Complement Factor D is a biomarker for progression of cutaneous squamous cell carcinoma

Cutaneous squamous cell carcinoma (cSCC) is the most prevalent metastatic skin cancer, and its incidence is increasing on a global scale. Previous studies have demonstrated the role of complement system in cSCC progression. Here, we have investigated the role of complement factor D (CFD), an activator of alternative pathway of complement, in development of cSCC. RT-qPCR analysis of cSCC cell lines (n=8) and normal human epidermal keratinocytes (NHEKs) (n=6), demonstrated significant up-regulation of CFD mRNA expression in cSCC cells compared to NHEKs. Western blot analysis of conditioned culture media showed, that production of CFD was higher in cSCC cell lines than in NHEKs. Significantly higher CFD mRNA levels were noted in cSCC tumors (n=6) compared to normal skin (n=6). Strong tumor cell-associated CFD staining was detected in the invasive edge of human cSCC xenografts established in SCID mice. Immunohistochemical analysis of human tissue microarrays revealed more intense tumor cell-specific labeling for CFD clustered in the tumor margin in primary and metastatic cSCCs (n=202), in metastases (n=9), and in recessive dystrophic epidermolysis bullosa-associated cSCCs (n=16), compared with cSCC in situ (n =57), actinic keratosis (n=64), and normal skin (n=80). The production of CFD by cSCC cells was upregulated by p38 MAPK pathway, and induced by interferon-γ, and interleukin-1β. Targeted inhibition of CFD activity by small molecule factor D inhibitor (Danicopan; ACH-4471), potently inhibited activation of ERK1/2 and significantly attenuated proliferation of cSCC cells. Altogether, these results provide evidence for the role of CFD in the development of cSCC and identify CFD as a novel putative biomarker and therapeutic target for cSCC progression.