Tumour cell repopulation during fractionated radiotherapy: correlation between flow cytometric and radiobiological data in three murine tumours

This study tested whether the potential doubling time of tumour cells measured before or during treatment could predict the repopulation rate of surviving clonogens during fractionated radiotherapy. Tumours used for the study were a fibrosarcoma (SSK 2), an adenocarcinoma (AT 7) and a squamous cell carcinoma (AT 478), all grown subcutaneously in the C3H mouse. Potential doubling times (Tpot) were measured using the thymidine nanalogue iododexyuridine (IUdR) and flow cytometry. Results were compared with previous radiobiological studies on these tumours in which repopulation rates during radiotherapy were estimated using the tumour growth delay and tumour cure assays. Fractionated treatments consisted of daily doses of 4 or 8 Gy to clamped (hypoxic) tumours, 6 days per week for 1-3 weeks. Tpot values increased markedly during therapy for two of the tumours (SSK 2 and AT 478), by a factor of more than 10 for AT 478 in the third treatment week. Tpot remained approximately constant for the third tumour (AT 7). In no case was there evidence from the labelling studies of a shortening of Tpot which would suggest accelerated repopulation. From the radiobiological data, effective clonogen doubling times during radiotherapy were calculated from the doses required to produce a given effect in short and long treatment schedules. In the second week of treatment, effective clonogen doubling times in two tumours were approximately equal to the pretreatment Tpot, and shorter than the pretreatment Tpot in the third tumour. At some time during treatment, the surviving clonogens in these tumours therefore proliferated at the same rate or faster than before treatment. The difference between the labelling and radiobiological measurements was ascribed to the fact that, shortly after the start of a fractionated treatment, the IUdR labelling technique measures primarily doomed cells. These results show that kinetic measurements using DNA labelling techniques made during fractionated radiotherapy in most cases do not reflect the proliferation status of the surviving cells which are responsible for treatment outcome. Pretreatment Tpot measurements give a much better indication of the proliferation rate of surviving cells but in some cases may underestimate repopulation during radiotherapy.

Antibodies against cisplatin-modified DNA and cisplatin-modified (di)nucleotides

Cytotoxic effects of cis-diamminedichloroplatinum-(II) (cis-DDP) are thought to be mediated by binding to DNA. Studies on binding of cis-DDP to cellular DNA rely heavily on the availability of specific antibodies. We therefore raised and characterized four rabbit antisera: one against cis-DDP-modified DNA (antiserum NKI-A59) and three others against the cis-DDP-modified (di)nucleotides cis-Pt(NH3)2d(pApG) (NKI-A68), cis-Pt(NH3)2d(GMP)2 (NKI-A10), and Pt(NH3)3dGMP (NKI-A39). Reactivities to platinum compounds were determined in an enzyme-linked immunosorbent assay (ELISA) and in a quantitative immunocytochemical assay. In the ELISA, NKI-A59 showed a high affinity for DNA heavily substituted with either cis-DDP or CBDCA [cis-diammine(1,1-cyclobutanedicarboxylato)platinum(II)]; amounts of platinum per well giving 50% inhibition (IA50) were as low as 15 and 76 fmol, respectively. NKI-A59 also showed affinity to cis-DDP-modified poly[d(G-C)].poly[d(G-C)], poly(dC), and poly(dG). No affinity was found for trans-DDP [trans-diamminedichloro-platinum(II)]-modified DNA, enzymatically digested cis-DDP-DNA, or cis-DDP-DNA, or cis-DDP-modified poly(dA).poly(dT), oligo(dA)15.oligo(dT)15, oligo(dG)21, oligo(dG)42, or oligo(dAAAG)10. The efficiency of binding to cis-DDP-DNA decreased with decreasing DNA modification levels. Although other cis-DDP-DNA- and cis-DDP-(di)nucleotide-specific antisera have been identified, NKI-A59 is the first antiserum described that is suitable for the in situ detection of cis-DDP-DNA adducts at clinically relevant platinum levels. Adduct-specific immunostaining signals in cultured RIF-1 cells or rat liver paralleled platinum-DNA binding as measured by atomic absorption spectroscopy. The antisera NKI-A68, NKI-A10, and NKI-A39 showed high affinity for their corresponding haptens and varying affinity for non-hapten cis-DDP-DNA adducts. Their affinity for digested cis-DDP-modified DNA was up to 30 times that for intact cis-DDP-DNA. Neither NKI-A68 nor NKI-A10 resulted in specific immunocytochemical staining of cis-DDP-DNA adducts. We conclude that NKI-A68, NKI-A10, and NKI-A39 are suitable for platinum-DNA adduct analysis of digested DNA in ELISA and that NKI-A59 is suitable for platinum-DNA adduct detection at the single-cell level using immunocytochemical methods.

