Treatment of cultured human colon carcinoma cells with fluorinated pyrimidines

Pharmacokinetic properties and antitumor efficacy of the 5-fluorouracil loaded PEG-hydrogel

Background

We have studied the in vitro and in vivo utility of polyethylene glycol (PEG)-hydrogels for the development of an anticancer drug 5-fluorouracil (5-FU) delivery system.

Methods

A 5-FU-loaded PEG-hydrogel was implanted subcutaneously to evaluate the drug retention time and the anticancer effect. For the pharmacokinetic study, two groups of male rats were administered either an aqueous solution of 5-FU (control group)/or a 5-FU-loaded PEG-hydrogel (treated group) at a dose of 100 mg/kg. For the pharmacodynamic study, a human non-small-cell lung adenocarcinoma (NSCLC) cell line, A549 was inoculated to male nude mice with a cell density of 3 × 10⁶. Once tumors start growing, the mice were injected with 5-FU/or 5-FU-loaded PEG-hydrogel once a week for 4 weeks. The growth of the tumors was monitored by measuring the tumor volume and calculating the tumor inhibition rate (IR) over the duration of the study.

Results

In the pharmacokinetic study, the 5-FU-loaded PEG-hydrogel gave a mean residence time (MRT) of 8.0 h and the elimination half-life of 0.9 h; these values were 14- and 6-fold, respectively, longer than those for the free solution of 5-FU (p < 0.05). In the pharmacodynamic study, A549 tumor growth was significantly inhibited in the 5-FU-loaded PEG-hydrogel group in comparison to the untreated group beginning on Day 14 (p < 0.05-0.01). Moreover, the 5-FU-loaded PEG-hydrogel group had a significantly enhanced tumor IR (p < 0.05) compared to the free 5-FU drug treatment group.

Conclusion

We suggest that 5-FU-loaded PEG-hydrogels could provide a useful tool for the development of an anticancer drug delivery system.

Limits to thymidylate synthase and TP53 genes as predictive determinants for fluoropyrimidine sensitivity and further evidence for RNA-based toxicity as a major influence

The major determinants of 5-flurouracil (5-FU) response would seem, based on accumulated literature, to be thymidylate synthase (TYMS, TS) expression levels, TS gene modifications, and TP53 status. We tested 5-FU sensitivity in yeast and human cancer cell models in which TS or TP53 alleles and expression were varied. Polymorphic TS tandem repeat status, TS expression levels reported, TS intragenic mutations, and TP53 status in outbred and experimental cancer cell lines did not predict 5-FU sensitivity or resistance. Novel observations included a dose-resistant persistence of unbound TS protein in many cancers and, upon 5-FU treatment of the colon cancer cell line, HCT116, evidence of allelic switching favoring transcripts of the mutant TS allele. The reported alleles having an intragenic mutation could not be causally associated with major degrees of 5-FU sensitivity. In yeast, TS protein was altered upon treatment with FdUMP, but 5-FU toxicity seemed to be largely RNA-based, being rescued by uridine rather than by thymidine. Cancer cell lines were also rescued from 5-FU toxicity with uridine rather than thymidine. Additionally, a TS (CDC21) knockout yeast strain, obviating any potential role for TS protein as a target, was hypersensitive to 5-FU. When denatured proteins from cancer cells treated with radiolabeled 5-FU were labeled, species with alternative molecular weights other than TS were visualized, providing further evidence for alternative 5-FU protein targets. These data emphasize that TS and TP53 status do not consistently explain the variance in responses of fluoropyrimidine-treated cancer cells, in part due to RNA-based toxicity.

Adenosine stimulation of proliferation of breast carcinoma cell lines: Evaluation of the [3H]thymidine assay system and modulatory effects of the cellular microenvironment in vitro

