Clinical course of ovarian cancer patients under repeated stimulation of HAMA using MAb OC125 and B43.13

Front-line chemoimmunotherapy for treating epithelial ovarian cancer: Part II promising results of phase 2 study of paclitaxel-carboplatin-oregovomab regimen

In the Part I, we have discussed the background of CA125 and the development of anti-CA125 monoclonal antibody (MAb) to highlight the potential role of CA125 and anti-CA125 MAb in the management of women with advanced stage epithelial ovarian cancer (EOC). Glycosylation change either by N-link or by O-link of CA125 is supposed to play a role in the modification of immunity. Anti-CA125 MAb, which can be classified as OC 125-like Abs, M11-like Abs, and OV197-like Abs, is often used for diagnosing, screening, monitoring and detecting the mesothelin-related diseases of the abdominal cavity, particular for those women with EOC. Additionally, anti-CA125 MAb also plays a therapeutic role, named as OvaRex MAb-B43.13 (oregovomab), which has also been extensively reviewed in the Part I review article. The main mechanisms include (a) forming CA125 immune complexes to activate the antigen-presenting cells; (b) triggering induction of CA125-specific immune responses, including anti-CA125 Abs against various epitopes and CA125-specific B and T cell responses; and (c) triggering CD4 and CD8 T-cell responses specific for B43.13 to produce specific and non-specific immune response. With success in vitro, in vivo and in primitive studies, phase II study was conducted to test the effectiveness of chemoimmunotherapy (CIT) for the management of EOC patients. In the 97 EOC patients after optimal debulking surgery (residual tumor <1 cm or no gross residual tumor), patients treated with CIT had a dramatical and statistically significant improvement of both progression-free survival (PFS) and overall survival (OS) compared to those treated with chemotherapy alone with a median PFS of 41.8 months versus 12.2 months (hazard ratio [HR] 0.46, 95 % confidence interval [CI] 0.28-0.7) and OS not yet been reached (NE) versus 42.3 months (HR 0.35, 95 % CI 0.16-0.74), respectively. The current review as Part II will explore the possibility of using CIT as front-line therapy in the management of advanced-stage EOC patients after maximal cytoreductive surgery based on the evidence by many phase 2 studies.

Front-line chemo-immunotherapy for treating epithelial ovarian cancer: Part I CA125 and anti-CA125

The current standard therapy of epithelial ovarian cancer (EOC) is the combination of surgery (primary cytoreductive surgery or interval cytoreductive surgery) and platinum-based chemotherapy (mainly using paclitaxel and carboplatin either by neoadjuvant chemotherapy and/or by postoperative adjuvant chemotherapy) with/without adding targeted therapy (mainly using anti-angiogenesis agent- bevacizumab). After front-line chemotherapy, the advanced-stage EOC can be successfully controlled and three-quarters of patients can achieve a complete clinical remission. Unfortunately, nearly all patients will recur and progression-free survival (PFS) of these patients is seldom more than 3 years with a dismal median PFS of 12-18 months. With each recurrence, patients finally develop resistance to standard chemotherapy regimen, contributing to fewer than half of women who survive for more than 5 years after diagnosis with a median overall survival (OS) of 40.7 months. Due to the lower PFS and OS, particularly for those advanced-stage patients, novel therapeutic options during the front-line therapy are desperately needed to decrease the occurrence of recurrence, and the majority of them are still under investigation. It is well-known that overexpression of CA125 has been associated with attenuated cellular apoptosis, platinum chemotherapy resistance, tumor proliferation and disease progression, suggesting that anti-CA125 may play a role in the management of patients with EOC. The current review is a Part I which will focus on development of anti-CA125 monoclonal antibody, hoping that alternation of the front-line therapy by chemo-immunotherapy will be beneficial for prolonged survival of patients with EOC.

Pre-existing antitherapeutic antibodies against the Fc region of the hu14.18K322A mAb are associated with outcome in patients with relapsed neuroblastoma

Purpose

Patients with cancer receiving tumor-reactive humanized monoclonal antibody (mAb) therapy can develop a human antihuman antibody (HAHA) response against the therapeutic mAb. We evaluated for HAHA in patients with neuroblastoma treated in a phase I study of humanized anti-GD2 mAb (immunoglobulin (Ig)G1 isotype), hu14.18K322A (NCT00743496). The pretreatment sera (collected prior to mAb treatment) from 9 of 38 patients contained antitherapeutic antibodies, even though they had no prior mAb exposure. We sought to characterize these pre-existing antitherapeutic antibodies (PATA).