Fluorescent markers for hypoxic cells. A study of novel heterocyclic compounds that undergo bio-reductive binding

The bioreductive metabolism and binding of nitroaromatic compounds has been suggested as a method for the identification of hypoxic tumour cells. Bound metabolites of suitable nitroaryl compounds (and some other reducible aromatic compounds) may fluoresce, offering an alternative to radiolabelling or NMR etc. as a diagnostic method. In this paper, the synthesis of some heteroaromatic nitro-compounds is given together with the results obtained from testing of these and other mainly nitroaromatic compounds in vitro as potential bioreductive fluorescent probes for hypoxic cells in tumours. Compounds were incubated with oxygenated or hypoxic mammalian cell suspensions for various times before evaluation of the cellular fluorescence from bioreductive metabolites by fluorescence microscopy and flow cytometry. Among those compounds yielding fluorescent metabolites in cells, considerable variation in hypoxic:oxic differential fluorescence was observed. The in vitro mammalian cell test system showed several of the compounds to be sufficiently promising to merit further investigation in vivo.

Formation of interaction products of carboplatin with DNA in vitro and in cancer patients

Binding of the cytostatic drug carboplatin to DNA was studied in solution, in RIF-1 and CHO cell lines and in human buccal cells after in vitro or in situ drug exposure. Results were compared with DNA adduction by cisplatin. The rate of binding in solution, determined by atomic absorption spectroscopy, was 35 times lower for carboplatin than for cisplatin. Adduct formation in cells in vitro was determined in a quantitative immunostaining assay. Staining intensities after carboplatin treatment were at least 29 times lower than after an equimolar dose of cisplatin. For RIF-1 and CHO cells, maximum levels of carboplatin-induced DNA modification were obtained 24 h after treatment; these levels correlated with cell killing. Adduct-specific staining in buccal cells from two carboplatin-treated patients increased 5-7 fold between 0 and 14 h after infusion, reaching a maximum at 10-14 h. This strongly contrasts with buccal cells from a cisplatin-treated patient, in which the adduct-specific staining signal increased by only 23% between 0 and 6 h after infusion, and then declined. This difference in the rate of adduct formation in vivo is consistent with the in vitro data.

Cell kinetic analysis of mixed populations using three-color fluorescence flow cytometry

The development of antibodies to DNA-incorporated thymidine analogs has in turn led to the development of flow cytometric techniques for rapidly measuring cell kinetics parameters. More recently, these techniques have been applied to clinical tumor material. One problem with such measurements has been the difficulty of distinguishing malignant cells from coexistent normal cells in the biopsy material. In the present study, the feasibility of selecting out the desired malignant cell population for kinetic analysis from a mixture of cells was tested in vitro. An anticytokeratin antibody was used to discriminate between a mixture of tumor cells (cytokeratin positive) and normal cells (cytokeratin negative). The cell lines chosen for the study, A549 human lung carcinoma cells and Chinese hamster ovary (CHO) cells, were pulse labeled with iododeoxyuridine (IdUrd) and sampled every hour up to 16 hours. Selecting out cells from the mixture required the application of three-color fluorescence flow cytometry, which was carried out using the fluorochromes FITC (fluorescein isothionate, green fluorescence, IdUrd-DNA antibody), PE (phycoerythrin, orange fluorescence, cytokeratin antibody), and PI (propidium iodide, red fluorescence, DNA). This allowed single laser excitation. The staining procedure involved incubation with the IdUrd antibodies (specific antibody plus FITC-conjugated second antibody) followed by the cytokeratin antibodies (specific antibody plus PE-conjugated second antibody) and lastly by the DNA stain containing RNase. Two analysis methods of the IdUrd/DNA cytograms were applied: a mid-S window analysis and a relative movement (RM) analysis. Results of the analyses for cells selected out of mixtures were compared with results of cells stained and analyzed separately. A clear separation of the two cell lines could be obtained on the basis of orange fluorescence (cytokeratin content) despite a large overlap of their DNA histograms. By gating on high or low orange fluorescence, almost pure populations of the individual cell types could be selected out for further kinetic analysis. Little difference was seen, with both the mid-S and RM analyses, between cells gated from mixtures or stained separately. It is concluded that this technique is feasible for use on clinical material, provided good cell suspensions can be obtained, leading to the hope of increasing the accuracy of kinetic measurements on human tumors.

