Optimization of radioimmunotherapy of solid tumors: biological impediments and their modulation

Transcatheter pseudo-vascular isolation for localization and concentration of a large molecule theranostic probe into a transgenic OncoPIG kidney tumor

INTRODUCTION

Great strides have been made identifying molecular and genetic changes expressed by various tumor types. These molecular and genetic changes are used as pharmacologic targets for precision treatment using large molecule (LM) proteins with high specificity. Theranostics exploits these LM biomolecules via radiochemistry, creating sensitive diagnostic and therapeutic agents. Intravenous (i.v.) LM drugs have an extended biopharmaceutical half-life thus resulting in an insufficient therapeutic index, permitting only palliative brachytherapy due to unacceptably high rates of systemic nontarget radiation doses to normal tissue. We employ tumor arteriole embolization isolating a tumor from the systemic circulation, and local intra-arterial (i.a.) infusion to improve uptake of a LM drug within a porcine renal tumor (RT).

METHODS

In an oncopig RT we assess the in vivo biodistribution of 99mTc-labeled macroaggregated albumin (MAA) a surrogate for a LM theranostics agent in the RT, kidney, liver, spleen, muscle, blood, and urine. Control animals underwent i.v. infusion and experimental group undergoing arteriography with pseudovascular isolation (PVI) followed by direct i.a. injection.

RESULTS

Injected dose per gram (%ID/g) of the LM at 1 min was 86.75 ± 3.76 and remained elevated up to 120 min (89.35 ± 5.77) with i.a. PVI, this increase was statistically significant (SS) compared to i.v. (13.38 ± 1.56 and 12.02 ± 1.05; p = 0.0003 p = 0.0006 at 1 and 120 min respectively). The circulating distribution of LM in the blood was less with i.a. vs i.v. infusion (2.28 ± 0.31 vs 25.17 ± 1.84 for i.v. p = 0.033 at 1 min). Other organs displayed a trend towards less exposure to radiation for i.a. with PVI compared to i.v. which was not SS.

CONCLUSION

PVI followed by i.a. infusion of a LM drug has the potential to significantly increase the first pass uptake within a tumor. This minimally invasive technique can be translated into clinical practice, potentially rendering monoclonal antibody based radioimmunotherapy a viable treatment for renal tumors.

Targeting neutrophil elastase is a promising direction for future cancer treatment

Neutrophil elastase (NE) is a proteolytic enzyme released extracellular during the formation of neutrophil extracellular traps (NETs) through degranulation. In addition to participating in the body's inflammatory response, NE also plays an important role in cancer. It can promote tumor proliferation, migration, and invasion, induce epithelial-mesenchymal transition (EMT), and change the tumor microenvironment (TME) to promote tumor progression. Concurrently, NE promotes systemic treatment resistance by inducing EMT. However, it can also selectively kill cancer cells and attenuate tumor development. Sivelestat is a specific NE inhibitor that can be used in the perioperative period of esophageal cancer patients to reduce the incidence of postoperative complications after esophagectomy. In addition, the combination of sivelestat and trastuzumab can enhance the efficacy of human epidermal growth factor receptor 2(HER 2) positive breast cancer patients. Meanwhile, targeting the human antibody domains and fragments of NE is also a new way to treat cancer and inflammation-related diseases. This review provides valuable insights into the role of NE in cancer treatment. Additionally, we discuss the challenges associated with the clinical application of sivelestat. By shedding light on the promising potential of NE, this review contributes to the advancement of cancer treatment strategies.

Multibarrier-penetrating drug delivery systems for deep tumor therapy based on synergistic penetration strategy

Nanotherapies, valued for their high efficacy and low toxicity, frequently serve as antitumor treatments, but do not readily penetrate deep into tumor tissues and cells. Here we developed an improved tumor-penetrating peptide (TPP)-based drug delivery system. Briefly, the established TPP iNGR was modified to generate a linear NGR peptide capable of transporting nanotherapeutic drugs into tumors through a CendR pathway-dependent, neuropilin-1 receptor-mediated process. Although TPPs have been reported to reach intended tumor targets, they often fail to penetrate cell membranes to deliver tumoricidal drugs to intracellular targets. We addressed this issue by harnessing cell penetrating peptide technology to develop a liposome-based multibarrier-penetrating delivery system (mbPDS) with improved synergistic drug penetration into deep tumor tissues and cells. The system incorporated doxorubicin-loaded liposomes coated with nona-arginine (R9) CPP and cyclic iNGR (CRNGRGPDC) molecules, yielding Lip-mbPDS. Lip-mbPDS tumor-targeting, tumor cell/tissue-penetrating and antitumor capabilities were assessed using CD13-positive human fibrosarcoma-derived cell (HT1080)-based in vitro and in vivo tumor models. Lip-mbPDS evaluation included three-dimensional layer-by-layer confocal laser scanning microscopy, cell internalization/toxicity assays, three-dimensional tumor spheroid-based penetration assays and antitumor efficacy assays conducted in an animal model. Lip-mbPDS provided enhanced synergistic drug penetration of multiple biointerfaces for potentially deep tumor therapeutic outcomes.

Approaches to Reducing Normal Tissue Radiation from Radiolabeled Antibodies

Radiolabeled antibodies are powerful tools for both imaging and therapy in the field of nuclear medicine. Radiolabeling methods that do not release radionuclides from parent antibodies are essential for radiolabeling antibodies, and practical radiolabeling protocols that provide high in vivo stability have been established for many radionuclides, with a few exceptions. However, several limitations remain, including undesirable side effects on the biodistribution profiles of antibodies. This review summarizes the numerous efforts made to tackle this problem and the recent advances, mainly in preclinical studies. These include pretargeting approaches, engineered antibody fragments and constructs, the secondary injection of clearing agents, and the insertion of metabolizable linkages. Finally, we discuss the potential of these approaches and their prospects for further clinical application.

Targeting Breast Cancer Signaling via Phytomedicine and Nanomedicine

BACKGROUND

The development of breast cancer (BC) and how it responds to treatment have both been linked to the involvement of inflammation. Chronic inflammation is critical in carcinogenesis, leading to elevated DNA damage, impaired DNA repair machinery, cell growth, apoptosis, angiogenesis, and invasion. Studies have found several targets that selectively modulate inflammation in cancer, limit BC's growth, and boost treatment effectiveness. Drug resistance and the absence of efficient therapeutics for metastatic and triple-negative BC contribute to the poor outlook of BC patients.

SUMMARY

To treat BC, small-molecule inhibitors, phytomedicines, and nanoparticles are conjugated to attenuate BC signaling pathways. Due to their numerous target mechanisms and strong safety records, phytomedicines and nanomedicines have received much attention in studies examining their prospects as anti-BC agents by such unfulfilled demands.

KEY MESSAGES

The processes involved in the affiliation across the progression of tumors and the spread of inflammation are highlighted in this review. Furthermore, we included many drugs now undergoing clinical trials that target cancer-mediated inflammatory pathways, cutting-edge nanotechnology-derived delivery systems, and a variety of phytomedicines that presently address BC.