Experimental design

The PATA+ pretreatment samples were characterized via ELISA; clinical associations with PATA status were evaluated.

Results

Pretreatment sera from eight of nine PATA+ patients also bound rituximab and demonstrated preferential ELISA reactivity against the Fc portions of hu14.18K322A and rituximab as compared with the Fab portions of these mAbs. These PATA+ sera also recognized dinutuximab (human IgG1 isotype) and mouse IgG2a isotype mAbs, but not a mouse IgG1 isotype or the fully human panitumumab (IgG2 isotype) mAb. Of the 38 treated patients, only 4 patients (all in the PATA+ cohort) demonstrated no disease progression for >2.5 years without receiving further therapy (p=0.002).

Conclusions

This study demonstrates an association between clinical outcome and the presence of PATA against determinant(s) on the Fc component of the therapeutic mAb, suggesting that the PATA may be playing a role in augmenting mAb-based antitumor effects. Further analyses for the presence of PATA in a larger cohort of patients with relapsed neuroblastoma, analyses of their clinical correlates, identification of their immunological targets, and potential antitumor mechanisms are warranted.

Oregovomab: an investigational agent for the treatment of advanced ovarian cancer

Introduction: Ovarian cancer (OC) represents the leading cause of death among gynecological cancers. Despite novel compound classes like vascular endothelial growth factor (VEGF) inhibitors or poly-ADP ribose polymerase (PARP) inhibitors are available, which improve significantly efficacy of platinum-based chemotherapy, OC prognosis remains poor and innovative strategies are needed. The induction of tumor specific immune response with a therapeutic intent is a very challenging approach. Oregovomab is a murine monoclonal antibody direct to the tumor-associated antigen CA125 that stimulate a host cytotoxic immune response against tumor cells expressing CA125. Areas covered: This paper reviews the preclinical and clinical published data underlying the use of oregovomab in advanced OC. A literature search was performed in PubMed for oregovomab, ovarian cancer, anti-CA125, and on ClinicalTrials.gov for currently ongoing trials. Expert opinion: Oregovomab demonstrated a significant improvement in progression-free and overall survival in advanced OC treatment when administered simultaneously with first-line chemotherapy. This promising schedule is currently investigated in a phase III trial. Since oral treatments as PARP-inhibitors have recently been approved in the OC first-line setting, the possible role of oregovomab needs still to be defined, also considering the intravenous route of administration. The easy to manage toxicity profile makes oregovomab an ideal candidate for association strategies.

Immuno-PET of epithelial ovarian cancer: harnessing the potential of CA125 for non-invasive imaging

Background

Epithelial ovarian cancer (EOC) is characterized by the overexpression of cancer antigen 125 (CA125), a mucinous glycoprotein that serves as a tumor biomarker. Early diagnosis of EOC is plagued by its asymptomatic nature of progression and the limitations of currently used immunoassay techniques that detect CA125 as a shed antigen in serum samples. Presently, there is no technique available for the in vivo evaluation of CA125 expression in malignant tissues. Moreover, there could be an unexplored pathophysiological time window for the detection of CA125 in EOC, during which it is expressed on tumor cells prior to being shed into the bloodstream. A method for the in vivo evaluation of CA125 expression on ovarian neoplasms earlier along disease progression and/or recurrence can potentially contribute to better disease management. To this end, the present work utilizes an anti-CA125 monoclonal antibody (MAb) and a single-chain variable fragment (scFv) labeled with the positron-emitting radionuclide ⁶⁴Cu for preclinical molecular imaging of CA125 expression in vivo.

Methods

Anti-CA125 MAb and scFv were prepared and functionally characterized for target binding prior to being tested as radiotracers in a preclinical setting.

