Radiolabeled-antibody therapy of B-cell lymphoma with autologous bone marrow support

Radioimmunotherapy for B-cell non-Hodgkin lymphoma

Radioimmunotherapy (RIT) combines the targeting advantage of a monoclonal antibody with the radiosensitivity of non-Hodgkin lymphoma (NHL) cells. There are now two radioimmunoconjugates (RICs) - ibritumomab tiuxetan (Zevalin) and tositumomab (Bexxar) - that are approved by the FDA in the US for relapsed low-grade or follicular B-cell NHL. Both agents target the CD20 antigen on B-cell lymphoma cells. In relapsed disease, single doses of RIT produce an 80% overall response rate, with approximately 20% of patients achieving durable responses. RIT is very well tolerated and is delivered on an outpatient basis over 1 week. The only significant toxicity is reversible myelosuppression. Both RIT agents have demonstrated high anti-tumor activity in patients who are refractory to rituximab. Current trials are testing RIT as initial therapy with rituximab maintenance, as adjuvant therapy after chemotherapy, or in high-dose protocols with stem-cell support.

Role of hematopoietic stem cell transplantation for advanced-stage diffuse large cell B-cell lymphoma-B

The prognosis of patients with relapsed or refractory diffuse large cell B-cell lymphoma-B (DLCL-B) is poor with conventional salvage chemotherapy; therefore, high-dose therapy (HDT) combined with autologous stem cell transplant (ASCT) has become the treatment of choice for these patients. The outcomes of transplant are better in patients with chemosensitive relapse: those with a longer duration of first remission (>12 month) and those with an age-adjusted low-risk International Prognostic Index (IPI) at relapse. Several high-dose regimens with or without total body irradiation (TBI) have been used with similar outcomes. Relapse remains the most common cause of treatment failure, and thus the use of radioimmunotherapy (RIT) in the high-dose regimens and incorporation of rituximab in the transplant setting have been explored. Several studies have shown that RIT both at conventional dose and at high dose can be given in combination with high-dose chemotherapy regimens without additional toxicity or delay in hematopoietic recovery after ASCT. Additional studies using RIT in combination with high-dose chemotherapy and ASCT are ongoing, and preliminary results suggest that these approaches may be superior to conventional high-dose regimens. Since rituximab is an effective therapy for B-cell non-Hodgkin's lymphoma and given its limited toxicity, rituximab has been incorporated into HDT and ASCT for DLCL-B as in vivo purging, as part of high-dose regimens, and as maintenance therapy to prevent relapse. Preliminary results suggested that rituximab during ASCT and as maintenance therapy post-transplant reduces the risk of relapse and improves survival; however, these results need to be confirmed in phase III randomized trials. The role of ASCT during first remission as consolidative therapy in patients with DLCL-B remains controversial and should not be performed outside of the clinical trial setting. Allogeneic stem cell transplant (allo-SCT) for patients with relapsed DLCL-B is associated with significant toxicity and should be reserved for patients who relapse after ASCT or those with persistent marrow involvement. Innovative approaches are needed for primary refractory and chemoresistant relapsed DLCL-B since these patients have very poor outcomes after ASCT.

Clinical development of radioimmunotherapy for B-cell non-Hodgkin's lymphoma

Over the past several decades, several biomolecules have been investigated for their ability to deliver radiation to cancer cells, but antibodies have been the carriers of choice in systemic targeted radionuclide therapy (STaRT). Two radioimmunotherapy agents that target the CD20 antigen, (131)I-tositumomab and (90)Y-ibritumomab tiuxetan, have been approved by the U.S. Food and Drug Administration for the treatment of patients with relapsed or refractory B-cell non-Hodgkin's lymphoma (NHL), and clinical trials have shown that they are effective as monotherapies in the salvage setting, producing response rates that are often higher and durations of response that are often longer than those with chemotherapy. Escalated doses of these agents can be supported with stem cell transplantation and can produce high rates of complete response and greater survival in patients with relapsed NHL. The quality and duration of responses are greater with radioimmunotherapy when it is used earlier in the course of treatment.

Systemic targeted radionuclide therapy: potential new areas

Radiation oncology is entering an exciting new era with therapies being delivered in a targeted fashion through an increasing number of novel approaches. External beam radiotherapy now integrates functional and anatomic tumor imaging to guide delivery of conformal radiation to the tumor target. Systemic targeted radionuclide therapy (STaRT) adds an important new dimension by making available to the radiation oncologist biologically targeted radiation therapy. Impressive clinical results with antibody-targeted radiotherapy, leading to the Food and Drug Administration's approval of two anti-CD20 radiolabeled antibodies, highlight the potential of STaRT. Optimization strategies will further improve the efficacy of STaRT by improving delivery systems, modifying the tumor microenvironment to increase targeted dose, and maximizing dose effect. Ultimately, the greatest potential for STaRT will not be as monotherapy, but as therapy integrated into established multimodality regimens and used as adjuvant or consolidative therapy in patients with minimal or micrometastatic disease.

Phase II trial of CHOP chemotherapy followed by tositumomab/iodine I-131 tositumomab for previously untreated follicular non-Hodgkin's lymphoma: five-year follow-up of Southwest Oncology Group Protocol S9911

PURPOSE

Advanced follicular lymphoma (FL) is incurable with conventional chemotherapy and radiotherapy, and optimal front-line management is controversial. This study was performed to determine the efficacy of cyclophosphamide, doxorubicin, vincristine, and prednisone (CHOP) chemotherapy followed by tositumomab/iodine I-131 tositumomab.

PATIENTS AND METHODS

From 1999 to 2000, the Southwest Oncology Group (SWOG) conducted a phase II trial (S9911) to test a novel new regimen consisting of six cycles of CHOP chemotherapy followed 4 to 8 weeks later by tositumomab/iodine I-131 tositumomab in 90 eligible patients with previously untreated, advanced-stage FL.

RESULTS

The overall response rate was 91%, including a 69% complete remission (CR) rate. After a median follow-up time of 5.1 years, the estimated 5-year overall survival (OS) rate was 87%, and the progression-free survival (PFS) rate was 67%. The 5-year estimates of OS and PFS were each 23% better (absolute difference) than the corresponding figures for patients treated on previous SWOG protocols with CHOP alone. An analysis according to the Follicular Lymphoma International Prognostic Index showed that 21% of patients had high-risk features, 44% had intermediate-risk features, and 34% had low-risk features. High-risk patients had worse OS than lower risk patients (P = .05), but differences in PFS were not statistically significant (P = .21). Serial monitoring of the t(14;18) translocation in bone marrow by polymerase chain reaction demonstrated that 32 of 38 informative patients obtained molecular CRs, including seven patients (18%) after CHOP and 24 additional patients (63%) after tositumomab/iodine I-131 tositumomab. (The timing of conversion of one patient was unclear.)

CONCLUSION

A prospective, phase III, randomized Intergroup Trial is currently underway comparing the efficacy of the promising CHOP + tositumomab/iodine I-131 tositumomab regimen with the efficacy of CHOP + rituximab.

A phase I trial of (90)Y-DOTA-anti-CEA chimeric T84.66 (cT84.66) radioimmunotherapy in patients with metastatic CEA-producing malignancies

PURPOSE/OBJECTIVE

Previous radioimmunotherapy (RIT) clinical trials at this institution with (90)Y-labeled cT84.66 anti-CEA (carcinoembryonic antigen) evaluated the antibody conjugated to diethylenetriaminepentaacetic acid (DTPA). The aim of this phase I therapy trial was to evaluate cT84.66 conjugated to the macrocyclic chelate (90)Y-DOTA and labeled with (90)Y in a comparable patient population.

EXPERIMENTAL DESIGN

Patients with metastatic CEA-producing cancers were entered in this trial. If antibody targeting to tumor was observed after the administration of (111)In-DTPA cT84.66, the patient then received the therapy infusion of (90)Y-DOTA-cT84.66 1 week later. Serial nuclear scans, blood and urine collections, and computed tomography (CT) scans were performed to assess antibody biodistribution, pharmacokinetics, toxicities, and antitumor effects.

