Secreted Antibody/Granzyme B Fusion Protein Stimulates Selective Killing of HER2-overexpressing Tumor Cells

Augmented antitumor immune responses of HER2-targeted pyroptotic induction by long-lasting recombinant immunopyroptotins

Pyroptosis is a well-documented form of programmed cell death caused by the gasdermin-driven perforation of cell membranes. Selective induction of pyroptosis in tumor cells represents a promising antitumor strategy to enhance the efficacy of immunotherapy. In this study, we established a recombinant protein-based immunopyroptotin strategy that led to the intratumoral induction of pyroptosis for HER2-directed therapy. Long-lasting immunopyroptotins were constructed by sequentially fusing the humanized anti-HER2 single-chain antibody P1h3, albumin-binding peptide (ABD035 or dAb7h8), cathepsin B-cleavable peptide B2, endosome-disruptive peptide E5C3, and active pyroptotic effector gasdermin D-N fragment (GN). After purification, we evaluated the cytotoxicity and antitumor immune responses primarily induced by the immunopyroptotins in HER2-overexpressing breast cancer cells. The resulting ABD035-immunoGN and dAb7h8-immunoGN showed improved in vitro cytotoxicity in HER2-overexpressing cancer cells compared with that in the immunotBid that we previously generated to induce tumor cell apoptosis. The binding of long-lasting immunopyroptotins to albumin increased the half-life by approximately 7-fold in nude mice. The enhanced antitumor efficacy of long-lasting immunopyroptotins was confirmed in both N87 tumor-bearing T cell-deficient mice and 4T1-hHER2 bilateral tumor-bearing immunocompetent mice. Immunopyroptotin treatment elicited systemic antitumor immune responses involving CD8+ T cells and mature dendritic cells and upregulated the expression of proinflammatory cytokines, leading to sustained remission of non-injected distant tumors. This study extends the repertoire of antibody-based therapeutics through the tumor-targeted delivery of a constitutively active pore-forming gasdermin-N fragment, which shows great potential for pyroptosis-based antitumor therapy.

Intracellular and Extracellular Roles of Granzyme K

Granzymes are a family of serine proteases stored in granules inside cytotoxic cells of the immune system. Granzyme K (GrK) has been only limitedly characterized and knowledge on its molecular functions is emerging. Traditionally GrK is described as a granule-secreted, pro-apoptotic serine protease. However, accumulating evidence is redefining the functions of GrK by the discovery of novel intracellular (e.g. cytotoxicity, inhibition of viral replication) and extracellular roles (e.g. endothelial activation and modulation of a pro-inflammatory immune cytokine response). Moreover, elevated GrK levels are associated with disease, including viral and bacterial infections, airway inflammation and thermal injury. This review aims to summarize and discuss the current knowledge of i) intracellular and extracellular GrK activity, ii) cytotoxic and non-cytotoxic GrK functioning, iii) the role of GrK in disease, and iv) GrK as a potential therapeutic target.

Antitumor effects of a recombinant baculovirus displaying anti-HER2 scFv expressing Apoptin in HER2 positive SK-BR-3 breast cancer cells

Aim: Since HER2 targeted therapies have shown clinical benefit in breast cancer, in the present study recombinant baculovirus (BV) displaying anti-HER2 single-chain variable domain fragment (scFv) expressing Apoptin was generated. Methods: The binding specificity and surface display of anti-HER2 scFv were evaluated using enzyme-linked immunosorbent assay (ELISA) and electron microscopy, respectively. The targeting properties and cytotoxic effect on breast cancer cells determined by fluorescence microscopy and MTT assays. Results: The results demonstrated that recombinant BV could specifically bind to HER2-overexpressing SK-BR-3 cells but not to the HER2 negative MCF-7 cells and reduced the viability of SK-BR-3 cells by expressing Apoptin. Conclusion: These results suggest that the antitumor effect of Apoptin in combination with HER2 targeting of this recombinant BV makes it a promising vector in targeted cancer therapy.

