Pharmacokinetics of trastuzumab deruxtecan (T-DXd), a novel anti-HER2 antibody-drug conjugate, in HER2-positive tumour-bearing mice

Antibody-drug conjugates for non-small cell lung cancer: Advantages and challenges in clinical translation

Lung cancer is the leading cause of cancer death, with non-small cell lung cancer (NSCLC) accounting for approximately 85 % of all lung cancers and having a poor treatment and prognosis. Conventional clinical chemotherapy and immunotherapy are challenged by systemic toxicity and drug resistance, so researchers are increasingly focusing on antibody-drug conjugate (ADC), an innovative concept combining chemotherapy and targeted therapy, in which a drug selectively binds to antigens on the surface of a tumor cell via antibodies, which internalize the ADC, and then transfers the ADC to the lysosome via the endosomes to degrade the drug and kill the tumor cell. Despite the promising nature of ADCs, no ADC product for any indication including NSCLC has been approved for marketing by the FDA to date. In this review, we summarize the main advantages of ADCs and discuss in depth the design of the most desirable ADCs for NSCLC therapy. In addition to preclinical studies, we focus on the current state of clinical research on ADCs as interventions for the treatment of NSCLC by summarizing real-time clinical trial data from ClinicalTrials.gov, and reasonably speculate on the direction of the design of future generations of ADCs.

Development of an ELISA with acidification treatment for an antibody conjugate incorporating Exatecans

The successful development of Sacituzumab Govitecan and Trastuzumab Deruxtecan has made camptothecin derivatives one of the most popular payloads for antibody-drug conjugates (ADCs). Camptothecin and its derivatives all exist in a pH-dependent equilibrium between the carboxylate and lactone forms. Such transformation may lead to differences in the ratio of the two molecular forms in calibration standards and biological matrix (bio-matrix) samples, thereby leading to inaccurate conjugated antibody results. In this study, we reported an enzyme-linked immunosorbent assay (ELISA) free of the aforementioned influence for the detection of the Exatecans-conjugated antibody (conjugated SM001) in cynomolgus monkey serum. The assay was developed by first acidifying all samples with glacial acetic acid (HAc), then performing neutralization and thereafter capturing conjugated SM001 with anti-Exatecan monoclonal antibody (mAb) and detecting it with biotinylated Nectin4 (hNectin4-Bio) and horseradish peroxidase-labeled streptavidin (SA-HRP). Results showed that all tested performance parameters met the acceptance criteria. The conjugated SM001 concentrations obtained were in parallel to but slightly lower than total antibody (TAb) throughout the pharmacokinetic (PK) study, revealing that the assay strategy implemented for conjugated SM001 measurement worked well for the elimination of interference triggered by the heterogeneous existence of the lactone and carboxylate forms of Exatecan (lactone-Exatecan and carboxylate-Exatecan).

Quantitative evaluation of trastuzumab deruxtecan pharmacokinetics and pharmacodynamics in mouse models of varying degrees of HER2 expression

Trastuzumab deruxtecan (T-DXd; DS-8201; ENHERTU®) is a human epithelial growth factor receptor 2 (HER2)-directed antibody drug conjugate (ADC) with demonstrated antitumor activity against a range of tumor types. Aiming to understand the relationship between antigen expression and downstream efficacy outcomes, T-DXd was administered in tumor-bearing mice carrying NCI-N87, Capan-1, JIMT-1, and MDA-MB-468 xenografts, characterized by varying HER2 levels. Plasma pharmacokinetics (PK) of total antibody, T-DXd, and released DXd and tumor concentrations of released DXd were evaluated, in addition to monitoring γΗ2AX and pRAD50 pharmacodynamic (PD) response. A positive relationship was observed between released DXd concentrations in tumor and HER2 expression, with NCI-N87 xenografts characterized by the highest exposures compared to the remaining cell lines. γΗ2AX and pRAD50 demonstrated a sustained increase over several days occurring with a time delay relative to tumoral-released DXd concentrations. In vitro investigations of cell-based DXd disposition facilitated the characterization of DXd kinetics across tumor cells. These outputs were incorporated into a mechanistic mathematical model, utilized to describe PK/PD trends. The model captured plasma PK across dosing arms as well as tumor PK in NCI-N87, Capan-1, and MDA-MB-468 models; tumor concentrations in JIMT-1 xenografts required additional parameter adjustments reflective of complex receptor dynamics. γΗ2AX longitudinal trends were well characterized via a unified PD model implemented across xenografts demonstrating the robustness of measured PD trends. This work supports the application of a mechanistic model as a quantitative tool, reliably projecting tumor payload concentrations upon T-DXd administration, as the first step towards preclinical-to-clinical translation.

Unveiling the intra-tumor fate of trastuzumab deruxtecan in a xenograft model to support its mechanism of action

Trastuzumab deruxtecan (T-DXd) is an antibody-drug conjugate used for cancer treatment comprising an anti-human epidermal growth factor receptor type 2 (HER2) antibody and the topoisomerase I inhibitor DXd. The present study investigated the intratumor fate of T-DXd. Fluorescence-labeled T-DXd was found to accumulate in tumors of HER2-positive tumor xenograft mice and was observed to be distributed within lysosomes of in vitro tumor cells in accordance with their HER2 expression. DXd was released by cysteine proteases, including cathepsins, in lysosomal fractions in vitro in response to the pH. Tumor slices obtained from HER2-positive tumor xenograft mice treated with T-DXd were examined by semi-quantitative and three-dimensional immunohistochemical assays using phosphor-integrated dots, which visualized DXd-related signals in the nucleus, the site of topoisomerase I inhibition. In addition, based on the data showing the antibody component of T-DXd barely distributed in the nucleus, it was suggested that the DXd-related signals detected in the nucleus were predominantly derived from free DXd. These observations help support the mode of action of T-DXd from the perspective of drug disposition.