Enhanced Therapeutic Effects of 177Lu-DOTA-M5A in Combination with Heat Shock Protein 90 Inhibitor Onalespib in Colorectal Cancer Xenografts

Carcinoembryonic antigen (CEA) has emerged as an attractive target for theranostic applications in colorectal cancers (CRCs). In the present study, the humanized anti-CEA antibody hT84.66-M5A (M5A) was labeled with 177Lu for potential CRC therapy. Moreover, the novel combination of 177Lu-DOTA-M5A with the heat shock protein 90 inhibitor onalespib, suggested to mediate radiosensitizing properties, was assessed in vivo for the first time. M5A antibody uptake and therapeutic effects, alone or in combination with onalespib, were assessed in human CRC xenografts and visualized using SPECT/CT imaging. Although both 177Lu-DOTA-M5A and onalespib monotherapies effectively reduced tumor growth rates, the combination therapy demonstrated the most substantial impact, achieving a fourfold reduction in tumor growth compared to the control group. Median survival increased by 33% compared to 177Lu-DOTA-M5A alone, and tripled compared to control and onalespib groups. Importantly, combination therapy yielded comparable or superior effects to the double dose of 177Lu-DOTA-M5A monotherapy. 177Lu-DOTA-M5A increased apoptotic cell levels, indicating its potential to induce tumor cell death. These findings show promise for 177Lu-DOTA-M5A as a CRC therapeutic agent, and its combination with onalespib could significantly enhance treatment efficacy. Further in vivo studies are warranted to validate these findings fully and explore the treatment's potential for clinical use.

Gas-assisted phototherapy for cancer treatment

Phototherapies, mainly including photodynamic and photothermal therapy, have made considerable strides in the field of cancer treatment. With the aid of phototherapeutic agents, reactive oxygen species (ROS) or heat are generated under light irradiation to selectively damage cancer cells. However, sole-modality phototherapy faces certain drawbacks, such as limited penetration of phototherapeutic agents into tumor tissues, inefficient ROS generation due to hypoxia, treatment-induced inflammation and resistance of tumor to treatment (e.g., high levels of antioxidants, expression of heat shock protein). Gas therapy, an emerging therapy approach that damages cancer cells by improving the level of certain gas at the tumor site, shows potential to overcome the challenges associated with phototherapies. In addition, with the rapid development of nanotechnology, gas-assisted phototherapy based on nanomedicines has emerged as a promising strategy to enhance the treatment efficacy. This review summarizes recent advances in gas-assisted phototherapy and discusses the prospects and challenges of this strategy in cancer phototherapy.

Direct In Vivo Comparison of 99mTc-Labeled Scaffold Proteins, DARPin G3 and ADAPT6, for Visualization of HER2 Expression and Monitoring of Early Response for Trastuzumab Therapy

Non-invasive radionuclide molecular visualization of human epidermal growth factor receptor type 2 (HER2) can provide stratification of patients for HER2-targeting therapy. This method can also enable monitoring of the response to such therapies, thereby making treatment personalized and more efficient. Clinical evaluation in a phase I study demonstrated that injections of two scaffold protein-based imaging probes, [^99mTc]Tc-(HE)₃-G3 and [^99mTc]Tc-ADAPT6, are safe, well-tolerated and cause a low level of radioactivity in healthy tissue. The goal of this preclinical study was to select the best probe for stratification of patients and response monitoring. Biodistribution of both tracers was compared in mice bearing SKOV-3 xenografts with high HER2 expression or MDA-MB-468 xenografts with very low expression. Changes in accumulation of the probes in SKOV-3 tumors 24 h after injection of trastuzumab were evaluated. Both [^99mTc]Tc-ADAPT6 and [^99mTc]Tc-(HE)₃-G3 permitted high contrast imaging of HER2-expressing tumors and a clear discrimination between tumors with high and low HER2 expression. However, [^99mTc]Tc-ADAPT6 has better preconditions for higher sensitivity and specificity of stratification. On the other hand, [^99mTc]Tc-(HE)₃-G3 is capable of detecting the decrease of HER2 expression on response to trastuzumab therapy only 24 h after injection of the loading dose. This indicates that the [^99mTc]Tc-(HE)₃-G3 tracer would be better for monitoring early response to such treatment. The results of this study should be considered in planning of further clinical development of HER2 imaging probes.

Multifunctional Nanosystems with Enhanced Cellular Uptake for Tumor Therapy

Rapid development of nanotechnology provides promising strategies in biomedicine, especially in tumor therapy. In particular, the cellular uptake of nanosystems is not only a basic premise to realize various biomedical applications, but also a fatal factor for determining the final therapeutic effect. Thus, a systematic and comprehensive summary is necessary to overview the recent research progress on the improvement of nanosystem cellular uptake for cancer treatment. According to the process of nanosystems entering the body, they can be classified into three categories. The first segment is to enhance the accumulation and permeation of nanosystems to tumor cells through extracellular microenvironment stimulation. The second segment is to improve cellular internalization from extracellular to intracellular via active targeting. The third segment is to enhance the intracellular retention of therapeutics by subcellular localization. The major factors in the delivery can be utilized to develop multifunctional nanosystems for strengthening the tumor therapy. Ultimately, the key challenges and prospective in the emerging research frontier are thoroughly outlined. This review is expected to provide inspiring ideas, promising strategies and potential pathways for developing advanced anticancer nanosystems in clinical practice.

Human Antibody Domains and Fragments Targeting Neutrophil Elastase as Candidate Therapeutics for Cancer and Inflammation-Related Diseases

Neutrophil elastase (NE) is a serine protease released during neutrophil maturation. High levels of NE are related to lung tissue damage and poor prognosis in cancer; thus, NE is a potential target for therapeutic immunotherapy for multiple lung diseases and cancers. Here, we isolate and characterize two high-affinity, specific, and noncompetitive anti-NE antibodies Fab 1C10 and V_H 1D1.43 from two large phage-displayed human Fab and V_H libraries. After fusion with human IgG1 Fc, both of them (V_H-Fc 1D1.43 and IgG1 1C10) inhibit NE enzymatic activity with V_H-Fc 1D1.43 showing comparable inhibitory effects to that of the small molecule NE inhibitor SPCK and IgG1 1C10 exhibiting even higher (2.6-fold) activity than SPCK. Their epitopes, as mapped by peptide arrays combined with structural modeling, indicate different mechanisms for blocking NE activity. Both V_H-Fc and IgG1 antibodies block NE uptake by cancer cells and fibroblast differentiation. V_H-Fc 1D1.43 and IgG1 1C10 are promising for the antibody-based immunotherapy of cancer and inflammatory diseases.

Radioimmunotherapy for solid tumors: spotlight on Glypican-1 as a radioimmunotherapy target

Radioimmunotherapy (i.e., the use of radiolabeled tumor targeting antibodies) is an emerging approach for the diagnosis, therapy, and monitoring of solid tumors. Often using paired agents, each targeting the same tumor molecule, but labelled with an imaging or therapeutic isotope, radioimmunotherapy has achieved promising clinical results in relatively radio-resistant solid tumors such as prostate. Several approaches to optimize therapeutic efficacy, such as dose fractionation and personalized dosimetry, have seen clinical success. The clinical use and optimization of a radioimmunotherapy approach is, in part, influenced by the targeted tumor antigen, several of which have been proposed for different solid tumors. Glypican-1 (GPC-1) is a heparan sulfate proteoglycan that is expressed in a variety of solid tumors, but whose expression is restricted in normal adult tissue. Here, we discuss the preclinical and clinical evidence for the potential of GPC-1 as a radioimmunotherapy target. We describe the current treatment paradigm for several solid tumors expressing GPC-1 and suggest the potential clinical utility of a GPC-1 directed radioimmunotherapy for these tumors.

