Iododeoxyuridine (IdUrd) incorporation into DNA of human hematopoietic cells, normal liver and hepatic metastases in man: as a radiosensitizer and as a marker for cell kinetic studies

Phase I and Pharmacology Study of Ropidoxuridine (IPdR) as Prodrug for Iododeoxyuridine-Mediated Tumor Radiosensitization in Advanced GI Cancer Undergoing Radiation

PURPOSE

Iododeoxyuridine (IUdR) is a potent radiosensitizer; however, its clinical utility is limited by dose-limiting systemic toxicities and the need for prolonged continuous infusion. 5-Iodo-2-pyrimidinone-2'-deoxyribose (IPdR) is an oral prodrug of IUdR that, compared with IUdR, is easier to administer and less toxic, with a more favorable therapeutic index in preclinical studies. Here, we report the clinical and pharmacologic results of a first-in-human phase I dose escalation study of IPdR + concurrent radiation therapy (RT) in patients with advanced metastatic gastrointestinal (GI) cancers.

PATIENTS AND METHODS

Adult patients with metastatic GI cancers referred for palliative RT to the chest, abdomen, or pelvis were eligible for study. Patients received IPdR orally once every day × 28 days beginning 7 days before the initiation of RT (37.5 Gy in 2.5 Gy × 15 fractions). A 2-part dose escalation scheme was used, pharmacokinetic studies were performed at multiple time points, and all patients were assessed for toxicity and response to Day 56.

RESULTS

Nineteen patients were entered on study. Dose-limiting toxicity was encountered at 1,800 mg every day, and the recommended phase II dose is 1,200 mg every day. Pharmacokinetic analyses demonstrated achievable and sustainable levels of plasma IUdR ≥1 μmol/L (levels previously shown to mediate radiosensitization). Two complete, 3 partial, and 9 stable responses were achieved in target lesions.

CONCLUSIONS

Administration of IPdR orally every day × 28 days with RT is feasible and tolerable at doses that produce plasma IUdR levels ≥1 μmol/L. These results support the investigation of IPdR + RT in phase II studies.

Dominant Pathways of Adenosyl Radical-Induced DNA Damage Revealed by QM/MM Metadynamics

Brominated nucleobases sensitize double stranded DNA to hydrated electrons, one of the dominant genotoxic species produced in hypoxic cancer cells during radiotherapy. Such radiosensitizers can therefore be administered locally to enhance treatment efficiency within the solid tumor while protecting the neighboring tissue. When a solvated electron attaches to 8-bromoadenosine, a potential sensitizer, the dissociation of bromide leads to a reactive C8 adenosyl radical known to generate a range of DNA lesions. In the current work, we propose a multiscale computational approach to elucidate the mechanism by which this unstable radical causes further damage in genomic DNA. We employed a combination of classical molecular dynamics conformational sampling and QM/MM metadynamics to study the thermodynamics and kinetics of plausible reaction pathways in a realistic model, bridging between different time scales of the key processes and accounting for the spatial constraints in DNA. The obtained data allowed us to build a kinetic model that correctly predicts the products predominantly observed in experimental settings-cyclopurine and β-elimination (single strand break) lesions-with their ratio and yield dependent on the effective lifetime of the radical species. To date, our study provides the most complete description of purine radical reactivity in double stranded DNA, explaining the radiosensitizing action of electrophilic purines in molecular detail as well as providing a conceptual framework for the computational modeling of competing reaction pathways in biomolecules.

Impact of IUdR on Rat 9L glioma cell survival for 25-35 keV photon-activated auger electron therapy