The purine nucleoside adenosine is produced at increased levels in the tissues of solid cancers as a result of local hypoxia. Adenosine inhibits the cell-mediated anti-tumor immune response, promotes tumor cell migration and angiogenesis, and stimulates the proliferation of tumor cells. We examined the stimulatory effect of adenosine on DNA synthesis, cell cycle progression, and cell proliferation in MCF7 and T-47D breast carcinoma cell lines in culture, and identified factors that modulate the growth response. The ability of adenosine to stimulate DNA synthesis, as measured by the incorporation of [(3)H]thymidine, was independent of the total radioactivity of the [(3)H]thymidine up to 10 microCi/ml, total thymidine concentrations up to 100 microM, and the labeling interval. It was also not affected by the presence of low-molecular-weight compounds (such as thymidine and adenosine) in the serum used to supplement the medium. Adenosine stimulated DNA synthesis and cell proliferation with an EC(50) of 4-6 microM and a maximum response at 30-100 microM, when given as a single addition. The stimulatory effect of adenosine involved progression through the cell cycle and a genuine increase in cell number, in the absence of significant apoptotic or necrotic cell death. The mitogenic effect of adenosine was dependent upon the culture cell density, with an optimum adenosine response at around 50% of confluent density. The response was also highly dependent upon the form of the serum addition to the growth medium, with the best response elicited in the presence of low concentrations of nonfetal bovine serum, although adenosine was mitogenic under standard culture conditions. The effects of serum supplementation and cell density were not due to differences in the rate of adenosine metabolism by either serum or cellular enzymes, but appeared to result from changes in the sensitivity to adenosine of the cell population in response to environmental cues. We, therefore, find that adenosine is consistently mitogenic for human breast carcinoma cells, and that the [(3)H]thymidine incorporation assay is a valid measure of this response. The data are consistent with the stimulatory effect of adenosine on cell proliferation being modulated by the local cellular environment.

Delivery of anticancer drugs via isolated hepatic perfusion: a promising strategy in the treatment of irresectable liver metastases?

The prognosis of patients with irresectable liver metastases derived from colorectal cancer is invariably poor; unfortunately, these tumours show only minor responses to conventional anticancer agents. The best responses have been obtained by fluoropyrimidines delivered as continuous infusion into the hepatic artery (HAI): their rapid uptake and detoxification by liver cells results in relatively low systemic drugs levels. This approach increases mean survival duration from 17 to 26 months and, in few patients, causes "down-staging" that may result in resectability. To improve opportunities for chemotherapy, the technique of 1-hour recirculating perfusion of the vascularly isolated liver (isolated hepatic perfusion, IHP) was developed. If leakage to the systemic circulation is negligible-and the compounds used do not readily cause hepatotoxicity-IHP allows usage of drug doses that would be fatal if delivered systemically. Because alkylating agents generally have steep dose-response curves, mitomycin C (MMC) and melphalan (L-PAM) entered phase I/II studies on IHP. Using these drugs, IHP was performed in principle as a single procedure in 60 otherwise untreated patients at our institution. However, despite preliminary data that indicate impressive clinical responses are obtained, improvement over HAI will probably be minor. Because IHP is a complicated way of drug delivery, one could argue that its use is justified only when it has the potential to kill all tumour cells in the liver. We critically discuss the possibilities of IHP and/or the use of gene therapy in an IHP setting.

Continuous infusion of chemotherapy: focus on 5-fluorouracil and fluorodeoxyuridine

Continuous infusion of chemotherapy is one of the developments to try to improve the treatment of metastatic cancer. There is a sound theoretical rationale to deliver cytotoxic drugs as a continuous infusion. Furthermore, the development of reliable venous access devices and portable infusion pumps enables patients to be treated in an ambulatory setting. This review focuses on the continuous infusion of the most frequently used drugs: 5-fluorouracil (5-FU) and fluorodeoxyuridine (FUDR). An overview is given of both preclinical studies and studies in humans. Continuous infusion of 5-FU and FUDR has proven to be feasible in all studies. However, the results (response rate and especially survival) are rather disappointing. So far, continuous infusion of cytostatic drugs can still be considered as an experimental procedure. Whether protracted, intermittent of circadian modulated continuous infusion is the optimal treatment schedule has still to be proven in future studies. Furthermore, studies are needed to demonstrate whether dose intensity for most tumours is important for treatment outcome. Also, studies are needed to investigate quality of life and economic issues.

