Cisplatin-DNA adduct formation in patients treated with cisplatin-based chemoradiation: lack of correlation between normal tissues and primary tumor

Purpose

In this study, the formation of cisplatin-DNA adducts after concurrent cisplatin-radiation and the relationship between adduct-formation in primary tumor tissue and normal tissue were investigated.

Methods

Three intravenous cisplatin-regimens, given concurrently with radiation, were studied: daily low-dose (6 mg/m²) cisplatin, weekly 40 mg/m², three-weekly 100 mg/m². A ³²P-postlabeling technique was used to quantify adducts in normal tissue [white blood cells (WBC) and buccal cells] and tumor.

Results

Normal tissue samples for adduct determination were obtained from 63 patients and tumor biopsies from 23 of these patients. Linear relationships and high correlations were observed between the levels of two guanosine- and adenosine–guanosine-adducts in normal and tumor tissue. Adduct levels in tumors were two to five times higher than those in WBC (P < 0.001). No significant correlations were found between adduct levels in normal tissues and primary tumor biopsies, nor between WBC and buccal cells.

Conclusions

In concurrent chemoradiotherapy schedules, cisplatin adduct levels in tumors were significantly higher than in normal tissues (WBC). No evidence of a correlation was found between adduct levels in normal tissues and primary tumor biopsies. This lack of correlation may, to some extent, explain the inconsistencies in the literature regarding whether or not cisplatin-DNA adducts can be used as a predictive test in anticancer platinum therapy.

Hypoxia in head and neck cancer: How much, how important?

BACKGROUND

Hypoxia develops in tumors because of a less ordered, often chaotic, and leaky vascular supply compared with that in normal tissues. In preclinical models, hypoxia has been shown to be associated with treatment resistance and increased malignant potential. In the clinic, several reports show the presence and extent of tumor hypoxia as a negative prognostic indicator. This article reviews the biology and importance of hypoxia in head and neck cancer.

METHODS

A review of literature was carried out and combined with our own experience on hypoxia measurements using exogenous and endogenous markers.

RESULTS

Hypoxia can increase resistance to radiation and cytotoxic drugs and lead to malignant progression, affecting all treatment modalities, including surgery. Hypoxia measurements using electrodes, exogenous bioreductive markers, or endogenous markers show the presence of hypoxia in most head and neck cancers, and correlations with outcome, although limited, consistently indicate hypoxia as an important negative factor. Each hypoxia measurement method has disadvantages, and no "gold standard" yet exists. Distinctions among chronic, acute, and intermediate hypoxia need to be made, because their biology and relevance to treatment resistance differ. Reliable methods for measuring these different forms in the clinic are still lacking. Several methods to overcome hypoxia have been tested clinically, with radiosensitizers (nimorazole), hypoxic cytotoxins (tirapazamine), and carbogen showing some success. New treatments such as hypoxia-mediated gene therapy await proper clinical testing.

CONCLUSIONS

The hypoxia problem in head and neck cancer needs to be addressed if improvements in current treatments are to be made. Increased knowledge of the molecular biology of intermediate, severe, and intermittent hypoxia is needed to assess their relevance and indicate strategies for overcoming their negative influence.

Rapid fluorescence ratio assay for detecting changes in radiosensitivity

To test modifications in sensitization to radiation or drugs in preclinical studies of cancer therapy, the colony-forming assay is regarded as the gold standard. Because this assay is time consuming, somewhat laborious, and unsuitable for rapid screening, development of other assays is desirable. We describe here an assay based on the detection of enhanced green fluorescence protein (EGFP) with flow cytometry that is particularly suitable for genetic manipulation studies in which the gene of interest is introduced together with EGFP as reporter. It is easily adaptable to other reporters, however, whether naturally fluorescent or requiring immunochemical staining. Cells are irradiated as mixed populations of a known standard cell line (nonfluorescent) together with the genetically manipulated cell line expressing EGFP. Ratios of fluorescent and nonfluorescent cells are measured before treatment and several days after treatment. If the cell populations have equal radiosensitivities, the ratio remains unchanged. Changes in the ratio indicate changes in radiosensitivity. The assay was validated for two situations in which dominant negative peptides inhibiting DNA repair were expressed in A549 human lung cells and affected radiosensitivity.

Hypoxia and perfusion measurements in human tumors--initial experience with pimonidazole and IUdR

We describe our preliminary studies on the development of methods to measure hypoxia in standard paraffin sections of human tumors. Three parameters were investigated. First, image analysis of tumor vascularity yielded the parameter diffusion limited fraction (DLF), which is the amount of tumor tissue greater than a fixed distance from the nearest blood vessel. Secondly, the amount of tumor tissue stained with antibodies against bound reduced products of the bioreductive marker pimonidazole was assessed. Finally, the fraction of blood vessels showing no surrounding tumor tissue labeled with lUdR, a cell kinetic marker, was measured. DLF and pimonidazole monitor primarily chronic hypoxia, while it is hypothesized that the IUdR-negative fraction monitors acute hypoxia. Feasibility was demonstrated in a series of 10 esophageal and 10 rectal tumors (no drug administration), 10 cervix tumors (pimonidazole) and 14 head and neck tumors (pimonidazole and lUdR). Significant differences between tumors were found for all parameters. DLF correlated significantly with the pimonidazole fraction when all images of all tumors were included, although mean values per tumor showed no correlation. The IUdR-negative fraction did not correlate with either of the other two parameters. We conclude that it is feasible to measure hypoxia-related, and possibly perfusion-related, parameters on paraffin sections for predictive purposes, although each method needs further validation. Each parameter will be correlated with outcome in a larger study on head and neck tumors treated with surgery with or without postoperative radiotherapy.

Accelerated hyperfractionation (AHF) compared to conventional fractionation (CF) in the postoperative radiotherapy of locally advanced head and neck cancer: influence of proliferation

Based on the assumption that an accelerated proliferation process prevails in tumour cell residues after surgery, the possibility that treatment acceleration would offer a therapeutic advantage in postoperative radiotherapy of locally advanced head and neck cancer was investigated. The value of T(pot) in predicting the treatment outcome and in selecting patients for accelerated fractionation was tested. Seventy patients with (T2/N1-N2) or (T3-4/any N) squamous cell carcinoma of the oral cavity, larynx and hypopharynx who underwent radical surgery, were randomized to either (a) accelerated hyperfractionation: 46.2 Gy per 12 days, 1.4 Gy per fraction, three fractions per day with 6 h interfraction interval, treating 6 days per week or (b) Conventional fractionation: 60 Gy per 6 weeks, 2 Gy per fraction, treating 5 days per week. The 3-year locoregional control rate was significantly better in the accelerated hyperfractionation (88 +/- 4%) than in the CF (57+/- 9%) group, P=0.01 (and this was confirmed by multivariate analysis), but the difference in survival (60 +/- 10% vs 46 +/- 9%) was not significant (P=0.29). The favourable influence of a short treatment time was further substantiated by demonstrating the importance of the gap between surgery and radiotherapy and the overall treatment time between surgery and end of radiotherapy. Early mucositis progressed more rapidly and was more severe in the accelerated hyperfractionation group; reflecting a faster rate of dose accumulation. Xerostomia was experienced by all patients with a tendency to be more severe after accelerated hyperfractionation. Fibrosis and oedema also tended to be more frequent after accelerated hyperfractionation and probably represent consequential reactions. T(pot) showed a correlation with disease-free survival in a univariate analysis but did not prove to be an independent factor. Moreover, the use of the minimum and corrected P-values did not identify a significant cut-off. Compared to conventional fractionation, accelerated hyperfractionation did not seem to offer a survival advantage in fast tumours though a better local control rate was noted. This limits the use of T(pot) as a guide for selecting patients for accelerated hyperfractionation. For slowly growing tumours, tumour control and survival probabilities were not significantly different in the conventional fractionation and accelerated hyperfractionation groups. A rapid tumour growth was associated with a higher risk of distant metastases (P=0.01). In conclusion, tumour cell repopulation seems to be an important determinant of postoperative radiotherapy of locally advanced head and neck cancer despite lack of a definite association between T(pot) and treatment outcome. In fast growing tumours accelerated hyperfractionation provided an improved local control but without a survival advantage. To gain a full benefit from treatment acceleration, the surgery-radiotherapy gap and the overall treatment time should not exceed 6 and 10 weeks respectively.

