Intravenous azidothymidine with fluorouracil and leucovorin: a phase I-II study in previously untreated metastatic colorectal cancer patients

Viruses in colorectal cancer

Increasing evidence suggests that microorganisms might represent at least highly interesting cofactors in colorectal cancer (CRC) oncogenesis and progression. Still, associated mechanisms, specifically in colonocytes and their microenvironmental interactions, are still poorly understood. Although, currently, at least seven viruses are being recognized as human carcinogens, only three of these – Epstein–Barr virus (EBV), human papillomavirus (HPV) and John Cunningham virus (JCV) – have been described, with varying levels of evidence, in CRC. In addition, cytomegalovirus (CMV) has been associated with CRC in some publications, albeit not being a fully acknowledged oncovirus. Moreover, recent microbiome studies set increasing grounds for new hypotheses on bacteriophages as interesting additional modulators in CRC carcinogenesis and progression. The present Review summarizes how particular groups of viruses, including bacteriophages, affect cells and the cellular and microbial microenvironment, thereby putatively contributing to foster CRC. This could be achieved, for example, by promoting several processes – such as DNA damage, chromosomal instability, or molecular aspects of cell proliferation, CRC progression and metastasis – not necessarily by direct infection of epithelial cells only, but also by interaction with the microenvironment of infected cells. In this context, there are striking common features of EBV, CMV, HPV and JCV that are able to promote oncogenesis, in terms of establishing latent infections and affecting p53‐/pRb‐driven, epithelial–mesenchymal transition (EMT)‐/EGFR‐associated and especially Wnt/β‐catenin‐driven pathways. We speculate that, at least in part, such viral impacts on particular pathways might be reflected in lasting (e.g. mutational or further genomic) fingerprints of viruses in cells. Also, the complex interplay between several species within the intestinal microbiome, involving a direct or indirect impact on colorectal and microenvironmental cells but also between, for example, phages and bacterial and viral pathogens, and further novel species certainly might, in part, explain ongoing difficulties to establish unequivocal monocausal links between specific viral infections and CRC.

Effects of the combination of As2O3 and AZT on proliferation inhibition and apoptosis induction of hepatoma HepG2 cells following silencing of Egr-1

Context

Previous studies have demonstrated that 3′-azido-3′-deoxythymidine (AZT) and arsenic trioxide (As₂O₃), traditional chemotherapy agents, can synergically inhibit the growth of hepatocellular carcinoma cells. However, the molecular mechanisms underlying As₂O₃ and AZT anti-hepatoma activity are unknown.

Objective

This study aimed to investigate the role of early growth response protein 1 (Egr-1) in the process of As₂O₃ combined with AZT inhibiting proliferation and inducing apoptosis of human hepatocellular carcinoma HepG2 cells, and explore the possible mechanism.

Materials and methods

The expression of Egr-1 was silenced using siRNA, and then HepG2 cells were treated with As₂O₃ (2 μM) and AZT (20 μM). The rates of cell inhibition and apoptosis were determined by the 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromide (MTT) method and flow cytometry, respectively. The mRNA and protein expression of p53, caspase-3, and Egr-1 were detected by real-time quantitative polymerase chain reaction and Western blotting, respectively.

Results

The inhibitory rate of As₂O₃ (2 μM) combined with AZT (20 μM) on proliferation of HepG2 cells was significantly higher than that of As₂O₃ alone. The combination index (CI) values were 0.2<CI<0.4, showing strong synergic effect. After silencing Egr-1, the proliferation inhibition and proapoptotic ability of As₂O₃ combined with AZT on HepG2 cells were decreased, and the CI value was greater than 1, showing antagonistic effect. In addition, the expression of p53 and caspase-3 mRNA/protein was also significantly decreased.

Conclusion

The present results show that AZT could increase the sensitization of As₂O₃ for inhibiting proliferation and promoting apoptosis of HepG2 cells through regulating the expression of Egr-1, which may control the expression of p53 and caspase-3.

Intrahepatic Chemotherapy with Floxuridine, Leucovorin and Dexamethasone in Continuous Infusion and Mitomycin-c Bolus in Unresectable Hepatic Metastases from Colorectal Cancer: A Phase II Study

Background

Intrahepatic continuous infusion FUDR induces a 50% response rate in patients with hepatic metastases from colorectal cancer. Lower rates have been observed in pretreated patients. The combination of floxuridine plus leucovorin has obtained over 70% responses, with high hepatic toxicity. The use of dexamethasone can decrease hepatic toxicity. A randomized study reported an increase in response rate and a decrease in hepatic toxicity in a group of patients treated with floxuridine plus dexamethasone compared to a group receiving only floxuridine. Moreover, the combination of mitomycin C, carmustine and floxuridine is also effective in pretreated patients.

