Labetuzumab govitecan (IMMU-130), an
antibody-drug conjugate (ADC) with an average of 7.6
SN-38/
IgG, was evaluated for its potential to enhance delivery of
SN-38 to human colonic
tumor xenografts. Mice bearing LS174T or GW-39 human colonic
tumor xenografts were injected with
irinotecan or
IMMU-130 (
SN-38 equivalents ∼500 or ∼16 μg, respectively). Serum and homogenates of
tumors, liver, and small intestine were extracted, and
SN-38,
SN-38G (glucuronidated SN-38), and
irinotecan concentrations determined by reversed-phase HPLC.
Irinotecan cleared quickly from serum, with only 1% to 2% injected dose/mL after 5 minutes; overall, approximately 20% was converted to
SN-38 and
SN-38G. At 1 hour with
IMMU-130, 45% to 63% injected dose/mL of the
SN-38 was in the serum, with >90% bound to the ADC over 3 days, and with low levels of
SN-38G. Total
SN-38 levels decreased more quickly than the
IgG, confirming a gradual
SN-38 release from the ADC. AUC analysis found that
SN-38 levels were approximately 11- and 16-fold higher in LS174T and GW-39
tumors, respectively, in IMMU-130-treated animals. This delivery advantage is amplified >30-fold when normalized to
SN-38 equivalents injected for each product. Levels of
SN-38 and
SN-38G were appreciably lower in the liver and small intestinal contents in animals given
IMMU-130. On the basis of the
SN-38 equivalents administered,
IMMU-130 potentially delivers >300-fold more
SN-38 to CEA-producing
tumors compared with
irinotecan, while also reducing levels of
SN-38 and
SN-38G in normal tissues. These observations are consistent with preclinical and clinical data showing efficacy and improved safety. Mol
Cancer Ther; 17(1); 196-203. ©2017 AACR.