Concepts in Ras-directed therapy

Oligomer β-amyloid Induces Hyperactivation of Ras to Impede NMDA Receptor-Dependent Long-Term Potentiation in Hippocampal CA1 of Mice

The activity of Ras, a small GTPase protein, is increased in brains with Alzheimer’s disease. The objective of this study was to determine the influence of oligomeric Aβ_1-42 on the activation of Ras, and the involvement of the Ras hyperactivity in Aβ_1-42-induced deficits in spatial cognition and hippocampal synaptic plasticity. Herein, we show that intracerebroventricular injection of Aβ_1-42 in mice (Aβ-mice) enhanced hippocampal Ras activation and expression, while 60 min incubation of hippocampal slices in Aβ_1-42 (Aβ-slices) only elevated Ras activity. Aβ-mice showed deficits in spatial cognition and NMDA receptor (NMDAR)-dependent long-term potentiation (LTP) in hippocampal CA1, but basal synaptic transmission was enhanced. The above effects of Aβ_1-42 were corrected by the Ras inhibitor farnesylthiosalicylic acid (FTS). ERK2 phosphorylation increased, and Src phosphorylation decreased in Aβ-mice and Aβ_1-42-slices. Both were corrected by FTS. In CA1 pyramidal cells of Aβ_1-42-slices, the response of AMPA receptor and phosphorylation of GluR1 were enhanced with dependence on Ras activation rather than ERK signaling. In contrast, NMDA receptor (NMDAR) function and GluN2A/2B phosphorylation were downregulated in Aβ_1-42-slices, which was recovered by application of FTS or the Src activator ouabain, and mimicked in control slices treated with the Src inhibitor PP2. The administration of PP2 impaired the spatial cognition and LTP induction in control mice and FTS-treated Aβ-mice. The treatment of Aβ-mice with ouabain rescued Aβ-impaired spatial cognition and LTP. Overall, the results indicate that the oligomeric Aβ_1-42 hyperactivates Ras and thereby causes the downregulation of Src which impedes NMDAR-dependent LTP induction resulting in cognitive deficits.

Neuroprotective Effect of S-trans, Trans-farnesylthiosalicylic Acid via Inhibition of RAS/ERK Pathway for the Treatment of Alzheimer's Disease

Background

Alzheimer’s disease (AD), a leading cause of dementia, becomes a serious health issue for individuals and society around the world. AD is a neurodegenerative disease characterized by the deposition of amyloid-β (Aβ) peptides and neurofibrillary tangles (NFT) and the loss of large numbers of neurons. To date, there is no effective treatment for AD, and thus, to enhance neurogenesis in the AD brain may be a therapeutic strategy. RAS signaling pathway involves in synaptic plasticity and memory formation, which is overexpressed in brains with AD. This study used Aβ_1-42-injected mice (Aβ_1-42-mice) as the AD model to investigate the effects of S-trans, trans-farnesylthiosalicylic acid (FTS), a synthetic Ras inhibitor, on the impairment of neurogenesis and the spatial cognitive deficits.

Materials and methods

AD model mice were manufactured through intracerebroventricular injection of Aβ_1-42. Morris water maze (MWM) was performed to evaluate the capacity of spatial memory, and Nissl staining was applied to assess neuronal damage in the hippocampus CA1. Immunohistochemistry of 5-bromo-2-deoxyuridine (BrdU), BrdU/neuronal nuclei (NeuN), and doublecortin (DCX) were used to detect progenitor cell proliferation, maturation, and neurite growth, respectively. And the expression levels of RAS, ERK/ERK phosphorylation (p-ERK) and CREB/CREB phosphorylation (p-CREB) were detected by Western blot.

Results

The results demonstrated that FTS could prevent Aβ_1-42 to impair survival and neurite growth of newborn neurons in the hippocampal dentate gyrus (DG) in Aβ_1-42-mice. Furthermore, behavioral indexes and morphological findings showed that FTS improved the learning and spatial memory abilities of Aβ_1-42-mice. In addition, FTS could inhibit the levels of hippocampal p-ERK and p-CREB activated by Aβ, which is the underlying molecular mechanism.

Conclusion

In conclusion, these findings suggest that FTS as a RAS inhibitor could be a potential therapeutic agent for the treatment of AD.

Local cortical circuit correlates of altered EEG in the mouse model of Fragile X syndrome

Electroencephalogram (EEG) recordings in Fragile X syndrome (FXS) patients have revealed enhanced sensory responses, enhanced resting "gamma frequency" (30-100 Hz) activity, and a decreased ability for sensory stimuli to modulate cortical activity at gamma frequencies. Similar changes are observed in the FXS model mouse - the Fmr1 knockout. These alterations may become effective biomarkers for diagnosis and treatment of FXS. Therefore, it is critical to better understand what circuit properties underlie these changes. We employed Channelrhodopsin2 to optically activate local circuits in the auditory cortical region in brain slices to examine how changes in local circuit function may be related to EEG changes. We focused on layers 2/3 and 5 (L2/3 and L5). In Fmr1 knockout mice, light-driven excitation of L2/3 revealed hyperexcitability and increased gamma frequency power in both local L2/3 and L5 circuits. Moreover, there is increased synchrony in the gamma frequency band between L2/3 and L5. Hyperexcitability and increased gamma power were not observed in L5 with L5 light-driven excitation, indicating that these changes were layer-specific. A component of L2/3 network hyperexcitability is independent of ionotropic receptor mediated synaptic transmission and may be mediated by increased intrinsic excitability of L2/3 neurons. Finally, lovastatin, a candidate therapeutic compound for FXS that targets ERK signaling did not normalize changes in gamma activity. In conclusion, hyperactivity and increased gamma activity in local neocortical circuits, together with increased gamma synchrony between circuits, provide a putative substrate for EEG alterations observed in both FXS patients and the FXS mouse model.

