In vitro radiosensitivity of human medulloblastoma cell lines

Treatment of medulloblastoma using an oncolytic measles virus encoding the thyroidal sodium iodide symporter shows enhanced efficacy with radioiodine

Background

Medulloblastoma is the most common malignant brain tumor of childhood. Although the clinical outcome for medulloblastoma patients has improved significantly, children afflicted with the disease frequently suffer from debilitating side effects related to the aggressive nature of currently available therapy. Alternative means for treating medulloblastoma are desperately needed. We have previously shown that oncolytic measles virus (MV) can selectively target and destroy medulloblastoma tumor cells in localized and disseminated models of the disease. MV-NIS, an oncolytic measles virus that encodes the human thyroidal sodium iodide symporter (NIS), has the potential to deliver targeted radiotherapy to the tumor site and promote a localized bystander effect above and beyond that achieved by MV alone.

Methods

We evaluated the efficacy of MV-NIS against medulloblastoma cells in vitro and examined their ability to incorporate radioiodine at various timepoints, finding peak uptake at 48 hours post infection. The effects of MV-NIS were also evaluated in mouse xenograft models of localized and disseminated medulloblastoma. Athymic nude mice were injected with D283med-Luc medulloblastoma cells in the caudate putamen (localized disease) or right lateral ventricle (disseminated disease) and subsequently treated with MV-NIS. Subsets of these mice were given a dose of ¹³¹I at 24, 48 or 72 hours later.

Results

MV-NIS treatment, both by itself and in combination with ¹³¹I, elicited tumor stabilization and regression in the treated mice and significantly extended their survival times. Mice given ¹³¹I were found to concentrate radioiodine at the site of their tumor implantations. In addition, mice with localized tumors that were given ¹³¹I either 24 or 48 hours after MV-NIS treatment exhibited a significant survival advantage over mice given MV-NIS alone.

Conclusions

These data suggest MV-NIS plus radioiodine may be a potentially useful therapy for the treatment of medulloblastoma.

Effects of surgical excision and radiation on medulloblastoma cell invasiveness

OBJECTIVES

Surgical resection and adjuvant radiation are mainstays of medulloblastoma (MB) patient management. We utilized a novel 3-dimensional assay to identify how (a) radiation, (b) excision of the primary tumour aggregate, and (c) both treatments combined influence MB cell invasiveness.

METHODS

Five MB cell lines (UW228-1, 2 and 3; Daoy, and Madsen) were implanted onto a 3-dimensional, type I collagen gel assay to assess tumour invasion distance over five days, in response to (1) needle-assisted excision of the central cell aggregate; (2) pre-exposure to single-dose and fractionated dose irradiation in doses from 6-25 and 8-24 Gy, respectively; and (3) excision plus either single-dose or fractionated radiation.

RESULTS

Within hours, individual MB cells detached from the surface of the cell aggregates and invaded the collagen matrix, to distances up to 1200 microm and at rates up to 300 microm daily. The UW228-1 cell line was less invasive than the other cell lines and was dropped from further analysis. In the four remaining lines, a dose-dependent decline in tumour invasiveness was identified, both for single-dose and fractionated radiation, which achieved statistically decreased invasion distances at higher doses, especially of fractionated irradiation. Excision of the central tumour aggregate tended towards exerting a late effect on cell invasion, but exerted no significant influence on the radio-sensitivity of residual cells.

CONCLUSIONS

Both single-dose and fractionated dose irradiation appear to inhibit MB cell invasiveness in a dose-dependent manner, whereas excision of the central cell aggregate exerts no effect on residual invading cells.

Correlation of 3D-planned and measured dosimetry of photon and electron craniospinal radiation in a pediatric anthropomorphic phantom

BACKGROUND AND PURPOSE

Improved radiotherapy techniques in pediatric craniospinal therapy (CSRT) strive to reduce risks of late morbidity. Using a pediatric anthropomorphic phantom, this research correlated measured target and normal tissue dose to that predicted from a 3D planning system (3D-RTP).