Quantitative systems pharmacology modeling of HER2-positive metastatic breast cancer for translational efficacy evaluation and combination assessment across therapeutic modalities

HER2-positive (HER2+) metastatic breast cancer (mBC) is highly aggressive and a major threat to human health. Despite the significant improvement in patients' prognosis given the drug development efforts during the past several decades, many clinical questions still remain to be addressed such as efficacy when combining different therapeutic modalities, best treatment sequences, interindividual variability as well as resistance and potential coping strategies. To better answer these questions, we developed a mechanistic quantitative systems pharmacology model of the pathophysiology of HER2+ mBC that was extensively calibrated and validated against multiscale data to quantitatively predict and characterize the signal transduction and preclinical tumor growth kinetics under different therapeutic interventions. Focusing on the second-line treatment for HER2+ mBC, e.g., antibody-drug conjugates (ADC), small molecule inhibitors/TKI and chemotherapy, the model accurately predicted the efficacy of various drug combinations and dosing regimens at the in vitro and in vivo levels. Sensitivity analyses and subsequent heterogeneous phenotype simulations revealed important insights into the design of new drug combinations to effectively overcome various resistance scenarios in HER2+ mBC treatments. In addition, the model predicted a better efficacy of the new TKI plus ADC combination which can potentially reduce drug dosage and toxicity, while it also shed light on the optimal treatment ordering of ADC versus TKI plus capecitabine regimens, and these findings were validated by new in vivo experiments. Our model is the first that mechanistically integrates multiple key drug modalities in HER2+ mBC research and it can serve as a high-throughput computational platform to guide future model-informed drug development and clinical translation.

Trastuzumab deruxtecan in breast cancer

Trastuzumab deruxtecan (T-DXd) is an antibody-drug conjugate (ADC) consisting of a humanised, anti-human epidermal growth factor receptor 2 (HER2) monoclonal antibody covalently linked to a topoisomerase I inhibitor cytotoxic payload (DXd). The high drug-to-antibody ratio (8:1) ensures a high DXd concentration is delivered to target tumour cells, following internalisation of T-DXd and subsequent cleavage of its tetrapeptide-based linker. DXd's membrane-permeable nature enables it to cross cell membranes and potentially exert antitumour activity on surrounding tumour cells regardless of HER2 expression. T-DXd's unique mechanism of action is reflected in its efficacy in clinical trials in patients with HER2-positive advanced breast cancer (in heavily pretreated populations and in those previously treated with a taxane and trastuzumab), as well as HER2-low metastatic breast cancer. Thus, ADCs such as T-DXd have the potential to change the treatment paradigm of targeting HER2 in metastatic breast cancer, including eventually within the adjuvant/neoadjuvant setting.

Prognosis and influencing factors of ER-positive, HER2-low breast cancer patients with residual disease after neoadjuvant chemotherapy: a retrospective study

Previously, we found that patients with estrogen receptor (ER)-positive, HER2-low breast cancer are resistant to neoadjuvant chemotherapy (NACT) and have worse outcomes than those who achieve pathological complete response (pCR) after NACT. This study aimed to investigate the prognosis and influencing factors in these patients. A total of 618 patients with ER-positive breast cancer who received standard thrice-weekly NACT were enrolled, including 411 patients with ER-positive, HER2-low breast cancer. Data on the clinicopathological features of these patients before and after NACT were collected. Univariate and multivariate Cox regression analyses were used to identify the independent factors affecting 5-year disease-free survival (DFS). Among the ER-positive, HER2-low patients, 49 (11.9%) achieved a pCR after NACT. A significant difference in survival was observed between patients with and without residual disease after NACT. Additionally, changes in immunohistochemical markers and tumor stages before and after NACT were found to be significant. According to univariate and multivariate analyses, cN_stage (P = 0.002), ER (P = 0.002) and Ki67 (P = 0.023) expression before NACT were significantly associated with 5-year DFS, while pT_stage (P = 0.015), pN_stage (P = 0.029), ER (P = 0.020) and Ki67 (P < 0.001) levels after NACT were related to 5-year DFS in ER-positive, HER2-low patients with residual disease. Our study suggested that high proliferation, low ER expression and advanced stage before and after NACT are associated with a poor prognosis, providing useful information for developing long-term treatment strategies for ER-positive, HER2-low breast cancer in patients with residual disease in the future.

Rational Identification of Novel Antibody-Drug Conjugate with High Bystander Killing Effect against Heterogeneous Tumors

Bystander-killing payloads can significantly overcome the tumor heterogeneity issue and enhance the clinical potential of antibody-drug conjugates (ADC), but the rational design and identification of effective bystander warheads constrain the broader implementation of this strategy. Here, graph attention networks (GAT) are constructed for a rational bystander killing scoring model and ADC construction workflow for the first time. To generate efficient bystander-killing payloads, this model is utilized for score-directed exatecan derivatives design. Among them, Ed9, the most potent payload with satisfactory permeability and bioactivity, is further used to construct ADC. Through linker optimization and conjugation, novel ADCs are constructed that perform excellent anti-tumor efficacy and bystander-killing effect in vivo and in vitro. The optimal conjugate T-VEd9 exhibited therapeutic efficacy superior to DS-8201 against heterogeneous tumors. These results demonstrate that the effective scoring approach can pave the way for the discovery of novel ADC with promising bystander payloads to combat tumor heterogeneity.