Ras inhibitor S-trans, trans-farnesylthiosalicylic acid enhances spatial memory and hippocampal long-term potentiation via up-regulation of NMDA receptor

Statins by reducing farnesyl-pyrophosphate or farnesyl transferase inhibitors have been demonstrated to enhance spatial memory and long-term potentiation (LTP). The objective of this study was to investigate effects of the synthetic Ras inhibitor S-trans, trans-farnesylthiosalicylic acid (FTS) on spatial cognitive function in adult mice, synaptic plasticity in hippocampal CA1 regions, and NMDA receptor (NMDAr) activity of pyramidal cells. Here, we show that administering FTS (5 mg/kg, i.p.) enhanced spatial cognitive performance, as assessed via Morris water maze and Y-maze tests. Treating hippocampal slices with FTS (5 μM) for 2 h enhanced selectively NMDAr-dependent LTP without changing the synaptic properties. In comparison with the controls, the FTS-treated slices showed increases in the amplitude of NMDA-evoked currents (I_NMDA) and the phosphorylation of NMDAr GluN2A/GluN2B subunits and Src. The Src inhibitor PP2 blocked the enhancing effects of FTS on the activity and phosphorylation of NMDAr. In FTS-treated slices, basal levels of CaMKII, ERK2 and CREB phosphorylation did not differ significantly from those of controls; however, high-frequency stimulation-induced increases in CaMKII, ERK2 and CREB phosphorylation were more significant than in the controls, which were sensitive to PP2 and NMDAr antagonist MK801. Furthermore, the phosphorylation of AMPA receptor GluR1 during LTP was higher in FTS-treated slices compared with the control, which depended on Src and ERK1/2 signaling. The results indicate that the Ras inhibition by FTS can enhance NMDAr-dependent LTP by increasing Src activity to promote NMDAr GluN2A/GluN2B phosphorylation, which then leads to spatial memory potentiation.

Ras Signaling Inhibitors Attenuate Disease in Adjuvant-Induced Arthritis via Targeting Pathogenic Antigen-Specific Th17-Type Cells

The Ras family of GTPases plays an important role in signaling nodes downstream to T cell receptor and CD28 activation, potentially lowering the threshold for T-cell receptor activation by autoantigens. Somatic mutation in NRAS or KRAS may cause a rare autoimmune disorder coupled with abnormal expansion of lymphocytes. T cells from rheumatoid arthritis (RA) patients show excessive activation of Ras/MEK/ERK pathway. The small molecule farnesylthiosalicylic acid (FTS) interferes with the interaction between Ras GTPases and their prenyl-binding chaperones to inhibit proper plasma membrane localization. In the present study, we tested the therapeutic and immunomodulatory effects of FTS and its derivative 5-fluoro-FTS (F-FTS) in the rat adjuvant-induced arthritis model (AIA). We show that AIA severity was significantly reduced by oral FTS and F-FTS treatment compared to vehicle control treatment. FTS was as effective as the mainstay anti-rheumatic drug methotrexate, and combining the two drugs significantly increased efficacy compared to each drug alone. We also discovered that FTS therapy inhibited both the CFA-driven in vivo induction of Th17 and IL-17/IFN-γ producing “double positive” as well as the upregulation of serum levels of the Th17-associated cytokines IL-17A and IL-22. By gene microarray analysis of effector CD4⁺ T cells from CFA-immunized rats, re-stimulated in vitro with the mycobacterium tuberculosis heat-shock protein 65 (Bhsp65), we determined that FTS abrogated the Bhsp65-induced transcription of a large list of genes (e.g., Il17a/f, Il22, Ifng, Csf2, Lta, and Il1a). The functional enrichment bioinformatics analysis showed significant overlap with predefined gene sets related to inflammation, immune system processes and autoimmunity. In conclusion, FTS and F-FTS display broad immunomodulatory effects in AIA with inhibition of the Th17-type response to a dominant arthritogenic antigen. Hence, targeting Ras signal-transduction cascade is a potential novel therapeutic approach for RA.

Intracellular oxygen determined by respiration regulates localization of Ras and prenylated proteins

Reduction of mitochondrial DNA (mtDNA) content induces the reduction of oxidative phosphorylation and dependence on fermentative glycolysis, that is, the Warburg effect. In aggressive prostate cancer (PCa), the reduction of mtDNA reduces oxygen consumption, increases intracellular oxygen concentration, and induces constitutive activation of Ras. Many essential proteins for cell death, growth, differentiation, and development, such as Ras, require prenylation for subcellular localization and activation. Prenylation of a protein is defined as the attachment of isoprenoids to a cysteine residue at or near the C-terminus. 3-Hydroxy-3-methyl-glutaryl-coenzyme A reductase (HMGR) produces isoprenoids, and is posttranslationally regulated by oxygen. We investigated a critical role of intracellular oxygen in membrane localization of prenylated proteins. Localization of prenylated proteins (H-Ras, prelamin A/C, and Rab5a) was observed in poorly differentiated PCa (PC-3) and well-differentiated PCa (LNCaP) cells. PC-3 cells exhibited high intracellular oxygen concentration, and H-Ras, prelamin A/C, and Rab5a were localized to various membranes (Golgi and plasma membrane, nuclear membrane, and early endosomes, respectively). Remarkably, exogenous hypoxia (0.2% O₂) in PC-3 cells induced intracellular hypoxia and changed the localization of the prenylated proteins. H-Ras and Rab5a were translocated to cytosol, and prelamin A/C was in the nucleus forming an abnormal nuclear envelope. The localization was reversed by mevalonate indicating the involvement of mevalonate pathway. In contrast, in LNCaP cells, exhibiting low intracellular oxygen concentration, H-Ras and Rab5a were localized in the cytosol, and prelamin A/C was inside the nucleus forming an inadequate nuclear envelope. Exogenous hyperoxia (40% O₂) increased the intracellular oxygen concentration and induced Ras translocation from cytosol to the membrane. Prelamin A/C was translocated to the nuclear membrane and formed a proper nuclear envelope. Rab5a was translocated to the early endosomes. The specific localizations of the prenylated proteins were dependent on intracellular oxygen concentration. These results demonstrate that intracellular oxygen concentration regulates the localization and activation of prenylated proteins.