Use of thymidine analogues to indicate vascular perfusion in tumours

Temporary reduction in blood-flow within tumour blood vessels can reduce oxygen supply leading to transient perfusion-limited hypoxia. Consequent selection of cells with mutations and reduced radiosensitivity can lead to disease progression and treatment-resistance. In the present study, we investigated whether heterogeneity of labelling after thymidine analogue administration is related to perfusion variations, and if so, could it be quantified and used as a perfusion indicator. Perfusion in murine RIF1 tumours was reduced by hydralazine or increased by nicotinamide and the mice subsequently injected with IdUrd. Tumours were halved for analysis by both flow cytometry and immunohistochemistry. Tumour sections were stained for vasculature and IdUrd. Each blood vessel was scored for the density of IdUrd-labelled cells surrounding it, using a semi-quantitative scoring system. Flow cytometry showed that the IdUrd labelling index and intensity decreased by approximately 50% after hydralazine. In tumour sections of control animals, 2.9% of vessels showed no IdUrd label. In contrast, after hydralazine almost 50% of vessels had no surrounding IdUrd labelling, whereas after nicotinamide there were fewer vessels with low labelling and a higher median score. In conclusion, changes of tumour perfusion by pharmacological agents is reflected in changes in tumour-cell labelling by the thymidine analogue IdUrd, suggesting that IdUrd labelling could be used to indicate perfusion in individual vessels in human tumours.

Diffusion limited hypoxia estimated by vascular image analysis: comparison with pimonidazole staining in human tumors

PURPOSE

To assess diffusion limited hypoxia in human tumors using image analysis of vasculature and to compare it with the bioreductive marker pimonidazole as an independent method.

MATERIALS AND METHODS

To set up the method, nine rectal adenocarcinomas and ten squamous cell carcinomas were analyzed. To validate the method, ten squamous cell carcinomas of the cervix were analyzed from patients who were injected with pimonidazole and biopsied approximately 24 h later. Sections of the rectal and esophageal tumors were stained for vasculature, while cervix tumor sections were double stained for vasculature and pimonidazole. Tumor areas were delineated on digitized images, and the proportion of tumor tissue greater than a fixed distance from the nearest blood vessel (called diffusion limited fraction, DLF) was then calculated. The proportion of tumor area stained for pimonidazole was also measured.

RESULTS

There was a wide variation between tumors in both the vascular-derived DLF and in the pimonidazole-stained fraction. Average DLFs varied between 1.5 and 92% for different tumors, with significant differences between them. The area stained by pimonidazole was significantly smaller than DLF for all tumors. The correlation between pimonidazole area and DLF was significant in three of seven tumors containing > or = 3 images. When images from all tumors (n=123) were analyzed together, the correlation was highly significant (r=0.47, P<0.0001).

CONCLUSION

The vascular derived DLF correlates significantly with pimonidazole staining, but there was large scatter. Both methods may underestimate perfusion limited hypoxia.

DNA-adduct levels as a predictor of outcome for NSCLC patients receiving daily cisplatin and radiotherapy

We aimed to investigate whether biological factors related to radiosensitivity and chemosensitivity have prognostic significance in non-small-cell-lung-cancer (NSCLC) patients treated with daily low doses of cisplatin and radiotherapy. We treated 27 NSCLC patients with concomitant daily low-dose cisplatin and radiotherapy between 1993 and 1995. Tumour specimens were analyzed for p53 and bcl-2 expression, and for cell proliferation using antibodies against ki-67. In addition, apoptosis was measured by an end-labeling technique (TUNEL). Finally, cisplatin-induced DNA modification in buccal cells was assessed immunocytochemically using a specific anti-serum. Univariate and multivariate analyses were performed to assess the association between the different variables and survival. The median follow-up was 41 months, and 21 patients (78%) have died. In a univariate analysis, age, tumour stage and cisplatin-DNA-adduct staining were the only factors significantly associated with survival (p < 0.05, log-rank test). p53, bcl-2, Ki-67 and apoptosis showed no relationship with outcome. Multivariate analysis revealed that cisplatin-DNA-adduct staining remained an independent prognostic factor (hazard ratio, 0.10, 95% CI, 0.02-0.49), with shorter survival times for patients with low adduct staining.

In vitro differentiation characteristics of human skin fibroblasts: correlations with radiotherapy-induced breast fibrosis in patients

PURPOSE

To determine whether there is an association between dermal fibroblast differentiation characteristics in vitro and breast fibrosis developing in patients following radiotherapy for breast cancer.

MATERIALS AND METHODS

Three hundred and eighty-five patients had been characterized for the degree of breast fibrosis and the level of clinical risk factors for fibrosis as established by logistic regression. Early-passage fibroblasts from 79 patients with a high (HR) or low (LR) level of risk factors were studied in vitro. The percentage differentiated cells (%DC) 7 days after 0 and 8 Gy was scored, and unirradiated colonies were scored for the ratio of early:late fibroblast differentiation stages (E:L ratio).

RESULTS

%DC: For the 0 Gy data there was a significant interpatient variation (CoV = 55%, p = 0.0001). HR patients with breast fibrosis had a higher %DC compared with patients without (p = 0.017). E:L ratio: for HR patients there was a significant interpatient variation (82%, p = 0.0030) and a lower E:L ratio for patients with fibrosis compared with those without (p = 0.086), but for LR patients this relationship was reversed (p = 0.079)

CONCLUSIONS

There was a true interpatient variation in the in vitro parameters of fibroblast differentiation but insufficient correlation with observed fibrosis after radiotherapy for use as a predictive test.

Translational research offers individually tailored treatments for cancer patients

The measurement of the effect of cisplatin on DNA has become feasible with the development of antibodies against DNA adducts. In a phase II dose escalation trial with concomitant radiotherapy and daily cisplatin in lung cancer, we found that patients with high DNA adduct levels measured in the buccal mucosa had a much higher survival rate than patients with a low or undetectable amount of cisplatin-DNA adducts. The use of this assay may therefore allow the selection of individual patients for concomitant treatment with cisplatin and radiotherapy, as has been shown to be effective in randomized trials in patients with lung, head and neck, and cervix malignancies. To predict the response to radiation treatment, assays have been developed for tumor growth potential by measuring the labeling index after intravenous injection of IdUrd or by estimating cyclin D1 expression. Intrinsic radiation sensitivity of human tumors can be estimated by conventional techniques, which are probably too slow or cumbersome for routine use, or with more rapid assays, such as those for chromosome damage with fluorescent probes. These assays should be able to guide us in the adaptation of the individual radiation doses that should be applied and to select patients for an accelerated or hyperfractionated regimen. Pretreatment levels of apoptosis may also be helpful in predicting treatment outcome, although the data so far show inconsistent results. A better understanding of the signal transduction pathways involved in radiation-induced apoptosis may help in the design of studies aimed at modulating the apoptotic response, thereby increasing cell kill. We have recently shown that alkyllysophospholipids, which inhibit mitogenic signaling, induce apoptosis in a variety of tumor cell lines. In combination with ionizing radiation, these compounds cause an enhancement of apoptotic cell kill. This type of a signaling-based intervention could form the basis for new therapeutic strategies. The role of hormonal therapy in breast cancer patients, both in an adjuvant setting and for the treatment of disseminated disease, is becoming increasingly important. The development of a functional assay for the estrogen receptor (ER-FASAY), based on a yeast growth assay, provides a better way than the classical immunohistochemistry assay of estimating abnormal function of the receptor in tumors. These assays are simply examples, illustrating how clinicians could improve the therapeutic outcome for their patients by implementing knowledge obtained in the laboratory in clinical decision making. With further optimization of these assays, this holds the promise for the future that the treatment for each patient can be tailored rationally to the biology of the individual.

