In this article, we will discuss Ofatumumab (Mechanism of Action). So, let’s get started.
Mechanism of Action
Ofatumumab binds specifically to both the small and large extracellular loops of the CD20 molecule. The CD20 molecule is expressed on normal B lymphocytes (pre–B- to mature B-lymphocyte) and on B-cell CLL. The CD20 molecule is not shed from the cell surface and is not internalized following antibody binding.
The Fab domain of ofatumumab binds to the CD20 molecule and the Fc domain mediates immune effector functions to result in B-cell lysis in vitro. Data suggest that possible mechanisms of cell lysis include complement-dependent cytotoxicity and antibody-dependent, cell-mediated cytotoxicity.
Pharmacodynamics
B-cell Depletion: In patients with previously untreated CLL, at 6 months after the last dose, the median reductions in CD19-positive B cells were >99% (n = 155) for Ofatumumab in combination with chlorambucil and 94% (n = 121) for chlorambucil alone.
In patients treated with extended treatment for CLL after response to therapy for their recurrent or progressive disease, the median decreases in B-cell counts were 61% (n = 168) after the first infusion and 80% (n = 114) prior to the sixth infusion; in the observation arm, the median changes in B-cell counts at the same time points were increases of 32% (n = 148) and 1,328% (n = 95).
In patients with CLL refractory to fludarabine and alemtuzumab, the median decrease in circulating CD19-positive B cells was 91% (n = 50) with the 8th infusion and 85% (n = 32) with the 12th infusion. The time to recovery of lymphocytes, including CD19-positive B cells, to normal levels has not been determined. Although the depletion of B-cells in the peripheral blood is a measurable pharmacodynamic effect, it is not directly correlated with the depletion of B cells in solid organs or in malignant deposits. B-cell depletion has not been shown to be directly correlated to clinical response.
Cardiac Electrophysiology: The effect of multiple doses of Ofatumumab on the QTc interval was evaluated in a pooled analysis of 3 open-label studies in patients with CLL (N = 85). Patients received Ofatumumab 300 mg on Day 1 followed by either 1,000 mg or 2,000 mg for subsequent doses. No large changes in the mean QTc interval (i.e., >20 milliseconds) were detected in the pooled analysis.