Standard-dose anti-CD20 antibody rituximab has efficacy in chronic lymphocytic leukaemia: results from a Nordic multicentre study

Phase I Trial: Cirmtuzumab Inhibits ROR1 Signaling and Stemness Signatures in Patients with Chronic Lymphocytic Leukemia

Cirmtuzumab is a humanized monoclonal antibody (mAb) that targets ROR1, an oncoembryonic orphan receptor for Wnt5a found on cancer stem cells (CSCs). Aberrant expression of ROR1 is seen in many malignancies and has been linked to Rho-GTPase activation and cancer stem cell self-renewal. For patients with chronic lymphocytic leukemia (CLL), self-renewing, neoplastic B cells express ROR1 in 95% of cases. High-level leukemia cell expression of ROR1 is associated with an unfavorable prognosis. We conducted a phase 1 study involving 26 patients with progressive, relapsed, or refractory CLL. Patients received four biweekly infusions, with doses ranging from 0.015 to 20 mg/kg. Cirmtuzumab had a long plasma half-life and did not have dose-limiting toxicity. Inhibition of ROR1 signaling was observed, including decreased activation of RhoA and HS1. Transcriptome analyses showed that therapy inhibited CLL stemness gene expression signatures in vivo. Cirmtuzumab is safe and effective at inhibiting tumor cell ROR1 signaling in patients with CLL.

Ibrutinib versus rituximab in relapsed or refractory chronic lymphocytic leukemia or small lymphocytic lymphoma: a randomized, open-label phase 3 study

In the Asia‐Pacific region, treatment options are limited for patients with relapsed/refractory chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma (SLL). Rituximab is widely used in this setting when purine analog‐based therapies are not appropriate. We evaluated the efficacy and safety of ibrutinib compared with rituximab in a randomized, open‐label phase 3 study in predominantly Asian patients with relapsed/refractory CLL/SLL. Patients (N = 160) were randomly assigned 2:1 to receive 420 mg ibrutinib (n = 106) until disease progression (PD) or unacceptable toxicity or up to six cycles of rituximab (n = 54). The primary endpoint was investigator‐assessed progression‐free survival (PFS); key secondary endpoints were overall response rate (ORR), overall survival (OS), and safety. Rituximab‐treated patients could crossover to receive ibrutinib after confirmed PD. At data cutoff, median treatment duration was 16.4 months for ibrutinib and 4.6 months for rituximab. Ibrutinib significantly improved PFS (hazard ratio [HR] = 0.180, 95% confidence interval [CI]: 0.105–0.308). ORR was significantly higher (P < 0.0001) with ibrutinib (53.8%) than with rituximab (7.4%). At a median follow‐up of 17.8 months, ibrutinib improved OS compared with rituximab (HR = 0.446; 95% CI: 0.221–0.900; P = 0.0206). Overall incidence of adverse events (AEs) was similar between treatments and was not exposure‐adjusted. With ibrutinib, most common AEs were diarrhea and platelet count decreased; with rituximab, most common AEs were neutrophil count decreased and platelet count decreased. Grade ≥3 AEs were reported in 82.7% of ibrutinib‐treated patients and 59.6% of rituximab‐treated patients. Ibrutinib improved PFS, ORR, and OS compared with rituximab and displayed a manageable safety profile in Asian patients with relapsed/refractory CLL/SLL.

The safety profile of monoclonal antibodies for chronic lymphocytic leukemia

INTRODUCTION

Monoclonal antibodies (MoAbs), non-chemotherapeutic agents targeting the antigens present on chronic lymphocytic leukemia (CLL) lymphocytes, are being implemented increasingly more often as treatment options. Areas covered: This article reviews the similarities and differences in the structure, mechanism of action, efficacy and safety profile of commercially-available MoAbs and prevents new agents potentially useful for CLL treatment. Publications in English before June 2016 were surveyed on the MEDLINE database for articles. Proceedings of the American Society of Hematology held during the last five years were also included. Expert opinion: MoAbs, especially those targeting CD20, are highly effective biological options for first-line and salvage treatment of CLL, particularly in chemoimmunotherapy, and possibly also as maintenance therapy. Treatment with MoAbs is associated with reduced risk of such adverse events as cytopenias, infections and secondary neoplasias and is generally well tolerated. Depending on antibody type, the most common adverse events are usually transient and limited to grade 1 and 2 infusion-related reactions. In addition to commercially available MoAbs, several other antibodies exist which are targeted against different antigens studied in the clinical trials.

Development of Novel Anti-Cd20 Monoclonal Antibodies and Modulation in Cd20 Levels on Cell Surface: Looking to Improve Immunotherapy Response

Rituximab has been revolutionized and validated CD20 targeting monoclonal antibody. Although, it is widely used for lymphoma therapy and many patients have been benefited. However significant numbers of patients are refractory or developed resistance to current therapies due to low level of CD20 expression and/or availability on cells surface. Thus development of novel anti-CD20 mAbs with great cell killing ability and enhance CD20 levels on cell surface can potentially exploit lymphoma therapy. In this scenario, we are summarizing the recently developed mAbs against CD20 and compounds that have ability to induce CD20 expression at significant level. We also are providing information regarding combination strategy for use of radiation and anti-CD20 mAbs in vitro. However, it will need to be determined by rigorous at pre-clinical and clinic testing. We hope this review will be beneficial for current research in the area of immunotherapy or radio-immunotherapy.

