Phenylacetate inhibits isoprenoid biosynthesis and suppresses growth of human pancreatic carcinoma

Evaluation of α-hydroxycinnamic acids as pyruvate carboxylase inhibitors

Through a structure-based drug design project (SBDD), potent small molecule inhibitors of pyruvate carboxylase (PC) have been discovered. A series of α-keto acids (7) and α-hydroxycinnamic acids (8) were prepared and evaluated for inhibition of PC in two assays. The two most potent inhibitors were 3,3'-(1,4-phenylene)bis[2-hydroxy-2-propenoic acid] (8u) and 2-hydroxy-3-(quinoline-2-yl)propenoic acid (8v) with IC₅₀ values of 3.0 ± 1.0 μM and 4.3 ± 1.5 μM respectively. Compound 8v is a competitive inhibitor with respect to pyruvate (K_i = 0.74 μM) and a mixed-type inhibitor with respect to ATP, indicating that it targets the unique carboxyltransferase (CT) domain of PC. Furthermore, compound 8v does not significantly inhibit human carbonic anhydrase II, matrix metalloproteinase-2, malate dehydrogenase or lactate dehydrogenase.

Randomized phase II study of 5-fluorouracil hepatic arterial infusion with or without antineoplastons as an adjuvant therapy after hepatectomy for liver metastases from colorectal cancer

Background

Antineoplastons are naturally occurring peptides and amino acid derivatives found in human blood and urine. Antineoplaston A10 and AS2-1 reportedly control neoplastic growth and do not significantly inhibit normal cell growth. Antineoplastons contain 3-phenylacetylamino-2, 6-piperidinedione (A10), phenylacetylglutamine plus phenylacetylisoglutamine (A10-I), and phenylacetylglutamine plus phenylacetate (AS2-1). This open label, non- blinded randomized phase II study compared the efficacy of hepatic arterial infusion (HAI) with 5-fluorouracil,with or without antineoplastons as a postoperative therapy for colorectal metastasis to the liver.

Methods

Sixty-five patients with histologically confirmed metastatic colon adenocarcinoma in liver, who had undergone hepatectomy, and/or thermal ablation for liver metastases were enrolled between 1998- 2004 in Kurume University Hospital. Patients were randomly assigned to receive systemic antineoplastons (A10-I infusion followed by per-oral AS2-1) plus HAI (AN arm) or HAI alone (control arm) based on the number of metastases and presence/ absence of extra-hepatic metastasis at the time of surgery. Primary endpoint was cancer-specific survival (CSS); secondary endpoints were relapse-free survival (RFS), status and extent of recurrence, salvage surgery (rate) and toxicity.

Findings

Overall survival was not statistically improved (p=0.105) in the AN arm (n=32). RFS was not significant (p=0.343). Nevertheless, the CSS rate was significantly higher in the AN arm versus the control arm (n=33) with a median survival time 67 months (95%CI 43-not calculated) versus 39 months (95%CI 28-47) (p=0.037) and 5 year CSS rate 60% versus 32% respectively. Cancer recurred more often in a single organ than in multiple organs in the AN arm versus the control arm. The limited extent of recurrent tumours in the AN arm meant more patients remained eligible for salvage surgery. Major adverse effects of antineoplastons were fullness of the stomach and phlebitis. No serious toxicity, including bone marrow suppression, liver or renal dysfunction, were found in the AN arm.

Interpretation

Antineoplastons (A10 Injection and AS2-1) might be useful as adjunctive therapy in addition to HAI after hepatectomy in colorectal metastases to the liver.

