Objectives: To investigate the biodistribution and specific targeting for tumour necrosis factor (TNF) of a fully human, radiolabelled anti-TNF monoclonal antibody (anti-TNF mAb) in patients with active rheumatoid arthritis (RA). To assess whether this agent is suitable for visualisation of synovitis.
Methods: Ten patients with RA underwent whole body scintigraphy after administration of a tracer—subtherapeutic dose of 100 μg 99mTc human anti-TNF mAb. After two weeks, the procedure was repeated to assess the specificity of the radiolabelled antibody for TNF and its sensitivity for changes in inflammation. Therefore, a competition study was performed in five patients, who received excess unlabelled anti-TNF mAb before the tracer dose of 99mTc-anti-TNF. Another five patients received 120 mg methylprednisolone two days before the second scintigraphy.
Results: Radiolabelled anti-TNF mAb allowed clear visualisation of inflamed joints in patients with active RA with a high specificity. Concomitant administration of excess unlabelled anti-TNF reduced the joint uptake of 99mTc-anti-TNF mAb by a median of 25% as a percentage of the injected dose after 24 hours, whereas uptake in liver and spleen remained unchanged. Systemic corticosteroids reduced the disease activity, which was mirrored by a decreased joint uptake of the tracer. The anti-TNF mAb retained its high affinity for TNFα after labelling and was cleared from the circulation with an elimination half life of 48 hours. The procedure was well tolerated.
Conclusions: Radiolabelled human anti-TNF mAb allows visualisation of synovitis in patients with RA. Joint accumulation of this agent is partly due to specific TNF targeting and is highly predictive for inflammation.
- monoclonal antibodies
- rheumatoid arthritis
- tumour necrosis factor α
- DAS, disease activity score
- HPLC, high performance liquid chromatography
- HYNIC, hydrazinicotinamide
- ID, injected dose
- mAb, monoclonal antibody
- RA, rheumatoid arthritis
- TNFα, tumour necrosis factor α
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