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Anti-prostate immunotoxins: cytotoxicity of E4 antibody-Pseudomonas exotoxin constructs
1Laboratory of Molecular Biology, Division of Basic Sciences, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA.
Abstract:
E4 is a monoclonal antibody (MAb) that reacts with a surface antigen present on normal prostate and prostate cancers. Using this antibody, 2 immunotoxins were generated, one being a chemical conjugate with a mutant truncated form of Pseudomonas exotoxin A (PE), E4-PE35KDEL. The other is a recombinant single chain immunotoxin, E4(Fv)-PE38KDEL. The affinity of the conjugated immunotoxin was similar to the hybridoma-produced MAb E4, revealing that conjugation did not impair the binding ability. The affinity of the recombinant immunotoxin (10 nM) was 10-fold lower than that of the MAb, probably reflecting differences of bivalent (MAb) vs. monovalent (Fv) binding. Antigen positive prostate, breast and colon carcinoma cell lines showed cytotoxic response to the E4 immunotoxins while antigen negative cells were not affected. The IC50 value, representing a 50% inhibition of cellular protein synthesis, ranged from 0.3 to 20 ng/ml for E4-PE35KDEL and from 2 to 100 ng/ml for E4(Fv)-PE38KDEL. Therefore, the E4-derived immunotoxins may be useful for the treatment of prostate as well as breast and colon cancers.
Insights
E4 immunotoxins targeting prostate cancer antigens show potent cytotoxicity against cancer cells. These novel agents demonstrate potential for treating prostate, breast, and colon cancers.
Area of Science:
- Immunology
- Oncology
- Biochemistry
Background:
- Monoclonal antibody E4 targets a surface antigen on normal and cancerous prostate cells.
- Immunotoxins combine antibody-mediated targeting with cytotoxic payloads for cancer therapy.
Purpose of the Study:
- To develop and characterize E4-based immunotoxins for cancer treatment.
- To evaluate the binding affinity and cytotoxic activity of E4 immunotoxins against various cancer cell lines.
Main Methods:
- Generation of two E4 immunotoxins: E4-PE35KDEL (chemical conjugate) and E4(Fv)-PE38KDEL (recombinant single chain).
- Assessment of antibody-antigen binding affinity using techniques like surface plasmon resonance.
- Evaluation of in vitro cytotoxicity against antigen-positive and antigen-negative cancer cell lines by measuring inhibition of protein synthesis (IC50 values).
Main Results:
- Both E4 immunotoxins retained binding affinity to the target antigen.
- E4 immunotoxins exhibited significant cytotoxic effects on antigen-positive prostate, breast, and colon carcinoma cell lines.
- Antigen-negative cell lines were unaffected, indicating target specificity.
- IC50 values ranged from 0.3 to 100 ng/ml, demonstrating potent cytotoxic activity.
Conclusions:
- E4-derived immunotoxins are effective in targeting and killing cancer cells expressing the E4 antigen.
- These immunotoxins hold promise as a therapeutic strategy for prostate, breast, and colon cancers.