Targeting and internalization of sterically stabilized liposome modified with ZCH-4-2E8

Successful construction and massive expression of a novel Anti-CD19 human-mouse chimeric antibody Hm2E8b

CD19 antigen is a major target for human B cell malignancies. Many studies have shown that the antibodies recognizing this antigen hold clinical therapeutic potential, while CD19 antibody of mouse origin requires genetic engineering to reduce the potential side effects of the antibody for their clinical use. There are many clones of CD19 antibodies available with different subclasses of immunoglobulin. IgM type antibody holds a high affinity and high complement activating capacities facilitating the targeting efficacy when it is used in targeting therapy. However, engineering the murine IgM antibody into a functional humanized antibody remains a challenge. The aim of this study was to construct a chimeric antibody composed of a CD19 specific murine IgM antibody 2E8 single-chain antibody fragment (scFv) and human IgG1 Fc region, which was named 2E8scFv-Fc or Hm2E8b. The function and the biological activities of this engineered antibody were characterized using a variety of approaches including cellular, immunological, flow cytometric, and molecular biological approaches. After switching from IgM- to IgG-like type antibody, Hm2E8b retained full antigen-binding activity to membrane CD19 antigen as its parental antibody 2E8, and the immune effector function analysis revealed that it could mediate complement-dependent cytotoxicity (CDC) to kill the target cells via IgG1 Fc domain. The yield of the engineered antibody Hm2E8b in the supernatant was 13.3 μg/mL expressed and secreted in the CHO cell system, which reached the secretory quantity of a regular mouse hybridoma cells. Our conclusion is that the IgM type of CD19 mouse antibody can be successfully engineered into an IgG1 type human-mouse chimeric antibody with similar affinity and biological activity. The yield of the Hm2E8b expression and secretion in CHO cell system was adequate to facilitate further development for therapeutic purpose.

CD19-antigen specific nanoscale liposomal formulation of a SYK P-site inhibitor causes apoptotic destruction of human B-precursor leukemia cells

We report the anti-leukemic potency of a unique biotargeted nanoscale liposomal nanoparticle (LNP) formulation of the spleen tyrosine kinase (SYK) P-site inhibitor C61. C61-loaded LNP were decorated with a murine CD19-specific monoclonal antibody directed against radiation-resistant CD19-receptor positive aggressive B-precursor acute lymphoblastic leukemia (ALL) cells. The biotargeted C61-LNP were more potent than untargeted C61-LNP and consistently caused apoptosis in B-precursor ALL cells. The CD19-directed C61-LNP also destroyed B-precursor ALL xenograft cells and their leukemia-initiating in vivo clonogenic fraction. This unique nanostructural therapeutic modality targeting the SYK-dependent anti-apoptotic blast cell survival machinery shows promise for overcoming the clinical radiochemotherapy resistance of B-precursor ALL cells.

Preparation and evaluation of norcantharidin-encapsulated liposomes modified with a novel CD19 monoclonal antibody 2E8

In this study, norcanthridin (NCTD)-encapsulated liposomes were modified with a novel murine anti-human CD19 monoclonal antibody 2E8 (2E8-NCTD-liposomes) and the targeting efficiency and specific cytotoxicity of 2E8-NCTD-liposomes to CD19(+) leukemia cells were evaluated. BALB/c mice were injected with 2E8 hybridoma cells to obtain 2E8 monoclonal antibody (mAb). NCTD-liposomes were prepared by using film dispersion method. 2E8 mAbs were linked to NCTD-liposomes using post-incorporation technology. Flow cytometry showed that the targeting efficiency of purified 2E8 mAbs on CD19(+) Nalm-6 cells was 99.93%. The purified 2E8 mAbs were conjugated with NCTD-liposomes to prepare 2E8-NCTD-liposomes whose targeting efficiency on CD19(+) Nalm-6 was also 95.82%. The average size of 2E8-NCTD-liposomes was 118.32 nm in diameter. HPLC showed that the encapsulation efficiency of NCTD was 46.51%. When the molar ratio of 2E8/Mal-PEG(2000)-DSPE reached 1:50, we obtained the liposomes with 9 2E8 molecules per liposome. The targeting efficiency of 2E8-NCTD-liposomes on CD19(+) leukemia cells was significantly higher than that on CD19-leukemia cells. Similarly, the targeting efficiency of the immunoliposomes was also higher than that of the NCTD-liposomes on CD19(+) leukemia cells. Those results were consistent with those observed by laser scanning confocal microscopy. 3-(4, 5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay demonstrated that 2E8-NCTD-liposomes specifically killed Nalm-6 cells in a dose- and time-dependent manner. The viability of Nalm-6 cells treated by 2E8-NCTD-liposomes was significantly lower than that of Molt-3 cells and it was also significantly lower than that of Nalm-6 cells treated with the same concentration of NCTD-liposomes or free NCTD. We are led to concluded that 2E8 antigen can serve as a specific targeting molecule of B lineage hematopoietic malignancies for liposome targeting, and 2E8-NCTD-liposomes can be used as a new and effective means for the treatment of B lineage hematopoietic malignancies.