Primary postoperative chemotherapy without radiotherapy for intracranial ependymoma in children: the UKCCSG/SIOP prospective study

BACKGROUND

Over half of childhood intracranial ependymomas occur in children younger than 5 years. As an adjuvant treatment, radiotherapy can be effective, but has the potential to damage the child's developing nervous system at a crucial time-with a resultant reduction in IQ and cognitive impairment, endocrinopathy, and risk of second malignancy. We aimed to assess the role of a primary chemotherapy strategy in avoiding or delaying radiotherapy in children younger than 3 years with intracranial ependymoma.

METHODS

Between December, 1992, and April, 2003, we enrolled 89 children with ependymoma who were aged 3 years or younger at diagnosis, of whom nine had metastatic disease on pre-operative imaging. After maximal surgical resection, children received alternating blocks of myelosuppressive and non-myelosuppressive chemotherapy every 14 days for an intended duration of 1 year. Radiotherapy was withheld unless local imaging (ie, from the child's treatment centre) showed progressive disease.

FINDINGS

50 of the 80 patients with non-metastatic disease progressed, 34 of whom were irradiated for progression. The 5-year cumulative incidence of freedom from radiotherapy for the 80 non-metastatic patients was 42% (95% CI 32-53). With a median follow-up of 6 years (range 1.5-11.3), overall survival for the non-metastatic patients at 3 years was 79.3% (95% CI 68.5-86.8) and at 5 years 63.4% (51.2-73.4). The corresponding values for event-free survival were 47.6% (36.2-58.1) and 41.8% (30.7-52.6). There was no significant difference in event-free or overall survival between complete and incomplete surgical resection, nor did survival differ according to histological grade, age at diagnosis, or site of disease. In 47 of 59 (80%) patients who progressed, relapse resulted from local control only. The median time to progression for the 59 patients who progressed was 1.6 years (range 0.1-10.2 years). The median age at irradiation of the whole group was 3.6 years (range 1.5-11.9). For the 80 non-metastatic patients, the 23 who achieved the highest relative dose intensity of chemotherapy had the highest post-chemotherapy 5-year overall survival of 76% (95% CI 46.6-91.2), compared with 52% (33.3-68.1) for the 32 patients who achieved the lowest relative dose intensity of chemotherapy.

INTERPRETATION

This protocol avoided or delayed radiotherapy in a substantial proportion of children younger than 3 years without compromising survival. These results suggest, therefore, that primary chemotherapy strategies have an important role in the treatment of very young children with intracranial ependymoma.

Analysis of patients with supratentorial primitive neuro-ectodermal tumours entered into the SIOP/UKCCSG PNET 3 study

The SIOP PNET 3 study was designed to determine whether 10 weeks of moderately intensive chemotherapy given after surgery and before radiotherapy (RT) would improve the outcome for patients with primitive neuroectodermal tumours (PNETs) compared with RT alone. Patients with a histological diagnosis of supratentorial PNET (StPNET) and no radiological evidence of metastatic disease were initially eligible for randomisation to either chemotherapy followed by craniospinal RT 35 Gy in 21 fractions with a boost of 20 Gy in 12 fractions to the primary site, or RT alone. In respect of the increasing recognition that StPNET were high-risk tumours, randomisation for this group closed in November 1999. This analysis includes both randomised and non-randomised patients with StPNET entered into the study database. Sixty-eight patients aged 2.9-16.6 years (median 6.5 years) were included in the analysis (chemotherapy+RT: 44, RT alone: 24). Fifty-four patients (79%) had a non-pineal and 14 (21%) a pineal site. At a median follow-up of 7.4 years, for all patients overall survival (OS) at 3 and 5 years was 54.4% and 48.3%, respectively. Event-free survival (EFS) at 3 and 5 years was 50.0% and 47.0%, respectively. There was no statistically significant difference in OS or EFS according to treatment received. OS (P=0.05) and EFS (P=0.03) were significantly better for patients with pineal primary sites. EFS for pineal tumours were 92.9% at 3 years and 71.4% at 5 years and for non-pineal primaries 40.7% at 3 years and 40.7% at 5 years. This study confirmed the relatively good survival for non-metastatic pineal PNETs but poor survival of non-pineal StPNETs. There was no evidence that pre-radiation chemotherapy improved outlook. Future treatment programs should be directed at the particular natural history of these tumours, to further define prognostic factors and to explore further biological characteristics.

Outcome for patients with metastatic (M2–3) medulloblastoma treated with SIOP/UKCCSG PNET-3 chemotherapy

The aim of this study was to determine the outcome for patients with Chang stage M2-3 medulloblastoma (MB) treated with surgery and pre-radiotherapy (RT) chemotherapy (CT). Between 1992 and 2000, 68 patients aged 2.8-16.4 years (median 7.8 years) with M2-3 MB were treated with CT comprising vincristine, etoposide, carboplatin and cyclophosphamide. For 61 patients, CT was followed by craniospinal RT 35 Gy/21 fractions with a posterior fossa (PF) boost, 20 Gy/12 fractions. Twenty-four (35%) irradiated patients received a metastatic boost (mean dose to metastases 47.4 Gy, range 40.0-55.1 Gy). With 7.2-years of median follow-up, overall survival (OS) rates at 3 and 5 years were 50.0% (95% Confidence Interval (CI): 38.1-61.9%) and 43.9% (95% CI: 32.0-55.7%), respectively, event-free survival (EFS) rates at 3 and 5 years were 39.7% (95% CI: 28.1-51.3%) and 34.7% (95% CI: 23.2-46.2%), respectively. Univariate analysis did not demonstrate an impact of age, gender, M stage, extent of resection, RT duration or metastatic boost. For patients commencing RT within 110 days of surgery, EFS was significantly (P=0.04) worse than for those who commenced RT later than this. Response to pre-RT CT was assessable from institutional reports for 44 (65%) patients, and 17 (39%) had a complete response (CR), 15 (34%) a partial response (PR), 4 (9%) stable disease (SD) and 8 (18%) progression. Although CT improved outcome for M0-1 patients in the primitive neuroectodermal tumour (PNET-3) randomised study, and resulted in a high response rate in this study, there has been no apparent improvement in outcome for M2-3 patients when compared with earlier multi-institutional series. Newer approaches such as more intensive CT and RT need to be explored.

Impact of radiotherapy parameters on outcome in the International Society of Paediatric Oncology/United Kingdom Children's Cancer Study Group PNET-3 study of preradiotherapy chemotherapy for M0-M1 medulloblastoma

PURPOSE

To analyze the impact of radiotherapy (RT) parameters on outcome in a randomized study of pre-RT chemotherapy for M0-M1 medulloblastoma.