Inverse electron demand Diels-Alder click chemistry for pretargeted PET imaging and radioimmunotherapy

Radiolabeled antibodies have shown promise as tools for both the nuclear imaging and endoradiotherapy of cancer, but the protracted circulation time of radioimmunoconjugates can lead to high radiation doses to healthy tissues. To circumvent this issue, we have developed an approach to positron emission tomography (PET) imaging and radioimmunotherapy (RIT) predicated on radiolabeling the antibody after it has reached its target within the body. This in vivo pretargeting strategy is based on the rapid and bio-orthogonal inverse electron demand Diels-Alder reaction between tetrazine (Tz) and trans-cyclooctene (TCO). Pretargeted PET imaging and RIT using TCO-modified antibodies in conjunction with Tz-bearing radioligands produce high activity concentrations in target tissues as well as reduced radiation doses to healthy organs compared to directly labeled radioimmunoconjugates. Herein, we describe how to prepare a TCO-modified antibody (humanized A33-TCO) as well as how to synthesize two Tz-bearing radioligands: one labeled with the positron-emitting radiometal copper-64 ([64Cu]Cu-SarAr-Tz) and one labeled with the β-emitting radiolanthanide lutetium-177 ([177Lu]Lu-DOTA-PEG7-Tz). We also provide a detailed description of pretargeted PET and pretargeted RIT experiments in a murine model of human colorectal carcinoma. Proper training in both radiation safety and the handling of laboratory mice is required for the successful execution of this protocol.

Cell-penetrating peptides (CPPs): an overview of applications for improving the potential of nanotherapeutics

In the field of nanotherapeutics, gaining cellular entry into the cytoplasm of the target cell continues to be an ultimate challenge. There are many physicochemical factors such as charge, size and molecular weight of the molecules and delivery vehicles, which restrict their cellular entry. Hence, to dodge such situations, a class of short peptides called cell-penetrating peptides (CPPs) was brought into use. CPPs can effectively interact with the cell membrane and can assist in achieving the desired intracellular entry. Such strategy is majorly employed in the field of cancer therapy and diagnosis, but now it is also used for other purposes such as evaluation of atherosclerotic plaques, determination of thrombin levels and HIV therapy. Thus, the current review expounds on each of these mentioned aspects. Further, the review briefly summarizes the basic know-how of CPPs, their utility as therapeutic molecules, their use in cancer therapy, tumor imaging and their assistance to nanocarriers in improving their membrane penetrability. The review also discusses the challenges faced with CPPs pertaining to their stability and also mentions the strategies to overcome them. Thus, in a nutshell, this review will assist in understanding how CPPs can present novel possibilities for resolving the conventional issues faced with the present-day nanotherapeutics.

Perspectives on metals-based radioimmunotherapy (RIT): moving forward

Radioimmunotherapy (RIT) is FDA-approved for the clinical management of liquid malignancies, however, its use for solid malignancies remains a challenge. The putative benefit of RIT lies in selective targeting of antigens expressed on the tumor surface using monoclonal antibodies, to systemically deliver cytotoxic radionuclides. The past several decades yielded dramatic improvements in the quality, quantity, recent commercial availability of alpha-, beta- and Auger Electron-emitting therapeutic radiometals. Investigators have created new or improved existing bifunctional chelators. These bifunctional chelators bind radiometals and can be coupled to antigen-specific antibodies. In this review, we discuss approaches to develop radiometal-based RITs, including the selection of radiometals, chelators and antibody platforms (i.e. full-length, F(ab')2, Fab, minibodies, diabodies, scFv-Fc and nanobodies). We cite examples of the performance of RIT in the clinic, describe challenges to its implementation, and offer insights to address gaps toward translation.

Potential of three-step pretargeting radioimmunotherapy using biotinylated bevacizumab and succinylated streptavidin in triple-negative breast cancer xenograft

OBJECTIVE

Pretargeting radioimmunotherapy (PRIT) is a promising approach that can reduce long-time retention of blood radioactivity and consequently reduce hematotoxicity. Among the PRIT strategies, the combination of biotin-conjugated mAb and radiolabeled streptavidin (StAv) is a simple and convenient method because of its ease of preparation. This study performed three-step (3-step) PRIT using the sequential injection of (1) biotinylated bevacizumab (Bt-BV), (2) avidin, and (3) radiolabeled StAv for the treatment of triple-negative breast cancer (TNBC).

METHODS

Four biodistribution studies were performed using ¹¹¹In in tumor-bearing mice to optimize each step of our PRIT methods. Further, a therapeutic study was performed with optimized 3-step PRIT using ⁹⁰Y-labeled StAv.

RESULTS

Based on the biodistribution studies, the protein dose of Bt-BV and avidin was optimized to 100 μg and 10 molar equivalent of BV, respectively. Succinylation of StAv significantly decreased the kidney accumulation level (with succinylation (6.96 ± 0.91) vs without succinylation (20.60 ± 1.47) at 1 h after injection, p < 0.0001) with little effect on the tumor accumulation level. In the therapeutic study, tumor growth was significantly suppressed in treatment groups with optimized 3-step PRIT using ⁹⁰Y-labeled succinylated StAv compared to that of the no-treatment group (p < 0.05).

CONCLUSIONS

The 3-step PRIT strategy of this study achieved fast blood clearance and low kidney uptake with little effect on the tumor accumulation level, and a certain degree of therapeutic effect was consequently observed. These results indicated that the pretargeting treatment of the current study may be effective for human TNBC treatment.

Molecular Imaging of a Zirconium-89 Labeled Antibody Targeting Plasmodium falciparum-Infected Human Erythrocytes

PURPOSE

Nuclear imaging is an important preclinical research tool to study infectious diseases in vivo and could be extended to investigate complex aspects of malaria infections. As such, we report for the first time successful radiolabeling of a novel antibody specific to Plasmodium-infected erythrocytes (IIIB6), its in vitro assessment and molecular imaging in nude mice.

PROCEDURES

In vitro confocal microscopy was used to determine the stage-specificity of Plasmodium-infected erythrocytes recognised by IIIB6. To enable micro-positron emission tomography (PET)/X-ray computed tomography (CT) imaging, IIIB6 was conjugated to Bz-DFO-NCS and subsequently radiolabeled with zirconium-89. Healthy nude mice were injected with [⁸⁹Zr]IIIB6, and pharmacokinetics and organ uptake were monitored over 24 h. This was followed by post-mortem animal dissection to determine the biodistribution of [⁸⁹Zr]IIIB6.

RESULTS

IIIB6 recognised all the relevant stages of Plasmodium falciparum-infected erythrocytes (trophozoites, schizonts and gametocytes) that are responsible for severe malaria pathology. [⁸⁹Zr]IIIB6-radiolabeling yields were efficient at 84-89 %. Blood pool imaging analysis indicated a pharmacological half-life of 9.6 ± 2.5 h for [⁸⁹Zr]IIIB6. The highest standard uptake values were determined at 2-6 h in the liver followed by the spleen, kidneys, heart, stomach and lung, respectively. Minimal activity was present in muscle and bone tissues.