Granzyme B-loaded, cell-selective penetrating and reduction-responsive polymersomes effectively inhibit progression of orthotopic human lung tumor in vivo

The clinical use of protein therapeutics with intracellular targets is hampered by its in vivo fragility and low cell permeability. Here, we report that cell-selective penetrating and reduction-responsive polymersomes (CPRPs) mediate high-efficiency targeted delivery of granzyme B (GrB) to orthotopic human lung tumor in vivo. Model protein studies using FITC-labeled cytochrome C (FITC-CC) revealed efficient and high protein loading up to 17.2 wt% for CPRPs. FITC-CC-loaded CPRPs exhibited a small size of 82-90 nm, reduction-responsive protein release, as well as greatly enhanced internalization and cytoplasmic protein release in A549 lung cancer cells compared with the non-targeted FITC-CC-loaded RPs control. GrB-loaded CPRPs showed a high potency toward A549 lung cancer cells with a half maximal inhibitory concentration (IC₅₀) of 20.7 nM. Under the same condition, free GrB was essentially non-toxic. Importantly, installing cell-selective penetrating peptide did not alter the circulation time but did enhance tumor accumulation of RPs. Orthotopic A549-Luc lung tumor-bearing nude mice administered with GrB-loaded CPRPs at a dosage of 2.88 nmol GrB equiv./kg showed complete tumor growth inhibition with little body weight loss throughout the treatment period, resulting in significantly improved survival rate over the non-targeted and non-treated controls. These cell-selective penetrating and reduction-responsive polymersomes provide a targeted protein therapy for cancers.

Protein Nanotherapeutics as an Emerging Modality for Cancer Therapy

Protein drugs are a unique and versatile class of biotherapeutics that have not only high biological activity but also superb specificity. This rapidly evolving biotechnology has rendered it possible to produce various proteins in a large scale and reproducible way. Many proteins have demonstrated striking anticancer activities and have emerged as advanced alternatives to cytotoxic chemotherapeutic agents for cancer therapy. The clinical translation of anticancer proteins with intracellular targets is, nevertheless, severely hindered by their fast degradation in vivo, poor cell penetration, and inefficient intracellular transportation. The past few years have witnessed tremendous effort and progress in developing polymeric protein delivery nanosystems, ranging from nanoparticles, nanocapsules, nanogels, micelles, to polymersomes, for the treatment of different tumors such as lung tumors, breast tumors, ovarian cancers, and glioblastoma. These proof-of-concept studies point out that protein nanotherapeutics, with rationally designed nanovehicles, are able to overcome the extracellular barriers, cell membrane barriers, and intracellular barriers, and systemically deliver proteins into targeted cancer cells, resulting in effective cancer protein therapy. Protein nanotherapeutics appear to be a novel modality for safe and efficient cancer treatment.

Human Granzyme B Based Targeted Cytolytic Fusion Proteins

Cancer immunotherapy aims to selectively target and kill tumor cells whilst limiting the damage to healthy tissues. Controlled delivery of plant, bacterial and human toxins or enzymes has been shown to promote the induction of apoptosis in cancerous cells. The 4th generation of targeted effectors are being designed to be as humanized as possible—a solution to the problem of immunogenicity encountered with existing generations. Granzymes are serine proteases which naturally function in humans as integral cytolytic effectors during the programmed cell death of cancerous and pathogen-infected cells. Secreted predominantly by cytotoxic T lymphocytes and natural killer cells, granzymes function mechanistically by caspase-dependent or caspase-independent pathways. These natural characteristics make granzymes one of the most promising human enzymes for use in the development of fusion protein-based targeted therapeutic strategies for various cancers. In this review, we explore research involving the use of granzymes as cytolytic effectors fused to antibody fragments as selective binding domains.