RESULTS

Thirteen (13) patients were treated in this study. Dose-limiting hematologic toxicity was experienced at initial starting activity levels of 12 and 8 mCi/m(2). Subsequent patients received systemic Ca-DTPA at 125 mg/m(2) every 12 hours for 3 days post-therapy to allow for a dose escalation to 16 mCi/m(2), where hematologic toxicity was observed with an associated maximum tolerated dose (MTD) of 13.4 mCi/m(2). Tumor doses ranged from 4.4 to 569 cGy/mCi, which translated to 97-12,500 cGy after a single infusion of (90)Y-DOTA-cT84.66. Human anti-chimeric antibody (HACA) response developed in 8 of 13 patients and prevented additional therapy in 4 patients.

CONCLUSIONS

This study demonstrates the feasibility of using (90)Y-DOTA-cT84.66 for antibody-guided radiation therapy. Immunogenicity of the DOTA-conjugated cT84.66 antibody was not appreciably greater than that observed with (90)Y-DTPA-cT84.66 in previous trials. Dose-limiting hematopoietic toxicity with (90)Y-DOTA-cT84.66 decreased with Ca-DTPA infusions post-therapy and appears to be comparable to previously published results for (90)Y-DTPA-cT84.66. The highest antibody uptake and tumor doses were to small nodal lesions, which supports the predictions from preclinical and clinical data that RIT may be best applied in the minimal tumor burden setting.

Improving the Efficacy of Reduced Intensity Allogeneic Transplantation for Lymphoma using Radioimmunotherapy

Nonmyeloablative allogeneic transplantation provides a valuable therapeutic option for patients with relapsed non-Hodgkin lymphomas, particularly those that have recurred after autologous transplantation. However, the absence of an intensive conditioning regimen renders this approach less effective for patients with aggressive or bulky lymphoma because rapid tumor growth may outpace the evolution of the graft-versus-lymphoma effect. Radioimmunotherapy provides an attractive, minimally toxic modality to safely prevent early progression of B-cell lymphomas and induce remissions without incurring the risks of traditional intensive therapy. This approach provides a time window during which a robust graft-versus-lymphoma effect may be established before tumor progression, thereby providing more effective long-term disease control. The rationale for incorporation of radioimmunotherapy into reduced intensity allogeneic transplantation regimens for non-Hodgkin lymphoma is discussed, as are current study designs, preliminary results, and future directions.

A genetically engineered anti-CD45 single-chain antibody-streptavidin fusion protein for pretargeted radioimmunotherapy of hematologic malignancies

Acute myelogenous leukemia (AML) currently kills the majority of afflicted patients despite combination chemotherapy and hematopoietic cell transplantation (HCT). Our group has documented the promise of radiolabeled anti-CD45 monoclonal antibodies (Ab) administered in the setting of allogeneic HCT for AML, but toxicity remains high, and cure rates are only 25% to 30% for relapsed AML. We now show the superiority of pretargeted radioimmunotherapy (PRIT) compared with conventional radioimmunotherapy using a recombinant tetravalent single-chain Ab-streptavidin (SA) fusion protein (scFv(4)SA) directed against human CD45, administered sequentially with a dendrimeric N-acetylgalactosamine-containing clearing agent and radiolabeled 1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic (DOTA)-biotin. The scFv(4)SA construct was genetically engineered by fusing Fv fragments of the human CD45-specific BC8 Ab to a full-length genomic SA gene and was expressed as a soluble tetramer in the periplasmic space of Escherichia coli. The fusion protein was purified to >95% homogeneity at an overall yield of approximately 50% using iminobiotin affinity chromatography. The immunoreactivity and avidity of the fusion protein were comparable with those of the intact BC8 Ab, and the scFv(4)SA construct bound an average of 3.9 biotin molecules out of four theoretically possible. Mouse lymphoma xenograft experiments showed minimal toxicity, excellent tumor-specific targeting of the fusion protein and radiolabeled DOTA-biotin in vivo, marked inhibition of tumor growth, and cured 100% of mice bearing CD45-expressing tumors. These promising results have prompted large-scale cGMP production of the BC8 fusion protein for clinical trials to be conducted in patients with hematologic malignancies.

Allogeneic hematopoietic cell transplantation following conditioning with 90Y-ibritumomab-tiuxetan

Radioimmunotherapy (RIT) of relapsed lymphoma is gaining increasing importance. Especially the commercially available anti-CD20 antibody 90Y-ibritumomab tiuxetan is currently under investigation in various trials including dose escalation and autologous hematopoietic progenitor cell support. It is not clear, however, whether the implementation of this radiolabeled antibody into another treatment option for relapsed or poor risk lymphoma patients-allogeneic hematopoietic cell transplantation-interferes with or delays successful engraftment. This study reports encouraging results with 2 relapsed lymphoma patients (1 transformed marginal zone lymphoma and 1 mantle cell lymphoma) who underwent allogeneic hematopoietic cell transplantation from HLA-matched donors. The conditioning regimen consisted of Rituximab 250 mg m(-2) on days -21 and -14, 0.4 mCi kg(-1) body weight 90Y-ibritumomab tiuxetan on day -14 and fludarabine (30 mg m(-2)) plus cyclophosphamide (500 mg m(-2)) on days -7 to -3. The data demonstrate that engraftment is fast and reliable with leukocytes >1 x 10(9) L(-1) on day 12 and platelets >50 x 10(9) L(-1) on day 10. Thus, the incorporation of radioimmunotherapy into allogeneic transplant protocols combines established modalities with proven anti-lymphoma activity and, hence, offers an attractive new therapeutic option for relapsed lymphoma patients.

Comparison of a tetravalent single-chain antibody-streptavidin fusion protein and an antibody-streptavidin chemical conjugate for pretargeted anti-CD20 radioimmunotherapy of B-cell lymphomas

The efficacy of radioimmunotherapy (RIT) for patients with relapsed non-Hodgkin lymphoma (NHL) is limited by nonspecific delivery of radiation to normal tissues due to the long circulating half-life of radiolabeled anti-CD20 antibodies (Abs). Pretargeted RIT using a covalent conjugate of the 1F5 anti-CD20 Ab with streptavidin (SA) has been shown to augment the efficacy of RIT and decrease toxicity compared with a directly labeled 1F5 Ab. We have engineered a tetravalent singlechain 1F5 (scFv)4SA fusion protein and compared it to the 1F5-SA conjugate. Athymic mice bearing Ramos lymphoma xenografts received either the conjugate or fusion protein, followed 20 hours later by a biotin-N-acetyl-galactosamine clearing agent, followed 4 hours later by 111In-DOTA-biotin. After 24 hours, 11.4% +/- 2.1% of the injected dose of radionuclide was present per gram of tumor (% ID/g) using 1F5 (scFv)4SA compared with 10.8% +/- 2.5% ID/g with 1F5 Ab-SA. Superior tumor-to-normal organ ratios of radioactivity were consistently seen using the fusion protein compared with the chemical conjugate (eg, tumor-to-blood ratio > 65:1 after 48 hours with the fusion protein, but < 7:1 with the conjugate). More than 90% of lymphomabearing mice could be cured with minimal toxicity using either reagent followed by 1200 muCi (44.4 MBq) 90Y-DOTA-biotin.

Review of clinical radioimmunotherapy

Radioimmunotherapy involves a form of biologically targeted radiopharmaceutical treatment in which a radioactive isotope (typically a short-range, high-energy beta-emitter) is chemically bound to a target-specific monoclonal antibody or fragment. Thus, these radioimmunoconjugates combine the exquisite targeting specificity of the humoral immune system with the known cancer-killing power of high-energy radiotherapy. To date, two radioimmunotherapy agents have been fully approved for commercial use: 90Yttrium ibritumomab tiuxetan and (131)Iodine tositumomab. Both compounds target the CD20 surface molecule found on normal and malignant B cells, and both are medically indicated for the treatment of indolent B-cell lymphoma and related conditions. Clinical results are excellent (20-40% complete response rates and 60-80% overall response rates) and toxicity is typically quite mild. Current research is now attempting to both explore the biology of these compounds and to expand the spectrum of CD20+ diseases that could be treated using either or both of these active agents. Concurrently, work is in progress to achieve the same excellent clinical results using antibodies specific for other, more common epithelial tumors. This work is at an earlier stage than the lymphoma work, partly due to the high innate radiosensitivity of the lymphoid system. Thus, various enhancement methodologies are being explored to increase clinical response rates for these solid tumors, and a number of solid tumor RIT agents are now in early-stage clinical trials. The most likely pattern of use for this field in the next 5 years will probably involve combination or sequential regimens incorporating both radioimmunotherapy and more conventional chemotherapy or external radiotherapy.