Potential of radiation-induced chromosome aberrations to predict radiosensitivity in human tumour cells

PURPOSE

To validate whether the number of aberrations could be used as a measure of the radiosensitivity of human tumour cells. If so, this would potentially provide a more rapid method than the colony assay to predict radiocurability in human tumour biopsy material.

MATERIALS AND METHODS

A panel of 13 human tumour cell lines was investigated, covering a wide range of radiosensitivities. Fluorescence in situ hybridization (FISH) employing whole chromosome probes was used to detect aberrations.

RESULTS

A dose-dependent increase in radiation-induced chromosome aberrations was observed in all cell lines. A good correlation (r=0.90) was found between cell survival and total chromosome aberrations in 12 of the 13 cell lines (92%), with one exception. A poorer correlation was observed between cell survival and stable- (r=0.85) and unstable-type aberrations (r=0.81). Survival-aberration correlations for individual radiation doses were worse, although statistically significant. The exceptional cell line showed significantly more aberrations for a given level of cell kill than expected based on data for the other lines.

CONCLUSION

This study indicates that radiation-induced chromosome aberrations can be used as a potential predictor of intrinsic radiosensitivity for the majority of human tumours when more than one dose level is tested. This could aid the design of radiotherapy schedules for each individual patient, or in the decision of whether to use an alternative therapy.

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.

The presence of wild-type TP53 is necessary for the radioprotective effect of the Bowman-Birk proteinase inhibitor in normal fibroblasts

In the present study we have demonstrated that the Bowman-Birk proteinase inhibitor (BBI) protected normal fibroblasts from a radiation-induced reduction in cell survival, whereas in transformed fibroblasts no radioprotective effect was observed. It was shown that BBI reduced the radiation-induced protein stabilization and DNA-binding activity of TP53 (formerly known as p53) in normal fibroblasts. In transformed fibroblasts, BBI failed to induce these effects. The analysis of the TP53 gene in transformed fibroblasts revealed a mutation in exon 5. As a consequence of this mutation, the expression of the TP53 downstream gene CDKN1A (p21/WAF1/Cip1) is blocked. Based on experiments using TP53 antisense oligonucleotides, the radioprotective effect of BBI could be correlated with the function of wild-type TP53. Thus BBI can be considered as a selective radioprotective agent for normal human fibroblasts.

Automatic detection of stable and unstable chromosome aberrations visualized by three-color imaging after fluorescence in situ hybridization with a painting and a pancentromeric DNA probe

Two-color fluorescence in situ hybridization (FISH) in combination with digital image analysis was used to develop an automatic system for the detection and classification of chromosome aberrations. Algorithms were developed for the automatic thresholding of the three digitized images: an FITC image representing specific painted chromosomes, a TRITC image representing the centromeres of all chromosomes, and a DAPI image representing all the counterstained chromosomes. A further algorithm was developed for the automatic classification of the different types of chromosome aberrations, such as translocations, dicentrics, and fragments. For this study, a dataset of 252 metaphases were digitized and analyzed automatically as well as manually. Of these metaphases, 81.3% could be correctly classified by the algorithm. The error rate was reduced to 9.3% by automatically excluding the detected clusters and artifacts. The average analysis time per metaphase was 34.5 s without any user intervention.

Low predictive value of intrinsic fibroblast radiosensitivity for fibrosis development following radiotherapy for breast cancer

PURPOSE

To test whether the intrinsic radiosensitivity of skin fibroblasts from breast cancer patients correlates with the degree of breast fibrosis after breast conserving therapy.

METHODS

In a systematic study design, 79 patients were selected from an earlier study group of 385 patients based on observed fibrosis and seven identified clinical risk factors for fibrosis development. In vitro radiosensitivity of patients' dermal fibroblasts was determined by clonogenic assay of early passage cultures. Survival was determined after irradiation at 0, 2 and 4 Gy, given in two fractions of 2 Gy with a 6 h interval.

RESULTS

There was a significant inter-patient variation for SF2 values (coefficient of variation = 40%). The ratio of SF2 values for fibroblasts from patients with breast fibrosis versus those without was 0.80 (95% CI: 0.60-1.07). This was a statistically non-significant trend (p = 0.13). The same ratio for a derived value for SF2 ((SF2 + square root of SF4)/2) was 0.88 (p = 0.19).

CONCLUSIONS

A significant variation in intrinsic radiosensitivity of breast cancer patients' dermal fibroblasts was observed. However, the degree of radiosensitivity did not show a significant correlation with fibrosis development. This indicates that the use of fibroblast radiosensitivity will have a limited usefulness for predicting fibrosis following breast irradiation.

Intraperitoneal cisplatin with regional hyperthermia in advanced ovarian cancer: pharmacokinetics and cisplatin-DNA adduct formation in patients and ovarian cancer cell lines

The purpose of this study was to investigate the influence of hyperthermia on cisplatin pharmacokinetics and DNA adduct formation. The latter was investigated both in tumour cell lines in vitro and in tumour cells and buccal cells from cancer patients. The patients had advanced ovarian carcinoma and were entered into a phase I study for cytoreductive surgery followed by hyperthermia in combination with intraperitoneal cisplatin administration. The cisplatin-DNA modifications in vivo and in vitro were studied by an immunocytochemical method with the polyclonal antiserum NKI-A59. The patient samples for pharmacokinetic determinations were analysed by flameless atomic absorption spectrometry. In vitro, the combination of hyperthermia and cisplatin enhanced cell killing compared with either treatment alone, such that the cisplatin-resistant ovarian cell line A2780/DDP became almost as sensitive as the parent A2780 cell line (resistance factor reduced from 30 to 2 at the IC50). In addition, increased cisplatin-DNA adducts were observed in the resistant cell line after the combined treatment compared with cisplatin alone. A good correlation was found between nuclear staining density and surviving fraction for all groups, indicating that the DNA adducts generated are an important determinant of toxicity and that the mechanism by which hyperthermia enhances kill is by increasing adduct levels. In the patients, the ratio of drug concentration in the peritoneal perfusate compared with that in plasma was found to be approximately 15, indicating a favourable pharmacokinetic ratio. Cisplatin-DNA adduct formation in tumour cells from patients was higher than in buccal cells, reflecting this higher drug exposure, i.e. local plus systemic versus systemic only. In addition, the tumour cells but not buccal cells were exposed to hyperthermia. The higher number of tumour adducts also suggests that a favourable therapeutic ratio could be achieved. Platinum-DNA adduct formation was found to decrease with distance from the surface of the tumour nodules. However, at a distance of 3-5 mm, the nuclear staining density levels were still measurable and higher than in buccal cells. In conclusion, the combined pharmacokinetic and adduct data in patients support the advantages of the intraperitoneal route for drug administration, and the addition of heat.

