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Methylcholanthrene-transformed AKR-2B mouse embryonal fibroblasts (AKR-MCA cells) were examined for cell surface alterations after growth in culture medium containing N,N-dimethylformamide (DMF) using the lactoperoxidase-glucose oxidase radioiodination procedure with subsequent electrophoresis. DMF has been shown to induce maturational changes in a variety of transformed cells in vitro and has been reported to produce a more normal phenotype when applied to cultured AKR-MCA cells. The electrophoretic profile of 125I-labeled surface proteins from AKR-MCA cells exhibited a prominent peak of labeled material with a molecular weight of approximately 85,000. After growth of AKR-MCA cells in medium containing DMF, the Mr 85,000 peak was substantially reduced, while there was a large increase in Mr 200,000 to 250,000 radioiodinated surface material. This cell surface labeling pattern was virtually identical to that of the nontransformed AKR-2B fibroblasts from which AKR-MCA cells were derived. The cell surface alterations observed upon exposure of AKR-MCA cells to DMF occurred as a function of time of growth in DMF and DMF concentration. Growth of AKR-MCA cells in DMF resulted in a steady increase in cell surface 125I incorporation up to the fourth day of exposure to DMF. At this time, the incorporation level was 22.9-fold greater than that for untreated AKR-MCA cells. Incorporation of radiolabel was decreased after the fifth and sixth days of AKR-MCA exposure to DMF. This trend was also manifested by AKR-2B fibroblasts grown in the presence of DMF. The data suggest that there was increased expression of the Mr 200,000 to 250,000 surface protein on both AKR-2B and AKR-MCA cells when grown in DMF. DMF also inhibited morphological transformation and the cell surface changes associated with transformation of AKR-2B cells by exogenous transforming growth factors.

Six cultured human colon cancer cell lines possessing different biological characteristics were enzymatically radiolabeled in situ with 125I and 3H, and the labeled cell surface proteins and glycoproteins were compared. The electrophoretic patterns of labeled cell surface material suggest correlations between biological properties and cell surface proteins. Highly aggressive cell lines (as assessed by in vitro parameters) had predominant peaks of 125I-labeled proteins between molecular weights 66,000 and 92,500. The major peak of radioiodinated material from the more indolent cell lines occurred between molecular weights 31,000 and 45,000. The profile of one 125I-labeled intermediately aggressive cell line was similar to the profiles of the more aggressive lines, whereas another intermediate line exhibited a profile different from those of both indolent and aggressive lines. Electrophoresis of tritiated material indicated that essentially all of the recovered labeled glycoprotein was of relatively high molecular weight (92,000-180,000) in the indolent lines, whereas the intermediate and highly aggressive lines had patterns with significant peaks between molecular weights 45,000 and 92,500.

A human colon carcinoma cell line resistant to mitomycin C (MMC) was obtained by repeated exposure of a previously described sensitive parental line, HCT 116, to MMC in vitro. Xenografts grown from the MMC-resistant phenotype were not inhibited in MMC-treated animals, while MMC treatment produced growth inhibition in parental cell xenografts. The MMC-resistant phenotype exhibited a greater amount of a Mr 148,000 cell surface protein than did the parental line. The increase in this Mr 148,000 cell surface protein correlated positively with the degree of MMC resistance. Alkaline elution of filter-bound DNA from resistant cells exposed to MMC in vitro showed a decrease in DNA cross-link formation such that a 10-fold higher MMC concentration was required to produce similar cross-link formation in the resistant cell as compared to the parental cell. The development of MMC resistance was not associated with in vitro cross-resistance to other natural product cytotoxic drugs. This model for resistance to MMC will be useful in future studies to define the mechanisms for MMC action and resistance in human colon carcinoma cells.