Abundant in vitro expression of the oncofetal ED-B-containing fibronectin translates into selective pharmacodelivery of 131I-L19SIP in a prostate cancer patient

Shielding and nurturing: Fibronectin as a modulator of cancer drug resistance

Resistance to chemotherapy and targeted therapies constitute a common hallmark of most cancers and represent a dominant factor fostering tumor relapse and metastasis. Fibronectin, an abundant extracellular matrix glycoprotein, has long been proposed to play an important role in the pathobiology of cancer. Recent research has unraveled the role of Fibronectin in the onset of chemoresistance against a variety of antineoplastic drugs including DNA-damaging agents, hormone receptor antagonists, tyrosine kinase inhibitors, microtubule destabilizing agents, etc. The current review summarizes the role played by Fibronectin in mediating drug resistance against diverse anticancer drugs. We have also discussed how the aberrant expression of Fibronectin drives the oncogenic signaling pathways ultimately leading to drug resistance through the inhibition of apoptosis, promotion of cancer cell growth and proliferation.

Emerging new therapeutic antibody derivatives for cancer treatment

Monoclonal antibodies constitute a promising class of targeted anticancer agents that enhance natural immune system functions to suppress cancer cell activity and eliminate cancer cells. The successful application of IgG monoclonal antibodies has inspired the development of various types of therapeutic antibodies, such as antibody fragments, bispecific antibodies, and antibody derivatives (e.g., antibody–drug conjugates and immunocytokines). The miniaturization and multifunctionalization of antibodies are flexible and viable strategies for diagnosing or treating malignant tumors in a complex tumor environment. In this review, we summarize antibodies of various molecular types, antibody applications in cancer therapy, and details of clinical study advances. We also discuss the rationale and mechanism of action of various antibody formats, including antibody–drug conjugates, antibody–oligonucleotide conjugates, bispecific/multispecific antibodies, immunocytokines, antibody fragments, and scaffold proteins. With advances in modern biotechnology, well-designed novel antibodies are finally paving the way for successful treatments of various cancers, including precise tumor immunotherapy, in the clinic.

The Functional Role of Extracellular Matrix Proteins in Cancer

The extracellular matrix (ECM) is highly dynamic as it is constantly deposited, remodeled and degraded to maintain tissue homeostasis. ECM is a major structural component of the tumor microenvironment, and cancer development and progression require its extensive reorganization. Cancerized ECM is biochemically different in its composition and is stiffer compared to normal ECM. The abnormal ECM affects cancer progression by directly promoting cell proliferation, survival, migration and differentiation. The restructured extracellular matrix and its degradation fragments (matrikines) also modulate the signaling cascades mediated by the interaction with cell-surface receptors, deregulate the stromal cell behavior and lead to emergence of an oncogenic microenvironment. Here, we summarize the current state of understanding how the composition and structure of ECM changes during cancer progression. We also describe the functional role of key proteins, especially tenascin C and fibronectin, and signaling molecules involved in the formation of the tumor microenvironment, as well as the signaling pathways that they activate in cancer cells.

Extracellular matrix and its therapeutic potential for cancer treatment

The extracellular matrix (ECM) is one of the major components of tumors that plays multiple crucial roles, including mechanical support, modulation of the microenvironment, and a source of signaling molecules. The quantity and cross-linking status of ECM components are major factors determining tissue stiffness. During tumorigenesis, the interplay between cancer cells and the tumor microenvironment (TME) often results in the stiffness of the ECM, leading to aberrant mechanotransduction and further malignant transformation. Therefore, a comprehensive understanding of ECM dysregulation in the TME would contribute to the discovery of promising therapeutic targets for cancer treatment. Herein, we summarized the knowledge concerning the following: (1) major ECM constituents and their functions in both normal and malignant conditions; (2) the interplay between cancer cells and the ECM in the TME; (3) key receptors for mechanotransduction and their alteration during carcinogenesis; and (4) the current therapeutic strategies targeting aberrant ECM for cancer treatment.

Extra-domain B of fibronectin as an alternative target for drug delivery and a cancer diagnostic and prognostic biomarker for malignant glioma

Extra-domain B of fibronectin (EDB-FN) is an alternatively spliced form of fibronectin with high expression in the extracellular matrix of neovascularized tissues and malignant cancer cells. In this study, we evaluated the practicality of using EDB-FN as a biomarker and therapeutic target for malignant gliomas (MGs), representative intractable diseases involving brain tumors.