Trial registration information

ClinicalTrials.gov UMIN000012099

HDAC inhibitor SAHA normalizes the levels of VLCFAs in human skin fibroblasts from X-ALD patients and downregulates the expression of proinflammatory cytokines in Abcd1/2-silenced mouse astrocytes

X-adrenoleukodystrophy (X-ALD) is a peroxisomal metabolic disorder caused by mutations in the ABCD1 gene encoding the peroxisomal ABC transporter adrenoleukodystrophy protein (ALDP). The consistent metabolic abnormality in all forms of X-ALD is an inherited defect in the peroxisomal β-oxidation of very long chain FAs (VLCFAs >C22:0) and the resultant pathognomic accumulation of VLCFA. The accumulation of VLCFA leads to a neuroinflammatory disease process associated with demyelination of the cerebral white matter. The present study underlines the importance of a potent histone deacetylase (HDAC) inhibitor, suberoylanilide hydroxamic acid (SAHA) in inducing the expression of ABCD2 [adrenoleukodystrophy-related protein (ALDRP)], and normalizing the peroxisomal β-oxidation, as well as the saturated and monounsaturated VLCFAs in cultured human skin fibroblasts of X-ALD patients. The expression of ELOVL1, the single elongase catalyzing the synthesis of both saturated VLCFA (C26:0) and monounsaturated VLCFA (C26:1), was also reduced by SAHA treatment. In addition, using Abcd1/Abcd2-silenced mouse primary astrocytes, we also examined the effects of SAHA in VLCFA-induced inflammatory response. SAHA treatment decreased the inflammatory response as expression of inducible nitric oxide synthase, inflammatory cytokine, and activation of NF-κB in Abcd1/Abcd2-silenced mouse primary astrocytes was reduced. These observations indicate that SAHA corrects both the metabolic disease of VLCFA as well as secondary inflammatory disease; therefore, it may be an ideal drug candidate to be tested for X-ALD therapy in humans.

d-δ-Tocotrienol-mediated suppression of the proliferation of human PANC-1, MIA PaCa-2, and BxPC-3 pancreatic carcinoma cells

OBJECTIVE

The rate-limiting activity of the mevalonate pathway, 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase, provides intermediates essential for growth. Competitive inhibitors of HMG CoA reductase, such as the statins, and down-regulators of reductase, such as the tocotrienols, suppress tumor growth. We evaluated the impact of d-delta-tocotrienol, the most potent vitamin E isomer, on human MIA PaCa-2 and PANC-1 pancreatic carcinoma cells and BxPC-3 pancreatic ductal adenocarcinoma cells.

METHODS

Cell proliferation was measured by using CellTiter 96 Aqueous One Solution (Promega, Madison, Wis). Cell cycle distribution was determined by flow cytometry. Apoptosis was evaluated by Annexin V staining and fluorescence microscopy after dual staining with acridine orange and ethidium bromide.

RESULTS

d-delta-Tocotrienol induced concentration-dependent suppression of cell proliferation with 50% inhibitory concentrations of 28 (6) micromol/L (MIA PaCa-2), 35 (7) micromol/L (PANC-1), and 35 (8) microL (BxPC-3), respectively. These effects are attributable to cell cycle arrest at the G1 phase and apoptosis. Mevalonate attenuated d-delta-tocotrienol-mediated growth inhibition. A physiologically attainable blend of d-delta-tocotrienol and lovastatin synergistically suppressed the proliferation of MIA PaCa-2 cells.

CONCLUSIONS

Suppression of mevalonate pathway activities, be it by modulators of HMG CoA reductase (statins, tocotrienols, and farnesol), farnesyl transferase (farnesyl transferase inhibitors), and/or mevalonate pyrophosphate decarboxylase (phenylacetate) activity, may have a potential in pancreatic cancer chemotherapy.

Multilevel modulation of the mevalonate and protein-prenylation circuitries as a novel strategy for anticancer therapy

The important role of the mevalonate and protein-prenylation circuitries in the process of carcinogenesis is increasingly being recognized. Accordingly, several enzymes within these pathways have been pharmacologically targeted for anticancer drug development. Despite promising activity in a plethora of preclinical models, clinical evaluation of these agents as monotherapy against various malignancies has been disappointing. Appropriate combinations of inhibitors of isoprenoid biosynthesis, inhibitors of prenylation and postprenylation modifications might be a more clinically effective strategy for anticancer therapy.