Targeting MAPK pathway in melanoma therapy

New drugs targeting the mitogen-activated protein kinase (MAPK) pathway have generated striking clinical response in melanoma therapy. From the discovery of BRAF mutation in melanoma in 2002, to the approval of first BRAF inhibitor vemurafenib for melanoma treatment by the US Food and Drug Administration in 2011, therapies targeting the MAPK pathway have been proven effective in less than a decade. The success of vemurafenib stimulated more intensive investigation of the molecular mechanisms of melanoma pathogenesis and development of new treatment strategies targeting specific molecules in MAPK pathway. Although selective BRAF inhibitors and MEK inhibitors demonstrated improved overall survival of metastatic melanoma patients, limited duration or development of resistance to BRAF inhibitors have been reported. Patients with metastatic melanoma still face very poor prognosis and lack of clarified therapies. Studies and multiple clinical trials on more potent and selective small molecule inhibitory compounds to further improve the clinical effects and overcome drug resistance are underway. In this review, we analyzed the therapeutic potentials of each member of the MAPK signaling pathway, summarized important MAPK-inhibiting drugs, and discussed the promising combination treatment targeting multiple targets in melanoma therapy, which may overcome the drawbacks of current drugs treatment.

PEG-farnesyl thiosalicylic acid telodendrimer micelles as an improved formulation for targeted delivery of paclitaxel

We have recently designed and developed a dual-functional drug carrier that is based on poly(ethylene glycol) (PEG)-derivatized farnesylthiosalicylate (FTS, a nontoxic Ras antagonist). PEG_5K-FTS₂ readily form micelles (20–30 nm) and hydrophobic drugs such as paclitaxel (PTX) could be effectively loaded into these micelles. PTX formulated in PEG_5K-FTS₂ micelles showed an antitumor activity that was more efficacious than Taxol in a syngeneic mouse model of breast cancer (4T1.2). In order to further improve our PEG-FTS micellar system, four PEG-FTS conjugates were developed that vary in the molecular weight of PEG (PEG_2K vs PEG_5K) and the molar ratio of PEG/FTS (1/2 vs 1/4) in the conjugates. These conjugates were characterized including CMC, drug loading capacity, stability, and their efficacy in delivery of anticancer drug PTX to tumor cells in vitro and in vivo. Our data showed that the conjugates with four FTS molecules were more effective than the conjugates with two molecules of FTS and that FTS conjugates with PEG_5K were more effective than the counterparts with PEG_2K in forming stable mixed micelles. PTX formulated in PEG_5K-FTS₄ micelles was the most effective formulation in inhibiting the tumor growth in vivo.

Targeted delivery of curcumin to tumors via PEG-derivatized FTS-based micellar system

Curcumin and S-trans, trans-farnesylthiosalicylic acid (FTS) are two promising anticancer agents. In this study, we demonstrated that the two agents exerted significant synergy in antitumor activity in various types of cancer cells with combination indices ranging from 0.46 to 0.98 (a value of less than unity indicates synergism). We have further shown that synergistic-targeted co-delivery of the two agents can be achieved via formulating curcumin in polyethylene glycol (PEG)-derivatized FTS-based nanomicellar system. Curcumin formulated in PEG-FTS micelles had small size of around 20 nm. The nanomicellar curcumin demonstrated enhanced cytotoxicity towards several cancer cell lines in vitro. Intravenous application of curcumin-loaded micelle (20 mg kg(-1) curcumin) led to a significantly more effective inhibition of tumor growth in a syngeneic mouse breast cancer model (4T1.2) than curcumin formulated in Cremophor/EL (P < 0.05).

Nanomicellar carriers for targeted delivery of anticancer agents

Clinical application of anticancer drugs is limited by problems such as low water solubility, lack of tissue-specificity and toxicity. Formulation development represents an important approach to these problems. Among the many delivery systems studied, polymeric micelles have gained considerable attention owing to ease in preparation, small sizes (10-100 nm), and ability to solubilize water-insoluble anticancer drugs and accumulate specifically at the tumors. This article provides a brief review of several promising micellar systems and their applications in tumor therapy. The emphasis is placed on the discussion of the authors' recent work on several nanomicellar systems that have both a delivery function and antitumor activity, named dual-function drug carriers.

PEG-farnesylthiosalicylate conjugate as a nanomicellar carrier for delivery of paclitaxel

S-trans, trans-farnesylthiosalicylic acid (FTS) is a synthetic small molecule that acts as a potent and especially nontoxic Ras antagonist. It inhibits both oncogenically activated Ras and growth factor receptor-mediated Ras activation, resulting in the inhibition of Ras-dependent tumor growth. In this work, an FTS conjugate with poly(ethylene glycol) (PEG) through a labile ester linkage, PEG5K-FTS2(L), was developed. PEG5K-FTS2 conjugate readily forms micelles in aqueous solutions with a critical micelle concentration of 0.68 μM, and hydrophobic drugs such as paclitaxel (PTX) could be effectively loaded into these particles. Both drug-free and PTX-loaded micelles were spherical in shape with a uniform size of 20-30 nm. The release of PTX from PTX-loaded PEG5K-FTS2 micelles was significantly slower than that from Taxol formulation. In vitro cytotoxicity studies with several tumor cell lines showed that PEG5K-FTS2(L) was comparable to FTS in antitumor activity. Western immunoblotting showed that total Ras levels were downregulated in several cancer cell lines treated with FTS or PEG5K-FTS2(L). The micellar formulation of PTX exhibited more in vitro cytotoxic activity against several tumor cell lines compared with free PTX, suggesting a possible synergistic effect between the carrier and the codelivered drug. The antitumor activity of the PTX loaded PEG5K-FTS2(L) micelles in a syngeneic murine breast cancer model was found to be significantly higher than that of Taxol, which may be attributed to their preferential tumor accumulation and a possible synergistic effect between PEG5K-FTS2 carrier and loaded PTX.

Lovastatin corrects excess protein synthesis and prevents epileptogenesis in a mouse model of fragile X syndrome

Many neuropsychiatric symptoms of fragile X syndrome (FXS) are believed to be a consequence of altered regulation of protein synthesis at synapses. We discovered that lovastatin, a drug that is widely prescribed for the treatment of high cholesterol, can correct excess hippocampal protein synthesis in the mouse model of FXS and can prevent one of the robust functional consequences of increased protein synthesis in FXS, epileptogenesis. These data suggest that lovastatin is potentially disease modifying and could be a viable prophylactic treatment for epileptogenesis in FXS.

