Population pharmacokinetics of trastuzumab emtansine (T-DM1), a HER2-targeted antibody-drug conjugate, in patients with HER2-positive metastatic breast cancer: clinical implications of the effect of covariates

Quantifying payloads of antibody‒drug conjugates using a postcolumn infused-internal standard strategy with LC‒MS

BACKGROUND

Antibody‒drug conjugates (ADCs) are innovative biopharmaceutics consisting of a monoclonal antibody, linkers, and cytotoxic payloads. Monitoring circulating payload concentrations has the potential to identify ADC toxicity; however, accurate quantification faces challenges, including low plasma concentrations, severe matrix effects, and the absence of stable isotope-labeled internal standards (SIL-IS) for payloads and their derivatives. Previous studies used structural analogs as internal standards, but different retention times between structural analogs and target analytes may hinder effective matrix correction. Therefore, a more flexible approach is required for precise payload quantification.

RESULTS

We developed an LC‒MS/MS method incorporating a postcolumn-infused internal standard (PCI-IS) strategy for quantifying payloads and their derivatives of trastuzumab emtansine, trastuzumab deruxtecan, and sacituzumab govitecan, including DM1, MCC-DM1, DXd, SN-38, and SN-38G. Structural analogs (maytansine, Lys-MCC-DM1, and exatecan) were selected as PCI-IS candidates, and their accuracy performance was evaluated based on the percentage of samples within 80%-120% quantification accuracy. Compared to the approach without PCI-IS correction, exatecan enhanced the accuracy performance from 30-40%-100% for SN-38 and DXd, while maytansine and Lys-MCC-DM1 showed comparable accuracy for DM1 and MCC-DM1. This validated PCI-IS analytical method showed superior normalization of matrix effect in all analytes compared to the conventional internal standard approach. The clinical application of this approach showed pronounced differences in DXd and SN-38 concentrations before and after PCI-IS correction. Moreover, only DXd concentrations after PCI-IS correction were significantly higher in patients with thrombocytopenia (p = 0.037).

SIGNIFICANCE

This approach effectively addressed the issue of unavailability of SIL-IS for novel ADC payloads and provided more accurate quantification, potentially yielding more robust statistical outcomes for understanding the exposure-toxicity relationship in ADCs. It is anticipated that this PCI-IS strategy may be extrapolated to quantify payloads and derivatives in diverse ADCs, thereby providing invaluable insights into drug toxicity and fortifying patient safety in ADC usage.

Antibody drug conjugates in older patients: State of the art

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

Pharmacokinetics and pharmacodynamics of antibody-drug conjugates for the treatment of patients with breast cancer

INTRODUCTION

Currently three antibody-drug-conjugates (ADC) are approved by the European Medicines Agency (EMA) for treatment of breast cancer (BC) patient: trastuzumab-emtansine, trastuzumab-deruxtecan and sacituzumab-govitecan. ADC are composed of a monoclonal antibody (mAb) targeting a specific antigen, a cytotoxic payload and a linker. Pharmacokinetics (PK) and pharmacodynamics (PD) distinguish ADC from conventional chemotherapy and must be understood by clinicians.

AREAS COVERED

Our review delineates the PK/PD profiles of ADC approved for the treatment of BC with insight for future development. This is an expert opinion literature review based on the EMA's Assessment Reports, enriched by a comprehensive literature search performed on Medline in August 2023.

EXPERT OPINION

All three ADC distributions are described by a two-compartment structure: tissue and serum. Payload concentration peak is immediate but remains at low concentration. The distribution varied for all ADC only with body weight. mAb will be metabolised firstly by the saturable complex formation of ADC/Tumour-Receptor and secondly by binding of FcgRs in immune cells. They are all excreted in the bile and faeces with minimal urine elimination. Dose adjustments, apart from weight, are not recommended. Novel ADC are composed of cleavable linkers with various targets/payloads with the same PK/PD properties, but novel structures of ADC are in development.

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.

The Challenges of Treating Patients with Breast Cancer and Obesity

Obesity is defined as a body mass index (BMI) of 30 kg/m² or more and is associated with worse outcomes in patients with breast cancer, resulting in an increased incidence of breast cancer, recurrence, and death. The incidence of obesity is increasing, with almost half of all individuals in the United States classified as obese. Patients with obesity present with unique pharmacokinetics and physiology and are at increased risk of developing diabetes mellitus and cardiovascular disease, which leads to specific challenges when treating these patients. The aim of this review is to summarize the impact of obesity on the efficacy and toxicity of systemic therapies used for breast cancer patients, describe the molecular mechanisms through which obesity can affect systemic therapies, outline the existing American Society of Clinical Oncology (ASCO) guidelines for treating patients with cancer and obesity, and highlight additional clinical considerations for treating patients with obesity and breast cancer. We conclude that further research on the biological mechanisms underlying the obesity-breast cancer link may offer new treatment strategies, and clinicals trials that focus on the treatment and outcomes of patients with obesity and all stages of breast cancer are needed to inform future treatment guidelines.

Complex PK-PD of an engineered IL-15/IL-15Rα-Fc fusion protein in cynomolgus monkeys: QSP modeling of lymphocyte dynamics

XmAb24306 is a lymphoproliferative interleukin (IL)-15/IL-15 receptor α (IL-15Rα) Fc-fusion protein currently under clinical investigation as an immunotherapeutic agent for cancer treatment. XmAb24306 contains mutations in IL-15 that attenuate its affinity to the heterodimeric IL-15 receptor βγ (IL-15R). We observe substantially prolonged pharmacokinetics (PK) (half-life ∼ 2.5 to 4.5 days) in single- and repeat-dose cynomolgus monkey (cyno) studies compared to wild-type IL-15 (half-life ∼ 1 hour), leading to increased exposure and enhanced and durable expansion of NK cells, CD8+ T cells and CD4-CD8- (double negative [DN]) T cells. Drug clearance varied with dose level and time post-dose, and PK exposure decreased upon repeated dosing, which we attribute to increased target-mediated drug disposition (TMDD) resulting from drug-induced lymphocyte expansion (i.e., pharmacodynamic (PD)-enhanced TMDD). We developed a quantitative systems pharmacology (QSP) model to quantify the complex PKPD behaviors due to the interactions of XmAb24306 with multiple cell types (CD8+, CD4+, DN T cells, and NK cells) in the peripheral blood (PB) and lymphoid tissues. The model, which includes nonspecific drug clearance, binding to and TMDD by IL15R differentially expressed on lymphocyte subsets, and resultant lymphocyte margination/migration out of PB, expansion in lymphoid tissues, and redistribution to the blood, successfully describes the systemic PK and lymphocyte kinetics observed in the cyno studies. Results suggest that after 3 doses of every-two-week (Q2W) doses up to 70 days, the relative contributions of each elimination pathway to XmAb24306 clearance are: DN T cells > NK cells > CD8+ T cells > nonspecific clearance > CD4+ T cells. Modeling suggests that observed cellular expansion in blood results from the influx of cells expanded by the drug in lymphoid tissues. The model is used to predict lymphoid tissue expansion and to simulate PK-PD for different dose regimens. Thus, the model provides insight into the mechanisms underlying the observed PK-PD behavior of an engineered cytokine and can serve as a framework for the rapid integration and analysis of data that emerges from ongoing clinical studies in cancer patients as single-agent or given in combination.

Phase I Study and Cell-Free DNA Analysis of T-DM1 and Metronomic Temozolomide for Secondary Prevention of HER2-Positive Breast Cancer Brain Metastases

PURPOSE

Preclinical data showed that prophylactic, low-dose temozolomide (TMZ) significantly prevented breast cancer brain metastasis. We present results of a phase I trial combining T-DM1 with TMZ for the prevention of additional brain metastases after previous occurrence and local treatment in patients with HER2+ breast cancer.