METHODS AND MATERIALS

Patients were randomized to RT alone or RT preceded by chemotherapy with vincristine, etoposide, carboplatin, and cyclophosphamide. RT consisted of craniospinal RT, 35 Gy in 21 fractions, followed by a posterior fossa (PF) boost of 20 Gy in 12 fractions. The accuracy of cribriform fossa, skull base, and PF field placement was assessed.

RESULTS

Between 1992 and 2000, 217 patients were randomized, of whom 179 were eligible for analysis. At a median follow-up of 5.4 years, the 3- and 5-year overall survival rate was 79.5% and 70.7%, respectively. The 3- and 5-year event-free survival (EFS) rate was 71.6% and 67.0%, respectively. EFS was significantly better for the chemotherapy plus RT group (3-year EFS rate 78.5% vs. 64.8%, p = 0.0366). Overall survival and EFS were significantly better for patients completing RT within 50 days compared with those taking >50 days to complete RT (3-year overall survival rate 84.1% vs. 70.9%, p = 0.0356, 3-year EFS rate 78.5% vs. 53.7%, p = 0.0092). Multivariate analysis identified the use of chemotherapy (p = 0.0248) and RT duration (p = 0.0100) as predictive of better EFS. Planning films were reviewed for 131 (74.4%) of 176 patients. Sixty-five (49.6%) had no targeting deviations and 58 (44.3%) had one or more deviations. PF recurrence occurred in 11 (34.4%) of 32 with a PF targeting deviation compared with 13 (16.3%) of 80 without (p = 0.043). No statistically significant impact of other targeting deviations on recurrence risk or EFS were found.

CONCLUSION

The results of this study have confirmed the importance of the duration of RT for medulloblastoma. Also, attention to detail when planning RT is important, as illustrated in the case of PF field placement.

Results of a randomized study of preradiation chemotherapy versus radiotherapy alone for nonmetastatic medulloblastoma: The International Society of Paediatric Oncology/United Kingdom Children's Cancer Study Group PNET-3 Study

PURPOSE

To determine whether preradiotherapy (RT) chemotherapy would improve outcome for Chang stage M0-1 medulloblastoma when compared with RT alone. Chemotherapy comprised vincristine 1.5 mg/m2 weekly for 10 weeks and four cycles of etoposide 100 mg/m2 daily for 3 days, and carboplatin 500 mg/m2 daily for 2 days alternating with cyclophosphamide 1.5 g/m2.

PATIENTS AND METHODS

Patients aged 3 to 16 years inclusive were randomly assigned to receive 35 Gy craniospinal RT with a 20 Gy posterior fossa boost, or chemotherapy followed by RT.

RESULTS

Of 217 patients randomly assigned to treatment, 179 were eligible for analysis (chemotherapy + RT, 90 patients; RT alone, 89 patients). Median age was 7.67 years, and median follow-up was 5.40 years. Overall survival (OS) at 3 and 5 years was 79.5% and 70.7%, respectively. Event-free survival (EFS) at 3 and 5 years was 71.6% and 67.0%, respectively. EFS was significantly better for chemotherapy and RT (P =.0366), with EFS of 78.5% at 3 years and 74.2% at 5 years compared with 64.8% at 3 years and 59.8% at 5 years for RT alone. There was no statistically significant difference in 3-year and 5-year OS between the two arms (P =.0928). Multivariate analysis identified use of chemotherapy (P =.0248) and time to complete RT (P =.0100) as having significant effect on EFS.

CONCLUSION

This is the first large multicenter randomized study to demonstrate improved EFS for chemotherapy compared with RT alone. It is anticipated that this regimen could reduce ototoxicity and nephrotoxicity compared with cisplatin-containing schedules. The importance of avoiding interruptions to RT has been confirmed.

Temozolomide in malignant gliomas of childhood: a United Kingdom Children's Cancer Study Group and French Society for Pediatric Oncology Intergroup Study

PURPOSE

To determine the response rate of the malignant gliomas of childhood to an oral, daily schedule of temozolomide.

PATIENTS AND METHODS

A multicenter, phase II evaluation of an oral, daily schedule of temozolomide (200 mg/m(2) on 5 consecutive days) was undertaken in children with relapsed or progressive, biopsy-proven, high-grade glioma (arm A) and progressive, diffuse, intrinsic brainstem glioma (arm B). Evidence of activity was defined by radiologic evidence of a sustained reduction in tumor size on serial magnetic resonance imaging scans.

RESULTS

Fifty-five patients were recruited (34 to arm A and 21 to arm B) and received 215 cycles of chemotherapy. Grade 3/4 thrombocytopenia was the most frequent toxic event (7% of cycles). Prolonged myelosuppression resulted in significant treatment delays and dose reductions (17% and 22% of cycles, respectively). Two toxic deaths were documented and were related to myelosuppression and sepsis in one patient and pneumonia in a second. The overall (best) response rate was 12% for arm A (95% confidence interval [CI], 3 to 28 in the study cohort, and 2 to 31 for eligible patients) and 5% and 6%, respectively, for arm B (95% CI, 0 to 26 in the study cohort, and 0 to 27 for eligible patients). Stabilization of disease was also documented and was most noteworthy for brainstem gliomas, where two patients achieved both radiologic static disease and discontinued steroid medication.

CONCLUSION

Despite moderate toxicity, objective response rates to temozolomide have been low, indicating that temozolomide has minimal activity in the high-grade gliomas of childhood.

Assays to predict the genotoxicity of the chromosomal mutagen etoposide -- focussing on the best assay

The topoisomerase II inhibitor etoposide is used routinely to treat a variety of cancers in patients of all ages. As a result of its extensive use in the clinic and its association with secondary malignancies it has become a compound of great interest with regard to its genotoxic activity in vivo. This paper describes a series of assays that were employed to determine the in vivo genotoxicity of etoposide in a murine model system. The alkaline comet assay detected DNA damage in the bone marrow mononuclear compartment over the dose range of 10--100mg/kg and was associated with a large and dose dependent rise in the proportion of cells with severely damaged DNA. In contrast, the bone marrow micronucleus assay was found to be sensitive to genotoxic damage between the doses of 0.1--1mg/kg without any corresponding increases in cytotoxicity. An increase in the mutant frequency was undetectable at the Hprt locus at administered doses of 1 and 10mg/kg of etoposide, however, an increase in the mutant frequency was seen at the Aprt locus at these doses. We conclude that the BMMN assay is a good short-term predictor of the clastogenicity of etoposide at doses that do not result in cytotoxic activity, giving an indication of potential mutagenic effects. Moreover, the detection of mutants at the Aprt locus gives an indication of the potential of etoposide to cause chromosomal mutations that may lead to secondary malignancy.