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.

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.

Potential role of Ras in cerebral vasospasm after experimental subarachnoid hemorrhage in rabbits

Previous studies have demonstrated that mitogen-activated protein kinase (MAPK) is involved in the pathogenesis of cerebral vasospasm after aneurysmal subarachnoid hemorrhage (SAH). Ras, an upstream regulator of MAPK, may be activated following SAH. The aim of this study was to investigate the role of Ras in cerebral vasospasm in a rabbit model of SAH. We first investigated the time course of Ras and ERK1/2 activation in the basilar artery after SAH. Next, for the time point at which Ras was maximally activated, we assessed the effect of FTI-277 (a Ras farnesyltransferase inhibitor) on cerebral vasospasm. SAH was induced by injecting autologous blood into the cisterna magna on both day 0 and day 2. FTI-277 was injected into the cisterna magna every 24 hours, beginning 30 minutes after blood injection to the last day of the experiment. Elevated expression of Ras-GTP and phosphorylated ERK1/2 was detected in the basilar artery after SAH and expression peaked on day 3. FTI-277 administration resulted in lower Ras-GTP and phosphorylated ERK1/2 levels and markedly attenuated vasospasm in the basilar arteries relative to animals that did not receive FTI-277. Our results suggest that Ras protein is activated in the arterial wall after SAH and contributes to vasospasm development.

Approaches for prevention of restenosis

Coronary artery disease is characterized by a narrowing (stenosis) of the arteries that supply blood to the tissue of the heart. Continued restriction of blood flow manifests itself as angina and ultimately myocardial infarction (heart attack) for the patient. Heart bypass was once the only treatment for this condition, but over the years percutaneous coronary intervention (PCI) has become an increasingly attractive alternative to medical therapy and surgical revascularization for the treatment of coronary artery disease. A vascular stent is a medical device designed to serve as a temporary or permanent internal scaffold, to maintain or increase the lumen of a blood vessel. Metallic coronary stents were first introduced to prevent arterial dissections and to eliminate vessel recoil and intimal hyperplasia associated with PCI. Further advancement in the treatment of coronary artery disease is the development of drug-eluting stents that dramatically reduce the incidence of in-stent restenosis to less than 5%. Local drug delivery offers the advantages of allowing a relatively high local concentration of drug at the treatment site while minimizing systemic toxic effect. This review describes approaches for prevention of restenosis. It focuses on drugs for prevention of restenosis, bare metal stents, and drug-eluting stents. It also describes recent advances in bioresorbable stents. One of the chapters is dedicated to our novel composite bioresorbable drug-eluting fibers, designed to be used as basic elements in drug-eluting stents.

Regulation of the nucleotide state of oncogenic ras proteins by nucleoside diphosphate kinase

Oncogenic forms of the Ras GTPase exhibit defective GTP hydrolase activity and are insensitive to the stimulatory activity of GTPase activating proteins. It has been suggested that a potential therapeutic strategy to inactivate such mutant forms of Ras could involve small molecules that restore GTP hydrolase activity to mutant Ras proteins; however, thus far, such molecules have not been developed. While characterizing the biochemical properties of several commonly detected K-Ras mutants, we made the unexpected observation that an activity in crude bacterial cell extracts was capable of stimulating the conversion of the oncogenic K-RasG13D mutant from a GTP-bound, active form to a GDP-bound, inactive form. The activity was purified, and the protein, nucleoside diphosphate kinase (NDK), was identified as being responsible for the Ras regulating activity. NDK is closely related to the human metastasis suppressor, NM23, which has previously been implicated in regulating the nucleotide state of small GTPases of the Ras family. Although the physiological relevance of such regulation has been controversial, our biochemical findings in in vitro assays indicate that it may be feasible to develop a therapeutic strategy to achieve the selective biochemical inactivation of oncogenic Ras proteins.

Neuroprotective Effects of the Ras Inhibitor S-Trans-Trans-Farnesylthiosalicylic Acid, Measured by Diffusion-Weighted Imaging after Traumatic Brain Injury in Rats

Ras proteins play a role in receptor-mediated signaling pathways and are activated after traumatic brain injury. S-trans-trans-farnesylthiosalicylic acid (FTS), a synthetic Ras inhibitor, acts primarily on the active, GTP-bound form of Ras and was shown to improve neurobehavioral outcome after closed head injury (CHI) in mice. To gain a better understanding of the neuroprotective mechanism of FTS, we used diffusion-weighted imaging (DWI) in a rat model of CHI. Apparent diffusion coefficients (ADC) and transverse relaxation times (T2) were measured in injured rat brains after treatment with vehicle or FTS (5 mg/kg). Neuroprotection by FTS was also assessed in terms of the neurological severity score. One week after injury, significantly better recovery was observed in the FTS-treated rats than in the controls (p = 0.0191). T2 analysis of the magnetic resonance images revealed no differences between the two groups. In contrast, they differed significantly in ADC, particularly at 24 h post-CHI (p < 0.05): in the vehicle-treated rats ADC had decreased to approximately 26% below baseline, whereas it had increased to about 10% above baseline in the FTS-treated rats. As the magnitude of ADC reduction is strongly linked to blood perfusion deficit, these results suggest that the neuroprotective mechanism of FTS might be related to an improvement in cerebral perfusion. We propose that FTS, which is currently being tested in humans for anti-cancer indications, should also be considered as a new strategy for the management of head injury.

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.

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

Neurofibromatosis type 1 (NF1) is characterized by a high incidence of benign and malignant tumors attributed to loss of function of Nf1, which encodes neurofibromin, a tumor suppressor with Ras-GAP activity. Neurofibromin deficiency typically causes chronic activation of Ras, considered the major contributor to manifestation of NF1. Resistance to radio- and chemotherapy are typical of NF1-associated tumors, but the underlying mechanism is unknown. Here, we investigated interrelationships between neurofibromin expression, Ras activity, and sensitivity to apoptosis. Neurofibromin-deficient mouse embryonic fibroblasts (MEFs) and human NF1 tumor cells were more resistant than neurofibromin-expressing cells to apoptosis. Moreover, Nf1(-/-), Nf1(+/-), and Nf1(+/+) MEFs exhibited gene-dosage-related resistance to apoptosis. Resistance of the Nf1-deficient cells was mediated by two survival pathways: a Ras-dependent pathway, and a Ras-independent pathway promoted by the lack of an NF1-GRD-independent proapoptotic action of neurofibromin. Therefore, besides its Ras-dependent growth inhibition, neurofibromin can exert tumor suppression via a proapoptotic effect.

