Implantable biodegradable polymers for IUdR radiosensitization of experimental human malignant glioma

Polifeprosan 20, 3.85% carmustine slow release wafer in malignant glioma: patient selection and perspectives on a low-burden therapy

Polifeprosan 20 with carmustine (GLIADEL^®) polymer implant wafer is a biodegradable compound containing 3.85% carmustine (BCNU, bischloroethylnitrosourea) implanted in the brain at the time of planned tumor surgery, which then slowly degrades to release the BCNU chemotherapy directly into the brain thereby bypassing the blood-brain barrier. Carmustine implant wafers were demonstrated to improve survival in randomized placebo-controlled trials in patients undergoing a near total resection of newly diagnosed or recurrent malignant glioma. Based on these trials and other supporting data, carmustine wafer therapy was approved for use for newly diagnosed and recurrent malignant glioma in the United States and the European Union. Adverse events are uncommon, and as this therapy is placed at the time of surgery, it does not add to patient treatment burden. Nevertheless, this therapy appears to be underutilized. This article reviews the evidence for a favorable therapeutic ratio for the patient and the potential barriers. Consideration of these issues is important for optimal use of this therapeutic approach and may be important as this technology and other local therapies are further developed in the future.

Polymeric drug delivery for the treatment of glioblastoma

Glioblastoma (GBM) remains an almost universally fatal diagnosis. The current therapeutic mainstay consists of maximal safe surgical resection followed by radiation therapy (RT) with concomitant temozolomide (TMZ), followed by monthly TMZ (the "Stupp regimen"). Several chemotherapeutic agents have been shown to have modest efficacy in the treatment of high-grade glioma (HGG), but blood-brain barrier impermeability remains a major delivery obstacle. Polymeric drug-delivery systems, developed to allow controlled local release of biologically active substances for a variety of conditions, can achieve high local concentrations of active agents while limiting systemic toxicities. Polymerically delivered carmustine (BCNU) wafers, placed on the surface of the tumor-resection cavity, can potentially provide immediate chemotherapy to residual tumor cells during the standard delay between surgery and chemoradiotherapy. BCNU wafer implantation as monochemotherapy (with RT) in newly diagnosed HGG has been investigated in 2 phase III studies that reported significant increases in median overall survival. A number of studies have investigated the tumoricidal synergies of combination chemotherapy with BCNU wafers in newly diagnosed or recurrent HGG, and a primary research focus has been the integration of BCNU wafers into multimodality therapy with the standard Stupp regimen. Overall, the results of these studies have been encouraging in terms of safety and efficacy. However, the data must be qualified by the nature of the studies conducted. Currently, there are no phase III studies of BCNU wafers with the standard Stupp regimen. We review the rationale, biochemistry, pharmacokinetics, and research history (including toxicity profile) of this modality.

Polifeprosan 20, 3.85% carmustine slow-release wafer in malignant glioma: evidence for role in era of standard adjuvant temozolomide

