Absorption, distribution, metabolism, and excretion considerations for the development of antibody-drug conjugates

Smart Cancer Nanomedicine for Synergetic Therapy

Cancer is the second leading cause of death. Notwithstanding endeavors to comprehend tumor causes and therapeutic modalities, no noteworthy advancements in cancer therapy have been identified. Nanomedicine has drawn interest for its diagnostic potential because of its ability to deliver therapeutic agents specifically to tumors with little adverse effects. Nanomedicines have become prevalent in the treatment of cancer. Here, we present four strategic suggestions for improvement in the functionality and use of nanomedicine. (1) Smart drug selection is a prerequisite for both medicinal and commercial achievement. Allocating resources to the advancement of modular (pro)drugs and nanocarrier design ought to consider the role of opportunistic decisions depending on drug availability. (2) Stimuli-responsive nanomedicine for cancer therapy is being designed to release medications at particular locations precisely. (3) The cornerstone of clinical cancer treatment is combination therapy. Nanomedicines should be included more frequently in multimodal combination therapy regimens since they complement pharmacological and physical co-treatments. (4) Regulation by the immune system is transforming cancer therapy. Nanomedicines can improve the effectiveness of the immune system and control the behavior of anticancer immunity. These four approaches, both separately and particularly in combination, will accelerate and promote the creation of effective cancer nanomedicine treatments.

Recent Advances in Targeted Cancer Therapy: Are PDCs the Next Generation of ADCs?

Antibody-drug conjugates (ADCs) comprise antibodies, cytotoxic payloads, and linkers, which can integrate the advantages of antibodies and small molecule drugs to achieve targeted cancer treatment. However, ADCs also have some shortcomings, such as non-negligible drug resistance, a low therapeutic index, and payload-related toxicity. Many studies have focused on changing the composition of ADCs, and some have even further extended the concept and types of targeted conjugated drugs by replacing the targeted antibodies in ADCs with peptides, revolutionarily introducing peptide-drug conjugates (PDCs). This Perspective summarizes the current research status of ADCs and PDCs and highlights the structural innovations of ADC components. In particular, PDCs are regarded as the next generation of potential targeted drugs after ADCs, and the current challenges of PDCs are analyzed. Our aim is to offer fresh insights for the efficient design and expedited development of innovative targeted conjugated drugs.

Antibody-Drug Conjugates in the Pipeline for Treatment of Melanoma: Target and Pharmacokinetic Considerations

Melanoma is an aggressive, rapidly developing form of skin cancer that affects about 22 per 100,000 individuals. Treatment options for melanoma patients are limited and typically involve surgical excision of moles and chemotherapy. Survival has been improved in recent years through targeted small molecule inhibitors and antibody-based immunotherapies. However, the long-term side effects that arise from taking chemotherapies can negatively impact the lives of patients because they lack specificity and impact healthy cells along with the cancer cells. Antibody-drug conjugates are a promising new class of drugs for the treatment of melanoma. This review focuses on the development of antibody-drug conjugates for melanoma and discusses the existing clinical trials of antibody-drug conjugates and their use as a melanoma treatment. So far, the antibody-drug conjugates have struggled from efficacy problems, with modest effects at best, leading many to be discontinued for melanoma. At the same time, conjugates such as AMT-253, targeting melanoma cell adhesion molecule, and mecbotamab vedotin  targeting AXL receptor tyrosine kinase, are among the most exciting for melanoma treatment in the future.

Antibody-Drug Conjugates: Advancing from Magic Bullet to Biological Missile

Precision drug development is focusing on targeting tumor cell surface proteins for therapeutic delivery, maximizing biomarker identified on-target damage to the tumor while minimizing toxicity. A recent article demonstrated high expression of B7-H4 antigen on resistant ovarian cancer cells and described preclinical activity of B7-H4-directed antibody-drug conjugate. See related article by Gitto et al., p. 1567.

Antibody-Drug Conjugates (ADC) in HER2/neu-Positive Gynecologic Tumors

Antibody-drug conjugates (ADCs) are a new class of targeted anti-cancer therapies that combine a monoclonal tumor-surface-receptor-targeting antibody with a highly cytotoxic molecule payload bonded through specifically designed cleavable or non-cleavable chemical linkers. One such tumor surface receptor is human epidermal growth factor 2 (HER2), which is of interest for the treatment of many gynecologic tumors. ADCs enable the targeted delivery of a variety of cytotoxic therapies to tumor cells while minimizing delivery to healthy tissues. This review summarizes the existing literature about HER2-targeting ADC therapies approved for use in gynecologic malignancies, relevant preclinical studies, strategies to address ADC resistance, and ongoing clinical trials.

Atypical Asparagine Deamidation of NW Motif Significantly Attenuates the Biological Activities of an Antibody Drug Conjugate

Asparagine deamidation is a post-translational modification (PTM) that converts asparagine residues into iso-aspartate and/or aspartate. Non-enzymatic asparagine deamidation is observed frequently during the manufacturing, processing, and/or storage of biotherapeutic proteins. Depending on the site of deamidation, this PTM can significantly impact the therapeutic's potency, stability, and/or immunogenicity. Thus, deamidation is routinely monitored as a potential critical quality attribute. The initial evaluation of an asparagine's potential to deamidate begins with identifying sequence liabilities, in which the n + 1 amino acid is of particular interest. NW is one motif that occurs frequently within the complementarity-determining region (CDR) of therapeutic antibodies, but according to the published literature, has a very low risk of deamidating. Here we report an unusual case of this NW motif readily deamidating within the CDR of an antibody drug conjugate (ADC), which greatly impacts the ADC's biological activities. Furthermore, this NW motif solely deamidates into iso-aspartate, rather than the typical mixture of iso-aspartate and aspartate. Interestingly, biological activities are more severely impacted by the conversion of asparagine into iso-aspartate via deamidation than by conversion into aspartate via mutagenesis. Here, we detail the discovery of this unusual NW deamidation occurrence, characterize its impact on biological activities, and utilize structural data and modeling to explain why conversion to iso-aspartate is favored and impacts biological activities more severely.

Pharmacokinetics and toxicity considerations for antibody-drug conjugates: an overview

Antibody-drug conjugates (ADCs) is one of the fastest-growing drug-delivery systems. It involves a monoclonal antibody conjugated with payload via a ligand that directly targets the expressive protein of diseased cell. Hence, it reduces systemic exposure and provides site-specific delivery along with reduced toxicity. Because of this advantage, researchers have gained interest in this novel system. ADCs have displayed great promise in drug delivery and biomedical applications. However, a lack of understanding exists on their mechanisms of biodistribution, metabolism and side effects. To gain a better understanding of the therapeutics, careful consideration of the pharmacokinetics and toxicity needs to be undertaken. In this review, different pharmacokinetics parameters including distribution, bioanalysis and heterogeneity are discussed for developing novel therapeutics.