Construction of humanized anti-HER2 single-chain variable fragments (husFvs) and achievement of potent tumor suppression with the reconstituted husFv-Fdt-tBid immunoapoptotin

As HER2 is frequently overexpressed in various malignancies, targeting HER2 is considered an efficient, highly selective antitumor therapy. HER2-targeted immunoconjugates are being developed and result in persistent remission of HER2-overexpressing tumors. However, many of the antibodies used as the targeting moiety are of murine origin and exhibit risk of inducing immunogenicity, limiting their antitumor therapeutic efficacy. Here, we humanized e23sFv, an HER2-targeting murine scFv with excellent affinity and specificity, using a human antibody consensus sequence engraftment strategy. The affinity of the initially humanized e23sFv was then rescued and improved by selective mutagenesis followed by phage-display-based affinity panning of the mutant pool. The resulting humanized e23sFv candidates (husFvs) exhibited up-to-94-fold increased affinity to recombinant HER2. The immunogenicity of e23sFv was dramatically alleviated after humanization, as indicated by the impaired production of cytokines by husFv-stimulated human PBMCs. Two internalizable husFvs with optimal affinity were applied to generate humanized immunoapoptotins by infusion with the translocation domain Fdt and the proapoptotic domain truncated Bid. The husFv-immunoapoptotins demonstrated improved HER2-targeting and tumor-killing capacities in vitro and in vivo compared with the e23sFv-immunoapoptotins and would enable the administration of multiple treatment cycles to patients, resulting in improved antitumor efficacy. Furthermore, the husFvs recognized distinct HER2 epitopes and could thus be used in combination with trastuzumab or pertuzumab to achieve robust synergistic antitumor effects in HER2-positive malignancies.

Immunoproapoptotic molecule scFv-Fdt-tBid modified mesenchymal stem cells for prostate cancer dual-targeted therapy

Highly efficient target therapy is urgently needed for prostate cancer with overexpression of γ-seminoprotein (γ-SM). Recent studies indicated that mesenchymal stem cells (MSCs) are attractive candidate for cell-based, targeted therapy due to their tumor tropism. Here we designed a dual-target therapeutic system in which MSCs were engineered to produce and deliver scFv-Fdt-tBid, a novel γ-SM-targeted immunoproapoptotic molecule. Such engineered MSCs (MSC.scFv-Fdt-tBid) would home to tumor sites and release the fusion protein to induce the apoptosis of prostate cancer cells. Our data demonstrated that scFv-Fdt-tBid showed a selective, potent and dose-dependent inhibition for γ-SM-positive cells (LNCaP, C4-2, 22Rv1) rather than γ-SM-negative cells and MSCs. Importantly, MSC.scFv-Fdt-tBid caused cell death through an apoptosis-dependent manner. Further, the tropism of MSC.scFv-Fdt-tBid to prostate cancer was verified both in vitro and in vivo. Finally, the in vivo experiments demonstrated that MSC.scFv-Fdt-tBid significantly inhibited γ-SM-positive tumor growth without toxic side effects. Collectively, this study represented a novel immunoproapoptotic molecule scFv-Fdt-tBid for γ-SM-positive tumors and demonstrated the therapeutic efficiency and safety of scFv-Fdt-tBid-modified MSCs against prostate cancers.

Dual targeting and enhanced cytotoxicity to HER2-overexpressing tumors by immunoapoptotin-armored mesenchymal stem cells

Mesenchymal stem cells (MSCs) are promising vehicles for the delivery of anticancer agents in cancer therapy. However, the tumor targeting of loaded therapeutics is essential. Here, we explored a dual-targeting strategy to incorporate tumor-tropic MSC delivery with HER2-specific killing by the immunoapoptotin e23sFv-Fdt-tBid generated in our previous studies. The MSC engineering allowed simultaneous immunoapoptotin secretion and bioluminescence detection of the modified MSCs. Systemic administration of the immunoapoptotin-engineered MSCs was investigated in human HER2-reconstituted syngeneic mouse models of orthotopic and metastatic breast cancer, as well as in a xenograft nude mouse model of orthotopic gastric cancer. In vivo dual tumor targeting was confirmed by local accumulation of the bioluminescence-imaged MSCs and persistence of His-immunostained immunoapoptotins in tumor sites. The added tumor preference of MSC-secreted immunoapoptotins resulted in a significantly stronger antitumor effect compared with purified immunoapoptotins and Jurkat-delivered immunoapoptotins. This immunoapoptotin-armored MSC strategy provides a rationale for its use in extended malignancies by combining MSC mobility with redirected immunoapoptotins against a given tumor antigen.

