Rituximab-mediated sensitization of B-non-Hodgkin's lymphoma (NHL) to cytotoxicity induced by paclitaxel, gemcitabine, and vinorelbine

Camptothecin enhances 131I-rituximab-induced G1-arrest and apoptosis in Burkitt lymphoma cells

Background

Rituximab is a chimeric monoclonal antibody against CD20. It is an established immunotherapeutic agent for non-Hodgkin's lymphoma. Even though rituximab has been used in clinics for decades, only 50% of the patients respond to rituximab therapy. To enhance the in vitro effect of rituximab, it was labeled with Iodine-131 (¹³¹I) and combined effect of ¹³¹I-rituximab and camptothecin (CPT) was studied on a tumor cell line expressing CD20.

Objective

The aim is to study the magnitude of cell killing and the underlying mechanism responsible for enhancing in vitro therapeutic efficacy.

Materials and

Methods

Rituximab was labeled with ¹³¹I by the iodogen method. Raji cells were pretreated with CPT (250 nM) for an hour followed by ¹³¹I-rituximab (0.37 and 3.7 MBq) and incubated for 24 h in a humidified atmosphere of CO₂ incubator at 37°C. Subsequently, Raji cells were harvested and thoroughly washed to carry out studies of cellular toxicity, apoptosis, cell cycle, and mitogen-activated protein kinase (MAPK) pathways.

Results

Maximal inhibition of cell proliferation and enhancement of apoptotic cell death was observed in the cells treated with the combination of CPT and ¹³¹I-rituximab, compared to controls of CPT-treated and ¹³¹I-rituximab-treated cells. Raji cells undergo G1 arrest after ¹³¹I-rituximab treatment, which leads to apoptosis and was confirmed by the downregulation of bcl_xl protein. Expression of p38 was decreased while an increase in phosphorylation of p38 was observed in the combination treatment of CPT and ¹³¹I-rituximab.

Conclusions

It was concluded from the findings that CPT enhanced ¹³¹I-rituximab-induced apoptosis, G1 cell cycle arrest and p38 MAPK phosphorylation in Raji cells.

Apoptosis-promoting effect of rituximab-conjugated magnetic nanoprobes on malignant lymphoma cells with CD20 overexpression

Background

Cancer targeting nanoprobes with precisely designed physicochemical properties may show enhanced pharmacological targeting and therapeutic efficacy. As a widely used commercialized antibody, rituximab has been in clinical use for three decades and has lengthened or even saved thousands of lives. However, many people cannot benefit from rituximab treatment because of drug resistance or side effects.

Methods

In this study, a 13-nm rituximab-conjugated magnetic nanoparticle was developed as a therapeutic nanoprobe targeting CD20 overexpressing malignant lymphoma cells to enhance the treatment effects of rituximab. The magnetic cores (2,3-dimercaptosuccinicacid modified Fe₃O₄ nanoparticles, Fe₃O₄@DMSA) of the nanoprobes with an average diameter of 6.5 nm were synthesized using a co-precipitation method. Rituximab was then conjugated on the surface of Fe₃O₄@DMSA using a cross-linking agent (carbodiimide/N-hydroxysulfosuccinimide sodium salt). Based on theoretical calculations, approximately one antibody was coupled with one nanoparticle, excluding the multivalent antibody effect.

Results

Cell targeting experiments and magnetic resonance (MR) signal and T2 measurements showed that the Fe₃O₄@DMSA@Ab nanoprobes have specific binding affinity for CD20-positive cells. Compared to rituximab and Fe₃O₄@DMSA, Fe₃O₄@DMSA@Ab nanoprobes significantly reduced cell viability and promoted Raji cell apoptosis. Initiating events of apoptosis, including increased intracellular calcium and reactive oxygen species, were observed in nanoprobe-treated Raji cells. Nanoprobe-treated Raji cells also showed the most drastic decrease in mitochondrial membrane potential and Bcl-2 expression, compared to rituximab and Fe₃O₄@DMSA-treated Raji cells.

Conclusion

These results indicate that Fe₃O₄@DMSA@Ab nanoprobes have the potential to serve as MRI tracers and therapeutic agents for CD20-positive cells.

Drug-Free Macromolecular Therapeutics Induce Apoptosis via Calcium Influx and Mitochondrial Signaling Pathway

Recently, an innovative paradigm has been proposed in macromolecular therapeutics for treatment of B-cell lymphomas that can specifically kill cancer cells without a drug. The design rationale of this drug-free macromolecular therapeutic (DFMT) system is crosslinking the cell surface receptor to initiate apoptosis. However, how the apoptosis signal is triggered after receptor hyper-crosslinking remains to be elucidated. Here, two pathways, calcium influx dependent pathway and mitochondrial signal pathway, are identified to play major roles in triggering the programmed cell death. With the first step pretargeting and second step multiple binding, receptor hyper-crosslinking is achieved in a highly specific, time-dependent manner and largely mediated by multivalence. As a consequence, extracellular calcium influx is triggered, which subsequently decreases the mitochondrial membrane potential and induces apoptosis. The mitochondrial depolarization also stems from the Bcl-2 inhibition mediated by DFMT, followed by the cytochrome c release that activates caspase signaling. With the participation of the two-pronged mechanism, a programmed apoptosis is induced in response to DFMT treatment. The current findings can offer important implications to optimize the anti-CD20 strategies to treat B-cell non-Hodgkin lymphomas.

