Enhanced efficacy of Escherichia coli nitroreductase/CB1954 prodrug activation gene therapy using an E1B-55K-deleted oncolytic adenovirus vector

Viruses that replicate selectively in cancer cells constitute an exciting new class of anticancer agent. The conditionally replicating adenovirus (CRAd) dl1520, which lacks the E1B-55K gene, has elicited significant clinical responses in humans when used in combination with chemotherapy. A convergent development has been to use replication-defective viruses to express prodrug-activating enzymes in cancer cells. This can sensitize the cancer to prodrug, but depends upon achieving sufficient level, distribution and specificity of enzyme expression within the tumour. In this study, we have expressed the prodrug-activating enzyme nitroreductase (NTR) in the context of an E1B-55K-deleted adenovirus, CRAd-NTR(PS1217H6). We show that CRAd-NTR(PS1217H6) retains oncolytic growth properties, and expresses substantially more NTR than a comparable, replication-defective adenovirus. The combination of viral oncolysis and NTR expression results in significantly greater sensitization of SW480 and WiDr colorectal cancer cells to the prodrug CB1954 in vitro. In vivo, CRAd-NTR(PS1217H6) was shown to replicate in subcutaneous SW480 tumour xenografts in immunodeficient mice, resulting in more NTR expression and greater sensitization to CB1954 than with replication-defective virus. Combination therapy of CRAd-NTR(PS1217H6) with CB1954 reduced tumour growth from 13.5- to 2.8-fold over 5 weeks, and extended median survival from 42 to 81 days, compared with no treatment.

Virus-directed enzyme prodrug therapy: intratumoral administration of a replication-deficient adenovirus encoding nitroreductase to patients with resectable liver cancer

PURPOSE

Virus-directed enzyme prodrug therapy depends on selective delivery of virus encoding a prodrug-activating enzyme to tumor, followed by systemic treatment with prodrug to achieve high levels of the activated cytotoxic at the intended site of action. The use of the bacterial enzyme nitroreductase to activate CB1954 (5-(aziridin-1-yl)-2,4-dinitrobenzamide) to a short lived, highly toxic DNA cross-linking agent has been demonstrated in tumor xenografts. In this study, we report the first clinical trial investigating the feasibility, safety, and transgene expression of a replication-defective adenovirus encoding nitroreductase (CTL102) in patients with liver tumors.

PATIENTS AND METHODS

Patients with resectable primary or secondary (colorectal) liver cancer received a single dose of CTL102 delivered by direct intratumoral inoculation 3 to 8 days before surgical resection.

RESULTS

Eighteen patients were treated with escalating doses of CTL102 (range, 10(8)-5 x 10(11) virus particles). The vector was well tolerated with minimal side effects, had a short half-life in the circulation, and stimulated a robust antibody response. Dose-related increases in tumoral nitroreductase expression measured by immunohistochemical analysis have been observed.

CONCLUSION

Direct intratumoral inoculation of CTL102 to patients with primary and secondary liver cancer is feasible and well tolerated. The high level of nitroreductase expression observed at 1 to 5 x 10(11) virus particles mandates further studies in patients with inoperable tumors who will receive CTL102 and CB1954.

A randomized trial of chemoradiotherapy and chemotherapy after resection of pancreatic cancer

BACKGROUND

The effect of adjuvant treatment on survival in pancreatic cancer is unclear. We report the final results of the European Study Group for Pancreatic Cancer 1 Trial and update the interim results.

METHODS

In a multicenter trial using a two-by-two factorial design, we randomly assigned 73 patients with resected pancreatic ductal adenocarcinoma to treatment with chemoradiotherapy alone (20 Gy over a two-week period plus fluorouracil), 75 patients to chemotherapy alone (fluorouracil), 72 patients to both chemoradiotherapy and chemotherapy, and 69 patients to observation.

