The efficient elimination of solid tumor cells by EGFR-specific and HER2-specific scFv-SNAP fusion proteins conjugated to benzylguanine-modified auristatin F

Reforming solid tumor treatment: the emerging potential of smaller format antibody-drug conjugate

In recent years, substantial therapeutic efficacy of antibody-drug conjugates (ADCs) has been validated through approvals of 16 ADCs for the treatment of malignant tumors. However, realization of the maximum clinical use of ADCs requires surmounting extant challenges, mainly the limitations in tumor penetration capabilities when targeting solid tumors. To resolve the hurdle of suboptimal tumor penetration, miniaturized antibody fragments with engineered formats have been harnessed for ADC assembly. By virtue of their reduced molecular sizes, antibody fragment-drug conjugates hold considerable promise for efficacious delivery of cytotoxic agents, thus conferring superior therapeutic outcomes. This review will focus on current advancements in novel ADC development utilizing smaller antibody formats from ~6 to 80 kDa, with particular emphasis on single-domain antibodies, which have been widely applied in novel ADC design. Additionally, strategies to optimize clinical translation are discussed, including half-life extension, acceleration of internalization, and reduction of immunogenic potential.

Machine learning and bioinformatic analyses link the cell surface receptor transcript levels to the drug response of breast cancer cells and drug off-target effects

Breast cancer responds variably to anticancer therapies, often leading to significant off-target effects. This study proposes that the variability in tumour responses and drug-induced adverse events is linked to the transcriptional profiles of cell surface receptors (CSRs) in breast tumours and normal tissues. We analysed multiple datasets to compare CSR expression in breast tumours with that in non-cancerous human tissues. Our findings correlate the drug responses of breast cancer cell lines with the expression levels of their targeted CSRs. Notably, we identified distinct differences in CSR expression between primary breast tumour subtypes and corresponding cell lines, which may influence drug response predictions. Additionally, we used clinical trial data to uncover associations between CSR gene expression in healthy tissues and the incidence of adverse drug reactions. This integrative approach facilitates the selection of optimal CSR targets for therapy, leveraging cell line dose-responses, CSR expression in normal tissues, and patient adverse event profiles.

Development of a sensitive direct competitive chemiluminescent enzyme immunoassay for gentamicin based on the construction of a specific single-chain variable fragment-alkaline phosphatase fusion protein

A sensitive chemiluminescent enzyme immunoassay (CLEIA) was established for the determination of gentamicin (GEN) residue levels in animal tissue. This assay is based on a fusion protein of single-chain variable fragment (scFv) and alkaline phosphatase (AP). Initially, VL and VH derived from anti-gentamicin monoclonal antibody were linked by a short peptide to construct a scFv. Subsequently, the constructed scFv sequence was accessed into the pLIP6/GN vector, and a soluble scFv-AP fusion protein was generated. The scFv-AP fusion protein was used to develop a direct competitive CLEIA (dcCLEIA) for the determination of gentamicin. In the dcCLEIA, the half inhibitory concentration (IC50) and limit of detection (LOD) were 1.073 ng/mL and 0.380 ng/mL, respectively. The average recoveries of gentamicin spiked in animal tissue samples ranged from 78% to 96%. These results showed a strong correlation with ultra performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS). The above results suggest that the anti-GEN scFv-AP fusion protein is suitable for detecting gentamicin residues in edible animal tissues.

CSPG4 as a target for the specific killing of triple-negative breast cancer cells by a recombinant SNAP-tag-based antibody-auristatin F drug conjugate

PURPOSE

Triple-negative breast cancer (TNBC) is phenotypic of breast tumors lacking expression of the estrogen receptor (ER), the progesterone receptor (PgR), and the human epidermal growth factor receptor 2 (HER2). The paucity of well-defined molecular targets in TNBC, coupled with the increasing burden of breast cancer-related mortality, emphasizes the need to develop targeted diagnostics and therapeutics. While antibody-drug conjugates (ADCs) have emerged as revolutionary tools in the selective delivery of drugs to malignant cells, their widespread clinical use has been hampered by traditional strategies which often give rise to heterogeneous mixtures of ADC products.

METHODS

Utilizing SNAP-tag technology as a cutting-edge site-specific conjugation method, a chondroitin sulfate proteoglycan 4 (CSPG4)-targeting ADC was engineered, encompassing a single-chain antibody fragment (scFv) conjugated to auristatin F (AURIF) via a click chemistry strategy.

RESULTS

After showcasing the self-labeling potential of the SNAP-tag component, surface binding and internalization of the fluorescently labeled product were demonstrated on CSPG4-positive TNBC cell lines through confocal microscopy and flow cytometry. The cell-killing ability of the novel AURIF-based recombinant ADC was illustrated by the induction of a 50% reduction in cell viability at nanomolar to micromolar concentrations on target cell lines.