Oral platinum analogue JM216, a radiosensitizer in oxic murine cells

This study was designed to compare radiosensitization by the oral platinum compound JM216 with cisplatin. RIF1 mouse tumour cells were treated at various doses and at various exposure times with JM216 and irradiated 15 min before the end of drug exposure. The fraction of cells surviving treatment was assessed by colony formation. Results were compared with those for equivalent treatments with cisplatin. JM216 alone showed exponential killing of RIF1 cells, being approximately three times less efficient than cisplatin on a molar basis. For radiosensitization studies, drug doses used gave approximately 50 or 90% cell killing alone. No radiosensitization was seen after 2-h drug exposures, but significant radiosensitization occurred after 1- and 0.5-h exposures (shorter times required proportionally higher drug doses, giving equivalent drug kill). The enhancement ratio and time dependence were similar for the two platinum compounds, reaching 1.5 at the highest concentrations tested. Drug DNA adduct formation was assessed using immunocytochemistry with the NKI-A59 antiserum raised to cisplatin-DNA adducts. The antiserum was shown to recognize JM216-DNA adducts in a dose-dependent manner and maximum nuclear staining was found to be correlated with cell kill for both drugs. However, neither the level of staining at the time of irradiation nor at the time of maximum adducts correlated with radiosensitization, indicating that the number of DNA adducts did not determine radiosensitization. Intracellular glutathione levels were shown to be decreased by the drug, but only by approximately 50%, implying that this was not the cause of the increased radiosensitivity. In summary, JM216 was shown capable of radiosensitizing a platinum-sensitive tumour line to an extent similar to cisplatin. Radiosensitization was exposure-time and drug-concentration dependent, but was not dependent on DNA adduct levels nor glutathione depletion. In contrast, cell kill after drug alone was well correlated with adduct levels. These data suggest that JM216 could replace cisplatin in combined radiotherapy-chemotherapy studies, and also indicate that the NKI-A59 antibody could be used to monitor exposure levels in vivo.

Accelerated fractionation (AF) compared to conventional fractionation (CF) improves loco-regional control in the radiotherapy of advanced head and neck cancers: results of the EORTC 22851 randomized trial

BACKGROUND AND PURPOSE

A 5 week-hyperfractionated and accelerated radiotherapy regimen without reduction of the total dose was developed to fight tumour repopulation during treatment and tumour hypoxia. The purpose of the study was to try to improve loco-regional control in high risk head and neck carcinoma treated with curative radiotherapy.

METHODS AND MATERIALS

From 1985 to 1995, a randomised controlled trial of the EORTC Cooperative Group of Radiotherapy (EORTC 22851) compared the experimental regimen (72 Gy/45 fractions/5 weeks) to standard fractionation and overall treatment time (70 Gy/35 fractions/7 weeks) in T2, T3 and T4 head and neck cancers (hypopharynx excluded). The end-point criteria were local and loco-regional control, overall and disease-free survival, and acute and late toxicities. Five hundred twelve patients were accrued.

RESULTS

Patients in the AF (accelerated fractionation) arm did significantly better with regard to loco-regional control (P = 0.02) resulting at 5 years in a 13% gain (95% CI 3-23% gain) in loco-regional control over the CF (conventional fractionation) arm. This improvement is of larger magnitude in patients with poorer prognosis (N2-3 any T, T4 any N) than in patients with more favourable stage. Multivariate analysis confirmed AF as an independent prognostic factor of good prognosis for loco-regional control (P = 0.03). Specific survival shows a trend (P = 0.06) in favour of the AF arm. ACUTE AND LATE TOXICITIES: Acute and late toxicity were increased in the AF arm. Late severe functional irradiation damage occurred in 14% of patients of the AF arm versus 4% in the CF arm. Two cases of radiation-induced myelitis occurred after doses of 42 and 48 Gy to the spinal cord.

CONCLUSIONS

This trial shows that accelerated radiotherapy improves loco-regional control in head and neck squamous cell carcinomas. A less toxic scheme should, however, be investigated and documented before using accelerated radiotherapy as a standard regimen of curative radiotherapy for head and neck cancers.

Cell kinetic measurements in prostate cancer

PURPOSE

Two approaches have been suggested for escalating the total dose in radiotherapy treatment of prostate cancer. One is conformal radiotherapy; the other is hyperfractionation using many small fractions. Both imply some possible prolongation in overall treatment time. To judge whether prolonged treatment schedules would be detrimental, it is necessary to know the proliferation rates in human prostate tumors, specifically, the potential doubling time (Tpot). There is a lack of data on this parameter in the literature.

METHODS AND MATERIALS

Seven patients with adenocarcinoma of the prostate were studied. A tracer dose of 100 mg/m2 of IUdR was infused intravenously 4-12 h before biopies were taken. Biopsies were fixed in 70% ethanol, stored at 4 degrees C, and later prepared and stained by standard methods for flow cytometry, using the red fluorescence signal for DNA and the green fluorescence signal (fluorescein isothiocyanate) for 5-iodo-2'-deoxyuridine. The duration of DNA synthesis (Ts) was determined by the relative movement (RM) method, knowing the interval between tracer administration and biopsy. Tpot was calculated as the quotient of Ts by labeling index (LI).

RESULTS

In two of the seven tumors the LI was too low (<0.6%) for a reliable estimate of RM to be made, so no determination of Tpot was possible for these tumors. The mean LI values in the other five tumors were 2.4%, 1.4%, 1.0%, 3.0%, and 0.9%. The durations of Ts were 13.2, 9.5, 10.0, 11.7, and 12.7 h, respectively. The resulting values of Tpot were 23, 28, 42, 16, and 61 days, respectively.

CONCLUSION

The low labeling indices in prostate tumors, also reported by others, made estimation of Ts by RM impossible in about a third of these tumors. However, five tumors yielded long estimates for Tpot, implying that prolongation from 6 to about 8 weeks should not be detrimental.

Detection of radiation-induced chromosome aberrations using fluorescence in situ hybridization in drug-induced premature chromosome condensations of tumour cell lines with different radiosensitivities

A potential assay for radiosensitivity of human tumours is that of radiation-induced chromosome damage determined on metaphase spreads of human solid tumours. It is often difficult, however, to obtain enough metaphases for cytogenetic analysis after radiation. A possible solution would be to use the technique of premature chromosome condensation (PCC), enabling the study of interphase cells. The induction of PCCs using mitotic inducer cells is technically difficult, however, and the frequency of induction relatively low. We have attempted to use another approach, to induce PCCs using the phosphatase inhibitors okadaic acid and calyculin A. Both inhibitors were found to induce PCCs in several human tumour cell lines, with calyculin A producing the higher incidence. Determination of radiation-induced chromosome aberrations using fluorescence in situ hybridization on these chemically induced PCCs showed a clear difference between a radiosensitive (SCC61) and a radioresistant (A549) tumour cell line, with more aberrations in the sensitive line. Owing to incomplete condensation compared with that in standard metaphases, accurate classification of aberration types was not possible. Despite this limitation, the present data indicate that this relatively quick and simple method may be useful for determining chromosome aberrations in interphase cells and potentially in human solid tumours for predictive assay purposes.

Enrichment of tumor cells for cell kinetic analysis in human tumor biopsies using cytokeratin gating

PURPOSE

To determine the feasibility of using cytokeratin antibodies to distinguish normal and malignant cells in human tumors using flow cytometry. The goal was ultimately to increase the accuracy of cell kinetic measurements on human tumor biopsies.

MATERIAL AND METHODS

A panel of four antibodies was screened on a series of 48 tumors from two centres; 22 head and neck tumors (Amsterdam) and 26 esophagus carcinomas (Leuven). First, screening was carried out by immunohistochemistry on frozen sections to test intensity of staining and the fraction of cytokeratin-positive tumor cells. The antibody showing the most positive staining was then used for flow cytometry on the same tumor.