Modified fatty acids and their possible therapeutic targets in malignant diseases

Fatty acids and other lipids have multiple roles in the cell, functioning as structural components, participating in intracellular signalling and serving as metabolic fuel. Various compounds that influence cellular lipid metabolism can reduce the growth of malignant cells, and dietary as well as pharmacological strategies for modulating lipid metabolism have therefore been suggested as possible approaches for cancer prevention and treatment. By chemically modifying fatty acids (e.g., butyrates, retinoids), new potential anticancer agents have been produced that possess increased metabolic stability and more specific and potent biological activity compared to the natural fatty acids. Possible therapeutic targets for such modified fatty acids include: i) Histone deacetylase; ii) nuclear hormone receptors (retinoid receptors), peroxisome proliferator-activated receptors; iii) cyclooxygenase-2; iv) intracellular signalling involving protein farnesylation and Ras activation; and v) various mitochondrial functions. Although several fatty acid derivatives have been thoroughly investigated in experimental models, clinical data on toxicity and pharmacological interactions are not available for the majority of these agents. However, several promising novel compounds are now being evaluated in preclinical and early clinical studies, and future research will hopefully reveal new formulations and therapy schedules that will improve the outcome of patients with malignant disorders.

Histone deacetylase inhibitors in clinical development

In addition to a variety of other novel agents, interest in histone deacetylase inhibitors (HDACIs) as antineoplastic drugs has recently accelerated and increasing numbers of these compounds have entered clinical trials in humans. HDACIs represent a prototype of molecularly targeted agents that perturb signal transduction, cell cycle-regulatory and survival-related pathways. Newer generation HDACIs have been introduced into the clinical arena that are considerably more potent on a molar basis than their predecessors and are beginning to show early evidence of activity, particularly in hematopoietic malignancies. In addition, there is an increasing appreciation of the fact that HDACIs may act through mechanisms other than induction of histone acetylation and, as in the case of other molecularly-targeted agents, it is conceivable that the ultimate role of HDACIs in cancer therapy will be as modulators of apoptosis induced by other cytotoxic agents. One particularly promising strategy involves attempts to combine HDACIs with other novel agents to promote tumour cell differentiation or apoptosis. The present review focuses on recent insights into the mechanisms by which HDACIs exert their anticancer effects, either alone or in combination with other compounds, as well as attempts to translate these findings into the clinic.

Multisite inhibition by phenylacetate of PC-3 cell growth

Phenylacetate (PA) is a reversible inhibitor of tumor cell growth and an inhibitor of mevalonate pyrophosphate decarboxylase (MPD). We hypothesized that MPD inhibition should lower rates of protein accumulation and accretion of cell number in all cell lines regardless of tumorigenic status or origin of the cell lines. PA treatment inhibited growth of MCF-7, NIH-3T3, Detroit 551, UT-2, NCTC-929, COS-1 and PC-3 cell lines. NCTC-929 cells lack cadherins and Cos-1 cells are deficient in PPARalpha and PPARgamma, proteins suggested to be central to the action of PA. Oxidative metabolism was not impeded by PA treatment. One-dimensional and two-dimensional FACS analysis of BrdU incorporation failed to demonstrate a redistribution of nuclei in the cell cycle or that the rate of cells entering S phase had changed. Time-lapse photo-microscopy studies reveal a process that left condensed nuclei with little or no cytoplasm. However, negative TUNEL assay results and failure to block cell loss with z-VAD-fmk suggest this type of cell death is not typical apoptosis, but cell death is responsible for the lower rates of cell and protein accumulation. Supplementation studies with mevalonate pathway intermediates during inhibition of the mevalonate pathway of cholesterol biosynthesis by lovastatin confirmed MPD as a site of PA inhibition of growth, but in the presence of lovastatin with or without farnesyl pyrophosphate plus geranylgeranyl pyrophosphate, additive inhibition by PA revealed additional site(s). The existence of site(s) in addition to MPD suggests effective PA-based agents might be developed that would not inhibit MPD.

