Abstract 19: Neurofibromatosis type 1 (NF1) status determines sensitivity of soft tissue sarcoma and melanoma cell lines to glutaminase inhibitors

• Published in: Cancer research (Chicago, Ill.) Ill.), 2016-07, Vol.76 (14_Supplement), p.19-19
• Main Authors: Sheikh, Tahir N., Patwardhan, Parag P., Schwartz, Gary K.
• Format: Article
• Language: English
• ISSN: 0008-5472; 1538-7445
• DOI: 10.1158/1538-7445.AM2016-19

Neurofibromatosis type 1 (NF1) is an autosomal dominant genetic syndrome caused by a mutation in or deletion of the NF1 gene. Mutations in the NF1 gene lead to the production of a nonfunctional version of neurofibromin that cannot regulate cell growth and division. As a result, tumors such as neurofibromas can form along nerves throughout the body. The NF1 phenotype is highly penetrant and occurs in 1 in 3,000 to 4,000 people worldwide. Individuals with an altered NF1 gene are at an increased risk of developing benign and/or malignant tumors. NF1 has been shown to negatively regulate Ras activity. Ras-driven cancer cells have also been known to alter glucose and glutamine metabolism. In the present study, we evaluated the role played by NF1 status in determining the sensitivity of sarcoma and melanoma cell lines to glutaminase inhibition and its effect on Ras activity. We tested a panel of soft tissue sarcoma and melanoma cell lines that were either wild-type, null or mutant for NF1. Results from our in vitro proliferation assay showed that compared to wild-type NF1 (STS26T, LS141) cell lines, NF1 mutant (MPNST) and NF1 null (ST88 and MeWo) cell lines showed greater sensitivity to inhibition of proliferation by glutaminase inhibitors CB-839 and BPTES. Western blot analysis showed induction of apoptosis and down regulation of mTORC1 targets such as phospho-S6K and phospho-S6 by glutaminase inhibitors only in NF1 null and NF1 mutant but not wild-type NF1 cell lines. Gene silencing experiments showed that siRNA mediated knockdown of NF1 sensitizes LS141and STS26T cell lines to glutaminase inhibition. Conversely, overexpression of wild-type NF1 GRD (GAP related domain) in MeWo cell line resulted in decreased sensitivity to glutaminase inhibition when tested in a cell proliferation assay, thus, confirming the role played by NF1. Previous reports have shown that mutation or deletion of NF1 results in activation of Ras. In order to test the effect of glutaminase inhibition on Ras activity, we carried out Ras-GTP pull down assay following the treatment with glutaminase inhibitors in NF1 null and wild-type NF1 cell lines. Our results showed that glutaminase inhibition leads to down regulation of activated RAS in NF1 null but not wild-type NF1 cells. SiRNA mediated knockdown of NF1 followed by glutaminase inhibition in wild-type NF1 cell line (LS141) resulted in decreased Ras activity, further confirming our hypothesis. Results from patient derived MPNST tumor xenog