Implantable polymers for tirapazamine treatments of experimental intracranial malignant glioma

Malignant gliomas remain refractory to intensive radiotherapy and cellular hypoxia enhances clinical radioresistance. Under hypoxic conditions, the benzotriazine di-N-oxide (3-amino-1,2,4-benzotriazine 1,4-dioxide) (tirapazamine) is reduced to yield a free-radical intermediate that results in DNA damage and cellular death. For extracranial xenografts, tirapazamine treatments have shown promise. We therefore incorporated tirapazamine into the synthetic, biodegradable polymer, measured the release, and tested the efficacy both alone and in combination with external beam radiotherapy in the treatment of experimental intracranial human malignant glioma xenografts. The [(poly(bis(p-carboxyphenoxy)-propane) (PCPP):sebacic acid (SA) (PCPP:SA ratio 20:80)] polymer was synthesized. The PCPP:SA polymer and solid tirapazamine were combined to yield proportions of 20% or 30% (wt/wt). Polymer discs (3 x 2 mm) (10 mg) were incubated (PBS, 37 degrees C), and the proportion of the drug released vs. time was recorded. Male nu/nu nude mice were anesthetized and received intracranial injections of 2 x 10(5) U251 human malignant glioma cells. For single intraperitoneal (i.p.) drug and/or external radiation treatments, groups of mice had i.p. 0.3 mmol/kg tirapazamine, 5 Gy cranial irradiation, or combined treatments on day 8 after inoculation. For fractionated drug and radiation treatments, mice had i.p. 0.15 mmol/kg tirapazamine, 5 Gy radiation, or combined treatments on days 8 and 9 after inoculation. For intracranial (i.c.) polymer treatments, mice had craniectomies and intracranial placement of polymer discs at the site of cellular inoculation. The maximally tolerated percentage loading of tirapazamine in the polymer.disc was determined. On day 7 after inoculation, groups of mice had i.c. empty or 3% tirapazamine alone or combined with radiation (5 Gy x 2 doses) or combined with i.p. drug (0.15 mmol/kg x 2 doses on days 8 and 9). Survival was recorded. Polymers showed controlled, protracted in vitro release for over 100 days. The 5 Gy x 1 treatment resulted in improved survival; 28.5 +/- 3.7 days (P = 0.01 vs. controls), while the single i.p. 0.3 mmol/kg tirapazamine treatment, 17.5 +/- 1.9 days (P = NS) and combined treatments; 21.5 +/- 5.0 days (P = NS) were not different. The fractionated treatments: 5 Gy x 2, i.p. 0.15 mmol/kg tirapazamine x 2 and the combined treatments resulted in improved survival: 44.5 +/- 3.9 (P < 0.001), 24.5 +/- 2.3 (P = 0.05) and 50.0 +/- 6.0 (P < 0.001), respectively. Survival after intracranial empty polymer was 16.5 +/- 3.0 days and increased to 31.0 +/- 3.0 (P = 0.003) days when combined with the 5 Gy x 2 treatment. The survival after the polymer bearing 3% tirapazamine alone vs. combined with radiation was not different. The combined 3% tirapazamine polymer, i.p. tirapazamine, and radiation treatments resulted in both early deaths and the highest long-term survivorship. The basis for potential toxicity is discussed. We conclude that implantable biodegradable polymers provide controlled intracranial release for treatment of experimental glioma. For treatment of malignant gliomas, the combination of continuous polymer-mediated delivery and fractionated systemic delivery of tirapazamine with external beam radiotherapy warrants further exploration.

Synthetic, implantable, biodegradable polymers for controlled release of radiosensitizers

INTRODUCTION

Synthetic, implantable, biodegradable polymers offer the sustained local release of disparate therapeutic agents for the treatment of human malignant brain tumors. The role of polymeric devices for the local delivery of radiosensitizers remains unexplored, however. We therefore quantified the release of the representative radiosensitizers IUdR (5-iodo-2'-deoxyuridine), tirapazamine (3-amino-1,2,4-benzotriazine-1,4-dioxide) and etanidazole [N-(2-hydroxyethyl)-2-nitro-1-imidazole-1-acetamide] from the [(poly(bis(p-carboxyphenoxy)-propane) (PCPP):sebacic acid (SA) (PCPP:SA ratio 20:80)] polymer.

