Follicular non-Hodgkin's lymphoma.

Follicular non-Hodgkin's lymphoma (NHL) is a unique subtype of NHL, which is indolent, incurable with a high prevalence of residual mass after treatment, and may transform to more aggressive NHL. The aim of this review is to (1) describe the histological and flow cytometry characteristics of follicular NHL; (2) introduce the Follicular Lymphoma International Prognostic Index 2 (FLIPI-2), which allows better treatment selection and patient stratification for clinical trials; (3) illustrate the classic and atypical ultrasound, computed tomography (CT), magnetic resonance imaging (MRI), and positron-emission tomography (PET)/CT appearance of follicular NHL; and (4) characterize the appearance of nodal and extranodal follicular NHL with pathological correlation. Imaging is essential in every step of the management of patients with follicular lymphoma. Overall survival is improved with better predictive tools and new targeted biological therapies. Radiologists should be aware of possible active residual mass, indolent recurrence, transformation, and association with other primary cancers in patients treated for follicular lymphoma.

111In-pentetreotide versus bone scintigraphy in the detection of bony metastases of neuroblastoma.

Bone scintigraphy (BS) is widely utilized for the assessment of bone metastases (BMs) of neuroblastoma (NB). Since 111In-pentetreotide scintigraphy (PS) has been used to image NB with high sensitivity, we compared the sensitivity and specificity of PS with that of BS for the detection of BMs of NB. Nine patients with NB underwent both PS and BS for staging and/or restaging of their disease. The sensitivity and specificity of both imaging approaches were compared based on the findings of histopathology, other conventional imaging methods and subsequent clinical follow-up. In five of the nine patients, both PS and BS were negative for BMs. Radiographic bone surveys (RBSs) were also negative in these patients, except in one who showed a suspicious tibial lesion, but a computed tomography-guided biopsy failed to show evidence of disease. These patients remained without clinical evidence of BMs after a median duration of more than 15 months (range, 6-19 months). In three of four remaining patients, both PS and BS were positive for BMs, whilst only PS was positive in one patient. Overall, PS showed a greater number of BMs (30 vs. 7) with greater conspicuity compared with BS. The initial experience comparing BS with PS suggests that PS may provide a better assessment of the extent of BMs of NB, and that it may be useful as an adjunct to BS at institutions in which 131I- or 123I-metaiodobenzylguanidine is not available, particularly if BS is negative. In patients with similarly positive BS, PS might still provide unique prognostic information beyond that provided by BS. Further studies are therefore warranted.

Role of radiation dosimetry in radioimmunotherapy planning and treatment dosing.

Cancer-seeking antibodies (Abs) carrying radionuclides can be powerful drugs for delivering radiotherapy to cancer. As with all radiotherapy, undesired radiation dose to critical organs is the limiting factor. It has been proposed that optimization of radioimmunotherapy (RIT), that is, maximization of therapeutic efficacy and minimization of normal tissue toxicity, depends on a foreknowledge of the radiation dose distributions to be expected. The necessary data can be acquired by established tracer techniques, in individual patients, using quantitative radionuclide imaging. Object-oriented software systems for estimating internal emitter radiation doses to the tissues of individual patients (patient-specific radiation dosimetry), using computer modules, are available for RIT, as well as for other radionuclide therapies. There is general agreement that radiation dosimetry (radiation absorbed dose distribution, cGy) should be utilized to establish the safety of RIT with a specific radiolabeled Ab in the early stages (i.e. phase I or II) of drug evaluation. However, it is less well established that radiation dose should be used to determine the radionuclide dose (amount of radioactivity, GBq) to be administered to a specific patient (i.e. radiation dose-based therapy). Although treatment planning for individual patients based upon tracer radiation dosimetry is an attractive concept and opportunity, particularly for multimodality RIT with intent to cure, practical considerations may dictate simpler solutions under some circumstances.

Initial experience with high-dose radioimmunotherapy of metastatic medullary thyroid cancer using 131I-MN-14 F(ab)2 anti-carcinoembryonic antigen MAb and AHSCR.

