Antibody-Drug Conjugates: A Clinical Pharmacy Perspective on an Emerging Cancer Therapy

Antibody-drug conjugates in breast cancer treatment: resistance mechanisms and the role of therapeutic sequencing

Antibody-drug conjugates (ADCs) are a transformative approach in breast cancer therapy, offering targeted treatment with reduced toxicity by selectively delivering cytotoxic agents to cancer cells. While ADCs like trastuzumab emtansine (T-DM1), trastuzumab deruxtecan (T-DXd), and sacituzumab govitecan have shown significant efficacy, resistance mechanisms such as antigen loss, impaired internalization, and efflux of cytotoxic payloads challenge their effectiveness. This review discusses these resistance mechanisms and explores advanced strategies to overcome them, including innovations in linker chemistry, multi-antigen targeting, and biomarker-driven personalization. Additionally, therapeutic sequencing - determining the optimal order of ADCs with other treatments such as chemotherapy, endocrine therapy, and immunotherapy - is examined as a crucial approach to maximize ADC efficacy and manage resistance. Evidence-based sequencing strategies, particularly for human epidermal growth factor receptor 2 (HER2)-positive and triple-negative breast cancer (TNBC), are supported by clinical trials demonstrating the benefits of ADCs in both early-stage and metastatic settings. The potential of combination therapies, such as ADCs with immune checkpoint inhibitors (ICIs), further highlights the evolving landscape of breast cancer treatment. As ADC technology advances, personalized approaches integrating biomarkers and optimized sequencing protocols offer promising avenues to enhance treatment outcomes and combat resistance in breast cancer.

Antibody drug conjugates in older patients: State of the art

More than half of cancer cases occur in patients aged 65 years or older. The efficacy and safety of antibody drug conjugates (ADCs) in older patients remains an unclear subject as available evidence is limited. Geriatric population is underrepresented in clinical trials. Consequently, most of our knowledge regarding innovative therapeutics was studied on a younger population. In this review of published literature, we report the available information on efficacy, safety and pharmacokinetics of FDA approved ADCs for hematologic malignancies and solid tumors in the geriatric population. We explore the results of clinical trials dedicated for older individuals as well as subgroup analyses of the geriatric population in major trials evaluating these drugs. Available data suggest a similar efficacy in older adults as compared to general population. However, older patients might be prone to a higher rate of adverse events in incidence with a potential impact on quality of life. We lack data to support primary dose reductions or schedule modifications in this category of patients. No pharmacokinetic differences were reported between age groups. It is crucial to encourage the development of clinical trials dedicated to older patients with geriatric parameters (G8 score, G-CODE…) so that results can be more representative of this population outside of clinical trials.

A CRISPR activation screen identifies MUC-21 as critical for resistance to NK and T cell-mediated cytotoxicity

BACKGROUND

Immunotherapy has significantly advanced cancer treatments, but many patients do not respond to it, partly due to immunosuppressive mechanisms used by tumor cells. These cells employ immunosuppressive ligands to evade detection and elimination by the immune system. Therefore, the discovery and characterization of novel immunosuppressive ligands that facilitate immune evasion are crucial for developing more potent anti-cancer therapies.

METHODS

We conducted gain-of-function screens using a CRISPRa (CRISPR activation) library that covered the entire human transmembrane sub-genome to identify surface molecules capable of hindering NK-mediated cytotoxicity. The immunosuppressive role and mechanism of MUC21 were validated using NK and T cell mediated cytotoxicity assays. Bioinformatics tools were employed to assess the clinical implications of mucin-21 (MUC21) in cancer cell immunity.

RESULTS

Our genetic screens revealed that MUC21 expression on cancer cell surfaces inhibits both the cytotoxic activity of NK cells and antibody-dependent cellular cytotoxicity, but not affecting complement-dependent cytotoxicity. Additionally, MUC21 expression hinders T cell activation by impeding antigen recognition, thereby diminishing the effectiveness of the immune checkpoint inhibitor, anti-PD-L1. Moreover, MUC21 expression suppress the antitumor function of both CAR-T cells and CAR-NK cells. Mechanistically, MUC21 facilitates immune evasion by creating steric hindrance, preventing interactions between cancer and immune cells. Bioinformatics analysis revealed elevated MUC21 expression in lung cancer, which correlated with reduced infiltration and activation of cytotoxic immune cells. Intriguingly, MUC21 expression was higher in non-small cell lung cancer (NSCLC) tumors that were non-responsive to anti-PD-(L)1 treatment compared to responsive tumors.