RESULTS

The analysis was based on 237 deaths among the 289 patients (82 percent) and a median follow-up of 47 months (interquartile range, 33 to 62). The estimated five-year survival rate was 10 percent among patients assigned to receive chemoradiotherapy and 20 percent among patients who did not receive chemoradiotherapy (P=0.05). The five-year survival rate was 21 percent among patients who received chemotherapy and 8 percent among patients who did not receive chemotherapy (P=0.009). The benefit of chemotherapy persisted after adjustment for major prognostic factors.

CONCLUSIONS

Adjuvant chemotherapy has a significant survival benefit in patients with resected pancreatic cancer, whereas adjuvant chemoradiotherapy has a deleterious effect on survival.

Establishing a national tissue bank for surgically harvested cancer tissue

Surgeons have a part to play

CB 1954: From the Walker Tumor to NQO2 and VDEPT

CB 1954 [5-(aziridin-1-yl)-2,4-dinitrobenzamide] has been the subject of continued interest for over 30 years. As an anti-cancer agent, it represents one of the very few examples of a compound that shows real anti-tumor selectivity. Unfortunately, for the treatment of human disease, this anti-tumor selectivity was seen only in certain rat tumors. The basis for the anti-tumor selectivity of CB 1954 is that it is a prodrug that is enzymatically activated to generate a difunctional agent, which can form DNA-DNA interstrand crosslinks. The bioactivation of CB 1954 in rat cells involves the aerobic reduction of its 4-nitro group to a 4-hydroxylamine by the enzyme NQO1 (DT-diaphorase). The human form of NQO1 metabolizes CB 1954 much less efficiently than rat NQO1. Thus human tumors are insensitive to CB 1954. In view of the proven success of CB 1954 in the rat system, it would be highly desirable to re-create its anti-tumor activity in man. This has led to the development of CB 1954 analogs and other prodrugs activated by nitroreduction such, as those based on a self-immolative activation mechanism. A gene therapy-based approach for targeting cancer cells and making them sensitive to CB 1954 and related compounds has been developed. VDEPT (gene-directed enzyme prodrug therapy) has been used to express an E. coli nitroreductase in tumor cells and human tumor cells transduced to express this enzyme are very sensitive to prodrugs activated by nitroreduction. CB 1954 is in clinical trial for this application. Recently it has been shown that a latent nitroreductase is present in some human tumors. This is NQO2--an enzyme that requires for activity, the non-biogenic compound dihydronicotinamide riboside (NRH) as a cosubstrate. When active, NQO2 is 3000 times more effective than human DT-diaphorase in the reduction of CB 1954. NRH and reduced pyridinium derivatives that, like NRH, act as co-substrates for NQO2, produce a dramatic increase in the cytotoxicity of CB 1954 against human cell lines in vitro and its anti-tumor activity against certain human xenografts in vivo. NQO2 activity is substantially raised in tumor samples from colorectal and hepatoma patients (up to 14-fold). A phase I clinical trial of an NQO2 co-substrate with CB 1954 is scheduled.

Mechanism of cell death induced by the novel enzyme-prodrug combination, nitroreductase/CB1954, and identification of synergism with 5-fluorouracil

Virus-directed enzyme prodrug therapy (VDEPT) utilising the bacterial enzyme nitroreductase delivered by a replication-defective adenovirus vector to activate the prodrug CB1954 is a promising strategy currently undergoing clinical trials in patients with a range of cancers. An understanding of the mechanism of tumour cell death induced by activated CB1954 will facilitate this clinical development. Here, we report that activated CB1954 kills cells predominantly by caspase-dependent apoptosis. This may have important implications for the generation of immune-mediated bystander effects. Further, the use of a replication-defective adenovirus vector to deliver nitroreductase may negatively affect cellular apoptotic pathways stimulated by activated CB1954. Finally, examination of nitroreductase/CB1954 in combination with conventional chemotherapy reveals a synergistic interaction with 5-fluorouracil. These data will facilitate the further development and future clinical trial design of this novel therapy.