Phenylacetate induces growth inhibition and apoptosis of human osteosarcoma cells

PURPOSE

Phenylacetate has potent antiproliferative effects in many malignant tumors. However, the exact mechanism as to how phenylacetate induces cell growth arrest remains unclear and very little is known about its effects on human osteosarcoma cells. In this study, we investigated whether phenylacetate is effective against two osteosarcoma cell lines (HOS and U-2 OS) in vitro.

MATERIALS AND METHODS

The viability of phenylacetate-treated cell lines was assessed by trypan blue exclusion assay, and the cell cycle distribution was measured by flow cytometry. To measure cell apoptosis, poly (ADP-ribose) polymerase cleavage assay and flow cytometry were employed. The expressions of cell cycle-regulatory proteins and the apoptosis-related genes were evaluated by western blot analysis.

RESULTS

Phenylacetate was found to inhibit the growth of osteosarcoma cells, induce cell cycle arrest in the G1 phase, and induce apoptosis. A significant decrease in Bcl-2 expression and a mild up-regulation of Bax were also observed in both phenylacetate-treated cell lines. Reduced phosphorylation of the pRb and the increased expression of p21(Cip1) were observed subsequent to treatment with phenylacetate.

CONCLUSION

These findings support the idea that phenylacetate may be an effective chemotherapeutic agent to be employed in the future against osteosarcoma, because phenylacetate acts to inhibit the growth of osteosarcoma cells through cell cycle arrest and apoptosis.

In vitro toxicity of bisphosphonates on human neuroblastoma cell lines

Neuroblastoma is the commonest extracranial solid tumor of childhood and frequently metastasizes to the bone. Bisphosphonates are standard treatment of osteolytic lesions by bone metastasis. Since recent studies suggested direct antitumor effects of bisphosphonates, we screened the toxicity of different bisphosphonates on neuroblastoma cell lines. The nitrogen-containing bisphosphonate pamidronate was significantly more toxic on a panel of eight neuroblastoma cell lines than the non-nitrogen-containing bisphosphonates, clodronate and tiludronate. After 72 h, GI50 concentrations (inhibiting cell growth by 50% compared to untreated controls) for pamidronate ranged from 12.8 to >500 microM. CHLA-90 and SH-SY5Y were the most sensitive cell lines. In CHLA-90, zoledronate was the most cytotoxic bisphosphonate, followed by alendronate, pamidronate and ibandronate. In SH-SY5Y, alendronate was the most cytotoxic bisphosphonate, followed by ibandronate, pamidronate and zoledronate. The GI50 values after 72 h were 34.1 (SH-SY5Y) and 3.97 microM (CHLA-90) for zoledronate, and 22.4 (SH-SY5Y) and 9.55 microM (CHLA-90) for alendronate. Neuroblastoma cells treated with bisphosphonates showed signs of differentiation and finally underwent apoptosis. The observed GI50 concentrations suggest that local nitrogen-containing bisphosphonate concentrations at the bone interface can directly target neuroblastoma cell penetration into the bone matrix. In summary, these observations warrant the investigation of adjuvant bisphosphonate treatment in controlled clinical trials.

Studies of the isoprenoid-mediated inhibition of mevalonate synthesis applied to cancer chemotherapy and chemoprevention