CONCLUSION

In vitro characterization of IIIB6 and pharmacokinetic characterization of [⁸⁹Zr]IIIB6 revealed that this antibody has potential for future use in Plasmodium-infected mouse models to study malaria in a preclinical in vivo setting with PET/CT imaging.

The Current Landscape of Antibody-based Therapies in Solid Malignancies

Over the past three decades, monoclonal antibodies (mAbs) have revolutionized the landscape of cancer therapy. Still, this benefit remains restricted to a small proportion of patients due to moderate response rates and resistance emergence. The field has started to embrace better mAb-based formats with advancements in molecular and protein engineering technologies. The development of a therapeutic mAb with long-lasting clinical impact demands a prodigious understanding of target antigen, effective mechanism of action, gene engineering technologies, complex interplay between tumor and host immune system, and biomarkers for prediction of clinical response. This review discusses the various approaches used by mAbs for tumor targeting and mechanisms of therapeutic resistance that is not only caused by the heterogeneity of tumor antigen, but also the resistance imposed by tumor microenvironment (TME), including inefficient delivery to the tumor, alteration of effector functions in the TME, and Fc-gamma receptor expression diversity and polymorphism. Further, this article provides a perspective on potential strategies to overcome these barriers and how diagnostic and prognostic biomarkers are being used in predicting response to mAb-based therapies. Overall, understanding these interdependent parameters can improve the current mAb-based formulations and develop novel mAb-based therapeutics for achieving durable clinical outcomes in a large subset of patients.

Ligand-Targeted Delivery of Photosensitizers for Cancer Treatment

Photodynamic therapy (PDT) is a promising cancer treatment which involves a photosensitizer (PS), light at a specific wavelength for PS activation and oxygen, which combine to elicit cell death. While the illumination required to activate a PS imparts a certain amount of selectivity to PDT treatments, poor tumor accumulation and cell internalization are still inherent properties of most intravenously administered PSs. As a result, common consequences of PDT include skin photosensitivity. To overcome the mentioned issues, PSs may be tailored to specifically target overexpressed biomarkers of tumors. This active targeting can be achieved by direct conjugation of the PS to a ligand with enhanced affinity for a target overexpressed on cancer cells and/or other cells of the tumor microenvironment. Alternatively, PSs may be incorporated into ligand-targeted nanocarriers, which may also encompass multi-functionalities, including diagnosis and therapy. In this review, we highlight the major advances in active targeting of PSs, either by means of ligand-derived bioconjugates or by exploiting ligand-targeting nanocarriers.

Breast cancer targeted/ therapeutic with double and triple fusion Immunotoxins

Target-specific transport of therapeutic agents holds promise to increase the efficacy of cancer treatment by decreasing injury to normal tissues and post treatment problems. HER2 is a tumor cell surface marker that is expressed in 25-30 % of breast cancer patients. The significant role of HER2 in cancer development and its biological feature makes it a highly appealing goal for the therapeutic treatment of cancer targeted therapy using HER2 monoclonal antibody. This approach is currently used as a special treatment against breast cancer in some research. In the present study, HER2 monoclonal antibody (mAb), (Herceptin) fused to PE38 by recombinant DNA technology and a new recombinant IT was developed. The scFv(Herceptin)-PE-STXA and scFv(Herceptin)-PE fusions cloned in pET28a and recombinant protein expression was carried out and then the proteins were purified. MCF-7 and SKBR-3 cells were used as HER2-negative and HER2-positive breast cancer cells, respectively. The cytotoxicity of its evaluated using MTT assay. The cell ELISA was used to determine the binding ability of immunotoxins (ITs) to the cell receptor and internalization and apoptosis were also assessed. The results revealed that cell cytotoxicity occurred in SKBR-3 cells in a dose-dependent manner but not in MCF-7 cells. It is possible that this ITs can attach to HER2-positive breast cancer cells and then, internalize and eradicate cancer cells by apoptosis. Here, we concluded that the recombinant ITs have therapeutic potential against HER2-positive breast cancer.

Preparation of an Actinium-228 Generator

Advances in targeted α-therapies have increased the interest in actinium (Ac), whose chemistry is poorly defined due to scarcity and radiological hazards. Challenges associated with characterizing Ac³⁺ chemistry are magnified by its 5f⁰6d⁰ electronic configuration, which precludes the use of many spectroscopic methods amenable to small amounts of material and low concentrations (like EPR, UV-vis, fluorescence). In terms of nuclear spectroscopy, many actinium isotopes (²²⁵Ac and ²²⁷Ac) are equally "unfriendly" because the actinium α-, β-, and γ-emissions are difficult to resolve from the actinium daughters. To address these issues, we developed a method for isolating an actinium isotope (²²⁸Ac) whose nuclear properties are well-suited for γ-spectroscopy. This four-step procedure isolates ²²⁸Ra from naturally occurring ²³²Th. The relatively long-lived ²²⁸Ra (t_1/2 = 5.75(3) years) radioisotope subsequently decays to ²²⁸Ac. Because the ²²⁸Ac decay rate [t_1/2 = 6.15(2) h] is fast, ²²⁸Ac rapidly regenerates after being harvested from the ²²⁸Ra parent. The resulting ²²⁸Ac generator provides frequent and long-term access (of many years) to the spectroscopically "friendly" ²²⁸Ac radionuclide. We have demonstrated that the ²²⁸Ac product can be routinely "milked" from this generator on a daily basis, in chemically pure form, with high specific activity and in excellent yield (∼95%). Hence, in the same way that developing synthesis routes to new starting materials has advanced coordination chemistry for many metals by broadening access, this ²²⁸Ac generator has the potential to broaden actinium access for the inorganic community, facilitating the characterization of actinium chemical behavior.

Radiolabeled Anti-Adenosine Triphosphate Synthase Monoclonal Antibody as a Theragnostic Agent Targeting Angiogenesis

INTRODUCTION

The potential of a radioiodine-labeled, anti-adenosine triphosphate synthase monoclonal antibody (ATPS mAb) as a theragnostic agent for simultaneous cancer imaging and treatment was evaluated.

METHODS

Adenosine triphosphate synthase monoclonal antibody was labeled with radioiodine, then radiotracer uptake was measured in 6 different cancer cell lines. In vivo biodistribution was evaluated 24 and 48 hours after intravenous injection of ¹²⁵I-ATPS mAb into MKN-45 tumor-bearing mice (n = 3). For radioimmunotherapy, 18.5 MBq ¹³¹I-ATPS mAb (n = 7), isotype immunoglobulin G (IgG) (n = 6), and vehicle (n = 6) were injected into MKN-45 tumor-bearing mice for 4 weeks, and tumor volume and percentage of tumor growth inhibition (TGI) were compared each week.