CONCLUSIONS

These findings indicate that surface MUC21 serves as a potent immunosuppressive ligand, shielding cancer cells from NK and CD8+T cell attacks. This suggests that inhibiting MUC21 could be a promising strategy to improve cancer immunotherapy.

Antibody-Drug Conjugates: Ushering in a New Era of Cancer Therapy

Antibody-drug conjugates (ADCs) have provided new therapeutic options and significant promise for patients with cancer, particularly where existing treatments are limited. Substantial effort in ADC development is underway globally, with 13 ADCs currently approved and many more in development. The therapeutic benefits of ADCs leverage the ability to selectively target cancer cells through antibody binding, resultant relative sparing of non-malignant tissues, and the targeted delivery of a cytotoxic payload. Consequently, this drug class has demonstrated activity in multiple malignancies refractory to standard therapeutic options. Despite this, limitations exist, including narrow therapeutic windows, unique toxicity profiles, development of therapeutic resistance, and appropriate biomarker selection. This review will describe the development of ADCs, their mechanisms of action, pivotal trials, and approved indications and identify common themes. Current challenges and opportunities will be discussed for this drug class in cancer therapeutics at a time when significant developments in antibody therapies, immunotherapy, and targeted agents are occurring.

Marginal Corneal Infiltration Following Treatment for Metastatic Breast Cancer with Triple Chemotherapy of Trastuzumab, Pertuzumab & Docetaxel

PURPOSE

To report a case of bilateral marginal corneal infiltration upon treatment with trastuzumab, pertuzumab, and docetaxel via novel proposed mechanisms.

CASE DESCRIPTION

A patient, diagnosed with metastatic breast cancer and positive for human epidermal growth factor receptor 2 (HER2) with high Ki67, presented with bilateral severe marginal corneal infiltration upon undergoing first cycle of triple chemotherapy: trastuzumab, pertuzumab, and docetaxel. Treatment with topical corticosteroids and antibiotics was unsuccessful and was replaced by allogeneic serum eye drops (SED). The case improved significantly 10 days upon starting allogeneic SED.

CONCLUSIONS

We propose that trastuzumab, pertuzumab, and docetaxel suppress HER2 and Ki67 in the cornea and lacrimal gland. To the best of our knowledge, our report is the first to highlight the potential impact of this triple chemotherapy on the lacrimal gland and cornea and the first to highlight the proposed role of Ki67 suppression in damaging corneal integrity.

Targeted sonodynamic destruction of glioblastoma cells using antibody-titanium dioxide nanoparticle conjugates

Aim: We present data on sonodynamic therapy (SDT) against glioblastoma cells utilizing titanium dioxide (TiO₂) nanoparticles conjugated to anti-EGFR antibody. Materials & methods: TiO₂ nanoparticles were bound to anti-EGFR antibody to form antibody-nanoparticle conjugates (ANCs), then characterized by x-ray photoelectron spectroscopy and transmission electron microscopy. Cells underwent ultrasound and assessment on viability, reactive oxygen species and apoptosis were performed. Results: X-ray photoelectron spectroscopy analysis revealed the formation of an ANC. Transmission electron microscopy showed internalization of the ANCs by glioblastoma cells. With SDT, cell viabilities were reduced in the presence of ANCs, reactive oxygen species production was formed, but minimal effect on apoptosis was seen. Conclusion: For the first time, an ANC can be used with SDT to kill glioblastoma cells.

Gemtuzumab ozogamicin in acute myeloid leukemia: past, present and future

After being in the therapeutic wilderness for several decades, acute myeloid leukemia has been recently thrust into the limelight with a series of drug approvals. Technical refinements in production, genetic manipulation and chemical modification of monoclonal antibodies led to growing interest in antibodies-based treatment strategies. Much of the focus of these efforts in acute myeloid leukemia has been on CD33 as a target. On September 2, 2017, the U.S. Food and Drug Administration approved gemtuzumab ozogamicin for treatment of relapsed or refractory CD33⁺ acute myeloid leukemia. This signals a new chapter in the long and unusual story of gemtuzumab ozogamicin, which was the first antibody-drug conjugate approved for human use by the Food and Drug Administration. In this review we have analyzed the history of this drug which, among several mishaps, is experiencing a second youth and still represents a field to be further explored.

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.