The goal of the current study was to measure the energy dependence of survival of rat 9L glioma cells labeled with iododeoxyuridine (IUdR) that underwent photon-activated Auger electron therapy using 25-35 keV monochromatic X rays, i.e., above and below the K-edge energy of iodine. Rat 9L glioma cells were selected because of their radioresistance, ability to be implanted for future in vivo studies and analogy to radioresistant human gliomas. Survival curves were measured for a 4 MV X-ray beam and synchrotron produced monochromatic 35, 30 and 25 keV X-ray beams. IUdR was incorporated into the DNA at levels of 0, 9 and 18% thymidine replacement for 4 MV and 35 keV and 0 and 18% thymidine replacement for 30 and 25 keV. For 10 combinations of beam energy and thymidine replacement, 62 data sets (3-13 per combination) provided 776 data points (47-148 per combination). Survival versus dose data taken for the same combination, but on different days, were merged by including the zero-dose points in the nonlinear, chi-squared data fitting using the linear-quadratic model and letting the best estimate to the zero-dose plating efficiency for each of the different days be a fitting parameter. When comparing two survival curves, the ratio of doses resulting in 10% survival gave sensitization enhancement ratios (SER10) from which contributions due to linear energy transfer (LET) (SER10,LET), IUdR radiosensitization (SER10,RS), the Auger effect (SER10,AE) and the total of all effects (SER10,T) were determined. At 4 MV and 35, 30 and 25 keV, SER10,LET values were 1.00, 1.08 ± 0.03, 1.22 ± 0.02 and 1.37 ± 0.02, respectively. At 4 MV SER10,RS values for 9 and 18% IUdR were 1.28 ± 0.02 and 1.40 ± 0.02, respectively. Assuming LET effects were independent of percentage IUdR and radiosensitization effects were independent of energy, SER10,AE values for 18% IUdR at 35, 30 and 25 keV were 1.35 ± 0.05, 1.06 ± 0.03 and 0.98 ± 0.03, respectively. The value for 9% IUdR at 35 keV was 1.01 ± 0.04. First, we found the radioresistant rat 9L glioma cell line exhibited an SER10 due to the Auger effect of 1.35 at (35 keV, 18% IUdR) and an SER10 due to the radiosensitizing effect of 1.40 at (4 MV, 18% IUdR), both significantly less than values for previously reported cell lines. These low individual values emphasize the benefit of their combined value (SER10 of approximately 1.9) for achieving clinical benefit. Second, as expected, we observed that energies below the K-edge of iodine (25 and 30 keV), for which there are L, M and higher shell photoelectric events creating Auger electrons, show no promise for Auger electron therapy. Third, to proceed with future in vivo studies, additional data from 35-65 keV are needed to determine the optimal X-ray energy for IUdR Auger electron therapy. Only then can there be an answer to the question, how well the energy dependence of in vitro survival data supports the potential for photon-activated Auger electron therapy with IUdR in cancer radiotherapy.

Iododeoxyuridine uptake in proliferating smooth muscle cells in vitro

PURPOSE

Iododeoxyuridine (IUdR) is a halogenated pyrimidine recognized as the thymidine substitute in DNA. When labeled with iodine 125, IUdR can be used as a carrier to incorporate the isotope into DNA and target the dividing cells. The purpose of this study was to assess the maximum uptake of IUdR by proliferating smooth muscle cells (SMCs) in vitro to determine the optimal concentration to be administered in an in vivo experiment. The long-term goal is to use radioactive IUdR to inhibit SMC proliferation and recurrent stenosis of arteries after balloon angioplasty in vivo.

MATERIALS AND METHODS

Porcine vascular SMCs were cultured in 5% fetal bovine serum medium and stimulated to proliferate by adding a medium containing 10% fetal bovine serum and insulin. IUdR was added to the proliferating SMCs at concentrations of 5, 10, 20, 30, and 40 micro mol/L on days 1, 3, 5, and 7 of incubation. One group of cells--the control group--did not receive IUdR. The SMCs were harvested and double-stained with an anti-IUdR antibody and propidium iodide, and fluorescence-activated cell scanning was performed to determine the ratio of IUdR-labeled cells to the total cell population for each IUdR concentration and at each time point. The data were measured three times at each time point. The doubling times, growth curve, and cell density of the proliferating SMCs were investigated by using the Coulter particle counter and digital microscopy.

RESULTS

The percentage of proliferating SMCs that showed IUdR uptake increased from 1 to 5 days incubation with all concentrations of IUdR; the incorporation rate reached a peak value at day 5 and then decreased by day 7. IUdR uptake on day 5 was higher with concentrations of 10 and 20 micro mol/L. When compared with that of the control group, the doubling times increased with an increase in IUdR concentration, whereas the proliferating cell number and density decreased significantly by days 5 (P < .05) and 7 (P < .01).