UNLABELLED: This phase I study was initiated to determine the toxicity and therapeutic potential of high-dose 131I-MN-14 F(ab)2 anti-carcinoembryonic antigen monoclonal antibody (MAb) combined with autologous hematopoietic stem cell rescue (AHSCR) in patients with rapidly progressing metastatic medullary thyroid cancer. METHODS: Twelve patients were entered into the study. Dose escalation was based on prescribed radiation doses to critical organs (i.e., kidney, lung, and liver). Starting doses were 900 cGy to the kidney and no more than 1200 cGy to the lung and liver, with dose increments of 300 cGy until the maximum tolerable dose is determined. Tumor targeting was assessed by external scintigraphy, toxicity was assessed according to the common toxicity criteria of the National Cancer Institute, and therapy responses were assessed by CT, serum carcinoembryonic antigen, and calcitonin. RESULTS: One patient received 9.95 GBq 131I-MN-14 F(ab)2, for an initial dose of 656 cGy to critical organs, 8 received 900 cGy (8.69-17.98 GBq), and 3 received 1200 cGy (15.17-17.69 GBq). The MAb scans of all patients showed positive findings. Autologous hematopoietic stem cells were given to all patients 1-2 wk after therapy, when the total body radiation exposure was less than 5.2 x 10(-7) C/kg/h. Dose-limiting toxicity, defined as grade 3 or 4 nonhematologic toxicity, was not seen in the patient who received the 656-cGy dose, and only 1 of the 8 patients treated at the 900-cGy dose level had grade 3 toxicity, which was gastrointestinal and reversible. No dose-limiting toxicity was seen in the 3 patients treated at the 1200-cGy dose level. Except for the instance of grade 3 gastrointestinal toxicity, nonhematologic toxicity was relatively mild, with only grade 1 or 2 toxicity observed in 9 patients. No renal toxicity was seen. Of the 12 patients, 1 had partial remission for 1 y, another had a minor response for 3 mo, and 10 had stabilization of disease lasting between 1 and 16 months. CONCLUSION: The results show the safety of administering high myeloablative doses of 131I-MN-14 F(ab)2 with AHSCR in patients with metastatic medullary thyroid cancer. The antitumor responses in patients with aggressive, rapidly progressing disease are encouraging and warrant further research to optimize the effectiveness of this new treatment.

Plasma FLT3-L levels predict bone marrow recovery from myelosuppressive therapy.

BACKGROUND: During the recovery period after anticancer myelosuppressive therapy, hematopoietic progenitor cells become mitotically active in order to replenish the bone marrow compartment and remain hyperproliferative even after normalization of peripheral white blood cells and platelets. At this stage, the progenitors are more radiosensitive and chemosensitive. Dosing patients with additional cytotoxic therapy during this phase will likely result in more severe toxicity. For example, the authors have noted that the red bone marrow (RM) dose resulting from radioantibody therapy does not correlate with observed bone marrow toxicity. Several patients given similar RM doses had Grade 3 or 4 toxicity, whereas others had Grade 0-2 toxicity even though their white blood cell (WBC) and (PLT) counts were normal at the time of dosing. The goal of these studies was to establish a noninvasive predictive marker of bone marrow activity that could determine stem cell and progenitor cell recovery from previous myelosuppressive therapy. METHODS: A retrospective study was conducted to quantitate plasma levels of 5 cytokines regulating hematopoiesis, namely, 2 stimulatory fms-like tyrosine kinase (FLT3-L) and stem cell factor (SCF) and 3 inhibitory growth factors tumor necrosis factor-alpha (TNFalpha), tumor growth factor-beta, and macrophage inflammatory protein (MIP-1alpha), by immunoassay in 43 patients enrolled in clinical trials at Garden State Cancer Center in Belleville, New Jersey. All patients had had previous chemotherapy with a duration of 1-24 months. The serum cytokine values were correlated with the magnitude of leukopenia or thrombocytopenia following a single dose of radioantibody as the cytotoxic therapy. RESULTS: Plasma FLT3-L levels predicted excess platelet toxicity in 13 of 16 patients (mean = 225 +/- 106 pg/mL) and resulted in a false-positive in only 3 of 27 other patients (mean = 80 +/- 41 pg/mL). Plasma FLT3-L > 135 pg/mL resulted in 81% sensitivity and 89% and 86% specificity and accuracy, respectively, for predicting excess toxicity caused by additional cytotoxic therapy. The positive likelihood ratio was 7.5 (95% confidence interval, 2.5-22.5) and the negative likelihood ratio was 0.19 (95% confidence interval, 0.05-0.67). CONCLUSIONS: Elevated plasma FLT3-L in patients who previously received chemotherapy is a predictive measure of the stage of recovery of the bone marrow compartment. FLT3-L seems to identify the likelihood that the patient will experience Grade > or = 3 thrombocytopenia if additional cytotoxic therapy is administered. Knowledge of bone marrow activity should permit therapy that is more aggressive by establishing the earliest possible time for dosing with any cytotoxic agent for which myelosuppression is the dose-limiting toxicity.

Progressive intermediate-grade non-Hodgkin's lymphoma after high-dose therapy and autologous peripheral stem-cell transplantation: changing the natural history with monoclonal antibody therapy.