METHODS

For measurements of controlled release, triplicate polymer discs were incubated for known intervals in 2 ml 0.1 phosphate-buffered saline, pH 7.4, 37 degrees C. Using a predefined schedule, the supernatant fractions were systematically removed and replaced with fresh solution. The supernatant fractions were measured. The cumulative percentage of the loaded drug that appeared in these serial supernatant fractions was plotted vs. time. The percentage of the drug that was loaded into each polymer and that was released vs. time was fit to the power function of the form y = (a) x tb, where y is the cumulative released agent, a and b are constants and t is time (days).

RESULTS

The IUdR was released over an interval of approximately one week, while the release of the tirapazimine persisted for over 100 days. The etanidazole was released most rapidly, over a period of hours. Modeling of release showed that regardless of percentage loading of the drug, the monoexponential function showed high correlation of the fit of the plot of the release vs. time.

CONCLUSIONS

These results suggest that the hydrophilicity and percentage loading of the drug predominantly determine the rate of release. Based upon these results, IUdR and tirapazamine warrant preclinical testing for radiosensitization of human malignant brain tumors via the synthetic, implantable, biodegradable polymeric devices.

Effect of interstitial and/or systemic delivery of tirapazamine on the radiosensitivity of human glioblastoma multiforme in nude mice

The purpose of this study was to investigate the feasibility and the efficacy of administering tirapazamine by a slow-releasing polymer disc that was implanted interstitially into a U251 (human glioblastoma multiforme) tumor grown in nude mice. Tumor-bearing animals, with a tumor nodule 0.8 cm3 in size, were distributed to groups receiving combinations of empty or drug-containing polymer implants in the tumor or contralateral leg, intraperitoneal (i.p.) drug, and/or irradiation. The drug (i.p.) alone (14 mg/kg x6) or in combination with tumor drug implant (2 mg) did not significantly increase the tumor volume doubling time compared to that of control animals. Given with 12 Gy of irradiation in twice a day 2-Gy fractions, combined i.p. drug and tumor drug implant significantly delayed tumor growth compared to irradiation alone, which was not achieved with either drug treatment alone added to irradiation. Toxicity, as manifested by transient weight loss, was primarily seen in animals receiving radiation and i.p. tirapazamine. These results indicated that a slow-releasing tirapazamine disc can be produced and the addition of an interstitially implanted tirapazamine disc further increased the effectiveness of i.p. tirapazamine.

Differential diagnosis of hot flashes

OBJECTIVE

The purpose of this study is to present the physiology and differential diagnosis of hot flashes, other than associated with menopause, in order to facilitate the proper evaluation of symptomatic patients with hot flashes.

STUDY DESIGN

Literature search using Med-Line computer access.

RESULTS

Interest in flushing reaction began in historic times. With the rapidly expanding population of women over the age of 45 and prevalence of hot flashes as menopausal symptoms, physicians need to be aware of other medical conditions which may mimic hot flashes. These include flushing due to systemic diseases, carcinoid syndrome, systemic mast cell disease, pheochromocytoma, medullary carcinoma of the thyroid, pancreatic islet-cell tumors, renal cell carcinoma, neurological flushing, emotional flushing, spinal cord injury, flushing reaction related to alcohol and drugs, flushing associated with food additives and eating.

CONCLUSION

There is a wide variety of disease processes that can cause hot flashes. Knowledge of the nature of these disease processes is necessary for quick recognition of patients with hot flashes who do not respond to estrogen replacement treatment, and to facilitate the proper evaluation of atypical patients.

Implantable biodegradable polymers for IUdR radiosensitization of experimental human malignant glioma

PURPOSE

The potential of halogenated pyrimidines for the radiosensitization of human malignant gliomas remains unrealized. To assess the role of local delivery for radiosensitization, we tested a synthetic, implantable biodegradable polymer for the controlled release of 5-iodo-2'-deoxyuridine (IUdR) both in vitro and in vivo and the resultant radiosensitization of human malignant glioma xenografts in vivo.

