CLINICAL PHARMACOLOGY
Mechanism Of Action
Selpercatinib is a kinase inhibitor. Selpercatinib inhibited wild-type RET and multiple mutated RET isoforms as well as VEGFR1 and VEGFR3 with IC50 values ranging from 0.92 nM to 67.8 nM. In other enzyme assays, selpercatinib also inhibited FGFR 1, 2, and 3 at higher concentrations that were still clinically achievable. In cellular assays, selpercatinib inhibited RET at approximately 60-fold lower concentrations than FGFR1 and 2 and approximately 8-fold lower concentration than VEGFR3.
Certain point mutations in RET or chromosomal rearrangements involving in-frame fusions of RET with various partners can result in constitutively activated chimeric RET fusion proteins that can act as oncogenic drivers by promoting cell proliferation of tumor cell lines. In in vitro and in vivo tumor models, selpercatinib demonstrated anti-tumor activity in cells harboring constitutive activation of RET protein resulting from gene fusions and mutations, including CCDC6-RET, KIF5B-RET, RET V804M, and RET M918T. In addition, selpercatinib showed anti-tumor activity in mice intracranially implanted with a patient-derived RET fusion positive tumor.
Pharmacodynamics
Exposure-Response Relationship
Selpercatinib exposure-response relationships and the time course of pharmacodynamic response have not been fully characterized.
Cardiac Electrophysiology
The effect of RETEVMO on the QTc interval was evaluated in a thorough QT study in healthy subjects. The largest mean increase in QTc is predicted to be 10.6 msec (upper 90% confidence interval: 12.1 msec) at the mean steady-state maximum concentration (Cmax) observed in patients after administration of 160 mg twice daily. The increase in QTc was concentration-dependent.
Pharmacokinetics
The pharmacokinetics of selpercatinib were evaluated in patients with locally advanced or metastatic solid tumors administered 160 mg twice daily unless otherwise specified. Steady-state selpercatinib AUC and Cmax increased in a slightly greater than dose proportional manner over the dose range of 20 mg once daily to 240 mg twice daily [0.06 to 1.5 times the maximum recommended total daily dosage].
Steady-state was reached by approximately 7 days and the median accumulation ratio after administration of 160 mg twice daily was 3.4-fold. Mean steady-state selpercatinib [coefficient of variation (CV%)] Cmax was 2,980 (53%) ng/mL and AUC0-24h was 51,600 (58%) ng*h/mL.
Absorption
The median tmax of selpercatinib is 2 hours. The mean absolute bioavailability of RETEVMO capsules is 73% (60% to 82%) in healthy subjects.
Effect Of Food
No clinically significant differences in selpercatinib AUC or Cmax were observed following administration of a high-fat meal (approximately 900 calories, 58 grams carbohydrate, 56 grams fat and 43 grams protein) in healthy subjects.
Distribution
The apparent volume of distribution (Vss/F) of selpercatinib is 191 L.
Protein binding of selpercatinib is 97% in vitro and is independent of concentration. The bloodto- plasma concentration ratio is 0.7.
Elimination
The apparent clearance (CL/F) of selpercatinib is 6 L/h in patients and the half-life is 32 hours following oral administration of RETEVMO in healthy subjects.
Metabolism
Selpercatinib is metabolized predominantly by CYP3A4. Following oral administration of a single radiolabeled 160 mg dose of selpercatinib to healthy subjects, unchanged selpercatinib constituted 86% of the radioactive drug components in plasma.
Excretion
Following oral administration of a single radiolabeled 160 mg dose of selpercatinib to healthy subjects, 69% of the administered dose was recovered in feces (14% unchanged) and 24% in urine (12% unchanged).
Specific Populations
The apparent volume of distribution and clearance of selpercatinib increase with increasing body weight (27 kg to 177 kg).
No clinically significant differences in the pharmacokinetics of selpercatinib were observed based on age (15 years to 90 years), sex, or mild or moderate renal impairment (CLcr ≥ 30 mL/min as estimated by Cockcroft-Gault). The effect of severe renal impairment (CLcr < 30 mL/min) on selpercatinib pharmacokinetics has not been adequately studied.
Patients With Hepatic Impairment
The selpercatinib AUC0-INF increased by 7%, 32%, and 77% in subjects with mild (total bilirubin less than or equal to ULN with AST greater than ULN or total bilirubin greater than 1 to 1.5 times ULN with any AST ), moderate (total bilirubin greater than 1.5 to 3 times ULN and any AST), and severe (total bilirubin greater than 3 to 10 times ULN and any AST) hepatic impairment, respectively, compared to subjects with normal hepatic function.
