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Modulation of apoptotic response of a radiation-resistant human carcinoma by Pseudomonas exotoxin-chimeric protein
S Seetharam1, E Nodzenski, M A Beckett
1Department of Radiation and Cellular Oncology, University of Chicago Hospitals, Illinois 60637, USA.
Abstract:
Strategies to sensitize human tumors that are resistant to apoptosis have been clinically unsuccessful. We demonstrate that a structurally modified chimeric Pseudomonas exotoxin, PEdelta53L/TGF-alpha/KDEL, with binding specificity for the epidermal growth factor receptor, markedly enhances sensitivity of human xenografts to radiation killing. Exposure to PEdelta53L/TGF-alpha/KDEL decreases the apoptotic threshold through protein synthesis inhibition and simultaneous production of ceramide in tumor cells that lack functional p53 protein. In contrast, no increase in local or systemic toxicity was observed with the chimeric toxin and radiation. We conclude that biochemical targeting of the chimeric toxin and physical targeting of ionizing radiation may increase the therapeutic ratio in the treatment of human cancers with alterations of p53 expression. This strategy offers a high therapeutic potential for Pseudomonas exotoxin A chimeric proteins and irradiation.
Insights
This study shows a new chimeric toxin enhances radiation therapy for human tumors resistant to apoptosis. The toxin targets cancer cells lacking p53 protein, increasing tumor cell death without added toxicity.
Area of Science:
- Oncology
- Molecular Biology
- Biochemistry
Background:
- Clinical strategies to overcome apoptosis resistance in human tumors have faced challenges.
- Targeting apoptosis pathways is crucial for effective cancer therapy.
Purpose of the Study:
- To investigate the efficacy of a modified chimeric Pseudomonas exotoxin (PEdelta53L/TGF-alpha/KDEL) in sensitizing human tumors to radiation.
- To evaluate the safety and therapeutic potential of this combined treatment approach.
Main Methods:
- Utilized a structurally modified chimeric Pseudomonas exotoxin with specificity for the epidermal growth factor receptor.
- Administered the chimeric toxin in conjunction with radiation therapy to human xenografts.
- Assessed tumor cell apoptosis, protein synthesis, ceramide production, and local/systemic toxicity.
Main Results:
- The chimeric toxin significantly enhanced tumor sensitivity to radiation killing in human xenografts.
- Treatment reduced the apoptotic threshold in p53-deficient tumor cells via protein synthesis inhibition and ceramide production.
- No significant increase in local or systemic toxicity was observed with the combined therapy.
Conclusions:
- Combining biochemical targeting with the chimeric toxin and physical targeting with ionizing radiation can improve the therapeutic ratio for cancers with p53 alterations.
- This strategy holds high therapeutic potential for treating human cancers using Pseudomonas exotoxin A chimeric proteins and irradiation.