Desmoid tumors (DTs) are rare mesenchymal lesions with a high rate of local recurrence. Their common feature is a deregulated WNT pathway, mainly caused by gain-of-function mutations in exon 3 of the CTNNB1 gene (encoding for β-catenin), resulting in nuclear accumulation of β-catenin. Sorafenib has emerged as a promising therapeutic strategy based on compassionate use, which has led to an ongoing nationally-denominated phase III clinical trial. Concurrently, we conducted a comprehensive analysis of sorafenib efficacy in a large panel of desmoid cell strains to probe for response mechanisms. While much is already known about the molecular mechanism of sorafenib action in other cancers, little is currently known about sorafenib in desmoid tumors. Our preliminary results have shown distinctive groups of higher- and lower-responder cells. Clustering the lower responder group, we observed CTNNB1 mutation was a determinant of outcome. Our results showed that even lower doses of sorafenib were able to inhibit cell viability, migration and invasion of wildtype and T41A-mutated DTs. Apoptosis induction was observed in those cells after treatment with sorafenib. On the other hand, lower doses of sorafenib were not able to inhibit cell viability, migration, and invasion or to induce apoptosis in the S45F-mutated DTs. In the first aim of this grant, we propose to investigate the differences between desmoids harboring different CTNNB1 mutations and their response to sorafenib. Multiple mechanisms contribute to drug resistance, including alterations in the tumor microenvironment (TME). The tumor microenvironment describes stromal and other cells that surround tumor cells. Several studies have shown that TME cells can affect tumor growth, invasion, local recurrence and drug resistance; however, to the best of our knowledge, the role of the microenvironment in desmoid tumor cells resistance to drugs has not been investigated to date. Moreover, in studies conducted within the premise of our previously funded DTRF seed grant, we showed that there was no significant induction of apoptosis in the S45F mutated desmoid cell strains when compared to the T41A mutated cells. Therefore, it is important to investigate if S45F desmoid-associated TME cells differ from TME sorted from T41A-mutated desmoid cells. In the second aim of this grant, we propose to investigate the role of the TME in the resistance of S45F-mutated desmoid tumors to therapy. Our preliminary results have shown that TME sorted from S45F-mutated DTs are more tolerant to doxorubicin when compared to T41A desmoid-associated TME. Interestingly, as opposed to results with mixed populations shown previously by our group, pure desmoid populations sorted from S45F-mutated cells did not show tolerance to doxorubicin, suggesting that TME may play a role in the resistance to drugs observed in some desmoid cells. Finally, we have shown that the pure population of T41A-mutated desmoids cultured with media collected from TME sorted from S45F-mutated desmoid tumors are more tolerant to doxorubicin treatment, as oppose to the sensitivity seen in the mixed population, suggesting that the TME releases factors that may play a critical role in the therapeutic resistance of desmoid tumors harboring the S45F mutation. These preliminary results are intriguing; however, these findings are in need of further investigation to identify the molecular mechanisms underlying the role of the TME in desmoid resistance to drugs. With such enhanced understanding, these findings may potentially have an impact on patients in the clinic.
LAY VERSION OF ABSTRACT- “The role of the tumor microenvironment in S45F desmoid tumor chemotherapeutic resistance.”