Targeting of K-Ras 4B by S-trans,trans-farnesyl thiosalicylic acid

Targeting KRAS mutant cancers by preventing signaling transduction in the MAPK pathway

KRAS genes are the most commonly mutated oncogenes in cancer. Unfortunately, effective therapeutic strategies for targeting KRAS mutant cancers have proven to be difficult to obtain. A key reason for this setback is due to the lack of success direct KRAS mutant inhibitors have received. Researchers have turned their efforts away from targeting the KRAS nucleotide-binding site directly and towards targeting other areas of the MAPK signaling pathway to block KRAS function. Researchers found that inhibiting enzymes and protein-protein interactions involved in the MAPK signaling pathway inhibit the activation of KRAS mutant therefore can lead to a potential therapeutic for KRAS mutated cancers. Throughout the past two decades, various indirect inhibitors have been designed and tested. EGFR and MEK inhibitors have presented with less success; however, significant advances have been made when targeting the plasma membrane localization process and the allosteric site of KRAS mutant. Farnesyltransferase and allosteric inhibitors have both advanced to human clinical trials. This comprehensive review presents the most recent developments of direct and indirect KRAS mutant inhibitors. This review summarizes published data on the inhibitory and anti-cancer activity of compounds that target KRAS activation as well as highlights the most promising strategies for targeting KRAS mutant cancers.

Celecoxib combined with salirasib strongly inhibits pancreatic cancer cells in 2D and 3D cultures

Background/Aim: Pancreatic adenocarcinoma is a highly malignant tumor. Synergistic combinations of anticancer agents for the effective treatment of pancreatic cancer patients are urgently needed. Here, we investigated the combined effect of celecoxib (CEL) and salirasib (SAL) on pancreatic cancer cells. Methods: Cell viability and apoptosis were measured by the trypan blue assay, three-dimensional cultures, propidium iodide staining, and caspase-3 assay. NF-κB activation and the protein levels of Akt, pAkt, and Bcl-2 were determined by the luciferase reporter assay and western blot. Results: Co-treatment with CEL and SAL had stronger effects on decreasing cell viability and inducing apoptosis in Panc-1 cells as compared with each agent individually. This combination strongly inhibited NF-κB activity and reduced pAkt and Bcl-2 levels in Panc-1 cells. Conclusion: SAL in combination with CEL may represent a new approach for effective inhibition of pancreatic cancer.

HRAS as a potential therapeutic target of salirasib RAS inhibitor in bladder cancer

The active form of the small GTPase RAS binds to downstream effectors to promote cell growth and proliferation. RAS signal enhancement contributes to tumorigenesis, invasion, and metastasis in various different cancers. HRAS proto-oncogene GTPase (HRAS), one of the RAS isoforms, was the first human oncogene for which mutations were reported in T24 bladder cancer (BC) cells in 1982, and HRAS mutation or upregulation has been reported in several cancers. According to data from The Cancer Genome Atlas, HRAS expression was significantly upregulated in clinical BC samples compared to healthy samples (P=0.0024). HRAS expression was also significantly upregulated in BC with HRAS mutation compared to patients without HRAS mutation (P<0.0001). The tumor suppressive effect of salirasib, a RAS inhibitor, has been reported in several cancer types, but only at relatively high concentrations. As such, RAS inhibitors have not been used for clinical applications. The aim of the current study was to investigate the therapeutic potential of targeting HRAS using salirasib and small interfering RNA (siRNA) and to characterize the mechanism by which HRAS functions using recently developed quantitative in vitro proteome-assisted multiple reaction monitoring for protein absolute quantification (iMPAQT), in BC cells. iMPAQT allows measurement of the absolute abundance of any human protein with the high quantitative accuracy. Salirasib and siRNA targeting of HRAS inhibited cell proliferation, migration and invasion in HRAS wild type and HRAS-mutated cell lines. Proteomic analyses revealed that several metabolic pathways, including the oxidative phosphorylation pathway and glycolysis, were significantly downregulated in salirasib-treated BC cells. However, the expression levels of hexokinase 2, phosphoglycerate kinase 1, pyruvate kinase, muscle (PKM)1, PKM2 and lactate dehydrogenase A, which are downstream of RAS and target genes of hypoxia inducible factor-1α, were not notably downregulated, which may explain the high concentration of salirasib required to inhibit cell viability. These findings provide insight into the mechanisms of salirasib, and suggest the need for novel therapeutic strategies to treat cancers such as BC.

Deubiquitinase USP18 Loss Mislocalizes and Destabilizes KRAS in Lung Cancer

KRAS is frequently mutated in lung cancers and is associated with aggressive biology and chemotherapy resistance. Therefore, innovative approaches are needed to treat these lung cancers. Prior work implicated the IFN-stimulated gene 15 (ISG15) deubiquitinase (DUB) USP18 as having antineoplastic activity by regulating lung cancer growth and oncoprotein stability. This study demonstrates that USP18 affects the stability of the KRAS oncoprotein. Interestingly, loss of USP18 reduced KRAS expression, and engineered gain of USP18 expression increased KRAS protein levels in lung cancer cells. Using the protein synthesis inhibitor cycloheximide, USP18 knockdown significantly reduced the half-life of KRAS, but gain of USP18 expression significantly increased its stability. Intriguingly, loss of USP18 altered KRAS subcellular localization by mislocalizing KRAS from the plasma membrane. To explore the biologic consequences, immunohistochemical (IHC) expression profiles of USP18 were compared in lung cancers of KrasLA2/+ versus cyclin E engineered mouse models. USP18 expression was higher in Kras-driven murine lung cancers, indicating a link between KRAS and USP18 expression in vivo To solidify this association, loss of Usp18 in KrasLA2/+ /Usp18-/- mice was found to significantly reduce lung cancers as compared with parental KrasLA2/+ mice. Finally, translational relevance was confirmed in a human lung cancer panel by showing that USP18 IHC expression was significantly higher in KRAS-mutant versus wild-type lung adenocarcinomas.Implications: Taken together, this study highlights a new way to combat the oncogenic consequences of activated KRAS in lung cancer by inhibiting the DUB USP18. Mol Cancer Res; 15(7); 905-14. ©2017 AACR.

Targeting RAS Membrane Association: Back to the Future for Anti-RAS Drug Discovery?

RAS proteins require membrane association for their biologic activity, making this association a logical target for anti-RAS therapeutics. Lipid modification of RAS proteins by a farnesyl isoprenoid is an obligate step in that association, and is an enzymatic process. Accordingly, farnesyltransferase inhibitors (FTI) were developed as potential anti-RAS drugs. The lack of efficacy of FTIs as anticancer drugs was widely seen as indicating that blocking RAS membrane association was a flawed approach to cancer treatment. However, a deeper understanding of RAS modification and trafficking has revealed that this was an erroneous conclusion. In the presence of FTIs, KRAS and NRAS, which are the RAS isoforms most frequently mutated in cancer, become substrates for alternative modification, can still associate with membranes, and can still function. Thus, FTIs failed not because blocking RAS membrane association is an ineffective approach, but because FTIs failed to accomplish that task. Recent findings regarding RAS isoform trafficking and the regulation of RAS subcellular localization have rekindled interest in efforts to target these processes. In particular, improved understanding of the palmitoylation/depalmitoylation cycle that regulates RAS interaction with the plasma membrane, endomembranes, and cytosol, and of the potential importance of RAS chaperones, have led to new approaches. Efforts to validate and target other enzymatically regulated posttranslational modifications are also ongoing. In this review, we revisit lessons learned, describe the current state of the art, and highlight challenging but promising directions to achieve the goal of disrupting RAS membrane association and subcellular localization for anti-RAS drug development. Clin Cancer Res; 21(8); 1819-27. ©2015 AACR. See all articles in this CCR Focus section, "Targeting RAS-Driven Cancers."