Antibody-guided radiation therapy of cancer

Radioimmunotherapy (RIT) using radiolabeled monoclonal antibodies (MAbs) directed against tumor-associated antigens has evolved from an appealing concept to one of the standard treatment options for patients with non-Hodgkin's lymphoma (NHL). Inefficient localization of radiolabeled MAbs to nonhematological cancers due to various tumor-related factors, however, has refrained RIT from outgrowing the experimental stage in solid tumors. Still, small volume or minimal residual disease has been recognized as a potentially suitable target for radiolabeled antibodies. Several strategies are being explored aimed at improving the targeting of radiolabeled MAbs to solid tumors thus improving their therapeutic efficacy. In this review, a historical overview of the application of RIT is given and various aspects of the application of radiolabeled MAbs as anti-cancer agents are discussed. Finally, the clinical results of RIT of NHL, colorectal cancer, ovarian cancer, breast cancer, and renal cell cancer are reviewed.

Radioimmunotherapy of B-cell lymphoma with radiolabelled anti-CD20 monoclonal antibodies

CD20 has proven to be an excellent target for the treatment of B-cell lymphoma, first for the chimeric monoclonal antibody rituximab (Rituxan), and more recently for the radiolabelled antibodies Y-90 ibritumomab tiuxetan (Zevalin) and I-131 tositumomab (Bexxar). Radiation therapy effects are due to beta emissions with path lengths of 1-5 mm; gamma radiation emitted by I-131 is the only radiation safety issue for either product. Dose-limiting toxicity for both radiolabelled antibodies is reversible bone marrow suppression. They produce response rates of 70%-90% in low-grade and follicular lymphoma and 40%-50% in transformed low-grade or intermediate-grade lymphomas. Both products produce higher response rates than related unlabelled antibodies, and both are highly active in patients who are relatively resistant to rituximab-based therapy. Median duration of response to a single course of treatment is about 1 year with complete remission rates that last 2 years or longer in about 25% of patients. Clinical trials suggest that anti- CD20 radioimmunotherapy is superior to total body irradiation in patients undergoing stem cell supported therapy for B-cell lymphoma, and that it is a safe and efficacious modality when used as consolidation therapy following chemotherapy. Among cytotoxic treatment options, current evidence suggests that one course of anti-CD20 radioimmunotherapy is as efficacious as six to eight cycles of combination chemotherapy. A major question that persists is how effective these agents are in the setting of rituximab- refractory lymphoma. These products have been underutilised because of the complexity of treatment coordination and concerns regarding reimbursement.

Pilot trial of unlabeled and indium-111-labeled anti-prostate-specific membrane antigen antibody J591 for castrate metastatic prostate cancer

BACKGROUND

Prostate-specific membrane antigen (PSMA) is a transmembrane glycoprotein primarily expressed on benign and malignant prostatic epithelial cells. J591 is an IgG1 monoclonal antibody that targets the external domain of the PSMA. The relationship among dose, safety, pharmacokinetics, and antibody-dependent cellular cytotoxicity (ADCC) activation for unlabeled J591 has not been explored.

PATIENTS AND METHODS

Patients with progressive metastatic prostate cancer despite androgen deprivation were eligible. Each patient received 10, 25, 50, and 100 mg of J591. Two milligrams of antibody, conjugated with the chelate 1,4,7,10-tetraazacyclododecane-N, N',N'',N'''-tetraacetic acid, were labeled with 5 mCi indium-111 (111In) as a tracer. One group of patients received unlabeled J591 before the labeled antibody; the other received both together. Toxicities, pharmacokinetic properties, biodistribution, ADCC induction, immunogenicity, and clinical antitumor effects were assessed.

RESULTS

Fourteen patients were treated (seven in each group). Treatment was well tolerated. Biodistribution of 111In-labeled J591 was comparable in both groups. The mean T1/2 was .96, 1.9, 2.75, and 3.47 days for the 10, 25, 50, and 100 mg doses, respectively. Selective targeting of 111In-labeled J591 to tumor was seen. Hepatic saturation occurred by the 25-mg dose. ADCC activity was proportional to dose. One patient showed a >50% prostate-specific antigen decline.

CONCLUSIONS

J591 is well tolerated in repetitive dose-escalating administrations. The rate of serum clearance decreases with increasing antibody mass. ADCC activation is proportional to antibody mass. The optimal dose is 25 mg for radioimmunotherapy and 100 mg for immunotherapy. Phase II studies using J591 as a radioconjugate are under way.

Recommendations for the use of Yttrium-90 ibritumomab tiuxetan in malignant lymphoma

Radioimmunotherapy (RIT) with Yttrium-90 (90Y) ibritumomab tiuxetan (Zevalin) combines the tumor targeting attributes of a monoclonal antibody against the CD20 antigen and the pure beta-radiation of 90Y. High efficacy and a favorable safety profile have been demonstrated in Phase II and III clinical trials enrolling patients with CD20+ B-cell non-Hodgkin lymphoma (B-NHL). On the basis of these results, 90Y-ibritumomab tiuxetan was approved in the United States for the treatment of patients with follicular lymphoma (FL) or transformed B-NHL. In the European Union its use was restricted to FL, refractory to or relapsed after rituximab. There are a number of important clinical trials currently evaluating 90Y-ibritumomab tiuxetan in other subtypes of lymphoma such as diffuse large-cell and mantle-cell lymphoma, as consolidation therapy or as part of myeloablative regimens. In light of the constantly increasing clinical experience with RIT, clinicians face the challenge of how to best integrate this promising new treatment option into existing established treatment algorithms. By incorporating the most recent data in this rapidly developing field, this review article focuses on current recommendations for the use of 90Y-ibritumomab tiuxetan in patients with malignant lymphoma, outlines future perspectives, and provides practical recommendations for patient management.

Current concepts of 131I therapy in oncology: Indications, methods and follow up

Radioiodine in various forms (as sodium iodide and as the iodinated compounds MIBG, LIPIODOL, et al.) has been used as a therapeutic agent in oncology. Differentiated thyroid carcinoma (DTC) has been successfully treated by 131I therapy. Neuroendocrine tumors can be treated by palliative therapy, including Meta 131Iodobenzylguanidine therapy (131I-MIBG). Diagnostic 131I or 123I-MIBG scintigraphy is usually performed to image neuroblastoma and malignant pheochromocytoma. Following the establishment of the diagnosis, 131I-MIBG may be applied as a therapeutic agent but with limited success. Hepatocellular carcinoma (HCC) is treated by surgery only in 10% of patients. In others, palliative therapy should be administered. Radionuclide therapy for this disease is a therapeutic option with a major advantage compared to systemic chemotherapy, estrogen and progesterone therapy, and immunotherapy. 131I-lipiodol can be used to treat HCC without side effects. Compared to untreated patients, those who received 131Ilipiodol, showed significantly better survival and a decreased recurrence rate. The modern aspect of the neoplasm treatment involves radioimmunotherapy with radioiodine and some other radionuclides. Monoclonal antibody therapy with radioiodine has been extensively succeeded in the therapy of B-cell non-Hodgkin?s lymphoma, prostate cancer. Radioimmunotherapy is also efficiently performed in some other malignancies such as: medullary thyroid carcinoma, breast cancer, colorectal cancer and malignant brain tumors. Radioimmunotherapy will play a key role in the treatment of malignant diseases, especially hematopoietic neoplasms during this millennium.

Tailoring antibodies for radionuclide delivery

Therapeutic antibodies are well established as an important class of drugs in modern medicine. The exquisite specificity and affinity for a specific target offered by antibodies has also encouraged their development as delivery vehicles for agents such as radionuclides to target tissues, for radioimmunoimaging and radioimmunotherapy. Specifically, in nuclear medicine, radionuclide-conjugated antibody molecules make it possible to image diseased loci with greater sensitivity than other imaging modalities such as magnetic resonance imaging. Furthermore, two radionuclide-conjugated antibodies have recently been approved for the therapy of non-Hodgkin's lymphoma. However, optimal implementation of antibodies has been limited by the extended circulation persistence that is characteristic of native antibodies, which is responsible for increased background activity in radioimmunoimaging applications and dose-related normal organ toxicities in radioimmunotherapy. In this article the current status of radiolabelled intact antibodies is reviewed, focusing on strategies to improve their pharmacokinetic properties to suit a desired application. Examples from the literature that represent different approaches to accomplishing this task in terms of their successes as well as limitations, and perspectives for the future are discussed.