The prognosis of patients with progressive intermediate-grade non-Hodgkin's lymphoma (NHL) after high-dose chemotherapy and autologous peripheral stem-cell transplantation (PSCT) is poor, with survival measured in months. The advent of monoclonal antibody therapy for NHL has created new options for effective therapy with relatively mild side effects. We report on two patients with progressive intermediate-grade NHL after PSCT who were treated with monoclonal antibody therapy. Both patients initially received rituximab (unlabeled anti-CD20 monoclonal antibody) and were subsequently treated with (90)Y-epratuzumab (yttrium-90-labeled humanized anti-CD22 monoclonal antibody) at relapse. One patient received (90)Y-epratuzumab alone while the other was treated with higher doses in combination with autologous peripheral stem-cell infusion. Both patients achieved a rapid response to the radiolabeled antibody with minimal toxicity. Monoclonal antibody therapy may be an effective and tolerable treatment for progressive NHL after PSCT.

Assessment of combined radioimmunotherapy and chemotherapy for treatment of medullary thyroid cancer.

We have shown previously significant antitumor effects using 90Y-MN-14 anti-CEA monoclonal antibody (MAb) for radioimmunotherapy (RAIT) of human medullary thyroid cancer (MTC) xenografts using the TT cell line. The purpose of this investigation was to determine the effect of combining chemotherapy and RAIT with 90Y-MN-14 in MTC. In particular, the toxicity and efficacy of various dose schedules of RAIT and doxorubicin were examined and compared with that at the maximum tolerated dose (MTD) of each single modality treatment. The MTD of RAIT of 105 microCi of 90Y-MN-14 was given alone and combined with 100 and 75% of the MTD of doxorubicin (60 mg/m2); and the MTD of doxorubicin was given alone and combined with 100 and 75% of the MTD of RAIT. In addition, 75% of each agent was also administered in combination. The MTD of RAIT was also evaluated in combination with 58 and 78% of the MTD of Taxol. Whereas 90Y-MN-14 (105 microCi) led to significant antitumor effects (P < 0.0001), doxorubicin at 60 mg/m2 or Taxol at 225 mg/m2 yielded only a slight tumor growth delay. The combinations of 100% of the MTD of RAIT and 75% of the MTD of doxorubicin and 100% of the MTD of doxorubicin and 75% of the MTD of RAIT were equitoxic to the MTD of RAIT alone and appear to result in improved efficacy compared with either RAIT or doxorubicin alone. For the 100% RAIT and 75% doxorubicin combination, the therapeutic efficacy was similar when doxorubicin was administered on the same day or 1 day after RAIT, but the treatment was less effective when doxorubicin was administered 2 days after RAIT (P < 0.03). Prolonged retardation of tumor progression was also observed in animals treated with the MTD of RAIT combined with 175 mg/m2 of Taxol, without increases in toxicity above that observed with RAIT alone. In conclusion, the combination of RAIT and chemotherapy appears to augment the antitumor effects of either treatment alone without a significant increase in toxicity. In addition, the timing of drug administration relative to RAIT in the combined therapy appears to be important.

Pharmacokinetics, dosimetry, and initial therapeutic results with 131I- and (111)In-/90Y-labeled humanized LL2 anti-CD22 monoclonal antibody in patients with relapsed, refractory non-Hodgkin's lymphoma.

The pharmacokinetics, dosimetry, and immunogenicity of 131I- and (111)In-/90Y-humanized LL2 (hLL2) anti-CD22 monoclonal antibodies were determined in patients with recurrent non-Hodgkin's lymphoma. Fourteen patients received tracer doses of 131I-hLL2 followed 1 week later by therapeutic doses intended to deliver 50-100 cGy to the bone marrow. Another eight patients received (111)In-hLL2 followed by therapy with 90Y-hLL2 also delivering 50 or 100 cGy to the bone marrow. The blood T(1/2) (hours) for the tracer infusions of 131I-hLL2 was 44.2 +/- 10.9 (mean +/- SD) compared with 54.2 +/- 25.0 for the therapy infusions, whereas the values were 70.7 +/- 17.6 for (111)In-hLL2 and 65.8 +/- 15.0 for 90Y-hLL2. The estimated average radiation dose from 131I-hLL2 in tumors >3 cm was 2.4 +/- 1.9 cGy/mCi and was only 0.9-, 1.0-, 1.1-, and 1.0-fold that of the bone marrow, lung, liver, and kidney, respectively. In contrast, the estimated average radiation dose from 90Y-hLL2 in tumors >3 cm was 21.5 +/- 10.0 cGy/mCi and was 3.7-, 2.5-, 1.8-, and 2.5-fold that of the bone marrow, lung, liver, and kidney, respectively. No evidence of significant anti-hLL2 antibodies was seen in any of the patients. Myelosuppression was the only dose-limiting toxicity and was greater in patients who had prior high-dose chemotherapy. Objective tumor responses were seen in 2 of 13 and 2 of 7 patients given 131I-hLL2 or 90Y-hLL2, respectively. In conclusion, 90Y-hLL2 results in a more favorable tumor dosimetry compared with 131I-hLL2. This finding, combined with the initial anti-tumor effects observed, encourage further studies of this agent in therapeutic trials.

