Abstract CT211: IMMU-130, an SN-38 antibody-drug conjugate (ADC) targeting CEACAM5, is therapeutically active in metastatic colorectal cancer (mCRC): Initial clinical results of two Phase I studies

Abstract IMMU-130, an ADC of the active metabolite of CPT-11, SN-38, conjugated by a pH-sensitive linker (7.6 average drug-antibody ratio) to the humanized anti-CEACAM5 antibody (labetuzumab), is completing two Phase I trials. In both, eligible patients with advanced mCRC were required to have failed/relapsed standard treatments, one being the topoisomerase-I inhibiting drug, CPT-11 (irinotecan), and an elevated plasma CEA (>5 ng/mL). IMMU-130 was administered every 14 days (EOW) at doses starting from 2.0 mg/kg in the first protocol (IMMU-130-01). Febrile neutropenia occurred in 2 of 3 patients at 24 mg/kg; otherwise at ≤16 mg/kg, neutropenia (≥ Grade 2) was observed in 7 patients, with one also experiencing thrombocytopenia. One patient [of 8 who received > 4 doses (2 cycles)] showed a 40.6% decrease in liver (starting at 7 cm) and lung target lesions (PR by RECIST) for 4.7 months, with no major toxicity, tolerating a total of 18 doses at 16 mg/kg. The study is continuing at 12 mg/kg EOW. Since SN-38 is most effective in S-phase cells, a more protracted exposure could improve efficacy. Thus, in a second Phase I trial (IMMU-130-02), dosing was intensified to twice-weekly, starting at 6 mg/kg/dose for 2 weeks (4 doses) with 1 week off, as a treatment cycle, in a 3+3 trial design. Neutropenia and manageable diarrhea were the major side effects, until dose reduction to 4.0 mg/kg twice-weekly, with early results indicating multiple cycles are well-tolerated. Currently, tumor shrinkage occurred in 3 patients, with 1 in continuing PR (-46%) by RECIST, among 6 patients who completed >4 doses (1 cycle). In both trials, CEA blood titers correlated with tumor response, and high levels did not interfere with therapy. There have been no anti-antibody or anti-SN-38 antibody reactions, based on ELISA tests. In each study, the ADC was cleared by 50% within the first 24 h, which is much longer exposure than with typical doses of the parental molecule, CPT-11. These results indicate that this novel ADC, given in different regimens averaging ∼16-24 mg/kg/cycle, shows therapeutic activity in advanced mCRC patients. Since CEACAM5 has elevated expression in breast and lung cancers, as well as other epithelial tumors, it may be a useful target in other cancers as well. A Phase II trial evaluating twice-weekly dosing and a new regimen, once-weekly x 2 every 21 days, is ongoing in mCRC. Citation Format: Neil H. Segal, Efrat Dotan, Jordan D. Berlin, Alexander N. Starodub, Michael J. Guarino, Leonard B. Saltz, Pius P. Maliakal, Serengulam V. Govindan, William A. Wegener, Robert M. Sharkey, David M. Goldenberg. IMMU-130, an SN-38 antibody-drug conjugate (ADC) targeting CEACAM5, is therapeutically active in metastatic colorectal cancer (mCRC): Initial clinical results of two Phase I studies. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr CT211. doi:10.1158/1538-7445.AM2014-CT211