Results

Immunoblotting, immunofluorescence, and flow cytometry revealed specific binding of CA125-targeting vectors to NIH:OVCAR-3 cells and no binding to antigen-negative SKOV3 cells. ⁶⁴Cu-labeled anti-CA125 MAb and scFv were obtained in specific activities of 296 and 122 MBq/mg, respectively. Both radioimmunoconjugate vectors demonstrated highly selective binding to NIH:OVCAR-3 cells and virtually no binding to SKOV3 cells. In vivo radiopharmacological evaluation using xenograft mouse models injected with ⁶⁴Cu-labeled anti-CA125 MAb provided a standardized uptake value (SUV) of 5.76 (29.70 %ID/g) in OVCAR3 tumors 24 h post-injection (p.i.) versus 1.80 (5.91 %ID/g) in SKOV3 tumors. ⁶⁴Cu-labeled anti-CA125 scFv provided an SUV of 0.64 (3.21 %ID/g) in OVCAR3 tumors 24 h p.i. versus 0.25 (1.49 %ID/g) in SKOV3 tumors. Results from small-animal PET imaging were confirmed by ex vivo autoradiography and immunohistochemistry.

Conclusions

Radiolabeling of anti-CA125 MAb and scFv with ⁶⁴Cu did not compromise their immunoreactivity. Both radioimmunoconjugates presented specific tumor uptake and expected biological clearance profiles. This renders them as potential immuno-PET probes for targeted in vivo molecular imaging of CA125 in EOC.

Electronic supplementary material

The online version of this article (doi:10.1186/s13550-014-0060-4) contains supplementary material, which is available to authorized users.

Immunological response induced by abagovomab as a maintenance therapy in patients with epithelial ovarian cancer: relationship with survival-a substudy of the MIMOSA trial

PURPOSE

To determine whether abagovomab induces protective immune responses in ovarian cancer patients in first clinical remission. The present analysis is a substudy of monoclonal antibody immunotherapy for malignancies of the ovary by subcutaneous abagovomab trial (NCT00418574).

METHODS

The study included 129 patients, 91 in the abagovomab arm and 38 in the placebo arm. Circulating CA125-specific cytotoxic T lymphocytes (CTL) were measured by a flow cytometry-based interferon-γ producing assay. Human antimouse antibody and anti-anti-idiotypic (Ab3) were assessed by ELISA. Patients were evaluated before starting the treatment and at different time points during induction and maintenance phases.

RESULTS

A similar percentage of patients in both the placebo and abagovomab arms had CA125-specific CTL (26.3 and 31.8 %, respectively; p = 0.673 by Fisher's exact test). Patients with CA125-specific CTL in both arms tended to have an increased relapse-free survival (RFS, log-rank test p = 0.095) compared to patients without. Patients (n = 27) in the abagovomab arm without CA125-specific CTL but that developed Ab3 above the cutoff (defined as median Ab3 level at week 22) had a prolonged RFS compared to patients (n = 24) that did not develop Ab3 above the cutoff (log-rank test p = 0.019).

CONCLUSION

Abagovomab does not induce CA125-specific CTL. However, patients with CA125-specific CTL perform better than patients without, irrespective of abagovomab treatment. Abagovomab-induced Ab3 associate with prolonged RFS in patients without CA125-specific CTL. Further studies are needed to confirm these data and to assess the potential utility of these immunological findings as a tool for patient selection in clinical trial.

MUC16 (CA125): tumor biomarker to cancer therapy, a work in progress

Over three decades have passed since the first report on the expression of CA125 by ovarian tumors. Since that time our understanding of ovarian cancer biology has changed significantly to the point that these tumors are now classified based on molecular phenotype and not purely on histological attributes. However, CA125 continues to be, with the recent exception of HE4, the only clinically reliable diagnostic marker for ovarian cancer. Many large-scale clinical trials have been conducted or are underway to determine potential use of serum CA125 levels as a screening modality or to distinguish between benign and malignant pelvic masses. CA125 is a peptide epitope of a 3-5 million Da mucin, MUC16. Here we provide an in-depth review of the literature to highlight the importance of CA125 as a prognostic and diagnostic marker for ovarian cancer. We focus on the increasing body of literature describing the biological role of MUC16 in the progression and metastasis of ovarian tumors. Finally, we consider previous and on-going efforts to develop therapeutic approaches to eradicate ovarian tumors by targeting MUC16. Even though CA125 is a crucial marker for ovarian cancer, the exact structural definition of this antigen continues to be elusive. The importance of MUC16/CA125 in the diagnosis, progression and therapy of ovarian cancer warrants the need for in-depth research on the biochemistry and biology of this mucin. A renewed focus on MUC16 is likely to culminate in novel and more efficient strategies for the detection and treatment of ovarian cancer.