Mechanisms of action of therapeutic antibodies for cancer

The therapeutic utility of antibodies and their derivatives is achieved by various means. The FDA has approved several targeted antibodies that disrupt signaling of various growth factor receptors for the treatment of a number of cancers. Rituximab, and other anti-CD20 monoclonal antibodies are active in B cell malignancies. As more experience has been gained with anti-CD20 monoclonal antibodies, the multifactorial nature of their anti-tumor mechanisms has emerged. Other targeted antibodies function to dampen inhibitory checkpoints. These checkpoint inhibitors have recently achieved dramatic results in several cancers, including melanoma. These and related antibodies continue to be investigated in the clinical and pre-clinical settings. Novel antibody structures that target two or more antigens have also made their way into clinical use. Tumor targeted antibodies can also be conjugated to chemo- or radiotherapeutic agents, or catalytic toxins, as a means to deliver toxic payloads to cancer cells. Here we provide a review of these mechanisms and a discussion of their relevance to current and future clinical applications.

Rituximab for the treatment of follicular lymphoma

Rituximab is the first and most widely adopted anti-CD20 monoclonal antibody, and has dramatically improved outcomes for patients with B-cell malignancies. Rituximab is active as a single agent and when combined with chemotherapy improves both response rates and survival compared with chemotherapy alone. This approach has become standard of care in this setting. A number of Phase III studies using extended applications of rituximab have demonstrated that patients achieve a significantly longer progression-free survival, at the cost of an increase in infective complications. This has resulted in the widespread adoption of maintenance rituximab following the completion of primary therapy. Rituximab is useful in both previously untreated patients and at relapse, although a subset of patients develop disease that is rituximab resistant, which along with histologic transformation remains a significant management problem for patients with follicular lymphoma. The toxicities are modest and manageable, including infusion reactions, late-onset neutropenia, impaired humoral immunity, reactivation of hepatitis and possibly pulmonary toxicity.

Pilot study of dacetuzumab in combination with rituximab and gemcitabine for relapsed or refractory diffuse large B-cell lymphoma

Dacetuzumab, a CD40-targeted, humanized antibody, mediates antitumor activity through effector cell functions and direct apoptotic signal transduction. Preclinical studies demonstrated synergistic activity between dacetuzumab, gemcitabine and rituximab against non-Hodgkin lymphoma in vivo. A phase 1b safety/efficacy study of dacetuzumab in combination with rituximab and gemcitabine was conducted in relapsed/refractory diffuse large B-cell lymphoma (DLBCL). Patients received dacetuzumab at doses of 8 or 12 mg/kg IV weekly with rituximab (375 mg/m(2) IV weekly in cycle 1, then every 28 days) and gemcitabine (1000 mg/m(2) IV, days 1, 8 and 15, or days 1 and 15). Thirty-three patients with a median age of 67 years were enrolled. Common adverse events (≥ 15%) were grade 1/2 cytokine release syndrome, nausea, fatigue, thrombocytopenia, headache, decreased appetite, dyspnea, neutropenia, pyrexia, anemia, diarrhea, edema, constipation and cough. Dacetuzumab-related grade 3/4 adverse events occurred infrequently. Six of 30 evaluable patients achieved a complete response (CR) and eight a partial response (PR) per investigator assessment for an overall response rate (ORR) of 47%.

Sepantronium bromide (YM155) enhances response of human B-cell non-Hodgkin lymphoma to rituximab

In the treatment of B-cell non-Hodgkin lymphoma (B-NHL) rituximab improves long-term survival in combination with conventional chemotherapy. However, because the majority of patients with B-NHL eventually relapse, the development of more effective therapies is needed. Here, we evaluated the antitumor effects of a combination treatment involving sepantronium bromide (YM155), a first-in-class survivin suppressant, and rituximab in B-NHL xenograft mice models. To determine the efficacy of the combination treatment, YM155- and rituximab-treated B-NHL cell xenografted mice were monitored for tumor size and survival and subjected to 2'-deoxy-2'-(18)F-fluoro-D-glucose ((18)F-FDG) and 3'-(18)F-fluoro-3'-deoxythymidine ((18)F-FLT) positron emission tomography (PET) imaging. In addition, the cell proliferation status of excised tumors was examined by Ki-67 immunohistochemistry. In DB, WSU-DLCL-2, and Mino xenograft-bearing mice, the combination treatment of YM155 and rituximab induced significant tumor growth inhibition and tumor regression compared with either single agent. On day 3 after the initiation of treatment a significant decrease in both (18)F-FDG and (18)F-FLT tumor uptake from pretreatment levels was observed in combination treatment groups. The Ki-67 proliferation index was significantly decreased on day 3 in the xenograft models treated with combination treatment, suggesting that the combination of YM155 and rituximab reduced cell proliferation and glucose metabolism. Furthermore, compared with monotherapy, combination treatment prolonged survival times of severe combined immunodeficient mice with disseminated WSU-FSCCL and Jeko B-NHL tumors. Our findings demonstrate that YM155 and rituximab combination treatment enhances antitumor activity in B-NHL xenografts, and (18)F-FLT and (18)F-FDG PET imaging may allow the early functional evaluation of treatment responses in patients with B-NHL.

Combinations of mTORC1 inhibitor RAD001 with gemcitabine and paclitaxel for treating non-Hodgkin lymphoma

Single-agent mammalian target of rapamycin complex 1 (mTORC1) inhibitors have recently been reported as effective salvage treatment in non-Hodgkin lymphoma (NHL). The combined effect of mTORC1 inhibitor, RAD001, with chemotherapeutic agents used for relapsed or refractory NHL was examined. Synergistic interactions were observed for RAD001 plus gemcitabine or paclitaxel in six NHL cell lines; enhanced gemcitabine- and paclitaxel-induced caspase-dependent apoptosis associated with down-regulation of mTOR signaling was detected. Synergistic interactions were also observed with RAD001 plus gemcitabine and paclitaxel. In conclusion, synergistic cytotoxicity was observed with RAD001 plus gemcitabine and paclitaxel in NHL cells. Combination therapy with these three drugs should be examined in patients with refractory or relapsed NHL.

