Clinical Pharmacology for Gavreto
Mechanism Of Action
Pralsetinib is a kinase inhibitor of wild-type RET and oncogenic RET fusions (CCDC6-RET) and mutations (RET V804L, RET V804M and RET M918T) with half maximal inhibitory concentrations (IC50s) less than 0.5 nM. In purified enzyme assays, pralsetinib inhibited DDR1, TRKC, FLT3, JAK1-2, TRKA, VEGFR2, PDGFRB, and FGFR1 at higher concentrations that were still clinically achievable at Cmax. In cellular assays, pralsetinib inhibited RET at approximately 14-, 40-, and 12-fold lower concentrations than VEGFR2, FGFR2, and JAK2, respectively.
Certain RET fusion proteins and activating point mutations can drive tumorigenic potential through hyperactivation of downstream signaling pathways leading to uncontrolled cell proliferation. Pralsetinib exhibited anti-tumor activity in cultured cells and animal tumor implantation models harboring oncogenic RET fusions or mutations including KIF5B-RET, CCDC6-RET, RET M918T, RET C634W, RET V804E, RET V804L and RET V804M. In addition, pralsetinib prolonged survival in mice implanted intracranially with tumor models expressing KIF5B-RET or CCDC6-RET.
Pharmacodynamics
Pralsetinib exposure-response relationships and the time course of pharmacodynamics response have not been fully characterized.
Cardiac Electrophysiology
The QT interval prolongation potential of pralsetinib was assessed in 34 patients with RET Âaltered solid tumors administered GAVRETO at the recommended dosage. No large mean increase in QTc (> 20 ms) was detected in the study.
Pharmacokinetics
At 400 mg GAVRETO once daily under fasting conditions, the steady state mean [% coefficient of variation (CV%)] of maximum observed plasma concentration (Cmax) and area under the concentration-time curve (AUC0-24h) of pralsetinib was 2,470 (55%) ng/mL and 36,700 (66%) h•ng/mL, respectively. Pralsetinib Cmax and AUC increased inconsistently over the dose range of 60 mg to 600 mg once daily (0.15 to 1.5 times the recommended dose). Pralsetinib plasma concentrations reached steady state by 3 to 5 days. The mean accumulation ratio was approximately 2-fold after once-daily oral administration.
Absorption
The median time to peak concentration (Tmax) ranged from 2 to 4 hours following single doses of pralsetinib 60 mg to 600 mg.
Food Effect
Following administration of a single dose of 200 mg with a high-fat meal, (approximately 800 to 1000 calories with 50 to 60% of calories from fat), the mean Cmax of pralsetinib was increased by 2.0-fold, the mean AUC0-INF was increased by 2.2-fold, and the median Tmax was delayed from 4 to 8.5 hours, compared to the fasted state.
Distribution
The mean (CV%) apparent volume of distribution (Vd/F) of pralsetinib is 303 L (68%). Protein binding of pralsetinib is 97% and is independent of concentration. The blood-to-plasma ratio is 0.6 to 0.7.
Elimination
The mean (±standard deviation) plasma elimination half-life (T½) of pralsetinib is 16 hours (10) following single doses and 20 hours (12) following multiple doses of pralsetinib. The mean (CV%) apparent oral clearance (CL/F) of pralsetinib is 11 L/h (66%) at steady state.
Metabolism
Pralsetinib is primarily metabolized by CYP3A4 and to a lesser extent by CYP2D6 and CYP1A2, in vitro. Following a single oral dose of 310 mg of radiolabeled pralsetinib, pralsetinib metabolites from oxidation and glucuronidation were detected as 5% or less.
Excretion
Approximately 73% (66% as unchanged) of the total administered radioactive dose [14C] pralsetinib was recovered in feces and 6% (4.8% as unchanged) was recovered in urine.
Specific Populations
No clinically significant differences in the PK of pralsetinib were observed based on age (19 to 87 years), sex, race (White, Black, or Asian), and body weight (32 to 128 kg). Mild and moderate renal impairment (CLcr 30 -89 mL/min) had no effect on the exposure of pralsetinib. Pralsetinib has not been studied in patients with severe renal impairment (CLcr < 15 mL/min).
Drug Interaction Studies
Clinical Studies And Model-Informed Approach
CYP3A Inhibitors
Coadministration of multiple doses of CYP3A inhibitors increases pralsetinib Cmax and AUC.