Effect of regional angiotensin II infusion on the relationship between tumour blood flow and fluorouracil uptake in a liver metastasis animal model

The aim of this study was to assess the relationship between tumour:liver blood flow and 5-fluorouracil (5-FU) uptake ratios in a hypovascular liver metastasis animal model, and examine whether they were similarly affected by a 5 min infusion of angiotension II via the hepatic artery. Tumour:liver blood flow ratio was measured using the isotope tracer 64Copper (II)-pyruvaldehyde bis(n-4 methyl thiosemicarbazone, and 5-FU was tritiated. There was a wide variation in tumour:liver blood flow and 5-FU uptake ratios which could only partly be explained by between animal variation, and was not related either to individual tumour size or overall tumour burden within the liver. There was a close correlation (r = 0.957, P < 0.0001) between tumour:liver blood flow and 5-FU uptake ratios. Angiotensin II infusion significantly increased tumour:liver blood flow (nested analysis of variance, P= 0.05) but not 5-FU uptake (P = 0.29) ratios. There was a poor correlation (r = 0.51, P = 0.13) between tumour:liver blood flow and 5-FU uptake ratios with angiotensin II infusion. Thus, despite an increased 5-FU blood concentration arising from angiotensin-induced reduction in blood flow at constant 5-FU infusion dose, tumour:liver 5-FU uptake ratio did not increase as expected, and there ceased to be a significant correlation between tumour:liver blood flow and 5-FU uptake ratios. We conclude that the vasoactive changes within the hypovascular tumour circulation produced by a 5 min angiotensin II infusion did not significantly increase tumour 5-FU uptake.

The effect of different routes of administration of 5-fluorouracil on thymidylate synthase inhibition in the rat

A rat colon tumour model of liver metastases was used to administer 5-fluorouracil (5FU) by intraperitoneal (i.p.) bolus injection (50 mg/kg), isolated liver perfusion (ILP, 150 mg/kg) and hepatic artery infusion (HAI, 50 mg/kg). The biochemical effect of 5FU, delivered by different routes, on its target enzyme thymidylate synthase (TS) was studied in both tumour and normal tissues of the rat. In tumour tissue, only small differences were observed in the extent of TS inhibition. A pronounced inhibition of TS was observed 3 h after 5FU administration by all routes, but was followed by a recovery of TS activity within 24 and 48 h. Effects of 5FU on normal tissues were diverse. In liver, TS activity increased 6-fold after ILP and HAI administration of 5FU, and a 2-fold increase of FdUMP binding to TS was seen for all routes of administration. In intestinal mucosa, both induction of TS activity (by ILP) and inhibition of TS activity (by HAI) were observed, while i.p. injection did not cause major changes. TS activity and FdUMP binding to TS in bone marrow was strongly inhibited after administration of 5FU by all routes, but administration by ILP seemed slightly advantageous, since a smaller extent of TS inhibition was observed compared to the other routes of administration. 5FU given by ILP had a small antitumour effect in this colon tumour model, while HAI administration had no antitumour activity. Since this difference in antitumour activity could not be related to differences in TS inhibition in the tumour, the RNA-directed mechanism of action of 5FU could be involved. Focusing on the effects of TS, we may conclude that the ILP administration of 5FU offered the important advantage of a lack of severe TS inhibition in normal tissues, which corresponds with the low systemic toxicity observed.

Phase II trial of intravenous melphalan in advanced colorectal carcinoma

BACKGROUND

Relatively few studies have examined the activity of alkylating agents in the treatment of advanced colorectal adenocarcinoma. Recent reports have suggested possible therapeutic activity for high-dose intravenous melphalan administered with autologous bone marrow transplantation (BMT) support. We conducted a phase II study to determine the efficacy of administering intravenous melphalan at doses that do not require BMT support in patients with advanced colorectal adenocarcinoma.

PATIENTS AND METHODS

Fifteen patients with histologically proven, bidimensionally measurable disease were treated. The starting dose of melphalan was 30 mg/m2, with dose escalation permitted.

RESULTS

No objective responses were observed. Toxic effects were primarily reversible granulocytopenia and thrombocytopenia. There were no treatment-associated deaths.

CONCLUSION

Melphalan's lack of efficacy at the doses administered does not disprove the steep chemotherapy dose-response relationship postulated for many solid tumors. However, we feel that it is unlikely that repetitive courses of high dose melphalan with autologous BMT support will be a practical approach to the management of advanced colorectal adenocarcinoma.