Rituximab: mechanism of action

Rituximab is a mainstay in the therapy for a broad variety of B-cell malignancies. Despite its undeniable therapeutic value, we still do not fully understand the mechanisms of action responsible for rituximab's anti-tumor effects. Direct signaling, complement-mediated cytotoxicity (CMC), and antibody-dependent cellular cytotoxicity (ADCC) all appear to play a role in rituximab efficacy. In vitro, animal model and clinical data addressing each of these mechanisms of action are reviewed, as are data speaking to the complexity of interactions between these mechanisms. Taken together, these data suggest different mechanisms are likely important in different scenarios. Study of the complex mechanisms of action that contribute to the clinical efficacy of rituximab have led to novel clinical trials including novel combinations, schedules, and generation of additional antibodies designed to have even greater effect. Such studies need to be accompanied by rigorous correlative analysis if we are to understand the importance of various mechanisms of action of rituximab and use that information to improve on what is already an indispensable component of therapy.

The use of single chain Fv as targeting agents for immunoliposomes: an update on immunoliposomal drugs for cancer treatment

IMPORTANCE OF THE FIELD

Targeted liposomal drugs represent the next evolution of liposomal drug delivery in cancer treatment. In various preclinical cancer models, antibody-targeted PEGylated liposomal drugs have demonstrated superior therapeutic effects over their non-targeted counterparts. Single chain Fv (scFv) has gained popularity in recent years as the targeting agent of choice over traditional targeting agents such as monoclonal antibodies (mAb) and antibody fragments (e.g., Fab').

AREAS COVERED IN THIS REVIEW

This review is focused mainly on advances in scFv-targeted liposomal drug delivery for the treatment of cancers, based on a survey of the recent literature, and on experiments done in a murine model of human B-lymphoma, using anti-CD19 targeted liposomes targeted with whole mAb, Fab' fragments and scFv fragments.

WHAT THE READER WILL GAIN

This review examines the recent advances in PEGylated immunoliposomal drug delivery, focusing on scFv fragments as targeting agents, in comparison with Fab' and mAb.

TAKE HOME MESSAGE

For clinical development, scFv are potentially preferred targeting agents for PEGylated liposomes over mAb and Fab', owing to factors such as decreased immunogenicity, and pharmacokinetics/biodistribution profiles that are similar to non-targeted PEGylated (Stealth) liposomes.

A natural compound, methyl angolensate, induces mitochondrial pathway of apoptosis in Daudi cells

Natural products discovered from medicinal plants have played an important role in the treatment of cancer. In an effort to identify novel small molecules which can affect the proliferation of lymphoma cells, we tested methyl angolensate (MA), a plant derived tetranortriterpenoid, purified from the crude extract of the root callus of Soymida febrifuga commonly known as Indian red wood tree. We have tested MA for its cytotoxic properties on Burkitt's lymphoma cell lines, using various cellular assays. We observed that MA induces cytotoxicity in Daudi cells in a dose-dependent manner using trypan blue, MTT and LDH assays. We find that the treatment with MA led to activation of DNA double-strand break repair proteins including KU70 and KU80, suggesting the activation of nonhomologous DNA end joining pathway in surviving cells. Further, we find that methyl angolensate could induce apoptosis by cell cycle analysis, annexin V-FITC staining, DNA fragmentation and PARP cleavage. Besides, MA treatment led to reactive oxygen species generation and loss of mitochondrial transmembrane potential. These results suggest the activation of mitochondrial pathway of apoptosis. Hence, we identify MA as a potential chemotherapeutic agent against Daudi cells.

CD20-directed small modular immunopharmaceutical, TRU-015, depletes normal and malignant B cells

PURPOSE

CD20-directed therapy with rituximab is effective in many patients with malignant lymphoma or follicular lymphoma. However, relapse frequently occurs within 1 year, and patients become increasingly refractory to retreatment. Our purpose was to produce a compact, single-chain CD20-targeting immunotherapeutic that could offer therapeutic advantages in the treatment of B-cell lymphoma.

EXPERIMENTAL DESIGN

Rituximab is a chimeric antibody containing two heavy chains and two light chains. Here, we describe the properties of TRU-015, a small modular immunopharmaceutical specific for CD20, encoded by a single-chain construct containing a single-chain Fv specific for CD20 linked to human IgG1 hinge, CH2, and CH3 domains but devoid of CH1 and CL domains.

RESULTS

TRU-015 mediates potent direct signaling and antibody-dependent cellular cytotoxicity but has reduced size and complement-mediated cytotoxicity activity compared with rituximab. TRU-015 is a compact dimer of 104 kDa that comigrates with albumin in size exclusion chromatography and retains a long half-life in vivo. TRU-015 induced growth arrest in multiple B lymphoma cell lines in vitro and showed effective antitumor activity against large, established subcutaneous Ramos or Daudi xenograft tumors in nude mice. TRU-015 also showed rapid, dose-dependent, and durable depletion of peripheral blood B cells following single-dose administration to nonhuman primates.

CONCLUSION

These results indicate that TRU-015 may improve CD20-directed therapy by effectively depleting embedded malignant B cells and nonmalignant pathogenic B cells and do so with reduced complement activation.

