Inhibition of protein farnesyltransferase: a possible mechanism of tumor prevention by dehydroepiandrosterone sulfate

Physiological implications of DHEAS-induced non-classical steroid hormone signaling

In the spermatogenic cell line GC-2, dehydroepiandrosterone sulfate (DHEAS), activates the Src/Ras/c-Raf/Erk1/2/CREB(ATF-1) signaling cascade. Since DHEAS is present in the gonads, and since spermatogenesis and maturation of spermatogonia to haploid spermatozoa requires activation of Erk1/2, the triggering of these signaling events by DHEAS might have physiological relevance. In the Sertoli cell line TM4, DHEAS-induces activation of Erk1/2, CREB, and ATF-1, stimulates expression of claudin-3 and claudin-5 and augments transepithelial resistance, indicating the formation of tight junctions between adjacent Sertoli cells. Thus, by influencing the formation and dynamics of tight junctions at the blood-testis barrier, which protects germ cells from cells of the immune system, DHEAS might play a crucial role in the regulation and maintenance of male fertility. In bEnd.3 brain-derived endothelial cells, DHEAS stimulates the expression of zonula occludens-1 and claudin-3 and promotes tight junction formation between neighboring cells, which at the blood-brain barrier protects the brain from harmful factors and cells. If DHEAS supports the integrity of the blood-brain barrier also in vivo, the current findings might lead to new strategies for the prevention or treatment of neurological disorders associated with barrier defects.

Cholesterol is essential for mitosis progression and its deficiency induces polyploid cell formation

As an essential component of mammalian cell membranes, cells require cholesterol for proliferation, which is either obtained from plasma lipoproteins or synthesized intracellularly from acetyl-CoA. In addition to cholesterol, other non-sterol mevalonate derivatives are necessary for DNA synthesis, such as the phosphorylated forms of isopentane, farnesol, geranylgeraniol, and dolichol. The aim of the present study was to elucidate the role of cholesterol in mitosis. For this, human leukemia cells (HL-60) were incubated in a cholesterol-free medium and treated with SKF 104976, which inhibits cholesterol biosynthesis by blocking sterol 14alpha-demethylase, and the expression of relevant cyclins in the different phases of the cell cycle was analyzed by flow cytometry. Prolonged cholesterol starvation induced the inhibition of cytokinesis and the formation of polyploid cells, which were multinucleated and had mitotic aberrations. Supplementing the medium with cholesterol completely abolished these effects, demonstrating they were specifically due to cholesterol deficiency. This is the first evidence that cholesterol is essential for mitosis completion and that, in the absence of cholesterol, the cells fail to undergo cytokinesis, entered G1 phase at higher DNA ploidy (tetraploidy), and then progressed through S (rereplication) into G2, generating polyploid cells.

Prostate intraepithelial neoplasia in Noble rats, a potential intermediate endpoint for chemoprevention studies

In most prostate chemoprevention studies conducted with animal models, the incidence and multiplicity of tumours have been used as endpoints for efficacy. However, the latency of tumours is usually over 1 year, making these studies costly and time consuming. The main purpose of this study was to assess the utility of prostate intraepithelial neoplasia (PIN), induced in Noble rats by continuous testosterone + oestradiol (T + E) administration, as a potential intermediate endpoint biomarker of efficacy in chemoprevention studies. Noble rats at the age of 12 weeks were treated for 36 weeks with T + E given subcutaneously via Silastic capsules. The incidence and multiplicity of PIN were assessed in various prostate glands by serial sections generated at three separate tissue levels. The efficacy of dehydroepiandrosterone (DHEA) and DHEA 8354 (1000 and 2000 mg/kg diet), difluoromethylornithine (DFMO) (1000 and 2000 mg/kg diet) and oltipraz (125 and 250 mg/kg diet) to inhibit PIN was assessed in two independent sets of experiments. T + E induced multiple PIN in the dorsolateral prostate (DLP) of 80-100% of the animals. DHEA and DHEA 8354 did not affect the incidence but decreased the multiplicity of PIN in the DLP, from 3.2 +/- 1.0 in control group to 1.5 +/- 1.0 in the low-dose and to 1.6 +/- 0.6 in the high-dose group for DHEA (P<0.05 and P<0.02, respectively), and to 1.9 +/- 0.8 in the high-dose (P<0.05) DHEA 8354. Both agents did not affect PIN in anterior prostate, seminal vesicles or ventral prostate. In a second experiment, DFMO and oltipraz were found not effective in inhibiting PIN. In this study, we provide new evidence that PIN in Noble rats, induced by continuous T + E treatment, is a useful intermediate endpoint for determining the efficacy of DHEA and other potential chemopreventive agents. The hormonal pathogenesis, high multiplicity, short latency, preferential location in the DLP, similarity in morphology and biology to PIN of human prostate, and the sensitivity to agents that suppress prostate carcinogenesis, makes PIN in Noble rats a promising intermediate endpoint for chemoprevention studies.

Colorectal cancer chemoprevention--an overview of the science

The development and dissemination of sophisticated detection technologies have recently exposed the high prevalence of preinvasive colorectal neoplasia in the adult U.S. population. Although cancer screening and surveillance provide opportunities for risk stratification, they achieve risk reduction only when coupled with effective interventions. This review surveys the lead compounds for colorectal cancer prevention and the measures by which they may be prioritized for clinical testing. Clinical trials remain the rate-limiting step in agent development, and novel trial designs are needed to hasten agent identification and testing for cancer prevention. Innovative research models include the nesting of prevention end points within cancer treatment trials and within trials testing promising preventive compounds intended for nononcologic indications.