PATIENTS AND METHODS

Eligible patients had HER2+ breast cancer with brain metastases and were within 12 weeks of whole brain radiation therapy (WBRT), stereotactic radiosurgery, and/or surgery. Standard doses of T-DM1 were administered intravenously every 21 days (3.6 mg/kg) and TMZ was given orally daily in a 3+3 phase I dose escalation design at 30, 40, or 50 mg/m2, continuously. DLT period was one 21-day cycle. Primary endpoint was safety and recommended phase II dose. Symptom questionnaires, brain MRI, and systemic CT scans were performed every 6 weeks. Cell-free DNA sequencing was performed on patients' plasma and CSF.

RESULTS

Twelve women enrolled, nine (75%) with prior SRS therapy and three (25%) with prior WBRT. Grade 3 or 4 AEs included thrombocytopenia (1/12), neutropenia (1/12), lymphopenia (6/12), and decreased CD4 (6/12), requiring pentamidine for Pneumocystis jirovecii pneumonia prophylaxis. No DLT was observed. Four patients on the highest TMZ dose underwent dose reductions. At trial entry, 6 of 12 patients had tumor mutations in CSF, indicating ongoing metastatic colonization despite a clear MRI. Median follow-up on study was 9.6 m (2.8-33.9); only 2 patients developed new parenchymal brain metastases. Tumor mutations varied with patient outcome.

CONCLUSIONS

Metronomic TMZ in combination with standard dose T-DM1 shows low-grade toxicity and potential activity in secondary prevention of HER2+ brain metastases.

Favorable Outcome and Safety of Neoadjuvant Trastuzumab Emtansine (T-DM1) in a HER2-Positive Early Breast Cancer Patient with Severe Renal Disease on Hemodialysis Ineligible for Conventional Chemotherapy: A Case Report

Breast cancer is the leading cause of cancer-related death among women worldwide. It is the most common malignancy in middle-age and elderly women already suffering from other comorbidities, such as chronic kidney disease (CKD). Being a heterogeneous disease, it has variable subtype-specific outcomes and responses towards treatment. Patients with human epidermal growth factor receptor 2 (HER2) overexpression are treated with anti-HER2-targeted drugs. With the advent of newer drugs, the usage of HER2 blockade and chemotherapy in the neoadjuvant treatment of HER2-positive early breast cancer management helps to increase the probability of achieving pathological complete response. We herein present a case of a patient with breast cancer with long-standing CKD and on maintenance hemodialysis where treatment with conventional chemotherapy regimens was a concern and managed with an antibody–drug conjugate (ADC), namely T-DM1, in a neoadjuvant setting. The patient showed a favorable outcome, and the tolerance of T-DM1 in this patient was predictable. This is a first-of-its-kind case report, where T-DM1 was used in a neoadjuvant setting for a patient on simultaneous hemodialysis.

Primary results of ELAINA: a randomized, multicenter, open-label, phase III study of the efficacy and safety of trastuzumab emtansine vs. lapatinib plus capecitabine in Chinese patients with HER2-positive locally advanced or metastatic breast cancer who have received prior trastuzumab-based therapy

Background

The antibody-drug conjugate (ADCs) trastuzumab emtansine (T-DM1) is approved for human epidermal growth factor receptor 2 (HER2)-positive metastatic breast cancer (mBC) previously treated with trastuzumab and a taxane. The phase III ELAINA trial aimed to determine the clinical utility of T-DM1 in Chinese patients.

Methods

ELAINA was a randomized, multicenter, open-label bridging study of Chinese patients with HER2-positive locally advanced breast cancer (LABC) or mBC previously treated with trastuzumab and a taxane. Using an interactive voice/internet response system, patients were randomized 3:1 to receive T-DM1 or lapatinib plus capecitabine. Patents were stratified by number of prior therapies in this disease setting and by presence of visceral disease using a permuted block randomization scheme. Patients received treatment until disease progression, unmanageable toxicity, or study termination. After that, data on survival and subsequent cancer therapies were collected at approximately 3-month intervals. The primary endpoint was investigator-assessed progression-free survival (PFS). Secondary endpoints were overall response rate, duration of response, overall survival (OS), safety, patient-reported quality of life, and pharmacokinetics (PKs).

Results

ELAINA was fully enrolled with 200 patients randomized to T-DM1 (n=151) or lapatinib plus capecitabine (n=49). Median treatment duration was approximately 6 months in each study arm. Median follow-up time was approximately 9 months for all analyses except for OS. T-DM1 was associated with a 15% reduction in risk of disease progression or death compared with lapatinib plus capecitabine [stratified hazard ratio (HR) =0.85; 95% confidence interval (CI): 0.56-1.29] in the intent-to-treat (ITT) population. The objective response rate (ORR) was similar with T-DM1 (50.4%) and lapatinib plus capecitabine (55.8%); median duration of response was 8.4 months for both treatments. At a median follow-up time of approximately 30 months, OS was similar in each treatment arm. Incidence of grade ≥3 adverse events (AEs) was similar with T-DM1 (54.3%) and lapatinib plus capecitabine (57.1%). Grade ≥3 thrombocytopenia was greater with T-DM1 (40.4%) than with lapatinib plus capecitabine (4.1%); there was no grade ≥3 hemorrhage with either treatment.

Conclusions

T-DM1 demonstrated an acceptable benefit-risk profile in Chinese patients with HER2-positive LABC/mBC previously treated with trastuzumab and a taxane. T-DM1 therefore provides a chemotherapy-free option in this setting.

Trial Registration

ClinicalTrials.gov identifier: NCT03084939.

Performance of Cox proportional hazard models on recovering the ground truth of confounded exposure-response relationships for large-molecule oncology drugs

A Cox proportional hazard (CoxPH) model is conventionally used to assess exposure-response (E-R), but its performance to uncover the ground truth when only one dose level of data is available has not been systematically evaluated. We established a simulation workflow to generate realistic E-R datasets to assess the performance of the CoxPH model in recovering the E-R ground truth in various scenarios, considering two potential reasons for the confounded E-R relationship. We found that at high doses, when the pharmacological effects are largely saturated, missing important confounders is the major reason for inferring false-positive E-R relationships. At low doses, when a positive E-R slope is the ground truth, either missing important confounders or mis-specifying the interactions can lead to inaccurate estimates of the E-R slope. This work constructed a simulation workflow generally applicable to clinical datasets to generate clinically relevant simulations and provide an in-depth interpretation on the E-R relationships with confounders inferred by the conventional CoxPH model.

Covariate analysis of tusamitamab ravtansine, a DM4 anti‐CEACAM5 antibody‐drug conjugate, based on first‐in‐human study

Tusamitamab ravtansine is an anti‐CEACAM5 antibody‐drug conjugate indicated in patients with solid tumors. Based on a previous developed semimechanistic model describing simultaneously pharmacokinetic (PK) of SAR408701, two of its active metabolites: DM4 and methyl‐DM4 and naked antibody, with integration of drug‐to‐antibody data, the main objective of the present analysis was to evaluate covariate’s impact in patients from phase I/II study (n = 254). Demographic and pathophysiologic baseline covariates were explored to explain interindividual variability on each entity PK parameter. Model parameters were estimated with good precision. Five covariates were included in the final PK model: body surface area (BSA), tumor burden, albumin, circulating target, and gender. Comparison of BSA‐adjusted dosing and flat dosing supported the current BSA‐based dosing regimen, to limit under and over exposure in patients with extreme BSA. Overall, this model characterized accurately the PKs of all entities and highlighted sources of PK variability. By integrating mechanistic considerations, this model aimed to improve understanding of the SAR408701 complex disposition while supporting key steps of clinical development.

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.