Splenic Volume Change and Nodal Tumor Response in Non-Hodgkin's Lymphoma Patients after Radioimmunotherapy Using Radiolabeled Lym-1 Antibody

Splenomegaly is frequently found in non-Hodgkin's lymphoma (NHL) patients. This study evaluated the implications of splenic volume change in response to radioimmunotherapy (RIT) using radiolabeled Lym- 1 antibody.

METHODS

Twenty-nine NHL patients treated with radiolabeled-Lym-1 and 9 breast cancer patients, the reference group, treated with radiolabeled ChL6, BrE-3, or m170, were analyzed using X-ray computer tomography (CT) splenic images obtained before and after RIT. Patient-specific radiation doses to the spleen were determined using actual splenic volume determined by CT and body weight.

RESULTS

Of 29 NHL patients, 13 that had splenic volumes equal or less than 310 mL, there was little or no change in splenic volume after RIT, despite splenic radiation doses as high as 23.1 Gy (median 8.0 Gy). Similarly, in a reference group of 9 breast cancer patients, there was little or no change in splenic volume after RIT, despite doses as high as 14.4 Gy (median 11.5 Gy). In the remaining 16 NHL patients, splenic volumes decreased in 13 patients, with initial volumes of 380-1,400 mL, by 68-548 mL despite splenic radiation doses as low as 1.1 Gy (median 3.2 Gy); splenic volumes increased in the other 3 patients after RIT. Although not statistically significant in this small series, therapeutic remission, defined conventionally by nodal tumor response, was more likely when splenic volume decreased after RIT. All 10 NHL patients with greater than a 15% decrease in their splenic volumes after RIT had nodal tumor response (5 complete response, 5 partial response). There were 12 responders (5 complete response and 7 partial response) in 19 NHL patients with less than a 15% decrease in splenic volume after RIT.

CONCLUSIONS

Splenic volume decreased in NHL patients with splenomegaly, despite splenic radiation dose as low as 1.1 Gy. In the absence of splenomegaly, splenic volume did not decrease, even after much higher radiation doses. RIT with radiolabeled-Lym-1 may benefit NHL patients with splenomegaly, with reduction in splenic volume likely owing to a therapeutic effect on malignant lymphocytes.

Improved conditioning regimens for autologous transplantation using targeted radiotherapy

Most patients undergoing autologous hematopoietic stem cell transplantation for malignant diseases suffer recurrences of their neoplasms and die due to the inability of conventional high-dose conditioning regimens to eradicate their malignancies. As a result, intensive efforts to develop more effective conditioning regimens are currently under way at many institutions. Encouraging results have been obtained using targeted radiotherapy with radiolabeled antibodies or bone-seeking isotopes as components of novel conditioning regimens for autologous transplantation of patients with lymphomas, multiple myeloma and bone metastases. Results with radiolabeled antibodies targeting epithelial antigens on solid tumors, however, have been less encouraging. This report reviews the status of clinical studies using myeloablative doses of targeted radiotherapy in patients undergoing autologous stem cell transplantation for hematological malignancies or solid tumors.

131I-anti-CD45 antibody plus busulfan and cyclophosphamide before allogeneic hematopoietic cell transplantation for treatment of acute myeloid leukemia in first remission

In an attempt to improve outcomes for patients with acute myeloid leukemia (AML) after allogeneic hematopoietic cell transplantation (HCT), we conducted a phase 1/2 study in which targeted irradiation delivered by 131I-anti-CD45 antibody was combined with targeted busulfan (BU; area-under-curve, 600-900 ng/mL) and cyclophosphamide (CY; 120 mg/kg). Fifty-two (88%) of 59 patients receiving a trace 131I-labeled dose of 0.5 mg/kg anti-CD45 murine antibody had higher estimated absorbed radiation in bone marrow and spleen than in any other organ. Forty-six patients were treated with 102 to 298 mCi (3774-11 026 MBq) 131I, delivering an estimated 5.3 to 19 (mean, 11.3) Gy to marrow, 17-72 (mean, 29.7) Gy to spleen, and 3.5 Gy (n = 4) to 5.25 Gy (n = 42) to the liver. The estimated 3-year nonrelapse mortality and disease-free survival (DFS) were 21% and 61%, respectively. These results were compared with those from 509 similar International Bone Marrow Transplant Registry patients who underwent transplantation using BU/CY alone. After adjusting for differences in age and cytogenetics risk, the hazard of mortality among all antibody-treated patients was 0.65 times that of the Registry patients (95% CI 0.39-1.08; P = .09). The addition of targeted hematopoietic irradiation to conventional BU/CY is feasible and well tolerated, and phase 2 results are sufficiently encouraging to warrant further study.

Dose-Fractionated Radioimmunotherapy in Non-Hodgkin's Lymphoma Using DOTA-Conjugated, 90Y-Radiolabeled, Humanized Anti-CD22 Monoclonal Antibody, Epratuzumab

PURPOSE

Fractionated radioimmunotherapy may improve therapeutic outcome by decreasing heterogeneity of the dose delivered to the tumor and by decreasing hematologic toxicity, thereby allowing an increased amount of radionuclide to be administered. Because humanized anti-CD22 epratuzumab can be given repeatedly, a single-center study was conducted to establish the feasibility, safety, optimal dosing, and preliminary efficacy of weekly administrations of 90Y-labeled 1,4,7,10-tetra-azacyclodecane-N,N',N'',N'''-tetraacetic acid-conjugated epratuzumab.

EXPERIMENTAL DESIGN

Cohorts of three to six patients with B-cell lymphoma received 185 MBq/m2 [90Y]epratuzumab with unconjugated epratuzumab (total protein dose 1.5 mg/kg) once weekly for two to four infusions, with [(111)In]epratuzumab coadministered at first infusion for scintigraphic imaging and dosimetry.

RESULTS

Sixteen patients received treatment without significant infusional reactions. The overall objective response rate was 62% (95% confidence interval, 39-86%) in both indolent (75%) and aggressive disease (50%). Complete responses (CR/CRu) occurred in 25% of patients and were durable (event-free survival, 14-41 months). Two patients receiving four infusions had hematologic dose-limiting toxicity. Serum epratuzumab levels increased with each weekly dose. Of 13 patients with tumor cell CD22 expression determined by flow cytometry, seven of eight with strongly positive results had objective responses, versus one of five with negative or weakly positive results (P = 0.032).

CONCLUSIONS

Radioimmunotherapy with weekly 185 MBq/m2 [90Y]epratuzumab achieved a high objective response rate (62%) across lymphoma subtypes, including durable CRs. The findings that three weekly infusions (555 MBq/m2, total dose) can be administered safely with only minor toxicity, that antibody levels increased during treatment weeks, and that therapeutic response predominantly occurs in patients with unequivocal CD22 tumor expression provide guidance for future studies.

A phase 1/2 trial of high-dose yttrium-90-ibritumomab tiuxetan in combination with high-dose etoposide and cyclophosphamide followed by autologous stem cell transplantation in patients with poor-risk or relapsed non-Hodgkin lymphoma

We conducted a phase 1/2 trial of high-dose 90Y-ibritumomab tiuxetan in combination with high-dose etoposide (VP-16) 40 to 60 mg/kg (day -4) and cyclophosphamide 100 mg/kg (day -2) followed by autologous stem cell transplantation (ASCT) in 31 patients with CD20+ non-Hodgkin lymphoma (NHL). Patients underwent dosimetry (day -21) with 5 mCi (185 MBq) 111In-ibritumomab tiuxetan following 250 mg/m2 rituximab, followed a week later by 90Y-ibritumomab tiuxetan to deliver a target dose of 1000 cGy to highest normal organ. Bone marrow biopsy was done on day -7 to estimate radiation dose and stem cells were reinfused when the radiation dose was estimated to be less than 5 cGy. The median 90Y-ibritumomab tiuxetan dose was 71.6 mCi (2649.2 MBq; range, 36.6-105 mCi; range, 1354.2-3885 MBq). Histology included follicular lymphoma (n = 12), diffuse large B-cell (n = 14), and mantle cell (n = 5). The median number of prior chemo-therapy treatments was 2. The treatment was well tolerated. The median times to reach an absolute neutrophil count greater than 500/microL and platelet count more than 20,000/microL were 10 days and 12 days, respectively. There were 2 deaths and 5 relapses. At a median follow-up of 22 months, the 2-year estimated overall survival and relapse-free survival rates are 92% and 78%, respectively. We conclude that high-dose 90Y-ibritumomab tiuxetan can be combined safely with high-dose etoposide and cyclophosphamide without an increase in transplant-related toxicity or delayed engraftment.

