Native liquid chromatography mass spectrometry (LC-MS) is a commonly used approach for intact analysis of inter-chain cysteine conjugated antibody-drug conjugates (ADCs). Coupling native LC-MS with affinity capture provides a platform for intact ADC analysis from in vivo samples and characterisation of individual drug load species, specifically the impact of drug linker deconjugation, hydrolysis, and differential clearance in a biological system.This manuscript describes data generated from native LC-MS analysis of ADCs from human plasma, both in vitro incubations and clinical samples. It also details the pharmacokinetic (PK) model built to specifically characterise the disposition of individual drug load species from MMAE and MMAF interchain cysteine conjugated ADCs.In vitro deconjugation and hydrolysis rates were similar across both ADCs. Differential clearance of higher loaded species in vivo was pronounced for the MMAE conjugated ADC, while systemic elimination after accounting for deconjugation was similar across drug loads for the MMAF conjugated ADC. This is the first report of affinity capture native LC-MS analysis, and subsequent modelling of deconjugation, hydrolysis and clearance rates of individual drug load species using clinical data from cysteine conjugated ADCs.

Background and ObjectiveTucatinib 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.MethodsA 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.ResultsA 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.ConclusionsThe 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 RegistrationNCT03723395, NCT03914755, NCT03826602, NCT03043313, NCT01983501, NCT02025192.

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.

BackgroundSEA-CD40 is an investigational, non-fucosylated, humanized monoclonal IgG1antibody that activates CD40, an immune-activating tumor necrosis factor receptor superfamily member. SEA-CD40 exhibits enhanced binding to activating FcγRIIIa, possibly enabling greater immune stimulation than other CD40 agonists. A first-in-human phase 1 trial was conducted to examine safety, pharmacokinetics, and pharmacodynamics of SEA-CD40 monotherapy in patients with advanced solid tumors and lymphoma.MethodsSEA-CD40 was administered intravenously to patients with solid tumors or lymphoma in 21-day cycles with standard 3+3 dose escalation at 0.6, 3, 10, 30, 45, and 60 µg/kg. An intensified dosing regimen was also studied. The primary objectives of the study were to evaluate the safety and tolerability and identify the maximum tolerated dose of SEA-CD40. Secondary objectives included evaluation of the pharmacokinetic parameters, antitherapeutic antibodies, pharmacodynamic effects and biomarker response, and antitumor activity.ResultsA total of 67 patients received SEA-CD40 including 56 patients with solid tumors and 11 patients with lymphoma. A manageable safety profile was observed, with predominant adverse events of infusion/hypersensitivity reactions (IHRs) reported in 73% of patients. IHRs were primarily ≤grade 2 with an incidence associated with infusion rate. To mitigate IHRs, a standardized infusion approach was implemented with routine premedication and a slowed infusion rate. SEA-CD40 infusion resulted in potent immune activation, illustrated by dose dependent cytokine induction with associated activation and trafficking of innate and adaptive immune cells. Results suggested that doses of 10–30 µg/kg may result in optimal immune activation. SEA-CD40 monotherapy exhibited evidence of antitumor activity, with a partial response in a patient with basal cell carcinoma and a complete response in a patient with follicular lymphoma.ConclusionsSEA-CD40 was tolerable as monotherapy and induced potent dose dependent immune cell activation and trafficking consistent with immune activation. Evidence of monotherapy antitumor activity was observed in patients with solid tumors and lymphoma. Further evaluation of SEA-CD40 is warranted, potentially as a component of a combination regimen.Trial registration numberNCT02376699.