Impact of Physiologically Based Pharmacokinetics, Population Pharmacokinetics and Pharmacokinetics/Pharmacodynamics in the Development of Antibody-Drug Conjugates

Antibody‐drug conjugates are important molecular entities in the treatment of cancer, with 8 antibody‐drug conjugates approved by the US Food and Drug Administration since 2000 and many more in early‐ and late‐stage clinical development. These conjugates combine the target specificity of monoclonal antibodies with the potent anticancer activity of small‐molecule therapeutics. The complex structure of antibody‐drug conjugates poses unique challenges to pharmacokinetic (PK) and pharmacodynamic (PD) characterization because it requires a quantitative understanding of the PK and PD properties of multiple different molecular species (eg, conjugate, total antibody, and unconjugated payload) in different tissues. Quantitative clinical pharmacology using mathematical modeling and simulation provides an excellent approach to overcome these challenges, as it can simultaneously integrate the disposition, PK, and PD of antibody‐drug conjugates and their components in a quantitative manner. In this review, we highlight diverse quantitative clinical pharmacology approaches, ranging from system models (eg, physiologically based pharmacokinetic [PBPK] modeling) to mechanistic and empirical models (eg, population PK/PD modeling for single or multiple analytes, exposure‐response modeling, platform modeling by pooling data across multiple antibody‐drug conjugates). The impact of these PBPK and PK/PD models to provide insights into clinical dosing justification and inform drug development decisions is also highlighted.

Assessment of racial differences in the incidence of thrombocytopenia induced by trastuzumab emtansine: a systematic review and meta-analysis

Background

Trastuzumab emtansine (T-DM1) has been proved to have value and efficacy in the treatment of advanced metastatic cancer, including in the adjuvant setting. However, there is increasing concern about T-DM1-induced thrombocytopenia (TCP), which shows racial differences in incidence. This meta-analysis aimed to evaluate differences in the incidence of T-DM1-related TCP between Asian and non-Asian patients by combining accessible information from all single-agent T-DM1 clinical trials published to date.

Methods

We conducted systematic searches of the PubMed, Embase, and the Cochrane Library databases to identify relevant clinical studies of T-DM1 that reported on safety, including the incidence of TCP, which were published between January 1980 and March 2020. Two reviewers were responsible for the screening and extraction of data. The pooled-effect estimate calculated with a fixed-effects or random-effects model was represented as incidence with 95% confidence intervals (CIs).

Results

A total of 29 studies involving 6,188 patients were included. The incidence of all-grade TCP in Asian patients and non-Asian patients was 0.39 (95% CI: 0.11–0.67) and 0.29 (95% CI: 0.23–0.35), respectively. The incidence of TCP of grade 3 or higher in Asians was 0.20 (95% CI: 0.10–0.29), compared with 0.02 (95% CI: 0.01–0.03) in non-Asians. Gastrointestinal cancer type and a T-DM1 treatment dose of 2.4 mg/kg Q3W were related to grade 3 or higher TCP events.

Discussion

Asian patients have a higher risk of developing TCP after receiving T-DM1 than non-Asian patients. Clinicians should be aware of the importance of careful observation of platelet count in patients receiving T-DM1 therapy.

Trastuzumab Emtansine: A Review of Its Adjuvant Use in Residual Invasive HER2-Positive Early Breast Cancer

Trastuzumab emtansine (Kadcyla^®), an antibody-drug conjugate of trastuzumab (Herceptin^®) connected by a thioether linker to the microtubule inhibitor DM1 (a cytotoxic derivative of maytansine), provides direct intracellular delivery of the potent cytotoxin DM1 to HER2-overexpressing cells, while retaining trastuzumab activity. Its approval in metastatic/advanced breast cancer (BC) has been extended to include single-agent adjuvant treatment of HER2-positive early BC in patients with residual invasive disease in the breast and/or lymph nodes after neoadjuvant taxane-based and HER2-targeted treatment. In the pivotal KATHERINE trial in this population, significantly more trastuzumab emtansine than trastuzumab recipients were estimated to be free of invasive disease recurrence at 3 years, with a 50% reduction in the risk of invasive disease recurrence or death. The tolerability of trastuzumab emtansine in early BC was consistent with its known safety profile; as expected, adverse events were more common with trastuzumab emtansine than with trastuzumab. Recently updated international and national treatment guidelines recommend trastuzumab emtansine as a preferred option in this high-risk BC population.

Neural-ODE for pharmacokinetics modeling and its advantage to alternative machine learning models in predicting new dosing regimens

Forecasting pharmacokinetics (PK) for individual patients is a fundamental problem in clinical pharmacology. One key challenge is that PK models constructed using data from one dosing regimen must predict PK data for different dosing regimen(s). We propose a deep learning approach based on neural ordinary differential equations (neural-ODE) and tested its generalizability against a variety of alternative models. Specifically, we used the PK data from two different treatment regimens of trastuzumab emtansine. The models performed similarly when the training and the test sets come from the same dosing regimen. However, for predicting a new treatment regimen, the neural-ODE model showed substantially better performance. To date, neural-ODE is the most accurate PK model in predicting untested treatment regimens. This study represents the first time neural-ODE has been applied to PK modeling and the results suggest it is a widely applicable algorithm with the potential to impact future studies.

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.

Clinical pharmacology strategies in supporting drug development and approval of antibody-drug conjugates in oncology

Antibody–drug conjugates (ADCs) are important molecular entities in the treatment of cancer. These conjugates combine the target specificity of monoclonal antibodies with the potent anti-cancer activity of small-molecule therapeutics. The complex structure of ADCs poses unique challenges to characterize the drug’s pharmacokinetics (PKs) and pharmacodynamics (PDs) since it requires a quantitative understanding of the PK and PD properties of multiple different molecular species (e.g., ADC conjugate, total antibody and unconjugated cytotoxic drug). As a result, clinical pharmacology strategy of an ADC is rather unique and dependent on the linker/cytotoxic drug technology, heterogeneity of the ADC, PK and safety/efficacy profile of the specific ADC in clinical development. In this review, we summarize the clinical pharmacology strategies in supporting development and approval of ADCs using the approved ADCs as specific examples to illustrate the customized approach to clinical pharmacology assessments in their clinical development.

Trastuzumab Emtansine (T-DM1) and stereotactic radiation in the management of HER2+ breast cancer brain metastases

Background

Due to recent concerns about the toxicity of trastuzumab emtansine (T-DM1) with stereotactic radiation, we assessed our institutional outcomes treating HER2-positive breast cancer brain metastases (BCBM) with T-DM1 and stereotactic radiation.

Methods

This is a single institution series of 16 patients with HER2-positive breast cancer who underwent 18 stereotactic sessions to 40 BCBM from 2013 to 2019 with T-DM1 delivered within 6 months. The Kaplan-Meier method was used to calculate overall survival (OS), local control (LC), distant intracranial control (DIC), and systemic progression-free survival (sPFS) from the date of SRS. A neuro-radiologist independently reviewed follow-up imaging.

Results

One patient had invasive lobular carcinoma, and 15 patients had invasive ductal carcinoma. All cases were HER2-positive, while 10 were hormone receptor (HR) positive. Twenty-four lesions were treated with stereotactic radiosurgery (SRS) to a median dose of 21 Gy (14–24 Gy). Sixteen lesions were treated with fractionated stereotactic radiation (FSRT) with a median dose of 25 Gy (20-30Gy) delivered in 3 to 5 fractions. Stereotactic radiation was delivered concurrently with T-DM1 in 19 lesions (48%). Median follow up time was 13.2 months from stereotactic radiation. The 1-year LC, DIC, sPFS, and OS were 75, 50, 30, and 67%, respectively. There was 1 case of leptomeningeal progression and 1 case (3%) of symptomatic radionecrosis.

Conclusions

We demonstrate that stereotactic radiation and T-DM1 is well-tolerated and effective for patients with HER2-positive BCBM. An increased risk for symptomatic radiation necrosis was not noted in our series.