Polymer-coated albumin microspheres as carriers for intravascular tumour targeting of cisplatin

We used a poly-lactide-co-glycolide polymer (PLAGA 50:50) to formulate cisplatin (cDDP) into microspheres designed for intravascular administration. Two systems were developed. PLAGA-coated albumin microspheres and microspheres consisting of PLAGA only. PLAGA-coated microspheres displayed a mean diameter of 31.8 +/- 0.9 microns and a payload of 7.5% cDDP (w/w). Solid PLAGA microspheres exhibited a mean diameter of 19.4 +/- 0.6 microns and a payload of 20% cDDP. Release characteristics and in vitro effects on L1210 leukemia and B16 melanoma cell lines were investigated. Both types of microsphere overcame the initial rapid release of cDDP (burst effect), and PLAGA-coated albumin microspheres also showed a lag phase of approximately 30 min before cDDP release began. PLAGA-coated albumin microspheres released most of their payload through diffusion, and the coating eventually cracked after 7 days' incubation in saline supplemented with 0.1% Tween at 37 degrees C, enabling the release of any cDDP remaining. Effects of platinum, pre-released from PLAGA-coated albumin microspheres on the in vitro growth of L1210 cells were comparable with those of standard formulations (dissolved) of cDDP. Material released from non-drug-loaded PLAGA microspheres had no effect on L1210 cell growth, suggesting the absence of cytotoxic compounds in the matrix. The colony-forming ability of B16 cells was also equally inhibited by standard cDDP and pre-released drug. These studies show that formulation of cDDP in PLAGA-based microspheres prevents the rapid burst effect of cDDP seen in previous preparations and offers an improved system of administration for hepatic artery infusion or adjuvant therapy, enabling better clinical handling and the promise of a higher ratio of tumour tissue to normal tissue.

The predictive value of cell kinetic measurements in a European trial of accelerated fractionation in advanced head and neck tumors: an interim report

The value of cell kinetic measurements in head and neck tumors in predicting which patients will benefit from accelerated fractionation radiotherapy regimens is being tested in a multicenter European trial (EORTC trial 22851). This paper reports on the first analysis of the correlation of kinetics with outcome in this trial. A proportion of patients in both the accelerated arm (72 Gy in 5 weeks, 1.6Gy per fraction, 45 fractions) and the conventional arm (70-72 Gy in 7-8 weeks, 1.8-2.0 Gy per fraction, 35-40 fractions) were given an i.v. injection of 100 mg/m2 IUdR (iododeoxyuridine) before treatment, and a tumor biopsy was taken several hours later. The potential doubling time of the tumor (Tpot) was obtained from a flow cytometric analysis of tumor cell nuclei using an anti-IUdR antibody. From a total of 260 patients entered in the trial, 53 have undergone kinetic analysis. Adequate IUdR labeling was seen in 47 patients (88.7%), from which the mean value for Tpot was found to be 4.5 +/- 2.5 days (+/- S.D.). Of the IUdR labeled patients, 30 have now been followed up for at least 1 year, 17 with conventional and 13 with accelerated radiotherapy. These patients were split into those with fast and those with slowly growing tumors, the dividing line being the median Tpot value of 4.6 days. After conventional 7-week radiotherapy, 2 of 6 patients with "fast" growing tumors obtained local control compared with 8 of 11 with "slow" growing tumors. A small difference in local control was seen been fast and slow tumors in the accelerated arm (5/9 vs. 3/4). These preliminary data support the hypothesis that patients with fast growing tumors do poorly with conventional radiotherapy and that pretreatment kinetic measurements can select patients at risk. The predictive power of the method must await the final analysis of trial results.

Cisplatin and radiation: interaction probabilities and therapeutic possibilities

This paper examines the probability of interactions occurring between drug lesions and radiation lesions in DNA for the cytotoxic and radiosensitizing agent cisplatin. The number of cisplatin-induced DNA adducts and radiation-induced strand breaks after a given dose of each agent are known for given cell systems, from which the probability that these lesions will interact can be estimated. Results of these calculations indicate that the probability of interaction could be high, depending on the distance over which two lesions can interact and the probability of repair of the interaction lesion. Calculated lesion numbers have been compared with known data on radiation modification, including illustrations of inconsistencies. In the second part of the paper, ways in which combined therapy with cisplatin and radiation can be improved are described. Development of methods to predict which types of tumor and which individual tumors within a given type are sensitive to the cytotoxic and radiosensitizing effects of the drug would aid rational selection of patients for combination treatments. Immunocytochemical methods sensitive enough to monitor cisplatin-DNA interactions in patients are available and may be useful in this context. The delivery and maintenance of higher tumour concentrations of radiosensitizer offers a further possibility for improvement. Studies of intratumoral injection of cisplatin have shown promise for achieving this goal while limiting normal tissue toxicity.

