Clinical Pharmacology for Tukysa
Mechanism Of Action
Tucatinib is a tyrosine kinase inhibitor of HER2. In vitro, tucatinib inhibits phosphorylation of HER2 and HER3, resulting in inhibition of downstream MAPK and AKT signaling and cell proliferation, and showed anti-tumor activity in HER2 expressing tumor cells. In vivo, tucatinib inhibited the growth of HER2 expressing tumors. The combination of tucatinib and trastuzumab showed increased anti-tumor activity in vitro and in vivo compared to either drug alone.
Pharmacodynamics
Exposure Response Relationship
Tucatinib exposure-response relationships and the time course of pharmacodynamics response have not been fully characterized.
Cardiac Electrophysiology
No large mean increase in QTc (i.e., > 20 ms) was detected following treatment with TUKYSA at the recommended dose of 300 mg taken orally twice daily.
Pharmacokinetics
Tucatinib AUC0-INF and Cmax increased proportionally over a dosage range from 50 mg to 300 mg (0.17 to 1 times the approved recommended dosage). Time to steady state was approximately 4 days. Steady-state pharmacokinetic parameters following administration of TUKYSA 300 mg twice daily for 7 days in patients with mBC and Mcrc are described in Table 9. The geometric mean (CV%) tucatinib AUC accumulation ratios ranged from 2.0 (26) fold to 2.5 (28) fold.
Table 9: Tucatinib Cmax and AUC
| Tumor Type |
AUCss (ng*h/mL) |
Cmax,ss (ng/mL) |
Ctrough,ss (ng/mL) |
| mBC |
5620 (43) |
747(45) |
288 (59) |
| mCRC |
3370 (49) |
405 (45) |
197 (63) |
Absorption
The median time to peak plasma concentration of tucatinib was approximately 2 hours (range 1 to 4 hours).
Effects Of Food
Following administration of a single oral dose of TUKYSA in 11 subjects after a high-fat meal (approximately 58% fat, 26% carbohydrate, and 16% protein), the mean AUC0-INF increased by 1.5-fold, the Tmax shifted from 1.5 hours to 4 hours, and Cmax was unaltered. The effect of food on the pharmacokinetics of tucatinib was not clinically meaningful.
Distribution
The geometric mean (CV%) apparent volume of distribution of tucatinib at steadystate were 903 (42) L and 829 (21) L in patients with mBC and mCRC, respectively. The plasma protein binding was 97.1% at clinically relevant concentrations.
At steady-state, concentrations of tucatinib and its metabolite ONT-993 in the cerebrospinal fluid were comparable to unbound plasma concentrations.
Elimination
At steady-state, tucatinib effective half-life was approximately 11.9 hours and geometric mean (CV%) apparent clearance was 53 (43) L/h in patients with mBC. Tucatinib effective half-life was approximately 16.4 hours and geometric mean (CV%) apparent clearance was 89 (49) L/h in patients with mCRC.
Metabolism
Tucatinib is metabolized primarily by CYP2C8 and to a lesser extent via CYP3A.
Excretion
Following a single oral dose of 300 mg radiolabeled tucatinib, approximately 86% of the total radiolabeled dose was recovered in feces (16% of the administered dose as unchanged tucatinib) and 4.1% in urine with an overall total recovery of 90% within 13 days post-dose. In plasma, approximately 76% of the plasma radioactivity was unchanged, 19% was attributed to identified metabolites, and approximately 5% was unassigned.
Specific Populations
Age (18-77 years), albumin (19 to 52 g/L), creatinine clearance (CLcr: 60 to 89 mL/min (n = 63); CLcr 30 to 59 mL/min (n = 6)), body weight (41 to 146 kg), sex (male (n = 170), female (n = 113)) and race (White (n = 205), Black (n = 37), or Asian (n = 25)) did not have a clinically meaningful effect on tucatinib exposure.
Renal Impairment
No clinically significant differences in the pharmacokinetics of tucatinib were observed in patients with mild to moderate renal impairment (CLcr: 30 to 89 mL/min by Cockcroft- Gault). The effect of severe renal impairment (CLcr: < 30 mL/min) on the pharmacokinetics of tucatinib is unknown.
