Effects of 3-deazaadenosine, an inducer of HL-60 cell differentiation, on human blood cells in vitro

Low-dose methotrexate: a mainstay in the treatment of rheumatoid arthritis

Methotrexate administered weekly in low doses is a mainstay in the therapy of rheumatoid arthritis. Although originally developed as a folate antagonist for the treatment of cancer, its mechanism of action in the therapy of rheumatoid arthritis remains less clear. Several mechanisms have been proposed including inhibition of T cell proliferation via its effects on purine and pyrimidine metabolism, inhibition of transmethylation reactions required for the prevention of T cell cytotoxicity, interference with glutathione metabolism leading to alterations in recruitment of monocytes and other cells to the inflamed joint, and promotion of the release of the endogenous anti-inflammatory mediator adenosine. These mechanisms of action and the role of methotrexate in the suppression of rheumatoid arthritis are reviewed.

Cotylenin A--a plant growth regulator as a differentiation-inducing agent against myeloid leukemia

Acute myeloid leukemia (AML) is characterized by the arrest of differentiation leading to the accumulation of immature cells. This maturation arrest can be reversed by certain agents. Although differentiation therapy for patients with acute promyelocytic leukemia (APL) using all-trans retinoic acid (ATRA) has been established, the clinical response of AML patients other than those with APL to ATRA is limited. We must consider novel therapeutic drugs against other forms of AML for the development of a differentiation therapy for leukemia. Regulators that play an important role in the differentiation and development of plants or invertebrates may also affect the differentiation of human leukemia cells through a common signal transduction system, and might be clinically useful for treating AML. Cotylenin A, a plant growth regulator, is a potent and novel inducer of the monocytic differentiation of human myeloid leukemia cell lines and leukemia cells freshly isolated from AML patients.

Effects of 3-deazaadenosine on apoptosis-related gene transcripts in HL-60 cells

The effect of the transmethylation inhibitor 3-deazaadenosine on transcription levels of genes associated with apoptosis was investigated in HL-60 cells. After incubation of HL-60 cells with 100 microM 3-deazaadenosine for 45 min., a schedule known to perturb transmethylation metabolites and initiate apoptosis in these cells, a 50% decrease in c-myc and a 50% increase in bcl-2 RNA steady-state levels compared to control cells were observed. Transcription levels of c-myc continued to decrease after extended exposure to 3-deazaadenosine, while bcl-2 mRNA levels dropped to 25% and 30% below those in control cells after 1.5 hr and 3 hr, respectively. The expression levels of the bcl-2 related bax gene, showed a similar pattern as bcl-2; a 60% increase was initially measured, but after 1.5 and 3 hr, bax transcripts were 80% and 70% respectively, of those found in untreated cells. Another bcl-2 related gene, bcl-x, was previously reported to generate two transcripts in human cells. The long variant bcl-x1 acts as bcl-2, while the short form bcl-xs induces apoptosis. We were unable to detect bcl-xs transcripts in untreated and 3-deazaadenosine treated cells by the highly sensitive reverse transcriptase polymerase chain reaction method. This suggests that this gene product may not be involved in 3-deazaadenosine induced apoptosis in HL-60 cells. Bcl-x1 mRNA levels, however, slowly decreased with about 50% after 1.5 or 3 hr 3-deazaadenosine treatment. It is concluded that 3-deazaadenosine initiated apoptosis affects c-myc, bcl-2, bax and bcl-x1 mRNA levels.

Effect of adenosine analogues on the expression of matrix metalloproteinases and their inhibitors from human dermal fibroblasts

The effect of the cytostatic and antiviral adenosine analogues 3-deazaadenosine (c3Ado) and 3-deaza-(+/-)-aristeromycin (c3Ari) on human skin fibroblasts was studied. Variables examined were cell morphology, viability, DNA fragmentation, expression of matrix metalloproteinases (MMPs) and matrix metalloproteinase inhibitors (TIMPs). None of these variables were changed when cells were exposed to c3Ari concentrations ranging from 10(-5) to 10(-3) M or 10(-5) M c3Ado. However, large changes in cell morphology, viability and expression of MMPs and MMP inhibitors occurred when fibroblasts were treated with 10(-4) or 10(-3) M c3Ado. Cells rounded up, shrank in volume, some detached and viability was lost without any detectable fragmentation of DNA. These changes in morphology and viability were associated with a differentiated expression of MMPs and MMP inhibitors. A large increase in collagenase activity occurred, and depending on the concentration of the adenosine analogue and the length of treatment, this change in activity could be shown to be due to one or a combination of the following factors: an increased synthesis of the collagenase protein, a decreased production of TIMP-1 or an increased activity of the collagenase superactivator, stromelysin. In contrast to this, treatment with c3Ado resulted in a decreased gelatinase activity, which in part could be attributed to an increased production of an inhibitor that seemed to affect gelatinase but not collagenase. The cellular changes induced by c3Ado seemed to reflect some of the alteration in the metabolic machinery that appears during a drug-induced or programmed/controlled death of a dermal cell. The different effects exerted by these two adenosine analogues on dermal fibroblasts can at least in part explain why c3Ado have previously been shown to be more toxic than c3Ari in animal models.

Differential cell cycle perturbation by transmethylation inhibitors

Cell cycle distribution of HL-60 cells was studied by flow cytometry after incubation with the transmethylation inhibitors 3-deaza-(+/-)-aristeromycin (c3 Ari) and 3-deazaadenosine (c3 Ado). Cells were incubated with the drugs (25 microM) for two cell doublings in control cells (36 hr). The presence of c3 Ari caused a dose-dependent, reversible G2 + M arrest, whereas c3 Ado-treated cells accumulated in G0/G1. The G2 + M arrest was also found in NIH/3T3 cells incubated for 36 hr with 25 microM c3 Ari, but not in U937 and K562 cells. Possible mechanisms for the described effects of c3 Ari are discussed from the perspective that inhibition of S-adenosyl homocysteine hydrolase, and subsequent inhibition of transmethylation reactions, at present is the only known site of action of c3 Ari.