Antibody-drug conjugates for the treatment of cancer

VHH Nanobody Versatility against Pentameric Ligand-Gated Ion Channels

Pentameric ligand-gated ion channels provide rapid chemical-electrical signal transmission between cells in the central and peripheral nervous system. Their dysfunction is associated with many nervous system disorders. They are composed of five identical (homomeric receptors) or homologous (heteromeric receptors) subunits. VHH nanobodies, or single-chain antibodies, are the variable domain, VHH, of antibodies that are composed of the heavy chain only from camelids. Their unique structure results in many specific biochemical and biophysical properties that make them an excellent alternative to conventional antibodies. This Perspective explores the published VHH nanobodies which have been isolated against pentameric ligand-gated ion channel subfamilies. It outlines the genetic and chemical modifications available to alter nanobody function. An assessment of the available functional and structural data indicate that it is feasible to create therapeutic agents and impart, through their modification, a given desired modulatory effect of its target receptor for current stoichiometric-specific VHH nanobodies.

Cancer therapy with antibodies

The greatest challenge in cancer therapy is to eradicate cancer cells with minimal damage to normal cells. Targeted therapy has been developed to meet that challenge, showing a substantially increased therapeutic index compared with conventional cancer therapies. Antibodies are important members of the family of targeted therapeutic agents because of their extraordinarily high specificity to the target antigens. Therapeutic antibodies use a range of mechanisms that directly or indirectly kill the cancer cells. Early antibodies were developed to directly antagonize targets on cancer cells. This was followed by advancements in linker technologies that allowed the production of antibody-drug conjugates (ADCs) that guide cytotoxic payloads to the cancer cells. Improvement in our understanding of the biology of T cells led to the production of immune checkpoint-inhibiting antibodies that indirectly kill the cancer cells through activation of the T cells. Even more recently, bispecific antibodies were synthetically designed to redirect the T cells of a patient to kill the cancer cells. In this Review, we summarize the different approaches used by therapeutic antibodies to target cancer cells. We discuss their mechanisms of action, the structural basis for target specificity, clinical applications and the ongoing research to improve efficacy and reduce toxicity.

Antibody-peptide conjugates deliver covalent inhibitors blocking oncogenic cathepsins

Cysteine cathepsins are a family of proteases that are relevant therapeutic targets for the treatment of different cancers and other diseases. However, no clinically approved drugs for these proteins exist, as their systemic inhibition can induce deleterious side effects. To address this problem, we developed a modular antibody-based platform for targeted drug delivery by conjugating non-natural peptide inhibitors (NNPIs) to antibodies. NNPIs were functionalized with reactive warheads for covalent inhibition, optimized with deep saturation mutagenesis and conjugated to antibodies to enable cell-type-specific delivery. Our antibody-peptide inhibitor conjugates specifically blocked the activity of cathepsins in different cancer cells, as well as osteoclasts, and showed therapeutic efficacy in vitro and in vivo. Overall, our approach allows for the rapid design of selective cathepsin inhibitors and can be generalized to inhibit a broad class of proteases in cancer and other diseases.

Targeted drug delivery using nanobodies to deliver effective molecules to breast cancer cells: the most attractive application of nanobodies

Targeted drug delivery is one of the attractive ways in which cancer treatment can significantly reduce side effects. In the last two decades, the use of antibodies as a tool for accurate detection of cancer has been noted. On the other hand, the binding of drugs and carriers containing drugs to the specific antibodies of cancer cells can specifically target only these cells. However, the use of whole antibodies brings challenges, including their large size, the complexity of conjugation, the high cost of production, and the creation of immunogenic reactions in the body. The use of nanobodies, or VHHs, which are a small part of camel heavy chain antibodies, is very popular due to their small size, high craftsmanship, and low production cost. In this article, in addition to a brief overview of the structure and characteristics of nanobodies, the use of this molecule in the targeted drug delivery of breast cancer has been reviewed.

Antibody-drug conjugates in cancer therapy: innovations, challenges, and future directions

The emergence of antibody-drug conjugates (ADCs) as a potential therapeutic avenue in cancer treatment has garnered significant attention. By combining the selective specificity of monoclonal antibodies with the cytotoxicity of drug molecules, ADCs aim to increase the therapeutic index, selectively targeting cancer cells while minimizing systemic toxicity. Various ADCs have been licensed for clinical usage, with ongoing research paving the way for additional options. However, the manufacture of ADCs faces several challenges. These include identifying suitable target antigens, enhancing antibodies, linkers, and payloads, and managing resistance mechanisms and side effects. This review focuses on the strategies to overcome these hurdles, such as site-specific conjugation techniques, novel antibody formats, and combination therapy. Our focus lies on current advancements in antibody engineering, linker technology, and cytotoxic payloads while addressing the challenges associated with ADC development. Furthermore, we explore the future potential of personalized medicine, leveraging individual patients' molecular profiles, to propel ADC treatments forward. As our understanding of the molecular mechanisms driving cancer progression continues to expand, we anticipate the development of new ADCs that offer more effective and personalized therapeutic options for cancer patients.

Multifunctional Poly(2-ethyl-2-oxazoline) Copolymers Containing Dithiolane and Pentafluorophenyl Esters as Effective Reactive Linkers for Gold Surface Coatings

Surface functionalization with biological macromolecules is an important task for the development of sensor materials, whereby the interaction with other biological materials should be suppressed. In this work, we developed a novel multifunctional poly(2-ethyl-2-oxazoline)-dithiolane conjugate as a versatile linker for gold surface immobilization of amine-containing biomolecules, containing poly(2-ethyl-2-oxazoline) as antifouling polymer, dithiolane for surface immobilization, and activated esters for protein conjugation. First, a well-defined carboxylic acid containing copoly(2-ethyl-2-oxazoline) was synthesized by cationic ring-opening copolymerization of 2-ethyl-2-oxazoline with a methyl ester-containing 2-oxazoline monomer, followed by postpolymerization modifications. The side-chain carboxylic groups were then converted to amine-reactive pentafluorophenyl (PFP) ester groups. Part of the PFP groups was used for the attachment of the dithiolane moiety, which can efficiently bind to gold surfaces. The final copolymer contained 1.4 mol% of dithiolane groups and 4.5 mol% of PFP groups. The copolymer structure was confirmed by several analytical techniques, including NMR spectroscopy and size-exclusion chromatography. The kinetics of the PFP ester aminolysis and hydrolysis demonstrated significantly faster amidation compared to hydrolysis, which is essential for subsequent protein conjugation. Successful coating of gold surfaces with the polymer was confirmed by spectroscopic ellipsometry, showing a polymer brush thickness of 4.77 nm. Subsequent modification of the coated surfaces was achieved using bovine serum albumin as a model protein. This study introduces a novel reactive polymer linker for gold surface functionalization and offers a versatile polymer platform for various applications including biosensing and surface functionalization.

