An anti-transferrin receptor antibody enhanced the growth inhibitory effects of chemotherapeutic drugs on human non-hematopoietic tumor cells

The Transferrin Receptor-Directed CAR for the Therapy of Hematologic Malignancies

As many patients ultimately relapse after chimeric antigen receptor (CAR) T-cell therapy, identification of alternative targets is currently being evaluated. Substantial research efforts are underway to develop new targets. The transferrin receptor (TfR) is prevalently expressed on rapidly proliferating tumor cells and holds the potential to be the alternative target. In order to investigate the efficacy and challenges of TfR-targeting on the CAR-based therapy strategy, we generated a TfR-specific CAR and established the TfR-CAR–modified T cells. To take the advantage of TfR being widely shared by multiple tumors, TfR-CAR T cells were assessed against several TfR⁺ hematological malignant cell lines. Data showed that TfR-CAR T cells were powerfully potent in killing all these types of cells in vitro and in killing T-ALL cells in vivo. These findings suggest that TfR could be a universal target to broaden and improve the therapeutic efficacy of CAR T cells and warrant further efforts to use these cells as an alternative CAR T cell product for the therapy of hematological malignancies.

Antibodies Targeting the Transferrin Receptor 1 (TfR1) as Direct Anti-cancer Agents

The transferrin receptor 1 (TfR1), also known as cluster of differentiation 71 (CD71), is a type II transmembrane glycoprotein that binds transferrin (Tf) and performs a critical role in cellular iron uptake through the interaction with iron-bound Tf. Iron is required for multiple cellular processes and is essential for DNA synthesis and, thus, cellular proliferation. Due to its central role in cancer cell pathology, malignant cells often overexpress TfR1 and this increased expression can be associated with poor prognosis in different types of cancer. The elevated levels of TfR1 expression on malignant cells, together with its extracellular accessibility, ability to internalize, and central role in cancer cell pathology make this receptor an attractive target for antibody-mediated therapy. The TfR1 can be targeted by antibodies for cancer therapy in two distinct ways: (1) indirectly through the use of antibodies conjugated to anti-cancer agents that are internalized by receptor-mediated endocytosis or (2) directly through the use of antibodies that disrupt the function of the receptor and/or induce Fc effector functions, such as antibody-dependent cell-mediated cytotoxicity (ADCC), antibody-dependent cell-mediated phagocytosis (ADCP), or complement-dependent cytotoxicity (CDC). Although TfR1 has been used extensively as a target for antibody-mediated cancer therapy over the years, interest continues to increase for both targeting the receptor for delivery purposes and for its use as direct anti-cancer agents. This review focuses on the developments in the use of antibodies targeting TfR1 as direct anti-tumor agents.

Monoclonal antibody AC10364 inhibits cell proliferation in 5-fluorouracil resistant hepatocellular carcinoma via apoptotic pathways

Background

This study was designed to investigate the antitumor activity of the mAb (AC10364) in vitro and elucidate the related mechanisms of inhibition to cell growth using bel/fu cells treated with AC10364.

Methods

The inhibitory effects of AC10364 on the proliferation of Bel/fu cells were examined using a cytotoxicity assay. Apoptosis of Bel/fu cells was detected using FITC annexin V and PI staining following treatment with AC10364 for 24 h. The factors regulating apoptosis were identified by Western blot using lysates of Bel/fu cells treated with AC10364 for 0, 12, 24, or 36 h. Genes associated with tumorigenesis or growth were analyzed by reverse transcription–quantitative polymerase chain reaction using Bel/fu cells treated for 12, 24, or 36 h with AC10364.