An Antibody-Drug Conjugate Targeting MUC1-Associated Carbohydrate CA6 Shows Promising Antitumor Activities

Glycosylation is a complex multienzyme-related process that is frequently deregulated in cancer. Aberrant glycosylation can lead to the generation of novel tumor surface-specific glycotopes that can be targeted by antibodies. Murine DS6 mAb (muDS6) was generated from serous ovary adenocarcinoma immunization. It recognizes CA6, a Mucin-1 (MUC1)-associated sialoglycotope that is highly detected in breast, ovarian, lung, and bladder carcinomas. SAR566658 antibody-drug conjugate (ADC) is a humanized DS6 (huDS6) antibody conjugated through a cleavable linker to the cytotoxic maytansinoid derivative drug, DM4. SAR566658 binds to tumor cells with subnanomolar affinity, allowing good ADC internalization and intracellular delivery of DM4, resulting in tumor cell death (IC₅₀ from 1 to 7.3 nmol/L). SAR566658 showed in vivo antitumor efficacy against CA6-positive human pancreas, cervix, bladder, and ovary tumor xenografts and against three breast patient-derived xenografts. Tumor regression was observed in all tumor models with minimal effective dose correlating with CA6 expression. SAR566658 displayed better efficacy than standard-of-care nontargeted tubulin binders. These data support the development of SAR566658 in patients with CA6-expressing tumors.

Novel Therapeutics for Recurrent Cervical Cancer: Moving Towards Personalized Therapy

While screening programs and HPV vaccination have decreased the incidence of cervical cancer, still over 13,000 cases occur in the USA annually. Early-stage cervical cancer has an excellent long-term prognosis, with 5-year survival for localized disease being > 90%. Survival decreases markedly for both locally advanced and metastatic disease, and both are associated with a higher risk of recurrence. Few effective treatment options exist for persistent, recurrent, or metastatic cervical cancer. In 2014, the anti-VEGF antibody bevacizumab was approved in combination with chemotherapy based on the results of the Phase III GOG-240 study. As the majority of cervical cancers have a viral etiology, which impairs the immune system, immunotherapy using checkpoint inhibitors and other agents, appears to be a promising approach. In June 2018, the US FDA approved the anti-PD1 antibody pembrolizumab for recurrent or metastatic cervical cancer with PD-L1 expression that progressed after one or more lines of chemotherapy. Another anti-PD1 antibody, cemiplimab also shows potential in this setting, either as monotherapy or combined with radiotherapy, and it is currently being evaluated in a Phase III trial. Additional checkpoint inhibitors including nivolumab, durvalumab, atezolizumab, and camrelizumab are in different stages of clinical development for the disease. Finally, an additional targeted approach being pursued involves PARP inhibitors (rucaparib and olaparib are both in Phase II) based on earlier study results.

Antibody-Drug Conjugates Targeting the Urokinase Receptor (uPAR) as a Possible Treatment of Aggressive Breast Cancer

A promising molecular target for aggressive cancers is the urokinase receptor (uPAR). A fully human, recombinant antibody that binds uPAR to form a stable complex that blocks uPA-uPAR interactions (2G10) and is internalized primarily through endocytosis showed efficacy in a mouse xenograft model of highly aggressive, triple negative breast cancer (TNBC). Antibody-drug conjugates (ADCs) of 2G10 were designed and produced bearing tubulin inhibitor payloads ligated through seven different linkers. Aldehyde tag technology was employed for linking, and either one or two tags were inserted into the antibody heavy chain, to produce site-specifically conjugated ADCs with drug-to-antibody ratios of either two or four. Both cleavable and non-cleavable linkers were combined with two different antimitotic toxins—MMAE (monomethylauristatin E) and maytansine. Nine different 2G10 ADCs were produced and tested for their ability to target uPAR in cell-based assays and a mouse model. The anti-uPAR ADC that resulted in tumor regression comprised an MMAE payload with a cathepsin B cleavable linker, 2G10-RED-244-MMAE. This work demonstrates in vitro activity of the 2G10-RED-244-MMAE in TNBC cell lines and validates uPAR as a therapeutic target for TNBC.

Development of a human immuno-oncology therapeutic agent targeting HER2: targeted delivery of granzyme B

Background

Immunotherapeutic approaches designed to augment T and B cell mediated killing of tumor cells has met with clinical success in recent years suggesting tremendous potential for treatment in a broad spectrum of tumor types. After complex recognition of target cells by T and B cells, delivery of the serine protease granzyme B (GrB) to tumor cells comprises the cytotoxic insult resulting in a well-characterized, multimodal apoptotic cascade.