Granzyme B-truncated VEGF fusion protein represses angiogenesis and tumor growth of OSCC

OBJECTIVE

To evaluate the antitumor effects of fusion protein hGrB-TV of human granzyme B (hGrB) and truncated vascular endothelial growth factor (tVEGF) on human oral squamous cell carcinoma (OSCC) in vitro and in vivo.

METHODS

The fusion protein hGrB-TV was expressed and purified from E. coli bacteria by affinity chromatography. The cytotoxcity of hGrB-TV on VEGFR-2 (Flk-1)(+) OSCC cells was analyzed in vitro. The antitumor therapeutic study was conducted on OSCC xenografts in vivo.

RESULTS

The purified hGrB-TV fusion protein was selectively internalized into VEGFR-2 (Flk-1)(+) OSCC cells and endothelial cells. It can cleave inactive caspase 3 into its active p20 form. The hGrB-TV showed dose-dependent cytotoxicity on VEGFR-2(+) SCC-9 cells. The morphological changes and cytolysis were appeared within dozen minutes. However, no cytotoxicity was observed on VEGFR-2(-) cells. The hGrB alone or tVEGF alone did not have any toxicity on SCC-9 cells. In addition, hGrB-TV treatment completely destroyed the vasculature of the chick chorioallantoic membrane (CAM) in vivo and consequently led to chick embryo development arrest. Most importantly, the fusion protein hGrB-TV inhibited tumor angiogenesis and growth of human OSCC xenografts in nude mice without any apparent toxicity.

CONCLUSIONS

The fusion protein hGrB-TV specifically inhibits angiogenesis and tumor growth of OSCC; hGrB-TV is a powerful and safe therapeutic molecule for tumor therapy.

A novel far-red fluorescent xenograft model of ovarian carcinoma for preclinical evaluation of HER2-targeted immunotoxins

We have created a novel fluorescent model of a human ovarian carcinoma xenograft overexpressing receptor HER2, a promising molecular target of solid tumors. The model is based on a newly generated SKOV-kat cell line stably expressing far-red fluorescent protein Katushka. Katushka is most suitable for the in vivo imaging due to an optimal combination of high brightness and emission in the "window of tissue transparency". The relevance of the fluorescent model for the in vivo monitoring of tumor growth and response to treatment was demonstrated using a newly created HER2-targeted recombinant immunotoxin based on the 4D5scFv antibody and a fragment of the Pseudomonas exotoxin A.

The functionalized human serine protease granzyme B/VEGF₁₂₁ targets tumor vasculature and ablates tumor growth

The serine protease granzyme B (GrB) induces apoptosis through both caspase-dependent and -independent multiple-cascade mechanisms. VEGF₁₂₁ binds to both VEGF receptor (VEGFR)-1 and VEGFR-2 receptors. We engineered a unique GrB/VEGF₁₂₁ fusion protein and characterized its properties in vitro and in vivo. Endothelial and tumor cell lines showed varying levels of sensitivity to GrB/VEGF₁₂₁ that correlated closely to total VEGFR-2 expression. GrB/VEGF₁₂₁ localized efficiently into VEGFR-2-expressing cells, whereas the internalization into VEGFR-1-expressing cells was significantly reduced. Treatment of VEGFR-2(+) cells caused mitochondrial depolarization in 48% of cells by 48 hours. Exposure to GrB/VEGF₁₂₁ induced apoptosis in VEGFR-2(+), but not in VEGFR-1(+), cells and rapid caspase activation was observed that could not be inhibited by treatment with a pan-caspase inhibitor. In vivo, GrB/VEGF₁₂₁ localized in perivascular tumor areas adjacent to microvessels and in other areas in the tumor less well vascularized, whereas free GrB did not specifically localize to tumor tissue. Administration (intravenous) of GrB/VEGF₁₂₁ to mice at doses up to 40 mg/kg showed no toxicity. Treatment of mice bearing established PC-3 tumor xenografts with GrB/VEGF₁₂₁ showed significant antitumor effect versus treatment with GrB or saline. Treatment with GrB/VEGF₁₂₁ at 27 mg/kg resulted in the regression of four of five tumors in this group. Tumors showed a two-fold lower Ki-67-labeling index compared with controls. Our results show that targeted delivery of GrB to tumor vascular endothelial cells or to tumor cells activates apoptotic cascades and this completely human construct may have significant therapeutic potential.