Correlation between cell killing by cis-diamminedichloroplatinum(II) in six mammalian cell lines and binding of a cis-diamminedichloroplatinum(II)-DNA antiserum

The relationship between cell killing and the binding of the anticancer drug cis-diamminedichloroplatinum(II) (cis-DDP) to DNA was studied in six mammalian cell lines. Two of the human cell lines (COV413B) were of the same origin, comprising one sensitive to cis-DDP and the other with induced resistance to the drug. The four other lines, two rodent (RIF-1, Chinese hamster ovary) and two human (A2780, A1847), were unrelated. The cell lines differed in their sensitivity to cis-DDP, as tested in a clonogenic assay. cis-DDP-DNA binding was determined by quantitative immunocytochemistry using an antiserum against cis-DDP-modified DNA. The resistance factors relative to RIF-1, calculated from full survival curves for cis-DDP, were 3.8 +/- 0.4 for Chinese hamster ovary cells and 8.8 +/- 0.7 for both A2780 and A1847 lines. Using quantitative immunocytochemistry, the levels of the adduct-specific nuclear staining density compared with RIF-1 cells were 4.8 +/- 0.2 for Chinese hamster ovary cells, 9.1 +/- 0.2 for A2780, and 10.0 +/- 0.1 for A1847 cells, i.e., in good agreement with the resistance factors. In studies with the COV413B cells and their cis-DDP-resistant counterpart COV413B-PtR, immunologically detected adduct levels again correlated closely with resistance factors (correlation coefficient = 0.97). The kinetics of cis-DDP-DNA adduct formation and loss was investigated in RIF-1, A2780, and A1847 cells by the immunocytochemistry technique. Adduct levels after a 1-h incubation with approximately equitoxic doses of cis-DDP increased by 18 to 32% (average, 27%) between 0 and 6.5 h after treatment and then declined. Adduct half-lives in this latter phase did not correlate with the sensitivities of the cells for cis-DDP. These results indicate that the initial level of cis-DDP-DNA binding measured by quantitative immunocytochemistry may be a reasonable predictor of sensitivity to this chemotherapeutic drug.

Intratumoural administration of cisplatin in slow-release devices. I. Tumour response and toxicity

In this study we investigated the effect of the incorporation of cisplatin in slow-release systems on tumour response and animal toxicity after intratumoural (i.t.) administration. Solid slow-release rods with incorporated cisplatin were prepared either from starch or from three different polyether-hydrogel formulations. In vitro release rates from these rods were widely different. With the starch system, approximately 100% release was obtained in 2 h. For the hydrogel formulations, release was approximately 100% in 1 day for a formulation with 40% water uptake (T3), 45% within 4 days for a formulation with 14% water uptake (T2) and 8% within 4 days for a formulation with 4% water uptake (T1). The slow-release rods containing graded amounts of cisplatin were implanted i.t. in s.c. RIF1 murine tumours. The i.t. administration of cisplatin in starch rods did not reduce animal toxicity or increase tumour response relative to i.t. injections of cisplatin in solution. For the hydrogel rods, the tumour response and animal toxicity for a given dose of cisplatin decreased with decreasing release rate. Higher doses of cisplatin could therefore be delivered with the slower-releasing hydrogel formulations. The slowest-release hydrogel rods (T1) had very little effect on either tumour (growth delay) or host (animal weight loss), even at cisplatin doses 8 times that tolerated as an i.p. injection. The fast (T3)- and intermediate (T2)-release hydrogel rods resulted in dose dependent tumour growth delays that were longer than those obtained with i.p. or i.t. administration of cisplatin. The highest response, a tumour growth delay of 55 days, was obtained with the intermediate-release hydrogel rods (T2) at a cisplatin dose of 40 mg/kg. Analysis of tumour growth delay for a given level of toxicity indicated that the intermediate-release formulation (T2) was slightly better than the fast-release formulation (T3) and confirmed the therapeutic advantage of i.t. implants over systemic therapy.

A new intraperitoneal tumor model in the rat

A new tumour model that is particularly suitable for testing intraperitoneal chemotherapy is described. Single tumours were induced to grow in the mesentery of rats by the implantation of small pieces taken from subcutaneous tumours. Tumour growth was monitored by repeated laparotomies at which the tumour size was measured with calipers. In this way, growth curves of treated and untreated tumours could be defined. The diameter of untreated intraperitoneal tumours increased linearly with time [diameter (mm) = 0.39 t (days) +2.4]. Tests using different numbers of laparotomies showed that the procedure itself had little influence on growth. Cell kinetic studies of 6-mm tumours showed a mean labelling index of 31% and a volume-doubling time of 3.9 days, resulting in cell-loss factors probably in excess of 70%. The model was tested by assessing the effect of the chemotherapeutic agent cisplatin. Regression and regrowth could be satisfactorily followed, leading to estimates of growth delay. This model therefore provides a quantitative way to assess the response of intraperitoneal tumours to chemotherapy.

