DR5-Selective TRAIL Variant DR5-B Functionalized with Tumor-Penetrating iRGD Peptide for Enhanced Antitumor Activity against Glioblastoma

TRAIL (TNF-related apoptosis-inducing ligand) and its derivatives are potentials for anticancer therapy due to the selective induction of apoptosis in tumor cells upon binding to death receptors DR4 or DR5. Previously, we generated a DR5-selective TRAIL mutant variant DR5-B overcoming receptor-dependent resistance of tumor cells to TRAIL. In the current study, we improved the antitumor activity of DR5-B by fusion with a tumor-homing iRGD peptide, which is known to enhance the drug penetration into tumor tissues. The obtained bispecific fusion protein DR5-B-iRGD exhibited dual affinity for DR5 and integrin αvβ3 receptors. DR5-B-iRGD penetrated into U-87 tumor spheroids faster than DR5-B and demonstrated an enhanced antitumor effect in human glioblastoma cell lines T98G and U-87, as well as in primary patient-derived glioblastoma neurospheres in vitro. Additionally, DR5-B-iRGD was highly effective in a xenograft mouse model of the U-87 human glioblastoma cell line in vivo. We suggest that DR5-B-iRGD may become a promising candidate for targeted therapy for glioblastoma.

A novel anti-HIV-1 bispecific bNAb-lectin fusion protein engineered in a plant-based transient expression system

The discovery of broadly neutralizing antibodies (bNAbs) has been a major step towards better prophylactic and therapeutic agents against human immunodeficiency virus type 1 (HIV-1). However, effective therapy will likely require a combination of anti-HIV agents to avoid viral evasion. One possible solution to this problem is the creation of bispecific molecules that can concurrently target two vulnerable sites providing synergistic inhibitory effects. Here, we describe the production in plants and anti-HIV activity of a novel bispecific fusion protein consisting of the antigen-binding fragment (Fab) of the CD4 binding site-specific bNAb VRC01 and the antiviral lectin Avaren, which targets the glycan shield of the HIV-1 envelope (VRC01Fab -Avaren). This combination was justified by a preliminary experiment demonstrating the synergistic HIV-1 neutralization activity of VRC01 and Fc-fused Avaren dimer (Avaren-Fc). Using the GENEWARE® tobacco mosaic virus vector, VRC01Fab -Avaren was expressed in Nicotiana benthamiana and purified using a three-step chromatography procedure. Surface plasmon resonance and ELISA demonstrated that both the Avaren and VRC01Fab moieties retain their individual binding specificities. VRC01Fab -Avaren demonstrated enhanced neutralizing activity against representative HIV-1 strains from A, B and C clades, compared to equimolar combinations of VRC01Fab and Avaren. Notably, VRC01Fab -Avaren showed significantly stronger neutralizing effects than the bivalent parent molecules VRC01 IgG and Avaren-Fc, with IC50 values ranging from 48 to 310 pm. These results support the continued development of bispecific anti-HIV proteins based on Avaren and bNAbs, to which plant-based transient overexpression systems will provide an efficient protein engineering and production platform.

A bispecific enediyne-energized fusion protein targeting both epidermal growth factor receptor and insulin-like growth factor 1 receptor showing enhanced antitumor efficacy against non-small cell lung cancer

Epidermal growth factor receptor (EGFR) and insulin-like growth factor 1 receptor (IGF-1R) both overexpressed on non-small cell lung cancer (NSCLC) and are known cooperatively to promote tumor progression and drug resistance. This study was to construct a novel bispecific fusion protein EGF-IGF-LDP-AE consisting of EGFR and IGF-IR specific ligands (EGF and IGF-1) and lidamycin, an enediyne antibiotic with potent antitumor activity, and investigate its antitumor efficacy against NSCLC. Binding and internalization assays showed that EGF-IGF-LDP protein could bind to NSCLC cells with high affinity and then internalized into cells with higher efficiency than that of monospecific proteins. In vitro, the enediyne-energized analogue of bispecific fusion protein (EGF-IGF-LDP-AE) displayed extremely potent cytotoxicity to NSCLC cell lines with IC₅₀<10⁻¹¹ mol/L. Moreover, the bispecific protein EGF-IGF-LDP-AE was more cytotoxic than monospecific proteins (EGF-LDP-AE and LDP-IGF-AE) and lidamycin. In vivo, EGF-IGF-LDP-AE markedly inhibited the growth of A549 xenografts, and the efficacy was more potent than that of lidamycin and monospecific counterparts. EGF-IGF-LDP-AE caused significant cell cycle arrest and it also induced cell apoptosis in a dosage-dependent manner. Pretreatment with EGF-IGF-LDP-AE inhibited EGF-, IGF-stimulated EGFR and IGF-1R phosphorylation, and blocked two main downstream signaling molecules AKT and ERK activation. These data suggested that EGF-LDP-IGF-AE protein would be a promising targeted agent for NSCLC patients with EGFR and/or IGF-1R overexpression.

Interleukin-15:Interleukin-15 receptor α scaffold for creation of multivalent targeted immune molecules

Human interleukin-15 (hIL-15) and its receptor α (hIL-15Rα) are co-expressed in antigen presenting cells allowing trans-presentation of the cytokine to immune effector cells. We exploited the high-affinity interactions between hIL-15 and the extracellular hIL-15Rα sushi domain (hIL-15RαSu) to create a functional scaffold for the design of multispecific fusion protein complexes. Using single-chain T cell receptors (scTCRs) as recognition domains linked to the IL-15:IL-15Rα scaffold, we generated both bivalent and bispecific complexes. In these fusions, the scTCR domains retain the antigen-binding activity and the hIL-15 domain exhibits receptor binding and biological activity. As expected, bivalent scTCR fusions exhibited improved antigen binding due to increased avidity, whereas fusions comprising two different scTCR domains were capable of binding two cognate peptide/MHC complexes. Bispecific molecules containing scTCR and scCD8αβ domains also exhibit enhanced binding to peptide/MHC complexes, demonstrating that the IL-15:IL-15Rα scaffold displays flexibility necessary to support multi-domain interactions with a given target. Surprisingly, functional heterodimeric molecules could be formed by co-expressing the TCR α and β chains separately as fusions to the hIL-15 and hIL-15RαSu domains. Together, these properties indicate that the hIL-15 and hIL-15RαSu domains can be used as versatile, functional scaffold for generating novel targeted immune molecules.