RESULTS

MKN-45 cells showed the highest in vitro cellular binding after 4 hours (0.00324 ± 0.00013%/μg), which was significantly inhibited by unlabeled ATPS mAb at concentrations of greater than 0.4 μM. The in vitro retention rate of ¹²⁵I-ATPS mAb in MKN-45 cells was 64.1% ± 1.0% at 60 minutes. The highest tumor uptake of ¹²⁵I-ATPS mAb in MKN-45 tumor-bearing mice was achieved 24 hours after injection (6.26% ± 0.47% injected dose [ID]/g), whereas tumor to muscle and tumor to blood ratios peaked at 48 hours. The 24-hour tumor uptake decreased to 3.43% ± 0.85% ID/g by blocking with unlabeled ATPS mAb. After 4 weeks of treatment, mice receiving ¹³¹I-ATPS mAb had significantly smaller tumors (679.4 ± 232.3 mm³) compared with control (1687.6 ± 420.4 mm³, P = .0431) and IgG-treated mice (2870.2 ± 484.1 mm³, P = .0010). The percentage of TGI of ¹³¹I-ATPS mAb was greater than 50% during the entire study period (range: 53.7%-75.9%).

CONCLUSION

The specific binding and antitumor effects of radioiodinated ATPS mAb were confirmed in in vitro and in vivo models of stomach cancer.

Selectivity Conversion of Protease Inhibitory Antibodies

Solid tumors are inherently difficult to treat because of large regions of hypoxia and are often chemotherapy- or radiotherapy-resistant. It seems that cancer stem cells reside in hypoxic and adjacent necrotic tumor areas. Therefore, new treatments that are highly selective for tumors and can eradicate cells in both hypoxic and necrotic tumor regions are desirable. Antibody α-radioconjugates couple an α-emitting radionuclide with the specificity of a tumor-targeting monoclonal antibody. The large mass and energy of α-particles result in radiation dose delivery within a smaller area independent of oxygen concentration, thus matching key criteria for killing hypoxic tumor cells. With advances in radionuclide production and chelation chemistry, α-radioconjugate therapy is regaining interest as a cancer therapy. Here, we will review current literature examining radioconjugate therapy specifically targeting necrotic and hypoxic tumor cells and outline how α-radioconjugate therapy could be used to treat tumor regions harboring more resistant cancer cell types.

Statement of Significance

Tumor-targeting antibodies are excellent vehicles for the delivery of toxic payloads directly to the tumor site. Tumor hypoxia and necrosis promote treatment recurrence, resistance, and metastasis. Targeting these areas with antibody α-radioconjugates would aid in overcoming treatment resistance.

Selectivity Conversion of Protease Inhibitory Antibodies

Background: Proteases are one of the largest pharmaceutical targets for drug developments. Their dysregulations result in a wide variety of diseases. Because proteolytic networks usually consist of protease family members that share high structural and catalytic homology, distinguishing them using small molecule inhibitors is often challenging. To achieve specific inhibition, this study described a novel approach for the generation of protease inhibitory antibodies. As a proof of concept, we aimed to convert a matrix metalloproteinase (MMP)-14 specific inhibitor to MMP-9 specific inhibitory antibodies with high selectivity. Methods: An error-prone single-chain Fv (scFv) library of an MMP-14 inhibitor 3A2 was generated for yeast surface display. A dual-color competitive FACS was developed for selection on MMP-9 catalytic domain (cdMMP-9) and counter-selection on cdMMP-14 simultaneously, which were fused/conjugated with different fluorophores. Isolated MMP-9 inhibitory scFvs were biochemically characterized by inhibition assays on MMP-2/-9/-12/-14, proteolytic stability tests, inhibition mode determination, competitive ELISA with TIMP-2 (a native inhibitor of MMPs), and paratope mutagenesis assays. Results: We converted an MMP-14 specific inhibitor 3A2 into a panel of MMP-9 specific inhibitory antibodies with dramatic selectivity shifts of 690-4,500 folds. Isolated scFvs inhibited cdMMP-9 at nM potency with high selectivity over MMP-2/-12/-14 and exhibited decent proteolytic stability. Biochemical characterizations revealed that these scFvs were competitive inhibitors binding to cdMMP-9 near its reaction cleft via their CDR-H3s. Conclusions: This study developed a novel approach able to convert the selectivity of inhibitory antibodies among closely related protease family members. This methodology can be directly applied for mAbs inhibiting many proteases of biomedical importance.

Targeted Optical Imaging Agents in Cancer: Focus on Clinical Applications

Molecular imaging is an emerging strategy for in vivo visualization of cancer over time based on biological mechanisms of disease activity. Optical imaging methods offer a number of advantages for real-time cancer detection, particularly in the epithelium of hollow organs and ducts, by using a broad spectral range of light that spans from visible to near-infrared. Targeted ligands are being developed for improved molecular specificity. These platforms include small molecule, peptide, affibody, activatable probes, lectin, and antibody. Fluorescence labeling is used to provide high image contrast. This emerging methodology is clinically useful for early cancer detection by identifying and localizing suspicious lesions that may not otherwise be seen and serves as a guide for tissue biopsy and surgical resection. Visualizing molecular expression patterns may also be useful to determine the best choice of therapy and to monitor efficacy. A number of these imaging agents are overcoming key challenges for clinical translation and are being validated in vivo for a wide range of human cancers.

PEGylated dendritic polyglycerol conjugate targeting NCAM-expressing neuroblastoma: Limitations and challenges

Neural cell adhesion molecule (NCAM) is found to be a stem-cell marker in several tumor types and its overexpression is known to correlate with increased metastatic capacity. To combine extravasation- and ligand-dependent targeting to NCAM overexpressing-cells in the tumor microenvironment, we developed a PEGylated NCAM-targeted dendritic polyglycerol (PG) conjugate. Here, we describe the synthesis, physico-chemical characterization and biological evaluation of a PG conjugate bearing the mitotic inhibitor paclitaxel (PTX) and an NCAM-targeting peptide (NTP). PG-NTP-PTX-PEG was evaluated for its ability to inhibit neuroblastoma progression in vitro and in vivo as compared to non-targeted derivatives and free drug. NCAM-targeted conjugate inhibited the migration of proliferating endothelial cells, suggesting it would be able to inhibit tumor angiogenesis. The targeting conjugate provided an improved binding and uptake on IMR-32 cells compared to non-targeted control. However, these results did not translate to our in vivo model on orthotopic neuroblastoma bearing mice.

Antibody or Antibody Fragments: Implications for Molecular Imaging and Targeted Therapy of Solid Tumors

The use of antibody-based therapeutics has proven very promising for clinical applications in cancer patients, with multiple examples of antibodies and antibody–drug conjugates successfully applied for the treatment of solid tumors and lymphomas. Given reported recurrence rates, improvements are clearly still necessary. A major factor limiting the efficacy of antibody-targeted cancer therapies may be the incomplete penetration of the antibody or antibody–drug conjugate into the tumor. Incomplete tumor penetration also affects the outcome of molecular imaging, when using such targeting agents. From the injection site until they arrive inside the tumor, targeting molecules are faced with several barriers that impact intratumoral distribution. The primary means of antibody transport inside tumors is based on diffusion. The diffusive penetration inside the tumor is influenced by both antibody properties, such as size and binding affinity, as well as tumor properties, such as microenvironment, vascularization, and targeted antigen availability. Engineering smaller antibody fragments has shown to improve the rate of tumor uptake and intratumoral distribution. However, it is often accompanied by more rapid clearance from the body and in several cases also by inherent destabilization and reduction of the binding affinity of the antibody. In this perspective, we discuss different cancer targeting approaches based on antibodies or their fragments. We carefully consider how their size and binding properties influence their intratumoral uptake and distribution, and how this may affect cancer imaging and therapy of solid tumors.