Hepatic Impairment
Mild (Child-Pugh A) and moderate (Child-Pugh B) hepatic impairment had no clinically relevant effect on tucatinib exposure. Tucatinib AUC0-INF was increased by 1.6 fold in subjects with severe (Child-Pugh C) hepatic impairment compared to subjects with normal hepatic function.
Drug Interaction Studies
Clinical Studies
Table 10: Effect of Other Drugs on TUKYSA
| Concomitant Drug (Dose) |
TUKYSA Dose |
Ratio (90% CI) of Tucatinib Exposure With and Without Concomitant Drug |
| Cmax |
AUC |
| Strona CYP3A Inhibitor Itraconazole (200 mg BID) |
300 mg single dose |
1.3 (1.2, 1.4) |
1.3 (1.3, 1.4) |
| Strona CYP3A/Moderate 2C8 Inducer Rifampin (600 mg once daily) |
0.6 (0.5, 0.8) |
0.5 (0.4, 0.6) |
| Strona CYP2C8 Inhibitor Gemfibrozil (600 mg BID) |
1.6 (1.5, 1.8) |
3.0 (2.7, 3.5) |
Table 11: Effect of TUKYSA on Other Drugs
| Concomitant Drug (Dose) |
TUKYSA Dose |
Ratio (90% CI) of Exposure Measures of Concomitant Drug with/without Tucatinib |
| Cmax |
AUC |
| CYP2C8 Substrate Repaglinide (0.5 mg single dose) |
300 mg twice daily |
1.7 (1.4, 2.1) |
1.7 (1.5, 1.9) |
| CYP3A Substrate Midazolam (2 mg single dose) |
3.0 (2.6, 3.4) |
5.7 (5.0, 6.5) |
| P-gp Substrate Digoxin (0.5 mg single dose) |
2.4 (1.9, 2.9) |
1.5 (1.3, 1.7) |
| MATE½-K substratea Metformin (850 mg single dose) |
1.1 (1.0, 1.2) |
1.4 (1.2, 1.5) |
| a Tucatinib reduced the renal clearance of metformin without any effect on glomerular filtration rate (GFR) as measured by iohexol clearance and serum cystatin C. |
No clinically significant difference in the pharmacokinetics of tucatinib were observed when used concomitantly with omeprazole (proton pump inhibitor) or tolbutamide (sensitive CYP2C9 substrate).
In Vitro Studies
Cytochrome P450 (CYP) Enzymes
Tucatinib is a reversible inhibitor of CYP2C8 and CYP3A and a time-dependent inhibitor of CYP3A, but is not an inhibitor of CYP1A2, CYP2B6, CYP2C9, CYP2C19, or CYP2D6.
Uridine diphosphate (UDP)-glucuronosyl transferase (UGT) Enzymes
Tucatinib is not an inhibitor of UGT1A1.
Transporter Systems
Tucatinib is a substrate of P-gp and BCRP, but is not a substrate of OAT1, OAT3, OCT1, OCT2, OATP1B1, OATP1B3, MATE1, MATE2-K, or BSEP.
Tucatinib inhibits MATE1/MATE2-K-mediated transport of metformin and OCT2/MATE1- mediated transport of creatinine. The observed serum creatinine increase in clinical studies with tucatinib is due to inhibition of tubular secretion of creatinine via OCT2 and MATE1.
Clinical Studies
HER2-Positive Metastatic Breast Cancer
The efficacy of TUKYSA in combination with trastuzumab and capecitabine was evaluated in 612 patients in HER2CLIMB (NCT02614794), a randomized (2:1), double-blind, placebo-controlled trial. Patients were required to have HER2-positive, unresectable locally advanced or metastatic breast cancer, with or without brain metastases, and prior treatment with trastuzumab, pertuzumab, and ado-trastuzumab emtansine (T-DM1) separately or in combination, in the neoadjuvant, adjuvant or metastatic setting. HER2 positivity was based on archival or fresh tissue tested with an FDA-approved test at a central laboratory prior to enrollment with HER2 positivity defined as HER2 IHC 3+ or ISH positive.
Patients with brain metastases, including those with progressing or untreated lesions, were eligible provided they were neurologically stable and did not require immediate radiation or surgery. The trial excluded patients with leptomeningeal disease. Randomization was stratified by the presence or history of brain metastases (yes vs. no), Eastern Cooperative Oncology Group (ECOG) performance status (0 vs. 1), and region (U.S., Canada, or rest of world).
