Suramin Analogues Research Articles

Breast cancer angiogenesis--new approaches to therapy via antiangiogenesis, hypoxic activated drugs, and vascular targeting.

Several groups have shown that quantitation of tumor angiogenesis by counting blood vessels in primary breast cancer gives an independent assessment of prognosis. Poor prognosis is associated with high blood vessel counts. We have shown that the rate of cell division in endothelial cells is much higher in breast tumours than in normal breast. Breast cancer cell lines and primary human breast tumours express a wide range of vascular growth factors, including VEGF, placenta growth factor, pleiotrophin, TGF beta 1, acidic and basic FGF, and platelet-derived endothelial cell growth factor. Inhibiting angiogenesis by blocking vascular growth factors would be difficult with highly specific agents, but drugs with a broader spectrum of antagonism may be effective. We have developed several suramin analogues which are less toxic than suramin in vivo but more potent in inhibiting angiogenesis, and these have been developed for Phase I. A combination of anti-angiogenesis agents with drugs activated by hypoxia may also be useful, because anti-angiogenesis alone may not kill cells, whereas activation of hypoxic drugs could synergize. New endpoints may be necessary because inhibition of new blood vessel formation may not cause tumour regression. Thus, the endpoint of stable disease and biochemical assessment of inhibition of angiogenesis may be much more important in therapeutic studies and for drug development in the future. The prognostic importance of angiogenesis suggests that this should be a major new therapeutic target.

Selective sensitivity of solid tumors to suramin in primary cultures of tumor cells from patients.

The antineoplastic activity of suramin is currently the subject of clinical trials. We therefore used the semi-automated fluorometric microculture cytotoxicity assay (FMCA) to evaluate the cytotoxicity of suramin in vitro in primary cultures of cells from patients with hematological or solid tumors. The activity patterns of some standard cytotoxic agents were included for comparison. A total of 159 samples were tested using continuous drug exposure. Suramin showed relatively high activity against solid tumors, with colorectal, adrenal and kidney carcinomas being the most sensitive, whereas hematological malignancies were more resistant. Suramin and standard drugs showed very low cross-resistance. The results indicate that suramin is differentially active against some solid tumors with comparatively little activity against hematological tumors. The study provides an experimental motive for evaluation of suramin therapy in patients with solid tumors and exploration of less toxic suramin analogues.

Suramin analogs, divalent cations and ATP gamma S as inhibitors of ecto-ATPase.

Ecto-nucleotidases are plasma membrane-bound enzymes that sequentially dephosphorylate extracellular nucleotides such as ATP. This breakdown of ATP and other nucleotides obscures the characterization and classification of P2 (nucleotide) receptors. We therefore studied suramin and several of its analogs, divalent cations and ATP gamma S for their ability to inhibit ecto-ATPase in human blood cells. Suramin itself and Ni2+ were the more potent, non-competitive inhibitors with micromolar affinity. ATP gamma S also displayed micromolar affinity and inhibited ecto-ATPase competitively. The data obtained with the divalent cations demonstrate that coordination of the phosphate chain but not the N7 of the adenine ring is required for the breakdown of ATP by ecto-ATPase. Divalent cations that coordinate both the phosphate chain and N7 inhibit ecto-ATPase in a non-competitive manner.

Suramin blocks the binding of interleukin-1 to its receptor and neutralizes IL-1 biological activities

This report demonstrates the ability of the anti-cancer drug suramin to interfere with the binding of interleukin (IL)-1 to its receptor and to inhibit IL-1-induced biological activities. In a radioreceptor cell based assay, suramin inhibits the binding of IL-1 α to several murine cell lines expressing predominantly type I and type II IL-1 receptors. Affinity cross-linking experiments using IL-1 α and EL-4.6.1 cells confirms that suramin inhibits the binding of the ligand to the kDa IL-1 type I receptor. In contrast, suramin fails to displace significantly prebound IL-1. In a cell-free system, suramin prevents the binding of IL-1 α and IL-1 β to murine and human recombinant soluble type I IL-1 receptors. For example, the IC 50 for suramin inhibiting IL-1 α and IL-1 β binding to soluble human IL-1 receptor were 204 μM and 186 μM, respectively. The suramin analogues, NF-058 and NF-103 (which bear the same number of sulfate groups as suramin), are between three-and ten-fold less active than suramin in inhibiting IL-1 binding to EL-4.6.1 cells, and to recombinant soluble IL-1 receptor. Furthermore, in a dose-dependent manner suramin prevents several IL-1 mediated biological responses, including thymocyte proliferation, PGE-2 synthesis and IL-6 production. The inhibitory effect of the drug can be significantly reversed by the addition of excess cytokine. Taken together, the results indicate that suramin is a competitive IL-1 receptor antagonist. Because IL-1 participates in a broad range of immunological and inflammatory functions, the data suggest that suramin administration may influence important activities beyond those associated strictly with tumor inhibition.