Efficacy of an adapted granzyme B-based anti-CD30 cytolytic fusion protein against PI-9-positive classical Hodgkin lymphoma cells in a murine model

Tumors develop when infiltrating immune cells contribute growth stimuli, and cancer cells are selected to survive within such a cytotoxic microenvironment. One possible immune-escape mechanism is the upregulation of PI-9 (Serpin B9) within cancer cells. This serine proteinase inhibitor selectively inactivates apoptosis-inducing granzyme B (GrB) from cytotoxic granules of innate immune cells. We demonstrate that most classical Hodgkin lymphoma (cHL)-derived cell lines express PI-9, which protects them against the GrB attack and thereby renders them resistant against GrB-based immunotherapeutics. To circumvent this disadvantage, we developed PI-9-insensitive human GrB mutants as fusion proteins to target the Hodgkin-selective receptor CD30. In contrast to the wild-type GrB, a R201K point-mutated GrB construct most efficiently killed PI-9-positive and -negative cHL cells. This was tested in vitro and also in vivo whereby a novel optical imaging-based tumor model with HL cell line L428 was applied. Therefore, this variant, as part of the next generation immunotherapeutics, also named cytolytic fusion proteins showing reduced immunogenicity, is a promising molecule for (targeted) therapy of patients with relapsing malignancies, such as cHL, and possibly other PI-9-positive malignancies, such as breast or lung carcinoma.

A novel recombinant immunocasp-6 fusion gene specifically and efficiently suppresses HER2-overexpressing osteosarcoma

Osteosarcoma is the most common primary malignant tumor of bone for adolescent or children. The poor prognosis of patients, due to its remote metastasis, has led to the exploration of more effective and less toxic treatments. Immunotherapy is a promising strategy for the treatment of human epidermal growth factor receptor 2 (HER2)-overexpressing tumors. Herein, we describe experiments conducted with a fusion gene, immunocasp-6, which was generated by fusing a HER2-specific single-chain Ab, a single-chain Pseudomonas exotoxin A and an active caspase-6 which can directly cleave lamin A leading to nucleus damage inducing programmed cell death. We demonstrated that immunocasp-6 can specifically and efficiently recognize and induce apoptosis in HER2-overexpressing osteosarcoma cells in vitro. The immunocasp-6 was transferred into BALB/c athymic mice bearing human osteosarcoma by i.m. injection of liposome-encapsulated pCMV-immunocap-6. Expression of immunocasp-6 not only strongly inhibited tumor growth and significantly prolonged animal survival, but also greatly prevented tumor metastasis. Our data showed that the immuno-casp-6 can specifically recognize HER2-overexpressing osteosarcoma cells, can also promptly attack their nucleus and induce apoptotic death, suggesting the potential of this strategy for the treatment of human HER2-overexpressing tumors.

Cancer gene therapy targeting cellular apoptosis machinery

The unraveling of cellular apoptosis machinery provides novel targets for cancer treatment, and gene therapy targeting this suicidal system has been corroborated to cause inflammation-free autonomous elimination of neoplastic cells. The apoptotic machinery can be targeted by introduction of a gene encoding an inducer, mediator or executioner of apoptotic cell death or by inhibition of anti-apoptotic gene expression. Strategies targeting cancer cells, which are achieved by selective gene delivery, specific gene expression or secretion of target proteins via genetic modification of autologous cells, dictate the outcome of apoptosis-based cancer gene therapy. Despite so far limited clinical success, gene therapy targeting the apoptotic machinery has great potential to benefit patients with threatening malignancies provided the availability of efficient and specific gene delivery and administration systems.