Radioimmunotherapy using 131I-rituximab in patients with advanced stage B-cell non-Hodgkin’s lymphoma: initial experience

PURPOSE

The aim of this study was to evaluate the safety, toxicity and therapeutic response of non-myeloablative radioimmunotherapy using 131I-rituximab in previously heavily treated patients with B-cell non-Hodgkin's lymphoma (B-NHL).

METHODS

Nine patients with relapsed, refractory or transformed B-NHL received ten radioimmunotherapies. Patients had a median of 5 (range 2-7) prior standard therapies. Four patients had received prior high-dose chemotherapy followed by autologous stem cell transplantation, and eight had received prior rituximab therapy. Histopathology consisted of four mantle cell, one follicular and four diffuse large B-cell lymphomas. Rituximab, a monoclonal chimeric anti-CD20 antibody (IDEC-C2B8), was labelled with 131I using the Iodogen method. The administered activity (2,200+/-600 MBq) was based on a dosimetrically calculated 45 cGy total-body radiation dose. All patients received an infusion of 2.5 mg/kg of rituximab prior to administration of the radiopharmaceutical.

RESULTS

No acute adverse effects were observed after the administration of 131I-rituximab. Radioimmunotherapy was safe in our patient group and achieved one complete response ongoing at 14 months and two partial responses progressing at 12 and 13 months after treatment. One partial responder was re-treated with radioimmunotherapy and achieved an additional progression-free interval of 7 months. Four non-responders with bulky disease died 4.8+/-2.0 months after therapy. Three patients had an elevated serum lactate dehydrogenase (LDH) level prior to radioimmunotherapy and none of the patients responded. Of two patients who received radioimmunotherapy as an additional treatment after salvage chemotherapy, one continues to be disease-free at 9 months and one relapsed at 5 months' follow-up. Reversible grade 3 or 4 haematological toxicity occurred in seven of nine patients. Median nadirs were 35 days for platelets, 44 days for leucocytes and 57 days for erythrocytes.

CONCLUSION

Radioimmunotherapy with 131I-rituximab in previously heavily treated B-NHL patients was safe and well tolerated, and four out of ten therapies induced responses. Radioimmunotherapy was less efficient in patients with bulky disease and elevated LDH. Severe haematological toxicity in seven patients did not cause significant clinical problems. Radioimmunotherapy seems to be an additional therapeutic option in carefully selected therapy-refractory B-NHL patients.

Follicular lymphoma: time for a re-think?

Follicular lymphoma (FL) is a malignancy of follicle centre B cells that have at least a partially follicular pattern, and is the commonest type of indolent Non-Hodgkin's lymphoma. Except in the subset of patients with localized disease, FL should still be regarded as an incurable malignancy with a relentless relapsing/remitting course. However, the provocative new data covered by this review (including anti-CD20 antibody therapy, BCL-2, radioimmunotherapy, new chemotherapeutic agents and anti-idiotype vaccination), provides much cause for excitement and guarded optimism. Rituximab represents a novel treatment approach for a variety of disease settings, with a proven excellent efficacy and toxicity profile. Long-term data is required to establish whether its use translates into survival benefit. As the clinical activity of rituximab and other new therapeutic approaches becomes established, it will be important to determine how best to integrate these results into the standard care of patients with follicular lymphoma.

A review of tositumomab and I131tositumomab radioimmunotherapy for the treatment of follicular lymphoma

The CD20 antigen has become a major therapeutic target in the management of follicular and other B cell non-Hodgkin's lymphomas. The murine monoclonal antibody, tositumomab, on binding CD20, is able to induce antibody-dependent cellular cytotoxicity, complement-dependent cytotoxicity and apoptosis. In addition, when radioiodinated, the antibody exploits the tumour's sensitivity to ionising radiation by direct targeting of the malignant cell. Tositumomab and Iodine (I(131)) tositumomab (Bexxar, GlaxoSmithKline, Philadelphia, PA, USA) is administered in two steps. The dosimetric step determines individual patient pharmacokinetics, allowing a patient- specific dose to be calculated. This is followed by the therapeutic step, with administration of the therapeutic dose between 7 and 14 days after the dosimetric dose. Over a decade's worth of experience in clinical trials has determined the efficacy and safety of the regimen in a variety of clinical circumstances; establishment of exactly where the regimen fits amongst the algorithm for the management of follicular lymphoma continues.

Radioimmunotherapy and colorectal cancer

BACKGROUND

Despite the success of radioimmunotherapy (RIT) using radiolabelled monoclonal antibodies (Mabs) directed against tumour-associated antigens in the treatment of non-Hodgkin's lymphoma, therapeutic success in solid tumours has been modest. In the past decade, a dozen Mabs have been investigated clinically for their potential usefulness in RIT of colorectal cancer.

METHODS

The application of radiolabelled Mabs for the treatment of solid cancers is discussed, and clinical trials investigating RIT for colorectal cancer listed in the Medline and Embase databases are reviewed.

RESULTS

Uptake of radiolabelled Mabs in tumour and, consequently, the therapeutic efficacy of RIT is inversely correlated with tumour size. The bone marrow is the most important dose-limiting organ. Twenty-three phase I/II studies were found that investigated the feasibility and efficacy of RIT using five radionuclides and 15 Mabs against carcinoembryonic antigen, tumour-associated glycoprotein 72, epithelial cellular adhesion molecule, A33 or colon-specific antigen p, mainly in patients with advanced colorectal cancer. A few responses were recorded but no particular antibody construct seemed superior.

CONCLUSION

RIT might be an effective adjuvant treatment modality in colorectal cancer. Future studies should focus on its application in patients with small-volume or minimal residual disease.

Overview of monoclonal antibodies in cancer therapy: present and promise

After 30 years of development, therapy with monoclonal antibodies has started to realize its promise. Clinical use is most widespread in the field of oncology, where half of the agents approved for routine clinical use are employed and a large number of molecules are currently undergoing clinical trials. In the past 2 years alone, three new compounds-the radiolabeled antibody (131)I-tositumomab and two antibodies targeting growth factor receptors (bevacizumab and cetuximab)-have received FDA approval for indications in oncology. This review summarizes the development of this exciting treatment modality over the last three decades, examines the outcome of treatment with these new antibodies and others available for routine clinical use (i.e. rituximab, trastuzumab, alemtuzumab, gemtuzumab ozogamicin, (90)Y-ibritumomab tiuxetan) in standard indications and in experimental settings, and gives a brief outlook on possible future developments.