Preparation of an Ultrahigh-DAR PDL1 monoclonal antibody-polymeric-SN38 conjugate for precise colon cancer therapy

Antibody-drug conjugates (ADCs) are the most potent active tumor-targeting agents used clinically. However, the preparation of ADCs with high drug-to-antibody ratios (DARs) remains a major challenge. Herein, a Fab-nondestructive SN38-loaded antibody-polymeric-drug conjugate (APDC), aPDL1-NPLG-SN38, was prepared that had a DAR as high as 72 for the first time, by increased numbers of payload binding sites via the carboxyl groups of poly (l-glutamic acid) (PLG). The bonding of Fc-III-4C peptide with PLG-graft-mPEG/SN38 (Fc-NPLG-SN38) was achieved using a click reaction between azide and DBCO groups. The aPDL1-NPLG-SN38 conjugate was then synthesized by the high-affinity interaction between the Fc-III-4C peptide in Fc-NPLG-SN38 and the crystallizable fragment (Fc) of PDL1 monoclonal antibody (aPDL1). This approach avoided the potential deleterious effects on the Fab structure of the monoclonal antibody. The aqueous environment used in its preparation helped maintain monoclonal antibody recognition capability. Through the specific recognition by aPDL1 of PDL1 that is highly expressed on MC38 tumors, the accumulation of aPDL1-NPLG-SN38 in the tumors was 2.8-fold greater than achieved with IgG-NPLG-SN38 that had no active tumor-targeting capability. aPDL1-NPLG-SN38 exhibited excellent therapeutic properties in both medium-sized and large MC38 tumor animal models. The present study provides the details of a novel preparation strategy for SN38-loaded ADCs having a high DAR.

Clickable Shiga Toxin B Subunit for Drug Delivery in Cancer Therapy

In recent years, receptor-mediated drug delivery has gained major attention in the treatment of cancer. The pathogen-derived Shiga Toxin B subunit (STxB) can be used as a carrier that detects the tumor-associated glycosphingolipid globotriaosylceramide (Gb3) receptors. While drug conjugation via lysine or cysteine offers random drug attachment to carriers, click chemistry has the potential to improve the engineering of delivery systems as the site specificity can eliminate interference with the active binding site of tumor ligands. We present the production of recombinant STxB in its wild-type (STxB_wt) version or incorporating the noncanonical amino acid azido lysine (STxB_AzK). The STxB_wt and STxB_AzK were manufactured using a growth-decoupled Escherichia coli (E. coli)-based expression strain and analyzed via flow cytometry for Gb3 receptor recognition and specificity on two human colorectal adenocarcinoma cell lines-HT-29 and LS-174-characterized by high and low Gb3 abundance, respectively. Furthermore, STxB_AzK was clicked to the antineoplastic agent monomethyl auristatin E (MMAE) and evaluated in cell-killing assays for its ability to deliver the drug to Gb3-expressing tumor cells. The STxB_AzK-MMAE conjugate induced uptake and release of the MMAE drug in Gb3-positive tumor cells, reaching 94% of HT-29 cell elimination at 72 h post-treatment and low nanomolar doses while sparing LS-174 cells. STxB_AzK is therefore presented as a well-functioning drug carrier, with a possible application in cancer therapy. This research demonstrates the feasibility of lectin carriers used in delivering drugs to tumor cells, with prospects for improved cancer therapy in terms of straightforward drug attachment and effective cancer cell elimination.

Knowledge atlas of antibody-drug conjugates on CiteSpace and clinical trial visualization analysis

Objective

Antibody-drugs conjugates (ADCs) are novel drugs with highly targeted and tumor-killing abilities and developing rapidly. This study aimed to evaluate drug discovery and clinical trials of and explore the hotspots and frontiers from 2012 to 2022 using bibliometric methods.

Methods

Publications on ADCs were retrieved between 2012 and 2022 from Web of Science (WoS) and analyzed with CiteSpace 6.1.R2 software for the time, region, journals, institutions, etc. Clinical trials were downloaded from clinical trial.org and visualized with Excel software.

Results

A total of 696 publications were obtained and 187 drug trials were retrieved. Since 2012, research on ADCs has increased year by year. Since 2020, ADC-related research has increased dramatically, with the number of relevant annual publications exceeding 100 for the first time. The United States is the most authoritative and superior country and region in the field of ADCs. The University of Texas MD Anderson Cancer Center is the most authoritative institution in this field. Research on ADCs includes two clinical trials and one review, which are the most influential references. Clinical trials of ADCs are currently focused on phase I and phase II. Comprehensive statistics and analysis of the published literature and clinical trials in the field of ADCs, have shown that the most studied drug is brentuximab vedotin (BV), the most popular target is human epidermal growth factor receptor 2 (HER2), and breast cancer may become the main trend and hotspot for ADCs indications in recent years.

Conclusion

Antibody-drug conjugates have become the focus of targeted therapies in the field of oncology. The innovation of technology and combination application strategy will become the main trend and hotspots in the future.

Adsorption of conjugates of lysozyme and fluorescein isothiocyanate in hydrophobic interaction chromatography

Bioconjugates, such as antibody-drug conjugates or fluorescent-labeled proteins, are highly interesting for various applications in medicine and biology. In their production, not only the synthesis is challenging but also the downstream processing, for which hydrophobic interaction chromatography (HIC) is often used. However, in-depth studies of the adsorption of bioconjugates in HIC are still rare. Therefore, in the present work, three different conjugates of lysozyme and fluorescein isothiocyanate (FITC) were synthesized and isolated, and their adsorption on the hydrophobic resin Toyopearl PPG-600 M was systematically studied in batch experiments. The influence of sodium chloride and ammonium sulfate with ionic strengths up to 2000 mM on the adsorption isotherms was investigated at pH 7.0 and 25 °C, and the results were compared to those for pure lysozyme. The conjugation leads to an increase of the adsorption in all studied cases. All studied conjugates contain only a single FITC and differ only in the position of the conjugation on the lysozyme. Despite this, strong differences in the adsorption behavior were observed. Moreover, a mathematical model was developed, which enables the prediction of the adsorption isotherms in the studied systems for varying ionic strengths.

Triggering of the immune response to MCF7 cell line using conjugated antibody with bacterial antigens: In-vitro and in-vivo study

The current study intended to trigger the immune response to cancer cells by using antibodies conjugated with bacterial antigens. The protein membrane of the MCF7 cell line was extracted and specific antibodies against cell membrane antigens was produced in rabbits. The specific antibodies were purified using chromatography methods and linked to E. coli antigens or doxorubicin using Diethylenetriamine pentaacetate (DTPA) linker. After confirmation of the conjugation process using SDS-PAGE and ATR-FTIR methods, the MCF7 and HUVEC cells were treated with various concentrations of the prepared conjugated antibodies along with human serum. The toxicity of each treatment against MCF7 and HUVEC cells was evaluated using the MTT assay. Also, polylactic acid scaffolds that contain 10×10⁴ MCF7 cells were surgically placed in the peritoneal cavity of the rats. After treatment of each group, induction of the inflammatory responses was evaluated on stained histological sections of the scaffolds. The lowest cytotoxic doses of the antigen conjugated-antibody, doxorubicin-conjugated-antibody was 4 and 1 μg/mL, respectively. Doxorubicin conjugated antibodies displayed greater toxicity on both MCF7 and HUVEC cells. The in vivo finding revealed that the inflammatory cells were significantly higher in treating animals with antigen conjugated-antibody. The current synthetic agent stimulated the serum toxicity and induced an inflammatory response to MCF7 cell lines. Targeting of the bacterial antigens on tumor sites by immune system elements, could limit the growth of the tumor cells.

