Evaluation of Safety and Clinically Relevant Drug-Drug Interactions with Tucatinib in Healthy Volunteers

Impact of variation in CYP3A and CYP2C8 on tucatinib metabolic clearance in human liver microsomes

Tucatinib is a small molecule tyrosine kinase inhibitor indicated for HER2-positive breast cancer. This recently approved drug is primarily metabolized by cytochrome P450 (P450) 2C8 and CYP3A. Given the interindividual variability in the pharmacokinetics of some kinase inhibitors, the present study explored how variability in CYP2C8 and CYP3A activities and concentrations can influence variability in overall tucatinib metabolic clearance in vitro. Tucatinib depletion, P450 activities, and P450 concentrations were measured in human liver microsomes from 21 donors (males n = 11, females n = 10). CYP2C8 and CYP3A activities were quantitated by liquid chromatography-tandem mass spectrometry analysis using the following marker reactions: amodiaquine N-deethylation and midazolam 1'-hydroxylation, respectively. CYP2C8, CYP3A4, and CYP3A5 protein concentrations were measured using quantitative targeted absolute proteomics. The minimum clearance rate was 2.01 μL/mg/min, and the maximum clearance rate was 28.9 μL/mg/min, indicating a 14.3-fold variation in the apparent tucatinib clearance between donors. Tucatinib clearance was significantly correlated with both CYP2C8 and CYP3A enzyme activities and protein concentrations in this donor cohort (r = 0.781, r = 0.904, r = 0.907, and r = 0.882, respectively). A multiple linear regression model was developed to determine the most significant parameters influencing tucatinib clearance. Overall, we found that CYP2C8 and CYP3A activities were significant predictors of tucatinib apparent clearance in human liver microsomes from individual donors. Proteomics data are available with identifier PXD057282 via ProteomeXchange. SIGNIFICANCE STATEMENT: The results from this study demonstrate a strong relationship between CYP2C8 and CYP3A phenotypes and interindividual variability in tucatinib metabolism. By elucidating how variability in CYP2C8 and CYP3A phenotypes influence tucatinib pharmacokinetics, this study has the potential to provide the framework for future studies that could inform dosing to minimize adverse events and improve therapeutic outcomes. Ultimately, understanding how individual cytochrome P450 phenotypes influence the clearance of cancer therapeutics will aid in the development of tailored regimens for diverse patient populations.

Population Pharmacokinetic Analysis of Tucatinib in Healthy Participants and Patients with Breast Cancer or Colorectal Cancer

BACKGROUND AND OBJECTIVE

Tucatinib is a highly selective, oral, reversible, human epidermal growth factor receptor 2 (HER2)-specific tyrosine kinase inhibitor. Tucatinib is approved at a 300-mg twice-daily dose in adults in combination with trastuzumab and capecitabine for advanced HER2-postitive (HER2+) unresectable or metastatic breast cancer and in combination with trastuzumab for RAS wild-type HER2+ unresectable or metastatic colorectal cancer. This study sought to characterize the pharmacokinetics (PK) and assess sources of PK variability of tucatinib in healthy volunteers and in patients with HER2+ metastatic breast or colorectal cancers.

METHODS

A population pharmacokinetic model was developed based on data from four healthy participant studies and three studies in patients with either HER2+ metastatic breast cancer or metastatic colorectal cancer using a nonlinear mixed-effects modeling approach. Clinically relevant covariates were evaluated to assess their impact on exposure, and overall model performance was evaluated by prediction-corrected visual predictive checks.

RESULTS

A two-compartment pharmacokinetic model with linear elimination and first-order absorption preceded by a lag time adequately described tucatinib pharmacokinetic profiles in 151 healthy participants and 132 patients. Tumor type was identified as a significant covariate affecting tucatinib bioavailability and clearance, resulting in a 1.2-fold and 2.1-fold increase in tucatinib steady-state exposure (area under the concentration-time curve) in HER2+ metastatic colorectal cancer and HER2+ metastatic breast cancer, respectively, compared with healthy participants. No other covariates, including mild renal or hepatic impairment, had an impact on tucatinib pharmacokinetics.

