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In vitro and in vivo variation in transferrin receptor expression on a human medulloblastoma cell line
1Department of Neurosurgery, University of Minnesota Hospital and Clinic, Minneapolis, USA.
Abstract:
The poor prognosis associated with pediatric central nervous system tumors such as medulloblastoma has led to the development and investigation of a variety of new treatment techniques. Therapeutic agents include targeted-toxin conjugates or immunotoxins that show significant in vitro activity against many brain tumors. Transferrin receptors (TRs) are specific, cell-surface antigens that are expressed preferentially on brain tumors rather than on normal human brain tissue. This antigen has been successfully targeted in human and nonhuman brain tumors in vitro and in vivo. In this study, when TRs were used as a target in the DAOY human medulloblastoma-derived cell line in vitro, a significant level of expression was confirmed by testing the sensitivity to different immunotoxins. To ensure the relevance of the in vitro data to the in vivo situation, we also analyzed TR expression in DAOY tumors growing in athymic mice and rats. Immunocytochemistry, immunohistochemistry, immunobead binding, immunofluorescence, 125iodine-transferrin binding, and Northern blot analysis were used to compare TR expression in DAOY cells in vitro and in vivo. All in vitro assays demonstrated significant TR expression, whereas in vivo, the TR expression was negligible in the DAOY tissue. The results caution against extrapolating in vitro antigen and receptor expression data directly to the in vivo situation. Using a transferrin-toxin conjugate in a nude rat model of leptomeningeal carcinomatosis, we achieved therapeutic efficacy, despite demonstrating reduced TR expression on tumor tissue. With respect to clinical efficacy, the reduced expression of TR on DAOY medulloblastoma in vivo may be less significant than expected because of the extreme potency of immunotoxins observed in central nervous system tumors.
Insights
Pediatric brain tumor treatments using transferrin receptor (TR)-targeted immunotoxins showed efficacy in vivo, despite lower TR expression than observed in vitro. This highlights the potent nature of immunotoxins in central nervous system tumors.
Area of Science:
- Oncology
- Neuroscience
- Pharmacology
Background:
- Pediatric central nervous system tumors, including medulloblastoma, have a poor prognosis, necessitating novel therapeutic strategies.
- Targeted-toxin conjugates, or immunotoxins, show promise against brain tumors by targeting specific cell-surface antigens like transferrin receptors (TRs).
- TRs are preferentially expressed on brain tumors compared to normal brain tissue, making them a viable therapeutic target.
Purpose of the Study:
- To investigate transferrin receptor (TR) expression in DAOY medulloblastoma cells in vitro and in vivo.
- To evaluate the therapeutic efficacy of a transferrin-toxin conjugate in a preclinical model of leptomeningeal carcinomatosis.
- To assess the relevance of in vitro TR expression data for in vivo therapeutic outcomes.
Main Methods:
- Cultured DAOY medulloblastoma cells and xenograft tumors in athymic mice/rats were analyzed for TR expression.
- Techniques included immunocytochemistry, immunohistochemistry, immunobead binding, immunofluorescence, 125iodine-transferrin binding, and Northern blot analysis.
- Therapeutic efficacy was tested using a transferrin-toxin conjugate in a nude rat model of leptomeningeal carcinomatosis.
Main Results:
- Significant TR expression was confirmed in DAOY cells in vitro across multiple assays.
- In vivo, TR expression in DAOY tumors was found to be negligible.
- Despite reduced in vivo TR expression, the transferrin-toxin conjugate demonstrated therapeutic efficacy in the leptomeningeal carcinomatosis model.
Conclusions:
- In vitro assessment of antigen and receptor expression may not accurately predict in vivo levels.
- The potent activity of immunotoxins against central nervous system tumors can overcome reduced target receptor expression.
- Transferrin receptor-targeted immunotoxins hold therapeutic potential for pediatric brain tumors, even with lower in vivo target expression.