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. Even though it is controversial, several studies have shown that the mutation S45F strongly correlates with increased propensity for desmoid recurrence as compared to T41A mutation. Therefore, it is important to investigate the differences between these two genetic alterations in order to identify potential targets for novel molecular therapies. In studies conducted within the premise of our previously funded DTRF seed grant we were able to establish a desmoid tissue and cell strain repository. Furthermore, we showed that the difference between the CTNNB1 T41A and S45F mutations is not due to differential protein expression levels, since β-catenin is equally expressed in both mutations. Our gene array analysis showed that pro-apoptotic genes are downregulated and anti-apoptotic genes are upregulated in the cells with the S45F mutation when compared to the T41A mutation. Moreover, we showed that there is no significant induction of apoptosis in the S45F mutated desmoid cell strains when compared to the T41A mutated cells. Interestingly, the impairment of apoptosis appears to be specific to the CTNNB1 S45F mutation and not to desmoid tumors per se. We also showed that RUNX3 seems to play a role in the cross-talk between the WNT and apoptosis pathway and that RUNX3 overexpression overcomes apoptotic resistance in S45F transfected cells. Interim results are promising, confirming our initial observation. However, these findings are in need of further investigation to better understand the molecular mechanisms driving the differences in the induction of apoptosis between the T41A and S45F mutated tumors. Once we understand these differences, these findings may potentially have an impact on patients in the clinic. Finally, we have also evaluated the effects of Sorafenib as potential alternative therapies for patients harboring the β-catenin S45F mutation. Our results showed that the mechanism of action of sorafenib might not rely on targeting of tyrosine kinases VEGFR2 and PDGFR-β in DTs. Interestingly, we showed that sorafenib inhibited the activation of ERK, but was not able to inhibit activation of MEK. We also showed that sorafenib exhibits significant anti-DT cell activity and elicits apoptosis in a subset of these cell strains based on mutation status. Lastly, our results suggest that autophagy plays a role in the sorafenib response in the S45F mutated DT cells, which seems to be highly dependent on autophagy for survival. These exciting results are in need of further investigation to find the specific kinase that plays a role in the response to sorafenib and to evaluate the impact of sorafenib in the autophagy pathway. This knowledge may lead us to the discovery of new deregulated pathways, which could help the development of new target therapies that will hopefully have an impact on patients in the clinic. In this third year of funding, we propose to:
- expand our desmoid tumor tissue repository as well as to continue trying to establish a desmoid tumor murine model
- unravel the molecular mechanism underlying the differences in the induction of apoptosis between the CTNNB1 T41A and S45F mutation
- further investigate the molecular mechanism of action of sorafenib, and additional possible therapeutic combinations;
- evaluate autophagy as a survival mechanism in S45F mutated desmoids as well as the impact of sorafenib in this pathway.