Importance of timing of radioimmunotherapy after granulocyte colony-stimulating factor administration for peripheral blood stem cell harvest.

Nine radioimmunotherapy (RAIT)-naive patients with medullary thyroid cancer received high doses of 131I-MN-14 F(ab)2 anti-carcinoembryonic antigen monoclonal antibody (232-486 mCi), five in combination with bone marrow harvest, without prior granulocyte colony stimulating factor (G-CSF) injections (group 1) and the other four using peripheral blood stem cell harvest (PBSCH) preceded by G-CSF administration of 10 microg/kg per day for 5 days for stem cell mobilization, 6-8 days before RAIT (group 2). The amounts of radioactivity (mCi) given in both groups were similar (312 +/- 93 versus 424 +/- 65; P = NS). The percent platelet loss at nadir, duration of grade 4 thrombocytopenia, and time to complete recovery (TTCR, measured from the day of treatment), were 83 +/- 17%, 2.5 +/- 0.7 days, and 45 +/- 8 days in group 1, respectively, compared with 88 +/- 6%, 3.0 +/- 2.6 days, and 50 +/- 24 days in group 2 (P = NS), respectively. In contrast, the percent WBC loss at nadir, duration of grade 4 leukopenia, and TTCR of WBCs were 72 +/- 12%, 0.0 +/- 0.0 day, and 42 +/- 12 days in group 1, respectively, compared with 93 +/- 3%, 8.0 +/- 3.6 days, and 263 +/- 136 days in group 2, respectively (P < 0.02, 0.03, and 0.05 for differences of percent loss, duration of nadir, and TTCR, respectively). The difference in WBC toxicity after RAIT with bone marrow harvest and PBSCH is thought to be due to the administration of G-CSF for stem cell mobilization within 1 week before RAIT, which may sensitize the "endogenous" granulocyte precursors to subsequent RAIT. Preclinical data of RAIT in mice showed that the time of G-CSF administration before RAIT is critical: increased WBC toxicity was seen in mice given RAIT 3 or 7 days after a 5-day course of G-CSF (81 and 57% WBC loss, respectively) compared with those given no G-CSF or G-CSF 10 or 14 days before RAIT (45-50%) WBC loss). In conclusion, our data indicate that the timing of RAIT after the administration of G-CSF for PBSCH may influence WBC toxicity and recovery after this treatment and may have important implications on the design of high-dose RAIT trials combined with PBSCH.

Prediction of hematologic toxicity after radioimmunotherapy with (131)I-labeled anticarcinoembryonic antigen monoclonal antibodies.

UNLABELLED: This study was undertaken to determine the factors affecting myelotoxicity after radioimmunotherapy (RAIT) with 131I-labeled anticarcinoembryonic antigen (anti-CEA) monoclonal antibodies (MAbs). METHODS: Ninety-nine patients who received 131I-labeled MN-14 or NP-4 anti-CEA MAbs for the treatment of CEA-producing cancers were assessed for platelet and white blood cell (WBC) toxicity based on the common Radiation Therapy Oncology Group (RTOG) criteria. Univariate and multivariate regression analyses were used to identify the statistically significant factors affecting toxicity among the following variables: red marrow dose, baseline platelet and WBC counts, bone or marrow (or both) metastases, prior chemo- or radiotherapy, timing of prior chemo- or radiotherapy in relation to RAIT, type and number of prior chemotherapeutic regimens, age, sex, antibody form and cancer type. RESULTS: Red marrow dose, baseline platelet or WBC counts and multiple bone or marrow (or both) metastases were the only significant factors affecting hematologic toxicity according to both univariate and multivariate analyses, whereas chemotherapy, 3-6 mo before RAIT, was significant according to multivariate analysis. In this retrospective study, the multivariate regression equations using these four variables provided an exact fit for postRAIT platelet toxicity grade (PltGr) and WBC toxicity grade (WBCGr) in 40% and 46%, respectively, of the 99 patients included in the analysis. Moreover, severe (grade 3 or 4) PltGr and WBCGr could be classified accurately in all cases, whereas nonsevere (grade 0, 1, or 2) PltGr and WBCGr could be classified accurately in all but 6 of 13 cases of grade 2 toxicity, in which a severe toxicity grade was estimated using the regression equations. CONCLUSION: Red marrow dose, baseline blood counts, multiple bone or marrow (or both) metastases and recent chemotherapy are the most important factors related to hematologic toxicity after RAIT. This study provides a simple model for predicting myelotoxicity with reasonable accuracy in most patients. In addition, the identification of bone or marrow (or both) metastases and recent chemotherapy as significant factors for myelotoxicity may be important in the future design of clinical trials.

