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

Modeling antibody drug conjugate potential using a granzyme B antibody fusion protein

BACKGROUND

Antibody drug conjugates (ADCs) constitute a promising class of targeted anti-tumor therapeutics that harness the selectivity of monoclonal antibodies with the potency of cytotoxic drugs. ADC development is best suited to initially screening antibody candidates for desired properties that potentiate target cell cytotoxicity. However, validating and producing an optimally designed ADC requires expertise and resources not readily available to certain laboratories.

RESULTS

In this study, we propose a novel approach to help streamline the identification of potential ADC candidates by utilizing a granzyme B (GrB)-based antibody fusion protein (AFP) for preliminary screening. GrB is a non-immunogenic serine protease expressed by immune effector cells such as CD8 + T cells that induces apoptotic activity and can be leveraged for targeted cell killing.

CONCLUSIONS

Our innovative model allows critical antibody parameters (including target cell binding, internalization, and cytotoxic potential) to be more reliably evaluated in vitro through the creation of an ADC surrogate. Successful incorporation of this AFP could also significantly expand and enhance ADC development pre-clinically, ultimately leading to the accelerated translation of ADC therapies for patients.

Therapeutic efficacy and safety of a human fusion construct targeting the TWEAK receptor Fn14 and containing a modified granzyme B

Background

Antibody-drug conjugates are an exceptional and useful therapeutic tool for multiple diseases, particularly for cancer treatment. We previously showed that the fusion of the serine protease granzyme B (GrB), the effector molecule or T and B cells, to a binding domain allows the controlled and effective delivery of the cytotoxic payload into the target cell. The production of these constructs induced the formation of high molecular aggregates with a potential impact on the efficacy and safety of the protein.

Methods

Our laboratory designed a new Fn14 targeted fusion construct designated GrB(C210A)-Fc-IT4 which contains a modified GrB payload for improved protein production and preserved biological activity. We assessed the construct’s enzymatic activity, as well as in vitro cytotoxicity and internalization into target cells. We also assessed pharmacokinetics, efficacy and toxicology parameters in vivo.

Results

GrB(C210A)-Fc-IT4 protein exhibited high affinity and selective cytotoxicity within the nanomolar range when tested against a panel of Fn14-positive human cancer cell lines. The construct rapidly internalized into target cells, activating the caspase cascade and causing mitochondrial membrane depolarization. Pharmacokinetic studies in mice revealed that GrB(C210A)-Fc-IT4 displayed a bi-exponential clearance from plasma with a fast initial clearance (t_1/2α=0.36 hour) followed by a prolonged terminal-phase plasma half-life (t_1/2β=35 hours). Mice bearing MDA-MB-231 orthotopic tumor xenografts treated with vehicle or GrB(C210A)-Fc-IT4 construct (QODx5) demonstrated tumor regression and long-term (>80 days) suppression of tumor growth. Treatment of mice bearing established, subcutaneous A549 lung tumors showed impressive, long-term tumor suppression compared with a control group treated with vehicle alone. Administration of GrB(C210A)-Fc-IT4 (100 mg/kg total dose) was well-tolerated by mice and resulted in significant reduction of tumor burden in a lung cancer patient-derived xenograft model. Toxicity studies revealed no statistically significant changes in aspartate transferase, alanine transferase or lactate dehydrogenase in treated mice. Histopathological analysis of tissues from treated mice did not demonstrate any specific drug-related changes.

Conclusion

GrB(C210A)-Fc-IT4 demonstrated excellent, specific cytotoxicity in vitro and impressive in vivo efficacy with no significant toxicity in normal murine models. These studies show GrB(C210A)-Fc-IT4 is an excellent candidate for further preclinical development.

A novel Granzyme B nanoparticle delivery system simulates immune cell functions for suppression of solid tumors

Cell-based immunotherapy for the treatment of hematologic malignancies, such as leukemia and lymphoma, has seen much success and played an increasingly important role in clinical studies. Nevertheless, the efficacy of immunotherapy in solid tumors still needs improvements due to the immunosuppressive properties of tumor cells and the microenvironment. To overcome these limitations, we prepared a novel tumor-targeting delivery system based on the underlying mechanism of immune-targeted cell death that encapsulated granzyme B protein within a porous polymeric nanocapsule.