Improving Prospects for Targeting RAS

RAS mutations are among the most common oncogenic drivers in human cancers, affecting nearly a third of all solid tumors and around a fifth of common myeloid malignancies, but they have evaded therapeutic interventions, despite being the focus of intense research over the last three decades. Recent discoveries lend new understanding about the structure, function, and signaling of RAS and have opened new avenues for development of much needed new therapies. We discuss the various approaches under investigation to target mutant RAS proteins. The recent development of direct RAS inhibitors specific to KRAS G12C mutations represents a landmark discovery that promises to change the perception about RAS's druggability. Multiple clinical trials targeting synthetically lethal partners and/or downstream signaling partners of RAS are underway. Novel inhibitors targeting various arms of RAS processing and signaling have yielded encouraging results in the laboratory, but refinement of the drug-like properties of these molecules is required before they will be ready for the clinic.

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

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.

Ras and autophagy in cancer development and therapy

Autophagy, a process of self-degradation and turnover of cellular components, plays a complex role in cancer. Evidence exists to show that autophagy may support tumor growth and cell survival, whereas it can also contribute to tumor suppression and have anti-survival characteristics in different cellular systems. Numerous studies have described the effects of various oncogenes and tumor suppressors on autophagy. The small GTPase Ras is an oncogene involved in the regulation of various cell-signaling pathways, and is mutated in 33% of human cancers. In the present review, we discuss the interplay between Ras and autophagy in relation to oncogenesis. It appears that Ras can upregulate or downregulate autophagy through several signaling pathways. In turn, autophagy can affect the tumorigenicity driven by Ras, resulting in either tumor progression or repression, depending on the cellular context. Furthermore, Ras inhibitors were shown to induce autophagy in several cancer cell lines.

Chloroquine synergizes with FTS to enhance cell growth inhibition and cell death

The Ras family of small GTPases transmits extracellular signals that regulate cell growth, differentiation, motility and death. Ras signaling is constitutively active in a large number of human cancers. Ras can also regulate autophagy by affecting several signaling pathways including the mTOR pathway. Autophagy is a process that regulates the balance between protein synthesis and protein degradation. It is important for normal growth control, but may be defective in diseases. Previously, we have shown that Ras inhibition by FTS induces autophagy, which partially protects cancer cells and may limit the use of FTS as an anti-cancer drug. Since FTS is a non toxic drug we hypothesized that FTS and chloroquine (an autophagy inhibitor) will synergize in cell growth inhibition and cell death. Thus, in the present study, we explored the mechanism of each individual drug and their combined action. Our results demonstrate that in HCT-116 and in Panc-1 cells, FTS induces autophagy, which can be inhibited by chloroquine. Furthermore, the combined treatment synergistically decreased the number of viable cells. Interestingly, the combined treatment enhanced apoptotic cell death as indicated by increased sub-G1 cell population, increased Hoechst staining, activation of caspase 3, decrease in survivin expression and release of cytochrome c. Thus, chloroquine treatment may promote FTS-mediated inhibition of tumor cell growth and may stimulate apoptotic cell death.

Rasfonin, a novel 2-pyrone derivative, induces ras-mutated Panc-1 pancreatic tumor cell death in nude mice

Rasfonin is a novel 2-pyrone derivative reported to induce apoptosis in ras-dependent cells. In this study, its effects on ras-mutated pancreatic cancer cells were investigated in vitro and in vivo. Two human pancreatic cancer cell lines Panc-1 (mutated K-ras) and BxPC-3 (wild-type K-ras) were selected to test the effects of rasfonin on cell proliferation, clone formation, migration and invasion in vitro. Immunoblotting was used to detect the expressions of EGFR-Ras-Raf-MEK-ERK signaling pathway proteins. Ras activity was measured using a pull-down ELISA kit and guanine exchange factor (GEF)/GTPase-activating proteins (GAP) activity was measured by [(3)H]-GDP radiometric ligand binding. For an in vivo study, CD1 nude mice bearing Panc-1 cells were treated with rasfonin or Salirasib (FTS). We found that rasfonin suppressed proliferation more strongly in Panc-1 cells (IC50=5.5 μM) than BxPC-3 cells (IC50=10 μM) in vitro. Clone formation, migration and invasion by Panc-1 cells were also reduced by rasfonin. Rasfonin had little effect on the farnesylation of Ras, but it strongly downregulated Ras activity and consequently phosphorylation of c-Raf/MEK/ERK. Further experiments indicated that rasfonin reduced Son of sevenless (Sos1) expression but did not alter GEF and GAP activities. The in vivo experiments also revealed that rasfonin (30 mg/kg) delayed the growth of xenograft tumors originating from Panc-1 cells. Tumor weight was ultimately decreased after 20 days of treatment of rasfonin. Rasfonin is a robust inhibitor of pancreatic cancers with the K-ras mutation. The reduction of Sos1 expression and the consequently depressed Ras-MAPK activity could be important in its anticancer activity.

Disrupting the oncogenic synergism between nucleolin and Ras results in cell growth inhibition and cell death

BACKGROUND

The ErbB receptors, Ras proteins and nucleolin are major contributors to malignant transformation. The pleiotropic protein nucleolin can bind to both Ras protein and ErbB receptors. Previously, we have demonstrated a crosstalk between Ras, nucleolin and the ErbB1 receptor. Activated Ras facilitates nucleolin interaction with ErbB1 and stabilizes ErbB1 levels. The three oncogenes synergistically facilitate anchorage independent growth and tumor growth in nude mice.

METHODOLOGY/PRINCIPAL FINDINGS

In the present study we used several cancer cell lines. The effect of Ras and nucleolin inhibition was determined using cell growth, cell death and cell motility assays. Protein expression was determined by immunohistochemistry. We found that inhibition of Ras and nucleolin reduces tumor cell growth, enhances cell death and inhibits anchorage independent growth. Our results reveal that the combined treatment affects Ras and nucleolin levels and localization. Our study also indicates that Salirasib (FTS, Ras inhibitor) reduces cell motility, which is not affected by the nucleolin inhibitor.

CONCLUSIONS/SIGNIFICANCE

These results suggest that targeting both nucleolin and Ras may represent an additional avenue for inhibiting cancers driven by these oncogenes.

Ras inhibition enhances autophagy, which partially protects cells from death

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.

