Differences in sensitivity of monkey and human to antisense oligonucleotide (ASO)-induced alternative pathway of complement (APC) activation were evaluated in monkeys or human, and in serum using biochemical assays. Transient APC activation was evident in monkeys at higher doses of two 2′-Methoxyethyl (MOE) ASOs (ISIS 426115 and ISIS 183750). No evidence of APC activation was observed in humans for either ASO, even with the plasma Cmax for ISIS 183750 that reached the threshold for activation in monkeys. The absence of APC activation in human was consistent with a query of the Isis Clinical Safety Database containing 767 subjects from fourteen studies. The in vivo difference in sensitivity was confirmed in monkey and human serum exposed to increasing concentrations of ASO indicating that monkeys are more sensitive to APC activation with this class of compounds. The mechanistic basis for greater sensitivity of monkeys to APC activation by 2′-MOE ASO was evaluated using purified human or monkey complement Factor H (CFH) protein. The binding affinities between a representative ASO and either purified CFH are similar. However, the IC50 of fluid-phase complement inhibition for monkey CFH was about 2-3 fold greater than that for human CFH using either monkey serum or Factor H-depleted human serum. Interestingly, there is a sequence variant in monkey CFH similar to a SNP in humans that is correlated with decreased CFH function. These findings show that monkeys are more sensitive to 2′-MOE ASO mediated complement activation than humans because of differences in CFH protein interactions and inhibitory capacity.
- The American Society for Pharmacology and Experimental Therapeutics