Besilesomab is a murine immunoglobulin of IgG1 isotype that specifically binds to NCA-95 (non specific cross-reacting antigen 95), an epitope expressed at the cell membrane of granulocytes and granulocyte precursors. Besilesomab cross-reacts with tumours expressing carcinoembryonic antigen (CEA). Besilesomab has no effect on activation of complement, granulocyte function or platelets.
At the recommended activities, it does not exert any clinically relevant pharmacodynamic effects.
Whole blood concentration-time radioactivity curves show a two-phase course, which can be subdivided into an early phase (0-2 h) and a late phase (5-24 h). After correcting for the decay of radionuclide, the calculated half-life of the early phase is 0.5 h whereas the late phase shows a half-life of elimination of 16 h.
Six hours after injection, about 1.5% of the whole body radioactivity is found in the liver whereas about 3.0% is found in the spleen. Twenty-four hours after injection, the percentages of radioactivity are 1.6% in the liver and 2.3% in the spleen.
Non pathological unusual accumulations may be observed in the spleen (up to 6% of the patients), in the bowel (up to 4% of the patients), in the liver and bone marrow (up to 3% of the patients), and in the thyroid and kidneys (up to 2% of patients).
Measurement of radioactivity levels in urine shows that up to 14% of the administered activity is excreted via the bladder during the 24 h post-injection. The low renal clearance of activity (0.2 L/h for a glomerular filtration rate around 7 L/h) indicates that the kidney is not the major route of besilesomab elimination.
Preclinical toxicity and safety studies were performed using commercial kits reconstituted with decayed technetium (99mTc) and thus the effect of radiation has not been assessed.
Preclinical data obtained with the non-radioactive compound reveal no special hazard for humans based on conventional studies of safety pharmacology, single-dose and repeated-dose toxicity, although antimurine antibodies were found in all dose groups (including controls) in a repeated-dose study in monkeys. Genotoxicity studies conducted to test for potentially genotoxic impurities were also negative. Long-term carcinogenicity studies and toxicity to reproduction have not been carried out.
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