DHAP in combination with rituximab vs DHAP alone as salvage treatment for patients with relapsed or refractory diffuse large B-cell lymphoma: a matched-pair analysis

The addition of rituximab to chemotherapy in patients with diffuse large B-cell lymphoma (DLBCL) has been shown to improve outcome in first-line therapy. However, in patients with relapsed or refractory disease, the value of adding rituximab to salvage chemotherapy is less clearly defined. This study performed a matched-pair analysis of patients with relapsed or refractory DLBCL by comparing the combination of dexamethasone, high-dose cytarabine and cisplatin (DHAP) with rituximab to DHAP alone. Sixty-seven patients with relapsed or refractory DLBCL were collected from two prospective phase II trials from Germany and Italy. Twenty-three patient pairs treated with either DHAP in combination with rituximab or DHAP alone could be analysed after matching for important prognostic factors. The addition of rituximab to the DHAP regimen led to higher complete and similar overall remission rates. However, differences with regard to complete remission rates failed to reach statistical significance, thereby necessitating further evaluation of the role of combined immunochemotherapy in this patient population.

Rituximab, gemcitabine and oxaliplatin: an effective salvage regimen for patients with relapsed or refractory B-cell lymphoma not candidates for high-dose therapy

BACKGROUND

High-dose therapy (HDT) with stem-cell support is the reference treatment for relapsed lymphoma, but is not appropriate for all patients. Conventional salvage chemotherapies have been used with limited efficacy and significant toxicity. Rituximab, gemcitabine and oxaliplatin are active as single agents in relapsed or refractory lymphoma, and have demonstrated synergistic effects in vitro and in vivo.

PATIENTS AND METHODS

Forty-six patients with relapsed or refractory B-cell lymphoma received up to eight cycles of R-GemOx (rituximab 375 mg/m(2) on day 1, gemcitabine 1000 mg/m(2) and oxaliplatin 100 mg/m(2) on day 2). The majority (72%) had diffuse large B-cell lymphoma.

RESULTS

After four cycles of R-GemOx, the overall response rate was 83% [50% complete response (CR)/unconfirmed CR (CRu)]. High CR/CRu rates were observed in all histological subtypes. In patients who had previously received rituximab, the CR/CRu rate after eight cycles was 65%. The 2-year event-free and overall survival rates (median follow-up of 28 months) were 43% and 66%, respectively. Among responders, the probability of being disease free for 2 years was 62%. Treatment was generally well tolerated.

CONCLUSION

R-GemOx shows promising activity with acceptable toxicity in patients with relapsed/refractory B-cell lymphoma who are not eligible for HDT.

The anti-CD20 antibody rituximab augments the immunospecific therapeutic effectiveness of an anti-CD19 immunotoxin directed against human B-cell lymphoma

The chimaeric anti-CD20 antibody rituximab (Rituxan) sensitises lymphoma cells to small molecule cytotoxic drugs and to protein toxins. We have explored the augmentive effect of rituximab on the anti-CD19 immunotoxin BU12-SAPORIN in a model of human lymphoma. Intact rituximab and its F(ab)2 derivative both augmented the immunospecific protein synthesis inhibitory effects of BU12-SAPORIN in a complement-independent manner. A combination of rituximab + BU12-SAPORIN completely abolished the proliferation of Ramos cells in vitro and also induced a significantly greater degree of apoptosis in these cells. Treatment with rituximab, BU12-SAPORIN or a combination of both induced poly(ADPribose) polymerase and caspase 3 cleavage, although this was always consistently greater in combination-treated cells. zVAD almost completely inhibited apoptosis in rituximab- or BU12-SAPORIN-treated cells but only partially in combination-treated cells. In severe combined immunodeficient (SCID)-Ramos mice the combination of rituximab + BU12-SAPORIN was significantly better therapeutically than either single agent. The immunological fidelity of the therapeutic effect because of combination treatment was demonstrated through the failure of rituximab to augment an irrelevant anti-CD7 immunotoxin. The therapeutic efficacy of rituximab and combination treatment was reduced in SCID-Ramos mice depleted of serum complement while natural killer cell depletion failed to show any convincing role for antibody-dependent cellular cytotoxicity. This study shows a clear therapeutic advantage from using rituximab to immunospecifically augment immunotoxin cytotoxicity warranting further investigation.

High efficacy of combined rituximab and gemcitabine on Epstein–Barr virus-associated human B-cell lymphoma obtained after Hodgkin's xenograft in immunodeficient mice

The objectives were to characterize an Epstein-Barr virus-associated human B-cell lymphoma obtained from Hodgkin's xenograft, and to evaluate the in-vivo combination of rituximab and/or gemcitabine. A lymph node biopsy sample from a patient with Hodgkin's disease was xenografted into Rag gamma(c)(-/-) mice. Immunohistochemical, cytogenetic and genetic analyses were performed on both the human biopsy and xenografted tumor from severe combined immunodeficient mice. Tumor-bearing mice were then treated with rituximab and/or gemcitabine. Histologic features of the patient's biopsy concluded on classical CD15/CD30-positive Hodgkin's disease without expression of Epstein-Barr virus proteins. In contrast, morphologic and immunophenotypic examination of the xenograft showed diffuse proliferation of large B cells with high Epstein-Barr virus protein expression. Comparative genomic hybridization showed a normal pattern in the first case and a gain of chromosomal 12 in the xenografted tumor. Finally, polymerase chain reaction detected an immunoglobulin heavy chain rearrangement in the xenografted tumor. Altogether, these results indicate that the xenograft grew from the patient's Epstein-Barr virus-infected B-lymphoid cells and could be assimilated to posttransplant lymphoproliferative disease. In-vivo treatments of xenografted tumors showed significant tumor growth inhibition induced either by rituximab or gemcitabine alone and an impressive efficacy of combined treatment. This result therefore indicates that combined rituximab and gemcitabine could be an alternative approach in patients with posttransplant lymphoproliferative disease.