Cellular and molecular signal transduction pathways modulated by rituximab (rituxan, anti-CD20 mAb) in non-Hodgkin's lymphoma: implications in chemosensitization and therapeutic intervention

The clinical application of rituximab (chimeric mouse anti-human CD20 mAb, Rituxan, IDEC-C2B8), alone and/or combined with chemotherapy, has significantly ameliorated the treatment outcome of patients with relapsed and refractory low-grade or follicular non-Hodgkin's lymphoma (NHL). The exact in vivo mechanisms of action of rituximab are not fully understood, although antibody-dependent cell-mediated cytotoxicity (ADCC), complement-dependent cytotoxicity (CDC), and apoptosis have been suggested. We have proposed that modifications of the cellular signaling pathways by rituximab may be crucial for its clinical response. The B-cell restricted cell surface phosphoprotein CD20 is involved in many cellular signaling events including proliferation, activation, differentiation, and apoptosis upon crosslinking. Monomeric rituximab chemosensitizes drug-resistant NHL cells via selective downregulation of antiapoptotic factors through the type II mitochondrial apoptotic pathway. Several signaling pathways are affected by rituximab which are implicated in the underlying molecular mechanisms of chemosensitization. ARL (acquired immunodeficiency syndrome (AIDS)-related lymphoma) and non-ARL cell lines have been examined as in vitro model systems. In ARL, rituximab diminishes the activity of the p38MAPK signaling pathway resulting in inhibition of the interleukin (IL)-10/IL-10R autocrine/paracrine cytokine autoregulatory loop leading to the inhibition of constitutive STAT-3 activity and subsequent downregulation of Bcl-2 expression leading to chemosensitization. Rituximab upregulates Raf-1 kinase inhibitor protein (RKIP) expression in non-ARL cells. Through physical association with Raf-1 and nuclear factor kappaB (NF-kappa B)-inducing kinase (NIK), RKIP negatively regulates two major survival pathways, namely, the extracellular signal-regulated kinase1/2 (ERK1/2) and the NF-kappa B pathways, respectively. Downmodulation of the ERK1/2 and NF-kappa B pathways inhibits the transcriptional activity of AP-1 and NF-kappa B transcription factors, respectively, both of which lead to the downregulation of Bcl-(xL) (Bcl-2 related gene (long alternatively spliced variant of Bcl-x gene)) transcription and expression and sensitization to drug-induced apoptosis. Bcl-(xL)-overexpressing cells corroborated the pivotal role of Bcl-(xL) in chemosensitization. The specificity of rituximab-mediated signaling and functional effects were corroborated by the use of specific pharmacological inhibitors. Many patients do not respond and/or relapse and the mechanisms of unresponsiveness are unknown. Rituximab-resistant B-NHL clones were generated to investigate the acquired resistance to rituximab-mediated signaling, and chemosensitization. Resistant clones display different phenotypic, genetic and functional properties compared to wild-type cells. This review summarizes the data highlighting a novel role of rituximab as a signal-inducing antibody and as a chemosensitizing agent through negative regulation of major survival pathways. Studies presented herein also reveal several intracellular targets modified by rituximab, which can be exploited for therapeutic and prognostic purposes in the treatment of patients with rituximab- and drug-refractory NHL.

Rituximab and other emerging monoclonal antibody therapies for lymphoma

The recent approval of rituximab, gemtuzumab ozogamicin, alemtuzumab and ibritumomab tiuxetan by the FDA in the US revealed clear evidence that monoclonal antibodies (mAbs) have significant roles in the current treatment of haematologic malignancies. Among the mAbs under clinical development, anti-CD20 mAbs have been most extensively investigated and have shown definitive clinical efficacy. Rituximab is a genetically engineered chimeric anti-CD20 mAb, with mouse variable and human constant regions. Consecutive clinical trials conducted in the US, Europe and Japan have revealed that rituximab is a highly effective agent with acceptable toxicities against indolent and aggressive B cell non-Hodgkin's lymphomas (B-NHLs) as a single agent and in combination with cytotoxic drugs. A recent French Phase III study in elderly patients with untreated aggressive B-NHL suggested that the addition of rituximab to standard CHOP (cyclophosphamide, doxorubicin, vincristine and prednisone) chemotherapy increases the complete response rate and prolongs event-free and overall survival. Lymphoma cells are inherently sensitive to radiation. The aim of radioimmunotherapy is to use the mAb to target radiation to lymphoma tissue while minimising toxicity to normal cells. The clinical trials of 90Y ibritumomab tiuxetan and (131)I tositumomab showed they have definitive efficacy in relapsed indolent B-NHL with acceptable toxicities. A recent comparative study in relapsed indolent B-NHL showed that 90Y ibritumomab tiuxetan produces higher response rates than rituximab. In addition, BL22, a recombinant anti-CD22 immunotoxin, showed significant efficacy in patients with chemotherapy-resistant hairy cell leukaemia. MAbs will have significant roles in the treatment of lymphoid malignancies in the future.

Combining yttrium 90-labeled ibritumomab tiuxetan with high-dose chemotherapy and stem cell support in patients with relapsed non-Hodgkin's lymphoma

Targeted radioimmunotherapy, including yttrium 90-labeled ibritumomab tiuxetan (Zevalin) and iodine I 131 tositumomab (Bexxar), has the potential to increase the cure rate for patients with CD20+ B-cell malignancies who are undergoing autologous hematopoietic stem cell transplantation. The results of phase I and II trials suggest that radioimmunoconjugates can be safely combined with high-dose chemotherapy, although the optimal approach remains to be established. This review focuses on the use of 90Y ibritumomab tiuxetan combined with high-dose chemotherapy in the setting of autologous hematopoietic stem cell transplantation.

Testicular Uptake and Radiation Dose in Patients Receiving Zevalin™ and Pretarget™ CC49Fusion Protein

OBJECTIVE

Radiation dose to the testes from radionuclide therapies is of concern. This study evaluated image-quantification methods for testicular uptake in a phantom and in patients.

METHODS

A 50-mL vial and a large water tank were used to simulate testes and the body, respectively. Activity concentration in the vial and water tank was prepared to generate testes-to-background concentrations of 1.3 and 1.1. Five male lymphoma patients who received a Zevalin (Biogen Idec, Cambridge, MA) regimen and 6 male colorectal cancer patients who received a Pretarget (Neo Rx, Seattle, WA) CC49Fusion protein were evaluated. Testicular activity was quantified using two methods: (1) geometric-mean, background-corrected testicular region of interest (ROI) counts as a fraction of body counts without explicit attenuation correction (Zevalin Kit); (2) background-corrected anterior testicular ROI counts with attenuation correction using known depth in the phantom and CT depth in patients.

RESULTS

In the phantom study, Method 1 underestimated 49% and 39%, at image contrast of 1.3 and 1.1, respectively. Quantification was improved using Method 2 (7% for a 1.3 contrast, -17% for a 1.1 contrast). Method 2 was used in patients because background-corrected posterior ROI counts were statistically unreliable due to poor image contrast. In patients receiving Zevalin, the median peak percent injected dose (%ID)/testis was 0.10 (range, 0.08-0.18) with a median biologic half-time (T(bio1/2)) of 156 (range, 91-4200) hours. The median dose was 2.4 (range, 1.5-3.6) Gy/GBq, compared to the originally reported mean dose of 9.1 (range, 5.4-11.4) Gy/GBq (Zevalin package insert). In patients receiving the Pretarget CC49Fusion protein, the median peak %ID/testis was 0.22 (range, 0.05-0.29) with a median T(bio1/2) of 44 (range, 37-64) hours. The median dose was 0.84 (range, 0.3-1.2) Gy/GBq.

CONCLUSION

This study found that testicular doses from Zevalin were much lower than that originally reported in the package insert. The median testicular dose from Pretarget CC49Fusion protein was less than half that of the median testicular dose from Zevalin.

Concepts in radioimmunotherapy and immunotherapy: Radioimmunotherapy from a Lym-1 perspective

Conventional chemotherapy regimens cure fewer than 50% of patients with aggressive non-Hodgkin's lymphoma, and fewer than 5% of patients with indolent lymphomas. However, the majority of patients remain responsive to remarkably low doses of external beam radiotherapy. A logical strategy for the treatment of non-Hodgkin's lymphoma is radioimmunotherapy (RIT); systemic radiation targeted to tumor cells using monoclonal antibodies. RIT involves continuous exposure to low-dose-rate radiation, with the intensity of the dose decreasing over time, and as such is distinct from conventional radiotherapy and chemotherapy. RIT has several advantages over monoclonal antibody therapy. For example, a functional immune system is not an absolute requirement to kill tumor cells, and, depending on the radiolabel used, beta-emissions are effective over 100 to 500 cell diameters, resulting in a crossfire effect on nearby tumor cells. The crossfire effect enables the eradication of cells that are not necessarily targeted by the antibody, but are affected by the radiation. The success of RIT depends on which antibody and radioisotope is used. This article examines how the antibody, radioisotope, chelator, and linker affect the safety and efficacy of RIT. The different approaches to dosing are also considered.