Nonconventional Trafficking of Ras Associated with Ras Signal Organization

Ras signaling to its downstream effectors appears to include combinations of extracellular-signal-regulated Ras activation at the plasma membrane (PM) and endomembranes, dynamic lateral segregation in the PM, and translocation of Ras from the PM to intracellular compartments. These processes are governed by the C-terminal polybasic farnesyl domain in K-Ras 4B and by the cysteine-palmitoylated C-terminal farnesyl domains in H-Ras and N-Ras. K-Ras 4B has no palmitoylated cysteines. Depalmitoylation/repalmitoylation of H-/N-Ras proteins promotes their cellular redistribution and signaling by mechanisms as yet unknown, possibly involving chaperones. Palmitoylation of H-/N-Ras also promotes their association with 'rasosomes', randomly diffusing nanoparticles that apparently provide a means by which multiple copies of activated Ras and its signal can spread rapidly. Ubiquitination of H-Ras evidently targets it to the endosomes. The polybasic farnesyl domain of K-Ras 4B was shown to act as a target for Ca++/calmodulin, which sequesters the active protein from the PM, thereby facilitating its trafficking to Golgi apparatus and early endosomes. Protein kinase C-dependent phosphorylation of S181 in K-Ras 4B was shown to provide a regulated farnesyl-electrostatic switch on K-Ras 4B, which promotes its translocation to the mitochondria. All these translocation events are characterized by nonconventional trafficking of the farnesyl-modified Ras proteins and seem to govern the selectivity and probably also the robustness of the Ras signal. In this review, we discuss the various modifications and interactions of the farnesylated C-terminus, the trafficking of Ras proteins in the PM and between the PM and the endomembranes, and the relevance of the subcellular localization of Ras for Ras function.

Spatiotemporal organization of Ras signaling: rasosomes and the galectin switch

1. Ras signaling and oncogenesis depend on the dynamic interplay of Ras with distinctive plasma membrane (PM) microdomains and various intracellular compartments. Such interaction is dictated by individual elements in the carboxy-terminal domain of the Ras proteins, including a farnesyl isoprenoid group, sequences in the hypervariable region (hvr)-linker, and palmitoyl groups in H/N-Ras isoforms. 2. The farnesyl group acts as a specific recognition unit that interacts with prenyl-binding pockets in galectin-1 (Gal-1), galectin-3 (Gal-3), and cGMP phosphodiesterase delta. This interaction appears to contribute to the prolongation of Ras signals in the PM, the determination of Ras effector usage, and perhaps also the transport of cytoplasmic Ras. Gal-1 promotes H-Ras signaling to Raf at the expense of phosphoinositide 3-kinase (PI3-K) and Ral guanine nucleotide exchange factor (RalGEF), while galectin-3 promotes K-Ras signaling to both Raf and PI3-K. 3. The hvr-linker and the palmitates of H-Ras and N-Ras determine the micro- and macro-localizations of these proteins in the PM and in the Golgi, as well as in 'rasosomes', randomly moving nanoparticles that carry palmitoylated Ras proteins and their signal through the cytoplasm.4. The dynamic compartmentalization of Ras proteins contributes to the spatial organization of Ras signaling, promotes redistribution of Ras, and provides an additional level of selectivity to the signal output of this regulatory GTPase.

Antiphospholipid antibodies, thrombin and LPS activate brain endothelial cells and Ras-dependent pathways through distinct mechanisms

BACKGROUND

The antiphospholipid syndrome (APS) commonly affects the central nervous system through mechanisms that may include small vessel pathology and activation of thrombin. Antiphospholipid antibodies (aPL) activate endothelial cells but the specific activation of brain vascular endothelial cells (BVEC) and the receptors and signaling pathways involved have not been fully characterized.

OBJECTIVE

To examine whether aPL, the inflammatory stimulant lipopolysacharide (LPS) and thrombin activate BVECs through a Ras-dependent pathway.

METHODS

Rat BVEC (G8) were grown to confluence on 24-well plates. IgG was purified from 8 APS patients on a protein G column. Phosphorylation of ERK in the BVEC was measured by immunoblot utilizing a specific antibody.

RESULTS

Significant phosphorylation of ERK was measured following exposure of the cells to LPS and thrombin and this was blocked by the Ras inhibitor farnesylthiosalicylate (FTS). aPL IgG (1:100 relative to serum) from 7/8 patients also induced phosphorylation of ERK.

CONCLUSIONS

Activation of the Ras-ERK pathway is an effect of both APS IgG and thrombin. This pathway is potentially amenable to drugs such as FTS and may serve as a therapeutic target in APS.

Inhibition of Ras attenuates the course of experimental autoimmune neuritis

EAN induced in Lewis rats by immunization with peripheral bovine myelin was treated by the Ras inhibitor farnesylthiosalicylate (FTS). Treatment from day 0 with FTS (5 mg/kg intraperitoneally twice daily) attenuated peak clinical scores (mean+/-S.E., 2.5+/-0.5 compared to 4.1+/-0.5 in saline treated controls, p=0.018, t-test) but not recovery. Treatment from day 10 with FTS attenuated peak disability (2.5+/-0.6, p=0.032 compared to saline treated controls) and improved recovery (0.84+/-0.42, untreated controls 2.4+/-0.6, p=0.028 by repeated measures ANOVA). Effects were confirmed by rotarod and nerve conduction studies. An inactive analogue, geranylthiosalicylate, had no clinical effect. Inhibition of Ras is of potential use in the treatment of inflammatory neuropathies.