K-ras 4A and 4B mRNA levels correlate with superoxide in lung adenocarcinoma cells, while at the protein level, only mutant K-ras 4A protein correlates with superoxide

The K-ras gene is frequently mutated in lung and other cancers. K-ras protein includes two splice variants, K-ras 4A and 4B. While K-ras 4B is more widely expressed, recent evidence implicates K-ras 4A in lung tumorigenesis. We found that K-ras 4A protein has a wide range of expression in a large panel of human lung adenocarcinoma cell lines. In cell lines with mutant K-ras, but not those with wildtype K-ras, the K-ras 4A protein had a strong positive correlation with levels of cellular superoxide. We investigated whether K-ras 4A protein was involved in superoxide production, or alternatively was modulated by elevated superoxide. Experiments with small interfering RNA targeting K-ras 4A did not confirm its role in superoxide generation. However, decreasing cellular superoxide with the scavenger Tiron tended to reduce levels of K-ras 4A protein. K-ras 4A and 4B mRNA were also quantified in a number of NSCLC cell lines. 4A mRNA correlated with 4A protein only in K-ras-mutant cells. K-ras 4A mRNA also correlated with superoxide, but with no difference between cell lines with mutant or wildtype K-ras. K-ras 4B mRNA correlated with 4A mRNA and with superoxide, in both K-ras mutant and wildtype cells. The results are consistent with superoxide directly or indirectly up-regulating expression of all K-ras genes, and also increasing the stability of K-ras 4A mutant protein selectively.

Ras nanoclusters: a new drug target?

Ras proteins on the plasma membrane are laterally segregated into transient nanoclusters that are essential for high-fidelity signal transmission by the Ras/MAPK cascade. The dynamics of Ras nanocluster assembly and disassembly control MAPK signal output. BRaf inhibitors paradoxically activate CRaf and MAPK signaling in Ras-transformed cells. In our recent study, we showed that BRaf inhibition significantly enhances nanoclustering of oncogenic K- and N-Ras, but not H-Ras by increasing the frequency of Ras nanocluster formation. This disrupted spatiotemporal dynamics of Ras nanocluster fully accounts for the observed effects of Raf inhibitors on Ras signal transmission. Here together with other studies, we propose that the dynamics of Ras nanoclusters may represent a novel target for future therapeutic intervention.

Synergistic effects of combined Wnt/KRAS inhibition in colorectal cancer cells

Activation of Wnt signalling due to inability to degrade β-catenin is found in >85% of colorectal cancers. Approximately half of colon cancers express a constitutively active KRAS protein. A significant fraction of patients show both abnormalities. We previously reported that simultaneous down-regulation of both β-catenin and KRAS was necessary to induce significant cell death and tumor growth inhibition of colorectal cancer cells. Although attractive, an RNAi-based therapeutic approach is still far from being employed in the clinical setting. Therefore, we sought to recapitulate our previous findings by the use of small-molecule inhibitors of β-catenin and KRAS. We show here that the β-catenin inhibitors PKF115-584 and pyrvinium pamoate block β-catenin-dependent transcriptional activity and synergize with the KRAS inhibitor S-trans, trans-farnesylthiosalicylic acid (FTS, salirasib) in colon cancer cells driven by Wnt and KRAS oncogenic signals, but not in cells carrying BRAF mutations. The combined use of these compounds was superior to the use of any drug alone in inducing cell growth arrest, cell death, MYC and survivin down-modulation, and inhibition of anchorage-independent growth. Expression analysis of selected cancer-relevant genes revealed down-regulation of CD44 as a common response to the combined treatments. These data provide a proof of principle for a combination therapeutic strategy in colorectal cancer.

IgM-mediated autoimmune responses directed against anchorage epitopes are greater in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) than in major depression

Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) and depression are considered to be neuro-immune disorders (Maes and Twisk, BMC Medicine 8:35, 2010). There is also evidence that depression and ME/CFS are accompanied by oxidative and nitrosative stress (O&NS) and by increased autoantibodies to a number of self-epitopes some of which have become immunogenic due to damage by O&NS. The aim of this study is to examine IgM-mediated autoimmune responses to different self-epitopes in ME/CFS versus depression. We examined serum IgM antibodies to three anchorage molecules (palmitic and myristic acid and S-farnesyl-L-cysteine); acetylcholine; and conjugated NO-modified adducts in 26 patients with major depression; 16 patients with ME/CFS, 15 with chronic fatigue; and 17 normal controls. Severity of fatigue and physio-somatic (F&S) symptoms was measured with the Fibromyalgia and Chronic Fatigue Syndrome Rating Scale. Serum IgM antibodies to the three anchorage molecules and NO-phenylalanine were significantly higher in ME/CFS than in depression. The autoimmune responses to oxidatively, but not nitrosatively, modified self-epitopes were significantly higher in ME/CFS than in depression and were associated with F&S symptoms. The autoimmune activity directed against conjugated acetylcholine did not differ significantly between ME/CFS and depression, but was greater in the patients than controls. Partially overlapping pathways, i.e. increased IgM antibodies to a multitude of neo-epitopes, underpin both ME/CFS and depression, while greater autoimmune responses directed against anchorage molecules and oxidatively modified neo-epitopes discriminate patients with ME/CFS from those with depression. These autoimmune responses directed against neoantigenic determinants may play a role in the dysregulation of key cellular functions in both disorders, e.g. intracellular signal transduction, cellular differentiation and apoptosis, but their impact may be more important in ME/CFS than in depression.

Fendiline inhibits K-Ras plasma membrane localization and blocks K-Ras signal transmission

Ras proteins regulate signaling pathways important for cell growth, differentiation, and survival. Oncogenic mutant Ras proteins are commonly expressed in human tumors, with mutations of the K-Ras isoform being most prevalent. To be active, K-Ras must undergo posttranslational processing and associate with the plasma membrane. We therefore devised a high-content screening assay to search for inhibitors of K-Ras plasma membrane association. Using this assay, we identified fendiline, an L-type calcium channel blocker, as a specific inhibitor of K-Ras plasma membrane targeting with no detectable effect on the localization of H- and N-Ras. Other classes of L-type calcium channel blockers did not mislocalize K-Ras, suggesting a mechanism that is unrelated to calcium channel blockade. Fendiline did not inhibit K-Ras posttranslational processing but significantly reduced nanoclustering of K-Ras and redistributed K-Ras from the plasma membrane to the endoplasmic reticulum (ER), Golgi apparatus, endosomes, and cytosol. Fendiline significantly inhibited signaling downstream of constitutively active K-Ras and endogenous K-Ras signaling in cells transformed by oncogenic H-Ras. Consistent with these effects, fendiline blocked the proliferation of pancreatic, colon, lung, and endometrial cancer cell lines expressing oncogenic mutant K-Ras. Taken together, these results suggest that inhibitors of K-Ras plasma membrane localization may have utility as novel K-Ras-specific anticancer therapeutics.

Staurosporines disrupt phosphatidylserine trafficking and mislocalize Ras proteins

Oncogenic mutant Ras is frequently expressed in human cancers, but no anti-Ras drugs have been developed. Since membrane association is essential for Ras biological activity, we developed a high content assay for inhibitors of Ras plasma membrane localization. We discovered that staurosporine and analogs potently inhibit Ras plasma membrane binding by blocking endosomal recycling of phosphatidylserine, resulting in redistribution of phosphatidylserine from plasma membrane to endomembrane. Staurosporines are more active against K-Ras than H-Ras. K-Ras is displaced to endosomes and undergoes proteasomal-independent degradation, whereas H-Ras redistributes to the Golgi and is not degraded. K-Ras nanoclustering on the plasma membrane is also inhibited. Ras mislocalization does not correlate with protein kinase C inhibition or induction of apoptosis. Staurosporines selectively abrogate K-Ras signaling and proliferation of K-Ras-transformed cells. These results identify staurosporines as novel inhibitors of phosphatidylserine trafficking, yield new insights into the role of phosphatidylserine and electrostatics in Ras plasma membrane targeting, and validate a new target for anti-Ras therapeutics.