CONCLUSION

This research underscores the applicability of SNAP-tag in the unambiguous generation of homogeneous and pharmaceutically relevant immunoconjugates that could potentially be instrumental in the management of a daunting disease like TNBC.

Antibody drug conjugates as targeted cancer therapy: past development, present challenges and future opportunities

Antibody drug conjugates (ADCs) are promising cancer therapeutics with minimal toxicity as compared to small cytotoxic molecules alone and have shown the evidence to overcome resistance against tumor and prevent relapse of cancer. The ADC has a potential to change the paradigm of cancer chemotherapeutic treatment. At present, 13 ADCs have been approved by USFDA for the treatment of various types of solid tumor and haematological malignancies. This review covers the three structural components of an ADC-antibody, linker, and cytotoxic payload-along with their respective structure, chemistry, mechanism of action, and influence on the activity of ADCs. It covers comprehensive insight on structural role of linker towards efficacy, stability & toxicity of ADCs, different types of linkers & various conjugation techniques. A brief overview of various analytical techniques used for the qualitative and quantitative analysis of ADC is summarized. The current challenges of ADCs, such as heterogeneity, bystander effect, protein aggregation, inefficient internalization or poor penetration into tumor cells, narrow therapeutic index, emergence of resistance, etc., are outlined along with recent advances and future opportunities for the development of more promising next-generation ADCs.

The Evolution of SNAP-Tag Labels

The conjugation of proteins with synthetic molecules can be conducted in many different ways. In this Perspective, we focus on tag-based techniques and specifically on the SNAP-tag technology. The SNAP-tag technology makes use of a fusion protein between a protein of interest and an enzyme tag that enables the actual conjugation reaction. The SNAP-tag is based on the O⁶-alkylguanine-DNA alkyltransferase (AGT) enzyme and is optimized to react selectively with O⁶-benzylguanine (BG) substrates. BG-containing dye derivatives have frequently been used to introduce a fluorescent tag to a specific protein. We believe that the site-specific conjugation of polymers to proteins can significantly benefit from the SNAP-tag technology. Especially, polymers synthesized via reversible deactivation radical polymerization allow for the facile introduction of a BG end group to enable SNAP-tag conjugation.

Monoclonal Antibodies: The Greatest Resource to Treat Multiple Myeloma

Multiple myeloma (MM) is a currently incurable hematologic cancer. This disease is characterized by immunological alterations of myeloid cells and lymphocytes. The first-line therapy involves the use of classic chemotherapy; however, many patients have a relapsed form that could evolve into a refractory MM. The new therapeutic frontiers involve the use of new monoclonal antibodies (Mab) such as daratumumab, isatuximab, and elotuzumab. In addition to monoclonal antibodies, new immunotherapies based on modern bispecific antibodies and chimeric antigen receptor (CAR) T cell therapy have been investigated. For this reason, immunotherapy represents the greatest hope for the treatment of MM. This review intends to focus the attention on the new approved antibody targets. The most important are: CD38 (daratumumab and isatuximab), SLAM7 (elotuzumab), and BCMA (belantamab mafodotin) for the treatment of MM currently used in clinical practice. Although the disease is still incurable, the future perspective is to find the best therapeutic combination among all available drugs.

Click Chemistry-Generated Auristatin F-Linker-Benzylguanine for a SNAP-Tag-Based Recombinant Antibody-Drug Conjugate Demonstrating Selective Cytotoxicity toward EGFR-Overexpressing Tumor Cells

Antibody-drug conjugates (ADCs) are bifunctional molecules combining the targeting potential of monoclonal antibodies with the cancer-killing ability of cytotoxic drugs. This simple yet intelligently designed system directly addresses the lack of specificity encountered with conventional anti-cancer treatment regimes. However, despite their initial success, the generation of clinically sustainable and effective ADCs has been plagued by poor tumor penetration, undefined chemical linkages, unpredictable pharmacokinetic profiles, and heterogeneous mixtures of products. To this end, we generated a SNAP-tag-based fusion protein targeting the epidermal growth factor receptor (EGFR)-a biomarker of aggressive and drug-resistant cancers. Here, we demonstrate the use of a novel click coupling strategy to engineer a benzylguanine (BG)-linker-auristatin F (AuriF) piece that can be covalently tethered to the EGFR-targeting SNAP-tag-based fusion protein in an irreversible 1:1 stoichiometric reaction to form a homogeneous product. Furthermore, using these recombinant ADCs to target EGFR-overexpressing tumor cells, we provide a proof-of-principle for generating biologically active antimitotic therapeutic proteins capable of inducing cell death in a dose-dependent manner, thus alleviating some of the challenges of early ADC development.