Antibody–Ferrocene Conjugates as a Platform for Electro-Chemical Detection of Low-Density Lipoprotein

Low-density lipoprotein (LDL) is a cardiac biomarker identified in the pathology of cardiovascular disease (CVD). Typically, the level of LDL is calculated using the Friedewald relationship based on measured values of total cholesterol, high-density lipoproteins (HDL), and triglycerides. Unfortunately, this approach leads to some errors in calculation. Therefore, direct methods that can be used for fast and accurate detection of LDL are needed. The purpose of this study was to develop an electrochemical platform for the detection of LDL based on an antibody–ferrocene conjugate. An anti-apolipoprotein B-100 antibody labeled with ferrocene was covalently immobilized on the layer of 4-aminothiophenol (4-ATP) on the surface of gold electrodes. Upon interaction between LDL and the antibody–ferrocene conjugate, a decrease in the ferrocene redox signal registered by square wave voltammetry was observed, which depends linearly on the concentration from 0.01 ng/mL to 1.0 ng/mL. The obtained limit of detection was equal to 0.53 ng/mL. Moreover, the satisfied selectivity toward human serum albumin (HSA), HDL, and malondialdehyde-modified low-density lipoprotein (MDA-LDL) was observed. In addition, the acceptable recovery rates of LDL in human serum samples indicate the possible application of immunosensors presented in clinical diagnostics.

Carbon dioxide enhances sulphur-selective conjugate addition reactions

Sulphur-selective conjugate addition reactions play a central role in synthetic chemistry and chemical biology. A general tool for conjugate addition reactions should provide high selectivity in the presence of competing nucleophilic functional groups, namely nitrogen nucleophiles. We report CO₂-mediated chemoselective S-Michael addition reactions where CO₂ can reversibly control the reaction pHs, thus providing practical reaction conditions. The increased chemoselectivity for sulphur-alkylation products was ascribed to CO₂ as a temporary and traceless protecting group for nitrogen nucleophiles, while CO₂ efficiently provide higher conversion and selectivity sulphur nucleophiles on peptides and human serum albumin (HSA) with various electrophiles. This method offers simple reaction conditions for cysteine modification reactions when high chemoselectivity is required.

A novel strategy for treatment of bladder cancer: Antibody-drug conjugates

In the past, there was no second-line chemotherapeutic agent suitable for use when urothelial carcinoma (UC) progressed to platinum-resistant UC. However, recently, several new treatment options, such as immune checkpoint inhibitors or targeted therapy have shifted the treatment paradigm regarding second-line therapeutic modalities. A novel class of therapeutic agents includes an antibody-drug conjugate (ADC). ADCs consist of three characteristics: a monoclonal antibody, linker, and payload. The specificity of the monoclonal antibody facilitates the delivery of a linked cytotoxic drug directly into the target tumor cell. Although various ADCs have been developed and approved for use in treating several solid tumors, almost all ADCs for the treatment of UC are still in the testing phase. Here, we review the key points about ADCs and summarize the novel ADCs that are approved or are involved in ongoing studies in UC.

Antibody drug conjugate: the "biological missile" for targeted cancer therapy

Antibody–drug conjugate (ADC) is typically composed of a monoclonal antibody (mAbs) covalently attached to a cytotoxic drug via a chemical linker. It combines both the advantages of highly specific targeting ability and highly potent killing effect to achieve accurate and efficient elimination of cancer cells, which has become one of the hotspots for the research and development of anticancer drugs. Since the first ADC, Mylotarg^® (gemtuzumab ozogamicin), was approved in 2000 by the US Food and Drug Administration (FDA), there have been 14 ADCs received market approval so far worldwide. Moreover, over 100 ADC candidates have been investigated in clinical stages at present. This kind of new anti-cancer drugs, known as “biological missiles”, is leading a new era of targeted cancer therapy. Herein, we conducted a review of the history and general mechanism of action of ADCs, and then briefly discussed the molecular aspects of key components of ADCs and the mechanisms by which these key factors influence the activities of ADCs. Moreover, we also reviewed the approved ADCs and other promising candidates in phase-3 clinical trials and discuss the current challenges and future perspectives for the development of next generations, which provide insights for the research and development of novel cancer therapeutics using ADCs.

Terminology and the naming of conjugates based on polymers or other substrates (IUPAC Recommendations 2021)

A number of human activities require that certain complex molecules, referred to as active species (drugs, dyes, peptides, proteins, genes, radioactive labels, etc.), be combined with substrates, often a macromolecule, to form temporary or permanent conjugates. The existing IUPAC organic, polymer, and inorganic nomenclature principles can be applied to name such conjugates but it is not always appropriate. These nomenclatures have two major shortcomings: (1) the resulting names are often excessively long and (2) identification of the components (substrate, active species, and link) can be difficult. The new IUPAC naming system elaborates rules for unambiguous and facile naming of any conjugate. This naming system is not intended to replace the existing nomenclature but to provide a suitable alternative when dictated by necessity. Although the rules are intended to be primarily applicable to the naming of polymer conjugates, they are also applicable to naming conjugates with other substrates, which include micelles, particles, minerals, surfaces, pores, etc. The naming system should be used when recognition of the substrate and active substance is essential and will also be useful when constraints of name length make the otherwise preferred IUPAC nomenclatures untenable. The proposed rules for the new naming system are complemented by a glossary of relevant terms.

Linkers: An Assurance for Controlled Delivery of Antibody-Drug Conjugate

As one of the major therapeutic options for cancer treatment, chemotherapy has limited selectivity against cancer cells. Consequently, this therapeutic strategy offers a small therapeutic window with potentially high toxicity and thus limited efficacy of doses that can be tolerated by patients. Antibody-drug conjugates (ADCs) are an emerging class of anti-cancer therapeutic drugs that can deliver highly cytotoxic molecules directly to cancer cells. To date, twelve ADCs have received market approval, with several others in clinical stages. ADCs have become a powerful class of therapeutic agents in oncology and hematology. ADCs consist of recombinant monoclonal antibodies that are covalently bound to cytotoxic chemicals via synthetic linkers. The linker has a key role in ADC outcomes because its characteristics substantially impact the therapeutic index efficacy and pharmacokinetics of these drugs. Stable linkers and ADCs can maintain antibody concentration in blood circulation, and they do not release the cytotoxic drug before it reaches its target, thus resulting in minimum off-target effects. The linkers used in ADC development can be classified as cleavable and non-cleavable. The former, in turn, can be grouped into three types: hydrazone, disulfide, or peptide linkers. In this review, we highlight the various linkers used in ADC development and their design strategy, release mechanisms, and future perspectives.