Loss of murine tumor thymidine kinase activity in vivo following 5-fluorouracil (FUra) treatment by incorporation of FUra into RNA

The effects of 5-fluorouracil (FUra) treatment on thymidine kinase (TKase) activity were examined in vivo in CD8F1 mice bearing first generation CD8F1 mouse mammary tumors. TKase activity was not affected by low dose FUra25 (25 mg/kg), a dose which substantially inhibited thymidylate synthase (TSase), but was severely inhibited 24 hr following treatment with FUra100, a weekly maximally tolerated dose, as judged by activity measurements and labeling of DNA with [3H]thymidine. The amount of (FU)RNA was increased markedly with increasing FUra dose from 0.4 nmol/mg DNA at FUra25 to 2.2 nmol/mg DNA at FUra100. At FUra100, TKase activity gradually declined over 24 hr to less than 10% of the control value, remained low for a further 48 hr, and then was gradually restored to control levels by 168 hr. The loss of TKase activity followed the incorporation of FUra into RNA which peaked at 4-5 hr. TKase activity was not restored by removal of endogenous inhibitors but was restored by treatment with uridine. TKase activity was not inhibited by therapeutic levels of methotrexate (300 mg/kg). TKase from murine colon 38 carcinoma was also severely inhibited, but the activity from colon 26 was only partially (50%) inhibited. Ornithine decarboxylase was also inhibited by FUra100 treatment in the CD8F1 tumor. These results demonstrate that certain short-lived, proliferation-related enzymes are affected by FUra doses higher than those required for TSase inhibition, and this effect appears to correlate with incorporation of FUra into RNA. Thus, in some tumors high doses of FUra can inhibit salvage as well as de novo synthesis of thymidylate providing an increased block of DNA synthesis and increased therapeutic advantage.

Kinetic analysis of 5-fluorouracil action against various cancer cells

Based on our recent kinetic analysis, which made it possible to distinguish between the cell-killing actions of cell cycle phase-specific and non-specific agents, we attempted to elucidate the actions of 5-fluorouracil (FUra) on three different cancer cell lines. By colony-forming assay, the concentrations of fluorouridine (FUrd), fluorodeoxyuridine (FdUrd) or FUra giving 90% cell kill (IC90) at various exposure times (texps) were obtained. With P388 cells, the curve of texps-IC90 for FUrd on a log-log scale was linear with a slope of -1, which is typical for cell cycle phase-nonspecific agents. In contrast, the curve for FdUrd showed a much steeper slope than -1, which is characteristic for cell cycle phase-specific agents. We found that the curve for FUra was exactly the same as that for FUrd, indicating that the mode of FUra action on P388 leukemia is analogous to that of FUrd. Similar results were observed with human colon and renal cancer cell lines, HT-29 and KU-2, although when the cells were exposed to relatively low concentrations of FUra for a long time, a cell cycle phase-specific action became evident.

Concentration and time dependence of the toxicity of fluorinated pyrimidines to HT 29 colorectal carcinoma cells

To determine the optimal concentration time factors for the fluoropyrimidines 5-fluorouracil (FU), 5-fluorouridine (FUR), and 5-fluoro-2'-deoxyuridine (FUdR) in regional chemotherapy, we tested these drugs against the colorectal carcinoma cell line HT 29 at various dosages and exposure times. The measure of cytotoxicity used was the degree of inhibition of colony formation in soft agar after drug treatment compared with untreated control cells. Colonies were visible after 6 days of growth in soft agar, so the initial evaluation of toxicity was done at this time. Additional colonies were found 10 and 16 days after the first evaluation, so the dishes containing the treated cells were also evaluated for this delayed growth phenomenon ("regrowth"), which we considered to be due to a cell growth inhibition effect of the drugs rather than a cytocidal effect. Exposure times of the cells to the drugs ranged from 5 min to 24 h and the doses, between 0.01 and 1000 micrograms/ml. The toxicity of FUdR was concentration-dependent, but its time dependence ceased after a relatively short exposure time. There was a cell population that was not susceptible to FUdR regardless of dose and exposure time; consequently, FUdR treatment was always accompanied by substantial regrowth of colonies. With FU and FUR, conditions could be achieved that resulted in complete cell death (no regrowth), but high concentrations and long exposure times were required with FU. With FUR, on the other hand, both cytostasis and cytotoxicity could be achieved with substantially lower doses and shorter exposure times than with FU. These results indicate that FUR has the potential to be an effective drug in chemotherapy protocols not involving systemic administration.