Functionalized Liposome and Albumin-Based Systems as Carriers for Poorly Water-Soluble Anticancer Drugs: An Updated Review

Cancer is one of the leading causes of death worldwide. In the available treatments, chemotherapy is one of the most used, but has several associated problems, namely the high toxicity to normal cells and the resistance acquired by cancer cells to the therapeutic agents. The scientific community has been battling against this disease, developing new strategies and new potential chemotherapeutic agents. However, new drugs often exhibit poor solubility in water, which led researchers to develop functionalized nanosystems to carry and, specifically deliver, the drugs to cancer cells, targeting overexpressed receptors, proteins, and organelles. Thus, this review is focused on the recent developments of functionalized nanosystems used to carry poorly water-soluble drugs, with special emphasis on liposomes and albumin-based nanosystems, two major classes of organic nanocarriers with formulations already approved by the U.S. Food and Drug Administration (FDA) for cancer therapeutics.

Antibody-Based Targeted Interventions for the Diagnosis and Treatment of Skin Cancers

BACKGROUND

Cutaneous malignancies most commonly arise from skin epidermal cells. These cancers may rapidly progress from benign to a metastatic phase. Surgical resection represents the gold standard therapeutic treatment of non-metastatic skin cancer while chemo- and/or radiotherapy are often used against metastatic tumors. However, these therapeutic treatments are limited by the development of resistance and toxic side effects, resulting from the passive accumulation of cytotoxic drugs within healthy cells.

OBJECTIVE

This review aims to elucidate how the use of monoclonal Antibodies (mAbs) targeting specific Tumor Associated Antigens (TAAs) is paving the way to improved treatment. These mAbs are used as therapeutic or diagnostic carriers that can specifically deliver cytotoxic molecules, fluorophores or radiolabels to cancer cells that overexpress specific target antigens.

RESULTS

mAbs raised against TAAs are widely in use for e.g. differential diagnosis, prognosis and therapy of skin cancers. Antibody-Drug Conjugates (ADCs) particularly show remarkable potential. The safest ADCs reported to date use non-toxic photo-activatable Photosensitizers (PSs), allowing targeted Photodynamic Therapy (PDT) resulting in targeted delivery of PS into cancer cells and selective killing after light activation without harming the normal cell population. The use of near-infrared-emitting PSs enables both diagnostic and therapeutic applications upon light activation at the specific wavelengths.

CONCLUSION

Antibody-based approaches are presenting an array of opportunities to complement and improve current methods employed for skin cancer diagnosis and treatment.

Selective recognition of tumor cells by molecularly imprinted polymers

Molecularly imprinted polymers, developed 50 years ago, have garnered enormous attention as receptor-like materials. Lately, molecularly imprinted polymers have been employed as a specific target tool in favor of cancer diagnosis and therapy by the selective recognition of tumor cells. Although the molecular imprinting technology has been well-innovated recently, the cell still remains the most challenging target for imprinting. In this review, we summarize the advances in the synthesis of molecularly imprinted polymers suitable for the selective recognition of tumor cells. Through a sustained effort, three strategies have been developed including peptide-imprinting, polysaccharide-imprinting, and whole-cell imprinting, which have resulted in inspiring applications in effective cancer diagnosis and therapy. The major challenges and perspectives on the further directions related to the synthesis of molecularly imprinted polymers were also outlined.

Toward Homogenous Antibody Drug Conjugates Using Enzyme-Based Conjugation Approaches

In the last few decades, antibody-based diagnostic and therapeutic applications have been well established in medicine and have revolutionized cancer managements by improving tumor detection and treatment. Antibodies are unique medical elements due to their powerful properties of being able to recognize specific antigens and their therapeutic mechanisms such as blocking specific pathways, antibody-dependent cellular cytotoxicity, and complement-dependent cytotoxicity. Furthermore, modification techniques have paved the way for improving antibody properties and to develop new classes of antibody-conjugate-based diagnostic and therapeutic agents. These techniques allow arming antibodies with various effector molecules. However, these techniques are utilizing the most frequently used amino acid residues for bioconjugation, such as cysteine and lysine. These bioconjugation approaches generate heterogeneous products with different functional and safety profiles. This is mainly due to the abundance of lysine and cysteine side chains. To overcome these limitations, different site-direct conjugation methods have been applied to arm the antibodies with therapeutic or diagnostics molecules to generate unified antibody conjugates with tailored properties. This review summarizes some of the enzyme-based site-specific conjugation approaches.