Gene therapy through signal transduction pathways and angiogenic growth factors as therapeutic targets in breast cancer.

Angiogenesis is a major new prognostic factor in breast cancer. Small vessels quantitatively assessed by staining with anti-CD31 antibodies correlate with lymph node involvement and are a better independent predictor of survival. There are many vascular growth factors, but predominant in primary tumors assessed by nuclease protection assays are vascular endothelial growth factor and platelet-derived endothelial cell growth factor. Acidic and basic fibroblast growth factor are also detectable. A common feature of these angiogenic factors is heparin binding, so novel analogues of suramin that can compete for heparin binding have been developed. These are more potent in vitro against endothelial cells and are less toxic in vivo, thereby giving a much better therapeutic ratio. Protein kinase C is also important in endothelial growth, as it is in carcinoma growth. Thus, a novel agent inhibiting this pathway, and inducing transforming growth factor-beta production has been assessed in a Phase I trial; this agent is bryostatin. It does not cause marrow suppression and has stimulatory effects of tumor necrosis factor-alpha and interleukin (IL)-6 production. High expression of epidermal growth factor (EGF) receptors and erbB-2 has been related to poor prognosis. EGF receptors are mainly regulated by transcription, as are some cases of high erbB-2 expression. Thus, a novel approach to gene therapy is being developed using direct tumor injection of cDNA, with a tumor specific promoter ligated to the IL-2 gene. This avoids many problems associated with targeting. Because IL-2 stimulation of cytotoxic T-cells will depend on appropriate antigen presentation, human lymphocyte antigen Class I expression was studied, as was the peptide transporter system RING4 (TAP1). Losses were found in 50% of cases, and in some cases only in lymph nodes but not primary cancers, thereby providing evidence for a role in suppressing metastasis. Thus, many new approaches to therapy are possible as a result of understanding growth factors and intracellular signaling pathways.

Double screening of suramin derivatives on human colon cancer cells and on neural cells provides new therapeutic agents with reduced toxicity

Suramin is a polyanionic compound currently used under evaluation for antineoplastic activity. One of the main problems encountered during clinical trials was an adverse neurotoxic effect, probably due to a direct cytotoxic effect on neural cells. Suramin is also known to trigger differentiation of human colon cancer cells, yet a chronic treatment induces a lysosomal storage disorder. The aim of this study was to evaluate suramin analogs for their effect: (i) on the lysosomal system of the human colon cancer cell clone HT29-D4; and (ii) on C6 glioma cell growth and morphology. One of the derivatives tested, NF036, induced terminal differentiation of HT29-D4 cells without any impairment of the lysosomal system. Furthermore, in contrast to suramin, NF036 did not alter C6 cell growth and morphology. We conclude that there is a relationship between the ability of a suramin derivative to induce a lysosomal storage disorder in human colon cancer cells and its neurotoxic effect. A double screening of suramin analogs on HT29-D4 and C6 cells allowed us to identify a new candidate antineoplastic drug: NF036.

