Reproducibility of measurements of potential doubling time of tumour cells in the multicentre National Cancer Institute protocol T92-0045

Spatially-resolved pharmacokinetic/pharmacodynamic modelling of bystander effects of a nitrochloromethylbenzindoline hypoxia-activated prodrug

PURPOSE

Hypoxia-activated prodrugs (HAPs) have the potential for eliminating chemo- and radiation-resistant hypoxic tumour cells, but their activity is often compromised by limited penetration into hypoxic zones. Nitrochloromethylbenzindoline (nitroCBI) HAPs are reduced in hypoxic cells to highly cytotoxic DNA minor groove alkylating aminoCBI metabolites. In this study, we investigate whether a lead nitroCBI, SN30548, generates a significant bystander effect through the diffusion of its aminoCBI metabolite and whether this compensates for any diffusion limitations of the prodrug in tumour tissue.

METHODS

Metabolism and uptake of the nitroCBI in oxic and anoxic cells, and diffusion through multicellular layer cultures, was characterised by LC-MS/MS. To quantify bystander effects, clonogenic cell killing of HCT116 cells was assessed in multicellular spheroid co-cultures comprising cells transfected with cytochrome P450 oxidoreductase (POR) or E. coli nitroreductase NfsA. Spatially-resolved pharmacokinetic/pharmacodynamic (PK/PD) models, parameterised by the above measurements, were developed for spheroids and tumours using agent-based and Green's function modelling, respectively.

RESULTS

NitroCBI was reduced to aminoCBI by POR under anoxia and by NfsA under oxia, and was the only significant cytotoxic metabolite in both cases. In spheroid co-cultures comprising 30% NfsA-expressing cells, non-metabolising cells were as sensitive as the NfsA cells, demonstrating a marked bystander effect. Agent-based PK/PD models provided good prediction of cytotoxicity in spheroids, while use of the same parameters in a Green's function model for a tumour microregion demonstrated that local diffusion of aminoCBI overcomes the penetration limitation of the prodrug.

CONCLUSIONS

The nitroCBI HAP SN30548 generates a highly efficient bystander effect through local diffusion of its active metabolite in tumour tissue.

Cell Kinetics Analysis in Patients Affected by Squamous Cell Carcinoma of the Head and Neck Treated with Primary Surgery and Adjuvant Radiotherapy

BACKGROUND

The increasing complexity of management strategies for patients with head and neck squamous cell carcinoma (HN-SCC) calls for the investigation of new objective prognostic parameters to subdivide patients according to the tumor's biological aggressiveness.

METHODS

We evaluated in 35 HN-SCC patients the pretreatment cell kinetics parameters and DNA ploidy after in vivo infusion of bromodeoxyuridine and flow cytometric analysis. Patients were treated with radical surgery followed by conventional radiation therapy. Locoregional control data are available for follow-up times above five years.

RESULTS

We found that the likelihood of locoregional control for patients with rapidly proliferating HN-SCC characterized by a short potential doubling time (Tpot <5 days) was significantly smaller than for HN-SCC patients with slow tumor proliferation (Tpot >5 days). Moreover, when patients were stratified according to DNA ploidy and Tpot value, we found that the locoregional failure rate for rapidly proliferating tumors was significantly higher for diploid HN-SCCs than for aneuploid HN-SCCs.

CONCLUSION

The present data suggest that patients with resectable HN-SCC characterized by fast growth might have a worse prognosis after surgery and adjuvant conventional radiotherapy and might benefit from more aggressive radiotherapeutic modalities.

Biological Predictors of Response to Radiotherapy in Head and Neck Cancer: Recent Advances and Emerging Perspectives

The study of new biological parameters has received considerable attention in radiotherapy during the last decade due to their potential value in predicting treatment response in squamous cell carcinoma of the head and neck (SCC-HN) and the foreseen possibility of selecting altered fractionation radiotherapy for the individual patient. Although there are established clinical parameters in SCC-HN patients that relate to radiation response (extent of disease, hemoglobin level), recent advances with direct measurement of tumor oxygenation, inherent radiosensitivity and proliferation rate have increased the promise of individualization of treatment strategy according to these radiobiologically based parameters. Molecular research has now identified a host of new biological parameters with potential predictive utility; oncogenes, tumor suppressor genes, cell-cycle control genes, apoptosis genes and angiogenesis genes have been extensively studied and correlated with radiation response. Moreover, study of the epidermal growth factor receptor signal-transduction system as a possible response modulator has recently fostered molecular strategies which employ blockade of the receptor to down-regulate tumor growth. This article briefly reviews and analyzes the main controversial issues and drawbacks that hinder the general use of biological parameters for predicting tumor response to radiotherapy. It highlights the future perspectives of radiotherapy predictive assay research and the need to shift from single-parameter analysis to multiparametric studies which take into account several potential predictors that together are involved in different biological and clinical pathways.

