A new screening model for safety evaluation of superantigen-antibody recombinant fusion proteins (mAb Fab-SEA/E) using telemetric monitoring in conscious rabbits.
BACKGROUND
Carcinoma recognising monoclonal antibodies (mAb) and mutated forms of the T-cell-activating bacterial staphylococcal enterotoxin A/E (SEA/E) have been combined in single hybrid constructs (mAb Fab-SEA/E). By introducing substitutions in an MHC class II binding site, these harmful toxins can be converted into tolerable immunotoxins. Rabbits and humans are sensitive to SE toxins, and cardiovascular effects in rabbits are similar to those seen in septic shock in man. A new screening model using telemetry in conscious rabbits was applied in the safety evaluation of different mAb Fab-SEA/E constructs administered intravenously.


METHODS
Telemetry transmitters were implanted in the peritoneal cavity of animals with a pressure catheter in the aorta and electrodes for ECG recording subcutaneously following administration of mAb Fab-SEA/E constructs intravenously.


RESULTS
The responses in body temperature, heart rate, and blood pressure varied depending on the treatment regimen and the mutations of the drug given. For example, 25 micro g/kg of C215 Fab-SEAmut9 were given as a first treatment cycle on days 1, 5, and 7 and as a second treatment cycle on days 13-15. The first dose induced high fever, whereas the second and third doses induced fever responses more rapidly and were of lower and shorter duration. The second treatment cycle, starting on day 13, did not induce any responses probably due to anti-SEA antibodies formed because of the treatment. Another construct, 5T4 Fab-SEA/E-11 at 50 micro g/kg, induced a similar response as C215 Fab-SEAmut9 on days 1, 5, and 7. In this case, the pharmacologic response was still present on days 13-15, though no clinical signs developed or no formation of anti-SEA antibodies occurred. When 50 micro g/kg of 5T4 Fab-SEA/E-11 was administered once daily for 4 days, body temperature after the first dose increased slowly during the first 24 h, whereas the second to fourth doses induced more rapid and higher responses. The fourth dose of another compound, K305 Fab-SEA/E-11 (50 micro g/kg), induced an even more pronounced response both in magnitude and in duration as well as in adverse clinical signs.


CONCLUSIONS
By using continuous telemetric registration in the rabbit as a tool in superantigen-antibody (mAb Fab-SEA/E) drug selection, it has been possible to evaluate the dynamics of drug-induced immune effects (fever) and concomitant engagement of the cardiovascular system, conditions that are essential before clinical trials can be initiated.
Toxicology Division, National Food Administration, Uppsala, Sweden. ngil@slv.se
Nils-Gunnar
NG
Ilbäck
Robert
R
Persson
Kjell
K
Gunnarsson
Torbjörn
T
Stålhandske
D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D001831:Body Temperature / Q000187:drug effects; D004353:Drug Evaluation, Preclinical / Q000295:instrumentation* / Q000379:methods*; D004562:Electrocardiography / Q000295:instrumentation; D006339:Heart Rate / Q000187:drug effects; D000922:Immunotoxins / Q000493:pharmacokinetics / Q000633:toxicity*; D007275:Injections, Intravenous; D008297:Male; D011817:Rabbits; D011994:Recombinant Proteins / Q000493:pharmacokinetics / Q000633:toxicity; D018089:Superantigens / Q000633:toxicity*; D013686:Telemetry / Q000295:instrumentation* / Q000379:methods*
D000922:Immunotoxins; D011994:Recombinant Proteins; D018089:Superantigens