A Novel Strategy Conjugating PD-L1 Polypeptide With Doxorubicin Alleviates Chemotherapeutic Resistance and Enhances Immune Response in Colon Cancer

Background

Modifying the structure of anti-tumor chemotherapy drug is of significance to enhance the specificity and efficacy of drug-delivery. A novel proteolysis resistant PD-L1-targeted peptide (PPA1) has been reported to bind to PD-L1 and disrupt the PD-1/PD-L1 interaction, thus appearing as an outstanding tumor-targeting modification of synergistic drug conjugate for effective anti-tumor treatment. However, the combination regimen of coupling PD-L1 polypeptide with chemotherapeutic drug in tumoricidal treatment has not been reported thus far.

Methods

We developed a novel synergistic strategy by conjugating PPA1 to doxorubicin (DOX) with a pH sensitive linker that can trigger the release of DOX near acidic tumor tissues. The binding affinity of PPA1-DOX with PD-L1 and the acid-sensitive cleavage of PPA1-DOX were investigated. A mouse xenograft model of colon cancer was used to evaluate the biodistribution, cytotoxicity and anti-tumor activity of PPA1-DOX.

Results

PPA1-DOX construct showed high binding affinity with PD-L1 in vitro and specifically enriched within tumor when administered in vivo. PPA1-DOX exhibited a significantly lower toxicity and a remarkably higher antitumor activity in vivo, as compared with free PPA1, random polypeptide-DOX conjugate, DOX, or 5-FU, respectively. Moreover, increased infiltration of both CD4⁺ and CD8⁺ T cells was found in tumors from PPA1-DOX treated mice.

Conclusions

We describe here for the first time that the dual-functional conjugate PPA1-DOX, which consist of the PD-L1-targeted polypeptide that renders both the tumor-specific drug delivery and inhibitory PD-1/PD-L1 immune checkpoint inhibition, and a cytotoxic agent that is released and kills tumor cells once reaching tumor tissues, thus representing a promising therapeutic option for colon cancer with improved efficacy and reduced toxicity.

Anti‑HER3 monoclonal antibody exerts antitumor activity in a mouse model of colorectal adenocarcinoma

HER3 belongs to the epidermal growth factor receptor (EGFR) family and is known to form an active heterodimer with other three family members EGFR, HER2, and HER4. HER3 is overexpressed in lung, breast, colon, prostate, and gastric cancers. In the present study, we developed and validated an anti-HER3 monoclonal antibody (mAb), H₃Mab-17 (IgG_2a, kappa), by immunizing mice with HER3-overexpressed CHO-K1 cells (CHO/HER3). H₃Mab-17 was found to react specifically with endogenous HER3 in colorectal carcinoma cell lines, using flow cytometry. The K_D for H₃Mab-17 in CHO/HER3 and Caco-2 (a colon cancer cell line) were determined to be 3.0×10⁻⁹ M and 1.5×10⁻⁹ M via flow cytometry, respectively, suggesting high binding affinity of H₃Mab-17 to HER3. Then, we assessed the H₃Mab-17 antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC) against Caco-2, and evaluated its antitumor capacity in a Caco-2 ×enograft model. In vitro experiments revealed H₃Mab-17 had strongly induced both ADCC and CDC against Caco-2 cells. In vivo experiments on Caco-2 ×enografts revealed that H₃Mab-17 treatment significantly reduced tumor growth compared with the control mouse IgG. These data indicated that H₃Mab-17 could be a promising treatment option for HER3-expressing colon cancers.

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.

Monoclonal Antibodies, Small Molecule Inhibitors and Antibody-drug Conjugates as HER2 Inhibitors

Overexpression of human epidermal growth factor receptor (HER)-2 is found in a variety of cancers, often portending poor clinical outcomes. Therefore, HER2 is an attractive target for treatment. This review describes the research progress of HER2 targeted inhibitors in recent years. Excellent reviews are available, so we focus on the development, mechanisms of action, and structure-activity relationships of different types of inhibitors, including monoclonal antibodies, small molecule inhibitors, and antibody-drug conjugates (ADCs). In addition, the differences among them are compared.

Nanobodies as efficient drug-carriers: Progress and trends in chemotherapy

Nanobodies (Nb) have a promising future as a part of next generation chemodrug delivery systems. Nb, or VHH, are small (15 kDa) monomeric antibody fragments consisting of the antigen binding region of heavy chain antibodies. Heavy chain antibodies are naturally produced by camelids, however the structure of their VHH regions can be readily reproduced in industrial expression systems, such as bacteria or yeast. Due to their small size, high solubility, remarkable stability, manipulatable characteristics, excellent in vivo tissue penetration, conjugation advantages, and ease of production, Nb have many advantages when compared against their antibody precursors. In this review, we discuss the generation and selection of Nbs via phage display libraries for easy screening, and the conjugation techniques involved in creating target-specific nanocarriers. Furthermore, we provide a comprehensive overview of recent developments and perspectives in the field of Nb drug conjugates (NDCs) and Nb-based drug vehicles (NDv) with respect to antitumor therapeutics.

Antibody-drug nanoparticle induces synergistic treatment efficacies in HER2 positive breast cancer cells

Chemotherapeutic drugs suffer from non-specific binding, undesired toxicity, and poor blood circulation which contribute to poor therapeutic efficacy. In this study, antibody–drug nanoparticles (ADNs) are engineered by synthesizing pure anti-cancer drug nanorods (NRs) in the core of nanoparticles with a therapeutic monoclonal antibody, Trastuzumab on the surface of NRs for specific targeting and synergistic treatments of human epidermal growth factor receptor 2 (HER2) positive breast cancer cells. ADNs were designed by first synthesizing ~ 95 nm diameter × ~ 500 nm long paclitaxel (PTX) NRs using the nanoprecipitation method. The surface of PTXNRs was functionalized at 2′ OH nucleophilic site using carbonyldiimidazole and conjugated to TTZ through the lysine residue interaction forming PTXNR-TTZ conjugates (ADNs). The size, shape, and surface charge of ADNs were characterized using scanning electron microscopy (SEM), SEM, and zeta potential, respectively. Using fluorophore labeling and response surface analysis, the percentage conjugation efficiency was found > 95% with a PTX to TTZ mass ratio of 4 (molar ratio ≈ 682). In vitro therapeutic efficiency of PTXNR-TTZ was evaluated in two HER2 positive breast cancer cell lines: BT-474 and SK-BR-3, and a HER2 negative MDA-MB-231 breast cancer cell using MTT assay. PTXNR-TTZ inhibited > 80% of BT-474 and SK-BR-3 cells at a higher efficiency than individual PTX and TTZ treatments alone after 72 h. A combination index analysis indicated a synergistic combination of PTXNR-TTZ compared with the doses of single-drug treatment. Relatively lower cytotoxicity was observed in MCF-10A human breast epithelial cell control. The molecular mechanisms of PTXNR-TTZ were investigated using cell cycle and Western blot analyses. The cell cycle analysis showed PTXNR-TTZ arrested > 80% of BT-474 breast cancer cells in the G2/M phase, while > 70% of untreated cells were found in the G0/G1 phase indicating that G2/M arrest induced apoptosis. A similar percentage of G2/M arrested cells was found to induce caspase-dependent apoptosis in PTXNR-TTZ treated BT-474 cells as revealed using Western blot analysis. PTXNR-TTZ treated BT-474 cells showed ~ 1.3, 1.4, and 1.6-fold higher expressions of cleaved caspase-9, cytochrome C, and cleaved caspase-3, respectively than untreated cells, indicating up-regulation of caspase-dependent activation of apoptotic pathways. The PTXNR-TTZ ADN represents a novel nanoparticle design that holds promise for targeted and efficient anti-cancer therapy by selective targeting and cancer cell death via apoptosis and mitotic cell cycle arrest.