FTS and 2-DG induce pancreatic cancer cell death and tumor shrinkage in mice

The Ras inhibitor S-trans-trans farnesylthiosalicylic acid (FTS) inhibits active Ras, which controls cell proliferation, differentiation, survival, and metabolism. FTS also inhibits HIF1α expression in cancer cells, leading to an energy crisis. The synthetic glucose analog 2-deoxy-D-glucose (2-DG), which inhibits glycolysis, is selectively directed to tumor cells that exhibit increased glucose consumption. The 2-DG enters tumor cells, where it competes with glucose for glycolytic enzymes. In cancer models, as well as in human phase 1 trials, 2-DG inhibits tumor growth without toxicity. We postulated that under normoxic conditions, tumor cells treated with FTS would be more sensitive than normal cells to 2-DG. We show here that combined treatment with FTS and 2-DG inhibited cancer cell proliferation additively, yet induced apoptotic cell death synergistically both in vitro and in vivo. The induced apoptosis was inferred from QVD-OPH inhibition, an increase in cleaved caspase 3, and loss of survivin. FTS and 2-DG when combined, but not separately, also induced an increase in fibrosis of the tumor tissue, chronic inflammation, and tumor shrinkage. Overall, these results suggest a possible new treatment of pancreatic tumors by the combined administration of FTS and 2-DG, which together induce pancreatic tumor cell death and tumor shrinkage under non-toxic conditions.

IgM-mediated autoimmune responses directed against multiple neoepitopes in depression: new pathways that underpin the inflammatory and neuroprogressive pathophysiology

BACKGROUND

There is evidence that depression is accompanied by oxidative and nitrosative stress (O&NS), as indicated by increased free radical levels, lipid peroxidation, and lowered antioxidant levels. The aims of the present study are to examine whether depression is accompanied by autoimmune responses directed against a) neoepitopes that are formed following O&NS damage; and b) the major anchorage molecules, i.e. palmitic and myristic acids and S-farnesyl-L-cysteine.

METHODS

We examined serum IgM antibodies to the conjugated fatty acids, palmitic and myristic acids; acetylcholine; S-farnesyl-L-cysteine; and NO-modified adducts in 26 depressed patients and 17 normal controls. Severity of depression was measured with the Hamilton Depression Rating Scale and severity of fatigue and somatic (F&S) symptoms with the Fibromyalgia and Chronic Fatigue Syndrome (FF) Rating Scale.

RESULTS

The prevalences and mean values for the serum IgM levels directed against conjugated palmitic and myristic acids, acetylcholine, S-farnesyl-L-cysteine; and the conjugated NO adducts, NO-tyrosine, NO-phenylalanine, NO-aspartate, NO-histidine, and NO-creatine were significantly higher in depressed patients than in normal controls. The autoimmune responses were significantly related to FF symptoms, such as fatigue and a flu-like malaise, whereas the indicants of nitrosative stress were related to gastro-intestinal and autonomic symptoms.

DISCUSSION

Depression is characterized by IgM-related autoimmune responses directed against a) neoepitopes that are normally not detected by the immune system but that due to damage by O&NS have become immunogenic; and b) anchorage epitopes, i.e. palmitic and myristic acids, and S-farnesyl-L-cysteine. These autoimmune responses play a role in the inflammatory and O&NS pathophysiology of depression and may mediate the cellular dysfunctions that contribute to neuroprogression, e.g. aberrations in signal transduction, cellular differentiation and apoptosis.

Farnesylthiosalicylic acid (salirasib) inhibits Rheb in TSC2-null ELT3 cells: a potential treatment for lymphangioleiomyomatosis

The small GTPase proteins, Ras and Rheb, serve as molecular switches regulating cell proliferation, differentiation and apoptosis. Ras also regulates Rheb by inactivating the tuberous sclerosis complex (TSC), which includes products of the TSC1 and TSC2 genes encoding hamartin (TSC1) and tuberin (TSC2), respectively, and acts as a Rheb-specific GTPase-activating protein. Loss of function of TSC1 or TSC2 results in an increase in active Rheb.GTP with the consequent translational abnormalities and excessive cell proliferation characteristic of the genetic disorders, tuberous sclerosis and lymphangioleiomyomatosis (LAM). To determine whether inactivation of Rheb, Ras or both might be a potential treatment for LAM, we used TSC2-null ELT3 cells as a LAM model. The cells were treated with the Ras inhibitor S-trans,trans-farnesylthiosalicylic acid (FTS; salirasib), which mimics the C-terminal S-farnesyl cysteine common to Ras and Rheb. This C-terminus is critical for their attachment to cellular membranes and for their biological activities. Untreated, the ELT3 cells expressed significant amounts of Rheb but little Ras.GTP, and this phenotype was reversed by TSC2 reexpression. Treatment with FTS decreased Ras.GTP only slightly in the TSC2-null cells, but reduced their overactive Rheb as well as their proliferation, migration and tumor growth. Notably, TSC2 reexpression in these ELT3 cells rescued them from the inhibitory effect of FTS. Evidently, therefore, FTS blocks active Rheb in TSC2-null ELT3 cells and may have therapeutic potential for LAM.

Inhibition of contact sensitivity by farnesylthiosalicylic acid-amide, a potential Rap1 inhibitor

We hypothesized that Ras proximate 1 (Rap1) functions as an additional target for farnesylthiosalicylic acid (FTS) or its derivatives, and that the inhibition of Rap1 in lymphocytes by these agents may represent a method for treating inflammatory disorders. Indeed, we found that FTS-amide (FTS-A) was able to inhibit the elicitation phase of delayed cutaneous hypersensitivity in vivo. This effect was associated with the inhibition of Rap1 more than with the inhibition of Harvey rat sarcoma viral oncogene (Ras). Moreover, FTS-A inhibited Rap1 and contact sensitivity far better than FTS. We suggest that FTS-A may serve as a possible therapeutic tool in contact sensitivity in particular and T-cell-mediated inflammation in general.

Phase 1 first-in-human clinical study of S-trans,trans-farnesylthiosalicylic acid (salirasib) in patients with solid tumors

PURPOSE

This phase I first-in-human trial evaluated salirasib, an S-prenyl derivative of thiosalicylic acid that competitively blocks RAS signaling.

METHODS

Patients with advanced cancers received salirasib twice daily for 21 days every 4 weeks. Doses were escalated from 100 to 200, 400, 600, and 800 mg.