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. 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). 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

Background: Oxaliplatin (OX)-containing regimens are frequently utilized to treat gastrointestinal (GI) cancers. OX is eliminated predominately via urinary excretion (GFR and active tubular secretion). The contribution of active transport via OCT2 and MATE1/2-K to OX clearance is not fully understood. Tyrosine kinase inhibitors (TKIs) are frequently found to interact with OCT2/MATE transporters; however, a gap in knowledge remains between their clinical potential to impact OX pharmacokinetics (PK) and in turn, impact renal function. Tucatinib (TUC) is a highly selective human epidermal growth factor receptor 2 (HER2)-directed TKI approved in multiple regions in combination with trastuzumab and capecitabine for adult patients with metastatic HER2+ breast cancer and is currently being investigated in other HER2+ tumors. TUC inhibits OCT2/MATE-mediated transport of metformin and creatinine in vitro and in vivo. In this study, we investigated the impact of TUC on OX plasma PK, OX renal clearance (Clr), and renal function. Methods: In vitro inhibition of OCT2/MATE-mediated transport of OX by TUC was assessed in OCT2, MATE1, or MATE2-K-expressing MDCK-II cells. SGNTUC-024 (NCT04430738) is a Ph1b/2 clinical study in patients with HER2+ GI cancers evaluating the impact of TUC on the safety and PK of OX. Patients received TUC 150 mg (Cohort 1A) or 300 mg (Cohort 1B) BID starting on C1D8 of a 2-week cycle in combination with modified FOLFOX6/7. Intensive PK was collected in plasma and urine for OX alone (C1D1) or with steady-state TUC (C2D1). Total plasma platinum (Pt, analyzed as a surrogate for OX and catabolites), plasma Pt ultrafiltrate (PUF, unbound), and urine Pt were quantitatively analyzed via ICP-MS. Serum Cystatin C (CysC) was measured as a pharmacodynamic (PD) renal function marker in Cohorts 1A and 1B. Results: TUC inhibited in vitro OX transport by MATE1 (IC50 = 0.0639 µM), MATE2-K (IC50 = 0.0382 µM), and OCT2 (IC50 = 0.491 µM). In 11 patients, total Pt and PUF AUC0-8h geometric mean ratio (GMR) and 90% confidence intervals (CI) between patients who received OX alone compared to in combination were 1.1 (0.98, 1.3) and 1.0 (0.78, 1.4) in Cohort 1A (n=4) and 1.1 (0.96, 1.2) and 1.0 (0.98, 1.1) in Cohort 1B (n=7), respectively. OX GM (%CV) renal clearance (Clr,0-8h in mL/min) and fraction excreted 24h post-dose (fe,0-24h) were similar with and without TUC in both Cohort 1A (C1D1 Clr0-8h = 277 (33), fe,0-24h = 22% (17); C2D1 Clr0-8h = 249 (78), fe,0-24h = 21% (15)) and Cohort 1B (C1D1 Clr0-8h = 189 (37), fe,0-24h = 17.7% (16); C2D1 Clr0-8h = 177 (40), fe,0-24h = 16.6% (35)). Reversible slight increases in CysC (normalized to baseline) on day 3 of each cycle, irrespective of tucatinib, were observed. Conclusions: This investigation of in vitro and in vivo determinants of OX PK demonstrates that TUC does not alter the renal clearance of oxaliplatin nor renal function when OX is administered in combination with TUC. Citation Format: Ariel R. Topletz-Erickson, Anthony Lee, Vineet Kumar, Michelle Ubowski, JoAl G. Mayor, Layth I. Abdulrasool, Clark M. Henderson, Joseph A. Ware, Christopher J. Endres. Tucatinib does not alter oxaliplatin PK or associated renal function: An OCT2 and MATE transport inhibition study. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5060.

