Inducible nitric oxide synthase (iNOS) produces nitric oxide (NO) and related reactive nitrogen species, which play key roles in the intracellular killing of bacterial and parasitic pathogens. The proteasomal degradation of iNOS is driven by the SPRY domain-containing SOCS box proteins SPSB11 and SPSB2.2 SPSB2-deficient macrophages show prolonged iNOS expression, increased NO production and enhanced killing of bacteria and parasites.2 Disrupting iNOS degradation by the proteasome thus represents a new strategy to treat infectious diseases, including respiratory infections such as tuberculosis and pneumonia.
We have designed several cyclic peptide inhibitors of the SPSB-iNOS interaction, with the aims of making them stable to proteolysis and relatively non-polar.3-5 However, even the least polar of these does not show significant passive membrane permeability in PAMPA assays.6 As the SPSB-iNOS interaction occurs in the cytoplasm of macrophages, we have investigated the ability of a range of cell-penetrating peptide conjugates, both linear and cyclic, to facilitate cytoplasmic delivery. We have also characterised the effects of treating activated macrophages with these conjugates on NO production and iNOS lifetime, and monitored their ability to escape from endosomes.7
1 Lewis, R. S., Kolesnik, T. B., Kuang, Z. et al. J. Immunol. 187, 3798-3805 (2011)
2 Kuang, Z., Lewis, R. S., Curtis, J. M. et al. J. Cell Biol. 190, 129-141 (2010)
3 Yap, B. K., Leung, E. W., Yagi, H. et al. J. Med. Chem. 57, 7006-7015 (2014)
4 Yap, B. K., Harjani, J. R., Leung, E. W. et al. FEBS Lett. 590, 696-704 (2016)
5 Sadek, M. M., Barlow, N., Leung, E. W. W. et al. ACS Chem Biol 13, 2930-2938 (2018)
6 Barlow, N., Chalmers, D. K., Williams-Noonan, B. J. et al. ACS Chem Biol 15, 2070-2078 (2020)
7 Teo, S. L. Y., Rennick, J. J., Yuen, D. et al. Nature Commun, in press (2021)