Chemical formula: C₂₁H₂₂F₂N₆O₂ Molecular mass: 428.444 g/mol
Larotrectinib is an adenosine triphosphate (ATP)-competitive and selective tropomyosin receptor kinase (TRK) inhibitor that was rationally designed to avoid activity with off-target kinases. The target for larotrectinib is the TRK family of proteins inclusive of TRKA, TRKB, and TRKC that are encoded by NTRK1, NTRK2 and NTRK3 genes, respectively. In a broad panel of purified enzyme assays, larotrectinib inhibited TRKA, TRKB, and TRKC with IC50 values between 5-11 nM. The only other kinase activity occurred at 100-fold higher concentrations. In in vitro and in vivo tumour models, larotrectinib demonstrated anti-tumour activity in cells with constitutive activation of TRK proteins resulting from gene fusions, deletion of a protein regulatory domain, or in cells with TRK protein overexpression.
In-frame gene fusion events resulting from chromosomal rearrangements of the human genes NTRK1, NTRK2, and NTRK3 lead to the formation of oncogenic TRK fusion proteins. These resultant novel chimeric oncogenic proteins are aberrantly expressed, driving constitutive kinase activity subsequently activating downstream cell signalling pathways involved in cell proliferation and survival leading to TRK fusion-positive cancer.
Acquired resistance mutations after progression on TRK inhibitors have been observed. Larotrectinib had minimal activity in cell lines with point mutations in the TRKA kinase domain, including the clinically identified acquired resistance mutation, G595R. Point mutations in the TRKC kinase domain with clinically identified acquired resistance to larotrectinib include G623R, G696A, and F617L.
The molecular causes for primary resistance to larotrectinib are not known. It is therefore not known if the presence of a concomitant oncogenic driver in addition to an NTRK gene fusion affects the efficacy of TRK inhibition.
In 36 healthy adult subjects receiving single doses ranging from 100 mg to 900 mg, larotrectinib did not prolong the QT interval to any clinically relevant extent. The 200 mg dose corresponds to a peak exposure (Cmax) similar to that observed with larotrectinib 100 mg BID at steady state. A shortening of QTcF was observed with larotrectinib dosing, with a maximum mean effect observed between 3 and 24 hours after Cmax, with a geometric mean decrease in QTcF from baseline of -13.2 msec (range -10 to -15.6 msec). Clinical relevance of this finding has not been established.
In cancer patients given larotrectinib capsules, peak plasma levels (Cmax) of larotrectinib were achieved at approximately 1 hour after dosing. Half-life (t½) is approximately 3 hours and steady state is reached within 8 days with a systemic accumulation of 1.6 fold. At the recommended dose of 100 mg taken twice daily, steady-state arithmetic mean (± standard deviation) Cmax and daily AUC in adults were 914 ± 445 ng/mL and 5410 ± 3813 ng*h/mL, respectively. In vitro studies indicate that larotrectinib is not a substrate for either OATP1B1 or OATP1B3.
In vitro studies indicate that larotrectinib does not inhibit CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C19, or CYP2D6 at clinically relevant concentrations and is unlikely to affect clearance of substrates of these CYPs.
In vitro studies indicate that larotrectinib does not inhibit the transporters BCRP, P-gp, OAT1, OAT3, OCT1, OCT2, OATP1B3, BSEP, MATE1 and MATE2-K at clinically relevant concentrations and is unlikely to affect clearance of substrates of these transporters.
Larotrectinib is available as a capsule and oral solution formulation. The mean absolute bioavailability of larotrectinib was 34% (range: 32% to 37%) following a single 100 mg oral dose. In healthy adult subjects, the AUC of larotrectinib in the oral solution formulation was similar to the capsule, with Cmax 36% higher with the oral solution formulation. Larotrectinib Cmax was reduced by approximately 35% and there was no effect on AUC in healthy subjects administered larotrectinib after a high-fat and high-calorie meal compared to the Cmax and AUC after overnight fasting.
Larotrectinib has pH-dependent solubility. In vitro studies show that in liquid volumes relevant to the gastrointestinal (GI) tract larotrectinib is fully soluble over entire pH range of the GI tract. Therefore, larotrectinib is unlikely to be affected by pH-modifying agents.
The mean volume of distribution of larotrectinib in healthy adult subjects was 48 L following intravenous administration of an IV microtracer in conjunction with a 100 mg oral dose. Binding of larotrectinib to human plasma proteins in vitro was approximately 70% and was independent of drug concentration. The blood-to-plasma concentration ratio was approximately 0.9.
Larotrectinib was metabolised predominantly by CYP3A4/5 in vitro. Following oral administration of a single 100 mg dose of radiolabeled larotrectinib to healthy adult subjects, unchanged larotrectinib (19%) and an O-glucuronide that is formed following loss of the hydroxypyrrolidine-urea moiety (26%) were the major circulating radioactive drug components.
The half-life of larotrectinib in plasma of cancer patients given 100 mg twice daily of larotrectinib was approximately 3 hours. Mean clearance (CL) of larotrectinib was approximately 34 L/h following intravenous administration of an IV microtracer in conjunction with a 100 mg oral dose of larotrectinib.
Following oral administration of 100 mg radiolabeled larotrectinib to healthy adult subjects, 58% of the administered radioactivity was recovered in faeces and 39% was recovered in urine and when an IV microtracer dose was given in conjunction with a 100 mg oral dose of larotrectinib, 35% of the administered radioactivity was recovered in faeces and 53% was recovered in urine. The fraction excreted as unchanged drug in urine was 29% following IV microtracer dose, indicating that direct renal excretion accounted for 29% of total clearance.