A phase 1 trial of the Fc-engineered CD19 antibody XmAb5574 (MOR00208) demonstrates safety and preliminary efficacy in relapsed CLL

CD19 is ubiquitously expressed on chronic lymphocytic leukemia (CLL) cells and is therefore an attractive candidate for antibody targeting. XmAb5574 (aka MOR00208) is a novel humanized CD19 monoclonal antibody with an engineered Fc region to enhance Fcγ receptor binding affinity. Here we report results of a first in human phase 1 trial of XmAb5574 in patients with relapsed or refractory CLL. Twenty-seven patients were enrolled to 6 escalating dose levels, with expansion at the highest dose level of 12 mg/kg. Nine doses of XmAb5574 were infused over 8 weeks. No maximal tolerated dose was reached, and the drug was generally well tolerated, with infusion reactions of grades 1 and 2 being the most common toxicities. Grade 3 and 4 toxicities occurred in 5 patients and included neutropenia, thrombocytopenia, increased aspartate aminotransferase, febrile neutropenia, and tumor lysis syndrome. XmAb5574 showed preliminary efficacy, with 18 patients (66.7%) responding by physical examination criteria and laboratory studies, and 8 patients (29.6%) responding by computed tomography criteria. Pharmacokinetics showed a half-life of 14 days with clearance that was not dose-dependent. In conclusion, this phase 1 trial demonstrates safety and preliminary efficacy of a novel Fc-engineered CD19 monoclonal antibody XmAb5574 and justifies movement into the phase 2 setting. This trial was registered at www.clinicaltrials.gov as #NCT01161511.

Current and emerging monoclonal antibody treatments for chronic lymphocytic leukemia: state of the art

Anti-CD20 monoclonal antibodies (mAbs), rituximab, ofatumumab and obinutuzumab, have a significant impact in the treatment of chronic lymphocytic leukemia (CLL), particularly in combination with chemotherapy. Over the last few years, several new mAbs have been developed and investigated in CLL. The most promising newer mAbs are directed against CD20, CD19, CD37 and CD40. Combinations of antibodies with targeted drugs like ibrutinib, idelalisib or lenalidomide will probably replace chemotherapy-based combinations in the near future. This review gives a critical overview of established mAbs as well as new antibodies potentially useful in CLL.

Idelalisib and rituximab in relapsed chronic lymphocytic leukemia

BACKGROUND

Patients with relapsed chronic lymphocytic leukemia (CLL) who have clinically significant coexisting medical conditions are less able to undergo standard chemotherapy. Effective therapies with acceptable side-effect profiles are needed for this patient population.

METHODS

In this multicenter, randomized, double-blind, placebo-controlled, phase 3 study, we assessed the efficacy and safety of idelalisib, an oral inhibitor of the delta isoform of phosphatidylinositol 3-kinase, in combination with rituximab versus rituximab plus placebo. We randomly assigned 220 patients with decreased renal function, previous therapy-induced myelosuppression, or major coexisting illnesses to receive rituximab and either idelalisib (at a dose of 150 mg) or placebo twice daily. The primary end point was progression-free survival. At the first prespecified interim analysis, the study was stopped early on the recommendation of the data and safety monitoring board owing to overwhelming efficacy.

RESULTS

The median progression-free survival was 5.5 months in the placebo group and was not reached in the idelalisib group (hazard ratio for progression or death in the idelalisib group, 0.15; P<0.001). Patients receiving idelalisib versus those receiving placebo had improved rates of overall response (81% vs. 13%; odds ratio, 29.92; P<0.001) and overall survival at 12 months (92% vs. 80%; hazard ratio for death, 0.28; P=0.02). Serious adverse events occurred in 40% of the patients receiving idelalisib and rituximab and in 35% of those receiving placebo and rituximab.

CONCLUSIONS

The combination of idelalisib and rituximab, as compared with placebo and rituximab, significantly improved progression-free survival, response rate, and overall survival among patients with relapsed CLL who were less able to undergo chemotherapy. (Funded by Gilead; ClinicalTrials.gov number, NCT01539512.).

Idelalisib, an inhibitor of phosphatidylinositol 3-kinase p110δ, for relapsed/refractory chronic lymphocytic leukemia

In a phase 1 trial, idelalisib (GS-1101, CAL-101), a selective inhibitor of the lipid kinase PI3Kδ, was evaluated in 54 patients with relapsed/refractory chronic lymphocytic leukemia (CLL) with adverse characteristics including bulky lymphadenopathy (80%), extensive prior therapy (median 5 [range 2-14] prior regimens), treatment-refractory disease (70%), unmutated IGHV (91%), and del17p and/or TP53 mutations (24%). Patients were treated at 6 dose levels of oral idelalisib (range 50-350 mg once or twice daily) and remained on continuous therapy while deriving clinical benefit. Idelalisib-mediated inhibition of PI3Kδ led to abrogation of Akt phosphorylation in patient CLL cells and significantly reduced serum levels of CLL-related chemokines. The most commonly observed grade ≥3 adverse events were pneumonia (20%), neutropenic fever (11%), and diarrhea (6%). Idelalisib treatment resulted in nodal responses in 81% of patients. The overall response rate was 72%, with 39% of patients meeting the criteria for partial response per IWCLL 2008 and 33% meeting the recently updated criteria of PR with treatment-induced lymphocytosis.(1,2) The median progression-free survival for all patients was 15.8 months. This study demonstrates the clinical utility of inhibiting the PI3Kδ pathway with idelalisib. Our findings support the further development of idelalisib in patients with CLL. These trials were registered at clinicaltrials.gov as #NCT00710528 and #NCT01090414.

Chemoimmunotherapy resistant follicular lymphoma: predictors of resistance, association with transformation and prognosis

Follicular lymphoma (FL) is characterized by an initial response to treatment with inevitable relapse. We evaluated chemoimmunotherapy resistance (CIR resistance) including transformation. We identified patients who received rituximab combination therapy for symptomatic FL. CIR resistance was defined as disease progression during rituximab-based chemoimmunotherapy, rituximab maintenance or within 6 months of treatment completion. Our primary outcome was time to early progression (CIR resistance). Between July 2006 and April 2010, 132 patients met the inclusion criteria and 22 (16.7%) demonstrated CIR resistance with a median follow-up of 33 months. High-risk Follicular Lymphoma International Prognostic Index (FLIPI) score was predictive of CIR resistance (hazard ratio [HR] 2.43; 95% confidence interval [CI], 1.4-4.1; p = 0.001). Overall, eight patients (36.3%) transformed (biopsy-proven), with no transformation in the chemoimmunotherapy responder group. Median overall survival in the CIR resistant group was 47 months. Patients with CIR resistance had high rates of histologic transformation and shorter survival with poor response to next therapy.

