New paper: Design and Characterization of SGK3-PROTAC1, an Isoform Specific SGK3 Kinase PROTAC Degrader

  • ToC graphics
  • Figure 1. Design and cellular activity of first generation SGK3 PROTACs.
  • Figure 2. Design and cellular evaluation of second and third generation SGK PROTACs.
  • Figure 3. Characterization of cellular activities of SGK3-PROTAC1 and cisSGK3-PROTAC1.
  • Figure 4. TMT proteomic analysis of HEK293 cells treated with SGK3-PROTAC1.
  • Figure 5. SGK3-PROTAC1-mediated degradation of SGK3 inhibits Akt-independent activation of mTORC1 in cancer cell lines treated with Akt or PI3K inhibitors.
  • Figure 6. SGK3-PROTAC1-mediated degradation of SGK3 further inhibiting the growth of cancer cell lines treated with PI3K-Akt pathway inhibitors.

Read the open access article here

Congratulations to Hannah in Dario Alessi's group for the great job on this study. Well done Andrea for the compound design and synthetic contributions to the project!


Title: Design and Characterization of SGK3-PROTAC1, an Isoform Specific SGK3 Kinase PROTAC Degrader

Authors: Hannah Tovell, Andrea Testa, Houjiang Zhou, Natalia Shpiro, Claire Crafter, Alessio Ciulli*, and Dario R. Alessi*


SGK3 is a PX domain containing protein kinase activated at endosomes downstream of class 1 and 3 PI3K family members by growth factors and oncogenic mutations. SGK3 plays a key role in mediating resistance of breast cancer cells to class 1 PI3K or Akt inhibitors, by substituting for the loss of Akt activity and restoring proliferative pathways such as mTORC1 signaling. It is therefore critical to develop tools to potently target SGK3 and obstruct its role in inhibitor resistance. Here, we describe the development of SGK3-PROTAC1, a PROTAC conjugate of the 308-R SGK inhibitor with the VH032 VHL binding ligand, targeting SGK3 for degradation.  SGK3-PROTAC1 (0.3 μM) induced 50% degradation of endogenous SGK3 within 2 h, with maximal 80% degradation observed within 8 h, accompanied by a loss of phosphorylation of NDRG1, an SGK3 substrate. SGK3-PROTAC1 did not degrade closely related SGK1 and SGK2 isoforms that are nevertheless engaged and inhibited by 308-R. Proteomic analysis revealed that SGK3 was the only cellular protein whose cellular levels were significantly reduced following treatment with SGK3-PROTAC1. Low doses of SGK3-PROTAC1 (0.1–0.3 μM) restored sensitivity of SGK3 dependent ZR-75-1 and CAMA-1 breast cancer cells to Akt (AZD5363) and PI3K (GDC0941) inhibitors, whereas the cis epimer analogue incapable of binding to the VHL E3 ligase had no impact. SGK3-PROTAC1 suppressed proliferation of ZR-75-1 and CAMA-1 cancer cell lines treated with a PI3K inhibitor (GDC0941) more effectively than could be achieved by a conventional SGK isoform inhibitor (14H). This work underscores the benefit of the PROTAC approach in targeting protein kinase signaling pathways with greater efficacy and selectivity than can be achieved with conventional inhibitors. SGK3-PROTAC1 will be an important reagent to explore the roles of the SGK3 pathway.