The effects of dose, route of administration, drug scheduling and MDR-1 gene transfer on the genotoxicity of etoposide in bone marrow

We have used the bone marrow micronucleus assay (BMMN) as a measure of clastogenicity, in response to etoposide exposure in murine bone marrow. Oral delivery of etoposide resulted in a reduced number of micronucleated polychromatic erythrocytes (MPE) relative to the same dose delivered intraperitoneally (P < 0.001). Daily fractionation of the oral schedule of etoposide led to a more than six-fold increase in cumulative MPE frequency over that observed with the same total, unfractionated dose, with the potency of the response increasing with serial exposure (r = 0.79). Retrovirally-mediated expression of MDR1 in murine bone marrow resulted in partial protection against the clastogenic activity of etoposide relative to mock transduced control mice. The model system developed has indicated a variety of factors able to influence the genotoxicity of etoposide. It should now be possible to further exploit this model in order to define other factors governing haemopoietic sensitivity to etoposide.

A radiation-controlled molecular switch for use in gene therapy of cancer

Ionising radiation induces the expression of a number of radiation-responsive genes and there is current interest in exploiting this to regulate the expression of exogenous therapeutic genes in gene therapy strategies for cancer. However, the radiation-responsive promoters used in these approaches are often associated with low and transient levels of therapeutic gene expression. We describe here a novel radiation-triggered molecular switching device based on promoter elements from the radiation-responsive Egr-1 gene and the cre-LoxP site-specific recombination system of the P1 bacteriophage. Using this system, a single, minimally toxic dose of radiation induced cre-mediated excision of a lox-P flanked stop cassette in a silenced expression vector and this resulted in amplified levels of CMV-promoter-driven expression of the exogenous tumour-sensitising gene, HSV-tk. This strategy could be used in combination with targeted delivery and tumour-specific promoters to elicit the tumour-targeted and prolonged expression of a variety of tumour-sensitising genes and provide an unprecedented level of control and tumour selectivity.

The expression of full length Gp91-phox protein is associated with reduced amphotropic retroviral production

BACKGROUND AND OBJECTIVE

As a single gene defect in mature bone marrow cells, chronic granulomatous disease (X-CGD) represents a disorder which may be amenable to gene therapy by the transfer of the missing subunit into hemopoietic stem cells. In the majority of cases lack of Gp91-phox causes the disease. So far, studies involving transfer of Gp91-phox cDNA, including a phase I clinical trial, have yielded disappointing results. Most often, low titers of virus have been reported. In the present study we investigated the possible reasons for low titer amphotropic viral production.

DESIGN AND METHODS

To investigate the effect of Gp91 cDNA on the efficiency of retroviral production from the packaging cell line, GP+envAm12, we constructed vectors containing either the native cDNA, truncated versions of the cDNA or a mutated form (LATG) in which the natural translational start codon was changed to a stop codon. Following derivation of clonal packaging cell lines, these were assessed for viral titer by RNA slot blot and analyzed by non-parametrical statistical analysis (Whitney-Mann U-test).

RESULTS

An improvement in viral titer of just over two-fold was found in packaging cells containing the start-codon mutant of Gp91 and no evidence of truncated viral RNA was seen in these cells. Further analysis revealed the presence of rearranged forms of the provirus in Gp91-expressing cells, and the production of truncated, unpackaged viral RNA. Protein analysis revealed that LATG-transduced cells did not express full-length Gp91-phox, whereas those containing the wild-type cDNA did. However, a truncated protein was seen in ATG-transduced cells which was also present in wild type cells. No evidence for the presence of a negative transcriptional regulatory element was found from studies with the deletion mutants.

INTERPRETATION AND CONCLUSIONS

A statistically significant effect of protein production on the production of virus from Gp91-expressing cells was found. Our data point to a need to restrict expression of the Gp91-phox protein and its derivatives in order to enhance retroviral production and suggest that improvements in current vectors for CGD gene therapy may need to include controlled, directed expression only in mature neutrophils.

Engineering drug resistance in human cells

Many of the problems with current anti-tumour therapies stem from a lack of specificity for tumour as opposed to normal tissues. To address the problem of collateral toxicity during anti-tumour chemotherapy we have been developing a gene therapy approach to protect normal tissues from the toxic and potentially mutagenic effects of chemotherapeutic agents. As a paradigm for this we have been examining the potential of the DNA repair protein O6-alkylguanine-DNA-alkyltransferase (ATase) to confer genetic chemoprotection to the bone marrow. By transfer and expression of a mutant form of this protein, which is resistant to inactivation by the tumour sensitising agent O6-benzylguanine (O6-beG), we have been able to demonstrate protection of murine bone marrow in vitro from the cytotoxic and clastogenic effects of O6-beG in combination with the anti-tumour agent temozolomide. This protection is seen in multiple lineages, including erythroid and granulocyte/macrophage progenitors, as well as more primitive cells. Importantly, significant protection of the platelet lineage is also seen, with faster recovery of platelets. The multi-lineage protection seen has encouraged us to take this approach forward to clinical trial in the near future.

Development of synthetic promoters for radiation-mediated gene therapy

Exposure of cells to ionising radiation results in the activation of specific transcriptional control (CArG) elements within the early growth response 1 (Egr1) gene promoter, leading to increased gene expression. As part of a study investigating the potential use of these elements in radiation-controlled gene therapy vectors, we have incorporated their sequences into a synthetic gene promoter and assayed for the ability to induce expression of a downstream reporter gene following irradiation. In vector-transfected MCF-7 breast adenocarcinoma cells, the synthetic promoter was more effective than the wild-type Egr1 counterpart in up-regulating expression of the reporter gene after exposure to a single 5 Gy dose, and equally effective as the wild-type in U87-MG glioma cells. The level of gene expression achieved using the synthetic promoter was dependent on the inducing radiation dose for both U87-MG and MCF-7 cells, being maximal at 3 Gy and decreasing at 5 and 10 Gy. Furthermore, induction could be repeated by additional radiation treatments. The latter indicates that up-regulation should be additive during fractionated radiotherapy schedules. To demonstrate the potential clinical benefit of such an approach, the synthetic promoters were also shown to drive expression of the herpes simplex virus thymidine kinase gene, leading to enhanced cell killing in the presence of the prodrug ganciclovir (GCV) when compared with cells treated with radiation alone. Our results demonstrate that the synthetic promoter is responsive to low doses of ionising radiation and therefore isolated CArG elements function as radiation-mediated transcriptional enhancers outside their normal sequence context. The continued development and optimisation of such radiation-responsive synthetic promoters is expected to make a valuable contribution to the development of future radiation-responsive vectors for cancer gene therapy.