Monoclonal antibodies in chronic lymphocytic leukemia

Multiple options are now available for the treatment of chronic lymphocytic leukemia. Over the last 10 years, monoclonal antibodies have become an integral part of the management of this disease. Alemtuzumab has received approval for use in patients with fludarabine-refractory chronic lymphocytic leukemia. Rituximab has been investigated extensively in chronic lymphocytic leukemia both as a single agent and in combination with chemotherapy and other monoclonal antibodies. Epratuzumab and lumiliximab are newer monoclonal antibodies in the early phase of clinical development. This article will review the monoclonal antibodies more commonly used to treat chronic lymphocytic leukemia, the results obtained with monoclonal antibodies as single agents and in combination with chemotherapy, and other biological agents and newer compounds undergoing clinical trials.

Selection of rituximab dosage in chronic lymphocytic leukemia: where is the evidence?

Rituximab prolongs survival in many CD20-expressing B- lymphoid malignancies. In non-Hodgkin lymphoma (NHL), a large number of clinical studies have established the 375 mg/m(2) dose of rituximab as standard. In chronic lymphocytic leukemia (CLL), response rates to single-agent rituximab at the NHL dose were low, but the use of higher doses or more frequent dosing have led to improved response rates, suggesting that a higher dose may be required. This led to the empiric decision to adopt rituximab at 500 mg/m(2) in combination with fludarabine and cyclophosphamide (FC) in phase II and III trials in CLL. The final result was the approval of rituximab at 500 mg/m(2) for treatment of CLL, in combination with FC. There is, however, preclinical evidence that full saturation of CD20 molecules may not be required to achieve chemosensitization in cancer cells, and it remains possible that the approved dose of 500 mg/m(2) is higher than what is required to achieve maximal in vivo synergy. Nevertheless, all of the randomized evidence for superiority of rituximab plus chemotherapy over chemotherapy alone comes from studies using the 500 mg/m(2) dose.

Chronic lymphocytic leukemia: inception to cure: are we there?

There have been remarkable advances in our understanding of the biology and therapeutics of chronic lymphocytic leukemia. B cell receptor signaling and micro-environment in CLL biology have been the most modern areas of research. In CLL therapeutics, we have come a long way from alkylating agents to chemo-immunotherapy. Despite this there remain significant lacunae in the disease biology that has hindered our quest to achieve the ultimate in CLL: Cure. This review aims to summarize the past, present and future in the biology and treatment of CLL.

Targeted drug delivery for cancer therapy: the other side of antibodies

Therapeutic monoclonal antibody (TMA) based therapies for cancer have advanced significantly over the past two decades both in their molecular sophistication and clinical efficacy. Initial development efforts focused mainly on humanizing the antibody protein to overcome problems of immunogenicity and on expanding of the target antigen repertoire. In parallel to naked TMAs, antibody-drug conjugates (ADCs) have been developed for targeted delivery of potent anti-cancer drugs with the aim of bypassing the morbidity common to conventional chemotherapy. This paper first presents a review of TMAs and ADCs approved for clinical use by the FDA and those in development, focusing on hematological malignancies. Despite advances in these areas, both TMAs and ADCs still carry limitations and we highlight the more important ones including cancer cell specificity, conjugation chemistry, tumor penetration, product heterogeneity and manufacturing issues. In view of the recognized importance of targeted drug delivery strategies for cancer therapy, we discuss the advantages of alternative drug carriers and where these should be applied, focusing on peptide-drug conjugates (PDCs), particularly those discovered through combinatorial peptide libraries. By defining the advantages and disadvantages of naked TMAs, ADCs and PDCs it should be possible to develop a more rational approach to the application of targeted drug delivery strategies in different situations and ultimately, to a broader basket of more effective therapies for cancer patients.

Treatment of relapsed or refractory chronic lymphocytic leukemia

BACKGROUND

Recent advances in the treatment of chronic lymphocytic leukemia (CLL) have moved beyond the traditional use of alkylating agents and purine analogs into regimens combining these two chemotherapy classes with monoclonal antibodies.

METHODS

This article reviews treatments options for patients with relapsed or refractory CLL.

RESULTS

Several studies have investigated novel agents in treating patients with 17p deletion, TP53 mutation, and fludarabine-refractory CLL, as well as patients with suboptimal response to intense treatment. These investigational agents include rituximab, alemtuzumab, ofatumumab, bendamustine, high-dose methylprednisolone, lenalidomide, lumiliximab, cyclin-dependent kinase inhibitors, small modular immunopharmaceuticals, Bcl-2 inhibitors, and histone deacetylase inhibitors. While these newer drugs and combination therapies have shown promise as treatment options for CLL, additional studies are needed to determine the immunosuppression, toxicities, and infections associated with their use.

CONCLUSIONS

Despite improvement in initial overall response rates, most patients relapse and require further treatment. CLL remains incurable with standard therapies due to development of disease refractoriness. As such, novel approaches such as those noted above warrant continued research to improve outcomes for patients with CLL.

Immunomodulating antibodies and drugs for the treatment of hematological malignancies

The aim of cancer immunotherapy is to induce immune cells to kill tumor and promote immunological memory that protects against tumor recurrence. Most current immunotherapies, such as monoclonal antibodies (mAb), target the tumor cells directly. Advances in our understanding of the immune system such as the role of co-stimulatory and co-inhibitory receptors, and the advent of new immunomodulatory agents provide new opportunities to target the immune system and enhance anti-tumor immune responses. These promising agents include immunomodulating mAbs, Toll-like receptor agonists, IMiDs, and cytokines. In this review, we discuss the current results of immunomodulating agents in the treatment of hematological malignancies and propose applications that include targeting of the innate and adaptive immune systems as well as combinations with tumor-specific mAbs.