In vivo isolated liver perfusion technique in a rat hepatic metastasis model: 5-fluorouracil concentrations in tumor tissue

An in vivo method of isolated rat liver perfusion was developed with true vascular isolation and recirculating perfusate. This new surgical technique to temporarily isolate the liver vascularly, and the perfusion procedure are described in depth. Twelve inbred WAG/RIJ rats were subjected to 25 min of normothermic liver perfusion without chemotherapy, and all rats survived the procedure. Hepatic functional and histological integrity were not significantly altered during perfusion. To determine the role of isolated liver perfusion (ILP) as a means of improved targeting of antitumor agents, 5-fluorouracil (5-FU) concentrations were monitored in hepatic tumor and liver tissues and in systemic plasma using high-performance liquid chromatography. Fifty-one rats with hepatic tumors of colonic origin were randomly assigned to one of three dosage groups (20, 40, or 80 mg/kg) receiving 5-FU by ILP, hepatic artery infusion (HAI), or jugular vein infusion (JVI). ILP resulted in significantly increased 5-FU concentrations in liver tissue. However, no significant differences were found in tumor tissue concentrations of 5-FU between the three treatment modalities. 5-FU concentrations in tumor tissue increased as a function of the dose with ILP, HAI, and JVI. ILP was associated with the lowest systemic drug concentrations. The low systemic 5-FU concentrations with ILP suggest a higher maximum tolerable dose. This mode of treatment deserves to be studied further in our model before conclusions can be drawn regarding its therapeutic potential.

The use of human cancer cell lines as a primary screening system for antineoplastic compounds

Exponentially growing cells of human cancer lines have been utilized to investigate the cytotoxic activity of antineoplastic agents. Different cancer cell lines differ greatly in their responsiveness to both clinical and experimental cytotoxic drugs. For example, sensitivities to 5-fluorouracil and cytosine arabinoside ranged over 15- and 30-fold respectively. Cell lines derived from carcinomas were more sensitive to 5-fluorouracil and less sensitive to cytosine arabinoside than was a leukaemic cell line. In general, colon carcinoma lines were most resistant to DNA-intercalating drugs, and a breast carcinoma and leukaemia line most sensitive. In a congeneric series of amsacrine analogues, in vitro patterns of activity against different lines were shown to correlate with activity against the Lewis lung mouse carcinoma in vivo. Results suggest that established cell lines manifest responsiveness to anticancer drugs consistent with that expected from their tumours of origin. This assay is economical, reproducible and convenient, and could be used to complement the human tumour stem cell assay in drug development studies.

Human tissues degrade uridine much less than thymidine. Possible consequence for 5-fluorouracil therapy

In view of clinical trials to improve FUra chemotherapy of cancer by combined application with Urd and dThd, we investigated the capacity of human tissues to split these nucleosides. All human normal and neoplastic tissues gave a uridine-splitting activity which can be inhibited by beta-L-pTdR and behaves in this respect as uridine-deoxyuridine phosphorylase (EC 2.4.2.3). dThd splitting, however, which is 2-9-fold higher than that of Urd, is insensitive towards beta-L-pTdR, confirming earlier results that it is due to thymidine phosphorylase (EC 2.4.2.4). On the other hand, tissues, e.g., spleen of rats and mice, in which dThd and Urd are split by uridine-deoxyuridine phosphorylase, degrade 2-5-fold more Urd than dThd. Thus, free pyrimidine base competing with FUra for degradation and thus prolonging the life time of the drug in the body, will be formed mainly from dThd in the human body but more so from Urd in the rat or mouse.