RESULTS

The most common toxicity was dose-related diarrhea (Grade 1-2, 79% of 24 patients). Other toxicities included abdominal pain, nausea, and vomiting. No Grade 3-4 toxicity was noted. Nineteen (79%) patients had no drug-related toxicity >Grade 1. Dose-limiting toxicity (DLT) was not reached, but all three patients treated with 800 mg experienced Grade 1-2 diarrhea, brogating dose escalation. Six patients were treated at a dose of 600 mg with no DLTs. Seven (29%) patients had stable disease on salirasib for ≥4 months (range 4-23+). The salirasib pharmacokinetic profile was characterized by slow absorption and a rapid elimination phase following oral administration. Salirasib exposure (C(max); day 1 AUC(inf) vs. day 15 AUC(0-12 h)) was similar between days 1 and 15 (P > 0.05). The T(1/2) (mean ± SD) was 3.6 ± 2.2 h on day 1.

CONCLUSIONS

Salirasib therapy was well tolerated. The recommended dose for phase II studies is 600 mg twice daily.

Novel nitric oxide-releasing derivatives of farnesylthiosalicylic acid: synthesis and evaluation of antihepatocellular carcinoma activity

Novel furoxan-based nitric oxide (NO) releasing derivatives (8a-p) of farnesylthiosalicylic acid (FTS) were synthesized. Compound 8l displayed the strongest inhibition on the proliferation of human hepatocellular carcinoma (HCC) cells in vitro, superior to FTS, sorafenib, and furoxan moiety, selectively induced high frequency of HCC cell apoptosis, and produced high levels of NO in HCC cells but not in nontumor liver cells. Furthermore, 8l exhibited low acute toxicity to mice and significantly inhibited the growth of HCC tumors in vivo and the Ras-related signaling in the tumors. Therefore, our novel findings may provide a new framework for the design of new NO-releasing furoxan/FTS hybrids for the intervention of human HCC.

The Ras antagonist, farnesylthiosalicylic acid (FTS), decreases fibrosis and improves muscle strength in dy/dy mouse model of muscular dystrophy

The Ras superfamily of guanosine-triphosphate (GTP)-binding proteins regulates a diverse spectrum of intracellular processes involved in inflammation and fibrosis. Farnesythiosalicylic acid (FTS) is a unique and potent Ras inhibitor which decreased inflammation and fibrosis in experimentally induced liver cirrhosis and ameliorated inflammatory processes in systemic lupus erythematosus, neuritis and nephritis animal models. FTS effect on Ras expression and activity, muscle strength and fibrosis was evaluated in the dy^2J/dy^2J mouse model of merosin deficient congenital muscular dystrophy. The dy^2J/dy^2J mice had significantly increased RAS expression and activity compared with the wild type mice. FTS treatment significantly decreased RAS expression and activity. In addition, phosphorylation of ERK, a Ras downstream protein, was significantly decreased following FTS treatment in the dy^2J/dy^2J mice. Clinically, FTS treated mice showed significant improvement in hind limb muscle strength measured by electronic grip strength meter. Significant reduction of fibrosis was demonstrated in the treated group by quantitative Sirius Red staining and lower muscle collagen content. FTS effect was associated with significantly inhibition of both MMP-2 and MMP-9 activities. We conclude that active RAS inhibition by FTS was associated with attenuated fibrosis and improved muscle strength in the dy^2J/dy^2J mouse model of congenital muscular dystrophy.

Multiple cellular proteins modulate the dynamics of K-ras association with the plasma membrane

Although specific proteins have been identified that regulate the membrane association and facilitate intracellular transport of prenylated Rho- and Rab-family proteins, it is not known whether cellular proteins fulfill similar roles for other prenylated species, such as Ras-family proteins. We used a previously described method to evaluate how several cellular proteins, previously identified as potential binding partners (but not effectors) of K-ras4B, influence the dynamics of K-ras association with the plasma membrane. Overexpression of either PDEδ or PRA1 enhances, whereas knockdown of either protein reduces, the rate of dissociation of K-ras from the plasma membrane. Inhibition of calmodulin likewise reduces the rate of K-ras dissociation from the plasma membrane, in this case in a manner specific for the activated form of K-ras. By contrast, galectin-3 specifically reduces the rate of plasma membrane dissociation of activated K-ras, an effect that is blocked by the K-ras antagonist farnesylthiosalicylic acid (salirasib). Multiple cellular proteins thus control the dynamics of membrane association and intercompartmental movement of K-ras to an important degree even under basal cellular conditions.

Salirasib in the treatment of pancreatic cancer

The Ras family of genes is involved in the cellular regulation of proliferation, differentiation, cell adhesion and apoptosis. The K-ras gene is mutated in over 90% of pancreatic cancer cases. Salirasib (S-trans,trans-farnesylthiosalycilic acid [FTS]) is a synthetic small molecule that acts as a potent Ras inhibitor. It is a farnesylcysteine mimetic that selectively disrupts the association of active RAS proteins with the plasma membrane. Animal studies demonstrated that salirasib inhibited tumor growth, downregulated gene expression in the cell cycle and Ras signaling pathways. In a clinical study of salirasib combined with standard doses of gemcitabine, it was demonstrated that the two drugs have no overlapping pharmacokinetics. The salirasib recommended dose was 600 mg twice daily and the progression-free survival was 4.7 months. Future studies will determine whether salirasib adds to the anti-tumor activity of drugs approved by the US FDA for pancreatic cancer.

Galectin-3 promotes chronic activation of K-Ras and differentiation block in malignant thyroid carcinomas

Anaplastic thyroid carcinomas are deadly tumors that are highly invasive, particularly into the bones. Although oncogenic Ras can transform thyroid cells into a severely malignant phenotype, thyroid carcinomas do not usually harbor ras gene mutations. Therefore, it is not known whether chronically active Ras contributes to thyroid carcinoma cell proliferation, although galectin-3 (Gal-3), which is strongly expressed in thyroid carcinomas but not in benign tumors or normal glands, is known to act as a K-Ras chaperone that stabilizes and drives K-Ras.GTP nanoclustering and signal robustness. Here, we examined the possibility that thyroid carcinomas expressing high levels of Gal-3 exhibit chronically active K-Ras. Using cell lines representing three types of malignant thyroid tumors--papillary, follicular, and anaplastic--we investigated the possible correlation between Gal-3 expression and active Ras content, and then examined the therapeutic potential of the Ras inhibitor S-trans, trans-farnesylthiosalicylic acid (FTS; Salirasib) for thyroid carcinoma. Thyroid carcinoma cells strongly expressing Gal-3 showed high levels of K-Ras.GTP expression, and K-Ras.GTP transmitted strong signals to extracellular signal-regulated kinase. FTS disrupted interactions between Gal-3 and K.Ras, strongly reduced K-Ras.GTP and phospho-extracellular signal-regulated kinase expression, and enhanced the expression of the cell cycle inhibitor p21 as well as of the thyroid transcription factor 1, which is involved in thyroid cell differentiation. FTS also inhibited anaplastic thyroid carcinoma cell proliferation in vitro and tumor growth in nude mice. We conclude that wild-type K-Ras.GTP in association with Gal-3 contributes to thyroid carcinoma malignancy and that Ras inhibition might be a useful treatment strategy against these deadly tumors.