Ofatumumab is active in patients with fludarabine-refractory CLL irrespective of prior rituximab: results from the phase 2 international study

Ofatumumab, the human CD20 monoclonal antibody that binds a distinct epitope from rituximab, has demonstrated clinical benefit as monotherapy for patients with chronic lymphocytic leukemia refractory to fludarabine and alemtuzumab (FA-ref) and patients refractory to fludarabine with bulky (> 5 cm) lymph nodes (BF-ref). To potentially gain insight into outcomes in patients previously treated with or refractory to rituximab, we performed an ad hoc retrospective analysis in the final 96 FA-ref and 111 BF-ref patients. There were 117 patients previously treated with rituximab (98 rituximab-refractory); 89 patients were rituximab-naive. For rituximab-treated, rituximab-refractory, and rituximab-naive patients, overall response rate was 43%, 44%, and 53%; median progression-free survival was 5.3, 5.5, and 5.6 months; and median overall survival was 15.5, 15.5, and 20.2 months. There were no significant differences in ofatumumab-related infusion reactions, or hematologic or infectious adverse events between subgroups. In summary, ofatumumab monotherapy was effective and well tolerated in patients with fludarabine-refractory chronic lymphocytic leukemia, including in patients with previous rituximab exposure. This trial was registered at www.clinicaltrials.gov as #NCT00349349.

Cancer immunotherapy

Cancer immunotherapy consists of approaches that modify the host immune system, and/or the utilization of components of the immune system, as cancer treatment. During the past 25 years, 17 immunologic products have received regulatory approval based on anticancer activity as single agents and/or in combination with chemotherapy. These include the nonspecific immune stimulants BCG and levamisole; the cytokines interferon-α and interleukin-2; the monoclonal antibodies rituximab, ofatumumab, alemtuzumab, trastuzumab, bevacizumab, cetuximab, and panitumumab; the radiolabeled antibodies Y-90 ibritumomab tiuxetan and I-131 tositumomab; the immunotoxins denileukin diftitox and gemtuzumab ozogamicin; nonmyeloablative allogeneic transplants with donor lymphocyte infusions; and the anti-prostate cancer cell-based therapy sipuleucel-T. All but two of these products are still regularly used to treat various B- and T-cell malignancies, and numerous solid tumors, including breast, lung, colorectal, prostate, melanoma, kidney, glioblastoma, bladder, and head and neck. Positive randomized trials have recently been reported for idiotype vaccines in lymphoma and a peptide vaccine in melanoma. The anti-CTLA-4 monoclonal antibody ipilumumab, which blocks regulatory T-cells, is expected to receive regulatory approval in the near future, based on a randomized trial in melanoma. As the fourth modality of cancer treatment, biotherapy/immunotherapy is an increasingly important component of the anticancer armamentarium.

Enhancing the action of rituximab by adding fresh frozen plasma for the treatment of fludarabine refractory chronic lymphocytic leukemia

Complement deficiencies have been identified in many chronic lymphocytic leukemia (CLL) patients. Supplying fresh frozen plasma (FFP)-derived complement can enhance complement-dependent cell lysis by the rituximab. The objective of our study was to evaluate the clinical efficacy and safety of the treatment by adding FFP to rituximab in fludarabine refractory CLL patients. Twenty-two patients were treated with two units of FFP followed with rituximab, 375 mg/m(2), as a single agent, repeated every 1-2 weeks. Patients received a median of four courses of the combined FFP and rituximab treatment (range: 2-6). Sixteen patients (72.7%) responded to treatment and seven (31.8%) achieved a complete remission. Three (13.6%) of which had no evidence of minimal residual disease after treatment. Patients with high expression of ZAP-70 or CD38, unmutated immunoglobulin heavy chain variable region, mutated p53, or adverse cytogenetic features, achieved response to treatment at rates that appeared similar to those who did not have such characteristics. With a median follow-up of 12 (4-19) months, the median overall survival and progression free survival have not been achieved. Toxicity was minimal, and the treatment was well tolerated. Our data suggest that the adding FFP to rituximab is an effective nonmyelotoxic regimen for the treatment of fludarabine refractory CLL patients.

The emerging role of ofatumumab in the treatment of chronic lymphocytic leukemia

The treatment of chronic lymphocytic leukemia (CLL) has evolved over the past decade. Our better understanding of disease biology and risk stratification has allowed delivering more effective therapies. In fact, front-line chemoimmunotherapy has demonstrated improvement in overall survival when compared to chemotherapy in randomized studies. Yet, treatment of relapsed CLL remains challenging and few agents are effective in that setting. Ofatumumab (Ofa) is a humanized monoclonal antibody targeted against CD20 with demonstrable activity in rituximab-resistant CLL cell lines. This agent was recently approved for the treatment of relapsed/refractory CLL patients who have failed fludarabine and alemtuzumab. In this review, we provide a historical perspective on approaches to CLL as front-line and in the relapsed setting. We further summarize novel anti-CD20 antibodies with specific emphasis on ofa. We review studies that led to ofatumumab's approval including pre-clinical data, trials using ofa in combination therapies, and adverse events/toxicities reported with this agent.

Chemoimmunotherapy with fludarabine and rituximab produces extended overall survival and progression-free survival in chronic lymphocytic leukemia: long-term follow-up of CALGB study 9712

PURPOSE

The addition of rituximab to fludarabine-based regimens in chronic lymphocytic leukemia (CLL) has been shown to produce high response rates with extended remissions. The long-term follow-up of these regimens with respect to progression, survival, risk of secondary leukemia, and impact of genomic risk factors has been limited.

METHODS

We report the long-term follow-up of the chemoimmunotherapy trial CALGB 9712 from the Cancer and Leukemia Group B, for which treatment regimen was previously reported, to examine end points of progression-free survival (PFS), overall survival (OS), impact of genomic features, and risk of therapy-related myeloid neoplasm (t-MN).

RESULTS

A total of 104 patients were enrolled on this study and now have a median follow-up of 117 months (range, 66 to 131 months). The median OS was 85 months, and 71% of patients were alive at 5 years. The median PFS was 42 months, and 27% were progression free at 5 years. An estimated 13% remained free of progression at almost 10 years of follow-up. Multivariable models of PFS and OS showed that immunoglobulin heavy chain variable region mutational status was significant for both, whereas cytogenetic abnormalities were significant only for OS. No patient developed t-MN before relapse.

