Radiosensitization of hematopoietic precursor cells (CFUc) in glioblastoma patients receiving intermittent intravenous infusions of bromodeoxyuridine (BUdR)

Genetic models to study quiescent stem cells and their niches

Hematopoietic stem cells (HSC) have been defined by their ability to establish long-term hematopoiesis in myelo-ablated hosts. Prospective isolation using combinations of cell-surface markers and/or dye exclusion can yield highly purified and nearly homogeneous phenotypically defined cells that repopulate irradiated hosts. Although highly informative, these types of analyses may not necessarily reflect ongoing homeostatic hematopoiesis. HSCs are also described as being quiescent. This has been demonstrated by cell cycle analysis of phenotypically defined HSCs. Some studies have challenged the existence of truly quiescent HSCs, suggesting that they continuously cycle, albeit with very slow kinetics. Here we present a pulse-chase system based on the controllable incorporation of H2B-GFP into nucleosomes, which allows the identification, purification, and functional analysis of viable label-retaining cells. Our data complement and extend recent studies using similar strategies. These, together with our present studies, find a rare, quiescent or dormant subset within the population of stringently defined HSC phenotypes. To date, three types of niches, endosteal, vascular, and reticular, have been described; herein we review the cellular and spatial nature of these microenvironments. We propose that HSC label-retention combined with genetically manipulated stem cell niches will allow us to determine their anatomical architecture, to address HSC cell fate proliferation kinetics, and to begin to dissect the molecular cross talk among stem cells and niche cells in vivo during both normal and perturbed homeostasis.

Hematopoietic stem cells reversibly switch from dormancy to self-renewal during homeostasis and repair

Bone marrow hematopoietic stem cells (HSCs) are crucial to maintain lifelong production of all blood cells. Although HSCs divide infrequently, it is thought that the entire HSC pool turns over every few weeks, suggesting that HSCs regularly enter and exit cell cycle. Here, we combine flow cytometry with label-retaining assays (BrdU and histone H2B-GFP) to identify a population of dormant mouse HSCs (d-HSCs) within the lin(-)Sca1+cKit+CD150+CD48(-)CD34(-) population. Computational modeling suggests that d-HSCs divide about every 145 days, or five times per lifetime. d-HSCs harbor the vast majority of multilineage long-term self-renewal activity. While they form a silent reservoir of the most potent HSCs during homeostasis, they are efficiently activated to self-renew in response to bone marrow injury or G-CSF stimulation. After re-establishment of homeostasis, activated HSCs return to dormancy, suggesting that HSCs are not stochastically entering the cell cycle but reversibly switch from dormancy to self-renewal under conditions of hematopoietic stress.

Continuous 28-day iododeoxyuridine infusion and hyperfractionated accelerated radiotherapy for malignant glioma: a phase I clinical study

PURPOSE

To investigate the maximal tolerated dose of a continuous 28-day iododeoxyuridine (IUdr) infusion combined with hyperfractionated accelerated radiotherapy (HART); to analyze the percentage of IUdr-thymidine replacement in peripheral granulocytes as a surrogate marker for IUdr incorporation into tumor cells; to measure the steady-state serum IUdr levels; and to assess the feasibility of continuous IUdr infusion and HART in the management of malignant glioma.

METHODS AND MATERIALS

Patients were required to have biopsy-proven malignant glioma. Patients received 100 (n = 4), 200 (n = 3), 300 (n = 3), 400 (n = 6), 500 (n = 4), 625 (n = 5), or 781 (n = 6) mg/m(2)/d of IUdr by continuous infusion for 28 days. HART was started 7 days after IUdr initiation. The total dose was 70 Gy (1.2 Gy b.i.d. for 25 days with a 10-Gy boost [2.0 Gy for 5 Saturdays]). Weekly assays were performed to determine the percentage of IUdr-DNA replacement in granulocytes and serum IUdr levels using standard high performance liquid chromatography methods. Standard Phase I toxicity methods were used.

RESULTS

Between June 1994 and August 1999, 31 patients were enrolled. No patient had Grade 3 or worse HART toxicity. Grade 3 or greater IUdr toxicity predominantly included neutropenia (n = 3), thrombocytopenia (n = 3), and elevated liver function studies (n = 3). The maximal tolerated dose was 625 mg/m(2)/d. Thymidine replacement in the peripheral granulocytes peaked at 3 weeks and increased with the dose (maximal thymidine replacement 4.9%). The steady-state plasma IUdr level increased with the dose (maximum, 1.5 microM).

CONCLUSION

In our study, continuous long-term IUdr i.v. infusion had a maximal tolerated dose of 625 mg/m(2)/d. Granulocyte incorporation data verified the concept that prolonged IUdr infusion results in IUdr-DNA replacement that corresponds to a high degree of cell labeling. IUdr steady-state plasma levels increased with increasing dose and attained levels needed for clinical radiosensitization. Continuous IUdr infusion and HART were both feasible and well tolerated.

Potential tumour doubling time: determination of Tpot for various canine and feline tumours

Spontaneous tumours in dogs and cats are an excellent model for clinical human research, such as in developing proton conformation radiotherapy for humans. The kinetics of tumour cells can be used effectively to predict prognosis and response to therapy in patients with tumours. Knowledge of the kinetic parameters in these tumours is therefore important. In the present study the kinetic parameters evaluated included the labelling index (LI), relative movement (RM), mitotic index (MI), and potential doubling time (Tpot). These parameters were determined using in vivo labelling with bromodeoxyuridine, flow cytometry and histological preparation. Samples were obtained and evaluated from 72 dogs and 20 cats, presenting as patients in our clinic. Within the groups of epithelial and mesenchymal tumours from dogs and cats, the kinetic parameters LI, RM and MI were compared with Tpot. Significant correlations were observed for the comparison Tpot and LI. No correlation was found between Tpot and RM.

Bromodeoxyuridine-mediated radiosensitization in human glioma: the effect of concentration, duration, and fluoropyrimidine modulation

PURPOSE

To define the relative influence of duration of exposure, concentration, and modulation by fluorodeoxyuridines (FdUrd) on the incorporation of 5-bromo-2-deoxyuridine (BrdUrd) into DNA of a human malignant glioma line (D-54) in vitro and in vivo.

MATERIALS AND METHODS

IN VITRO STUDIES

an established human malignant glioma line (D-54) was exposed to a clinically achievable concentration of BrdUrd to model intravenous (1 microM BrdUrd) and intraarterial (4 microM BrdUrd) conditions. The influence of modulation was assessed using 1 nM FdUrd. Incorporation of BrdUrd, radiosensitization, and cytotoxicity were determined after 24, 72, and 120 h drug exposures. In Vivo studies: nude mice bearing D-54 xenografts were infused with BrdUrd at 100 mg/kg/day for 7 and 14 days or BrdUrd at 400 mg/kg/day for 5 days. The influence of modulation was assessed by combining 100 mg/kg/day of BrdUrd with 0.1, 0.3, and 1 mg/kg/day FdUrd for 7 days. Incorporation of BrdUrd into the DNA of tumor, gut, and marrow were determined.