Current strategies for the discovery and bioconjugation of smaller, targetable drug conjugates tailored for solid tumor therapy

Introduction: Antibody-Drug Conjugates (ADCs) have undergone a recent resurgence with 5 product approvals over the last 2 years but for those close to the field, it's been repeated cycles of setbacks and new innovations. A new wave of innovation is in the type of format used to deliver the cytotoxic payloads, with smaller bio-molecules being designed to have more optimal penetration and elimination properties tailored for solid tumors.Areas covered: In this review, the authors cover many of the recently described smaller-format drug conjugates (including formats such as diabodies, Fabs, scFvs, domain antibodies) with an emphasis on the types of conjugation technologies used to attach the chemical linker-payload.Expert opinion: Smaller formats are highly influenced by the structure of the linker-payload, arguably more-so than larger ADCs, so careful consideration is needed where solublising and pharmacokinetic modulation is required. High-quality conjugates are being developed with in vivo tumor efficacy and tolerability properties competitive with ADCs and with a few formats already in clinical development, we expect the pipeline to expand and to reach the market.

Using the SNAP-Tag technology to easily measure and demonstrate apoptotic changes in cancer and blood cells with different dyes

In vitro and ex vivo development of novel therapeutic agents requires reliable and accurate analyses of the cell conditions they were preclinical tested for, such as apoptosis. The detection of apoptotic cells by annexin V (AV) coupled to fluorophores has often shown limitations in the choice of the dye due to interference with other fluorescent-labeled cell markers. The SNAP-tag technology is an easy, rapid and versatile method for functionalization of proteins and was therefore used for labeling AV with various fluorophores. We generated the fusion protein AV-SNAP and analyzed its capacity for the specific display of apoptotic cells in various assays with therapeutic agents. AV-SNAP showed an efficient coupling reaction with five different fluorescent dyes. Two selected fluorophores were tested with suspension, adherent and peripheral blood cells, treated by heat-shock or apoptosis-inducing therapeutic agents. Flow cytometry analysis of apoptotic cells revealed a strong visualization using AV-SNAP coupled to these two fluorophores exemplary, which was comparable to a commercial AV-Assay-kit. The combination of the apoptosis-specific binding protein AV with the SNAP-tag provides a novel solid method to facilitate protein labeling using several, easy to change, fluorescent dyes at once. It avoids high costs and allows an ordinary exchange of dyes and easier use of other fluorescent-labeled cell markers, which is of high interest for the preclinical testing of therapeutic agents in e.g. cancer research.

Advances in epidermal growth factor receptor specific immunotherapy: lessons to be learned from armed antibodies

The epidermal growth factor receptor (EGFR) has been recognized as an important therapeutic target in oncology. It is commonly overexpressed in a variety of solid tumors and is critically involved in cell survival, proliferation, metastasis, and angiogenesis. This multi-dimensional role of EGFR in the progression and aggressiveness of cancer, has evolved from conventional to more targeted therapeutic approaches. With the advent of hybridoma technology and phage display techniques, the first anti-EGFR monoclonal antibodies (mAbs) (Cetuximab and Panitumumab) were developed. Due to major limitations including host immune reactions and poor tumor penetration, these antibodies were modified and used as guiding mechanisms for the specific delivery of readily available chemotherapeutic agents or plants/bacterial toxins, giving rise to antibody-drug conjugates (ADCs) and immunotoxins (ITs), respectively. Continued refinement of ITs led to deimmunization strategies based on depletion of B and T-cell epitopes or substitution of non-human toxins leading to a growing repertoire of human enzymes capable of inducing cell death. Similarly, the modification of classical ADCs has resulted in the first, fully recombinant versions. In this review, we discuss significant advancements in EGFR-targeting immunoconjugates, including ITs and recombinant photoactivable ADCs, which serve as a blueprint for further developments in the evolving domain of cancer immunotherapy.

Antibody-Based Immunotherapy: Alternative Approaches for the Treatment of Metastatic Melanoma

Melanoma is the least common form of skin cancer and is associated with the highest mortality. Where melanoma is mostly unresponsive to conventional therapies (e.g., chemotherapy), BRAF inhibitor treatment has shown improved therapeutic outcomes. Photodynamic therapy (PDT) relies on a light-activated compound to produce death-inducing amounts of reactive oxygen species (ROS). Their capacity to selectively accumulate in tumor cells has been confirmed in melanoma treatment with some encouraging results. However, this treatment approach has not reached clinical fruition for melanoma due to major limitations associated with the development of resistance and subsequent side effects. These adverse effects might be bypassed by immunotherapy in the form of antibody–drug conjugates (ADCs) relying on the ability of monoclonal antibodies (mAbs) to target specific tumor-associated antigens (TAAs) and to be used as carriers to specifically deliver cytotoxic warheads into corresponding tumor cells. Of late, the continued refinement of ADC therapeutic efficacy has given rise to photoimmunotherapy (PIT) (a light-sensitive compound conjugated to mAbs), which by virtue of requiring light activation only exerts its toxic effect on light-irradiated cells. As such, this review aims to highlight the potential clinical benefits of various armed antibody-based immunotherapies, including PDT, as alternative approaches for the treatment of metastatic melanoma.