Peptide ligand-modified nanomedicines for targeting cells at the tumor microenvironment

Since their initial discovery more than 30years ago, tumor-homing peptides have become an increasingly useful tool for targeted delivery of therapeutic and diagnostic agents into tumors. Today, it is well accepted that cells at the tumor microenvironment (TME) contribute in many ways to cancer development and progression. Tumor-homing peptide-decorated nanomedicines can interact specifically with surface receptors expressed on cells in the TME, improve cellular uptake of nanomedicines by target cells, and impair tumor growth and progression. Moreover, peptide ligand-modified nanomedicines can potentially accumulate in the target tissue at higher concentrations than would small conjugates, thus increasing overall target tissue exposure to the therapeutic agent, enhance therapeutic efficacy and reduce side effects. This review describes the most studied peptide ligands aimed at targeting cells in the TME, discusses major obstacles and principles in the design of ligands for drug targeting and provides an overview of homing peptides in ligand-targeted nanomedicines that are currently in development for cancer therapy and diagnosis.

Pretargeting for imaging and therapy in oncological nuclear medicine

Background

Oncological pretargeting has been implemented and tested in several different ways in preclinical models and clinical trials over more than 30 years. Despite highly promising results, pretargeting has not achieved market approval even though it could be considered the ultimate theranostic, combining PET imaging with short-lived positron emitters and therapy with radionuclides emitting beta or alpha particles.

Results

We have reviewed the pretargeting approaches proposed over the years, discussing their suitability for imaging, particularly PET imaging, and therapy, as well as their limitations. The reviewed pretargeting modalities are the avidin-biotin system, bispecific anti-tumour x anti-hapten antibodies and bivalent haptens, antibody-oligonucleotide conjugates and radiolabelled complementary oligonucleotides, and approaches using click chemistry. Finally, we discuss recent developments, such as the use of small binding proteins for pretargeting that may offer new perspectives to cancer pretargeting.

Conclusions

While pretargeting has shown promise and demonstrated preclinical and clinical proof of principle, full-scale clinical development programs are needed to translate pretargeting into a clinical reality that could ideally fit into current theranostic and precision medicine perspectives.

Novel Tumor Pretargeting System Based on Complementary l-Configured Oligonucleotides

Unnatural mirror image l-configured oligonucleotides (L-ONs) are a convenient substance class for the application as complementary in vivo recognition system between a tumor specific antibody and a smaller radiolabeled effector molecule in pretargeting approaches. The high hybridization velocity and defined melting conditions are excellent preconditions of the L-ON based methodology. Their high metabolic stability and negligible unspecific binding to endogenous targets are superior characteristics in comparison to their d-configured analogs. In this study, a radiopharmacological evaluation of a new l-ONs based pretargeting system using the epidermal growth factor receptor (EGFR) specific antibody cetuximab (C225) as target-seeking component is presented. An optimized PEGylated 17mer-L-DNA was conjugated with p-SCN-Bn-NOTA (NOTA') to permit radiolabeling with the radionuclide ⁶⁴Cu. C225 was modified with the complementary 17mer-L-DNA (c-L-DNA) strand as well as with NOTA' for radiolabeling and use for positron emission tomography (PET). Two C225 conjugates were coupled with 1.5 and 5.0 c-L-DNA molecules, respectively. In vitro characterization was done with respect to hybridization studies, competition and saturation binding assays in EGFR expressing squamous cell carcinoma cell lines A431 and FaDu. The modified C225 derivatives exhibited high binding affinities in the low nanomolar range to the EGFR. PET and biodistribution experiments on FaDu tumor bearing mice with directly ⁶⁴Cu-labeled NOTA'₃-C225-(c-L-DNA)_1.5 conjugate revealed that a pretargeting interval of 24 h might be a good compromise between tumor accumulation, internalization, blood background, and liver uptake of the antibody. Despite internalization of the antibody in vivo pretargeting experiments showed an adequate hybridization of ⁶⁴Cu-radiolabeled NOTA'-L-DNA to the tumor located antibody and a good tumor-to-muscle ratio of about 11 resulting in a clearly visible image of the tumor after 24 h up to 72 h. Furthermore, low accumulation of radioactivity in organs responsible for metabolism and excretion was determined. The presented results indicate a high potential of complementary L-ONs for the pretargeting approach which can also be applied to therapeutic radionuclides such as ¹⁷⁷Lu, ⁹⁰Y, ¹⁸⁶Re, or ¹⁸⁸Re.

Antibody-drug conjugates and other nanomedicines: the frontier of gynaecological cancer treatment

Gynaecological cancers: malignancies of the cervix, uterus, ovaries, vagina and vulva, are responsible for over 1.1 million new cancer cases and almost half a million deaths annually. Ovarian cancer in particular is difficult to treat due to often being diagnosed at a late stage, and the incidence of uterine and vulvar malignancies are both on the rise. The field of nanomedicine is beginning to introduce drugs into the clinic for oncological applications exemplified by the liposomal drugs, Doxil and Myocet, the nanoparticle, Abraxane and antibody-drug conjugates (ADCs), Kadcyla and Adcetris. With many more agents currently undergoing clinical trials, the field of nanomedicine promises to have a significant impact on cancer therapy. This review considers the state of the art for nanomedicines currently on the market and those being clinically evaluated for the treatment of gynaecological cancers. In particular, it focuses on ADCs and presents a methodology for their rational design and evaluation.

Overview of Methods for Overcoming Hindrance to Drug Delivery to Tumors, with Special Attention to Tumor Interstitial Fluid

Every drug used to treat cancer (chemotherapeutics, immunological, monoclonal antibodies, nanoparticles, radionuclides) must reach the targeted cells through the tumor environment at adequate concentrations, in order to exert their cell-killing effects. For any of these agents to reach the goal cells, they must overcome a number of impediments created by the tumor microenvironment (TME), beginning with tumor interstitial fluid pressure (TIFP), and a multifactorial increase in composition of the extracellular matrix (ECM). A primary modifier of TME is hypoxia, which increases the production of growth factors, such as vascular endothelial growth factor and platelet-derived growth factor. These growth factors released by both tumor cells and bone marrow recruited myeloid cells form abnormal vasculature characterized by vessels that are tortuous and more permeable. Increased leakiness combined with increased inflammatory byproducts accumulates fluid within the tumor mass (tumor interstitial fluid), ultimately creating an increased pressure (TIFP). Fibroblasts are also up-regulated by the TME, and deposit fibers that further augment the density of the ECM, thus, further worsening the TIFP. Increased TIFP with the ECM are the major obstacles to adequate drug delivery. By decreasing TIFP and ECM density, we can expect an associated rise in drug concentration within the tumor itself. In this overview, we will describe all the methods (drugs, nutraceuticals, and physical methods of treatment) able to lower TIFP and to modify ECM used for increasing drug concentration within the tumor tissue.