Bioanalytical Assays for Pharmacokinetic and Biodistribution Study of Antibody-Drug Conjugates

Antibody-drug conjugates (ADCs) are produced by the chemical linkage of cytotoxic agents and monoclonal antibodies. The complexity and heterogeneity of ADCs and the low concentration of cytotoxic agent released in vivo poses big challenges to their bioanalysis. Understanding the pharmacokinetic behavior, exposure-safety, and exposure-efficacy relationships of ADCs is needed for their successful development. Accurate analytical methods are required to evaluate intact ADCs, total antibody, released small molecule cytotoxins, and related metabolites. The selection of appropriate bioanalysis methods for comprehensive analysis of ADCs is mainly dependent on the properties of cytotoxic agents, the chemical linker, and the attachment sites. The quality of the information about the whole pharmacokinetic profile of ADCs has been improved due to the development and improvement of analytical strategies for detection of ADCs, such as ligand-binding assays and mass spectrometry-related techniques. In this article, we will focus on the bioanalytical assays that have been used in the pharmacokinetic study of ADCs and discuss their advantages, current limitations, and potential challenges. SIGNIFICANCE STATEMENT: This article describes bioanalysis methods which have been used in pharmacokinetic study of ADCs and discusses the advantages, disadvantages and potential challenges of these assays. This review is useful and helpful and will provide insights and reference for bioanalysis and development of ADCs.

Optimizing the safety of antibody-drug conjugates for patients with solid tumours

Over the past 5 years, improvements in the design of antibody-drug conjugates (ADCs) have enabled major advances that have reshaped the treatment of several advanced-stage solid tumours. Considering the intended rationale behind the design of ADCs, which is to achieve targeted delivery of cytotoxic molecules by linking them to antibodies targeting tumour-specific antigens, ADCs would be expected to be less toxic than conventional chemotherapy. However, most ADCs are still burdened by off-target toxicities that resemble those of the cytotoxic payload as well as on-target toxicities and other poorly understood and potentially life-threatening adverse effects. Given the rapid expansion in the clinical indications of ADCs, including use in curative settings and various combinations, extensive efforts are ongoing to improve their safety. Approaches currently being pursued include clinical trials optimizing the dose and treatment schedule, modifications of each ADC component, identification of predictive biomarkers for toxicities, and the development of innovative diagnostic tools. In this Review, we describe the determinants of the toxicities of ADCs in patients with solid tumours, highlighting key strategies that are expected to improve tolerability and enable improvements in the treatment outcomes of patients with advanced-stage and those with early stage cancers in the years to come.

Application of Modelling and Simulation Approaches to Predict Pharmacokinetics of Therapeutic Monoclonal Antibodies in Pediatric Population

Ethical regulations and limited paediatric participants are key challenges that contribute to a median delay of 6 years in paediatric mAb approval. To overcome these barriers, modelling and simulation methodologies have been adopted to design optimized paediatric clinical studies and reduce patient burden. The classical modelling approach in paediatric pharmacokinetic studies for regulatory submissions is to apply body weight-based or body surface area-based allometric scaling to adult PK parameters derived from a popPK model to inform the paediatric dosing regimen. However, this approach is limited in its ability to account for the rapidly changing physiology in paediatrics, especially in younger infants. To overcome this limitation, PBPK modelling, which accounts for the ontogeny of key physiological processes in paediatrics, is emerging as an alternative modelling strategy. While only a few mAb PBPK models have been published, PBPK modelling shows great promise demonstrating a similar prediction accuracy to popPK modelling in an Infliximab paediatric case study. To facilitate future PBPK studies, this review consolidated comprehensive data on the ontogeny of key physiological processes in paediatric mAb disposition. To conclude, this review discussed different use-cases for pop-PK and PBPK modelling and how they can complement each other to increase confidence in pharmacokinetic predictions.

Detection and Characterization of In Vitro Payload-Containing Catabolites of Noncleavable Antibody-Drug Conjugates by High-Resolution Mass Spectrometry and Multiple Data Mining Tools

The formation and accumulation of payload-containing catabolites (PCCs) from a noncleavable antibody-drug conjugate (ADC) in targeted and normal tissues are directly associated with the therapeutic effect and toxicity of the ADC, respectively. Understanding the PCC formation is important for supporting the payload design and facilitating preclinical evaluation of ADCs. However, detection and identification of PCCs of a noncleavable ADC are challenging due to their low concentrations and unknown structures. The main objective of this study was to develop and apply a generic liquid chromatography-high-resolution mass spectrometry (LC-HRMS) method for profiling PCCs in vitro. Noncleavable ADCs, ado-trastuzumab emtansine (T-DM1) and ADC-1, were incubated in liver lysosomes, liver S9, and/or cancer cells followed by data acquisition using LC-HRMS. Profiling PCCs mainly relied on processing LC-HRMS datasets using untargeted precise and thorough background subtraction (PATBS) processing and targeted product ion filtering (PIF). As a result, 12 PCCs of T-DM1 were detected and structurally characterized in human liver lysosomal incubation, a majority of which consisted of 4-[N-maleimidomethyl]cyclohexane-1-carboxylate (MCC)-DM1 and a few amino acids. Additionally, the incubation of ADC-1 in human, rat, and monkey liver S9 and cancer cells generated one major and three very minor PCCs, verifying the payload design. The results demonstrate that PATBS enabled the comprehensive profiling of PCCs regardless of their molecular weights, charge states, and fragmentations. As a complementary tool, PIF detected specific PCCs with superior sensitivity. The combination of the in vitro metabolism systems and the LC-HRMS method is a useful approach to profiling in vitro PCCs of noncleavable ADCs in support of drug discovery programs. SIGNIFICANCE STATEMENT: Profiling in vitro payload-containing catabolites (PCCs) of a noncleavable antibody-drug conjugate (ADC) is important for optimization of the payload design and preclinical evaluation of ADC. However, currently used analytical approaches often fail to quickly provide reliable PCC profiling results. The work introduces a new liquid chromatography high resolution mass spectrometry method for comprehensive and rapid detection and characterization of PCCs released from a noncleavable ADC in liver lysosomes and S9 incubations.

Antibody-Drug Conjugates for the Treatment of HER2-Positive Breast Cancer

Human epidermal growth factor receptor 2 (HER2) receptor tyrosine kinase is overexpressed in 20-30% of breast cancers and is associated with poor prognosis and worse overall patient survival. Most women with HER2-positive breast cancer receive neoadjuvant chemotherapy plus HER2-targeted therapies. The development of HER2-directed therapeutics is an important advancement in targeting invasive breast cancer. Despite the efficacy of anti-HER2 monoclonal antibodies, they are still being combined with adjuvant chemotherapy to improve overall patient outcomes. Recently, significant progress has been made towards the development of a class of therapeutics known as antibody-drug conjugates (ADCs), which leverage the high specificity of HER2-targeted monoclonal antibodies with the potent cytotoxic effects of various small molecules, such as tubulin inhibitors and topoisomerase inhibitors. To date, two HER2-targeting ADCs have been approved by the FDA for the treatment of HER2-positive breast cancer: Ado-trastuzumab emtansine (T-DM1; Kadcyla®) and fam-trastuzumab deruxtecan-nxki (T-Dxd; Enhertu®). Kadcyla and Enhertu are approved for use as a second-line treatment after trastuzumab-taxane-based therapy in patients with HER2-positive breast cancer. The success of ADCs in the treatment of HER2-positive breast cancer provides novel therapeutic advancements in the management of the disease. In this review, we discuss the basic biology of HER2, its downstream signaling pathways, currently available anti-HER2 therapeutic modalities and their mechanisms of action, and the latest clinical and safety characteristics of ADCs used for the treatment of HER2-positive breast cancer.