PATIENTS AND METHODS

A pediatric anthropomorphic phantom was planned following French Society of Pediatric Oncology (SFOP) protocols. Thermoluminescent detectors (TLDs) were used to perform dosimetric measurements during treatment. 4 and 6MV photon fields with multi leaf collimation (MLC) or custom blocks were compared to 3D-RTP computer (ADAC Pinnacle) predictions for cranial fields. Spinal dosimetry was studied using photons (4 and 6MV) and electrons (9 and 12MeV).

RESULTS

3D-RTP predictions generally concurred with dose received in cranial and spinal sites. The measured dose was over-predicted significantly by the 3D-RTP in the anterior cranial fossa. Normal tissue doses were reduced when treating the spine using megavoltage electron beams instead of photons.

CONCLUSIONS

Treating the spinal field with electrons minimises the risk of pulmonary sequelae, however electron energy selection is critical to achieve adequate spinal field coverage. Despite adhering to a major trial protocol guideline, dose at the floor of the anterior cranial fossa remains a potential clinical problem and 3D-RTP do not predict this well.

Radiosensitive human tumour cell lines show misrepair of DNA termini

Physical measures of the rejoining of radiation-induced breaks in DNA strands are limited in terms of sensitivity and the fact that they do not assess the fidelity with which the rejoining occurs. In this report, transfection of cleaved plasmid has been used as a probe for repair in three radiosensitive tumour cell lines and shown them to have low repair fidelity compared with resistant cells. Errors in the repair of linear plasmid were found by Southern analysis, in keeping with the measured repair fidelity. Radiosensitive tumour cells showed few errors in the uptake and integration of circular plasmid, in contrast to ataxia-telangiectasia (A-T) cells. In the neuroblastoma HX142, the repair of blunt-ended linear plasmid was associated with deletions of > 1 kb; staggered-ended linear plasmid was repaired with small insertions and circular plasmid integration was intact in > 60% of the copies. The neuroblastoma SKN.SH, processed staggered-ended plasmid by insertions of a variety of sizes, but processed circular plasmid largely error-free. In contrast, A-T cells (AT5BIVA) had the same spectrum of errors irrespective of the form of plasmid transfected. Cell fusion between HX142 and AT5BIVA showed complementation to a resistant phenotype, suggesting that misrepair in the tumour cell did not result from somatic mutation in the ATM gene. In conclusion, radiosensitive tumours show evidence of misrepair of DNA termini, with a mechanism which is functionally and genetically distinct from that in A-T cells.

Impact of radiation technique upon the outcome of treatment for medulloblastoma

Craniospinal irradiation (CSI) is an essential component of the therapy of medulloblastoma. Because medulloblastoma disseminates via the cerebrospinal fluid (CSF), CSI technique involves the irradiation of all CSF-bearing areas which are at risk for tumor seeding. Underdosing with radiation because of inadequacies in CSI technique will produce dose "cold spots" which have the potential of serving as a nidus for tumor recurrence. A simple mathematic model of subclinical disease in medulloblastoma based on the available data concerning the radiosensitivity of medulloblastoma cell lines as well as the known clinical dose-response relationships support the hypothesis that for most cases of medulloblastoma, the radiotherapist is working in a range of doses arrayed on the steep portion of the tumor control probability curve. Underdosing of CSF-bearing areas because of technical problems at the junction of the cranial and spinal fields of irradiation, placement of shielding blocks in the cribiform plate-subfrontal region, and/or anatomic errors in the design of the caudal end of the CSI fields may lead to significant risks of tumor relapse. One may debate the necessity of a posterior fossa boost encompassing the entire anatomic posterior fossa rather than the primary tumor volume with a margin. This review critically evaluates the potential impact of CSI technique upon the outcome of treatment for medulloblastoma, and suggests future areas of inquiry.

Fabrication and testing of a device capable of reducing the incidence of ventricular shunt promoted metastasis

PURPOSE/OBJECTIVE

Some malignant brain tumors shed cells into the cerebrospinal fluid (CSF). These tumors may implant throughout the neuroaxis via the CSF. With the placement of a ventriculoperitoneal (VP) or ventriculoatrial (VA) shunt, tumor cells free-floating in the CSF may be carried through the shunt to the remainder of the body. Mechanical filtration devices to prevent this are not reliable. We report the development of a new device capable of reducing the incidence of shunt promoted metastasis.