The effect of cisplatin on the repair of radiation damage in RIF1 mouse tumours in vivo

The effect of the antitumour agent cisplatin on repair of X-ray-induced damage was studied in RIF1 mouse tumours treated in situ. The response of tumours, assessed by growth delay, to 4 fractions of X-rays given at 5-h intervals was compared with that after single doses. The displacement between the curves was taken as a measure of repair. A single dose of 6 mg.kg-1 cisplatin given 0.5 h before the first fraction resulted in no detectable inhibition of repair despite a significant growth delay caused by drug alone. A dose of 2 mg/kg cisplatin given 0.5 h before each of the X-ray fractions did, however, cause some repair inhibition; a result confirmed by tumour control experiments. The schedule dependence for repair inhibition was the same whether the irradiations were carried out on clamped (fully hypoxic) tumours or under ambient conditions. Significant enhancement of radiation damage was seen after correcting for the effects of drug alone, whether or not repair inhibition occurred. The effects of cisplatin on normal stroma within the tumour (vascular damage) was also investigated by monitoring the regrowth rates of recurrent tumours. In contrast to the effects on tumour cells, no enhancement of damage or inhibition of repair was seen for this assay in the combined treatment schedules.

Rapid fluorescence-based assay for radiosensitivity and chemosensitivity testing in mammalian cells in vitro

An efficient and rapid cytotoxicity assay has been developed, particularly for radiobiological studies, utilizing 96-well microtiter plates. Several days after treatment, cell numbers per well were measured by fluorescent intensity using an automatic reader after staining with the DNA specific dye Hoechst 33258. For radiobiological applications, a microtiter plate irradiation box was designed and built which allowed a variable number of wells (minimum 4, maximum 16) to be irradiated at one time. In this manner, complete dose-response curves could be obtained from one plate. The assay depends on the growth of surviving and untreated cells, and by appropriate choice of conditions (cell numbers plated, time of assay), cell survival curves for this quick fluorescence assay were in reasonable agreement with those from a clonogenic assay for cisplatin and X-ray-induced cell killing. The assay can span 1.5-2 decades of cell survival and is suitable for any cell line which grows as a monolayer. Radiobiological applications were tested using agents or conditions which modified radiation damage. Firstly, sublethal damage repair could be demonstrated in RIF1 mouse tumor cells by comparing the survival curve for a single X-ray dose with that for two fractions separated by 4 h. Secondly, incorporation of 5-iodo-2'-deoxyuridine into cellular DNA was shown to radiosensitize Chinese Hamster cells, with similar enhancement ratios obtained from the fluorescence and clonogenic assays. Thirdly, radiosensitization by cisplatin and radioprotection by cysteamine could be readily measured using the quick fluorescence assay. The ability to have multiple dose groups per plate makes it an efficient assay for both radiosensitivity and chemosensitivity testing.

Monitoring of interaction products of cis-diamminedichloroplatinum(II) and cis-diammine(1,1-cyclobutanedicarboxylato)platinum(II) with DNA in cells from platinum-treated cancer patients

The formation and stability of interaction products between the anti-cancer drug cis-diamminedichloroplatinum(II) (cis-DDP) and DNA were studied in buccal epithelial and urinary cells from ten cancer patients who received cis-DDP-based therapy. Buccal cells were collected 1 h before and 1-2 h after i.v. infusions with cis-DDP. The interaction products were visualized in an immunocytochemical peroxidase assay, using an antiserum against cis-DDP-modified calf thymus DNA. The nuclear staining density was measured by microdensitometry. Nuclear staining densities in buccal cells after infusions of greater than or equal to 20 mg/m2 cis-DDP were always higher than pretreatment values. Repeated sampling from individual patients treated for 2-5 consecutive days with daily doses of 20-70 mg/m2 cis-DDP indicated that cis-DDP-DNA binding in buccal cells increased in proportion to the cumulative total dose of cis-DDP. The variation in dose-density response between patients was 17%. Apparent adduct loss in buccal cells from four patients, as measured 8-17 days after the last infusion, amounted to 67-86%. Platinum-induced DNA modifications could also be detected in buccal cells from two cis-diammine(1,1-cyclobutanedicarboxylato)platinum(II)-treated patients. In vitro experiments with human buccal cells and lymphocytes indicated linear relationships between DNA modification and either cis-DDP concentration or incubation time. Nuclear staining densities in pretreatment buccal cells from ten cancer patients treated in vitro with 33 microM cis-DDP for 1 h revealed that interpatient variation in in vitro DNA modification by cis-DDP was low. No quantitative correlation was found between in situ and in vitro DNA modification.