Antibody-enzyme fusion proteins for cancer therapy

Advances in biomolecular technology have allowed the development of genetically fused antibody-enzymes. Antibody-enzyme fusion proteins have been used to target tumors for cancer therapy in two ways. In one system, an antibody-enzyme is pretargeted to the tumor followed by administration of an inactive prodrug that is converted to its active form by the pretargeted enzyme. This system has been described as antibody-directed enzyme prodrug therapy. The other system uses antibody-enzyme fusion proteins as direct therapeutics, where the enzyme is toxic in its own right. The key feature in this approach is that the antibody is used to internalize the toxic enzyme into the tumor cell, which activates cell-death processes. This antibody-enzyme system has been largely applied to deliver ribonucleases. This article addresses these two antibody-enzyme targeting strategies for cancer therapy from concept to (pre)clinical trials.

Delivery and therapeutic potential of human granzyme B

Granzyme B (GzmB) is used by cytotoxic lymphocytes as a molecular weapon for the defense against virus-infected and malignantly transformed host cells. It belongs to a family of small serine proteases that are stored in secretory vesicles of killer cells. After secretion of these cytolytic granules during killer cell attack, GzmB is translocated into the cytosol of target cells with the help of the pore-forming protein perforin. GzmB has adopted similar protease specificity as caspase-8, and once delivered, it activates major executioner apoptosis pathways. Since GzmB is very effective in killing human tumor cell lines that are otherwise resistant against many cytotoxic drugs and since GzmB of human origin can be recombinantly expressed, its use as part of a 'magic bullet' in tumor therapy is a very tempting idea. In this review, we emphasize the peculiar characteristics of GzmB that make it suited for use as an effector domain in potential immunoconjugates. We discuss what is known about its uptake into target cells and the trials performed with GzmB-armed immunoconjugates, and we assess the prospects of its potential therapeutic value.

The role of HER2 in cancer therapy and targeted drug delivery

HER2 is highly expressed in a significant proportion of breast cancer, ovarian cancer, and gastric cancer. Since the discovery of its role in tumorigenesis, HER2 has received great attention in cancer research during the past two decades. Successful development of the humanized monoclonal anti-HER2 antibody (Trastuzumab) for the treatment of breast cancer further spurred scientists to develop various HER2 specific antibodies, dimerization inhibitors and kinase inhibitors for cancer therapy. On the other hand, the high expression of HER2 and the accessibility of its extracellular domain make HER2 an ideal target for the targeted delivery of anti-tumor drugs as well as imaging agents. Although there is no natural ligand for HER2, artificial ligands targeting HER2 have been developed and applied in various targeted drug delivery systems. The emphasis of this review is to elucidate the roles of HER2 in cancer therapy and targeted drug delivery. The structure and signal pathway of HER2 will be briefly described. The role of HER2 in tumorigenesis and its relationship with other tumor markers will be discussed. For the HER2 targeted cancer therapy, numerous strategies including the blockage of receptor dimerization, inhibition of the tyrosine kinase activity, and interruption of the downstream signal pathway will be summarized. For the targeted drug delivery to HER2 positive tumor cells, various targeting ligands and their delivery systems will be described in details.

Granzyme B-H22(scFv), a human immunotoxin targeting CD64 in acute myeloid leukemia of monocytic subtypes

