Ratio of 2'-deoxyadenosine-5'-triphosphate/thymidine-5'-triphosphate influences the commitment of human colon carcinoma cells to thymineless death

In colon cancers induction of a thymineless state following inhibition of thymidylate synthase (TS) by 5-fluorouracil combined with leucovorin can initiate a cytotoxic response. Using a 5-fluorouracil-leucovorin-treated human colon carcinoma cell line (GC3/cl) and a clonally derived TS- mutant, initiation events that dictate the onset of and commitment to thymineless death have been examined. Initial events related to a temporally associated decrease in dTTP and elevation in the dATP pools; no depletion of dGTP or elevation in dCTP was detected. Nucleosomal degradation of DNA commenced at 24 h in TS- and 49 h in GC3/c1, and was associated with the more rapid development of an imbalance in the dATP and dTTP pools and a higher dATP:dTTP ratio in TS- cells. The contribution of elevated dATP or depleted dTTP pools to thymineless death was subsequently determined by treatment of GC3/cl or TS- cells with deoxyadenosine to elevate the dATP pool either under thymidine-replete or thymineless conditions. Thus, deoxyadenosine supplementation under dTTP-replete conditions elevated the dATP pool for 16 h and was cytotoxic to cells. During dTTP depletion elevated dATP was maintained, and cytotoxicity was significantly and rapidly enhanced by deoxyadenosine but could be reversed by thymidine. Data suggest that maintenance of elevated dATP and the dATP:dTTP ratio are essential initiation events in the commitment of colon carcinoma cells to thymineless death.

Limbal epithelium is more resistant to 5-fluorouracil toxicity than corneal epithelium

There is increasing evidence indicating that the limbal epithelium contains slow-cycling stem cells, whereas both limbal and corneal epithelia contain rapid-cycling transit amplifying cells. 5-Fluorouracil (5-FU), an antimetabolite used in glaucoma filtering procedures, is reported to inhibit rapid-cycling cells. After a 1-day subconjunctival (20 mg/eye) 5-FU injection followed by a 2-day rest, continuous BrdU labeling for 5 additional days (to also label slow-cycling stem cells) revealed that the limbal labeling index was not changed, whereas the corneal labeling index was markedly suppressed (p < 0.001). Following subconjunctival 5-FU treatments, peripheral and central corneal explant cultures showed a significantly higher magnitude of reduction of epithelial outgrowth size than limbal cultures (p < 0.05). Such a resistant nature of limbal epithelium to 5-FU toxicity was further confirmed by two different single-cell clonal growth assays. Taken together, these results indicate that the limbal epithelium has more slow-cycling cells than the corneal epithelium, and these cells selectively harvested by the subconjunctival 5-FU treatment can be used for future studies of their regulatory mechanism.

An optimal, generalized sampling time of 30 +/- 6 h after double dosing in the mouse peripheral blood micronucleus test

Double dosing and single sampling seems to be the simplest and most reliable method for detecting clastogens in the mouse peripheral blood micronucleus test. Optimal sampling times after double dosing are studied here. Eleven clastogens [water soluble: colchicine, cyclophosphamide, cytosine arabinoside, 5-fluoro-2'-deoxyuridine, 5-fluorouracil (5-FU), 6-mercaptopurine, methotrexate (MTX), mitomycin C; water insoluble: N-2-acetylaminofluorene, diethyl sulfate, 7,12-dimethyl-benz[a]anthracene (DMBA)] were given i.p. twice to MS/Ae mice and peripheral blood samples were collected at 6 h intervals starting 24 h after the second treatment. Samples collected at 30 +/- 6 h were nearly optimal for all 11 chemicals. When DMBA, 5-FU and MTX were given, elevated micronucleus frequencies tended to last longer relative to those induced by direct-acting chemicals. Since samples collected 30 +/- 6 h after the second treatment with these three chemicals showed almost the same micronucleus frequencies observed in later samples, the time 30 +/- 6 h could be applied for these long-acting chemicals. Micronucleated reticulocytes persist in the peripheral blood (PB) longer than micronucleated polychromatic erythrocytes are retained in the bone marrow, which thus provides a simple, effective and generalized protocol for the mouse short-term PB micronucleus test, namely double dosing and sampling 30 +/- 6 h after the second dose. When one sample time has to be selected, 30 h after the second treatment is recommended.