The Polifeprosan 20 with carmustine (BCNU, bis-chloroethylnitrosourea, Gliadel^®) polymer implant wafer is a biodegradable compound containing 3.85% carmustine which slowly degrades to release carmustine and protects it from exposure to water with resultant hydrolysis until the time of release. The carmustine implant wafer was demonstrated to improve survival in blinded placebo-controlled trials in selected patients with newly diagnosed or recurrent malignant glioma, with little increased risk of adverse events. Based on these trials and other supporting data, US and European regulatory authorities granted approval for its use in recurrent and newly diagnosed malignant glioma, and it remains the only approved local treatment. The preclinical and clinical data suggest that it is optimally utilized primarily in the proportion of patients who may have total or near total removal of gross tumor. The aim of this work was to review the evidence for the use of carmustine implants in the management of malignant astrocytoma (World Health Organization grades III and IV), including newly diagnosed and recurrent disease, especially in the setting of a standard of care that has changed since the randomized trials were completed. Therapy has evolved such that patients now generally receive temozolomide chemotherapy during and after radiotherapy treatment. For patients undergoing repeat resection for malignant glioma, a randomized, blinded, placebo-controlled trial demonstrated a median survival for 110 patients who received carmustine polymers of 31 weeks compared with 23 weeks for 122 patients who only received placebo polymers. The benefit achieved statistical significance only on analysis adjusting for prognostic factors rather than for the randomized groups as a whole (hazard ratio = 0.67, P = 0.006). A blinded, placebo-controlled trial has also been performed for carmustine implant placement in newly diagnosed patients prior to standard radiotherapy. Median survival was improved from 11.6 to 13.9 months (P = 0.03), with a 29% reduction in the risk of death. When patients with glioblastoma multiforme alone were analyzed, the median survival improved from 11.4 to 13.5 months, but this improvement was not statistically significant. When a Cox’s proportional hazard model was utilized to account for other potential prognostic factors, there was a significant 31% reduction in the risk of death (P = 0.04) in this subgroup. Data from other small reports support these results and confirm that the incidence of adverse events does not appear to be increased meaningfully. Given the poor prognosis without possibility of cure, these benefits from a treatment with a favorable safety profile were considered meaningful. There is randomized evidence to support the use of carmustine wafers placed during resection of recurrent disease. Therefore, although there is limited specific evidence, this treatment is likely to be efficacious in an environment when nearly all patients receive temozolomide as part of initial management. Given that half of the patients in the randomized trial assessing the value of carmustine implants in recurrent disease had received prior chemotherapy, it is likely that this remains a valuable treatment at the time of repeat resection, even after temozolomide. There are data from multiple reports to support safety. Although there is randomized evidence to support the use of this therapy in newly diagnosed patients who will receive radiotherapy alone, it is now standard to administer both adjuvant temozolomide and radiotherapy. There are survival outcome reports for small cohorts of patients receiving temozolomide with radiotherapy, but this information is not sufficient to support firm recommendations. Based on the rationale and evidence of safety, this approach appears to be a reasonable option as more information is acquired. Available data support the safety of using carmustine wafers in this circumstance, although special attention to surgical guidelines for implanting the wafers is warranted.

Drug delivery strategies for the treatment of malignant gliomas

As primary brain tumors, malignant gliomas are known to be one of the most insidious types of brain cancer afflicting the humans. The current standard strategy for the treatment of malignant gliomas includes the surgical resection of the tumor when possible, followed by a combination of radiotherapy and/or a certain chemotherapeutic protocol. However, due to the short mean survival, frequent recurrences, and poor prognosis associated with the tumors, new therapeutic strategies are investigated consecutively. These novel drug delivery approaches can be subdivided as systemic and local drug administration. This review focuses on localized drug delivery strategies for the treatment of malignant gliomas, including the injections, infusions, trans-nasal delivery systems, convection enhanced delivery (CED) systems, and various types of polymeric implants. Furthermore, systemic strategies to increase the drug penetration into the brain, such as temporary disruption of the blood brain barrier (BBB), chemical modification of the available therapeutic substances, and utilization of endogenous transport systems will be briefly discussed.

Carmustine wafers: localized delivery of chemotherapeutic agents in CNS malignancies

High-grade glioma is a devastating disease that leaves the majority of its victims dead within 2 years. To meaningfully increase survival, a trimodality approach of surgery, radiation, and chemotherapy is needed. Carmustine (1,3-bis (2-chloroethyl)-1-nitrosourea) is a nitrosourea alkylating agent that exerts its antitumor effect by akylating DNA and RNA. Systemic administration of nitrosoureas as a single agent or as part of procarbazine/3-cyclohexyl-1-nitroso-urea/vincristine has demonstrated little efficacy in the treatment of high-grade glioma. The development of carmustine wafers (Gliadel((R)) Wafer) as a method for controlled released delivery of carmustine from biodegradable polymer wafers enhances the therapeutic ratio by fully containing the drug within the confines of the brain tumor environment while minimizing systemic toxicities. Preclinical and clinical studies have proven the safety and efficacy of Gliadel in the management of glioblastoma. From these results, Gliadel is currently approved for use in patients with recurrent glioblastoma as an adjunct to surgery and in newly diagnosed patients with high-grade glioma as an adjunct to surgery and radiation. Other promising advances in the use of locally delivered chemotherapy for CNS malignancies, including Gliadel for brain metastases and combination therapies with systemic or biologic agents, are discussed.

Advances in brain tumor surgery

Advances in the fields of molecular and translational research, oncology, and surgery have emboldened the medical community to believe that intrinsic brain tumors may be treatable. Intraoperative imaging and brain mapping allow operations adjacent to eloquent cortex and more radical resection of tumors with increased confidence and safety. Despite these advances, the infiltrating edge of a neoplasm and distant microscopic satellite lesions will never be amendable to a surgical cure. Indeed, it is continued research into the delivery of an efficacious chemobiologic agent that will eventually allows us to manage this primary cause of treatment failure.