An integrated approach to analyze EG2-hFc monoclonal antibody N-glycosylation by MALDI-MS

The characterization of the N-glycan portion of antibodies has been the subject of several studies involving mass spectrometry. In this article, a workflow is presented that starts with the expression of a monoclonal antibody (EG2-hFc) in Chinese hamster ovary cells and continues with Protein A purification of the antibody. Then the protocol continues with gel electrophoresis. Bands containing the heavy chain are cut and isolated from the gel followed by tryptic digestion to obtain peptides and glycopeptides. The enrichment of glycopeptides by C18 chromatography is described followed by characterization using positive and negative modes MALDI-MS and MS/MS. An exoglycosidase, beta-galactosidase, is used to verify anomericity of linkages in the glycan portion of glycopeptides. In the last step, glycans are detached from glycopeptides using PNGase F labelled with phehylhydrazine and characterized by MALDI-MS/MS. This workflow is reported for the first time for this particular antibody and presents a valuable approach for the analysis of N-glycans on most antibodies and glycoproteins.

Building better monoclonal antibody-based therapeutics

For 20 years, monoclonal antibodies (mAbs) have been a standard component of cancer therapy, but there is still much room for improvement. Efforts continue to build better cancer therapeutics based on mAbs. Anticancer mAbs function through various mechanisms, including directly targeting the malignant cells, modifying the host response, delivering cytotoxic moieties and retargeting cellular immunity towards the malignant cells. Characteristics of mAbs that affect their efficacy include antigen specificity, overall structure, affinity for the target antigen and how a mAb component is incorporated into a construct that can trigger target cell death. This Review discusses the various approaches to using mAb-based therapeutics to treat cancer and the strategies used to take advantage of the unique potential of each approach, and provides examples of current mAb-based treatments.

A pretargeting system for tumor PET imaging and radioimmunotherapy

Labeled antibodies, as well as their fragments and antibody-derived recombinant constructs, have long been proposed as general vectors to target radionuclides to tumor lesions for imaging and therapy. They have indeed shown promise in both imaging and therapeutic applications, but they have not fulfilled the original expectations of achieving sufficient image contrast for tumor detection or sufficient radiation dose delivered to tumors for therapy. Pretargeting was originally developed for tumor immunoscintigraphy. It was assumed that directly-radiolabled antibodies could be replaced by an unlabeled immunoconjugate capable of binding both a tumor-specific antigen and a small molecular weight molecule. The small molecular weight molecule would carry the radioactive payload and would be injected after the bispecific immunoconjugate. It has been demonstrated that this approach does allow for both antibody-specific recognition and fast clearance of the radioactive molecule, thus resulting in improved tumor-to-normal tissue contrast ratios. It was subsequently shown that pretargeting also held promise for tumor therapy, translating improved tumor-to-normal tissue contrast ratios into more specific delivery of absorbed radiation doses. Many technical approaches have been proposed to implement pretargeting, and two have been extensively documented. One is based on the avidin-biotin system, and the other on bispecific antibodies binding a tumor-specific antigen and a hapten. Both have been studied in preclinical models, as well as in several clinical studies, and have shown improved targeting efficiency. This article reviews the historical and recent preclinical and clinical advances in the use of bispecific-antibody-based pretargeting for radioimmunodetection and radioimmunotherapy of cancer. The results of recent evaluation of pretargeting in PET imaging also are discussed.

Change in cell death markers during (177)Lu-mAb radioimmunotherapy-induced rejection of syngeneic rat colon carcinoma

PURPOSE

To monitor cell death in tumors during the rejection process after treatment with an antibody radiolabeled with a β-emitter.

METHODS

Tumors during rejection after treatment with (177)Lu-labeled antibody BR96 and after administration of unlabeled BR96 were compared with untreated tumors from the same immunocompetent syngeneic rat tumor model. Cell death was monitored with the terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay and immunohistochemical staining of activated caspase-3 and γH2AX. These data were evaluated together with histopathological morphology, BR96-binding antigen expression, and (177)Lu radioactivity distribution imaged by digital autoradiography.

RESULTS

The untreated tumors showed staining for all the markers, mainly in and around the necrotic areas. One to 2 days p.i. large areas were stained with anti-γH2AX, followed by a slight decrease. Staining of activated caspase-3 was intense and extensive 1-2 days p.i., while found in and around necrotic areas 3-8 days p.i. TUNEL staining was similar to activated caspase-3 staining 1-2 days p.i. but more extensive than activated caspase-3 staining 3-4 days p.i. Digital autoradiography revealed activity concentration in granulation tissue from 1 day p.i.

CONCLUSION

Following radioimmunotherapy in an immunocompetent syngeneic colon carcinoma model, tumor cells did not only die through caspase-3-dependent apoptosis, but also by other mechanisms.

General overview of radioimmunotherapy of solid tumors

Radioimmunotherapy (RIT) represents an attractive tool for the treatment of local and/or diffuse tumors with radiation. In RIT, cytotoxic radionuclides are delivered by monoclonal antibodies that specifically target tumor-associated antigens or the tumor microenvironment. While RIT has been successfully employed for the treatment of lymphoma, mostly with radiolabeled antibodies against CD20 (Bexxar(®); Corixa Corp., WA, USA and Zevalin(®); Biogen Idec Inc., CA, USA and Schering AG, Berlin, Germany), its use in solid tumors is more challenging and, so far, few trials have progressed beyond Phase II. This review provides an update on antibody-radionuclide conjugates and their use in RIT. It also discusses possible optimization strategies to improve the clinical response by considering biological, radiobiological and physical features.

Emerging trends for radioimmunotherapy in solid tumors

Due to its ability to target both known and occult lesions, radioimmunotherapy (RIT) is an attractive therapeutic modality for solid tumors. Poor tumor uptake and undesirable pharmacokinetics, however, have precluded the administration of radioimmunoconjugates at therapeutically relevant doses thereby limiting the clinical utility of RIT. In solid tumors, efficacy of RIT is further compromised by heterogeneities in blood flow, tumor stroma, expression of target antigens and radioresistance. As a result significant efforts have been invested toward developing strategies to overcome these impediments. Further, there is an emerging interest in exploiting short-range, high energy α-particle emitting radionuclides for the eradication of minimal residual and micrometastatic disease. As a result several modalities for localized therapy and models of minimal disease have been developed for preclinical evaluation. This review provides a brief update on the recent efforts toward improving the efficacy of RIT for solid tumors, and development of RIT strategies for minimal disease associated with solid tumors. Further, some of promising approaches to improve tumor targeting, which showed promise in the past, but have now been ignored are also discussed.