RESULTS

In Vitro: thymidine replacement and radiosensitization were a function of concentration, and incorporation began to plateau after 2 to 3 population doublings. Modulation with 1 nM FdUrd significantly increased incorporation. Radiosensitization was a linear function of thymidine replacement under all conditions tested. In Vivo: infusion with 400 mg/kg/day for 5 days resulted in greater tumor incorporation (10.3 +/- 0.4% thymidine replaced) than treatment with 100 mg/kg/day for 14 days (6.0 +/- 0.6% of thymidine replaced). Infusion of FdUrd with BrdUrd increased normal tissue incorporation of BrdUrd, but failed to increase BrdUrd incorporation in tumor cells.

CONCLUSION

These results suggest that relatively short, high dose rate infusions may be preferable to long, low dose rate infusions. The potential benefit of FdUrd modulation demonstrated in vitro may be difficult to realize using continuous systemic infusions.

Prospective evaluation of cell kinetics in head and neck squamous carcinoma: the relationship to tumour factors and survival

Tumour growth rates were measured in 105 patients using in vivo incorporation of bromodeoxyuridine (BrdU) and investigated for any relationship to tumour factors or survival. The median labelling index (LI) was 8.7%, the duration of S-phase (Ts) was 14 h and the potential doubling time (Tpot) was 5.9 days. The labelling index in aneuploid tumours was significantly higher than that in diploid tumours. However the total labelling index (TLI) did not differ significantly between aneuploid and diploid tumours, and so it would seem likely that the difference in LI is due to the dilutional effect of benign tissue upon the calculation of LI in diploid tumours. The total labelling index, duration of S-phase and potential doubling time were not related to the tumour factors examined (site, T stage, N stage, stage grouping). Interim survival analysis was carried out and there was no difference in survival between those patients with high values for TLI, Ts, and Tpot and those with low values.

Correlation of sensitizer enhancement ratio with bromodeoxyuridine concentration and exposure time in human cervical carcinoma cells treated with low dose rate irradiation

The effect of a range of bromodeoxyuridine concentrations and exposure times on the sensitizer enhancement ratio of two human cervical carcinoma cell lines treated with low rate irradiation was evaluated. Both cell lines show a linear, though different, dose response to low dose rate irradiation at dose rates up to 0.62 Gy/hr. Cells were pre-incubated with 0, 1, 5, or 10 microM bromodeoxyuridine for 0, 24, or 48 hr prior to low dose rate irradiation. Based on the survival of cells exposed to 4 Gy, delivered at 0.62 Gy/hr, a slope was determined for an exponential survival curve for each bromodeoxyuridine concentration and exposure time. Sensitizer enhancement ratios were calculated as the ratio of the slopes of the treated and untreated cells from a particular exposure time. Ratios increased linearly initially with a plateauing at higher levels with respect to the product of bromodeoxyuridine concentration and time of exposure for both cell lines with similar degrees of enhancement. A linear relationship has been noted previously for acute irradiation of hamster cells over a similar range of sensitizer concentrations and exposure times. At the highest dose-time points (540 microM-hr) ratios of greater than 2 were attained, which were comparable to results obtained following acute radiation exposures of V-79 cells. These results demonstrate that significant sensitizer enhancement ratios with low dose irradiation can be obtained in human tumor cells after exposures of 2 to 3 doubling times using relatively low concentrations of sensitizer.

Low dose rate irradiation and halogenated pyrimidine effects on human cervical carcinoma cells

The response of two human cervical carcinoma cell lines to the combination of bromodeoxyuridine (BrdUrd) incorporation and low dose rate irradiation (LDRI) was assessed. Survival curves were generated following both acute (67.2 Gy/hr) and low dose rate (0.11-0.62 Gy/hr) 137Cs gamma-ray irradiation. The two cell lines exhibited markedly different radiation responses, but for the chronic irradiation, there was no significant difference in response between the low dose rates for either cell line. In all cases, the low dose rate radiation response could be described using a single exponential y = e-alpha D. The sensitizer enhancement ratio (SER) at 10% survival was determined and for the first cell line the low dose rate slope (alpha) was approximately 0.7 Gy-1 with an SER of 1.3-1.5 and an SER of approximately 1.6 for the acute response. In contrast, the second cell line had a low dose rate slope (alpha) of approximately 0.4 Gy-1, an SER of 1.3-1.5, and an SER of approximately 1.7 for the acute response. The similarity of the SER's is notable in light of the marked differences between the intrinsic radiation response of the cells. As the concentration and/or time of exposure to BrdUrd increased, both cytotoxicity and the degree of sensitization also increased. This study demonstrates that SER's with BrdUrd and LDRI are comparable to those obtained for acute exposures in two cervical carcinoma cell lines. The results suggest that this combination of modalities may have clinical applications.

Primary treatment of large and massive adult sarcomas with iododeoxyuridine and aggressive hyperfractionated irradiation

For a decade, the authors have experimented with treatment for unresectable adult soft tissue and bony sarcomas. Over the last 6 years, they have combined hyperfractionated radiation therapy and intravenous iododeoxyuridine as a radiosensitizer, in regimens designed to minimize toxicity and permit delivery of aggressive radiation therapy. Patients with solitary lesions and those with metastasis (38%) were treated in the hope of both potential cure in some and durable palliation in others. The most formidable of these cancers have been those that are large or massive, often requiring five or more fields and extensive treatment planning. The authors report results from 36 patients with large unresectable sarcomas (tumors ranging from 5 to 35 cm; average 14 cm) treated with hyperfractionated radiation therapy, with a minimum follow-up of 1 year, follow-up of 4 or more years (in 50%), or follow-up until death. Overall local control has been 60%, with control of 66% of lesions from 5 to 9 cm, 63% of those from 10 to 14 cm, 63% of those from 15 to 19 cm, and 57% of those greater than 20 to 40 cm. Morbidity has been modest. This experience compares favorably with the authors' earlier trials with misonidazole, and toxicity has been reduced considerably.

Analysis of 5-iodo-2'-deoxyuridine incorporation in murine melanoma for photon activation therapy

Quantitative evaluation of the dose enhancement obtained with analog nucleoside agents such as iododeoxyuridine (IdUrd) requires knowledge of the degree to which the thymidine (Thd) in DNA is replaced by IdUrd. In the present investigation, mice were infused with IdUrd using an intravenous infusion apparatus capable of delivering continuous multi-day infusions without restraining the mice. The absolute incorporation of IdUrd in DNA was measured by 125IdUrd label, both in whole tissue and extracted DNA, showing a good correlation between levels observed in DNA and whole tissue. Replacement in a Harding-Passey murine melanoma tumor carried in BALB/c mice approached 10%. In addition, a Neutron Activation Analysis (NAA) technique was developed which showed in vitro, a sensitivity sufficient to evaluate the % replacement of Thd by IdUrd in small biological samples with a sensitivity greater than 0.1 ppm, at 1% replacement in mg samples. This method can provide information on iodine substitution in DNA in humans where the use of a radioactive DNA-seeking substance would be undesirable. Analyses of IdUrd incorporation in cultured cells by NAA and 125I counting showed good agreement.

