F8-IL10: A New Potential Antirheumatic Drug Evaluated by a PET-Guided Translational Approach

Abstract

Antibody fragment F8-mediated interleukin 10 (IL10) delivery is a novel treatment for rheumatoid arthritis (RA). F8 binds to the extra-domain-A of fibronectin (ED-A). In this study, in vivo biodistribution and arthritis targeting of radiolabeled F8-IL10 were investigated in RA patients, followed by further animal studies. Therefore, three RA patients (DAS28 > 3.2) received 0.4 mg of 30-74 megabecquerel [¹²⁴I]I-F8-IL10 for PET-CT and blood sampling. In visually identified PET-positive joints, target-to-background was calculated. Healthy mice, rats, and arthritic rats were injected with iodinated F8-IL10 or KSF-IL10 control antibody. Various organs were excised, weighed, and counted for radioactivity. Tissue sections were stained for fibronectin ED-A. In RA patients, [¹²⁴I]I-F8-IL10 was cleared rapidly from the circulation with less than 1% present in blood after 5 min. PET-CT showed targeting in 38 joints (11-15 per patient) and high uptake in the liver and spleen. Mean target-to-background ratios of PET-positive joints were 2.5 ± 1.2, 1.5 times higher for clinically active than clinically silent joints. Biodistribution of radioiodinated F8-IL10 in healthy mice showed no effect of the radioiodination method. [¹²⁴I]I-F8-IL10 joint uptake was also demonstrated in arthritic rats, ∼14-fold higher than that of the control antibody [¹²⁴I]I-KSF-IL10 ( p < 0.001). Interestingly, liver and spleen uptake were twice as high in arthritic than in healthy rats and were related to increased (∼7×) fibronectin ED-A expression in these tissues. In conclusion, [¹²⁴I]I-F8-IL10 uptake was observed in arthritic joints in RA patients holding promise for visualization of inflamed joints by PET-CT imaging and therapeutic targeting. Patient observations and, subsequently, arthritic animal studies pointed to awareness of increased [¹²⁴I]I-F8-IL10 uptake in the liver and spleen associated with moderate systemic inflammation. This translational study demonstrated the value of in vivo biodistribution and PET-CT-guided imaging in development of new and potential antirheumatic drugs'.

Keywords: IL10; computed tomography; fibronectin (ED-A); pharmacokinetics; positron emission tomography; rheumatoid arthritis.

Figure 1

(A) Example of a [¹²⁴I]I–F8–IL10 PET-CT scan of the hands of RA patient 3 with clinically active disease. (B) [¹²⁴I]I–F8–IL10 PET scan of RA patient 1 showing clear tracer uptake in liver and spleen. %ID = percentage of the injected dose.

Figure 2

Pharmacokinetic analysis of [¹²⁴I]I–F8–IL10 in (A) whole blood and (B) plasma of three RA patients.

Figure 3

Ex vivo tissue distribution of healthy mice with [¹³¹I]I–F8–IL10 (iodogen) and [¹²⁴I]-F8-IL10 (chloramine-T) at 10 min and 24 h. The results are expressed as a percentage of the injected dose per gram (%ID/g ± SD).

Figure 4

Ex vivo tissue distribution at 24 h p.i. in healthy rats, [¹²⁴I]I–F8–IL10^low (white bars), and in arthritic rats, [¹²⁴I]I-KSF-IL10-control (black bars), [¹²⁴I]I–F8–IL10^low (light gray bars), and [¹²⁴I]I–F8–IL10^high (dark gray bars). The results are expressed as percentage injected dose per gram (%ID/g ± SD).

Figure 5

Histopathology and immunofluorescence images of fibronectin ED-A stainings on arthritic and healthy rats spleen and liver sections. (A) HE staining of spleen (10× magnification). (B, C) Fibronectin ED-A staining (40× magnification) of healthy spleen (B) and arthritic spleen (C). (D) The total fluorescence intensity of healthy spleen vs the arthritic spleen (total fluorescence intensity E+06 ± SD). (E) HE staining of liver (10× magnification). (F, G) Fibronectin ED-A staining (blue channel, nucleus, and green channel, fibronectin ED-A) of healthy (F) and arthritic liver (G). (H) The total fluorescence intensity of healthy liver vs the arthritic liver (total fluorescence intensity E+06 ± SD).