Patients received TUKYSA 300 mg or placebo orally twice daily with a trastuzumab or a non-US approved trastuzumab product loading dose of 8 mg/kg on Day 1 of Cycle 1 if needed and then a maintenance dose of 6 mg/kg on Day 1 of every 21-day cycle thereafter and capecitabine 1000 mg/m² orally twice daily on Days 1 through 14 of every 21-day cycle. An alternate trastuzumab dosing regimen was 600 mg administered subcutaneously on Day 1 of every 21-day cycle. Patients were treated until disease progression or unacceptable toxicity. Tumor assessments, including brain-MRI in patients with presence or history of brain metastases at baseline, occurred every 6 weeks for the first 24 weeks and every 9 weeks thereafter.
The major efficacy outcome measure was progression-free survival (PFS) in the first 480 randomized patients assessed by blinded independent central review (BICR) using Response Evaluation Criteria in Solid Tumors (RECIST) v1.1. Additional efficacy outcome measures were evaluated in all randomized patients and included overall survival (OS), PFS among patients with a history or presence of brain metastases (PFSBrainMets), and confirmed objective response rate (ORR).
The median age was 54 years (range: 22 - 82); 116 (19%) patients were age 65 or older. The majority were White (73%) and female (99%) and 51% had an ECOG performance status of 1. Sixty percent had estrogen and/or progesterone receptor-positive disease. Forty-eight percent had a presence or history of brain metastases; of these patients, 23% had untreated brain metastases, 40% had treated but stable brain metastases, and 37% had treated but radiographically progressing brain metastases. Seventy-four percent of patients had visceral metastases. Patients had received a median of 4 (range, 2 to 17) prior lines of systemic therapy and a median of 3 (range, 1 to 14) prior lines of systemic therapy in the metastatic setting. All patients received prior trastuzumab and T-DM1 and all but two patients had prior pertuzumab.
Efficacy results are summarized in Table 12 and Figure 1 and 2. Efficacy results were consistent across patient subgroups defined by stratification factors (presence or history of brain metastases, ECOG status, region of world) and hormone receptor status.
Table 12: Efficacy Results in HER2CLIMB
|
TUKYSA + Trastuzumab + Capecitabine |
Placebo + Trastuzumab + Capecitabine |
| PFS1 |
N=320 |
N=160 |
| Number of events (%) |
178 (56) |
97 (61) |
| Median, months (95% CI) |
7.8 (7.5, 9.6) |
5.6 (4.2, 7.1) |
| Hazard ratio (95% CI) 2 |
0.54 (0.42, 0.71) |
| P-value3 |
<0.00001 |
| OS |
N=410 |
N=202 |
| Number of deaths (%) |
130 (32) |
85 (42) |
| Median, months (95% CI) |
21.9 (18.3, 31.0) |
17.4 (13.6, 19.9) |
| Hazard ratio (95% CI)2 |
0.66 (0.50, 0.87) |
| P-value4 |
0.00480 |
| PFSBrainMets5 |
N=198 |
N=93 |
| Number of events (%) |
106 (53.5) |
51 (54.8) |
| Median, months (95% CI) |
7.6 (6.2, 9.5) |
5.4 (4.1, 5.7) |
| Hazard ratio (95% CI)2 |
0.48 (0.34, 0.69) |
| P-value6 |
<0.00001 |
| Confirmed ORR for Patients with Measurable Disease |
N=340 |
N=171 |
| ORR (95% CI)7 |
40.6 (35.3, 46.0) |
22.8 (16.7, 29.8) |
| CR (%) |
3 (0.9) |
2 (1.2) |
| PR (%) |
135 (39.7) |
37 (21.6) |
| P-value3 |
0.00008 |
| DOR |
| Median, months (95% CI)8 |
8.3 (6.2, 9.7) |
6.3 (5.8, 8.9) |
BICR=blinded independent central review; CI=confidence interval; PFS=progression-free survival; OS=overall survival; ORR=objective response rate; CR=complete response; PR=partial response; DOR=duration of response.