Radiation, pool size and incorporation studies in mice with 5-chloro-2'-deoxycytidine

Bolus doses of 5-chlorodeoxycytidine (CldC) administered with modulators of pyrimidine metabolism, followed by X-irradiation, resulted in a 2-fold dose increase effect against RIF-1 tumors in C3H mice. Pool size studies of the fate of [14C]-CldC in BDF1 mice bearing Sarcoma-180 tumors, which demonstrated the rapid formation of 5-chlorodeoxycytidylate (CldCMP), and incorporation of CldC as such in RIF-1 tumor DNA, indicate that CldC is a substrate for deoxycytidine kinase, as our past Km studies have shown. Our data indicate that 5-chlorodeoxyuridine triphosphate (CldUTP) accumulates from both the cytidine deaminase-thymidine kinase pathway, as well as from the deoxycytidine kinase-dCMP deaminase pathway, in tumor tissue. As shown in a previous study, tetrahydrouridine (H4U), a potent inhibitor of cytidine deaminase, can effectively inhibit the enzyme in the normal tissues of BDF1 mice. When H4U was administered with the modulators N-(phosphonacetyl)-L-aspartic acid (PALA) and 5-fluorodeoxycytidine (FdC), the levels of CldC-derived RNA and DNA directed metabolites increased in tumor and decreased in normal tissues compared to when CldC was administered alone. These modulators inhibit the de novo pathway of thymidine biosynthesis, lowering thymidine triphosphate (TTP) levels, which compete with CldUTP for incorporation into DNA. 5-Benzylacyclouridine (BAU), an inhibitor of uridine phosphorylase, was also utilized. DNA incorporation studies using C3H mice bearing RIF-1 tumors showed that the extent of incorporation of 5-chlorodeoxyuridine (CldU) into DNA correlates with the levels of cytidine and dCMP deaminases; this is encouraging in view of their high activity in many human malignancies and the low activities in normal tissues, including those undergoing active replication. Up to 3.9% replacement of thymidine by CldU took place in RIF-1 tumors, whereas incorporation into bone marrow was below our limit of detection. CldC did not result in photosensitization under conditions in cell culture in which radiosensitization to X rays was obtained. Thus, the combination of CldC with modulators of its metabolism has potential as a modality of selective radiosensitization for ultimate clinical use in a wider range of tumors than those of the brain.

S-phase fraction of human prostate adenocarcinoma studied with in vivo bromodeoxyuridine labeling

Forty-six patients with adenocarcinoma of the prostate were given an intravenous infusion of the thymidine analogue, bromodeoxyuridine (BrdU), 200 mg/m2, at the time of needle biopsy or transurethral resection to label tumor cells in the DNA synthesis phase. The tumor specimens were stained by an indirect immunoperoxidase method with anti-BrdU monoclonal antibody. The BrdU labeling index, S-phase fraction, was determined by counting the number of BrdU-labeled cells in the tissue sections. S-phase fraction correlates with the results of histologic tumor grade, Gleason score, and growth patterns. The higher S-phase fraction may indicate biologic malignancy. Moreover, the degree of heterogeneity concerning S-phase fraction distribution within prostate cancer tissue could be evaluated and the findings compared with the morphologic appearance. The authors results suggest that the measurement of BrdU labeling index in prostate cancer may prove to be a new objective and quantitative assay for biologic potential of individual tumors.

The dependence of halogenated pyrimidine incorporation and radiosensitization on the duration of drug exposure

The influence of the duration of exposure to the halogenated pyrimidines iododeoxyuridine (IdUrd) and bromodeoxyuridine (BrdUrd) on incorporation into DNA and the resulting radiosensitization was studied in cultured human colon cancer cells. Cells were incubated with either 10 microM BrdUrd or IdUrd for periods up to 7 days. They were also assessed for up to 4 days after removal of drug from the medium. Replacement of thymidine by fraudulent bases was measured using a sensitive gas chromatographic, mass spectrometric (GC/MS) assay. Incorporation of BrdUrd and IdUrd plateaued at 35% and 30%, respectively, after 4 days of exposure. Prolonging the time of exposure to 7 days increased cytotoxicity without affecting either incorporation or radiosensitization. Incorporation remained constant for 1-2 days after removal of drug from the medium. Radiosensitization was linearly related to incorporation throughout the range of conditions assessed. These data suggest that it may be possible to develop a predictive assay for radiosensitization based on measurements of halogenated pyrimidine incorporation in a tumor biopsy specimen. They also suggest that a clinical approach based on repeated short exposures to halogenated pyrimidines may present certain advantages over the current practice of prolonged continuous exposure. A Phase I/II trial using IdUrd and external beam irradiation for the treatment of patients with poor prognosis soft tissue sarcomas has been initiated based on this concept.

Adjunctive therapy (whole body hyperthermia versus lonidamine) to total body irradiation for the treatment of favorable B-cell neoplasms: a report of two pilot clinical trials and laboratory investigations

Based on earlier clinical and preclinical investigations, we designed two different pilot trials for patients with nodular lymphoma or chronic lymphocytic leukemia. These studies evaluated the use of either 41.8 degrees C whole body hyperthermia (WBH), or the nonmyelosuppressive chemotherapeutic drug, lonidamine (LON), as an adjunct to total body irradiation (TBI) (12.5 cGy twice a week, every other week for a planned total dose of 150 cGy). Whole body hyperthermia was initiated approximately 10 min after total body irradiation; lonidamine was administered orally (420 mg/m2) on a daily basis. Although entry to the studies was nonrandomized, the two patient populations were accrued during the same time frame and were comparable in terms of histology, stage of disease, performance status, and prior therapy. Of 8 patients entered on the TBI/WBH study, we observed 3 complete responses (CR), 4 partial responses (PR), and 1 improvement (i.e., a 48% decrease in tumor burden). Of 10 patients entered in the TBI/LON study, there was 1 CR and 4 PR. For the TBI/WBH study, myelosuppression was not treatment-limiting; there were no instances of infection or bleeding and platelet support was never required. The median survival time for the TBI/WBH study is 52.5 months based on Kaplan Meir estimates. Two patients remain in a CR. The median time to treatment failure (MTTF) is 9.4 months (90% confidence interval = 7-15.4 months). In the TBI/LON study, 50% of patients receiving TBI required treatment modification due to platelet-count depression during therapy, but there were no instances of infection or bleeding. Frequently observed LON-related toxicities included myalgias, testicular pain, photophobia and ototoxicity. For the TBI/LON study, median survival is 7.6 months; MTTF was 2.4 months. In analyzing the results of these pilot studies, our subjective clinical impressions lead to the hypothesis that WBH protected against TBI-induced thrombocytopenia during therapy, whereas LON had no effect on TBI-induced myelosuppression. This speculation was tested and confirmed in a series of in vitro and in vivo experiments.

The ocular effects of intracarotid bromodeoxyuridine and radiation therapy in the treatment of malignant glioma

Since July 1985, 23 patients have been entered into a phase I/II clinical trial using intraarterial 5-bromodeoxyuridine (BUdR) (400-600 mg/m2 daily for 8.5 weeks) and focal external beam radiotherapy (59.4 Gy at 1.8 Gy daily in 6.5 weeks) in the treatment of malignant gliomas (Kernohan grades 3 and 4). The side effects in all patients have included varying degrees of anorexia, fatigue, ipsilateral forehead dermatitis, blepharitis, and conjunctivitis. Mucopurulent conjunctivitis and exposure keratitis developed in several patients and spontaneous corneal perforation developed in one. Eyes from two individuals examined at autopsy showed significant changes. Animal studies that predated clinical trials using rhesus monkeys did not predict the ophthalmologic complications seen in human subjects.