Treatment of intracranial rat glioma model with implant of radiosensitizer and biomodulator drug combined with external beam radiotherapy

PURPOSE

To evaluate an intracranial polymer implant containing bromodeoxyuridine (BrdUrd) and N-(phosphonacetyl)-L-aspartic acid (PALA) in combination with external beam radiotherapy (EBRT) in the treatment of a rat glioma.

METHODS AND MATERIALS

Combinations of the biomodulators 5-fluorouracil, methotrexate, or PALA with BrdUrd were evaluated as radiosensitizers in vitro by clonogenic assay. In in vivo experiments, BrdUrd and PALA were incorporated into a polyanhydride-based polymer, bis(p-carboxyphenoxy)propane sebacic acid, and implanted in the C6 rat glioma growing intracranially. The effectiveness of treatment was evaluated on the basis of survival. EBRT was given as 10-MV X-rays.

RESULTS

In tissue culture experiments, C6 cells were refractory to radiosensitization by BrdUrd even when the thymidine analog was combined with a biomodulator intended to reduce de novo thymidine synthesis. The most effective compound in vitro was PALA. When PALA and BrdUrd in a polymer formulation were implanted intracranially and combined with 10-Gy EBRT, the treatment was highly effective, with 83% of treated rats surviving 180 days.

CONCLUSION

Although the in vitro results were not encouraging, the combination of intratumoral BrdUrd and PAL with 10-Gy EBRT was highly effective in treating a rat glioma. These results indicate the clinical potential of combined and mixed modality treatments involving intratumoral sustained-release drug delivery.

Toxicities and therapeutic effect of 5-fluorouracil controlled release implant on tumor-bearing rats

AIM: To investigate the toxicities, biodistribution and anticancer effect of 5-fluorouracil controlled release implant (5-FUCI) on Walker 256 carcinosarcoma cells in Wistar rats.

METHODS: Experiment 1: Wistar rats were randomly divided into three groups (27 rats per group). Blank implant was implanted in left lobe of the liver, and rats were treated with saline solution (in group A) or 5-fluorouracil (subcutaneous injection, group B). 5-FUCI was inserted in left lobe of the liver (group C). The gastrointestinal and hematological toxicities were observed and contents of element F in group C were assayed. Experiment 2: on day 6 after Walker-256 carcinosarcoma transplantation in left lobe of the liver, 5-FUCI was implanted in right lobe of the liver (group E) or left lobe (group F), and rats in control group (group D) were inserted blank implant. Tumor inhibition rate and survival time were investigated.

RESULTS: 5-FUCI showed no obvious toxic effect, extraction of Evan’s blue from gastrointestinal tissue was normal, the peripheral white blood cells and bone marrow nucleated cells were not reduced, compared with control group (P > 0.05). Histological examination revealed that there were no visible changes in small intestinal mucosa, The concentration of 5-fluorouracil in left lobe of the liver was 9.84, 28, 34 times as much as those of right lobe of the liver, heart and kidney respectively after the implantation in group C. They kept a high level of fluorouracil in left lobe of the liver, ranging from (4.414% ± 0.482%) to (7.800% ± 0.804%), for eight weeks. Survival days were 28.0 ± 2.2, 30.0 ± 3.2 and 38.7 ± 6.7 d in group D, E and F, respectively.

CONCLUSION: 5-FUCI shows no obvious toxicities to gastrointestinal tract and myelotoxicity. After implantation, it kept a high level of 5- fluorouracil in surrounding tissues of the implant for eight weeks. Its antitumor effect on Walker-256 carcinosarcoma is demonstrated.

The surgical bed after BCNU polymer wafer placement for recurrent glioma: serial assessment on CT and MR imaging

OBJECTIVE

The objective of our study was to describe the CT and MR imaging appearances of the surgical bed in the brains of patients receiving biodegradable polymers impregnated with N, N'1, 3-Bis-(2-chloroethyl)-N-nitrosourea (BCNU) for recurrent glioma and to determine whether patients receiving placebos could be differentiated from those receiving BCNU based on the pattern and growth kinetics of tumor recurrence.

