A characterization of the NTCU mouse model of lung squamous cell carcinoma: The role of vitamin D
Mazzilli, Sarah A.
MetadataShow full item record
Lung cancer has the highest rate of mortality amongst the major cancer subtypes, in part due to the limited number of effective screening methods or treatment modalities, which leads to late stage diagnoses and progression to more advanced and often aggressive disease. Progression has been made in identifying populations at risk for lung cancer using clinical and demographic information. Therefore, identifying chemoprevention strategies for lung cancer is a potential way to reduce the high mortality rate. Chemoprevention studies in lung cancer have not been successful in the past, possibly as a result of poor study design or lack of relevant pre-clinical testing. The N-nitroso-tris-chloroethylurea (NTCU) mouse model of lung SCC develops similar histopathology premalignant lesions as seen in human disease, providing a relevant model to examine chemoprevention agents. We demonstrate that the optimal dose of NTCU for chemoprevention studies is 25 ml of 40 mM NTCU once per week. At this dose, topical treatments of NTCU induce the development of atypic lesions as soon as 2 weeks after the first treatment and develop predominantly low-grade dysplasia lesions (squamous metaplasia and mild dysplasia) by 15 weeks and high-grade dysplasia lesions (moderate and severe dysplasia) by 25 weeks. Additionally we show that NTCU stimulates a state of chronic inflammation that supports the development of disease. Vitamin D, an essential mediator of calcium homeostasis, acts through the vitamin D receptor to promote cellular differentiation and inhibit proliferation, inflammation, apoptosis, and angiogenesis. Epidemiologic studies indicate that there is an inverse relationship between UVB exposure, vitamin D intake, and serum levels of 25D3 and the increased risk and poor prognosis of a number of cancers, including lung cancer. Pre-clinical studies in mice show that dietary vitamin D and calcium deficiency promote carcinogenesis in mouse models of breast, colon and prostate cancer. All these data suggest that vitamin D may have a role as a chemopreventive agent. We have conducted studies investigating the effects of vitamin D on cancer progression using dietary vitamin D3 (0 or 2000 IU/kg) and injections of the active metabolite of vitamin D, calcitriol (1,25D3) in the NTCU model. In this study, 12 week-old female mice were randomized to 6 treatment groups at two time points (15 and 25 weeks of NTCU treatment). Disease burden, as measured by scoring serial H&E sections of the lung per mouse, was more aggressive in the vitamin D deficient groups (25D3 < 4ng/ml) as demonstrated by an increase in high-grade dysplasia at both 15 and 25 weeks of NTCU treatment compared to mice with sufficient (25D3 ∼21 ng/ml) levels of vitamin D. This study supports the concept that vitamin D deficiency promotes the development of more aggressive disease. This study also demonstrated that calcitriol administration reduces the progression of lung squamous cell carcinoma (SCC) in particular in early stages of disease and in mice that were vitamin D deficient. Furthermore, subsequent studies suggest that vitamin D sufficiency reduces proliferation, suppresses inflammation, and promotes DNA repair. In conclusion these studies in the NTCU model of lung SCC suggest that vitamin D sufficiency reduces the number and severity of premalignant lesions through the modulation of multiple mechanisms, whereas vitamin D deficiency promotes the development of disease.