MATERIALS AND METHODS

In vitro: To measure release, increasing (10%, 30%, 50%) proportions (weight/weight) of IUdR in the polyanhydride [(poly(bis(p-carboxyphenoxy)-propane) (PCPP): sebacic acid (SA) (PCPP : SA ratio 20:80)] polymer discs were incubated (1 ml phosphate-buffered saline, 37 degrees C). The supernatant fractions were serially assayed using high performance liquid chromatography. To measure modulation of release, polymer discs were co-loaded with 20 microCi 5-125-iodo-2'-deoxyuridine (125-IUdR) and increasing (10%, 30%, or 50%) proportions of D-glucose. To test radiosensitization, cells (U251 human malignant glioma) were sequentially exposed to increasing (0 or 10 microM) concentrations of IUdR and increasing (0, 2.5, 5.0, or 10 Gy) doses of acute radiation. In vivo. To measure release, PCPP : SA polymer discs having 200 microCi 125-IUdR were surgically placed in U251 xenografts (0.1-0.2 cc) growing in the flanks of nude mice. The flanks were reproducibly positioned over a collimated scintillation detector and counted. To measure radiosensitization, PCPP : SA polymer discs having 0% (empty) or 50% IUdR were placed in the tumor or contralateral flank. After five days, the tumors were acutely irradiated (500 cGy x 2 daily fractions).

RESULTS

In vitro: Intact IUdR was released from the PCPP : SA polymer discs in proportion to the percentage loading. After 4 days the cumulative percentages of loaded IUdR that were released were 43.7 +/- 0.1, 70.0 +/- 0.2, and 90.2 +/- 0.2 (p < 0.001 ANOVA) for the 10, 30, and 50% loadings. With 0, 10, 30, or 50% D-glucose co-loading, the cumulative release of 125-IUdR from PCPP : SA polymers was 21, 70, 92, or 97% (p < 0.001), respectively, measured 26 days after incubation. IUdR radiosensitized U251 cells in vitro. Cell survival (log10) was -2.02 +/- 0.02 and -3.68 +/- 0.11 (p < 0.001) after the 10 Gy treatment and no (control) or 10 microM IUdR exposures, respectively. In vivo: 125-IUdR Release: The average counts (log10 cpm +/- SEM) (hours after implant) were 5.2 +/- 0.05 (0.5), 4.3 +/- 0.07 (17), 3.9 +/- 0.08 (64), and 2.8 +/- 0.06 (284). Radiosensitization: After intratumoral implantation of empty polymer or intratumoral 50% IUdR polymer, or implantation of 50% IUdR polymers contralateral to tumors the average growth delays of tumors to 4 times the initial volumes were 15.4 +/- 1.8, 20.1 + 0.1, and 20.3 + 3.6 (mean + SEM) days, respectively (p = 0.488 one-way ANOVA). After empty polymer and radiation treatments, no tumors regressed and the growth delay was 31.1 + 2.1 (p = 0.046 vs. empty polymer alone) days. After implantation of 50% IUdR polymers either contralateral to the tumors or inside the tumors, followed by radiation, tumors regressed; growth delays to return to the initial average volumes of 14.0 + 3.6 or 24.2 + 0.2 (p < 0.01) days, respectively.

CONCLUSIONS

Synthetic, implantable biodegradable polymers hold promise for the controlled release and local delivery of IUdR for radiosensitization of gliomas.

Local delivery of chemotherapy and concurrent external beam radiotherapy prolongs survival in metastatic brain tumor models

Local chemotherapy with biodegradable polymers prolongs survival with minimal morbidity in patients with intracranial high-grade gliomas. However, use of local chemotherapy for metastatic brain tumors has not been defined. We studied the safety and the efficacy of locally delivered chemotherapy with and without concurrent radiation therapy in treating tumors that frequently metastasize to the brain. The chemotherapeutic agents 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU), carboplatin, and camptothecin were incorporated into controlled-release polymers and tested individually against intracranial challenges with one of four tumors (lung carcinoma, renal cell carcinoma, colon carcinoma, and melanoma). For each combination of drug and tumor type, four groups were tested: (a) empty polymer (no drug); (b) external beam radiotherapy (XRT) alone; (c) local chemotherapy from biodegradable polymer alone; and (d) local chemotherapy and XRT together. Polymers were implanted 5 days after tumor inoculation; XRT was given on days 7-9 (300 cGy/day). BCNU and XRT together were effective against all four tumors. BCNU polymer alone significantly prolonged survival in mice with intracranial melanoma or renal cell carcinoma. Carboplatin alone was effective against both melanoma and colon carcinoma and in combination with XRT against colon and renal cell carcinomas. Camptothecin was effective only with XRT against melanoma. These studies demonstrate that local delivery of chemotherapy with concurrent radiation therapy is safe and can significantly prolong survival in models of common intracranial metastatic tumors. Concurrent use of local chemotherapy with standard XRT appears to be more effective than either treatment alone. Local chemotherapy may also be of benefit to patients who have previously received maximal cranial irradiation but suffer an intracranial recurrence.