Faculty Bibliography

Although the principles that balance stem cell self-renewal and differentiation in normal tissue homeostasis are beginning to emerge, it is still unclear whether cancer cells with tumour initiating potential are similarly governed, or whether they have acquired distinct mechanisms to sustain self-renewal and long-term tumour growth. Here we show that the transcription factor Sox2, which is not expressed in normal skin epithelium and is dispensable for epidermal homeostasis, marks tumour initiating cells (TICs) in cutaneous squamous cell carcinomas (SCCs). We demonstrate that Sox2 is required for SCC growth in mouse and human, where it enhances Nrp1/Vegf signalling to promote the expansion of TICs along the tumour-stroma interface. Our findings suggest that distinct transcriptional programmes govern self-renewal and long-term growth of TICs and normal skin epithelial stem and progenitor cells. These programmes present promising diagnostic markers and targets for cancer-specific therapies.

The precise mechanisms governing invasion at the leading edge of squamous cell carcinoma (SCC) and its subsequent metastasis are not fully understood. We aimed to define the cancer-related molecular changes that distinguish noninvasive tumor from invasive SCC. To this end, we combined laser capture microdissection with complementary DNA (cDNA) microarray analysis. We defined invasion-associated genes as those differentially regulated only in invasive SCC nests, but not in actinic keratosis or in situ SCC, compared with normal epidermis. There were 383 upregulated and 354 downregulated genes in the "invasion set." SCC invasion was characterized by aberrant expression of various proteolytic molecules. We noted increased expression of MMP7 and IL-24 in invasive SCC. IL-24 induced the expression of matrix metallopeptidase 7 (MMP7) in SCC cells in culture. In addition, blocking of MMP7 by a specific antibody significantly delayed the migration of SCC cells in culture. These results suggest a possible contribution of IL-24 to SCC invasion via enhancing focal expression of MMP7, although IL-24 has been suggested to have antitumor growth effects in other cancer types. Identification of regional molecular changes that regulate cancer invasion may facilitate the development of new targeted treatments for aggressive cancer.

The pathogenesis of BCC is associated with sonic hedgehog (SHH) signaling. Vismodegib, a smoothened inhibitor that targets this pathway, is now in clinical use for advanced BCC patients, but its efficacy is limited. Therefore, new therapeutic options for this cancer are required. We studied gene expression profiling of BCC tumour tissues coupled with laser capture microdissection to identify tumour specific receptor tyrosine kinase expression that can be targeted by small molecule inhibitors. We found a >250 fold increase (FDR<10-4) of the oncogene, anaplastic lymphoma kinase (ALK) as well as its ligands, pleiotrophin and midkine in BCC compared to microdissected normal epidermis. qRT-PCR confirmed increased expression of ALK (p<0.05). Stronger expression of phosphorylated ALK in BCC tumour nests than normal skin was observed by immunohistochemistry. Crizotinib, an FDA-approved ALK inhibitor, reduced keratinocyte proliferation in culture, whereas a c-Met inhibitor did not. Crizotinib significantly reduced the expression of GLI1 and CCND2 (members of SHH-pathway) mRNA by approximately 60% and 20%, respectively (p<0.01). Our data suggest that ALK may increase GLI1 expression in parallel with the conventional SHH-pathway and promote keratinocyte proliferation. Hence, an ALK inhibitor alone or in combination with targeting SHH-pathway molecules may be a potential treatment for BCC patients.

Organ transplant recipients suffer from an increased incidence and recurrence rate of nonmelanoma skin cancers. These cancers are often more aggressive than those in the general population, resulting in significant morbidity and mortality. Often times, routine treatment modalities are not adequate and the use of different management strategies is necessary. Treatment modalities, including surgical excision, Mohs micrographic surgery, physically destructive modalities, topical therapy, and photodynamic therapy may be used. Combinations of these therapies may be used in rotation for treatment of extensive field disease. Chemoprophylaxis with oral retinoids and alteration of the immune suppression regimen may be indicated for specific cases. In addition, newly emerging therapies for squamous cell carcinomas including cetuximab and capecitabine may offer heightened control in organ transplant patients with significant cutaneous disease.

The development of vismodegib and its recent approval by the United States Food and Drug Administration for use in patients with locally advanced or metastatic basal cell carcinoma (BCC) carries with it a renewed sense of optimism. Once BCC has progressed to an advanced, or so-called inoperable stage, there has been a paucity of effective therapies, making the new small molecule inhibitors targeting the hedgehog pathway particularly hopeful prospects. In order to better understand the utility of these new treatments, it is important to assess the existing economic, physical, and psychological burden of advanced BCC. This review aims to recognize the impact of inoperable and metastatic BCC, as well as to better characterize the various types of advanced BCC. The use of vismodegib as a prophylactic treatment in patients with basal cell nevus syndrome is also addressed, including possible adverse events, tumor resistance, and new onset malignancies.