Validation of an immunohistochemical assay, CEACAM5 IHC 769, under development for use with the antibody-drug conjugate tusamitamab ravtansine (SAR408701).
Authors: LaPointe Nichole , Hertle Nick , Hsu Shu Chi , Kellis James , King Nita , Littrell Joshua , Nguyen Quyen , Ren Jianan , Srdanov Marko Romeo , Tanna Vaishali , Thakrar Sanchit , Zhao Tianxun , Saiz Robert , Le Bail Nathalie , Bauchet Anne-Laure , Lacoste-Bourgeacq Anne-Sophie , Chadjaa Mustapha , Ferrari Paul 
Published: June 2021

e21030 Background: Despite recent advances in non-small cell lung cancer (NSCLC) treatment, a need remains for treatment options at disease progression. Tusamitamab ravtansine (SAR408701) is an antibody-drug conjugate of a humanized CEACAM5-specific monoclonal antibody linked to the maytansinoid DM4, a potent anti-tubulin agent. In a Phase 1/2 study, tusamitamab ravtansine showed promising antitumor activity in pretreated advanced non-squamous NSCLC (NSQ NSCLC) patients with high CEACAM5 expression, defined as ≥ 50% of the tumor cells per specimen with CEACAM5 positive staining at ≥ 2+ intensity (Gazzah A et al. J Clin Oncol 2020;38[15]: 9505). Sanofi and Agilent have partnered to develop an immunohistochemical (IHC) assay, CEACAM5 IHC 769, for detection of CEACAM5 protein in formalin-fixed paraffin-embedded (FFPE) NSQ NSCLC tissue using the EnVision FLEX visualization system on Dako Omnis. This assay is in development for the assessment of patients for whom tusamitamab ravtansine is being considered. Methods: CEACAM5 IHC 769 is a qualitative IHC assay using mouse monoclonal anti-CEACAM5 clone 769. Murine anti-CEACAM5 clone 769 is based on tusamitamab ravtansine, with the same specificity as the drug for CEACAM5. The clone was developed by Sanofi and used to evaluate CEACAM5 expression in a Phase 1/2 trial. The CEACAM5 IHC 769 scoring algorithm defines positive staining as any partial or complete tumor cell plasma membrane staining at ≥ 2+ intensity. Membrane staining may be linear or punctate. Staining may appear as complete or partial staining involving the basal, lateral, or basolateral aspects of the membrane, or as apical staining of the luminal aspect of the cell. CEACAM5 IHC 769 is being validated by Agilent Technologies for NSQ NSCLC at the cutoff of ≥ 50% at ≥ 2+ intensity. Internal studies included sensitivity, specificity, intra-block heterogeneity, observer precision, laboratory repeatability/precision, and robustness. Results: Sensitivity studies demonstrated detection across a dynamic range of CEACAM5 expression. Specificity studies indicated that the antibody is specific for CEACAM5. An intra-block heterogeneity study showed good overall diagnostic agreement for sections from the same tumor (point estimate ≥ 85%). Inter- and intra-observer precision, laboratory repeatability/precision, and robustness validation studies met acceptance criteria; the lower bound of the two-sided 95% confidence interval was ≥ 85% for positive, negative, and overall percent agreement. Conclusions: Internal validation studies demonstrated that CEACAM5 IHC 769 is sensitive, specific, precise, reproducible and robust in evaluating CEACAM5 expression in NSQ NSCLC tissue at the cutoff of ≥ 50% at ≥ 2+ intensity. CEACAM5 IHC 769 is being used for patient selection/stratification in ongoing Phase 2 and 3 clinical trials of tusamitamab ravtansine.