PEG Linker Improves Antitumor Efficacy and Safety of Affibody-Based Drug Conjugates

Antibody drug conjugates (ADCs) have become an important modality of clinical cancer treatment. However, traditional ADCs have some limitations, such as reduced permeability in solid tumors due to the high molecular weight of monoclonal antibodies, difficulty in preparation and heterogeneity of products due to the high drug/antibody ratio (4-8 small molecules per antibody). Miniaturized ADCs may be a potential solution, although their short circulation half-life may lead to new problems. In this study, we propose a novel design strategy for miniaturized ADCs in which drug molecules and small ligand proteins are site-specifically coupled via a bifunctional poly(ethylene glycol) (PEG) chain. The results showed that the inserted PEG chains significantly prolonged the circulation half-life but also obviously reduced the cytotoxicity of the conjugates. Compared with the conjugate Z_HER2-SMCC-MMAE (HM), which has no PEG insertion, Z_HER2-PEG4K-MMAE (HP4KM) and Z_HER2-PEG10K-MMAE (HP10KM) with 4 or 10 kDa PEG insertions have 2.5- and 11.2-fold half-life extensions and 4.5- and 22-fold in vitro cytotoxicity reductions, respectively. The combined effect leads to HP10KM having the most ideal tumor therapeutic ability at the same dosages in the animal model, and its off-target toxicity was also reduced by more than 4 times compared with that of HM. These results may indicate that prolonging the half-life is very helpful in improving the therapeutic capacity of miniaturized ADCs. In the future, the design of better strategies that can prolong half-life without affecting cytotoxicity may be useful for further improving the therapeutic potential of these molecules.

Evaluation of PNU-159682 antibody drug conjugates (ADCs)

PNU-159682 is a highly potent secondary metabolite of nemorubicin belonging to the anthracycline class of natural products. Due to its extremely high potency and only partially understood mechanism of action, it was deemed an interesting starting point for the development of a new suite of linker drugs for antibody drug conjugates (ADCs). Structure activity relationships were explored on the small molecule which led to six linker drugs being developed for conjugation to antibodies. Herein we describe the synthesis of novel PNU-159682 derivatives and the subsequent linker drugs as well as the corresponding biological evaluations of the small molecules and ADCs.

Nucleic Acid Aptamers as a Potential Nucleus Targeted Drug Delivery System

BACKGROUND

Nucleus targeted drug delivery provides several opportunities for the treatment of fatal diseases such as cancer. However, the complex nucleocytoplasmic barriers pose significant challenges for delivering a drug directly and efficiently into the nucleus. Aptamers representing singlestranded DNA and RNA qualify as next-generation highly advanced and personalized medicinal agents that successfully inhibit the expression of certain proteins; possess extraordinary gene-expression for manoeuvring the diseased cell's fate with negligible toxicity. In addition, the precisely directed aptamers to the site of action present a tremendous potential to reach the nucleus by escaping the ensuing barriers to exhibit a better drug activity and gene expression.

OBJECTIVE

This review epigrammatically highlights the significance of targeted drug delivery and presents a comprehensive description of the principal barriers faced by the nucleus targeted drug delivery paradigm and ensuing complexities thereof. Eventually, the progress of nucleus targeting with nucleic acid aptamers and success achieved so far have also been reviewed.

METHODS

Systematic literature search was conducted of research published to date in the field of nucleic acid aptamers.

CONCLUSION

The review specifically points out the contribution of individual aptamers as the nucleustargeting agent rather than aptamers in conjugated form.

Two Patient Studies of a Companion Diagnostic Immuno-Positron Emission Tomography (PET) Tracer for Measuring Human CA6 Expression in Cancer for Antibody Drug Conjugate (ADC) Therapy

An antigen binding fragment (BFab) derived from a tumor-associated mucin 1–sialoglycotope antigen (CA6) targeting antibody (huDS6) was engineered. We synthesized a companion diagnostic positron emission tomography (PET) tracer by radiolabeling BFab with [⁶⁴Cu] to measure CA6 expression on cancer tissues prior to anti-human CA6 (huDS6-DM4 antibody-drug conjugate) therapy for ovarian and breast cancer patients. After chemotherapy, the ovarian patient received PET scan with ¹⁸F-2-fluoro-2-deoxyglucose ([¹⁸F]FDG: 10 mCi), followed by [⁶⁴Cu]-DOTA-BFab ([⁶⁴Cu]BFab; 5.5 mCi) 1 week later for PET scanning of CA6 expression and subsequent surgery. The breast cancer patient was treated with chemotherapy before primary tumor resection and subsequent [¹⁸F]FDG-PET scan. 4 weeks later the patient received of [⁶⁴Cu]BFab (11.7 mCi) for CA6 PET scan. Whole body [¹⁸F]FDG-PET of the breast cancer patient indicated FDG-avid tumor metastases to the liver, bilateral hila and thoracic spine, but no uptake was observed for the ovarian patient. Each patient was also imaged by PET/CT with [⁶⁴Cu]BFab at 1 and 24 hours after tracer administration. The [⁶⁴Cu]BFab tracer was well tolerated by both patients without adverse effects, and no significant tracer uptake was observed in both patients. Immunohistochemistry (IHC) data indicated CA6 expressions were weak to intermediate and matched with the [⁶⁴Cu]BFab-PET signals.

Antibody stability: A key to performance - Analysis, influences and improvement

An antibody's stability greatly influences its performance (i.e. its specificity and affinity). Thus, stability is a major issue for researchers and manufacturers, especially with the increasing use of antibodies in therapeutics, diagnostics and rapid analytical platforms. Here we review antibody stability under five headings: (i) measurement techniques; (ii) stability issues in expression and production (expression, proteolysis, aggregation); (iii) effects of antibody format and engineering on stability and (iv) formulation, drying and storage conditions. We consider more than 100 sources, including patents, and conclude with (v) recommendations to promote antibody stability.