Development of 131I-tositumomab

The median survival for patients with advanced indolent non-Hodgkin's lymphoma (NHL) has remained at 7 to 8 years since the 1960s. Targeted treatment using radioimmunotherapy (RIT), radiolabeled monoclonal antibodies directed against tumor-specific antigens, is an attractive option for this patient population, combining the advantages of an active biologic therapy with low dose-rate irradiation of an inherently radiosensitive tumor. Two anti-CD20 RIT agents have now been approved for the treatment of refractory NHL: 90Y-ibritumomab tiuxetan (Zevalin; Biogen Idec Inc, San Diego, CA, and Schering AG, Berlin, Germany) is approved in both the United States and Europe, and 131I-tositumomab (Bexxar; Corixa Corp, Seattle, WA) is approved only in the United States. This article discusses the development of 131I-tositumomab. Because 131I-labeled antibody clearance varies significantly among patients, prescription of 131I-tositumomab activity must be based on a calculated total-body dose derived from quantitative whole-body imaging. The maximum tolerated total-body dose has been established at 75 cGy in patients with adequate bone marrow reserves and less than 25% bone marrow involvement by lymphoma (65 cGy in patients with mild thrombocytopenia; 45 cGy in patients who have received stem cell transplantation). In a phase III trial, overall response rate (ORR) and complete response (CR) rate were significantly higher following 131I-tositumomab than following the patient's last qualifying chemotherapy (ORR, 65% v 28%; P <.001; CR, 20% v 3%; P <.001). 131I-tositumomab has also been shown to be effective in patients who are refractory to rituximab (ORR, 70%; CR, 32%) and as first-line therapy in patients with NHL (ORR, 97%; CR, 63%). The major side effects of 131I-tositumomab are hematologic. In the phase III study, 20% of patients experienced grade 4 neutropenia and 22% experienced grade 4 thrombocytopenia. Myelodysplastic syndromes or secondary acute myeloid leukemia have been reported in 8.4% of patients with chemotherapy-refractory disease treated with 131I-tositumomab, but have not been observed to date in patients receiving 131I-tositumomab as first-line therapy. Future progress in NHL management is likely to include RIT as part of a multi-modality approach; trials are planned or currently underway to investigate the combination of RIT with chemotherapy regimens.

Dosimetry model for radioactivity localized to intestinal mucosa

BACKGROUND

This paper provides a new model for calculating radiation-absorbed doses to the full thickness of the small and large intestinal walls, and to the mucosal layers. The model was used to estimate the intestinal radiation doses from yttrium-90-labeled-DOTA-biotin binding to NR-LU-10-streptavidin in patients.

METHODS

We selected model parameters from published data and observations, and used the model to calculate energy-absorbed fractions using the EGS4 radiation transport code. We determined the cumulated (90)Y activity in the small and large intestines of patients from gamma camera images, and calculated absorbed doses to the mucosal layer and to the whole intestinal wall.

RESULTS

The mean absorbed dose to the wall of the small intestine was 16.2 mGy/MBq (60 cGy/mCi) administered from (90)Y localized in the mucosa, and 70 mGy/MBq (260 cGy/mCi) to the mucosal layer within the wall. Doses to the large intestinal wall and to the mucosa of the large intestine were lower than those for the small intestine by a factor of about 2.5. These doses are greater by factors of about 5 to 6 than those that would have been calculated using the standard MIRD models that assume the intestinal activity is in the bowel contents.

CONCLUSIONS

The specific uptake of radiopharmaceuticals in mucosal tissues may lead to dose-related intestinal toxicities. Tissue dosimetry at the sub-organ level is useful for a better understanding of intestinal tract radiotoxicity and associated dose-response relationships.

Comparison of Radiation Dose Estimation for Myeloablative Radioimmunotherapy for Relapsed or Recurrent Mantle Cell Lymphoma Using131I Tositumomab to That of Other Types of Non-Hodgkin's Lymphoma

Patients with relapsed or refractory mantle cell lymphoma (MCL) demonstrate poor survival after standard treatment. Myeloablative radioimmunotherapy (RIT) using (131)I tositumomab (anti-CD20) has the ability to deliver specific radiation-absorbed dose to antigen-bearing tumor. We reviewed normal organ radiation- absorbed doses in MCL patients.

METHODS

Records of patients with MCL (n =25), who received myeloablative RIT between January 1996 and December 2003 were reviewed. Individual patient radiation dosimetry was performed on all patients after a trace-labeled infusion of (131)I tositumomab (mean = 348 MBq), to calculate the required amount of radioactivity for therapy, based on medical internal radiation dose (MIRD) schema.

RESULTS

Mean organ residence times (hour) corrected for computed tomography (CT) derived organ volumes for MCL, were as follows: Lungs: 9.0; Liver: 12.4; Kidneys: 1.7; Spleen: 2.17; Whole Body: 62.4 and mean radiation absorbed doses mGy/Mbq were: Lungs: 1.2; Liver: 1.1; Kidneys: 0.85; Spleen: 1.7; Whole Body: 0.21. This is similar to patients with other non-Hodgkin's lymphoma (NHL). Patients received a mean activity of 21 GBq of (131)I (range, 11.5-41.4) for therapy estimated to deliver 25 Gy to the normal organ receiving the highest radiation-absorbed dose.

CONCLUSION

Myeloablative RIT using (131)I tositumomab results in normal organ radiation-absorbed doses similar to those in patients with other non-Hodgkin's lymphoma, and is suitable for treating patients with relapsed or refractory MCL.

Cellular immunotherapy for follicular lymphoma using genetically modified CD20-specific CD8+ cytotoxic T lymphocytes

Humoral immunotherapy using the monoclonal anti-CD20 antibody rituximab induces remissions in approximately 60% of patients with relapsed follicular lymphoma; however, most patients eventually relapse despite continued expression of CD20 on lymphoma cells. We have hypothesized that cellular immunotherapy targeting CD20(+) cells might provide a more effective mechanism for eliminating lymphoma cells than anti-CD20 antibodies and are therefore investigating the utility of cytotoxic T lymphocytes (CTL) genetically modified to target the CD20 antigen. Peripheral blood mononuclear cells were activated with anti-CD3 antibody (OKT3) and recombinant human interleukin-2 and electroporated with a plasmid containing a CD20-specific scFvFc:zeta chimeric T cell receptor gene and a neomycin phosphotransferase gene (neo(R)). Transfected cells were selected using the antibiotic G418 and cloned by limiting dilution. Using this approach, we have generated CD8(+) CTL clones with CD20-specific cytotoxicity, which specifically lysed CD20(+) target cells, including actual tumor cells from patients with follicular lymphoma, small lymphocytic lymphoma, splenic marginal zone lymphoma, diffuse large B cell lymphoma, and chronic lymphocytic leukemia. The CTL clones have been expanded to numbers sufficient for therapy ( approximately 10(9) cells). Our data indicate the feasibility of generating and expanding CD20-specific CTL and, for the first time, demonstrate that such CTL exhibit specific cytotoxicity against actual tumor cells isolated from patients with a variety of B lymphoid malignancies. In view of these promising findings, a Phase I clinical trial for relapsed follicular lymphoma is being initiated.

Phase I trial of iodine-131 tositumomab with high-dose chemotherapy and autologous stem-cell transplantation for relapsed non-Hodgkin's lymphoma

PURPOSE

To determine the maximum outpatient dose of iodine-131 tositumomab (up to 0.75 Gy) combined with high-dose carmustine, etoposide, cytarabine, and melphalan (BEAM) followed by autologous stem-cell transplantation (ASCT) for the treatment of chemotherapy-resistant relapsed or refractory B-cell non-Hodgkin's lymphoma (NHL).

PATIENTS AND METHODS

Twenty-three patients with chemotherapy-refractory or multiply-relapsed B-cell NHL were treated in a phase I trial combining iodine-131 tositumomab (ranging from 0.30 to 0.75 Gy total-body dose [TBD]) with high-dose BEAM followed by ASCT.

RESULTS

The complete response rate after transplantation was 57%, and the overall response rate was 65%. Short-term and long-term toxicities were similar to historical control patients treated with BEAM alone. With a median follow-up of 38 months (range, 27 to 60 months), the overall survival (OS) rate was 55%, and the event-free survival (EFS) rate was 39%.

CONCLUSION

There were no significant added toxicities apparent with the addition of iodine-131 tositumomab up to a dose of 0.75 Gy TBD to high-dose BEAM chemotherapy followed by ASCT. The EFS and OS were encouraging in this group of chemotherapy-resistant or refractory B-cell NHL patients. A follow-up phase II trial with iodine-131 tositumomab at the dose of 0.75 Gy TBD with BEAM is currently ongoing.