Cell proliferation in the murine epidermis and subcutaneous vascular endothelium after hyperthermia

The skin of mouse legs was exposed to 44 degrees C hyperthermia using a thermostatically controlled waterbath. Treatment at 44 degrees C, for 15 or 30 min, led to oedema in the dermis immediately after treatment and to an infiltration by neutrophils within 7 h. The oedema disappeared in 2 days. Treatment for 60 min at 44 degrees C led to subepidermal blistering and as a result of this a considerable area of the tissue became necrotic 4 days after treatment. A repair reaction followed, and 3 weeks after heating for 60 min at 44 degrees C the epithelium was again completely or almost completely covering the underlying tissue. Shortly (7 h) after 15 or 30 min at 44 degrees C an increase was observed in the number of basal cells in the epithelium incorporating [3H]thymidine. This increase declined slowly with time: 3 weeks after treatment the number of labelled basal cells was not significantly different from that in untreated skin. Shortly after 60 min at 44 degrees C some basal cells of the epidermis still incorporated [3H]thymidine. The labelling index dropped to near-zero at day 2 after 60 min at 44 degrees C. Thereafter repopulation started and in the areas next to the granulation tissue the labelling index of basal cells reached values close to 100 per cent, 2 or 3 weeks after treatment. Treatment for 15 min at 44 degrees C did not lead to a stimulation of the proliferation of subcutaneous endothelial cells. Both 30 min and 60 min at 44 degrees C led to a greatly enhanced proportion of labelled subcutaneous endothelial cells after 2 days and 4 weeks, respectively (labelling index between 35 and 40 per cent). After this peak value the labelling index declined rapidly. However, in granulation tissue it remained high for about 10 days after the peak on day 4. The stimulated proliferation of subcutaneous endothelial cells after heating for 30 and 60 min at 44 degrees C correlated well with the finding that these heat treatments, given after or shortly before X-irradiation, led to a greatly reduced (X-ray-induced) tumour bed effect.

Human tumour cell kinetics using a monoclonal antibody against iododeoxyuridine: intratumour sampling variations

Cell kinetic parameters in human tumours were determined by in vivo labelling with iododeoxyuridine (IUdR) followed by flow cytometric analysis of tumour biopsies after staining with a monoclonal antibody against IUdR-DNA. The purpose of this study was to determine the variation in these kinetic parameters from area to area within the same tumour. Each patient received a single i.v. injection of IUdR and the biopsy or operation specimen was taken several hours later. Multiple biopsies were taken or the operation specimen was cut into several pieces. Tumour material was stored in ethanol. Each piece was subsequently processed and stained for analysis separately. The duration of DNA synthesis (Ts), the labelling index (L.I., percent IUdR-labelled cells) and the potential doubling time (Tpot) were determined for each sample. The mean and standard deviation (variation between pieces) for each parameter was calculated for each tumour. The coefficient of variation (C.V.) provided the measure of intratumoural variation. Thirteen tumours were investigated, 6 of which were transitional cell carcinomas of the bladder and 7 of which were squamous cell carcinomas, mostly of the head and neck. Ts values ranged from 4.1 to 17.2 h (mean 9.5 h), L.I. values from 1.6 to 18.6% (mean 9.7%) and Tpot values from 2.3 to 15.1 days (mean 7.2 days). Mean C.V.s for Ts, L.I. and Tpot were 10, 24 and 27%, respectively. Most of the variation in Tpot (calculated from the other two parameters), came from the L.I., with Ts showing much less intratumoural variations. It is concluded that this kinetic method using low IUdR doses can be successfully applied in human tumours and has sufficient accuracy for predictive assay applications in which tumours need to be classified according to their proliferation rates. Further developments are required to distinguish normal and malignant cells flow cytometrically, particularly for diploid tumours.

Validation of the fluorescent dye Hoechst 33342 as a vascular space marker in tumours

The DNA-binding fluorescent dye Hoechst 33342 (H33342) has been used in a series of investigations of the vascular parameters of two murine tumours. This dye has been shown, to have a short half-life in the circulation (T1/2 less than 2 min), but is stably bound for at least 2 h after it enters cells. It can be used in morphometric studies on frozen sections to determine the effective vascular volume, the capillary fraction and the size distribution of blood vessels in each tumour. These latter two parameters cannot be deduced from the less labour intensive techniques using radioactive isotopes. The effective vascular volume perfused in 1 min by H33342 was compared with the volume perfused in 30 min with 51Cr labelled erythrocytes. Similar volumes were estimated with the two techniques in a murine carcinoma and in a sarcoma. Both techniques showed that the vascular volume decreased in larger tumours. The H33342 analysis of vessel size showed the decrease in capillary vessels in the carcinomas was even greater, falling from 70% in small tumours to 20% in larger tumours. The deteriorating vascular network in larger tumours is associated with an increasing fraction of necrotic tissue. Experiments in which the isotopes and dye were co-injected suggest that at 40 mgkg-1 the dye may rapidly lead to a partial shutdown of the tumour vascular bed. This is less marked with 20 mg kg-1. In spite of this effect there is in general a close correlation between the volumes perfused by labelled red blood cells and the fluorescent dye.

