IntronA (Interferon alpha 2b)

Function

IFNα2b is a naturally secreted protein that is produced by the human body via antigen-presenting cells (APCs) ^[2]. When introduced to the body for treatment, IFNα2b is injected into the body subcutaneously and binds to the surface of cells ^[3]. When this occurs, IFNα2b produces many possible outcomes. This includes inhibiting replication of viruses within virus-infected cells, suppressing cell proliferation, enhancing activity of macrophages, stimulating certain types of enzymes, and increasing lymphocytes’ specific cytotoxicity ^[3]. Specifically, in viral infections and malignancy the interferon specifically targets CD8+ effector T cells and CD4+ immunomodulatory T cells to amplify the body’s immune response ^[2]. It can also help induce a caspase cascade to activate cell death in virally infected and malignant cells ^[2]. Overall, INFα2b is crucial for activation and regulation of the protective immune response.

Structural highlights

Each IFNα2b monomer consists of five alpha helices and five coiled loops ^[4]. A zinc molecule is held within each IFNα2b monomer ^[4]. There are four significant cysteine residues on IFNα2b that create two disulfide bonds ^[1]. The first disulfide bond is between Cys29 and Cys138 ^[1]. The second disulfide bond is between Cys1 and Cys98 ^[1]. IFNα2b is considered a Type I interferon and recognizes interferon alpha receptors 1 and 2 located on the target protein’s surface ^[1]. Amino acid residues on IFNα2b that participate in binding to IFNAR 1 and 2 are present on one coiled loop and four alpha helices ^[1]. These residues include: Arg22, Leu26, Phe27, Leu30, Lys31, Arg33, His34, Ser68, Thr79, Lys83, Tyr85, Tyr89, Arg120, Lys121, Gln124, Lys131 Glu132, Arg144, and Glu146 ^[1].

Mechanism

There are several pathways in that IFNα2b has an effect on the target cell ^[1]. These pathways include the caspase cascade and the JAK-STAT pathway ^{[1] [2]}. The caspase cascade results in apoptosis, thereby participating in both anti-viral and anti-cancer mechanisms ^[2]. Once IFNα2b binds to either IFNAR 1 or 2 receptors, cytochrome c and tumor necrosis alpha factor trigger the caspase cascade, which in turn signals apoptosis ^[1]. In the binding of IFNα2b to an IFNAR receptor, the protein JAK (a tyrosine kinase) is activated ^[1]. JAK is phosphorylated and in turn phosphorylates the IFNAR receptors ^[1]. The IFNAR receptors bind to STAT proteins resulting in a cascade pathway that signals the release of antiviral proteins ^[1].

Disease

Hepatitis Virus

Hepatitis B

IFNα2b treats chronic Hepatitis B (HBV) by interfering with viral DNA synthesis and enhancing the cellular immune response ^[5]. The cytokine enhances T-cell and natural killer cell activity by interacting with the infected cell’s surface ^[5]. IFNα2b also activates antiviral enzymes to inhibit proliferation of HBV ^[5].

Hepatitis C

Hepatitis C (HCV) can range from acute to chronic conditions and progression occurs in more than half of these cases ^[6]. HCV attacks the liver tissues causing inflammation and cirrhosis, which can lead to chronic liver disease ^[6]. IFNα2b is used to treat the acute stage of HVC to prevent progression into the chronic disease ^[6]. IFNα2b overall reduces the viral amplification and allows T-cells to effectively respond to the infection ^[7].

Cancer

Multiple Myeloma

IFNα2b has been shown to prolong patients with multiple myeloma ^[8]. Multiple myeloma is diagnosed when multiple clones of a specific plasma cell are found or when apparent genetic mutations are affecting the cell’s normal functions ^[8]. IFNα2b therapy causes tumor stabilization and prolongation of the aggressive stage of multiple myeloma with maintained therapy ^[8].

Hairy cell Leukemia

IFNα2b is a major treatment for patients with hairy cell leukemia ^[1]. The disease is characterized by B cells in the blood, bone marrow, and spleen ^[1]. Patients who receive the therapeutic treatment experience partial to complete remission ^[1]. The treatment is especially effective because there is rarely relapse of the cancer with consistent therapy and mild side effects ^[1]. The presence of malignant cells decreases, predominantly in the bone marrow, and hematologic levels normalized ^[9]