c-Myc regulation by TGF-beta signaling as a therapeutic target in Osteosarcoma

PROJECT SUMMARY Osteosarcoma (OS) is an aggressive malignant primary bone cancer with a high propensity for lung metastasis. Since the development of aggressive chemotherapy and surgery, the 5-year event-free survival rate for non- metastatic patients has attained 70%. In contrast, the outcome for pulmonary metastatic osteosarcoma (pOS)

remains poor and the 5-year event-free survival has not improved significantly over the past 3 decades (20%). Therefore, treating pOS effectively remains a challenge. Transforming growth factor-β (TGF-β) is one of the most potent immune suppressive cytokines in tumor microenvironment (TME) and can promote metastasis in solid

tumors. TGF-β production is increased in the sera of OS patients. This increase in TGF-β production is correlated with high grade OS and associated with the presence of lung metastases. Therefore, target TGF-β is the new therapeutic approach for the treatment of OS. In this proposal, we will demonstrate the therapeutic effects of a

novel inhibitor of TGF-β signaling, TEW-7197, on OS growth in vitro and in vivo and associated immune responses in the OS TME. TEW-7197 (“Vactosertib”) is the first-in-class small molecule inhibitor of the TGF-β type I Receptor (TβRI) kinase and currently in Phase I clinical trial at UH Seidman Cancer Center for Multiple

Myeloma, another disease with high TGF-β (#NCT03143985). TEW-7197 is orally available (taken qD or BID) and well tolerated with minimal side effects. Our preliminary data show that blocking TGF-β signaling with TEW- 7197 inhibited OS proliferation in vitro and oral administration of TEW-7197 to OS-bearing mice significantly

reduced established pOS in vivo. Our preliminary observation has resulted in an Orphan Drug Designation authorization by the FDA in August 2021 as well as Fast-track IND issuance in January 2023 for the use of TEW- 7197 in OS. More recently, a multi-center phase I/II clinical trial using Vactosertib as monotherapy for the

treatment of advanced osteosarcoma in patients age 14 and up been organized and planned for accrual in spring 2023 (#NCT05588648) at 21 sites across US, Europe and Asia. Recently, we have made the additional observation that TGF-β induced c-Myc expression in OS cells and those inductions were completely inhibited by

TEW-7197 in OS cells. c-Myc is a major proto-oncogene which is highly amplified in OS. c-Myc overexpression in human OS correlates with aggressive tumor cell invasion and metastasis and worsens overall patient clinical prognosis. Therefore, these new results suggest that c-Myc regulation by TGF-β may be an important therapeutic

target in OS. We hypothesize that TGF-β signaling inhibition may be an effective therapeutic strategy against metastatic pOS by modifying tumor-intrinsic signaling (c-Myc regulation) and extrinsic immune-related TME to achieve optimal immune-effector function and maximal clinical response in pOS. To confirm this hypothesis, we

will utilize various mouse and human OS cell lines and PDX models in vitro and in vivo. Two specific aims will be pursued to accomplish the overall objective. Specific aim 1 will Determine effects of TGF-β inhibition on c- Myc regulation in OS cells in vitro. Specific aim 2 will Determine whether daily oral administration of TEW-7197

suppresses pOS tumor progression in the syngeneic and humanized mouse models. A fully humanized mouse model will be employed to interrogate TEW-7197 effects on cellular immune responses with preclinical human OS TME in vivo. This research will establish a critical role of TGF-β signaling in pOS progression and provide

scientific rationale that targeting TGF-β signaling with orally available small molecule inhibitor should be developed as a viable therapeutic arsenal for pOS patients.