Monoclonal antibodies therapies for ovarian cancer

INTRODUCTION

Despite aggressive debulking surgery, intraperitoneal therapies and the use of new drugs for chemotherapy, patients with ovarian cancer (OC) still have poor prognosis and, therefore, new strategies for its management are needed. Molecular-targeted agents can be considered a new option in drug research. Several antigens related to OC have been isolated and they could be potential target of monoclonal antibodies (mAbs); therefore, different mAbs have been developed and are emerging as new potential OC treatments.

AREAS COVERED

This article aims to review the literature on the use of mAbs in the treatment of OC. The purposes of this manuscript are to offer a brief explanation of the mechanisms of action of mAbs and to help readers in understanding the current role of mAbs in the treatment of OC.

EXPERT OPINION

A deeper knowledge of the molecular biology of OC has brought new developments in targeted therapies. Among these therapies, bevacizumab demonstrated the higher clinical efficacy. Further larger trials are needed to better define the role of the other mAbs in OC treatment. There is a strong need to identify and validate robust biomarkers for a more focused patient selection and for tailoring therapies, optimizing dose and assessing response.

Monoclonal antibodies in gynecological cancer: a critical point of view

During the last decades, several improvements in treating gynecological malignancies have been achieved. In particular, target therapies, mostly monoclonal antibodies, have emerged as an attractive option for the treatment of these malignancies. In fact, various molecular-targeted agents have been developed for a variety of malignancies with the objective to interfere with a precise tumor associated receptor, essential for cancer cell survival or proliferation, blocking its function, of the cancer cells. Alternatively, monoclonal antibodies have been developed to block immune suppression or enhance functions of immune effector cells. So far, several monoclonal antibodies have been tested for clinical efficacy for the treatment of gynecological cancers. Antibodies against Vascular Endothelial Growth Factor (VEGF) and Epidermal Growth Factor Receptor (EGFR) have been used in different neoplasms such as ovarian and cervical cancer. Catumazumab, a bivalent antibody against CD3 and EpCAM, is effective in the treatment of neoplastic ascites. Other antibodies are peculiar for specific cancer-associated antigen such as Oregovomab against CA125 or Farletuzumab against the folate receptor. Here we describe the preclinical and clinical experience gained up to now with monoclonal antibodies in tumors of the female genital tract and trace future therapeutic and research venues.

Abagovomab: an anti-idiotypic CA-125 targeted immunotherapeutic agent for ovarian cancer

Ovarian cancer remains the leading cause of death due to gynecologic malignancies. Most patients present with advanced disease at the time of diagnosis. Although many have a good initial response to surgical debulking and platinum-based chemotherapy, relapse is common, with the eventual development of chemotherapy resistance. Innovative treatments are needed in the remission setting to prolong the disease-free interval or prevent recurrence. Abagovomab is a murine monoclonal anti-idiotypic antibody (molecular weight: 165-175 kDa) that functionally imitates the tumor-associated antigen, CA-125. It has been shown to be well tolerated and to induce a sustained immune response in initial Phase I and II clinical trials. An ongoing, double-blind, placebo-controlled, multicenter, Phase III trial (MIMOSA) completed its double-blind period in December 2010 and will compare abagovomab maintenance therapy to placebo, which will definitively determine the efficacy of this immunotherapeutic approach in patients with ovarian cancer.