MATERIALS & METHODS

The device exposes the draining CSF, as it passes through a baffle system, to a localized high-intensity radiation field adequately shielded from surrounding normal tissue. The prototype consists of geometrically fixed iodine-125 (125I) sources. The device accommodates the maximum CSF flow rate of 500 ml/24 hours. Radiation exposure to clonogenic cells occurs as they transit through the baffle system. Since the volume of the prototype device is 14 ml, a tumor cell floating through the device will be exposed to radiation for 40 minutes. Utilizing the human medulloblastoma cell line D425 MED, a limiting dilution clonogenic assay was performed. Suspensions of tumor cells in liquid medium were pumped through the device at the maximum anticipated CSF production rate of 0.35 ml/min. After the cells, with their tissue culture medium, were received from the device, a series of nine 5-fold dilutions were prepared from the suspensions which initially contained 10(6) tumor cell/ml. Plates were then incubated and growth was demonstrated by visual scoring of colonies of more than 20 cells. Limiting dilution data analysis was performed. Radiation surveys of the fully loaded (approximately 1.8 Ci) 125I prototype were conducted. A well calibrator was used to measure the activity of the fully loaded device.

RESULTS

When the device was loaded with 125I seeds providing a dose of 364-479 cGy the probability of clonogen survival was 0.033. Radiation exposure levels at the exterior surface of the shielded device were in the range of 2-5 mR/hr and thus fell within guidelines for acceptable normal tissue exposure. Attenuation of radiation by the shielding case for the fully loaded device was 10(-5).

CONCLUSION

The device kills medulloblastoma cells as they are pumped through it. If the risk of metastasis is linearly related to the number of clonogenic cells, then the device would, we infer, reduce the risk of shunt-born metastasis by a factor of 0.033 and merits further investigation.

Intrinsic and extrinsic characteristics of human tumors relevant to radiosurgery: comparative cellular radiosensitivity and hypoxic percentages

We have collected the in vitro x-ray radiation survival characteristics of 181 lines from 12 different classes of exponentially growing human tumor cells (sarcomas, lung cancers, colo-rectal cancers, medulloblastomas, melanoma, breast cancers, prostate cancers, renal cell cancers, grades III and IV brain tumors, ovarian, and head and neck cancers). This information was used to intercompare survival after single high doses of 20-40 Gy for each tumor line. Radiosensitivities could roughly be divided into two groups. The more radiosensitive group included: sarcoma, small-cell lung cancer, non-small cell lung cancer, colorectal cancer, medulloblastoma and melanoma. The more radioresistant group included breast, prostate, renal cell, primary brain tumors, ovarian tumors, and head and neck cancers. Using a model of a 3 cm diameter brain lesion containing about 1.4 x 10(9) oxic cells, the single doses calculated to reduce survival to 1 cell were: sarcoma and small cell lung cancers-22-23 Gy; melanoma-25 Gy; non-small cell lung and colorectal cancer-26 Gy; medullo-blastoma-28 Gy; breast, prostate, renal cell, primary brain tumors, ovarian tumors, and head and neck cancers-30-36 Gy. If, however, tumors contained on average 20 percent hypoxic cells, the dose needed for equivalent cell killing increased by about a factor of 2.6-2.8. Also, there was no correlation between the ranking of relative radiosensitivities of the various classes of tumor cells at high doses (as in radiosurgery) to the sensitivity at low doses (as in conventional fractionated radiotherapy).

CONCLUSION

available information on the intrinsic radiosensitivity of human tumor cells indicates that meaningful differences exist among different histological classes of neoplasm that are relevant to the single high doses used in radioneurosurgery, and which could constitute a basis for "tailoring" the administered dose to the particular neoplasm. However, if intracerebral lesions contain a large number of hypoxic cells (e.g., 20%), this may constitute a significant problem.