Engineered scPDL1-DM1 drug conjugate with improved in vitro analysis to target PD-L1 positive cancer cells and intracellular trafficking studies in cancer therapy

Antibody-drug conjugates (ADC), precisely deliver a cytotoxic agent to antigen-expressing tumor cells by using specific binding strategies of antibodies. The ADC has shown the ability of potent bio-therapeutics development but indefinite stoichiometric linkage and full-length antibody penetration compromised the field of its advancement. Single chain variable fragments convention instead of the full-length antibody may overcome the challenge of rapid penetration and internalization. Programmed cell death ligand-1 interaction with PD-1 has recently revolutionized the field of immunotherapy. We systematically designed scPDL1-DM1 drug conjugate by linking scFv-PD-L1 proteins (scFv) with maytansinoids (DM1) cytotoxic agent through succinimidyl trans-4-maleimidylmethyl cyclohexane-1- carboxylate (SMCC) linker. Binding affinity was confirmed by immunocytochemistry, spectrophotometry and gel electrophoresis analysis. The scPDL1-DM1 showed specific binding with PD-L1 positive tumor cells and retained in vitro anti-cell proliferation activity. The intracellular trafficking of the drug was evaluated in A549 cancer cell lines, and maximum trafficking was observed after two hours of incubation. The generated drug can be utilized as a potent tool for site-specific conjugation, predicting specificity in vitro activities with extended range against PD-L1 positive cancer cells and can be utilized for further in vivo testing and clinical therapeutics development.

Antibody-drug conjugates in clinical trials for lymphoid malignancies and multiple myeloma

Antibody-drug conjugates (ADC) represent a distinct family of chemoimmunotherapy agents. ADCs are composed of monoclonal antibodies conjugated to cytotoxic payloads via specialized chemical linkers. ADCs therefore combine the immune therapy with targeted chemotherapy. Due to the distinct biomarkers associated with lymphocytes and plasma cells, ADCs have emerged as a promising treatment option for lymphoid malignancies and multiple myeloma. Several ADCs have been approved for clinical applications: brentuximab vedotin, inotuzumab ozogamicin, moxetumomab pasudotox, and polatuzumab vedotin. More novel ADCs are under clinical development. In this article, we summarized the general principles for ADC design, and updated novel ADCs under various stages of clinical trials for lymphoid malignancies and multiple myeloma.

Photoimmunoconjugates: novel synthetic strategies to target and treat cancer by photodynamic therapy

Photodynamic therapy (PDT) combines a photosensitizer (PS) with the physical energy of non-ionizing light to trigger cell death pathways. PDT has potential as a therapeutic modality to be used in alternative or in combination with other conventional cancer treatment protocols (e.g. surgery, chemotherapy and radiotherapy). Still, due to the lack of specificity of the current PSs to target the tumor cells, several studies have exploited their conjugation with targeting moieties. PSs conjugated with antibodies (Abs) or their fragments, able to bind antigens overexpressed in the tumors, have demonstrated potential in PDT of tumors. This review provides an overview of the most recent advances on photoimmunoconjugates (PICs) for cancer PDT, which involve the first and second-generation PSs conjugated to Abs. This is an update of our previous review "Antibodies armed with photosensitizers: from chemical synthesis to photobiological applications", published in 2015 in Org. Biomol. Chem.

Biomolecular engineering of antidehydroepiandrosterone antibodies: a new perspective in cancer diagnosis and treatment using single-chain antibody variable fragment

Aim: To develop a monoclonal antibody against dehydroepiandrosterone (DHEA) and miniaturize it, generating a single-chain antibody variable fragment (scFv) against DHEA as an adrenocortical carcinoma (ACC) marker. Material & methods: DHEA conjugated to keyhole limpet hemocyanin was used as an immunogen to obtain anti-DHEA hybridomas. Variable fragments were cloned from hybridoma 5B7 total RNA, and used to detect DHEA in normal adrenal tissue and ACC cells. Results: IgM monoclonal antibody was highly specific, and the recombinant scFv preserved parental antibody characteristics, allowing tissue localization of DHEA. Conclusion: Undefined small lesions are challenges for clinicians and impact clinical adrenocortical tumor management. Generating an anti-DHEA scFv facilitates development of imaging tests for early diagnosis of pediatric ACC.

Applications of SNAP-tag technology in skin cancer therapy

BACKGROUND

Cancer treatment in the 21st century has seen immense advances in optical imaging and immunotherapy. Significant progress has been made in the bioengineering and production of immunoconjugates to achieve the goal of specifically targeting tumors.