Enhancing hemopoietic drug resistance: a rationale for reconsidering the clinical use of mitozolomide

Retroviral gene transfer was used to achieve expression in mouse bone marrow of a mutant form of the DNA repair protein O6-alkylguanine-DNA alkyltransferase (hATPA/GA), which exhibits resistance to inactivation by O6-benzylguanine (O6-beG). After reconstitution of mice with transduced bone marrow, approximately 50% of the bipotent granulocyte-macrophage colony-forming cell (GM-CFC) and multipotent spleen colony-forming unit (CFU-S) hemopoietic populations showed expression of the transgene; this expression was associated with resistance to either mitozolomide or to a combination of O6-beG and mitozolomide, relative to mock-transduced controls. Thus, at a dose of mitozolomide in vivo that allowed only 70% and 62% survival of mock-transduced GM-CFC and CFU-S, respectively, the hATPA/GA CFC were totally resistant to the same dose of mitozolomide (P < .05 and .001, respectively). In the presence of O6-beG, the toxicity of mitozolomide was greatly potentiated. Only 24% and 18%, respectively, of mock-transduced GM-CFC and CFU-S survived combination treatment, whereas 45% (P < .05) and 37% (P < .01) of GM-CFC and CFU-S, respectively, from hATPA/GA mice survived the same combination of doses. Furthermore, as a result of transgene expression, the number of micronucleated polychromatic erythrocytes induced by mitozolomide was significantly reduced (P < .05) by 40% relative to mock-transduced controls, indicating the potential of this approach to reduce the frequency of mutation associated with chemotherapy exposure. The protection against the toxic and clastogenic effects of mitozolomide in both primitive and more mature hemopoietic cells suggests that the severe myelosuppression that halted further clinical investigation of this drug could be substantially ameliorated by the exogenous expression of O6-alkylguanine-DNA alkyltransferase. Therefore, these data raise the prospect for the reinvestigation of mitozolomide and other proscribed drugs in the context of genetically protected hemopoiesis.

Leptomeningeal melanoma in childhood

BACKGROUND

Malignant melanoma (MM) is one of the least common types of childhood cancer, accounting for less than 1% of all pediatric malignancies. Neurocutaneous melanosis (NCM) is a rare phakomatosis consisting of congenital abnormal pigmentation of the skin and meninges. The meningeal lesions are particularly prone to malignant change.

METHODS

The authors describe 5 patients with NCM and 1 with primary leptomeningeal melanoma (LMM) seen at 2 treatment centers in the north of England over a 13-year period (1984-1997).

RESULTS

The clinical features, progress, radiological findings, and treatment of these patients are discussed. All six died within eight months of their diagnosis, illustrating the difficulties faced in treating patients with these conditions. The authors reviewed the published literature on NCM, concentrating on the various therapeutic strategies that have been tried. Very little consistency in approach was found. Malignant skin lesions in NCM may be less responsive than primary malignant melanoma, but the small number of patients with primary LMM or brain metastases of MM make comparisons with NCM difficult. The authors' own series illustrates well the piecemeal nature of therapy for patients with these rare conditions.

CONCLUSIONS

The rate of incidence of MM melanoma in the U.K. is increasing, and it will represent an increasing proportion of the pediatric oncologist's workload. A consistent approach to the therapy of patients with metastatic MM and NCM is needed if we are to have any hope of offering more than palliative therapy to these children in the future.

New perspectives for cancer chemotherapy by genetic protection of haematopoietic cells

The effectiveness of anti-cancer chemotherapy can be limited by acute suppression of the bone marrow (myelosuppression). There is also a risk of therapy-related secondary haematopoietic malignancy as well as acute and longer term effects in other tissues. Clinical strategies have been established to address some of these problems, particularly toxic effects on the bone marrow (acute myelotoxicity); however, there is still substantial scope for improving the management of chronic toxicity and mutagenicity to haematopoietic cells and collateral damage to non-haematopoietic cells during chemotherapy. In this review, we have discussed a novel strategy that involves the transfer and expression of drug-resistance functions into haematopoietic stem cells and more-mature blood progenitor cells, to overcome both the acute and long-term deleterious effects of anti-tumour treatment in bone marrow. The potential advantages of this approach include: (1) the in vivo selection of protected cell populations, which offers the possibility of intensification or escalation of chemotherapeutic drug doses; (2) a reduction in the frequency of therapy-related leukaemia and (3) tumour sensitisation to chemotherapy at the same time as haematopoietic protection.

A novel dual function retrovirus expressing multidrug resistance 1 and O6-alkylguanine-DNA-alkyltransferase for engineering resistance of haemopoietic progenitor cells to multiple chemotherapeutic agents

Following transduction with a retrovirus (SF1MIH) expressing both the multidrug resistance 1 (MDR1) and O6-alkylguanine-DNA-alkyltransferase (ATase) proteins, human erythroleukaemic progenitor (K562) cells were isolated which were resistant to killing by the MDR1 substrate, colchicine. In colony-forming survival assays, K562-SF1MIH cells exhibited resistance to colchicine and doxorubicin, as well as to the O6-alkylating agents N-Methyl-N-nitrosourea (MNU) and temozolomide. Furthermore, the resistance to doxorubicin was abolished by preincubation with the MDR1 inhibitor verapamil while resistance to MNU was ablated by the specific ATase inactivator, O6-benzylguanine (O6-beG) confirming that resistance to doxorubicin and MNU was conferred by MDR1 and ATase, respectively. When K562-SF1MIH were exposed to combinations of colchicine and MNU or doxorubicin and temozolomide, simultaneous resistance to these agents was observed. Thus, transduction of K562 with SF1MIH conferred dual resistance to these cells. These data offer the prospect of designing vectors that will confer resistance to entire regimens of chemotherapy rather than just to individual components of such drug cocktails, thereby substantially increasing the efficacy of therapy. Furthermore, the use of such dual expression constructs is likely to be highly informative for the design of effective in vivo selection protocols, an issue likely to make a major impact in a clinical context in gene therapy in the near future.