Vitamin E protects intestinal basolateral membrane from CMF-induced damages in rat

CMF is a combination of anticancer chemotherapeutic agents Cyclophosphamide, Methotrexate and 5-Fluorouracil. Vitamin E protects the basolateral membrane (BSM) from CMF induced lipid peroxidative damages. Rats were treated intravenously with cyclophosphamide-10 mg, methotrexate-1.0 mg and 5-fluorouracil-10 mg per kg body weight for six cycles. Vitamin E (600 mg/kg body weight) was administered orally, daily. Intestinal basolateral membrane bound ATPases (3.6.1.3), Alkalinephosphatase (3.1.1) and 5'-Nucleotidase (3.1.3.5) were protected by co-administration of vitamin E with CMF. In CMF treated rats the lipid peroxidation levels were found to be elevated with a significant depletion in membrane sulfhydryl groups. In vitamin E co-administered animals, the enzyme activities were found to be restored with concomitant reduction in malondialdehyde levels and an increase in the sulfhydryl groups. The membrane cholesterol and phospholipid levels which were altered in CMF treated rats were bought back to the normal in co-administration of vitamin E.

Lymphohematopoietic progenitors of normal mice

We have identified and characterized the lymphohematopoietic progenitors in the bone marrow of normal mice using a single-step methylcellulose culture assay. Lineage-negative Ly-6A/E (Sca-1)+ progenitors isolated from normal mice were plated in methylcellulose culture containing steel factor (SF), interleukin-7 (IL-7), erythropoietin (Ep), and IL-11. After 16 to 17 days of culture, pre-B-cell-containing multilineage myeloid colonies can be microscopically identified; however, flow-cytometric analysis of individual colonies for B220-positive cells proved superior to in situ microscopic identification of lymphomyeloid colonies. Approximately 10% (6/66) of the mixed colonies without a conspicuous B-cell component had B220-positive cells. The single cell origin of the lymphomyeloid colonies was confirmed by micromanipulation. Although the combination of SF, IL-7, and Ep was sufficient to support formation of lymphomyeloid colonies, addition of IL-11, granulocyte colony-stimulating factor or IL-12 to the combination of SF, IL-7, and Ep increased the number of lymphomyeloid colonies. IL-1 alpha and IL-3 independently inhibited the expression of the B-lymphoid lineage when added to the combination of SF, IL-7, Ep, and IL-11. Approximately four times more lymphohematopoietic progenitors are present in normal mice than in mice treated with 5-fluorouracil.

The influence of 5-fluorouracil on the endothelium in small arteries. An electron microscopic study in rabbits

5-Fluorouracil (5-FU) is a widely used antineoplastic agent. 5-FU induced cardiotoxicity is a still relatively unknown side-effect of this drug. This phenomenon could be due to a direct cytotoxic effect on the endothelial cells. We tested this hypothesis in an experimental study in rabbits, by scanning or transmission electron microscopic evaluation of endothelium in small arteries (the central artery of the ear) after in vivo treatment with 5-FU. Both local and systemic effects of 5-FU on endothelium were studied 15, 30, 60 and 120 minutes after intra-arterial or intraperitoneal treatment. Perfusion fixation at physiological pressure and temperature was used in order to minimize damage to the endothelium during the preparation procedure. Eighteen rabbits weighing 2.5-3.0 kg were used, and 6 animals served as controls. The following parameters were evaluated: vessel wall and endothelial cell contraction, cell edema, cytolysis, occurrence of denuded areas, platelet adhesion/aggregation and fibrin formation. For the description of each parameter a scale of negative points was used. Irreversible cell damage was observed in 5-FU treated animals: disruption of the endothelial sheet and patchy exposure of the subendothelium, sometimes as a focus for thrombus formation. Our findings support the hypothesis that the thrombogenic effect of 5-FU secondary to its direct cytotoxic effect on endothelium might be one of the pathophysiological mechanisms behind 5-FU induced cardiotoxicity.

