RT Journal Article SR Electronic T1 Antibody Drug Conjugates Differentiate Uptake and DNA Alkylation of Pyrrolobenzodiazepines in Tumors from Organs of Xenograft Mice JF Drug Metabolism and Disposition JO Drug Metab Dispos FD American Society for Pharmacology and Experimental Therapeutics SP 1958 OP 1962 DO 10.1124/dmd.116.073031 VO 44 IS 12 A1 Yong Ma A1 S. Cyrus Khojasteh A1 Cornelis E.C.A. Hop A1 Hans K. Erickson A1 Andrew Polson A1 Thomas H. Pillow A1 Shang-Fan Yu A1 Hong Wang A1 Peter S. Dragovich A1 Donglu Zhang YR 2016 UL http://dmd.aspetjournals.org/content/44/12/1958.abstract AB Pyrrolobenzodiazepine (PBD)-dimer is a DNA minor groove alkylator, and its CD22 THIOMAB antibody drug conjugate (ADC) demonstrated, through a disulfide linker, an efficacy in tumor reduction for more than 7 weeks with minimal body weight loss in xenograft mice after a single 0.5–1 mg/kg i.v. dose. The DNA alkylation was investigated here in tumors and healthy organs of mice to understand the sustained efficacy and tolerability. The experimental procedures included the collection of tumors and organ tissues of xenograft mice treated with the ADC followed by DNA isolation/hydrolysis/quantitation and payload recovery from reversible DNA alkylation. PBD-dimer formed a considerable amount of adducts with tissue DNA, representing approximately 98% (at 24 hours), and 99% (at 96 hours) of the total PBD-dimer in tumors, and 78–89% in liver and lung tissues, suggesting highly efficient covalent binding of the released PBD-dimer to tissue DNA. The amount of PBD-DNA adducts in tumor tissues was approximately 24-fold (at 24 hours) and 70-fold (at 96 hours) greater than the corresponding amount of adducts in liver and lung tissues. In addition, the DNA alkylation levels increased 3-fold to 4-fold from 24 to 96 hours in tumors [41/106 base pairs (bp) at 96 hours] but remained at the same level (1/106 bp) in livers and lungs. These results support the typical target-mediated cumulative uptake of ADC into tumors and payload release that offers an explanation for its sustained antitumor efficacy. In addition, the low level of DNA alkylation in normal tissues is consistent with the tolerability observed in mice.