Construction and characterization of a new chimeric antibody against HER2

Differential Effects of Inhibitory and Stimulatory Anti-HER2 Monoclonal Antibodies on AKT/ERK Signaling Pathways

Objective:

Homo- and heterodimerization of the receptor tyrosine kinase HER2 hyperactivate several downstream signaling pathways, leading to uncontrolled growth and proliferation of tumor cells. Anti-HER2 monoclonal antibodies (mAbs) may induce different effects on HER2 dimerization and signaling.

Methods:

The effect of two inhibitory (2A8, 1T0) and one stimulatory (1H9) anti-HER2 mAbs either alone or in combination with trastuzumab was investigated on AKT and ERK signaling pathways and HER2 degradation in a human breast cancer cell line (BT-474) by Western blotting.

Result:

While 1H9 mAb had no significant effect on AKT and ERK signaling pathways, 1T0 and 2A8 mAbs inhibited phosphorylation of both pathways. Combination of 1T0 mAb with trastuzumab resulted in significant synergistic inhibition of both pathways and HER2 degradation, much more potently than the combination of trastuzumab and pertuzumab.

Conclusion:

Our data indicate that anti-HER2 mAbs may induce different signaling pathways depending on their effect on tumor cell growth and proliferation. The significant inhibition of ERK and AKT phosphorylation by 1T0 alone or particularly in combination with trastuzumab suggests its potential therapeutic application for targeted immunotherapy of HER2 overexpressing malignancies.

All-trans retinoic acid in combination with sodium butyrate enhances specific monoclonal antibody productivity in recombinant CHO cell line

The effects of all-trans retinoic acid (RA) and sodium butyrate (NaBu) on growth, viability and antibody production of two types of transfected Chinese hamster ovary cell lines (CHO-K1 and CHO-S) were investigated using a batch mode cell culture. By adding 0.5 mM NaBu in the CHO-K1 cell culture, the cell specific productivity (Q_p) and antibody concentration increased by five- and threefold, respectively. The optimal concentration of RA was 100 nM which resulted in twofold increase in antibody production. In a combination model, RA applied at early growth phase of CHO-K1 cells followed by addition of NaBu with lowering culture temperature at the end of stationary phase resulted in two- and threefold increase in Q_p and final antibody concentration, respectively. The latter strategy was also applied on suspended CHO-S cells with enhanced Q_p and antibody concentration, but to a lesser extent than the CHO-K1 cells. In conclusion, our results demonstrate that the addition of RA and NaBu along with lowering the culture temperature can increase cell culture period as well as Q_p and the final concentration of recombinant monoclonal antibody in both CHO-K1 and CHO-S cells without any significant change in binding affinity of the mAb.

Immunization with HER2 extracellular subdomain proteins induces cellular response and tumor growth inhibition in mice

AIM

We investigated cellular and protective immune responses in mice vaccinated with recombinant HER2 extracellular subdomains.

MATERIALS & METHODS

Balb/C mice were immunized with recombinant full HER2 extracellular domain and subdomain proteins. Humoral and cellular immune response and antitumor effect was evaluated using a syngeneic mice tumor model.

RESULTS

All recombinant proteins induced secretion of IL-4 and particularly IFN-γ and IL-17 cytokines. Challenging of immunized mice with stable 4T1-HER2 transfected cells resulted in partial but significant tumor growth inhibition in all groups of mice particularly those immunized with fHER2-ECD together with CPG.

CONCLUSION

Our results suggest that the recombinant HER2-ECD subdomains induce mainly Th1 and Th17 responses, which seem to contribute to tumor growth inhibition in syngeneic mice.

Epitope Mapping of Human HER2 Specific Mouse Monoclonal Antibodies Using Recombinant Extracellular Subdomains

