An overview of the pharmacokinetics and pharmacodynamics of efalizumab: a monoclonal antibody approved for use in psoriasis.

Efalizumab is a recombinant humanized monoclonal IgG(1) antibody shown to be efficacious for the treatment of moderate to severe chronic plaque psoriasis. Efalizumab, a targeted inhibitor of T cell interactions, binds to the CD11a subunit of lymphocyte function-associated antigen 1 (LFA-1), thereby preventing LFA-1 binding to intercellular adhesion molecule 1 (ICAM-1). The authors review the pharmacokinetic and pharmacodynamic data from the efalizumab clinical development program and discuss how these data led to selection of the optimal weekly subcutaneous (SC) dose of efalizumab (1.0 mg/kg) in adults. Efalizumab SC dosages of 1.0 mg/kg/wk or greater exerted maximal pharmacodynamic effects for CD11a expression and available CD11a binding sites on T lymphocytes. Dosages greater than 1.0 mg/kg/wk SC did not provide additional benefits; moreover, higher doses did not alter the safety profile. During long-term administration of efalizumab, serum levels were generally stable and pharmacodynamic markers remained maximally affected.

Evaluation of a surrogate antibody for preclinical safety testing of an anti-CD11a monoclonal antibody.

Surrogate antibodies are a potential solution to the limited safety testing possible with humanized monoclonal antibodies with restricted species cross-reactivity. However, there are currently no defined criteria by which a potential surrogate antibody should be judged prior to its use in determining safety issues for the clinical agent. We propose that, potential surrogates should undergo rigorous evaluation to assess pharmacological and toxicological activities in comparison to the clinical agent. The current studies evaluated a chimeric mouse/rat anti-mouse CD11a monoclonal antibody (muM17) as a potential surrogate for efalizumab, a humanized anti-CD11a antibody in development for psoriasis. CD11a is a subunit of lymphocyte function associated antigen-1, an integrin involved in cell-cell interactions important to immune responses and inflammation. In vitro pharmacology studies included binding affinity to whole mouse blood and inhibitory activity of muM17 in a mixed lymphocyte response assay. In vivo pharmacology was examined using a delayed type hypersensitivity assay in female CD-1 mice. The toxicology evaluation included a murine tissue cross-reactivity study and in vivo multiple dose studies in female CD-1 mice which were administered muM17 (0.1-30 mg/kg) via subcutaneous injections once a week for 4 weeks. Clinical observations, body weight, clinical pathology, T cell CD11a expression, immunogenicity, toxicokinetics, and lymphoid organ histopathology were evaluated. Finally, since reproductive safety testing would be an important application of the proposed surrogate antibody, a pilot study in pregnant mice was conducted that demonstrated proportional transfer of muM17 into the fetus. These studies demonstrated that muM17 has pharmacological and toxicological activities similar to efalizumab. The selection of dose and regimen for GLP (Good Laboratory Practice) toxicology studies and extrapolation to clinical dose levels was based on pharmacodynamic activity (CD11a downmodulation on T cells).