Antibody-drug conjugates as targeted therapies: Are we there yet? A critical review of the current clinical landscape

Antibody-drug conjugates (ADCs) are targeted therapies with the expectation of broadened therapeutic window due to tumor-specific drug delivery. Recent approvals, including ADCs with a novel payload class, topoisomerase-1 inhibitors, generated renewed excitement in the field. We provide a critical review of approved and late-stage molecules, discuss strategies in solid tumors and ADCs outside oncology. Our pharmacokinetics-based assessment of targeting suggests that ADCs, especially in solid tumors, rely on additional mechanisms for efficacy including slow-release of the payload to the circulation at potentially efficacious levels. Further adjustments in the technology are needed to fulfill the promise of true targeted drug delivery.

Antibody-Drug Conjugates: Patient and Treatment Selection

Antibody-drug conjugates (ADCs) are a promising drug platform designed to enhance the therapeutic index and minimize the toxicity of anticancer agents. ADCs have experienced substantial progress and technological growth over the past decades; however, several challenges to patient selection and treatment remain. Methods to optimally capture all patients who may benefit from a particular ADC are still largely unknown. Although target antigen expression remains a biomarker for patient selection, the impact of intratumor heterogeneity on antigen expression, as well as the dynamic changes in expression with treatment and disease progression, are important considerations in patient selection. Better understanding of these factors, as well as minimum levels of target antigen expression required to achieve therapeutic efficacy, will enable further optimization of selection strategies. Other important considerations include understanding mechanisms of primary and acquired resistance to ADCs. Ongoing efforts in the design of its constituent parts to possess the intrinsic ability to overcome these mechanisms, including use of the "bystander effect" to enhance efficacy in heterogeneous or low target antigen-expressing tumors, as well as modulation of the chemical and immunophenotypic properties of antibodies and linker molecules to improve payload sensitivity and therapeutic efficacy, are under way. These strategies may also lead to improved safety profiles. Similarly, combination strategies using ADCs with other cytotoxic or immunomodulatory agents are also under development. Great strides have been made in ADC technology. With further refinements, this therapeutic modality has the potential to make an important clinical impact on a wider range of tumor types.

Trastuzumab emtansine: a game changer in HER2-positive early breast cancer

Trastuzumab emtansine (T-DM1), given postoperatively for 14 cycles to patients with human epidermal growth factor receptor 2-positive (HER2-positive) early breast cancer (EBC) who failed to achieve a pathological complete response after standard chemotherapy and HER2 blockade, represents probably the greatest progress in the management of this aggressive form of breast cancer since the adjuvant trastuzumab pivotal trials. This article addresses the rationale behind the conception of the KATHERINE trial, T-DM1's structure and pharmacokinetics data, clinical efficacy data of the KATHERINE trial and of other EBC trials with T-DM1, safety aspects, implications of the KATHERINE trial results to clinical practice and future perspectives in the management of HER2-positive EBC.

Population Pharmacokinetics of Trastuzumab Deruxtecan in Patients With HER2-Positive Breast Cancer and Other Solid Tumors

Trastuzumab deruxtecan (DS‐8201) is a human epidermal growth factor receptor 2 (HER2)–targeting antibody–drug conjugate with a novel enzyme‐cleavable linker, a topoisomerase I inhibitor payload, and a drug‐to‐antibody ratio of ≈ 8. We have characterized the population pharmacokinetics (PK) of trastuzumab deruxtecan and released drug (topoisomerase I inhibitor) in patients with HER2‐positive breast cancer or other solid tumor malignancies. This analysis includes pooled data from five clinical studies with 639 patients. Trastuzumab deruxtecan doses ranged from 0.8 to 8.0 mg/kg every 3 weeks. Serum concentrations of trastuzumab deruxtecan and released drug were analyzed using a sequential two‐step approach, with the nonlinear mixed‐effects modeling methods. Covariate assessment was based upon stepwise forward‐addition and backward‐elimination process, followed by both univariate and multivariate analysis quantifying their impact on steady‐state exposure of trastuzumab deruxtecan and released drug. A two‐compartment model with linear elimination best described PK profiles of intact trastuzumab deruxtecan, while a one‐compartment model with time‐varying release‐rate constant and linear elimination described released‐drug PK profiles. Statistically significant covariates (country, tumor size, sex, formulation, age, body weight, albumin, total bilirubin, and aspartate aminotransferase) resulted in < 20% change in steady‐state area under the concentration‐time curve of trastuzumab deruxtecan and released drug, except for increased body weight (95th percentile, 86 kg) and decreased albumin (5th percentile, 31 g/L). Analysis of patients stratified by country, race, renal function, and hepatic function found no clinically meaningful differences in steady‐state exposure of intact trastuzumab deruxtecan or released drug. Overall, results suggest that no dose adjustment based on tested covariates or in specific patient populations is warranted.

Capturing the Magic Bullet: Pharmacokinetic Principles and Modeling of Antibody-Drug Conjugates

Over the past two decades, antibody-drug conjugates (ADCs) have emerged as a promising class of drugs for cancer therapy and have expanded to nononcology fields such as inflammatory diseases, atherosclerosis, and bacteremia. Eight ADCs are currently approved by FDA for clinical applications, with more novel ADCs under clinical development. Compared with traditional chemotherapy, ADCs combine the target specificity of antibodies with chemotherapeutic capabilities of cytotoxic drugs. The benefits include reduced systemic toxicity and enhanced therapeutic index for patients. However, the heterogeneous structures of ADCs and their dynamic changes following administration create challenges in their development. The understanding of ADC pharmacokinetics (PK) is crucial for the optimization of clinical dosing regimens when translating from animal to human. In addition, it contributes to the optimization of dose selection and clinical monitoring with regard to safety and efficacy. This manuscript reviews the PK characteristics of ADCs and summarizes the diverse approaches for PK modeling that can be used to evaluate an ADC at the preclinical and clinical stages to support their successful development. Despite the numerous available options, fit-for-purpose modeling approaches for the PK and PD of ADCs should be critically planned and well-thought-out to adequately support the development of an ADC.

Influence of Antigen Mass on the Pharmacokinetics of Therapeutic Antibodies in Humans

Therapeutic antibodies are increasingly used to treat various diseases, including neoplasms and chronic inflammatory diseases. Antibodies exhibit complex pharmacokinetic properties, notably owing to the influence of antigen mass, i.e. the amount of antigenic targets to which the monoclonal antibody binds specifically. This review focuses on the influence of antigen mass on the pharmacokinetics of therapeutic antibodies quantified by pharmacokinetic modelling in humans. Out of 159 pharmacokinetic studies, 85 reported an influence of antigen mass. This influence led to non-linear elimination decay in 50 publications, which was described using target-mediated drug disposition or derived models, as quasi-steady-state, irreversible binding and Michaelis-Menten models. In 35 publications, the pharmacokinetics was apparently linear and the influence of antigen mass was described as a covariate of pharmacokinetic parameters. If some reported covariates, such as the circulating antigen level or tumour size, are likely to be correlated to antigen mass, others, such as disease activity or disease type, may contain little information on the amount of antigenic targets. In some cases, antigen targets exist in different forms, notably in the circulation and expressed at the cell surface. The influence of antigen mass should be soundly described during the early clinical phases of drug development. To maximise therapeutic efficacy, sufficient antibody doses should be administered to ensure the saturation of antigen targets by therapeutic antibodies in all patients. If necessary, antigen mass should be taken into account in routine clinical practice.

Predicting Thrombocytopenia in Patients With Breast Cancer Treated With Ado-trastuzumab Emtansine

INTRODUCTION

Thrombocytopenia is a common and potentially serious adverse event of ado-trastuzumab emtansine (T-DM1) use in patients with advanced breast cancer. However, the risk factors have been minimally explored. Our aim was to develop a clinical prediction model from the clinicopathologic data that would allow for quantification of the personalized risks of thrombocytopenia from T-DM1 usage.

