An enediyne-energized single-domain antibody-containing fusion protein shows potent antitumor activity

Challenges and Opportunities to Develop Enediyne Natural Products as Payloads for Antibody-Drug Conjugates

Calicheamicin, the payload of the antibody-drug-conjugates (ADCs) gemtuzumab ozogamicin (Mylotarg^®) and inotuzumab ozogamicin (Besponsa^®), belongs to the class of enediyne natural products. Since the isolation and structural determination of the neocarzinostatin chromophore in 1985, the enediynes have attracted considerable attention for their value as DNA damaging agents in cancer chemotherapy. Due to their non-discriminatory cytotoxicity towards both cancer and healthy cells, the clinical utilization of enediyne natural products relies on conjugation to an appropriate delivery system, such as an antibody. Here we review the current landscape of enediynes as payloads of first-generation and next-generation ADCs.

A novel anti-p21Ras scFv antibody reacting specifically with human tumour cell lines and primary tumour tissues

BACKGROUND

The ras genes play an important role in the development and progression of human tumours. Neutralizing Ras proteins in the cytoplasm could be an effective approach to blocking ras signalling. In this study, we prepared anti-p21Ras single chain fragment variable antibody (scFv) and investigated its immunoreactivity with human tumours.

METHODS

The coding sequences of H-ras, K-ras, and N-ras were separately ligated into the vector pET-28a(+). Then, recombinant expressing plasmids were induced by IPTG for p21Ras expression in E. coli. Hybridoma cell lines producing anti-p21Ras monoclonal antibodies were isolated using wildtype p21Ras proteins as immunogens. Anti-p21Ras scFv antibody was prepared from the hybridoma by the phage scFv display method. The immunoreactivity of the anti-p21Ras monoclonal antibody and the scFv antibody was identified by ELISA and immunocytochemistry.

RESULTS

We prokaryotically expressed wildtype H-p21Ras, K-p21Ras and N-p21Ras and generated the hybridoma cell line KGH-R1, producing anti-p21Ras monoclonal antibodies. It was demonstrated that KGH-R1 monoclonal antibody could recognize wildtype and mutated H-p21Ras, K-p21Ras and N-p21Ras in human tumour cell lines. In all 14 types of primary human cancer tissues tested, the monoclonal antibody presented strong immunoreactivity but showed weak or negative immunoreactivity in the corresponding normal tissues. Subsequently, we prepared anti-p21Ras scFv from hybridoma KGH-R1, which showed the same immunoreactivity as the original monoclonal antibody. Sequence analysis demonstrated that the nucleotides and amino acids of the scFv exhibited an approximately 50 % difference from the anti-p21Ras scFv reported previously.

CONCLUSIONS

This study presents a novel anti-p21Ras scFv antibody. Our data suggest that the scFv may be useful for ras signalling blockage and may be a potential therapeutic antibody for ras-derived tumours.

A Gelatinases-targeting scFv-based Fusion Protein Shows Enhanced Antitumour Activity with Endostar against Hepatoma

Gelatinases play important roles in tumour invasion and metastasis and are thus considered promising targets for cancer therapy. In this study, a new single-chain variable fragment (scFv)-based fusion protein Fv-LDP, composed of the anti-gelatinases scFv and lidamycin apoprotein (LDP), was prepared, and its combination with angiogenesis inhibitor Endostar was then investigated. The fusion protein Fv-LDP specifically bound to various tumour cells, and its binding capability to human pulmonary giant cell carcinoma (PG) cells was higher than that of LDP. Fv-LDP inhibited the expression and secretion of gelatinases and could be internalized into tumour cells via endocytosis. Fv-LDP also suppressed the growth of human hepatoma cells and murine hepatoma 22 transplanted in Kunming mice in various degrees. In addition, Endostar could enhance the synergistic or additive inhibition of Fv-LDP on the growth, migration or invasion of human hepatoma cells shown by a colony formation assay and a transwell-based migration or invasion assay, respectively. In vivo, Fv-LDP/Endostar combination showed a significantly synergistic effect on the growth of a human hepatoma xenograft, with an inhibition rate of 80.8% compared with the Fv-LDP (44.1%) or Endostar (8.9%)-treated group. The above-mentioned results indicate that the fusion protein Fv-LDP is effective against transplantable hepatoma in mice and human hepatoma xenografts in athymic mice. Moreover, Endostar can potentiate the inhibition effect of Fv-LDP on the growth of human hepatoma cells and xenografts. These data will provide a new combined strategy for improving the therapeutic efficacy of treatments for hepatoma or other gelatinase-overexpressing tumours.