CA125 in ovarian cancer

A quarter of a century since its discovery, circulating CA125 antigen is recommended for clinical use in the USA for ovarian cancer screening of high-risk women with ovaries, despite its limited sensitivity and specificity. Recent findings suggest that CA125 might also serve as a predictive marker for pre-invasive ovarian carcinoma. Methods to quantify circulating CA125 evolved toward sensitive and reliable double-determinant ELISA assays. The CA125 gene, MUC16, was cloned 20 years after the protein discovery and revealed a very complex and unusual glycoprotein structure, suggesting an immunological role. Recent evidence points toward CA125 function in the induction of materno-fetal tolerance through the alteration of natural killer phenotype. Two receptors for CA125 have been described: mesothelin and galectin-1. The specific location and functional proprieties of CA125 make it a therapeutic target of choice; clinical trials have demonstrated that anti-CA125 injections are well tolerated and suggest a potential survival benefit.

The detection, treatment, and biology of epithelial ovarian cancer

Ovarian cancer is particularly insidious in nature. Its ability to go undetected until late stages coupled with its non-descript signs and symptoms make it the seventh leading cause of cancer related deaths in women. Additionally, the lack of sensitive diagnostic tools and resistance to widely accepted chemotherapy regimens make ovarian cancer devastating to patients and families and frustrating to medical practitioners and researchers. Here, we provide an in-depth review of the theories describing the origin of ovarian cancer, molecular factors that influence its growth and development, and standard methods for detection and treatment. Special emphasis is focused on interactions between ovarian tumors and the innate and adaptive immune system and attempts that are currently underway to devise novel immunotherapeutic approaches for the treatment of ovarian tumors.

Consolidation Therapy in Ovarian Cancer: A Clinical Update

Objectives:

To evaluate current strategies under investigation for use as consolidation or maintenance treatment in patients with ovarian cancer.

Patients with epithelial ovarian cancer often enter a complete remission after primary treatment. Many relapse, unfortunately, but some can return to remission after additional treatment. Outcomes can be improved by applying effective consolidation or maintenance approaches to patients in a complete primary or subsequent remission.

Methods:

A selective review of the literature is undertaken to consider strategies that are being or will likely be evaluated in randomized trials while we assess whether consolidation or maintenance will have a place in the treatment of patients with ovarian cancer.

Results:

The application of extended standard cytotoxic agents has been generally disappointing, and no strategy applied in the first remission setting has prolonged overall survival.

Conclusions:

As treatment options move beyond classic chemotherapy to novel hormones, immune interventions, and biologic agents, the consolidation strategy is regaining interest. This is particularly attractive in that many of these agents have stable disease as best outcome, and this is most appropriate to evaluate in patients with minimal volume disease. A consideration of toxicity is paramount, and any strategy to be considered in an otherwise asymptomatic patient in remission must be well tolerated. In addition, patients in second or third complete remission are also being considered as an appropriate group in which to evaluate new agents. Numerous other phase 2 trials with novel agents not considered here are underway, and it is to be hoped that some will emerge as contenders for randomized trials. Participation in these trials remains a priority for patients who otherwise must pursue a difficult watch-and-wait strategy.

Preclinical studies and clinical utilization of monoclonal antibodies in epithelial ovarian cancer

OBJECTIVE

To present an overview of selected monoclonal antibodies (mAbs) that have been studied in epithelial ovarian cancer with a focus on combination treatment with conventional chemotherapy.

METHODS

The authors perform a narrative review of the literature. Preclinical studies that provided rationale for mAb use are examined, and selected clinical trials that evaluated efficacy and tolerability are reviewed.

RESULTS

Numerous mAbs have been utilized in epithelial ovarian cancer, including bevacizumab (anti-vascular endothelial growth factor), trastuzumab (anti-human epidermal growth factor-2), cetuximab (anti-epidermal growth factor receptor), and oregovomab (anti-CA125). Favorable preclinical results have lead to the development of a number of clinical trials. Side-effects have been minimal and combination therapy has been well-tolerated. Efficacy has been variable in the clinical trials.

CONCLUSIONS

Targeted treatment with mAbs in conjunction with cytotoxic chemotherapy has been an important research area during the last decade. This therapeutic approach holds promise for improved outcomes in patients with ovarian cancer.

New therapeutic agents in ovarian cancer

PURPOSE OF REVIEW

Despite advances in management over recent years, epithelial ovarian cancer remains the most lethal gynaecological malignancy. Methods of early detection, as well as improved therapeutic options, are urgently needed.