Colorectal cancer

Colorectal cancer (CRC) is one of the leading causes of mortality and accounts for approximately 200000 deaths per year in Europe and the USA. Chemotherapy and radiotherapy have established roles in the treatment of colorectal cancer and can contribute to cure rate, prolongation of survival, reduction of local rates of recurrence and enhanced quality of life in patients with advanced disease. However, over the past few years there have been major advances in our understanding of the molecular basis of this tumour and its progression from adenoma to carcinoma that hold potential for translation into novel strategies for the treatment of CRC. Furthermore, newer agents directed against different intracellular targets have also been shown to be efficacious in CRC treatment. Such improvements should continue to lead to increased cure rates in early disease and better overall survival in advanced cases. The aim of this review is to provide an overview of the pathogenesis of CRC and to present the evidence base for chemotherapy and some of the novel strategies that are currently being evaluated in phase I and II trials.

Gene therapy for colorectal cancer

Colorectal cancer is an important public health problem worldwide. Gene therapy has therapeutic potential for patients with advanced or recurrent colorectal cancer, incurable by conventional treatments. To date, many strategies of gene therapy have been explored, including mutant gene correction, prodrug activation, immune stimulation and genetically-modified oncolytic viruses. Although the preclinical results of gene therapy for colorectal cancer have shown promise, gene therapy is still at an early stage of clinical development and has not yet shown a significant therapeutic benefit for patients. The main obstacles for introduction of gene therapy to patients are poor targeting selectivity of the vectors and inefficient gene transfer. As the science supporting tumour-selective vectors evolves, gene therapy may expand rapidly in the clinical practice of colorectal cancer treatment.

A pilot study of adjuvant intraperitoneal 5-fluorouracil using 4% icodextrin as a novel carrier solution

AIM

This pilot study utilised the sustained intraperitoneal (i.p.) dwell properties of an iso-osmotic solution of 4% icodextrin to investigate the tolerability, toxicity and feasibility of home-based i.p. 5FU adjuvant chemotherapy following resective surgery for colorectal cancer.

METHODS

Twenty eligible patients (Dukes' stage B and C with potentially curative resection) underwent perioperative Tenckhoff catheter placement. Ten (6 male, 4 female, aged 46-85; mean 67.5 years) received 5FU chemotherapy. After initial flushing and gradual increase in volumes of 4% icodextrin alone, patients received home-based i.p. 5FU (150-300 mg/m(2)/day given as equal doses at 12-hourly intervals) for 14 days, with a 14-day recovery period, for a maximum of 6 courses. Two incurable patients, treated on compassionate grounds, provided further safety data.

RESULTS

Nine of the 10 patients became proficient in self-treatment with 5FU and two completed 6 courses. Frequent abdominal pain was the main dose-limiting toxicity of 5FU, causing withdrawal of three patients after a high (300 mg/m(2)/day) first course and one following a third course at lower doses. I.p. 5FU concentrations (mean>30000 ngml(-1)) were 1000 fold higher than systemic venous levels. Bacterial peritonitis led to two withdrawals but was not a frequent event (microbiologically confirmed incidence of 1 per 27 catheter-months).

CONCLUSIONS

Home-based i.p. adjuvant chemotherapy is a feasible treatment option in patients with surgically resected colorectal carcinoma.

Effect of specimen length: are the mechanics of individual motion segments comparable in functional spinal units and multisegment specimens?

Functional spinal units (FSUs) are frequently used for in vitro mechanical testing. This approach assumes that the mechanical behavior of the FSUs is equivalent to the mechanics of these segments within the intact spine. The purpose of this study was to determine whether normal spinal mechanics are compromised in FSU preparations. Flexion-extension pure-moment flexibility testing was performed on 13 L2-L5 porcine specimens. The moment-angle relationship of the L3/L4 segment was recorded, and then the multisegment specimens were cut down to L3/L4 FSUs and retested. Comparisons of stiffness, range of motion, and laxity zone were made between conditions. The neutral zone and range of motion parameters were significantly larger in the L3/L4 motion segment compared to the L3/L4 segment tested within the multisegment specimen; the stiffness was not significantly different. These differences were attributed to cutting the supraspinous ligament as this ligament spans several vertebral levels. Flexion mechanical tests performed on FSUs should be interpreted cautiously as the biomechanics of FSUs is altered from normal. Although the choice of spine length depends on the experimental purpose, spinal flexion studies should be performed on multisegment specimens to appropriately represent the anatomical boundary conditions.

