Sarcoma is a heterogeneous disease with at least 50 different subtypes. This genetic diversity makes the development of new targeted therapies particularly challenging. However, one consistent theme now emerging is that activation of the IGF-1R/PI3K/Akt and mTOR pathways are critical for sarcoma tumor oncogenesis, proliferation, and survival across histologic subtypes. Despite the compelling rationale to target mTOR in sarcomas, results from clinical studies examining the efficacy of rapamycin analogues ("rapalogues") have been disappointing. Several studies to date have suggested that persistent or increased Akt activation in the context of mTOR inhibitors may represent a mechanism of resistance to this class of therapies. Our own data in a panel of sarcoma cell lines confirms that rapamycin induces increased Akt phosphorylation. We hypothesize that persistent or increased Akt activation is a critical mechanism of clinical sarcoma resistance to mTOR inhibition with rapamycin analogues and that future therapeutic strategies must be focused upon combined mTOR and Akt inhibition. Towards this end, we have identified two classes of sarcoma cell lines: 1) "IGF-1R dependent" cells for which combined IGF-1R and mTOR targeting results in decreased p-Akt levels and hence enhanced anti-proliferative effects;and 2) "IGF-1R independent" cells for which IGF-1R inhibition fails to decrease p-Akt levels or enhance anti-tumor effects. These classifications not only will provide the framework by which to clinically evaluate mTOR targeting agents in clinical trials, but also highlight differences in sarcoma biology that suggest novel strategies for overcoming Akt mediated resistance. Additionally, we have identified a high rate of PIK3CA mutations in myxoid-round cell liposarcomas and observed that different classes of PIK3CA mutations correspond to dramatically different levels of Akt activation in patient tumor samples. In order to advance our understanding of how to manipulate these pathways for sarcoma therapy, the specific aims of this project are to 1) conduct clinical trials in sarcoma with combinations of TORC1 and IGF-1R inhibitors, as well as a first-in-class TORC1/2 inhibitor;2) evaluate strategies for reducing activated Akt in the context of TORC1 inhibition in IGF-1R -dependent and -independent sarcoma cells;and 3) study the impact of PIK3CA mutations upon myxoid-round cell liposarcoma biology and the susceptibility of these tumors to mTOR targeting.
Given the lack of effective chemotherapy, patients with advanced and metastatic sarcoma are in great need of new therapies. Combining new generation drugs that specifically inhibit pathways that promote sarcoma tumor growth (mTOR and IGF- 1R/PI3K/Akt) should result in major advances in the treatment and cure of this disease.
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