Can Inhibiting Ubiquitin Target Undruggable Tumor Proteins?

The paper summarized Genentech’s “in-house efforts to develop inhibitors for deubiquitinating enzymes and detailed the mechanistic and structural characterization of inhibitors of the deubiquitinase USP7,” said senior author Ingrid E. Wertz, MD, PhD, a senior scientist at Genentech in South San Francisco, California.

“We found that our USP7 inhibitors attenuate ubiquitin binding to USP7, [and] that in turn disables USP7 from adopting an active conformation,” Dr Wertz told Cancer Therapy Advisor. “These compounds activate cell death in tumor cells in vitro and in vivo. In terms of next steps, we are interested in targeting deubiquitinases for maximal therapeutic benefit with wide safety margins.”

Researchers at the University of Oxford, the University of Chicago, and several biotechnology companies have separately reported findings with 2 selective small-molecule USP7 inhibitors, FT671 and FT827, also in Nature.² They found that these agents show high affinity and specificity for USP7, both in vitro and in human cells; FT671 destabilized MDM2, increasing p53 levels and upregulating transcription of p53’s target genes, inducing the p21 tumor suppressor protein and blocking tumor growth in mice.

Dr Zhang and colleagues are developing USP7 and USP10 inhibitors to restore unmutated p53 activity in tumor cells with TP53 mutations.⁹ They determined the structure of one, UbV.7.2, that exhibits high affinity to USP7 and inhibits its deubiquitination activity.

Researchers at Harvard Medical School and the Novartis Institutes for Biomedical Research reported in 2016 that cells must reach a threshold level of p53 protein to trigger and complete apoptosis and that cell-to-cell variations in p53 levels might contribute to chemotherapy resistance.¹¹

“We found that cell death was increased significantly by UbV.7.2 expression (by p53 stabilization) in a colon cancer cell line that was treated with the chemotherapy drug cisplatin, demonstrating the therapeutic potential of UbV.7.2,” Dr Zhang said.

The USP7 inhibitors reported thus far will not be the final page for ubiquitin pathway modulation in cancer control drug development research, Dr Zhang emphasized.

“A general platform for targeted inhibition of DUBs is urgently needed,” he said. “Our structure-based combinatorial protein engineering enabled rapid and efficient development of Ub [ubiquitin] variant (UbV) inhibitors for not only USP7 but also other human and viral DUBs.”^8,9,12

These reagents may help in the design and screening of additional candidate anticancer USP inhibitors.

References

1. Kategaya L, Di Lello P, Rouge L, et al. USP7 small-molecule inhibitors interfere with ubiquitin binding. Nature. 2017;550(7677):534-8. doi: 10.1038/nature24006
2. Turnbull AP, Ioannidis S, Krajewski WW, et al. Molecular basis of USP7 inhibition by selective small-molecule inhibitors. Nature. 2017;550:481-6. doi: 10.1038/nature24451
3. Salami J, Crews CM. Waste disposal—an attractive strategy for cancer therapy. Science. 2017;355:1163-7. doi: 10.1126/science.aam7340
4. He MJ, Zhou Z, Shah AA, et al. The emerging role of deubiquitinating enzymes in genomic integrity, diseases, and therapeutics. Cell Biosci. 2016;6:62. doi: 10.1186/S13578-016-0127-1
5. Goto Y, Koyasu S, Kobayashi M, Harada H. The emerging roles of the ubiquitination/deubiquitination system in tumor radioresistance regarding DNA damage responses, cell cycle regulation, hypoxic responses, and antioxidant properties: insight into the development of novel radiosensitizing strategies. Mutat Res. 2017;803-805:76-81. doi: 10.1016/j.mrfmmm.2017.07.007
6. Lei H, Shan H, Wu Y. Targeting deubiquitinating enzymes in cancer stem cells. Cancer Cell Int. 2017;17:101. doi: 10.1186/s12935-017-0472-0
7. Huang X, Dixit VM. Drugging the undruggables: exploring the ubiquitin system for drug development. Cell Res. 2016;26:484-98. doi: 10.1038/cr.2016.31
8. Ernst A, Avvakumov G, Tong J, et al. A strategy for modulation of enzymes in the ubiquitin system. Science. 2013;339(6119):590-5. doi: 10.1126/science.1230161
9. Zhang W, Sartori MA, Makhnevych T, et al. Generation and validation of intracellular ubiquitin variant inhibitors for USP7 and USP10. J Molec Biol. 2017;429:3546-60. doi: 10.1016/j.jmb.2017.05.025
10. Malapelle U, Morra F, Ilardi G, et al. USP7 inhibitors, downregulating CCDC6, sensitize lung neuroendocrine cancer cells to PARP-inhibitor drugs. Lung Cancer. 2017;107:41-9. doi: 10.1016/j.lungcan.2016.06.015
11. Paek AL, Liu JC, Loewer A, Forrester WC, Lahav G. Cell-to-cell variation in p53 dynamics leads to fractional killing. Cell. 2016;165:631-42.
12. Zhang W, Bailey-Elkin BA, Knaap RC, et al. Potent and selective inhibition of pathogenic viruses by engineered ubiquitin variants. PLoS Pathog. 2017;13(5):e1006372. doi: 10.1371/journal.ppat.1006372