3-D tumor model for in vitro evaluation of anticancer drugs

The efficacy of potential anticancer drugs during preclinical development is generally tested in vitro using cancer cells grown in monolayer; however, a significant discrepancy in their efficacy is observed when these drugs are evaluated in vivo. This discrepancy, in part, could be due to the three-dimensional (3-D) nature of tumors as compared to the two-dimensional (2-D) nature of monolayer cultures. Therefore, there is a need for an in vitro model that would mimic the 3-D nature of tumors. With this objective, we have developed surface-engineered, large and porous biodegradable polymeric microparticles as a scaffold for 3-D growth of cancer cells. Using the MCF-7 cell line as model breast cancer cells, we evaluated the antiproliferative effect of three anticancer drugs: doxorubicin, paclitaxel and tamoxifen in 3-D model vs in 2-D monolayer. With optimized composition of microparticles and cell culture conditions, a density of 4.5 x 10 (6) MCF-7 cells/mg of microparticles, which is an 18-fold increase from the seeding density, was achieved in six days of culture. Cells were observed to have grown in clumps on the microparticle surface as well as in their interior matrix structure. The antiproliferative effect of the drugs in 3-D model was significantly lower than in 2-D monolayer, which was evident from the 12- to 23-fold differences in their IC 50 values. Using doxorubicin, the flow cytometry data demonstrated approximately 2.6-fold lower drug accumulation in the cells grown in 3-D model than in the cells grown as 2-D monolayer. Further, only 26% of the cells in 3-D model had the same concentration of drug as the cells in monolayer, thus explaining the reduced activity of the drugs in 3-D model. The collagen content of the cells grown in 3-D model was 2-fold greater than that of the cells grown in 2-D, suggesting greater synthesis of extracellular matrix in 3-D model, which acted as a barrier to drug diffusion. The microarray analysis showed changes in several genes in cells grown in 3-D, which could also influence the drug effect. In conclusion, the cells grown in 3-D are more resistant to chemotherapy than those grown in 2-D culture, suggesting the significant roles of cellular architecture, phenotypic variations, and extracellular matrix barrier to drug transport in drug efficacy. We propose that our model provides a better assessment of drug efficacy than the currently used 2-D monolayer as many of its characteristic features are similar to an actual tumor. A well-characterized 3-D model can particularly be useful for rapid screening of a large number of therapeutics for their efficacy during the drug discovery phase.

Prediction of Tumour Tissue Diffusion Coefficients of Hypoxia-Activated Prodrugs from Physicochemical Parameters

The therapeutic activity of anticancer agents depends critically on their ability to penetrate through tumour tissue to reach their target cells, a requirement that is especially important for hypoxia-activated prodrugs. Here we use multicellular layers (MCL) grown in vitro from HT29 colon carcinoma cells to measure tissue diffusion coefficients (Dmcl) of 67 structurally diverse benzotriazine di-N-oxides (analogues of the hypoxia-activated prodrug tirapazamine) plus four miscellaneous compounds. An algorithm was developed to predict Dmcl from physicochemical parameters (molecular weight, octanol/water partition coefficient at pH 7.4, number of hydrogen bond donors and acceptors); the fitted multivariate relationship had an explained variance (R2) of 0.907 and predictive power (Q2) of 0.879. Using a subset of nine compounds tested as a single cassette, the algorithm was shown to apply, with some adjustment of coefficients, to MCLs from three other tumour cell lines with differing cell packing densities (SiHa, HCT8-Ea, and HCT8-Ra). The demonstrated relationships provide tools for optimizing extravascular transport of anticancer agents during lead optimization.