CONCLUSIONS

IUdR uptake peaked on day 5, and the optimal concentration of IUdR for in vitro uptake in proliferating SMCs was 10-20 micro mol/L. IUdR inhibited the proliferation of the SMCs, and the inhibitory effect was related to the concentration.

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.

Cell production rates in human tissues and tumours and their significance. Part 1: an introduction to the techniques of measurement and their limitations

In the past two decades, the technology of laser cytometry and use of the halogenated thymidine (HP) analogues bromodeoxyuridine and iododeoxyuridine as proliferation labels, have allowed us to quantify the rate of cell turnover in tissues and tumours, in clinical samples as in laboratory models. The principal studies have used injection of bromo- or iododeoxyuridine to measure cell production rates in vivo. Flow cytometry (FCM) has been used to estimate the S phase labelling index (LI) and the S phase duration (Ts) and calculate the cell production rate, represented by the potential doubling time (Tpot). This has allowed calculation of time-dependent indices of proliferation from single biopsies of HP pulse labelled human tissues and tumours. In the first part of this two-part review, we describe the technique and its limitations as a biological assay. The second part summarizes the knowledge gained about cell production rates and the relevance that this information may have to future investigative, prognostic and treatment strategies.

A molecular cytogenetic approach to studying platinum resistance

The technique of comparative genomic hybridisation (CGH) has until recently been used to screen for common genomic abnormalities in fresh tumour material; it has identified previously unrecognised regions of amplification associated with poor prognosis subtypes of breast cancer and lymphoma. Our group has applied this technique to resistant cell lines and their sensitive counterparts in order to define chromosomal abnormalities associated with acquired drug resistance. We have demonstrated the applicability of this technique to the study of drug resistance using cell lines with known mechanisms of resistance. The ability to detect novel genomic alterations in cell lines with novel mechanisms of resistance was also demonstrated. We subsequently examined the CGH profiles of seven different cell lines made resistant to three platinum analogues and showed the most consistent abnormalities to involve over-representation of regions 4q and 6q. More recently, we have applied the CGH technique to a series of testicular germ cell tumours (TGCTs) collected as formalin-fixed paraffin-embedded biopsy specimens from patients, both pre- and post-therapy using a platinum-based regimen (POMB/ACE). Previous reports have shown over-representation of X, 7q, 8q and 12p and loss of 13q to occur in 25% of primary TGCTs. Over-representation of 12p was confirmed in the majority of these biopsy samples; deletion of 13q was noted in the initial biopsies of several patients. We also demonstrated alterations of 4p, 4q, 5q and 6q in this series of patients. Newly acquired deletions of 2q and 18q and amplifications of 8q were frequently observed in post-chemotherapy samples from resistant tumours. The CGH studies on these patients with TGCT will not only enable us to correlate our observations on clinical material with those from long-term cell lines, but should also identify sites of key genes involved in clinical platinum resistance.

A phase I trial of hepatic arterial bromodeoxyuridine and conformal radiation therapy for patients with primary hepatobiliary cancers or colorectal liver metastases

PURPOSE

We have previously found that conformal radiation therapy (RT) and hepatic arterial fluorodeoxyuridine was associated with durable responses and long-term survival for patients treated for nondiffuse primary hepatobiliary tumors and colorectal liver metastases. Further improvements in hepatic control may result from the addition of selective radiosensitization using bromodeoxyuridine (BrdU) infused through the hepatic artery (HA) concurrently with RT. This is a Phase I study of escalating doses of HA BrdU combined with our standard hepatic RT.

METHODS AND MATERIALS

Patients with unresectable primary hepatobiliary cancer or colorectal liver metastases were treated with concurrent HA BrdU and conformal RT (1.5 Gy per fraction, twice a day). Three-dimensional treatment planning was used to define both the target and normal liver volumes. The total dose of RT (24, 48, or 66 Gy) was determined by the fractional volume of normal liver excluded from the high dose volume. HA BrdU was escalated in standard Phase I fashion with at least three patients receiving each combination of RT dose and BrdU dose. The starting dose of HA BrdU was 10 mg/kg/day, with two potential escalations to a maximum of 25 mg/kg/day (the maximum tolerable dose of HA BrdU when given alone on this same schedule). Grade > or = 3 toxicity was considered dose limiting. Patients receiving 24 Gy had one cycle of HA BrdU, while those receiving either 48 or 66 Gy had two cycles. Patients were followed for toxicity, complications, and response (when evaluable).

