Antibody drug conjugates (ADCs) have demonstrated clinical benefits which have led to the recent FDA approval of KADCYLA® and ADCETRIS®. Most ADCs that are currently in clinical use or development, including ADCETRIS®, are produced by chemical conjugation of a toxin via either lysine or cysteine residues, inevitably leading to heterogeneous products with variable drug-to-antibody ratios (DARs). Here, we describe the in vitro and in vivo characterization of four novel ADCs that are based on the anti-CD30 antibody cAC10, which has the same polypeptide backbone as ADCETRIS®, and compare the results with the latter. Bacterial transglutaminase (BTG) was exploited to site-specifically conjugate derivatives of monomethyl auristatin E (all comprising a cleavable linker) to the glutamines at position 295 and 297 of cAC10, thereby yielding homogeneous ADCs with a DAR of 4. In vitro cell toxicity experiments using two different CD30-positive cell lines (Karpas 299 and Raji-CD30+) revealed comparable EC50-values for ADCETRIS® (1.8±0.4 and 3.6±0.6 ng/ml, respectively) and the four cAC10-based ADCs (2.0±0.4 to 4.9±1.0 ng/ml). Quantitative time-dependent in vivo biodistribution studies (3-96 h p.i.) in normal and xenografted (Karpas 299 cells) SCID mice were performed with a selected 125I-radioiodinated cAC10 ADC and compared with 125I-ADCETRIS®. The chemo-enzymatically conjugated, radioiodinated ADC showed higher tumor uptake (17.84±2.2 %ID/g 24 h p.i.) than 125I-ADCETRIS® (10.5± 1.8 %ID/g 24 h p.i.). Moreover, 125I-ADCETRIS® exhibited higher non-targeted liver and spleen uptakes. In line with these results, the maximum tolerated dose of the BTG-coupled ADC (&gt; 60 mg/kg) was significantly higher than that of ADCETRIS® (18 mg/kg) in rats. These results suggest that homogenous ADCs display improved pharmacokinetics and better therapeutic indexes compared to chemically modified ADCs with variable DARs.

Site-specific conjugation of monomethyl auristatin E to anti-CD30 antibodies improves their pharmacokinetics and therapeutic index in rodent models

251st National Meeting (2016)

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