Dosimetry of intrathecal iodine131 monoclonal antibody in cases of neoplastic meningitis

Clinical trial design and scoring of radionuclide therapy endpoints: normal organ toxicity and tumor response

Like other cancer therapy agents under development, radionuclide therapies are usually evaluated in a progressive series of clinical trials after basic science, human cell culture and animal model studies. Toxicities during these trials are graded using common scoring systems that are in widespread use such as the Common Toxicity Criteria from the National Cancer Institute. Information on normal tissue toxicity from radionuclides is more limited than that from external beam radiation and is more variable. Variability is likely due to many biologic factors as well as less precise dose quantitation than those used in external beam radiation practice. As expected based on known radiobiologic effects, tolerance to radionuclide therapy appears to exceed that from high dose rate external beam radiation in most organs. Although the correlation between reported dose estimates and toxicity has progressively and substantially improved over the past two decades, further progress is needed to establish optimal toxicity predictive relationships. Continued refinement of dosimetry techniques and standardization is expected to increase the accuracy and comparability of radiation dose reports between institutions as well as improve dose/response correlation.

Experimental radioimmunotherapy

Experimental radioimmunotherapy (RIT) studies in animal models have contributed significantly to the design of clinical RIT protocols, although the results have not always been directly translated. Reviewed in this article are current areas of active research in experimental RIT to increase the therapeutic ratio that are likely to have a significant impact on the design of future clinical studies. Approaches for increasing the therapeutic efficacy of RIT include the development of new targeting molecules (genetically engineered monoclonal antibodies, antibody fragments, single-chain antibodies, diabodies and minibodies, fusion toxins, or peptides); improved labeling chemistry; novel radionuclide use and fractionation; locoregional administration; pretargeting; use of biological response modifiers or gene transfer techniques to increase target receptor expression; bone marrow transplantation; and combined modality therapy with external-beam radiation therapy, chemotherapy, or gene therapy. Further research with these new experimental approaches in preclinical animal models is necessary to contribute to advances in the treatment of cancer patients using radiolabeled antibodies and peptides.

Treatment of neoplastic meningitis by targeted radiation using (131)I-radiolabelled monoclonal antibodies. Results of responses and long term follow-up in 40 patients

Between 1984 and 1993, monoclonal antibodies (MAbs) radiolabelled with (131)I were administered into the CSF of 52 patients with neoplastic meningitis (meningosis) with progressive disease despite active conventional therapy. Selection of MAbs was based on immunoreactivity with patients' tumour and lack of binding to normal central nervous system (CNS) tissue. Following full clinical assessment and neuro-imaging which included isotope flow study of CSF pathways, (131)I-MAb was administered via a ventricular access device, lumbar catheter or both. Radioisotope activity varied from 25 mCi to 160 mCi in adults. Dose escalation was carried out and some patients received multiple doses. Distribution of (131)I-MAb and clearance kinetics were derived from serial scintigraphy and CSF/blood sampling. Evidence of localisation to tumour was frequently observed. Toxicity was minimal and easily treated, although one death occurred, possibly due to a seizure. The best results were obtained in primitive neuroectodermal tumour (n=22), where 53% of evaluable cases had responses and 11% had stable disease, adults responding better than children. Three exceptional survivals have been recorded; one patient leads a normal life at 10 years 11 months, one case is alive and normal at 3 years, 2 months. A third case survived in good condition for 8 years. The mean survival of responders was 39 months and non-responders 4 months. In the total series, 50% of patients survived for at least one year with 2 long term survivors. CSF therapy with (131)I-MAb appears to be valuable as a single agent or when used in combination with other modalities. Results of treating leukaemia and carcinoma cases suggest that re-seeding into the CSF compartment from active systemic disease may account for early relapse in the CNS. One carcinoma case with no apparent systemic disease made a remarkable response and survival for 4 years following a single treatment. Neoplastic meningitis generally carries a dismal prognosis. The results obtained in this initial trial are sufficiently encouraging to stimulate further attempts at CSF therapy with (131)I-MAbs.

Pharmacokinetics and dose estimates following intrathecal administration of 131I-monoclonal antibodies for the treatment of central nervous system malignancies

PURPOSE

Treatment of malignant disease in the central nervous system (CNS) with systemic radiolabeled monoclonal antibodies (MoAbs) is compromised by poor penetration into the cerebrospinal fluid (CSF), limited diffusion into solid tumors, and the generation of anti-mouse antibodies. To attempt to avoid these problems we have treated patients with diffuse neoplastic meningitis with radioimmunoconjugates injected directly into the intrathecal space.

METHODS AND MATERIALS

Tumor-specific MoAbs were conjugated to Iodine-131 (131I) (629-3331 MBq) by the Iodogen technique, and administered via an intraventricular reservoir. A clinical response rate of approximately 33% was achieved, with better results in more radiosensitive tumors. Here, we present detailed pharmacodynamic data on patients receiving this intracompartmental targeted therapy.