Methods

On such premises, since July 1993 we have treated 39 patients affected by unresectable hepatic metastases from colon carcinoma (26 patients) and rectal carcinoma (13 patients) with the combination continuous infusion of floxuridine (0.20 mg/kg per day) + leucovorin (7.5 mg/m2/day) + dexamethasone (20 mg on days 1 to 14) and bolus mitomycin C (10 mg/m2 on day 1) via the hepatic artery. Cycles were administered every four weeks. There were as 28 males and 11 females, with a median age of 64 years (range, 39-75) and a median PS = 0. Twenty-two patients were pretreated with systemic chemotherapy including 5-fluorouracil plus leucovorin. Total number of cycles was 189, with a median of 6 cycles per patient (range, 1-12).

Results

Of 39 patients 37 were assessable for response (2 patients were not assessable because they stopped chemotherapy for occlusion of the catheter after the first cycle). There were 3 complete responses (1 in a naive patient and 2 in pretreated patients), 16 partial responses (11 in pretreated patients and 5 in chemonaive patients), 4 minor responses, 4 stable disease and 10 progressive disease. The overall response rate was 51.3% (95 CI, 51.3-86.7%). Median time to progression was 6 months (range, 1-34+). Overall survival was 18 months (range, 1-34+). Of 39 patients, 36 were assessable for toxicity (WHO) (3 patients died after the first cycle for progression of disease): diarrhea and nausea-vomiting grade 3-4 occurred respectively in 15 (41%) and 3 patients (8%); hepatic toxicity was mild.

Conclusions

The treatment we used showed an elevated activity in liver metastases from colorectal cancer even in patients pretreated and resistant to systemic chemotherapy, although toxicity grade 3-4 diarrhea occurred in approximately 40% of the patients.

Could adult hippocampal neurogenesis be relevant for human behavior?

Although the function of adult neurogenesis is still unclear, tools for directly studying the behavioral role of new hippocampal neurons now exist in rodents. Since similar studies are impossible to do in humans, it is important to assess whether the role of new neurons in rodents is likely to be similar to that in humans. One feature of adult neurogenesis that varies tremendously across species is the number of neurons that are generated, so a key question is whether there are enough neurons generated in humans to impact function. In this review we examine neuroanatomy and circuit function in the hippocampus to ask how many granule neurons are needed to impact hippocampal function and then discuss what is known about numbers of new neurons produced in adult rats and humans. We conclude that relatively small numbers of neurons could affect hippocampal circuits and that the magnitude of adult neurogenesis in adult rats and humans is probably larger than generally believed.

Long-term exposure to zidovudine delays cell cycle progression, induces apoptosis, and decreases telomerase activity in human hepatocytes

Zidovudine (3'-azido-3'-deoxythymidine; AZT), which is currently used in the treatment of acquired immunodeficiency syndrome, has been shown to have anticancer properties. In the present study, we examined the mechanisms contributing to increased sensitivity of cancer cells to the growth-inhibitory effects of AZT. This was accomplished by incubating a hepatoma cell line (HepG2) and a normal liver cell line (THLE2) with AZT in continuous culture for up to 4 weeks and evaluating the number of viable and necrotic cells, the induction of apoptosis, cell cycle alterations, and telomerase activity. In HepG2 cells, AZT (2-100 microM) caused significant dose-dependent decreases in the number of viable cells at exposures > 24 h. During a 1-week recover period, there was only a slight increase in the number of viable cells treated with AZT. The decrease in viable cells was associated with an induction of apoptosis, a decrease in telomerase activity, and S and G2/M phase arrest of the cell cycle. During the recovery period, the extent of apoptosis and telomerase activity returned to control levels, whereas the disruption of cell cycle progression persisted. Western blot analysis indicated that AZT caused a decrease in checkpoint kinase 1 (Chk1) and kinase 2 (Chk2) and an increase in phosphorylated Chk1 (Ser345) and Chk2 (Thr68). Similar effects, to lesser extent, were observed in THLE2 cells given much higher concentrations of AZT (50-2500 microM). These data show that HepG2 cells are much more sensitive than THLE2 cells to AZT. They also indicate that a combination of a delay of cell cycle progression, an induction of apoptosis, and a decrease in telomerase activity is contributing to the decrease in the number of viable cells from AZT treatment, and that checkpoint enzymes Chk1 and Chk2 may play an important role in the delay of cell cycle progression.