Modulation of growth and proliferation in squamous cell carcinoma by retinoic acid: a rationale for combination therapy with chemotherapeutic agents

We have previously shown that beta-all trans retinoic acid (RA) inhibits macrocellular growth of a multicellular tumor spheroid model for squamous carcinoma, as measured by spheroid size, but allows for continuing DNA synthesis and cell cycle progression, the two being reconciled by a cell death effect. DNA synthesis in the presence of growth inhibition suggested a rationale for examining combination chemotherapy with RA-inhibited cells. To this aim, we have extended this observation to a series of 8 squamous carcinoma cell lines. Cells were treated with 1 microM RA for 7 days and cell growth parameters monitored. Although growth inhibition ranged from 0% (A431) to approx. 80% (MDA 886Ln), [3H]-thymidine incorporation (cpm/microgram protein) and percent S-phase (by flow cytometry) in 7-day RA-treated cells was equal or higher than in their control vehicle-treated cells in 7/8 SCC cell lines. Thus RA-induced growth inhibition is not just cytostasis. Combination therapy was examined with MDA 886Ln, MDA 686Ln, 1483 and A431 cells pre-treated for 7 days with 1 microM RA followed by cisplatin or 5-fluorouracil treatment. An increased effectiveness for the combination was shown using 5-day tetrazolium dye (MTT) growth assays when cells were growth-inhibited by RA. Computerized analysis of data using median-effect and isobologram techniques indicated that the interaction of RA with these chemotherapeutic agents was synergistic. With squamous carcinoma, RA treatment inhibits growth while allowing for continuing DNA synthesis, and these RA-treated, growth-inhibited cells exhibit increased sensitivity to chemotherapeutic agents.

5-Fluoro-2-pyrimidinone, a liver aldehyde oxidase-activated prodrug of 5-fluorouracil

5-Fluorouracil (5-FU) is an effective antitumor agent used in treating various cancers. Because of its metabolism by intestinal and other cells, 5-FU has an inconsistent bioavailability that limits its oral use. 5-Fluoro-2-pyrimidione (5-FP), a 5-FU prodrug, was synthesized and found to be converted to 5-FU by aldehyde oxidase, an enzyme present in high concentrations in the livers of mice and humans but not in the gastrointestinal tract. Using BDF1 mice, the pharmacokinetics of 5-FP were studied and compared with those of 5-FU. The bioavailability of 5-FP given orally was 100% at a dosage of 25 mg/kg and 78% at a dosage of 50 mg/kg. The half-lives of both doses of 5-FP were at least 2-fold longer than the half-lives of the same doses of 5-FU, and the clearance rates of 5-FP were 3-fold slower. 5-FP was converted rapidly to 5-FU, in vivo. The resulting 5-FU was measured at a steady-state level of 40-70 microM in plasma, at a dosage of 25 mg/kg, that was sustained for at least 4 hr. Also, when given orally, 5-FP was shown to have potent activity against Colon 38 tumor cells and P388 leukemia cells in mice. The therapeutic index of 5-FP was similar to that of 5-FU in these mouse tumor models. The potential clinical use of 5-FP as a prodrug of 5-FU should be considered.

5-fluorouracil induced cardiotoxicity in albino rats

Since 1975, many cases of 5-fluorouracil (5-FU) associated cardiotoxicity have been described in the literature. A histopathological study of 5-FU induced cardiotoxicity was performed on 50 Swiss albino rats. Multiple interstitial myocardial hemorrhages, multifocal myofibre necroses, inflammatory reaction, vascular changes, valvulitis and pericarditis have been noted especially in the left heart ventricles of rats under study. The mechanism of 5-FU associated cardiotoxicity is controversial. A probable mechanism has been proposed; it explains the endothelial damage leading to extravasation of the drug containing blood into myocardium resulting in myofibre necroses and inflammatory reaction.

Influence of various immunosuppressive agents on the occurrence of endogenous bacteraemia in mice

The influence of six immunosuppressive agents on the occurrence of endogenous bacteraemia in mice was evaluated. The mortality rates in conventional ddY mice given cyclophosphamide (CY), fluorouracil (5-FU), methotrexate (MTX), cisplatin (CDDP) or FK-506 intraperitoneally, or dexamethasone (DXM) subcutaneously were 70, 100, 100, 100, 0 and 0%, respectively. Pseudomonas aeruginosa was isolated from 70% of mice treated with CY but from only 10% of mice treated with 5-FU and 30% treated with MTX. Enterobacteria were isolated from 90% of mice treated with 5-FU. Specific-pathogen-free (SPF) mice fed P. aeruginosa were also treated with these agents. All mice in the CY, 5-FU, MTX and CDDP groups died whereas mice treated with DXM and FK-506 showed 20% and 0% mortality, respectively. Pure cultures of P. aeruginosa were obtained from all of the mice treated with CY. Polymicrobial bacteraemia with P. aeruginosa and enterobacteria occurred in 5, 25, 5 and 5% of mice treated with 5-FU, MTX, CDDP and DXM, respectively. Enterobacterial bacteraemia was observed in 70% of mice treated with CDDP and in 5% of the DXM group. Different types of bacteraemia were induced by different immunosuppressive agents. The mechanism of immunosuppression may affect the frequency of bacteraemia and the causative organism.

