Background: Imatinib functions as a specific inhibitor of a number of tyrosine kinase enzymes, such as KIT and PDGFR, by occupying the TK active site, and thus improves the prognosis of gastrointestinal stromal tumor (GIST) patients. However, resistance to the drug appears with prolonged usage. Mechanisms of acquired resistance are still under elucidation. Methods: To evaluate mechanisms of acquired resistance for imatinib, we established a imatinib-resistant GIST cell line, so-called T1R, by culturing the GIST cell line, GIST-T1, with increasing concentrations of imatinib. Next, we analyzed receptor tyrosine kinases (RTKs) and intracellular signals strongly expressed in T1R by western blotting and phosphorylated arrays. Finally, we examined the antitumor effect of an agent which was confirmed to inhibit upregulated RTKs in T1R. Results: Interestingly, imatinib-resistant T1R showed cross resistance to sunitinib, which offers patients with imatinib-resistant GIST a new treatment option to stop further disease progression. By western blotting, T1R showed a suppression of phosphorylation in KIT in contrast to a promotion of phosphorylation in PDGFRA, which never observed before imatinib treatment. A phosphorylation multiplex array also revealed that T1R had additional promotion of phosphorylation in FGFR, Met, Eph, Axl, and Tie2. Therefore we considered activation of PDGFRA owing to one of the candidate machinery of acquired resistance for imatinib as well as sunitinib. HSP90 inhibitors is known to effective against both imatinib-sensitive and resistant GIST models. Therefore, we examined whether HSP90 inhibitors interact with PDGFRA TK kinase activity in T1R. HSP90 inhibitors inhibited the phosphorylation and protein expression of PDGFRA and other RTKs, resulted to inhibit cell proliferation and induce apoptosis in T1R. Conclusions: Activation of multiple RTKs is an essential for acquired resistance for imatinib in GIST. Inhibition of PDGFRA and other RTKs by HSP90 inhibitors has a potential to the next treatment option for GIST which acquired drug resistance for conventional small-molecule, multi-targeted RTK inhibitors. Legal entity responsible for the study: Department of Medical Oncology, Kawasaki Medical School Hospital. Funding: Has not received any funding. Disclosure: All authors have declared no conflicts of interest.

OBJECTIVES To evaluate the diagnostic value of MRI for odontogenic tumours. MATERIALS AND METHODS 51 patients with odontogenic tumours were subjected to pre-operative MRI examinations. For tumours with liquid components, i.e. ameloblastomas and keratocystic odontogenic tumours (KCOTs), the signal intensity (SI) uniformity of their cystic components (UΣ) was calculated and then their UΣ values were compared. For tumours with solid components that had been examined using dynamic contrast-enhanced MRI (DCE-MRI), their CImax (maximum contrast index), Tmax (the time when CImax occurred), CIpeak (CImax × 0.90), Tpeak (the time when CIpeak occurred) and CI300 (i.e. the CI observed at 300 s after contrast medium injection) values were determined from CI curves. We then classified the odontogenic tumours according to their DCE-MRI parameters. RESULTS Significant differences between the UΣ values of the ameloblastomas and KCOT were observed on T1 weighted images, T2 weighted images and short TI inversion recovery images. Depending on their DCE-MRI parameters, we classified the odontogenic tumours into the following five types: Type A, CIpeak > 2.0 and Tpeak < 200 s; Type B, CIpeak < 2.0 and Tpeak < 200 s; Type C, CI300 > 2.0 and Tmax < 600 s; Type D, CI300 > 2.0 and Tmax > 600 s; Type E, CI300 < 2.0 and Tmax > 600 s. CONCLUSION Cystic component SI uniformity was found to be useful for differentiating between ameloblastomas and KCOT. However, the DCE-MRI parameters of odontogenic tumours, except for odontogenic fibromas and odontogenic myxomas, contributed little to their differential diagnosis.

Ameloblastoma is the most frequent odontogenic tumor and is considered a benign, but locally invasive, neoplasm with variable clinico-pathological expression. Syndecan-1 is a cell surface proteoglycan that binds cells to the extracellular matrix and its expression is down-regulated in many cellular transformation models. The aims of this study were to examine the pattern of syndecan-1 expression, to evaluate the proliferating activity in a large series of solid/multicystic (SA) and unicystic ameloblastomas (UA), and to study its possible correlation to their biological behavior. Immunohistochemical studies were performed for syndecan-1 (clone MI15) and Ki-67 (clone MIB-1) in 120 ameloblastomas (75 SA and 45 UA). The salient finding was that expression of syndecan-1 was related to the histological subtype of tumors, as there was a lower expression in SA (40.2%) as compared to UA (49.7%) (p < 0.05). These findings did not correlate with Ki-67 expression, as this was similar in both types of ameloblastomas. Our results suggest that the reduced expression of syndecan-1 supports the view that SA has a more aggressive biological behavior than the UA. The lack of correlation between reduction of the syndecan-1 and Ki-67 index may be due to the different histomorphologies of both types of ameloblastoma, and more studies are necessary to better understand the role of this protein in the biological behavior of these tumors.

OBJECTIVES AND DESIGN: The expressions of human beta defensin-1 (HBD-1), -2 (HBD-2) and -3 (HBD-3) in non-inflamed pseudocysts such as mucoceles were investigated immunohistochemically in this study.MATERIALS AND METHODS: Mucocele specimens were obtained from 21 patients. The expression of HBDs was studied immunohistochemically by using antibodies directed against HBD-1, -2, and -3. Statistical analyses were carried out on serial sections stained with antibodies.RESULTS: Cells expressing HBDs were found in mucoceles. The expression of HBD-2 was observed in floating cells in all the specimens, whereas HBD-1 and HBD-3-expressing cells were detected in 93% and 73% of the mucoceles, respectively. The HBD-2 signal was the most intense and the HBD-3 signal intensity was weaker than that of HBD-1. HBDs were expressed in neutrophils and in other floating cells. Interestingly, the signal intensity and the population of positive cells located close to the centers of cysts were higher than those located in the peripheral areas of cysts.CONCLUSION: The expression of HBDs was found even in non-inflamed pseudocysts such as mucoceles. These results suggest that an unknown mechanism not involved in biophylaxis for the expression of HBDs may exist.

Type IV collagen, the major component of basement membrane (BM), demonstrates a stageand position-specific distribution of its isoforms during tooth development. To determine its localization in BM of odontogenic neoplasms, immunohistochemistry using six anti-α(IV) chain-specific monoclonal antibodies was performed. Expression of α1(IV)/ α2(IV) and α5(IV)/ α6(IV) chains was stronger in the desmoplastic than in ordinary ameloblastomas. The adenomatoid odontogenic tumor distinctly expressed these chains in BM of cribriform areas and hyaline materials (which was also α4(IV)-positive. These five chains also stained BM and tumor cells of ameloblastic fibroma. Present results suggest that collagen IV composition and distribution in the basement membranes of odontogenic neoplasms plays a key role in tumor growth and progression.