Concurrent administration of granulocyte colony-stimulating factor or granulocyte-monocyte colony-stimulating factor enhances the biological activity of rituximab in a severe combined immunodeficiency mouse lymphoma model

A predominant percentage of the in vivo antitumor activity of rituximab occurs through antibody-dependent cellular cytotoxicity (ADCC) via FcgammaRIII receptors. Co-expression of CD11b/CD18 (MAC-1), an adhesion molecule present in activated neutrophils, plays an important role in the induction of ADCC. The effects of granulocyte-monocyte colony-stimulating factor (GM-CSF) and granulocyte colony-stimulating factor (G-CSF) on the biological activity of rituximab were studied in a non-Hodgkin's lymphoma (NHL)-bearing severe combined immunodeficiency (SCID) mouse model. Natural killer (NK) cell-depleted SCID mice were inoculated intravenously with Raji cells. Animals were divided into 6 cohorts: group A: placebo (saline injection); group B: murine (m)-G-CSF; group C: m-GM-CSF; group D: rituximab alone; group E: concurrent m-G-CSF and rituximab; and group F: concurrent m-GM-CSF and rituximab. Treatment with G-CSF or GM-CSF led to a 1.5- to 2-fold increase of CD11b/CD18 expression in neutrophils. Treatment with G-CSF led to the highest expression of CD11b/CD18 on neutrophils. No antitumor activity was observed among mice treated with G-CSF or GM-CSF alone. After 3 months, survival rates were highest in animals treated with rituximab and G-CSF (53.3%) compared to rituximab alone (13.3%) or in combination with peg-GM-CSF (26.7%). Increasing neutrophil counts via cytokine stimulation may play an important role in augmenting rituximab-associated antitumor activity.

Antitumor efficacy of a combination of CMC-544 (inotuzumab ozogamicin), a CD22-targeted cytotoxic immunoconjugate of calicheamicin, and rituximab against non-Hodgkin's B-cell lymphoma

PURPOSE

CMC-544 is a CD22-targeted cytotoxic immunoconjugate, currently being evaluated in B-cell non-Hodgkin's lymphoma (B-NHL) patients. Rituximab is a CD20-targeted antibody commonly used in B-NHL therapy. Here, we describe antitumor efficacy of a combination of CMC-544 and rituximab against B-cell lymphoma (BCL) in preclinical models.

EXPERIMENTAL DESIGN

BCLs were cultured in vitro with CMC-544, rituximab, or their combination. BCLs were injected either s.c. or i.v. to establish localized s.c. BCL in nude mice or disseminated BCL in severe combined immunodeficient mice, respectively. I.p. treatment with CMC-544 or rituximab was initiated at various times either alone or in combination and its effect on s.c. BCL growth or survival of mice with disseminated BCL was monitored.

RESULTS

In vitro growth-inhibitory activity of CMC-544 combined with rituximab was additive. Rituximab but not CMC-544 exhibited effector functions, such as antibody-dependent cellular cytotoxicity and complement-dependent cytotoxicity. Rituximab was less effective in inhibiting growth of established BCL xenografts than developing xenografts. In contrast, CMC-544 was equally effective against both developing and established BCL xenografts. Although CMC-544 and rituximab individually caused partial inhibition of the growth of BCL xenografts at suboptimal doses examined, their combination suppressed xenograft growth by >90%. In a disseminated BCL model, 60% of CMC-544-treated mice and 20% of rituximab-treated mice survived for 125 days. In contrast, 90% of mice treated with the combination of CMC-544 and rituximab survived for longer than 125 days.

CONCLUSION

The demonstration of superior antitumor activity of a combination of CMC-544 and rituximab described here provides the preclinical basis for its clinical evaluation as a treatment option for B-NHL.

Enhanced efficacy of gemcitabine in combination with anti-CD20 monoclonal antibody against CD20+ non-Hodgkin's lymphoma cell lines in vitro and in scid mice

Background

Despite exciting new targeted therapeutics against non-Hodgkin's lymphoma (NHL), chemotherapy remains a cornerstone of therapy. While purine nucleoside analogs have significant activity in low grade NHL, the pyrimidine nucleoside analog gemcitabine has been less extensively studied, but has important activity. Use of the anti-CD20 monoclonal antibody rituximab in combination with chemotherapy for B-NHL is becoming prevalent in clinical practice, but has not been extensively studied in pre-clinical models.

Methods

We have tested the activity of gemcitabine ± rituximab in vitro and in scid/human NHL xenograft models. We used two t(14;18)+, CD20+ follicular B cell NHL cell lines, DoHH2 a transformed NHL line and WSU-FSCCL isolated from pleural fluid of a patient with indolent NHL.

Results

Gemcitabine is cytotoxic to DoHH2 and WSU-FSCCL cells in vitro, and the IC₅₀ is 2–3 fold lower in the presence of rituximab. Apoptosis is also enhanced in the presence of rituximab. Clearance of NHL cells from ascites in scid mice is prolonged by the combination, as compared with either agent alone. Most importantly, survival of scid mice bearing human NHL cells is significantly prolonged by the combination of gemcitabine + rituximab.

Conclusion

Based on our pre-clinical data showing prolonged survival of mice bearing human lymphoma cell line xenografts after treatment with gemcitabine + anti-CD20 antibody, this combination, expected to have non-overlapping toxicity profiles, should be explored in clinical trials.