DISCUSSION

In the 21st century, antibody drug conjugates (ADCs) have been the focus of immunotherapeutic strategies in cancer. ADCs combine the unique targeting of monoclonal antibodies (mAbs) with the cancer killing ability of cytotoxic drugs. However, due to random conjugation methods of drug to antibody, ADCs are associated with poor antigen specificity and low cytotoxicity, resulting in a drug to antibody ratio (DAR) >1. This means that the cytotoxic drugs in ADCs are conjugated randomly to antibodies, by cysteine or lysine residues. This generates heterogeneous ADC populations with 0 to 8 drugs per an antibody, each with distinct pharmacokinetic, efficacy, and toxicity properties. Additionally, heterogeneity is created not only by different antibody to ligand ratios but also by different sites of conjugation. Hence, much effort has been made to find and establish antibody conjugation strategies that enable us to better control stoichiometry and site-specificity. This includes utilizing protein self-labeling tags as fusion partners to the original protein. Site-specific conjugation is a significant characteristic of these engineered proteins. SNAP-tag is one such engineered self-labeling protein tag shown to have promising potential in cancer treatment. The SNAP-tag is fused to an antibody of choice and covalently reacts specifically in a 1:1 ratio with benzylguanine (BG) substrates, eg, fluorophores or photosensitizers, to target skin cancer. This makes SNAP-tag a versatile technique in optical imaging and photoimmunotherapy of skin cancer.

CONCLUSION

SNAP-tag technology has the potential to contribute greatly to a broad range of molecular oncological applications because it combines efficacious tumor targeting, minimized local and systemic toxicity, and noninvasive assessment of diagnostic/prognostic molecular biomarkers of cancer.

Revival of a potent therapeutic maytansinoid agent using a strategy that combines covalent drug conjugation with sequential nanoparticle assembly

Maytansine and its related analogues are a class of highly potent anti-proliferation agents that have failed to be exploited as clinical drugs for human therapy due to unacceptable systemic toxicity. Here, we delineate a novel strategy that combines rational drug conjugation with subsequent nanoparticle assembly to systemically deliver this highly potent and toxic drug. To demonstrate this concept, we covalently coupled the thiolated maytansine derivative, the DM1 agent, to amphiphilic block co-polymers, polyethylene glycol (PEG)-block-polylactide (PLA), in varying molecular weights to generate two prodrug constructs (i.e., PEG_2K-PLA_2K-DM1 and PEG_2K-PLA_4K-DM1) via the maleimide-thiol reaction. The resulting two constructs are amenable to self-assembly in aqueous solutions and are systemically injectable for preclinical studies. In vivo evaluations indicate that PEG-PLA-DM1 conjugate-assembled nanoparticles (NPs) display substantially reduced drug toxicity compared to the free drug forms and NPs that physically encapsulate DM1. Furthermore, following systemic administration, these nanodrugs produced superior therapeutic efficacy over free DM1 in a colon tumor xenograft-bearing mouse model. Therefore, this study provides evidence that the conjugation of toxic drugs to assembling copolymers enables the alleviation of cancer drug toxicity and effective delivery of anticancer drugs. Thus, this DM1-formulated platform represents a new generation of nanotherapeutics that are available for further clinical evaluation.

Specific Drug Delivery to Cancer Cells with Double-Imprinted Nanoparticles against Epidermal Growth Factor Receptor

Epidermal growth factor receptor (EGFR), a tyrosine kinase receptor, is over-expressed in many tumors, including almost half of triple-negative breast cancers. The latter belong to a very-aggressive and drug-resistant form of malignancy. Although humanized anti-EGFR antibodies can work efficiently against these cancers both as monotherapy and in combination with genotoxic drugs, instability and high production costs are some of their known drawbacks in clinical use. In addition, the development of antibodies to target membrane proteins is a very challenging task. Accordingly, the main focus of the present work is the design of supramolecular agents for the targeting of membrane proteins in cancer cells and, hence, more-specific drug delivery. These were produced using a novel double-imprinting approach based on the solid-phase method for preparation of molecularly imprinted polymer nanoparticles (nanoMIPs), which were loaded with doxorubicin and targeted toward a linear epitope of EGFR. Additionally, upon binding, doxorubicin-loaded anti-EGFR nanoMIPs elicited cytotoxicity and apoptosis only in those cells that over-expressed EGFR. Thus, this approach can provide a plausible alternative to conventional antibodies and sets up a new paradigm for the therapeutic application of this class of materials against clinically relevant targets. Furthermore, nanoMIPs can promote the development of cell imaging tools against difficult targets such as membrane proteins.

