AZATERO

Indications

• Myelodysplastic syndromes (MDS)
• Acute myeloid leukemia (AML)
• Chronic myelomonocytic leukemia (CMML)

Dosage

Adults: The recommended dosage of azacitidine for adults

Mechanism of action

Azacitidine induces its antineoplastic activity by inhibiting DNA methyltransferase at low doses, which leads to DNA hypomethylation and prevents DNA synthesis. At high doses, it incorporates into RNA and DNA, disrupting RNA metabolism and protein synthesis. After cellular uptake, it is phosphorylated to form 5-azacytidine monophosphate, which is further phosphorylated to diphosphate and triphosphate forms. Azacitidine triphosphate incorporates into RNA, while 5-aza-deoxycytidine triphosphate incorporates into DNA, inhibiting DNA synthesis and leading to cell death, particularly during the S-phase of the cell cycle.

Pharmacodynamics

Azacitidine demonstrates a unique pharmacodynamic profile where it can inhibit DNA methylation without significantly suppressing DNA synthesis initially. This hypomethylation can restore normal gene function critical for cell differentiation and proliferation. Clinical use has shown that azacitidine treatment leads to reduced genome-wide DNA methylation levels in bone marrow cells, corroborating its mechanism of action. However, it is associated with side effects such as anemia, neutropenia, and thrombocytopenia, and may pose risks of renal toxicity and hepatotoxicity in susceptible individuals.

Pharmacokinetics

After administration, azacitidine is rapidly absorbed and undergoes extensive metabolism. It is phosphorylated in cells to active forms, which are involved in its incorporation into nucleic acids. The drug has a variable half-life and is primarily eliminated through renal pathways. The pharmacokinetic profile indicates that azacitidine reaches peak concentrations shortly after administration, with effects noted predominantly during the S-phase of the cell cycle.

Contra-indications

• Active severe infection
• Unstable cardiac disease
• History of cardiovascular disease
• Previous therapy with anthracyclines or anthracenediones
• Previous radiotherapy to the mediastinal area

Adverse effects

• Anemia
• Neutropenia
• Thrombocytopenia
• Nausea
• Vomiting
• Diarrhea
• Constipation
• Fatigue
• Chills
• Dizziness
• Mucositis
• Pulmonary toxicity
• Skin reactions
• Altered taste
• Oliguria
• Chest pain
• Confusion
• Dry eye
• Eosinophilia
• Hyperbilirubinemia
• Hyperuricemia
• Alopecia
• Arthralgia
• Asthenia
• Local reactions at the injection site
• Night sweats

Interactions

• Concurrent use with other cytotoxic agents may increase the risk of hematologic toxicity.
• Caution is advised when combined with drugs that affect liver enzymes.

Precautions

• Monitor full blood count and cardiac function throughout treatment.
• Consider secondary assessment before and during treatment in patients with unstable malignancy or pulmonary disease.
• Handle with care as it is an irritant to tissues.

Pregnancy

Azacitidine may cause embryo-fetal toxicity and is not recommended during pregnancy.

Breast-feeding

The effects on breastfed infants are unknown; caution is advised.

Storage

Store in a refrigerator (2 to 8 degrees Celsius). Protect from light. Do not freeze.

