Salirasib

Salirasib (S-trans,trans-farnesylthiosalycilic acid [FTS]) is a synthetic small molecule that acts as a potent Ras inhibitor.[1]

The Ras family of small GTPases transmits extracellular signals, which are initiated by cell-surface receptors and serve to regulate various cellular processes including cell growth, differentiation, motility and cell death. Signals transmitted by activated Ras induce activation of multiple effectors. Ras signaling is activated in a large number of human cancers. Mutations of codons 12, 13 and 61 in Ras result in constitutively active Ras, and activating mutations of the three major Ras isoforms (H, K and N) have been found in more than 33% of human cancers. [2]

Salirasib mimics the carboxy-terminal farnesylcysteine carboxymethyl ester common to all Ras proteins, which acts as part of a recognition unit for anchorage and dislodges the active Ras protein from the cell membrane. Salirasib is readily taken up by cells, and once inside the cell it specifically disrupts the association of active forms of all Ras proteins (H-ras, K-ras and N-ras) with the inner surface of the cell membrane and with other cellular membranes. [1]

The in vitro activity of salirasib has been demonstrated in pancreatic cell lines and xenograft models. In the Panc-1 cell line, salirasib decreased the amount of RAS in a dosedependent manner, with a maximum decrease in Ras of approximately 50 % seen at concentrations of 25 to 50 μM. In the mouse xenograft models, salirasib inhibites Panc-1 tumor growth and is shown to be synergistic with gemcitabine, both inhibiting tumor growth and prolonging survival. Salirasib is tested in a phase I study in patients with solid tumors twice daily for 21 days every 4 weeks. Doses are escalated from 100 to 200, 400, 600, and 800 mg. Dose-limiting toxicity is not reached, but all three patients treated with 800 mg experienced Grade 1–2 diarrhea, preventing further dose escalation. The recommended dose for phase II studies is 600 mg bid. [3]

References:
[1] Ernesto Bustinza-Linares, Razelle Kurzrock , Apostolia-Maria Tsimberidou.  Salirasib in the treatment of pancreatic cance. Future Oncol. (2010) 6(6), 885–891.
[2] Sari Schokoroy, Dolly Juster, Yoel Kloog, Ronit Pinkas-Kramarski.  Disrupting the Oncogenic Synergism between Nucleolin and Ras Results in Cell Growth Inhibition and Cell Death. PLOS ONESeptember 2013, Volume 8, Issue 9, e75269.
[3] Daniel Laheru , Preeti Shah, N.  V. Rajeshkumar et al. Integrated preclinical and clinical development of S-trans, trans-farnesylthiosalicylic acid (FTS, Salirasib) in pancreatic cancer. Invest New Drugs (2012) 30:2391–2399.

Enhancing FTS (Salirasib) efficiency via combinatorial treatment.[Pubmed:25735913]

Biol Cell. 2015 May;107(5):130-43.

The Ras oncogene transmits signals, which regulate various cellular processes including cell motility, differentiation, growth and death. Since Ras signalling is abnormally activated in more than 30% of human cancers, Ras and its downstream signalling pathways are considered good targets for therapeutic interference. Ras is post-translationally modified by the addition of a farnesyl group, which permits its attachment to the plasma membrane. Exploiting this knowledge, a synthetic Ras inhibitor, S-trans, trans-farnesylthiosalicylic acid (FTS; Salirasib), was developed. FTS resembles the farnesylcysteine group of Ras, and acts as an effective Ras antagonist. In the present review, the effect of FTS in combination with various other drugs, as tested in vitro and in vivo, and its therapeutic potential are discussed. As reviewed, FTS cooperates with diverse therapeutic agents, which significantly improves treatment outcome. Therefore, combinations of FTS with other agents have a potential to serve as anti-cancer or anti-inflammatory therapies.

Phase I study of S-trans, trans-farnesylthiosalicylic acid (salirasib), a novel oral RAS inhibitor in patients with refractory hematologic malignancies.[Pubmed:25795639]

Clin Lymphoma Myeloma Leuk. 2015 Jul;15(7):433-438.e2.