Phase I/II trial of (131)I-MN-14F(ab)2 anti-carcinoembryonic antigen monoclonal antibody in the treatment of patients with metastatic medullary thyroid carcinoma.

BACKGROUND: Monoclonal antibodies (MAbs) against carcinoembryonic antigen (CEA) have been recognized as targeting agents for medullary thyroid carcinoma (MTC). This Phase I/II study was initiated to determine the safety, maximum tolerated dose (MTD), and therapeutic potential of (131)I-MN-14 F(ab)2 anti-CEA MAb for patients with metastatic MTC. METHODS: Fifteen patients were enrolled in this study. Dose escalation was based on estimates of radiation dose to the bone marrow, and the radioactive dose given was determined by a pretherapy diagnostic study in which 8 mCi (0.6-20 mg) of (131)I-MN-14 F(ab)2 was administered 1 week prior to therapy. RESULTS: Three patients received an initial dose of 140 centigray (cGy) to bone marrow, 11 received 180 cGy, and 1 received 220 cGy. Myelosuppression was the only significant treatment-related dose-limiting toxicity (DLT), and the MTD appeared to be 180 cGy to the bone marrow. Human antimouse antibodies (HAMA) developed in 8 patients 2-6 weeks after therapy. Seven patients had a median of 55% reduction of tumor markers. One patient showed a dramatic improvement in the mass effect on the airways caused by 3 tumor lesions in the neck, with a 45% reduction of overall tumor burden. The disease has continued to be radiologically stable in 11 of 12 assessable patients for periods ranging from 3+ to 26+ months. CONCLUSIONS: Therapy with (131)I-MN-14 F(ab)2 is well tolerated and shows evidence of biochemical and radiologic antitumor activity. HAMA development suggests that humanized MAbs will be required in trials with repeated dose schedules. Further dose escalation, alone or in combination with other therapy modalities, is indicated for future trials, preferably with humanized anti-CEA MAbs.

Carcinoembryonic antigen as a target for radioimmunotherapy of human medullary thyroid carcinoma: antibody processing, targeting, and experimental therapy with 131I and 90Y labeled MAbs.

The poor prognosis of patients with advanced medullary thyroid carcinoma (MTC) has prompted a search for new treatment modalities. In this report we explore the characteristics of carcinoembyronic antigen (CEA) as a target for radioimmunotherapy (RAIT) of MTC, with respect to antibody processing, targeting, and experimental therapy. In vitro studies showed a high level of CEA expression on the cell surface of the MTC cell line TT. MAbs bound to the cell were predominantly retained for several days, although there was also a significant level of internalization and catabolism. Immunohistology of frozen sections of tumor xenografts demonstrated that approximately half of the cells were darkly stained, however, some cells expressed little or no CEA. In biodistribution studies in nude mice bearing TT tumors, the mean percent injected dose per gram of tumor observed at three days post injection (time of maximum uptake) of 125I-MN-14 was 19.7%. When the MAb was labeled with 88Y, a residualizing label, a much higher accretion, 50.5%, was observed at the time of maximum uptake (7 days). Significant anti-tumor effects were seen at the maximum tolerated doses of 131I- and 90Y-MN-14, compared with relatively rapid tumor growth in untreated animals or those treated with the same dose of control MAbs. Importantly, it was observed that 90Y-MN-14 yielded significantly improved therapeutic efficacy in comparison to 131I-MN-14, which may have important implications for design and conduct of future clinical trials for the treatment of MTC.

Pharmacokinetics, dosimetry and toxicity of rhenium-188-labeled anti-carcinoembryonic antigen monoclonal antibody, MN-14, in gastrointestinal cancer.