MATERIALS AND METHODS

The CT and MR images of 20 patients who underwent surgery for resection of recurrent high-grade gliomas and placement of intratumoral wafers (11 received BCNU polymer wafers, nine received control wafers) were analyzed for wafer appearance, volume of gas in the tumor bed, and volume of enhancement on serial scans.

RESULTS

Wafers appeared as linear hyperdense structures on CT and as linear low-signal-intensity structures on MR imaging and caused no significant enhancement. In the BCNU polymer group, gas volume was 4.0 +/- 3.4 cm(3) (mean +/- SD), whereas gas volume was 1.6 +/- 3.0 cm(3) for the placebo group (Mann-Whitney test, p = 0.03). A trend toward linear rather than exponential recurrent tumor growth was identified for the BCNU polymer group but not for the placebo group.

CONCLUSION

BCNU polymer wafers have a specific appearance on CT and MR imaging with which radiologists should be familiar: gas in the surgical bed is an expected transient finding, and tumor regrowth in patients receiving BCNU polymer wafers appeared to occur at a slower rate than in those receiving the placebo.

Tumor treatment by sustained intratumoral release of 5-fluorouracil: effects of drug alone and in combined treatments

PURPOSE

To evaluate an intratumoral polymer implant for sustained delivery of 5-fluorouracil (5-FU) in a mouse tumor model.

METHODS AND MATERIALS

5-FU was incorporated into a polyanhydride-based polymer, bis(p-carboxyphenoxy)propane sebacic acid (CPP:SA) and implanted in RIF-1 mouse fibrosarcoma growing s.c. The effectiveness of treatment was evaluated by tumor growth delay. External beam radiation was 60Co gamma rays, and the source of interstitial radiation was implanted 125I seeds. A second drug, cis-diamminedichloroplatinum (cis-DDP), was administered by intraperitoneal injection or by osmotic pump.

RESULTS

For drug/polymer implant alone, the tumor growth delay was proportional to the amount of drug in the implant. The 5-FU polymer implant was most effective when combined with cis-DDP or with acute or fractionated radiation, and in some cases, the effects of combined treatments were greater than additive. The most effective combination was intratumoral 5-FU and low-dose-rate radiation delivered from an interstitial radiation source.

CONCLUSION

Results indicate that 5-FU can be effectively delivered by polymer implant and that this mode of delivery is particularly appropriate for combined treatments.

Local drug delivery to the brain

The controlled local delivery of antineoplastic agents by biodegradable polymers is a technique that allows for exposure of tumor cells to therapeutic doses of an active agent for prolonged periods of time while avoiding high systemic doses associated with debilitating toxicities. The use of polymers for chemotherapy delivery expands the spectrum of available treatment of neoplasms in the central nervous system, and facilitates new approaches for the treatment of malignant gliomas. In this article, we discuss the rationale and history of the development and use of these polymers, and review the various agents that have used this technology to treat malignant brain tumors.

Daily low-dose carboplatin as a radiation sensitizer for newly diagnosed malignant glioma

Surgical resection followed by local field radiotherapy is currently our most effective approach to treatment for most patients with malignant glioma. Carboplatin chemotherapy has direct cytotoxic effects on glioma cells and acts as a radiation sensitizer to enhance cell killing. Its demonstrated efficacy as a sensitizer in other solid tumors led to this clinical trial of carboplatin as a radiation sensitizer in the treatment of newly diagnosed glioblastoma multiforme (GBM) and anaplastic astrocytoma (AA). Fourteen patients (nine GBM and five AA) were treated with daily low-dose carboplatin 25 mg/m2 intravenously within 2 h of their fractionated radiotherapy to a total dose of 600 mg/m2. No significant toxicities attributable to this combined therapy were observed. All patients have progressed, with median time to progression of 16 weeks. Eleven patients have died, with median survival of 38 weeks for the entire cohort. Although this regimen appeared safe, there was no benefit in survival time compared to historical patients treated with radiotherapy. The limitations and future potential for the strategy of radiation sensitization are discussed.