The area under the plasma concentration-time curve (AUC) and maximum plasma concentration (Cmax) of larotrectinib after a single dose in healthy adult subjects were dose proportional up to 400 mg and slightly greater than proportional at doses of 600 to 900 mg.
Based on population pharmacokinetic analyses exposure (Cmax and AUC) in paediatric patients (1 month to <3 months of age) at the recommended dose of 100 mg/m² with a maximum of 100 mg BID was 3-fold higher than in adults (≥18 years of age) given the dose of 100 mg BID. At the recommended dose, the Cmax in paediatric patients (≥3 months to <12 years of age) was higher than in adults, but the AUC was similar to that in adults. For paediatric patients older than 12 years of age, the recommended dose is likely to give similar Cmax and AUC as observed in adults. Data defining exposure in small children (1 month to <6 years of age) at the recommended dose is limited (n=33).
There are limited data in elderly. PK data is available only in 2 patients over 65 years.
A pharmacokinetic study was conducted in subjects with mild (Child-Pugh A), moderate (Child-Pugh B) and severe (Child-Pugh C) hepatic impairment, and in healthy adult control subjects with normal hepatic function matched for age, body mass index and sex. All subjects received a single 100 mg dose of larotrectinib. An increase in larotrectinib AUC0-inf was observed in subjects with mild, moderate and severe hepatic impairment of 1.3, 2 and 3.2-fold respectively versus those with normal hepatic function. Cmax was observed to increase slightly by 1.1, 1.1 and 1.5-fold respectively.
A pharmacokinetic study was conducted in subjects with end stage renal disease requiring dialysis, and in healthy adult control subjects with normal renal function matched for age, body mass index and sex. All subjects received a single 100 mg dose of larotrectinib. An increase in larotrectinib Cmax and AUC0-inf, of 1.25 and 1.46-fold respectively was observed in renally impaired subjects versus those with normal renal function.
Gender did not appear to influence larotrectinib pharmacokinetics to a clinically significant extent. There was not enough data to investigate the potential influence of race on the systemic exposure of larotrectinib.
Systemic toxicity was assessed in studies with daily oral administration up to 3 months in rats and monkeys. Dose limiting skin lesions were only seen in rats and were primarily responsible for mortality and morbidity. Skin lesions were not seen in monkeys. Clinical signs of gastrointestinal toxicity were dose limiting in monkeys. In rats, severe toxicity (STD10) was observed at doses corresponding to 1- to 2-times the human AUC at the recommended clinical dose. No relevant systemic toxicity was observed in monkeys at doses which correspond to >10-times the human AUC at the recommended clinical dose.
Larotrectinib was not teratogenic and embryotoxic when dosed daily during the period of organogenesis to pregnant rats and rabbits at maternotoxic doses, i.e. corresponding to 32-times (rats) and 16-times (rabbits) the human AUC at the recommended clinical dose. Larotrectinib crosses the placenta in both species.
Fertility studies with larotrectinib have not been conducted. In 3-months toxicity studies, larotrectinib had no histological effect on the male reproductive organs in rats and monkeys at the highest tested doses corresponding to approximately 7-times (male rats) and 10-times (male monkeys) the human AUC at the recommended clinical dose. In addition, larotrectinib had no effect on spermatogenesis in rats.
In a 1-month repeat-dose study in rats, fewer corpora lutea, increased incidence of anestrus and decreased uterine weight with uterine atrophy were observed and these effects were reversible. No effects on female reproductive organs were seen in the 3-months toxicity studies in rats and monkeys at doses corresponding to approximately 3-times (female rats) and 17-times (female monkeys) the human AUC at the recommended clinical dose. Larotrectinib was administered to juvenile rats from postnatal day (PND) 7 to 70. Pre-weaning mortality (before PND 21) was observed at the high dose level corresponding to 2.5- to 4-times the AUC at the recommended dose. Growth and nervous system effects were seen at 0.5- to 4-times the AUC at the recommended dose. Body weight gain was decreased in pre-weaning male and female pups, with a post-weaning increase in females at the end of exposure whereas reduced body weight gain was seen in males also post-weaning without recovery. The male growth reduction was associated with delayed puberty. Nervous system effects (i.e. altered hindlimb functionality and, likely, increases in eyelid closure) demonstrated partial recovery. A decrease in pregnancy rate was also reported despite normal mating at the high-dose level.
Carcinogenicity studies have not been performed with larotrectinib. Larotrectinib was not mutagenic in bacterial reverse mutation (Ames) assays and in in vitro mammalian mutagenesis assays. Larotrectinib was negative in the in vivo mouse micronucleus test at the maximum tolerated dose of 500 mg/kg.
The safety pharmacology of larotrectinib was evaluated in several in vitro and in vivo studies that assessed effects on the CV, CNS, respiratory, and GI systems in various species. Larotrectinib had no adverse effect on haemodynamic parameters and ECG intervals in telemetered monkeys at exposures (Cmax) which are approximately 6-fold the human therapeutic exposures. Larotrectinib had no neurobehavioural findings in adult animals (rats, mice, cynomolgus monkeys) at exposure (Cmax) at least 7-fold higher than the human exposure. Larotrectinib had no effect on respiratory function in rats; at exposures (Cmax) at least 8-times the human therapeutic exposure. In rats, larotrectinib accelerated intestinal transit and increased gastric secretion and acidity.
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