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Characterization of human cells transformed by chemical and physical carcinogens in vitro
Abstract:
Several different classes of chemical carcinogens induced the transformation of human fibroblasts grown in vitro. Characteristics of the events that occur from time of treatment through the expression of neoplastic transformation are presented. The S-phase appeared to be the portion of the cell cycle most vulnerable to insult. Staging of the cells by blocking them in G1 before releasing them to proceed through scheduled DNA synthesis (S) was required to induce reproducible transformation. Compounds such as insulin were added to the cells upon release from the block to sensitize the cells to the carcinogen that was added during S. Growth of the transformed cells as distinct from nontransformed cells was promoted by growth in medium supplemented with 8X nonessential amino acids. Carcinogen-treated cells in the early stage of transformation exhibited abnormal colony morphology and were able to grow at 41 degrees C, in air atmosphere, and in medium supplemented with only 1% serum. In addition, the transformed cells were insensitive to KB cell lysate and exhibited density independent, as well as anchorage independent, growth (i.e., growth in 0.33% agar). Cells that grew in soft agar also produced undifferentiated mesenchymal tumors in preirradiated nude mice.
Insights
Chemical carcinogens transform human fibroblasts by targeting the S-phase of the cell cycle. Optimized conditions, including insulin and specific media, enhance this neoplastic transformation, leading to tumor formation in mice.
Area of Science:
- Cell Biology
- Cancer Research
- Toxicology
Background:
- Chemical carcinogens can induce neoplastic transformation in human fibroblasts in vitro.
- Understanding the cell cycle events during transformation is crucial for cancer research.
Purpose of the Study:
- To characterize the events leading to neoplastic transformation of human fibroblasts induced by chemical carcinogens.
- To identify optimal conditions for reproducible in vitro transformation.
Main Methods:
- Human fibroblasts were treated with chemical carcinogens, with cell cycle staging (G1 block) and specific sensitization protocols (insulin).
- Transformed cells were cultured in specialized media (8X nonessential amino acids, 1% serum) and assessed for growth characteristics.
- In vivo studies involved injecting agar-cloning cells into nude mice to assess tumor formation.
Main Results:
- The S-phase of the cell cycle was identified as the most vulnerable period for carcinogen insult.
- Optimized conditions, including insulin and specific media supplements, promoted reproducible transformation.
- Transformed cells exhibited altered morphology and exhibited anchorage-independent growth in soft agar.
- Cells grown in soft agar formed undifferentiated mesenchymal tumors in vivo.
Conclusions:
- Neoplastic transformation of human fibroblasts by chemical carcinogens is reproducible under specific cell cycle and culture conditions.
- In vitro transformed cells display hallmarks of cancer, including anchorage independence and tumorigenicity in vivo.
- This model provides a platform for studying chemical carcinogenesis and developing anti-cancer strategies.