RESULTS

A total of 41 patients (18 with colorectal liver metastases, 16 with cholangiocarcinoma and 7 with hepatoma) were treated. Five patients were removed from the protocol (three had HA catheter complications, one developed atrial fibrillation, and one was removed due to recurrent Grade 4 toxicity), although all five are included for toxicity purposes. Dose-limiting toxicity was primarily thrombocytopenia and there was no obvious relationship with the RT dose. Only 2 of 17 cycles given at 25 mg/kg/day had Grade > or = 3 toxicity. Complications developed in four patients, including one patient with radiation-induced liver disease. Response rates were not improved compared to our previous experience.

CONCLUSIONS

The appropriate dose of HA BrdU for Phase II evaluation is 25 mg/kg/day. Neither the hepatic parenchyma nor the gastrointestinal mucosa appeared to be sensitized by this method of BrdU administration. It is anticipated that these, or still newer methods of therapy, can improve treatment results in the near future.

Survival improvement in anaplastic astrocytoma, combining external radiation with halogenated pyrimidines: final report of RTOG 86-12, Phase I-II study

PURPOSE

This study evaluated the toxicity and tumor efficacy of the halopyrimidine IUdR as a chemical modifier of radiation response in patients with malignant glioma. The preliminary results published in 1993 demonstrated no real advantage in the group of patients with glioblastoma. However, a benefit appeared to be evolving in the group of patients with Anaplastic Astrocytoma (AA). We are now presenting the results on the long-term follow-up of patients with AA.

METHODS AND MATERIALS

Between August 1987 and October 1991, 79 patients were entered in a prospective study with newly diagnosed malignant glioma. Twenty-one of 79 were AA. The study was designed to have a fixed dose of radiation consisting of 60.16 Gy in 32 fractions in 6.5 weeks but varying the dose schedule of IUdR, delivered in a continuous intravenous infusion of long (96 h) or short (48 and 24 h) duration, every week for the 6.5 weeks of radiation treatment.

RESULTS

The last AA patient was entered in March 1991. Ninety-five percent of the AA patients were under 59 years of age and 86% had a Karnofsky score 80. Thirty-eight percent had a tumor diameter of less than 5 cm and 52% had a tumor diameter between 5-10 cm. Seventy-six percent had partial or total tumor resection. The toxicity of this treatment was acceptable and has already been published elsewhere. At the time of this report, 14 out of 21 patients with AA are dead. The median survival, calculated from the Kaplan-Meier, is 3.2 years. Thirty-three percent of the patients have survived 5 years. These results compare favorably with the best results reported in the literature with postoperative external radiation plus chemotherapy, median survival time (MST) of 3 years, and previous Radiation Therapy Oncology Group (RTOG) experience with radiation alone, MST of 2 years.

CONCLUSIONS

Our findings in patients with AA corroborate the improved therapeutic results published recently when combining external radiation with "long" infusion of i.v. BUdR and indicate the need to proceed with randomized Phase III studies utilizing halogenated pyrimidines and radiation. One such study has already been activated, RTOG # 94-04.

Mechanisms of radiosensitization in iododeoxyuridine-substituted cells

The radiosensitization caused by iododeoxyuridine (IdU)-substitution of thymidine in V79-171 cells is decreased by the presence of acetone during irradiation. Acetone, at 1 mol dm-3, removes almost all the increase in double strand breaks (dsbs) caused by IdU substitution, but removes only about two-thirds of the enhancement in killing. Similar observations were made with BrdU-substituted cells. The decrease in cell radiosensitization coincides with the removal of the additional dsbs. The protection afforded by acetone is assumed to be due to its scavenging of hydrated electrons, thought to be the active species causing enhanced DNA damage in the presence of halogenated pyrimidines. The residual component of IdU radiosensitization, which could not be removed by treatment with acetone, is manifest largely as a shoulder effect (Dq) and may be due to either a subset of non-scavengable, lethal dsbs and/or the influence of IdU on the fixation of potentially lethal damage. This study further demonstrates that halogenated pyrimidine-mediated radiosensitization consists of at least distinct components each associated with a different phenomenon.

