Affinity and formulation of a phenyl glycolipid for stimulation of invariant natural killer T cells to inhibit tumor growth

α-galactosylceramide (α-GalCer) can activate invariant natural killer T (iNKT) cells to modulate immune system. We have synthesized and tested many α-GalCer analogs and found the most potent iNKT-stimulating agent C34, which has two phenyl rings on the acyl chain. The complex of C34 and CD1d showed the highest binding affinity to the T cell receptor of iNKT cells. Moreover, C34 can induce strong Th1-biased cytokines and exhibit potent anticancer efficacy in tumor animal models. However, poor water solubility of C34 limits its clinical application. In this study, we incorporated C34 into PEGylated lipid nanocarriers (PLN), which improves the water solubility of C34. The PLN-C34 shortened the activation time of iNKT cells and maintained C34's ability to activate iNKT cells to secrete cytokines in vitro. Furthermore, PLN-C34 showed similar anticancer efficacy as C34 dissolved in dimethyl sulfoxide to prolong the survival of mice bearing with TC1 or B16F10 tumor. In general, the PLN-C34 preserved the ability to activate iNKT cells and inhibited tumor growth, suggesting that PLN-C34 is a promising candidate for cancer therapy in clinical settings.