Rilonacept is a recombinant dimeric fusion protein and interleukin-1 (IL-1) cytokine trap used as a targeted anti-inflammatory active pharmaceutical ingredient. Unlike conventional small-molecule APIs, rilonacept is a biologic protein and therefore requires control of protein identity, molecular integrity, purity, aggregation, potency, host-cell impurities and other critical quality attributes.
Rilonacept consists of the ligand-binding domains of the extracellular portions of the human interleukin-1 receptor type I (IL-1R1) and IL-1 receptor accessory protein (IL-1RAcP) linked to the Fc portion of human IgG1. It is produced using recombinant Chinese hamster ovary (CHO) cells. The FDA reports an approximate molecular weight of 251 kDa.
Rilonacept API
The FDA Substance Registration System confirms CAS 501081-76-1 and UNII 8K80YB5GMG for rilonacept.
Because rilonacept is a recombinant biologic, a conventional small-molecule molecular formula is not appropriate for CMS use. NCBI lists a very large composition-based formula, C9030H13932N2400O2670S74, but for pharmaceutical API presentation it is more appropriate to report the protein as an approximately 251-kDa recombinant fusion protein.
Rilonacept is a dimeric glycoprotein fusion protein containing extracellular IL-1 receptor components fused to a human IgG1 Fc region.
The protein architecture provides high-affinity binding to inflammatory IL-1 cytokines. FDA characterization reported equilibrium dissociation constants of approximately:
The principal pharmacological activity is associated with binding IL-1α and IL-1β and preventing their interaction with cell-surface IL-1 receptors.
Rilonacept is manufactured using recombinant CHO-cell technology and has an approximate molecular weight of 251 kDa.
Rilonacept API is used in the development and manufacture of biologic pharmaceutical products for inflammatory and autoinflammatory diseases.
Current U.S. labeling includes:
Rilonacept is administered by subcutaneous injection. The current product is supplied as a 220 mg lyophilized powder for reconstitution, providing up to 160 mg from a single vial after reconstitution.
Rilonacept functions as a soluble IL-1 cytokine trap.
It binds both IL-1α and IL-1β, preventing these cytokines from interacting with their cell-surface receptors. This suppresses downstream IL-1-mediated inflammatory signaling.
In CAPS, mutations affecting the NLRP3 inflammasome can result in excessive production of active IL-1β. By capturing IL-1, rilonacept reduces inflammatory signaling and associated inflammatory manifestations.
As a recombinant fusion protein, rilonacept requires a biologic-specific analytical control strategy rather than conventional small-molecule API tests.
Important analytical controls can include:
FDA's original quality review specifically characterized rilonacept as a ~251-kDa dimeric glycoprotein and evaluated ligand-binding specificity and affinity.
Rilonacept is produced using recombinant CHO-cell technology.
A pharmaceutical-grade manufacturing process generally requires controlled upstream cell culture followed by downstream purification and formulation.
Key stages include:
Because rilonacept is a complex protein, manufacturing consistency depends on control of molecular integrity, glycosylation, aggregation, charge heterogeneity and biological activity.
| Parameter | Specification |
|---|---|
| Appearance | white to off-white crystalline powder |
| Identification | IR & HPLC compliant |
| Assay (HPLC) | 98.0% – 102.0% |
| Loss on Drying | NMT 1.0% |
| Residue on Ignition | NMT 0.1% |
| pH (1% Solution) | 6.5 |
| Individual Impurity | NMT 0.5% |
| Total Impurities | NMT 2.0% |
| Water Content | NMT 1.0% |