Drug Interaction Studies
Clinical Studies And Model-Informed Approaches
Proton-Pump Inhibitors (PPI)
Coadministration with multiple daily doses of omeprazole (PPI) decreased selpercatinib AUC0-INF and Cmax when RETEVMO was administered fasting. Coadministration with multiple daily doses of omeprazole did not significantly change the selpercatinib AUC0-INF and Cmax when RETEVMO was administered with food (Table 7).
Table 7 : Change in Selpercatinib Exposure After Coadministration with PPI
| Selpercatinib AUC0-INF | Selpercatinib Cmax |
RETEVMO fasting | Reference | Reference |
RETEVMO fasting + PPI | ↓69% | ↓88% |
RETEVMO with a high-fat meal1 + PPI | ↑ 2% | ↓ 49% |
RETEVMO with a low-fat meal2 + PPI | No change | ↓22% |
1 High-fat meal: approximately 150, 250, and 500-600 calories from protein, carbohydrate, and fat, respectively; approximately 800 to 1000 calories total. 2 Low-fat meal: approximately 390 calories and 10 g of fat |
H2 Receptor Antagonists
No clinically significant differences in selpercatinib pharmacokinetics were observed when coadministered with multiple daily doses of ranitidine (H2 receptor antagonist) given 10 hours prior to and 2 hours after the RETEVMO dose (administered fasting).
Strong CYP3A Inhibitors
Coadministration of multiple doses of itraconazole (strong CYP3A inhibitor) increased the selpercatinib AUC0-INF by 133% and Cmax by 30%.
Moderate CYP3A Inhibitors
Coadministration of multiple doses of diltiazem, fluconazole, or verapamil (moderate CYP3A inhibitors) is predicted to increase the selpercatinib AUC by 60-99% and Cmax by 46-76%.
Strong CYP3A Inducers
Coadministration of multiple doses of rifampin (strong CYP3A inducer) decreased the selpercatinib AUC0-INF by 87% and Cmax by 70%.
Moderate CYP3A Inducers
Coadministration of multiple doses of bosentan or efavirenz (moderate CYP3A inducers) is predicted to decrease the selpercatinib AUC by 40-70% and Cmax by 34-57%.
Weak CYP3A Inducers
Coadministration of multiple doses of modafinil (weak CYP3A inducer) is predicted to decrease the selpercatinib AUC by 33% and Cmax by 26%.
CYP2C8 Substrates
Coadministration of RETEVMO with repaglinide (sensitive CYP2C8 substrate) increased the repaglinide AUC0-INF by 188% and Cmax by 91%.
CYP3A Substrates
Coadministration of RETEVMO with midazolam (sensitive CYP3A) increased the midazolam AUC0-INF by 54% and Cmax by 39%.
P-glycoprotein (P-gp) Inhibitors
No clinically significant differences in selpercatinib pharmacokinetics were observed when coadministered with a single dose of rifampin (P-gp inhibitor).
MATE1 Substrates
No clinically significant differences in glucose levels were observed when metformin (MATE1 substrate) was coadministered with selpercatinib.
In Vitro Studies
CYP Enzymes
Selpercatinib does not inhibit or induce CYP1A2, CYP2B6, CYP2C9, CYP2C19, or CYP2D6 at clinically relevant concentrations.
Transporter Systems
Selpercatinib inhibits MATE1, P-gp, and BCRP, but does not inhibit OAT1, OAT3, OCT1, OCT2, OATP1B1, OATP1B3, BSEP, and MATE2-K at clinically relevant concentrations. Selpercatinib may increase serum creatinine by decreasing renal tubular secretion of creatinine via inhibition of MATE1 [see Adverse Effects]. Selpercatinib is a substrate for P-gp and BCRP, but not for OAT1, OAT3, OCT1, OCT2, OATP1B1, OATP1B3, MATE1, or MATE2-K.
Clinical Studies
Metastatic RET Fusion-Positive Non-Small Cell Lung Cancer
The efficacy of RETEVMO was evaluated in patients with advanced RET fusion-positive NSCLC enrolled in a multicenter, open-label, multi-cohort clinical trial (LIBRETTO-001, NCT03157128). The study enrolled patients with advanced or metastatic RET fusion-positive NSCLC who had progressed on platinum-based chemotherapy and patients with advanced or metastatic NSCLC without prior systemic therapy in separate cohorts. Identification of a RET gene alteration was prospectively determined in local laboratories using next generation sequencing (NGS), polymerase chain reaction (PCR), or fluorescence in situ hybridization (FISH). Adult patients received RETEVMO 160 mg orally twice daily until unacceptable toxicity or disease progression. The major efficacy outcome measures were confirmed overall response rate (ORR) and duration of response (DOR), as determined by a blinded independent review committee (BIRC) according to RECIST v1.1.