Tucatinib is a highly selective human epidermal growth factor receptor 2 (HER2) -directed tyrosine kinase inhibitor approved in multiple countries for metastatic HER2-positive breast cancer and in the US for metastatic HER2-postive metastatic colorectal cancer. This phase Ⅰ study (N＝36) compared the pharmacokinetic (PK) and safety profiles of tucatinib administered at 50-, 150-, and 300-mg doses taken twice daily orally in healthy Japanese (n＝18［n＝6 per tucatinib dose cohort］) and Caucasian volunteers (n＝18［n＝6 per tucatinib dose cohort］) to assess ethnicity effects on PK and dose proportionality of tucatinib. Ethnicity effects between both populations were evaluated using an analysis of covariance (ANCOVA) model and dose proportionality of tucatinib was assessed using a log-transformed linear regression model. Tucatinib steady-state exposure (AUCss) and maximum plasma concentration (Cmax) geometric mean values were similar between Japanese and Caucasian volunteers, with ANCOVA-adjusted geometric mean ratios (90％ confidence intervals) of 2.63 (1.04, 6.62), 1.11 (0.76, 1.62), and 1.33 (0.91, 1.95) for Cmax and 1.97 (0.85, 4.56), 1.05 (0.70, 1.58), and 1.04 (0.72, 1.49) for AUCss in the tucatinib 50-, 150-, and 300-mg cohorts, respectively. Thirty-three treatment-emergent adverse events (TEAEs) in 13 Caucasian volunteers and 2 TEAEs in 2 Japanese volunteers were reported. All TEAEs were grade 1, and the majority resolved by the end of study. At the approved therapeutic dose of 300 mg twice daily, tucatinib had a manageable safety profile and exposures were similar between Japanese and Caucasian volunteers. These findings indicate there is no need for dose alteration of tucatinib based on ethnicity.

Tucatinib is approved for treatment of human epidermal growth factor receptor 2-positive metastatic breast cancer. Understanding potential drug–drug interactions (DDIs) informs proper dosing when co-administering tucatinib with other therapies. The aim of this study was to evaluate DDIs between tucatinib and metabolizing enzymes and transporters in healthy volunteers. Parts A–C assessed the impact of itraconazole (cytochrome P450 [CYP] 3A4 inhibitor), rifampin (CYP3A4/CYP2C8 inducer), or gemfibrozil (CYP2C8 inhibitor) on the pharmacokinetics of a single 300 mg dose of tucatinib administered orally and its primary metabolite, ONT-993. Parts D and E assessed the effect of steady-state tucatinib on the pharmacokinetics of repaglinide (CYP2C8 substrate), tolbutamide (CYP2C9 substrate), midazolam (CYP3A4 substrate), and digoxin (P-glycoprotein substrate). Tucatinib area under the concentration–time curve from time 0 extrapolated to infinity (AUC0–inf) increased by ~ 1.3- and 3.0-fold with itraconazole and gemfibrozil, respectively, and decreased by 48% with rifampin, indicating that tucatinib is metabolized primarily by CYP2C8, and to a lesser extent via CYP3A. Tucatinib was a strong inhibitor of CYP3A (midazolam AUC0–inf increased 5.7-fold), a weak inhibitor of CYP2C8 and P-glycoprotein, and had no impact on CYP2C9-mediated metabolism in humans. Tucatinib was well tolerated, alone and with co-administered drugs. The potential DDIs identified here may be mitigated by avoiding concomitant use of tucatinib with strong CYP3A inducers, moderate CYP2C8 inducers, CYP3A substrates with a narrow therapeutic window (modifying substrate dose where concomitant use is unavoidable), and strong CYP2C8 inhibitors (decreasing tucatinib dose where concomitant use is unavoidable), or by reducing the dose of P-glycoprotein substrates with a narrow therapeutic window. This trial (NCT03723395) was registered on October 29, 2018.