Ifosfamide/etoposide alternating with high-dose methotrexate: evaluation of a chemotherapy regimen for poor-risk osteosarcoma

Fifteen patients with relapsed osteosarcoma were treated with an intensive combination chemotherapy schedule. Ifosfamide 2.5 g m(-2) daily and etoposide 150 mg m(-2) daily coincidentally for 3 days and high-dose methotrexate 8 g m(-2) (with folinic acid rescue) on days 10-14 in a planned 21 -day cycle. Feasibility, toxicity and response to this alternative combination for the treatment of relapsed osteosarcoma was assessed. There were 98 evaluable cycles for toxicity and tolerability. The majority of cycles were well tolerated. Haematological toxicity of grade 3/4 (common toxicity criteria) was seen in all courses. Renal tubular loss of electrolytes, particularly magnesium, occurred in 71% of cycles. Thirteen per cent of cycles were repeated within 21 days and 61% within 28 days. In the thirteen patients evaluable for response, a partial response rate of 31% was seen after two cycles. However, patients with stable disease continued on therapy, and an overall consequent response rate of 62% was observed. Four patients were alive with no evidence of disease at 8-74 months. Three are alive with disease (at 8-19 months). There were six deaths, all disease related. This regimen exhibits an encouraging response rate in a group of children with poor prognosis disease, with a tolerable toxicity profile.

Chemoprotective gene transfer I: transduction of human haemopoietic progenitors with O6-benzylguanine-resistant O6-alkylguanine-DNA alkyltransferase attenuates the toxic effects of O6-alkylating agents in vitro

Retroviral transduction was used to introduce cDNAs encoding two mutants of human O6-alkylguanine-DNA alkyltransferase (hAT), one of which (hATPA) is 16 times more resistant to O6-benzylguanine (O6-beG), and the other (hATPA/GA) which is almost totally refractory to inactivation relative to the wild-type protein, into K562 human erythroleukaemic cells. A colony-forming assay was used to demonstrate significant protection (P < 0.001) against mitozolomide or temozolomide toxicity in K562 clones expressing either hAT mutant, as determined from an in vitro assay of activity. However, protection against these agents was reduced in hATPA expressing cells in the presence of 1 microM O6-beG and was lost in the presence of 20 microM O6-beG while cells expressing hATPA/GA retained protection even in the presence of 20 microM O6-beG (P < 0.001). Using primary human cord blood-derived CD34+ haemopoietic cells in which PCR analysis indicated that up to 70% of progenitors were transduced with retroviral constructs harbouring hATPA/GA, we observed significant protection of the granulocyte-macrophage colony-forming cells against mitozolomide (P < 0.05) and temozolomide (P < 0.001) induced toxicity in the presence of O6-beG. These findings indicate that retrovirus-mediated expression of hATPA/GA in primitive primary human haemopoietic cells is possible and does provide O6-beG-resistant protection for these cells. Using this strategy in patients may simultaneously permit attenuated myelosuppression and increased sensitivity of tumour cells to the effects of O6-alkylating agent chemotherapy. These data, taken together with the study reported by Chinnasamy et al in the accompanying article in this issue showing reduced toxicity and clastogenicity in murine haemopoietic progenitors, make a compelling case to test this strategy clinically.

Chemoprotective gene transfer II: multilineage in vivo protection of haemopoiesis against the effects of an antitumour agent by expression of a mutant human O6-alkylguanine-DNA alkyltransferase

Murine bone marrow cells were transduced ex vivo with a retrovirus encoding an O6-benzylguanine (O6-beG) insensitive, double mutant form of the human DNA repair protein O6-alkylguanine-DNA alkyltransferase (hATPA/GA). In animals reconstituted with the transduced bone marrow, about 50% of cells in the multipotent spleen colony-forming cells (CFU-S) and lineage restricted granulocyte-macrophage (GM-CFC) haemopoietic progenitor populations were found to be carrying the transgene and this correlated with the frequency of bone marrow cells and spleen colonies which stained positive for hATPA/GA by immunocyto-chemistry. Expression of hATPA/GA was associated with significant in vivo protection of both CFU-S (P = 0.001) and GM-CFC (P < 0.024) against the toxicity of the antitumour methylating agent, temozolomide, given in combination with O6-beG. Expression of hATPA/GA also led to a reduction in the frequency of combined O6-beG/temozolomide-induced micronuclei seen in polychromatic erythrocytes (P < 0.003). This study is the first to demonstrate in vivo protection of multipotent haemopoietic progenitors against the toxic and clastogenic effects of an O6-alkylating agent in the presence of O6-beG. It also represents the first report of reduced clastogenesis as a consequence of expression of an O6-beG-resistant ATase. In the accompanying article we report hATPA/GA-mediated resistance of human CD34+ haemopoietic progenitors to combined O6-beG/O6-alkylating agent toxicity. Together these two reports suggest that a gene therapy strategy whereby protection of normal haemopoietic tissue may be combined with O6-beG-mediated tumour sensitisation may be efficacious in achieving an increase in therapeutic index.

Accelerated telomere shortening in young recipients of allogeneic bone-marrow transplants

BACKGROUND

The establishment of donor-derived haemopoiesis in the recipients of allogeneic bone-marrow transplants (BMT) involves extensive proliferation of haemopoietic stem cells. The biological consequences of this replicative stress are ill defined, but any "ageing" effect would carry the risk of an increased frequency of clonal disorders during later life. We compared blood-cell mean telomere lengths in donor/recipient pairs.

METHODS

Mean telomere length was calculated by in-gel hybridisation to leucocyte DNA from 56 normal individuals aged 0-96 years, and from 14 consecutive BMT recipients (aged 2-14 years) plus their respective donors (aged 2-46 years). Engraftment was confirmed by variable numbers of tandem repeats (VNTR) or gender analysis.

FINDINGS

On average, blood-cell telomeres of transplant recipients were 0.4 kb (95% CI -0.2 to -0.6) shorter than those of their respective donors. This degree of telomere loss is equivalent to a median of 15 years' (range 0-40) ageing in the healthy controls.

INTERPRETATION

The kinetics of haemopoietic engraftment impose replicative stress on the haemopoietic stem cells, resulting in a pronounced ageing effect, which may be sufficient to accelerate the onset of clonal haemopoietic disorders usually associated with later life. Monitoring of haemopoietic status in BMT recipients as time since BMT increases will be important. Assessment of transplant protocols under development in terms of their effects on telomere shortening is also indicated.

