Effect of ribonucleotide reductase inhibitors on the growth of human colon carcinoma HT-29 cells in culture

Synthesis and antitumor activity of 5-bromo-1-mesyluracil

Large-scale preparation of 5-bromo-1-mesyluracil (BMsU) 4 has been optimized. BMsU was synthesized by condensation of silylated 5-bromouracil and MsCl in acetonitrile or by the reaction of 5-bromouracil with MsCl in pyridine. The same product was obtained by bromination of 1-mesyluracil. The purpose of this study was to elucidate the effects of BMsU on the biosynthetic activity of tumor cell enzymes involved in DNA, RNA and protein syntheses, and in de novo and salvage pyrimidine and purine syntheses. Investigations were performed in vitro on human cervix carcinoma cells (HeLa). BMsU displayed inhibitory effects on DNA and RNA syntheses in HeLa cells after 24 h of treatment. De nova biosynthesis of pyrimidine and purine was also affected. Antitumor activity of BMsU is closely associated with its inhibitory activity on the enzymes that play an important role in the metabolism of tumor cells. In vivo antitumor activity of BMsU was also investigated. The model used in investigations was a mouse anaplastic mammary carcinoma transplanted into the thigh of the right leg of CBA mice. Significant reduction in tumor growth time was achieved with BmsU administered at a dose of 50 mg/kg.

Metabolic effects of novel N-1-sulfonylpyrimidine derivatives on human colon carcinoma cells

Novel N-1-sulfonylpyrimidine derivatives have a strong antiproliferative activity and an ability to induce apoptosis in treated tumor cells. The purpose of this study was to elucidate the effects of two N-1-sulfonylpyrimidine nucleobases on catalytic activity of tumor cells' enzymes involved in DNA and RNA synthesis, and in de novo and salvage pyrimidine and purine syntheses. Investigations were performed in vitro on colon carcinoma cells (Caco2). The biosynthetic activity of the tumor cells' enzymes was determined using sensitive radio-assays. Enzyme activity in treated cells was calculated relative to untreated control cells. Both of the investigated compounds, 1-(p-toluenesulfonyl) cytosine (TsC) and 5-bromo-1-(methanesulfonyl) uracil (BMsU) inhibited activities of specific enzymes involved in nucleic acid synthesis. BMsU strongly inhibited activities of DNA polymerase alpha (53%), thymidine kinase (68%), thymidilate synthase (43%), and ribonucleotide reductase (46%). De novo biosynthesis of pyrimidine and purine was reduced by 20%. TsC was able to inhibit RNA polymerase (37%), orotate phosphoribosyltransferase (39%), uridine kinase (44%), ribonucleotid reductase (47%), and de novo purine synthesis (61%). Antitumor activity of 1-(p-toluenesulfonyl) cytosine (TsC) and 5-bromo-1-(methanesulfonyl) uracil (BMsU) is closely associated with their inhibitory activity on enzymes that play an important role in the metabolism of tumor cells.

Structure-based rationalization of antitumor drugs mechanism of action by a MIF approach

Structural patterns for antitumor drugs, evidenced by means of a molecular interaction field (MIF) approach using grid independent descriptors (GRIND), resembled closely those of a previous independent pharmacological classification based on their antitumor mechanism of action. For topoisomerase II inhibitors, antimitotic agents and DNA antimetabolites, systematic structural patterns were evidenced by MIF and the structural features of "outliers" in these classes corresponded to peculiar pharmacological mechanisms of action supported by literature evidences. Alkylating agents and DNA/RNA antimetabolites, interacting with a large variety of targets by different molecular mechanisms, did not exhibit clustering in the structure-based MIF approach. Moreover MIFS were able to point out similarities between drugs which, in spite of apparent dramatic differences in chemical structure, exhibit the same pharmacological behaviour.

Adenosine analogs as possible differentiation-inducing agents against acute myeloid leukemia

Several adenosine analogs induce the functional and morphological differentiation of myelomonocytic leukemia cells. They can be classified into two types; i.e., those that do/do not require phosphorylation to induce the differentiation of leukemia cells. Neplanocin A, a potent S-adenosylhomocysteine hydrolase inhibitor, induces the differentiation of some leukemia cells without phosphorylation. On the other hand, deoxycoformycin (dCF), a potent adenosine deaminase inhibitor, also induces the myelomonocytic differentiation of leukemia cells when it is treated with deoxyadenosine (dAdo). This differentiation is inhibited by 5'-amino-deoxyadenosine, an inhibitor of (deoxy)adenosine kinase, suggesting that kinase-dependent phosphorylation is involved in the differentiation-inducing effect of dCF plus dAdo. Retinoids induce the differentiation of NB4 cells, a cell line derived from human promyelocytic leukemia. When used in combination with all-trans retinoic acid (ATRA), both NPA and dCF plus dAdo greatly enhance the granulocytic differentiation of NB4 cells. This enhancing effect is greatest when the cells are pretreated with NPA and then with ATRA. On the other hand, pre-exposure of NB4 cells to ATRA greatly potentiates the differentiation induced by dCF plus dAdo, while pretreatment with dCF plus dAdo before exposure to ATRA is less effective. The ATRA-induced differentiation of NB4 cells is effectively augmented by clinically applicable concentrations of these analogs. A clinical strategy that combines intermittent treatment with these analogs and a low dose of ATRA may increase the clinical response and decrease the adverse effects of ATRA.