CONCLUSION

Long-term follow-up of CALGB 9712 demonstrates extended OS and PFS with fludarabine plus rituximab. Patients treated with fludarabine plus rituximab administered concurrently or sequentially have a low risk of t-MN. These long-term data support fludarabine plus rituximab as one acceptable first-line treatment for symptomatic patients with CLL.

The spectrum of use of rituximab in chronic lymphocytic leukemia

The monoclonal chimeric anti-CD20 antibody, rituximab, has considerably improved therapeutic outcome in B-cell chronic lymphocytic leukemia. Rituximab has limited clinical activity when used as a single agent. The combination of the monoclonal antibody with fludarabine-based regimens clearly demonstrated, in Phase II and randomized trials, an increase in clinical efficacy in previously untreated and pretreated patients. Furthermore the addition of rituximab enabled the eradication of minimal residual disease, which is correlated with the prognosis in a high proportion of patients. Although the combination of rituximab with fludarabine-based regimens increased myelosuppression and immunosuppression, incidence of infections did not increase. The benefit of adding rituximab to other purine analogs or other chemotherapeutic combination regimens has also been explored. Moreover there could be a role for achieving better quality of responses with the combination of different monoclonal antibodies, considering that they target different antigens and exert different mechanism of action. Although the role of rituximab as maintenance therapy in low grade non-Hodgkin's lymphomas has been determined, the benefit and optimal schedule in chronic lymphocytic leukemia are still under investigation. This review brings together knowledge of the pharmacokinetics, mechanism of action and clinical use of rituximab in chronic lymphocytic leukemia.

Ofatumumab: a new CD20 monoclonal antibody therapy for B-cell chronic lymphocytic leukemia

Though most patients with chronic lymphocytic leukemia (CLL) respond to first-line therapy, all patients eventually relapse, after which therapeutic options are limited. Fludarabine-refractory patients have a particularly poor prognosis. The addition of the CD20 monoclonal antibody (MoAb) rituximab to chemotherapy in CLL has improved outcomes, particularly in early lines of therapy; however, the efficacy of rituximab monotherapy in CLL is limited, potentially in part because of reduced cell lysis via complement-dependent cytotoxicity (CDC) in this setting. Rituximab CDC is dependent on CD20 expression; CLL cells underexpress CD20. Ofatumumab is a human MoAb that targets an epitope encompassing the membrane-proximal small-loop on the CD20 molecule, which differs from the binding location of rituximab. In vitro studies with ofatumumab have demonstrated that it is significantly more effective than rituximab at corresponding dose levels at lysing CLL cells and B-cell lines, especially those with low CD20 copy numbers. In patients with CLL refractory to both fludarabine and alemtuzumab or refractory to fludarabine with bulky lymphadenopathy and, therefore, less suitable for treatment with the CD52 MoAb alemtuzumab, results from the planned interim analysis showed an encouraging response rate with ofatumumab (Independent Endpoint Review Committee evaluated) and survival parameters, which seemed to be higher than those reported from a historical assessment of other salvage therapies in a corresponding group of patients. Ofatumumab was also well tolerated; the most common adverse events were transient grade 1 or 2 infusion reactions and infections. Ongoing trials will help confirm the role of ofatumumab in CLL, in addition to the effect of this agent in combination with chemotherapies and other MoAbs.

Rituximab in chronic lymphocytic leukemia

Rituximab is a class I chimeric anti-CD20 antibody that has shown efficacy in chronic lymphocytic leukemia (CLL), both as a single agent and in combination with traditional chemotherapies. The modest activity demonstrated in early studies evaluating rituximab in relapsed CLL was improved with higher doses or more dose-intensive regimens that overcame the unfavorable pharmacokinetic features commonly found in CLL. These studies led to a variety of combination trials of rituximab with chemotherapy, where both phase II and later phase III studies have shown great promise for the advancement of CLL therapy. Despite the therapeutic success of rituximab in CLL, studies demonstrating the definitive relative mechanism of tumor clearance are still lacking and this requires further investigation. In addition to being used as a therapy for CLL, rituximab is an effective treatment for autoimmune CLL complications such as hemolytic anemia and immune thrombocytopenia (ITP). Patients with CLL may experience early infusion-related side effects that can be diminished with corticosteroid pretreatment and stepped-up dosing. Risk factors for infusion-related toxicity may relate to atypical CLL expressing bright CD20 antigen expression, although several different studies have not clearly implicated elevated white blood cell count as a risk factor. Other adverse events, including delayed cytopenias, reactivation of hepatitis B, and development of progressive multifocal leukoencephalopathy, are rare. Future efforts focusing on novel combination-based strategies will be required to fully appreciate the benefit of this therapy in CLL.

Role of CD20 monoclonal antibodies in previously untreated chronic lymphocytic leukemia

Monoclonal antibodies (MoAbs) directed against the CD20 antigen on B cells have dramatically altered the treatment landscape for patients with chronic lymphocytic leukemia (CLL). Rituximab, a chimeric mouse/human MoAb, was the first antibody to be approved for the treatment of indolent B-cell lymphomas. Although single-agent, standard-dose rituximab has limited activity as first-line therapy for patients with CLL, it has synergistic therapeutic activity when combined with chemotherapy. Indeed, chemoimmunotherapy with combined fludarabine (F), cyclophosphamide (C), and rituximab was shown to improve both progression-free and overall survival in a randomized phase III clinical trial compared with FC in previously untreated patients with CLL. In this article, we review important clinical trials that have incorporated rituximab with other agents for treatment-naive patients with CLL. We also highlight second- and third-generation CD20 MoAbs approved or in development for the treatment of CLL.

Pharmacokinetics and pharmacokinetic/pharmacodynamic associations of ofatumumab, a human monoclonal CD20 antibody, in patients with relapsed or refractory chronic lymphocytic leukaemia: a phase 1-2 study

The purpose of this phase 1-2 study was to investigate the association between the pharmacokinetic properties of ofatumumab, a human monoclonal CD20 antibody, and outcomes in 33 patients with relapsed/refractory chronic lymphocytic leukaemia receiving 4 weekly infusions of ofatumumab. The ofatumumab concentration profiles were fitted well by a two-compartment model with different elimination rate constant at first infusion compared to the remaining infusions in line with the observed rapid and sustained B-cell depletion. Exposure to ofatumumab was linked to clinical outcomes: high exposure was associated with higher probability of overall clinical response and longer progression-free survival. This association still remained statistically significant even when adjusting for relevant baseline covariates including tumour burden.