Pools of farnesyl diphosphate and other phosphorylated products of the mevalonate pathway are essential to the post-translational processing and physiological function of small G proteins, nuclear lamins, and growth factor receptors. Inhibitors of enzyme activities providing those pools, namely, 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase and mevalonic acid-pyrophosphate decarboxylase, and of activities requiring substrates from the pools, the prenyl protein transferases, have potential for development as novel chemotherapeutic agents. Their potentials as suggested by the clinical responses recorded in Phase I and II investigations of inhibitors of HMG CoA reductase (the statins), of mevalonic acid-pyrophosphate decarboxylase (sodium phenylacetate and sodium phenylbutyrate), and of farnesyl protein transferase (R115777, SCH66336, BMS-214662, Tipifarnib, L-778,123, and, prematurely, perillyl alcohol) are dimmed by dose-limiting toxicities. These nondiscriminant growth-suppressive agents induce G1 arrest and initiate apoptosis and differentiation, effects attributed to modulation of cell signaling pathways either by modulating gene expression, suppressing the post-translational processing of signaling proteins and growth factor receptors, or altering diacylglycerol signaling. Diverse isoprenoids and the HMG CoA reductase inhibitor, lovastatin, modulate cell growth, induce cell cycle arrest, initiate apoptosis, and suppress cellular signaling activities. Perillyl alcohol, the isoprenoid of greatest clinical interest, initially was considered to inhibit farnesyl protein transferase; follow-up studies revealed that perillyl alcohol suppresses the synthesis of small G proteins and HMG CoA reductase. In sterologenic tissues, sterol feedback control, mediated by sterol regulatory element binding proteins (SREBPs) 1a and 2, exerts the primary regulation on HMG CoA reductase activity at the transcriptional level. Secondary regulation, a nonsterol isoprenoid-mediated fine-tuning of reductase activity, occurs at the levels of reductase translation and degradation. HMG CoA reductase activity in tumors is elevated and resistant to sterol feedback regulation, possibly as a consequence of aberrant SREBP activities. Nonetheless, tumor reductase remains sensitive to isoprenoid-mediated post-transcriptional downregulation. Farnesol, an acyclic sesquiterpene, and farnesyl homologs, gamma-tocotrienol and various farnesyl derivatives, inhibit reductase synthesis and accelerate reductase degradation. Cyclic monoterpenes, d-limonene, menthol and perillyl alcohol and beta-ionone, a carotenoid fragment, lower reductase mass; perillyl alcohol and d-limonene lower reductase mass by modulating translational efficiency. The elevated reductase expression and greater demand for nonsterol products to maintain growth amplify the susceptibility of tumor reductase to isoprenoids, therein rendering tumor cells more responsive than normal cells to isoprenoid-mediated growth suppression. Blends of lovastatin, a potent nondiscriminant inhibitor of HMG CoA reductase, and gamma-tocotrienol, a potent isoprenoid shown to post-transcription-ally attenuate reductase activity with specificity for tumors, synergistically affect the growth of human DU145 and LNCaP prostate carcinoma cells and pending extensive preclinical evaluation, potentially offer a novel chemotherapeutic strategy free of the dose-limiting toxicity associated with high-dose lovastatin and other nondiscriminant mevalonate pathway inhibitors.

Complementary and alternative therapies for cancer

Many cancer patients use therapies promoted as literal alternatives to conventional medical care. Such "alternative" modalities are unproven or were studied and found worthless. These can be harmful. An even greater proportion of cancer patients uses "complementary" therapies along with mainstream cancer treatment. Most are helpful adjunctive approaches that control symptoms and enhance quality of life. This review describes alternative as well as complementary therapies commonly used today by cancer patients. Herbal remedies also are discussed. Evidence regarding the efficacy and safety of complementary/alternative medicine (CAM) is reviewed, and implications for oncologists are discussed. To encourage open communication of CAM use by patients, oncologists should be knowledgeable about the most popular remedies and know where to find reliable information for themselves and for their patients.

Osteoblasts produce soluble factors that induce a gene expression pattern in non-metastatic prostate cancer cells, similar to that found in bone metastatic prostate cancer cells

BACKGROUND

Progressive prostate cancer typically metastasizes to bone where prostate cancer cells gain an osteoblast-like phenotype and induce osteoblastic metastases through unknown mechanisms. To investigate the biology of prostate cancer skeletal metastases, we compared gene expression between the non-metastatic LNCaP cell line and its derivative cell line C4-2B that metastasizes to bone.