Taking Gene Therapy into the Clinic

Gene therapy represents a promising novel treatment strategy for colorectal cancer. Preclinical data has been encouraging and several clinical trials are underway. Many phase 1 trials have proven the safety of the reagents but have yet to demonstrate significant therapeutic benefit. Ongoing efforts are being made to improve the efficiency of gene delivery and accuracy of gene targeting with the aim of enhancing antitumor potency. It is envisaged that gene therapy will be used in combination with other therapies including surgery, chemotherapy, and radiotherapy to facilitate the improvements in cancer treatments in the future.

Immune enhancement of nitroreductase-induced cytotoxicity: studies using a bicistronic adenovirus vector

The nitroreductase (NR)/CB1954 enzyme prodrug system has given promising results in preclinical studies and is currently being assessed in phase I clinical trials. It is well established that there is an immune component to the bystander effect observed with other systems such as thymidine kinase and cytosine deaminase; however, such an effect has not previously been described using NR. We have preliminary data suggesting an immune bystander effect with NR to further examine these effects and their potential enhancement by cytokines, an adenoviral vector containing CMV-NR, an internal ribosome entry site (IRES) and the gene for murine GM-CSF (mGM-CSF) was constructed. The NR-GM-CSF virus was validated in 2 experimental models and demonstrated increased therapeutic efficacy in the MC26 murine colorectal tumour model. These data illustrate that the combination of suicide gene therapy using NR and CB1954 with immune stimulation via GM-CSF gives an improved response compared to either modality alone and suggests that the immune component of this response may be beneficial in combating unresectable, metastatic disease and preventing tumour recurrence.

Comparison of intermittent and continuous palliative chemotherapy for advanced colorectal cancer: a multicentre randomised trial

BACKGROUND

Policies of UK clinicians regarding the duration of chemotherapy for patients with advanced colorectal cancer are not consistent. We aimed to compare effectiveness of continuous and intermittent chemotherapy in such patients.

METHODS

Patients who responded or had stable disease after receiving 12 weeks of the regimens described by de Gramont and Lokich, or raltitrexed chemotherapy, were randomised to either intermittent (a break in chemotherapy, re-starting on the same drug on progression), or continuous chemotherapy until progression.

FINDINGS

354 patients (178 intermittent, 176 continuous) were enrolled from 42 UK centres. At randomisation, 41% of participants had part or complete response; 59% were stable. Only 66 (37%) patients allocated to intermittent treatment restarted as planned, after a median of 130 days. Median time on treatment after restarting was 84 days. Patients in the continuous group remained on treatment for a median of a further 92 days. Similar proportions of patients in both groups received second-line therapy. Patients on intermittent chemotherapy had significantly fewer toxic effects and serious adverse events than those in the continuous group. There was no clear evidence of a difference in overall survival (hazard ratio 0.87 favouring intermittent, 95% CI 0.69-1.09, p=0.23).

INTERPRETATION

Our findings provided no clear evidence of a benefit in continuing therapy indefinitely until disease progression. They showed that it is safe to stop chemotherapy after 12 weeks and re-start the same treatment on progression in patients with chemosensitive advanced colorectal cancer.

