CD200-expressing human basal cell carcinoma cells initiate tumor growth

Chantal S Colmont,Jonathan C Vogel,Carole L Yee,Mark C Udey,Nga V Hawk,Manabu Ohyama,William G Telford,Simon H Reed,Antisar Benketah,Girish K Patel

doi:10.1073/pnas.1211655110

Abstract

Smoothened antagonists directly target the genetic basis of human basal cell carcinoma (BCC), the most common of all cancers. These drugs inhibit BCC growth, but they are not curative. Although BCC cells are monomorphic, immunofluorescence microscopy reveals a complex hierarchical pattern of growth with inward differentiation along hair follicle lineages. Most BCC cells express the transcription factor KLF4 and are committed to terminal differentiation. A small CD200(+) CD45(-) BCC subpopulation that represents 1.63 ± 1.11% of all BCC cells resides in small clusters at the tumor periphery. By using reproducible in vivo xenograft growth assays, we determined that tumor initiating cell frequencies approximate one per 1.5 million unsorted BCC cells. The CD200(+) CD45(-) BCC subpopulation recreated BCC tumor growth in vivo with typical histological architecture and expression of sonic hedgehog-regulated genes. Reproducible in vivo BCC growth was achieved with as few as 10,000 CD200(+) CD45(-) cells, representing ~1,500-fold enrichment. CD200(-) CD45(-) BCC cells were unable to form tumors. These findings establish a platform to study the effects of Smoothened antagonists on BCC tumor initiating cell and also suggest that currently available anti-CD200 therapy be considered, either as monotherapy or an adjunct to Smoothened antagonists, in the treatment of inoperable BCC.

Highlights

Smoothened antagonists directly target the genetic basis of human basal cell carcinoma (BCC), the most common of all cancers
BCC arise from keratinocytes with mutations leading to constitutively active sonic hedgehog (SHH) growth factor signaling
Unlike the multiple genetic lesions required during stepwise carcinogenesis in many other cancers, fewer “hits” are required for the development of BCC, perhaps explaining the absence of precursor lesions and why BCC is the most common malignancy in subjects of white race

Summary

Introduction

Smoothened antagonists directly target the genetic basis of human basal cell carcinoma (BCC), the most common of all cancers. These drugs inhibit BCC growth, but they are not curative. An autosomal-dominant genetic disease resulting in BCC, basal cell nevus syndrome (i.e., Gorlin syndrome), is caused by germ-line mutations in the human homologue of patched 1 (PTCH1) receptor, a component of the sonic hedgehog (SHH) growth factor signaling pathway [2]. Sporadic BCC tumors harbor inactivating mutations in PTCH1 (80–90%) or activating mutations in SMO (10–20%) [9] Together, these finding indicate that BCCs arise from constitutive activation of the SHH growth factor signaling pathway in keratinocytes. By using in vitro and in vivo assays, we demonstrate that the CD200+ BCC population is enriched for in vitro colony forming ability and contains TICs that can recreate BCC growth in vivo

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Conclusion