Development of Traceable Rituximab-Modified PEO-Polyester Micelles by Postinsertion of PEG-phospholipids for Targeting of B-cell Lymphoma

[Image: see text] The objective of this work was to develop rituximab (RTX)-modified polymeric micelles for targeting of B-cell lymphoma cells, through postinsertion of RTX-poly(ethylene glycol)-1,2-distearoyl-sn-glycero-3-phosphoethanolamine (RTX-PEG-DSPE) into methoxy poly(ethylene oxide)-poly(ε-caprolactone) (PEO-PCL) or methoxy poly(ethylene oxide)-poly(ε-benzylcarboxylate-ε-caprolactone) (PEO-PBCL) micelles. Mixed micelles were made traceable by introducing Cy5.5 to RTX and conjugating Cy3 to propargyl moiety, end-capped PCL or PBCL. Successful adaptation of the postinsertion method for the formation of immunomicelles was evidenced by measurement of RTX levels on the micellar surface, purified from free RTX by size exclusion chromatography, using microBSA assay. A change in the micellar diameter, from 50–70 nm for PEO-PCL and PEO-PBCL micelles and 20 nm for PEG-DSPE micelles, to 80–95 nm for the mixed micellar population as well as the critical micellar concentration of mixed micelles provided further proof for the success of the postinsertion method applied here. Mixed micelles containing PCL or PBCL with a degree of polymerization of 22 (PCL(22) and PBCL(22)) were thermodynamically and kinetically more stable than those with PCL(15). Accordingly, RTX micelles containing PCL(22) or PBCL(22) showed a higher percentage of Cy(3+)/Cy(5.5+) cell population in CD20(+) KG-15 cells, than those with PCL(15). The percentage of Cy(3+)/Cy(5.5+) cell population drastically reduced in the presence of competing RTX for micelles containing PCL(22) or PBCL(22) cores, indicating the superiority of these structures for active targeting of CD20(+) cells. No significant difference in the cytotoxicity of paclitaxel in RTX-micelles versus plain ones was observed, reflecting the noninternalizing function of CD20. The results show that traceable mixed micelles prepared through postinsertion of RTX-PEG-DSPE to PEO-PCL(22) or PEO-PBCL(22) micelles can be used for targeting and/or imaging of CD20(+) B cell lymphoma cells. The postinsertion method can be adopted to prepare other PEO-poly(ester)-based immunomicelles for active targeting of other diseased cells.