Purpose: To characterize in vivo features of HPV-immortalized and carcinogen transformed oral keratinocytes.
Methods: The growth and squamous differentiation of IHGK (immortalized human gingival keratinocyte with HPV), IHGKN [4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone, (NNK)]-carcinogen transformed keratinocytes, and two head and neck squamous cell carcinoma (HNSCC) cell lines, HN30 and HN12, were tested by injecting these cells into SCID mice. The growth, histological features, and expression of PCNA, Involucrin, and high molecular weight keratin of the tumors formed were compared among these cell lines.
Results: All cell lines formed a palpable lesion at 2 weeks; however, only HN30 continued to grow. IHGK and IHGKN cells formed palpable nodules within 2 weeks with no further growth after 4 to 5 weeks, and no regression of the nodule was noted at 12 weeks. HN12 cells did not form tumor nodules unless these cells were co-injected with immortalized fibroblasts. Both IHGK and IHGKN cells formed a well-circumscribed epithelial lesion with islands of differentiated squamous cells bound by a myxoid matrix. Nests of basal-horny squamous cells centrally differentiated into anucleate squamous cells. IHGK and IHGKN nodules had more squamous differentiation than HN12 and HN30 and further differentiated over time. IHGK and IHGKN cells expressed differentiation (involucrin and high molecular weight keratin) and proliferation (PCNA) markers that suggest that IHGK and IHGKN behave as well-differentiated squamous lesions when compared with malignant HN12 and HN30 nodules. IHGK and IHGKN cells showed an initial growth phase followed by terminal differentiation, and then a phase characterized by regression and host inflammatory stage.
Conclusions: The growth, histology, and expression of differentiation and proliferation markers of IHGK and IHGKN lesions into SCID mice demonstrate that these cells are endowed with a limited malignant potential. Our in vivo model with these intermediate cell lines can provide a short-term analysis for studying the biology of HNSCC progression and the activity of chemoprevention agents.