Acute myeloid leukemia (AML) cells of subtypes M4 and M5 show enhanced expression of CD64 (FcgammaRI), the high-affinity receptor for IgG, which is normally expressed at high levels only on activated cells of the myeloid lineage. CD64 is therefore a prime target for the specific delivery of cytotoxic agents. A promising toxin candidate is granzyme B, a human serine protease originating from cytotoxic granules of CD8+ T lymphocytes and natural killer cells. After evaluating the sensitivity of the AML-related cell line U937 toward cytosolic granzyme B, we genetically fused granzyme B to H22, a humanized single-chain antibody fragment (scFv) specific for CD64, to obtain Gb-H22(scFv), a fusion protein lacking the immunogenic properties of nonhuman immunofusions. Gb-H22(scFv) was successfully expressed in human 293T cells, secreted, and purified from cell culture supernatants. The purified protein bound specifically to CD64+ U937 cells. Despite linkage to the binding domain, the proteolytic activity of functional Gb-H22(scFv) was identical to that of free granzyme B. Target cell-specific cytotoxicity was observed with a half-maximal inhibitory concentration (IC50) between 1.7 and 17 nmol/L. In addition, the induction of apoptosis in U937 cells was confirmed by Annexin A5 staining and the detection of activated caspase-3 in the cytosol. Finally, apoptosis was observed in primary CD64+ AML cells, whereas CD64(-) AML cells were unaffected. This is the first report of a completely human granzyme B-based immunotoxin directed against CD64, with activity against an AML-related cell line and primary AML cells.

Single-chain antibody/activated BID chimeric protein effectively suppresses HER2-positive tumor growth

BH3-interacting domain death agonist (BID) is a crucial element in death signaling pathways and is recognized as an intracellular link connecting the intrinsic mitochondrial apoptotic and extrinsic death receptor-mediated apoptotic pathways. Herein, we describe experiments conducted with a fusion protein, which was generated by fusing a human epidermal growth factor receptor-2 (HER2)-specific single-chain antibody with domain II of Pseudomonas exotoxin A and the truncated active BID (tBID). These experiments extend our previous work on several other immuno-proapoptotic proteins. Specifically, by excluding cells with undetectable HER2, we showed that the secreted immuno-tBID molecule selectively recognized and killed HER2-overexpressing tumor cells in vitro by attacking their mitochondria and inducing their apoptotic death. This apoptosis could only be inhibited partially by caspase pan-inhibitor zVAD and mitochondrial protector TAT-BH4. Subsequently, we transferred the immuno-tbid gene into BALB/c athymic mice bearing HER2-positive tumors together with other immuno-proapoptotic proteins using i.m. injections of liposome-encapsulated vectors. The expression of the immuno-tbid gene suppressed tumor growth and prolonged animal survival significantly. We also shortened the translocation domain of Pseudomonas exotoxin A II to only 10-amino acid sequence, which were crucial for furin cleavage. The new recombinant molecule retained the translocation efficiency and the ability of specific killing HER2-positive tumor cells. Our data showed that, compared with the toxins employed before, the chimeric immuno-tBID molecule can not only specifically recognize HER2-positive tumor cells but also certainly induce apoptosis even in the presence of zVAD and TAT-BH4, thereby suggesting an alternative approach to treating HER2/neu-positive tumors.

Targeted apoptosis activation with GrB/scFvMEL modulates melanoma growth, metastatic spread, chemosensitivity, and radiosensitivity

GrB/scFvMEL, a fusion protein composed of human granzyme B (GrB) and the single-chain antibody scFvMEL, targets melanoma gp240 antigen and exerts impressive cytotoxic effects by inducing apoptosis. We evaluated the effects of GrB/scFvMEL on chemotherapy, radiation therapy, metastasis in vitro, and the growth of human melanoma A375 xenograft tumors in nude mice. GrB/scFvMEL showed synergistic cytotoxicity when coadministered with doxorubicin, vincristine or cisplatin, and additive effects, in combination with etoposide or cytarabine. Optimal cytotoxic effects were obtained when cells were treated first with GrB/scFvMEL followed by exposure to the agent (rather than the reverse). Pretreatment of A375 cells with GrB/scFvMEL significantly sensitized melanoma cells to ionizing radiation assessed using a clonogenic survival assay. Subtoxic doses of GrB/scFvMEL inhibited the invasion of A375 cells into Matrigel. GrB/scFvMEL (37.5 mg/kg) was administered intravenously to nude mice bearing A375 tumors. Saline-treated tumors increased 24-fold, whereas tumors treated with GrB/scFvMEL showed a significant tumor growth delay increasing four-fold. Tumor tissue displayed an increase in apoptotic nuclei compared to control. Thus, the targeted delivery of GrB to tumors may have a significant potential for cancer treatment. Targeted therapeutic agents specifically designed to impact cellular apoptotic pathways may represent a novel class of therapeutic agents.