Table 9: Observed or Predicted Increase in Pralsetinib Exposure after Coadministration of CYP3A Inhibitors
| Type of inhibitor |
Coadministered CYP3A Inhibitor |
Increase in pralsetinib Cmax |
Increase in pralsetinib AUC |
| Observed |
| P-gp and Strong CYP3A Inhibitor |
Itraconazole (200 mg twice daily on Day 1, followed by 200 mg once daily) |
1.8-fold |
3.5-fold |
| Predicted |
| Strong CYP3A Inhibitors |
Voriconazole (400 mg twice daily on Day 1, followed by 200 mg twice daily) |
1.2-fold |
2.2-fold |
| Combined P-gp and Moderate CYP3A Inhibitors |
Verapamil (80 mg three times daily) |
1.6-fold |
2.1-fold |
| Moderate CYP3A Inhibitors |
Fluconazole (400 mg once daily) |
1.2-fold |
1.7-fold |
P-gp Inhibitors
Coadministration of cyclosporine (single 600 mg dose) with a single 200 mg dose of pralsetinib in healthy subjects increased pralsetinib AUC0-inf by 1.8-fold and Cmax by 1.5Âfold, relative to a 200 mg dose of pralsetinib administered alone.
Strong CYP3A Inducers
Coadministration of rifampin 600 mg once daily with a single GAVRETO 400 mg dose decreased pralsetinib AUC0-INF by 68% and Cmax by 30%.
Moderate CYP3A Inducers
Coadministration of multiple doses of efavirenz (600 mg once daily) is predicted to decrease the pralsetinib AUC by 45% and Cmax by 18%.
Mild CYP3A Inducers
No clinically significant differences in the PK of pralsetinib were identified when GAVRETO was coadministered with mild CYP3A inducers.
Acid-Reducing Agents
No clinically significant differences in the PK of pralsetinib were observed when GAVRETO was coadministered with gastric acid reducing agents.
In Vitro Studies
Cytochrome P450 (CYP) Enzymes
Pralsetinib is a time-dependent inhibitor of CYP3A and an inhibitor of CYP2C8, CYP2C9, and CYP3A, but not an inhibitor of CYP1A2, CYP2B6, CYP2C19 or CYP2D6 at clinically relevant concentrations.
Pralsetinib is an inducer of CYP2C8, CYP2C9, and CYP3A, but not an inducer of CYP1A2, CYP2B6, or CYP2C19 at clinically relevant concentrations.
Transporter Systems
Pralsetinib is a substrate of P-gp and BCRP, but not a substrate of BSEP, OCT1, OCT2, OATP1B1, OATP1B3, MATE1, MATE2-K, OAT1, or OAT3.
Pralsetinib is an inhibitor of P-gp, BCRP, OATP1B1, OATP1B3, OAT1, MATE1, MATE2-K, and BSEP, but not an inhibitor of OCT1, OCT2, and OAT1A3 at clinically relevant concentrations.
Animal Toxicology And/Or Pharmacology
In 28-day rat and monkey toxicology studies, once daily oral administration of pralsetinib resulted in histologic necrosis and hemorrhage in the heart of preterm decedents at exposures ≥ 1.3 times and ≥ 3.1 times, respectively, the human exposure based on AUC at the clinical dose of 400 mg. Pralsetinib induced hyperphosphatemia (rats) and multi-organ mineralization (rats and monkeys) in 13-week toxicology studies at exposures approximately 2.8 times and ≥ 0.13 times, respectively, the human exposure based on AUC at the clinical dose of 400 mg.
Clinical Studies
Metastatic RET Fusion-Positive Non-Small Cell Lung Cancer
The efficacy of GAVRETO was evaluated in patients with RET fusion-positive metastatic NSCLC in a multicenter, non-randomized, open-label, multi-cohort clinical trial (ARROW, NCT03037385). The study enrolled, in separate cohorts, patients with metastatic RET fusion-positive NSCLC who had progressed on platinum-based chemotherapy and treatment-naïve patients with metastatic NSCLC. Identification of a RET gene fusion was determined by local laboratories using next generation sequencing (NGS), fluorescence in situ hybridization (FISH), and other tests. Among the 237 patients in the efficacy population(s) described in this section, samples from 40% of patients were retrospectively tested with the LIFE Technologies Corporation Oncomine Dx Target Test (ODxTT). Patients with asymptomatic central nervous system (CNS) metastases, including patients with stable or decreasing steroid use within 2 weeks prior to study entry, were enrolled. Patients received GAVRETO 400 mg orally once daily until disease progression or unacceptable toxicity.
The major efficacy outcome measures were overall response rate (ORR) and duration of response (DOR), as assessed by a blinded independent central review (BICR) according to RECIST v1.1.
Metastatic RET Fusion-Positive NSCLC Previously Treated With Platinum Chemotherapy
Efficacy was evaluated in 130 patients with RET fusion-positive NSCLC with measurable disease who were previously treated with platinum chemotherapy enrolled into a cohort of ARROW.