Rituximab for the treatment of patients with chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is a lymphoproliferative disorder that originates from antigen-experienced B lymphocytes that do not die and hence accumulate due to external survival signals or undergo apoptosis and are replenished by proliferating precursors. These neoplastic lymphocytes exhibit a characteristic immunophenotype of CD5(+)/CD19(+)/CD20(+)/HLA-DR+/CD23(+)/sIgdim. Thus, the CD20 antigen has been an appealing target for therapy. The introduction of the monoclonal antibody rituximab (anti-CD20) enabled an outstanding advance in CLL treatment. The introduction of this monoclonal antibody into chemotherapy regimens has dramatically improved complete response rates and progression-free survival in patients with both untreated and relapsed CLL. Although only preliminary data from phase III confirmatory trials have been reported, the FCR regimen, which combines fludarabine and cyclophosphamide with rituximab, is currently the most effective treatment regimen for CLL patients, and has also been demonstrated to significantly improve overall survival. The success of rituximab and the identification of other CLL lymphocyte surface antigens have spurred the development of a multitude of monoclonal antibodies targeting distinct proteins and epitopes in an attempt to target CLL cells more effectively.

Ofatumumab as single-agent CD20 immunotherapy in fludarabine-refractory chronic lymphocytic leukemia

PURPOSE

New treatments are needed for patients with fludarabine- and alemtuzumab-refractory (FA-ref) chronic lymphocytic leukemia (CLL) or patients with fludarabine-refractory CLL with bulky (> 5 cm) lymphadenopathy (BF-ref) who are less suitable for alemtuzumab treatment; these groups have poor outcomes with available salvage regimens. Ofatumumab (HuMax-CD20) is a human monoclonal antibody targeting a distinct small-loop epitope on the CD20 molecule. We conducted an international clinical study to evaluate the efficacy and safety of ofatumumab in patients with FA-ref and BF-ref CLL.

PATIENTS AND METHODS

Patients received eight weekly infusions of ofatumumab followed by four monthly infusions during a 24-week period (dose 1 = 300 mg; doses 2 to 12 = 2,000 mg); response by an independent review committee (1996 National Cancer Institute Working Group criteria) was assessed every 4 weeks until week 24 and then every 3 months until month 24.

RESULTS

This planned interim analysis included 138 treated patients with FA-ref (n = 59) and BF-ref (n = 79) CLL. The overall response rates (primary end point) were 58% [corrected] and 47% in the FA-ref and BF-ref groups, respectively. Complete resolution of constitutional symptoms and improved performance status occurred in 57% and 48% of patients, respectively. Median progression-free survival and overall survival times were 5.7 and 13.7 months in the FA-ref group, respectively, and 5.9 and 15.4 months in the BF-ref group, respectively. The most common adverse events during treatment were infusion reactions and infections, which were primarily grade 1 or 2 events. Hematologic events during treatment included anemia and neutropenia.

CONCLUSION

Ofatumumab is an active, well-tolerated treatment providing clear clinical improvements for fludarabine-refractory patients with very poor-prognosis CLL.

Investigational immunotherapeutics for B-cell malignancies

The use of rituximab-based chemoimmunotherapy regimens has remarkably improved the response rates, long-term outcomes, and quality of life of patients with B-cell malignancies. However, a substantial number of patients exhibit either primary or acquired resistance to rituximab, which suggests that novel immunotherapeutics with distinct mechanisms of action are necessary. A series of monoclonal antibodies with specificity against different surface antigens expressed on malignant B cells (eg, CD22, CD23, CD40, CD70) and novel immunotherapeutics (eg, bispecific monoclonal antibodies, small-modular immunopharmaceuticals, T-cell engagers) are currently in clinical or final preclinical stages of development. Although these agents offer reason for optimism, considerable challenges lie ahead in establishing their real clinical value, as well as in integrating them into current therapeutic algorithms for patients with B-cell malignancies. This review describes some of the most promising investigational immunotherapeutics for the treatment of B-cell malignancies.

Engineered anti-CD20 antibodies with enhanced complement-activating capacity mediate potent anti-lymphoma activity

One of the major issues in current antibody therapy is insufficient efficacy. Various biological factors relating to the host's immune system or tumor cells have been suggested to reduce the efficacy of anti-CD20 therapy in B-cell malignancies. In this study, we characterized the in vitro anti-lymphoma activity of anti-CD20 antibodies having a novel engineered heavy chain with enhanced complement-dependent cytotoxicity (CDC). Anti-CD20 antibodies having a variant heavy constant region of mixed IgG1/IgG3 isotype, which have previously been found to enhance CDC, were investigated for their in vitro CDC against lymphoma cells and whole blood B-cell depletion activity. Use of the variant constant region greatly increased the CDC of an anti-CD20 antibody having variable regions identical to those of rituximab to the level shown by an IgG1 antibody of ofatumumab. Although the whole blood assay showed different cytotoxicity patterns among individual blood donors, the CDC-enhancing variant of rituximab showed higher activity than the parent IgG1 and consistently showed maximized activity when further combined with antibody-dependent cellular cytotoxicity (ADCC)-enhancing modification by fucose removal from Fc-linked oligosaccharides. In addition, the rituximab variant showed potent CDC against transfectant cells with lower CD20 expression and chronic lymphocytic leukemia-derived cell lines with higher complement regulatory proteins. These findings suggest that CDC enhancement, both alone and in combination with ADCC enhancement, increases the anti-lymphoma activity of anti-CD20 antibodies irrespective of individual differences in effector functions, and renders current anti-CD20 therapy capable of overcoming the potential resistance mechanisms.