CONCLUSIONS

The impact of statistically significant covariates identified was not considered clinically meaningful. No tucatinib dose adjustments are required based on the covariates tested in the final population pharmacokinetic model.

CLINICAL TRIAL REGISTRATION

NCT03723395, NCT03914755, NCT03826602, NCT03043313, NCT01983501, NCT02025192.

Kinase Inhibitors FDA Approved 2018-2023: Drug Targets, Metabolic Pathways, and Drug-Induced Toxicities

Small molecule kinase inhibitors are one of the fastest growing classes of drugs, which are approved by the US Food and Drug Administration (FDA) for cancer and noncancer indications. As of September 2023, there were over 70 FDA-approved small molecule kinase inhibitors on the market, 42 of which were approved in the past five years (2018-2023). This minireview discusses recent advances in our understanding of the pharmacology, metabolism, and toxicity profiles of recently approved kinase inhibitors with a central focus on tyrosine kinase inhibitors (TKIs). In this minireview we discuss the most common therapeutic indications and molecular target(s) of kinase inhibitors FDA approved 2018-2023. We also describe unique aspects of the metabolism, bioactivation, and drug-drug interaction (DDI) potential of kinase inhibitors; discuss drug toxicity concerns related to kinase inhibitors, such as drug-induced liver injury; and highlight clinical outcomes and challenges relevant to TKI therapy. Case examples are provided for common TKI targets, metabolism pathways, DDI potential, and risks for serious adverse drug reactions. The minireview concludes with a discussion of perspectives on future research to optimize TKI therapy to maximize efficacy and minimize drug toxicity. SIGNIFICANCE STATEMENT: This minireview highlights important aspects of the clinical pharmacology and toxicology of small molecule kinase inhibitors FDA approved 2018-2023. We describe key advances in the therapeutic indications and molecular targets of TKIs. The major metabolism pathways and toxicity profiles of recently approved TKIs are discussed. Clinically relevant case examples are provided that demonstrate the risk for hepatotoxic drug interactions involving TKIs and coadministered drugs.

Creation of Novel Sensitive Probe Substrate and Moderate Inhibitor Models for a Comprehensive Prediction of CYP2C8 Interactions for Tucatinib

A physiologically-based pharmacokinetic (PBPK) model was developed to simulate plasma concentrations of tucatinib (TUKYSA®) after single-dose or multiple-dose administration of 300 mg b.i.d. orally. This PBPK model was subsequently applied to support evaluation of drug-drug interaction (DDI) risk as a perpetrator resulting from tucatinib inhibition of CYP3A4, CYP2C8, CYP2C9, P-gp, or MATE1/2-K. The PBPK model was also applied to support evaluation of DDI risk as a victim resulting from co-administration with CYP3A4 or CYP2C8 inhibitors, or a CYP3A4 inducer. After refinement with clinical DDI data, the final PBPK model was able to recover the clinically observed single and multiple-dose plasma concentrations for tucatinib when tucatinib was administered as a single agent in healthy subjects. In addition, the final model was able to recover clinically observed plasma concentrations of tucatinib when administered in combination with itraconazole, rifampin, or gemfibrozil as well as clinically observed plasma concentrations of probe substrates of CYP3A4, CYP2C8, CYP2C9, P-gp, or MATE1/2-K. The PBPK model was then applied to prospectively predict the potential perpetrator or victim DDIs with other substrates, inducers, or inhibitors. To simulate a potential interaction with a moderate CYP2C8 inhibitor, two novel PBPK models representing a moderate CYP2C8 inhibitor and a sensitive CYP2C8 substrate were developed based on the existing PBPK models for gemfibrozil and rosiglitazone, respectively. The simulated population geometric mean area under the curve ratio of tucatinib with a moderate CYP2C8 inhibitor ranged from 1.98- to 3.08-fold, and based on these results, no dose modifications were proposed for moderate CYP2C8 inhibitors for the tucatinib label.