Formulations

• Powder for solution for infusion
• Solution for infusion

Mechanism of action

Azacitidine (5-azacytidine) is a chemical analogue of the cytosine nucleoside present in DNA and RNA. It induces antineoplastic activity by inhibiting DNA methyltransferase at low doses and inducing cytotoxicity by incorporating itself into RNA and DNA at high doses. Covalent binding to DNA methyltransferase results in DNA hypomethylation and prevents DNA synthesis. On the other hand, the incorporation of azacitidine into RNA and DNA leads to cytotoxicity as follows: Following cellular uptake, azacitidine is phosphorylated by uridine-cytidine kinase to form 5-azacytidine monophosphate. Afterwards, pyrimidine monophosphate and diphosphate kinases phosphorylate 5-azacytidine monophosphate to form 5-azacytidine diphosphate and triphosphate, respectively. Azacitidine triphosphate is able to incorporate into RNA, disrupting RNA metabolism and protein synthesis. The reduction of azacytidine diphosphate leads to the formation of 5-aza-deoxycytidine diphosphate, which is then phosphorylated to form 5-azadeoxycitidine triphosphate, a compound able to incorporate into DNA and inhibit DNA synthesis. As a ribonucleoside, azacitidine incorporates into RNA to a larger extent than into DNA. Incorporating into RNA leads to the disassembly of polyribosomes, defective methylation and acceptor function of transfer RNA, and the inhibition of protein production, resulting in cell death. During the S-phase of the cell cycle, azacitidine exhibits the highest toxicity; however, the predominant mechanism of cytotoxicity has not been elucidated. The cytotoxic effects of azacitidine cause the death of rapidly dividing cells, including cancer cells that are no longer responsive to normal growth control mechanisms. Non-proliferating cells are relatively insensitive to azacitidine. It is believed that azacitidine exerts its antineoplastic effects through direct cytotoxicity on abnormal hematopoietic cells in the bone marrow. Telomerase activation is thought to be a critical step in cellular immortality and oncogenesis. Several reagents including differentiation-inducing and antineoplastic agents are known to inhibit telomerase activity, although the molecular mechanisms through which they inhibit telomerase activity remain unclear. Demethylating reagents have recently been used as potential antineoplastic drugs for some types of cancers including those of the prostate. In the present study, we examined the effect of the demethylating reagent 5-azacytidine (5-aza-CR) on telomerase activity using cells of two prostate cancer cell lines, DU-145 and TSU-PR1. 5-aza-CR treatment significantly reduced telomerase activity in TSU-PR1 cells, but not in DU-145 cells, although growth inhibition was observed to a similar extent in both cell lines. Reverse transcription-PCR analyses revealed that inhibition of telomerase activity was accompanied by down-regulation of telomerase catalytic subunit (hTERT) mRNA expression. Transient expression assays showed that 5-aza-CR repressed the transcriptional activity of the hTERT promoter and that the E-box within the core promoter was responsible for this down-regulation. Western blot analyses revealed that 5-aza-CR reactivated p16 expression and repressed c-Myc expression in TSU-PR1 cells but not in DU-145 cells. Overexpression of p16 in TSU-PR1 cells led to significant repression of c-Myc transcription. These findings suggest that 5-aza-CR inhibits telomerase activity via transcriptional repression of hTERT, in which p16 and c-Myc may play a key role. Cellular differentiation is controlled by a variety of factors including gene methylation, which represses particular genes as cell fate is determined. The incorporation of 5-azacytidine (5azaC) into DNA in vitro prevents methylation and thus can alter cellular differentiation pathways. Human bone marrow fibroblasts and MG63 cells treated with 5azaC were used as models of osteogenic progenitors and of a more mature osteoblast phenotype, respectively. The capacity for different

Pharmacodynamics

The concentration of azacitidine required for maximum inhibition of DNA methylation in vitro does not cause major suppression of DNA synthesis, and hypomethylation may restore normal function to genes critical for differentiation and proliferation. Genome-wide DNA methylation levels in bone marrow granulocytes were reduced in patients with juvenile myelomonocytic leukemia after the first treatment cycle of azacitidine (75 mg/m² or 2.5 mg/kg), confirming the DNA-hypomethylating activity of azacitidine. The use of azacitidine causes anemia, neutropenia and thrombocytopenia in adult patients with myelodysplastic syndrome and pediatric patients with juvenile myelomonocytic leukemia. Azacitidine may cause renal toxicity, tumor lysis syndrome and embryo-fetal toxicity. It may also lead to the development of hepatotoxicity in patients with severe pre-existing hepatic impairment.