IUdR polymers for combined continuous low-dose rate and high-dose rate sensitization of experimental human malignant gliomas

Local polymeric delivery enhances IUdR radiosensitization of human malignant gliomas (MG). The combined low-dose rate (LDR) (0.03 Gy/h) and fractionated high-dose rate (HDR) treatments result in cures of experimental MGs. To enhance efficacy, we combined polymeric IUdR delivery, LDR, and HDR for treatments of both subcutaneous and intracranial MGs. In vitro: Cells (U251 MG) were trypsinized and replated in triplicate 1 day prior to LDR irradiation in media either without (control) or with 10 microM IUdR. After 72 hr, LDR irradiation cells were acutely irradiated (1.1 Gy/min) with increasing (0, 1.25, 2.5, 5.0, or 10 Gy) single doses. Implantable IUdR polymers [(poly(bis(p-carboxyphenoxy)-propane) (PCPP): sebaic acid (PCPP:SA), 20:80] (50% loading; 10 mg) were synthesized. In vivo: For flank vs. intracranial tumors, mice had 6 x 10(6) subcutaneous vs. 2 x 10(5) intracranial cells. For intracranial or subcutaneous MGs, mice had intratumoral blank (empty) vs. IUdR polymer treatments. One day after implantation, mice had immediate external LDR (3 cGy/h x 3 days total body irradiation) or HDR (2 Gy BID x 4 days to tumor site) or concurrent treatments. For the in vitro IUdR treatments, LDR resulted in a striking increase in cell-killing when combined with HDR. For the in vivo LDR treatments of flank tumors, the growth delay was greater for the IUdR vs. blank polymer treatments. For the combined LDR and HDR, the IUdR treatments resulted in a dramatic decrease in tumor volumes. On day 60 the log V/V0 were -1.7 +/- 0.22 for combined LDR + HDR + IUdR polymer (P < 0.05 vs. combined LDR + HDR + blank polymer). Survival for the intracranial controls was 22.9 +/- 1.2 days. For the blank polymer + LDR vs. blank polymer + LDR + HDR treatments, survival was 25.3 +/- 1.7 (P = NS) vs. 48.1 +/- 3.5 days (P < 0.05). For IUdR polymer + LDR treatment survival was 27.3 +/- 2.3 days (P = NS). The most striking improvement in survival followed the IUdR polymer + LDR + HDR treatment: 66.0 + 6.4 days (P < 0.05 vs. blank polymer + LDR + HDR). The polymeric IUdR delivery plus combined continuous LDR and HDR treatments results in growth delay and improved survival in animals bearing the MG xenografts. This treatment may hold promise for the treatment of human MGs.

Regional drug delivery with radiation for the treatment of Ewing's sarcoma. In vitro development of a taxol release system

Recently, several studies have suggested the radiosensitizing effect of taxol, a microtubular inhibitor. Our overall hypothesis is that a combination of radiation and taxol may demonstrate therapeutic efficacy over doses of either individually. Studies examining taxol use have mostly focused on systemic administration, which can lead to undesired effects. To circumvent these side effects, we propose a locally administered polymeric microsphere delivery system combined with radiation therapy for the treatment of Ewing's sarcoma. The present study focuses on the in vitro ability of taxol when present as a microencapsulated drug delivery system, and delivered locally at the site of the sarcoma/tumor, to block cells in the G2/M phase of the cell cycle and potentially enhance the radiation sensitivity of cells. Using the bioresorbable poly(anhydride-co-imide), poly[pyromellityl-imidoalanine-1,6-bis(carboxy-phenoxy)hexane] (PMA-CPH), and the radiosensitizing agent taxol, a microsphere based delivery system was fabricated. A solvent evaporation technique was used to encapsulate taxol at doses of 1%, 5%, and 10% in PMA-CPH microspheres. Release kinetics studies demonstrated that the total amount of taxol released and the release rate were directly dependent on loading percentage. Taxol's bioactivity and radiosensitizing ability were measured using flow cytometry. Co-culture of Ewing's sarcoma cells with and without taxol-loaded microspheres demonstrated that released taxol retained its bioactivity and effectively blocked cells in the radiosensitive G2/M phase of mitosis. The taxol-radiation delivery system studied achieved an 83% decrease in tumor cell count compared to control. Taxol effectively sensitized Ewing's sarcoma cells to radiation with radiosensitivity shown to be independent of radiation dose at levels of dosages studied. This work has demonstrated that taxol can be effectively released from a biodegradable PMA-CPH microsphere delivery system while maintaining potent combined cytotoxic and radiosensitizing abilities.

