| Anticancer drug therapy can have significant adverse effects, resulting from nonselective toxicities. Treatment with antibody-targeted liposomes such as StealthRTM immunoliposomes (SIL) results in improved selectivity of chemotherapeutics for cancer cells that can be easily accessed from the vasculature, e.g., haematological malignancies. This thesis examined, in an animal model of a B-cell malignancy, the activity of doxorubicin (DXR) encapsulated in SIL and targeted via an anti-CD 19 whole monoclonal antibody (mAb), its Fab' fragment (Fab') or a single chain Fv fragment (scFv), all directed against the same epitope of CD 19. The therapeutic effect of DXR-loaded SIL (SIL-DXR) was hypothesized to be influenced by the differences in the pharmacokinetics (PK) properties of the targeted liposomes.;SIL-DXR targeted via mAb, Fab' or scFv had improved cytotoxicity to B cells, over untargeted liposomal DXR, via CD19-mediated mechanisms. PK studies demonstrated that Fab'-targeted SIL-DXR had long circulation times, similar to untargeted liposomes, while mAb-targeted SIL-DXR was rapidly cleared by the liver and spleen. The presence of poly-histidine and c-myc tags on the scFv increased their uptake into liver, compared to tagless scFv. However, the differences in PK between the various formulations of SIL-DXR did not result in differences in their therapeutic effects. These results suggested that, in the treatment of haematological malignancies, the choice between mAb, Fab' or scFv as targeting agents for SIL may be dependent on other factors, such as immunogenicity, toxicity, or production cost, rather than the PK properties of the individual construct.;Various anti-CD19 scFv constructs were compared for their stability, production yield, and affinity. Production yield and activity of native scFv from the periplasmic space of E. coli were compared with those of refolded scFv from denatured inclusion bodies. The ability to refold the scFv and the stability of the resulting construct were the major factors in determining its success as a targeting agent. Of the several scFv constructs tested, only one demonstrated suitable properties for targeting SIL. The coupling of scFv to polyethylene glycol-lipid micelles was found to increase their storage stability, making it possible to generate the amounts of scFv required for the in vivo experiments. |