Estimation of growth fraction in situ in human bladder cancer with bromodeoxyuridine labelling

A group of 8 patients with invasive bladder cancer received fractionated intra-arterial infusions of the thymidine analogue bromodeoxyuridine (BrdU), 150 mg, every 6 to 10 h for 3 days before endoscopic cold cup biopsy to label tumour cells in the proliferative pool (growth fraction). The tumour specimens were fixed and stained by an indirect immunoperoxidase method using anti-BrdU monoclonal antibody. There was an area which could not be stained with anti-BrdU monoclonal antibody surrounding the stained area where diffusion effects could be excluded. This indicates a growth fraction less than 1 and implies that a proportion of the tumour cells in bladder tumours are cycling and contributing to growth. The BrdU labelling index (growth fraction) was determined by counting the number of BrdU labelled cells in the well labelled tissue sections. The average growth fraction of invasive bladder cancer was 38.4 +/- 7.7% (range 26.9-48.1%). Grade 3 tumours averaged 42.8 +/- 5.4% labelling versus 31.0 +/- 4.4% in grade 2. The higher growth fraction may indicate greater biological malignancy. These results indicate that immunohistochemical studies of cell kinetics using BrdU monoclonal antibodies may provide information about the biological characteristics of bladder tumours in situ.

Mucocutaneous complications of intraarterial 5-bromodeoxyuridine and radiation

5-Bromodeoxyuridine (BUDR), a halopyrimidine thymidine analogue, is incorporated into the DNA of dividing cells and causes photoradiosensitization. Twenty-five patients with malignant astrocytomas were treated with continuous intracarotid BUDR radiosensitization and radiotherapy for 8 1/2 weeks. Unique dose-limiting mucocutaneous complications were encountered. Ipsilateral facial dermatitis with epilation of eyebrows and eyelashes, ocular irritation, and bilateral nail dystrophy developed in all patients. Less common reactions included oral ulceration in six patients, body exanthem on the trunk in five, and atypical erythema multiforme major in one.

Radiobiology and clinical application of halogenated pyrimidine radiosensitizers

Halogenated pyrimidines (HP) represent a unique class of non-hypoxic cell radiosensitizers currently under clinical re-investigation. In order for halogenated pyrimidines to sensitize cells to radiation, they must be incorporated into cellular DNA. In the case of human tumors, which have in general rather long cell cycle times, this may require many days of continuous drug infusion to achieve adequate replacement of the DNA base thymidine with HP. In vitro studies support the relationship between the extent of radiosensitization and the percentage of thymidine replacement. Recent clinical studies evaluating the role of iododeoxyuridine (IdUrd) as a radiation sensitizer in large unresectable sarcomas have been extremely encouraging. To support and expand upon these positive clinical findings more information and research is needed regarding: (1) the mechanism of HP-induced radiosensitization; (2) the percentage of HP thymidine replacement in human tumors achievable and how it relates to treatment outcome; (3) the means of increasing HP incorporation in tumor and minimizing incorporation in normal tissues; (4) a better understanding of optimal timing between HP administration and radiation treatment; and (5) methods to evaluate which tumors are appropriate candidates for HP therapy. While presently limited to use in conventional high dose-rate X-ray therapy, laboratory studies suggest that HP might also be effective in low dose-rate brachytherapy and for selected high LET clinical beams. HPs probably will not be 'general' non-hypoxic cell radiosensitizers for all tumor types, but with appropriate tumor-type/anatomical site selection and refinement in their administration, HPs may prove beneficial in cancer treatment.

Application of non-hypoxic cell sensitizers in radiobiology and radiotherapy: rationale and future prospects

The effects of commonly used non-hypoxic cell radiosensitizers are briefly reviewed. Emphasis is placed on the effects and the mechanism of action of halogenated pyrimidines, since recent clinical trials indicated the potential importance of these compounds in the treatment of certain types of human tumors. Evidence is presented suggesting that halogenated pyrimidines sensitize cells to radiation by increasing induction of DNA and chromosome damage per cell per unit absorbed dose, as well as by increasing the susceptibility to fixation of radiation induced PLD. The former mode of action correlates with an increase in survival curve slope, whereas the latter probably causes the reduction observed in shoulder width. The effects of repair inhibitors such as the nucleoside analogs are briefly reviewed and their possible clinical importance discussed. Results are presented indicating that combined treatment with halogenated pyrimidines and nucleoside analogs may enhance the radiosensitizing effect of the former and the specificity on tumor cells of the latter. Finally, the effects of other radiation sensitizers such as 3-aminobenzamide and diamide are briefly summarized.

Immunocytochemical demonstration of S phase cells by anti-bromodeoxyuridine monoclonal antibody in human prostate adenocarcinoma

Using a monoclonal antibody to bromodeoxyuridine and immunohistochemistry, we measured the incorporation of this thymidine analogue into the deoxyribonucleic acid of human prostate adenocarcinoma cells exposed in situ. Fifteen patients with prostate cancer were given an intravenous infusion of 500 mg. bromodeoxyuridine at needle biopsy to label tumor cells in the deoxyribonucleic acid synthesis phase (S phase). The tumor specimens were fixed with 70 per cent ethanol, embedded in paraffin, sectioned and stained by an indirect immunoperoxidase method using anti-bromodeoxyuridine monoclonal antibody as the first antibody. The results showed that this method demonstrated bromodeoxyuridine-labeled nuclei satisfactorily in tissue section. The bromodeoxyuridine labeling index, S phase fraction, was determined by counting the number of bromodeoxyuridine-labeled cells in the tissue sections. Grade 3 tumors averaged 4.37 +/- 0.48 per cent labeling versus 2.41 +/- 0.49 per cent in grade 2 tumors, and grade 1 tumor in the series had an S phase fraction of 1.36 +/- 0.39 per cent. The average S phase fractions for single gland, cribriform, fused and medullary were 1.16, 2.30, 3.74 and 4.95 per cent, respectively. The results obtained with S phase fraction measured with bromodeoxyuridine labeling proved to be comparable to the results of histological grade and growth pattern. Thus, the higher S phase fraction may indicate biological malignancy. Moreover, the degree of heterogeneity concerning S phase fraction distribution within prostate cancer tissue could be compared to the morphological appearance. Our preliminary results suggest that the measurement of bromodeoxyuridine labeling index in prostate cancer may prove to be a new objective and quantitative assay of biological potential of individual tumor.

DNA cell cycle studies in uveal melanoma

We histologically studied uveal melanomas treated with surgery only (enucleation or ciliochoroidectomy), low-dose (20 Gy) preenucleation radiation followed by enucleation, or enucleated melanomas after high-dose (50 to 80 Gy) charged-particle beam therapy. There was significantly less bromodeoxyuridine uptake in irradiated vs nonradiated melanomas (P less than .0001). Similarly, tissue culture growth of irradiated tumors was significantly less (P less than .007). These data demonstrate destruction of reproductive integrity of helium ion-irradiated melanomas. The incorporation of bromodeoxyuridine and fine needle aspiration biopsy techniques may be useful in the delineation of successfully irradiated tumors from tumors with apparent growth secondary to radiation vasculopathy.