Methods

We designed a recombinant fusion construct, GrB-Fc-4D5, composed of a humanized anti-HER2 scFv fused to active GrB for recognition of tumor cells and internal delivery of GrB, simulating T and B cell therapy. We assessed the construct’s antigen-binding specificity and GrB enzymatic activity, as well as in vitro cytotoxicity and internalization into target and control cells. We also assessed pharmacokinetic and toxicology parameters in vivo.

Results

GrB-Fc-4D5 was highly cytotoxic to Her2 positive cells such as SKBR3, MCF7 and MDA-MB-231 with IC₅₀ values of 56, 99 and 27 nM, respectively, and against a panel of HER2+ cell lines regardless of endogenous expression levels of the PI-9 inhibitor. Contemporaneous studies with Kadcyla demonstrated similar levels of in vitro activity against virtually all cells tested. GrB-Fc-4D5 internalized rapidly into target SKOV3 cells within 1 h of exposure rapidly delivering GrB to the cytoplasmic compartment. In keeping with its relatively high molecular weight (160 kDa), the construct demonstrated a terminal-phase serum half-life in mice of 39.2 h. Toxicity studies conducted on BALB/c mice demonstrated no statistically significant changes in SGPT, SGOT or serum LDH. Histopathologic analysis of tissues from treated mice demonstrated no drug-related changes in any tissues examined.

Conclusion

GrB-Fc-4D5 shows excellent, specific cytotoxicity and demonstrates no significant toxicity in normal, antigen-negative murine models. This construct constitutes a novel approach against HER2-expressing tumors and is an excellent candidate for further development.

MEN1309/OBT076, a First-In-Class Antibody-Drug Conjugate Targeting CD205 in Solid Tumors

CD205 is a type I transmembrane glycoprotein and is a member of the C-type lectin receptor family. Analysis by mass spectrometry revealed that CD205 was robustly expressed and highly prevalent in a variety of solid malignancies from different histotypes. IHC confirmed the increased expression of CD205 in pancreatic, bladder, and triple-negative breast cancer (TNBC) compared with that in the corresponding normal tissues. Using immunofluorescence microscopy, rapid internalization of the CD205 antigen was observed. These results supported the development of MEN1309/OBT076, a fully humanized CD205-targeting mAb conjugated to DM4, a potent maytansinoid derivate, via a cleavable N-succinimidyl-4-(2-pyridyldithio) butanoate linker. MEN1309/OBT076 was characterized in vitro for target binding affinity, mechanism of action, and cytotoxic activity against a panel of cancer cell lines. MEN1309/OBT076 displayed selective and potent cytotoxic effects against tumor cells exhibiting strong and low to moderate CD205 expression. In vivo, MEN1309/OBT076 showed potent antitumor activity resulting in durable responses and complete tumor regressions in many TNBC, pancreatic, and bladder cancer cell line-derived and patient-derived xenograft models, independent of antigen expression levels. Finally, the pharmacokinetics and pharmacodynamic profile of MEN1309/OBT076 was characterized in pancreatic tumor-bearing mice, demonstrating that the serum level of antibody-drug conjugate (ADC) achieved through dosing was consistent with the kinetics of its antitumor activity. Overall, our data demonstrate that MEN1309/OBT076 is a novel and selective ADC with potent activity against CD205-positive tumors. These data supported the clinical development of MEN1309/OBT076, and further evaluation of this ADC is currently ongoing in the first-in-human SHUTTLE clinical trial.

Corneal features in trastuzumab emtansine treatment: not a rare occurrence

PURPOSE

Ado-trastuzumab emtansine (T-DM1/Kadcyla^®;Genentech) is an antibody-drug conjugate used in the treatment of human epidermal growth factor receptor-2-positive metastasized breast cancer. Few studies report a spectrum of corneal changes in patients treated with this drug. Our aim is to specify the nature and prevalence of corneal features of T-DM1 treatment in order to formulate guidelines as to which findings necessitate systemic treatment cessation or dose reduction.

METHODS

We performed a cross-sectional, prospective study in all patients currently treated with T-DM1 or recently stopped in Ghent University Hospital, Belgium.

