SKY59: A Long-Lasting Engineered Anti-C5 Antibody for Subcutaneously Injectable Anti-Complement Therapy

Modulating the complement system is a promising approach in drug discovery for overcoming uncontrolled complement activation, which is known to cause various disorders. While these disorders can be effectively treated by inhibiting complement C5 with a therapeutic antibody, the high concentration of C5 in plasma requires a huge dosage and frequent intravenous administration of the antibody. We have generated SKY59, an engineered humanized anti-C5 monoclonal antibody that shows long-lasting neutralization of C5 in cynomolgus monkeys, which enables subcutaneous delivery or less frequent administration. We found that, although the effective duration of the antibody was prolonged by engineering a pH-dependent C5 binding, it was not sufficient to achieve subcutaneous delivery with less frequent administration. Here, we further improved the effectiveness of the pH-dependent anti-C5 antibody by applying a novel approach: surface charge engineering.

Intravenous injection of 40 mg/kg CFA0322, a high affinity anti-C5 monoclonal antibody that is not pH-dependent, caused about 3-fold increase of total C5 concentration in the plasma of cynomolgus monkeys. This is because the C5-antibody immune complexes (ICs) have slower clearance than C5 alone. The increase in total C5 concentration then requires an even higher dosage of the antibody to neutralize the increased amount of C5.

To reduce the required dosage of anti-C5 antibody, pH-dependent antibodies were identified from rabbit immunization. A humanized lead antibody, 305LO1, showed a pH-dependent binding property and reduced the plasma total C5 concentration compared to CFA0322. However, we still observed an increase in total C5 plasma concentration over the baseline. We assumed that this was due to a slow uptake rate of the C5-antibody ICs into the cell. We hypothesized that the surface charges of the ICs partially contributed to the slow uptake rate.

Surface-charge engineered antibodies were generated by engineering both the variable and the constant regions. Both approaches successfully reduced the increase of plasma C5 in cynomolgus monkey and the combination of the two completely suppressed the accumulation. Interestingly, surface-charge engineering did not affect the pharmacokinetics of the antibody. The effect of surface-charge engineering on C5 reduction correlated clearly with the retention time of the C5-antibody ICs in cation exchange chromatography, indicating the contribution of positive surface charges of the ICs.

After further engineering to optimize various properties such as immunogenicity and physicochemical properties, SKY59 was successfully generated. Our surface-charge engineered pH-dependent antibody suppressed the increase of total C5 concentration in vivo by accelerating the rate of IC uptake into cells, C5 release from the antibody in endosomes, and salvage of the antigen-free antibody. Thus, SKY59 can be expected to provide significant benefits for patients with complement-mediated disorders.