Tuftsin-based, EGFR-targeting fusion protein and its enediyne-energized analog show high antitumor efficacy associated with CD47 down-regulation

Tuftsin (TF) is an immunomodulator tetrapeptide (Thr-Lys-Pro-Arg) that binds to the receptor neuropilin-1 (Nrp1) on the surface of cells. Many reports have described anti-tumor activity of tuftsin to relate with nonspecific activation of the host immune system. Lidamycin (LDM) that displays extremely potent cytotoxicity to cancer cells is composed of an apoprotein (LDP) and an enediyne chromophore (AE). In addition, Ec is an EGFR-targeting oligopeptide. In the present study, LDP was used as protein scaffold and the specific carrier for the highly potent AE. Genetically engineered fusion proteins LDP-TF and Ec-LDP-TF were prepared; then, the enediyne-energized fusion protein Ec-LDM-TF was generated by integration of AE into Ec-LDP-TF. The tuftsin-based fusion proteins LDP-TF and Ec-LDP-TF significantly enhanced the phagocytotic activity of macrophages as compared with LDP (P < 0.05). Ec-LDP-TF effectively bound to tumor cells and macrophages; furthermore, it markedly suppressed the growth of human epidermoid carcinoma A431 xenograft in athymic mice by 84.2 % (P < 0.05) with up-regulated expression of TNF-α and IFN-γ. Ec-LDM-TF further augmented the therapeutic efficacy, inhibiting the growth of A431 xenograft by 90.9 % (P < 0.05); notably, the Ec-LDM-TF caused marked down-regulation of CD47 in A431 cells. Moreover, the best therapeutic effect was recorded in the group of animals treated with the combination of Ec-LDP-TF with Ec-LDM-TF. The results suggest that tuftsin-based, enediyne-energized, and EGFR-targeting fusion proteins exert highly antitumor efficacy with CD47 modulation. Tuftsin-based fusion proteins are potentially useful for treatment of EGFR- and CD47-overexpressing cancers.

A cell penetrating peptide-integrated and enediyne-energized fusion protein shows potent antitumor activity

Arginine-rich peptides belong to a subclass of cell penetrating peptides that are taken up by living cells and can be detected freely diffusing inside the cytoplasm and nucleoplasm. This phenomenon has been attributed to either an endocytotic mode of uptake and a subsequent release from vesicles or a direct membrane penetration. Lidamycin is an antitumor antibiotic, which consists of an active enediyne chromophore (AE) and a noncovalently bound apoprotein (LDP). In the present study, a fusion protein (Arg)(9)-LDP composed of cell penetrating peptide (Arg)(9) and LDP was prepared by DNA recombination, and the enediyne-energized fusion protein (Arg)(9)-LDP-AE was prepared by molecular reconstitution. The data in fixed cells demonstrated that (Arg)(9)-LDP could rapidly enter cells, and the results based on fluorescence activated cell sorting indicated that the major route for (Arg)(9)-mediated cellular uptake of protein molecules was endocytosis. (Arg)(9)-LDP-AE demonstrated more potent cytotoxicity against different carcinoma cell lines than lidamycin in vitro. In the mouse hepatoma 22 model, (Arg)(9)-LDP-AE (0.3mg/kg) suppressed the tumor growth by 89.2%, whereas lidamycin (0.05 mg/kg) by 74.6%. Furthermore, in the glioma U87 xenograft model in nude mice, (Arg)(9)-LDP-AE at 0.2mg/kg suppressed tumor growth by 88.8%, compared with that of lidamycin by 62.9% at 0.05 mg/kg. No obvious toxic effects were observed in all groups during treatments. The results showed that energized fusion protein (Arg)(9)-LDP-AE was more effective than lidamycin and would be a promising candidate for glioma therapy. In addition, this approach to manufacturing fusion proteins might serve as a technology platform for the development of new cell penetrating peptides-based drugs.

Factor VII light chain-targeted lidamycin shows intensified therapeutic efficacy for liver cancer

The overexpression of tissue factor (TF) observed in numerous cancer cells and clinical samples of human cancers makes TF an ideal target for cancer therapy. The purpose of this study is to develop a TF-targeting energized fusion protein hlFVII-LDP-AE, which is composed of a human Factor VII light chain (hlFVII) as the targeting domain conjugated to the cytotoxic antibiotic lidamycin (LDM, LDP-AE) as the effector domain. The potential efficacy of hlFVII-LDP-AE for cancer therapy was tested in vitro by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and colony formation assays and in vivo with a BALB/c nude mouse xenograft model of human liver cancer line HepG2. The inhibitory concentration (IC(50)) value of hlFVII-LDP-AE varied from 0.15 to 0.64 nM for the various human tumor lines. hlFVII-LDP-AE showed a tumor growth inhibition rate of 90.6% at the dose of 0.6 mg/kg in in vivo animal experiments. The mechanism through which hlFVII-LDP-AE inhibits tumor growth also was determined by Hoechst 33342 staining and Tdt-mediated dUTP nick-end labeling (TUNEL) assay. hlFVII-LDP-AE causes tumor cell death through inducing chromatin condensation and cleavage of genomic DNA. These findings suggest that the hlFVII-LDP-AE protocol is efficacious and tolerated in the mouse model of human liver cancer HepG2 and has clinical applicability for treating cancer patients.