Cell kinetics

Cell kinetic concepts have pervaded radiation therapy since the early part of the 20th century and have been instrumental in the development of modern radiotherapy. In this review, the fundamental radiobiological concepts that have been developed based on cell kinetic knowledge will be revisited and discussed in the context of contemporary radiation therapy. This will include how the proliferation characteristics, variation in sensitivity during the cell cycle and the extent of radiation-induced cell cycle delay translate into a variable time for the expression of damage, how cell kinetics interacts with hypoxia and how the response to fractionated radiation schedules is influenced by cell kinetics in terms of repair, redistribution, reoxygenation and repopulation. The promise of combining radiation with new biologically targeted agents and the potential of non-invasive positron emission tomography imaging of proliferation are areas where cell kinetics will continue to influence radiotherapy practice.

Cell Proliferation in Breast Cancer is a Major Determinant of Clinical Outcome in Node-Positive but Not in Node-Negative Patients

The growth rate of a tumor cell population depends on two major factors: the percentage of proliferating cells (cell growth fraction) and the rapidity of their duplication (cell proliferation rate). The authors evaluated the prognostic and predictive value of both kinetics parameters in a large series of breast cancer patients (n=504). The cell growth fraction was determined by MIB-1 immunostaining, the cell proliferation rate by AgNOR analysis. Ki-67 LI (labeling index) and AgNOR area were significantly associated with histotype, histologic grade, tumor size, estrogen/progesterone receptor status, patient age, and lymph node involvement (P<0.005). In the entire series of patients, both kinetics variables were significantly and independently associated with the clinical outcome, but their prognostic relevance was quite different when node-negative and node-positive patients were considered separately. Although in node-positive patients Ki-67 LI and AgNOR area were the unique independent predictors of disease-free and overall survival, they were excluded by the multivariate Cox model in node-negative patients, where only tumor size and estrogen receptor status retained a significant P-value. These results show that in breast carcinoma the cell growth fraction and the cell proliferation rate have a different prognostic impact with respect to the lymph node status and are major determinants of clinical outcome in node-positive patients only. Within this subgroup, the rapidity of cell proliferation as assessed by AgNOR analysis also served as a sensitive predictor of the response to adjuvant treatments.

Drug penetration in solid tumours

To be most effective anticancer drugs must penetrate tissue efficiently, reaching all the cancer cells that comprise the target population in a concentration sufficient to exert a therapeutic effect. Most research into the resistance of cancers to chemotherapy has concentrated on molecular mechanisms of resistance, whereas the role of limited drug distribution within tumours has been neglected. We summarize the evidence that indicates that the distribution of many anticancer drugs in tumour tissue is incomplete, and we suggest strategies that might be used either to improve drug penetration through tumour tissue or to select compounds based on their abilities to penetrate tissue, thereby increasing the therapeutic index.

An audit of delays before and during radical radiotherapy for cervical cancer--effect on tumour cure probability

AIM

To evaluate the potential impact of time delay before and during radical radiotherapy for cervical carcinoma at Addenbrooke's Hospital.

MATERIALS AND METHODS

An audit was undertaken which recorded the number of gaps during external beam radiotherapy (EBRT), overall treatment time, and delay between first oncology consultation to start of radiotherapy, for patients receiving primary radical radiotherapy for cervical cancer in 1996, 1998 and 2001. Radiobiological modelling was used to calculate the tumour control probability (TCP). A questionnaire survey of 62 oncology departments in the U.K. was carried out for comparison.

RESULTS

The percentage of patients completing EBRT without any interruptions was 22, 67 and 94% in 1996, 1998, and 2001, respectively (P = 0.0009). The median overall treatment time was 49, 42 and 39 days in 1996, 1998 and 2001, respectively (P = 0.001). However, the median waiting time to start of radiotherapy increased from 14 days in 1996 to 18 days in 1998 and 35 days in 2001 (P = 0.007).

CONCLUSION

The results from the national survey showed that this pattern of improved overall treatment times accompanied by deterioration in waiting times was also seen in most other U.K. centres. Radiobiological modelling showed that any potential gain in TCP resulting from shorter overall treatment times could be offset entirely by the adverse effect of increasing waiting times. The calculations suggest that the tumours most likely to be adversely affected by long waiting times are those with shorter volume doubling times or a medium chance of tumour control at the outset of treatment. A system of patient triage, and prioritization of patients deemed most likely to benefit from a reduced waiting time, may be necessary in the current climate of limited radiotherapy resources.

