The Ras Inhibitor Farnesylthiosalicylic Acid as a Potential Therapy for Neurofibromatosis Type 1

Abstract

Purpose: Farnesylthiosalicylic acid (FTS) is a Ras inhibitor that dislodges all active Ras isoforms from the membrane.We assessed the ability of FTS to reverse the transformed phenotype of neurofibromatosis type 1 (NF1)^associated tumor cell lines of malignant peripheral nerve sheath tumor (MPNST). Experimental Design: nf1 mutations were genotyped, allelic losses were analyzed, and neurofibromin expression levels were determined in MPNST cell lines ST88-14, S265P21, and 90-8. The effects of FTS on GTP-bound Ras (Ras-GTP) and its prominent downstream targets, as well as on cell morphology, anchorage-dependent and anchorage-independent growth, and tumor growth in mice, were assessed. Results: The MPNSTcell lines were biallelic, NF1inactive, and neurofibromin deficient. We show that FTS treatment shortened the relatively long duration of Ras activation and signaling to extracellular signal-regulated kinase, Akt, and RalA in all NF1-deficient MPNST cell lines (NF1 cells) to that observed in a non-NF1, normally expressing neurofibromin MPNSTcell line. These effects of FTS led to lower steady-state levels of Ras-GTP and its activated targets. Both anchoragedependent and anchorage-independent growth of NF1cells were dose dependently inhibited by FTS, and the inhibition correlated positively with Ras-GTP levels. NF1cells were found to possess strong actin stress fibers, and this phenotype was also corrected by FTS. NF1tumor growth in a nude mouse model was inhibited by oral FTS. Conclusions: FTS treatment of NF1cells normalized Ras-GTP levels, resulting in reversal of the transformed phenotype and inhibition of tumor growth. FTS may therefore be considered as a potential drug for the treatment of NF1.

The tumor suppressor neurofibromin confers sensitivity to apoptosis by Ras-dependent and Ras-independent pathways

“…Notably, the range of FTS concentrations used in these experiments and in all subsequent experiments in which cells were grown in low serum was 2.5-30 mM; FTS is more effective in low serum than in high serum because it binds to serum proteins; thus in low serum the concentration of free FTS is higher than in high serum. [26][27][28] Last, FTS induced a reduction in steady-state Ras-GTP levels in the serum-starved Nf1 SV40 MEFs with no appreciable effect on total Ras levels (Figure 3c and d). The extent of inhibition correlated well with the Nf1 gene dosage and with the levels of Ras-GTP shown in Figure 1a and b: the lower the gene dosage, the higher the levels of Ras-GTP and the sensitivity to FTS.…”

“…Recently, we showed that FTS effectively reduces steady-state levels of Ras-GTP and inhibits growth of ST88-14 cells. 27 We therefore treated serum-starved ST88-14 and STS26T cells with FTS or with its vehicle for 24 h, and then determined the numbers of live and dead cells. In the absence of FTS, the serum-starved ST88-14 and STS26T cells showed similar viability (Figure 7f) possibly because the survival of these two schwannoma cell lines under these conditions is dependent on numerous factors in addition to the presence of neurofibromin.…”

Phenotypic Reversion of Invasive Neurofibromin-Deficient Schwannoma by FTS: Ras Inhibition Reduces BMP4/Erk/Smad Signaling

“…The role of Ras in NF1-based malignancy suggests that Ras inhibitors, such as S-trans,trans-farnesylthiosalicylic acid (FTS; salirasib) that interferes with Ras-membrane anchorage (19), are an efficient therapeutic approach. Importantly, FTS interferes with the transformed phenotype of NF1-associated MPNST cell lines in vitro and in vivo (20).…”

Experimental therapeutic approaches to peripheral nerve tumors

“…One such alternative approach designed to directly achieve Ras inhibition has been accomplished through use of farnesylthiosalicylic acid, an agent that inhibits all Ras isoforms by competing with Ras-GTP for saturable binding sites in the cell membrane. 7 The same authors demonstrated reversal of the 83 The neurofibromin GRD reduces the ability of the NIH 3T3 NF1-deficient fibroblast and hematopoietic cell lines to form colonies in an in vitro environment. 54 Further, depression of K-Ras and N-Ras activity, in association with inhibited proliferation of acute myeloid leukemia cells has been demonstrated through expression of the neurofibromin GRD in cells deficient for this protein.…”