A bispecific enediyne-energized fusion protein containing ligand-based and antibody-based oligopeptides against epidermal growth factor receptor and human epidermal growth factor receptor 2 shows potent antitumor activity

PURPOSE

The cooverexpression of epidermal growth factor receptor (EGFR) and human epidermal growth factor receptor 2 (HER2) observed in many human tumors and their synergistic interaction in the transformation of cells make these receptors important targets for the development of new targeted therapeutics. Targeting of EGFR and HER2 simultaneously has been pursued as a strategy with which to potentially increase efficiency and selectivity in therapy of certain cancers. This study was set to construct a bispecific energized fusion protein (Ec-LDP-Hr-AE) consisting of two oligopeptides against EGFR and HER2, and lidamycin, and investigate its antitumor efficacy.

EXPERIMENTAL DESIGN

In vitro experiments measured the binding and internalization of bispecific Ec-LDP-Hr fusion protein. The potency of energized fusion proteins was also done in which the bispecific Ec-LDP-Hr-AE was compared with lidamycin (LDM) and its monospecific counterparts, Ec-LDP-AE and LDP-Hr-AE. In vivo, Ec-LDP-Hr-AE was given i.v. to nude mice bearing human ovarian carcinoma SK-OV-3 xenografts.

RESULTS

Binding and internalization studies showed that bispecific fusion protein Ec-LDP-Hr bound to carcinoma cells specifically and then were internalized into the cytoplasm. Bispecific Ec-LDP-Hr-AE was more potent and selective in its cytotoxicity against different carcinoma cell lines than corresponding momospecific agents and LDM in vitro. In addition, Ec-LDP-Hr-AE significantly inhibited the growth of SK-OV-3 xenografts in nude mouse model. In vivo imaging study showed that FITC-labeled Ec-LDP-Hr was targeted and accumulated in the tumors.

CONCLUSION

A ligand-based and an antibody-based oligopeptide fused to the enediyne antibiotic LDM created a new bispecific fusion protein with low molecular weight and more potent in vitro and in vivo antitumor activity (than momospecific fusion proteins).

A tandem scFv-based fusion protein and its enediyne-energized analogue show intensified therapeutic efficacy against lung carcinoma xenograft in athymic mice

Gelatinases play important roles in tumor progression and are abundantly expressed in a variety of malignant tumors. Antibody targeting gelatinases is a possible avenue to fight against cancer. However, antibody alone can not achieve curative efficacy. Herein, we demonstrated the intensified targeting therapy of a tandem scFv-based fusion protein and its enediyne-energized analogue against gelatinases-overexpressed tumor. A fusion protein dFv-LDP, comprising a tandem scFv of anti-gelatinases linked to the apoprotein (LDP) of lidamycin, was generated and showed strong tumor targeting capability in three different tumor xenografts. In PG-BE1 lung carcinoma xenograft, the tumor inhibition rate was 77.5% by dFv-LDP versus 94.2% by dFv-LDP-AE, the product of dFv-LDP assembled with the active enediyne chromophore (AE) of lidamycin. Moreover, the combination of dFv-LDP with dFv-LDP-AE further augmented the therapeutic efficacy, producing initial tumor shrinkage in five of six mice. The microvessel density (P<0.05) and proliferation index (P<0.05) were also stepwise decreased in groups of dFv-LDP, dFv-LDP-AE and the combination. In conclusion, our results demonstrated that the antibody-based therapy against gelatinases was stepwise intensified in use of dFv-LDP, dFv-LDP-AE and dFv-LDP plus dFv-LDP-AE, and indicated that the combination of an antibody with its drug-armed analogue might be of interest as a new approach to augment antitumor efficacy.

Binding capability of the enediyne-associated apoprotein to human tumors and constitution of a ligand oligopeptide-integrated protein

The molecule of lidamycin that belongs to the chromoprotein family of antitumor antibiotics is composed of an apoprotein (LDP) and an enediyne chromophore. The enediyne moiety of the molecule is responsible for the potent cytotoxicity; however, the biological function of the apoprotein moiety, particularly its interaction with cancer cells, remains unclear. In present study, the binding capability of LDP to human tumors was detected for the first time by tissue microarray. LDP bound to various human tumors with significant difference from the corresponding normal tissues. Positive correlation between binding activity and the overexpression of VEGF and EGFR was confirmed by lung carcinoma tissue microarray. A fusion protein LG-LDP that consists of LDP and a ligand oligopeptide to EGFR was constructed by DNA recombination. LG-LDP showed augmented binding to EGFR-overexpressing cancer cells. Furthermore, an energized fusion protein LG-LDP-AE was prepared by integrating the active enediyne (AE) into LG-LDP molecule. By MTT assay, LG-LDP-AE displayed extremely potent cytotoxicity to cancer cells with IC50 approximate to 0.01nM. The results indicate that LDP binds to various human tumors and it might serve as a delivery carrier by integration of ligand oligopeptide to manufacture motif-based, targeted fusion proteins for cancer.