Tumor cord and growth in human brain tumors based on mathematical morphology

The growth of human brain tumor was quantitatively investigated by using the anti-bromodeoxyuridine (BrdU) monoclonal antibody and the texture analyzing system (TAS). Tissues from thirty eight patients consisting of 22 gliomas, 8 brain metastases, 1 cerebellar hemangioblastoma and 7 normal white matters were applied in this study. Mean values of growth fractions (GFs) were 29.4% in group 1, 14.8% in group 2, and 6.5% in group 3. The higher value of GFs showed a significantly larger degree of perivascular aggregation of S-phase cells (DPAS). The mean number of cells in each tumor cord was approximately 20, which is not significantly larger than that of the normal group. But there was a significant difference between the non-selected area of the histologically malignant or benign gliomas and the proliferating area of the biologically malignant or benign brain tumors (t-value; p less than 0.001). A significant difference was also noticed in the mean area and diameter of tumor cords (t-value; p less than 0.001). From the point of view of biological behavior in human brain tumor, it is suggested that one tumor cord contains approximately 20 viable cells in the proliferating area in both benign and malignant brain tumors, and that if viable cells increase to more than 20 cells in one TC, necrotic cells and the diameter and area of the TC will increase, because the vessel-density is decreased by the occlusion of the vessels and the death of the endothels.

S phase fraction of human bladder tumor measured in situ with bromodeoxyuridine labeling

A total of 18 patients with transitional cell bladder cancer was given a 0.5-hour intravenous infusion of bromodeoxyuridine at the time of endoscopic biopsy or transurethral resection to label tumor cells in the deoxyribonucleic acid synthesis phase (S phase). The tumor specimens were fixed with 70 per cent ethanol, embedded in paraffin, sectioned and stained by an indirect immunoperoxidase method with anti-bromodeoxyuridine monoclonal antibody as the first antibody. The bromodeoxyuridine labeling index, S phase fraction, was determined by counting the number of bromodeoxyuridine-labeled cells in the tissue sections. All grade 1 tumors had an S phase fraction of lower than 10 per cent. The average S phase fractions for noninvasive (11 cases) and invasive (7) tumors were 9.8 and 20.0 per cent, respectively. Two distant metastatic bladder tumors showed an average S phase fraction of 25.3 and 30.0 per cent. Thus, transitional cell bladder cancers with an S phase fraction of greater than 10 per cent appears to grow faster and be more invasive more often than those with an S phase fraction of less than 10 per cent. The higher S phase fraction may indicate greater biological malignancy. Our preliminary results suggest that measurement of the bromodeoxyuridine labeling index in bladder tumors may be a new objective and quantitative assay of biological potential of individual tumors.

Technique for detection of DNA nucleobases by reversed-phase high-performance liquid chromatography optimized for quantitative determination of thymidine substitution by iododeoxyuridine

A reversed-phase high-performance liquid chromatographic (HPLC) method for quantification of iododeoxyuridine (IdUrd) substitution for thymidine in DNA was developed. IdUrd substitution was determined by HPLC with ultraviolet absorbance in two cell lines (L1210 and HT-29) after incubation in vitro with IdUrd alone or with IdUrd and fluorodeoxyuridine. In addition, radiolabeled IdUrd was used concomitantly with HPLC to evaluate the degree of dehalogenation. This HPLC technique has also been applied to the measurement of IdUrd incorporation in vivo into DNA from peripheral granulocytes of patients receiving IdUrd. This method provides an interesting tool for the quantification of drug substitution into DNA and can be applied to multiple sampling sites in animal and human studies.

Cytotoxic effect and induction of sister chromatid exchange in exponentially growing rat 9L gliosarcoma cells after brief exposure to BrdU

The magnitude of DNA modulation in rat 9L gliosarcoma cells after a brief exposure to bromodeoxyuridine (BrdU) was studied by assaying colony-forming efficiency (CFE) and the number of sister chromatid exchanges (SCEs) per metaphase. The CFE assay showed that a 1-hr exposure to BrdU, at concentrations ranging from 10 to 1000 microM, produced a maximum cell kill of 5%. After a 2-hr exposure to 20 microM BrdU, the surviving fraction was 0.99, and even at a BrdU concentration of 1000 microM, 77% of the 9L cells survived. Compared with control cultures, the relative number of SCEs per metaphase in treated cultures was increased after a 1-hr exposure to BrdU at concentrations of 100 microM or more and after a 2-hr exposure to concentrations of 20 microM or more; no increase was observed in cells treated for 30 min with BrdU at concentrations up to 1000 microM. When the treated cells were allowed to grow in BrdU-free growth medium, the number of SCEs per metaphase returned to the control level within 24 hr, even after exposure to BrdU at concentrations as high as 1000 microM. These results demonstrate that exposure to BrdU at concentrations of up to 1000 microM for 30 min, 100 microM for 1 hr, and 20 microM for 2 hr causes little modulation of DNA.

Enhancement of X ray induced DNA damage by pre-treatment with halogenated pyrimidine analogs

The use of the halogenated pyrimidine analogs, including bromodeoxyuridine (BrdUrd) and iododeoxyuridine (IdUrd), as potential clinical radiosensitizers is an area of renewed clinical research. Cellular radiation effects of these analogs using clinically achievable steady state plasma levels (10(-7)-10(-5) M) were measured in vitro using exponentially growing Chinese hamster V79 cells. Radiation response was determined by clonogenic survival and by the production of DNA single strand (SSB) and double strand breaks (DSB) using filter elution techniques. Replacement of thymidine in DNA by BrdUrd or IdUrd was also determined. Drug exposure of BrdUrd or IdUrd for two population doublings (17 hr) prior to irradiation resulted in a progressive reduction of n and D0 compared to untreated controls over the drug dose range of 10(-7)-10(-5) M. The percent thymidine replacement increased from 1% at 10(-7) M to 5% at 10(-6) M to 23% at 10(-5) M. Using a 17 hr exposure at 10(-5) of BrdUrd or IdUrd, the production of SSB and DSB was increased by greater than or equal to 2X and greater than or equal to 1.5X respectively. No differences in the kinetics of repair of SSB and DSB were found following 3 hr of post-irradiation repair. We conclude that in this in vitro model, there appears to be a direct relationship between percent thymidine replacement, reduction of radiation survival parameters (n, D0), and the production of DNA strand breaks in the clinically achievable dose range of these halogenated pyrimidine analogs. These filter elution assays may be adapted to in vivo studies and possibly may allow for monitoring of radiation-induced DNA damage and repair in clinical tumor specimens treated with these radiosensitizers.

Analysis of cell cycle characteristics and course of the disease in ANLL

The cell cycle characteristics of a newly diagnosed patient with acute nonlymphocytic leukemia (ANLL) were studied by using intravenous bromodeoxyuridine (BrdU) and our previously described "double-label" technique. The percentage of S-phase cells in the bone marrow (BM) biopsy were 25% compared to 7% from the simultaneously obtained BM aspirate. The duration of S-phase (Ts) was determined to be 4 hr and the total cell cycle time (Tc) was 16 hr. We demonstrated that the actual clinical course of this patient's illness corresponded well with the course predicted on the basis of these cell cycle measurements. Although he achieved aplasia in response to two successive courses of induction chemotherapy, leukemic cells repopulated the marrow, producing a rapidly rising PB white blood cell (WBC) count with a T1/2 of approximately 20 hr each time. It is likely that the resistance of this patient's leukemia to therapy was a result of the rapid proliferative rate of his leukemic cells and not due to the inability of chemotherapeutic agents to kill a large number of cells. Since the measurements can be completed within 48 hr, measuring Ts and Tc will provide a better understanding of the biological differences that exist between patients with ANLL.