Methods: A cell-penetrating peptide TAT was attached onto granzyme B (GrB) to enhance its transmembrane transport efficiency and potency to induce cell apoptosis. The endocytosis and internalization pathways of GrB-TAT (GrB-T) were analyzed in comparison with perforin by confocal microscopy and flow cytometry. Furthermore, the positively charged GrB-T was wrapped into nanoparticles by p-2-methacryloyloxy ethyl phosphorylcholine (PMPC)-modified HA (hyaluronic acid). The nanoparticles (called TCiGNPs) were characterized in terms of zeta potential and by transmission electron microscopy (TEM). The in vitro anti-tumor effects of GrB-T were examined by cell apoptosis assay and Western blotting analysis. The in vivo anti-tumor therapeutic efficacy of TCiGNPs was evaluated in a mouse tumor model.

Results: The TAT peptide could play a role similar to perforin to mediate direct transmembrane transfer of GrB and improve GrB-induced cell apoptosis. The TCiGNPs were successfully synthesized and accumulated in the solid tumor through enhanced permeability and retention (EPR) effect. In the tumor microenvironment, TCiGNPs could be degraded by hyaluronidase and triggered the release of GrB-T. The TAT peptide enabled the translocation of GrB across the plasma membrane to induce tumor cell apoptosis in vivo.

Conclusion: We successfully developed a granzyme B delivery system with a GrB-T core and a PMPC/HA shell that simulated CTL/NK cell-mediated cancer immunotherapy mechanism. The GrB delivery system holds great promise for cancer treatment analogous to the CTL/NK cell-induced immunotherapy.

Development of a human immuno-oncology therapeutic agent targeting HER2: targeted delivery of granzyme B

Background

Immunotherapeutic approaches designed to augment T and B cell mediated killing of tumor cells has met with clinical success in recent years suggesting tremendous potential for treatment in a broad spectrum of tumor types. After complex recognition of target cells by T and B cells, delivery of the serine protease granzyme B (GrB) to tumor cells comprises the cytotoxic insult resulting in a well-characterized, multimodal apoptotic cascade.

Methods

We designed a recombinant fusion construct, GrB-Fc-4D5, composed of a humanized anti-HER2 scFv fused to active GrB for recognition of tumor cells and internal delivery of GrB, simulating T and B cell therapy. We assessed the construct’s antigen-binding specificity and GrB enzymatic activity, as well as in vitro cytotoxicity and internalization into target and control cells. We also assessed pharmacokinetic and toxicology parameters in vivo.

Results

GrB-Fc-4D5 was highly cytotoxic to Her2 positive cells such as SKBR3, MCF7 and MDA-MB-231 with IC₅₀ values of 56, 99 and 27 nM, respectively, and against a panel of HER2+ cell lines regardless of endogenous expression levels of the PI-9 inhibitor. Contemporaneous studies with Kadcyla demonstrated similar levels of in vitro activity against virtually all cells tested. GrB-Fc-4D5 internalized rapidly into target SKOV3 cells within 1 h of exposure rapidly delivering GrB to the cytoplasmic compartment. In keeping with its relatively high molecular weight (160 kDa), the construct demonstrated a terminal-phase serum half-life in mice of 39.2 h. Toxicity studies conducted on BALB/c mice demonstrated no statistically significant changes in SGPT, SGOT or serum LDH. Histopathologic analysis of tissues from treated mice demonstrated no drug-related changes in any tissues examined.

Conclusion

GrB-Fc-4D5 shows excellent, specific cytotoxicity and demonstrates no significant toxicity in normal, antigen-negative murine models. This construct constitutes a novel approach against HER2-expressing tumors and is an excellent candidate for further development.

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.

