Immunoreactivity, pharmacokinetics and bone marrow dosimetry of intrathecal radioimmunoconjugates

A phase II study of radioimmunotherapy with intraventricular 131 I-3F8 for medulloblastoma

BACKGROUND

High-risk and recurrent medulloblastoma (MB) is associated with significant mortality. The murine monoclonal antibody 3F8 targets the cell-surface disialoganglioside GD2 on MB. We tested the efficacy, toxicity, and dosimetry of compartmental radioimmunotherapy (cRIT) with intraventricular ¹³¹ I-labeled 3F8 in patients with MB on a phase II clinical trial.

METHODS

Patients with histopathologically confirmed high-risk or recurrent MB were eligible for cRIT. After determining adequate cerebrospinal fluid (CSF) flow, patients received 2 mCi (where Ci is Curie) ¹²⁴ I-3F8 or ¹³¹ I-3F8 with nuclear imaging for dosimetry, followed by up to four therapeutic (10 mCi/dose) ¹³¹ I-3F8 injections. Dosimetry estimates were based on serial CSF and blood samplings over 48 hr plus region-of-interest analyses on serial imaging scans. Disease evaluation included pre- and posttherapy brain/spine magnetic resonance imaging approximately every 3 months for the first year after treatment, and every 6-12 months thereafter.

RESULTS

Forty-three patients received a total of 167 injections; 42 patients were evaluable for outcome. No treatment-related deaths occurred. Toxicities related to drug administration included acute bradycardia with somnolence, headache, fatigue, and CSF pleocytosis consistent with chemical meningitis and dystonic reaction. Total CSF absorbed dose was 1,453 cGy (where Gy is Gray; 350.0-2,784). Median overall survival from first dose of cRIT was 24.9 months (95% confidence interval [CI]:16.3-55.8). Patients treated in radiographic and cytologic remission were at a lower risk of death compared to patients with radiographically measurable disease (hazard ratio: 0.40, 95% CI: 0.18-0.88, P = 0.024).

CONCLUSIONS

cRIT with ¹³¹ I-3F8 is safe, has favorable dosimetry to CSF, and when added to salvage therapy using conventional modalities, may have clinical utility in maintaining remission in high-risk or recurrent MB.

Dose distribution to spinal structures from intrathecally administered yttrium-90

Previous treatment of cerebrospinal fluid (CSF) malignancies by intrathecal administration of (131)I-radiolabelled monoclonal antibodies has led to the assumption that more healthy tissue will be spared when a pure beta-emitter such as (90)Y replaces (131)I. The purpose of this study is to compare and quantitatively evaluate the dose distribution from (90)Y to the CSF space and its surrounding spinal structures to (131)I. A 3D digital phantom of a section of the T-spine was constructed from the visible human project series of images which included the spinal cord, central canal, subarachnoid space, pia mater, arachnoid, dura mater, vertebral bone marrow and intervertebral disc. Monte Carlo N-particle (MCNP4C) was used to model the (90)Y and (131)I radiation distribution. Images of the CSF compartment were convolved with the radiation distribution to determine the dose within the subarachnoid space and surrounding tissues. (90)Y appears to be a suitable radionuclide in the treatment of central nervous system (CNS) malignancies when attached to mAb's and the dose distribution would be confined largely within the vertebral foramen. This choice may offer favourable dose improvement to the subarachnoid and surface of spinal cord over (131)I in such an application.

Current treatment of leptomeningeal metastases: systemic chemotherapy, intrathecal chemotherapy and symptom management

Treatment of leptomeningeal metastases is multifaceted and includes symptomatic therapy, intrathecal and systemic chemotherapy, and radiotherapy. As the majority of patients have widespread incurable systemic tumor, treatment is predominantly palliative; however, some patients with leukemia, lymphoma or breast cancer may have prolonged remissions and the possibility of cure.

Systemic chemotherapy, intrathecal chemotherapy, and symptom management in the treatment of leptomeningeal metastasis

Metastasis to the leptomeninges occurs in many common cancers, including leukemia; lung, breast, and gastrointestinal cancers; and tumors of the brain. By way of the flow of cerebrospinal fluid, leptomeningeal metastasis spreads throughout the neuraxis. Consequently, therapy for leptomeningeal metastasis must be directed to the entire central nervous system (CNS). Treatment often consists of involved-field radiotherapy, systemic chemotherapy, and intrathecal chemotherapy. However, because meningeal spread occurs most often in advanced disease, treatment is mainly palliative, except in childhood leukemia, where durable remission has been reported. This article outlines the role of systemic and intrathecal chemotherapy in patients with leptomeningeal metastases. Strategies for symptom management in these patients are also described.