The median age was 59 years (range: 26 to 85); 51% were female, 40% were White, 50% were Asian, 4.6% were Hispanic/Latino. ECOG performance status was 0-1 (95%) or 2 (3.8%), 99% of patients had metastatic disease, and 41% had either a history of or current CNS metastasis. Patients received a median of 2 prior systemic therapies (range 1–6); 42% had prior anti-PDÂ1/PD-L1 therapy and 27% had prior kinase inhibitors. A total of 48% of the patients received prior radiation therapy. RET fusions were detected in 80% of patients using NGS (37% tumor samples; 15% blood or plasma samples, 28% unknown), 13% using FISH, and 2% using other methods. The most common RET fusion partners were KIF5B (70%) and CCDC6 (19%).
Efficacy results for RET fusion-positive NSCLC patients who received prior platinum-based chemotherapy are summarized in Table 10.
Table 10: Efficacy Results in ARROW ( Metastatic RET Fusion-Positive NSCLC Previously Treated with Platinum Chemotherapy)
| Efficacy Parameter |
GAVRETO
N=130 |
| Overall Response Rate (ORR)a (95% CI) |
63 (54, 71) |
| Complete Response, % |
6 |
| Partial Response, % |
57 |
| Duration of Response (DOR) |
N=82 |
| Median, months (95% CI) |
38.8 (14.8, NE) |
| Patients with DOR ≥ 12-monthsb, % |
66 |
NE = not estimable
a Confirmed overall response rate assessed by BICR
b Based on observed duration of response |
For the 54 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 59% (95% CI: 45, 72) and the median DOR was 22.3 months (95% CI: 8.0, NE).
Among the 130 patients with RET-fusion positive NSCLC, 10 had measurable CNS metastases at baseline as assessed by BICR. No patients received radiation therapy (RT) to the brain within 2 months prior to study entry. Responses in intracranial lesions were observed in 7 of these 10 patients including 2 patients with a CNS complete response; 71% of responders had a DOR of ≥ 6 months.
Treatment-naïve RET Fusion-Positive NSCLC
Efficacy was evaluated in 107 patients with treatment-naïve RET fusion-positive NSCLC with measurable disease enrolled into ARROW.
The median age was 62 years (range 30 to 87); 53% were female, 49% were White, 45% were Asian, and 2.8% were Hispanic or Latino. ECOG performance status was 0-1 for 99% of the patients and 98% of patients had metastatic disease; 28% had either history of or current CNS metastasis. RET fusions were detected in 68% of patients using NGS (30% tumor samples; 17% blood or plasma; 22% unknown) and 19% using FISH. The most common RET fusion partners were KIF5B (71%) and CCDC6 (18%).
Efficacy results for treatment-naïve RET fusion-positive NSCLC are summarized in Table 11.
Table 11: Efficacy Results for ARROW (Treatment-Naïve Metastatic RET Fusion-Positive NSCLC)
| Efficacy Parameter |
GAVRETO
N=107 |
| Overall Response Rate (ORR)a (95% CI) |
78 (68,85) |
| Complete Response, % |
7 |
| Partial Response, % |
71 |
| Duration of Response (DOR) |
N=83 |
| Median, months (95% CI) |
13.4 (9.4, 23.1) |
| Patients with DOR ≥ 12-monthsb, % |
45 |
a Confirmed overall response rate assessed by BICR
b Based on observed duration of response |
RET Fusion-Positive Thyroid Cancer
The efficacy of GAVRETO was evaluated in RET fusion-positive metastatic thyroid cancer patients in a multicenter, open-label, multi-cohort clinical trial (ARROW, NCT03037385). All patients with RET fusion-positive thyroid cancer were required to have disease progression following standard therapy, measurable disease by RECIST version 1.1, and have RET fusion status as detected by local testing (89% NGS tumor samples and 11% using FISH).
The median age was 61 years (range: 46 to 74); 67% were male, 78% were White, 22% were Asian, 11% were Hispanic/Latino. All patients (100%) had papillary thyroid cancer. ECOG performance status was 0-1 (100%), all patients (100%) had metastatic disease, and 56% had a history of CNS metastases. Patients had received a median of 2 prior therapies (range 1-8). Prior systemic treatments included prior radioactive iodine (100%) and prior sorafenib and/or lenvatinib (56%).
Efficacy results are summarized in Table 12.
Table 12: Efficacy Results for RET Fusion-Positive Thyroid Cancer (ARROW)
| Efficacy Parameters |
GAVRETO
N=9 |
| Overall Response Rate (ORR)a (95% CI) |
89 (52, 100) |
| Complete Response, % |
0 |
| Partial Response, % |
89 |
| Duration of Response (DOR) |
N=8 |
| Median in months (95% CI) |
NR (NE, NE) |
| Patients with DOR ≥ 6 monthsb, % |
100 |
NR = Not Reached; NE = Not Estimable
a Confirmed overall response rate assessed by BICR
b Based on observed duration of response |