Development and approval of novel injectables: enhancing therapeutic innovations

INTRODUCTION

Novel injectables possess applications in both local and systemic therapeutics delivery. The advancement in utilized materials for the construction of complex injectables has tremendously upgraded their safety and efficacy.

AREAS COVERED

This review focuses on various strategies to produce novel injectables, including oily dispersions, in situ forming implants, injectable suspensions, microspheres, liposomes, and antibody-drug conjugates. We herein present a detailed description of complex injectable technologies and their related drug formulations permitted for clinical use by the United States Food and Drug Administration (USFDA). The excipients used, their purpose and the challenges faced during manufacturing such formulations have been critically discussed.

EXPERT OPINION

Novel injectables can deliver therapeutic agents in a controlled way at the desired site. However, several challenges persist with respect to their genericization. Astronomical costs incurred by innovator companies during product development, complexity of the product itself, supply limitations with respect to raw materials, intricate manufacturing processes, patent evergreening, product life-cycle extensions, relatively few and protracted generic approvals contribute to the exorbitant prices and access crunch. Moreover, regulatory guidance are grossly underdeveloped and significant efforts have to be directed toward development of effective characterization techniques.

Delivery of a BET protein degrader via a CEACAM6-targeted antibody-drug conjugate inhibits tumour growth in pancreatic cancer models

Pancreatic ductal adenocarcinoma (PDAC) has the worst prognosis of all cancers. To improve PDAC therapy, we establish screening systems based on organoid and co-culture technologies and find a payload of antibody-drug conjugate (ADC), a bromodomain and extra-terminal (BET) protein degrader named EBET. We select CEACAM6/CD66c as an ADC target and developed an antibody, #84.7, with minimal reactivity to CEACAM6-expressing normal cells. EBET-conjugated #84.7 (84-EBET) has lethal effects on various PDAC organoids and bystander efficacy on CEACAM6-negative PDAC cells and cancer-associated fibroblasts. In mouse studies, a single injection of 84-EBET induces marked tumor regression in various PDAC-patient-derived xenografts, with a decrease in the inflammatory phenotype of stromal cells and without significant body weight loss. Combination with standard chemotherapy or PD-1 antibody induces more profound and sustained regression without toxicity enhancement. Our preclinical evidence demonstrates potential efficacy by delivering BET protein degrader to PDAC and its microenvironment via CEACAM6-targeted ADC.

Drug conjugates for the treatment of lung cancer: from drug discovery to clinical practice

A drug conjugate consists of a cytotoxic drug bound via a linker to a targeted ligand, allowing the targeted delivery of the drug to one or more tumor sites. This approach simultaneously reduces drug toxicity and increases efficacy, with a powerful combination of efficient killing and precise targeting. Antibody‒drug conjugates (ADCs) are the best-known type of drug conjugate, combining the specificity of antibodies with the cytotoxicity of chemotherapeutic drugs to reduce adverse reactions by preferentially targeting the payload to the tumor. The structure of ADCs has also provided inspiration for the development of additional drug conjugates. In recent years, drug conjugates such as ADCs, peptide‒drug conjugates (PDCs) and radionuclide drug conjugates (RDCs) have been approved by the Food and Drug Administration (FDA). The scope and application of drug conjugates have been expanding, including combination therapy and precise drug delivery, and a variety of new conjugation technology concepts have emerged. Additionally, new conjugation technology-based drugs have been developed in industry. In addition to chemotherapy, targeted therapy and immunotherapy, drug conjugate therapy has undergone continuous development and made significant progress in treating lung cancer in recent years, offering a promising strategy for the treatment of this disease. In this review, we discuss recent advances in the use of drug conjugates for lung cancer treatment, including structure-based drug design, mechanisms of action, clinical trials, and side effects. Furthermore, challenges, potential approaches and future prospects are presented.

Impact of Complex Apoptotic Signaling Pathways on Cancer Cell Sensitivity to Therapy

Anticancer drugs induce apoptotic and non-apoptotic cell death in various cancer types. The signaling pathways for anticancer drug-induced apoptotic cell death have been shown to differ between drug-sensitive and drug-resistant cells. In atypical multidrug-resistant leukemia cells, the c-Jun/activator protein 1 (AP-1)/p53 signaling pathway leading to apoptotic death is altered. Cancer cells treated with anticancer drugs undergo c-Jun/AP-1-mediated apoptotic death and are involved in c-Jun N-terminal kinase activation and growth arrest- and DNA damage-inducible gene 153 (Gadd153)/CCAAT/enhancer-binding protein homologous protein pathway induction, regardless of the p53 genotype. Gadd153 induction is associated with mitochondrial membrane permeabilization after anticancer drug treatment and involves a coupled endoplasmic reticulum stress response. The induction of apoptosis by anticancer drugs is mediated by the intrinsic pathway (cytochrome c, Cyt c) and subsequent activation of the caspase cascade via proapoptotic genes (e.g., Bax and Bcl-xS) and their interactions. Anticancer drug-induced apoptosis involves caspase-dependent and caspase-independent pathways and occurs via intrinsic and extrinsic pathways. The targeting of antiapoptotic genes such as Bcl-2 enhances anticancer drug efficacy. The modulation of apoptotic signaling by Bcl-xS transduction increases the sensitivity of multidrug resistance-related protein-overexpressing epidermoid carcinoma cells to anticancer drugs. The significance of autophagy in cancer therapy remains to be elucidated. In this review, we summarize current knowledge of cancer cell death-related signaling pathways and their alterations during anticancer drug treatment and discuss potential strategies to enhance treatment efficacy.