Studies of variation in inherent sensitivities to radiation, 5-fluorouracil and methotrexate in a series of human and murine tumor cell lines in vitro

Clinical studies have reported reduced response rates to subsequent chemotherapy in certain tumors recurring after radiotherapy. We have investigated whether there are any correlations between radiation and drug responses in vitro using a range of murine and human tumor cell lines. We have compared sensitivities to X-irradiation and to 24 hr exposures to two widely used antitumor drugs, methotrexate and 5-fluorouracil. The 4 murine lines selected showed a range of radiation responses with Do values of 0.48-0.76 Gy. Methotrexate sensitivities also exhibited an 800-fold difference (IC50 values of 0.018-14.9 micrograms/ml) which appeared to correlate inversely with radiation response. Sensitivity to 5-FU was less variable in these cells with a range of IC50 values of 0.056-0.43 microgram/ml and was unrelated to radiation response. In contrast, in the human lines tested, no correlations were observed between drug sensitivities and radiation response. The six lines tested (3 derived from epidermoid head and neck tumors, 2 from neuroblastomas and 1 from a colon carcinoma) showed a range of radiation responses with Do values of 0.66-1.59 Gy. Methotrexate sensitivities ranged only over a 150-fold concentration but, contrasting with data from the murine cells, no correlation with radiation response was apparent. Similarly, no correlations between response to 5-fluorouracil and radiation or 5-fluorouracil and methotrexate were noted, which is inconsistent with results using murine cells.

Pharmacologic requirements for obtaining sensitization of human tumor cells in vitro to combined 5-Fluorouracil or ftorafur and X rays

The combined effects of X ray and 5-Fluorouracil (5-FU) in tissue culture have been studied using two human adenocarcinoma lines (HeLa and HT-29 cells). Both showed similar sensitivities to 5-FU, HeLa cells appearing somewhat more resistant to higher concentrations. Combined treatment of both cell types with 5-FU and X rays led to a time-dependent enhancement of cell killing ("radiosensitization"). Only post-radiation incubation had any effect, prior exposure to 5-FU being strictly additive. Enhanced cell killing by combined 5-FU and X rays could not be explained by either the infliction of additional acute damage in the immediate post-radiation period or an inhibitory effect of 5-FU on the repair of sub-lethal X ray injury. Rather, the enhanced cytotoxicity proved to be dependent on a damage expressed in time periods exceeding the duration of a cell doubling time in vitro. Overall, the data equally suggest that X rays may sensitize the cells to 5-FU. The enhanced cell killing is maximized if the cells are continuously exposed to 5-FU for 48 hours following the X ray exposure. These results indicate that clinical treatment regimens might be useful in evaluating 5-FU infusional scheduling in accordance with these unique requirements, which are not met by conventional bolus 5-FU and X ray therapy fractionation regimens. Ftorafur, a drug proposed to act as a slow release form of 5-FU, was found to show limited cytotoxic potential in vitro and did not significantly enhance cell killing after X ray exposure.

Surgical adjuvant therapy in colon carcinoma: a human tumor spheroid model for evaluating radiation sensitizing agents

HT-29 human colon tumor cells growing as spheroids have been evaluated as a model system for measuring the response of human colon tumor cell to antineoplastic agents. HT-29 cells have been capacity to form spheroids up to 1 mm or more in diameter when grown in spinner culture. The multicellular HT-29 spheroids develop hypoxic centers reflecting the cellular conditions found in human cancer treatment, i.e., nutritionally deficient hypoxic cells that are felt to be a significant source of both radiation and chemotherapy clinical treatment failures. Spheroids of increasing size were radiated and then dispersed into single cells for colony survival assay. Compared with irradiated single cell suspensions, the spheroid cells demonstrated a significant increase in radioresistance. Growing spheroids developed a complex radiation survival curve which was variable with respect to size of the spheroid. The drug 5-Fu was studied to examine in a preliminary fashion its interaction with these resistant cell fractions. In direct cytotoxicity assay, 5-fluorouracil (5-FU) exhibited both cytotoxic and cytostatic effects when the drug was present at a concentration greater than 0.4 microgram/ml. The interaction of 5-FU with x-rays in the HT-29 spheroids was complex and dependent on the type of assay employed (spheroid size versus clonogenicity). The effect of allopurinol, an agent that protects cells from 5-FU toxicity was examined. Allopurinol at a concentration of 100 microgram/ml was found to protect these human colonic carcinoma cells from the cytotoxic effects of 5-FU under conditions resembling those found in vivo. Overall, this HT-29 spheroid system appears to b an interesting model for studying a variety of drug/x-ray interactions in vitro and may prove capable of answering specific questions of preclinical and clinical relevance.