Methods: The microarray- and sequence-based patient transcriptomic database 'Oncopression' and tissue microarray of MG patient tissue samples were analyzed. EDB-FN data were extracted and evaluated from 23,344 patient samples of 17 types of cancer to assess its effectiveness and selectivity as a molecular target. To strengthen the results of the patient data analysis, the utility of EDB-FN as a molecular marker and target for MG was verified using active EDB-FN-targeting ultrasmall lipidic micellar nanoparticles (~12 nm), which had a high drug-loading capacity and were efficiently internalized by MG cells in vitro and in vivo.

Results: Brain tumors had a 1.42-fold cancer-to-normal ratio (p < 0.0001), the second highest among 17 cancers after head and neck cancer. Patient tissue microarray analysis showed that the EDB-FN high-expression group had a 5.5-fold higher risk of progression than the EDB-FN low-expression group (p < 0.03). By labeling docetaxel-containing ultrasmall micelles with a bipodal aptide targeting EDB-FN (termed APT_EDB-DSPE-DTX), we generated micelles that could specifically bind to MG cells, leading to superior antitumor efficacy of EDB-FN-targeting nanoparticles compared to nontargeting controls.

Conclusions: Taken together, these results show that EDB-FN can be an effective drug delivery target and biomarker for MG.

Extradomain-B Fibronectin-Targeted Dextran-Based Chemical Exchange Saturation Transfer Magnetic Resonance Imaging Probe for Detecting Pancreatic Cancer

A dextran-peptide conjugate was developed for magnetic resonance (MR) molecular imaging of pancreatic ductal adenocarcinoma (PDAC) through its overexpressed microenvironment biomarker, extradomain-B fibronectin (EDB-FN). This new agent consists of diamagnetic and biocompatible dextran and a targeting peptide. Dextrans can be directly detected by chemical exchange saturation transfer magnetic resonance imaging (CEST MRI) without the need for radionuclide or metallic labeling. In addition, large molecular weight dextran, dextran 10 (MW ∼ 10 kDa), provides an approximately 50 times higher sensitivity per molecule than a single glucose unit. The potential of this highly biocompatible diamagnetic probe is demonstrated in a murine syngeneic allograft PDAC tumor model. The biocompatibility and sensitivity of this new agent clearly show potential for a path to clinical translation.

Preparation and Evaluation of ZD2 Peptide 64Cu-DOTA Conjugate as a Positron Emission Tomography Probe for Detection and Characterization of Prostate Cancer

Positron emission tomography (PET) is a sensitive modality for cancer molecular imaging. We aim to develop a PET probe for sensitive detection and risk stratification of prostate cancer by targeting an abundant microenvironment oncoprotein, extradomain-B fibronectin (EDB-FN). The probe consists of a small ZD2 peptide specific to EDB-FN and a ⁶⁴Cu-DOTA chelate. The probe was synthesized using standard solid-phase peptide chemistry and chelated to ⁶⁴Cu prior to imaging. PET images were acquired at 4 and 22 h after intravenously injecting a 200 μCi probe into mice bearing human PC3 and LNCaP tumors, which represent highly aggressive and slow-growing prostate tumors, respectively. At 4 and 22 h postinjection, tumors could be clearly identified in the PET images. A significant higher signal was observed in PC3 tumors than in LNCaP tumors at 22 h (p = 0.01). Probe accumulation was also higher in PC3 tumors at 24 h. These data demonstrated that PET molecular imaging of EDB-FN in the tumor microenvironment of prostate cancer allows efficient differentiation of PC3 and LNCaP tumors in vivo. The ZD2 peptide-targeted PET probe shows potential in the detection and characterization of high-risk prostate cancer to improve the clinical management of prostate cancer.

ED-B fibronectin expression is a marker of epithelial-mesenchymal transition in translational oncology

Fibronectin is a component of the extracellular matrix that links collagen fibers to integrins on the cell's surface. The splicing isoforms, containing the ED-B domain, are not expressed in adult tissues but only in tumor stroma or during embryonic development. Fibroblasts and endothelial cells express ED-B fibronectin during angiogenesis. Also cancer cells can synthetize ED-B fibronectin, but its function in tumor growth needs to be further elucidated.