Development and Validation of an ADA-Tolerant Assay for Quantification of an Exatecan-Based ADC in Monkey Plasma

BACKGROUND

The development of an anti-drug antibody (ADA)-tolerant pharmacokinetic (PK) assay is important when the drug exposure is irrelevant to toxicity in the presence of ADA. We aimed to develop and validate an ADA-tolerant assay for an exatecan-based antibody-drug conjugate (ADC) in monkey plasma.

RESULTS

The assay tolerated 5.00 µg/mL of ADA at 12 µg/mL of ADC. Its accuracy and precision results satisfied the acceptance criteria. Furthermore, the assay was free from hook and matrix effects and exhibited good dilutional linearity. Additionally, the ADC in plasma samples was stable under different storage conditions.

METHOD

An ADA-tolerant ADC assay was configured with an anti-payload antibody for capture, and a drug-target protein combined with a horseradish peroxidase (HRP)-labeled antibody against a drug-target-protein tag for detection. Samples were firstly acidified to dissociate drug and ADA complexes, and to convert the carboxylate form to the lactone form of exatecan molecules; then, the ADAs in the samples were removed with a naked antibody-coated microplate. The treated samples were further incubated with coated anti-payload antibody and captured ADC molecules were quantified by the detection reagent. The developed assay was optimized and validated against regulatory guidelines.

CONCLUSIONS

The assay met both methodological and sample-related ADA tolerance requirements, and was applicable to a nonclinical study in cynomolgus monkeys.

Exploring DESTINY: the Past, Present, and Future of Trastuzumab Deruxtecan

PURPOSE OF REVIEW

HER2-positive breast cancer accounts for 10-15% of all breast cancers and fam-trastuzumab deruxtecan (T-DXd) has played a major role in moving the treatment of HER2-expressing disease forward.

RECENT FINDINGS

T-DXd is a novel antibody-drug conjugate (ADC) composed of a humanized IgG1 monoclonal antibody against HER2 receptor bound to a potent topoisomerase I cytotoxin payload by a cleavable peptide linker. It has been shown to have robust preclinical activity in pretreated cancer cell lines, as well as meaningful clinical activity in advanced HER2-expressing breast cancer. Recent studies have demonstrated T-DXd as an active agent for metastatic HER2-positive patients, and as a viable additional line for heavily pretreated patients with HER2-low disease. The toxicity of T-DXd remains manageable and burden of side effects seems to be lower when offered as an earlier line of therapy over the course of treatment. In this review, we discuss the pharmacology of T-DXd, review pertinent preclinical and clinical data, and address potential challenges and future directions related to the use of T-DXd in clinical practice.

Synthesis and biological evaluation of novel quaternary ammonium antibody drug conjugates based on camptothecin derivatives

Antibody drug conjugates (ADCs) have emerged as a highly promising class of cancer therapeutics, comprising antibodies, effector molecules, and linkers. Among them, DS-8201a with DXd as the effector molecule, has shown remarkable anti-tumor efficacy against solid tumors, sparking a surge of interest in ADCs with camptothecin derivatives as ADC effector molecules. In this study, we introduced and successfully constructed quaternary ammonium ADCs utilizing camptothecin derivatives WL-14 and CPTS-1 for the first time. All four ADCs displayed excellent stability under physiological conditions and in plasma, facilitating their prolonged circulation in vivo. Moreover, the four ADCs, employing Val-Cit or Val-Ala dipeptide linkers effectively achieved complete release of the effector molecules via cathepsin B. Although, the in vitro antitumor activity of these ADCs was comparatively limited, the development of quaternary ammonium ADCs based on novel camptothecin derivatives as effector molecules is still a viable and promising strategy. Significantly, our study provides valuable insights into the crucial role of linker optimization in ADCs design.

Towards a platform quantitative systems pharmacology (QSP) model for preclinical to clinical translation of antibody drug conjugates (ADCs)

A next generation multiscale quantitative systems pharmacology (QSP) model for antibody drug conjugates (ADCs) is presented, for preclinical to clinical translation of ADC efficacy. Two HER2 ADCs (trastuzumab-DM1 and trastuzumab-DXd) were used for model development, calibration, and validation. The model integrates drug specific experimental data including in vitro cellular disposition data, pharmacokinetic (PK) and tumor growth inhibition (TGI) data for T-DM1 and T-DXd, as well as system specific data such as properties of HER2, tumor growth rates, and volumes. The model incorporates mechanistic detail at the intracellular level, to account for different mechanisms of ADC processing and payload release. It describes the disposition of the ADC, antibody, and payload inside and outside of the tumor, including binding to off-tumor, on-target sinks. The resulting multiscale PK model predicts plasma and tumor concentrations of ADC and payload. Tumor payload concentrations predicted by the model were linked to a TGI model and used to describe responses following ADC administration to xenograft mice. The model was translated to humans and virtual clinical trial simulations were performed that successfully predicted progression free survival response for T-DM1 and T-DXd for the treatment of HER2+ metastatic breast cancer, including differential efficacy based upon HER2 expression status. In conclusion, the presented model is a step toward a platform QSP model and strategy for ADCs, integrating multiple types of data and knowledge to predict ADC efficacy. The model has potential application to facilitate ADC design, lead candidate selection, and clinical dosing schedule optimization.