A phase 2 study of yttrium-90 ibritumomab tiuxetan (Zevalin) in patients with chronic lymphocytic leukemia

BACKGROUND

Radioimmunotherapy (RIT) with radio-labeled monoclonal antibodies to CD20 produce a high response rate in patients with relapsed lymphoma. Use of this modality in patients with chronic lymphocytic leukemia (CLL) has been hampered by the extensive marrow involvement seen in patients with CLL, which would produce a high risk for marrow aplasia after treatment with RIT. Patients with lymphoma and marrow involvement have been treated with RIT if involved marrow was less than 25% of the total marrow. Thus, we adapted this approach as consolidation therapy in patients with CLL responding to chemoimmunotherapy.

METHODS

Fourteen patients with relapsed CLL either in partial remission or in complete remission but with disease documented by flow cytometry were treated with (90)Y ibritumomab tiuxetan.

RESULTS

One patient responded and achieved a complete remission but with residual disease detected by flow cytometry. Of note was that grade 3 or 4 hematologic toxicity was seen in 12 of the 13 (92%) evaluable patients, with grade 3 or 4 thrombocytopenia noted in 11 (85%) of the patients. In addition, myelosuppression was prolonged with a median duration of grade 3 or 4 thrombocytopenia of 37 days. Five patients had persistent thrombocytopenia 3 months post-therapy.

CONCLUSIONS

Even in patients with CLL and limited marrow involvement, the use of RIT results in unacceptable hematologic toxicity.

Chronic lymphocytic leukemia: treatment options for patients with refractory disease

Patients with purine analogue-refractory chronic lymphocytic leukemia (CLL) have short survival and limited treatment options. Defining the best salvage strategies for this population is challenging, because limited data are available from clinical trials, and because studies have enrolled mixed populations (patients with recurrent and refractory disease or patients with refractory disease and Richter transformation). Moreover, patients with refractory CLL have a high incidence of unfavorable molecular and clinical features, such as high-risk genomic profiles, unmutated immunoglobulin heavy-chain genes, expression of zeta-chain-associated protein kinase 70, and bulky lymphadenopathies. These patients are also severely immunosuppressed because of the underlying disease and the treatments received, and experience a high rate of infectious complications that pose an additional difficulty in selecting treatment. Despite these challenges, in parallel with better characterizations of the biologic features of refractory CLL, the number of available treatment modalities for this population has increased. Several chemoimmunotherapy combinations have been developed, and novel agents with a different mechanism of action are being investigated in clinical trials. Furthermore, allogeneic stem cell transplantation with nonmyeloablative conditioning regimens is a therapeutic strategy that is increasingly offered to patients with refractory CLL.

Incorporating the use of GM-CSF in the treatment of chronic lymphocytic leukemia

We evaluated the clinical activity of GM-CSF in combination with standard dose rituximab in patients with chronic lymphocytic leukemia (CLL). The rationale for exploring this combination is provided by the ability of GM-CSF to increase surface expression of CD20 in CLL cells and potentially render them a better target for rituximab. GM-CSF also enhances antibody-dependent cellular cytotoxicity against CLL cells. The combination of GM-CSF and rituximab was evaluated as initial treatment in elderly patients with indication for treatment and in patients at high risk for progression identified by elevated beta(2) microglobulin. This combination was also evaluated in patients with recurrent CLL. On the basis of the results of 118 patients, we observed an overall response rate of 65 and 9% complete remission and these results compare favourably with the results obtained with rituximab single agent. This combination was well tolerated with the most common toxicity consisting in mild GM-CSF injection site erythema. On the basis of this experience, we are currently evaluating the use of GM-CSF in combination with the chemoimmunotherapy regimen fludarabine, cyclophosphamide and rituximab.

Treatment of fludarabine-refractory chronic lymphocytic leukemia

The development of resistance to purine analogs defines a poor-risk subset of patients with chronic lymphocytic leukemia (CLL). Although in recent years chemoimmunotherapeutic combinations such as fludarabine, cyclophosphamide, and rituximab have induced response rates of 95% in previously untreated patients and increased the rates of failure-free survival, CLL remains incurable for many patients because of a lack of disease response or the development of refractoriness to fludarabine. Fludarabine-refractory disease is defined as CLL that does not respond to fludarabine or that recurs within 6 months of treatment with a fludarabine-containing regimen. The natural course of the disease is associated with poor survival. Salvage therapeutic strategies include alemtuzumab-containing regimens, targeted agents, and allogeneic stem cell transplantation. Single-agent alemtuzumab induces response in up to 40% of patients with fludarabine-refractory CLL, but responses are not durable, and the median survival is approximately 1 to 2 years. Alemtuzumab is also combined with fludarabine, cyclophosphamide, and/or rituximab, and other agents such as lenalidomide and flavopiridol, as well as targeted agents, and used in fludarabine-refractory CLL. Cumulative evidence suggests that allogeneic stem cell transplantation is an efficacious therapeutic strategy for patients who do not respond to fludarabine or who develop disease recurrence within 12 months after purine analog treatment. In conclusion, chemoimmunotherapy regimens that include alemtuzumab and/or rituximab and allogeneic stem cell transplantation improve the prognosis of this disease, but there is a continued need for novel, more effective therapies.

Binding of submaximal C1q promotes complement-dependent cytotoxicity (CDC) of B cells opsonized with anti-CD20 mAbs ofatumumab (OFA) or rituximab (RTX): considerably higher levels of CDC are induced by OFA than by RTX

The CD20 mAb ofatumumab (OFA) is more effective than rituximab (RTX) in promoting complement-dependent cytotoxicity (CDC) of B cells via the classical pathway (CP) of complement. CP activation is initiated by C1q binding to cell-bound IgG. Therefore, we examined the role of C1q in the dynamics of complement activation and CDC of B cell lines and primary cells from patients with chronic lymphocytic leukemia, reacted with OFA or RTX. C1q binding, complement activation, and colocalization of C1q with cell-bound mAbs were determined by flow cytometry and high-resolution digital imaging. C1q binds avidly to OFA-opsonized Raji and Daudi cells (K(D) = 12-16 nM) and colocalizes substantially with cell-bound OFA. Cells opsonized with OFA undergo high levels of complement activation and CDC in C1q-depleted serum supplemented with low concentrations of C1q. Under comparable conditions, RTX-opsonized cells bind less C1q; in addition, even when higher concentrations of C1q are used to achieve comparable C1q binding to RTX-opsonized cells, less complement activation and CDC are observed. Greater CDC induced by OFA may occur because C1q is bound in close proximity and with high avidity to OFA, resulting in effective CP activation. Moreover, OFA binds to the small, extracellular CD20 loop, placing the mAb considerably closer to the cell membrane than does RTX. This may facilitate effective capture and concentration of activated complement components closer to the cell membrane, potentially shielding them from inactivation by fluid phase agents and promoting efficient generation of the membrane attack complex.