Survival and late effects in medulloblastoma patients treated with craniospinal irradiation under three years old

Conventional treatment of medulloblastoma has involved surgery to the primary tumour and radiotherapy to the primary site and craniospinal axis. However CNS irradiation in a young child may result in significant side effects. Thus new treatment strategies have emerged which include chemotherapy, given in order to delay radiotherapy, to enable radiation dose reduction to the primary site and craniospinal axis, or even to eliminate radiotherapy completely. Such treatments have not yet been adequately evaluated in terms of survival and late effects. We report a retrospective study of 37 patients under the age of 36 months treated with postoperative craniospinal irradiation, in which the radiation dose to the neuroaxis was below conventional dosage. The overall actuarial 10-year survival rate was 44% and the actuarial 10-year relapse tree survival rate was 54%. Both radiotherapy and chemotherapy contributed to morbidity and mortality. Tour of 16 patients who survived longer than 10 years had no hard neurological signs; all but one patient have required extra support at school. Of nine patients available for work, two have obtained employment but only one has maintained this. No young adults have married. Despite lower doses of radiation, all but 1 survivor has significant spine shortening, and all who reached final height were short. Further work is needed to complete the profile of late effects in this group, which should include the survivors own perceptions of quality of life. It is hoped that multimodality treatment and supportive care can sustain acceptable survival rates but reduce the burden of late effects.

Pediatric oncology and hematology in Manchester, England

The Manchester pediatric oncology unit is the third largest unit in the United Kingdom, with approximately 120 new referred cases per annum (10% of the U.K. total). Research activities include a gene therapy program, peripheral blood stem cell studies, the genetic epidemiology of childhood cancer, late-effects research (growth, body composition, pulmonary, quality of life), psychosocial studies, and clinical trial organization. Both the clinical oncology service and research activities involve close team coordination and collaboration with scientists both within and outside Manchester. A comprehensive pediatric hematology service is provided. The unit contains the second largest children's hemophilia service in the United Kingdom, serving 200 patients with congenital blood disorders. Twenty-five bone marrow transplants are performed each year (allogeneic, unrelated donor, autologous, and peripheral stem cell) for malignant and nonmalignant disorders. These activities are closely related to local, national, and international research groups.

Possibilities of gene therapies for cancer

Cancer is an acquired disease in which it is possible to identify a variety of abnormalities at a genetic level. This holds a promise that genetic manipulation of tumour cells will lead to novel therapies. As yet these approaches are constrained by available methods for obtaining gene transfer and subsequent genetic control. However, a number of strategies are already reaching the clinic, including attempts at immunotherapy, prodrug activation and improving host defence against conventional chemotherapy. Further clinical opportunities will occur with improved vector development.

Towards gene therapy of Hurler syndrome

Allogeneic bone marrow transplantation is the most effective treatment for Hurler's syndrome. However, due to a lack of matched related donors and unacceptable morbidity of matched unrelated transplants, this therapy is not available to all patients. Therefore we have been developing an alternative approach based on transfer and expression of the normal gene in autologous bone marrow. A retroviral vector carrying the full length cDNA for alpha-L-iduronidase has been constructed and used to transduce bone marrow from patients with this disorder. A number of different gene transfer protocols have been assessed including the effect of intensive schedules of exposure of bone marrow to viral supernatant and the influence of growth factors. With these protocols we have demonstrated successful gene transfer into primitive CD34+ cells and subsequent enzyme expression in their maturing progeny. Also, using long-term bone marrow cultures, we have demonstrated high levels of enzyme expression sustained for several months. The efficiency of gene transfer has been assessed by PCR analysis of haemopoietic colonies as around 50%. No advantage has been demonstrated for the addition of growth factors or intensive viral exposure schedules. Indeed a possible disadvantage has been identified for the use of intensive transduction procedures. The enzyme is secreted into the medium and functional localisation has been demonstrated by reversal of the phenotypic effects of lysosomal storage in macrophages. This pre-clinical work forms the basis for a clinical trial of gene therapy for Hurler syndrome.

Uptake of alpha-(L)-iduronidase produced by retrovirally transduced fibroblasts into neuronal and glial cells in vitro

The uptake of recombinant alpha-(L)-iduronidase into glial and neuronal cells, produced by retrovirally transduced NIH3T3 fibroblasts, was studied. We demonstrate that: (1) neuronal and glial cells take up alpha-(L)-iduronidase released into the medium by retrovirally transduced fibroblasts expressing high levels of alpha-(L)-iduronidase; (2) both glial and neuronal cells express the cation independent mannose-6-phosphate receptor responsible for lysosomal enzyme uptake; and (3) uptake of the lysosomal enzyme can be blocked by excess free mannose-6-phosphate, but not glucose-6-phosphate. Thus, various brain cells take up alpha-(L)-iduronidase, possibly through a cation independent mannose-6-phosphate receptor mediated pathway, and this uptake is higher in actively dividing or immature brain cells. Consequently, (1) neuronal metabolism ought to be capable of cross correction by enzyme provided by genetically engineered and transplanted cells provided by bone marrow transplantation (BMT); (2) that BMT could have a more beneficial effect on neurological function if performed as early as possible; and (3) given that the uptake mechanism of glial cells has a higher capacity, it might be easier to target diseases like the leukodystrophies in which lysosomal enzymes are needed in glial cells, compared to diseases where lysosomal enzymes ought to be delivered into neurons.

Chemoprotection of normal tissues by transfer of drug resistance genes

The effectiveness of many types of antitumour agent is limited by (i) acute dose limiting cytotoxicity, principally myelosuppression but also lung, liver and gastrointestinal tract toxicity, (ii) the risk of therapy related secondary malignancy and (iii) the inherent or acquired drug-resistance of tumour cells. As the management of the acute toxic effects improve, the more insidious effects, and particularly haematological malignancies, are anticipated to increase. Furthermore, attempts to overcome tumour cell resistance to treatment can lead to increased collateral damage in normal tissues. One approach to circumventing both the acute toxic and chronic carcinogenic effects of chemotherapy would be to use gene therapy to achieve high levels of expression of drug resistance proteins in otherwise drug-sensitive tissues. To date the products of the multi-drug resistance (MDR-1) and the human O6-alkylguanine-DNA-alkyltransferase (ATase) gene have been used in preclinical experiments to demonstrate proof of principle, and the former of these is now being tested in a clinical situation. Here we discuss the potential of drug-resistance gene therapy to provide chemoprotection to normal tissues and examine the prospects for a dual approach which combines this with pharmacological sensitisation of tumours to chemotherapeutic agents.

