Abstract A37: Development of biologics targeting soluble ligands: Novel biomarker and PK-PD analyzes examining free and total ligand profile following treatment with carlumab (anti-CCL2 mAb).
Authors: Seetharam Shobha , Puchalski Thomas A. , McIntosh Thomas , Chaturvedi Shalini , Dawkins Fitzroy , Elsayed Yusri , Tolcher Anthony W. , Pienta Kenneth J. , de Bono Johann S. , Takimoto Chris H. 
Published: June 2012

Abstract
Background: Despite the large numbers of antibodies targeting soluble ligands in development in oncology and other therapeutic areas, very few reports have described pharmacodynamic (PD)/ mechanism of action (MOA) biomarkers of free ligand or total (antibody-complexed) ligand and their PK-PD relationship. Carlumab is a human IgG1 monoclonal antibody that binds the chemokine CCL2, which is a potent chemoattractant for tumor associated macrophages and promotes tumor growth and metastasis. Therapeutic targeting of CCL2 was based on the hypothesis that carlumab binding would inhibit chemokine activity and block tumor inflammation and macrophage differentiation thereby impairing tumor growth and metastases. Because proof of concept (POC) is a major milestone in early drug development, the objective of this study was to develop key PD/MOA biomarkers to facilitate the clinical evaluation of POC for carlumab. This required the development of robust analytical assays to accurately measure free and total CCL2 concentrations in the serum, and mechanistic PK-PD modeling for data analysis.
Methods: Carlumab was evaluated in three oncology clinical studies (as monotherapy in a Phase 1 first-in-human trial in patients with solid tumors, a Phase 1b chemotherapy combination study, and as a single agent Phase 2a study in patients with advanced prostate cancer). Biomarkers evaluated included free and total CCL2 concentrations in serum, a broad panel of soluble biomarkers, bone turnover markers, and circulating tumor cell (CTC) enumeration. Sequential tumor biopsies in ten patients from Phase 1 study yielded 4 paired specimens for immunohistochemical analysis of tumor associated macrophages (TAMs). A mechanistic PK-PD model that simultaneously characterized free and total CCL2, and carlumab concentrations in serum was used to estimate biologically effective doses that would inhibit CCL2 signaling.
Results: Analysis of CCL2 levels following carlumab administration revealed a rapid fall in free CCL2 as expected; however, post-treatment free CCL2 levels rapidly rebounded and quickly exceeded pretreatment serum concentrations. Two different analytical methods showed that carlumab suppressed CCL2 levels for only ∼24 hrs followed by a sustained increase in CCL2 concentration with subsequent treatment. These surprising results suggest that carlumab was ineffective at neutralizing free CCL2. PK-PD modeling confirmed the transient suppression of free CCL2 consistent with a higher carlumab dissociation constant (Kd) for CCL2 binding in vivo. Finally, carlumab did not affect other biomarkers including bone turnover markers or CTC numbers, consistent with an inability to impact CCL2 signaling. No evidence of clinical efficacy was observed in any of carlumab clinical trials.
Conclusion: Development of robust analytical assays to measure free and total CCL2 concentration and utilization of mechanistic PK-PD modeling facilitated the clinical evaluation of POC for carlumab. The unexpected increase in free CCL2 concentration and the lack of CCL2 target suppression likely explain the absence of carlumab clinical activity. Supportive biomarker analyzes and mechanistic PK-PD modeling are important components of the early development clinical plan for developing biologics against soluble ligands.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr A37.