Granzyme M Directly Cleaves Inhibitor of Caspase-Activated DNase (CAD) to Unleash CAD Leading to DNA Fragmentation

Granzyme (Gzm)M is constitutively highly expressed in NK cells that may play a critical role in NK cell-mediated cytolysis. However, the function of GzmM has been less defined. Just one report showed GzmM induces a caspase-independent death pathway. In this study, we demonstrate a protein transfection reagent Pro-Ject can efficiently transport GzmM into target cells. GzmM initiates caspase-dependent apoptosis with typical apoptotic nuclear morphology. GzmM induces DNA fragmentation, not DNA nicking. GzmM can directly degrade inhibitor of caspase-activated DNase to release the nuclease activity of caspase-activated DNase for damaging DNA. Furthermore, GzmM cleaves the DNA damage sensor enzyme poly(ADP-ribose) polymerase to prevent cellular DNA repair and force apoptosis.

Eukaryotic expression vectors and immunoconjugates for cancer therapy

This review considers ways to address specificity to therapeutic targeted anticancer agents. These include transcriptional activation of tissue- and tumor-specific promoters in eukaryotic expression vectors and use of antitumor-directed immunoconjugates. The review deals with analysis of strategies used for selection of targeted promoters and examples of antibody fusion proteins exhibiting antitumor activity. A new direction in antitumor treatment pooling together methods of gene therapy and antibody therapy has appeared. This direction is based on the development of vectors encoding secreted forms of immunoconjugates. After vector introduction into a cell, the latter is capable of synthesizing and secreting antibody fusion protein composed of a therapeutic anticancer agent and antibody specifically targeted to cancer cells.

Selective proapoptotic activity of a secreted recombinant antibody/AIF fusion protein in carcinomas overexpressing HER2

Apoptosis-inducing factor (AIF) represents a caspase-independent apoptotic pathway in the cell, and a mitochondrial localization sequence-truncated AIF (AIFDelta1-120) can be relocated from the cytoplasm to the nucleus and exhibit a constitutive proapoptotic activity. Here, we generated a chimeric immuno-AIF protein, which comprised an HER2 antibody, a Pseudomonas exotoxin translocation domain and AIFDelta1-120. Human Jurkat cells transfected with the immuno-AIF gene could express and secrete the chimeric protein, which selectively recognized HER2-overexpressing tumor cells and was endocytosed. Subsequent cleavage of truncated AIF from immuno-AIF and its release from the internalized vesicles resulted in apoptosis of tumor cells. Intramuscular injection of the immuno-AIF gene caused significant suppression of tumors and substantially prolonged mice survival in an HER2-overexpressing xenograft tumor model. Our study demonstrates the feasibility of the immuno-AIF gene as a novel approach to treating cancers that overexpress HER2.

Targeted induction of apoptosis by chimeric granzyme B fusion proteins carrying antibody and growth factor domains for cell recognition

The serine protease granzyme B (GrB) of cytotoxic lymphocytes efficiently induces apoptosis by direct activation of caspases and cleavage of central caspase substrates. We employed human GrB as an effector function in chimeric fusion proteins that also contain the EGFR ligand TGFalpha or an ErbB2-specific single-chain antibody fragment (scFv) for selective targeting to tumor cells. GrB-TGFalpha (GrB-T) and GrB-scFv(FRP5) (GrB-5) molecules expressed in the yeast Pichia pastoris were bifunctional, cleaving synthetic and natural GrB substrates, and binding specifically to cells expressing EGFR or ErbB2 target receptors. Upon cell binding the chimeric molecules were internalized into intracellular vesicles, but could be released into the cytosol by the endosomolytic reagent chloroquine. Treatment with picomolar to nanomolar concentrations of GrB-5 and GrB-T resulted in selective and rapid tumor cell killing, accompanied by clear signs of apoptosis such as chromatin condensation, membrane blebbing, formation of apoptotic bodies and activation of endogenous initiator and effector caspases.