Does the Number of Bifunctional Chelators Conjugated to a mAb Affect the Biological Activity of Its Radio-Labeled Counterpart? Discussion Using the Example of mAb against CD-20 Labeled with 90Y or 177Lu

There has been considerable interest in developing a monoclonal antibody (mAb) against-CD-20 (for example, Rituximab) modified by bifunctional chelating agents (BCA) for non-Hodgkin's lymphoma radioimmunotherapy. Therefore, many researchers have modified this monoclonal antibody by attaching different BCA moieties and evaluated their biological activities in terms of in vitro study and in vivo study in healthy and tumor xenografted rodents. This mini-perspective reviews the in vitro studies, the immunoreactivity and physiological distribution studies: organ-to-blood and the tumor-to-organ ratio of conjugates with different numbers of chelators per mAb. We set up a null hypothesis that states there is no statistical significance between the biological activity of monoclonal antibody (Rituximab) and the number of conjugated bifunctional chelators. Overall, we have concluded that there is no strong evidence for this hypothesis. However, the literature data should be questioned due to the potential lack of uniform study methodology.

Bioanalytical Methods and Strategic Perspectives Addressing the Rising Complexity of Novel Bioconjugates and Delivery Routes for Biotherapeutics

In recent years, an increase in the discovery and development of biotherapeutics employing new modalities, such as bioconjugates or novel routes of delivery, has created bioanalytical challenges. The inherent complexity of conjugated molecular structures means that quantification of the bioconjugate and its multiple components is critical for preclinical/clinical studies to inform drug discovery and development. Moreover, bioconjugates involve additional multifactorial complexity because of the potential for in vivo catabolism and biotransformation, which may require thorough investigations in multiple biological matrices. Furthermore, excipients that enhance absorption are frequently evaluated and employed for the development of oral and inhaled biotherapeutics. Risk-benefit assessments are required for novel or existing excipients that utilize dosages above previously approved levels. Bioanalytical methods that can measure both excipients and potential drug metabolites in biological matrices are highly relevant to these emerging bioanalysis challenges. We discuss the bioanalytical strategies for analyzing bioconjugates such as antibody-drug conjugates and antibody-oligonucleotide conjugates and review recent advances in bioanalytical methods for the quantification and characterization of novel bioconjugates. We also discuss bioanalytical considerations for both biotherapeutics and excipients through novel administration routes and review analyses in various biological matrices, from the extensively studied serum or plasma to tissue biopsy in the context of preclinical and clinical studies from both technical and regulatory perspectives.

Development of a Physiologically-Based Pharmacokinetic Model for Whole-Body Disposition of MMAE Containing Antibody-Drug Conjugate in Mice

PURPOSE

To quantitate and mathematically characterize the whole-body pharmacokinetics (PK) of different ADC analytes following administration of an MMAE-conjugated ADC in tumor-bearing mice.

METHODS

The PK of different ADC analytes (total antibody, total drug, unconjugated drug) was measured following administration of an MMAE-conjugated ADC in tumor-bearing mice. The PK of ADC analytes was compared with the whole-body PK of the antibody and drug obtained following administration of these molecules alone. An ADC PBPK model was developed by linking antibody PBPK model with small-molecule PBPK model, where the drug was assumed to deconjugate in DAR-dependent manner.

RESULTS

Comparison of antibody biodistribution coefficient (ABC) values for total antibody suggests that conjugation of drug did not significantly affect the PK of antibody. Comparison of tissue:plasma AUC ratio (T/P) for the conjugated drug and total antibody suggests that in certain tissues (e.g., spleen) ADC may demonstrate higher deconjugation. It was observed that the tissue distribution profile of the drug can be altered following its conjugation to antibody. For example, MMAE distribution to the liver was found to increase while its distribution to the heart was found to decrease upon conjugation to antibody. MMAE exposure in the tumor was found to increase by ~20-fold following administration as conjugate (i.e., ADC). The PBPK model was able to a priori predict the PK of all three ADC analytes in plasma, tissues, and tumor reasonably well.

CONCLUSIONS

The ADC PBPK model developed here serves as a platform for translational and clinical investigations of MMAE containing ADCs.

Antibody-drug conjugates: Recent advances in linker chemistry

Antibody–drug conjugates (ADCs) are gradually revolutionizing clinical cancer therapy. The antibody–drug conjugate linker molecule determines both the efficacy and the adverse effects, and so has a major influence on the fate of ADCs. An ideal linker should be stable in the circulatory system and release the cytotoxic payload specifically in the tumor. However, existing linkers often release payloads nonspecifically and inevitably lead to off-target toxicity. This defect is becoming an increasingly important factor that restricts the development of ADCs. The pursuit of ADCs with optimal therapeutic windows has resulted in remarkable progress in the discovery and development of novel linkers. The present review summarizes the advance of the chemical trigger, linker‒antibody attachment and linker‒payload attachment over the last 5 years, and describes the ADMET properties of ADCs. This work also helps clarify future developmental directions for the linkers.

Clinical Pharmacology of Antibody-Drug Conjugates

Antibody-drug conjugates (ADCs) are biopharmaceutical products where a monoclonal antibody is linked to a biologically active drug (a small molecule) forming a conjugate. Since the approval of first ADC (Gemtuzumab ozogamicin (trade name: Mylotarg)) for the treatment of CD33-positive acute myelogenous leukemia, several ADCs have been developed for the treatment of cancer. The goal of an ADC as a cancer agent is to release the cytotoxic drug to kill the tumor cells without harming the normal or healthy cells. With time, it is being realized that ADCS can also be used to manage or cure other diseases such as inflammatory diseases, atherosclerosis, and bacteremia and some research in this direction is ongoing. The focus of this review is on the clinical pharmacology aspects of ADC development. From the selection of an appropriate antibody to the finished product, the entire process of the development of an ADC is a difficult and challenging task. Clinical pharmacology is one of the most important tools of drug development since this tool helps in finding the optimum dose of a product, thus preserving the safety and efficacy of the product in a patient population. Unlike other small or large molecules where only one moiety and/or metabolite(s) is generally measured for the pharmacokinetic profiling, there are several moieties that need to be measured for characterizing the PK profiles of an ADC. Therefore, knowledge and understanding of clinical pharmacology of ADCs is vital for the selection of a safe and efficacious dose in a patient population.

Model-Informed Therapeutic Dose Optimization Strategies for Antibody-Drug Conjugates in Oncology: What Can We Learn From US Food and Drug Administration-Approved Antibody-Drug Conjugates?