METHODS

Total RNA from LNCaP and C4-2B cell lines was isolated and used to probe membrane-based gene arrays (Comparison 1). Additionally, LNCaP cells were incubated in the absence or presence of conditioned media (CM) from a human osteoblast-like cell line (HOBIT) and total RNA from these cells was used to probe gene arrays (Comparison 2). Differential expression of genes was confirmed by RT-PCR.

RESULTS

Of the 1,176 genes screened, 35 were differentially expressed between LNCaP and C4-2B cells (Comparison 1). HOBIT-CM induced differential expression of 30 genes in LNCaP cells (Comparison 2). Interestingly, 19 genes that were differentially expressed in C4-2B vs. LNCaP also displayed a similar expression pattern in LNCaPs grown in HOBIT-CM. These genes are primarily involved in motility, metabolism, signal transduction, tumorigenesis, and apoptosis.

CONCLUSIONS

These results suggest that osteoblasts produce soluble factors that contribute to the progression of prostate cancer skeletal metastases, including their transition to an osteoblast-like phenotype. Additionally, these data provide targets to explore for further investigations towards defining the biology of skeletal metastases.

Exposure to a deuterated analogue of phenylbutyrate retards S-phase progression in HT-29 colon cancer cells

Differentiation agents that induce neoplastic cells to regain a normal phenotype and/or cause growth arrest without significantly affecting normal cells represent an attractive option for cancer treatment. Analogues of short chain fatty acids, such as phenylbutyrate (PB), have been studied as clinically relevant agents. In an attempt to improve its pharmacokinetic profile, structural modifications of PB and other fatty acids have been studied. We hypothesize that strategic isotopic modification of PB would result in a longer half-life and thus translate into a more potent differentiation agent for clinical use. Using a colon cancer model, we demonstrated that 2,2,3,3-tetradeuterated PB (D4PB) significantly increased induction of apoptosis and inhibition of cell proliferation as compared with PB and butyrate. Difference in potency could not be explained by the effect of D4PB on the expression of specific regulatory proteins of the apoptotic cascade or from the inhibitory effect of D4PB on histone deacetylase activity. Interestingly, exposure of HT-29 colon cancer cells to D4PB resulted in a slowing of S transit, in contrast to butyrate and PB, which induced a G2/M cell cycle block. This difference in cell cycle effect may explain the differences seen in the potency of the phenotypic changes seen with treatment with D4PB. Further studies are needed to elucidate the mechanisms underlying effects of D4PB on the cell cycle.

Investigations into tumor accumulation and peroxisome proliferator activated receptor binding by F-18 and C-11 fatty acids

[11C]Acetate, a myocardial PET imaging agent for analysis of oxidative metabolism, has potential use in tumor imaging. Aromatic fatty acids display antitumor effects with phenylacetate currently in clinical trial. Tumor differentiation and cytostasis resulting from phenylacetate treatment may involve the peroxisome proliferator-activated receptor alpha (PPARalpha). To examine whether aromatic fatty acids are potential imaging agents for PPARalpha or tumors in general, [11C]phenylacetic acid (PAA) and [18F]fluorophenyl-acetic acid (FPAA) were synthesized and evaluated in EMT-6 tumor bearing mice and 9L-Glioma tumor bearing rats and compared to [11C]acetate. [11C]Acetate showed better tumor accumulation than PAA or FPAA. The aromatic fatty acids did not directly bind PPARalpha as confirmed by a biodistribution study of PAA in PPARalpha -/- mice.