We evaluated the expression of ED-B fibronectin in prostate cancer cell lines: PC3 and DU145. Using TGF-β, we induced epithelial to mesenchymal transition in culture and observed an increase of ED-B fibronectin expression. Thereafter, we evaluated the expression of ED-B fibronectin in multipotent mesangiogenic progenitor cells, and in mesenchymal stromal cells. The expression of ED-B fibronectin was much higher in mesenchymal than prostate cancer cells even after the epithelial to mesenchymal transition.

Epithelial to mesenchymal transition is a key step for tumor progression contributing to the metastatic spread. Therefore, circulating cancer cells could seed into the metastatic niche taking advantage from the ED-B fibronectin that secrete their own.

Antibody-based delivery of tumor necrosis factor (L19-TNFα) and interleukin-2 (L19-IL2) to tumor-associated blood vessels has potent immunological and anticancer activity in the syngeneic J558L BALB/c myeloma model

PURPOSE

To analyze the impact of TNFα or IL2 on human lymphocytes in vitro and the anti-tumor and immune-modifying effects of L19-IL2 and L19-TNFα on subcutaneously growing J558L myeloma in immunocompetent mice.

METHODS

PBMCs from three healthy volunteers were incubated with IL2, TNFα, or with IL2 plus addition of TNFα (final 20 h). BALB/c J558L mice with subcutaneous tumors were treated with intravenous L19-TNFα plus L19-IL2, or controls. Tumor growth and intra- and peri-tumoral tissues were analyzed for micro-vessel density, necrosis, immune cell composition, and PD1 or PD-L1 expressing cells.

RESULTS

Exposure of PBMC in vitro to IL2, TNFα, or to IL2 over 3 and 5 days plus TNFα for the final 20 h resulted in an approximately 50 and 75% reduction of the CD25low effector cell/CD25high Treg cell ratio, respectively, compared to medium control. IL2 or TNFα increased the proportion of CD4- CD25low effector lymphocytes while reducing the proportion of CD4+ CD25low Teff cells. In the J558L myeloma model, tumor eradication was observed in 58, 42, 25, and 0% of mice treated with L19-TNFα plus L19-IL2, L19-TNFα, L19-IL2, and PBS, respectively. L19-TNFα/L19-IL2 combination caused tumor necrosis, capillary density doubling, peri-tumoral T cell and PD1+ T cell reduction (- 50%), and an increase in PD-L1+ myeloma cells.

CONCLUSION

IL2, TNFα, or IL2 plus TNFα (final 20 h) increased the proportion of CD4- CD25low effector lymphocytes possibly indicating immune activation. L19-TNFα/L19-IL2 combination therapy eradicated tumors in J558L myeloma BALB/c mice likely via TNFα-induced tumor necrosis and L19-TNFα/L19-IL2-mediated local cellular immune reactions.

Magnetic resonance molecular imaging of metastatic breast cancer by targeting extradomain-B fibronectin in the tumor microenvironment

PURPOSE

Non-invasive early accurate detection of malignant breast cancer is paramount to the clinical management of the life-threatening disease. Here, we aim to test a small peptide targeted MRI contrast agent, ZD2-Gd(HP-DO3A), specific to an oncoprotein, extradomain-B fibronectin (EDB-FN), in the tumor microenvironment for MR molecular imaging of breast cancer.

METHOD

EDB-FN expression in 4T1 and MDA-MB-231 cancers was analyzed with quantitative real-time PCR and western blot. Primary and metastatic triple negative breast cancer mouse models were developed using 4T1 and MDA-MB-231 cells. Contrast-enhanced MRI was carried out to evaluate the use of ZD2-Gd(HP-DO3A) in detecting 4T1 and MDA-MB-231 primary and metastatic tumors.

RESULTS

EDB-FN was abundantly expressed in the extracellular matrix (ECM) of both the primary and metastatic TNBC tumors. In T₁ -weighted MRI, ZD2-Gd(HP-DO3A) generated superior contrast enhancement in primary TNBC tumors than a nonspecific clinical agent Gd(HP-DO3A), during 30 min after contrast injection. ZD2-Gd(HP-DO3A) also produced a significant increase in contrast-to-noise ratio (CNR) of TNBC metastases, enabling sensitive localization and delineation of metastases that occulted in non-contrast-enhanced or Gd(HP-DO3A)-enhanced MRI.