Galectin-3/MAC-2, Ras and PI3K activate complement receptor-3 and scavenger receptor-AI/II mediated myelin phagocytosis in microglia

The removal of degenerated myelin is essential for repair in Wallerian degeneration that follows traumatic injury to axons and in autoimmune demyelinating diseases (e.g., multiple sclerosis). Microglia can remove degenerated myelin through phosphatidylinositol-3-kinase (PI3K)-dependent phagocytosis mediated by complement receptor-3 (CR3/MAC-1) and scavenger receptor-AI/II (SRAI/II). Paradoxically, these receptors are expressed in microglia after injury but myelin is not phagocytosed. Additionally, Galectin-3/MAC-2 is expressed in microglia that phagocytose but not in microglia that do not phagocytose, suggesting that Galectin-3/MAC-2 is instrumental in activating phagocytosis. S-trans, trans-farnesylthiosalicylic (FTS), which inhibits Galectin-3/MAC-2 dependent activation of PI3K through Ras, inhibited phagocytosis. K-Ras-GTP levels and PI3K activity increased during normal phagocytosis and decreased during FTS-inhibited phagocytosis. Galectin-3/MAC-2, which binds and stabilizes active Ras, coimmunoprecipitated with Ras and levels of the coimmunoprecipitate increased during normal phagocytosis. A role for Galectin-3/MAC-2 dependent activation of PI3K through Ras, mostly K-Ras, is thus suggested. An explanation may thus be offered for deficient phagocytosis by microglia that express CR3/MAC-1 and SRAI/II without Galectin-3/MAC-2 and efficient phagocytosis when CR3/MAC-1 and SRAI/II are co-expressed with Galectin-3/MAC-2.

Determination of salirasib (S-trans,trans-farnesylthiosalicylic acid) in human plasma using liquid chromatography-tandem mass spectrometry

A liquid chromatography/tandem mass spectrometric (LC/MS/MS) assay was developed for the quantitative determination of salirasib (S-trans,trans-farnesylthiosalicylic acid, FTS) in human plasma. Sample pretreatment involved liquid-liquid extraction with methyl t-butyl ether of 0.5-mL aliquots of lithium heparin plasma spiked with the internal standard, S-trans,trans-5-fluoro-farnesylthiosalicylic acid (5-F-FTS). Separation was achieved on Waters X-Terra C(18) (50 mm x 2.1 mm i.d., 3.5 microm) at room temperature using isocratic elution with acetonitrile/10 mM ammonium acetate buffer mobile phase (80:20, v/v) containing 0.1% formic acid at a flow rate of 0.20 mL/min. Detection was performed using electrospray MS/MS by monitoring the ion transitions from m/z 357.2-->153.0 (salirasib) and m/z 375.1-->138.8 (5-F-FTS). Calibration curves were linear in the concentration range of 1-1000 ng/mL. A 5000 ng/mL sample that was diluted 1:10 (v/v) with plasma was accurately quantitated. The values for both within day and between day precision and accuracy were well within the generally accepted criteria for analytical method (<8.0%). This assay was subsequently used for the determination of salirasib concentrations in plasma of cancer patients after oral administration of salirasib at a dose of 400 mg.

Rapamycin and mTOR kinase inhibitors

Mammalian target of rapamycin (mTOR) is a protein kinase that controls cell growth, proliferation, and survival. mTOR signaling is often upregulated in cancer and there is great interest in developing drugs that target this enzyme. Rapamycin and its analogs bind to a domain separate from the catalytic site to block a subset of mTOR functions. These drugs are extremely selective for mTOR and are already in clinical use for treating cancers, but they could potentially activate an mTOR-dependent survival pathway that could lead to treatment failure. By contrast, small molecules that compete with ATP in the catalytic site would inhibit all of the kinase-dependent functions of mTOR without activating the survival pathway. Several non-selective mTOR kinase inhibitors have been described and here we review their chemical and cellular properties. Further development of selective mTOR kinase inhibitors holds the promise of yielding potent anticancer drugs with a novel mechanism of action.

The Ras inhibitor farnesylthiosalicylic acid (Salirasib) disrupts the spatiotemporal localization of active Ras: a potential treatment for cancer

Chronic activation of Ras proteins by mutational activation or by growth factor stimulation is a common occurrence in many human cancers and was shown to induce and be required for tumor growth. Even if additional genetic defects are present, "correction" of the Ras defect has been shown to reverse Ras-dependent tumorigenesis. One way to block Ras protein activity is by interfering with their spatiotemporal localization in cellular membranes or in membrane microdomains, a prerequisite for Ras signaling and biological activity. Detailed reports describe the use of this method in studies employing farnesylthiosalicylic acid (FTS, Salirasib), a Ras farnesylcysteine mimetic, which selectively disrupts the association of chronically active Ras proteins with the plasma membrane. FTS competes with Ras for binding to Ras-escort proteins, which possess putative farnesyl-binding domains and interact only with the activated form of Ras proteins, thereby promoting Ras nanoclusterization in the plasma membrane and robust signals. This chapter presents three-dimensional time-lapse images that track the FTS-induced inhibition of membrane-activated Ras in live cells on a real-time scale. It also describes a mechanistic model that explains FTS selectivity toward activated Ras. Selective blocking of activated Ras proteins results in the inhibition of Ras transformation in vitro and in animal models, with no accompanying toxicity. Phase I clinical trials have demonstrated a safe profile for oral FTS, with minimal side effects and promising activity in hematological malignancies. Salirasib is currently undergoing trials in patients with pancreatic cancer and with nonsmall cell lung cancer, with or without identified K-Ras mutations. The findings might indicate whether with the disruption of the spatiotemporal localization of oncogenic Ras proteins and the targeting of prenyl-binding domains by anticancer drugs is worth developing as a means of cancer treatment.

Ras as a therapeutic target in hematologic malignancies

The RAS gene product is normally a membrane-localized G protein (N-Ras, K-Ras and H-Ras) of 21 kDa classically described as a molecular off/on switch. It is inactive when bound to guanosine diphosphate and active when bound to GTP. When mutated, the gene produces an abnormal protein resistant to GTP hydrolysis by GTPase, resulting in a constitutively active GTP-bound protein that stimulates a critical network of signal transduction pathways that lead to cellular proliferation, survival and differentiation. At least three downstream effector pathways have been described, including Raf/MEK/ERK, PI3K/AKT and RalGDS, but they are not completely understood. Ras pathways are also important downstream effectors of several receptor tyrosine kinases localized in the cell membrane, most notably the BCR-ABL fusion protein seen in patients with Philadelphia chromosome positive chronic myelogenous leukemia. An important consideration in designing strategies to block Ras stimulatory effect is that Ras proteins are synthesized in the cytosol, but require post-translational modifications and attachment to anchor proteins or membrane binding sites in the cell membrane to be biologically active. Farnesyl transferase inhibitors (FTIs) are probably the best-studied class of Ras inhibitors in hematologic malignancies. They block the enzyme farnesyl-transferase (FTase), which is essential for post-translational modification. However, it has been observed that the Ras proteins also can be geranylgeranylated in the presence of FTIs, thus allowing membrane localization and activation, which limits their effectiveness. It is now hypothesized that their mechanism of action may be through FTase inhibition involving other signal transduction pathways. S-trans, trans-farnesylthiosalicylic acid, which was first designed as a prenylated protein methyltransferase inhibitor, has shown in vitro activity against all activated Ras proteins by dislodging them from their membrane-anchoring sites. Here, Ras biology, its signaling pathways and its implications as a therapeutic target in hematologic malignancies are reviewed.