Preoperative radiation therapy and iododeoxyuridine for large retroperitoneal sarcomas

PURPOSE

Local failure is frequent after conventional therapy for patients with retroperitoneal sarcomas. A Phase I/II multimodality approach was used, combining iododeoxyuridine (IdUrd) and radiation therapy, followed by attempted surgical resection, with the goal of improving local control.

METHODS AND MATERIALS

Patients with retroperitoneal sarcomas were treated with three to five consecutive cycles of treatment. Each 14-day cycle consisted of a continuous intravenous infusion of IdUrd on days 1-5, twice a day radiation therapy (1.25 Gy/fraction) on days 8-12, and a break on day 13 and 14. Surgical resection was attempted after three or five cycles. Patients resected after three cycles received an additional two cycles of treatment with radiation directed to the tumor bed. IdUrd dose was escalated in Phase I fashion (1000 mg/m2/day, 1333 mg/m2/day, and 1600 mg/m2/day). The median potential follow-up was 31 months.

RESULTS

Sixteen patients (13 with high grade tumors) were treated. The median maximum tumor size was 17 cm. Resection margins were negative in four patients, microscopically positive in four patients, and grossly positive in three patients. Five patients were not resected. The only grade 4 acute toxicity observed was vomiting which occurred in three patients receiving upper abdominal radiation. Postsurgical and long-term complications were rare. Median survival overall and for resected patients were 18 and 32 months, respectively. Local control was observed in three out of four patients with negative margins (9, 40+, and 51+ months), two out of four patients with microscopically positive margins (4 and 22 months), and one out of three patients with grossly positive margins (46+ months). The overall freedom from local progression was 45% at 24 months.

CONCLUSION

Retroperitoneal sarcomas can be resected after preoperative radiation therapy and IdUrd, with encouraging local control in patients resected with negative or microscopically positive margins. The recommended dose using this drug and radiation schedule appears to be 1600 mg/m2/day, which will form the basis for a Phase II trial.

Azidothymidine (AZT) as a potential modifier of radiation response in vitro

The potential effect of AZT as a thymidine analogue on radiation response in vitro was investigated. Two human cell lines (WiDr and HeLa) were used. The effect of 10 microM AZT on exponentially growing cells was studied after different exposure times (24, 48 and 72 h). The surviving fraction (clonogenic assay) or metabolic activity (MTT assay) after irradiation of AZT-exposed cells, was compared to unexposed irradiated controls. Flow cytometry was used to assess the cell-cycle effect of pre-exposure of exponentially growing cells to AZT. AZT had a radioprotective effect for all experimental time points as far as WiDr was concerned. For HeLa the effect was significant at 24 h. Cell-cycle analysis showed a significant accumulation in S-phase at 72 h for WiDr. For HeLa there was a significant accumulation in S-phase at 48 h. We conclude that under the reported experimental conditions, AZT as a thymidine analogue seems to reduce the cytotoxic effect of irradiation.

Kinetics of cell labeling and thymidine replacement after continuous infusion of halogenated pyrimidines in vivo

PURPOSE

Iododeoxyuridine (IdUrd) is a halogenated pyrimidine which has been recognized as a clinical radiosensitizer. It is generally agreed that the extent of radiosensitization correlates with the degree of thymidine substitution in DNA. Controversy exists regarding the optimal administration schedule to achieve maximum radiosensitization. To obtain more information relating to this problem, we present experiments on an in vivo human tumor xenograft continuously exposed to a fixed serum concentration of halogenated pyrimidines so as to study the kinetics of cell labeling and thymidine replacement.

METHODS AND MATERIALS

Human colon tumor (HCT-116) cells were injected subcutaneously into nude mice. After 10 days, most animals (> 90%) developed measurable tumor nodules with a volume doubling time of 5 +/- 1 days. Once the tumors reached a cross-sectional area of 0.25-0.30 cm2, miniosmotic pumps were implanted to deliver a dose of 100 mg/kg/day of IdUrd by continuous infusion. After an IdUrd exposure time of 1-7 days, blood and tumor tissue were collected.