Antibody–drug conjugates (ADCs) combine the specificity of an antibody with the cytotoxicity of a chemical agent. They represent a rapidly evolving area of oncology drug development and hold significant promise. There are currently nine ADCs on the market, more than half of which gained US Food and Drug Administration approval more recently, since 2019. Despite their enormous promise, the therapeutic window for these ADCs remains relatively narrow, especially when compared with other oncology drugs, such as targeted therapies or checkpoint inhibitors. In this review, we provide a detailed overview of the five dosing regimen optimization strategies that have been leveraged to broaden the therapeutic window by mitigating the safety risks while maintaining efficacy. These include body weight cap dosing; treatment duration capping; dose schedule (e.g., dosing frequency and dose fractionation); response‐guided dosing recommendations; and randomized dose‐finding. We then discuss how the lessons learned from these studies can inform ADC development going forward. Informed application of these dosing strategies should allow researchers to maximize the safety and efficacy for next‐generation ADCs.

Preclinical Studies of OBI-999: A Novel Globo H-Targeting Antibody-Drug Conjugate

Globo H (GH), a hexasaccharide, is expressed at low levels in normal tissues but is highly expressed in multiple cancer types, rendering it a promising target for cancer immunotherapy. OBI-999, a novel antibody-drug conjugate, is derived from a conjugation of a GH-specific mAb with a monomethyl auristatin E (MMAE) payload through a site-specific ThioBridge and a cleavable linker. OBI-999 high homogeneity with a drug-to-antibody ratio of 4 (>95%) was achieved using ThioBridge. OBI-999 displayed GH-dependent cellular internalization and trafficked to endosome and lysosome within 1 and 5 hours, respectively. Furthermore, OBI-999 showed low nanomolar cytotoxicity in the assay with high GH expression on tumor cells and exhibited a bystander killing effect on tumor cells with minimal GH expression. Tissue distribution indicated that OBI-999 and free MMAE gradually accumulated in the tumor, reaching maximum level at 168 hours after treatment, whereas OBI-999 and free MMAE decreased quickly at 4 hours after treatment in normal organs. Maximum MMAE level in the tumor was 16-fold higher than in serum, suggesting that OBI-999 is stable during circulation and MMAE is selectively released in the tumor. Excellent tumor growth inhibition of OBI-999 was demonstrated in breast, gastric, and pancreatic cancer xenograft or lung patient-derived xenograft models in a dose-dependent manner. The highest nonseverely toxic dose in cynomolgus monkeys is 10 mg/kg determined by a 3-week repeated-dose toxicology study demonstrating an acceptable safety margin. Taken together, these results support further clinical development of OBI-999, which is currently in a phase I/II clinical study in multiple solid tumors (NCT04084366). OBI-999, the first GH-targeting ADC, displayed excellent tumor inhibition in animal models across multiple cancer types, including breast, gastric, pancreatic, and lung cancers, warranting further investigation in the treatment of solid tumors.

Specific Cytotoxic Effect of an Auristatin Nanoconjugate Towards CXCR4+ Diffuse Large B-Cell Lymphoma Cells

BACKGROUND AND PURPOSE

Around 40-50% of diffuse large-B cell lymphoma (DLBCL) patients suffer from refractory disease or relapse after R-CHOP first-line treatment. Many ongoing clinical trials for DLBCL patients involve microtubule targeting agents (MTAs), however, their anticancer activity is limited by severe side effects. Therefore, we chose to improve the therapeutic window of the MTA monomethyl auristatin E developing a nanoconjugate, T22-AUR, that selectively targets the CXCR4 receptor, which is overexpressed in many DLBCL cells (CXCR4+) and associated with poor prognosis.

METHODS

The T22-AUR specificity towards CXCR4 receptor was performed by flow cytometry in different DLBCL cell lines and running biodistribution assays in a subcutaneous mouse model bearing CXCR4+ DLBCL cells. Moreover, we determined T22-AUR cytotoxicity using cell viability assays, cell cycle analysis, DAPI staining and immunohistochemistry. Finally, the T22-AUR antineoplastic effect was evaluated in vivo in an extranodal CXCR4+ DLBCL mouse model whereas the toxicity analysis was assessed by histopathology in non-infiltrated mouse organs and by in vitro cytotoxic assays in human PBMCs.

RESULTS

We demonstrate that the T22-AUR nanoconjugate displays CXCR4-dependent targeting and internalization in CXCR4+ DLBCL cells in vitro as well as in a subcutaneous DLBCL mouse model. Moreover, it shows high cytotoxic effect in CXCR4+ DLBCL cells, including induction of G2/M mitotic arrest, DNA damage, mitotic catastrophe and apoptosis. Furthermore, the nanoconjugate shows a potent reduction in lymphoma mouse dissemination without histopathological alterations in non-DLBCL infiltrated organs. Importantly, T22-AUR also exhibits lack of toxicity in human PBMCs.

CONCLUSION

T22-AUR exerts in vitro and in vivo anticancer effect on CXCR4+ DLBCL cells without off-target toxicity. Thus, T22-AUR promises to become an effective therapy for CXCR4+ DLBCL patients.

Environmental Effects on Salt Bridge Stability in the Protein-Protein Interface: The Case of Hen Egg-White Lysozyme and Its Antibody, HyHEL-10

We studied the stability of two salt bridges between hen egg-white lysozyme (HEL) and its antibody, HyHEL-10, by using molecular dynamics simulations. It was observed that one salt bridge, D32^H-K97^Y, was stable, whereas the other, D99^H-K97^Y, was not. To understand this difference, we compared several reduced salt bridge models that incorporated the salt bridges and nearby residues. The results showed the importance of nearby residues, especially Y33^H and W98^H. Furthermore, to understand the effects of nearby salt bridges, we investigated two mutants, D32^HA and D99^HA. We found that the D32^HA mutation considerably stabilized the D99^H-K97^Y salt bridge. The reduced model analysis indicated that this can be largely attributed to a conformational change of the main chain.

2020 FDA TIDES (Peptides and Oligonucleotides) Harvest

2020 has been an extremely difficult and challenging year as a result of the coronavirus disease 2019 (COVID-19) pandemic and one in which most efforts have been channeled into tackling the global health crisis. The US Food and Drug Administration (FDA) has approved 53 new drug entities, six of which fall in the peptides and oligonucleotides (TIDES) category. The number of authorizations for these kinds of drugs has been similar to that of previous years, thereby reflecting the consolidation of the TIDES market. Here, the TIDES approved in 2020 are analyzed in terms of chemical structure, medical target, mode of action, and adverse effects.

Enfortumab vedotin - next game-changer in urothelial cancer

Introduction: The therapeutic landscape of metastatic urothelial carcinoma (mUC) becomes increasingly dense: standard therapy remains cisplatin-based chemotherapy, followed by immunotherapy with checkpoint inhibitors as maintenance or second-line. New directions include erdafitinib, a fibroblast growth factor receptor (FGFR) inhibitor in patients with corresponding mutations in FGFR2/3 receptor. Enfortumab vedotin (EV) is an antibody-drug conjugate targeting nectin-4 and is conjugated with monomethyl auristatin E (MMAE). It received FDA approval based on phase I/II data recently and thus represents an alternative to established third-line chemotherapies with vinflunine, paclitaxel, or docetaxel.Areas covered: The aim of this review was to evaluate the added value of Enfortumab vedotin in the therapeutic landscape of mUC. Current therapeutic options and alternatives for the affected patients are described, followed by a detailed description of the characteristics and available results of EV. Ongoing studies are explained, the present significance of the substance is assessed and its further future potential is outlined.Expert opinion Enfortumab vedotin has shown encouraging efficacy and a good tolerability in phase I/II trials, especially in heavily pretreated patients and patients with liver metastases. It appears to outperform third-line chemotherapies; ongoing studies will show the future potential of EV in treatment sequence.