A phase I study of 153Sm-EDTMP with fixed high-dose melphalan as a peripheral blood stem cell conditioning regimen in patients with multiple myeloma

Despite response rates of 30% after high-dose chemotherapy with autologous hematopoietic stem cell transplant, patients with multiple myeloma are not cured. 153Samarium ethylenediaminetetramethylenephosphonate (153Sm-EDTMP; Quadramet) is a short-range, beta-emitting therapeutic radiopharmaceutical with avid skeletal uptake. In total, 12 patients were treated with escalating doses of 153Sm-EDTMP (N=3/group; 6, 12, 19.8, and 30 mCi/kg) and a fixed dose of melphalan (200 mg/m(2)). No dose limiting toxicity was seen. To better standardize the marrow compartment radiation dose, the study was modified such that an additional six patients were treated at a targeted absorbed radiation dose to the red marrow of 40 Gy based on a trace labeled infusion 1 week prior to the therapy. Despite rapid elimination of unbound radiopharmaceutical via kidneys and bladder, no episodes of nephrotoxicity, hemorrhagic cystitis, or delayed radiation nephritis were observed with a median follow-up of 31 months (range 8.5-44). Median times to ANC>0.5 and platelet >20 x 10(6)/l were 12 and 11 days, respectively, with no graft failures. Overall response rate was 94% including seven very good partial responses and five complete responses. Addition of 153Sm EDTMP to melphalan conditioning appears to be safe, well-tolerated and worthy of further study.

Long-term disease-free survival of patients with advanced follicular lymphoma after allogeneic bone marrow transplantation

Myeloablative allogeneic bone marrow transplantation (BMT) may be curative in patients with follicular non-Hodgkin's lymphoma, however, the impact of this therapy on long-term survival, disease progression and functional status is less clear. Twenty-nine patients (median age 42 years, range: 20-53) with advanced stage follicular lymphoma proceeded to allogeneic BMT a median of 25 (range: 8-154) months postdiagnosis, between 1985 and 2001, and have been followed for a minimum of 2 years. Eleven of 29 (38%) had refractory disease (n = 5 induction failure, n = 6 resistant relapse). Most (27 of 29, 93%) received total body irradiation-based conditioning; stem cell source was marrow from a related donor (n = 20) or unrelated donor (n = 9). Seventeen of 29 patients (59%) were alive a median of 5 years (range: 2-11) post-BMT with a median Karnofsky Performance Score of 100%. Death occurred because of transplant complications in seven patients (cumulative incidence of non-relapse mortality 24%), and progressive lymphoma in five patients (cumulative incidence of refractory/recurrent lymphoma 23%). The 5-year probability of overall and event-free survival was 58% and 53% respectively. Allogeneic BMT has resulted in long-term disease-free survival for approximately 50% of this cohort of patients with advanced follicular lymphoma and most of them now enjoy robust health.

A Single Treatment of Yttrium-90-labeled CHX-A″–C6.5 Diabody Inhibits the Growth of Established Human Tumor Xenografts in Immunodeficient Mice

Antitumor diabody molecules are noncovalent single-chain Fv dimers that recapitulate the divalent binding properties of native IgG antibodies. Diabodies are capable of substantial accumulation in tumor xenografts expressing relevant antigens in immunodeficient mouse models. With a Mr of approximately 55,000, diabodies are rapidly cleared from the circulation, resulting in tumor-to-blood ratios that significantly exceed those achieved early after the administration of monoclonal antibodies. We have evaluated the therapeutic potential of the beta-emitting isotope yttrium-90 (t1/2, 64 hours) conjugated to the C6.5K-A diabody that specifically targets the HER2/neu human tumor-associated antigen. We have found that a single intravenous dose of 150 microCi (200 microg) 90Y-CHX-A"-C6.5K-A diabody substantially inhibits the growth rates of established MDA-361/DYT2 human breast tumor xenografts in athymic nude mice. In contrast, 300 microCi (300 microg) 90Y-CHX-A"-C6.5K-A diabody resulted in only a minor delay in the growth of SK-OV-3 human ovarian cancer xenografts. The maximum tolerated dose was also dependent on the tumor xenograft model used. These studies indicate that genetically engineered antitumor diabody molecules can be used as effective vehicles for radioimmunotherapy.

Current treatment options in aggressive lymphoma

The overall percentage of patients achieving long-term remissions in aggressive non-Hodgkin's lymphoma (NHL) using CHOP or CHOP-based primary chemotherapy is only 40%. Much effort has therefore been concentrated on developing strategies to improve this figure. More intensive variants of CHOP chemotherapy, such as multi-agent "third-generation" regimens, have failed to improve long-term survival, and are also associated with increased toxicity. Hence, there is a need for improved treatment regimens, both as primary therapy and for patients in first and subsequent relapse. This need is most acute in elderly patients (> 60 years of age), who comprise more than 50% of NHL cases and who may not be able to tolerate subsequent intensive chemotherapy at relapse. Approaches currently being examined to improve outcome include: the use of clinical, histological and molecular prognostic factors to establish a patient's risk group, and so define those patients most likely to benefit from early aggressive therapy; the inclusion of high-dose therapy and autologous transplantation; and the integration of novel therapies, such as immunotherapy and radioimmunotherapy, into existing treatment strategies. The impact of these approaches on the treatment of diffuse, large B-cell lymphoma and mantle cell lymphoma is discussed below.

Targeted cancer therapy and immunosuppression using radiolabeled monoclonal antibodies

Radioimmunotherapy (RIT) as a means to target radiation therapy to tumor cells or to specifically suppress host immunity specifically in the setting of allogeneic transplantation is a promising new strategy in the armory of today's oncologist. Different approaches of RIT such as injection of a stable radioimmunoconjugate or the use of pretargeting are available. The choice of the radionuclide used for RIT depends on its radiation characteristics with respect to the malignancy or cells targeted. beta-Emitters with their lower energy and longer path length are more suitable for targeting bulky, solid tumors, whereas alpha-emitters with their high linear energy transfer and short path length are better suited to target cells or tumors of the hematologic system. Encouraging results have been obtained using these approaches treating patients with hematologic malignancies. While the results in solid tumors are somewhat less favorable, new strategies for patients with minimal residual disease (MRD), using adjuvant and locoregional treatment, are currently being investigated. In this report, we outline basic principles of RIT, give an overview of available radioimmunoconjugates and their clinical applications with special emphasis on their use in hematologic malignancies, including use in conditioning regimens for stem cell transplantation (SCT).

Antibody-induced intracellular signaling works in combination with radiation to eradicate lymphoma in radioimmunotherapy

Radioimmunotherapy (RIT) has emerged as an effective treatment for lymphoma, however the underlying mechanisms are poorly understood. We therefore investigated the relative contributions of antibody and targeted radiation to the clearance of tumor in vivo, using 2 different syngeneic murine B-cell lymphoma models. Although RIT with 131I–anti–major histocompatibility complex class II (MHCII) was effective in targeting radiation to tumor, no improvement in survival was seen by escalating the radiation dose alone and there were no long-term survivors. In contrast, using the combination of 131I anti-MHCII in the presence of unlabeled anti-idiotype (anti-Id), 100% prolonged disease-free survival was seen in both B-cell lymphoma models at the higher radiation dose. Using in vivo tracking we show that treatment with radiation plus anti-Id monoclonal antibody (mAb) results in a substantially greater reduction of splenic tumor cells than with either treatment alone. Prolonged survival could also be achieved using 131I anti-MHCII plus the signaling anti-CD19 mAb. Furthermore, the ability of these anti–B-cell mAbs to improve survival with targeted radiotherapy appeared to correlate with their ability to initiate intracellular signal transduction. Together these data illustrate that using 1 mAb to target radiation to tumor and a second to induce cell signaling is an effective new strategy in RIT.

Ibritumomab; Tositumomab

The increasing complexity of cancer chemotherapy makes it mandatory that pharmacists be familiar with these highly toxic agents. This column focuses on the commercially available and investigational agents used to treat malignant diseases and reviews issues related to the preparation, dispensing, and administration of cancer chemotherapy.