Conjugation Site Influences Antibody-Conjugated Drug PK Assays: Case Studies for Disulfide-Linked, Self-Immolating Next-Generation Antibody Drug Conjugates

Immunoaffinity (IA) LC-MS/MS pharmacokinetic (PK) assays are widely used in the field for antibody drug conjugates (ADCs) containing peptide linkers that are enzymatically cleavable, such as MC-ValCit-PAB. Conjugate PK assay strategies for these ADCs involve cleavage with cathepsin B or papain to release and measure the antibody-conjugated drug (acDrug) concentration. However, robust acDrug PK methods for disulfide-linked self-immolating ADCs are lacking as they are a different conjugation modality. We developed acDrug PK assays for next-generation disulfide-linked ADCs involving immunoaffinity capture, chemical cleavage, and LC-MS/MS. Disulfide-linked ADCs captured from plasma were chemically reduced at basic pH to release the linker-drug, followed by self-immolation to liberate the active drug, and quantified by MRM LC-MS/MS. Herein, we detail the development and optimization of this chemical cleavage acDrug PK assay, resulting in robust accuracy and precision (±20%). The conjugation site of the linker-drug on the antibody was found to affect the kinetics of drug release. Multiple biophysical and chemical characteristics, such as tertiary structure, fractional solvent accessibility, pK_a of the conjugation site, surrounding residue's pI, and electrostatic charge, may directly impact the drug release kinetics. Similar site-specific stability has been previously reported for ADCs in vivo. The assay development and qualification data for this original assay format are presented along with its application to multiple in vitro and in vivo studies across species.

Therapeutic Monoclonal Antibodies in Clinical Practice against Cancer

The importance of monoclonal antibodies in oncology has increased drastically following the discovery of Milstein and Kohler. Since the first approval of the monoclonal antibody, i.e. Rituximab in 1997 by the FDA, there was a decline in further applications but this number has significantly increased over the last three decades for various therapeutic applications due to the lesser side effects in comparison to the traditional chemotherapy methods. Presently, numerous monoclonal antibodies have been approved and many are in queue for approval as a strong therapeutic agent for treating hematologic malignancies and solid tumors. The main target checkpoints for the monoclonal antibodies against cancer cells include EGFR, VEGF, CD and tyrosine kinase which are overexpressed in malignant cells. Other immune checkpoints like CTLA-4, PD-1 and PD-1 receptors targeted by the recently developed antibodies increase the capability of the immune system in destroying the cancerous cells. Here, in this review, the mechanism of action, uses and target points of the approved mAbs against cancer have been summarized.

Antibody-Drug Conjugates and Targeted Treatment Strategies for Hepatocellular Carcinoma: A Drug-Delivery Perspective

Increased understanding of cancer biology, pharmacology and drug delivery has provided a new framework for drug discovery and product development that relies on the unique expression of specific macromolecules (i.e., antigens) on the surface of tumour cells. This has enabled the development of anti-cancer treatments that combine the selectivity of antibodies with the efficacy of highly potent chemotherapeutic small molecules, called antibody-drug conjugates (ADCs). ADCs are composed of a cytotoxic drug covalently linked to an antibody which then selectively binds to a highly expressed antigen on a cancer cell; the conjugate is then internalized by the cell where it releases the potent cytotoxic drug and efficiently kills the tumour cell. There are, however, many challenges in the development of ADCs, mainly around optimizing the therapeutic/safety benefits. These challenges are discussed in this review; they include issues with the plasma stability and half-life of the ADC, its transport from blood into and distribution throughout the tumour compartment, cancer cell antigen expression and the ADC binding affinity to the target antigen, the cell internalization process, cleaving of the cytotoxic drug from the ADC, and the cytotoxic effect of the drug on the target cells. Finally, we present a summary of some of the experimental ADC strategies used in the treatment of hepatocellular carcinoma, from the recent literature.

Synthesis of Potent Cytotoxic Epidithiodiketopiperazines Designed for Derivatization

We describe our design, synthesis, and chemical study of a set of functional epidithiodiketopiperazines (ETPs) and evaluation of their activity against five human cancer cell lines. Our structure-activity relationship-guided substitution of ETP alkaloids offers versatile derivatization while maintaining potent anticancer activity, offering exciting opportunity for their use as there are no examples of complex and potently anticancer (nM) ETPs being directly used as conjugatable probes or warheads. Our synthetic solutions to strategically designed ETPs with functional linkers required advances in stereoselective late-stage oxidation and thiolation chemistry in complex settings, including the application of novel reagents for dihydroxylation and cis-sulfidation of diketopiperazines. We demonstrate that complex ETPs equipped with a strategically substituted azide functional group are readily derivatized to the corresponding ETP-triazoles without compromising anticancer activity. Our chemical stability studies of ETPs along with cytotoxic evaluation of our designed ETPs against A549, DU 145, HeLa, HCT 116, and MCF7 human cancer cell lines provide insights into the impact of structural features on potency and chemical stability, informing future utility of ETPs in chemical and biological studies.

A Simple Long-wavelength Fluorescent Probe for Simultaneous Discrimination of Cysteine/Homocysteine and Glutathione/Hydrogen Sulfide with Two Separated Fluorescence Emission Channels by Single Wavelength Excitation

Small molecular biothiols, such as cysteine (Cys), homocysteine (Hcy), reduced glutathione (GSH), and hydrogen sulfide (H₂S), play crucial parts in regulating the redox balance of life activities, regulating normal physiological activities and preventing various diseases. Quantitative analysis of these important small molecular substances is very important for revealing their diverse physiological and pathological effects. Although many fluorescent probes have been reported to detect biothiols in cells, it is still not sufficiently advanced to detect biothiols with separated fluorescence emission peak by same wavelength excitation. In our work, we designed a simple conjugate of Nile red and NBD (7-nitro-1,2,3-benzoxadiazole) as long-wavelength fluorescent probe NR-NBD for the simultaneous discrimination of these biothiols at single wavelength excitation. Probe NR-NBD could efficiently discriminate Cys/Hcy, GSH and H₂S by two separated fluorescence emission channels and absorption spectra. Importantly, probe NR-NBD has excellent specificity and sensitivity towards the monitoring of endogenous/exogenous Cys/Hcy and GSH/H₂S in living cells and zebrafish.

ADCs, as Novel Revolutionary Weapons for Providing a Step Forward in Targeted Therapy of Malignancies

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Antibody drug conjugates (ADCs), as potent pharmaceutical trojan horses for cancer treatment, provide superior efficacy and specific targeting along with low risk of adverse reactions compared to traditional chemotherapeutics. In fact, the development of these agents combines the selective targeting capability of monoclonal antibody (mAb) with high cytotoxicity of chemotherapeutics for controlling the neoplastic mass growth. Different ADCs (more than 60 ADCs) in preclinical and clinical trials were introduced in this novel pharmaceutical field. Various design-based factors must be taken into account for improving the functionality of ADC technology, including selection of appropriate target antigen and high binding affinity of fragment (miniaturized ADCs) or full mAbs (preferentially use of humanized or fully human antibodies compared to murine and chimeric ones), use of bispecific antibodies for dual targeting effect, linker engineering and conjugation method efficacy to obtain more controlled drug to antibody ratio (DAR). Challenging issues affecting therapeutic efficacy and safety of ADCs, including bystander effect, on- and off-target toxicities, multi drug resistance (MDR) are also addressed. 4 FDA-approved ADCs in the market, including ADCETRIS ®, MYLOTARG®, BESPONSA ®, KADCYLA®. The goal of the current review is to evaluate the key parameters affecting ADCs development.