PURPOSE:Tucatinib, a small molecule for the treatment of metastatic HER2-positive breast cancer, was extensively metabolized in humans to multiple oxidative metabolites. To fully understand the elimination and biotransformation pathways of tucatinib, we investigated the in vitro and in vivo metabolism of tucatinib, and also conducted a Phase I trial using [14C]tucatinib.METHODS:To identify the responsible enzymes for tucatinib clearance, we investigated the in vitro metabolism of tucatinib including enzyme phenotyping, which facilitated the discovery of several metabolites in human and monkey plasma and excreta, in particular M1 (ONT-993, an aliphatic hydroxylated metabolite). Stereoselective formation of M1 was further investigated in vitro, in vivo, and in silico.RESULTS:In humans, approximately 86% of the total radiolabeled dose was recovered in feces and 4% in urine; in plasma, approximately 76% of radioactivity circulated as parent drug, with 19% attributed to multiple metabolites. The primary isoforms responsible for the elimination of tucatinib were CYP2C8 and CYP3A4/5. CYP2C8 was shown to possess sole catalytic activity for the formation of M1, whereas CYP3A4/5 and aldehyde oxidase catalyzed the formation of the remaining metabolites. Subsequent investigation revealed that M1 was formed in a stereoselective manner. Examination of the enantiomeric ratio of M1 stereoisomers observed in humans relative to cynomolgus monkeys revealed comparable results, suggesting that the enantiomers that comprise M1 were not considered to be unique or disproportionately high in human.CONCLUSION:CYP2C8 and CYP3A4/5 are the primary drug-metabolizing enzymes involved in the in vitro metabolism of tucatinib, which provided the basis to describe human disposition of tucatinib and formation of the observed metabolites.

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. 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. 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. 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.

Abstract Background: Tucatinib (TUKYSA®) is a selective HER2-targeted tyrosine kinase inhibitor indicated in combination with trastuzumab and capecitabine for adult patients with metastatic HER2+ breast cancer who have received ≥1 prior HER2-based regimen, including patients with brain metastases. Tucatinib is cleared via CYP2C8-mediated metabolism, to a lesser extent by CYP3A, and biliary excretion. Impaired hepatic function (HI) can cause alterations in drug disposition and pharmacokinetics (PK), thus characterizing PK in subjects with HI was necessary to inform dosing recommendations. ONT-380-009 was a clinical study conducted to evaluate the PK of tucatinib in volunteers with HI based on Child-Pugh (CP) score compared to matched healthy subject controls. Methods: Volunteers (N=37) at 4 centers were enrolled in the study. Subjects with mild (CP Class A; n=8), moderate (CP Class B; n=8) or severe (CP Class C; n=6) HI were matched to subjects with normal hepatic function (n=15) by age, BMI and sex. Tucatinib was administered as a single 300 mg oral dose. Plasma samples were collected for PK analysis and tucatinib concentrations measured using validated LC-MS/MS methods. The PK and safety profiles between each HI group and matched controls were compared. Results: Tucatinib single dose PK was similar between subjects with mild HI and matched controls (AUCinf and Cmax geometric mean ratios (GMR) [90% CI] were 99.0% [76.3%, 128%] and 104% [61.6%, 175%], respectively). Tucatinib plasma exposures were generally higher in subjects with moderate or severe HI compared to matched controls (AUCinf GMR [90% CI] were 115% [65.3%, 202%] and 161% [67.3%, 385%], respectively; Cmax GMR [90% CI] were 88.5% [42.1%, 186%] and 117% [36.6%, 377%], respectively). Changes were highly variable, and ratios crossed 1.0 (or 100%). The observed trend of increased plasma exposure for tucatinib by degree of HI did not reach statistical significance due to high inter-subject variability. Three subjects experienced a total of two Grade 1 (nausea, dermatitis) and one Grade 2 (increased transaminases) treatment-emergent adverse events (TEAEs) in the study, two of which were considered tucatinib-related. All three TEAEs recovered. No TEAEs were observed in patients with moderate or severe hepatic impairment. Conclusions: Subjects with mild HI had similar tucatinib exposures compared to subjects with normal hepatic function. Tucatinib exposure was generally increased in subjects with moderate and severe HI, however GMR values were less than 2-fold and exhibited large inter-subject variability. Overall, a single 300 mg oral dose of tucatinib was considered safe and well tolerated in this study for subjects with normal hepatic function or with mild, moderate, or severe HI. The 1.6-fold GMR AUCinf increase in severe HI subjects support dose reduction from 300 mg BID to 200 mg BID in those subjects; no dose adjustment is recommended for subjects with mild or moderate HI. Citation Format: Ariel R. Topletz-Erickson, Anthony Lee, JoAl G. Mayor, Hao Sun, Layth I. Abdulrasool, Evelyn L. Rustia, Luke Walker, Christopher J. Endres. Pharmacokinetics of tucatinib in healthy and hepatically-impaired volunteers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1371.