Anti-HIV drugs for cancer therapeutics: back to the future?

The use of anti-HIV drugs as cancer treatments is not new. Azidothymidine was studied as an antineoplastic in the 1990s, but despite promising in vitro data, clinical trials showed little antitumour activity. HIV protease inhibitors were developed in the early 1990s, and their subsequent incorporation into highly active antiretroviral therapy (HAART) has profoundly changed the natural history of HIV infection. The potential antitumour properties of these drugs have been investigated because of their success in treating HIV-related Kaposi's sarcoma. HAART's effects on Kaposi's sarcoma did not always correlate with immune reconstitution, and activity against other solid and haematological malignancies has been established. Inhibition of tumour-cell invasion and angiogenesis were properties first ascribed to inhibition of HIV protease; however, they have pleiotropic antitumour effects, including inhibition of inflammatory cytokine production, proteasome activity, cell proliferation and survival, and induction of apoptosis. HIV protease inhibitors are thus a new class of anticancer drugs with multiple effects, and other anti-HIV drugs might hold similar promise.

Simultaneous alteration of de novo and salvage pathway to the deoxynucleoside triphosphate pool by (E)-2'-deoxy-(fluoromethylene)cytidine (FMdC) and zidovudine (AZT) results in increased radiosensitivity in vitro

To test whether a thymidine analog zidovudine (=AZT), is able to modify the radiosensitizing effects of (E)-2'-Deoxy-(fluoromethylene)cytidine (FMdC). A human colon cancer cell line Widr was exposed for 48 hours prior to irradiation to FMdC. Zidovudine was added at various concentrations immediately before irradiation. We measured cell survival and the effect of FMdC, AZT and FMdC + AZT on deoxynucleotide triphosphate pool. FMdC results in a significant increase of radiosensitivity. The enhancement ratios (ER =surviving fraction irradiated cells/surviving fraction drug treated and irradiated cells), obtained by FMdC or AZT alone are significantly increased by the combination of both compounds. Adding FMdC to AZT yields enhancement ratios ranging from 1.25 to 2.26. FMdC reduces dATP significantly, with a corresponding increase of TTP, dCTP and dGTP. This increase of TTP, dCTP and dGTP is abolished with the addition of AZT. Adding AZT to FMdC results in a significant increase of the radiosensitizing effect of FMdC. This combination appears to reduce the reactive enhancement of TTP, dCTP and dGTP induced by FMdC while it does not affect the inhibitory effect on dATP.

Induction of thymidine phosphorylase expression by AZT contributes to enhancement of 5'-DFUR cytotoxicity

Thymidine phosphorylase (TP) regulates intracellular thymidine metabolism and can enhance the anti-tumor effectiveness of 5'-deoxy-5-fluorouridine (5'-DFUR) by conversion of the pro-drug 5'-DFUR to 5-fluorouracil (5-FU) in tumor tissues. 5'-DFUR is an effective anti-tumor drug in cells expressing high levels of TP. 3'-Azido 3'-deoxythymidine (AZT) is a thymidine analog that has been proven useful in the treatment of acquired immunodefiency syndrome (AIDS). In this study, we found that AZT induces TP expression and enhances the sensitivity of human myeloid leukemia U937 cells to 5'-DFUR. Both the protein level and the activity of TP in U937 cells were elevated for 48h after exposure to AZT (20, 100 or 300muM). AZT enhanced TP promoter activity in a dose-dependent manner. AZT also increased TP mRNA levels in U937 cells as assayed by Real-time reverse-transcription PCR. AZT enhanced the cytotoxic effect of 5'-DFUR on U937 cells. A TP inhibitor, TPI, abrogated the cytotoxic activity of 5'-DFUR, and attenuated the combined cytotoxicity of AZT and 5'-DFUR. These results suggest that AZT enhances the cytotoxic effect of 5'-DFUR on U937 cells by upregulating TP activity in addition to its inhibition of thymidine kinase (TK) activity and reduction of intracellular dTTP pools.