Effect of Tucatinib on Cardiac Repolarization in Healthy Volunteers

BACKGROUND AND OBJECTIVE

Tucatinib is a selective tyrosine kinase inhibitor of the human epidermal growth factor receptor 2 (HER2) approved to treat metastatic HER2-positive breast and colorectal cancers. The International Council for Harmonisation of Technical Requirements for Human Use (ICH) E14 guideline mandates that new drugs are assessed for potential effects on cardiac repolarization through electrocardiogram (ECG) evaluation in a QT/corrected QT (TQT) study.

METHODS

We evaluated the effect of tucatinib on cardiac repolarization in healthy volunteers in a phase I, randomized, partially double-blind, placebo-and positive-controlled three-period crossover study. The primary endpoint was the placebo-corrected change from baseline in QT interval values, corrected for heart rate using Fridericia's method (ΔΔQTcF).

RESULTS

After achieving steady-state tucatinib exposures with 300 mg twice daily, the observed ΔΔQTcF ranged from -2.9 msec at 2 hours post-dose to 0 msec at 4 hours post-dose. The upper bound of the 90% confidence interval (CI) was below 5 ms at all post-dose timepoints. Assay sensitivity was confirmed as the lower bound of the 90% CI and was >5 ms following moxifloxacin dosing. As the mean ΔΔQTcF of tucatinib was predicted to be -  1.80 ms (90% CI -  3.90, 0.30) at clinically relevant tucatinib concentrations (511 ng/mL), an effect of tucatinib on QTcF exceeding 10 ms was excluded within observed ranges of tucatinib (up to ~1000 ng/mL). Tucatinib had no clinically relevant effect on heart rate or cardiac conduction. The safety profile of tucatinib was manageable after multiple doses.

CONCLUSION

Tucatinib had no clinically relevant effects on studied ECG parameters. This study constitutes a clearly negative TQT study per ICH E14 guidance.

CLINICAL TRIAL REGISTRATION

This trial (NCT03777761) was registered on 17 December 2018.

HER2-Selective and Reversible Tyrosine Kinase Inhibitor Tucatinib Potentiates the Activity of T-DM1 in Preclinical Models of HER2-positive Breast Cancer

The oncogenic receptor HER2 is overexpressed in many cancers, including up to 20% of breast cancers. Despite the availability of HER2-targeted treatments, patients’ disease often progresses during therapy, underscoring the need for novel treatment strategies. The addition of tucatinib, a reversible, highly selective HER2 tyrosine kinase inhibitor (TKI), to treatment with trastuzumab and capecitabine significantly improved survival outcomes of patients with HER2-positive metastatic breast cancer, including those with active brain metastases. We rationalized that combining tucatinib with other HER2-targeting agents with complementary mechanisms of action would further increase efficacy against tumors. We characterized the activity of tucatinib with the antibody–drug conjugate T-DM1 in preclinical models of breast cancer, including HER2-positive breast cancer cells and patient-derived xenograft (PDX) models. Mechanistic details on tucatinib activity were obtained in internalization and catabolism studies. In combination, tucatinib and T-DM1 showed an enhanced, often synergistic, cytotoxic response and demonstrated improved antitumor activity in vivo, including in PDX models refractory to T-DM1 single-agent activity. Mechanistically, tucatinib mediated an increase in inactive HER2 molecules at the cell surface through inhibition of HER2 ubiquitination, resulting in increased internalization and catabolism of T-DM1. The combination was correlated with enhanced HER2 pathway inhibition, decreased proliferation, and increased apoptosis. In a xenograft model of brain metastasis, tucatinib penetrated intracranial tumor tissues, inhibiting tumor growth and improving survival. These results suggest that tucatinib may be the optimal TKI partner for HER2-targeted therapies and support clinical studies of its combination with T-DM1, including in patients with brain metastases.

SIGNIFICANCE

The preclinical findings in breast cancer models presented here demonstrate that combining tucatinib with T-DM1 enhances the antitumor activity of either agent alone, supporting clinical studies of the combination in HER2-positive breast cancer, including in patients with brain metastases, which remains an important unmet medical need.