Disruption of Cooperation Between Ras and MycN in Human Neuroblastoma Cells Promotes Growth Arrest

PURPOSE

Our aim was to examine whether active Ras and MycN cooperation contributes to the malignant phenotype of human neuroblastoma with amplified MycN gene, an aggressive incurable tumor.

EXPERIMENTAL DESIGN

Human neuroblastoma LAN-1 cells, in which the MycN gene is amplified, were used to examine the impact of the Ras inhibitor farnesylthiosalicylic acid on cell growth, on the levels Ras and MycN proteins, and on profiles of gene expression.

RESULTS

We show that LAN-1 cells express relatively large amounts of MycN and active Ras-GTP. Inhibition of active Ras by farnesylthiosalicylic acid led to attenuation of the Raf-MEK-ERK and phosphoinositide 3-kinase-Akt-glycogen synthase-3 (GSK-3) pathways, to reduction in cyclin D1, phospho-retinoblastoma, and E2F, and to increase in the cyclin-dependent kinase inhibitor p27 and in retinoblastoma-binding protein-1, an inhibitor of E2F transcriptional activity. Ras inhibition by farnesylthiosalicylic acid or by a dominant-negative Ras also led to complete disappearance of MycN protein from the nuclei of LAN-1 cells. This was a result of blocking of Akt inactivation of GSK-3, leading to GSK-3-dependent phosphorylation with consequent proteosomal degradation of MycN. Loss of active Ras and of MycN in LAN-1 cells was manifested in profiles of gene expression that could be expected from the loss of MycN transcriptional activity and of Ras signaling. These changes explain the farnesylthiosalicylic acid-induced inhibition of LAN-1 cell growth.

CONCLUSIONS

Active Ras is needed to block MycN degradation, promoting cooperative Ras- and MycN-dependent cell cycle progression in LAN-1 cells. Ras inhibitors are therefore likely candidates for the treatment of advanced neuroblastoma characterized by high expression of MycN.

TGF-β1-Induced Connective Tissue Growth Factor (CCN2) Expression in Human Renal Proximal Tubule Epithelial Cells Requires Ras/MEK/ERK and Smad Signalling

BACKGROUND

Connective tissue growth factor (CTGF, CCN2) plays a fundamental role in the development of tissue fibrosis by stimulating matrix deposition and mediating many of the pro-fibrotic effects of transforming growth factor (TGF)-beta. CCN2 induction by TGF-beta in renal proximal tubule epithelial cells (PTECs) is likely to play an important role in the development of tubulointerstitial fibrosis. In this study, we investigated the induction of CCN2 by TGF-beta1 and the possible mechanisms of this induction in human PTECs.

METHODS

Experiments were performed on primary and transformed (human kidney cell (HKC)-clone 8) human PTECs. Induction of CCN2 in response to TGF-beta1 was studied at the gene promoter level by reporter gene assay, mRNA by semi-quantitative RT-PCR and protein by immunoblotting. While chemical inhibitors were used to assess the role of Ras/MEK/ERK1,2 signalling, an HKC cell line over-expressing Smad7 was used to assess the role of Smad signalling in induction of CCN2 by TGF-beta1.

RESULTS

TGF-beta1 induced CCN2 promoter activity, mRNA and protein in human PTECs. TGF-beta1-dependent CCN2 promoter activity was reduced by inhibiting Ras and MEK activation. MEK inhibition also resulted in inhibition of the TGF-beta1-induced secreted CCN2 protein. There was no significant increase in CCN2 gene promoter activity or protein by TGF-beta1 in Smad7 over-expressing HKCs.

CONCLUSIONS

TGF-beta1 induces the expression of CCN2 in human PTECs. This induction is dependent on Ras/MEK/ERK and Smad signalling. Inhibiting TGF-beta induced CCN2 by targeting Smad and/or Ras/MEK/ERK1,2 signalling pathways could be of therapeutic value in renal fibrosis.

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.

Ras Inhibition in Glioblastoma Down-regulates Hypoxia-Inducible Factor-1α, Causing Glycolysis Shutdown and Cell Death

Active Ras and phosphatidylinositol-3-kinase–dependent pathways contribute to the malignant phenotype of glioblastoma multiformes (GBM). Here we show that the Ras inhibitor trans-farnesylthiosalicylic acid (FTS) exhibits profound antioncogenic effects in U87 GBM cells. FTS inhibited active Ras and attenuated Ras signaling to extracellular signal-regulated kinase, phosphatidylinositol-3-kinase, and Akt. Concomitantly, hypoxia-inducible factor 1α (HIF-1α) disappeared, expression of key glycolysis pathway enzymes and of other HIF-1α–regulated genes (including vascular endothelial growth factor and the Glut-1 glucose transporter) was down-regulated, and glycolysis was halted. This led to a dramatic reduction in ATP, resulting in a severe energy crisis. In addition, the expression of E2F-regulated genes was down-regulated in the FTS-treated cells. Consequently, U87 cell growth was arrested and the cells died. These results show that FTS is a potent down-regulator of HIF-1α and might therefore block invasiveness, survival, and angiogenesis in GBM.

The novel Ras antagonist, farnesylthiosalicylate, suppresses growth of prostate cancer in vitro

BACKGROUND

The majority of men with advanced prostate cancer (PCa) respond to androgen deprivation therapy (ADT) with objective evidence of tumor regression. However, these tumors will regrow in the presence of low-androgen levels after 12-18 months. Regrowth after ADT is associated with upregulation of growth factor (GF) mediated pathways. The compound farnesylthiosalicylate (FTS), a specific antagonist of the 21 kDa Ras protein, suppresses GF signaling and it might be a useful therapy against advanced PCa.

METHODS

We measured androgen and GF dependent growth of androgen dependent LNCaP and androgen hypersensitive CWR-R1 PCa cells in response to specific inhibitors of GF pathways, including FTS. Inhibition of GF mediated signaling and cell-cycle pathways was confirmed by Western blotting of extracts from treated cells.

RESULTS

Both LNCaP and CWR-R1 cells were dependent on GF signaling pathways for cell growth. FTS, as well as suppressing cell growth, inhibited GF signaling pathway activity and reduced the levels of E2F1, p-Rb, and p-cdc2, all GF dependent mediators of cell-cycle progression.