Long-term in vitro correction of alpha-L-iduronidase deficiency (Hurler syndrome) in human bone marrow

Allogeneic bone marrow transplantation is the most effective treatment for Hurler syndrome but, since this therapy is not available to all patients, we have considered an alternative approach based on transfer and expression of the normal gene in autologous bone marrow. A retroviral vector carrying the full-length cDNA for alpha-L-iduronidase has been constructed and used to transduce bone marrow from patients with this disorder. Various gene-transfer protocols have been assessed including the effect of intensive schedules of exposure of bone marrow to viral supernatant and the influence of growth factors. With these protocols, we have demonstrated successful gene transfer into primitive CD34+ cells and subsequent enzyme expression in their maturing progeny. Also, by using long-term bone marrow cultures, we have demonstrated high levels of enzyme expression sustained for several months. The efficiency of gene transfer has been assessed by PCR analysis of hemopoietic colonies as 25-56%. No advantage has been demonstrated for the addition of growth factors or intensive viral exposure schedules. The enzyme is secreted into the medium and functional localization has been demonstrated by reversal of the phenotypic effects of lysosomal storage in macrophages. This work suggests that retroviral gene transfer into human bone marrow may offer the prospect for gene therapy of Hurler syndrome in young patients without a matched sibling donor.

An intensive multiagent chemotherapy regimen for brain tumours occurring in very young children

Standard treatment for the majority of malignant brain tumours consists of surgery and radiotherapy. This treatment has late morbidity which is accentuated in the very young child. As part of a strategy to improve quality of life and overall survival of young children with brain tumours, members of the United Kingdom Children's Cancer Study Group (UKCCSG) have piloted an intensive chemotherapy regimen which aims to avoid or delay radiotherapy following surgery. Twenty eight children with a variety of malignant brain tumours have received the regimen, which contains carboplatin, vincristine, cyclophosphamide, methotrexate, and cisplatin. The treatment is toxic, resulting in one death from infection. The bulk of the toxicity was associated with the administration of carboplatin. All but three children eventually required adjuvant radiotherapy and this was given between 1.5 and 27 months from diagnosis (median delay to radiotherapy, 12 months). Using this treatment regimen, overall survival at four years is 35% (confidence intervals 10% to 60%). While there is no evidence from this study that radiotherapy can be abandoned in the management of malignant brain tumours, its introduction may be delayed using suitable chemotherapy, thus allowing time for further CNS development. This treatment strategy has been taken forward as an international clinical trial run through the International Society for Paediatric Oncology, but using a smaller dose of carboplatin to reduce toxicity.

Presenting a scientific paper, including the pitfalls

The tone of the presentation is set with the writing of the abstract. Wanting a trip to Vienna is not a good enough reason for framing an abstract unless the data are really interesting. If you don't find them so, you can bet your life that nobody else will. Have you presented the work before? Increasingly, the forms inviting abstracts stipulate that they should contain novel data. This protects the audience from boredom and your reputation from the aspersion that you never have anything new to say. It has been my practice to communicate similar data at a second meeting provided it contains some new results and that it is targeted at a totally unrelated specialist group. Hopefully, no one will have heard the information before. However, it is not acceptable to simply rehash the same abstract but should reflect the special interests of the second group. If one genuinely wants the abstract accepted for oral presentation it must contain a clear hypothesis, a brief description of methods, an exposition of results, and a conclusion. That well worn phrase 'results will be presented' simply raises the suspicion that the author is hoping that the data will be ready by the time that the conference begins. Sometimes, in the rush to meet deadlines for abstract submission, the needs of coauthors are overlooked. This is a sensitive area and can easily temporarily wreck what appeared to be a harmonious collaboration. Do make sure that all coauthors have seen the abstract before submission and are happy with the content--it is good research practice and important to the smooth running of the research group.

Phase I/II study of iodine 131 metaiodobenzylguanidine in chemoresistant neuroblastoma: a United Kingdom Children's Cancer Study Group investigation

PURPOSE

The goal of this study was to evaluate the toxicity of iodine 131 metaiodobenzylguanidine (mIBG) in metastatic neuroblastoma.

PATIENTS AND METHODS

A multicenter phase I study of 131I mIBG has been undertaken by the United Kingdom Children's Cancer Study Group (UKCCSG) in children with advanced chemoresistant neuroblastoma. Activity prescription was based on a prescribed whole-body radiation dose, which was established for individual patients by performing an initial tracer investigation with 75 MBq of 131I mIBG. An activity was derived from this pharmacokinetic study that would deliver an initial whole-body-absorbed radiation dose of 1 Gy. Subsequent dose escalations were based on observed toxicity.

RESULTS

Twenty-five patients, aged 1 to 10 years, were treated with prescribed whole-body dose levels of 1.0 Gy (n = 2), 2.0 Gy (n = 13), and 2.5 Gy (n = 10). This necessitated administration of 2.4 to 12.1 GBq of activity. Hematologic, hepatic, kidney, and adrenal toxicity were observed, with bone marrow suppression being the principal dose-limiting toxicity. Bone marrow toxicity increased with prescribed whole-body-absorbed radiation dose, with 80% of patients developing grade 3 or 4 thrombocytopenia at a prescribed whole-body radiation dose of 2.5 Gy. Objective evidence of tumor response was seen in soft tissue (primary or nodal disease), bone, and bone marrow, with an overall response rate of 33% (partial response, n = 8; static disease, n = 9; progressive disease, n = 7).

CONCLUSIONS

This study has established an effective method of activity prescription that predicts subsequent toxicity, with the maximally tolerated dose being sufficient activity to deliver a whole-body-absorbed radiation dose of 2.5 Gy. The objective response rate is comparable to other single agents in chemoresistant neuroblastoma and suggests that 131I mIBG may be a useful method for targeting radiotherapy in metastatic neuroblastoma.

The treatment of resistant neuroblastoma with 131I-mIBG: alternative methods of dose prescription

A UK multi-centre study has been carried out to collect medical and dosimetry data from treatments with 131I-metaiodobenzylguanidine (mIBG) for patients suffering from resistant neuroblastoma. All data have been acquired in a standardised way, following strict physics and clinical protocols. The accuracy of three different methods of dose prescription was studied. The results show that the most accurate method involved the use of an initial tracer study to determine the therapeutic activity required to deliver a predetermined absorbed whole-body (WB) dose.