Transition of average drug-to-antibody ratio of trastuzumab deruxtecan in systemic circulation in monkeys using a hybrid affinity capture liquid chromatography-tandem mass spectrometry

Trastuzumab deruxtecan (T-DXd, DS-8201a) is an antibody-drug conjugate, comprising an anti-HER2 antibody at a drug-to-antibody ratio of 7-8 with the topoisomerase I inhibitor DXd. In this study, the concentrations of antibody-conjugated DXd and total antibody were determined and observed to decrease over time following intravenous administration of T-DXd to monkeys. The drug-to-antibody ratio of T-DXd also decreased in a time-dependent manner, which reached approximately 2.5 in 21 days after administration. It was suggested that antibody-conjugated DXd of T-DXd was relatively stable in vivo compared with that of other reported antibody-drug conjugates.

The emergence of targeted therapy for HER2-low triple-negative breast cancer: a review of fam-trastuzumab deruxtecan

INTRODUCTION

Metastatic triple-negative breast cancer (TNBC) is an aggressive sub-type of breast cancer. Despite recent advances, metastatic TNBC remains difficult to treat with limited targeted treatment options. Fam-trastuzumab deruxtecan (T-DXd), is a novel antibody-drug conjugate (ADC) targeting human epidermal growth factor receptor 2 (HER2) and is composed of a unique linker bound to the topoisomerase I inhibitor DXd. T-DXd has significant anti-tumor activity in patients with HER2-low TNBC.

AREAS COVERED

This review reports on the mechanism, pre-clinical/clinical studies, efficacy, and tolerability of T-DXd. A literature search was conducted via PubMed using keywords such as 'fam-trastuzumab deruxtecan,' 'Enhertu,' and 'HER2-low cancers.'

EXPERT OPINION

The Phase III Destiny-Breast04 Trial showed benefit in progression-free and overall survival in patients with HER2-low metastatic breast cancers treated with T-DXd compared to treatment of physician's choice chemotherapy. T-DXd is the first pharmaceutical to effectively target a HER2-low population with clinically meaningful efficacy in patients with HER2-low TNBC. Compared to chemotherapy, T-DXd has a similar safety profile, with the additional need for close monitoring for interstitial lung disease. Given the clinical activity of T-DXd in TNBC, it is likely there will be continued efforts to refine HER2-low diagnostics and to develop additional ADCs with other protein targets.

Population Pharmacokinetics of Patritumab Deruxtecan in Patients With Solid Tumors

Patritumab deruxtecan is an antibody-drug conjugate consisting of a fully human monoclonal antibody against human epidermal growth factor receptor 3 (HER3) attached to a topoisomerase I inhibitor payload via a tetrapeptide-based cleavable linker. As part of the pharmacometric analysis informing dose selection for later-stage development, population pharmacokinetics (PK) analysis of patritumab deruxtecan was conducted with pooled serum PK data from patients with HER3-expressing solid tumors (from 3 phase 1/2 studies in breast, lung, and colorectal cancer; N = 425) treated over the dose range of 1.6 to 8.0 mg/kg intravenously every 3 weeks. Population PK modeling for deruxtecan (DXd)-conjugated antibody (representing patritumab deruxtecan) and unconjugated MAAA-1181a (DXd, payload) was carried out sequentially. DXd-conjugated antibody PK was described using a 2-compartment model with parallel linear and nonlinear clearance. Unconjugated DXd PK was described using a 1-compartment model with linear clearance and release of DXd as a first-order, time-dependent function of the level of DXd-conjugated antibody in the central compartment. Preliminary covariate evaluation was conducted for prespecified covariates of pharmacological plausibility and clinical interest. The final model retained weight (on linear clearance and central volume) and albumin level, sex, and tumor type (on linear clearance) for DXd-conjugated antibody, and weight (on release rate constant) and hepatic function (on clearance) for unconjugated DXd. Effects of these covariates on the exposure metrics were generally mild and did not require dose adjustment for subpopulations in subsequent development. Further PK characterization for patritumab deruxtecan will evolve with emerging data.

An Enzymatically Cleavable Tripeptide Linker for Maximizing the Therapeutic Index of Antibody-Drug Conjugates

Valine-citrulline is a protease-cleavable linker commonly used in many drug delivery systems, including antibody-drug conjugates (ADC) for cancer therapy. However, its suboptimal in vivo stability can cause various adverse effects such as neutropenia and hepatotoxicity, leading to dose delays or treatment discontinuation. Here, we report that glutamic acid-glycine-citrulline (EGCit) linkers have the potential to solve this clinical issue without compromising the ability of traceless drug release and ADC therapeutic efficacy. We demonstrate that our EGCit ADC resists neutrophil protease-mediated degradation and spares differentiating human neutrophils. Notably, our anti-HER2 ADC shows almost no sign of blood and liver toxicity in healthy mice at 80 mg kg-1. In contrast, at the same dose level, the FDA-approved anti-HER2 ADCs Kadcyla and Enhertu show increased levels of serum alanine aminotransferase and aspartate aminotransferase and morphologic changes in liver tissues. Our EGCit conjugates also exert greater antitumor efficacy in multiple xenograft tumor models compared with Kadcyla and Enhertu. This linker technology could substantially broaden the therapeutic windows of ADCs and other drug delivery agents, providing clinical options with improved efficacy and safety.

