Monoclonal Antibodies in Advanced B- cell Lymphomas

Transcription

1 Monoclonal Antibodies in Advanced B- cell Lymphomas By Chaitra Ujjani, MD Bruce D. Cheson, MD Georgetown University Hospital Lombardi Comprehensive Cancer Center Washington, DC February 9, 2010 Financial Disclosure: Dr. Cheson is on the advisory boards of GlaxoSmithKline, Seattle Genetics, Genentech, and Trubion. ABSTRACT The treatment of B-cell malignancies has been revolutionized by the availability of safe and effective monoclonal antibodies. The addition of rituximab to standard chemotherapy regimens prolongs the survival of patients with diffuse large B-cell lymphoma (DLBCL) and follicular non-hodgkin lymphoma. Nevertheless, indolent and mantle cell lymphomas remain incurable, and 30% to 40% of patients with DLBCL still die from their disease. Much ongoing research has focused on optimizing monoclonal antibody use, integrating them into multiagent regimens, and developing newer antibodies. Attempts to improve on the efficacy of monoclonal antibody based therapy have included altering the dosing schedule, optimizing patient selection, maintenance therapy, improving upon the rituximab molecule, radioimmunotherapy, as well as combinations with cytotoxic molecules and other novel agents. Preliminary data with a number of treatment regimens are promising in indolent and aggressive lymphomas. The eventual goal of targeted therapies is to individualize treatment to increase response and survival, while reducing treatment-related toxicity. B-cell malignancies include the non-hodgkin lymphomas (NHLs), with an estimated incidence of 65,980 in the United States for 2009, and chronic lymphocytic leukemia (CLL), with about 15,000 newly diagnosed patients per year. The NHLs include a wide spectrum of diseases that range from those that are indolent to others that are highly aggressive. In the US, 85% are of B-cell origin and only 15% are T-cell NHLs. Traditionally, advanced B-cell malignancies have been treated with either single-agent or combination chemotherapy. However, over the past decade the availability of safe and effective monoclonal antibodies has altered treatment strategies resulting in improved outcomes. Whereas, as single agents, these antibodies have demonstrated clinically meaningful activity, much of the ongoing research has focused on optimizing their use, finding how best to integrate them into multiagent regimens, and developing newer monoclonal antibodies. Mechanisms of Action and Resistance For an antibody to be effective, it needs to target an appropriate antigen, preferably one

2 that is expressed abundantly and exclusively on the malignant cells. Once the antibody binds to its target antigen, it induces cell death through a variety of mechanisms, including complement-dependent cytotoxicity (CDC), antibody-dependent cellular cytotoxicity (ADCC), and apoptosis.[1] Other hypothesized mechanisms of action include cytokine inhibition, cytotoxic T-lymphocyte generation, and phagocytosis. The mechanisms by which malignant lymphocytes become resistant to antibody therapy are not fully elucidated, but include impairment to the above-mentioned mechanisms of action.[1] For example, upregulation of complement inhibitory proteins, such as CD55 and CD59, can lead to decreased CDC.[2,3] ADCC, which occurs as a result of the Fc portion of the monoclonal antibody binding to the Fc! receptor on the effector cell, can vary with certain Fc!-receptor polymorphisms. Some are associated with rituximab (Rituxan) resistance, while others are associated with hypersensitivity in NHL.[4-6] Similarly, impaired apoptosis can result in resistance to a variety of therapeutics.[7,8] Retrospective data suggest that certain gene-expression patterns may be associated with rituximab resistance.