Controlled release of vancomycin from biodegradable microcapsules

Poly D,L-lactic acid (PLA) and its copolymers with glycolide PLGA 90:10 and 70:30 were polymerized under various conditions to yield polymers in the molecular weight range 12000-40000 daltons, as determined by gel permeation chromatography. Vancomycin hydrochloride was the hydrophilic drug of choice for the treatment of methicillin resistant Staphyloccoccal infections. It was microencapsulated in the synthesized polymers using water-oil-water (w/o/w) double emulsion and solvent evaporation. The influence of microcapsule preparation medium on product properties was investigated. An increase in polymer-to-drug ratio from 1:1 to 3:1 caused an increase in the encapsulation efficiency (i.e. from 44-97% with PLGA). An increase in the emulsifier (PVA) molecular weight from 14-72 kD caused an increase in encapsulation efficiency and microcapsule size. The in vitro release of vancomycin from microcapsules in phosphate buffer saline (pH 7.4) was found to be dependent on molecular weight and copolymer type. The kinetic behaviour was controlled by both diffusion and degradation. Sterilization with 60Co (2.5 Mrad) also affected the degradation rate and release profiles. Degradation of microcapsules could be seen by scanning electron microscopy, by the increase in the release rate from PLA and by the decrease in the Tg values of microcapsules. In vitro bactericidal effects of the microcapsule formulations on S. aureus were determined with a special diffusion cell after the preparations had been sterilized, and were found to have bactericidal effects lasting for 4 days.

Potentiation of ovarian OCa-1 tumor radioresponse by poly (L-glutamic acid)-paclitaxel conjugate

PURPOSE

It has been shown that paclitaxel (TXL) can strongly enhance tumor cells' sensitivity to radiation. We examined whether the radiosensitizing effect of paclitaxel can be further enhanced when it is delivered systemically as a polymer-drug conjugate that provides enhanced tumor uptake and prolonged release of TXL in the tumor.

METHODS AND MATERIALS

C3Hf/Kam mice bearing 8-mm murine ovarian OCa-1 tumors were treated with i.v.-injected Poly(L-glutamic acid)-paclitaxel (PG-TXL) at an equivalent TXL dose of 80 mg/kg, followed 24 h later by single doses of local radiation ranging from 5 to 15 Gy. To determine how long the radiopotentiation persisted at extended times after PG-TXL administration, mice with OCa-1 tumors were given i.v. PG-TXL and 4, 24, 48, 72, 120, or 168 h later their tumors were irradiated at a dose of 10 Gy. Antitumor activity was determined by delay in tumor growth. Cell cycle distribution was assayed using flow cytometry. Tumor vascular volume was estimated using Tc-99 m-labeled red blood cells.

RESULTS

PG-TXL strongly potentiated the radioresponse of the OCa-1 tumor. The enhancement factors ranged from 2.79 to 4.28, depending on radiation dose, when PG-TXL preceded radiation by 24 h. The enhancement factor derived from radiation dose-response curves was as high as 5.13. The radiosensitizing effect of PG-TXL was also dependent on the interval between PG-TXL administration and radiation delivery, with greater enhancement been observed when the interval was decreased. The percentage of G2/M cells was significantly increased to 21.4% 48 h after PG-TXL but declined to a preinjection level of 14.8% 72 h after PG-TXL. PG-TXL only moderately increased the tumor vascular volume by 37% 24 h after PG-TXL administration.

CONCLUSION

PG-TXL markedly potentiated response of OCa-1 tumor to radiation. When compared to literature data obtained from the same tumor model used here, PG-TXL exhibited stronger radiosensitization effect than TXL. Although its action is possibly mediated by arrest of cells in G2/M phases of cell cycle and by increased tumor blood supply, PG-TXL may exert its radiopotentiation activity through increased tumor uptake of PG-TXL and sustained release of TXL in the tumor. Our results show that conjugation of TXL to a polymer has the potential to further enhance its radiosensitizing activity and that clinical trials of PG-TXL in combination with radiation is warranted.

Local drug delivery

Intensive research efforts are now focused on the development of new strategies for more effective delivery of drugs to the central nervous system. These strategies include chemical modification of drugs, disruption of the blood-brain barrier, and utilization of alternative routes for drug delivery. This paper focuses on local drug delivery for the treatment of brain tumors. It reviews papers published in the past year on local chemotherapy and immunotherapy. Other aspects of local drug delivery are discussed, including convection-enhanced delivery and drug delivery via a controlled-release microchip.