BACKGROUND: Rat sarcoma (RAS)/rapidly accelerated fibrosarcoma (RAF)/mitogen-activated protein kinase activation (mutational or nonmutational) is a key pathway for survival and proliferative advantage of leukemic cells. Salirasib (Concordia Pharmaceuticals) is an oral RAS inhibitor that causes dislocation of RAS by competing directly with farnesylated RAS in binding to its putative membrane-binding proteins. Salirasib does not inhibit farnesyl transferase enzyme. PATIENTS AND METHODS: We report on a phase I study of Salirasib in patients with relapsed/refractory hematologic malignancies. Salirasib was administered orally twice daily on days 1 to 21 of a 28-day cycle in a "3+3" dose escalation design. RESULTS: Seventeen patients with relapsed/refractory leukemia were treated for a median of 4 cycles (range, 1-29). Three patients each were enrolled at a dose level of 100, 200, 400, 600, and 800 mg twice daily and 2 patients at a dose level of 900 mg twice daily. No dose-limiting toxicities were encountered. Grade 1/2 diarrhea was the only frequent nonhematologic toxicity observed in 14 of 17 (82%) patients and was resolved with oral antidiarrheal agents. Eight (47%) patients (4 with myelodysplastic syndrome, 2 with acute myeloid leukemia, 1 with chronic myelomonocytic leukemia, and 1 with chronic myeloid leukemia) had hematological improvement; 1 in 3 lineages, 1 in 2 lineages, and 6 in 1 lineage. None of the patients achieved complete remission. The responses lasted for a median of 10 weeks (range, 5-115). The study was discontinued because of financial constraints. CONCLUSION: Salirasib was well tolerated and showed modest activity in relapsed/refractory hematological malignancies. The safety profile of Salirasib and its hematological malignancy relevant target makes it a potential drug to be used in combination therapy.

Salirasib sensitizes hepatocarcinoma cells to TRAIL-induced apoptosis through DR5 and survivin-dependent mechanisms.[Pubmed:23348585]

Cell Death Dis. 2013 Jan 24;4:e471.

Ras activation is a frequent event in human hepatocarcinoma that may contribute to resistance towards apoptosis. Salirasib is a ras and mTOR inhibitor that induces a pro-apoptotic phenotype in human hepatocarcinoma cell lines. In this work, we evaluate whether Salirasib sensitizes those cells to TRAIL-induced apoptosis. Cell viability, cell death and apoptosis were evaluated in vitro in HepG2, Hep3B and Huh7 cells treated with DMSO, Salirasib and YM155 (a survivin inhibitor), alone or in combination with recombinant TRAIL. Our results show that pretreatment with Salirasib sensitized human hepatocarcinoma cell lines, but not normal human hepatocytes, to TRAIL-induced apoptosis. Indeed, FACS analysis showed that 25 (Huh7) to 50 (HepG2 and Hep3B) percent of the cells treated with both drugs were apoptotic. This occurred through activation of the extrinsic and the intrinsic pathways, as evidenced by a marked increase in caspase 3/7 (five to ninefold), caspase 8 (four to sevenfold) and caspase 9 (eight to 12-fold) activities in cells treated with Salirasib and TRAIL compared with control. Survivin inhibition had an important role in this process and was sufficient to sensitize hepatocarcinoma cells to apoptosis. Furthermore, TRAIL-induced apoptosis in HCC cells pretreated with Salirasib was dependent on activation of death receptor (DR) 5. In conclusion, Salirasib sensitizes hepatocarcinoma cells to TRAIL-induced apoptosis by a mechanism involving the DR5 receptor and survivin inhibition. These results in human hepatocarcinoma cell lines and primary hepatocytes provide a rationale for testing the combination of Salirasib and TRAIL agonists in human hepatocarcinoma.

Growth of poorly differentiated endometrial carcinoma is inhibited by combined action of medroxyprogesterone acetate and the Ras inhibitor Salirasib.[Pubmed:23530112]

Oncotarget. 2013 Feb;4(2):316-28.