Combination chemotherapy with gemcitabine and vinorelbine in the treatment of relapsed or refractory diffuse large B-cell lymphoma: a phase-II trial by the Hellenic Cooperative Oncology Group

To investigate the efficacy and toxicity of the combination of gemcitabine and vinorelbine in patients with relapsed or refractory diffuse large B-cell lymphoma (DLBL), 22 patients with relapsed or refractory DLBL were treated with gemcitabine 1000 mg/m2 and vinorelbine 30 mg/m2 on days 1 and 8 every 3 wk for a maximum of six cycles. Fourteen patients were considered chemosensitive while eight patients were considered chemoresistant to the last treatment regimen. All 22 patients were assessed for response to treatment. Three patients (14%) achieved complete remission and eight patients (36%) had partial remission of their disease, with an overall response rate of 50%. With a median follow up of 44 months, the median time to progression (TTP) for all patients was 8.1 months while the median overall survival (OS) was 12.9 months. Toxicity was minimal and all patients were treated on an outpatient basis. The combination of gemcitabine and vinorelbine is an effective and well-tolerated regimen for patients with relapsed of refractory DLBL.

Signaling via the anti-CD30 mAb SGN-30 sensitizes Hodgkin's disease cells to conventional chemotherapeutics

SGN-30, a monoclonal antibody with activity against CD30+ malignancies, is currently in phase II clinical evaluation for treatment of Hodgkin's disease (HD) and anaplastic large cell lymphoma. The mechanisms underlying SGN-30's antitumor activity were investigated using cDNA array of L540 cells. SGN-30 treatment activated NF-kappaB and modulation of several messages including the growth regulator p21WAF1/CIP1 (p21) and cellular adhesion marker ICAM-1. p21 protein levels increased coincident with growth arrest and Annexin V/PI staining in treated HD cells. To determine if SGN-30-induced growth arrest would sensitize tumor cells to chemotherapeutics used against HD, L540cy and L428 cells were exposed to SGN-30 in combination with a panel of cytotoxic agents and resultant interactions quantified by the Combination Effects Method. Interactions between SGN-30 and all cytotoxic agents examined were additive or better. These in vitro data translated to increased efficacy of SGN-30 and bleomycin against L540cy tumor xenografts. In addition to direct cell killing, SGN-30 affects growth arrest and drug sensitization through growth regulating and proapoptotic machinery. Importantly, these data suggest that SGN-30 can enhance the efficacy of standard chemotherapies used to treat patients with CD30+ malignancies.

Gemcitabine, cisplatin and methylprednisolone (GEM-P) is an effective salvage regimen in patients with relapsed and refractory lymphoma

There is currently no standard salvage chemotherapy regimen in relapsed and refractory lymphoma. Gemcitabine is a novel nucleoside analogue, which acts synergistically with cisplatin both in vitro and in clinical studies. We evaluated the combination of gemcitabine, cisplatin and methylprednisolone (GEM-P) in 41 heavily pretreated patients with relapsed and refractory Hodgkin's and non-Hodgkin's lymphoma. The best-achieved response rate (RR) was 79% (95% CI 64-91), with a complete RR of 21%. In patients with chemo-resistant disease, the RR was 63%. Myelosuppression was the main toxicity, the incidence of Grade 3 or 4 anaemia, neutropenia and thrombocytopenia was 17.1, 61.0 and 53.7% respectively. Only one patient had neutropenic sepsis and none of the patients suffered from haemorrhage. Grade 3 or 4 nonhaematological toxicity was minimal and stem cell mobilisation was not inhibited. GEM-P is an effective salvage regimen and its use prior to autologous stem cell transplant warrants further investigation.

Carcinoembryonic antigen antibody inhibits lung metastasis and augments chemotherapy in a human colonic carcinoma xenograft

PURPOSE

In addition to its use as a blood marker for many carcinomas, elevated expression of carcinoembryonic antigen (CEA, CD66e, CEACAM5) has been implicated in various biological aspects of neoplasia, especially tumor cell adhesion, metastasis, the blocking of cellular immune mechanisms, and having antiapoptosis functions. However, it is not known if treatment with anti-CEA antibodies can affect tumor metastasis or alter the effects of cytotoxic drugs.

METHODS

In vitro, human colon cancer cell lines were treated with anti-CEA MAb IgG1, hMN-14 (labetuzumab), to assess direct effects on proliferation, as well as antibody-dependent cellular cytotoxicity (ADCC), and complement-dependent cytotoxicity (CDC). In vivo studies were undertaken in nude mice bearing s.c. (local growth) or i.v. (metastatic model) GW-39 and LS174T human colon cancer grafts, to evaluate the MAb alone and in combination with either CPT-11 or 5-fluorouracil (5FU).

RESULTS

In vitro, labetuzumab did not induce apoptosis, nor did it affect tumor cell proliferation directly or by CDC, but it did inhibit tumor cell proliferation by ADCC. In vivo, labetuzumab did not increase median survival in the GW-39 metastatic model unless the mice were pretreated with GM-CSF to increase their peripheral WBC counts; GM-CSF alone was ineffective. Also, if GW-39 tumors were pretreated with IFN-gamma to up-regulate CEA expression threefold prior to i.v. injection, labetuzumab significantly increased median survival of the mice. When nude mice received labetuzumab with CPT-11 or 5FU, median survival increased significantly as compared to the drug or antibody alone.

CONCLUSIONS

Labetuzumab, a CEA-specific MAb, induces effector-cell function in vitro against CEA-positive colonic tumor cells, and also inhibits growth of lung metastasis when CEA expression is up-regulated or if peripheral WBCs are increased. The MAb also shows chemosensitizing properties.