RESULTS

The two broadest spectrum antibodies (AE1/AE3, E3/C4) showed overall the best results with immunohistochemical staining, being positive in over 95% of tumors. Good cell suspensions for DNA flow cytometry could be made from frozen material by a mechanical method, whereas enzymatic methods with trypsin or collagenase were judged failures in almost all cases. From fresh material, both collagenase and trypsin produced good suspensions for flow cytometry, although the fraction of tumor cells, judged by proportion aneuploid cells, was markedly higher for trypsin. Using the best cytokeratin antibody for each tumor, two parameter flow cytometry was done (cytokeratin versus DNA content). Enrichment of tumor cells was then tested by measuring the fraction of aneuploid cells (the presumed malignant population) of cytokeratin-positive cells versus all cells. An enrichment factor ranging between 0 (no enrichment) and 1 (perfect enrichment, tumor cells only) was then calculated. The average enrichment was 0.60 for head and neck tumors and 0.59 for esophagus tumors.

CONCLUSIONS

We conclude that this method can substantially enrich the proportion of tumor cells in biopsies from carcinomas. Application of this method could significantly enhance accuracy of tumor cell kinetic measurements.

Radiation-induced differentiation of human skin fibroblasts: relationship with cell survival and collagen production

The aim of this study was to determine whether significant inter-individual differences exist between skin fibroblast strains obtained from radiotherapy patients in both radiation-induced differentiation and collagen production in vitro, for use as potential parameters for a predictive assay for fibrosis following radiotherapy in patients. Morphological cell differentiation was determined 7 days after irradiation in seven early-passage primary human fibroblast cell strains and correlated with cell survival. Collagen production was measured in two cell strains by flow cytometry and incorporation of 3H-proline. There was a wide variation in the extent of radiation-induced differentiation for the seven cell strains, each showing a dose-related increase. The correlation between induced differentiation and cell survival was poor (r = 0.64) but statistically significant (p < 0.01). Collagen synthesis increased 7 days after irradiation for one cell strain (HF-48), as measured by incorporation of 3H-proline, but not in radiation sensitive AT-1 cells. The collagen I content of the two cell strains was assessed by flow cytometry but no significant differences were observed between the strains tested or with increasing dose. In conclusion, marked variations in radiation-induced fibroblast differentiation were observed between patients, this being an important criterion for a predictive assay.

Lethality of radiation-induced chromosome aberrations in human tumour cell lines with different radiosensitivities

In order to find an explanation for the eventual disappearance of all chromosome aberrations in two radiosensitive human tumour cell lines, the type and stability of different aberration types was investigated in more detail. To classify the aberrations into unstable and stable types, three-colour fluorescence in situ hybridization was performed, including a whole-chromosome probe, a pancentromere probe, and a stain for total DNA. This technique enables the appropriate classification of the aberrations principally by the presence (stable) or not (unstable) of a single centromere per chromosome. Unstable-type aberrations were found to disappear within 7 days (several divisions) in the two radiosensitive and the two radioresistant tumour lines investigated. Stable-type aberrations were found to remain at an approximately constant level over the duration of the experiment (14 days; 8-10 divisions) in the two radioresistant lines. In contrast, the majority of these stable-type aberrations had disappeared by 14 days in the two radiosensitive lines. The previous findings of disappearance of total aberrations in radiosensitive cells was therefore not due to a reduced induction of stable-type aberrations, but the complete disappearance of cells with this aberration type. These results could not be explained by differences in apoptosis or G1 blocks. Two possible explanations for these unexpected findings involve non-random induction of unstable-type aberrations, or lethality of stable-type aberrations. The results suggest caution in the use of stable-type aberration numbers as a predictor for radiosensitivity.

Use of fluorescence in situ hybridization to determine the relationship between chromosome aberrations and cell survival in eight human fibroblast strains

A predictive assay of normal tissue radiosensitivity could benefit 'treatment tailoring' of radiotherapy for certain categories of tumour. The use of present clonogenic cell survival assays for this purpose would be impractical in routine clinical practice because of the lengthy assay time. Fluorescence in situ hybridization (FISH) using whole chromosome probes on metaphases was investigated as a potential substitute. Eight human fibroblast cell strains with a range of radiosensitivities were tested. For each strain, cell survival curves were determined and correlated with chromosome aberrations detected by FISH performed on metaphase cells collected 52 h after irradiation. A whole chromosome probe for chromosome 4 was used for all cell strains. The results revealed an increase in the percentage of metaphases with aberrant chromosomes (translocations and/or breaks) with increasing radiation dose for all strains. For the more radiosensitive cell strains there were relatively more aberrant metaphases for a given radiation dose when compared with fibroblasts from a normal donor. The relationship between surviving fraction and chromosome aberrations showed some variation between strains, but a linear regression for all data showed a highly statistically significant correlation (r = 0.89, p < 0.0005). These results suggest that an assay of chromosome damage using FISH could substitute for the clonogenic assay to predict the radiation sensitivity of human fibroblasts.

Defective repair of DNA double-strand breaks and chromosome damage in fibroblasts from a radiosensitive leukemia patient

A radiation-sensitive fibroblast culture (180BR) established from an acute lymphoblastic leukemia patient who died following radiotherapy is defective in the repair of radiation-induced DNA double-strand breaks. The cells also show a reduced capacity to repair interphase chromosome damage visualized by means of premature chromosome condensation and metaphase chromosome aberrations measured by fluorescence in situ hybridization on chromosome 4. This case represents the first example in humans where hypersensitivity to ionizing radiation can be ascribed directly to a defect in DNA and chromosome repair, and the defect may underlie the cancerous phenotype observed.

Can measurements of potential doubling time (Tpot) be compared between laboratories? A quality control study

The purpose of this study was to investigate the reproducibility of potential doubling time measurements of human tumors in different laboratories and to distinguish which steps in the measurement procedure were subject to the greatest variation. This was achieved by comparing measurements on the same source material in two different laboratories in which three aspects of the technique were separately studied, namely, preparation and staining of the nuclear suspensions, running the samples on the flow cytometer (FCM), and analyzing the two-parameter FCM data. This involved exchange between the two centers of fixed tumor material, stained nuclear suspensions, and FCM data on floppy disks. The analysis step was found to be the least variable step. For DNA synthesis time, Ts, and the labeling index, LI, the coefficients of determination (R2) ranged from 92% to 95.4%. A small systematic bias was observed, with one center measuring approximately 15% higher values for both LI and Ts. Different criteria for window placements were found to be a contributing factor. Variations in the FCM step were approximately equal to those for analysis, with no systematic deviations. Variations for the preparation and staining step were the largest (R2 = 60.5% and 38.1% for LI and Ts, respectively). However, this step was the only one subject to intratumoral variability, which was the largest contributing factor to the variations observed. In addition, however, LI was on average 41% higher in one center compared to the other, resulting in a systematic bias. Differences in the level of green fluorescence of the labeled cells implicated antibody differences as a possible cause. The variations found here for the three procedural aspects were significantly smaller than variations observed between tumors, a requirement for a predictive assay. Suggestions for implementation of quality control procedures include objective (computer-assisted) data analysis on two-parameter histograms and optimization of antibody combinations.