RECENT FINDINGS

Currently, a number of targeted therapies, including vascular endothelial growth factor inhibitors, poly-ADP-ribose polymerase inhibitors and folate receptor inhibitors look promising in this arena and this article will review a number of these drugs and the evidence pertaining to their use.

SUMMARY

Much further research is required to define if, when and how best to integrate these novel therapies, and also to define associated biomarkers that predict toxicity and select patients most likely to derive benefit. Individualized therapy is not an impossible dream, but there is still a long way to go.

Harnessing the immune system for ovarian cancer therapy

The clinical course of ovarian cancer is often marked by periods of relapse and remission until chemo-resistance develops. Patients in remission with minimal disease burdens are ideally suited for the evaluation of immune-based strategies. Major obstacles to the development of successful immune strategies include the identification of tumor-restricted immunogenic targets, generation of a sufficient immune response to cause tumor rejection, and approaches to overcome evasion of immune attack. Many questions remain as optimal strategies are developed, which include: (i) What is the best antigen form (e.g. peptides, proteins or tumor lysates)? (ii) What are the appropriate adjuvants? (iii) Are mono-valent or multi-valent vaccines likely to be more effective? (iv) What is the optimal frequency and duration of vaccination? (v) How should antigen-specific responses be monitored? and (vi) How should the anti-cancer response be maintained? In this review, we explore representative examples of immune strategies under investigation for patients with ovarian carcinoma which illustrate many of these issues. Basic principles generic to all these immunotherapeutic approaches will also be discussed.

Immunologic approaches to ovarian cancer treatment

The clinical course of ovarian cancer is often marked by periods of relapse and remission until chemotherapy resistance develops. Patients in remission with minimal disease burdens are ideally suited for the evaluation of immune-based strategies. The role of immune surveillance in improving outcome has been supported by the correlation of increased survival with the presence or absence of tumor-infiltrating lymphocytes in a given patient. Major obstacles to the development of successful immune strategies include the identification of tumor-restricted immunogenic targets, generation of a sufficient immune response to cause tumor rejection, and approaches to overcome evasion of immune attack. As optimal strategies are being developed, many questions remain. Some of the questions are as follows: What is the best antigen form (eg, peptides, proteins, or tumor lysates)? What are the appropriate adjuvants? Are monovalent or multivalent vaccines likely to be more effective? What is the optimal frequency and duration of vaccination? How should antigen-specific responses be monitored? How should the anticancer response be maintained? In this review, we will explore representative examples of immune strategies under investigation for patients with ovarian carcinoma that illustrate many of these issues. We will review ongoing phase III studies for patients in first clinical remission. Basic principles generic to all these immunotherapeutic approaches will be discussed in the hopes of yielding the most promising results as the field continues to evolve.

Design of a bifunctional fusion protein for ovarian cancer drug delivery: single-chain anti-CA125 core-streptavidin fusion protein

We have developed a universal ovarian cancer cell targeting vehicle that can deliver biotinylated therapeutic drugs. A single-chain antibody variable domain (scFv) that recognizes the CA125 antigen of ovarian cancer cells was fused with a core-streptavidin domain (core-streptavidin-VL-VH and VL-VH-core-streptavidin orientations) using recombinant DNA technology and then expressed in Escherichia coli using the T7 expression system. The bifunctional fusion protein (bfFp) was expressed in a shaker flask culture, extracted from the periplasmic soluble protein, and affinity purified using an IMAC column. The two distinct activities (biotin binding and anti-CA125) of the bfFp were demonstrated using ELISA, Western blot and confocal laser-scanning microscopy (CLSM). The ELISA method utilized human NIH OVCAR-3 cells along with biotinylated bovine serum albumin (B-BSA) or biotinylated liposomes, whereas, the Western blot involved probing with B-BSA. The CLSM study has shown specificity in binding to the OVCAR-3 cell-line. ELISA and Western blot studies have confirmed the bifunctional activity and specificity. In the presence of bfFp, there was enhanced binding of biotinylated antigen and liposome to OVCAR-3 cells. In contrast, the control EMT6 cells, which do not express the CA125 antigen, showed minimal binding of the bfFp. Consequently, bfFp based targeting of biotinylated therapeutic drugs, proteins, liposomes, or nanoparticles could be an alternative, convenient method to deliver effective therapy to ovarian cancer patients. Peritoneal infusion of the bfFp-therapeutic complex could also be effective in locally targeting the most common site of metastatic spread.