Immunocytochemical detection of interaction products of cis-diamminedichloroplatinum(II) and cis-diammine(1,1-cyclobutanedicarboxylato)platinum(II) with DNA in rodent tissue sections

Calf thymus DNA was modified in vitro by cis-diamminedichloroplatinum(II) (cisDDP), complexed with methylated bovine serum albumin and used to immunize rabbits. The anti-cisDDP-DNA antiserum obtained was applied in a double peroxidase-antiperoxidase staining procedure to localize cisDDP-DNA and cis-diammine(1,1-cyclobutanedicarboxylato)platinum(II) (CBDCA)-DNA interaction products in cryostat tissue sections of mice and rats. Rats received cisDDP (0-10 mg/kg) and were killed after 24 h. Mice received cisDDP (0-15 mg/kg) or CBDCA (200 mg/kg), and were killed after 2 h-162 days. For each time-dose combination two mice or one rat were used; agents were given i.p. Specific nuclear staining was observed in all tissues examined from cisDDP- or CBDCA-treated animals. No significant nuclear staining could be observed in tissue sections from control rats and mice. The extent of staining after cisDDP was dose and time dependent. The lowest dose of cisDDP after which specific nuclear staining could be detected varied from tissue to tissue [e.g., 0.1 mg/kg, pancreas (mouse); 0.5 mg/kg, liver, kidney (mouse, rat)]. The longest time interval after a single dose of 6 mg/kg cisDDP in which adducts could be visualized also depended on the tissue and varied between 9 days (spleen, testis) and 162 days (kidney). The staining intensity in liver and kidney, measured microdensitometrically, decreased relatively fast in the first days after treatment, but much slower thereafter. In the kidney, cisDDP-induced DNA modification showed regional variation: inner cortex greater than outer cortex greater than medulla (rat) and cortex greater than medulla (mouse). In the mouse kidney, a small subpopulation of tubular cells in close association with the renal corpuscles showed a remarkably high staining intensity after both cisDDP and CBDCA administration. Tissues that showed clear cisDDP-induced histological alterations (kidney, pancreas, testis, and duodenum) also showed moderate to high levels of cisDDP-DNA interaction products. A correlation between cell damage (measured histologically) and cisDDP-DNA binding within one tissue type was demonstrated in the rat inner renal cortex, the murine renal cortex, and in duodenal epithelial cells of both mice and rats.

Radiosensitization in vitro by cis-diammine (1,1-cyclobutanedicarboxylato) platinum(II) (carboplatin, JM8) and ethylenediammine-malonatoplatinum(II) (JM40)

The radiosensitizing ability of two analogues of cisplatin have been tested in vitro. The analogues, CBDCA (JM8) and EDMP (JM40), are currently undergoing clinical tests in the search for an active but less toxic cancer chemotherapeutic agent than cisplatin. The compounds were cytotoxic to log phase RIF1 cells in culture, but at higher concentrations than the parent compound. Both analogues were radiosensitizers of oxic cells when given as 1 h exposures beginning either 3 h before, 1 h before or 2 h after irradiation, giving modest enhancements of approximately 1.2. Each drug caused an inhibition of the repair of sublethal damage which was greatest after CBDCA treatment. Although neither analogue was as good a radiosensitizer as cisplatin, CBDCA appears to show promise as a potential radioenhancing platinum compound.

Additivity versus repair inhibition in fractionated treatments combining drugs and X rays: a theoretical analysis

Drugs which inhibit the repair of radiation damage could potentially be useful for enhancing the effects of radiotherapy. In pre-clinical combined modality studies, however, it is often difficult to state with certainty whether or not a drug has inhibited radiation damage repair. This paper shows that several commonly used parameters for assessing repair can give the wrong answer regarding the presence of drug-induced repair inhibition. These parameters are; the difference in radiation dose between 1 and n fractions to give the same effect, the fractional recovered dose per fraction interval, FR, and the related parameter FREC. A further parameter used for treatment comparisons is the enhancement ratio for the drug (D.E.R.; ratio of radiation doses, with and without drug, to cause a given effect). An increasing D.E.R. with increasing number of radiation fractions has been taken as an indication that the drug inhibited repair. The present report demonstrates that this, too, can be misleading. From an analysis based on a linear-quadratic survival curve for X rays, it is suggested that deriving and comparing alpha/beta ratios (ratio of the linea to quadratic coefficients) gives the best indication of drug-induced changes in survival curve shape which may reflect underlying changes in repair capacity.