[9] The role of genes such as Bcl-2 as prognostic factors has yet to be established. Mounier et al[8] published data from a phase III trial in which diffuse large B-cell lymphoma (DLBCL) patients were randomized to cyclophosphamide, doxorubicin, vincristine, and prednisone (CHOP) alone or with rituximab (R-CHOP). In patients whose tumors were bcl-2 positive (greater than 50% expression of the bcl-2 protein), those who received R-CHOP had a higher overall response rate (78% vs 60%, P =.01), longer 2-year overall survival rate (67% vs 48%, P =.004), and longer event-free survival rate (58% vs 32%, P <.001) than those who were treated with CHOP alone. The investigators found no statistically significant difference in overall response rate or overall survival in the bcl-2 negative population. These data suggest that rituximab overcomes bcl-2 resistance. Wilson et al[9] demonstrated that the addition of rituximab to dose-adjusted etoposide, prednisone, vincristine, cyclophosphamide, and doxorubicin (DA-EPOCH) was also beneficial for DLBCL patients with bcl-2 overexpression, improving the 5-year progression-free survival from 50% to 80%. However, in a study by Winter et al,[10] the addition of rituximab did not improve overall survival or failure-free survival in patients with bcl-2 or bcl-6 overexpression. Discrepancies among the studies may be explained by differences in distribution of activated B-cell vs germinal center B-cell lymphomas, assay techniques, sample size, or other unknown factors. Rituximab Rituximab, a chimeric anti-cd20 monoclonal antibody, was initially approved by the US Food and Drug Administration (FDA) in 1997 as the first monoclonal antibody for the treatment of a human malignancy relapsed or refractory, follicular or low-grade NHL. This approval was based largely on a study involving 166 patients who received 375 mg/m 2 of rituximab weekly for 4 weeks.[11] The overall response rate was 48%, with 6% complete responses (CRs) and a median duration of response of about 1 year. Subsequent trials have confirmed its efficacy as a single agent in both the upfront and refractory disease settings (Table 1).[11-16] Moreover, addition of the antibody to standard chemotherapy regimens has prolonged the survival of patients with DLBCL and follicular NHL (Table 2).[17-27]

3 Nevertheless, indolent and mantle cell lymphomas remain incurable, and 30% to 40% of patients with DLBCL still die from their disease. Attempts to improve on the efficacy of rituximab have included strategies such as altering the dosing schedule, rituximab as maintenance therapy, improving on the molecule, radioimmunotherapy, and combinations with novel agents including immunomodulators, apoptosis targeting drugs, cytotoxic molecules, or other monoclonal antibodies. Other antibodies and related molecules are also in development. Dose and Schedule Intensification of dose and schedule of rituximab has been evaluated in a phase I/II trial by Poeschel et al, in which elderly patients (aged years, stages I IV) received six cycles of CHOP every 2 weeks along with 12 infusions of rituximab at 375 mg/m2 on days 0, 1, 4, 8, 15, 22, 29, 43, 57, 71, 85, and 99.[28] Of the first 20 patients, 3 died from therapy-associated complications (1 sepsis, 2 interstitial pneumonitis). Another 4 patients developed interstitial pneumonia. Prophylaxis for Pneumocystis carinii (cotrimoxazole) and cytomegalovirus (acyclovir) was initiated after the first 20 patients, with no additional episodes of interstitial pneumonia. Disease progression was not seen in the 46 patients who completed this regimen during the 9 months of followup. The RICOVER trial (Rituximab With CHOP Over Age 60 Years) was a phase III comparison of six or eight cycles of CHOP or R-CHOP in a 14-day dosing regimen in 1,222 elderly patients with aggressive B-cell lymphoma.[26] Patients who received rituximab had a longer progression-free and overall survival. Fifty patients in the eight-cycle group and 42 patients in the six-cycle group experienced treatment-related deaths, the majority due to infection. However, whether R-CHOP should be administered every 2 (R-CHOP-14) or 3 (R- CHOP-21) weeks remains controversial. Studies evaluating this question have been conducted by the Groupe d Etude des Lymphomes de l Adulte (GELA) and the National Cancer Research Institute (NCRI).