Results

The early apoptotic ratios of Bel/fu cells treated with AC10364 increased in a dose-dependent manner. The levels of caspases, including cleaved caspase-3, caspase-3 and caspase-9, were significantly high in Bel/fu cells treated with AC10364 (P<0.001). Compared with untreated cells, those exposed to AC10364 had showed significant downregulation of the expression of binding protein gene (G protein subunit α 15, GNA15) and other protein-coding genes, including fms-related tyrosine kinase 1(FLT1), nicotinamide phosphoribosyltransferase (NAMPT), netrin 4 (NTN4), platelet-derived growth factor subunit A (PDGFA), S100 calcium binding protein A11 (S100A11), tubulin β 3 class III (TUBB3), aldo-keto reductase family 1 member C3 (AKR1C3), endothelial PAS domain protein 1 (EPAS1), and interferon α-inducible protein 27 (IFI27) (P<0.001). Two other genes, AXL receptor tyrosine kinase (AXL) and carboxypeptidase A4 (CPA4), were significantly upregulated (P<0.001).

Conclusion

AC10364 inhibited cell viability and proliferation through aberrant expression of multiple genes associated with tumorigenesis or growth, which suggests that these genes may be promising therapeutic candidates for cancer therapy.

Endocytosis of a functionally enhanced GFP-tagged transferrin receptor in CHO cells

The endocytosis of transferrin receptor (TfR) has served as a model to study the receptor-targeted cargo delivery system for cancer therapy for many years. To accurately evaluate and optically measure this TfR targeting delivery in vitro, a CHO cell line with enhanced green fluorescent protein (EGFP)-tagged human TfR was established. A chimera of the hTfR and EGFP was engineered by fusing EGFP to the amino terminus of hTfR. Data were provided to demonstrate that hTfR-EGFP chimera was predominantly localized on the plasma membrane with some intracellular fluorescent structures on CHO cells and the EGFP moiety did not affect the endocytosis property of hTfR. Receptor internalization occurred similarly to that of HepG2 cells expressing wild-type hTfR. The internalization percentage of this chimeric receptor was about 81±3% of wild type. Time-dependent co-localization of hTfR-EGFP and PE-conjugated anti-hTfR mAb in living cells demonstrated the trafficking of mAb-receptor complexes through the endosomes followed by segregation of part of the mAb and receptor at the late stages of endocytosis. The CHO-hTfR cells preferentially took up anti-hTfR mAb conjugated nanoparticles. This CHO-hTfR cell line makes it feasible for accurate evaluation and visualization of intracellular trafficking of therapeutic agents conjugated with transferrin or Abs targeting the hTfRs.

Development of a complete human anti-human transferrin receptor C antibody as a novel marker of oral dysplasia and oral cancer

Oral squamous cell carcinoma (OSCC) is the sixth most common cancer worldwide. Up to 20% of oral dysplasia cases have been suggested to undergo malignant transformation to OSCC; however, there are no methods to predict OSCC development. In this study, to identify the genes associated with oral dysplasia progression, we performed genomic copy number analyses of genomic DNA samples isolated from primary oral dysplasia and OSCC via the microdissection method and found elevated expression of transferrin receptor C (TfR1/TFRC) with genomic amplification in oral dysplasia and OSCC. The expression rate of TFRC in OSCC was significantly higher than that in dysplasia, suggesting that OSCC disease progression might be related to TFRC expression. Additionally, we investigated the in vitro and in vivo impacts of a newly established anti-human TFRC monoclonal antibody, which was isolated from a human cDNA library using the phage-display method, on cell proliferation and survival. The anti-TFRC antibody blocked the interaction between transferrin and TFRC and consequently inhibited iron uptake, leading to the iron deprivation-mediated suppression of cell growth and induction of apoptosis. Moreover, we demonstrated that the anti-TFRC antibody efficiently inhibited tumor growth in a murine xenograft OSCC model. Therefore, we suggest our developed complete human anti-human TFRC antibody as a useful, novel treatment for oral dysplasia and OSCC.