The effect of radiation on G2 blocks, cyclin B expression and cdc2 expression in human squamous carcinoma cell lines with different radiosensitivities

The purpose of the present study was to investigate the role of cyclin B and cdc2 in the G2 delay and to test whether the magnitude of the G2 delay correlated with sensitivity to ionizing radiation in two human cell lines. Cell cycle delays were measured by flow cytometry after pulse labeling with bromodeoxyuridine, and expression of cell cycle control genes were measured in Western blots in radiosensitive SCC61 and radioresistant SQ20B cell lines. Flow cytometry data demonstrated that the duration of the G2 arrest was dose dependent in both cell lines, amounting to approximately 1.1 h/Gy. No difference was found between the cell lines in the length of the G2 block. Radiation exposure did not result in a decrease of cyclin B. Cyclin B protein levels in both asynchronous and synchronized populations in fact showed a dose dependent increase, concomitant with the rise in the fraction of cells in G2/M. Similarly, the cdc2 protein levels did not decrease after irradiation. However, it was found that the levels of hyperphosphorylated, and therefore inactive, kinase were significantly higher in irradiated cells than in unirradiated cells. The accumulation of this hyperphosphorylated form correlated with the arrest of cells in the G2 phase. Finally, immunocytochemical staining of cyclin B revealed an increase of this protein in the cytoplasm after irradiation and a decrease in nuclear staining. This differential localization could possibly account for the reduced nuclear phosphorylation of cdc2 kinase leading to the G2 arrest.

Differential repair of radiation-induced DNA damage in cells of human squamous cell carcinoma and the effect of caffeine and cysteamine on induction and repair of DNA double-strand breaks

The goal of these experiments was to investigate further the relationship between DNA double-strand breaks and cell killing in human tumor cells, first by comparing different cell lines, and second by radiomodification studies. Field-inversion gel electrophoresis was used to quantify double-strand breaks. Two subclones of the radioresistant human squamous cell carcinoma line SQ20B (SQD9 and SQG6) were compared. These subclones differed in DNA index by a factor of 1.7 but showed the same resistance to radiation as cells of the parental cell line. It was found that, although induction of DSBs was not significantly different in the two cell lines, the t1/2 of the fast component of repair was significantly shorter for SQD9 cells, leading to greater overall repair which was not reflected in increased survival. Caffeine and cysteamine were tested as modifiers of radiosensitivity, using the radioresistant SQ20B line and the radiosensitive SCC61 cell line. No effect of caffeine was seen when the drug was present only during irradiation. Postirradiation incubations with caffeine, however, resulted in a dose reduction factor greater than 2.0 in cell survival for both cell lines. In contrast, induction of DSBs was reduced by caffeine, and no effect on DSB repair was observed. Cysteamine led to a dose protection factor greater than 1.8 in cell survival in both cell lines. A reduction in induced DSBs was found at high doses corresponding approximately with the increase in cell survival. Over the same (low) dose range, however, the correlation between DSB induction and cell killing was poor. These data indicate that DSB induction does not correlate well with cell killing either for different cell lines, for radiochemical modification (cysteamine) or for some other types of modification (caffeine).

Use of fluorescence in situ hybridization to measure chromosome aberrations as a predictor of radiosensitivity in human tumour cells

Fluorescence in situ hybridization (FISH) is a potential assay for determining cellular radiosensitivity based on the detection of chromosome damage. This approach was chosen because of its relative simplicity and short assay time. Two radiosensitive and two radioresistant human tumour cell lines were used. The radiosensitive lines were an ovarian carcinoma line (A1847) and a squamous carcinoma line (SCC61). The radioresistant cells were a lung adenocarcinoma line (A549) and a second squamous line (SQ20B). Whole chromosome-specific probes were used to detect radiation-induced chromosome aberrations in mitotic cells. Available probes were first screened to characterize the intrinsic chromosome aberrations before irradiation and the appropriate probes (minimum fluorescent spots) were selected for each cell line. Maximum radiation-induced aberrations were found 24 h after irradiation. Dose-response curves corrected for target size (proportion of genome probed) differed for all cell lines. The radiosensitive A1847 cell line showed more induced aberrations compared with the radioresistant A549 cell line, in agreement with the survival data. In contrast, the SQ20B cell line showed more induced chromosome aberrations than the more radiosensitive SCC61 cell line, leading to the hypothesis that the SQ20B cells could tolerate more aberrations. Dose-response curves obtained in surviving cells 14 days postirradiation indeed showed elevated levels of chromosome aberrations for SQ20B cells. The difference in chromosome aberrations between 1 and 14 days showed a good correlation with the survival data for all four cell lines. In conclusion, FISH of mitotic cells with whole chromosome probes appears to be a suitable assay to predict radiosensitivity. It seems necessary, however, to determine both induced and remaining chromosome aberrations, since different processing or tolerance of radiation-induced aberrations, including stable types, could lead to different correlations with cell survival.

Improvement of combined modality therapy with cisplatin and radiation using intratumoral drug administration in murine tumors

The aim of these studies was to increase the therapeutic ratio by achieving higher tumor concentrations of cisplatin during the course of a fractionated irradiation treatment. Specific goals were to test, firstly, whether multiple drug injections could be replaced by a single slow release implant of cisplatin, and secondly, whether the therapeutic potential of the combined treatment could be increased by administering the drug intratumorally. Drug administration routes tested were intraperitoneal (i.p.) of drug in solution, intratumoral (i.t.) of drug in solution, and intratumoral of drug in a slow release formulation. The latter consisted of a hydrogel polymer formulated into rods which were implanted into the center of subcutaneous tumors. For drug alone, both i.t. routes (solution or polymer) produced higher therapeutic gains than i.p. administration, as judged by tumor growth delay for a given weight loss. When combined with radiation, dose response curves were always shifted to lower doses and were steeper than for radiation or drug alone, although isobologram analysis indicated additivity. In a first series, drug enhancement ratios ranged from 1.6 to 2.6, and were highest for the i.t. groups. In a second series, X-ray enhancement ratios ranged from 1.1 to 1.7, with overlap between results from the different routes. Therapeutic ratios, however, were highest for the i.t. groups in both series. Slow release rods produced the highest therapeutic gains in the first series, while i.t. administration of drug in solution was approximately as effective in the second series.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetics in melanoma-bearing mice of 5-dihydroxyboryl-6-propyl-2-thiouracil (BPTU), a candidate compound for boron neutron capture therapy

Blood pharmacokinetics and tissue distribution of 5-dihydroxyboryl-6-propyl-2-thiouracil (BPTU), a boron carrier with postulated melanin-seeking properties for boron neutron capture therapy, were determined in C57/BL mice with subcutaneous pigmented or non-pigmented B16 melanomas. Borocaptate sodium (BSH) was used as a boron compound without melanin-seeking properties in a comparative biodistribution study in the same animal tumour models. Administration of single doses showed that BPTU was retained better in the pigmented B16 tumour than in the non-pigmented variant. BPTU was found in large concentrations in kidney and liver. Brain boron was approximately 10-fold lower than tumour boron. On a molar basis, BPTU demonstrated higher affinity for B16 tumours than BSH. Owing to solubility limits, tumour boron concentrations in this mouse study were too low for effective application of BNCT. However, the high tumour-to-blood and tumour-to-normal tissues ratios indicate that, with appropriate formulation, BPTU could be a promising candidate for clinical BNCT.

Intrinsic radiosensitivity and chromosome aberration analysis using fluorescence in situ hybridization in cells of two human tumor cell lines

The survival curves for cells of two human tumor cell lines, HT29 and MeWo, have been defined using a Dynamic Microscopic Imaging Processing Scanner (DMIPS). There are two major differences between these two cell lines: (a) HT29 is more radioresistant than MeWo (surviving fraction at 2 Gy of 74 and 27%, respectively) and (b) HT29 presents a marked multiphasic survival curve with hypersensitivity at low doses (< 0.5 Gy) followed by an increase in radioresistance at higher doses which we have interpreted as "induced radioresistance"; this phenomenon is much less pronounced for the more radiosensitive cell line MeWo. We have now measured in these two cell lines the stable chromosomal aberrations and fragments, with the method of fluorescence in situ hybridization (FISH). We have analyzed chromosome 4, which does not have spontaneous translocations in either of these two cell lines. A dose-effect relationship was studied for radiation doses up to 5 Gy. At all doses, both translocations and breaks are more frequent in the radiosensitive cell line MeWo compared to the radioresistant cell line HT29. The correlation between survival and translocations is different for HT29 and MeWo, thus indicating that another factor(s) may be involved in cell killing in these lines.

