Optical studies of nonconventional drug interaction with human invariant natural killer T cells: Prediction from molecular simulations

This study examines sulfamethoxazole (SMX), a sulfonamide antibiotic strongly associated with severe cutaneous adverse effects, as a potential regulator of invariant natural killer T (iNKT) cells. This work combines molecular docking (to evaluate the likelihood of SMX binding to residues within a conventional binding pocket), molecular dynamics (to assess the stability of SMX binding and the forces that may destabilize the interaction), flow cytometry (to evaluate iNKT-cell activation in the presence of SMX within the context of established antigen presentation models), and particularly Raman spectroscopy (to investigate whether SMX-associated spectral features are retained after co-incubation and interaction) directly on sorted iNKT cells. Functional activation was assessed through IFN-γ production from sorted iNKT cells and correlated with Raman spectral data to support our hypothesis. The Raman spectroscopy was performed on both CD1d dimer (in isolation) as the presenter molecule of the drug and in sorted iNKT cells (in isolation), to identify spectroscopic evidence of drug–CD1dimer or drug-cell interactions under near-physiological conditions. From the CD1d experiment, we observed spectral features consistent with potential interactions between CD1d and serum-derived lipids, in a manner comparable to the positive control (α-GalCer). From the iNKT experiment, peaks at 1610 and 1663 cm−1 are the representative peaks that emerge under SMX stimulation conditions in iNKT cells (through TCR binding), as identified by second principal component (PC2) analysis. From the complete experiment, (CD1d + iNKT) suggests the possibility of a direct interaction between SMX and iNKT TCRs. Flow cytometry analysis further demonstrated a significant increase in ZAP-70 phosphorylation in sorted iNKT cells exposed to SMX under serum-free conditions, supporting the possibility of proximal TCR-associated signaling in the absence of CD1d.