Transferrin-targeted magnetic/fluorescence micelles as a specific bi-functional nanoprobe for imaging liver tumor

In order to delineate the location of the tumor both before and during operation, we developed targeted bi-functional polymeric micelles for magnetic resonance (MR) and fluorescence imaging in liver tumors. Hydrophobic superparamagnetic iron oxide nanoparticles (SPIONs) were loaded into the polymeric micelles through self-assembly of an amphiphilic block copolymer poly(ethylene glycol)-poly(ϵ-caprolactone). After, transferrin (Tf) and near-infrared fluorescence molecule Cy5.5 were conjugated onto the surface of the polymeric micelles to obtain the nanosized probe SPIO@PEG-b-PCL-Tf/Cy5.5 (SPPTC). Imaging capabilities of this nanoprobe were evaluated both in vitro and in vivo. The accumulation of SPPTC in HepG2 cells increased over SPIO@PEG-b-PCL-Cy5.5 (SPPC) by confocal microscopy. The targeted nanoprobe SPPTC possessed favorable properties on the MR and fluorescence imaging both in vitro and in vivo. The MTT results showed that the nanoprobes were well tolerated. SPPTC had the potential for pre-operation evaluation and intra-operation navigation of tumors in clinic.

Enhanced expression of transferrin receptor 1 contributes to oncogenic signalling by sphingosine kinase 1

Sphingosine kinase 1 (SK1) is a lipid kinase that catalyses the formation of sphingosine-1-phosphate (S1P). Considerable evidence has implicated elevated cellular SK1 in tumour development, progression and disease severity. In particular, SK1 has been shown to enhance cell survival and proliferation and induce neoplastic transformation. Although S1P has been found to have both cell-surface G-protein-coupled receptors and intracellular targets, the specific downstream pathways mediating oncogenic signalling by SK1 remain poorly defined. Here, using a gene expression array approach, we have demonstrated a novel mechanism whereby SK1 regulates cell survival, proliferation and neoplastic transformation through enhancing expression of transferrin receptor 1 (TFR1). We showed that elevated levels of SK1 enhanced total as well as cell-surface TFR1 expression, resulting in increased transferrin uptake into cells. Notably, we also found that SK1 activation and localization to the plasma membrane, which are critical for its oncogenic effects, are necessary for regulation of TFR1 expression specifically through engagement of the S1P G-protein coupled receptor, S1P2. Furthermore, we showed that blocking TFR1 function with a neutralizing antibody inhibits SK1-induced cell proliferation, survival and neoplastic transformation of NIH3T3 fibroblasts. Similar effects were observed following antagonism of S1P2. Together these findings suggest that TFR1 has an important role in SK1-mediated oncogenesis.

Comparison of two functional kappa light-chain transcripts amplified from a hybridoma

Three heavy-chain and three kappa (κ)-chain transcripts were amplified from hybridoma cells secreting a monoclonal antibody (mAb) against transferrin receptor. Sequence analysis via IMGT/V-QUEST yielded the functional/aberrant prediction. Two functional κ-chain transcripts, Vκ2 and Vκ3, and one functional VH1 were revealed. Comprehensive bioinformatics analyses including sequence alignment, phylogenetic tree, somatic hypermutation prediction, and three-dimensional-molecular structure modeling were used to predict the origin of the two κ-chain transcripts. The results of bioinformatics analysis suggest that Vκ3 is derived from the myeloma partner of the hybridoma; Vκ2 is derived from B-cell. Functional transcripts VH1 and Vκ2 and Vκ3 were then used to construct two chimeric antibodies chi-C2 (Vκ2-VH1) and chi-C3 (Vκ3-VH1), respectively. Antigen-binding experiments showed that only chi-C2 remained the same affinity as its parental mAb. Possible explanations for the coexistence of two functional κ-chain transcripts and the different affinity of the two chimeric antibodies are discussed.