Rituximab plus gemcitabine: a therapeutic option for elderly or frail patients with aggressive non Hodgkin's lymphoma?

The standard treatment for patients with aggressive B-cell lymphoma--particularly diffuse large-B-cell lymphoma [DLBCL)--is cyclophosphamide, doxorubicin, vincristine and prednisone [CHOP) plus rituximab, a chimeric monoclonal antibody against the CD20 antigen. However, some patients are not fit enough to tolerate CHOP or they relapse after previous therapy with CHOP. Gemcitabine as a monotherapy is active and relatively non-toxic in the treatment of NHL. We investigated the toxicity and efficacy of a combination of gemcitabine with rituximab in a small series of elderly patients with high-grade B-cell lymphoma who had either a relapse after CHOP, or were medically unfit to tolerate CHOP as a first-line therapy. Gemcitabine was given at 1000 mg/m2/week x 3, q28 days; rituximab at 325 mg/m2/week x 4 in the first cycle, and on day 1 of all subsequent cycles. Seven patients have been treated. The median number of cycles given was 4. The major toxicity was haematologic: grade 3/4 leukocytopenia occurred in 4 patients, grade 3/4 thrombocytopenia in 3 patients. There were no episodes of clinically significant bleeding. One patient developed febrile neutropenia and died in the course of treatment; another patient developed non-Q-wave myocardial infarction possibly related to hydration pre-treatment to rituximab and erythrocyte transfusion. He recovered well after symptomatic therapy. In 7 patients, 2 complete and 3 partial remissions were achieved, with an estimated median time to progression of 12 months. This series of patients shows that the combination of gemcitabine and rituximab is feasible in this population not able to undergo standard poly-chemotherapy, shows promising activity, and merits further evaluation.

A phase I trial of gemcitabine plus cladribine in patients with advanced hematologic malignant diseases

PURPOSE

Gemcitabine and cladribine (2CdA) are nucleoside analogues that decrease DNA synthesis via inhibition of ribonucleotide reductase; the combination could be additive or synergistic. We conducted a dose escalation study to establish the maximum tolerable doses (MTD) of gemcitabine and 2CdA when given in combination in patients with advanced hematologic malignancies and to describe the toxicity profile of this combination.

PATIENTS AND METHODS

A total of 45 patients with advanced hematologic diseases were enrolled into two groups. Group A had adequate baseline hematopoiesis, defined as absolute neutrophil count (ANC) >1 x 10(9)/l and platelet count >50 x 10(9)/l. Group B did not meet these criteria. Hematologic dose-limiting toxicity (DLT) for group A was defined as grade 4 neutropenia or thrombocytopenia lasting >28 days; group B was not evaluated for hematologic toxicity. Nonhematologic DLT was defined similarly for both groups. Death occurring during the first cycle of treatment was considered a DLT event only if it was related to drug toxicity. Gemcitabine was administered as a 4-h intravenous infusion once every 28 days. 2CdA was administered over 1 h daily for the first 3 days of each 28-day cycle.

RESULTS

The MTD was not reached in either group. Myelosuppression was common, but not dose-limiting. Febrile neutropenia and infections were also common, particularly in group B, and judged in most cases to be due to bone marrow failure at baseline. Nonhematologic toxicities were generally mild, and skin rash, the most frequently observed, was dose-limiting in one patient enrolled in each group. Four deaths (three during the first cycle of treatment) occurred at the highest dose level tested in group B (gemcitabine 5000 mg/m2 and 2CdA 16 mg/m2). Although only one of these deaths was dose-limiting by stated criteria, this dose level did not appear to be safely tolerated in this patient population. Several responses were observed in patients with Hodgkin's disease.

CONCLUSIONS

The combination of gemcitabine and 2CdA is feasible in patients with hematologic malignancies. Phase II studies of this combination should be considered, particularly in patients with Hodgkin's disease.

Empowering targeted therapy: lessons from rituximab

Rituximab, a monoclonal antibody directed against the B cell-specific protein CD20, has revolutionized lymphoma treatment by providing a highly effective form of therapy with relatively mild toxic side effects. Effective as a single agent against some forms of B cell lymphoma, rituximab also has a chemosensitizing effect, enhancing the efficacy of chemotherapy against other forms of the disease. Although the mechanisms whereby rituximab achieves its effects remain incompletely understood, these seem to involve at least three distinct phenomena: (i) antibody-dependent cell-mediated cytotoxicity, (ii) complement-mediated cell lysis, and (iii) stimulation of apoptosis in target cells. The latter occurs through interaction of complexes of rituximab and CD20 in lipid rafts, with elements of a signaling pathway involving Src kinases. Effector molecules trigger various gene expression events, leading to sensitization of malignant cells to proapoptotic stimuli. Lessons learned from the research on rituximab may be applied to the rational development of antibody-based therapies against other forms of cancer.

Rituximab and ICE as second-line therapy before autologous stem cell transplantation for relapsed or primary refractory diffuse large B-cell lymphoma

Patients with relapsed or primary refractory diffuse large B-cell lymphoma (DLBCL) who achieve complete response (CR) before autologous stem cell transplantation (ASCT) generally have better outcomes than those who achieve only partial response (PR). We investigated whether adding rituximab to the ifosfamide-carboplatin-etoposide (ICE) chemotherapy regimen (RICE) could increase the CR rate of patients with DLBCL under consideration for ASCT. Thirty-six eligible patients were treated with RICE, and 34 received all 3 planned cycles. The CR rate was 53%, significantly better than the 27% CR rate (P = .01) achieved among 147 similar consecutive historical control patients with DLBCL treated with ICE; the PR rate was 25%. Febrile neutropenia was the most frequent grade 3 or 4 nonhematologic toxicity; it occurred in 7.5% of delivered cycles. No patient had RICE-related toxicity that precluded ASCT. The median number of CD34+ cells per kilogram mobilized was 6.3 × 106. Progression-free survival rates of patients who underwent transplantation after RICE were marginally better than those of 95 consecutive historical control patients who underwent transplantation after ICE (54% vs 43% at 2 years; P = .25). RICE appears to induce very high CR rates in patients with relapsed and refractory DLBCL; however, further studies are necessary to determine whether this treatment regimen will improve outcomes after ASCT.