RESULTS

A total of 12 patients completed a full ophthalmic workup. Ten patients were currently using T-DM1, and two patients had recently (< 10 weeks) stopped treatment because of clinical non-response. Twenty eyes of 10 patients currently on T-DM1-treatment all exhibited coarse cystoid lesions to the deep corneal epithelial cells, primarily in the midperipheral area, both biomicroscopically and on confocal microscopy. The two patients who stopped treatment, displayed no corneal epithelial changes. Only three patients reported symptoms which were attributed to other ocular factors, likely not to be related to T-DM1 treatment.

CONCLUSIONS

This case series shows that asymptomatic, low-grade corneal epithelial changes are hallmark features in T-DM1-treatment and should not alarm clinicians. These findings are relatively stationary, reversible and thus do not require ocular treatment or cessation of systemic treatment.

Trastuzumab gold-conjugates: synthetic approach and in vitro evaluation of anticancer activities in breast cancer cell lines

We describe the preparation of gold(i)-compounds that are amenable to efficient bioconjugation with monoclonal antibodies via activated ester or maleimide linkers. New Trastuzumab-gold conjugates were synthesized and fully characterized. These bioconjugates are significantly more cytotoxic (sub-micromolar range) to HER2-positive breast cancer cells than the gold complexes and Trastuzumab.

Fully synthetic macromolecular prodrug chemotherapeutics with EGFR targeting and controlled camptothecin release kinetics

Herein, we developed a fully polymerizable, peptide-targeted, camptothecin polymeric prodrug system. Two prodrug monomers were synthesized via esterification of campothecin (20Cam) and 10-hydroxycamptothecin (10Cam) with mono-2-(methacryloyloxy)ethyl succinate (SMA) resulting in polymerizable forms of the aliphatic ester- and aromatic ester-linked drugs respectively. These monomers were then incorporated into zwitterionic polymers via RAFT copolymerization of the prodrug monomers with a tert-butyl ester protected carboxy betaine monomer. Subsequent deprotection of the tert-butyl residues with TFA yielded carboxy betaine methacrylate (CBM) scaffolds with controlled prodrug incorporation. Reverse phase HPLC was then employed to establish drug release kinetics in human serum at 37 oC for the resultant polymeric prodrugs. Copolymers containing 10Cam residues linked via aromatic esters showed faster hydrolysis rates with 59 % drug released at 7 days, while copolymers with Cam residues linked via aliphatic esters showed only 28 % drug release over the same time period. These differences in drug release kinetics were then shown to correlate with large differences in cytotoxic activity in SKOV3 ovarian cancer cell cultures. At 72 hours, the IC50s of aromatic- and aliphatic- ester linked prodrugs were 56 nM and 4776 nM, respectively. An EGFR-targeting peptide sequence, GE11, was then directly incorporated into the polymeric prodrugs via RAFT copolymerization of the polymeric prodrugs with a peptide macronomer. The GE11-targeted polymeric prodrugs showed enhanced targeting and cytotoxic activity in SKOV3 cell cultures relative to untargeted polymers containing the negative control sequence HW12. Following pulse-chase treatment (15 min, 37 °C), the 72 hour IC50 of GE11 targeted prodrug was determined to be 1597 nM, in contrast to 3399 nM for the non-targeted control.

Intracellular GSH-activated galactoside photosensitizers for targeted photodynamic therapy and chemotherapy

Ligand-targeted cancer therapeutics has been developed to minimize non-specific cytotoxicity via ligand-drug conjugates during the past few decades. We present here the design and synthesis of a GSH-activated amphiphilic photosensitizer conjugated with galactose (TPP-S-S-Gal) for targeted photodynamic therapy. Furthermore, the galactoside photosensitizer as supramolecular amphiphiles can self-assemble into micelles, which can be applied in integrative cancer treatment with chemotherapy drugs such as camptothecin (CPT) encapsulated in the hydrophobic core of micelles. Upon reaction with free thiol GSH that is relatively abundant in tumor cells, disulfide bond cleavage occurs as well as the active photosensitizer TPP and chemotherapy drug CPT release, which can cause cell apoptosis. The in vitro biological assessment of TPP-S-S-Gal micelles against the A549 cell line was evaluated by MTT assay, flow cytometry and confocal scanning laser microscopy, respectively. According to the MTT assay, TPP-S-S-Gal micelles exhibited low dark toxicity and efficient integrative efficacy of PDT and chemotherapy towards A549 cells after light irradiation.