CONCLUSIONS

These findings potentiate the use of ZD2-Gd(HP-DO3A) for MR molecular imaging of malignant breast cancers to improve the healthcare of breast cancer patients. Magn Reson Med 79:3135-3143, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

EDB Fibronectin-Specific SPECT Probe 99mTc-HYNIC-ZD2 for Breast Cancer Detection

Extradomain-B fibronectin (EDB-FN), an oncofetal isoform of FN, is a promising diagnostic and therapeutic target of tumors, including breast cancer. Many EDB-FN-targeted drugs have been developed and have shown therapeutic effects in clinical trials. Molecular imaging to visualize EDB-FN-positive cancers may help select the right patients who will be benefit from EDB-FN-targeted therapy. Although a few EDB-FN-targeted imaging probes have been developed, the complicated manufacturing procedure and expensive material and equipment required limit their application for large-scale screening of EDB-FN-positive cancer patients. Thus, more simple and economic EDB-FN-targeted imaging probes are still urgently needed. Previously, we have identified a breast cancer-targeted peptide, CTVRTSADC. Coincidently, it was later identified as an EDB-FN-targeted peptide and named ZD2. In this study, we found a positive correlation between the binding activity of the ZD2 phage and the expression level of EDB-FN in breast cancer cells. Moreover, we observed the colocalization of the ZD2 peptide with EDB-FN in breast cancer cells. Furthermore, in vivo tumor targeting of the ZD2 phage, near-infrared fluorescence imaging, and flow cytometry showed tumor-specific homing of the ZD2 peptide in mice bearing EDB-FN-positive breast cancers. Importantly, on the basis of this EDB-FN-targeted ZD2 peptide, we developed a kit-formulated probe, ^99mTc-HYNIC-ZD2, for single-photon-emission computed tomography (SPECT) imaging of breast cancer. The high tumor uptake of ^99mTc-HYNIC-ZD2 demonstrated its feasibility for use in visualizing EDB-FN-positive breast cancers in vivo. This kit-formulated EDB-FN-targeted SPECT probe has potential clinical applications for precision screening of EDB-FN-positive cancer patients who may benefit from EDB-FN-targeted therapy.

Targeted Contrast Agent Specific to an Oncoprotein in Tumor Microenvironment with the Potential for Detection and Risk Stratification of Prostate Cancer with MRI

Accurate detection and risk stratification are paramount to the clinical management of prostate cancer. Current diagnostic methods, including prostate specific antigen (PSA) screening, are unable to differentiate high-risk tumors from low-risk tumors, resulting in overdiagnosis and overtreatment. A peptide targeted contrast agent, ZD2-Gd(HP-DO3A), specific to an oncoprotein in tumor microenvironment, EDB-FN, was synthesized for noninvasive detection and characterization of aggressive prostate cancer. EDB-FN, one of the subtypes of oncofetal fibronectin, is involved in tumor epithelial-to-mesenchymal transition (EMT), which is implicated in drug resistance and metastasis. The EDB-FN mRNA level in the metastatic PC3 cells was at least three times higher than that in non-metastatic LNCaP cells. In tumors, EDB-FN protein was highly expressed in PC3 tumor xenografts, but not in LNCaP tumors, as revealed by Western blot analysis. ZD2-Gd(HP-DO3A) produced over two times higher contrast-to-noise ratio in the PC3 tumors than in the LNCaP tumors in contrast-enhanced MRI during 30 min after injection. ZD2-Gd(HP-DO3A) possessed high chelate stability against transmetalation and minimal tissue accumulation. Our results demonstrate that molecular MRI of EDB-FN with ZD2-Gd(HP-DO3A) can potentially be used for noninvasive detection and risk stratification of human prostate cancer. Incorporation of this targeted contrast agent in the existing clinical contrast enhanced MRI procedures has the potential to improve diagnostic accuracy of prostate cancer.

Targeting Fibronectin for Cancer Imaging and Therapy

During cancer progression, the extracellular matrix (ECM) undergoes dramatic changes, which promote cancer cell migration and invasion. In the remodeled tumor ECM, fibronectin (FN) level is upregulated to assist tumor growth, progression, and invasion. FN serves as a central organizer of ECM molecules and mediates the crosstalk between the tumor microenvironment and cancer cells. Its upregulation is correlated with angiogenesis, cancer progression, metastasis, and drug resistance. A number of FN-targeting ligands have been developed for cancer imaging and therapy. Thus far, FN-targeting imaging agents have been tested for nuclear imaging, MRI, and fluorescence imaging, for tumor detection and localization. FN-targeting therapeutics, including nuclear medicine, chemotherapy drugs, cytokines, and photothermal moieties, were also developed in cancer therapy. Because of the prevalence of FN overexpression in cancer, FN targeting imaging agents and therapeutics have the promise of broad applications in the diagnosis, treatment, and image-guided interventions of many types of cancers. This review will summarize current understanding on the role of FN in cancer, discuss the design and development of FN-targeting agents, and highlight the applications of these FN-targeting agents in cancer imaging and therapy.