Preliminary biological evaluation of 123I-labelled anti-CD30-LDM in CD30-positive lymphomas murine models

Overexpression of CD30 has been reported on the surface of some T-cell lymphomas, especially on Hodgkin's lymphoma (HL) and anaplastic large cell lymphoma (ALCL). CD30 targeted immunotherapy has good clinical therapy response. We have produced a novel antibody drug conjugates (ADCs)-anti-CD30-LDM, which shows attractive tumour-targeting capability and extremely potent antitumor efficacy. To further investigate biological characteristics and promote clinical translation of anti-CD30-LDM, we constructed a radiolabeled 123I-anti-CD30-LDM to evaluate the biodistribution characteristics. The anti-CD30-LDM was radioiodinated by the Iodogen method. The radiochemical purity of 123I-anti-CD30-LDM was more over 98%, and the specific activity of 240.5 MBq/mg. The stability and the specificity of 123I-anti-CD30-LDM were evaluated in vitro. Cellular binding assays were used to evaluate the binding capabilities in CD30-positive Karpas299 cells and CD30-negative Raji cells. B-NDG mice bearing Karpas 299 and Raji xenografts were used for in vivo biodistribution studies. Our results demonstrated that anti-CD30-LDM as an ideal ADC targeted to CD30, which was labelled easily with 123I and obtained the sufficient yields. The 123I-anti-CD30-LDM preserved specific binding to CD30 in vitro and uptake in tumour xenografts in B-NDG mice. These results are encouraging for anti-CD30-LDM as a promising clinical translational candidate for various CD30 positive lymphomas and other diseases.

Considerations for setting occupational exposure limits for novel pharmaceutical modalities

In order to develop new and effective medicines, pharmaceutical companies must be modality agnostic. As science reveals an enhanced understanding of biological processes, new therapeutic modalities are becoming important in developing breakthrough therapies to treat both rare and common diseases. As these new modalities progress, concern and uncertainty arise regarding their safe handling by the researchers developing them, employees manufacturing them and nurses administering them. This manuscript reviews the available literature for emerging modalities (including oligonucleotides, monoclonal antibodies, fusion proteins and bispecific antibodies, antibody-drug conjugates, peptides, vaccines, genetically modified organisms, and several others) and provides considerations for occupational health and safety-oriented hazard identification and risk assessments to enable timely, consistent and well-informed hazard identification, hazard communication and risk-management decisions. This manuscript also points out instances where historical exposure control banding systems may not be applicable (e.g. oncolytic viruses, biologics) and where other occupational exposure limit systems are more applicable (e.g. Biosafety Levels, Biologic Control Categories).

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Review of toxicology and pharmacology information for novel therapeutic modalities.

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Identification of occupational hazards associated with novel therapeutic modalities.

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Occupational hazards and exposure risks differ across pharmaceutical modalities.

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Occupational exposure control banding systems are not one size fits all.

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Banding system variations offer benefits while enabling proper exposure controls.

Mechanistic Modeling of Intra-Tumor Spatial Distribution of Antibody-Drug Conjugates: Insights into Dosing Strategies in Oncology

Antibody drug conjugates (ADCs) provide targeted delivery of cytotoxic agents directly inside tumor cells. However, many ADCs targeting solid tumors have exhibited limited clinical efficacy, in part, due to insufficient penetration within tumors. To better understand the relationship between ADC tumor penetration and efficacy, previously applied Krogh cylinder models that explore tumor growth dynamics following ADC administration in preclinical species were expanded to a clinical framework by integrating clinical pharmacokinetics, tumor penetration, and tumor growth inhibition. The objective of this framework is to link ADC tumor penetration and distribution to clinical efficacy. The model was validated by comparing virtual patient population simulations to observed overall response rates from trastuzumab‐DM1 treated patients with metastatic breast cancer. To capture clinical outcomes, we expanded upon previous Krogh cylinder models to include the additional mechanism of heterogeneous tumor growth inhibition spatially across the tumor. This expansion mechanistically captures clinical response rates by describing heterogeneous ADC binding and tumor cell killing; high binding and tumor cell death close to capillaries vs. low binding, and high tumor cell proliferation far from capillaries. Sensitivity analyses suggest that clinical efficacy could be optimized through dose fractionation, and that clinical efficacy is primarily dependent on the ADC‐target affinity, payload potency, and tumor growth rate. This work offers a mechanistic basis to predict and optimize ADC clinical efficacy for solid tumors, allowing dosing strategy optimization to improve patient outcomes.

Polatuzumab vedotin, an anti-CD79b antibody-drug conjugate for the treatment of relapsed/refractory diffuse large B-cell lymphoma

Refractory/relapsed diffuse large B-cell lymphoma remains a major unmet medical need with poor outcome, especially for patients considered ineligible for stem cell transplant. Polatuzumab vedotin (PV) is a first-in-class anti-CD79b antibody-drug conjugate that contains the microtubule inhibitor monomethyl auristatin E. The development of PV is currently very active. This drug was US FDA approved in 2019 in combination with bendamustine and rituximab for the treatment of refractory/relapsed diffuse large B-cell lymphoma in third line and more, after demonstrating relevant efficacy and acceptable safety in a pivotal randomized Phase II trial. This review summarizes the features of this new drug with the primary focus on the clinical work supporting efficacy, relevance and tolerability of PV.

Enfortumab Vedotin-ejfv: A First-in-Class Anti-Nectin-4 Antibody-Drug Conjugate for the Management of Urothelial Carcinoma

OBJECTIVE

To evaluate the pharmacology, pharmacokinetics, clinical efficacy, safety, dosing, cost, and clinical implications of enfortumab vedotin-ejfv (EV) in the treatment of locally advanced or metastatic urothelial carcinoma (UC).

DATA SOURCES

A literature search of PubMed (inception to August 2020) was conducted using the terms enfortumab, vedotin, Padcev, and Nectin. Data were also obtained from package inserts, meeting abstracts, and ongoing studies from ClinicalTrials.gov.

STUDY SELECTION AND DATA EXTRACTION

All relevant published articles, package inserts, and meeting abstracts evaluating EV for the treatment of UC were analyzed.

DATA SYNTHESIS

Antibody-drug conjugates (ADCs) deliver potent cytotoxic agents using highly selective monoclonal antibodies. Targeting the near-universal expression of Nectin-4 on UC cells is a viable therapeutic strategy. In a pivotal phase II trial, EV demonstrated an overall response rate of 44%, and a median duration of response of 7.6 months. Estimated overall survival was 11.7 months with a median estimated progression-free survival of 5.6 months. Results were similar among difficult-to-treat patients, including those with liver metastases. Unique toxicity concerns with EV require careful consideration and monitoring.

RELEVANCE TO PATIENT CARE AND CLINICAL PRACTICE

EV, a first-in-class anti-Nectin-4 ADC, provides impressive response rates with manageable toxicities, making it a promising treatment option for patients with multiply relapsed or refractory UC.

