BACKGROUND: 5-aminolevulinic acid-mediated PDT (ALA-PDT) has been used in a 
variety of skin diseases including cSCC (cutaneous squamous cell carcinoma). 
Halofuginone (HL) is a less-toxic febrifugine derivative and has inhibitory 
effects on a variety of cancer cells. For now, there are no published study 
focusing on the combination use of ALA-PDT with HL to improve clinical efficacy 
of cSCC.
OBJECTIVE: In this study, we will examine the effectiveness of combined 
treatment of ALA-PDT and HL in cSCC as well as its underlying mechanism.
METHODS: The human epidermoid carcinoma cell line SCL-1 was treated with ALA-PDT 
or/ and HL, and cell viability, cell migration, ROS production, apoptosis were 
evaluated by CCK-8, colony formation, scratch assay, DCFH-DA probe, flow 
cytometry, respectively. The protein expression of NRF2 signaling was examined 
by western blot.
RESULTS: HL strengthened ALA-PDT's inhibition of SCL-1 cell viability, 
migration, as well as NRF2 related β-catenin, p-Erk1/2, p-Akt and p-S6K1 
expression. Overexpression of NRF2 conferred resistance to co-treatment's 
effects on c-Myc, Cyclin D1, Bcl-2, as well as cell proliferation. HL also 
strengthened ALA-PDT's inhibition of tumor volume in cSCC mouse model and 
elevated ROS generation of ALA-PDT.
CONCLUSION: HL enhances the anti-tumor effect of ALA-PDT in vitro and in vivo. 
HL has the potential to enhance the anti-tumor effect of ALA-PDT in cSCC via 
inhibiting NRF2 signaling.