Characteristics of peripheral blood monocytes and bone marrow macrophages from rats treated with mitomycin C, 5-fluorouracil or phenylhydrazine

We examined the cellular functional changes in bone marrow macrophages obtained from rats treated intraperitoneally with mitomycin C (MMC), subcutaneously with 5-fluorouracil (5FU) or intraperitoneally with phenylhydrazine (PHZ) for 7 days to define the mechanisms of toxicity in the bone marrow. The functions of peripheral blood monocytes and bone marrow macrophages were also compared. MMC and PHZ caused anemia, and MMC and 5FU leukocytopenia. Changes in nucleated cell counts were different among the three drug-treatment groups, and MMC- and PHZ-treated bone marrow macrophages were activated for responsiveness to interleukin-1 (IL-1), and their migration activity, intracellular components and enzyme activities were increased. On the other hand, cellular functions of bone marrow macrophages of rats treated with 5FU were suppressed.

Induction of resistance to 1-beta-D-arabinofuranosylcytosine in human H9 cell line by simian immunodeficiency virus

We examined drug sensitivity of human T cell acute lymphoblastic leukemia H9 cells chronically infected with simian immunodeficiency virus (SIVmac) and found that the retrovirus-infected H9 cells showed 8.2-fold resistance to 1-beta-D-arabinofuranosylcytosine (Ara-C). In the infected cells, Ara-CTP levels decreased to 20% of that found in uninfected H9 cells after 3 h incubation at Ara-C concentration of 1 microM, and 8.1-fold increase of cytidine deaminase activity was observed in the infected H9 cells. A competitive inhibitor of cytidine deaminase, 3, 4, 5, 6-tetrahydrouridine (THU), at 100 microM reversed Ara-C resistance in the infected cells. These results indicate that inducing increased cytidine deaminase activity by SIVmac infection conferred Ara-C resistance to H9 cells. An understanding of these cellular differences in drug sensitivity may aid in the development of therapeutic strategies against retrovirus-infected cells.

Antitumor effect of intratumoral administration of fluorouracil/epinephrine injectable gel in C3H mice

Fluorouracil/epinephrine injectable gel (5-FU/epi gel) was evaluated in vitro for its drug-release profile characteristics and in a mouse tumor model for its antitumor effectiveness. In vitro chemosensitivity studies with 5-FU in RIF-1 fibrosarcoma cells showed less than 1 log of cell kill at 1 mM after 2 h of exposure. Increasing the exposure time to 24 h resulted in greater cell killing (approximately 2.5 log cell kill at 0.5 mM), suggesting that sustained drug levels in tumors would result in an increased efficacy outcome in vivo. A 5-FU/epi injectable gel was designed, providing drug release in vitro of 50% by approximately 4 h and of 80% by 24 h. The retention of 5-FU in RIF-1 mouse tumors was determined after intratumoral administration of 5-FU/epi gel or various combinations of the formulation components. Area-under-the-curve (AUC0-24 h) calculations resulted in an AUC value of 146.4% h for the 5-FU/epi gel formulation as compared with 45.7% h for 5-FU solution. Tumor growth was significantly delayed (P < 0.05) with the 5-FU/epi gel (60 mg/kg) as compared with 5-FU solution given intratumorally or systemically. A fluorouracil dose of 150 mg/kg in the 5-FU/epi gel given weekly for 13 weeks was not lethally toxic, whereas the same dose given as drug solution was 100% lethal, suggesting that the therapeutic index for 5-FU in the gel formulation may be much greater than that for aqueous drug solution delivered intratumorally.