Comparison of different methods of intracerebral administration of radioiododeoxyuridine for glioma therapy using a rat model

The Auger electron emitting agent 5-[125I]iodo-2'-deoxyuridine (i.e. [125I]IUdR) holds promise for the treatment of residual glioma after surgery because this thymidine analogue kills only proliferating cells. However, malignant cells which are not synthesizing DNA during exposure to the radiopharmaceutical will be spared. To determine whether tumour incorporation of [125I]IUdR could be enhanced by protracted administration, we used a C6 cell line, growing in the brains of Wistar rats, as a glioma model and compared three methods of intracerebral delivery of [125I]IUdR. Twenty-four hours after administration of drug, autoradiography of brain sections demonstrated nuclear uptake of the radiopharmaceutical in cells throughout tumour while normal brain cells remained free of radioactivity. The [125I]IUdR labelling indices (% +/- s.e.m.) achieved were 6.2 (0.4) by single injection, 22.5 (4.1) using a sustained release polymer implant (poly(lactide-co-glycolide)) and 34.3 (2.0) by mini-osmotic pump. These results emphasize the need for a sustained delivery system as a prerequisite for effective treatment. These findings are also encouraging for the development of a sustained release system for radiolabelled IUdR for use in the treatment of intracranial tumours, particularly in the immediate postoperative setting.

Allogeneic astrocytoma in immune competent dogs

We have induced in canines long-term immune tolerance to an allogeneic cell line derived from a spontaneous canine astrocytoma. Allogeneic astrocytoma cells were implanted endoscopically into the subcutaneous space of fetal dogs before the onset of immune competency (< 40th gestational day). At adulthood, dogs rendered tolerant successfully serve as recipients of intracranial transplants of their growing allogeneic, subcutaneous tumor. Transplanted dogs subsequently develop a solid brain tumor with histological features similar to the original astrocytoma. This model may allow rapid development and evaluation of new therapies for brain tumors, as well as afford tumor biology studies that are untenable in smaller, immune incompetent, or inbred animals harboring less representative tumors.

Comparison of spontaneous and idoxuridine-induced micronuclei by chromosome painting

Fluorescence in situ hybridisation (FISH) technique with chromosome specific library (CSL) DNA probes for all human chromosomes were used to study about 9000 micronuclei (MN) in normal and idoxuridine (IUdR)-treated lymphocyte cultures of female and male donors. In addition, MN rates and structural chromosome aberrations were scored in Giemsa-stained chromosome spreads of these cultures. IUdR treatment (40 microg/ml) induced on the average a 12-fold increase of the MN rate. Metaphase analysis revealed no distinct increase of chromosome breaks but a preferential decondensation at chromosome 9q12 (28-79%) and to a lower extend at 1q12 (8-21%). Application of FISH technique with CSL probes to one male and one female untreated proband showed that all human chromosomes except chromosome 12 (and to a striking high frequency chromosomes 9, X and Y) occurred in spontaneous MN. In cultures containing IUdR, the chromosomal spectrum found in MN was reduced to 10 chromosomes in the male and 13 in the female proband. Eight chromosomes (2, 6, 12, 13, 14, 15, 17 and 18) did not occur in MN of both probands. On the contrary chromosomes 1 and especially 9 were found much more frequently in the MN of IUdR-treated cultures than in MN of control cultures. DAPI-staining revealed heterochromatin signals in most of the IUdR-induced MN. In an additional study, spontaneous and IUdR-induced MN were investigated in lymphocytes of another female donor using CSL probes only for chromosomes 1, 6, 9, 15, 16 and X. The results confirmed the previous finding that chromosomes 1 and 9 occur very often in MN after IUdR-treatment. The results indicate that decondensation of heterochromatic regions on chromosomes 1 and 9 caused by IUdR treatment strongly correlates with MN formation by these chromosomes.

Innovative therapies for pediatric brain tumors

Success in the treatment of pediatric brain tumors has lagged behind that of other pediatric cancers. This paper highlights many of the advances that have taken place over the past few years in the surgical, radiotherapeutic, and chemotherapeutic approaches to central nervous system lesions that we hope will lead to a dramatic improvement in outcome. Innovations in neurosurgical and radiotherapeutic techniques have resulted in decreasing toxicity although substantial improvement in cure rates has not been observed. Many new techniques such as gene therapy, angiogenesis inhibitors, immunotherapy, and others that have not been part of the classic approach to these lesions are now in clinical trials in the hope that they will impact on the survival of these patients. The scientific basis for these new treatment modalities and preliminary clinical results are discussed.