Metastatic RET Fusion-Positive NSCLC Previously Treated With Platinum Chemotherapy
Efficacy was evaluated in 105 patients with RET fusion-positive NSCLC previously treated with platinum chemotherapy enrolled into a cohort of LIBRETTO-001.
The median age was 61 years (range: 23 to 81); 59% were female; 52% were White, 38% were Asian, 4.8% were Black, and 3.8% were Hispanic/Latino. ECOG performance status was 0-1 (98%) or 2 (2%) and 98% of patients had metastatic disease. Patients received a median of 3 prior systemic therapies (range 1–15); 55% had prior anti-PD-1/PD-L1 therapy. RET fusions were detected in 90% of patients using NGS (81.9% tumor samples; 7.6% blood or plasma samples), 8.6% using FISH, and 1.9% using PCR.
Efficacy results for RET fusion-positive NSCLC are summarized in Table 8.
Table 8 : Efficacy Results in LIBRETTO-001 (Metastatic RET Fusion-Positive NSCLC Previously Treated with Platinum Chemotherapy)
| RETEVMO (n = 105) |
Overall Response Rate1 (95% CI) | 64% (54%, 73%) |
Complete response | 1.9% |
Partial response | 62% |
Duration of Response |
Median in months (95% CI) | 17.5 (12, NE) |
% with ≥ 6 months2 | 81 |
1 Confirmed overall response rate assessed by BICR. 2 Based on observed duration of response NE = not estimable |
For the 58 patients who received an anti-PD-1 or anti-PD-L1 therapy, either sequentially or concurrently with platinum-based chemotherapy, an exploratory subgroup analysis of ORR was 66% (95% CI: 52%, 78%) and the median DOR was 12.5 months (95% CI: 8.3, NE).
Among the 105 patients with RET fusion-positive NSCLC, 11 had measurable CNS metastases at baseline as assessed by BIRC. No patients received radiation therapy (RT) to the brain within 2 months prior to study entry. Responses in intracranial lesions were observed in 10 of these 11 patients; all responders had a DOR of ≥ 6 months.
Treatment-naïve RET Fusion-Positive NSCLC
Efficacy was evaluated in 39 patients with treatment-naïve RET fusion-positive NSCLC enrolled into a cohort of LIBRETTO-001.
The median age was 61 years (range 23 to 86); 56% were female; 72% were White, 18% were Asian, and 8% were Black. ECOG performance status was 0-1 in all patients (100%) and all patients (100%) had metastatic disease. RET fusions were detected in 92% of patients using NGS (69% tumor samples; 23% in blood) and 8% using FISH.
Efficacy results for treatment naïve RET fusion-positive NSCLC are summarized in Table 9.
Table 9 : Efficacy Results in LIBRETTO-001 (Treatment-Naïve Metastatic RET Fusion-Positive NSCLC)
| RETEVMO (n =39) |
Overall Response Rate1 (95% CI) | 85% (70%, 94%) |
Complete response | 0 |
Partial response | 85% |
Duration of Response |
Median in months (95% CI) | NE (12, NE) |
% with ≥ 6 months2 | 58 |
1 Confirmed overall response rate assessed by BICR. 2 Based on observed duration of response NE = not estimable |
RET-Mutant Medullary Thyroid Cancer
The efficacy of RETEVMO was evaluated in patients with RET-mutant MTC enrolled in a multicenter, open-label, multi-cohort clinical trial (LIBRETTO-001, NCT03157128). The study enrolled patients with advanced or metastatic RET-mutant MTC who had been previously treated with cabozantinib or vandetanib (or both) and patients with advanced or metastatic RET-mutant MTC who were naïve to cabozantinib and vandetanib in separate cohorts.
RET-Mutant MTC Previously Treated With Cabozantinib Or Vandetanib
Efficacy was evaluated in 55 patients with RET-mutant advanced MTC who had previously treated with cabozantinib or vandetanib enrolled into a cohort of LIBRETTO-001.
The median age was 57 years (range: 17 to 84); 66% were male; 89% were White, 7% were Hispanic/Latino, and 1.8% were Black. ECOG performance status was 0-1 (95%) or 2 (5%) and 98% of patients had metastatic disease. Patients received a median of 2 prior systemic therapies (range 1 – 8). RET mutation status was detected in 82% of patients using NGS (78% tumor samples; 4% blood or plasma), 16% using PCR, and 2% using an unknown test. The protocol excluded patients with synonymous, frameshift or nonsense RET mutations; the specific mutations used to identify and enroll patients are described in Table 10.
