Radiation Dosimetry Study of [89Zr]rituximab Tracer for Clinical Translation of B cell NHL Imaging using Positron Emission Tomography

We evaluated the dosimetry of [Zr-89]rituximab, an anti-CD20 immunoPET tracer to image B cell non-Hodgkin's lymphoma (NHL) using a humanized transgenic mouse model that expresses human CD20 transgenic mice (huCD20TM). Rituximab was conjugated to desferrioxamine (Df) for radiolabeling of Zirconium-89. [Zr-89]rituximab (2.8 +/- 0.2 MBq) was tail vein-injected into huCD20T mice. Positron emission tomography (PET)/CT imaging was performed on the two groups of mice (blocking = 2 mg/kg pre-dose of rituximab and non-blocking; n = 5) at eight time points (1, 4, 24, 48, 72, 96, 120, and 168 h) post injection. The novel [Zr-89]rituximab PET tracer had good immunoreactivity, was stable in human serum, and was able to specifically target human CD20 in mice. The human equivalents of highest dose (mean +/- SD) organs with and without pre-dose are liver (345 +/- 284 mu Sv/MBq) and spleen (1165 +/- 149 mu Sv/MBq), respectively. Dosimetry of the human patient whole-body dose was found to be 145 MBq per annum, and the patient dose-limiting organ will be the liver (with rituximab pre-dose blocking) and spleen for non-blocking. The [Zr-89]rituximab (tA1/2 = 78.4 h) imaging of B cell NHL patients could permit the observation of targeting lesions in NHL patients over an extended period due to longer half-life as compared to the [Cu-64] rituximab (tA1/2 = 12.7 h).