Immunotherapy for colorectal cancer

There have been significant improvements in the diagnosis and treatment of colorectal cancer over the past 15 years. However, some 30% of patients with colorectal cancer have disseminated disease at presentation, and furthermore, 50% of patients initially believed to be cured by surgery subsequently relapse and die of the disease. Novel treatment concepts based on understanding the molecular signatures that separate tumor from normal epithelium, such as immunotherapy, are aimed at abolishing microscopic residual disease post standard treatment. The authors provide an overview of progress in the development of specific and nonspecific immunotherapies and explain why definition of end-points and early translation of immunotherapy into the adjuvant field are key to effective use of such agents in the clinical setting.

Intrahepatic arterial versus intravenous fluorouracil and folinic acid for colorectal cancer liver metastases: a multicentre randomised trial

BACKGROUND

The liver is the most frequent site for metastases of colorectal cancer, which is the second largest contributor to cancer deaths in Europe. We did a randomised trial to compare an intrahepatic arterial (IHA) fluorouracil and folinic acid regimen with the standard intravenous de Gramont fluorouracil and folinic acid regimen for patients with adenocarcinoma of the colon or rectum, with metastases confined to the liver.

METHODS

We randomly allocated 290 patients from 16 centres to receive either intravenous chemotherapy (folinic acid 200 mg/m2, fluorouracil bolus 400 mg2 and 22-h infusion 600 mg/m2, day 1 and 2, repeated every 14 days), or IHA chemotherapy designed to be equitoxic (folinic acid 200 mg/m2, fluorouracil 400 mg/m2 over 15 mins and 22-h infusion 1600 mg/m2, day 1 and 2, repeated every 14 days). The primary endpoint was overall survival, and analysis was by intention to treat.

FINDINGS

50 (37%) patients allocated to IHA did not start their treatment, and another 39 (29%) had to stop before receiving six cycles of treatment because of catheter failure. The IHA group received a median of two cycles (0-6), compared with 8.5 (6-12) for the intravenous group. 45 (51%) IHA patients who did not start or did not receive six cycles switched to intravenous treatment. In both groups, grade 3 or 4 toxicity was uncommon. Median overall survival was 14.7 months for the IHA group and 14.8 months for the intravenous group (hazard ratio 1.04 [95% CI 0.80-1.33], log-rank test p=0.79). Similarly, there was no significant difference in progression-free survival.

INTERPRETATION

Our results showed no evidence of an advantage in progression-free survival or overall survival for the IHA group; thus continued use of this regimen cannot be recommended outside of a clinical trial.

Use of a phage display library to identify oligopeptides binding to the lumenal surface of polarized endothelium by ex vivo perfusion of human umbilical veins

Human endothelial-specific targeting peptides were identified by biopanning within freshly-obtained human umbilical cords. Umbilical veins were cleaned in situ and M13 phage display libraries were passed through the cords. Tightly bound phage were recovered following isolation of endothelial cells by collagenase digestion and homogenisation, allowing production of enriched phage libraries for subsequent rounds of panning. After five rounds of biopanning, five promising sequences were selected and the binding of the corresponding phage clones was compared in perfused umbilical veins. Each of these peptides showed substantial binding, although the clone encoding the heptapeptide KPSGLTY showed the greatest, some 89-times greater than insertless phage. Binding of this phage clone was examined to cells in vitro, where it demonstrated at least five-times greater binding to isolated human umbilical vein endothelial cells than to 911, SKOV3, B16F10 and Cos7 cells. These initial peptides may prove useful targeting agents for endothelial-selective delivery, and this powerful approach should be readily applicable to biopanning in a broad range of human vessels ex vivo.

European Study Group for Pancreatic Cancer-1 interim results: a European randomized study to assess the roles of adjuvant chemotherapy and chemoradiation in resectable pancreatic cancer

Background

Pancreatic cancer affects 8–12 per 100 000 population per year in Europe. Following resection, the long-term survival rate is only 10–15 per cent and the role of adjuvant treatment is uncertain. The aims of the study were to answer two questions: (1) whether there is a role for chemoradiation (40 Gy and 5-fluorouracil (5-FU), and (2) whether there is a role for chemotherapy (5-FU–folinic acid (FA)) weekly).