Table 10 : Mutations used to Identify and Enroll Patients with RET-Mutant MTC in LIBRETTO-001
RET Mutation Type1 | Previously Treated (n = 55) | Cabozantinib/ Vandetanib Naive (n = 88) | Total (n = 143) |
M918T | 33 | 49 | 82 |
Extracellular cysteine mutation2 | 7 | 20 | 27 |
V804M or V804L | 54 | 6 | 11 |
Other3 | 10 | 13 | 23 |
1 Somatic or germline mutations; protein change. 2 Extracellular cysteine mutations involving cysteine residues 609, 611, 618, 620, 630, and 634 3 Other included: K666N (1), D631_L633delinsV (2), D631_L633delinsE (5), D378_G385delinsE (1), D898_E901del (2), A883F (4), E632_L633del (4), L790F (2), T636_V637insCRT(1), D898_E901del + D903_S904delinsEP (1) 4 One patient also had a M918T mutation |
Efficacy results for RET-mutant MTC are summarized in Table 11.
Table 11 : Efficacy Results in LIBRETTO-001 (RET-Mutant MTC Previously Treated with Cabozantinib or Vandetanib)
| RETEVMO (n = 55) |
Overall Response Rate1 (95% CI) | 69% (55%, 81%) |
Complete response | 9% |
Partial response | 60% |
Duration of Response |
Median in months (95% CI) | NE (19.1, NE) |
% with ≥ 6 months2 | 76 |
1 Confirmed overall response rate assessed by BICR. 2 Based on observed duration of response NE = not estimable |
Cabozantinib And Vandetanib-naïve RET-Mutant MTC
Efficacy was evaluated in 88 patients with RET-mutant MTC who were cabozantinib and vandetanib treatment-naïve enrolled into a cohort of LIBRETTO-001.
The median age was 58 years (range: 15 to 82) with two patients (2.3%) aged 12 to 16 years; 66% were male; and 86% were White, 4.5% were Asian, and 2.3% were Hispanic/Latino. ECOG performance status was 0-1 (97%) or 2 (3.4%). All patients (100%) had metastatic disease and 18% had received 1 or 2 prior systemic therapies (including 8% kinase inhibitors, 4.5% chemotherapy, 2.3% anti-PD1/PD-L1 therapy, and 1.1% radioactive iodine). RET mutation status was detected in 78.4% of patients using NGS (76.1 % tumor samples; 2.3% blood samples), 18.2% using PCR, and 3.4% using an unknown test. The mutations used to identify and enroll patients are described in Table 10.
Efficacy results for cabozantinib and vandetanib-naïve RET-mutant MTC are summarized in Table 12.
Table 12 : Efficacy Results in LIBRETTO-001 (Cabozantinib and Vandetanib-naïve RET-Mutant MTC)
| RETEVMO (n = 88) |
Overall Response Rate1 (95% CI) | 73% (62%, 82%) |
Complete response | 11% |
Partial response | 61% |
Duration of Response |
Median in months (95% CI) | 22.0 (NE, NE) |
% with ≥ 6 months2 | 61 |
1 Confirmed overall response rate assessed by BICR. 2 Based on observed duration of response NE = not estimable |
RET Fusion-Positive Thyroid Cancer
The efficacy of RETEVMO was evaluated in patients with advanced RET fusion-positive thyroid cancer enrolled in a multicenter, open-label, multi-cohort clinical trial (LIBRETTO-001, NCT03157128). Efficacy was evaluated in 27 patients with RET fusion-positive thyroid cancer who were radioactive iodine (RAI)-refractory (if RAI was an appropriate treatment option) and were systemic therapy naïve and patients with RET fusion-positive thyroid cancer who were RAI-refractory and had received sorafenib, lenvatinib, or both, in separate cohorts.
The median age was 54 years (range 20 to 88); 52% were male; 74% were White, 11% were Hispanic/Latino, 7.4% were Asian, and 3.7% were Black. ECOG performance status was 0-1 (89%) or 2 (11%). All (100%) patients had metastatic disease with primary tumor histologies including papillary thyroid cancer (78%), poorly differentiated thyroid cancer (11%), anaplastic thyroid cancer (7%) and Hurthle cell thyroid cancer (4%). Patients had received a median of 3 prior therapies (range 1–7). RET fusion-positive status was detected in 93% of patients using NGS tumor samples and in 7% using blood samples.
Efficacy results for RET fusion-positive thyroid cancer are summarized in Table 13.
Table 13 : Efficacy Results in LIBRETTO-001 (RET Fusion-Positive Thyroid Cancer)
| RETEVMO Previously Treated (n = 19) | RETEVMO Systemic Therapy Naive (n = 8) |
Overall Response Rate1 (95% CI) | 79% (54%, 94%) | 100% (63%, 100%) |
Complete response | 5.3% | 12.5% |
Partial response | 74% | 88% |
Duration of Response |
Median in months (95% CI) | 18.4 (7.6, NE) | NE (NE, NE) |
% with ≥ 6 months2 | 87 | 75 |
1Confirmed overall response rate assessed by BICR. 2 Based on observed duration of response NE = not estimable |