4 Preliminary results from the NCRI trial show similar complete response rates between R-CHOP-21 and R-CHOP-14 (47% in both arms), but no final data regarding overall survival are yet available.[29] Nevertheless, CR rates tend to correlate with timedependent endpoints. The most common grade 3 and 4 toxicities include neutropenia in 57% of patients given R-CHOP-21 and 31% of R-CHOP-14 recipients. Of note, patients in the latter group received granulocyte colony-stimulating factor (Neupogen) with each cycle, which likely contributed to the decreased frequency of neutropenia. Other adverse effects include thrombocytopenia occurring in 5% and 9% and infection in 22% and 17% of patients, respectively. Maintenance Therapy Another method of enhancing the benefit of rituximab is to use it as maintenance following induction therapy (Table 3).[20,25,30-38] Hainsworth et al[30] first published a phase II trial of 62 previously untreated patients with follicular lymphoma or small lymphocytic lymphoma (SLL) who received rituximab as four weekly infusions followed by an additional four weekly doses every 6 months until disease progression, or to a maximum of 2 years. The overall and complete response rates increased from 47% and 7% following the initial infusions to 73% and 37%, respectively, at the end of maintenance. With a median follow-up of 30 months, the progression-free survival was an encouraging 34 months. Nevertheless, randomized studies have failed to show a survival benefit with maintenance rituximab. Ghielmini et al reported 202 patients with untreated or previously treated follicular lymphoma treated with four weekly infusions of rituximab followed by observation or maintenance.[31] At a median follow-up of 8.9 years, the median event-free survival was 13 months for the observation arm and 24 months for the consolidation arm (P =.0012).[32] Overall survival revealed a trend favoring prolonged treatment (P =.09). Van Oers et al randomized 474 minimally pretreated follicular lymphoma patients to CHOP or R- CHOP with a second randomization to observation or maintenance rituximab.[20] Progression-free survival was longer with maintenance therapy (3.7 vs 1.3 years, P <.0001). An initial suggestion of a survival benefit disappeared with additional followup (5-year overall survival rates were 74% with maintenance and 64% with observation, P =.07). Forstpointner et al[33] randomized 195 patients with relapsed follicular or mantle cell lymphoma to fludarabine, cyclosphosphamide, and mitoxantrone (FCM) alone or with rituximab maintenance. They reported a significant prolongation of the duration of response in both follicular lymphoma (P =.035) and mantle cell lymphoma (P =.049), but the estimated 3-year overall survival was not different (77% with maintenance and 57% with observation, P =.1). In the mantle cell cohort, a higher rate of ongoing remissions was noted beyond 2 years with maintenance rituximab 45% vs 9% with observation. Whether a survival benefit will emerge requires longer follow-up. The European Mantle Cell Lymphoma Network is currently studying the efficacy of

5 maintenance rituximab vs maintenance interferon following R-CHOP or the combination of rituximab, fludarabine, and cyclophosphamide in mantle cell lymphoma (NCT ). Hochster et al conducted a phase III trial in which 311 patients with untreated advanced indolent NHL underwent induction therapy with cyclophosphamide, vincristine, and prednisone (CVP) and subsequently were stratified to either observation or maintenance rituximab.[34] Progression-free survival was significantly longer with maintenance therapy (68% vs 33%), but there was no improvement in overall survival. In a meta-analysis of five trials of approximately 1,000 follicular lymphoma patients randomized to rituximab maintenance or observation after induction, patients who received maintenance appeared to have a significantly longer survival.[35] However, this analysis was problematic: Whereas the Eastern Cooperative Oncology Group (ECOG) 1496 study cohorts were included individually, the final analysis was not.[34,36,37] Second, only the earlier data from both van Oers et al suggesting survival prolongation were used, not the longer follow-up showing no difference.[20,38] Similarly, only the initial data from the ECOG 1496 trial were included.[36] Preliminary results of patients who received CVP induction showed an improvement in overall survival with maintenance therapy, but with long-term followup this disappeared as well.[34] The meta-analysis may have produced different results with longer follow-up of this indolent patient population.