Therapeutic efficacy and imaging assessment of the HER2-targeting chemotherapy drug ZHER2:V2-pemetrexed in lung adenocarcinoma Xenografts

Chemotherapy has always been the first therapeutic option for patients with advanced non-small cell lung cancer (NSCLC) with untreatable oncogenic mutations. However, chemotherapy has demonstrated limited success and is associated with severe side effects. This research aimed to investigate the antitumor efficacy and cytotoxic safety of the conjugate Z_HER2:V2-pemetrexed, a novel targeted chemotherapeutic drug. In this context, human epidermal growth factor receptor 2 (HER2) + A549 lung xenografts were treated using Z_HER2:V2-pemetrexed, pemetrexed or physiological saline. Therapeutic efficacy was monitored by single photon emission computed tomography (SPECT) imaging using the ^99mTc-labeled Z_HER2:V2-pemetrexed conjugate and further confirmed by performing apoptosis assays using flow cytometry analysis and hematoxylin-eosin (H&E) staining. To evaluate the expression of HER2 in tumor tissues, immunohistochemistry was performed, accompanied by quantitative analysis using flow cytometry. A toxicological evaluation was also conducted. Imaging with ^99mTc-Z_HER2:V2-pemetrexed demonstrated that in HER2+ A549 models, Z_HER2:V2-pemetrexed showed better antineoplastic effects than pemetrexed. Compared with pemetrexed, the results from the pathological and flow cytometry analyses also revealed that Z_HER2:V2-pemetrexed exhibits high antitumor activity against A549 tumors, inducing necrosis, apoptosis and cell cycle arrest. In addition, the clinical signs of toxicity in the Z_HER2:V2-pemetrexed treated group were reduced compared with those in the pemetrexed treated group. These data revealed that the Z_HER2:V2-pemetrexed conjugate encompasses promising targeted antitumor activity against HER2-positive lung adenocarcinoma, with reduced side effects compared with pemetrexed. Thus, the Z_HER2:V2-pemetrexed conjugate may serve as a novel molecular agent with tremendous clinical breakthrough potential in the diagnosis and treatment of HER2-positive lung adenocarcinoma.

Tumor-Targeted Drug Conjugates as an Emerging Novel Therapeutic Approach in Small Cell Lung Cancer (SCLC)

There are few effective therapies for small cell lung cancer (SCLC), a highly aggressive disease representing 15% of total lung cancers. With median survival <2 years, SCLC is one of the most lethal cancers. At present, chemotherapies and radiation therapy are commonly used for SCLC management. Few protein-targeted therapies have shown efficacy in improving overall survival; immune checkpoint inhibitors (ICIs) are promising agents, but many SCLC tumors do not express ICI targets such as PD-L1. This article presents an alternative approach to the treatment of SCLC: the use of drug conjugates, where a targeting moiety concentrates otherwise toxic agents in the vicinity of tumors, maximizing the differential between tumor killing and the cytotoxicity of normal tissues. Several tumor-targeted drug conjugate delivery systems exist and are currently being actively tested in the setting of SCLC. These include antibody-drug conjugates (ADCs), radioimmunoconjugates (RICs), small molecule-drug conjugates (SMDCs), and polymer-drug conjugates (PDCs). We summarize the basis of action for these targeting compounds, discussing principles of construction and providing examples of effective versus ineffective compounds, as established by preclinical and clinical testing. Such agents may offer new therapeutic options for the clinical management of this challenging disease in the future.

Carfilzomib Is Not an Appropriate Payload of Antibody-Drug Conjugates Due to Rapid Inactivation by Lysosomal Enzymes

Carfilzomib (CFZ) is a proteasome inhibitor used for oncology indications including treating multiple myeloma. CFZ is a potent cytotoxic agent with an IC₅₀ value in the nanomolar range in various cancer cell lines and was considered as a potential payload for antibody drug conjugates (ADCs); however, the conjugated CFZ to anti-CD22 or anti-HER2 antibody totally abolishes the in vitro potency. This was a surprise since with other payloads such as monomethyl auristatin E (MMAE), where potent antiproliferation efficacy was retained as MMAE alone or as a payload in an ADC. Further investigations were conducted using CFZ alone, CFZ with a linker, and CFZ-ADC with tissue matrices including lysosomal enzymes. With CFZ linked to the ADC, cathepsin B (a lysosomal enzyme) was efficient in liberating CFZ from the ADC by cleavage of the valine-citrulline linker. At the same time, the liberated CFZ in the lysosome was inactivated due to further metabolism by lysosomal enzymes. The products from epoxide and amide hydrolysis were identified from these incubations. These results suggested that the CFZ-ADC upon uptake and internalization specifically delivers CFZ payload to the lysosomes, where CFZ was inactivated. On the other hand, CFZ by itself is not as vulnerable and could reach its target. Therefore, lysosomal stability is an important criterion in the selection of a payload for making the next generation of potent ADC therapeutics.

Application of triple quadrupole mass spectrometry for the characterization of antibody-drug conjugates

Antibody–drug conjugates (ADCs) are an inherently heterogeneous class of biotherapeutics, the development of which requires extensive characterization throughout. During the earliest phases of preclinical development, when synthetic routes towards the desired conjugate are being assessed, the main interest lies in the determination of the average drug-to-antibody ratio (DAR) of a given batch as well as information about different conjugation species. There has been a trend in mass spectrometry (MS)–based characterization of ADCs towards the use of high-resolving mass spectrometry for many of these analyses. Considering the high cost for such an instrument, the evaluation of cheaper and more accessible alternatives is highly motivated. We have therefore tested the applicability of a quadrupole mass analyzer for the aforementioned characterizations. Eight ADCs consisting of trastuzumab and varying stoichiometries of Mc-Val-Cit-PABC-monomethyl auristatin E conjugated to native cysteines were synthesized and served as test analytes. The average DAR value and molecular weights (Mw) of all detected chains from the quadrupole mass analyzer showed surprisingly high agreement with results obtained from a time-of-flight (TOF) mass analyzer and hydrophobic interaction chromatography (HIC)–derived values for all investigated ADC batches. Acquired Mw were within 80 ppm of TOF-derived values, and DAR was on average within 0.32 DAR units of HIC-derived values. Quadrupole mass spectrometers therefore represent a viable alternative for the characterization of ADC in early-stage development.