RESULTS

Elimination from the ventricular CSF appeared biphasic, with more rapid clearance occurring in the first 24 h. Radioimmunoconjugate entered the subarachnoid space and subsequently the vascular compartment. From this information, the areas under the effective activity curves for ventricular CSF, blood, and subarachnoid CSF were calculated to permit dosimetry. Critical organ doses were calculated using conventional medical internal radiation dose (MIRD) formalism. Where available, S-values were taken from standard tables. To calculate the doses to CSF, brain, and spinal cord, S-values were evaluated using the models described in the text.

CONCLUSION

A marked advantage could be demonstrated for the dose delivered to tumor cells within the CSF as compared to other neural elements.

The potential of targeted radiotherapy in the treatment of central nervous system leukaemia

We describe the results of clinical studies investigating the role of monoclonal antibody (MoAb) targeted radiotherapy in the treatment of central nervous system (CNS) leukaemia. Seven children, aged 3-16 years, in second or subsequent meningeal relapse of acute lymphoblastic leukaemia (ALL), have been treated. Each patient received a single injection into the cerebrospinal fluid (CSF) of between 629 and 1,702 MBq of 131-Iodine (131I) conjugated to MoAb HD37 (CD19, n = 2), WCMH 15.14 (CD10, n = 4) or both antibodies (n = 1). One patient underwent a course of repeated targeted therapy following his initial treatment. Acute toxicity was manifest in five patients by a transient aseptic meningitis. Myelosuppression was observed in four children. Pharmacokinetic studies investigated whole body, blood and CSF clearance of radioisotope. Progressively more rapid systemic clearance of 131I was noted in the patient receiving repeated therapy, indicating the development of the human anti-mouse Ig (HAMA) response. Dosimetric studies revealed a radiation dose to the red bone marrow of between 0.6 and 2.2 Gy. The dose to the subarachnoid CSF was between 12.2 and 25.3 Gy, over six times higher than that to the surface tissue of the brain and spinal cord and between 40 and 140 times higher than that to the whole brain. In all but one patient, a transient complete response, in terms of disappearance of lymphoblasts from the CSF, was observed. These studies demonstrate the feasibility of targeted radiotherapy in CNS ALL.(ABSTRACT TRUNCATED AT 250 WORDS)

A dosimetric model for intrathecal treatment with 131I and 67Ga

PURPOSE

Calculations were performed of absorbed dose distributions of the beta-emitter 131I and the Auger emitter 67Ga for intrathecal administration.

METHODS AND MATERIALS

The proposed dosimetric model accounts for the macroscopic distribution of the activity, by means of a Medical Internal Radiation Dose Committee approach, and for the microscopic distribution of activity, by means of a point kernel technique. This point kernel approach was used in combination with a distance histogram technique, to study in more detail the absorbed dose distribution in the cerebro-spinal fluid, in the surface of the central nervous system, and in tumor sites. We simulated decreased uptake, as well as highly selective uptake in free-floating tumor cells and in meningeal lesions (1-16 cells thick).

RESULTS

In case of limited access to lesions adherent to the pia mater, the beta-emitter 131I provides crossfire from the CSF, resulting in a higher absorbed dose (Gy/MBq) in these lesions as compared with the Auger emitter 67Ga. In case of increasing radionuclide uptake, the increment of the absorbed dose in the adherent lesions and the free floating cells from 67Ga is considerable because of the local deposition of energy by this radionuclide.

CONCLUSIONS

The model might be useful to select the optimal emission characteristics of radionuclides applicable for intrathecal therapy, which is demonstrated in a comparison of the Auger emitter 67Ga and the beta-emitter 131I.

Progress review: intrathecal and intratumoral injection of radiolabelled monoclonal antibodies (MoAbs) for the treatment of central nervous system (CNS) malignancies

The systemic administration of monoclonal antibodies (MoAbs) as delivery vehicles for targeted radiation therapy is associated with many problems. Most studies show that insufficient isotope is taken up into the tumour to elicit a tumoricidal effect. This has led several groups to explore the administration of radiolabelled MoAbs into body compartments, specifically for the treatment of minimal tumour deposits that present either as malignant ascites or small nodules on the lining of body cavities. The use of 131Iodine (131I) labelled MoAbs in the treatment of disseminated disease in the central nervous system (CNS) is described and the possibility of administering radiolabelled MoAbs to a cavity generated after debulking surgery for malignant glioma in order to overcome the problem of poor MoAb uptake into solid tumour deposits is discussed together with the rationale for substituting 90Yttrium (90Y) for 131I.

Radionuclide therapy revisited

Apart from its use in endocrinology and rheumatology, therapeutic nuclear medicine is developing rapidly as an additional treatment modality in oncology. Many different specific tumour-seeking radiopharmaceuticals are being applied both for diagnostic scintigraphy and treatment, using multiple routes and mechanisms to target radionuclides at tumours. After a brief introduction of some basic principles of radionuclide targeting, the therapeutic radiopharmaceuticals available are reviewed according to the accumulation site in relation to the cell nucleus; the results of their current clinical use for therapy are also reviewed. The response observed to a number of these applications, the non-invasiveness of the procedure and the relative lack of toxicity and late effects in comparison with chemotherapy and external beam radiotherapy make radionuclide therapy an attractive and realistic alternative in the management of malignant disease, as well as in the treatment of a few benign disorders.