Quantification of patient to patient variation of skin erythema developing as a response to radiotherapy

A method is described to determine accurately skin redness during a course of radiotherapy using reflectance spectroscopy utilizing information from across the visible spectrum according to the L*a*b* color coordinate system. The method was used to quantify the development of skin erythema during and after electron beam irradiation of the chest wall following mastectomy. A number of factors were identified which could influence the wide variation in response seen between patients. These were: intra- and inter-observer variation; intra- and inter-patient variation and variation in the actual dose delivered. Statistical analysis, including an analysis of variance of inter- and intra-patient variation, revealed that the major factor that accounts for the observed difference between patients is a true inter-patient variation, with a coefficient of variation, corrected for intra-patient variation, of 43%. Within the narrow dose range administered in this study, there was no demonstrable dose-effect relationship, raising questions about the role of cell death in the basal layer of the epidermis in the pathogenesis of radiation induced erythema.

A comprehensive PC-based computer model for microdosimetry of BNCT

A computer model is described that performs microdosimetric calculations of the radiation dose delivered to tumour and normal tissue in boron neutron capture therapy (BNCT) by simulating capture reactions in a predefined three-dimensional space. The role of intracellular boron distributions and cellular dimensions on the radiation dose in clinical and experimental BNCT has been studied using a PC-based computer model. In order to calculate the radiation dose to low boron uptake cells, the extent of irradiation by boron containing adjacent cells (cross fire) is also dealt with. Radiation doses from boron and nitrogen neutron capture are converted to a biological effect by means of relative individual ion track segment efficacies, based on linear energy transfer along the particle track. A good correlation was found after comparing predicted values with previously published experimental data. A number of examples is given to illustrate the program's features.

Characterization of resistance mechanisms to cis-diamminedichloroplatinum(II) in three sublines of the CC531 colon adenocarcinoma cell line in vitro

Cisplatin resistance was developed in sublines of the CC531 rat colon adenocarcinoma cell line by continued low level drug exposure. Two relatively stable lines were obtained (RL2 and RL4) which were 6- and 20-fold more resistant to cisplatin. In addition, a subline more sensitive than the parent line by a factor of 2 (RLS) was obtained by subculture from a treated tumor. Mechanisms of resistance to cisplatin were investigated in these four lines, with the aim of determining the relative contributions of different resistance mechanisms at various resistance levels. Drug accumulation linearly decreased with increasing drug resistance. A 20-fold resistance was associated with only a 5-fold decrease in accumulation, suggesting that other resistance mechanisms may be involved in the total degree of resistance. Intracellular glutathione, measured fluorometrically, also increased with increasing resistance, varying by a factor of 4 between the most and least resistant lines. Reduction of glutathione levels by buthionine sulfoximine to parent line levels increased sensitivity but the cells remained considerably more resistant than parent cells. Resistant lines cultured in the absence of drug became progressively more sensitive, without accompanying changes in total glutathione levels. DNA-drug adducts, the presumed toxic lesion, were measured immunocytochemically. Initial levels decreased with increasing platinum resistance, although not proportional to resistance (factor of 5 decrease for 20-fold resistance). Drug dose ratios for equal initial adducts were similar to dose ratios for equal drug accumulation, implying that intracellular concentrations solely determine DNA adduction and that differences in glutathione level had little influence on the proportion of drug which eventually formed adducts. After 48 h, a better correlation between remaining adducts and resistance was found (factor 12 less adducts for 20-fold resistance). This implies that repair of adducts was important in determining survival. These data indicate that decreased drug accumulation played a proportionally greater role in the moderately resistant cell line and that adduct repair played a progressively greater role in the highly resistant cell line.

Prediction of repopulation rates and radiosensitivity in human tumours

An accurate prediction of response to radiotherapy would allow treatments to be modified for those individuals where a relatively poor response is expected with conventional treatment. Present assays receiving most attention are those for repopulation, radiosensitivity and hypoxia. This paper discusses our experience with the first two, together with relevant data from other groups. Attention is focussed particularly on correlations with outcome in clinical trials, and the accuracy of present assay methods.

Cell kinetic analysis of murine squamous cell carcinomas: a comparison of single versus double labelling using flow cytometry and immunohistochemistry

The study was originally set up to measure accurate cell kinetic parameters in two murine squamous cell carcinomas (scc) for comparison with radiobiological data on proliferation during radiotherapy. The tumours, AT84 and AT478, were both moderately well differentiated aneuploid scc. In the course of the study, several comparisons of techniques were made in two different centres. This paper reports on the results of those comparisons involving two different detection methods (flow cytometry and immunohistochemistry), single vs double labelling, and in vivo and in vitro labelling, the latter using tissue slices incubated under high pressure oxygen. Pulse labelling studies with bromodeoxyuridine (BrdUrd) showed that the labelling indices (LI) were not significantly different after in vitro or in vivo labelling. In addition, the flow cytometry (FCM) and immunohistochemistry (IHC) methods also gave labelling indices which were not significantly different. Only tumour cells were analysed in these studies by selecting cells on the basis of aneuploidy (FCM) or morphology (IHC). The DNA synthesis time of the tumour cells were analysed by both techniques. For FCM, the Relative Movement method was used (Begg et al., 1985). For IHC, a double labelling method was used, employing BrdUrd and triated thymidine (3H-TdR) administered several hours apart, detected simultaneously using immunoperoxidase and autoradiography, respectively. When both labels were administered in vivo, there was good agreement for Ts between the FCM and IHC methods. Attempts were also made to measure Ts in vitro using both techniques. With double labelling, it was found that cells did not take up the second label, implying a failure of cycle progression. This was confirmed by FCM results, showing no movement of labelled cells through the S-phase, despite an initially high uptake. This could not be influenced by lowering the DNA precursor concentration or by adding foetal calf serum. This indicates that DNA synthesis times are difficult or impossible to measure in vitro in fresh tumour explants. Finally, the double labelling IHC method allowed intratumoural variations of both LI and Ts to be studied. Both parameters were found to vary markedly throughout the tumour volume, particularly for larger tumours (600 mg), giving calculated local potential doubling time values (Tpot) ranging from 1-7 days.

Lack of correlation of human fibroblast radiosensitivity in vitro with early skin reactions in patients undergoing radiotherapy

Fibroblasts from breast cancer patients were obtained as outgrowths in vitro from punch biopsies and their radiosensitivity tested in early passages. Skin erythema reactions in the same patients were also measured, as degree of redness using reflectance spectrophotometry. Measurements were taken before and during a 4-week radiotherapy treatment with electrons to the thoracic wall. Of 59 biopsies studied, radiosensitivity and erythema were concurrently studied in 32. In 24, evaluable data from both clinic and laboratory were obtained. A population growth assay in 96-well plates, using absorption of sulphur rhodamine B as the stain for cell numbers, showed good agreement with the colony-formation assay. Plating efficiencies and growth rates in the colony assay were higher using human serum in place of foetal calf serum. Cell survival curves with human serum were mostly exponential with little shoulder. The parameters of survival at 2 Gy (SF2) and the dose required to give 10% survival (D10) were used in the correlations with clinical data; these were 0.25 +/- 0.09 and 3.03 +/- 0.50 Gy, respectively. There was a strong correlation between these two survival curve parameters (r = 0.98). Skin redness was found to linearly increase with time during radiotherapy. The slope of the increase differed markedly from patient to patient, with a range of a factor approx. 10. No correlation was found between SF2 and erythema response in the 24 evaluable patients (r = 0.13, p > 0.5). A similar lack of correlation was found using D10 as the radiosensitivity parameter (r = 0.12, p > 0.5). These data indicate that fibroblast radiosensitivity measured in vitro cannot be used to predict erythema reactions to radiotherapy in breast cancer patients.