Methods

A multicentre European prospective randomized controlled trial was organized by the European Study Group for Pancreatic Cancer (ESPAC). A 2 × 2 factorial design was used, asking both questions of the same patient, and a pragmatic design asking only one of the two questions of each patient. The data were reviewed at regular intervals by the Independent Data and Safety Monitoring Committee (IDSMC).

Results

Some 531 patients with pancreatic ductal adenocarcinoma were randomized from 80 clinicians in 11 countries. Randomization was stratified by resection margin involvement; 82 per cent of patients were negative. Some 239 patients (45 per cent) are alive to date, at a median follow-up of 9 (interquartile range 1–24) months. Preliminary results show no evidence of a benefit for chemoradiation treatment (median survival 14 months with chemoradiation versus 15·7 months without; P = 0·24). There is some evidence of a survival benefit for patients having chemotherapy (median survival 19·5 months versus 13·5 months with no chemotherapy; P = 0·003). The effect is reduced when taking into account whether patients received radiotherapy (P = 0·01), indicating that radiotherapy may reduce the overall benefit of the chemotherapy. The IDSMC recommended closing recruitment to the chemoradiotherapy arm.

Conclusion

There is no role for adjuvant chemoradiotherapy in pancreatic cancer, but there may be a role for chemotherapy. ESPAC-3 is now randomizing between (1) surgery alone, (2) 5FU–FA and (3) gemcitabine.

Ras as a target in cancer therapy

Ras proteins are guanine nucleotide-binding proteins that are central to the control of normal and transformed cell growth and that are mutated in approximately 30% of human cancers. Binding of ligands to various growth factor receptors activates Ras and subsequently a plethora of downstream effectors including the Raf-1/mitogen-activated protein kinase pathway. For effective ras functioning and for transformation, Ras proteins must undergo post-translational modifications that facilitate their attachment to the plasma membrane. Farnesylation, catalysed by farnesyl protein transferase (FPT), is the first and the most important of these modifications; inhibition of which ablates ras activity, resulting in significant anti-proliferative effect in vitro and in human cancer xenograft models. FPT inhibitors are being assessed in a range of phase I and phase II trials, which incorporate both pharmacokinetic and dynamic end-points. In addition, ras mutations can also generate neo-epitopes for cytotoxic and helper T-cell recognition, rendering ras-mutated tumours a potential target for immunotherapy. Though their clinical evaluation is still in infancy, these two modes of ras targeting represent rational therapeutic strategies that can undergo mechanistic evaluation in the clinic.

Clinical experience with adenovirus in cancer therapy

Gene therapy is emerging as a novel treatment for cancer. Preclinical data utilizing adenovirus vectors have been promising and several clinical trials employing this employing this vector are underway. Data from many phase I trials have established the safety of adenovirus vectors, but have not as yet demonstrated significant therapeutic benefit. In order to refine this approach, continuing efforts are being made to improve antitumor potency, efficiency of gene delivery and accuracy of vector targeting. It is anticipated that adenovirus-mediated gene therapy will be integrated with existing treatment modalities, including surgery, chemotherapy and radiotherapy, to facilitate improvement in cancer treatments in the future.

Breast cancer cell-derived EMMPRIN stimulates fibroblast MMP2 release through a phospholipase A(2) and 5-lipoxygenase catalyzed pathway

Metalloproteinases (MMP) produced by both cancer and normal stromal fibroblast cells play a critical role in the metastatic spread of tumours, however little is known of the regulation of their release. In this report we demonstrate that breast cancer cells in culture release apparently full length soluble EMMPRIN that promotes the release of pro-MMP2 from fibroblasts. The generation of MMP2 is mediated by activation of phospholipase A(2) and 5-lipoxygenase. These results suggest that the production of soluble EMMPRIN, phospholipase A(2) and 5-lipoxygenase activities are sites for potential therapeutic intervention.