Dosimetry of iodine 131 metaiodobenzylguanidine for treatment of resistant neuroblastoma: results of a UK study

In 1987, the United Kingdom Children's Cancer Study Group (UKCCSG) set up a multi-centre study to investigate the toxicity of iodine 131 metaiodobenzylguanidine (mIBG) in the treatment of resistant neuroblastoma. Since December 1987, 25 children suffering from neuroblastoma have been treated with 131I-mIBG at six UK centres. All centres followed standardised physics and clinical protocols to provide consistent toxicity and dosimetry data. These protocols describe the methods employed for both the tracer study using 131I-mIBG and the subsequent therapy. Whole-body dosimetry calculations were performed on data from the tracer study. The activity administered for therapy was the amount predicted to deliver a predefined whole-body dose. Estimates of doses delivered to various organs during treatment are given in Table 1.

Meta-iodobenzylguanidine (mIBG) uptake and storage in the human neuroblastoma cell line SK-N-BE(2C)

Whilst many human neuroblastoma cell lines have been studied to see if they are capable of taking up mIBG, few appear to have this ability. This contrasts markedly to the situation in vivo, where uptake has been demonstrated in the majority of tumours investigated. Here we report on the human neuroblastoma cell line SK-N-BE(2C) and demonstrate that mIBG uptake can occur in this cell line through 2 mechanisms. At low concentrations of mIBG (approximately 10(-8) M) an active transport process predominates, whereas at non-physiological levels (10(-4) M) uptake occurs through passive diffusion. The active transport process is ATP-, Na(+)- and temperature-dependent. Uptake is blocked by 10(-6) M desipramine, an inhibitor of the uptake-I mechanism involved in amine transport. In contrast, desipramine has no effect on the passive diffusion of mIBG into cells. The active transport mechanism for mIBG uptake appears rather promiscuous for biogenic amines, as dopamine, tyramine and nor-adrenaline were highly efficient at blocking mIBG entry to the cell. Serotonin and histamine were capable of interfering with mIBG uptake only at much higher concentrations. Electron microscopy of SK-N-BE(2C) cells revealed a paucity of neurosecretory granules. Biochemical investigations demonstrated the majority of mIBG to be present in the cytoplasm of cells. The availability of a human neuroblastoma cell line that grows well, both as xenograft and in culture, should further our understanding of the cytotoxic effects of mIBG and thus enhance its clinical usefulness.

Dosimetry of intrathecal iodine131 monoclonal antibody in cases of neoplastic meningitis

Radioiodinated monoclonal antibodies (MCA) were administered by the lumbar route into the cerebrospinal fluid (CSF) of four patients with malignant leptomeningeal disease. Evidence suggesting uptake of 131I-MCA by tumour sites was seen in scintigrams. Dosimetry calculations were carried out, assuming that a proportion of the administered radionuclide was bound as a thin layer on the CSF surfaces of the meninges. The percentage injected dose and the clearance curves for the head and four spinal segments were obtained by scintigraphy after administration of tracer amounts of 131I-MCA (7-18 MBq). Although radioisotope levels in the central nervous system (CNS) fell, as determined by both external scintillation counting and direct CSF sampling, a marked difference in the measurements developed with respect to time. The ratio of these two measurements reached a maximum of 49:1, 7 days after monoclonal antibody administration. Patients subsequently received therapeutic amounts (870-1600 MBq) of 131I-MCAs, resulting in clinical remissions and prolonged survival. The mean absorbed radiation dose was estimated as 3.9 cGy.MBq-1 to the thoraco-lumbar region of the spine and 0.51 cGy.MBq-1 to the outer surface of the brain. The maximal dose delivered to the surface of the CNS in the region of the spine and brain was 5800 and 600 cGy, respectively.

Monoclonal antibodies M340 and UJ181.4 recognize antigens associated with primitive neuroectodermal tumours/tissues

Monoclonal antibodies UJ181.4 and M340 were raised from separate fusions using either human foetal brain or medulloblastoma tissue as immunogens. The antibodies are both of IgG isotype and bind to their target antigens with affinities in excess of 10(-9) M. Both monoclonal antibodies have been shown to bind to primitive neuroectodermal tumours and human foetal brain. Expression of the two antigens is developmentally regulated as no binding is detected on adult brain as determined by a variety of indirect binding assays. The two monoclonal antibodies can be clearly distinguished by their migration in a pH gradient (isoelectric focussing gels). UJ181.4 and M340 clearly recognize two different epitopes, as it is not possible to block the binding of one antibody with an excess of the other. In addition, careful study of the binding profiles of the two reagents suggest that they recognize two distinct antigens, although these have not been biochemically characterized. The reagents have proved particularly useful in both the differential diagnosis of the small round cell tumours of childhood and anaplastic brain tumours. In addition, they have formed part of a panel of reagents used for the immunomagnetic depletion of neuroblasts from bone marrow and have been used for targeting radionuclides to tumour cells in the intrathecal compartment.

A pilot study of 131I monoclonal antibodies in the therapy of leptomeningeal tumors

A pilot study was performed to investigate the toxicity and therapeutic effect of radiolabeled antibody administered intrathecally in patients with leptomeningeal tumors. Five patients who failed conventional therapy received between 11 mCi and 40 mCi of radiolabeled antibody. The choice of antibody varied depending on the immunophenotype of the tumor. Therapy was well tolerated generally, with minimal acute toxicity. Four of five patients achieved an objective response to treatment that has been sustained for a period varying from 7 months to 2 years. No clinical signs of chronic toxicity have been observed in patients 1 and 2 years after therapy.

The biodistribution and pharmacokinetics of meta-iodobenzylguanidine in childhood neuroblastoma

MIBG is generating considerable interest for the treatment of neuroblastoma. This study has investigated the biological variation in handling of the compound in children with neuroblastoma. The biodistribution of the compound has been characterised in children undergoing tracer administrations of 123I and 131I-mIBG. Estimates of hepatic and whole body radiation dose delivery have been made. The results indicate substantial interpatient variation in hepatic dose delivery. This organ may be critical in some patients undergoing targeted radiotherapy with mIBG.

Diagnosis and therapy of neuroectodermally associated tumours using targeted radiation

Monoclonal antibodies have been proposed as targeting agents for cytotoxic compounds in vivo. We have undertaken a phase 1 study of 131I UJ13A in patients with neuroblastoma as well as a pilot study for the intrathecal use of radiolabelled conjugates for diffuse malignant meningitis. Access to solid tumour deposits appears to be a major problem in targeting sufficient isotope to elicit a therapeutic response. This, however, is overcome in the intrathecal use of antibodies for diffuse disease. Problems have also been identified in changes in the pharmacokinetics of antibody handling that occur on repeated administration of conjugate to patient. This is presumably due to the generation of an anti-mouse Ig response. These studies indicate some of the limitations in using murine antibodies as targeting agents and point to areas where their use may be of maximal effect.