CONCLUSION

The US Food and Drug Administration-approved EV demonstrates antitumor activity in heavily pretreated patients with UC but harbors important adverse effects and financial concerns. Additional studies are required to identify the optimal sequencing, patient population, and place in therapy for EV.

Nonclinical Development of Next-generation Site-specific HER2-targeting Antibody-drug Conjugate (ARX788) for Breast Cancer Treatment

Conventional antibody-drug conjugates (ADC) utilize native surface-exposed lysines or cysteines on the antibody of interest to conjugate cytotoxic payload. The nonspecific conjugation results in a mixture with variable drug-to-antibody ratios (DAR), conjugation sites, and ADCs that are often unstable in systemic circulation. ARX788 is an ADC consisting of a HER2-targeting antibody site-specifically conjugated with a potent antitubulin cytotoxic drug-linker, AS269. The site-specific conjugation is achieved by first incorporating the nonnatural amino acid, para-acetyl phenylalanine (pAF), into the antibody, followed by covalent conjugation of AS269 to the pAF to form a highly stable oxime bond resulting in a DAR 2 ADC. ARX788 exhibits significant, dose-dependent antitumor activity against HER2- expressing breast and gastric xenograft tumors. Pharmacokinetic (PK) studies in multiple species showed the highly stable nature of ARX788 with overlapping PK profiles for the intact ADC and total antibody. Metabolism studies demonstrated that pAF-AS269 was the sole major metabolite of ARX788, with no evidence for the release of free drug often observed in conventional ADCs and responsible for adverse side effects. Furthermore, ARX788 demonstrated a favorable safety profile in monkeys with a highest nonseverely toxic dose of 10 mg/kg, which was well above the efficacious dose level observed in preclinical tumor models, thus supporting clinical development of ARX788.

A novel semi-mechanistic tumor growth fraction model for translation of preclinical efficacy of anti-glypican 3 antibody drug conjugate to human

The growing fraction (GF) of tumor has been reported as one of the predictive markers of the efficacy of chemotherapeutics. Therefore, a semi-mechanistic model has been developed that describes tumor growth on the basis of cell cycle, allowing the incorporation of the GF of a tumor in pharmacokinetic/pharmacodynamic (PK/PD) modeling. Efficacy data of anti-glypican 3 (GPC3) antibody drug conjugate (ADC) in a hepatocellular carcinoma (HCC) patient derived xenograft (PDX) model was used for evaluation of this proposed model. Our model was able to describe the kinetics of growth inhibition of HCC PDX models following treatment with anti-GPC3 ADC remarkably well. The estimated tumurostatic concentrations were used in tandem with human PKs translated from cynomolgus monkey for prediction of the efficacious dose. The projected efficacious human dose of anti-GPC3 ADC was in the range 0.20-0.63 mg/kg for the Q3W dosing regimen, with a median dose of 0.50 mg/kg. This publication is the first step in evaluating the applicability of GF in PK/PD modeling of ADCs. The authors are hopeful that incorporation of GF will result in an improved translation of the preclinical efficacy of ADCs to clinical settings and thereby better prediction of the efficacious human dose.

Stimuli-responsive prodrug-based cancer nanomedicine

The rapid development of nanotechnology results in the emergence of nanomedicines, but the effective delivery of drugs to tumor sites remains a great challenge. Prodrug-based cancer nanomedicines thus emerged due to their unique advantages, including high drug load efficiency, reduced side effects, efficient targeting, and real-time controllability. A distinctive characteristic of prodrug-based nanomedicines is that they need to be activated by a stimulus or multi-stimulus to produce an anti-tumor effect. A better understanding of various responsive approaches could allow researchers to perceive the mechanism of prodrug-based nanomedicines effectively and further optimize their design strategy. In this review, we highlight the stimuli-responsive pathway of prodrug-based nanomedicines and their anticancer applications. Furthermore, various types of prodrug-based nanomedicines, recent progress and prospects of stimuli-responsive prodrug-based nanomedicines and patient data in the clinical application are also summarized. Additionally, the current development and future challenges of prodrug-based nanomedicines are discussed. We expect that this review will be valuable for readers to gain a deeper understanding of the structure and development of prodrug-based cancer nanomedicines to design rational and effective drugs for clinical use.

Pharmacokinetics of polatuzumab vedotin in combination with R/G-CHP in patients with B-cell non-Hodgkin lymphoma

Purpose

The phase Ib/II open-label study (NCT01992653) evaluated the antibody-drug conjugate polatuzumab vedotin (pola) plus rituximab/obinutuzumab, cyclophosphamide, doxorubicin, and prednisone (R/G-CHP) as first-line therapy for B-cell non-Hodgkin lymphoma (B-NHL). We report the pharmacokinetics (PK) and drug–drug interaction (DDI) for pola.

Methods

Six or eight cycles of pola 1.0–1.8 mg/kg were administered intravenously every 3 weeks (q3w) with R/G-CHP. Exposures of pola [including antibody-conjugated monomethyl auristatin E (acMMAE) and unconjugated MMAE] and R/G-CHP were assessed by non-compartmental analysis and/or descriptive statistics with cross-cycle comparisons to cycle 1 and/or after multiple cycles. Pola was evaluated as a potential victim and perpetrator of a PK drug–drug interaction with R/G-CHP. Population PK (popPK) analysis assessed the impact of prior treatment status (naïve vs. relapsed/refractory) on pola PK.

Results

Pola PK was similar between treatment arms and independent of line of therapy. Pola PK was dose proportional from 1.0 to 1.8 mg/kg with R/G-CHP. Geometric mean volume of distribution and clearance of acMMAE ranged from 57.3 to 95.6 mL/kg and 12.7 to 18.2 mL/kg/day, respectively. acMMAE exhibited multi-exponential decay (elimination half-life ~ 1 week). Unconjugated MMAE exhibited formation rate-limited kinetics. Exposures of pola with R/G-CHP were similar to those in the absence of CHP; exposures of R/G-CHP in the presence of pola were comparable to those in the absence of pola.

Conclusions

Pola PK was well characterized with no clinically meaningful DDIs with R/G-CHP. Findings are consistent with previous studies of pola + R/G, and support pola + R/G-CHP use in previously untreated diffuse large B-cell lymphoma.

Electronic supplementary material

The online version of this article (10.1007/s00280-020-04054-8) contains supplementary material, which is available to authorized users.

2019 FDA TIDES (Peptides and Oligonucleotides) Harvest

2019 has been an excellent year in terms of peptides and oligonucleotides (TIDES) approved by the FDA. Despite the drop in the number of total drugs approved by the FDA in 2019 in comparison with 2018 (48 vs. 59), the total number of TIDES authorized increased (seven vs. three). Year after year, TIDES are increasingly present in therapy, as imaging agents, theragnostic and constituent moieties of other complex drugs, such as antibody drug conjugates. This means a consolidation of these kinds of drugs in the pharmaceutical arena, paving the way in the coming years for the approval of others for diverse medical indications. Here the TIDES approved in 2019 are analyzed in terms of chemical structure, medical target, mode of action, and adverse effects.

