C11-conjugated soft glucocorticoid antibody-drug conjugates for precision immunomodulation

Glucocorticoids (GCs) are highly effective therapies for inflammatory diseases, but their clinical use is severely limited by systemic toxicities. To address this liability, we developed a modular antibody-drug conjugate (ADC) platform for targeted delivery of GC to immune cells, thereby minimizing systemic exposure to free GC. The platform integrates three key design features: (i) fluticasone furoate (FF), a potent metabolically soft glucocorticoid; (ii) a legumain-cleavable AsnAsnGlyPro self-immolative linker for lysosome-selective payload release; and (iii) C11 hydroxyl conjugation to enhance resistance to serum esterase-mediated hydrolysis. ADCs targeting TNFα, CD38, and CD11a exhibited nanomolar potency in glucocorticoid-responsive reporter assays and excellent serum stability enabled by the C11 conjugation. Across all three targets, the ADCs displayed nanomolar potency in glucocorticoid-responsive reporter assays, achieving over 50-fold selectivity over non-targeting isotype controls. Functional assays in primary bone marrow-derived macrophages (BMDMs) and THP-1 cells confirmed potent inhibition of NF-κB signaling and pro-inflammatory cytokine secretion (IL-6, IL-8). Extensive stability assays in human and mouse serum revealed that the C11-conjugated constructs are highly resistant to premature cleavage. These findings establish a robust, highly stable soft glucocorticoid ADC platform for targeted immunosuppression with the potential to improve the safety and efficacy of glucocorticoid therapy for inflammatory diseases.