Targeting of Tumor Neovasculature with GrB/VEGF121, a Novel Cytotoxic Fusion Protein

Angiogenesis is a critical process in numerous diseases, and intervention in neovascularization has therapeutic value in several disease settings, including ocular diseases, arthritis, and in tumor progression and metastatic spread. Various vascular targeting agents have been developed, including those that inhibit growth factor receptor tyrosine kinases, blocking antibodies that interfere with receptor signal transduction, and strategies that trap growth factor ligands. Limited anti-tumor efficacy studies have suggested that the targeted delivery of the human pro-apoptotic molecule Granzyme B to tumor cells has significant potential for cancer treatment. Here, we review biological vascular targeting agents, and describe a unique vascular targeting agent composed of Granzyme B and the VEGF receptor ligand VEGF₁₂₁. The fusion protein GrB/VEGF₁₂₁ demonstrates cytotoxicity at nanomolar or sub-nanomolar levels, excellent pharmacokinetic and efficacy profiles, and has significant therapeutic potential targeting tumor vasculature.

A novel fully-human cytolytic fusion protein based on granzyme B shows in vitro cytotoxicity and ex vivo binding to solid tumors overexpressing the epidermal growth factor receptor

Human cytolytic fusion proteins (hCFPs) offer a promising immunotherapeutic approach for the treatment of solid tumors, avoiding the immunogenicity and undesirable side-effects caused by immunotoxins derived from plants or bacteria. The well-characterized human serine protease granzyme B has already been used as a therapeutic pro-apoptotic effector domain. We therefore developed a novel recombinant hCFP (GbR201K-scFv1711) consisting of an epidermal growth factor receptor-specific human antibody fragment and a granzyme B point mutant (R201K) that is insensitive to serpin B9 (PI9), a natural inhibitor of wild-type granzyme B that is often expressed in solid tumors. We found that GbR201K-scFv1711 selectively bound to epidermoid cancer and rhabdomyosarcoma cells and was rapidly internalized by them. Nanomolar concentrations of GbR201K-scFv1711 achieved the specific killing of epidermoid cancer cells by inducing apoptosis, and similar effects were observed in rhabdomyosarcoma cells when GbR201K-scFv1711 was combined with the endosomolytic substance chloroquine. The novel hCFP was stable in serum and bound to human rhabdomyosarcoma tissue ex vivo. These data confirm that GbR201K-scFv1711 is a promising therapeutic candidate suitable for further clinical investigation.

Development of human serine protease-based therapeutics targeting Fn14 and identification of Fn14 as a new target overexpressed in TNBC

The cytokine TWEAK and its receptor, Fn14, have emerged as potentially valuable targets for cancer therapy. Granzyme B (GrB)-containing Fn14-targeted constructs were generated containing either the Fn14 ligand TWEAK (GrB-TWEAK) or an anti-Fn14 humanized single-chain antibody (GrB-Fc-IT4) as the targeting moieties. Both constructs showed high affinity and selective cytotoxicity against a panel of Fn14-expressing human tumor cells including triple-negative breast cancer (TNBC) lines. Cellular expression of the GrB inhibitor PI-9 in target cells had no impact on the cytotoxic effect of either construct. Cellular expression of MDR1 showed no cross-resistance to the fusion constructs. GrB-TWEAK and GrB-Fc-IT4 activated intracellular caspase cascades and cytochrome c-related proapoptotic pathways consistent with the known intracellular functions of GrB in target cells. Treatment of mice bearing established HT-29 xenografts with GrB-TWEAK showed significant tumor growth inhibition compared with vehicle alone (P < 0.05). Both GrB-TWEAK and GrB-Fc-IT4 displayed significant tumor growth inhibition when administered to mice bearing orthotopic MDA-MB-231 (TNBC) tumor xenografts. The Cancer Genome Atlas analysis revealed that Fn14 mRNA expression was significantly higher in TNBC and in HER2-positive disease (P < 0.0001) compared with hormone receptor-positive breast cancer, and in basal-like 2 tumors (P = 0.01) compared with other TNBC molecular subtypes. IHC analysis of a 101 patient TNBC tumor microarray showed that 55 of 101 (54%) of tumors stained positive for Fn14, suggesting that this may be an excellent potential target for precision therapeutic approaches. Targeting Fn14 using fully human, GrB-containing fusion constructs may form the basis for a new class of novel, potent, and highly effective constructs for targeted therapeutic applications.