[31] It is also not clear if maintenance rituximab is more efficacious than re-treatment at time of progression. Hainsworth et al randomized 114 patients with relapsed indolent NHL to 4 weeks of rituximab followed by 4 weeks of maintenance rituximab every 6 months or rituximab retreatment at time of progression.[39] A longer progression-free survival was seen with maintenance therapy, but there was no difference in survival. The ECOG 4402 Rituximab Extended Schedule or Re-treatment Trial (RESORT) investigated this question in untreated indolent NHL, and results are pending. A number of factors should enter into the decision regarding the use of maintenance rituximab. First is the expense without an associated survival benefit. Second, there is no standard maintenance regimen, as schedules vary in frequency and duration (Table 3). Moreover, toxicities associated with maintenance rituximab include an increase in grade 3/4 infections as well as less common consequences such as progressive multifocal leukoencephalopathy.[40] In addition, maintenance may compromise response to subsequent therapies. Finally, none of the published studies in follicular lymphoma involve maintenance that follows the current standard of chemoimmunotherapy as the initial approach to the disease. In the Primary Rituximab and Maintenance (PRIMA) study, patients with untreated stage III/IV follicular lymphoma were treated with rituximab in combination with CHOP, CVP, or FCM, selected on an institutional basis. Patients who responded to induction were randomized to maintenance rituximab or observation. The study was closed early due to a planned interim analysis in which the primary endpoint of progression-free survival was prolonged with maintenance rituximab. Response rates, toxicity, and overall survival data are pending. Since no studies to date demonstrate a survival advantage for maintenance rituximab in follicular NHL, yet there is an increase in toxicities, maintenance is hard to justify on the basis of the available data. The lack of a role for maintenance in DLBCL is demonstrated by Habermann et al,[25] who conducted a phase III trial in which elderly patients with untreated DLBCL were

6 randomized to CHOP or R-CHOP followed by four weekly doses of rituximab every 6 months or observation. Although the primary endpoint of the study was reached with an improvement in failure-free survival (53% vs 46%), no survival benefit was seen from maintenance rituximab with R-CHOP. Other CD20 Monoclonal Antibodies Based on the efficacy, relative safety, and ubiquitous use of rituximab in B-cell NHL, attempts have been made to develop more effective anti-cd20 antibodies (Table 4). The farthest along in development is ofatumumab (Arzerra), a fully human IgG" anti- CD20 monoclonal antibody that targets a novel epitope of CD20 and appears to have stronger complement-dependent cytotoxicity, a slower disassociation rate, and more stability in binding to B cells than rituximab in vitro, even on cells with a low expression of CD20. In a multicenter, doseescalation phase I/II study including 40 patients with relapsed or refractory grade 1 or 2 follicular lymphoma, ofatumumab administered at four weekly doses from 300 mg to 1,000 mg produced a response rate of 43%.[41] Of the four patients reportedly rituximab-resistant, three showed a response to ofatumumab. A trial focusing on ofatumumab in rituximab-resistant follicular lymphoma patients is currently undergoing analysis (NCT ). Preliminary results indicate a 10% overall response rate.[42] Both the median duration of response and progression-free survival were 6 months. Ofatumumab was approved by the FDA in October 2009 for patients with CLL who are refractory to both fludarabine and alemtuzumab (Campath) based on the results of a phase I/II trial of single agent by Österborg et al in which single-agent ofatumumab produced an overall response rate of 42%.[43] Ongoing studies are evaluating ofatumumab in combination with other chemotherapeutic regimens such as CHOP (NCT ) and bendamustine (Treanda) in untreated follicular lymphoma. Ofatumumab is generally well tolerated in NHL, with the most common adverse effect being infusion-related. Other humanized CD20 antibodies currently being investigated include veltuzumab, GA101, and AME-133. In a phase I/II study of 82 patients with relapsed or refractory B-cell NHL who were given varying doses of veltuzumab ( mg), response rates of 44%, 83%, and 43% were seen in patients with follicular lymphoma, marginal zone lymphoma, and DLBCL, respectively.[44] Salles et al presented the interim analysis of a phase I/II trial of patients with relapsed or refractory CD20-positive malignancies. The follicular NHL patients showed a response rate of 43%.[45] Thus, it is not yet clear that there are major clinical differences among these agents. Epratuzumab Epratuzumab (LymphoCIDE) is a humanized monoclonal antibody directed against CD22, a B-cell marker thought to play a role in B-cell activation, cell-surface receptor

