Antibody-drug conjugates (ADC) contain targeted antibodies with effective small molecule payloads. The ADC is produced against different receptors on the anaplastic large cell lymphoma L-82 line, but delivers the same cytotoxic payload (monomethyl auristatin E, MMAE). ADC-mediated cytotoxicity is not related to target expression or drug: antibody ratio. LC-MS was used to measure the concentration of MMAE in the L-82 tumor parallel cohort by the same treatment protocol. Although there was no difference in tumor volume between the treatment groups 3 days after administration, intratumoral MMAE measurements showed two patterns. First, the MMAE concentration in the tumor increases in proportion to the ADC dose, which corresponds to stronger antitumor activity. Second, intra-tumor MMAE concentrations obtained after treatment with cOKT9-vcMMAE and cAC10-vcMMAE were similar at each dose, which is consistent with the observation that tumors responded similarly to these two ADCs.

In tumor xenograft models, the MMAE concentration in the tumor is always correlated with the degree of tumor growth inhibition. IHC analysis showed that tumors that were not combined with control treatment consisted of CD30 + and CD30 cells, presumably because they did not kill CD30 + or CD30- Karpas 299 cells. Only CD30-cells were found in tumors treated with cAC10-vcMMAF, indicating that cAC10-vcMMAF eliminated most CD30 + cells. Interestingly, at the end of the study, two tumors recurring from the treatment of cAC10-vcMMAE were also found to be CD30-, indicating that in the remaining two tumors, a small portion of CD30-cells may have escaped bystanders Kill.