Iodo-2'-deoxyuridine (IUdR) and 125IUdR loaded biodegradable microspheres for controlled delivery to the brain

The aim of this work was to develop sustained local release systems for radioiodinated iodo-2'-deoxyuridine (125IUdR) from biodegradable polymeric microspheres to facilitate the controlled delivery of 125IUdR to brain tumours. The selective uptake of IUdR into the cell nucleus results in cell disruption over the short range of the low energy Auger electrons. The biodegradable microspheres can be precisely implanted in the brain by stereotactic techniques and the IUdR within the microspheres is protected from degradation and thus a sustained source of radiolabelled IUdR is available in the vicinity of the residual tumour cells. Poly(lactic-co-glycolic acid), PLGA (85:15), microspheres containing cold IUdR and the Auger-electron emitter 125I, as 125IUdR were prepared using the O/W, O/O and W/O/W emulsion-solvent evaporation methods. The W/O/W emulsion method was most effective in achieving good drug loading with the use of bovine plasma in the internal water phase. Also effective in improving the drug loading was the use of 20% acetone in the dichloromethane and the presence of Span 40 in the organic phase. Electrolytes (NaCl and IUdR) in the external aqueous phase also improved drug loading. After an initial rapid release from the microspheres, a sustained release was observed over 15 days for the 'cold' IUdR. The sustained release portions of the release curves showed Higuchi (t1/2), diffusion controlled release kinetics. The radiolabelled IUdR microspheres showed a burst release effect of 30-40% followed by a sustained release over 35 days.

Synthetic, implantable polymers for local delivery of IUdR to experimental human malignant glioma

PURPOSE

Recently, polymeric controlled delivery of chemotherapy has been shown to improve survival of patients with malignant glioma. We evaluated whether we could similarly deliver halogenated pyrimidines to experimental intracranial human malignant glioma. To address this issue we studied the in vitro release from polymers and the in vivo drug delivery of IUdR to experimental human U251 glioblastoma xenografts.

METHODS AND MATERIALS

In vitro: To measure release, increasing (10%, 30%, 50%) proportions of IUdR in synthetic [(poly(bis(p-carboxyphenoxy)-propane) (PCPP):sebacic acid (SA) polymer discs were serially incubated in buffered saline and the supernatant fractions were assayed. In vivo: To compare local versus systemic delivery, mice bearing flank xenografts had intratumoral or contralateral flank IUdR polymer (50% loading) treatments. Mice bearing intracranial (i.c.) xenografts had i.c. versus flank IUdR polymer treatments. Four or 8 days after implantation of polymers, mice were sacrificed and the percentage tumor cells that were labeled with IUdR was measured using quantitative microscopic immunohistochemistry.

RESULTS

In vitro: Increasing percentage loadings of IUdR resulted in higher percentages of release: 43.7 + 0.1, 70.0 + 0.2, and 90.2 + 0.2 (p < 0.001 ANOVA) for the 10%, 30%, and 50% loadings, respectively. In vivo: For the flank tumors, both the ipsilateral and contralateral IUdR polymers resulted in similarly high percentages labeling of the tumors versus time. For the ipsilateral IUdR polymers, the percentage of tumor cellular labeling after 4 days versus 8 days was 45.8 +/- 7.0 versus 40.6 +/- 3.9 (p = NS). For the contralateral polymer implants, the percentage of tumor cellular labeling were 43.9 +/- 10.1 versus 35.9 +/- 5.2 (p = NS) measured 4 days versus 8 days after implantation. For the i.c. tumors treated with extracranial IUdR polymers, the percentage of tumor cellular labeling was low: 13.9 +/- 8.8 and 11.2 +/- 5.7 measured 4 and 8 days after implantation. For the i.c. tumors having the i.c. IUdR polymers, however, the percentage labeling was comparatively much higher: 34.3 +/- 4.9 and 35.3 +/- 4.0 on days 4 and 8, respectively. For the i.c. tumors, examination of the percentage cellular labeling versus distance from the implanted IUdR polymer showed that labeling was highest closest to the polymer disc.

CONCLUSION

Synthetic, implantable biodegradable polymers provide the local, controlled release of IUdR and result in the high, local delivery of IUdR to experimental intracranial human malignant glioma. This technique holds promise for the local delivery of IUdR for radiosensitization of human brain tumors.