Preparation of (177Lu-DOTA)n-PAMAM-[Nimotuzumab-F(ab’)2] as a Therapeutic Radioimmunoconjugate for EGFR Overexpressed Cancers Treatment

Intact monoclonal antibodies with a high molecular weight tend to have a poor pharmacokinetic profile and tumor penetration, and potential for eliciting host antibody responses. F(ab’) 2 fragments smaller than intact monoclonal antibodies that still maintain antigen binding could solve this problem. The objective of this study was to optimize the digestion process of nimotuzumab, an anti-EGFR monoclonal antibody, into its F(ab’) 2 fragment and investigate its potential as a therapeutic radioimmunoconjugate. Optimal conditions for digestion of nimotuzumab to its F(ab’) 2 fragment were found to be 6 hours of digestion time with a pH of 3.5 and 1:100 mol ratio of pepsin to nimotuzumab. The purity of the F(ab’) 2 -nimotuzumab was confirmed by SDS-PAGE and HPLC analysis. Prior to its labeling with lutetium-177 radionuclide, the nimotuzumab-F(ab’) 2 was conjugated to DOTA-PAMAM dendrimer [DOTA denotes 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid, PAMAM denotes poly(amidoamine)] to form conjugate of (DOTA) n -PAMAM-[nimotuzumab-F(ab’) 2 ]. Radiolabeling of DOTA-PAMAM-[nimotuzumab-F(ab’) 2 ] conjugate with 177 Lu resulted in ( 177 Lu-DOTA) n -PAMAM-[nimotuzumab-F(ab’) 2 ] with radiochemical purity > 99% after purification with a PD-10 column. Further studies still need to be performed in order to confirm the potential of this radioimmunoconjugate as a radioimmunotherapeutic agent for EGFR overexpressed cancers.