Growth inhibition of human melanoma tumor cells by the combination of sodium phenylacetate (NaPA) and substituted dextrans and one NaPA-dextran conjugate

We have studied the cytostatic effects of sodium phenylacetate (NaPA) in association with several substituted dextrans on human tumor melanoma 1205LU cells. We show that NaPA alone inhibits the growth of these cells (IC50 = 3.9 mM) while a weak inhibitory effect appears at a concentration of 37 microM (10 microg/ml) for a dextran methyl carboxylate benzylamide (LS17-DMCB). The precursors of LS17-DMCB [T40 Dextran and carboxymethyl dextran (LS17-DMC)] did not affect the growth of 1205LU cells. To potentiate the inhibitory activity of NaPA at low concentrations (below 5.6 mM), we have tested NaPA and LS17-DMCB in physical mixture (association) or linked together covalently (this conjugate is termed 'LS17-NaPaC'). We have observed an increase of the 1205LU cell growth inhibition effect with NaPA in association (IC50 1.8 mM). For a concentration of 5 mM of NaPA (free in the case of association or linked in the case of conjugate), the association with dextran derivative exhibits a 4.6-fold higher efficacy than with NaPA alone (9 versus 41% surviving fraction), while the conjugate is 1.3-fold smaller (52% growth inhibition). By performing isobologram analysis of the IC50 data, we have shown a synergistic effect for a particular molar ratio of NaPA and LS17-DMCB (NaPA:LS17-DMCB = 0.35).

Tributyrin, an oral butyrate analogue, induces apoptosis through the activation of caspase-3

The purpose of this study was to investigate the anti-proliferative and pro-apoptotic effects of the butyrate analogues, tributyrin (TB) and phenylbutyrate (PB), in a colon cancer model. We demonstrate that HT-29 colon cancer cells exposed to PB and TB result in growth inhibition associated with an induction of apoptosis mediated through the activation of caspase-3 activity. A block in the G1/S cell cycle traverse associated with a decrease in CDK2 (cyclin dependent kinase) protein levels and retinoblastoma protein hypophosphorylation was also noted after PB and TB exposure. Importantly, TB proved to be the most potent agent in its ability to induce these phenotypic changes, and potentially may represent a novel therapy for patients with advanced colorectal cancer.

Current prospects for controlling cancer growth with non-cytotoxic agents--nutrients, phytochemicals, herbal extracts, and available drugs

In animal or cell culture studies, the growth and spread of cancer can be slowed by many nutrients, food factors, herbal extracts, and well-tolerated, available drugs that are still rarely used in the clinical management of cancer, in part because they seem unlikely to constitute definitive therapies in themselves. However, it is reasonable to expect that mechanistically complementary combinations of these measures could have a worthwhile impact on survival times and, when used as adjuvants, could improve the cure rates achievable with standard therapies. The therapeutic options available in this regard include measures that: down-regulate serum free IGF-I; suppress the synthesis of mevalonic acid and/or certain derivatives thereof; modulate arachidonate metabolism by inhibiting 5-lipoxygenase, 12-lipoxygenase, or COX-2; antagonize the activation of AP-1 transcription factors; promote the activation of PPAR-gamma transcription factors; and that suppress angiogenesis by additional mechanisms. Many of these measures appear suitable for use in cancer prevention.

Suppression of dolichol synthesis with isoprenoids and statins may potentiate the cancer-retardant efficacy of IGF-I down-regulation

Agents that inhibit the synthesis of mevalonate or of downstream isoprenoids block the G1-S transition and induce apoptosis in many cell lines; these agents include statins, phenylacetate, and a range of cyclic and acyclic isoprenoids. This cytostatic effect is mediated primarily by decreased availability of dolichol; this deficit impedes the glycosylation of nascent IGF-I receptors, preventing their transfer to the cell surface. In most tissues as well as transformed cell lines, IGF-I activity is crucial for transition to S phase, and also prevents apoptosis. Thus, down-regulation of serum levels of free IGF-I - as may be achieved by caloric restriction, low-fat vegan diets, and various estrogen agonists/antagonists - may represent a useful strategy for preventing and controlling cancer; however, a compensatory up-regulation of tissue expression of IGF-I receptors limits the efficacy of such an approach. Concurrent use of agents that inhibit dolichol synthesis can be expected to prevent an increase in plasma membrane IGF-I receptors, thus potentiating the cancer-retardant efficacy of IGF-I down-regulation. Since dolichol and IGF-I appear to be essential for angiogenesis, these measures may also prove useful for control of pathogenic neovascularization.