Trastuzumab Deruxtecan, Antibody-Drug Conjugate Targeting HER2, Is Effective in Pediatric Malignancies: A Report by the Pediatric Preclinical Testing Consortium

HER2 is expressed in many pediatric solid tumors and is a target for innovative immune therapies including CAR-T cells and antibody-drug conjugates (ADC). We evaluated the preclinical efficacy of trastuzumab deruxtecan (T-DXd, DS-8201a), a humanized monoclonal HER2-targeting antibody conjugated to a topoisomerase 1 inhibitor, DXd, in patient- and cell line-derived xenograft (PDX/CDX) models. HER2 mRNA expression was determined using RNA-seq and protein expression via IHC across multiple pediatric tumor PDX models. Osteosarcoma (OS), malignant rhabdoid tumor (MRT), and Wilms tumor (WT) models with varying HER2 expression were tested using 10 mice per group. Additional histologies such as Ewing sarcoma (EWS), rhabdomyosarcoma (RMS), neuroblastoma (NB), and brain tumors were evaluated using single mouse testing (SMT) experiments. T-DXd or vehicle control was administered intravenously to mice harboring established flank tumors at a dose of 5 mg/kg on day 1. Event-free survival (EFS) and objective response were compared between treatment and control groups. HER2 mRNA expression was observed across histologies, with the highest expression in WT (median = 22 FPKM), followed by MRT, OS, and EWS. The relationship between HER2 protein and mRNA expression was inconsistent. T-DXd significantly prolonged EFS in 6/7 OS, 2/2 MRT, and 3/3 WT PDX models. Complete response (CR) or maintained CR (MCR) were observed for 4/5 WT and MRT models, whereas stable disease was the best response among OS models. SMT experiments also demonstrated activity across multiple solid tumors. Clinical trials assessing the efficacy of a HER2-directed ADC in pediatric patients with HER2-expressing tumors should be considered.

ABBV-011, A Novel, Calicheamicin-Based Antibody-Drug Conjugate, Targets SEZ6 to Eradicate Small Cell Lung Cancer Tumors

In the past year, four antibody-drug conjugates (ADC) were approved, nearly doubling the marketed ADCs in oncology. Among other attributes, successful ADCs optimize targeting antibody, conjugation chemistry, and payload mechanism of action. Here, we describe the development of ABBV-011, a novel SEZ6-targeted, calicheamicin-based ADC for the treatment of small cell lung cancer (SCLC). We engineered a calicheamicin conjugate that lacks the acid-labile hydrazine linker that leads to systemic release of a toxic catabolite. We then screened a patient-derived xenograft library to identify SCLC as a tumor type with enhanced sensitivity to calicheamicin ADCs. Using RNA sequencing (RNA-seq) data from primary and xenograft SCLC samples, we identified seizure-related homolog 6 (SEZ6) as a surface-expressed SCLC target with broad expression in SCLC and minimal normal tissue expression by both RNA-seq and IHC. We developed an antibody targeting SEZ6 that is rapidly internalized upon receptor binding and, when conjugated to the calicheamicin linker drug, drives potent tumor regression in vitro and in vivo. These preclinical data suggest that ABBV-011 may provide a novel treatment for patients with SCLC and a rationale for ongoing phase I studies (NCT03639194).

Antibody-drug conjugates: Resurgent anticancer agents with multi-targeted therapeutic potential

Antibody-drug conjugates (ADCs) constitute a relatively new group of anticancer agents, whose first appearance took place about two decades ago, but a renewed interest occurred in recent years, following the success of anti-cancer immunotherapy with monoclonal antibodies. Indeed, an ADC combines the selectivity of a monoclonal antibody with the cell killing properties of a chemotherapeutic agent (payload), joined together through an appropriate linker. The antibody moiety targets a specific cell surface antigen expressed by tumor cells and/or cells of the tumor microenvironment and acts as a carrier that delivers the cytotoxic payload within the tumor mass. Despite advantages in terms of selectivity and potency, the development of ADCs is not devoid of challenges, due to: i) low tumor selectivity when the target antigens are not exclusively expressed by cancer cells; ii) premature release of the cytotoxic drug into the bloodstream as a consequence of linker instability; iii) development of tumor resistance mechanisms to the payload. All these factors may result in lack of efficacy and/or in no safety improvement compared to unconjugated cytotoxic agents. Nevertheless, the development of antibodies engineered to remain inert until activated in the tumor (e.g., antibodies activated proteolytically after internalization or by the acidic conditions of the tumor microenvironment) together with the discovery of innovative targets and cytotoxic or immunomodulatory payloads, have allowed the design of next-generation ADCs that are expected to possess improved therapeutic properties. This review provides an overview of approved ADCs, with related advantages and limitations, and of novel targets exploited by ADCs that are presently under clinical investigation.

Datopotamab Deruxtecan, a Novel TROP2-directed Antibody-drug Conjugate, Demonstrates Potent Antitumor Activity by Efficient Drug Delivery to Tumor Cells

Trophoblast cell surface antigen 2 (TROP2) is highly expressed on various epithelial tumors and correlates with poor prognosis. We developed the novel TROP2-directed antibody-drug conjugate (ADC), datopotamab deruxtecan (Dato-DXd, DS-1062a), with a potent DNA topoisomerase I inhibitor (DXd), and evaluated its antitumor activity and safety profiles in preclinical models.The pharmacologic activity and mechanism of action of Dato-DXd were investigated in several human cancer cell lines and xenograft mouse models including patient-derived xenograft (PDX) models. Safety profiles were also assessed in rats and cynomolgus monkeys.Dato-DXd bound specifically to TROP2 and was internalized into tumor cells followed by intracellular trafficking to lysosome and DXd release, which induced DNA damage and apoptosis in TROP2-expressing tumor cells in vitro. Dato-DXd exhibited in vivo antitumor activity with DNA damage induced by the accumulated DXd in TROP2-expressing xenograft tumors, but neither isotype control IgG-ADC nor anti-TROP2 antibody had this effect. Dato-DXd also showed potent antitumor activity with tumor regression in several TROP2-expressing xenograft tumors including NSCLC PDX models. Safety profiles of Dato-DXd in rats and cynomolgus monkeys were acceptable.Dato-DXd demonstrated potent antitumor activity against TROP2-expressing tumors by efficient payload delivery into tumors and acceptable safety profiles in preclinical models. These results suggest Dato-DXd could be a valuable treatment option for patients with TROP2-expressing tumors in the clinical setting.