Azidothymidine induces apoptosis and inhibits cell growth and telomerase activity of human parathyroid cancer cells in culture

Telomerase activity has been correlated to parathyroid carcinoma. Because its role in acquisition of a malignant phenotype by parathyroid cells is unclear, we treated telomerase-positive cultured human parathyroid cancer cells with the telomerase inhibitor AZT, evaluating cell telomerase activity, cytotoxic effects, growth, and morphological changes. In vitro exposure of these cells to AZT correlated with inhibition of cell proliferation.

INTRODUCTION

Parathyroid carcinoma represents an uncommon cause of primary hyperparathyroidism, whose spectrum of clinical presentation, degree of malignancy, and prognosis are difficult to be properly identified. Neck surgery, specifically an en bloc resection of primary tumor, is the only curative treatment. Alternatively, affected patients could undergo repetitive palliative surgical exeresis of metastatic nodules. It has been previously shown that telomerase activity is specifically present in parathyroid carcinoma cells, being absent in hyperplastic and adenomatous tissues. Thus, determination of telomerase activity could represent either a useful diagnostic molecular marker for human parathyroid carcinoma or a potential target for pharmacological intervention in a malignant neoplasia usually resistant to chemo- and radiotherapeutic interventions.

MATERIALS AND METHODS

To further investigate the role of telomerase activity in acquisition of a malignant phenotype by parathyroid cells, we treated telomeric repeat amplification protocol-positive cultured human parathyroid cells with the telomerase inhibitor zidovudine, 3'-azido-3'deoxythymidine (AZT), evaluating cell telomerase activity, growth characteristics, potential cytotoxic effects, and morphological changes.

RESULTS

Our findings indicate that in vitro exposure of human parathyroid cancer cells to AZT resulted in intracellular accumulation of AZT-monophosphate (AZT-MP) and inhibition of telomerase, which correlate with inhibition of human parathyroid cancer cell proliferation. Moreover, we also found that AZT induced an apoptotic rather than a necrotic type of cellular death. None of these effects were observed in human adenomatous parathyroid cells in culture.

CONCLUSIONS

Altogether these results indicate that AZT may be a highly effective agent against cancer parathyroid cells proliferation, which is an extremely important observation for a neoplasia which shows lack of response to classical pharmacological and physical antiblastic treatments.

Telomerase Inhibition Using Azidothymidine in the HT-29 Colon Cancer Cell Line

BACKGROUND

We investigated the effects of telomerase inhibition by using the reverse transcriptase inhibitor azidothymidine (AZT) in the human colorectal cancer cell line HT-29 in the presence and absence of 5-fluorouracil (5-FU).

METHODS

HT-29 cells were cultured in the presence of AZT. Telomerase activity was measured by using the telomerase repeat amplification protocol. Telomere length was determined by Southern analysis. The colorimetric microtiter assay was performed to determine the cytotoxic effects of AZT, alone and in combination with 5-FU.

RESULTS

The presence of 3'-azido-3'-deoxythymidine triphosphate (AZT-TP) effectively inhibited telomerase extracted from HT-29 cells. HT-29 cells cultured with 125 microM of AZT underwent fewer total population doublings over 91 days. Southern analysis revealed that telomere attrition occurred within this period. Exposure to 125 microM of AZT resulted in slightly reduced viability (10%) of HT-29 cells. However, the presence of AZT increased 5-FU cytotoxicity, suggesting that the effects of these two drugs are synergistic.

CONCLUSIONS

The data are consistent with telomerase inhibition having growth-inhibitory effects in addition to those predicted to accompany loss of telomere function. Further studies using specific small-molecule inhibitors will confirm whether the growth-inhibitory and 5-FU-sensitivity effects seen here are a direct result of telomerase inhibition.

Chronic in vitro exposure to 3'-azido-2', 3'-dideoxythymidine induces senescence and apoptosis and reduces tumorigenicity of metastatic mouse mammary tumor cells

Normal cells in culture divide a certain amount of times and undergo a process termed replicative senescence. Telomere loss is thought to control entry into senescence. Activation of telomerase in tumors bypasses cellular senescence and is thus a requirement for tumor progression. We reported previously the preferential incorporation of 3'-azido-2', 3'-dideoxythymidine (AZT) in telomeric sequences of immortalized cells in culture. In this work, we have investigated the effects of chronic in vitro AZT exposure on F3II mouse mammary carcinoma cells. We demonstrate, for the first time, that AZT-treated tumor cells have a reduced tumorigenicity in syngeneic BALB/c mice. Tumor incidence was reduced and survival was prolonged in animals inoculated with AZT-treated cells when comparing with control counterparts. The number and size of spontaneous metastases were also decreased in animals inoculated with AZT-treated cells. In addition, we present evidence of morphological and biochemical signs of senescence, as shown by the staining for senescence associated beta-galactosidase activity, and induction of programmed cell death, as demonstrated by an increase of caspase-3 activity, in tumor cells exposed to AZT. These data indicate that chronic exposure of mammary carcinoma cells to AZT may be sufficient to induce a senescent phenotype and to reduce tumorigenicity.