Raf-1 Kinase Inhibitor Protein: Structure, Function, Regulation of Cell Signaling, and Pivotal Role in Apoptosis

The acquisition of resistance to conventional therapies such as radiation and chemotherapeutic drugs remains the major obstacle in the successful treatment of cancer patients. Tumor cells acquire resistance to apoptotic stimuli and it has been demonstrated that conventional therapies exert their cytotoxic activities primarily by inducing apoptosis in the cells. Resistance to radiation and chemotherapeutic drugs has led to the development of immunotherapy and gene therapy approaches with the intent of overcoming resistance to drugs and radiation as well as enhancing the specificity to eliminate tumor cells. However, cytotoxic lymphocytes primarily kill by apoptosis and, therefore, drug-resistant tumor cells may also be cross-resistant to immunotherapy. To evade apoptosis, tumor cells have adopted various mechanisms that interfere with the apoptotic signaling pathways and promote constitutive activation of cellular proliferation and survival pathways. Thus, modifications of the antiapoptotic genes in cancer cells are warranted for the effectiveness of conventional therapies as well as novel immunotherapeutic approaches. Such modifications will avert the resistant phenotype of the tumor cells and will render them susceptible to apoptosis. Current studies, both in vitro and preclinically in vivo, have been aimed at the modification and regulation of expression of apoptosis-related gene products and their activities. A novel protein designated Raf-1 kinase inhibitor protein (RKIP) has been partially characterized. RKIP is a member of the phosphatidylethanolamine-binding protein family. RKIP has been shown to disrupt the Raf-1-MEK1/2 [mitogen-activated protein kinase-ERK (extracellular signal-regulated kinase) kinase-1/2]-ERK1/2 and NF-kappaB signaling pathways, via physical interaction with Raf-1-MEK1/2 and NF-kappaB-inducing kinase or transforming growth factor beta-activated kinase-1, respectively, thereby abrogating the survival and antiapoptotic properties of these signaling pathways. In addition, RKIP has been shown to act as a signal modifier that enhances receptor signaling by inhibiting G protein-coupled receptor kinase-2. By regulating cell signaling, growth, and survival through its expression and activity, RKIP is considered to play a pivotal role in cancer, regulating apoptosis induced by drugs or immune-mediated stimuli. Overexpression of RKIP sensitizes tumor cells to chemotherapeutic drug-induced apoptosis. Also, induction of RKIP by drugs or anti-receptor antibodies sensitizes cancer cells to drug-induced apoptosis. In this review, we discuss the discovery, structure, function, and significance of RKIP in cancer.

Resveratrol modifies the expression of apoptotic regulatory proteins and sensitizes non-Hodgkin's lymphoma and multiple myeloma cell lines to paclitaxel-induced apoptosis

Resveratrol (trans-3,4,5-trihydroxystilbene) has received attention for its potential chemopreventive and antitumor effects in experimental systems. Recent evidence suggests that paclitaxel, alone or in combination with other drugs, can be effectively used in the treatment of non-Hodgkin's lymphoma (NHL) and multiple myeloma (MM). This study investigated whether resveratrol can sensitize NHL and MM cell lines to paclitaxel-mediated apoptosis and to delineate the underlying molecular mechanism of sensitization. Both resveratrol and paclitaxel negatively modulated tumor cell growth by arresting the cells at the G2-M phase of the cell cycle. Low concentrations of resveratrol exerted a sensitizing effect on drug-refractory NHL and MM cells to apoptosis induced by paclitaxel. Resveratrol selectively down-regulated the expression of antiapoptotic proteins Bcl-xL and myeloid cell differentiation factor-1 (Mcl-1) and up-regulated the expression of proapoptotic proteins Bax and apoptosis protease activating factor-1 (Apaf-1). Paclitaxel down-regulated the expression of Bcl-xL, Mcl-1, and cellular inhibitor of apoptosis protein-1 antiapoptotic proteins and up-regulated Bid and Apaf-1. Combination treatment resulted in apoptosis through the formation of tBid, mitochondrial membrane depolarization, cytosolic release of cytochrome c and Smac/DIABLO, activation of the caspase cascade, and cleavage of poly(adenosine diphosphate-ribose) polymerase. Combination of resveratrol with paclitaxel had minimal cytotoxicity against quiescent and mitogenically stimulated human peripheral blood mononuclear cells. Inhibition of Bcl-xL expression by resveratrol was critical for chemosensitization and its functional impairment mimics resveratrol-mediated sensitization to paclitaxel-induced apoptosis. Inhibition of Bcl-xL expression by resveratrol was due to the inhibition of the extracellular signal-regulated kinase 1/2 (ERK1/2) pathway and diminished activator protein-1-dependent Bcl-xL expression. The findings by resveratrol were corroborated with inhibitors of the ERK1/2 pathway. This study demonstrates that in resistant NHL and MM cell lines resveratrol and paclitaxel selectively modify the expression of regulatory proteins in the apoptotic signaling pathway and the combination, via functional complementation, results in synergistic apoptotic activity.