Background: Tucatinib (TUKYSA®) is a selective HER2-targeted tyrosine kinase inhibitor indicated in combination with trastuzumab and capecitabine for adult patients with metastatic HER2+ breast cancer who have received ≥1 prior HER2-based regimen, including patients with brain metastases. Tucatinib is cleared via CYP2C8-mediated metabolism, to a lesser extent by CYP3A, and biliary excretion. Impaired hepatic function (HI) can cause alterations in drug disposition and pharmacokinetics (PK), thus characterizing PK in subjects with HI was necessary to inform dosing recommendations. ONT-380-009 was a clinical study conducted to evaluate the PK of tucatinib in volunteers with HI based on Child-Pugh (CP) score compared to matched healthy subject controls. Methods: Volunteers (N=37) at 4 centers were enrolled in the study. Subjects with mild (CP Class A; n=8), moderate (CP Class B; n=8) or severe (CP Class C; n=6) HI were matched to subjects with normal hepatic function (n=15) by age, BMI and sex. Tucatinib was administered as a single 300 mg oral dose. Plasma samples were collected for PK analysis and tucatinib concentrations measured using validated LC-MS/MS methods. The PK and safety profiles between each HI group and matched controls were compared. Results: Tucatinib single dose PK was similar between subjects with mild HI and matched controls (AUCinf and Cmax geometric mean ratios (GMR) [90% CI] were 99.0% [76.3%, 128%] and 104% [61.6%, 175%], respectively). Tucatinib plasma exposures were generally higher in subjects with moderate or severe HI compared to matched controls (AUCinf GMR [90% CI] were 115% [65.3%, 202%] and 161% [67.3%, 385%], respectively; Cmax GMR [90% CI] were 88.5% [42.1%, 186%] and 117% [36.6%, 377%], respectively). Changes were highly variable, and ratios crossed 1.0 (or 100%). The observed trend of increased plasma exposure for tucatinib by degree of HI did not reach statistical significance due to high inter-subject variability. Three subjects experienced a total of two Grade 1 (nausea, dermatitis) and one Grade 2 (increased transaminases) treatment-emergent adverse events (TEAEs) in the study, two of which were considered tucatinib-related. All three TEAEs recovered. No TEAEs were observed in patients with moderate or severe hepatic impairment. Conclusions: Subjects with mild HI had similar tucatinib exposures compared to subjects with normal hepatic function. Tucatinib exposure was generally increased in subjects with moderate and severe HI, however GMR values were less than 2-fold and exhibited large inter-subject variability. Overall, a single 300 mg oral dose of tucatinib was considered safe and well tolerated in this study for subjects with normal hepatic function or with mild, moderate, or severe HI. The 1.6-fold GMR AUCinf increase in severe HI subjects support dose reduction from 300 mg BID to 200 mg BID in those subjects; no dose adjustment is recommended for subjects with mild or moderate HI. Citation Format: Ariel R. Topletz-Erickson, Anthony Lee, JoAl G. Mayor, Hao Sun, Layth I. Abdulrasool, Evelyn L. Rustia, Luke Walker, Christopher J. Endres. Pharmacokinetics of tucatinib in healthy and hepatically-impaired volunteers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1371.