Radiation-induced DNA damage and repair in radiosensitive and radioresistant human tumour cells measured by field inversion gel electrophoresis

Radiation-induced DNA damage induction and repair was measured in two human squamous carcinoma cell lines with differing radiosensitive. Experiments were carried out with field inversion gel electrophoresis (FIGE), adapted to measure DNA double strand break (DSB) induction and repair in unlabelled cells. The sensitivity of the method was increased by introducing a hybridization membrane into the agarose gel. Damaged DNA accumulated on one spot on the membrane resulting in high local concentrations. This DNA was quantified using radioactively-labelled total human DNA as a probe. Dose response experiments for damage induction correlated well with the results using prelabelled cells. Linear DNA damage induction curves were observed with a sensitivity for the post-labelling method of 1 Gy. No differences in DSB induction were found, however, between the radiosensitive SCC61 and the radioresistant SQ20B cell line. Repair experiments were carried out with trypsinized cells with different doses and repair temperatures. The 10, 25 and 50 Gy doses resulted in 6, 13 and 50% of the DNA migrating out of the plug at 0 h. For both the cell lines 75-85% of the initial damage was repaired within 1 h at 37 degrees C at all three radiation doses, i.e. no significant differences were observed in repair rates or extent between the two cell lines. At 24 degrees C repair was slower than at 37 degrees C, and at 0 degree C no repair was observed. In summary, radiosensitivity differences at physiological temperatures could not be explained by differences in either induction or repair of DNA damage as measured by pulsed field gel electrophoresis.

Ploidy status and the response of T1 glottic carcinoma to radiotherapy

Flow cytometric DNA ploidy measurements were performed on formalin fixed paraffin embedded tumour specimens from patients with a T1 glottic laryngeal carcinoma in order to evaluate the role of DNA content in relation to local control. From 1980 to 1987, a consecutive series of 90 patients with a T1 glottic laryngeal carcinoma were treated by radiotherapy with curative intent. Biopsies from 44 of these patients were readily available for DNA flow cytometry. In this group aneuploidy was associated with a significantly higher risk (P = 0.018) of local recurrence within 2 years after completion of radiotherapy (38% vs. 9% in the diploid group).

Selectivity of boron carriers for boron neutron capture therapy: pharmacological studies with borocaptate sodium, L-boronophenylalanine and boric acid in murine tumors

Borocaptate sodium (BSH) and L-boronophenylalanine (L-BPA) are two boron carriers used for boron neutron capture therapy (BNCT) in the treatment of glioblastoma and melanoma, respectively. The suitability of these two compounds was evaluated on the basis of pharmacokinetic studies aiming at characterizing their biodistribution, tumor uptake and tumor selectivity. Boric acid was also used as a reference compound since it is nonselective and relatively freely diffusible. The compounds were investigated in two tumor models, a B16 pigmented melanoma and the RIF1 sarcoma. Mice were sacrificed after different boron doses at various post-injection times and tissue and plasma levels measured using inductively coupled plasma atomic emission spectroscopy (ICP-AES). The proposed minimum effective tumor boron concentration of 15 ppm was achieved in both tumor models for the three compounds tested, although only for L-BPA in the melanoma was this achieved when tumor-plasma ratios were above 1. In the RIF1 model, maximum tumor concentrations of 44 and 31 ppm B were reached after administration of 50 micrograms B/g body weight for boric acid and BSH, respectively. After administration of 12.5 micrograms B/g of L-BPA, maximum concentrations of 15 and 21 ppm were found in the RIF1 and B16 models, respectively. Tumor-plasma ratios (TPR) for BSH remained close to or below unity at all times studied in both tumors. Brain levels of BSH were very low, however, leading to tumor-brain ratios markedly greater than 1 at all times. L-BPA and boric acid showed TPR values above unity in both tumor models, reaching 3.2 in B16.(ABSTRACT TRUNCATED AT 250 WORDS)

Reduction of systemic exposure and toxicity of cisplatin by encapsulation in poly-lactide-co-glycolide

The tissue distribution and normal tissue toxicity of cisplatin (cDDP) administered as poly-lactide-co-glycolide (PLAGA) microspheres, developed for loco-regional administration of cDDP to the liver, were studied in Wag/Rij rats. Venoportal administration of this formulation resulted in a reduction in total systemic and renal toxicity, which correlated with a decrease in normal tissue exposure to cDDP while maintaining high liver platinum levels. Liver-to-kidney platinum level ratios were 28 times higher after 4 h and 19 times higher after 24 h with PLAGA-cDDP microspheres than with free cDDP. Liver-to-blood platinum ratios at these times were 38 times and 36 times higher using PLAGA-cDDP. In a CC531 colon carcinoma liver micrometastases model, cytotoxicity of microsphere-released cDDP was confirmed in vivo by equal inhibition of tumor growth by PLAGA-cDDP and free cDDP over a period of 26 days. Free cDDP, however, caused significantly more histological renal damage and total body weight loss. The results were supported by the finding of higher plasma creatinine and urea concentrations 26 days after administration of free cDDP. Kidney platinum levels were 7 times lower when PLAGA-cDDP was used. These findings indicate a sparing effect on normal tissues when cDDP is targeted to the liver by formulation in PLAGA. PLAGA-cDDP microspheres may, therefore, be a useful and effective addition to current techniques of loco-regional chemotherapy for disseminated hepatic tumors.

Intratumoural administration of cisplatin in slow-release devices: II. Pharmacokinetics and intratumoural distribution

The pharmacokinetics of cisplatin in mice with s.c. RIF 1 tumours was studied after intratumoural (i.t.) administration of drug in solution and in different slow-release devices. The data were compared with those obtained after i.p. administration of cisplatin. The slow-release devices under test were manufactured from either starch (ST) or polymeric hydrogels with different water uptakes (named T1, T2 and T3). In vitro release from these devices was approximately 100% in 2 h for starch rods, 100% in 24 h for T3 hydrogels, 45% in 4 days for T2 hydrogels and less than 10% in 4 days for T1 hydrogels. In vivo release rates agreed well with the in vitro data for T1 and T2 rods and were slightly slower in vivo for the T3 rods. The ST rods released the drug 6 times slower in vivo than in vitro. Plasma concentrations after i.t. administration were lower than those measured after i.p. administration. Systemic exposure to both total and free platinum was reduced to 70% for i.t. as compared with i.p. administration. Tumour concentrations were 4 times higher after i.t. than after i.p. administration. Tumour and peak plasma levels of platinum increased with increasing release rates. With the faster-releasing formulations (ST and T3), tumour platinum concentrations were 100 times higher than after i.p. administration. With the slower releasing formulations (T1 and T2), total tumour platinum concentrations were 2 and 9 times higher, respectively, than after i.t. administration of cisplatin in solution. Platinum distribution within the tumour was homogeneous after i.p. administration. After i.t. administration of cisplatin in solution, platinum concentrations in the centre of the tumour were approximately 4 times higher than in peripheral tumour tissue. Implantation of cisplatin in T2 and T3 hydrogel rods resulted in large concentrations of platinum in the centre of the tumour (the site of implant), which decreased steeply towards the tumour periphery. In summary, i.t. administration of cisplatin solution produced better results than did systemic (i.p.) administration in terms of tumour versus plasma drug-concentration ratios. Administration of drug in slow-release rods proved even more advantageous, although this was offset by inhomogeneous drug distributions within the tumour.