7 circulation, and modulation of antigen-receptor signaling. When epratuzumab was administered to 40 patients with follicular lymphoma in a phase I trial at doses escalating from 120 mg/m 2 to 1,000 mg/ m 2, the overall response rate was 24%. The highest response rate was 43% in patients who received epratuzumab at 360 mg/m 2 (Table 5).[46] No responses were seen in patients receiving less than 360 mg/m 2 or more than 480 mg/m 2. The investigators found no dose-limiting toxicities, but common adverse effects included infusion-related reactions and nausea. Leonard et al[47] conducted a phase II trial evaluating the effect of prior rituximab in follicular lymphoma or SLL patients receiving rituximab in conjunction with epratuzumab. The overall and complete response rates for follicular lymphoma were 54% and 24%, respectively, while the overall response rate for SLL was 57%. The median duration of response for all patients with follicular lymphoma was 13.4 months. In the 10 patients who achieved either a CR or complete response, unconfirmed (CRu), the median duration of response improved to 29 months. The median duration of response for SLL was 20 months. Moreover, while rituximab-naive patients had a response rate of 50% to the combination, patients who previously responded to rituximab had a response of 64%. Strauss et al[48] conducted a phase II trial of a combination of rituximab and epratuzumab in patients with refractory or relapsed NHL. Objective response rates for follicular lymphoma and DLBCL were 64% and 47%, respectively, while 24% and 33% of patients achieved either a CR or CRu. The median duration of response was 16 months for follicular lymphoma and 6 months for DLCBL. In a study from Micallef et al, epratuzumab was added to R-CHOP as first-line therapy for DLBCL.[49] Although 107 patients were initially enrolled in the study, only 78 were eligible for the analysis because patients who were CD22-negative were removed. The overall response rate was 95%, and the CR rate was 73%. Similar results were seen even when patients were separated into low- and high-risk International Prognostic Index (IPI) groups. The Cancer and Leukemia Group B (CALGB) recently completed a phase II trial of rituximab and epratuzumab in previously untreated follicular lymphoma with a low or intermediate Follicular Lymphoma IPI (FLIPI) score (NCT ), the results of which are undergoing analysis. Lumiliximab Lumiliximab is a chimeric macaque-human monoclonal antibody targeting CD23, an IgE receptor that naturally occurs on CLL/SLL B cells and which may play a role in stimulation of germinal center B cells. In preclinical studies, lumiliximab induced apoptosis in both CLL and CD23-positive B cells.

8 Byrd et al conducted a phase I trial of lumiliximab in relapsed or refractory CLL.[50] A total of 46 patients received lumiliximab at 125, 250, or 375 mg/m 2 weekly for 4 weeks; 500 mg/m 2 weekly for 4 weeks; 500 mg/m 2 three times during week 1, then 500 mg/m 2 weekly for the next 3 weeks; or 500 mg/m 2 three times weekly for 4 weeks, respectively. Although no partial responses (PRs) or CRs were achieved, 52% of patients experienced decreased lymph node bulk (> 50% in 8% of patients). Approximately 91% of patients had some improvement in degree of lymphocytosis, and no dose-limiting toxicities were seen. Lumiliximab exhibited synergy when combined with rituximab or fludarabine in preclinical studies. In a phase I/II trial of 31 patients with relapsed CLL treated with a combination of lumiliximab with fludarabine, cyclophosphamide, and rituximab (FCR), the overall response rate was 65%, with 52% CRs.[51] The median progression-free survival for responders was 19 months. Data from this trial were compared to previously published data by Wierda et al[52] in relapsed/refractory CLL patients who received FCR alone. While the overall response rates from both trials were similar 71% and 73% the complete response rate appeared higher with the addition of lumiliximab, (52% vs 25%), with no increase in toxicity. A randomized phase III trial (LUCID, Evaluation of Lumiliximab in Combination With FCR in Patients With Relapsed CLL) to compare the efficacy of these regimens was recently closed following an interim analysis. Galiximab Galiximab is a chimeric human-macaque monoclonal antibody that targets CD80, an immune costimulatory molecule important to the regulation of T-cell activity. Although only transiently expressed on the surface of activated B and T cells, CD80 is consistently present in various B-cell lymphomas. In a phase I/II trial of single-agent galiximab in 34 patients with relapsed or refractory follicular lymphoma, 11% of patients had a response (two CRs, two PRs) and 34% had stable disease.