AbstractTucatinib is a potent tyrosine kinase inhibitor selective for human epidermal growth factor receptor 2 (HER2) approved by the US Food and Drug Administration for the treatment of HER2‐positive metastatic breast cancer and in development for other HER2‐positive solid tumors. Modest, reversible serum creatinine (SCr) elevations have been observed in tucatinib clinical trials. SCr is conveyed by the renal drug transporters organic cation transporter 2 (OCT2) and multidrug and toxin extrusion protein 1 (MATE1) and 2‐K (MATE2‐K) and can increase in the presence of inhibitors of these transporters. In vitro, tucatinib inhibited OCT2‐, MATE1‐, and MATE2‐K‐mediated transport of metformin, with IC50 values of 14.7, 0.340, and 0.135 µM, respectively. Tucatinib also inhibited OCT2‐ and MATE1‐mediated transport of creatinine, with IC50 values of 0.107 and 0.0855 µM, respectively. A phase 1 study with metformin administered orally in the absence and presence of tucatinib was conducted in 18 healthy subjects. Renal function was assessed by measuring glomerular filtration rate (GFR; based on iohexol plasma clearance) and endogenous markers (SCr, cystatin C‐based estimated glomerular filtration rate [eGFR]) with and without tucatinib. Metformin exposure increased (1.4‐fold) and renal clearance decreased (29.99‐17.64 L/h) with tucatinib, with no effect on metformin maximum concentration. Creatinine clearance transiently decreased 23% with tucatinib. GFR and eGFR, which are unaffected by OCT2 and/or MATE1/2‐K transport, were unchanged with tucatinib. These data demonstrate that tucatinib inhibits OCT2‐ and MATE1/2‐K‐mediated tubular secretion of creatinine, which may manifest as mild SCr elevations that are not indicative of renal impairment.

Abstract Background: Tucatinib (TUC) is a potent, highly selective investigational HER2 tyrosine kinase inhibitor in development for treatment of patients with HER2+ metastatic breast cancer (MBC). In HER2CLIMB (H2C), a pivotal study of patients with HER2+ MBC, a modest transient, reversible increase in serum creatinine (SCr) levels was observed in patients who received TUC. Similarly, in a study with healthy volunteers, SCr increased after 300 mg BID TUC and returned to baseline levels after TUC discontinuation. Clinically, SCr is used as a biomarker for glomerular filtration rate (GFR) and is routinely measured to monitor for potential renal injury. However, SCr renal elimination also depends on the kidney transporters OCT2 (uptake), MATE1 (efflux) and MATE2-K (efflux). Inhibition of OCT2 and MATE1/2-K has been associated with SCr increases in the absence of kidney damage (e.g., abemaciclib). In vitro assessments and a clinical study were performed to assess the impact of TUC on OCT2 and MATE1/2-K-mediated transport. Methods: Inhibition of OCT2, MATE1, and MATE2-K-mediated transport by TUC was estimated in transfected MDCK-II cells using creatinine and metformin (MF), a sensitive OCT2 and MATE1/2-K substrate used to quantify transport inhibition in vivo, as probe substrates. Subsequently, a single-arm drug-drug interaction study was performed in 17 healthy volunteers to evaluate the effects of TUC on MF PK. MF (850 mg, PO) was administered in the absence and presence of TUC (300 mg BID, PO). Iohexol was administered to calculate actual GFR (aGFR) in the absence and presence of TUC. Plasma (iohexol, MF and TUC) and urine (MF) samples were collected for PK analysis; drug concentrations were measured using validated LC-MS/MS methods. Serum and urine creatinine levels were also measured. Results: In MDCK II cells, TUC inhibited creatinine transport by OCT2 (IC50 = 0.107 µM) and MATE1 (IC50 = 0.086 µM) and MF transport by MATE1 (IC50 = 0.340 µM) and MATE2-K (IC50 = 0.135 µM), but not by OCT2 (IC50 = 14.7 µM). Using these IC50 values, physiologically-based pharmacokinetic (PBPK) model simulations predicted a 1.16 to 1.35-fold increase of MF exposure in the presence of TUC. Consistent with the PBPK prediction, in healthy volunteers MF exposure (AUCinf) increased ~1.4-fold and renal clearance decreased from 29.99 L/h to 17.64 L/h in the presence of TUC with no effect on MF Cmax. Iohexol clearance was unaffected in the presence of TUC indicating no change in aGFR. SCr increased in the presence of TUC and returned to baseline 8 days after TUC discontinuation. Conclusions: Together, these data demonstrate that the observed SCr increase in clinical studies with TUC is due to inhibition of tubular secretion of creatinine via OCT2 and MATE1 and not due to an effect on kidney function. An alternative, non-creatinine-based measure of renal function should be considered for tucatinib. Citation Format: Ariel R. Topletz-Erickson, Anthony Lee, JoAl Mayor, Evelyn Rustia, Layth Abdulrasool, Luke Walker, Christopher J. Endres. Tucatinib inhibits creatinine and metformin renal tubule secretion but has no effect on renal function (GFR) [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3015.