Spotlight on Trastuzumab Deruxtecan (DS-8201,T-DXd) for HER2 Mutation Positive Non-Small Cell Lung Cancer

Human epidermal growth factor receptor 2 (HER2) is a proto-oncogene that, when mutated or overexpressed, plays an important role in oncogenesis. The landscape of HER2-positive breast cancer has changed dramatically over the past 2 decades with the FDA approval of a growing number of agents (antibodies, tyrosine kinase inhibitors, and antibody-drug conjugates) targeting the HER2 receptor. HER2 inhibition has also been approved for HER2-positive gastric cancer. HER2 is amplified in 9% and mutated in 3% of lung cancer. Historically, HER2-targeted therapy for lung cancer with trastuzumab, pertuzumab, and trastuzumab emtansine has failed to demonstrate a survival benefit. Trastuzumab deruxtecan (T-DXd) is a novel antibody–drug conjugate with a tetrapeptide linker, which delivers a topoisomerase I inhibitor with a drug-to-antibody ratio of 7~8. The potency of the active payload, as well as its significant bystander effect, resulted in significant anti-tumor activity. The DESTINY-Lung01 trial evaluated T-DXd in HER2-positive non-squamous non-small cell lung cancer (NSCLC) and reported a progression-free survival of 14 months in HER2-mutated NSCLC, earning its breakthrough designation by the FDA. In this review, we will discuss the structural characteristics, pharmacodynamics, and pharmacokinetics of T-DXd. We will also shed light on the preclinical and ongoing clinical trials of T-DXd along with future directions in the management of HER2 positive lung cancer.

Trial watch: intratumoral immunotherapy

While chemotherapy and radiotherapy remain the first-line approaches for the management of most unresectable tumors, immunotherapy has emerged in the past two decades as a game-changing treatment, notably with the clinical success of immune checkpoint inhibitors. Immunotherapies aim at (re)activating anticancer immune responses which occur in two main steps: (1) the activation and expansion of tumor-specific T cells following cross-presentation of tumor antigens by specialized myeloid cells (priming phase); and (2) the immunological clearance of malignant cells by these antitumor T lymphocytes (effector phase). Therapeutic vaccines, adjuvants, monoclonal antibodies, cytokines, immunogenic cell death-inducing agents including oncolytic viruses, anthracycline-based chemotherapy and radiotherapy, as well as adoptive cell transfer, all act at different levels of this cascade to (re)instate cancer immunosurveillance. Intratumoral delivery of these immunotherapeutics is being tested in clinical trials to promote superior antitumor immune activity in the context of limited systemic toxicity.

Preclinical Evaluation of a Fluorescent Probe Targeting Receptor CDCP1 for Identification of Ovarian Cancer

Optimal cytoreduction for ovarian cancer is often challenging because of aggressive tumor biology and advanced stage. It is a critical issue since the extent of residual disease after surgery is the key predictor of ovarian cancer patient survival. For a limited number of cancers, fluorescence-guided surgery has emerged as an effective aid for tumor delineation and effective cytoreduction. The intravenously administered fluorescent agent, most commonly indocyanine green (ICG), accumulates preferentially in tumors, which are visualized under a fluorescent light source to aid surgery. Insufficient tumor specificity has limited the broad application of these agents in surgical oncology including for ovarian cancer. In this study, we developed a novel tumor-selective fluorescent agent by chemically linking ICG to mouse monoclonal antibody 10D7 that specifically recognizes an ovarian cancer-enriched cell surface receptor, CUB-domain-containing protein 1 (CDCP1). 10D7^ICG has high affinity for purified recombinant CDCP1 and CDCP1 that is located on the surface of ovarian cancer cells in vitro and in vivo. Our results show that intravenously administered 10D7^ICG accumulates preferentially in ovarian cancer, permitting visualization of xenograft tumors in mice. The data suggest CDCP1 as a rational target for tumor-specific fluorescence-guided surgery for ovarian cancer.

Trastuzumab deruxtecan for the treatment of HER2-positive gastric cancer

Introduction: Trastuzumab deruxtecan (T-DXd) is a novel human epidermal growth factor receptor 2 (HER2)-targeted antibody-drug conjugate with a humanized anti-HER2 antibody, cleavable peptide-based linker, and topoisomerase I inhibitor payload. The phase II trial DESTINY-Gastric01 has demonstrated that T-DXd exhibits antitumor activity in patients with HER2-positive advanced gastric cancer (AGC) who had received at least two previous therapies, including trastuzumab.Area covered: T-DXd was approved for previously treated HER2-positive AGC in Japan. The US Food and Drug Administration also approved on 15 January 2021. In this article, we review the development of T-DXd, its pharmacology, and its safety profile in patients with HER2-positive AGC.Expert opinion: T-DXd has demonstrated a significantly higher objective response rate and a longer overall survival in HER2-positive AGC patients with two or more previous lines of systemic chemotherapy, including trastuzumab. Safety profile was acceptable. Currently, there are several ongoing clinical trials of T-DXd in combination with cytotoxic chemotherapy or an immune checkpoint inhibitor.