Optochemical Control of Biological Processes in Cells and Animals

Biological processes are naturally regulated with high spatial and temporal control, as is perhaps most evident in metazoan embryogenesis. Chemical tools have been extensively utilized in cell and developmental biology to investigate cellular processes, and conditional control methods have expanded applications of these technologies toward resolving complex biological questions. Light represents an excellent external trigger since it can be controlled with very high spatial and temporal precision. To this end, several optically regulated tools have been developed and applied to living systems. In this review we discuss recent developments of optochemical tools, including small molecules, peptides, proteins, and nucleic acids that can be irreversibly or reversibly controlled through light irradiation, with a focus on applications in cells and animals.

Evolution of the magic bullet: Single chain antibody fragments for the targeted delivery of immunomodulatory proteins

Immunocytokines are fusion proteins that combine the specific antigen binding capacities of an antibody or derivative thereof and the potent bioactivity of a cytokine partner. These novel biopharmaceuticals have been directed to various targets of oncological as well as non-oncological origin and a handful of promising constructs are currently advancing in the clinical trial pipeline. Several factors such as the choice of a disease specific antigen, the antibody format and the modulatory nature of the payload are crucial, not only for therapeutic efficacy and safety but also for the commercial success of such a product. In this review, we provide an overview of the basic principles and obstacles in immunocytokine design with a specific focus on single chain antibody fragment-based constructs that employ interleukins as the immunoactive component. Impact statement Selective activation of the immune system in a variety of malignancies represents an attractive approach when existing strategies have failed to provide adequate treatment options. Immunocytokines as a novel class of bifunctional protein therapeutics have emerged recently and generated promising results in preclinical and clinical studies. In order to harness their full potential, multiple different aspects have to be taken into consideration. Several key points of these fusion constructs are discussed here and should provide an outline for the development of novel products based on an overview of selected formats.

Understanding preanalytical variables and their effects on clinical biomarkers of oncology and immunotherapy

Identifying a suitable course of immunotherapy treatment for a given patient as well as monitoring treatment response is heavily reliant on biomarkers detected and quantified in blood and tissue biospecimens. Suboptimal or variable biospecimen collection, processing, and storage practices have the potential to alter clinically relevant biomarkers, including those used in cancer immunotherapy. In the present review, we summarize effects reported for immunologically relevant biomarkers and highlight preanalytical factors associated with specific analytical platforms and assays used to predict and gauge immunotherapy response. Given that many of the effects introduced by preanalytical variability are gene-, transcript-, and protein-specific, biospecimen practices should be standardized and validated for each biomarker and assay to ensure accurate results and facilitate clinical implementation of newly identified immunotherapy approaches.

The state-of-play and future of antibody therapeutics

It has been over four decades since the development of monoclonal antibodies (mAbs) using a hybridoma cell line was first reported. Since then more than thirty therapeutic antibodies have been marketed, mostly as oncology, autoimmune and inflammatory therapeutics. While antibodies are very efficient, their cost-effectiveness has always been discussed owing to their high costs, accumulating to more than one billion dollars from preclinical development through to market approval. Because of this, therapeutic antibodies are inaccessible to some patients in both developed and developing countries. The growing interest in biosimilar antibodies as affordable versions of therapeutic antibodies may provide alternative treatment options as well potentially decreasing costs. As certain markets begin to capitalize on this opportunity, regulatory authorities continue to refine the requirements for demonstrating quality, efficacy and safety of biosimilar compared to originator products. In addition to biosimilars, innovations in antibody engineering are providing the opportunity to design biobetter antibodies with improved properties to maximize efficacy. Enhancing effector function, antibody drug conjugates (ADC) or targeting multiple disease pathways via multi-specific antibodies are being explored. The manufacturing process of antibodies is also moving forward with advancements relating to host cell production and purification processes. Studies into the physical and chemical degradation pathways of antibodies are contributing to the design of more stable proteins guided by computational tools. Moreover, the delivery and pharmacokinetics of antibody-based therapeutics are improving as optimized formulations are pursued through the implementation of recent innovations in the field.

