Targeted delivery of anti-CD19 liposomal doxorubicin in B-cell lymphoma: A comparison of whole monoclonal antibody, Fab′ fragments and single chain Fv

As part of an ongoing effort to develop a clinically acceptable doxorubicin formulation, targeted against B-cell malignancies, this study compared long-circulating (Stealth®) immunoliposomes (SIL) that were targeted against the B-cell antigen CD19, via a whole HD37 monoclonal antibody (HD37 mAb), versus its Fab′ fragment (HD37 Fab′) or an HD37–c-myc–Cys–His5 single chain Fv fragment (scFv, HD37-CCH) directed against the same epitope. Compared to untargeted liposomes (SL), SIL showed increased binding in vitro to CD19-expressing Raji cells and, when loaded with doxorubicin (SIL–DXR), increased cytotoxicity against Raji (CD19+), but not Molt4 (CD19−) cells. Pharmacokinetics and biodistribution studies using dual-labeled liposomes (lipid and drug) in naïve and Raji-bearing mice showed that SIL–DXR targeted via HD37 Fab′ exhibited the same long circulation half-life as SL–DXR. SIL–DXR targeted via HD37-CCH was cleared faster than SL–DXR due to increased liver uptake, which was related to the poly-His and/or the c-myc tags in the scFv construct. SIL–DXR targeted via HD37 mAb was cleared rapidly from circulation due to Fc-mediated uptake in the liver and spleen. All three formulations of SIL–DXR extended the mean survival time of Raji-bearing mice compared to SL–DXR or free DXR. SIL–DXR targeted via HD37 Fab′, which had the longest circulation half-life, appeared to be slightly more effective in prolonging survival times than SIL–DXR targeted via either HD37-CCH or HD37 mAb.