Efficacy of Belimumab for refractory systemic lupus erythematosus (SLE) involving the central nervous system

Determinants of neuropsychiatric flares in patients with systemic lupus erythematosus: results from five phase III trials of belimumab

OBJECTIVE

To identify determinants of neuropsychiatric (NP) flares in patients with SLE treated for active SLE yet no ongoing severe NPSLE with non-biologic standard therapy plus belimumab or placebo.

METHODS

We analysed data from five phase III trials (BLISS-52, BLISS-76, BLISS-NEA, BLISS-SC, EMBRACE; n = 3638) after exclusion of patients with baseline NP BILAG A. Factors associated with NPSLE flare, defined as a new NP BILAG A or B, were investigated using Cox regression. In a subgroup analysis, we studied patients with baseline NP BILAG E for determinants of de novo NPSLE flare. Organ damage was assessed using the SLICC/ACR Damage Index (SDI).

RESULTS

We documented 105 (2.9%) NPSLE flares. In multivariable analysis, male sex (HR = 2.37; 95% CI: 1.31, 4.28; P = 0.004), baseline NP BILAG B-D (HR = 5.91; 95% CI: 3.86, 9.06; P < 0.001), and increasing SDI scores (HR = 1.35; 95% CI: 1.21, 1.50; P < 0.001) were strongly associated with NPSLE flare. Belimumab use yielded no association at any dose or administration form. In analysis of SDI domains, NP damage was the strongest determinant of NPSLE flare (HR = 3.25; 95% CI: 2.72, 3.88; P < 0.001), holding true for cognitive impairment (HR = 14.29; 95% CI: 9.22, 22.14; P < 0.001), transverse myelitis (HR = 21.89; 95% CI: 5.40, 88.72; P < 0.001), and neuropathy (HR = 8.87; 95% CI: 5.59, 14.09; P < 0.001). Male sex was the strongest determinant of de novo NPSLE flare (HR = 3.26; 95% CI: 1.51, 7.04; P = 0.003).

CONCLUSION

Male sex, NPSLE history, and NP damage were strong determinants of impending NPSLE flare. No clear protection or predisposition was conferred from add-on belimumab.

Distinct binding mode of BAFF antagonist antibodies belimumab and tabalumab, analyzed by computer simulation

B cell-activating factor (BAFF) can bind with specific receptors to activate signalling pathways associated with the B cell activation. Belimumab and tabalumab are anti-BAFF (B cell depleting) monoclonal antibodies, with therapeutic efficacy demonstrated for the treatment of autoimmune disorders, while belimumab was approved by FDA in 2011 as a targeted therapy for systemic lupus erythematosus (SLE) and exhibited better clinical outcome than tabalumab. In this investigation, the combination modes of BAFF-belimumab and BAFF-tabalumab complexes were simulated in silico to better understand the reason for the comparative inhibitory difference between belimumab and tabalumab. The structures of belimumab and tabalumab were constructed through homology modelling. The combination mode of BAFF-belimumab complex was analyzed by molecular dynamics simulation, while that of BAFF-tabalumab complex was analyzed by protein-protein docking following the molecular dynamics simulation. Both belimumab and tabalumab were bound with BAFF at the same hydrophobic center to which the natural receptors of BAFF bind as well. Belimumab heavy chain components I51, F54, K58, D100, D101, L102, L103, and P105 and R27, Y30, K49, and S65 of belimumab light chain contribute to the BAFF-belimumab interaction mainly via hydrogen bonds, salt bridges, and hydrophobic interactions. More importantly, belimumab could bind to L83 of BAFF and produce steric hindrance with the adjacent BAFF trimers, while tabalumab could not. Therefore, our results indicated that belimumab has a better clinical outcome compared with tabalumab mainly because belimumab could bind to L83 of BAFF and interfere the formation of a BAFF 60-mer, besides mediating inhibition of the interaction of BAFF with its receptors.