Mertansine Inhibits mRNA Expression and Enzyme Activities of Cytochrome P450s and Uridine 5′-Diphospho-Glucuronosyltransferases in Human Hepatocytes and Liver Microsomes

Mertansine, a tubulin inhibitor, is used as the cytotoxic component of antibody–drug conjugates (ADCs) for cancer therapy. The effects of mertansine on uridine 5′-diphospho-glucuronosyltransferase (UGT) activities in human liver microsomes and its effects on the mRNA expression of cytochrome P450s (CYPs) and UGTs in human hepatocytes were evaluated to assess the potential for drug–drug interactions (DDIs). Mertansine potently inhibited UGT1A1-catalyzed SN-38 glucuronidation, UGT1A3-catalyzed chenodeoxycholic acid 24-acyl-β-glucuronidation, and UGT1A4-catalyzed trifluoperazine N-β-d-glucuronidation, with K_i values of 13.5 µM, 4.3 µM, and 21.2 µM, respectively, but no inhibition of UGT1A6, UGT1A9, and UGT2B7 enzyme activities was observed in human liver microsomes. A 48 h treatment of mertansine (1.25–2500 nM) in human hepatocytes resulted in the dose-dependent suppression of mRNA levels of CYP1A2, CYP2B6, CYP3A4, CYP2C8, CYP2C9, CYP2C19, UGT1A1, and UGT1A9, with IC₅₀ values of 93.7 ± 109.1, 36.8 ± 18.3, 160.6 ± 167.4, 32.1 ± 14.9, 578.4 ± 452.0, 539.5 ± 233.4, 856.7 ± 781.9, and 54.1 ± 29.1 nM, respectively, and decreased the activities of CYP1A2-mediated phenacetin O-deethylase, CYP2B6-mediated bupropion hydroxylase, and CYP3A4-mediated midazolam 1′-hydroxylase. These in vitro DDI potentials of mertansine with CYP1A2, CYP2B6, CYP2C8/9/19, CYP3A4, UGT1A1, and UGT1A9 substrates suggest that it is necessary to carefully characterize the DDI potentials of ADC candidates with mertansine as a payload in the clinic.

HER2-Overexpressing/Amplified Breast Cancer as a Testing Ground for Antibody-Drug Conjugate Drug Development in Solid Tumors

Efficacy data from the KATHERINE clinical trial, comparing the HER2-directed antibody-drug conjugate (ADC) ado-trastuzumab emtansine (T-DM1) to trastuzumab in patients with early-stage HER2-amplified/overexpressing breast cancer with residual disease after neoadjuvant therapy, demonstrates superiority of T-DM1 (HR for invasive disease or death, 0.50; P < 0.001). This establishes foundational precedent for ADCs as effective therapy for treatment of subclinical micrometastasis in an adjuvant (or post-neoadjuvant) early-stage solid tumor setting. Despite this achievement, general principles from proposed systems pharmacokinetic modeling for intracellular processing of ADCs indicate potential shortcomings of T-DM1: (i) C _max limited by toxicities; (ii) slow internalization rate; (iii) resistance mechanisms due to defects in intracellular trafficking [loss of lysosomal transporter solute carrier family 46 member 3, (SLC46A3)], and increased expression of drug transporters MDR1 and MRP1; and (iv) lack of payload bystander effects limiting utility in tumors with heterogeneous HER2 expression. These handicaps may explain the inferiority of T-DM1-based therapy in the neoadjuvant and first-line metastatic HER2⁺ breast cancer settings, and lack of superiority to chemotherapy in HER2⁺ advanced gastric cancer. In this review, we discuss how each of these limitations is being addressed by manipulating internalization and trafficking using HER2:HER2 bispecific or biparatopic antibody backbones, using site-specific, fixed DAR conjugation chemistry, and payload swapping to exploit alternative intracellular targets and to promote bystander effects. Newer HER2-directed ADCs have impressive clinical activity even against tumors with lower levels of HER2 receptor expression. Finally, we highlight ongoing clinical efforts to combine HER2 ADCs with other treatment modalities, including chemotherapy, molecularly targeted therapies, and immunotherapy.

Enfortumab Vedotin, a fully human monoclonal antibody against Nectin 4 conjugated to monomethyl auristatin E for metastatic urothelial Carcinoma

Introduction: The conventional management of most patients with metastatic urothelial carcinoma (UC) is platinum-based chemotherapy followed by immunotherapy. Erdafitinib is an option in post-platinum patients with activating mutations in fibroblast growth factor receptor (FGFR)-3 and -2. Salvage therapy with taxanes or vinflunine has demonstrated minimal efficacy. Enfortumab Vedotin (EV), a monoclonal antibody-drug conjugate (ADC) targeting nectin-4 is under investigation in patients with advanced UC. Areas covered: This review describes the epidemiology and unmet needs of patients with metastatic UC and is focused specifically on heavily treated patients. We explore the rationale for targeting nectin 4 and the clinical development of EV; efficacy and safety data from the completed phase I and II studies are examined. Ongoing trials to definitively assess clinical outcomes in comparison to current therapy and trials exploring EV in combination are also highlighted. Expert opinion: There is an unmet need for new therapies in most patients with advanced UC and who progress after platinum and immunotherapy. EV has shown promising efficacy and safety in this population in phase 1 and 2 trials including those with poor prognostic factors such as liver metastases. Ongoing trials exploring this agent in combination will continue to advance the treatment of UC.

An evaluation of brentuximab vedotin as a treatment option for stage III/IV Hodgkin lymphoma

Introduction: Outcomes of patients with classical Hodgkin lymphoma are excellent, and the intent of frontline therapy for even advanced-stage disease has been curative. This review summarizes the role of brentuximab vedotin in the upfront treatment of advanced stage classical Hodgkin lymphoma in the context of reducing therapy-related toxicity without compromising the high cure rate. Areas covered: Strategies to reduce bleomycin-induced lung toxicity include a response-adapted approach investigated in the RATHL study and a replacement of bleomycin with brentuximab vedotin in frontline chemotherapy regimens. In both studies, omission of bleomycin in the non-standard arms decreased the rate of pulmonary toxicity while maintaining high progression-free survival and overall survival rates. Expert opinion: The approval of A+AVD in North America offers a new bleomycin-free regimen for the treatment of advanced-stage HL, but it must be balanced against a risk-adapted approach. Recently presented subset analyses raise a question about which patients benefit most from this therapy.

Antibody-Drug Conjugates for the Therapy of Thoracic Malignancies

Antibody-drug conjugates (ADCs) are a novel class of therapeutic agents incorporating both target-specific monoclonal antibodies and cytotoxic small molecules via a chemical linker. They were first introduced into the clinic for the treatment of advanced hematologic malignancies. The only approved ADC for solid tumors targets erb-b2 receptor tyrosine kinase (HER2), a validated antigen in breast cancer. Many ADCs are under active investigation for various types of solid tumors. In this article, we review the literature from several perspectives including the design, pharmacology, and mechanism-based toxicities of antibody-drug conjugates. We then discuss ADCs currently in clinical development for thoracic malignancies.