Effect of diets on 5-fluorouracil and cyclophosphamide toxicity

Feeding rats a semipurified diet containing casein as a protein source results in severe gastrointestinal (GI) toxicity when the chemotherapeutic drug methotrexate (MTX) is given. However, when soy concentrate protein is used in place of casein, rats are completely protected from toxicity. The purpose of this study was to determine whether soy protein was also protective against two other chemotherapeutic agents, 5-fluorouracil (5-FU) and cyclophosphamide (CY), which are routinely used in a multidrug regimen with MTX in a clinical setting. Three diets were tested; they consisted of a control complex diet (rat chow) and two semipurified diets containing casein or soy concentrate as the protein fraction given to non-tumor-bearing rats receiving a single injection of 5-FU or CY at three different levels (Experiment I: 5-FU: 100, 260, and 420 mg/kg; Experiment II: CY: 120, 180, and 240 mg/kg). Each diet was fed to seven rats for seven days before injection and seven days after injection. Food intake decreased at Day 3 in all groups receiving 5-FU (35-90% reduction from preinjection level), with the greatest decrease associated with the group receiving the highest drug level. Animals fed the control diet ate consistently less than animals fed the other two diets regardless of the drug level. Intake was not significantly different between the casein and soy concentrate groups at any drug level. Animals gained weight on the low-dose treatment regardless of diets. At 260 and 420 mg/kg 5-FU, all diet groups lost weight, but the difference was significant only between the control and the two other diets (p < 0.05). Diarrhea was absent in the casein diet groups, regardless of drug dose, and present in the other diet groups. Food intake decreased on Day 1 for all groups receiving CY. At any dose, the control diet group maintained a greater intake on Day 1 than the other two diet groups. The difference in intake was significant between the control and the two other diet groups at low dose, between the control and the casein diet groups at 180 mg/kg, and between the control and the soy concentrate diet groups at high dose (p < 0.05). All animals lost weight regardless of diet and drug dose. A third experiment was conducted to evaluate histological damage to the intestine when these three diets were fed to animals injected with 420 mg/kg 5-FU.(ABSTRACT TRUNCATED AT 250 WORDS)

Clonogenic survival studies of human colon tumor cell lines in vitro: combined hyperthermia, 5-fluorouracil/leucovorin, carboplatin and tumor necrosis factor

The responses of DLD-1 and HCT-15 human colon adenocarcinoma cells to hyperthermia, 5-fluorouracil (5-FU)/leucovorin, carboplatin and tumor necrosis factor-alpha, singly and in multiple combinations, were evaluated in clonogenic assays. The combination of hyperthermia with the lower dose combination resulted in a survival fraction of about 0.005 to 0.001 for both cell types, whereas estimated additive interactions alone would have resulted in a survival fraction of about 0.5 (DLD-1) or 0.05 (HCT-15). A survival fraction of 0.00001 or greater was observed when the higher dose levels were combined with hyperthermia, whereas additive interactions alone would have achieved a decrease of only 0.001 or 0.0001 in the surviving fraction. The combination of the three other modalities at either dose level under conditions of hyperthermia or normothermia achieved statistically significant apparently supra-additive losses of clonogenicity in HCT-15 cells; similar results were obtained with the lower dose level in DLD-1 cells. Our results suggest that human colon tumor cells are markedly sensitive to this combination of modalities when used at clinically achievable dose levels.

Antibiotic C3368-A, a fungus-derived nucleoside transport inhibitor, potentiates the activity of antitumor drugs

Antibiotic C3368-A (CA) is produced by a fungus strain from a soil sample collected in Antarctica. CA markedly inhibited radiolabeled thymidine and uridine transport in mouse Ehrlich carcinoma cells, its 50% inhibitory concentration (IC50) being 4.6 and 7.7 microM, respectively. In clonogenic assay, CA displayed a synergistic effect with methotrexate (MTX), mitomycin C (MMC), 5-fluorouracil (5FU), and Adriamycin (ADR) against human oral epidermoid carcinoma KB cells. CA also markedly enhanced the inhibitory effect of 5FU and ADR on the proliferation of human hepatoma BEL-7402 cells as determined by the p-nitrophenyl-N-acetyl-beta-D-glucosaminide (NAG) enzyme-reaction assay. 5FU or ADR cytotoxicity was not augmented by CA in human fetal lung 2BS cells. In vivo, CA significantly potentiated the inhibitory effect of MMC against colon carcinoma 26 in mice. No significant augmentation of toxicity by the combination was found in treated mice. The results suggest that CA, the newly found nucleoside-transport inhibitor, may be useful in potentiation of the effect of antitumor drugs.