UNLABELLED: The biodistribution, pharmacokinetics and dosimetry of 188Re-labeled MN-14, an IgG anti-carcinoembryonic antigen monoclonal antibody (MAb), were assessed in patients in advanced gastrointestinal cancer. In addition, the dose-limiting toxicity (DLT) and maximum tolerated dose of fractionated doses of this agent were determined. METHODS: Eleven patients were administered radioactive doses of directly labeled 188Re-MN-14 IgG, ranging from 20.5 mCi to 161.0 mCi (2.0 mg-4.9 mg). Ten of these patients received two or three MAb infusions, given 3-4 days apart, delivering total doses of 30 mCi/m2-80 mCi/m2. External scintigraphy was used to evaluate the MAb biodistribution, and quantitative external scintigraphic methods were used to determine the organ and tumor radiation doses. RESULTS: The biodistribution studies showed enhanced 188Re-MN-14 uptake in the liver, spleen and kidneys, compared to that of 131I-MN-14. The biological T(1/2) values for 188Re-MN-14 in the blood and whole body (in hours) were 8.2 +/- 4.1 (n = 7) and 107.8 +/- 104.2 (n = 9), respectively (mean +/- s.d.). The radiation absorbed doses (cGy/mCi) delivered to the total body, red marrow, lungs, liver, spleen and kidneys were 0.5 +/- 0.05, 3.6 +/- 1.6, 2.0 +/- 0.8, 5.9 +/- 2.5, 7.1 +/- 1.9 and 8.5 +/- 2.8, respectively. Red marrow suppression was the only DLT observed. The maximum tolerated dose of fractionated doses of 188Re-MN-14 was estimated to be 60 mCi/m2. CONCLUSION: Despite its relatively increased renal and hepatic uptake, red marrow suppression is the only DLT of 188Re-MN-14. The feasibility of administering relatively high doses of 188Re on a completely outpatient basis may make this agent a preferred candidate for radioimmunotherapy.

Defining the optimal spacing between repeat radioantibody doses in experimental models: is there an accurate measurement for hematopoietic recovery?

BACKGROUND: Single doses of radioantibody are effective at treating single cells or small clusters of cancer cells. However, large tumor masses require either multiple doses of radioantibody or a multimodal approach to therapy using two or more therapeutic agents. Timing of the second dose in a multiple cycle scheme or the second treatment in a multimodal protocol will depend on recovery from toxicity associated with the first treatment. METHODS: BALB/c mice were dosed with a maximal tolerated dose (MTD) of I-131-MN-14 anti-carcinoembryonic antigen immunoglobulin G (IgG) (250 microCi) or F(ab')2 (1.2 mCi). Mice were redosed with the MTD at one of four time points, either Day 28, 35, 42, or 49 after IgG or Day 14, 21, 28, or 35 after F(ab')2. Survival was monitored to determine the earliest time to redose without lethality. Several studies were then performed to identify an accurate measure of true myelorecovery. Mice were bled retroorbitally on the day of the first dose and at weekly intervals thereafter. Total peripheral white blood cell counts, granulocyte counts, and lymphocyte counts were determined for each animal. GR-1hi expression (percentage of positive cells) and mean channel florescence were determined by FACScan analysis of a blood sample incubated with fluorescein isothiocyanate-anti-mouse Ly-6G (GR-1). In other studies, two mice were killed weekly from a group treated with a single MTD of radioantibody. The weights of their spleens and thymus glands were determined. At that time, femoral marrow was collected from these animals and plated in Methocult M3430 methylcellulose medium (Stemcell Technologies, Vancouver, Canada), and total colony-forming cells in culture were determined. Another population of mice was used to assess normal tissue metabolic activity following radioantibody therapy by quantitating the 4-hour utilization of I-125-dUrd. RESULTS: The ability to redose mice with a second MTD of 1-131-IgG or F(ab')2 required 49 days and 35 days, respectively. Granulocyte and lymphocyte counts did not accurately predict myelorecovery from the first dose. Hematopoietic tissue weight, tissue metabolic activity, and marrow colony forming cells all suggested that redosing was possible 1-2 weeks before it could actually be done without lethality. Percent of cells expressing GR-1hi (>60%) and absolute numbers of GR-1hi cells (>1400 cells/mm3) suggested myelorecovery in most animals. A greater degree of accuracy was achieved when trends in GR-1hi expression were noted over 2 or more weeks (i.e., the absolute amount of GR-1hi had to exceed levels in untreated mice, as evidence that the hyperproliferative phase of recovery was complete). CONCLUSIONS: The only approach that accurately predicted the ability to retreat with myelosuppressive therapy without risk of lethality was an increase in GR-1hi-positive cells above untreated levels. Other approaches are currently being investigated, including the expression of proliferation antigens (e.g., proliferating cell nuclear antigen and Ki-67) in both murine and human samples and differentiation antigens (CD33 and CD34) in humans.