RESULTS

The steady state serum IdUrd concentration was 0.95 +/- 0.1 microM, which is a clinically relevant concentration for a prolonged continuous intravenous infusion. The tumor cell potential doubling time (Tpot) was 25 +/- 2 h. The percent IdUrd thymidine replacement and the fraction of cells labeled, followed exponential saturation kinetics with a halflife of 33 +/- 9 and 27 +/- 2 h, respectively. After 5 days of exposure (congruent to 5 x Tpot), the thymidine replacement in tumor cells was 2.0 +/- 0.2% and the fraction of tumor cells labeled was 94 +/- 1%. Immunohistochemical staining of IdUrd labeled tumor tissues showed an exposure dependent gradient of cellular labeling that was initially highest in regions close to blood vessels. After 4 days of exposure at 100 mg/kg/day, there was an increase in the fraction of cells in G(0) + G1 and a decrease in the S phase population, suggesting a block between G1 and S phase.

CONCLUSION

We conclude that the in vivo kinetics of IdUrd thymidine replacement and fraction of cells labeled after continuous exposure followed exponential saturation kinetics with a halflife of approximately the potential doubling time of the tumor cell population. Simple modeling suggests that some form of prolonged, or briefly interrupted, continuous infusion should be considered for clinical administration because such schedules would leave fewer cells unsensitized than shorter infusions would. Even 10% of unlabeled clonogenic cells could explain the lack of dramatic clinical successes with IdUrd or BrdUrd sensitization.

Preclinical and clinical aspects of biomodulation of 5-fluorouracil

Although single agent 5-FU has for many years been the standard therapy for advanced colorectal malignancies, a number of recent clinical trials show higher response rates with biomodulation of 5-FU by several different agents. In general, trials of leucovorin, methotrexate, interferon, and PALA given in biomodulatory doses and sequences with 5-FU have demonstrated comparable response rates over a broad range. However, in the absence of controlled direct comparative phase III trials, final judgement on clinical superiority of a particular regimen must be reserved. Nevertheless, on the basis of current data, certain approaches appear promising and warrant further investigation. Compared to single agent 5-FU, survival benefit has been demonstrated with both low and high dose leucovorin/5-FU regimens and response rates in the 20-50% range appear reproducibly higher than those of 5-FU alone. Low dose and either continuous infusion or repetitive dosing of leucovorin, as well as the effect of treatment sequence and intervals between drugs, require additional investigation. When given 20-24 h before 5-FU, methotrexate achieves response rates similar to leucovorin modulated 5-FU, but the potential role of rescue leucovorin used in many of the trials makes definitive interpretation difficult. Interferon/5-FU regimens attaining response rates of 30-40% are promising but need to be carefully and rationally designed. Low dose PALA with effective doses of 5-FU achieving responses in 35-45% of patients represent a marked improvement in earlier trials of high dose PALA, but additional studies with higher doses not compromising 5-FU dose intensity should be considered. Certainly, the concomitant use of multiple modulating agents also needs further investigation. While many such trials already performed attained results no better than single agent biomodulation, the preliminary results obtained by Grem and colleagues with IFN/LV/5-FU in untreated patients, and by Conti et al. using TMTX/LV/5-FU in previously treated patients are encouraging. Further understanding of the mechanisms of action and interaction of modulating agents should allow additional rational combinations to be explored clinically. Cisplatin biomodulation of 5-FU has been studied in gastrointestinal and head and neck malignancies achieving excellent results in the latter group. Preclinical evidence exists which suggests, however, that 5-FU modulation of cisplatin may be more effective, especially when 5-FU is administered 24 h or more before cisplatin. Clinical investigation of this sequence is currently lacking. Data to support the clinical promise of AZT, IdUrd, uridine, and the benzylacyclouridines are not yet available, although preclinical and preliminary clinical studies are promising.