Flow cytometric detection of abnormal fetal erythropoiesis: application to 5-fluorouracil-induced anemia

We sought to determine whether flow cytometric analysis of circulating fetal blood cells could be used to rapidly detect perturbations of fetal erythropoiesis. In addition, we wanted to determine whether this approach would allow sample collection by exsanguination instead of fetal cardiac puncture, a difficult technique used to prevent contamination of samples with maternal erythrocytes. To monitor fetal erythropoiesis from gestational day (GD) 14-20, we analyzed the cell size, RNA content, and percentage of circulating liver-derived reticulocytes relative to yolk-sac-derived erythroblasts. As a model toxicant, we chose 5-fluorouracil (5-FU), since we previously observed that maternal administration at 20-40 mg/kg on gestational day (GD) 14 produced fetal anemia on GD 16-17, as evidenced by dose-dependent decreases in the cell counts, hematocrit, and hemoglobin content of fetal blood obtained by cardiac puncture. We report herein that 48 hr after maternal 5-FU administration, both cardiac and peripheral blood samples exhibited a dose-dependent decrease in the relative percentage of reticulocytes, indicating a reduced rate of reticulocyte release from the fetal liver. Moreover, at 30 and 40 mg/kg, reticulocytes exhibited increased size and reduced RNA content on GD 16, but elevated RNA content (indicative of premature release) by GD 18. These data suggest that 5-FU inhibits both erythroid cell proliferation and RNA synthesis reversibly, resulting in an anemia that triggers compensatory release of immature reticulocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

5-Fluorouracil cytotoxicity in human colon HT-29 cells with moderately increased or decreased cellular glutathione level

Little is known whether diet or certain components in the diet can modulate the efficacy of 5-fluorouracil (5FU) in patients with colon carcinoma. Glutathione (GSH), an important antioxidant and anticarcinogen, is present in many foods in varying amounts. This study examined whether a moderately increased or decreased cellular GSH level had any effect on the growth of human colon adenocarcinoma cells HT-29 and on the cytotoxic activity of 5FU in these cells. GSH and buthionine sulfoximine were used to enhance or reduce the GSH level respectively in these cells. A 34% increase in cellular GSH level had no effect on the growth of HT-29 cells, nor on the cytotoxic activity of 5FU as determined by the MTT colorimetric assay and cell counts. A 50% reduction in the cellular GSH level was found to enhance 5FU cytotoxicity by 20% to 31% as determined by the MTT colorimetric assay, depending on the 5FU concentration. This study shows that a moderate change in the GSH level in HT-29 cells had little or no effect on the cells' growth, but a decrease in cellular GSH level slightly enhanced the cytotoxic activity of 5FU in these cells.

Synchronization of cells in the S phase of the cell cycle by 3'-azido-3'-deoxythymidine: implications for cell cytotoxicity

The mechanism of synergy between 3'-azido-3'-deoxythymidine (AZT) and anticancer agents was investigated with emphasis on cell-cycle events. Exposure of exponentially growing WiDr human colon carcinoma cells to AZT resulted in synchronization of cells in the S phase of the cell cycle. Following treatment with AZT at 50 or 200 microM, 62% +/- 3% or 82% +/- 4% of the cells were in the S phase as compared with 36% +/- 2% in the control. Bromodeoxyuridine uptake studies revealed that the synchronized cells actively synthesized DNA. At concentrations of up to 200 microM, AZT produced a cytostatic rather than cytotoxic effect as indicated by viability and cell growth measurements. At 200 microM, AZT-induced synchronization was significant (P = < 0.001) after 12 h of drug exposure, reached a maximum at 24 h, and reversed to baseline levels by 72 h even in the continued presence of the drug. This indicates that AZT-induced cytostasis is a transient and reversible effect. The cell-cycle events seen with AZT in WiDr cells were also observed in eight of nine human tumor cell lines tested. Isobologram analysis of WiDr cells preexposed to AZT for 24 h and then exposed to either AZT-5-fluorouracil or AZT-methotrexate for a further 72 h revealed synergy between AZT and the anticancer agents, indicating that AZT-induced synchronization may have therapeutic benefits.