An overview of process development for antibody-drug conjugates produced by chemical conjugation technology

Introduction: We discuss chemical conjugation strategies for antibody-drug conjugates (ADCs) from an industrial perspective and compare three promising chemical conjugation technologies to produce site-specific ADCs.Areas covered: Currently, nine ADCs are commercially approved and all are produced by chemical conjugation technology. However, seven of these ADCs contain a relatively broad drug distribution, potentially limiting their therapeutic indices. In 2019, the first site-specific ADC was launched on the market by Daiichi-Sankyo. This achievement, and an analysis of clinical trials over the last decade, indicates that current industrial interest in the ADC field is shifting toward site-specific conjugation technologies. From an industrial point of view, we aim to provide guidance regarding established conjugation methodologies that have already been applied to scale-up stages. With an emphasis on highly productive, scalable, and synthetic process robustness, conjugation methodologies for ADC production is discussed herein.Expert opinion: All three chemical conjugation technologies described in this review have various advantages and disadvantages, therefore drug developers can utilize these depending on their biological and/or protein targets. The future landscape of the ADC field is also discussed.

HER2 splice variants in breast cancer: investigating their impact on diagnosis and treatment outcomes

Overexpression of the HER2 receptor occurs in approximately 20% of breast cancer patients. HER2 positivity is associated with poor prognosis and aggressive tumour phenotypes, which led to rapid progress in HER2 targeted therapeutics and diagnostic testing. Whilst these advances have greatly increased patients' chances of survival, resistance to HER2 targeted therapies, be that intrinsic or acquired, remains a problem. Different forms of the HER2 protein exist within tumours in tandem and can display altered biological activities. Interest in HER2 variants in breast cancer increased when links between resistance to anti-HER2 therapies and a particular variant, Δ16-HER2, were identified. Moreover, the P100 variant potentially reduces the efficacy of the anti-HER2 therapy trastuzumab. Another variant, Herstatin, exhibits 'auto-inhibitory' behaviour. More recently, new HER2 variants have been identified and are currently being assessed for their pro- and anti-cancer properties. It is important when directing the care of patients to consider HER2 variants collectively. This review considers HER2 variants in the context of the tumour environment where multiple variants are co-expressed at altered ratios. This study also provides an up to date account of the landscape of HER2 variants and links this to patterns of resistance against HER2 therapies and treatment plans.

Fluorescent Dye Labeling Changes the Biodistribution of Tumor-Targeted Nanoparticles

Fluorescent dye labeling is a common strategy to analyze the fate of administered nanoparticles in living organisms. However, to which extent the labeling processes can alter the original nanoparticle biodistribution has been so far neglected. In this work, two widely used fluorescent dye molecules, namely, ATTO488 (ATTO) and Sulfo-Cy5 (S-Cy5), have been covalently attached to a well-characterized CXCR4-targeted self-assembling protein nanoparticle (known as T22-GFP-H6). The biodistribution of labeled T22-GFP-H6-ATTO and T22-GFP-H6-S-Cy5 nanoparticles has been then compared to that of the non-labeled nanoparticle in different CXCR4+ tumor mouse models. We observed that while parental T22-GFP-H6 nanoparticles accumulated mostly and specifically in CXCR4+ tumor cells, labeled T22-GFP-H6-ATTO and T22-GFP-H6-S-Cy5 nanoparticles showed a dramatic change in the biodistribution pattern, accumulating in non-target organs such as liver or kidney while reducing tumor targeting capacity. Therefore, the use of such labeling molecules should be avoided in target and non-target tissue uptake studies during the design and development of targeted nanoscale drug delivery systems, since their effect over the fate of the nanomaterial can lead to considerable miss-interpretations of the actual nanoparticle biodistribution.

Development and biological assessment of MMAE-trastuzumab antibody-drug conjugates (ADCs)

BACKGROUND

Trastuzumab, a humanized monoclonal antibody targeting Human Epidermal growth factor Receptor 2 (HER2), is a therapeutic option used for the treatment of patients with HER2-overexpressing breast cancers. The primary purpose of the present study was to establish a trastuzumab-based antibody drug conjugate (ADC) to enhance the biopharmaceutical profile of trastuzumab.

METHODS

In this study, trastuzumab was linked to the microtubule-disrupting agent monomethyl auristatin E (MMAE) through a peptide linker. Following conjugation, MMAE-trastuzumab ADCs were characterized using SDS-PAGE, UV/VIS, and cell-based ELISA. The inhibitory effects of the ADCs were measured on MDA-MB-453 (HER2-positive cells) and HEK-293 (HER2-negative cells) using in vitro cell cytotoxicity and colony formation assays.

RESULTS

Our findings showed that approximately 3.4 MMAE payloads were conjugated to trastuzumab. MMAE-trastuzumab ADCs produced six bands, including H2L2, H2L, HL, H2, H, and L in non-reducing SDS-PAGE. The conjugates exhibited the same binding ability to MDA-MB-453 as unconjugated trastuzumab. The MTT assay showed a significant improvement in the trastuzumab activity following MMAE conjugation, representing a higher antitumor activity as compared with unconjugated trastuzumab. Furthermore, ADCs were capable of potentially inhibiting colony formation in HER2-positive cells, as compared with trastuzumab.

CONCLUSION

MMAE-trastuzumab ADCs represent a promising therapeutic strategy to treat HER2-positive breast cancer.