A Macropinocytosis-Intensifying Albumin Domain-Based scFv Antibody and Its Conjugate Directed against K-Ras Mutant Pancreatic Cancer

Enhanced macropinocytosis has been found in K-Ras mutant pancreatic cancer cells, through which albumin can massively enter into the K-Ras-driven cancer cells, suggesting its role in serving as a macropinocytosis-intensifying drug delivery carrier. In the present study, a novel recombinant protein Fv-LDP-D3 and its reconstituted analogue Fv-LDP-D3-AE were designed and prepared. Fv is the fragment of an anti-EGFR antibody, D3 is the domain III of human serum albumin (HSA), LDP is the apoprotein of the antitumor antibiotic lidamycin (LDM), and AE is an extremely cytotoxic enediyne chromophore derived from LDM. As shown, the recombinant protein Fv-LDP-D3 presented intensive and selective binding capacity to pancreatic cancer cells and inhibited cell proliferation by blocking EGFR signaling. Moreover, Fv-LDP-D3 showed prominent tumor imaging in pancreatic carcinoma xenograft. The reconstituted, enediyne-integrated analogue Fv-LDP-D3-AE displayed highly potent cytotoxicity to pancreatic cancer cells through apoptosis induction and G2/M arrest. Fv-LDP-D3 and Fv-LDP-D3-AE markedly inhibited the tumor growth of the pancreatic carcinoma AsPC-1 xenograft. Study results indicated that the novel recombinant protein displays both EGFR-targeting and macropinocytosis-intensifying attributes, presenting a new format of scFv antibody that integrates with albumin domain III. It might be a feasible strategy to develop targeted drugs for K-Ras mutant pancreatic cancer.

Antibody-Drug Conjugates as Cancer Therapeutics: Past, Present, and Future

Antibody-drug conjugates (ADCs) represent an innovative therapeutic approach that provides novel treatment options and hope for patients with cancer. By coupling monoclonal antibodies (mAbs) to cytotoxic small-molecule payloads with a plasma-stable linker, ADCs offer the potential for increased drug specificity and fewer off-target effects than systemic chemotherapy. As evidence for the potential of these therapies, many new ADCs are in various stages of clinical development. Because their structure poses unique challenges to pharmacokinetic and pharmacodynamic characterization, it is critical to recognize the differences between ADCs and conventional chemotherapy in the design of ADC clinical development strategies. Although some properties may be determined mainly by either the mAb or the small-molecule portion, the behavior of these agents is not always predictable. Furthermore, because the absorption, distribution, metabolism, and excretion (ADME) of ADCs are influenced by all 3 of its components (mAb, linker, and payload), it is important to characterize the intact molecule, any target-mediated catabolic clearance of the mAb, and the ADME properties of the small-molecule payload. Here we describe key issues in the clinical development of ADCs, including considerations for designing first-in-human studies for ADCs. We discuss some difficulties of ADC pharmacokinetic characterization and current approaches to overcoming these challenges. Finally, we consider all aspects of clinical pharmacology assessment required during drug development, using examples from the literature to illustrate the discussion.

Novel PSCA targeting scFv-fusion proteins for diagnosis and immunotherapy of prostate cancer

PURPOSE

Despite great progress in the diagnosis and treatment of localized prostate cancer (PCa), there remains a need for new diagnostic markers that can accurately distinguish indolent and aggressive variants. One promising approach is the antibody-based targeting of prostate stem cell antigen (PSCA), which is frequently overexpressed in PCa. Here, we show the construction of a molecular imaging probe comprising a humanized scFv fragment recognizing PSCA genetically fused to an engineered version of the human DNA repair enzyme O6-alkylguanine-DNA alkyltransferase (AGT), the SNAP-tag, enabling specific covalent coupling to various fluorophores for diagnosis of PCa. Furthermore, the recombinant immunotoxin (IT) PSCA(scFv)-ETA' comprising the PSCA(scFv) and a truncated version of Pseudomonas exotoxin A (PE, ETA') was generated.

METHODS

We analyzed the specific binding and internalization behavior of the molecular imaging probe PSCA(scFv)-SNAP in vitro by flow cytometry and live cell imaging, compared to the corresponding IT PSCA(scFv)-ETA'. The cytotoxic activity of PSCA(scFv)-ETA' was tested using cell viability assays. Specific binding was confirmed on formalin-fixed paraffin-embedded tissue specimen of early and advanced PCa.

RESULTS

Alexa Fluor® 647 labeling of PSCA(scFv)-SNAP confirmed selective binding to PSCA, leading to rapid internalization into the target cells. The recombinant IT PSCA(scFv)-ETA' showed selective binding leading to internalization and efficient elimination of target cells.

CONCLUSIONS

Our data demonstrate, for the first time, the specific binding, internalization, and cytotoxicity of a scFv-based fusion protein targeting PSCA. Immunohistochemical staining confirmed the specific ex vivo binding to primary PCa material.