Fibronectin-targeted drug delivery in cancer

Fibronectin is an extracellular matrix protein with pivotal physiological and pathological functions in development and adulthood. Alternative splicing of the precursor mRNA, produced from the single copy fibronectin gene, occurs at three sites coding for the EDA, EDB and IIICS domains. Fibronectin isoforms comprising the EDA or EDB domains are known as oncofetal forms due to their developmental importance and their re-expression in tumors, contrasting with restricted presence in normal adult tissues. These isoforms are also recognized as important markers of angiogenesis, a crucial physiological process in development and required by tumor cells in cancer progression. Attributed to this feature, EDA and EDB domains have been extensively used for the targeted delivery of cytokines, cytotoxic agents, chemotherapy drugs and radioisotopes to fibronectin-expressing tumors to exert therapeutic effects on primary cancers and metastatic lesions. In addition to drug delivery, the EDA and EDB domains of fibronectin have also been utilized to develop imaging strategies for tumor tissues. Furthermore, EDA and EDB based vaccines seem to be promising for the treatment and prevention of certain cancer types. In this review, we will summarize recent advances in fibronectin EDA and EDB-based therapeutic strategies developed to treat cancer.

EDB Fibronectin Specific Peptide for Prostate Cancer Targeting

Extradomain-B fibronectin (EDB-FN), one of the oncofetal fibronectin (onfFN) isoforms, is a high-molecular-weight glycoprotein that mediates cell adhesion and migration. The expression of EDB-FN is associated with a number of cancer-related biological processes such as tumorigenesis, angiogenesis, and epithelial-to-mesenchymal transition (EMT). Here, we report the development of a small peptide specific to EDB-FN for targeting prostate cancer. A cyclic nonapeptide, CTVRTSADC (ZD2), was identified using peptide phage display. A ZD2-Cy5 conjugate was synthesized to accomplish molecular imaging of prostate cancer in vitro and in vivo. ZD2-Cy5 demonstrated effective binding to up-regulated EDB-FN secreted by TGF-β-induced PC3 cancer cells following EMT. Following intravenous injections, the targeted fluorescent probe specifically bound to and delineated PC3-GFP prostate tumors in nude mice bearing the tumor xenografts. ZD2-Cy5 also showed stronger binding to human prostate tumor specimens with a higher Gleason score (GS9) compared to those with a lower score (GS 7), with no binding in benign prostatic hyperplasia (BPH). Thus, the ZD2 peptide is a promising strategy for molecular imaging and targeted therapy of prostate cancer.

A fibrin-specific monoclonal antibody from a designed phage display library inhibits clot formation and localizes to tumors in vivo

Fibrin formation from fibrinogen is a rare process in the healthy organism but is a pathological feature of thrombotic events, cancer and a wide range of inflammatory conditions. We have designed and constructed an antibody phage display library (containing 13 billion clones) for the selective recognition of the N-terminal peptide of fibrin alpha chain. The key structural feature for selective fibrin binding was a K94E mutation in the VH domain. From this library, an antibody was isolated (termed AP2), which recognizes the five N-terminal amino acids of fibrin with high affinity (Kd=44nM), but does not bind to fibrinogen. The AP2 antibody could be expressed in various formats (scFv, small immune protein and IgG) and inhibited fibrin clot formation in a concentration-dependent manner. Moreover, the AP2 antibody stained the fibrin-rich provisional stroma in solid tumors but did not exhibit any detectable staining toward normal tissues. Using a radioiodinated antibody preparation and quantitative biodistribution studies in tumor-bearing mice, AP2 was shown to selectively localize to fibrin-rich F9 murine teratocarcinomas, but not to SKRC-52 human kidney cancer xenografts. Collectively, the experiments indicate that the AP2 antibody recognizes fibrin in vitro and in vivo. The antibody may facilitate the development of fibrin-specific therapeutic agents.