MATERIALS AND METHODS

Data from 3 clinical trials, EMILIA (a study of trastuzumab emtansine versus capecitabine + lapatinib in participants with HER2 [human epidermal growth factor receptor 2]-positive locally advanced or metastatic breast cancer), TH3RESA (a study of trastuzumab emtansine in comparison with treatment of physician's choice in participants with HER2-positive breast cancer who have received at least two prior regimens of HER2-directed therapy), and MARIANNE [a study of trastuzumab emtansine (T-DM1) plus pertuzumab/pertuzumab placebo versus trastuzumab (Herceptin) plus a taxane in participants with metastatic breast cancer], were pooled. Cox proportional hazard analysis was used to assess the association between the pretreatment clinicopathologic data and grade ≥ 3 thrombocytopenia occurring within the first 365 days of T-DM1 use. A multivariable clinical prediction model was developed using a backward elimination process.

RESULTS

Of the 1620 participants, 141 (9%) had experienced grade ≥ 3 thrombocytopenia. On univariable analysis, the body mass index, race, presence of brain metastasis, platelet count, white blood cell count, and concomitant corticosteroid use were significantly associated with the occurrence of grade ≥ 3 thrombocytopenia (P < .05). The multivariable prediction model was optimally defined by race (Asian vs. non-Asian) and platelet count (100-220 vs. 220-300 vs. >300 × 10⁹/L). A large discrimination between the prognostic subgroups was observed. The highest risk subgroup (Asian and platelet count of 100-220 cells ×10⁹/L) had a 40% probability of grade ≥ 3 thrombocytopenia within the first 365 days of T-DM1 therapy compared with 2% for the lowest risk subgroup (non-Asian and platelet count > 300 × 10⁹/L).

CONCLUSION

A clinical prediction model, defined by race and pretreatment platelet count, was able to discriminate subgroups with a significantly different risk of grade ≥ 3 thrombocytopenia after T-DM1 initiation. The model allows for improved interpretation of the personalized risks and risk/benefit ratio of T-DM1.

Nanomedicines - Tiny particles and big challenges

After decades of research, nanotechnology has been used in a broad array of biomedical products including medical devices, drug products, drug substances, and pharmaceutical-grade excipients. But like many great achievements in science, there is a fine balance between the risks and opportunities of this new technology. Some materials and surface structures in the nanosize range can exert unexpected toxicities and merit a more detailed safety assessment. Regulatory agencies such as the United States Food and Drug Administration or the European Medicines Agency have started dealing with the potential risks posed by nanomaterials. Considering that a thorough characterization is one of the key aspects of controlling such risks this review presents the regulatory background of nanosafety assessment and provides some practical advice on how to characterize nanomaterials and drug formulations. Further, the challenges of how to maintain and monitor pharmaceutical quality through a highly complex production processes will be discussed.

Long-time Response with Ado-trastuzumab Emtansine in a Recurrent Metastatic Breast Cancer

Breast cancer is the most common cancer in a woman with a five-year survival of patients with metastatic disease is estimated at 23%. Ado-trastuzumab emtansine (T-DM1) is a HER2-antibody drug conjugate currently approved for the treatment of HER2-positive pre-treated metastatic breast cancer (BC). We report a case of recurrent metastatic breast cancer with unusually lengthy progression-free survival (PFS) on T-DM1 chemotherapy. She was diagnosed with Triple Positive Stage IIIC multifocal invasive ductal carcinoma of the left breast. After completing neoadjuvant chemotherapy, she underwent a bilateral mastectomy. Final pathology showed partial response. Postoperatively, she received adjuvant chemotherapy and radiation therapy. She was started on Q21 days trastuzumab following completion of adjuvant chemotherapy. Systemic imaging showed liver lesions and biopsy confirmed recurrence. She was started on T-DM1, endocrine therapy with anastrozole was continued. She is currently status post 45 cycles. T-DM1 was approved for the treatment (single-agent) of HER2-positive, metastatic BC based on phase III data from the EMILIA and TH3RESA study. Median PFS in the T-DM1 arm was 9.6 months. Herein, we present a case of a woman with recurrent triple positive metastatic BC with a lengthy progression-free survival on T-DM1 chemotherapy.

Pharmacokinetic and exposure-response analysis of pertuzumab in patients with HER2-positive metastatic gastric or gastroesophageal junction cancer

PURPOSE

To characterize the pharmacokinetics (PK) of pertuzumab and trastuzumab in patients with HER2-positive metastatic gastric or gastroesophageal junction cancer in the randomized, double-blind, phase III JACOB study (NCT01774786), and to evaluate the appropriateness of the pertuzumab regimen in these patients.

METHODS

Patients received 840 mg intravenous pertuzumab or placebo plus trastuzumab q3w and chemotherapy. Pertuzumab and trastuzumab were administered until disease progression or unacceptable toxicity. Chemotherapy was administered for up to six cycles or disease progression or unacceptable toxicity. Serum concentrations of pertuzumab and trastuzumab were measured. Pertuzumab PK was characterized across treatment cycles. The impact of anti-drug antibodies (ADAs) on pertuzumab PK and the impact of pertuzumab on trastuzumab PK were assessed. An exploratory exposure-efficacy analysis was also conducted.

RESULTS

In total, 374 patients in the pertuzumab arm had evaluable PK data. The mean observed pertuzumab steady-state serum trough (minimum) concentration (Cmin,ss) ± standard deviation was 114 ± 51.8 μg/mL. The target pertuzumab Cmin,ss of ≥ 20 μg/mL was reached in 99.3% of patients at Cycle 5 (steady state) and beyond. Greater than 90% of patients were above the PK target right after the first pertuzumab dose. There was no apparent impact of ADAs on pertuzumab PK nor of pertuzumab on trastuzumab PK. There were no differences in overall survival across Cycle 1 pertuzumab (Cmin) or Cycle 5 pertuzumab (Cmin,ss) exposure quartiles.

CONCLUSIONS

Pertuzumab exposure in JACOB was consistent with prior studies in advanced gastric cancer and breast cancer. The 840 mg q3w dose allowed the majority of patients in JACOB to achieve target pertuzumab concentrations and appears to be an appropriate dose selection.

Antibody-Drug Conjugates: Pharmacokinetic/Pharmacodynamic Modeling, Preclinical Characterization, Clinical Studies, and Lessons Learned

Antibody-drug conjugates are an emerging class of biopharmaceuticals changing the landscape of targeted chemotherapy. These conjugates combine the target specificity of monoclonal antibodies with the anti-cancer activity of small-molecule therapeutics. Several antibody-drug conjugates have received approval for the treatment of various types of cancer including gemtuzumab ozogamicin (Mylotarg^®), brentuximab vedotin (Adcetris^®), trastuzumab emtansine (Kadcyla^®), and inotuzumab ozogamicin, which recently received approval (Besponsa^®). In addition to these approved therapies, there are many antibody-drug conjugates in the drug development pipeline and in clinical trials, although these fall outside the scope of this article. Understanding the pharmacokinetics and pharmacodynamics of antibody-drug conjugates and the development of pharmacokinetic/pharmacodynamic models is indispensable, albeit challenging as there are many parameters to incorporate including the disposition of the intact antibody-drug conjugate complex, the antibody, and the drug agents following their dissociation in the body. In this review, we discuss how antibody-drug conjugates progressed over time, the challenges in their development, and how our understanding of their pharmacokinetics/pharmacodynamics led to greater strides towards successful targeted therapy programs.