Can occult metastases be treated by radioimmunotherapy?

BACKGROUND: Tumor lesions in the millimeter (mm) range may escape detection with nuclear medicine imaging methods (including single photon emission computed tomography [SPECT]) using radiolabeled monoclonal antibodies (MoAbs). We hypothesized that these lesions still could receive a potentially therapeutic radiation absorbed dose, and therefore should be treated, despite the lack of detection. METHODS: To simulate this situation, 2-mm beads (0.004 mL) containing approximately 1.15 microCi of iodine-131 (131I) were used. The beads were placed centrally in a 1200-mL liver phantom containing approximately 3 mCi of 131I. The resultant activity concentration on the beads was approximately 288 microCi/mL compared with approximately 2.5 microCi/mL in the phantom, corresponding to a maximum tumor uptake of approximately 0.3% injected dose per gram (%ID/g) if 100 mCi of 131I-labeled immunoglobulin G were administered. The phantom, containing the beads, was imaged by both planar and SPECT techniques at hypothetical Day 1 (time of maximum tumor uptake) and at hypothetical Day 7 to examine the improved target-to-nontarget ratio over time. In addition to imaging the beads, the radiation absorbed dose to the simulated lesions from the beta component emissions of 131I was calculated using absorbed fractions based on Berger's point kernels. RESULTS: Regardless of the conditions used, the beads could not be observed by either planar or SPECT imaging. However, the radiation-absorbed dose to the simulated lesion was calculated to be as high as approximately 6200 centigray (cGy), with an average dose rate of approximately 89.5 cGy/hour. CONCLUSIONS: This simulation demonstrates that a relatively high absorbed dose and dose rate can be delivered to mm-sized lesions not observed by conventional nuclear imaging methods, and that these lesions should be considered for radioimmunotherapy with 1311 MoAbs. However, for micrometastases of <1 mm, other radionuclides with shorter path length beta particles than 131I, Auger electrons, or alpha particles should be considered.

Factors influencing hematologic toxicity of radioimmunotherapy with 131I-labeled anti-carcinoembryonic antigen antibodies.

BACKGROUND: Several investigators have reported a considerable variability in the observed hematologic toxicity after radioimmunotherapy (RAIT) with monoclonal antibodies (MoAb) given at similar amounts of radioactivity based on body surface area and/or similar radiation absorbed doses given to the red marrow. The authors investigated various factors potentially affecting hematologic toxicity after RAIT with 131I-labeled anti-carcinoembryonic antigen (CEA) MoAb to identify the statistically significant factors from those commonly perceived clinically to substantially contribute to this toxicity. METHODS: Ninety-nine patients who received 131I-labeled anti-CEA MoAb for the treatment of CEA-producing cancers were assessed for platelet and white blood cell toxicity based on the common Radiation Therapy Oncology Group criteria. Multivariate regression analysis was used to identify the statistically significant factors affecting toxicity among the following variables: red marrow dose, baseline platelet and white blood cell counts, bone and/or marrow metastases, prior chemotherapy or radiotherapy, timing of prior chemotherapy or radiotherapy in relationship to RAIT, type and number of prior chemotherapeutic regimens, age, sex, antibody form, and cancer type. RESULTS AND CONCLUSIONS: Red marrow dose, baseline platelet or white blood cell counts, multiple bone and/or marrow metastases, and chemotherapy 3-6 months before RAIT were the only four significant factors affecting hematologic toxicity according to multivariate analysis. The identification of bone and/or marrow metastases and recent chemotherapy as significant factors for hematologic toxicity could be important in the design of future clinical trials.

Phase I/II clinical radioimmunotherapy with an iodine-131-labeled anti-carcinoembryonic antigen murine monoclonal antibody IgG.