Design optimization and characterization of Her2/neu-targeted immunotoxins: comparative in vitro and in vivo efficacy studies

Targeted therapeutics are potential therapeutic agents because of their selectivity and efficacy against tumors resistant to conventional therapy. The goal of this study was to determine the comparative activity of monovalent, engineered anti-Her2/neu immunotoxins fused to recombinant gelonin (rGel) to the activity of bivalent IgG-containing immunoconjugates. Utilizing Herceptin and its derived humanized single-chain antibody (single-chain fragment variable, designated 4D5), we generated bivalent chemical Herceptin/rGel conjugate, and the corresponding monovalent recombinant immunotoxins in two orientations, 4D5/rGel and rGel/4D5. All the constructs showed similar affinity to Her2/neu-overexpressing cancer cells, but significantly different antitumor activities. The rGel/4D5 orientation construct and Herceptin/rGel conjugate were superior to 4D5/rGel construct in in vitro and in vivo efficacy. The enhanced activity was attributed to improved intracellular toxin uptake into target cells and efficient downregulation of Her2/neu-related signaling pathways. The Her2/neu-targeted immunotoxins effectively targeted cells with Her2/neu expression level >1.5 × 10(5) sites per cell. Cells resistant to Herceptin or chemotherapeutic agents were not cross-resistant to rGel-based immunotoxins. Against SK-OV-3 tumor xenografts, the rGel/4D5 construct with excellent tumor penetration showed impressive tumor inhibition. Although Herceptin/rGel conjugate demonstrated comparatively longer serum half-life, the in vivo efficacy of the conjugate was similar to the rGel/4D5 fusion. These comparative studies demonstrate that the monovalent, engineered rGel/4D5 construct displayed comparable in vitro and in vivo antitumor efficacy as bivalent Herceptin/rGel conjugate. Immunotoxin orientation can significantly impact the overall functionality and performance of these agents. The recombinant rGel/4D5 construct with excellent tumor penetration and rapid blood clearance may reduce the unwanted toxicity when administrating to patients, and warrants consideration for further clinical evaluation.

Synthesis and application of a novel cysteine-based DTPA-NCS for targeted radioimmunotherapy

INTRODUCTION

For the development of safe and effective protein-based radiolabeled complexes such as radioimmunotherapy (RIT), the selection of the radionuclides and the chelating agents used for the radiolabeling of tumor-targeting molecules is a critical factor. We aim to synthesize a novel bifunctional chelating agent containing the isothiocyanate group for easy conjugation with antibodies having the characteristics of high stable chelation with therapeutic radionuclides.

METHODS

We have synthesized the DTPA analogue retaining L-cysteine as a core ligand of the thiol group. The chelating power of cysteine-based DTPA-NCS (cys-DTPA-NCS) was compared with that of commercial ρ-SCN-Bn-DTPA. In an application, the cetuximab was radioimmunoconjugated with (177)Lu using cys-DTPA-NCS. The affinity was tested in a cell line overexpressing EGFR. A therapy study was conducted in nude mice with subcutaneous HT-29 xenografts.

RESULTS

The cys-DTPA-NCS presents an excellent ability to chelate as compared to the ρ-SCN-Bn-DTPA. For mean ratio chemical labeling yields of 95%, the result was 0.97. (177)Lu-cys-DTPA-NCS-cetuximab was prepared under ambient condition with a high radiolabeling yield and the radiochemical purity was sustained for at least 6days. The IC50 value of the (177)Lu-labeled cetuximab was 10nM (95% confidence). The stability and therapeutic efficacy of the candidate radiopharmaceutical were verified.

CONCLUSION

The new DTPA derivative, cys-DTPA-NCS, is a good bifunctional chelating agent that can be used for protein-based radiopharmaceutical using lanthanides such as (177)Lu and (90)Y. The prepared (177)Lu-cys-DTPA-NCS-cetuximab can be used for the diagnosis and treatment of human colorectal tumor.

Endocytosis and intracellular trafficking as gateways for nanomedicine delivery: opportunities and challenges

More than 40 nanomedicines are already in routine clinical use with a growing number following in preclinical and clinical development. The therapeutic objectives are often enhanced disease-specific targeting (with simultaneously reduced access to sites of toxicity) and, especially in the case of macromolecular biotech drugs, improving access to intracellular pharmacological target receptors. Successful navigation of the endocytic pathways is usually a prerequisite to achieve these goals. Thus a comprehensive understanding of endocytosis and intracellular trafficking pathways in both the target and bystander normal cell type(s) is essential to enable optimal nanomedicine design. It is becoming evident that endocytic pathways can become disregulated in disease and this, together with the potential changes induced during exposure to the nanocarrier itself, has the potential to significantly impact nanomedicine performance in terms of safety and efficacy. Here we overview the endomembrane trafficking pathways, discuss the methods used to determine and quantitate the intracellular fate of nanomedicines, and review the current status of lysosomotropic and endosomotropic delivery. Based on the lessons learned during more than 3 decades of clinical development, the need to use endocytosis-relevant clinical biomarkers to better select those patients most likely to benefit from nanomedicine therapy is also discussed.

Intracellular CXCR4⁺ cell targeting with T22-empowered protein-only nanoparticles

BACKGROUND

Cell-targeting peptides or proteins are appealing tools in nanomedicine and innovative medicines because they increase the local drug concentration and reduce potential side effects. CXC chemokine receptor 4 (CXCR4) is a cell surface marker associated with several severe human pathologies, including colorectal cancer, for which intracellular targeting agents are currently missing.

RESULTS

Four different peptides that bind CXCR4 were tested for their ability to internalize a green fluorescent protein-based reporter nanoparticle into CXCR4⁺ cells. Among them, only the 18 mer peptide T22, an engineered segment derivative of polyphemusin II from the horseshoe crab, efficiently penetrated target cells via a rapid, receptor-specific endosomal route. This resulted in accumulation of the reporter nanoparticle in a fully fluorescent and stable form in the perinuclear region of the target cells, without toxicity either in cell culture or in an in vivo model of metastatic colorectal cancer.

CONCLUSION

Given the urgent demand for targeting agents in the research, diagnosis, and treatment of CXCR4-linked diseases, including colorectal cancer and human immunodeficiency virus infection, T22 appears to be a promising tag for the intracellular delivery of protein drugs, nanoparticles, and imaging agents.

In vivo therapeutic effect of CDH3/P-cadherin-targeting radioimmunotherapy

PURPOSE

We examined the possible efficacy of the yttrium-90 ((90)Y)-labeled anti-CDH3/P-cadherin mouse monoclonal antibody (MAb-6) in radioimmunotherapy (RIT) for lung and colorectal cancers that express CDH3/P-cadherin.

EXPERIMENTAL DESIGN

MAb-6 was established using genetic immunization. The biodistribution of MAb-6 in nude mice with lung and colorectal cancers was examined by administering indium-111((111)In)-labeled MAb-6 to mice. The mice were prepared by inoculation of CDH3/P-cadherin-positive (EBC1, H1373, and SW948) and CDH3/P-cadherin-negative (A549 and RKO) tumor cells. Therapeutic effects and toxicity were investigated by administration of (90)Y-labeled MAb-6 ((90)Y-MAb-6) to EBC, H1373, and SW948-inoculated mice.

RESULTS

Our in vivo results confirmed the specific binding of MAb-6 to tumor cells after intravenous injections of (111)In-labeled MAb-6 to mice with tumors expressing CDH3/P-cadherin. A single intravenous injection of (90)Y-MAb-6 (100 μCi) significantly suppressed tumor growth in mice with tumors expressing CDH3/P-cadherin. Furthermore, two injections of (90)Y-MAb-6 led to complete tumor regression in H1373-inoculated mice without any detectable toxicity.

CONCLUSIONS

Our findings demonstrate that CDH3/P-cadherin-targeting RIT with (90)Y-MAb-6 is a promising strategy for the treatment for cancers expressing CDH3/P-cadherin.