Iododeoxyuridine (IUdR) combined with radiation in the treatment of malignant glioma: a comparison of short versus long intravenous dose schedules (RTOG 86-12)

PURPOSE

To evaluate the toxicity and tumor efficacy of the halopyrimidine IUdR (NSC #39661, IND 22475) as a chemical modifier of radiation response when used in a high dose short time infusion versus the acceptable 4 day infusion.

METHODS AND MATERIALS

In August 1987 we initiated a prospective study in patients with newly diagnosed anaplastic astrocytoma and glioblastoma. The study was designed to have a fixed dose of radiation (60.16 Gy = 1.88 Gy in 32 fractions in 6.5 weeks) but varying the dose schedule of IUdR, keeping the total dose between 21 and 24 g/m2. IUdR was delivered in a 96, 48, or 24 hr continuous intravenous infusion per week for 6.5 weeks during radiation treatment.

RESULTS

The study was closed for patient accrual on October 1, 1991. Twenty-two patients were treated on the 96 hrs, 32 on the 48 hr and 25 on the 24 hr schedules. The incidence of glioblastoma ranged between 68 and 75% in the three arms. Seventy percent of the patients had a Karnofsky of 80-90% at the onset of treatment. Over 50% of the patient population were under age 55. Drug tolerance was related to the duration of the IUdR infusion. Toxicities were most pronounced in the 96 hr IUdR infusion schedule where 27.4% of the patients reported a grade 3 drug toxicity. No fatal or grade 4 toxicities were observed. More patients on the 24 and 48 hr schedule received at least 80% of the IUdR dose specified per protocol. We did not observe a trend in acute normal tissue radiation reactions in any of the three arms. The median survivals calculated from the Kaplan-Meier plot are 13.4, 10.5, and 11 months, respectively, for the 96, 48, and 24 hr infusions. The Cox Proportional Hazards model showed that any difference in survival can be attributed to histological grade, type of previous surgery and, to some extent, age of the patient. Dose schedule was not a significant predictor of survival, although statistically nonsignificant trend toward longer survival is seen in those patients with glioblastoma treated in the "long" 4 day schedule.

CONCLUSION

Overall, our treatment combination, particularly for patients with glioblastoma, has not shown convincing evidence of an improvement in survival. Of interest, however, it is the 2 year survival rate of 68% for patients with anaplastic astrocytoma. In our experience, the administration of IUdR is laborious, time consuming and with bothersome acute gastrointestinal and hematological toxicities.

The influence of high dose hydroxyurea on the incorporation of 5-iodo-2-deoxyuridine (IUdR) by human bone marrow and tumour cells in vivo

Resistance to cytotoxics precludes the successful treatment of many solid tumours. Inhibition of DNA synthesis in normal tissues with antimetabolites such as hydroxyurea (HU) may be a useful means of improving the selective uptake of toxic thymidine analogues by the relatively resistant tumour cells. HU also inhibits DNA repair by the critical depletion of intracellular deoxyribonucleotides. Twenty-five patients with various malignancies received 5-iodo-2-deoxyuridine (IUdR) 100 mg m-2 as a 20 min i.v. infusion and the uptake of IUdR was determined 1 h later immunocytochemically. Of these patients, 14 received IUdR 23 h from the start of a continuous i.v. infusion of HU (36 g over 36 h). Uptake of IUdR was equally suppressed in bone marrow and tumour aspirates, 0.1% (+/- 0.2%) of marrow precursor cells and 0.5% (+/- 0.4%) of tumour cells respectively, in patients who received HU compared to the uptake of IUdR in 11 patients who were not given HU 6.8% (+/- 1.1%) and 12.2% (+/- 1.8%) respectively. Mean HU plasma concentrations at the time of IUdR administration was 1.7 +/- 0.2 mM. The growth fraction of tumour cells (using Ki67 labelling) was not changed after treatment with HU. It is concluded that (1) since DNA synthesis is effectively inhibited by HU in tumour cells, differential uptake of radiolabelled IUdR by those cells will not be feasible using the current schedule of HU administration, (2) HU may be used as an inhibitor of DNA repair in vivo since the degree of inhibition correlates with that required to inhibit repair experimentally and that (3) Ki67 labelling index is not useful in studying cell kinetics in patients treated with HU.