Sinomenine hydrochloride enhancement of the inhibitory effects of anti-transferrin receptor antibody-dependent on the COX-2 pathway in human hepatoma cells

Transferrin receptor (TfR) has been used as a target for the antibody-based therapy of cancer due to its higher expression in tumors relative to normal tissues. Great potential has been shown by anti-TfR antibodies combined with chemotherapeutic drugs as a possible cancer therapeutic strategy. In our study, we investigated the anti-tumor effects of anti-TfR monoclonal antibody (mAb) alone or in combination with sinomenine hydrochloride in vitro. Results suggested that anti-TfR mAb or sinomenine hydrochloride could induce apoptosis, inhibit proliferation, and affect the cell cycle. A synergistic effect was found in relation to tumor growth inhibition and the induction of apoptosis when anti-TfR mAb and sinomenine hydrochloride were used simultaneously. The expression of COX-2 and VEGF protein in HepG2 cells treated with anti-TfR mAb alone was increased in line with increasing dosage of the agent. In contrast, COX-2 expression was dramatically decreased in HepG2 cells treated with sinomenine hydrochloride alone. Furthermore, we demonstrated that the inhibitory effects of sinomenine hydrochloride and anti-TfR mAb administered in combination were more prominent than when the agents were administered singly. To sum up, these results showed that the combined use of sinomenine hydrochloride and anti-TfR mAb may exert synergistic inhibitory effects on human hepatoma HepG2 cells in a COX-2-dependent manner. This finding provides new insight into how tumor cells overcome the interference of iron intake to survive and forms the basis of a new therapeutic strategy involving the development of anti-TfR mAb combined with sinomenine hydrochloride for liver cancer.

Generation and functional characterization of the anti-transferrin receptor single-chain antibody-GAL4 (TfRscFv-GAL4) fusion protein

BACKGROUND

The development of vectors for cell-specific gene delivery is a major goal of gene therapeutic strategies. Transferrin receptor (TfR) is an endocytic receptor and identified as tumor relative specific due to its overexpression on most tumor cells or tissues, and TfR binds and intakes of transferrin-iron complex. We have previously generated an anti-TfR single-chain variable fragments of immunoglobulin (scFv) which were cloned from hybridoma cell line producing antibody against TfR linked with a 20 aa-long linker sequence (G4S)4. In the present study, the anti-TfR single-chain antibody (TfRscFv) was fused to DNA-binding domain of the yeast transcription factor GAL4. The recombinant fusion protein, designated as TfRscFv-GAL4, is expected to mediate the entry of DNA-protein complex into targeted tumor cells.

RESULTS

Fusion protein TfRscFv-GAL4 was expressed in an E. coli bacterial expression system and was recovered from inclusion bodies with subsequent purification by metal-chelate chromatography. The resulting proteins were predominantly monomeric and, upon refolding, became a soluble biologically active bifunctional protein. In biological assays, the antigen-binding activity of the re-natured protein, TfRscFv-GAL4, was confirmed by specific binding to different cancer cells and tumor tissues. The cell binding rates, as indicated by flow cytometry (FCM) analysis, ranged from 54.11% to 8.23% in seven different human carcinoma cell lines. It showed similar affinity and binding potency as those of parent full-length mouse anti-TfR antibody. The positive binding rates to tumor tissues by tissue microarrays (TMA) assays were 75.32% and 63.25%, but it showed weakly binding with hepatic tissue in 5 cases, and normal tissues such as heart, spleen, adrenal cortex blood vessel and stomach. In addition, the re-natured fusion protein TfRscFv-GAL4 was used in an ELISA with rabbit anti-GAL4 antibody. The GAL4-DNA functional assay through the GAL4 complementary conjugation with the GAL4rec-GFP-pGes plasmid to verify the GLA4 activity and GAL4rec-recognized specificity functions. It also shows the complex, TfRscFv-GAL4-GAL4rec-GFP-pGes, could be taken into endochylema to express the green fluorescent protein (GFP) with 8 to 10-fold transfection efficiency.

CONCLUSIONS

Results of our study demonstrated that the biofunctianality of genetically engineered fusion protein, TfRscFv-GAL4, was retained, as the fusion protein could both carry the plasmid of GAL4rec-pGes and bind TfR on tumour cells. This product was able to transfect target cells effectively in an immuno-specific manner, resulting in transient gene expression. This protein that can be applied as an effective therapeutic and diagnostic delivery to the tumor using endogenous membrane transport system with potential widespread utility.