Drug targeting to myofibroblasts: Implications for fibrosis and cancer

Myofibroblasts are the key players in extracellular matrix remodeling, a core phenomenon in numerous devastating fibrotic diseases. Not only in organ fibrosis, but also the pivotal role of myofibroblasts in tumor progression, invasion and metastasis has recently been highlighted. Myofibroblast targeting has gained tremendous attention in order to inhibit the progression of incurable fibrotic diseases, or to limit the myofibroblast-induced tumor progression and metastasis. In this review, we outline the origin of myofibroblasts, their general characteristics and functions during fibrosis progression in three major organs: liver, kidneys and lungs as well as in cancer. We will then discuss the state-of-the art drug targeting technologies to myofibroblasts in context of the above-mentioned organs and tumor microenvironment. The overall objective of this review is therefore to advance our understanding in drug targeting to myofibroblasts, and concurrently identify opportunities and challenges for designing new strategies to develop novel diagnostics and therapeutics against fibrosis and cancer.

PSMA-Targeted Theranostic Nanocarrier for Prostate Cancer

Herein, we report the use of a theranostic nanocarrier (Folate-HBPE(CT20p)) to deliver a therapeutic peptide to prostate cancer tumors that express PSMA (folate hydrolase 1). The therapeutic peptide (CT20p) targets and inhibits the chaperonin-containing TCP-1 (CCT) protein-folding complex, is selectively cytotoxic to cancer cells, and is non-toxic to normal tissue. With the delivery of CT20p to prostate cancer cells via PSMA, a dual level of cancer specificity is achieved: (1) selective targeting to PSMA-expressing prostate tumors, and (2) specific cytotoxicity to cancer cells with minimal toxicity to normal cells. The PSMA-targeting theranostic nanocarrier can image PSMA-expressing cells and tumors when a near infrared dye is used as cargo. Meanwhile, it can be used to treat PSMA-expressing tumors when a therapeutic, such as the CT20p peptide, is encapsulated within the nanocarrier. Even when these PSMA-targeting nanocarriers are taken up by macrophages, minimal cell death is observed in these cells, in contrast with doxorubicin-based therapeutics that result in significant macrophage death. Incubation of PSMA-expressing prostate cancer cells with the Folate-HBPE(CT20p) nanocarriers induces considerable changes in cell morphology, reduction in the levels of integrin β1, and lower cell adhesion, eventually resulting in cell death. These results are relevant as integrin β1 plays a key role in prostate cancer invasion and metastatic potential. In addition, the use of the developed PSMA-targeting nanocarrier facilitates the selective in vivo delivery of CT20p to PSMA-positive tumor, inducing significant reduction in tumor size.

Efficient Preparation of Site-Specific Antibody-Drug Conjugates Using Cysteine Insertion

Antibody-drug conjugates (ADCs) are a class of biopharmaceuticals that combine the specificity of antibodies with the high-potency of cytotoxic drugs. Engineering cysteine residues in the antibodies using mutagenesis is a common method to prepare site-specific ADCs. With this approach, solvent accessible amino acids in the antibody have been selected for substitution with cysteine for conjugating maleimide-bearing cytotoxic drugs, resulting in homogeneous and stable site-specific ADCs. Here we describe a cysteine engineering approach based on the insertion of cysteines before and after selected sites in the antibody, which can be used for site-specific preparation of ADCs. Cysteine-inserted antibodies have expression level and monomeric content similar to the native antibodies. Conjugation to a pyrrolobenzodiazepine dimer (SG3249) resulted in comparable efficiency of site-specific conjugation between cysteine-inserted and cysteine-substituted antibodies. Cysteine-inserted ADCs were shown to have biophysical properties, FcRn, and antigen binding affinity similar to the cysteine-substituted ADCs. These ADCs were comparable for serum stability to the ADCs prepared using cysteine-mutagenesis and had selective and potent cytotoxicity against human prostate cancer cells. Two of the cysteine-inserted variants abolish binding of the resulting ADCs to FcγRs in vitro, thereby potentially preventing non-target mediated uptake of the ADCs by cells of the innate immune system that express FcγRs, which may result in mitigating off-target toxicities. A selected cysteine-inserted ADC demonstrated potent dose-dependent anti-tumor activity in a xenograph tumor mouse model of human breast adenocarcinoma expressing the oncofetal antigen 5T4.

