The Identification of Potential Therapeutic Targets for Cutaneous Squamous Cell Carcinoma

Angela Mchugh,Kenneth Fernandes,Nerime Chinner,Adel F.M Ibrahim,Amit K Garg,Garry Boag,Lydia A Hepburn,Charlotte M Proby,Irene M Leigh,Mark K Saville

doi:10.1016/j.jid.2019.09.024

Abstract

We performed a small interfering RNA screen to identify targets for cutaneous squamous cell carcinoma (cSCC) therapy in the ubiquitin/ubiquitin-like system. We provide evidence for selective anti-cSCC activity of knockdown of the E3 ubiquitin ligase MARCH4, the ATPase p97/VCP, the deubiquitinating enzyme USP8, the cullin-RING ligase (CRL) 4 substrate receptor CDT2/DTL, and components of the anaphase-promoting complex/cyclosome (APC/C). Specifically attenuating CRL4CDT2 by CDT2 knockdown can be more potent in killing cSCC cells than targeting CRLs or CRL4s in general by RBX1 or DDB1 depletion. Suppression of the APC/C or forced APC/C activation by targeting its repressor EMI1 are both potential therapeutic approaches. We observed that cSCC cells can be selectively killed by small-molecule inhibitors of USP8 (DUBs-IN-3/compound 22c) and the NEDD8 E1 activating enzyme/CRLs (MLN4924/pevonedistat). A substantial proportion of cSCC cell lines are very highly MLN4924-sensitive. Pathways that respond to defects in proteostasis are involved in the anti-cSCC activity of p97 suppression. Targeting USP8 can reduce the expression of growth factor receptors that participate in cSCC development. EMI1 and CDT2 depletion can selectively cause DNA re-replication and DNA damage in cSCC cells.

Highlights

There is a need for improved treatment for cutaneous squamous cell carcinoma in high-risk recessive dystrophic epidermolysis bullosa (RDEB) and immunocompromised patients, including transplant recipients and in the general population (Harwood et al, 2016; Mellerio et al, 2016)
We screened using a small interfering RNA library complementary to more than 1,000 genes to identify additional components of the ubiquitin/ ubiquitin-like system that could be targeted for cutaneous squamous cell carcinoma (cSCC) therapy
AND DISCUSSION small interfering RNA (siRNA) screening for potential therapeutic targets A cell line derived from a primary RDEB cSCC (SCCRDEB4) was transfected with pools of four siRNAs targeting 1,186 ubiquitin/ubiquitin-like pathway-linked genes (MacKay et al, 2014)

Summary

INTRODUCTION

There is a need for improved treatment for cutaneous squamous cell carcinoma (cSCC) in high-risk recessive dystrophic epidermolysis bullosa (RDEB) and immunocompromised patients, including transplant recipients and in the general population (Harwood et al, 2016; Mellerio et al, 2016). This includes better systemically and locally delivered therapy. We screened using a small interfering RNA (siRNA) library complementary to more than 1,000 genes to identify additional components of the ubiquitin/ ubiquitin-like system that could be targeted for cSCC therapy. Received 5 October 2018; revised 27 August 2019; accepted 23 September 2019; accepted manuscript published online 6 November 2019; corrected proof published online 16 December 2019

RESULTS

A McHugh et al Targeting the Ubiquitin System in cSCC

MATERIALS AND METHODS