In vivo cell kinetic measurements in a randomized trial of continuous hyperfractionated accelerated radiotherapy with or without mitomycin C in head-and-neck cancer

PURPOSE

Tumor cell repopulation is still considered to be a major cause of failure in radiotherapy. In this study, we investigated the influence of cell kinetic parameters on the outcome of patients treated in a randomized trial of accelerated fractionation, with or without mitomycin C, vs. conventional fractionation.

METHODS AND MATERIALS

Sixty-two patients were studied using administration of bromodeoxyuridine (BrdUrd), and cell kinetic parameters were measured using flow cytometry. The patients were treated with either 70 Gy for 7 weeks or 55.3 Gy for 17 continuous days (V-CHART) with or without 20 mg/m(2) mitomycin C on day 5.

RESULTS

The potential doubling time (Tpot) and labeling index (LI) failed to provide any prognostic information with regard to local control or survival. However, the duration of the S phase (Ts) revealed patients whose tumors had a long Ts had significantly worse local control (p = 0.028) and survival (p = 0.034) irrespective of treatment. A similar trend was evident within the different treatment arms particularly associated with overall survival.

CONCLUSIONS

The Ts values of head-and-neck squamous cell cancers provided prognostic information that predicted clinical outcome irrespective of treatment schedule in this study. This neglected parameter of the Tpot method might provide information related to redistribution of cells during fractionated radiotherapy.

Methods for measuring the infrared spectra of biological cells

Infrared (IR) spectroscopy of biological cells is a growing area of research, with many papers focusing on differences between the spectra of cancerous and noncancerous cells. Much of this research has been performed using a monolayer of dehydrated cells. We posit that the use of monolayers can introduce artefacts that lead to an apparent but inaccurate measurement of differences between cancerous and noncancerous cells. Additionally, the use of dried cells complicates the extraction of biochemical information from the IR spectra. We demonstrate that using suspensions of viable cells in aqueous suspension reduces measurement artefacts and facilitates determining the concentration of the major biochemical components via a linear least-squares fit of the component spectra to the spectrum of the cells.

Is there a future for cell kinetic measurements using IdUrd or BdUrd?

PURPOSE

The analysis of causes of radiation failure both in retrospective series of patients with head and neck cancer and in several randomized clinical trials suggests a loss of local control as the overall treatment time increases for the same total dose. This is attributed to tumor cell proliferation during fractionated radiotherapy. As longer treatment times lead to loss of local control, it has been suggested that shorter treatment times could lead to an increase in local control. For this reason accelerated treatment regimens have been and are being designed. However, these treatments may cause severe acute reactions. Due to this, lower total doses are sometimes given. Slowly proliferating tumors, therefore, may do worse when treated with accelerated schedules compared with conventional schedules. In addition, it is not desirable to subject all patients to the more intense acute reactions of accelerated schedules. It would thus be useful to predict which tumors will rapidly proliferate during treatment and are likely to benefit from accelerated radiotherapy. The potential doubling time (Tpot) is defined as the time within which the cell population of a tumor would double if there were no cell loss. The hypothesis is that the median Tpot measured before treatment might correlate with the effective doubling time (Tp) during treatment.

CONCLUSION

Tpot can be calculated knowing the labeling index (LI; proportion of cells incorporating the DNA precursor IdUrd or BdUrd) and Ts (the DNA synthesis time) measured by flow cytometry. A recent multicenter analysis has shown that the only pretreatment kinetic parameter for which some evidence is found for an association with local control is LI, not Tpot. Pitfalls associated with cell kinetic measurements such as assay variability, intratumor and intertumor variability, interlaboratory variability and the problem of an admixture of normal and malignant cells make Tpot not accurate and reproducible enough for a robust predictive assay. It therefore appears that pretreatment Tpot measurements using flow cytometry, provide only a relatively weak predictor of outcome after radiotherapy in head and neck cancer. Immunohistochemistry allows a simple measure of LI and may give additional independent information from labeling patterns, suggesting that this method is the (short term) future for clinical cell kinetic measurements using BdUrd or IdUrd.

