PIK-III (Synonyms: Vacuolar Protein Sorting 34 Inhibitor 2, Vps34-IN2, Vps34 Inhibitor 2)

IC50: 18 nM for VPS34

PIK-III is a VPS34 inhibitor and is able to inhibit autophagy.

VPS34 kinase has been found to be responsible for synthesis and deposition of phosphatidylinositol-3-phosphate at autophagosome formation sites, resulting in the recruitment of PtdIns(3)P-binding proteins.

In vitro: In previous study, PIK-III was identified as a selective inhibitor of VPS34 binding in a hydrophobic pocket. In addition, PIK-III could acutely inhibit the autophagy and lipidation of LC3, which led to the stabilization of autophagy substrates. Moreover, substrates such as NCOA4 were identified by conducting ubiquitin-affinity proteomic assay on PIK-III-treated cells, which accumulated in cells with ATG7 deficience and co-localized with autolysosomes. NCOA4 could bind ferritin heavy chain-1 directly to target the iron-binding ferritin complex following starvation or iron depletion [1].

In vivo: Animal study showed that PIK-III-treated Ncoa4-/- mice had a profound accumulation of iron in splenic macrophages that were important for iron reutilization from engulfed red blood cells. In summary, such in vivo results provided a novel mechanism for selective autophagy of ferritin and revealed a previously untouched role for autophagy and NCOA4 in the control of in-vivo iron homeostasis [1].

Clinical trial: Up to now, PIK-III is still in the preclinical development stage.

Reference:
[1] Dowdle WE et al.  Selective VPS34 inhibitor blocks autophagy and uncovers a role for NCOA4 in ferritin degradation and iron homeostasis in vivo. Nat Cell Biol. 2014 Nov;16(11):1069-79.