Preclinical and translational pharmacokinetics of a novel THIOMAB™ antibody-antibiotic conjugate against Staphylococcus aureus

DSTA4637S, a novel THIOMAB™ antibody-antibiotic conjugate (TAC) against Staphylococcus aureus (S. aureus), is currently being investigated as a potential therapy for complicated S. aureus bloodstream infections. DSTA4637S is composed of a monoclonal THIOMAB^TM IgG1 recognizing S. aureus linked to a rifamycin-class antibiotic (dmDNA31) via a protease-cleavable linker. The pharmacokinetics (PK) of DSTA4637A (a liquid formulation of DSTA4637S) and its unconjugated antibody MSTA3852A were characterized in rats and monkeys. Systemic concentrations of three analytes, total antibody (TAb), antibody-conjugated dmDNA31 (ac-dmDNA31), and unconjugated dmDNA31, were measured to describe complex TAC PK in nonclinical studies. In rats and monkeys, following intravenous administration of a single dose of DSTA4637A, systemic concentration-time profiles of both TAb and ac-dmDNA31 were bi-exponential, characterized by a short distribution phase and a long elimination phase as expected for a monoclonal antibody-based therapeutic. Systemic exposures of both TAb and ac-dmDNA31 were dose proportional over the dose range tested, and ac-dmDNA31 cleared 2-3 times faster than TAb. Unconjugated dmDNA31 plasma concentrations were low (<4 ng/mL) in every study regardless of dose. In this report, an integrated semi-mechanistic PK model for two analytes (TAb and ac-dmDNA31) was successfully developed and was able to well describe the complicated DSTA4637A PK in mice, rats and monkeys. DSTA4637S human PK was predicted reasonably well using this model with allometric scaling of PK parameters from monkey data. This work provides insights into PK behaviors of DSTA4637A in preclinical species and informs clinical translatability of these observed results and further clinical development. Abbreviations: ADC: Antibody-drug conjugate; AUC_inf: time curve extrapolated to infinity; ac-dmDNA31: antibody-conjugated dmDNA31; C_max: maximum concentration observed; DAR: drug-to-antibody ratio; CL: clearance; CL_D: distribution clearance; CL₁: systemic clearance of all DAR species; k_DC: deconjugation rate constant; PK: Pharmacokinetics; IV: Intravenous; IgG: Immunoglobulin G; mAb: monoclonal antibody; S. aureus: Staphylococcus aureus; TAC: THIOMAB^TM antibody-antibiotic conjugate; TDC: THIOMAB^TM antibody-drug conjugate; TAb: total antibody; t_{1/2, λz}: terminal half-life; vc linker: valine-citrulline linker; V_ss: volume of distribution at steady state; V_c: volume of distribution for the central compartment; V_p: the volume of distribution for the peripheral compartment.

Pharmacokinetics of trastuzumab emtansine (T-DM1) as a single agent or in combination with pertuzumab in HER2-positive breast cancer patients with recurrent or locally advanced metastatic breast cancer

PURPOSE

The phase III MARIANNE study investigated single-agent trastuzumab emtansine (T-DM1) and combination T-DM1 plus pertuzumab as the first-line treatment for human epidermal growth factor receptor 2 (HER2)-positive metastatic breast cancer (MBC). Pharmacokinetic properties of T-DM1 and pertuzumab in these patients and the potential for drug-drug interactions (DDIs) were assessed.

METHODS

Pharmacokinetic samples of T-DM1-related analytes (T-DM1 conjugate, total trastuzumab, DM1) and pertuzumab were analyzed. Observed pharmacokinetic data were summarized for all analytes. Historical population pharmacokinetic models for T-DM1 conjugate and pertuzumab in HER2-positive MBC were used to derive empirical Bayes estimates of pharmacokinetic parameters.

RESULTS

In MARIANNE (N = 375), mean ± standard deviation population pharmacokinetic model-predicted Cycle 1 C_max for T-DM1 conjugate was 74.4 ± 10.1 µg/mL, Cycle 1 C_trough was 1.34 ± 0.802 µg/mL, and area under the concentration-time curve from time zero to infinity after first dose (AUC_inf) was 338 ± 69.5 µg*day/mL. These values were similar to other T-DM1 studies. Pharmacokinetics of T-DM1 conjugate and other analytes (total trastuzumab, DM1) were similar with or without pertuzumab. In the pertuzumab plus T-DM1 arm, mean model-predicted Cycle 1 pertuzumab C_max, C_trough, and AUC_inf were 276 ± 50.0 µg/mL, 64.8 ± 17.9 μg/mL, and 4470 ± 1360 µg*day/mL, respectively. These values were similar to other pertuzumab studies.

CONCLUSIONS

Based on the population pharmacokinetic analysis of T-DM1 conjugate and pertuzumab, pharmacokinetics are similar across different lines of treatment and stages of disease including previously untreated MBC patients, and no DDIs were identified for combined use of T-DM1 and pertuzumab.

An Integrated Population Pharmacokinetic Model Versus Individual Models of Depatuxizumab Mafodotin, an Anti-EGFR Antibody Drug Conjugate, in Patients With Solid Tumors Likely to Overexpress EGFR

Depatuxizumab mafodotin (depatux-m) is an antibody-drug conjugate (ADC) designed for the treatment of tumors expressing epidermal growth factor receptor (EGFR), consisting of a veneered "humanized" recombinant IgG1κ antibody that has binding properties specific to a unique epitope of human EGFR with noncleavable maleimido-caproyl linkers each attached to a potent antimitotic cytotoxin, monomethyl auristatin F. We aimed to describe the development and comparison of 2 population pharmacokinetic modeling approaches. Data from 2 phase 1 studies enrolling patients with glioblastoma multiforme or advanced solid tumors were included in the analysis. Patients in these studies received doses of depatux-m ranging from 0.5 to 4.0 mg/kg as monotherapy, in combination with temozolomide, or radiation plus temozolomide depending on the study and/or arm. First, an integrated ADC model to simultaneously describe the concentration-time data for ADC, total antibody, and cys-mafodotin was built using a 2-compartment model for ADC for each drug-to-antibody ratio. Then, 3 individual models were developed for ADC, total antibody, and cys-mafodotin separately using 2-compartment models for ADC and total antibody and a 1-compartment model for cys-mafodotin. Visual predictive checks suggested accurate model fitting across a range of concentrations. The analysis showed that both an integrated complex ADC model and the individual models that have shorter computational time would result in similar outcomes.

Pharmacologic Considerations in the Disposition of Antibodies and Antibody-Drug Conjugates in Preclinical Models and in Patients

The rapid advancement in the development of therapeutic proteins, including monoclonal antibodies (mAbs) and antibody-drug conjugates (ADCs), has created a novel mechanism to selectively deliver highly potent cytotoxic agents in the treatment of cancer. These agents provide numerous benefits compared to traditional small molecule drugs, though their clinical use still requires optimization. The pharmacology of mAbs/ADCs is complex and because ADCs are comprised of multiple components, individual agent characteristics and patient variables can affect their disposition. To further improve the clinical use and rational development of these agents, it is imperative to comprehend the complex mechanisms employed by antibody-based agents in traversing numerous biological barriers and how agent/patient factors affect tumor delivery, toxicities, efficacy, and ultimately, biodistribution. This review provides an updated summary of factors known to affect the disposition of mAbs/ADCs in development and in clinical use, as well as how these factors should be considered in the selection and design of preclinical studies of ADC agents in development.

Population pharmacokinetic and covariate analyses of intravenous trastuzumab (Herceptin®), a HER2-targeted monoclonal antibody, in patients with a variety of solid tumors

PURPOSE

The aim of the study was to characterize the population pharmacokinetics (PK) of the intravenous formulation of trastuzumab, assess the impact of patient and pathological covariates on trastuzumab PK, and perform simulations to support dosing recommendations in special situations.

METHODS

Serum trastuzumab concentrations were obtained from 1582 patients with metastatic breast cancer (MBC), early breast cancer (EBC), advanced gastric cancer (AGC), or other tumor types/healthy volunteers in 18 phase I, II, and III trials and analyzed by nonlinear mixed-effects modeling.

RESULTS

A two-compartment model with parallel linear and nonlinear elimination best described the data. During treatment, linear clearance (CL) dominated, resulting in a total CL of 0.173-0.337 L/day, which is similar to other IgG1 monoclonal antibodies. Covariates influencing CL were baseline body weight, aspartate aminotransferase, albumin, gastric cancer, and the presence of liver metastases. MBC and EBC had similar PK parameters, while CL was higher in AGC. Simulations indicated that at least 95% of patients with BC reach concentrations < 1 µg/mL (~ 97% washout) by 7 months. A dose delay in BC or AGC patients of > 1 week would take approximately 6 weeks to get back within steady-state exposure range.

