Activation of the TGF Beta Signaling Pathway in Nonresponders to Induction Chemotherapy in Sinonasal Undifferentiated Carcinoma

Background Sinonasal undifferentiated carcinoma (SNUC) is a rare, highly aggressive cancer that arises in the nasal cavity and paranasal sinuses. Despite aggressive multimodal therapy, the prognosis remains poor. Because of its locally advanced nature, cisplatin-based induction chemotherapy has been used in our institution to downstage locoregionally advanced tumors before definitive surgery or radiation therapy. Unfortunately, nearly 50% of SNUC patients do not respond to induction chemotherapy, and this event is associated with poor survival rate. Therefore, developing strategies to overcome resistance to induction chemotherapy is crucial. Our previous gene expression analysis in specimens harvested from responders and nonresponders to induction chemotherapy showed that the TGFβ signaling pathway might be activated in the nonresponders. In this study, we examined the mechanism of TGFβ activation in nonresponders by using a SNUC cell line derived from one of those nonresponders. We also investigated whether inhibition of the TGFβ signaling pathway would be able to concur chemoresistance in the SNUC cell line.

Methods The MDA8788–6 cell lines established from a nonresponder to induction chemotherapy was used in this study. Activation of the TGFβ signaling pathway was accessed by phosphorylation of SMAD2. Two commercially available TGFβ receptor I (TGFßRI/ALK5) inhibitors LY2157299 and EW-7197 were used to inhibit the pathway. The cell line was also treated by serum-free conditioned medium collected from the same cell line to explore the mechanisms of the TGFβ signaling activation. Cell growth and cell survival were evaluated by Hoechst 33342 staining and clonogenic assay, previously.

Results First, basal level of TGFβ signaling was assessed by phosphorylation of SMAD2 under the condition of serum starvation. Interestingly, phosphorylation of SMAD2 was enhanced by serum starvation and the TGFβ1 ligand did not increase the signal further. This phosphorylation of SMAD2 by serum starvation was inhibited by the TGFßRI (ALK5) inhibitors LY2157299 and EW-7197 indicating the phosphorylation of SMAD2 went through TGFßRI. The SNUC cell line treated with conditioned media collected from the same cell line also induced the TGFβ signaling pathway, indicating this activation may occur in an autocrine manner. Treatment of the cells with the TGFßRI inhibitor successfully showed inhibition of growth and survival combined with cisplatin.

Conclusion Our study suggested activation of the TGFβ signaling pathway in the nonresponders may occur through an autocrine loop. Inhibition of this pathway in the SNUC cell line successfully showed inhibition of growth and survival under cisplatin. Our study may offer hope to SNUC patients struggling with chemoresistance.