Payload of T-DM1 binds to cell surface cytoskeleton-associated protein 5 to mediate cytotoxicity of hepatocytes

Off-target toxicity is a major cause of dose-limiting toxicity for antibody-drug conjugates (ADCs), mechanisms of which remain poorly understood. Here, we demonstrate that cytoskeleton-associated protein 5 (CKAP5) serves as a cell surface target for T-DM1 and that binding of T-DM1 to CKAP5 is mediated by payload (DM1). This study introduces a novel molecular mechanism of ADC payload-mediated interaction with cell surface molecules to induce cytotoxicity. Upon binding to CKAP5, T-DM1 causes cell membrane damage and leads to calcium influx into the cells, resulting in disorganized microtubule network and apoptosis. While binding of T-DM1 with HER2 is critical for killing HER2-positive tumor cells, our data suggest that cytotoxicity induced by T-DM1 interaction with CKAP5 may preferentially damage normal cells/tissues where HER2 expression is low or missing to cause off-target toxicity. This study provides molecular basis of ADC-induced off-target cytotoxicity and opens a new avenue for developing next generation of ADCs.

ADME Considerations and Bioanalytical Strategies for Pharmacokinetic Assessments of Antibody-Drug Conjugates

Antibody-drug conjugates (ADCs) are a unique class of biotherapeutics of inherent heterogeneity and correspondingly complex absorption, distribution, metabolism, and excretion (ADME) properties. Herein, we consider the contribution of various components of ADCs such as various classes of warheads, linkers, and conjugation strategies on ADME of ADCs. Understanding the metabolism and disposition of ADCs and interpreting exposure-efficacy and exposure-safety relationships of ADCs in the context of their various catabolites is critical for design and subsequent development of a clinically successful ADCs. Sophisticated bioanalytical assays are required for the assessments of intact ADC, total antibody, released warhead and relevant metabolites. Both ligand-binding assays (LBA) and hybrid LBA-liquid chromatography coupled with tandem mass spectrometry (LBA-LC-MS/MS) methods have been employed to assess pharmacokinetics (PK) of ADCs. Future advances in bioanalytical techniques will need to address the rising complexity of this biotherapeutic modality as more innovative conjugation strategies, antibody scaffolds and novel classes of warheads are employed for the next generation of ADCs. This review reflects our considerations on ADME of ADCs and provides a perspective on the current bioanalytical strategies for pharmacokinetic assessments of ADCs.

Bioanalytical workflow for novel scaffold protein–drug conjugates: quantitation of total Centyrin protein, conjugated Centyrin and free payload for Centyrin–drug conjugate in plasma and tissue samples using liquid chromatography–tandem mass spectrometry

Aim: Alternative scaffold proteins have emerged as novel platforms for development of therapeutic applications. One such application is in protein–drug conjugates (PDCs), which are analogous to antibody–drug conjugates. Methodology: Liquid chromatography–mass spectrometry methods for quantitation of total protein, conjugate and free payload for a PDC based on Centyrin scaffold were developed. Tryptic peptides generated from a region of the Centyrin that does not contain a conjugation site, and another that has the conjugation site with the linker-payload attached were used as surrogates of the total and conjugated Centyrin, respectively. Conclusion: The methods were successfully applied to analysis of samples from mice to quantify the plasma and tissue concentrations. This same workflow can potentially be applied to other PDCs and site-specific antibody–drug conjugates.

Recent preclinical and clinical advances in oligonucleotide conjugates

INTRODUCTION

Oligonucleotide therapeutics have the potential to change the way disease is treated due to their ability to modulate gene expression of any therapeutic target in a highly specific and potent manner. Unfortunately, this drug class is plagued with inherently poor pharmacological characteristics, which need to be overcome. The development of a chemical modification library for oligonucleotides has addressed many of the initial challenges, but delivery of these payloads across plasma membranes remains difficult. The latest technological advances in oligonucleotide therapeutics utilizes direct conjugation to targeting ligands, which has improved bioavailability and target tissue exposure many-fold. The success of this approach has resulted in numerous clinical programs over the past 5 years.

AREAS COVERED

We review the literature on oligonucleotide conjugate strategies which have proven effective preclinically and clinically. We summarize the chemical modifications which allow parenteral administration as well as evaluate the efficacy of a multitude of conjugate approaches including lipids, peptides, carbohydrates, and antibodies.

EXPERT OPINION

The success of future conjugate strategies will likely rely on the effective combination of characteristics from earlier technologies. High-affinity ligand-receptor interactions can be critical to achieving meaningful accumulation in target tissues, but pharmacokinetic modulators which increase the circulating half-life may also be necessary. Synthesis of these approaches has the potential to bring the next breakthrough in oligonucleotide therapeutics.

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

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

Noninvasive Trafficking of Brentuximab Vedotin and PET Imaging of CD30 in Lung Cancer Murine Models

CD30 has been considered a unique diagnostic and therapeutic target for CD30-positive lymphomas and some lung diseases. Additionally, CD30 has shown high expression in clinical lung cancer samples. In this study, ⁸⁹Zr-radiolabeled brentuximab vedotin (BV) was developed for in vivo tracking of BV and imaging CD30 expression in lung cancer models via conjugation with desferrioxamine (Df). CD30 expression in three lung cancer cell lines (H460, H358, and A549) was quantified by Western blot. Flow cytometry and saturation binding assays were used to evaluate the binding capabilities of the tracer in vitro. After longitudinal positron emission tomography (PET) imaging and quantitative analysis were performed, ex vivo biodistribution and histological studies were used to verify PET results. Finally, dosimetric extrapolation of murine data to humans was performed. At the cellular level, CD30 was found to be expressed on H460 and A549 cells with the highest and lowest levels of expression, respectively. Both Df-BV and ⁸⁹Zr-Df-BV displayed high binding affinity to H460 cells. PET images and their quantification verified that BV accumulated in H460 tumor models (9.93 ± 2.70% ID/g at 24 h after injection; n = 4) at the highest level, followed by H358 and A549 tumors (8.05 ± 2.43 and 5.00 ± 1.56% ID/g; n = 4). The nonspecific ⁸⁹Zr-labeled IgG showed a low tumor uptake of 5.2 ± 1.0% ID/g for H460 models. Ex vivo biodistribution and fluorescence immunohistochemistry also corroborated these findings. Dosimetric results displayed safe dose estimations. Therefore, ⁸⁹Zr-Df-BV provides a potential agent for evaluating CD30 expression noninvasively in lung cancer, and also for imaging of brentuximab vedotin for better understanding of its pharmacokinetics.

Antibody structure and engineering considerations for the design and function of Antibody Drug Conjugates (ADCs)

Antibody-drug conjugates (ADCs) are emerging as effective tools in cancer therapy, combining the antibody's exquisite specificity for the target antigen-expressing cancer cell together with the cytotoxic potency of the payload. Much success stems from the rational design of "toxic warheads", chemically linked to antibodies, and from fine-tuning the intricate properties of chemical linkers. Here, we focus on the antibody moiety of ADCs, dissecting the impact of Fab, linkers, isotype and Fc structure on the anti-tumoral and immune-activating functions of ADCs. Novel design approaches informed by antibody structural attributes present opportunities that may contribute to the success of next generation ADCs.