UNLABELLED: The aim of this study was to determine, in a Phase I/II clinical trial, the pharmacokinetics, dosimetry and toxicity, as well as antitumor activity, of the 131I-labeled murine anti-carcinoembryonic antigen (CEA) monoclonal antibody, NP-4 (IgG1 subtype). METHODS: A total of 57 patients with CEA-expressing tumors (29 colorectal, 9 lung, 7 pancreas, 6 breast and 4 medullary thyroid cancer patients), mostly in very advanced stages, were treated. The patients underwent a diagnostic study (1-3 mg of IgG and 8-30 mCi of 131I) to assess tumor targeting and to estimate dosimetry, followed by the therapeutic dose (4-23 mg and 44-268 mCi), based on the radiation dose to the red marrow. Imaging was performed from 4-240 hr postinjection (planar and SPECT). Blood and whole-body clearance were determined; radiation doses were calculated by the Medical Internal Radiation Dose scheme. RESULTS: Red marrow doses ranged from 45 to 706 cGy, and whole-body doses ranged from 31 to 344 cGy. Differences in pharmacokinetics were found between different types of CEA-producing tumors: blood T 1/2 was significantly lower in colorectal cancer when compared to all other tumor types (21.4 +/- 11.1 hr versus 35.8 +/- 13.2 hr, p < 0.01), as was also whole-body t 1/2. Myelotoxicity was dose-limiting, and its severity was related to the types of prior therapy and extent of bone marrow involvement. In patients without prior radiation or chemotherapy, marrow doses as high as 600 cGy were tolerated without evidence of dose-limiting toxicity. No major toxicity to other organs was observed. Tumor doses were inversely related to the tumor mass and ranged between 2 and 218 cGy/mCi. Modest antitumor effects were seen in 12 of 35 assessable patients (1 partial remission, 4 minor/mixed responses and 7 with stabilization of previously rapidly progressing disease). CONCLUSION: These results suggest that prior chemotherapy or external beam radiation is an important risk factor for the development of hematological toxicity in radioimmunotherapy and that higher radiation doses may be delivered to tumors of patients without prior therapy compromising the bone marrow reserve. The different and, in the individual cases, unpredictable clearance rates suggest the necessity of dosimetry-based treatment planning rather than mCi/m2 dosing. Small tumors seem to be more suitable for radioimmunotherapy because of their favorable dosimetry, but to achieve better therapeutic results in patients with bulky disease, the application of higher, potentially myeloablative doses is indicated.

Advantage of residualizing radiolabels for an internalizing antibody against the B-cell lymphoma antigen, CD22.

LL2 is an anti-CD22 pan-B-cell monoclonal antibody which, when radiolabeled, has a high sensitivity for detecting B-cell, non-Hodgkin's lymphoma (NHL), as well as an antitumor efficacy in therapeutic applications. The aim of this study was to determine whether intracellularly retained radiolabels have an advantage in the diagnosis and therapy of lymphoma with LL2. In vitro studies showed that iodinated LL2 is intracellularly catabolized, with a rapid release of the radioiodine from the cell. In contrast, residualizing radiolabels, such as radioactive metals, are retained intracellularly for substantially longer. In vivo studies were performed using LL2-labeled with radioiodine by a non-residualizing (chloramine-T) or a residualizing method (dilactitol-tyramine, DLT), or with a radioactive metal (111In). The biodistribution of a mixture of 125I (non-residualizing chloramine-T compared to residualizing DLT), 111In-labeled LL2 murine IgG2a or its fragments [F(ab')2, Fab'], as well as its humanized, CDR-grafted form, was studied in nude mice bearing the RL human B-cell NHL cell line. Radiation doses were calculated from the biodistribution data according to the Medical International Radiation Dose scheme to assess the potential advantage for therapeutic applications. At all assay times, tumor uptake was higher with the residualizing labels (i.e., 111In and DLT-125I) than with the non-residualizing iodine label. For example, tumor/blood ratios of 111In-labeled IgG were 3.2-, 3.5- and 2.8-fold higher than for non-residualizing iodinated IgG on days 3, 7 and 14, respectively. Similar results were obtained for DLT-labeled IgG and fragments with residualized radiolabels. Tumor/organ ratios also were higher with residualizing labels. No significant differences in tumor, blood and organ uptake were observed between murine and humanized LL2. The conventionally iodinated anti-CD20 antibody, 1F5, had tumor uptake values comparable to those of iodinated LL2, the uptake of both antibodies being strongly dependent on tumor size. These data suggest that, with internalizing antibodies such as LL2, labeling with intracellularly retained isotopes has an advantage over released ones, which justifies further clinical trials with residualizing 111In-labeled LL2 for diagnosis, and residualizing 131I and 90Y labels for therapy.

Cancer imaging with radiolabeled antibodies: new advances with technetium-99m-labeled monoclonal antibody Fab' fragments, especially CEA-Scan and prospects for therapy.

The use of radiolabeled anticancer antibodies to detect cancer sites by external scintigraphy has had a relatively long history. With the advent of monoclonal antibodies (MAbs), which precluded the need for purifying the antibodies by laborious purification steps, there was a surge of interest and efforts to develop these reagents for both imaging and therapy applications (1). Today, many thousands of patients have received different forms and doses of MAbs for various purposes, and four MAb-based products have been licensed for manufacture and sale in the U.S. (2,3). This article describes the most recent MAb product to be approved in the U.S. for colorectal cancer imaging, including discussions of using this agent and its therapeutic counterpart in several cancer types.