Naphthalenesulphonic Acid Derivatives as Potential anti-HIV-1 Agents. Chemistry, Biology and Molecular Modelling of Their Inhibition of Reverse Transcriptase

Activity against human immunodeficiency virus (HIV) in the naphthalenesulphonic acid series is most pronounced in the disulphonic acid series. In this class of compounds, N-acyl derivatives of 4-amino-5-hydroxy-2,7-naphthalenedisulphonic acid demonstrate significant anti-HIV activity at non-toxic doses. The most potent compounds in this group of agents are bis naphthalenedisulphonic acids. A bis derivative containing a decamethylene spacer demonstrated activity against HIV-1, HIV-2 giant cell formation and reverse transcriptase (RT). This compound also demonstrated an in vitro therapeutic index (ratio of 50% cytotoxic concentration to 50% inhibitory antiviral concentration) of 10.6. Molecular modelling analyses of this agent, suramin, and several suramin analogues were undertaken to explain the potent anti-HIV-1 RT activity. These studies were carried out using the molecular decomposition/recomposition strategy, conformational searching, energy minimization and molecular dynamics (MD) simulation. The bis naphthalenedisulphonic acid derivative compound 1, having a flexible decamethylene spacer, was shown to be able to mimic the helical twist of the B-DNA backbone as a low energy conformer state.

Inhibition of Human Immunodeficiency Virus Type I Reverse Transcriptase by Suramin-related Compounds

Ninety analogues of suramin have been examined for their ability to inhibit the exogenous reverse transcriptase (RT) of human immunodeficiency virus type I (HIV-I). Of these compounds, 57 inhibited the poly(rC).oligo(dG)-dependent RT activity. Three classes of dose-response curves could be discriminated. Allocation of a compound to one class did not correspond with obvious structural features. Twenty-four substances were superior to suramin in our RT inhibition assay. The RT-inhibitory activity of these compounds did not correlate with their effect against filariae or trypanosomes. Preliminary antiviral evaluation in susceptible human T cells inoculated with HIV-I demonstrated in vitro therapeutic efficacy for some compounds with lower drug-related cellular toxicity than suramin. Certain structural features relevant for the RT-inhibitory effect of these compounds were recognized. Predictions are made for the design of more effective RT inhibitors. Such compounds will help to understand the molecular mechanism of reverse transcription and might be useful in the therapy of retroviral infections.

The solubility of calcite and aragonite in seawater at various salinities, temperatures, and one atmosphere total pressure

We have previously identified the suramin analog 4,4′,4″,4″′-(carbonylbis(imino-5,1,3-benzenetriylbis(carbonylimino)))tetrakis-benzene-1,3-disulfonic acid (NF449) as a low nanomolar potency antagonist of recombinant P2X₁ receptors. Here, we characterize, by two-electrode voltage-clamp electrophysiology, three isomeric suramin analogs designated <i>para</i>-4,4′,4″,4″″-(carbonylbis(imino-5,1,3-benzenetriylbis (carbonylimino)))tetrakis-benzenesulfonic acid (NF110), <i>meta</i>-(3,3′,3″,3″″-(carbonylbis(imino-5,1,3-benzenetriylbis (carbonylimino)))tetra-kis-benzenesulfonic acid (NF448), and <i>ortho</i>-(2,2′,2″,2″″-(carbonylbis(imino-5,1,3-benzenetriylbis (carbonylimino)))tetra-kis-benzenesulfonic acid (MK3) with respect to their potency in antagonizing rat P2X receptor-mediated inward currents in <i>Xenopus laevis</i> oocytes. <i>Meta</i>, <i>para</i>, and <i>ortho</i> refer to the position of the single sulfonic acid group relative to the amide bond linking the four symmetrically oriented benzenesulfonic acid moieties to the central, invariant suramin core. NF448, NF110, and MK3 were &gt;200-fold less potent in blocking P2X₁ receptors than NF449, from which they differ structurally only by having one instead of two sulfonic acid residues per benzene ring. Although the <i>meta</i>- and <i>ortho</i>-isomers retained P2X₁ receptor selectivity, the <i>para</i>-isomer NF110 exhibited a significantly increased activity at P2X₃ receptors (<i>K</i>_i ∼ 36 nM) and displayed the following unique selectivity profile among suramin derivatives: P2X₂₊₃ = P2X₃ &gt; P2X₁ &gt; P2X₂ &gt;&gt; P2X₄ &gt; P2X₇. The usefulness of NF110 as a P2X₃ receptor antagonist in native tissues could be demonstrated by showing that NF110 blocks αβ-methylene-ATP-induced currents in rat dorsal root ganglia neurons with similar potency as recombinant rat P2X₃ receptors. Together, these data highlight the importance of both the number and exact location of negatively charged groups for P2X subtype potency and selectivity.