Orally administered FTS (salirasib) inhibits human pancreatic tumor growth in nude mice

BACKGROUND

S-trans,trans-farnesylthiosalicylic acid (salirasib, FTS) is a synthetic small molecule that acts as a potent Ras inhibitor. Salirasib inhibits specifically both oncogenically activated Ras and growth factor receptor-mediated Ras activation, resulting in the inhibition of Ras-dependent tumor growth. The objectives of this study were to develop a sensitive LC-MS/MS assay for determination of FTS in plasma, to assess the bioavailabilty of FTS after oral administration to mice, and then to examine the efficacy of orally administered FTS for inhibition of tumor growth in a nude mouse model.

METHODS

FTS was isolated from mouse plasma by liquid chromatography on a Columbus 5-mum particle size, 50 x 2 mm id column with a methanol/5 mM ammonium acetate (80/20) mobile phase (isocratic elution) at a flow rate of 0.3 ml/min. MS/MS was performed on a PE Sciex API 365 with Turbo Ion Spray as interface and negative ion ionization; parent ion (m/z): 357.2; daughter ion (m/z) 153.2; retention time 2.3 min. For plasma analysis, the amount of analyte in each sample was calculated by comparing response of the analyte in that sample to a nine-point standard curve linear over the range 3-1000 ng/ml. Pharmacokinetic studies were performed in mice following intraperitoneal dosing (20 mk/kg in PBS) or oral dosing (40 mg/kg in either 0.5% aqueous CMC or corn oil). Panc-1 tumor growth in nude mice was determined following daily oral dosing with FTS in 0.5% CMC (40, 60, or 80 mg/kg), or in combination with weekly gemcitabine (30 mg/kg).

RESULTS

Salirasib was readily detected in mouse plasma by LC-MS/MS at a detection limit of 3 ng/ml. For each route of administration, t (max) was 1 h and t (1/2) ranged from 1.86 to 2.66 h. Compared to IP administration, the oral bioavailabilty of FTS was 69.5% for oral CMC and 55% for oral corn oil suspensions, while clearance and volume of distribution were higher in both oral preparations. The orally administered salirasib inhibited panc-1 tumor growth in a dose dependent manner (67% reduction in tumor weight at the highest dose, P < 0.002 vs. control, n = 10 mice per group) and at a 40 mg/kg daily dose was synergistic with gemcitabine (83% increase in survival rate, n = 8 mice per group).

CONCLUSIONS

Salirasib exhibits good bioavailabilty after oral administration, as determined by a highly sensitive method for quantification in plasma. The orally available Ras inhibitor salirasib inhibited growth in nude mice, and may thus be considered for clinical trials.

Farnesylthiosalicylic acid: inhibition of proliferation and enhancement of apoptosis of hormone-dependent breast cancer cells

Farnesyltransferase inhibitors (FTIs) are being developed to block Ras-mediated actions, but current data suggest that the FTIs act through other non-Ras pathways. A new agent, farnesylthiosalicylic acid (FTS), blocks the binding of Ras to membrane acceptor sites and causes a marked reduction in Ras levels. Accordingly, FTS could be a useful new agent for the treatment of hormone-dependent breast cancer. We examined the dose-response effects of FTS on the growth of MCF-7 breast cancer cells in vitro and in vivo. Further, we dissected out its specific effects on cell proliferation and apoptosis by measuring BrdU incorporation into DNA and by using an ELISA assay to quantitate the magnitude of apoptosis. FTS and its solubilized conjoiner FTS-cyclodextrin markedly inhibited cell growth in MCF-7 breast cancer cells in culture and in xenografts. This agent exerted dual effects to reduce cell proliferation as assessed by BrdU incorporation and to enhance apoptosis as quantitated by ELISA assay. These data suggest that FTS is a promising agent to be developed for treatment of hormone-dependent breast cancer.

Ras inhibition results in growth arrest and death of androgen-dependent and androgen-independent prostate cancer cells

Prostate cancer is one of the most frequently diagnosed cancers in human males. Progression of these tumors is facilitated by autocrine/paracrine growth factors which activate critical signaling cascades that promote prostate cancer cell growth, survival and migration. Among these, Ras pathways have a major role. Here we examined the effect of the Ras inhibitor S-trans, trans-farnesylthiosalicylic acid (FTS), on growth and viability of androgen-dependent and androgen-independent prostate cancer cells. FTS downregulated Ras, inhibited signaling to Akt and reduced the levels of cell-cycle regulatory proteins including cyclin D1, p-RB, E2F-1 and cdc42 in LNCaP and PC3 cells. Consequently the anchorage-dependent and anchorage-independent growth of LNCaP and PC3 cells were inhibited. FTS also induced apoptotic cell death which was inhibited by the broad-spectrum caspases inhibitor, Boc-asp-FMK. Our study demonstrated that androgen-dependent and androgen-independent prostate cancer cells require active Ras for growth and survival. Ras inhibition by FTS results in growth arrest and cell death. FTS may be qualified as a potential agent for the treatment of prostate cancer.

Ras antagonist inhibits growth and chemosensitizes human epithelial ovarian cancer cells

The objective of this article was to determine whether human ovarian carcinoma cells (OVCAR-3) express significant amounts of Ras oncogene and active Ras-guanosine triphosphate (GTP) and, if so, whether the Ras inhibitor farnesyl thiosalicylic acid (FTS) inhibits their growth and chemosensitizes them to cisplatin. We assayed Ras and Ras-GTP in OVCAR-3 cells before and after FTS treatment. The effect of FTS on OVCAR-3 cell growth was assessed in terms of cell number. Because the OVCAR-3 cell line was derived from a patient who was refractory to cisplatin, we examined whether FTS enables cisplatin to induce death of these cells. Significant amounts of Ras and active Ras-GTP were expressed by OVCAR-3 cells and were reduced by 40% by FTS. FTS inhibited OVCAR-3 cell growth in a dose-dependent manner. When combined with cisplatin, FTS reduced the number of OVCAR-3 cells by 80%, demonstrating synergism between FTS and cisplatin. FTS, at a concentration range that allows downregulation of Ras and Ras-GTP in OVCAR-3 cells, also chemosensitizes these cells and inhibits their growth. These results suggest that ovarian carcinomas might respond well to Ras inhibition, both alone and when combined with cisplatin. The combined treatment would allow the use of smaller doses of chemotherapy, resulting in decreased cytotoxicity.

The inhibition of human mesangial cell proliferation by S-trans, trans-farnesylthiosalicylic acid

BACKGROUND

Many of the proliferative cytokines implicated in human mesangial cell (HMC) proliferation signal through the superfamily of Ras GTPases. The Ras antagonist, S-trans, trans- farnesylthiosalicylic acid (FTS), was used to investigate the effects of the inhibition of Ras signaling on HMC proliferation.