Background: Human epidermal growth factor receptor 2 (HER2) is overexpressed in several human malignancies and numerous studies have indicated that it plays important roles in the development and maintenance of the malignant phenotype. Targeting of HER2 molecules with monoclonal antibodies (mAbs) is a promising therapeutic approach. However, anti-HER2 mAbs affect cancer cells differently, depending on the distinct epitopes which are the targets. Methods: Reactivity of a panel of 8 mouse anti-HER2 mAbs was investigated by ELISA and Western blotting using different subdomains of the extracellular domain (ECD) of HER2. All subdomains, including I, II, III, IV, I+II, III+IV and full HER2-ECD were constructed and expressed in CHO cells. Cross-reactivity of the mAbs with other members of the human HER family and Cynomolgus HER2 was also studied by ELISA. The mAbs were also tested by immunohistochemistry (IHC) using HER2 positive breast cancer tissues. Results: Our results demonstrated that 3 out of 8 mAbs detected conformational epitopes (1T0, 2A8 and 1B5), while 5 mAbs identified linear epitopes (1F2, 1H9, 4C7, 1H6 and 2A9). Three of the mAbs recognized subdomain I, one reacted with subdomain I+II, 2 recognized either subdomain III or IV and 2 recognized subdomain III+IV. However, none of our mAbs recognized the subdomain II alone. The mAbs displayed either inhibitory or stimulatory effects on HER2-overexpressing tumor cells and did not react with other members of the human HER family. The pattern of IHC results implied better reactivity of the mAbs recognizing linear epitopes. Conclusions: Our findings suggest that paired subdomains of HER2 are essential for mapping of mAbs recognizing conformational epitopes. Moreover, there seems to be no association between subdomain specificity and antitumor activity of our anti-HER2 mAbs.

Hersintuzumab: A novel humanized anti-HER2 monoclonal antibody induces potent tumor growth inhibition

Humanized monoclonal antibodies (mAbs) against HER2 including trastuzumab and pertuzumab are widely used to treat HER2 overexpressing metastatic breast cancers. These two mAbs recognize distinct epitopes on HER2 and their combination induces a more potent blockade of HER2 signaling than trastuzumab alone. Recently, we have reported characterization of a new chimeric mAb (c-1T0) which binds to an epitope different from that recognized by trastuzumab and significantly inhibits proliferation of HER2 overexpressing tumor cells. Here, we describe humanization of this mAb by grafting all six complementarity determining regions (CDRs) onto human variable germline genes. Humanized VH and VL sequences were synthesized and ligated to human γ1 and κ constant region genes using splice overlap extension (SOE) PCR. Subsequently, the humanized antibody designated hersintuzumab was expressed and characterized by ELISA, Western blot and flow cytometry. The purified humanized mAb binds to recombinant HER2 and HER2-overexpressing tumor cells with an affinity comparable with the chimeric and parental mouse mAbs. It recognizes an epitope distinct from those recognized by trastuzumab and pertuzumab. Binding of hersintuzumab to HER2 overexpressing tumor cells induces G1 cell cycle arrest, inhibition of ERK and AKT signaling pathways and growth inhibition. Moreover, hersintuzumab could induce antibody-dependent cell cytotoxicity (ADCC) on BT-474 cells. This new humanized mAb is a potentially valuable tool for single or combination breast cancer therapy.

Monoclonal antibodies to various epitopes of hepatitis B surface antigen inhibit hepatitis B virus infection

BACKGROUND AND AIM

Antibodies against the "a" determinant of hepatitis B surface antigen (HBsAg) are able to neutralize circulating hepatitis B virus (HBV) particles and prevent HBV infection. It has been proposed that a single amino acid exchange may allow the virus to escape the immune response. We used a set of monoclonal antibodies (MAbs) to investigate whether a single mutation may account for virus escape from humoral immunity.

METHODS

Nine murine HBsAg-specific MAbs were raised. Reactivity of all antibodies with 14 recombinant mutants of HBsAg was assessed by ELISA. HBV infection of HepaRG cells was used to evaluate viral neutralization capacity of MAbs in vitro.

RESULTS

All MAbs were able to inhibit the establishment of HBV infection in a dose-dependent fashion, but recognition of HBsAg variants varied. The MAbs were classified into three subgroups based on their pattern of reactivity to the HBsAg variants. Accordingly, three MAbs showed weak reactivity (< 40%) to variants with mutations within the first loop of "a" determinant, five MAbs displayed negligible binding to variants with mutations within the second loop, and one MAb lost its binding to variants having mutations in both loops of the "a" determinant.

CONCLUSIONS

Our results indicate that antibodies against different epitopes of the "a" determinant of HBsAg are able to neutralize HBV. It seems that mutations within a single or a limited number of amino acids within this determinant can hardly result in viral escape. These results have important implications for the development of antibody-based therapies against HBV.