Type 2 endometrial carcinoma (EC) is a poorly differentiated EC. Unlike type 1 EC, which responds to hormonal treatment (progestins), type 2 EC is refractory to hormonal treatment because of its low expression of active estrogen and progesterone receptors (ER, PR). The aim of this study was to develop a novel drug combination designed to treat these aggressive type 2 EC tumors without surgery and with fertility potential preserved. We examined the effects of combined treatment with the progestin medroxyprogesterone acetate (MPA) and the Ras inhibitor S-farnesylthiosalicylic acid (FTS; Salirasib). Because FTS can induce cell differentiation in tumor cells, we examined whether FTS could induce re-differentiation of type 2 EC cells, thereby sensitizing them to MPA. We found that FTS reduced Ras-GTP, phospho- Akt, and phospho-ERK, and that these reductions all correlated with a decrease in ERalpha phosphorylation. Combined treatment with FTS and MPA induced stronger reduction in USPC1 type 2 EC cell numbers than the reduction induced by either drug alone. MPA caused ERalpha degradation. Death of the cells was caused by MPA but not by FTS. The phosphorylated ERalpha induces gene transcription manifested by enhanced cell proliferation and survival. The combination of FTS and MPA, by reducing the mRNA expression of ERalpha-mediated genes (i.e. PR, c-fos and ps2/TFF1), inhibited tumor growth and enhanced the death of type 2 EC cells. These promising results might herald a novel treatment for the highly aggressive, incurable type 2 endometrial carcinoma.

Ras inhibition enhances autophagy, which partially protects cells from death.[Pubmed:23370967]

Oncotarget. 2013 Jan;4(1):145-55.

Autophagy, a process of regulated turnover of cellular constituents, is essential for normal growth control but may be defective under pathological conditions. The Ras/PI3K/mTOR signaling pathway negatively regulates autophagy. Ras signaling has been documented in a large number of human cancers. In this in-vitro study we examined the effect of the Ras inhibitor Salirasib (S-trans, trans-farnesylthiosalicylic acid; FTS) on autophagy induction and cell viability. We show that Ras inhibition by FTS induced autophagy in several cell lines, including mouse embryonic fibroblasts and the human cancer cell lines HeLa, HCT-116 and DLD-1. The autophagy induced by FTS seems to inhibit the cell death induced by FTS, since in the absence of autophagy the death of FTS-treated cells was enhanced. Therefore, inhibition of autophagy may promote the inhibition of tumor cell growth and the cell death mediated by FTS.

Dislodgment and accelerated degradation of Ras.[Pubmed:9477957]

Biochemistry. 1998 Feb 3;37(5):1306-14.

Membrane anchorage of Ras oncoproteins, required for transforming activity, depends on their carboxy-terminal farnesylcysteine. We previously showed that S-trans,trans-farnesylthiosalicylic acid (FTS), a synthetic farnesylcysteine mimetic, inhibits growth of ErbB2- and Ras-transformed cells, but not of v-Raf-transformed cells, suggesting that FTS interferes specifically with Ras functions. Here we demonstrate that FTS dislodges Ras from membranes of H-Ras-transformed (EJ) cells, facilitating its degradation and decreasing total cellular Ras. The dislodged Ras that was transiently present in the cytosol was degraded relatively rapidly, causing a decrease of up to 80% in total cellular Ras. The half-life of Ras was 10 +/- 4 h in FTS-treated EJ cells and 27 +/- 4 h in controls. The dislodgment of membrane Ras and decrease in total cellular Ras were dose-dependent: 50% of the effects occurred at 10-15 microM, comparable to concentrations (7-10 microM) required for 50% growth inhibition in EJ cells. Higher concentrations of FTS (25-50 microM) were required to dislodge Ras from Rat-1 cell membranes expressing normal Ras, suggesting some selectivity of FTS toward oncogenic Ras. Membrane localization of the prenylated G beta gamma of heterotrimeric G proteins was not affected by FTS in EJ cells. An FTS-related compound, N-acetyl-S-farnesyl-L-cysteine, which does not inhibit EJ cell growth, did not affect Ras. FTS did not inhibit growth of Rat-1 cells transformed by N-myristylated H-Ras and did not reduce the total amount of this Ras isoform. The results suggest that FTS affects docking of Ras in the cell membrane in a rather specific manner, rendering the protein susceptible to proteolytic degradation.

Salirasib is a Ras inhibitor that inhibits specifically both oncogenically activated Ras and growth factor receptor-mediated Ras activation, resulting in the inhibition of Ras-dependent tumor growth.

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