (Dq, grays) and extrapolation number (n) were obtained. For the human colon adenocarcinoma system, these values for the 3 tumor lines were: DLD-1, 0.95, 2.34 and 11.7; clone A, 1.06, 2.23 and 8.20; and clone D, 1.08, 1.89 and 5.80. For the human lung carcinoma system, these values for the 5 sublines were: LX1, 1.14, 0.19 and 1.20; LX1-1, 0.96, 2.06 and 8.54; LX1-2, 0.96, 0.88 and 2.48; LX1-3, 0.68, 2.05 and 20.3; and LX1-9, 1.12. 0.00 and 1.00. These 2 human tumor systems therefore exhibit variability in their intrinsic sensitivity to X-irradiation. Failure of some human carcinomas to respond to physical treatment modalities can be due to preexisting resistant subpopulations.