[53] Almost half of the patients experienced a decrease in size of their indicator lesion. The investigators noted a delay in response. Galiximab is well tolerated, with major adverse effects of fatigue, nausea, and headache. The drug has also been studied in combination with rituximab. In a phase I/II trial of relapsed or refractory follicular lymphoma, this combination produced a response rate of 66% and median progression-free survival of 12 months.[54] Czuczman et al conducted a phase II study of the combination as first-line treatment for patients with follicular lymphoma.[55] Of the 61 patients, 44% had a CR or CRu and 26% had a PR. Both response rate and progression-free survival appeared to inversely correlate with FLIPI score. Specifically, patients with FLIPI scores of 0 1, 2, and 3 5 had overall response rates of 92%, 80%, and 55%, respectively. The median progression-free survival was not reached for FLIPI scores of 0 2 and 1.62 years for scores 3 5. A trial of rituximab with or without galiximab in relapsed and refractory follicular lymphoma was recently prematurely closed. Thus, the future of this antibody is uncertain. Dacetuzumab Dacetuzumab (SGN-40) is a chimeric murine-human monoclonal antibody directed against CD40, a tumor necrosis factor receptor that naturally exists on the surface of normal B cells as well most B-cell malignancies. In a phase I trial of 50 patients with refractory or recurrent NHL, investigators reported one CR and five PRs.[56] The most

9 frequent side effects were fever, headache, and chills. A randomized trial of RICE (rituximab, ifosfamide, carboplatin, etoposide) with or without dacetuzumab prior to autologous stem cell transplantation for patients with relapsed DLBCL showed insufficient benefit to pursue this direction (NCT ). Lucatumumab Lucatumumab (HCD122), a fully humanized CD40 monoclonal antibody, has shown antitumor activity in NHL cells and is undergoing clinical evaluation for NHL and Hodgkin lymphoma in a phase I/II trial.[57] Alemtuzumab Alemtuzumab is a humanized monoclonal antibody against CD52, a marker present on both normal and malignant B cells and T cells as well as the majority of monocytes, macrophages, and natural killer cells. It was approved by the FDA for relapsed and refractory CLL/SLL in 2001, and for previously untreated patients in Alemtuzumab s initial approval was based on the results of a study by Keating et al in which 93 patients with disease relapsed or refractory to fludarabine and an alkylating agent were treated with escalating doses of alemtuzumab (3 30 mg).[58] The overall response rate was 33%, and the median overall survival was 16 months. The approved indications for alemtuzumab were expanded to include initial treatment of CLL based on the results of a randomized trial by Hillmen et al[59] in which 292 previously untreated patients were randomized to either alemtuzumab, 30 mg three times a week, or chlorambucil (Leukeran), 40 mg/m 2 every 28 days. Patients were treated for up to 12 months. Those who received alemtuzumab had a significantly longer progression-free survival (14.6 vs 11.7 months, P =.0001), and a higher overall response rate (83% vs 55%, P <.0001) and complete response rate (24% vs 2%, P <.0001) compared to chlorambucil. Adverse effects from alemtuzumab include thrombocytopenia, neutropenia, infusion reactions, and cytomegalovirus reactivation. Alemtuzumab has also been combined with other agents such as FCR for CLL, with promising results.[60] It is currently being investigated in combination with bendamustine (NCT ) and R-CHOP (NCT ) for refractory CLL. Anti-TRAIL Tumor necrosis factor related apoptosis ligand (TRAIL), a member of the tumor necrosis factor ligand family, binds cell surface receptors, including TRAIL-R1 and TRAIL-R2, which function as death receptors. These receptors are present on a variety of malignant cells including NHL. Mapatumumab and lexatumumab are fully humanized agonistic monoclonal antibodies that induce apoptosis by targeting TRAIL- R1 and TRAIL-R2, respectively. Other mechanisms of action include cell growth arrest, ADCC, and CDC. Mapatumumab has significant activity in vitro in NHL cell lines, inducing apoptosis in 30% to 50% of cell lines and reducing cellular proliferation in 60%.[61] Younes et al conducted a phase II trial in which mapatumumab was administered to 40 patients with relapsed or refractory NHL, at one of two dose levels.[62] The overall response rate was 8%, all in patients with follicular lymphoma. Lexatumumab is currently being studied in a phase I study of patients with relapsed or refractory lymphoma as well as other solid malignancies.