Native Reversed-Phase Liquid Chromatography: A Technique for LCMS of Intact Antibody-Drug Conjugates

The synthesis of antibody-drug conjugates (ADCs) using the interchain cysteines of the antibody inherently gives a mixture of proteins with varying drug-to-antibody ratio. The drug distribution profiles of ADCs are routinely characterized by hydrophobic interaction chromatography (HIC). Because HIC is not in-line compatible with mass spectrometry (MS) due to the high salt levels, it is laborious to identify the constituents of HIC peaks. An MS-compatible alternative to HIC is reported here: native reversed phase liquid chromatography (nRPLC). This novel technique employs a mobile phase 50 mM ammonium acetate for high sensitivity in MS and elution with a gradient of water/isopropanol. The key to the enhancement is a bonded phase giving weaker drug-surface interactions compared to the noncovalent interactions holding the antibody-drug conjugates together. The hydrophobicity of the bonded phase is varied, and the least hydrophobic bonded phase in the series, poly(methyl methacrylate), is found to resolve the intact constituents of a model ADC (Ab095-PZ) and a commercial ADC (brentuximab vedotin) under the MS-compatible conditions. The nRPLC-MS data show that all species, ranging from drug-to-antibody ratios of 1 to 8, remained intact in the column. Another desired advantage of the nRPLC is the ability of resolving multiple positional isomers of ADC that are not well-resolved in other chromatographic modes. This supports the premise that lower hydrophobicity of the bonded phase is the key to enabling online nRPLC-MS analysis of antibody-drug conjugates.

Antibody conjugation and formulation

In an era where ultra-high antibody concentrations, high viscosities, low volumes, auto-injectors and long storage requirements are already complex problems with the current unconjugated monoclonal antibodies on the market, the formulation demands for antibody-drug conjugates (ADCs) are significant. Antibodies have historically been administered at relatively low concentrations through intravenous (IV) infusion due to their large size and the inability to formulate for oral delivery. Due to the high demands associated with IV infusion and the development of novel antibody targets and unique antibody conjugates, more accessible routes of administration such as intramuscular and subcutaneous are being explored. This review will summarize various site-specific and non-site-specific antibody conjugation techniques in the context of ADCs and the demands of formulation for high concentration clinical implementation.

Biological and chemical diversity go hand in hand: Basidiomycota as source of new pharmaceuticals and agrochemicals

The Basidiomycota constitutes the second largest higher taxonomic group of the Fungi after the Ascomycota and comprises over 30.000 species. Mycelial cultures of Basidiomycota have already been studied since the 1950s for production of antibiotics and other beneficial secondary metabolites. Despite the fact that unique and selective compounds like pleuromutilin were obtained early on, it took several decades more until they were subjected to a systematic screening for antimicrobial and anticancer activities. These efforts led to the discovery of the strobilurins and several hundreds of further compounds that mainly constitute terpenoids. In parallel the traditional medicinal mushrooms of Asia were also studied intensively for metabolite production, aimed at finding new therapeutic agents for treatment of various diseases including metabolic disorders and the central nervous system. While the evaluation of this organism group has in general been more tedious as compared to the Ascomycota, the chances to discover new metabolites and to develop them further to candidates for drugs, agrochemicals and other products for the Life Science industry have substantially increased over the past decade. This is owing to the revolutionary developments in -OMICS techniques, bioinformatics, analytical chemistry and biotechnological process technology, which are steadily being developed further. On the other hand, the new developments in polythetic fungal taxonomy now also allow a more concise selection of previously untapped organisms. The current review is dedicated to summarize the state of the art and to give an outlook to further developments.

Lysine Bioconjugation on Native Albumin with a Sulfonyl Acrylate Reagent

This protocol details a novel bioconjugation strategy that uses a methanesulfonyl acrylate reagent that is directed to the most reactive lysine on human serum albumin, which enables the construction of chemically defined and stable bioconjugates. The reaction proceeds rapidly and a regioselective modification is achieved using a single molar equivalent of the reagent under biocompatible conditions (37 °C, pH 8.0). Importantly, the bioconjugate retains both the secondary structural content and function of the unmodified protein. During the reaction of the amino group of lysine and the sulfonyl acrylate reagent, methanesulfinic acid is released after the conjugate addition, which then generates an electrophilic acrylate moiety on the protein. This acrylate can be further used for site-specific protein labeling using a synthetic molecule bearing a reactive amine under biocompatible conditions (21 °C, pH 8.0).

The molecularly imprinted polymer essentials: curation of anticancer, ophthalmic, and projected gene therapy drug delivery systems

The development of polymeric materials as drug delivery systems has advanced from systems that rely on classical passive targeting to carriers that can sustain the precisely controlled release of payloads upon physicochemical triggers in desired microenvironment. Molecularly imprinted polymers (MIP), materials designed to capture specific molecules based on their molecular shape and charge distribution, are attractive candidates for fulfilling these purposes. In particular, drug-imprinted polymers coupled with active targeting mechanisms have been explored as potential drug delivery systems. In this review, we have curated important recent efforts in the development of drug-imprinted polymers in a variety of clinical applications, especially oncology and ophthalmology. MIP possesses properties that may complement the traditional delivery systems of these two disciplines, such as passive enhanced permeability and retention effect (EPR) in cancer tumors, and passive drug diffusion in delivering ophthalmic therapeutics. Furthermore, the prospects of MIP integration with the emerging gene therapies will be discussed.

Emerging functional markers for cancer stem cell-based therapies: Understanding signaling networks for targeting metastasis

Metastasis is one of the most challenging issues in cancer patient management, and effective therapies to specifically target disease progression are missing, emphasizing the urgent need for developing novel anti-metastatic therapeutics. Cancer stem cells (CSCs) gained fast attention as a minor population of highly malignant cells within liquid and solid tumors that are responsible for tumor onset, self-renewal, resistance to radio- and chemotherapies, and evasion of immune surveillance accelerating recurrence and metastasis. Recent progress in the identification of their phenotypic and molecular characteristics and interactions with the tumor microenvironment provides great potential for the development of CSC-based targeted therapies and radical improvement in metastasis prevention and cancer patient prognosis. Here, we report on newly uncovered signaling mechanisms controlling CSC's aggressiveness and treatment resistance, and CSC-specific agents and molecular therapeutics, some of which are currently under investigation in clinical trials, gearing towards decisive functional CSC intrinsic or surface markers. One special research focus rests upon subverted regulatory pathways such as insulin-like growth factor 1 receptor signaling and its interactors in metastasis-initiating cell populations directly related to the gain of stem cell- and EMT-associated properties, as well as key components of the E2F transcription factor network regulating metastatic progression, microenvironmental changes, and chemoresistance. In addition, the study provides insight into systems biology tools to establish complex molecular relationships behind the emergence of aggressive phenotypes from high-throughput data that rely on network-based analysis and their use to investigate immune escape mechanisms or predict clinical outcome-relevant CSC receptor signaling signatures. We further propose that customized vector technologies could drastically enhance systemic drug delivery to target sites, and summarize recent progress and remaining challenges. This review integrates available knowledge on CSC biology, computational modeling approaches, molecular targeting strategies, and delivery techniques to envision future clinical therapies designed to conquer metastasis-initiating cells.