Eradication of Minimal Residual Disease with Alemtuzumab in B-Cell Chronic Lymphocytic Leukemia (B-CLL) Patients: The Need for a Standard Method of Detection and the Potential Impact of Bone Marrow Clearance on Disease Outcome

The introduction of new therapeutic agents, such as fludarabine phosphate (Fludara) and alemtuzumab (MabCampath, Campath), has made it possible to treat B-cell chronic lymphocytic leukemia (B-CLL) more effectively, compared with alkylating agents. However, although an increasing number of patients are able to achieve complete remission (CR), relapse is almost inevitable, because of the re-emergence of the malignant clone from small numbers of residual malignant cells. This phenomenon has introduced a need for a more sensitive assessment of low-level disease which, in turn, has encouraged the development of therapies aimed at the eradication of all residual disease in CR patients. The eradication of residual disease is associated with improved remission durability and has great potential in offering the possibility of cure. Alemtuzumab is the foundation of many eradication-based treatment approaches because of its ability to achieve clinical remissions and to successfully purge minimal residual disease (MRD) from both blood and bone marrow in B-CLL patients. This article describes and compares polymerase chain reaction (PCR) and flow cytometric methodologies for the assessment of MRD, and presents data demonstrating that alemtuzumab can eliminate residual malignant cells from blood and bone marrow (whether assessed by PCR or flow cytometry) at the highest levels of sensitivity currently available. The ability to clear MRD from bone marrow in patients achieving clinical CR using alemtuzumab is a significant step forward in the treatment of B-CLL, and supports treatment strategies in which alemtuzumab is used in combination with other agents. Purging of MRD from both blood and bone marrow also enables patients to proceed to autologous hematopoietic stem cell transplantation, a strategy that is able to achieve long-term remission.

Targeted therapy for chronic lymphocytic leukemia

The introduction of targeted agents such as the monoclonal antibodies rituximab (anti-CD20) and alemtuzumab (anti-CD52) has brought about a remarkable change in the therapy of chronic lymphocytic leukemia (CLL). Although it is unclear whether overall survival has been improved, the incorporation of these monoclonal antibodies into chemoimmunotherapy regimens has dramatically improved complete response rates and progression-free survival in patients with both newly-diagnosed and relapsed CLL. The success of rituximab and alemtuzumab has spurred the development of other monoclonal antibodies targeting distinct proteins and epitopes on the surface of CLL cells and an exciting array of novel immunotherapeutics. The judicious use of these agents provides the opportunity to develop risk-adapted therapeutic strategies to optimize responses and quality of life in patients with CLL.

Antibody therapy for chronic lymphocytic leukemia

The introduction of the monoclonal antibodies rituximab (anti-CD20) and alemtuzumab (anti-CD52) has revolutionized the treatment of chronic lymphocytic leukemia (CLL). Both antibodies were first studied as single agents in relapsed CLL, but rituximab is increasingly used in combination chemoimmunotherapy regimens in previously untreated patients. Phase II studies demonstrated that the addition of rituximab to fludarabine-based chemotherapy improves complete response (CR) rates and prolongs progression-free survival (PFS), but a long-term survival benefit has not been shown. Alemtuzumab is less commonly used, due to the greater likelihood of infusion toxicity, as well as hematologic and immune toxicities. Subcutaneous (SC) administration significantly reduces infusion toxicity, but hematologic and infectious complications, most notably cytomegalovirus (CMV) reactivation, still occur with SC dosing. Alemtuzumab's unique clinical properties include its clinical activity in relapsed CLL patients with del(17p13) and its ability to eradicate minimal residual disease (MRD) in bone marrow. Its use as consolidation therapy to eradicate MRD after nucleoside analog therapy is under active study. Several investigational monoclonal antibodies are in preclinical or clinical studies, most notably lumiliximab (anti-CD23) and ofatumumab (HuMax CD20), and are briefly discussed in this review.

Safety and efficacy of ofatumumab, a fully human monoclonal anti-CD20 antibody, in patients with relapsed or refractory B-cell chronic lymphocytic leukemia: a phase 1-2 study

Safety and efficacy of the fully human anti-CD20 monoclonal antibody, ofatumumab, was analyzed in a multicenter dose-escalating study including 33 patients with relapsed or refractory chronic lymphocytic leukemia. Three cohorts of 3 (A), 3 (B), and 27 (C) patients received 4, once weekly, infusions of ofatumumab at the following doses: (A) one 100 mg and three 500 mg; (B) one 300 mg and three 1000 mg; (C) one 500 mg and three 2000 mg. Sixty-seven percent of the patients were Binet stage B, and the median number of previous treatments was 3. The maximum tolerated dose was not reached. The majority of related adverse events occurred at first infusion, and the number of adverse events decreased at each subsequent infusion. Seventeen (51%) of 33 patients experienced infections, 88% of them of grade 1-2. One event of interstitial pneumonia was fatal; all other cases resolved within one month. The response rate of cohort C was 50% (13/26), one patient having a nodular partial remission and 12 patients partial remission. In conclusion, ofatumumab was found to be well tolerated in patients with chronic lymphocytic leukemia (CLL) in doses up to 2000 mg. Preliminary data on safety and objective response are encouraging and support further studies on the role of ofatumumab in CLL patients. This trial was registered at www.clinicaltrials.gov as no. NCT00093314.