10 SMIPs Small modular immunopharmaceuticals (SMIPs) are single polypeptide chains consisting of a single-chain Fv linked to human IgG hinge, CH2, and CH3 domains, but exist in solution as homodimers.[63] TRU-016, a SMIP targeting CD37-positive B cells via both apoptosis and ADCC, has demonstrated both single-agent activity as well as synergy with bendamustine, rituximab, and rapamycin and additive benefit with doxorubicin.[64] Synergy of TRU-016 and bendamustine was also seen in vivo with follicular lymphoma murine xenografts. Andritsos et al[65] presented preliminary data from a phase I trial of 10 patients with refractory or relapsed CLL who were treated with TRU-016 at escalating doses of 0.03 mg/kg to 3 mg/kg IV once a week for four doses. The investigators found no dose-limiting toxicities and reported only three mild infusion reactions. All patients treated to at least 0.3 mg/kg were noted to have a response with either partial clearing of leukemia cutis or a 27% to 94% reduction in peripheral lymphocyte counts. One patient was noted to have a 36% reduction in lymph node size. BITEs Bi-specific T-cell engager molecules (BITEs) are antibodies that target both an antigen on a malignant cell and CD3 on the surface of T cells. BITEs are composed of two single-chain antibodies that bind not only the target antigen on malignant cells but also stimulate cytotoxic T cells for directed tumor cell lysis. Blinatumumab (MEDI-538) and MT110 are examples of BITEs that target CD19 and EpCam respectively. Bargou et al conducted a phase I trial of blinatumumab at doses of 0.5 µg/m 2 /24 h to 60 µg/m 2 /24 h in relapsed NHL.[66] Responses among the 38 patients included four CRs and 11 PRs, all at doses of at least 15 µg/ m 2 /24 h. The response rate for the seven patients treated at 60 µg/ m 2 /24 h was 100%. Common side effects included fever, chills, leukopenia, and lymphopenia. Adverse events leading to discontinuation of blinatumumab included metabolic acidosis, confusion, coma, and cerebellar ataxia. This trial is continuing to accrue patients, with a target dose of 120 µg/m 2 /24 h. Drug-Antibody Conjugates Drug-antibody conjugates (DACs) involve monoclonal antibodies attached to cytotoxic drugs via chemical linkers. Anti-CD79b-Vc-MMAE is a humanized CD79b antibody linked to cytotoxic monomethylauristatin E. CD79b is a part of the B-cell receptor and is involved in both apoptosis and cellular proliferation. As it is expressed only on B cells as well as most NHLs, it is an ideal target. Preclinical studies with anti-cd79b- Vc-MMAE show significant efficacy for cellular death against NHL cell lines and xenograft models of follicular, Burkitt s, and mantle cell lymphoma.[67] Inotuzumab ozogamicin (CMC-544) is composed of inotuzumab, an anti-cd22 antibody, and calicheamicin, a cytotoxic agent derived from the bacteria Micromonospora echinospora, which acts by cleaving DNA. In a phase I trial of 48 patients with refractory or relapsed lymphoma, the overall response rates for follicular lymphoma and DLBCL were 69% and 33%, respectively.[68] Inotuzumab ozogamicin was well tolerated, with the most significant side effect being thrombocytopenia. When combined with rituximab in a phase I/II trial in patients with relapsed follicular lymphoma or DLBCL, the response rates and 6-month progression-free survival were 88% and 100% for follicular lymphoma and 71% and 66% for DLBCL.[69]

11 Radioimmunotherapy Radioimmunotherapy involves binding of a radioisotope to a monoclonal antibody. While the antibody binds to the target cell, the radioactive portion of the molecule attacks not only the cells to which the antibody is bound, but also cells that either are not accessible to the antibody or do not express sufficient antigen to bind the antibody. Two extensively studied radioimmunotherapeutics are yttrium-90 ( 90 Y)-ibritumomab tiuxetan (Zevalin) and tositumomab/iodine-131 ( 131 I)-tositumomab (Bexxar). 90 Y-ibritumomab was approved by the FDA for the treatment of relapsed or refractory follicular and low-grade NHL. When administered to patients with rituximab-refractory indolent lymphomas, the overall response rate with 90 Y-ibritumomab tiuxetan was 74%, with 15% CRs.[70] Compared with rituximab in rituximab-naive patients with relapsed or refractory follicular or low-grade lymphomas, 90 Y-labeled ibritumomab tiuxetan produced significantly higher overall response rates (80% vs 56%) and complete response rates (30% vs 16%).[71] The median duration of response was 14.2 months in the 90Y-ibritumomab tiuxetan group vs 12.1 months in the control group (P =.6). Time to progression was 11.2 vs 10.1 months (P =.173) in all patients. 90 Y-ibritumomab tiuxetan has also been evaluated as consolidation following induction chemotherapy for patients with follicular lymphoma. In the First-line Indolent Trial (FIT), 414 patients in CR or PR after induction therapy, most regimens not including rituximab, were randomized to consolidation with radioimmunotherapy or not.