Evidence of cell kinetics as predictive factor of response to radiotherapy alone or chemoradiotherapy in patients with advanced head and neck cancer

PURPOSE

The aim of this study was to investigate the potential clinical relevance of cell kinetics parameters to the locoregional control (LRC) and overall survival of patients affected by head and neck squamous cell carcinoma (HN-SCC) treated by conventional radiotherapy, partly accelerated radiotherapy, or alternating chemoradiotherapy.

METHODS AND MATERIALS

Between January 1993 and June 1996,115 patients with HN-SCC at Stage III and IV entered the study. Multiple primary tumor biopsies were obtained 6 h after in vivo infusion of bromodeoxyuridine (BrdUrd), an analogue of thymidine that is incorporated in DNA-synthesizing cells. In vivo S-phase fraction labeling index (LI), duration of S-phase (Ts), and potential doubling time (Tpot) were obtained by analysis of the flow cytometric content of BrdUrd and DNA. Eighty-two patients were randomly assigned to receive either alternating chemoradiotherapy or partly accelerated radiotherapy, whereas 33 other matching patients received conventional radiotherapy.

RESULTS

Univariate LRC analysis showed that LI value was a prognostically significant factor, independent of type of therapy. Multivariate analysis failed to show cell kinetics parameters as statistically significant factors affecting LRC probability and overall survival. However, subgroup analysis showed that LRC probability at 4 years for fast proliferating tumors characterized by a LI >/= 8% was significantly better for patients treated either with alternating chemoradiotherapy or partly accelerated radiotherapy than it was for those treated with conventional radiotherapy. Conversely, LRC probability for slow proliferating tumors (LI < 8%) treated with the three treatment modalities was similar.

CONCLUSIONS

These results showed that, independent of type of treatment, pretreatment cell kinetics provided only a weak prognostic role of outcome in HN-SCC. However, this report raises the hypothesis that fast growing HN-SCC may be more likely to benefit from intensified therapy, as given in this series. Cell kinetics parameters studied by the in vivo BrdUrd/flow cytometry method might be considered predictive factors of response, providing information on which type of treatment may be selected according to tumor proliferation rate.

The value of pretreatment cell kinetic parameters as predictors for radiotherapy outcome in head and neck cancer: a multicenter analysis

PURPOSE

The aim of this study was to assess the potential of pre-treatment cell kinetic parameters to predict outcome in head and neck cancer patients treated by conventional radiotherapy.

MATERIALS AND METHODS

Data from 11 different centers were pooled. Inclusion criteria were such that the patients received radiotherapy alone, and that the radiotherapy was given in an overall time of at least 6 weeks with a dose of at least 60 Gy. All patients received a tracer dose of either iododeoxyuridine (IdUrd) or bromodeoxyuridine (BrdUrd) intravenously prior to treatment and a tumor biopsy was taken several hours later. The cell kinetic parameters labeling index (LI), DNA synthesis time (Ts) and potential doubling time (Tpot) were subsequently calculated from flow cytometry data, obtained on the biopsies using antibodies against I/BrdUrd incorporated into DNA. Each center carried out their own flow cytometry analysis.

RESULTS

From the 11 centers, a total of 476 patients conforming to the inclusion criteria were analyzed. Median values for overall time and total dose were 49 days and 69 Gy, respectively. Fifty one percent of patients had local recurrences and 53% patients had died, the majority from their disease. Median follow-up was 20 months; being 30 months for surviving patients. Multivariate analysis revealed that T-stage, maximum tumor diameter, differentiation grade, N-stage, tumor localization and overall time correlated with locoregional control, in decreasing order of significance. For the cell kinetic parameters, univariate analysis showed that only LI was significantly associated with local control (P=0.02), with higher values correlating with a worse outcome. Ts showed some evidence that patients with longer values did worse, but this was not significant (P=0.06). Tpot showed no trend (P=0.8). When assessing survival in a univariate analysis, neither LI nor Tpot associated with outcome (P=0.4, 0.4, respectively). Surprisingly, Ts did correlate with survival, with longer values being worse (P=0.02). In the multivariate analysis of local control, LI lost its significance (P=0.16).

CONCLUSIONS

The only pretreatment kinetic parameter for which some evidence was found for an association with local control (the best end-point for testing the present hypothesis) was LI, not Tpot, and this evidence disappeared in a multivariate analysis. It therefore appears that pretreatment cell kinetic measurements carried out using flow cytometry, only provide a relatively weak predictor of outcome after radiotherapy in head and neck cancer.