Human Antibody Fusion Proteins/Antibody Drug Conjugates in Breast and Ovarian Cancer

Considerable research efforts have been dedicated to understanding ovarian and breast cancer mechanisms, but there has been little progress translating the research into effective clinical applications. Hence, personalized/precision medicine has emerged because of its potential to improve the accuracy of tumor targeting and minimize toxicity to normal tissue. Targeted therapy in both breast and ovarian cancer has focused on antibodies, antibody drug conjugates (ADCs), and very recently the introduction of human antibody fusion proteins. Small molecule inhibitors and monoclonal antibodies (mAbs) are used in conjunction with chemotherapeutic drugs as a form of treatment but problems arise from a board expression of the target antigen in healthy tissues. Also, insufficient tumor penetration due to tight binding affinity and macromolecular size of mAbs compromise the efficacy of these ADCs. A more targeted approach is thus needed, and ADCs were designed to meet this need. However, in ADCs the method of conjugation of drug to antibody is >1, altering the structure of the drug which leads to off-target effects. Random conjugation also causes the drug to affect the pharmokinetics and biodistribution of the antibody and may cause nonspecific binding and internalization. Recombinant therapeutic proteins achieve controlled conjugation reactions and combine cytotoxicity and targeting in one molecule. They can also be engineered to extend half-life, stability and mechanism of action, and offer novel delivery routes. SNAP-tag fusion proteins are an example of a theranostic recombinant protein as they provide a unique antibody format to conjugate a variety of benzyl guanine modified labels, e.g. fluorophores and photosensitizers in a 1:1 stoichiometry. On the one hand, SNAP tag fusions can be used to optically image tumors when conjugated to a fluorophore, and on the other hand the recombinant proteins can induce necrosis/apoptosis in the tumor when conjugated to a photosensitizer upon exposure to a changeable wavelength of light. The dual nature of SNAP-tag fusions as both a diagnostic and therapeutic tool reinforces its significant role in cancer treatment in an era of precision medicine.

Comparison of a mouse and a novel human scFv-SNAP-auristatin F drug conjugate with potent activity against EGFR-overexpressing human solid tumor cells

Antibody–drug conjugates (ADCs) can deliver toxins to specific targets such as tumor cells. They have shown promise in preclinical/clinical development but feature stoichiometrically undefined chemical linkages, and those based on full-size antibodies achieve only limited tumor penetration. SNAP-tag technology can overcome these challenges by conjugating benzylguanine-modified toxins to single-chain fragment variables (scFvs) with 1:1 stoichiometry while preserving antigen binding. Two (human and mouse) scFv-SNAP fusion proteins recognizing the epidermal growth factor receptor (EGFR) were expressed in HEK 293T cells. The purified fusion proteins were conjugated to auristatin F (AURIF). Binding activity was confirmed by flow cytometry/immunohistochemistry, and cytotoxic activity was confirmed by cell viability/apoptosis and cell cycle arrest assays, and a novel microtubule dynamics disassembly assay was performed. Both ADCs bound specifically to their target cells in vitro and ex vivo, indicating that the binding activity of the scFv-SNAP fusions was unaffected by conjugation to AURIF. Cytotoxic assays confirmed that the ADCs induced apoptosis and cell cycle arrest at nanomolar concentrations and microtubule disassembly. The SNAP-tag technology provides a platform for the development of novel ADCs with defined conjugation sites and stoichiometry. We achieved the stable and efficient linkage of AURIF to human or murine scFvs using the SNAP-tag technology, offering a strategy to improve the development of personalized medicines.

Up-regulation of plakophilin-2 is correlated with the progression of glioma

Glioma is the most common type of primary brain tumor in the CNS. Due to its poor prognosis and high mortality rates, it is urgent to find out more effective therapies. Plakophilin-2 (PKP2) is a widespread desmosomal plaque protein. Recently, the important roles of PKP2 in the proliferation and migration of cancer cells and tumor progression has been shown. However, the expression and potential function of PKP2 in glioma was still unclear. In this study, we demonstrated that PKP2 protein expression level was increased in glioma tissues compared with normal brain tissues, and its level was significantly associated with the Ki-67 expression and WHO grade by Western blot analysis and immunohistochemistry. Clinically, high PKP2 expression was tightly related to poor prognosis of glioma patients. Interestingly, we found that down-regulated PKP2 expression was shown to inhibit the migration of cells in glioma. Moreover, cell counting kit (CCK)-8 and colony formation analyses proved that reduced expression of PKP2 could weaken glioma cell proliferation. Taken together, these data uncover a potential role for PKP2 in the pathogenic process of glioma, suggesting that PKP2 may be a promising therapeutic target of glioma.