Chemical formula: C₁₄H₁₉BCl₂N₂O₄ Molecular mass: 361.03 g/mol PubChem compound: 25183872
Ixazomib citrate, a prodrug, is a substance that rapidly hydrolyses under physiological conditions to its biologically active form, ixazomib.
Ixazomib is an oral, highly selective and reversible proteasome inhibitor. Ixazomib preferentially binds and inhibits the chymotrypsin-like activity of the beta 5 subunit of the 20S proteasome.
Ixazomib induced apoptosis of several tumour cell types in vitro. Ixazomib demonstrated in vitro cytotoxicity against myeloma cells from patients who had relapsed after multiple prior therapies, including bortezomib, lenalidomide, and dexamethasone. The combination of ixazomib and lenalidomide demonstrated synergistic cytotoxic effects in multiple myeloma cell lines. In vivo, ixazomib demonstrated antitumour activity in various tumour xenograft models, including models of multiple myeloma. In vitro, ixazomib affected cell types found in the bone marrow microenvironment including vascular endothelial cells, osteoclasts and osteoblasts.
Ixazomib did not prolong the QTc interval at clinically relevant exposures based on the results of a pharmacokinetic-pharmacodynamic analysis of data from 245 patients. At the 4 mg dose, mean change from baseline in QTcF was estimated to be 0.07 msec (90% CI; -0.22, 0.36) from the model based analysis. There was no discernible relationship between ixazomib concentration and the RR interval suggesting no clinically meaningful effect of ixazomib on heart rate.
After oral administration, peak plasma concentrations of ixazomib were achieved at approximately one hour after dosing. The mean absolute oral bioavailability is 58%. Ixazomib AUC increases in a dose proportional manner over a dose range of 0.2-10.6 mg.
Administration with a high-fat meal decreased ixazomib AUC by 28% compared with administration after an overnight fast.
Ixazomib is 99% bound to plasma proteins and distributes into red blood cells with a blood-to-plasma AUC ratio of 10. The steady-state volume of distribution is 543 L.
After oral administration of a radiolabeled dose, 70% of total drug-related material in plasma was accounted for by ixazomib. Metabolism by multiple CYP enzymes and non-CYP proteins is expected to be the major clearance mechanism for ixazomib. At clinically relevant ixazomib concentrations, in vitro studies using human cDNA-expressed cytochrome P450 isozymes indicate that no specific CYP isozyme predominantly contributes to ixazomib metabolism and non-CYP proteins contribute to overall metabolism. At concentrations exceeding those observed clinically, ixazomib was metabolized by multiple CYP isoforms with estimated relative contributions of 3A4 (42.3%), 1A2 (26.1%), 2B6 (16.0%), 2C8 (6.0%), 2D6 (4.8%), 2C19 (4.8%) and 2C9 (<1%).
Ixazomib exhibits a multi-exponential disposition profile. Based on a population PK analysis, systemic clearance (CL) was approximately 1.86 L/hr with inter-individual variability of 44%. The terminal half-life (t½) of ixazomib was 9.5 days. Approximately 2-fold accumulation in AUC was observed with weekly oral dosing on Day 15.
After administration of a single oral dose of 14C-ixazomib to 5 patients with advanced cancer, 62% of the administered radioactivity was excreted in urine and 22% in the faeces. Unchanged ixazomib accounted for <3.5% of the administered dose recovered in urine.
The PK of ixazomib is similar in patients with normal hepatic function and in patients with mild hepatic impairment (total bilirubin ≤ ULN and AST > ULN or total bilirubin >1-1.5 x ULN and any AST) based on the results of a population PK analysis.
The PK of ixazomib was characterized in patients with normal hepatic function at 4 mg (N=12), moderate hepatic impairment at 2.3 mg (total bilirubin >1.5-3 x ULN, N=13) or severe hepatic impairment at 1.5 mg (total bilirubin >3 x ULN, N=18). Unbound dose-normalized AUC was 27% higher in patients with moderate or severe hepatic impairment as compared to patients with normal hepatic function.
The PK of ixazomib is similar in patients with normal renal function and in patients with mild or moderate renal impairment (creatinine clearance ≥30 mL/min) based on the results of a population PK analysis.
The PK of ixazomib was characterized at a dose of 3 mg in patients with normal renal function (creatinine clearance ≥90 mL/min, N=18), severe renal impairment (creatinine clearance <30 mL/min, N=14), or ESRD requiring dialysis (N=6). Unbound AUC was 38% higher in patients with severe renal impairment or ESRD requiring dialysis as compared to patients with normal renal function. Pre- and post-dialyzer concentrations of ixazomib measured during the haemodialysis session were similar, suggesting that ixazomib is not dialyzable.
There was no clinically meaningful effect of age (23-91 years), sex, body surface area (1.2-2.7 m²), or race on the clearance of ixazomib based on the results of a population PK analysis. The mean AUC was 35% higher in Asian patients; however, there was overlap in the AUC of ixazomib across White and Asian patients.
Ixazomib was not mutagenic in a bacterial reverse mutation assay (Ames assay) or clastogenic in a bone marrow micronucleus assay in mice. Ixazomib was positive in an in vitro clastogenicity test in human peripheral blood lymphocytes. However, ixazomib was negative in an in vivo comet assay in mice, in which percent tail DNA was assessed in the stomach and liver. Therefore, the weight of evidence indicates that ixazomib is not considered to present a genotoxic risk.
Ixazomib caused embryo-foetal toxicity in pregnant rats and rabbits only at maternally toxic doses and at exposures that were slightly higher than those observed in patients receiving the recommended dose. Studies of fertility and early embryonic development and pre- and post-natal toxicology were not conducted with ixazomib, but evaluation of reproductive tissues was conducted in the general toxicity studies. There were no effects due to ixazomib treatment on male or female reproductive organs in studies up to 6-months duration in rats and up to 9-months duration in dogs.
In multi-cycle repeated-dose toxicity studies conducted in rats and dogs, the principal target organs included the gastrointestinal tract, lymphoid tissues, and the nervous system. In the 9-month study (10 cycles) in dogs orally administered with a dosing schedule mimicking the clinical regimen (28-day cycle), microscopic neuronal effects were generally minimal in nature and only observed at 0.2 mg/kg (4 mg/m2). The majority of target organ findings demonstrated partial to full recovery following discontinuation of treatment, with the exception of neuronal findings in the lumbar dorsal root ganglion and dorsal column.
Following oral administration, a tissue distribution study in rats revealed that the brain and spinal cord were amongst the tissues with the lowest levels, suggesting that the penetration of ixazomib through the blood-brain barrier appears to be limited. However, the relevance to humans is unknown.
Non-clinical safety pharmacology studies both in vitro (on hERG channels) and in vivo (in telemetered dogs following single oral administration) demonstrated no effects of ixazomib on cardiovascular or respiratory functions at AUC more than 8-fold higher than the clinical value.
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