CONCLUSIONS

These data suggest that FTS might be a useful agent against PCa that has relapsed after ADT.

Inhibition of Intimal Thickening in the Rat Carotid Artery Injury Model by a Nontoxic Ras Inhibitor

BACKGROUND

Neointimal formation with and without previous vascular injury is common after balloon dilation and in transplant arteriosclerosis. It involves proliferation and migration of medial smooth muscle cells and inflammation, processes that are regulated by Ras proteins and their down-stream effectors. Farnesylthiosalicylate (FTS) is a Ras inhibitor that interferes with Ras membrane anchorage and affects Ras proteins in their active state. In the present study, we tested the hypothesis that systemic administration of FTS will suppress intimal thickening in the rat carotid injury model.

METHODS AND RESULTS

The effects of FTS on rat vascular smooth muscle cells (VSMC) and splenocytes proliferation were evaluated in vitro. The in vivo effects of FTS on the neointima of balloon-injured male Wistar rats, treated daily for 2 weeks with FTS (5 mg/kg weight, intraperitoneally) were evaluated by determination of Ras, Ras-GTP, and active ERK levels (3 days after injury), and by quantitative determination of the extent of intimal thickening and immunohistochemistry for Ras, iNOS, NFkB, and Ki-67 (2 weeks after injury). FTS inhibited VSMC and splenocyte proliferation as well as interferon-gamma secretion by splenocytes in a dose-dependent manner. Compared with controls, FTS treatment resulted in a strong decrease in Ras-GTP and active ERK, and it significantly reduced intimal thickening after the injury. Ras expression appeared predominantly at areas of neointima regardless of the treatment group. NFkB and iNOS-positive cell numbers were reduced in sections of FTS treated rats.

CONCLUSIONS

FTS appears to act as a potent inhibitor of intimal thickening in a model of experimental arterial injury.

The Ras inhibitor S-trans, trans-farnesylthiosalicylic acid exerts long-lasting neuroprotection in a mouse closed head injury model

Traumatic brain injury activates N-methyl-d-aspartate receptors (NMDAR) inducing activation of the Ras protein (a key regulator of cell growth, survival, and death) and its effectors. Thus, trauma-induced increase in active Ras-GTP might contribute to traumatic brain injury pathology. Based on this hypothesis, a new concept of neuroprotection is proposed, examined here by investigating the effect of the Ras inhibitor S-trans, trans-farnesylthiosalicylic acid (FTS) in a mouse model of closed head injury (CHI). Mice subjected to CHI were treated systemically 1 h later with FTS (5 mg/kg) or vehicle. After 1 h, Ras-GTP in the contused hemisphere showed a significant (3.8-fold) increase, which was strongly inhibited by FTS (82% inhibition) or by the NMDA-receptor antagonist MK-801 (53%). Both drugs also decreased active (phosphorylated) extracellular signal-regulated kinase. FTS prevented the CHI-induced reduction in NMDAR binding in cortical, striatal, and hippocampal regions, measured by [3H]-MK-801 autoradiography, and decreased lesion size by 50%. It also reduced CHI-induced neurologic deficits, indicated by the highly significant (P < 0.0001) 60% increase in extent of recovery. Thus, FTS provided long-term neuroprotection after CHI, rescuing NMDAR binding in the contused hemisphere and profoundly reducing neurologic deficits. These findings suggest that nontoxic Ras inhibitors such as FTS may qualify as neuroprotective drugs.

Farnesyl thiosalicylic acid chemosensitizes human melanoma in vivo

Malignant melanoma is well known for its poor response to a variety of chemotherapeutic agents. Testing of numerous treatment strategies has identified dacarbazine as the most active single drug; however, its response rates in various clinical settings are quite limited. Defective apoptosis in combination with oncogenic proteins (such as activated Ras) in cell proliferation pathways plays a key part in both the development and disease progression of human melanoma. Farnesyl thiosalicylic acid, a novel Ras inhibitor, dislodges Ras proteins from the cell membrane, leading to inhibition of cell transformation and tumor growth. In this study we evaluated the effect of farnesyl thiosalicylic acid treatment on established human melanoma xenografts grown in mice with severe combined immunodeficiency as well as the chemosensitizing effect of farnesyl thiosalicylic acid in combination with dacarbazine. Daily administration of 10, 20, or 40 mg per kg of farnesyl thiosalicylic acid resulted in a concentration-dependent reduction in tumor growth, with growth inhibition reaching a mean value of 45+/-7%, at the highest concentration. The combination of farnesyl thiosalicylic acid (10 mg per kg per day) and dacarbazine (80 mg per kg per day) resulted in a significant reduction of 56%+/-9%, in mean tumor growth. Analysis of toxicologic parameters (mouse weight, blood cell counts, and blood chemistry) showed an acceptable and similar toxicity profile for both the single-agent farnesyl thiosalicylic acid treatment and the combination of farnesyl thiosalicylic acid plus dacarbazine treatment. Given the observed preclinical treatment responses and the low toxicity, our results support the notion that farnesyl thiosalicylic acid in combination with dacarbazine may qualify as a rational treatment approach for human melanoma.

Targeting RAS signalling pathways in cancer therapy

The RAS proteins control signalling pathways that are key regulators of several aspects of normal cell growth and malignant transformation. They are aberrant in most human tumours due to activating mutations in the RAS genes themselves or to alterations in upstream or downstream signalling components. Rational therapies that target the RAS pathways might inhibit tumour growth, survival and spread. Several of these new therapeutic agents are showing promise in the clinic and many more are being developed.