[72] After a median follow-up of 3.5 years, radioimmunotherapy consolidation was associated with a significant increase in median progression-free survival (36.5 vs 13.3 months P <.0001). Of the 101 patients who achieved a PR with induction, 78% of them converted to a CR with radioimmunotherapy, increasing the final CR/CRu rate to 84.7% (vs 53.3% in the control arm). The most common toxicities were hematologic, and grade 3/4 infections occurred in 8% of patients. Based on these data, 90Yibritumomab tiuexetan was recently approved by the FDA as consolidation for patients with follicular lymphoma who have achieved a CR or PR to initial chemotherapy. There also appears to be a role for 90 Y-ibritumomab tiuxetan in the transplant setting. When added to BEAM (carmustine [BiCNU], etoposide, cytarabine [Ara-C], melphalan [Alkeran]) prior to autologous transplant for NHL patients who were ineligible for total-body irradiation, the 2-year overall survival and progression-free survival rates were 89% and 70%, respectively.[73] The toxicity profile was similar to BEAM alone, suggesting that the combination is reasonable for this population of patients and deserves further research. 90 Y-ibritumomab tiuxetan has activity in relapsed or refractory DLBCL as well, inducing overall response rates of 53% in rituximab-naive patients and 19% in patients with prior exposure to the antibody.[74] With a median follow-up of 21.7 months, median overall survival was 21.4 to 22.4 months and 4.6 months, respectively. A phase III trial investigating the efficacy of 90 Y-labeled ibritumomab tiuxetan as maintenance therapy for DLCBL patients who achieve a complete remission after R-CHOP is currently underway (NCT ). Tositumomab/ 131 I-tositumomab is approved for the treatment of CD20-positive rituximab and chemotherapy-refractory lymphomas. When administered to rituximabnaive patients with chemotherapy-refractory NHL, 131I-tositumomab induces a 65%

12 response rate with 20% complete remissions.[75] In patients with rituximab-refractory NHL, 131 I-tositumomab produced an overall response rate of 65% and complete response rate of 38%.[76] Kaminski et al conducted a phase II study of 131 I- tositumomab as first-line therapy for patients with follicular lymphoma; 95% of patients responded, including 75% complete remissions.[77] The 5-year progressionfree survival was 59% for all patients. In a Southwest Oncology Group (SWOG) phase II trial, patients with advanced-stage, previously untreated follicular lymphoma received six cycles of CHOP followed by 131 I-tositumomab if they were in CR or PR.[78] Of the 90 eligible patients, 84 subsequently received 131 I-tositumomab, which produced an overall response rate of 98% and complete response rate of 74%. 131 I-tositumomab increased the best overall response rate in 57% of patients who achieved a PR or CRu with CHOP alone. A total of 23 patients improved from a PR to a CRu or CR, while 4 patients increased from a CRu to a CR. The 4-year progression-free survival rate was 70% and 4-year overall survival rate was 91%. A phase III multicenter trial (SWOG 0016/CALGB 50102) comparing CHOP followed by 131 I- tositumomab to R-CHOP for previously untreated follicular lymphoma has completed accrual, and the results are pending. The most significant adverse effect associated with radioimmunotherapy is delayed myelosuppression, occurring at approximately 6 to 8 weeks after therapy. Given the risk of severe myelosuppression, patients with significant cytopenias are not candidates for these agents. Specifically, patients with absolute neutrophil counts < 1.5 # 10 3, platelets < 100,000, hemoglobin < 9 g/dl, > 25% disease involvement of marrow, or prior radiotherapy to > 25% of marrow are not eligible for radioimmunotherapy.[79] Whether radioimmunotherapeutics induce secondary acute myelogenous leukemia or myelodysplastic syndromes is controversial. Conclusion The availability of rituximab and radioimmunotherapy has revolutionized the treatment of B-cell NHL. Numerous new antibodies are now being evaluated. Whether they will prove superior to rituximab remains to be demonstrated. New directions to enhance antibody efficacy include maintenance, as well as combinations with cytotoxic agents, other monoclonal antibodies, apoptosis-inducing drugs, and immunomodulatory drugs. Correlative trials are integral to moving the field forward by providing a better understanding of how these drugs work and how cells develop resistance, as well as affording better insights into the biology of tumor cells and the microenvironment. The eventual goal of targeted therapy is to individualize treatment to increase response and

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