Early events following maternal exposure to 5-fluorouracil lead to dysmorphology in cultured embryonic tissues

The chemotherapeutic agent 5-fluorouracil (5-FU) is teratogenic in a number of species, yet the mechanism(s) of its developmental toxicity are not fully understood. Administration of 5-FU to the pregnant CD rat on day 14 of gestation results in dose-dependent growth retardation and numerous malformations in near-term fetuses, including hindlimb defects and cleft palate. Following treatment, a number of rapid biochemical and cellular alterations are detectable in embryonic hindlimbs, craniofacial and other tissues, which include thymidylate synthetase (TS) inhibition and altered cell cycle progression. In order to assess the importance of these early events in 5-FU-induced dysmorphogenesis, embryonic mid-facial tissues and hindlimbs were dissected 3 or 6 hr after administration of 5-FU to the dam and placed in explant culture. After 5 days in culture, craniofacial explants were evaluated morphologically for palatal closure and growth was assessed by measuring total protein and DNA content. Hindlimb explants were stained for cartilage using alcian blue to evaluate development of the digits. Craniofacial explants cultured at either 3 or 6 hr after exposure exhibited dose-dependent growth retardation and defects of palatal fusion at the end of the culture period. Deficits in protein and DNA content were similar to those in craniofacial tissues that continued to develop in utero after treatment, although morphological defects in cultured explants did not correlate well with the incidence of cleft palate in vivo. Dose-dependent deficits in metatarsal and phalanx development were observed in hindlimb explants dissected either 3 or 6 hr after maternal treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Ocular toxicity of mitomycin C and 5-fluorouracil in the rabbit

We studied the histotoxic effects of mitomycin C and 5-fluorouracil (5-FU) in the eyes of New Zealand white rabbits using light microscopy. Twenty-four eyes of 24 rabbits received subconjunctival injections of mitomycin C (0.025, 0.05, 0.10, 0.20, 0.40 or 0.80 mg/mL) or 5-FU (10.0 mg/mL), either alone (0.25 mL) or in combination with anterior chamber injections (0.05 mL), once daily for 4 consecutive days. Two eyes of two rabbits received subconjunctival and anterior chamber injections of unpreserved sterile saline. The eyes were examined regularly for external signs of toxicity and were enucleated 4 weeks after the last injection. Mitomycin C produced considerable tissue damage in the anterior segment, the severity being related to both the concentration and the route of administration. Eyes that received both subconjunctival and anterior chamber injections showed more damage than those that received subconjunctival injections alone. At the highest concentration of mitomycin C the cornea was inflamed, with stromal necrosis and marked endothelial loss. Hemorrhagic iris necrosis was also seen. In contrast, the 5-FU-treated eyes showed no microscopic evidence of toxicity. We conclude that there is greater risk of toxic anterior segment effects when mitomycin C is used as adjunctive therapy following filtration or pterygium surgery.

Effects of prostaglandin E2 on the micronucleus formation in mouse bone marrow cells by various mutagens

The effects of prostaglandin E2 (PGE2), as a trigger of erythroid progenitor cells into the cell cycle, were studied on the induction of micronuclei by various mutagens; with mitomicin C (MMC) the optimal protocol was established. PGE2 itself did not induce any micronuclei in this experiment. The highest frequency of micronuclei and dose-response relationship between PGE2 doses and micronucleus frequency were observed 30 h after injection of MMC to mice administered PGE2 24 h previously. Sensitization by PGE2 pretreatment was also found for other mutagens, such as vincristine, 5-fluorouracil, benzo[a]pyrene, 1,1-dimethylhydrazine and 2-naphthylamine. These results support the hypothesis that accelerating the erythropoiesis increases the frequency of micronuclei induced by mutagens.

Effect of conagenin on thrombocytopenia induced by antitumor agents in mice

The effect of conagenin (CNG) on myelosuppression induced by antitumor agents was investigated. The daily administration of CNG prevented reduction in the number of platelets (PLT) observed in peripheral blood of mice given mitomycin C (10 mg/kg) but did not prevent reduction in the number of leukocytes (WBC). The effect on PLT was also confirmed in mice given cyclophosphamide (100 mg/kg). In mice given repeated doses of 5-fluorouracil (10 mg/kg), CNG prevented the reduction of PLT as well as WBC and maintained them at normal levels. CNG prevented reduction of the production of interleukin-2, 3 and 6 in cultured supernatants of spleen cells taken from mice given 5-fluorouracil. These results suggest that CNG modulates production of lymphokines which are responsible for thrombopoiesis.