Abstract Background: Tucatinib is a potent, highly selective HER2 tyrosine kinase inhibitor in development for the treatment of patients with HER2+ metastatic breast cancer. In vitro metabolism studies suggest that drug metabolizing enzymes CYP2C8 and CYP3A play a role in tucatinib metabolism. Tucatinib exhibits competitive inhibition of CYP2C8, CYP2C9, CYP3A, and P-gp, and metabolism-dependent inactivation of CYP3A in vitro. ONT-380-012 was a clinical drug interaction study conducted to evaluate the magnitude of potential enzyme and transporter interactions for tucatinib (both as a victim and perpetrator), and the safety of healthy subjects when administered tucatinib doses at therapeutic levels (300 mg BID). Methods: Healthy volunteers (n=116) at multiple centers were enrolled in the study. Parts A-C evaluated the effects of a strong CYP2C8 inhibitor (gemfibrozil), a strong CYP3A inhibitor (itraconazole), and a CYP3A/CYP2C8 inducer (rifampin) on single-dose tucatinib (300 mg) PK. Parts D and E assessed the effects of steady-state tucatinib (300 mg BID) on single-dose PK of substrate probes for CYP2C8 (repaglinide), CYP2C9 (tolbutamide), CYP3A (midazolam), and P-gp (digoxin). Plasma samples were collected for PK analysis and drug concentrations were measured using validated LC-MS/MS methods. Results: A strong CYP3A inhibitor (itraconazole) increased tucatinib AUCinf and Cmax 1.3-fold. A CYP3A/CYP2C8 inducer (rifampin) decreased tucatinib AUCinf and Cmax 48% and 37%, respectively. A strong CYP2C8 inhibitor (gemfibrozil) increased tucatinib AUCinf and Cmax 3.1- and 1.6-fold, respectively. Tucatinib increased the AUCinf and Cmax of the CYP3A substrate (midazolam) 5.7- and 3.0-fold, respectively, the AUCinf and Cmax of the CYP2C8 substrate (repaglinide) 1.7-fold, and the AUCinf of the P-gp substrate (digoxin) 1.5-fold. Tucatinib had no impact on the PK of the CYP2C9 substrate (tolbutamide). Overall, tucatinib was well tolerated in healthy volunteers when administered 300 mg BID. Conclusions: Together, these data indicate tucatinib is metabolized primarily by CYP2C8 and to a lesser extent via CYP3A. Tucatinib was found to be a strong inhibitor of CYP3A, a weak inhibitor of CYP2C8 and P-gp, and had no impact on CYP2C9-mediated metabolism in vivo. Citation Format: Ariel R. Topletz-Erickson, Anthony Lee, Hao Sun, JoAl Mayor, Luke Walker, Christopher J. Endres. Tucatinib inhibits CYP3A, CYP2C8 and P-gp-mediated elimination and is impacted by CYP2C8 inhibition in healthy volunteers [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3016.