Comparative Benefits of the Non-Human Primate in Long-Term Toxicity Studies with Iron Chelators: 12-Month Studies with Deferiprone.

Cynomolgus monkeys and rats have been the species of choice for evaluation of general toxicity during the non-clinical development of iron chelators. Each model has its advantages in safety assessment studies, although the relatively poor conservation of iron in rats and other differences in their iron handling compared with primates, including man, have raised questions about their appropriateness. It was reported that in a study in cynomolgus monkeys conducted during the early development of deferiprone, doses greater than 150 mg/kg caused deaths when given orally once daily for c. 20 days of a scheduled 3-month treatment period. We present results from a 12-month oral toxicity study of deferiprone in naive and iron-loaded cynomolgus monkeys, using twice daily dosing and compare them with findings in a similar study in rats. Cynomolgus monkeys (4–6/sex/group) and rats (20/sex/group), iron loaded by intraperitoneal injection of iron dextran, were given deferiprone as two equal daily oral doses totalling 0, 75, 150 and 200 (250 after 3 months in monkeys) mg/kg/day; naive monkeys were given 0 and 150 mg/kg/day for 12 months. Measurement of all standard parameters, including toxicokinetics, was included. No mortalities, no adverse clinical signs, and no effects on body weight gain, food intake, cardiovascular function or eye morphology, were observed in either iron-loaded or naive monkeys. Haematological and plasma chemistry parameters were largely unaffected by treatment with deferiprone; intermittent increases in serum activities of some hepatic enzymes were related to iron loading. Similarly, histopathological changes were limited to those associated with iron deposition in tissues. Plasma deferiprone concentrations achieved were significantly in excess of clinical exposures. Both naive and iron-loaded rats were less tolerant of long-term administration of deferiprone.

Both divided daily dosing and iron loading may have contributed to the markedly better survival of monkeys in the 12-month study compared with the earlier investigation, and the results of this work confirm the value of the model in the evaluation of the safety of iron chelators.