Estimation of growth fraction with bromodeoxyuridine in human central nervous system tumors

Twenty-five patients with tumors of the central nervous system received bromodeoxyuridine (BUdR), 200 mg/sq m, by intravenous infusion every 8 hours for 3 days before surgery. Excised tumor specimens were fixed in chilled 70% ethanol, embedded in paraffin, and cut into 6-micron sections. Each section was reacted with monoclonal antibodies against BUdR and stained with immunoperoxidase to identify nuclei that had incorporated BUdR. The growth fraction of each tumor was estimated by calculating the ratio of BUdR-positive nuclei to the total number of tumor cells in three to six microscopic fields in viable areas of the tumor. In seven cases, the tumor doubling time was measured from the serial computerized tomography scans and an attempt was made to estimate the cell cycle time. The growth fractions ranged from 9.1% to 46.5% in malignant gliomas, 2.0% to 6.7% in low-grade gliomas, 11.2% to 43.2% in metastatic brain tumors, 0.8% to 1.9% in pituitary adenomas, 3.9% to 4.6% in acoustic neurinomas, and 6.2% to 8.2% in meningiomas and cerebellar hemangioblastomas. The estimated cell cycle time was 5 to 12 days in most malignant gliomas and brain metastases; however, the actual cell cycle time should be substantially shorter because cell loss was not considered in the calculation. Although the growth fraction appeared to correlate with the biological malignancy of each tumor, the tumor doubling time did not reflect growth potential. It is possible that unpredictable cell loss plays an important role in tumor growth at certain sizes. Therefore, the cell cycle times calculated in this study are considerably overestimated and should be interpreted with caution.

Proliferative potential of human meningiomas of the brain. A cell kinetics study with bromodeoxyuridine

Twenty patients with intracranial meningiomas were given a 1-hour intravenous infusion of bromodeoxyuridine (BrdU), 200 mg/m2, at the time of surgery to label tumor cells in the DNA synthesis phase (S phase). The excised tumor specimens were fixed with 70% ethanol, embedded in paraffin, sectioned, and stained by an indirect immunoperoxidase method using anti-BrdU monoclonal antibody as the first antibody. The BrdU labeling index (LI), or S-phase fraction, was determined by counting the number of BrdU-labeled cells in the tissue sections. The average LIs for nonmalignant (11 cases) and histologically malignant meningiomas (seven cases) were 0.45% and 3.9% respectively (P less than 0.05). Two hemangiopericytic variants showed average LIs of 0.53% and 4.1%. Four of seven malignant meningiomas and both hemangiopericytomas were recurrent tumors. Nine of 20 meningiomas had an LI greater than 1%, and six of those nine (67%) were recurrent. Thus, meningiomas with an LI greater than 1% appear to grow faster and recur more frequently than those with LIs less than 1%; the higher LI may indicate biological malignancy. The measurement of BrdU LI in meningioma may prove valuable in establishing the diagnosis of "malignant meningioma."

Cell kinetics analysis in a case of teratoma of the thoracic spine

The authors report cell kinetics studies in an infant who had multiple operations for removal of a rare benign thoracic spinal teratoma with retroperitoneal extension. Before the final surgical procedure for recurrent tumor, bromodeoxyuridine (BUdR), 200 mg/sq m, was administered intravenously to label tumor cells in the S (deoxyribonucleic acid (DNA) synthesis) phase of the cell cycle. Histologically, the tumor was a mature teratoma consisting of components derived from all three germ-cell layers. Cells labeled with BUdR were found in the basal layer of stratified squamous epithelia, in respiratory epithelia, in the cartilage and surrounding perichondrial mesenchyme, and in loose mesenchymal tissue throughout the teratoma. In contrast to neuroectodermal tumors, which show widespread BUdR uptake throughout the tissue and which have different average labeling indices according to their histological type (range less than 1% to 15.2%), the teratoma showed BUdR labeling only in certain areas, indicating fairly organized growth patterns; the labeling indices in these areas ranged from 0.39% to 1.9%.

Potentiation of chemotherapy cytotoxicity following iododeoxyuridine incorporation in Chinese hamster cells

This study reports on the potentiation of selected chemotherapy drugs following halogenated pyrimidine incorporation into cellular DNA. Exponentially growing cultures of Chinese hamster V79 cells were exposed to 10(-5) M IdUrd or BrdUrd for 17 hr (approximately 2 cell doublings). This exposure resulted in approximately 16% replacement of thymidine by IdUrd or BrdUrd in the cellular DNA. Following the IdUrd exposure, dose response curves were determined for a 1 hr exposure to the various drugs. IdUrd pre-treatment was shown to enhance the cytotoxicity of melphalan, adriamycin, cisplatin, and neocarzinostatin with enhancement ratios at 1% survival of 1.5, 1.8, 1.5, and 1.4 respectively. BrdUrd pre-treatment also enhanced cisplatin cytotoxicity. A combination of BrdUrd pretreatment, cisplatin, and X rays was shown to yield additive survival effects. These findings are discussed in the context of possible clinical application of local drug perfusion of tumor-containing organs.

In situ cell kinetics studies on human neuroectodermal tumors with bromodeoxyuridine labeling

Thirty-eight patients undergoing surgical removal of neuroectodermal tumors of the central nervous system were given a 1-hour intravenous infusion of bromodeoxyuridine (BUdR), 150 to 200 mg/sq m, to label tumor cells in the deoxyribonucleic acid (DNA) synthesis phase (S-phase). The excised tumor specimens were divided into two portions: one was fixed with 70% ethanol and embedded in paraffin and the other was digested with an enzyme cocktail to make a single-cell suspension. The paraffin-embedded tissues were stained by an indirect peroxidase method using anti-BUdR monoclonal antibody (MA) as the first antibody. Single-cell suspensions were reacted with fluorescein isothiocyanate (FITC)-conjugated anti-BUdR MA's for flow cytometric analysis. S-phase cells that had incorporated BUdR into their DNA were well stained by both methods. The percentage of BUdR-labeled cells, or S-phase fraction, was calculated in tissue sections by microscopic examination and in single-cell suspensions by flow cytometric analysis. The biological malignancy of the tumors was reflected in the S-phase fractions, which were 5% to 20% for glioblastoma multiforme, medulloblastoma, and highly anaplastic astrocytoma, but less than 1% in most moderately anaplastic astrocytomas, ependymomas, and mixed gliomas. Two juvenile pilocytic astrocytomas and two low-grade astrocytomas from children had high S-phase fraction despite the fairly benign and slow-growing nature of these tumors. These results indicate that the S-phase fraction obtained immunocytochemically with anti-BUdR MA's may provide useful information in estimating the biological malignancy of human central nervous system tumors in situ.

