Amrubicin

Uses

Investigated for use/treatment in lung cancer .

How Amrubicin works

As an anthracycline, amrubicin has antimitotic and cytotoxic activity through a variety of mechanisms of action. Amrubicin is found to form complexes with DNA via intercalation between base pairs, and it inhibits topoisomerase II enzyme activity by stabilizing the DNA-topoisomerase II complex, which prevents the re-ligation portion of the ligation-religation reaction that topoisomerase II normally catalyzes .

Topoisomerase II is an enzyme located in the nucleus that regulates DNA structure through double-strand breakage and re-ligation, therefore modulating DNA replication and transcription. Inhibition of the enzyme leads to inhibition of DNA replication and halt cell growth with an arrest of the cell cycle occurring at the G2/M phase. The mechanism by which amrubicin inhibits DNA topoisomerase II is believed to be through stabilization of the cleavable DNA–topo II complex, ending in re-ligation failure and DNA strand breakage .

DNA damage triggers activation of caspase-3 and -7 and cleavage of the enzyme PARP (Poly ADP ribose polymerase), leading to apoptosis and a loss of mitochondrial membrane potential. Amrubicin, like all anthracyclines, intercalates into DNA and produces reactive oxygen free radicals via interaction with NADPH, which causes cell damage .

Compared with doxorubicin, another member of the anthracycline drug class, amrubicin binds DNA with a 7-fold lower affinity and therefore, higher concentrations of amrubicin are necessary to promote DNA unwinding .

Toxicity

Based on acute intravenous dose toxicity studies, the lethal dose to 50% of animals was estimated to be 42 mg/kg in mice, 14 mg/kg in rats, and 4 mg/kg in dogs .

Myelosuppression, with the primary clinical manifestation of neutropenia and leucopenia, is the dose-limiting toxicity of this drug. In addition to this, mucositis, nausea, vomiting, and alopecia are frequent. Hepatopathy, observed with elevated bilirubin concentrations, occurs less frequently. Cardiotoxicity is a major adverse effect of the anthracycline antibiotics and may be acute or chronic; in the acute setting, electrocardiographic (ECG) abnormalities may be observed, demonstrating ST-T elevations and arrhythmias, however, chronic cardiotoxicity poses a serious risk that may be lethal due to the slow development of irreversible, cardiomyopathy. The occurrence of toxicity shows a significant interindividual variation, and for this reason, the pharmacokinetics and pharmacodynamics of anthracyclines have been heavily investigated in order to identify models that may be used in the clinical setting to prevent the development of serious toxicity, mainly leucopenia, and maximize tumor exposure . Interestingly, a recent study was done to further examine genetic predisposition neutropenia/amrubicin toxicity. It was determined that C3435T polymorphisms of the ABCB1 gene might be able to predict severe amrubicin-induced neutropenia .

Secondary alcohol metabolites of earlier generation anthracyclines have been shown to lead to cardiac toxicity which is a major toxicity of conventional anthracyclines and thus limits the amount that can be delivered safely to patients. Clinical manifestations of toxicity observed on the acute and repeated administration of amrubicin in rats and dogs were dose-related and reversible including fecal changes (mucoid or bloody feces/diarrhea), body weight decreases, decreased food consumption, decreased activity, and alopecia. Similar findings were observed at doses of doxorubicin approximately one half those of amrubicin .

Volume of Distribution

Moderate volume of distribution (1.4 times total body water) .

Elimination Route

Peak plasma concentrations of the active metabolite amrubicinol were observed from immediately after administration of amrubicin to 1h after administration. Plasma concentrations of amrubicinol were low compared with amrubicin plasma concentrations. The plasma amrubicinol AUC (area under the curve) was approximately 10-fold lower than the amrubicin plasma AUC. Concentrations of amrubicinol were higher in RBCs as compared with plasma. Amrubicinol AUCs ranged from 2.5-fold to 57.9-fold higher in red blood cells (RBCs) compared to plasma. Because amrubicinol distributes itself into RBCs more than amrubicin, the concentrations of amrubicinol and amrubicin in RBCs were quite similar. The AUC of amrubicinol in RBCs was approximately twofold lower than the amrubicin RBC AUC .

In one study, after repeated daily amrubicin administration, amrubicinol accumulation was observed in plasma and RBCs. On day 3, the amrubicinol plasma AUC was 1.2-fold to 6-fold higher than day 1 values; the RBC AUC was 1.2-fold to 1.7-fold higher than day 1 values. After 5 consecutive daily doses, plasma and RBC amrubicinol AUCs were 1.2-fold to 2.0-fold higher than day 1 values .

Half Life

20-30 h

In a study of dogs, Amrubicin plasma concentrations followed a biphasic pattern with peak concentrations observed immediately after dosing followed by α and β half-lives (t1/2) ± SD of 0.06 ± 0.01 and 2.0 ± 0.3 hours, respectively .

Clearance

The plasma pharmacokinetics of amrubicin in cancer patients are characterized by low total clearance (22% of total liver blood flow) .

Elimination Route

In one study, urinary excretion of amrubicin and amrubicinol after ingestion of amrubicin accounted for 2.7% to 19.6% of the administered dose. The amount of excreted amrubicinol was approximately 10-fold greater than excreted amrubicin .

Excretion of amrubicin and its metabolites is primarily hepatobiliary. Enterohepatic recycling was demonstrated in rats .

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