New drugs in the treatment of colorectal carcinoma

BACKGROUND

Treatment with 5-fluorouracil (5-FU) plus leucovorin has been the unofficial standard therapy for patients with colorectal carcinoma (CRC) for more than a decade; however, the optimal dose and schedule remain a matter of debate. Recently several new drugs have shown activity in this disease. These include irinotecan (CPT-11); oxaliplatin; the thymidylate synthase inhibitors raltitrexed, uracil/tegafur (UFT), capecitabine, and S-1; the biochemical modulators trimetrexate and 5-ethynyluracil; and the monoclonal antibody 17-1A.

METHODS

The results of clinical trials with these and other new agents, as well as their current status and main characteristics, were reviewed.

RESULTS

Several of these agents, some with a novel mechanism of action, show promising activity in CRC. In combination with 5-FU and leucovorin, trimetrexate showed encouraging response rates in Phase II studies. Other interesting agents include capecitabine, UFT, and S-1. The biochemical modulator 5-ethynyluracil may allow the oral administration of 5-FU; however, results of Phase II clinical trials are not yet available. CPT-11 is in the most advanced stage of development and, based on consistent data generated in extensive Phase II studies, currently appears to be a reasonable choice for 5-FU-resistant or refractory disease. Another promising agent is oxaliplatin, which showed activity as first-line and second-line treatment.

CONCLUSIONS

Several new agents have shown promise in the treatment of CRC, and changes in the standard treatment of advanced or high risk CRC appear likely in the near future.

Maximum tolerable doses of intravenous zidovudine in combination with 5-fluorouracil and leucovorin in metastatic colorectal cancer patients. Clinical evidence of significant antitumor activity and enhancement of zidovudine-induced DNA single strand breaks in peripheral nuclear blood cells

BACKGROUND

Experimental studies have demonstrated that 5-fluorouracil (5-FU) enhances zidovudine (AZT)-induced DNA strand breaks and cytotoxicity. Phase I studies have demonstrated that the maximum tolerable dose (MTD) of AZT is 8000 mg/sqm when administered i.v. over two hours after weekly 5-FU + l-leucovorin (LV), and that this combination has promising antitumor activity. The purpose of this study was therefore to evaluate the antitumor activity of weekly bolus 5-FU + LV + AZT, administered at its MTD, and to determine whether 5-FU enhances AZT-induced DNA strand breaks in blood nuclear cells.

PATIENTS AND METHODS

Twenty-nine chemotherapy-naïve metastatic colorectal cancer patients with measurable disease entered the study to evaluate the activity of a weekly 5-FU 500 mg/m2 i.v. bolus + LV 250 mg/m2 i.v. two-hour infusion + AZT 8000 mg/m2 i.v. two-hour infusion. In 10 different patients, who during three different weeks received 5-FU + LV, AZT and 5-FU + LV + AZT, DNA strand breaks in blood nuclear cells were determined by a fluorescent analysis of DNA unwinding.

RESULTS

Treatment was generally well tolerated and WHO grades III-IV toxicities, consisting mostly of diarrhea (17%), were uncommon. One patient died of severe diarrhea with consequent hypokalemia and cardiac arrhythmia. All patients were considered evaluable for response, and 3 (10%) complete and 10 (35%) partial responses were observed, for an objective response rate of 45% (95% confidence limit interval 26%-64%). Both 5-FU + LV and AZT decreased the percentage of double stranded DNA in nuclear blood cells. The greatest effect was observed with 5-FU + LV + AZT, which reduced the percentage of double stranded DNA to 50% and 36% after 24 and 48 hours, respectively, and this interaction between 5-FU + LV and AZT was found to be cumulative.

CONCLUSIONS

These studies demonstrate that the present dose and schedule of AZT in combination with 5-FU + LV has significant activity in metastatic colorectal cancer and that the combination of 5-FU + LV with AZT increases the amount of DNA damage. Therefore, AZT in combination with 5-FU + LV warrants further study in colorectal cancer.