METHODS

Ras expression and membrane localization, MAPK, and Akt activation were analyzed by Western blotting. Ras activation was determined with a pull-down assay using the Ras-binding domain of Raf. HMC growth curves were assessed using the MTS assay of viable cell number, while DNA synthesis was measured with BrdU incorporation. Hoechst 33342 staining was used to determine apoptosis.

RESULTS

FTS reduced the membrane localization of Ras in both serum and platelet-derived growth factor (PDGF). FTS (7.5-20 micromol/L) potently inhibited PDGF-induced HMC proliferation but had no effect on serum-induced proliferation. FTS (10-20 micromol/L) inhibited both Ras and phospho-MAPK activation by serum and PDGF. Furthermore, FTS (10-20 micromol/L) increased HMC apoptosis in the presence of PDGF but not in serum. Moreover, PDGF-stimulated activation of the survival protein Akt was inhibited by FTS. In contrast, serum-stimulated activation of Akt was unaffected by FTS.

CONCLUSION

FTS (5-20 micromol/L) inhibits PDGF-induced but not serum-induced HMC proliferation. FTS (10-20 micromol/L) also promotes HMC apoptosis in the presence of PDGF but not serum. These effects appear to be mediated by inhibitory effects on Ras-dependent signaling that occur as a result of the dislodgment of Ras from its membrane-anchorage sites by FTS. The selectivity of FTS toward PDGF-driven HMC proliferation suggests that FTS may be a valuable therapeutic in mesangioproliferative renal disease.

Ras inhibition leads to transcriptional activation of p53 and down-regulation of Mdm2: two mechanisms that cooperatively increase p53 function in colon cancer cells

Activated Ras, operating through the Raf/MEK/ERK pathway, is known to regulate transcription of both Mdm2 and its inhibitor p19ARF, resulting in opposing effects on the tumor suppressor protein p53. We show here that a decrease in Ras in SW480 cells induced either by the Ras inhibitor farnesylthiosalicylic acid (FTS) or by K-Ras antisense oligonucleotides, resulted in a similar increase in p53 protein. The increase in p53 was accompanied by an increase in p21(waf1/cip1) mRNA transcripts and protein. Consistent with the Ras/Raf/MEK/ERK-mediated control of Mdm2, treatment of SW480 cells with the Ras inhibitor FTS caused a marked (80%) decrease in Mdm2, which itself would account for the increase in p53. However, FTS also caused a 1.6-fold increase in p53 mRNA, indicative of a Ras-dependent mechanism that regulates p53 transcription. Thus, oncogenic Ras appears to attenuate p53 in SW480 cells by two independent regulatory mechanisms, the one leading to increased Mdm2-dependent p53 degradation and the other leading to a decrease in p53 transcription.

Human leukaemic stem cells: a novel target of therapy

Acute myeloid leukaemia (AML) is a life-threatening haematopoietic disease that is characterized by clonal growth and the accumulation of myelopoietic progenitor cells. Although AML cells only have a limited potential to undergo differentiation and maturation, each AML clone is organized in a hierarchical manner similar to normal haematopoiesis. Recent data have shown that each AML clone consists of leukaemic stem cells and their progeny, and that AML stem cells differ from more mature cells in several aspects, including survival and target antigen profiles. Most importantly, AML stem cells, but not their progeny, have the capacity to repopulate haematopoietic tissues with leukaemias in NOD/SCID mice. Furthermore, AML stem cells are thought to be responsible for the infinite growth of leukaemias in patients with AML. The phenotypic properties of AML stem cells have also been described. In most cases, these cells are detectable within the CD34+, CD38-, Lin-, CD123+ subpopulation of AML cells. Because of their AML-initiating and -renewing capacity and their unique phenotype, which includes several molecular targets of drug therapy, AML stem cells have recently been proposed as novel important target cell populations in the context of curative therapies. The present article gives an overview of our knowledge about AML stem cells, their phenotype, and their role as a 'therapy-target' in new concepts to treat and to cure patients with AML.

Treatment of thioacetamide-induced liver cirrhosis by the Ras antagonist, farnesylthiosalicylic acid

BACKGROUND/AIMS

Several studies have indicated increased expression of the Ras protooncogenes in liver cirrhosis. In a previous study in rats, we have shown that a synthetic Ras antagonist, S-farnesylthiosalicylic acid (FTS), could inhibit the development of liver cirrhosis. The aim of the current study was to examine whether FTS will accelerate the resolution of liver cirrhosis induced in rats by thioacetamide.

METHODS

Cirrhosis was induced in male Wistar rats by intraperitoneal (i.p.) administration of thioacetamide (200 mg/kg twice weekly for 12 weeks). In the treated group, the Ras antagonist FTS (5 mg/kg, i.p./3 times/week) was administered for 8 weeks after liver cirrhosis has already been established. Control cirrhotic rats received PBS injections for 8 weeks.

RESULTS

Rats treated with FTS for 8 weeks had lower histopathologic score of fibrosis (P = 0.01), lower hepatic hydroxyproline levels (P = 0.0002) and lower spleen weight (P = 0.02) than the cirrhotic rats treated with PBS. Following FTS treatment, the MMP-2 and MMP-9-induced collagenolytic activity and TIMP-2 expression, were increased in FTS-compared to PBS-treated rats. TUNEL assay of liver sections performed 8 weeks after thioacetamide withdrawal showed increased apoptotic figures in both groups (P = NS).

CONCLUSIONS

These results indicate that the Ras antagonist FTS accelerates the regression of experimentally-induced hepatic cirrhosis. The mechanism may involve increased collagenolytic activity.

Terpenes arrest parasite development and inhibit biosynthesis of isoprenoids in Plasmodium falciparum

Development of new drugs is one of the strategies for malaria control. The biosynthesis of several isoprenoids in Plasmodium falciparum was recently described. Interestingly, some intermediates and final products biosynthesized by this pathway in mammals differ from those biosynthesized in P. falciparum. These facts prompted us to evaluate various terpenes, molecules with a similar chemical structure to the intermediates of the isoprenoids pathway, as potential antimalarial drugs. Different terpenes and S-farnesylthiosalicylic acid were tested on cultures of the intraerythrocytic stages of P. falciparum, and the 50% inhibitory concentrations for each one were found: farnesol, 64 microM; nerolidol, 760 nM; limonene, 1.22 mM; linalool, 0.28 mM; and S-farnesylthiosalicylic acid, 14 microM. All the terpenes tested inhibited dolichol biosynthesis in the trophozoite and schizont stages when [1-(n)-(3)H]farnesyl pyrophosphate triammonium salt ([(3)H]FPP) was used as precursor. Farnesol, nerolidol, and linalool showed stronger inhibitory activity on the biosynthesis of the isoprenic side chain of the benzoquinone ring of ubiquinones in the schizont stage. Treatment of schizont stages with S-farnesylthiosalicylic acid led to a decrease in intensity of the band corresponding a p21(ras) protein. The inhibitory effect of terpenes and S-farnesylthiosalicylic acid on the biosynthesis of both dolichol and the isoprenic side chain of ubiquinones and the isoprenylation of proteins in the intraerythrocytic stages of P. falciparum appears to be specific, because overall protein biosynthesis was not affected. Combinations of some terpenes or S-farnesylthiosalicylic acid tested in this work with other antimalarial drugs, like fosmidomycin, could be a new strategy for the treatment of malaria.