Repair of sublethal radiation injury after multiple small doses in mouse kidney: an estimate of flexure dose

Functional kidney damage in mice was measured after a series of fractionated X-irradiations. Doses per fraction of 0.75-12.5 Gy were given as 2, 5, 10, 30, 40, 60, or 80 equal doses in a total treatment time of 4 weeks. Renal function (measured by clearance of 51CrEDTA or hematocrit levels) deteriorated progressively, in a dose related manner, from 20 to 46 weeks after the start of treatment. The changes in renal function versus time were fitted by a polynomial regression through all data and interpolated values for 51CrEDTA clearance were then calculated at 30 and 40 weeks after treatment. Steep dose response curves were obtained and these were used to calculate isoeffective doses for the different fractionation schedules. There was a marked increase in total isoeffective doses from 2-30 fractions and these data were well described by a linear quadratic (L.Q.) expression for damage with an alpha/beta ratio of 2.3 +/- 0.2 Gy. There was only a slight increase in the total isoeffect dose as the size of the dose per fraction was decreased below 2 Gy and the measured isoeffect doses after 40 to 80 fractions were lower than predicted on the basis of an L.Q. model assuming complete repair between successive irradiations. The flexure dose for mouse kidneys irradiated 3 times per day was, effectively, 1 to 2 Gy and hyperfractionation using lower doses per fraction did not lead to significant, additional repair.

Tolerance of previously irradiated mouse kidneys to cis-diamminedichloroplatinum(II)

In this study the tolerance of previously irradiated kidneys to retreatment with chemotherapy was assessed. cis-Diamminedichloroplatinum(II) (c-DDP) was given to groups of mice at 1, 3, or 6 months after bilateral renal irradiation with single doses of 8-14 Gy. Renal function was measured monthly (by clearance of 51Cr ethylenediaminetetraacetic acid) from 4-35 weeks after c-DDP injection and results were compared with function after X-rays alone or drug alone. At early testing times (during the first 11 weeks after c-DDP injection) the renal function of mice given drug at 1 or 3 months after irradiation was very similar to that seen after drug alone. c-DDP given at 6 months caused slightly more damage than either drug or X-rays alone, but these results could be explained in terms of additive toxicities. At later testing times (11-35 weeks after c-DDP injection), renal function was much worse in all animals which had received previous irradiation, with the greatest damage when c-DDP was given 6 months after X-rays. This may be partly due to additional cell killing by the drug causing the expression of subclinical radiation injury. It is also possible that c-DDP pharmacokinetics was altered in animals with previously irradiated kidneys, leading to higher drug exposures in these mice.

Radiosensitization by cisplatin of RIF1 tumour cells in vitro

The ability of cis-diamminedichloroplatinum (II) (c-DDP) to enhance radiation-induced cell killing was tested on oxic RIF1 tumour cells in monolayer culture. Marked radiosensitization of the survivors of a 1 h drug treatment was found with all c-DDP doses tested, with enhancement ratios increasing from 1.2 to 2.2 with increasing drug dose. Isobologram analyses showed that the interactions of c-DDP with X-rays were supra-additive. To test whether part of the enhancement was due to a selection of subpopulations, the diploid and tetraploid RIF1 cells, which normally coexist in culture, were separated by unit gravity velocity sedimentation, and by developing diploid and tetraploid clones. Both methods showed that there was little difference in either drug sensitivity or radiation sensitivity between diploid and tetraploid cells. DNA histograms obtained by flow cytometry showed little or no cycle progression during the 1 h drug treatment. These data indicate that the radiosensitization was not the result of the drug exposure leaving cells in a radiosensitive phase. The observed radiosensitization, therefore, appears to have resulted from a true drug/X-ray interaction.

Effects of hyperthermia and X-irradiation on mouse stromal tissue

The sensitivity of normal stroma to heat, irradiation and heat combined with irradiation has been studied using the tumour bed effect (TBE) assay. Irradiation before implantation led to a TBE. This TBE was dose dependent below 15 Gy, the TBE remaining relatively constant above 15 Gy. The interval (0-90 days) between irradiation and tumour implantation did not influence the magnitude of the TBE. Hyperthermia with large heat doses (45-60 min at 44 degrees C) before implantation may lead to a TBE. The interval between hyperthermia and tumour implantation proved to be very important. Our results show that the recovery from heat-induced stromal damage is very rapid. When the interval between hyperthermia and tumour implantation is 10 days or longer, no TBE could be observed. Irradiation combined with large heat doses (30-60 min at 44 degrees C) decreased the radiation-induced TBE. However, the combination of irradiation with mild heat treatments (15 min at 44 degrees C) could lead to a larger TBE than after irradiation alone. When hyperthermia was given prior to irradiation, the interval between heat and irradiation proved to be very important. With large intervals (21 days or longer) the TBE values were about the same as with irradiation alone. When heat was given after irradiation it always reduced the irradiation-induced TBE.