Novel anticarcinoembryonic antigen antibody-drug conjugate has antitumor activity in the existence of soluble antigen

Carcinoembryonic antigen (CEA) is a classic tumor‐specific antigen that is overexpressed in several cancers, including gastric cancer. Although some anti‐CEA antibodies have been tested, to the best of our knowledge, there are currently no clinically approved anti‐CEA antibody therapies. Because of this, we have created the novel anti‐CEA antibody, 15‐1‐32, which exhibits stronger binding to membrane‐bound CEA on cancer cells than existing anti‐CEA antibodies. 15‐1‐32 also shows poor affinity for soluble CEA; thus, the binding activity of 15‐1‐32 to membrane‐bound CEA is not influenced by soluble CEA. In addition, we constructed a 15‐1‐32‐monomethyl auristatin E conjugate (15‐1‐32‐vcMMAE) to improve the therapeutic efficacy of 15‐1‐32. 15‐1‐32‐vcMMAE showed enhanced antitumor activity against gastric cancer cell lines. Unlike with existing anti‐CEA antibody therapies, antitumor activity of 15‐1‐32‐vcMMAE was retained in the presence of high concentrations of soluble CEA.

High throughput cytotoxicity screening of anti-HER2 immunotoxins conjugated with antibody fragments from phage-displayed synthetic antibody libraries

Immunotoxins are an important class of antibody-based therapeutics. The potency of the immunotoxins depends on the antibody fragments as the guiding modules targeting designated molecules on cell surfaces. Phage-displayed synthetic antibody scFv libraries provide abundant antibody fragment candidates as targeting modules for the immunoconjugates, but the discovery of optimally functional immunoconjugates is limited by the scFv-payload conjugation procedure. In this work, cytotoxicity screening of non-covalently assembled immunotoxins was developed in high throughput format to discover highly functional synthetic antibody fragments for delivering toxin payloads. The principles governing the efficiency of the antibodies as targeting modules have been elucidated from large volume of cytotoxicity data: (a) epitope and paratope of the antibody-based targeting module are major determinants for the potency of the immunotoxins; (b) immunotoxins with bivalent antibody-based targeting modules are generally superior in cytotoxic potency to those with corresponding monovalent targeting module; and (c) the potency of the immunotoxins is positively correlated with the densities of the cell surface antigen. These findings suggest that screening against the target cells with a large pool of antibodies from synthetic antibody libraries without the limitations of natural antibody responses can lead to optimal potency and minimal off-target toxicity of the immunoconjugates.

Strategies for designing synthetic immune agonists

Enhancing the immune system is a validated strategy to combat infectious disease, cancer and allergy. Nevertheless, the development of immune adjuvants has been hampered by safety concerns. Agents that can stimulate the immune system often bear structural similarities with pathogen-associated molecular patterns found in bacteria or viruses and are recognized by pattern recognition receptors (PRRs). Activation of these PRRs results in the immediate release of inflammatory cytokines, up-regulation of co-stimulatory molecules, and recruitment of innate immune cells. The distribution and duration of these early inflammatory events are crucial in the development of antigen-specific adaptive immunity in the forms of antibody and/or T cells capable of searching for and destroying the infectious pathogens or cancer cells. However, systemic activation of these PRRs is often poorly tolerated. Hence, different strategies have been employed to modify or deliver immune agonists in an attempt to control the early innate receptor activation through temporal or spatial restriction. These approaches include physicochemical manipulation, covalent conjugation, formulation and conditional activation/deactivation. This review will describe recent examples of discovery and optimization of synthetic immune agonists towards clinical application.

Cardioprotective Potentials of Plant-Derived Small Molecules against Doxorubicin Associated Cardiotoxicity

Doxorubicin (DOX) is a potent and widely used anthracycline antibiotic for the treatment of several malignancies. Unfortunately, the clinical utility of DOX is often restricted due to the elicitation of organ toxicity. Particularly, the increased risk for the development of dilated cardiomyopathy by DOX among the cancer survivors warrants major attention from the physicians as well as researchers to develop adjuvant agents to neutralize the noxious effects of DOX on the healthy myocardium. Despite these pitfalls, the use of traditional cytotoxic drugs continues to be the mainstay treatment for several types of cancer. Recently, phytochemicals have gained attention for their anticancer, chemopreventive, and cardioprotective activities. The ideal cardioprotective agents should not compromise the clinical efficacy of DOX and should be devoid of cumulative or irreversible toxicity on the naïve tissues. Furthermore, adjuvants possessing synergistic anticancer activity and quelling of chemoresistance would significantly enhance the clinical utility in combating DOX-induced cardiotoxicity. The present review renders an overview of cardioprotective effects of plant-derived small molecules and their purported mechanisms against DOX-induced cardiotoxicity. Phytochemicals serve as the reservoirs of pharmacophore which can be utilized as templates for developing safe and potential novel cardioprotective agents in combating DOX-induced cardiotoxicity.