CONCLUSIONS

Trastuzumab PK for the intravenous formulation was well-described across cancer types, disease status, and regimens. No dose adjustment is required for any of the identified patient covariates. A 7-month serum washout period for trastuzumab is recommended. A reloading dose is required if a maintenance dose is missed by > 1 week.

A Phase I Pharmacokinetic Study of Trastuzumab Emtansine (T-DM1) in Patients with Human Epidermal Growth Factor Receptor 2-Positive Metastatic Breast Cancer and Normal or Reduced Hepatic Function

OBJECTIVE

The aim of this study was to evaluate the pharmacokinetics (PK) of trastuzumab emtansine (T-DM1) and relevant analytes in patients with human epidermal growth factor receptor 2 (HER2)-positive metastatic breast cancer and hepatic impairment.

METHODS

Patients were enrolled in three independent parallel cohorts based on hepatic function per Child-Pugh criteria: normal hepatic function, mild hepatic impairment, and moderate hepatic impairment. Patients received T-DM1 3.6 mg/kg intravenously every 3 weeks. PK samples were collected during cycles 1 and 3, and the PK of T-DM1 and relevant analytes were characterized and compared across cohorts.

RESULTS

Compared with patients with normal hepatic function (n = 10), T-DM1 clearance at cycle 1 was 1.8- and 4.0-fold faster in the mild (n = 10) and moderate (n = 8) cohorts, respectively. The trend of faster clearance was less apparent in cycle 3, with similar T-DM1 clearance across cohorts (mean ± standard deviation 8.16 ± 3.27 [n = 9], 9.74 ± 3.62 [n = 7], and 8.99 and 10.2 [individual values, n = 2] mL/day/kg for the normal, mild, and moderate cohorts, respectively). T-DM1 clearance at cycle 1 correlated significantly with baseline albumin, aspartate aminotransferase, and HER2 extracellular domain concentrations (p < 0.05). Plasma concentrations of DM1 and DM1-containing catabolites were low and were comparable across cohorts.

CONCLUSIONS

No increase in systemic DM1 concentration was observed in patients with mild or moderate hepatic impairment versus those with normal hepatic function. The faster T-DM1 clearance observed at cycle 1 in patients with hepatic impairment appeared to be transient. After repeated dosing (three cycles), T-DM1 exposure in patients with mild and moderate hepatic impairment was within the range seen in those with normal hepatic function.

Seek and destroy: improving PK/PD profiles of anticancer agents with nanoparticles

INTRODUCTION

The Pharmacokinetics/pharmacodynamics (PK/PD) relationships with cytotoxics are usually based on a steepening concentration-effect relationship; the greater the drug amount, the greater the effect. The Maximum Tolerated Dose paradigm, finding the balance between efficacy, while keeping toxicities at their manageable level, has been the rule of thumb for the last 50-years. Developing nanodrugs is an appealing strategy to help broaden this therapeutic window. The fact that efficacy and toxicity with cytotoxics are intricately linked is primarily due to the complete lack of specificity toward the tumor tissue during their distribution phase. Because nanoparticles are expected to better target tumor tissue while sparing healthy cells, accumulating large amounts of cytotoxics in tumors could be achieved in a safer way. Areas covered: This review aims at presenting how nanodrugs present unique features leading to reconsidering PK/PD relationships of anticancer agents. Expert commentary: The constant interplay between carrier PK, interactions with cancer cells, payload release, payload PK, target expression and target engagement, makes picturing the exact PK/PD relationships of nanodrugs particularly challenging. However, those improved PK/PD relationships now make the once contradictory higher efficacy and lower toxicities requirement an achievable goal in cancer patients.

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.

A Pharmacometric Analysis of Patient-Reported Outcomes in Breast Cancer Patients Through Item Response Theory

PURPOSE

An item response theory (IRT) pharmacometric framework is presented to characterize Functional Assessment of Cancer Therapy-Breast (FACT-B) data in locally-advanced or metastatic breast cancer patients treated with ado-trastuzumab emtansine (T-DM1) or capecitabine-plus-lapatinib.

METHODS

In the IRT model, four latent well-being variables, based on FACT-B general subscales, were used to describe the physical, social/family, emotional and functional well-being. Each breast cancer subscale item was reassigned to one of the other subscales. Longitudinal changes in FACT-B responses and covariate effects were investigated.

RESULTS

The IRT model could describe both item-level and subscale-level FACT-B data. Non-Asian patients showed better baseline social/family and functional well-being than Asian patients. Moreover, patients with Eastern Cooperative Oncology Group performance status of 0 had better baseline physical and functional well-being. Well-being was described as initially increasing or decreasing before reaching a steady-state, which varied substantially between patients and subscales. T-DM1 exposure was not related to any of the latent variables. Physical well-being worsening was identified in capecitabine-plus-lapatinib-treated patients, whereas T-DM1-treated patients typically stayed stable.

CONCLUSION

The developed framework provides a thorough description of FACT-B longitudinal data. It acknowledges the multi-dimensional nature of the questionnaire and allows covariate and exposure effects to be evaluated on responses.

Population PK and Exposure-Response Relationships for the Antibody-Drug Conjugate Brentuximab Vedotin in CTCL Patients in the Phase III ALCANZA Study

The antibody–drug conjugate (ADC) brentuximab vedotin consists of the CD30‐directed antibody attached to the microtubule‐disrupting agent monomethyl auristatin E (MMAE). In pharmacokinetic models, including data from six studies (380 patients with classical Hodgkin's, systemic anaplastic large‐cell, and cutaneous T‐cell (CTCL) lymphomas), lower clearance of ADC and modestly higher ADC exposure in CTCL patients did not translate into higher MMAE exposure. In CTCL patients from the phase III ALCANZA study (n = 66), improved progression‐free survival with brentuximab vedotin vs. controls was not related to ADC exposure. ADC exposure was a predictor of grade ≥3 treatment‐emergent adverse events (TEAEs). Results support the consistent benefit observed with brentuximab vedotin 1.8 mg/kg every 3 weeks across the range of exposures in ALCANZA and support dose reductions in patients experiencing TEAEs at the starting dose.

Factors Affecting the Pharmacology of Antibody-Drug Conjugates

Major advances in therapeutic proteins, including antibody–drug conjugates (ADCs), have created revolutionary drug delivery systems in cancer over the past decade. While these immunoconjugate agents provide several advantages compared to their small-molecule counterparts, their clinical use is still in its infancy. The considerations in their development and clinical use are complex, and consist of multiple components and variables that can affect the pharmacologic characteristics. It is critical to understand the mechanisms employed by ADCs in navigating biological barriers and how these factors affect their biodistribution, delivery to tumors, efficacy, and toxicity. Thus, future studies are warranted to better understand the complex pharmacology and interaction between ADC carriers and biological systems, such as the mononuclear phagocyte system (MPS) and tumor microenvironment. This review provides an overview of factors that affect the pharmacologic profiles of ADC therapies that are currently in clinical use and development.