Antiproliferative and cytotoxic effects of geldanamycin, cytochalasin E, suramin and thiacetazone in human prostate xenograft tumor histocultures

PURPOSE

We have shown that the three human prostate xenograft tumors, i.e. the androgen-dependent CWR22 tumor, and the androgen-resistant CWR22R and CWR91 tumors, are comparable to patient tumors in their expression of prostate specific antigen, multidrug resistance p-glycoprotein, p53 and Bcl-2 and in their sensitivity to doxorubicin and paclitaxel. The present study used histocultures of these xenograft tumors to evaluate the antiproliferative and cytotoxic effects of several drugs (geldanamycin, cytochalasin E and thiacetazone), which have diverse action mechanisms and have shown activity against primary cultures of human prostate cancer cells. Suramin, a clinically active compound was included for comparison. Methods. The antiproliferative effect of 96 h drug treatment was measured by inhibition of DNA precursor incorporation, and the cytotoxic or cell kill effect was measured by in situ DNA end labeling of apoptotic and necrotic cells and by reduction of live cell density.

RESULTS

The rank order of molar potency was geldanamycin > cytochalasin E > suramin > or = thiacetazone. Thiacetazone produced antiproliferation only in CWR22 tumor and had no cytotoxicity, whereas the other three drugs produced both antiproliferation and cytotoxicity in all three tumors. Geldanamycin, but not cytochalasin E and suramin, showed greater antiproliferation and cytotoxicity in tumor cells compared to normal stromal cells. The two androgen-resistant tumors were 4 to >40-fold less sensitive than the androgen-dependent tumor to drug-induced antiproliferation but were about equally or 4 to >20-fold more sensitive to drug-induced cytotoxicity. The ratios of drug concentrations that produced 50% antiproliferation to the concentrations that produced 50% cytotoxicity ranged from <0.04 to 0.3 in CWR22 tumor, but ranged from 0.3 to 2.7 in CWR22R and CWR91 tumors, indicating a shift from antiproliferation as the predominant drug effect in the androgen-dependent tumor to cytotoxicity in the androgen-resistant tumors.

CONCLUSIONS

Our results indicate (a) differential drug effects in human prostate xenograft tumors with antiproliferation and cytotoxicity as the predominant drug effect in the androgen-dependent and androgen-resistant tumors, respectively, (b) that progression of tumors from androgen-dependent state to androgen-resistant state appears to be associated with a lower sensitivity to drug-induced antiproliferation and an equal or greater sensitivity to drug-induced cytotoxicity, and (c) that geldanamycin but not thiacetazone warrants further development.

Purine enzyme profile in human colon-carcinoma cell lines and differential sensitivity to deoxycoformycin and 2'-deoxyadenosine in combination

Different cell lines, 2 from human colon carcinoma (LoVo and HT29) and 1 from Chinese hamster ovary (CHO K-I), were examined to assess the effect of deoxycoformycin (dCF), an inhibitor of adenosine deaminase (ADA), and 2'-deoxyadenosine (dAdo) on their growth. When used alone, neither dCF or dAdo were cytotoxic for the 3 cell lines, while their combination caused inhibition of cell growth, with the following sensitivity: CHO K-I > LoVo > HT29. We studied the pattern of enzymatic activities involved in the metabolism of dAdo in the 3 cell lines. The phosphorylation of dAdo by adenosine kinase appears to play a central role in the toxicity of the deoxynucleoside in combination with dCF. In fact, CHO K-I cells, which are the most sensitive, possess the highest level of this enzyme. Moreover, the cytotoxic effect was almost completely reversed in the 3 cell lines when inhibitors of adenosine kinase, such as 5'-amino-5'-deoxyadenosine and iodotubercidine, were added to the culture medium together with dCF and dAdo. In addition, baby hamster kidney (BHK) adenosine-kinase-deficient (AK-) cells were highly resistant to this treatment. Uptake inhibition of dAdo using dipyridamole also caused reversal of the toxicity. The AMP and deoxyAMP dephosphorylating activities, much lower in the CHO K-I cells, also appear to play a central role in the toxicity of dAdo when adenosine deaminase is inhibited. However, our data suggest that other factors may modulate the toxic effect, such as S-adenosyl-homocysteine-hydrolase inhibition by dAdo at high concentrations.

The lectin Griffonia simplicifolia I-A4 (GS I-A4) specifically recognizes terminal alpha-linked N-acetylgalactosaminyl groups and is cytotoxic to the human colon cancer cell lines LS174t and SW1116

The lectin GS I-A4 binds to terminal alpha-N-acetylgalactosaminyl (GalNAc) groups (which include the Tn antigen), but not to the closely related tumor-associated epitope, sialylated Tn antigen. The lectin also precipitates asialo OSM, but not its native sialylated form. Lectin histochemistry with human colonic tissues showed that GS I-A4 specifically stained specimens of colon cancer and colonic tissues from individuals with FAP; however, normal colonic tissues from patients without colonic disease were rarely stained with this lectin. Glycoconjugates bound by GS I-A4 were observed on the surface membranes of 2 human colon cancer cell lines, LS174t and SW1116, when fluorescein isothiocyanate (FITC)-conjugated GS I-A4 was used. GS I-A4 was toxic to these 2 human colon cancer cell lines in monolayer culture. A dose-response study conducted using 10-160 micrograms/ml, of GS I-A4 demonstrated significant dose-related toxicity against LS174t and SW1116 cells. At concentrations > 80 micrograms/ml, > 99% of LS174t and > 90% of SW1116 cells were killed. Four mM GalNAc specifically inhibited the cytotoxic effect of GS I-A4 (p < 0.001), whereas 4mM N-acetylglucosamine (GlcNAc) had no effect. Two other lectins that recognize terminal alpha-GalNAc residues, DBA and LBL, were significantly less cytotoxic to the colon cancer cells than GS I-A4. In the light of these findings, we speculate that GS I-A4 may have potential use as a diagnostic agent against colorectal cancer.