Tissue distribution and radiation dosimetry of astatine-211-labeled chimeric 81C6, an alpha-particle-emitting immunoconjugate

A paired-label study was performed in athymic mice bearing subcutaneous D-54 MG human glioma xenografts to compare the localization of human/mouse anti-tenascin chimeric antibody 81C6 labeled by reaction with N-succinimidyl 3-[211At]astatobenzoate and N-succinimidyl 3-[131I]iodobenzoate. Over the 48-h observation period, the distribution of 211At- and 131I-labeled antibody were quite similar in tumor and normal tissues except stomach. These data were used to calculate human radiation doses for both intravenously and intrathecal administered 211At-labeled chimeric 81C6 using a quality factor of 5 for alpha-emissions.

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.

Phase I studies of treatment of malignant gliomas and neoplastic meningitis with 131I-radiolabeled monoclonal antibodies anti-tenascin 81C6 and anti-chondroitin proteoglycan sulfate Me1-14 F (ab')2--a preliminary report

The advent of monoclonal antibody (MAb) technology has made Ehrlich's postulate of the 'magic bullet' an attainable goal. Although specific localization of polyvalent antibodies to human gliomas was demonstrated in the 1960s, the lack of specific, high affinity antibody populations and of defined target antigens of sufficient density precluded therapeutic applications. Not until the identification of operationally specific tumor-associated antigens (present in tumor tissue but not normal central nervous system tissue); production of homogeneous, high affinity MAbs to such antigens; and the use of compartmental administration (intrathecal or intracystic), has the promise of passive immunotherapy of primary and metastatic central nervous system neoplasms been recognized. We report here preliminary data from Phase I studies of the compartmental administration of the anti-tenascin MAb 81C6 and F(ab2)2 fragments of MAb Me1-14, which recognizes the proteoglycan chondroitin sulfate-associated protein of gliomas and melanomas, to patients with primary central nervous system tumors or tumors metastatic to the central nervous system. Phase I dose escalation studies of intracystically administered 131I-labeled anti-tenascin MAb 81C6 to either spontaneous cysts of recurrent gliomas or surgically created cystic resection cavities have resulted in striking responses. Of five patients with recurrent cystic gliomas treated, four had partial responses, clinically or radiographically. Similarly, in patients with surgically created resection cavities, a partial response at the treatment site and extended stable disease status has been obtained following intracystic administration of 131I-labeled 81C6. No evidence of hematologic or neurologic toxicity has been observed in either patient population, with the exception of transient exacerbation of a pre-existing seizure disorder in a single patient. Dosimetry calculations indicated high intracystic retention for four to six weeks with little or no systemic dissemination; estimated total doses intracystically ranged from 12,700-70,290 rad. Intrathecal administration of labeled MAbs to patients with neoplastic meningitis is more difficult to assess in terms of clinical responsiveness. Of patients so treated with either 131I-labeled 81C6 or 131I-labeled Me1-14 (F(ab)2, cerebrospinal fluid and radiographic responses have been achieved, and survival prolongation through maintenance of stable disease has been observed in several cases. Initial results from pHase I dose escalation trials are encouraging in terms of the proportion of cases of disease stabilization and partial and complete responses obtained. Importantly, neurotoxicity has been virtually nonexistent, and hematologic toxicity rare and rapidly responsive to treatment.(ABSTRACT TRUNCATED AT 400 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.

In vivo efficacy of intrathecal transferrin-Pseudomonas exotoxin A immunotoxin against LOX melanoma

Neoplastic meningitis due to the dissemination of systemic cancer or primary central nervous system tumors through the cerebrospinal fluid carries a very poor prognosis. Current treatments for this disease are ineffective, and new therapeutic modalities such as immunotoxins may be beneficial. We created an animal model of human carcinomatous meningitis with LOX melanoma-derived tissue-culture cells in athymic rats for testing the efficacy of intrathecal therapy with transferrin-Pseudomonas exotoxin A (Tfn-PE) immunotoxin. An injection of 5 x 10(5) LOX cells into the intrathecal space through an indwelling catheter resulted in the reproducible development of lower-extremity paraplegia at 9.24 +/- 1.77 days because of focal deposits of tumor growth adjacent to the thoracic and lumbar spinal cord. A dose of 2.5 or 5 micrograms of intrathecal Tfn-PE immunotoxin was neurotoxic and resulted in the deaths of 8 of 10 animals within 24 hours. Histological evidence of central nervous system damage was seen as hemorrhagic degeneration around the central canal or a pathological cleft at the level of the cervical spinal cord. Because no neurotoxicity was seen with 1 microgram of intrathecal Tfn-PE immunotoxin, this dose was administered in treatment experiments. Twenty-four hours after the intrathecal instillation of LOX cells, 10 animals received intrathecally either 1 microgram of Tfn-PE or phosphate-buffered saline with 0.1% human serum albumin (control group).(ABSTRACT TRUNCATED AT 250 WORDS)