Trastuzumab Emtansine: Antibody-drug Conjugate in Treatment of Human Epidermal Growth Factor Receptor-2-Positive Metastatic Breast Cancer

The human epidermal growth factor receptor-2 (HER2)-targeted therapies have improved clinical outcomes for patients at any stage of HER2-positive breast cancer (BC). Trastuzumab, a monoclonal antibody that targets the HER2 receptor on BC cells, showed improved survival in metastatic BC (MBC). However, resistance to therapy arises in the majority of patients with advanced disease. Antibody–drug conjugate (ADC) is a relatively new development to deliver cytotoxic drugs specifically to cancer cells. Trastuzumab emtansine (T-DM1) is a HER2-targeted ADC, composed of trastuzumab, a stable thioether linker, and the potent cytotoxic agent, emtansine (DM1, derivative of maytansine). T-DM1 has been approved for use in patients with MBC who have failed prior therapy with trastuzumab and a taxane. Dose finding Phase I study established the maximum tolerated dose at 3.6 mg/kg every 3 weeks. Phase I and II studies of T-DM1 have shown clinical activity and a favorable safety profile in HER2-positive MBC patients. The Phase III randomized EMILIA and TR3RESA trials demonstrated that T-DM1 significantly improves progression-free and overall survival in pretreated HER2-positive MBC patients. Nausea and fatigue are most commonly reported adverse drug reactions with T-DM1 and cardiac toxicity comparable with standard of care therapies. The drug is well tolerated in most patients, with a predictable pharmacokinetic profile and minimal systemic exposure to free cytotoxic DM1. T-DM1 has emerged as an effective therapeutic option for the management of patients with HER2-positive MBC.

Population pharmacokinetics of trastuzumab emtansine in previously treated patients with HER2-positive advanced gastric cancer (AGC)

PURPOSE

Ado-trastuzumab emtansine (T-DM1) is an antibody-drug conjugate comprising trastuzumab conjugated via a stable thioether linker to DM1, a highly potent cytotoxic agent. A population pharmacokinetics (PK) analysis was performed to characterize T-DM1 PK and evaluate the impact of patient characteristics on T-DM1 PK in previously treated patients with HER2-positive advanced gastric cancer (AGC).

METHODS

Following T-DM1 weekly or every three weeks dosing, T-DM1 concentration measurements (n = 780) were collected from 136 patients in the GATSBY (NCT01641939) study and analyzed using nonlinear mixed effects modeling. The influence of demographic, baseline laboratory, and disease characteristics on T-DM1 PK was examined.

RESULTS

T-DM1 PK was best described by a two-compartment model with parallel linear and nonlinear (Michaelis-Menten) elimination from the central compartment. The final population model estimated linear clearance (CL) of 0.79 L/day, volume of distribution in the central compartment (V _c) of 4.48 L, distribution clearance (Q) of 0.62 L/day, volume of distribution in the peripheral compartment (V _p) of 1.49 L, nonlinear CL of 2.06 L/day, and KM of 1.63 μg/mL. Parameter uncertainty was low to moderate for fixed effects, except KM (estimated with poor precision). Patients with high body weight and low baseline trastuzumab concentrations had significantly faster linear CL; those with higher body weight had significantly larger V _c.

CONCLUSIONS

In a HER2-positive AGC population, T-DM1 PK was best described by a two-compartment model with parallel linear and nonlinear elimination. Baseline body weight and trastuzumab concentration were identified as significant covariates for T-DM1 PK in a HER2-positive AGC population.

Exposure-response analyses of trastuzumab emtansine in patients with HER2-positive advanced breast cancer previously treated with trastuzumab and a taxane

PURPOSE

In the phase III EMILIA study, trastuzumab emtansine (T-DM1) significantly improved progression-free survival (PFS) and overall survival (OS) versus capecitabine plus lapatinib (control) in previously treated human epidermal growth factor receptor 2-positive advanced breast cancer. Using EMILIA data, we evaluated the T-DM1 exposure-response relationship.

METHODS

Exposure-response relationships were examined with four exposure metrics [model-predicted and observed minimum concentration (C _min) and area under the concentration-time curve from time zero to day 21 of T-DM1 at cycle 1] and multiple efficacy (OS, PFS, objective response rate) and safety (grade ≥ 3 adverse events, grade ≥ 3 thrombocytopenia, grade ≥ 3 hepatotoxicity) endpoints.

RESULTS

An apparent exposure-response trend was observed between model-predicted exposure metrics and efficacy; trends for observed exposure metrics were shallower and often not significant. Although median OS and PFS were numerically longer in patients with higher versus lower model-predicted cycle 1 C _min, OS and PFS hazard ratios for T-DM1-treated patients in the lowest exposure quartile (Q1) versus control were < 1 after adjusting for baseline risk factors (e.g., ECOG status, tumor burden, measurable disease, and number of disease sites). No meaningful exposure-response relationship was observed for any safety endpoints.

CONCLUSION

Exposure-response relationships for efficacy were inconsistent across exposure metrics; model-predicted cycle 1 C _min showed the strongest exposure-response trend. The Q1 subgroup based on model-predicted cycle 1 C _min had numerically similar or better OS and PFS versus control following covariate adjustment. The approved T-DM1 dose (3.6 mg/kg every 3 weeks) has a positive benefit-risk ratio versus control, even for the T-DM1 Q1 subgroup.

Pharmacokinetic Considerations for Antibody-Drug Conjugates against Cancer

Antibody-drug conjugates (ADCs) are ushering in the next era of targeted therapy against cancer. An ADC for cancer therapy consists of a potent cytotoxic payload that is attached to a tumour-targeted antibody by a chemical linker, usually with an average drug-to-antibody ratio (DAR) of 3.5-4. The theory is to deliver potent cytotoxic payloads directly to tumour cells while sparing healthy cells. However, practical application has proven to be more difficult. At present there are only two ADCs approved for clinical use. Nevertheless, in the last decade there has been an explosion of options for ADC engineering to optimize target selection, Fc receptor interactions, linker, payload and more. Evaluation of these strategies requires an understanding of the mechanistic underpinnings of ADC pharmacokinetics. Development of ADCs for use in cancer further requires an understanding of tumour properties and kinetics within the tumour environment, and how the presence of cancer as a disease will impact distribution and elimination. Key pharmacokinetic considerations for the successful design and clinical application of ADCs in oncology are explored in this review, with a focus on the mechanistic determinants of distribution and elimination.

Population pharmacokinetics and exposure-response of trastuzumab emtansine in advanced breast cancer previously treated with ≥2 HER2-targeted regimens

AIMS

We conducted population pharmacokinetic (PopPK) and exposure-response analyses for trastuzumab emtansine (T-DM1), to assess the need for T-DM1 dose optimization in patients with low exposure by using TH3RESA [A Study of Trastuzumab Emtansine in Comparison With Treatment of Physician's Choice in Patients With human epidermal growth factor receptor 2 (HER2)-positive Breast Cancer Who Have Received at Least Two Prior Regimens of HER2-directed Therapy] study data (NCT01419197). The randomized phase III TH3RESA study investigated T-DM1 vs. treatment of physician's choice (TPC) in patients with heavily pretreated HER2-positive advanced breast cancer.

METHODS

We compared a historical T-DM1 PopPK model with T-DM1 pharmacokinetics in TH3RESA and performed exposure-response analyses using model-predicted cycle 1 maximum concentration (C_max ), cycle 1 minimum concentration (C_min ) and area under the concentration-time curve at steady state (AUC_ss ). Kaplan-Meier analyses [overall survival (OS), progression-free survival (PFS)] and logistic regression [overall response rate (ORR), safety] were stratified by T-DM1 exposure metrics. Survival hazard ratios (HRs) in the lowest exposure quartile (Q1) of cycle 1 C_min were compared with matched TPC-treated patients.

RESULTS

T-DM1 concentrations in TH3RESA were described well by the historical PopPK model. Patients with higher cycle 1 C_min and AUC_ss exhibited numerically longer median OS and PFS and higher ORR than patients with lower exposure. Exposure-response relationships were less evident for cycle 1 C_max . No relationship between exposure and safety was identified. HRs for the comparison of T-DM1-treated patients in the Q1 subgroup with matched TPC-treated patients were 0.96 [95% confidence interval (CI) 0.63, 1.47] for OS and 0.92 (95% CI 0.64, 1.32) for PFS.

CONCLUSIONS

Exposure-response relationships for efficacy were inconsistent across exposure metrics. HRs for survival in patients in the lowest T-DM1 exposure quartile vs. matched TPC-treated patients suggest that, compared with TCP, the approved T-DM1 dose is unlikely to be detrimental to patients with low exposure.