Inhibitors of the ras oncogene as therapeutic targets

Advances in our understanding of the molecular pathways and genetic mutations that control tumor cell proliferation and metastasis present an opportunity to develop novel, mechanism-based therapeutic strategies. Ras mutations are the most frequently activated oncogenes in human tumors, with over 30% expressing ras mutations. Molecular dissection of the signaling pathway and the mechanisms of ras anchorage, post-translational modification, and downstream effector signaling of ras now under intensive investigation will help us to design additional methods for ras-directed therapy in an effort to reach an optimal treatment for human tumors that will most likely comprise a combination of modalities targeted at the different underlying genetic defects. The successes and limitations of ras-targeted therapies must be viewed in light of the increasing understanding of the complexity of the ras-signaling pathway. Only now are we beginning to discover the many functions of this integrated pathway, such as the differences between the actions of various ras isoforms that may affect our choice of therapeutic approach. Many of these Ras therapeutic targets have shown success in preclinical studies, and some have shown efficacy in clinical trials with minimal toxicities. Compounds that block ras-transforming activity without affecting normal ras function seem more attractive for the future development of ras-targeted therapy. FTIs may partially fulfill such requirements. Based on their specific, novel, and mechanism-based action; minimal toxicity; and encouraging responses in clinical trials, the development of Ras therapeutic targets as single agents or in combination with conventional chemotherapy and radiotherapy should be pursued.

Functional inhibition of Ras by S-trans,trans-farnesyl thiosalicylic acid attenuates atherosclerosis in apolipoprotein E knockout mice

BACKGROUND

Atherosclerosis is a multifactorial disorder involving inflammatory processes. These responses are associated with robust activation of signaling cascades by diverse cell surface receptors in a variety of cell types. The processes that are involved in atherosclerosis would likely require intact Ras pathways, which play a key role in the control of cell growth, differentiation, and apoptosis.

METHODS AND RESULTS

We examined whether the Ras inhibitor farnesyl thiosalicylic acid (FTS) can suppress atherogenesis in the apolipoprotein E-deficient mouse model. Mice were treated with FTS or a control regimen 3 times weekly for 6 weeks and fed a normal chow diet. Two additional groups included FTS-treated and control-treated mice that were fed a high-fat diet for 10 weeks. FTS reduced both fatty streaks and advanced lesions compared with the control treatment. Ras inhibition in vivo was evidenced by the reduced content of the active form of Ras (Ras-GTP) in aortas of FTS-treated mice. Splenocytes from the FTS-treated versus control mice exhibited reduced proliferation to oxidized LDL (OxLDL) but not to concanavalin A. IgG anti-OxLDL antibody levels were reduced in FTS-treated mice compared with controls. Whereas no effect of FTS was evident on plaque T lymphocyte and macrophage content, lesional vascular cell adhesion molecule-1 and nuclear factor-kappaB expression were considerably reduced compared with controls.

CONCLUSIONS

FTS suppressed atherosclerotic plaques in apolipoprotein E-deficient mice, providing a useful tool for research in atherosclerosis.

Galectin-1 binds oncogenic H-Ras to mediate Ras membrane anchorage and cell transformation

Ras genes, frequently mutated in human tumors, promote malignant transformation. Ras transformation requires membrane anchorage, which is promoted by Ras farnesylcysteine carboxymethylester and by a second signal. Previously we showed that the farnesylcysteine mimetic, farnesylthiosalicylic acid (FTS) disrupts Ras membrane anchorage. To understand how this disruption contributes to inhibition of cell transformation we searched for new Ras-interacting proteins and identified galectin-1, a lectin implicated in human tumors, as a selective binding partner of oncogenic H-Ras(12V). The observed size of H-Ras(12V)-galectin-1 complex, which is equal to the sum of the molecular weights of Ras and galectin-1 indicates a direct binding interaction between the two proteins. FTS disrupted H-Ras(12V)-galectin-1 interactions. Overexpression of galectin-1 increased membrane-associated Ras, Ras-GTP, and active ERK resulting in cell transformation, which was blocked by dominant negative Ras. Galectin-1 antisense RNA inhibited transformation by H-Ras(12V) and abolished membrane anchorage of green fluorescent protein (GFP)-H-Ras(12V) but not of GFP-H-Ras wild-type (wt), GFP-K-Ras(12V), or GFP-N-Ras(13V). H-Ras(12V)-galectin-1 interactions establish an essential link between two proteins associated with cell transformation and human malignancies that can be exploited to selectively target oncogenic Ras proteins.

Theoretical concepts and the emerging role of taxanes in adjuvant therapy

The proven benefits of adjuvant chemotherapy on disease-free and overall survival in breast cancer can be explained by concepts of cell kill. Interventions which result in greater log kill can be expected to produce improved clinical results. The application of log-kill concepts to human breast cancer growth, which appears to follow Gompertzian kinetics, suggests not only that the use of non-cross-resistant drugs is important, but that dose-dense schedules may have an advantage over conventional schedules of drug administration. Sequential therapy may allow dose-dense administration of cytotoxic agents and encourage the integration of new biological agents into combination regimens, particularly with the taxanes. Ongoing trials in these concepts are reviewed.

Novel compounds in the therapy of breast cancer: opportunities for integration with docetaxel

Increasingly, novel agents are being developed specifically at inhibition of growth factor receptors and events within the signal transduction pathway. These agents include the epidermal growth factor tyrosine kinase inhibitors, the farnesyl transferase inhibitors, and bcl-2 antisense oligonucleotides. Along with these new approaches to molecular targeting, it will be necessary to develop new study designs for drug evaluation. Target validation in both normal surrogate tissues and tumor tissue becomes increasingly relevant in early clinical trials. Furthermore, antitumor efficacy may no longer correlate with normal hematological or nonhematological toxicity, and it may be more appropriate in phase I trials to identify the maximum target inhibition dose rather than the maximum tolerated dose. Moreover, measures of cytoreduction, such as complete and partial response, may be less relevant than disease stabilization for some of these novel agents which have limited cytotoxic effects and would be considered cytostatic agents. Assessment of single-agent activity and the future role in conjunction with cytostatic agents represents the single most important challenge facing the clinical development of these molecular targeted therapies.

RAS inhibitors: potential for cancer therapeutics

As RAS oncoproteins play a major role in human malignancy, inhibiting RAS function is a promising approach for developing anticancer therapies. Among these approaches are agents such as farnesyltransferase inhibitors (FTIs) and the nontoxic farnesylcysteine analogue farnesylthiosalicylic acid (FTS) that dislodges all RAS isoforms from the membrane, as well as methods to restore regulation of RAS-GTP levels and to alter the interaction of RAS-GTP with downstream targets.