Quantitative Consideration of Clinical Increases in Serum Creatinine Caused by Renal Transporter Inhibition

Creatinine is a common biomarker of renal function and is secreted in the renal tubular cells via drug transporters, such as organic cation transporter 2 and multidrug and toxin extrusion (MATE) 1/2-K. To differentiate between drug-induced acute kidney injury (AKI) and drug interactions through the renal transporter, it has been examined whether these transporter inhibitions quantitatively explained increases in serum creatinine (SCr) at their clinically relevant concentrations using drugs without any changes in renal function. For such renal transporter inhibitors and recently approved tyrosine kinase inhibitors (TKIs), this mini-review describes clinical increases in SCr and inhibitory potentials against the renal transporters. Most cases of SCr elevations can be explained by considering the renal transporter inhibitions based on unbound maximum plasma concentrations, except for drugs associated with obvious changes in renal function. SCr increases for cobicistat, dolutegravir, and dronedarone, and some TKIs were significantly underestimated, and these underestimations were suggested to be associated with low plasma unbound fractions. Sensitivity analysis of SCr elevations regarding inhibitory potentials of MATE1/2-K demonstrated that typical inhibitors such as cimetidine, DX-619, pyrimethamine, and trimethoprim could give false interpretations of AKI according to the criteria based on relative or absolute levels of SCr elevations. Recent progress and current challenges of physiologically-based pharmacokinetics modeling for creatinine disposition were also summarized. Although it should be noted for the potential impact of in vitro assay designs on clinical translatability of transporter inhibitions data, mechanistic approaches could support decision-making in clinical development to differentiate between AKI and creatinine-drug interactions. SIGNIFICANCE STATEMENT: Serum creatinine (SCr) is widely used as an indicator of kidney function, but it increases due to inhibitions of renal transporters, such as multidrug and toxin extrusion protein 1/2-K despite no functional changes in the kidney. Such SCr elevations were quantitatively explained by renal transporter inhibitions except for some drugs with high protein binding. The present analysis demonstrated that clinically relevant inhibitors of the renal transporters could cause SCr elevations above levels corresponding to acute kidney injury criteria.

The Pharmacokinetics and Safety of Tucatinib in Volunteers with Hepatic Impairment

BACKGROUND AND OBJECTIVE

Tucatinib, a highly selective tyrosine kinase inhibitor of the human epidermal growth factor receptor 2 (HER2) approved for HER2-positive metastatic breast cancer, is cleared by hepatic metabolism and subsequent biliary excretion. Liver disease can alter drug disposition and pharmacokinetics (PK). The objective of this study is to characterize PK and safety of tucatinib in volunteers with hepatic impairment.

METHODS

This Phase 1 study compared the PK and safety of a single 300-mg oral dose of tucatinib in volunteers with mild, moderate, and severe hepatic impairment (Child-Pugh A/B/C) to healthy volunteers matched for sex, age, and body mass index. Pharmacokinetic parameters were determined for tucatinib and its predominant metabolite ONT-993.

RESULTS

Compared with healthy volunteers, tucatinib exposure was similar in volunteers with mild impairment and increased in those with moderate or severe impairment without reaching statistical significance. Respective fold increases in geometric mean ratios for AUC0-t and AUC0-∞ were 1.13 and 1.15 in moderate impairment, and 1.43 and 1.61 in severe impairment compared with healthy volunteers. Three treatment-emergent adverse events (nausea, dermatitis, and increased transaminases) were reported in three volunteers and showed no obvious association with hepatic impairment status.

CONCLUSION

The 1.61-fold geometric mean ratio AUC0-∞ increase in volunteers with severe hepatic impairment supports the recommendation in the tucatinib prescribing information to reduce the dose from 300 mg twice daily to 200 mg twice daily in patients with severe impairment; no dose adjustment is recommended for patients with mild or moderate hepatic impairment. This trial (NCT03722823) was registered on October 29, 2018.