Double labeling and in vitro versus in vivo incorporation of bromodeoxyuridine in patients with acute nonlymphocytic leukemia

A monoclonal antibody against bromodeoxyuridine (BrdUrd) was produced, and a rapid slide technique (RPMB technique) was developed for the estimation of S-phase cells in a population using this antibody. Bone marrow cells from patients with acute nonlymphocytic leukemia (ANLL) were studied by both the RPMB technique and tritiated thymidine (3HdThd) labeling index studies. The percentage of S-phase cells obtained by each method was compared in 50 samples, and the correlation coefficient was r = 0.89. A "double label" method is also described in which cells were simultaneously incubated with either BrdUrd and 3HdThd or BrdUrd and tritiated cytosine arabinoside (3HAra-C). The samples were first processed by the RPMB technique and then by autoradiography. Results showed only black grains overlying the nuclei of fluorescent cells in each group. An automated microphotometer was used to quantitate grains and fluorescence from each cell. This demonstrated an almost direct relationship between grains and fluorescence from BrdUrd + 3HdThd slides, whereas different patterns of relationship were noted from BrdU + 3HAra-C slides of leukemic patients. Their implications are discussed in the text. Finally, intravenous infusions of BrdUrd was given to five leukemic patients. S-phase cells were recognized distinctly within 5 min of starting the infusion. The percentage of S-phase cells was almost identical from in vivo and in vitro samples. Various possibilities of studying the biological behavior of acute leukemias and analyzing cell cycle characteristics are discussed.

Cell kinetic studies of in situ human brain tumors with bromodeoxyuridine

At the time of surgery, 18 patients with various brain tumors were given a 1-h i.v. infusion of bromodeoxyuridine (BrdUrd), 150-200 mg/m2. At an infusion rate of 200 mg/m2/h, serum BrdUrd levels of 8 microM were achieved. After the infusion, tumor tissue was obtained and divided into two portions. One portion was fixed in 70% ethanol, embedded in paraffin, and sectioned; the sections were deparaffinized, denatured with 2 N HCl, and reacted with monoclonal antibodies against BrdUrd (anti-BrdUrd MAb). BrdUrd-labeled nuclei were demonstrated satisfactorily by an indirect peroxidase method. The other portion was dissociated into single cells with a DNase enzyme cocktail and reacted with FITC-conjugated anti-BrdUrd MAb to determine the percentage of BrdUrd-labeled cells or with chromomycin A3 for DNA analysis. The single-cell suspensions were analyzed by flow cytometry. The fraction of S-phase cells in the tissue sections was similar to both the percentage of BrdUrd-labeled nuclei and the S-phase fraction determined by flow cytometric analysis. The results obtained with BrdUrd-labeled nuclei were similar to those obtained from previous autoradiographic studies of various brain tumors exposed to a pulse of 3H-thymidine. Since BrdUrd is not radioactive and is nontoxic at the dosage used, these techniques, together with the histopathological diagnosis, may help to predict the biological malignancy of individual tumors.

Rapid detection of S-phase cells by anti-bromodeoxyuridine monoclonal antibody in 9L brain tumor cells in vitro and in situ

FITC-conjugated anti-bromodeoxyuridine (BrdUrd) monoclonal antibody (anti-BU-MAb) was used to detect S-phase cells of 9L rat brain tumor cells in vitro and in situ. Monolayer 9L cells were treated with 0.625-20 microM of BrdUrd for 30 min, harvested, and reacted with a 1:100 dilution of FITC-conjugated anti-BU-MAb and analyzed with a flow cytometer. BrdUrd-treated cells stained satisfactorily with antibody. Values obtained for the labeling index using this method (48.6%) were 10%-20% higher than the fraction of cells in S-phase calculated from DNA histograms or as the labeling index calculated from autoradiographs of cells pulse-labeled with 3H-thymidine. BrdUrd (1-40 mg/kg) was administered by i.p. injection to rats bearing 9L brain tumors. Single cell suspensions obtained by disaggregation of excised tumors were stained with anti-BU-MAb. The percentage of fluorescent cells (15.9%) calculated using this method was similar to that of S-phase cells (17.2%) calculated from DNA histograms and from autoradiographics for tumor bearing rats pulse-labeled with 3H-thymidine in situ. The antibody staining technique is a rapid and accurate method for various cell kinetic studies both in vitro and in vivo in a rat model, and has promise as a technique for the study of cell kinetics in humans.

Immunocytochemical demonstration of S-phase cells by anti-bromodeoxyuridine monoclonal antibody in human brain tumor tissues

Five patients with various brain tumors received bromodeoxyuridine (BrdU), 150-200 mg/m2 i.v., at the time of craniotomy. Biopsied materials were fixed in 70% ethanol, sectioned, denatured with hydrochloric acid, and reacted with monoclonal antibodies against BrdU. Immunofluorescence and immunocytochemical methods were used to visualize BrdU-labeled nuclei. Our results showed that both methods demonstrated BrdU-labeled nuclei satisfactorily in tissue sections. Thus, BrdU can be used to measure the proliferative potential of human tumors in situ.

New therapeutic approaches for brain tumors

In the last decade, advances in the treatment of primary neuroglial tumors of the central nervous system in adults have been modest. Theories regarding their resistance to treatment have changed little, although now the heterogeneity of anaplastic astrocytomas is recognized. The most effective chemotherapeutic agents--the nitrosoureas and procarbazine--have been used for more than a decade, with no comparably active drugs identified in the meantime. The authors have initiated clinical trials using inhibitors of polyamine synthesis and augmentation of the known effectiveness of irradiation. These programs will be described with preliminary observations.

Phase I study of intravenous bromodeoxyuridine used concomitantly with radiation therapy in patients with primary malignant brain tumors

We report here the results of a Phase I study conducted to determine the toxicity and serum levels that could be tolerated by patients receiving i.v. bromodeoxyuridine (BUdR) concomitantly with radiation therapy. Because of severe thrombocytopenia and leukopenia that was produced in three patients treated by a 96 hour infusion of BUdR at a dose of 1.5 g/m2/24 hours, the dose was reduced to 0.8 g/m2/24 hours in these patients and the remaining 9 patients in the study group. Even at this dosage, myelotoxicity was observed. BUdR levels were measured by an isocratic high performance liquid chromatographic (HPLC) method developed for this study. Results of in vitro studies conducted by others suggest that serum levels produced in our patients by administration of doses of 0.6 to 0.8 g/m2/24 hours should be adequate to achieve a therapeutic effect.

131-iodine conjugated antibody cell kill enhanced by bromodeoxyuridine

131I-conjugated monoclonal and polyclonal antibodies are being administered in vivo to kill human tumor cells. Although these conjugates deliver relatively large doses of radiation to tumors (10 to 50 Gy), the rate of dose delivery is low (0.05 to 0.2 Gy/hour). Radiation delivered at low dose rates kills fewer cells that exhibit large shoulders on radiation survival curves than radiation delivered at high dose rates. To determine whether the cell kill produced by low dose rate radiation is enhanced by a radiation sensitizer (bromodeoxyuridine, BUdR) we studied the cell kill produced by an 131I-conjugated polyclonal antibody against Chinese hamster V79 cells. V79 cells were labeled with 131I-conjugated antibody (10-20 microCi/micrograms) and unconjugated antibody, and frozen for up to 30 days in liquid nitrogen. The surviving fraction of cells was measured at intervals of 5 to 10 days. Cells not containing BUdR were also studied. The 131I-conjugated antibody produced up to 40% cell kill and BUdR increased the fraction of cells killed to 75%. Our studies demonstrate that cells frozen at -196 degrees C are useful for the investigation of the cell kill produced by isotopes that deliver radiation at low dose rates and that the cell kill caused by 131I-conjugated antibodies can be enhanced by BUdR.