1 Primary PFS analysis conducted in first 480 randomized patients.
2 Hazard ratio and 95% confidence intervals are based on stratified Cox proportional hazards regression model controlling for stratification factors (presence or history of brain metastases, ECOG status, and region of world)
3 Two-sided p-value based on re-randomization procedure (Rosenberger and Lachin 2002) controlling for stratification factors, compared with the allocated alpha of 0.05
4 Two-sided p-value based on re-randomization procedure (Rosenberger and Lachin 2002) controlling for stratification factors, compared with the allocated alpha of 0.0074 for this interim analysis (with 60% of the planned number of events for final analysis)
5 Analysis includes patients with history or presence of parenchymal brain metastases at baseline, including target and non-target lesions. Does not include patients with dural lesions only.
6 Two-sided p-value based on re-randomization procedure (Rosenberger and Lachin 2002) controlling for stratification factors, compared with the allocated alpha of 0.0080 for this interim analysis (with 71% of the planned number of events for final analysis)
7 Two-sided 95% exact confidence interval, computed using the Clopper-Pearson method (1934)
8 Calculated using the complementary log-log transformation method (Collett, 1994) |
Figure 1: Kaplan-Meier Curve of PFS per BICR in HER2CLIMB
Figure 2: Kaplan-Meier Curve of Overall Survival in HER2CLIMB
HER2-Positive Metastatic Colorectal Cancer
The efficacy of TUKYSA in combination with trastuzumab was evaluated in 84 patients in MOUNTAINEER (NCT03043313), an open-label, multicenter trial. Patients were required to have HER2-positive, RAS wild-type, unresectable or metastatic colorectal cancer and prior treatment with fluoropyrimidines, oxaliplatin, irinotecan, and antivascular endothelial growth factor (VEGF) monoclonal antibody (mAb). Patients whose disease had deficient mismatch repair (dMMR) proteins or microsatellite instability-high (MSI-H) must have also received an anti-programmed cell death protein-1 (PD-1) mAb. Patients who received prior anti-HER2 targeting therapy were excluded. HER2 positivity as defined by HER2 overexpression or gene amplification was prospectively determined in local laboratories using immunohistochemistry (IHC), in situ hybridization (ISH), and/or next generation sequencing (NGS) on tumor tissue. RAS status was performed as standard of care prior to study entry based on expanded RAS testing including KRAS exons 2, 3, and 4 and NRAS exons 2, 3, and 4.
The median age was 55 years (range: 24 to 77); 12 (14%) patients were age 65 or older. Seventy-seven percent of patients were White, 4% were Black, 4% were Asian, and 4% were Hispanic or Latino. Sixty-one percent of patients were male. Seventy percent of patients had lung metastases, 64% had liver metastases, 60% had an ECOG performance status of 0, 37% had an ECOG performance status of 1, and 4% had an ECOG performance status of 2. Ninety-nine percent of patients received prior treatment with fluoropyrimidine, oxaliplatin, and irinotecan and 83% and 52% received anti-VEGF antibodies and anti-EGFR antibodies respectively; 23%, 38%, and 39% received 1, 2, or ≥3 prior lines of therapy, respectively.
Patients received TUKYSA 300 mg orally twice per day with a loading dose of trastuzumab or a non-US approved trastuzumab product 8 mg/kg intravenously on Day 1 of Cycle 1, followed by a maintenance dose of trastuzumab 6 mg/kg on Day 1 of each subsequent 21-day cycle. Patients were treated until disease progression or unacceptable toxicity.
The major efficacy outcome measures were overall response rate (ORR) and duration of response (DOR) as assessed by blinded independent central review (BICR) according to RECIST version 1.1.
Efficacy results are summarized in Table 13.
Table 13: Efficacy Results in MOUNTAINEER
|
TUKYSA + trastuzumab
N=84 |
| Overall Response Rate (%) (95% CI) |
38 (28, 49) |
| CR (%) |
3 (3.6) |
| PR (%) |
29 (35) |
| Duration of Response |
N=32 |
| Median1, months (95% CI) |
12.4 (8.5, 20.5) |
| Patients with DOR≥6 months2 |
81% |
| Patients with DOR≥12 months2 |
34% |
1 Based on Kaplan-Meier method.
2 Based on observed duration of response. |