Identification of bromodeoxyuridine in malignant and normal cells following therapy: relationship to complications

During a clinical Phase I study of bromodeoxyuridine (BUdR) as a radiation sensitizer we identified the normal and malignant cells that incorporated the BUdR. BUdR was infused for up to 14 days and the in vivo incorporation of BUdR into DNA was assessed using an immunohistochemical technique and a monoclonal antibody directed against BUdR. BUdR was identified in 50% of breast cancer cells and 10% of cells in a malignant melanoma. BUdR was also found in the basal layer of the normal epidermis and in 50% of cells in the marrow. The incorporation of BUdR into cells in the epidermis and marrow may produce the phototoxicity and myelosuppression observed in patients treated with BUdR. Sequential biopsies from a breast cancer taken prior to and following radiotherapy suggested that cells that incorporated BUdR may have been selectively killed by the radiation. The immunohistochemical technique used to identify BUdR appeared to be useful for studies of in vivo and in vitro cell proliferation.

Differing sensitivity to fluorescent light in Chinese hamster cells containing equally incorporated quantities of BUdR versus IUdR

Chinese hamster V79 cells that had incorporated approximately equal levels of either BUdR or IUdR into their DNA were found to be equal sensitizers to X rays. However, BUdR-substituted cells were much more sensitive to fluorescent light than IUdR-substituted cells, both on a cell survival basis and by the initial number of single strand DNA breaks induced. Since a major toxicity to the use of BUdR clinically has been light-induced skin rash, these data indicate that the use of IUdR clinically might cause less untoward toxicity but yet provide the same radiosensitization as BUdR.

The use of halogenated thymidine analogs as clinical radiosensitizers: rationale, current status, and future prospects: non-hypoxic cell sensitizers

The halogenated pyrimidine analogs, bromodeoxyuridine (BUdR) and iododeoxyuridine (IUdR) have been recognized as potential clinical radiosensitizers for over two decades. In vivo and in vitro experimental studies document that radiosensitization is directly dependent on the amount of thymidine replacement in DNA by these analogs. Early clinical studies in Japan using selective intra-arterial infusions of BUdR and conventional fractionated radiation suggested improved survival in patients with primary brain tumors, although there were significant catheter-related complications. Based on recent in vivo and clinical pharmacology studies on continuous intravenous infusions of these drugs, clinical trials are underway evaluating the potential of radiosensitization in high grade gliomas and other poorly radioresponsive tumors using the technically safer intravenous route of administration. In this paper, we review the basic strategy for the use of these analogs, the ongoing clinical trials and the potential areas for future experimental and clinical studies.

Marked radiosensitization of cells in culture to X ray by 5-chlorodeoxycytidine coadministered with tetrahydrouridine, and inhibitors of pyrimidine biosynthesis

Our approach to overcome the problem of rapid catabolism and general toxicity encountered with 5-halogenated analogues of deoxyuridine (5-bromo, chloro or iododeoxyuridine), which has limited their use as tumor radiosensitizers, is to utilize 5-chlorodeoxycytidine (CldC) with tetrahydrouridine (H4U). We propose that CldC, coadministered with H4U, is metabolized in the following manner: CldC----CldCMP----CldUMP---- ----CldUTP----DNA. All the enzymes of this pathway are elevated in many human malignant tumors and in HEp-2 cells. In X irradiation studies with HEp-2 cells, limited to 1 or 2 radiation doses, we have obtained 3.0 to 3.8 apparent dose enhancement ratios (these represent upper limits) when cells are preincubated with inhibitors of pyrimidine biosynthesis: N-(Phosphonacetyl)-L-aspartate (PALA) and 5-fluorodeoxyuridine (FdU) or 5-fluorodeoxycytidine (FdC) + H4U. Optimum conditions for radiosensitization are: PALA (0.1 mg/ml) 18-20 hr prior to FdU (0.1 microM) or FdC (0.02 microM) + H4U (0.1 mM) followed 6 hr later by CldC (0.1-0.2 mM) + H4U (0.1 mM) for 56-68 hr. Viabilities of 10 +/- 4% to 15 +/- 1% (+/- S.E.) were obtained for drug-treated unirradiated cells. Enzymatic studies indicate that this toxicity may be tumor selective. CldC + H4U alone (at these concentrations) results in 20% substitution of CldU for thymidine in DNA (determined by HPLC analysis). Preliminary toxicity studies indicate that mice will tolerate treatment protocols involving a single dose of PALA (200 mg/kg) followed by a dose of FdU (50 mg/kg) and 3 cycles of CldC (500 mg/kg) + H4U (100 mg/kg) at 10 hour intervals, with marginal weight loss (4%). In this approach we seek to obtain preferential conversion of CldC to CldUTP at the tumor site by taking advantage of quantitative differences in enzyme levels between tumors and normal tissues.

A Phase I study of intermittent intravenous bromodeoxyuridine (BUdR) with conventional fractionated irradiation

A Phase I trial of intravenous bromodeoxyuridine (BUdR) and conventional fractionated radiation therapy was performed in 14 patients with glioblastoma multiforme and 7 patients with other poorly radioresponsive tumors. The BUdR was given as a constant intravenous infusion for 12 hr/day for up to 14 days. Thirteen patients received a second 14 day infusion following a 10 to 14 day interruption for bone marrow recovery. Local toxicity (within the radiation field) was minor, with 7 of the 21 patients requiring a brief treatment break for moist skin desquamation. There was no significant CNS toxicity noted clinically nor by autopsy examination. Additionally, no significant enhancement of radiation injury was noted to bowel or liver. However, one patient treated for multiple pulmonary metastases experienced a clinical and radiographic pattern consistent with radiation pneumonitis. Dose-dependent systemic toxicity occurred in bone marrow and skin. Moderate myelosuppression, especially thrombocytopenia, was found following a 14 day cycle of BUdR at and above 650 mg/m2/12 hr infusion. Approximately one-third of patients developed a maculo-papular erythematous rash to the scalp, neck and upper chest. In two patients, the rash became generalized with evidence of epidermolysis on skin biopsy. Pharmacology studies revealed steady-state arterial plasma levels of 2 X 10(-6) M/1 during the 12 hr infusion of 650 to 700 mg/m2. Radiosensitization was measured by a change in the D0 of radiation survival curves of human bone marrow CFUc prior to and following the 14 day infusion in 4 patients. A trend of increasing radiosensitization was noted in most patients as the infusion rate of BUdR was increased from 500 to 870 mg/m2/12 hr. We conclude that the maximum tolerable dose of BUdR is 650 to 700 mg/m2/12 hrs when given as a 2 week intermittent intravenous infusion. Local toxicity is acceptable. The major systemic toxicities are myelosuppression and a maculopapular skin rash.

Bromodeoxyuridine in tumors and chromosomes detected with a monoclonal antibody

Using a monoclonal antibody to bromodeoxyuridine (BUdR) and immunohistochemistry, we measured the incorporation of this thymidine analogue into the DNA of human normal and malignant cells exposed in vivo. BUdR given as a constant intravenous infusion for 12 or 24 h daily for up to 13 d resulted in a steady-state plasma level of 10(-6) M during the infusion. We demonstrated extensive incorporation of BUdR into both normal skin, normal bone marrow, and malignant melanoma cells. In addition, this infusion of BUdR was adequate to identify sister chromatid exchanges from human marrow chromosomes exposed in vivo. Using this constant infusion, significant but reversible (acute) toxicity was observed with myelosuppression and skin photosensitivity. These techniques, which are considerably less cumbersome and time-consuming than the use of radioactive isotopes of thymidine, can be used for further human studies of cell kinetics and chromosomal replication in both normal and malignant cells.