A pilot phase 2 study of oregovomab murine monoclonal antibody to CA125 as an immunotherapeutic agent for recurrent ovarian cancer

This prospective, open-label, pilot phase 2 study examined the clinical and immunologic effects of oregovomab (OvaRex) in heavily pretreated patients with recurrent ovarian cancer (OC). Thirteen women were administered intravenous oregovomab (2 mg) at weeks 0, 2, 4, 8, and 12, followed by quarterly doses for up to 2 years or disease progression. Concomitant chemotherapy was not permitted. Eligibility criteria included recurrence after one or more platinum-based chemotherapy regimens, CA125 >35 U/mL, evaluable or measurable disease. Tumor burden was evaluated by physical or radiologic methods pretreatment, weeks 12, 24, and every 24 weeks thereafter. Immune responses, including antibodies and T cells to oregovomab and CA125, were demonstrated in over half the patients. Stabilization of disease and survival >2 years was observed in 3 of 13 patients and coincided with robust immune responses. Shrinkage of marker lesions was not observed; however, four patients showed decreases in CA125 levels. Treatment was well tolerated without serious adverse events or discontinuations due to therapy. This pilot study supports immunologic activity and safety of oregovomab in recurrent OC. Further study of this agent in the consolidation and adjuvant setting is ongoing to establish its clinical utility.

Immune responses to murine monoclonal antibody-B43.13 correlate with prolonged survival of women with recurrent ovarian cancer

OBJECTIVE

We evaluated the therapeutic efficiency of the murine monoclonal antibody-B43.13 in the treatment of patients with recurrent ovarian cancer.

STUDY DESIGN

This was a retrospective study of immune responses and survival in 44 patients who were treated with technetium 99m-labeled monoclonal antibody-B43.13, a murine monoclonal antibody that is directed against the tumor-associated antigen CA125. Most patients were pretreated heavily. Biologic activity was quantified by the assay of immune responses to the human anti-murine antibodies against the monoclonal antibody-B43.13 variable region (Ab(2)) and antibodies that target the CA 125 antigen itself (anti-CA 125 antibody).

RESULTS

More than one half of patients (56.8%) survived for >12 months after the first dose of monoclonal antibody B43.13; 34.1% of the patients survived >24 months. To date, 6 of the 44 patients are alive, with survival times of 4 to 7.5 years after the start of the antibody treatment. More than 60% of the evaluable patients met predefined criteria for robust, treatment-emergent human anti-murine antibodies and Ab(2) responses, and these responses were associated with improved survival rates. Median survival time increased approximately 3-fold for human anti-murine antibody responders (22.6 months) versus nonresponders (7.2 months; P <.0016, log-rank test) and 2-fold for Ab(2) responders (18.3 months) versus nonresponders (9.3 months). No serious drug-associated adverse events were reported.

CONCLUSION

The associations between multiple types of immune response and improved clinical outcomes suggest that monoclonal antibody-B43.13 should be further evaluated for potential use as an immunotherapy for CA125-expressing malignancies.

Induction of CA125-specific B and T cell responses in patients injected with MAb-B43.13--evidence for antibody-mediated antigen-processing and presentation of CA125 in vivo

The murine monoclonal anti-CA125 antibody MAb-B43.13 has previously been administered as an immunoscintigraphic agent in order to monitor recurrence of ovarian cancer in patients, and a long-term follow-up demonstrated a survival benefit for these patients. The clinical benefit was initially attributed to the activation of the idiotypic network. The objective of this study was to investigate the role of CA125-MAb-B43.13 immune complex formation on the induction of CA125-specific immune responses. Analysis of patient serum samples from pharmacokinetic studies demonstrated that the antibody forms immune complexes with CA125 in circulation within 30 minutes of injection. Induction of humoral and cellular anti-CA125 responses correlated with the amount of circulating CA125 antigen present at time of antibody injection. Subsequent to the injection of MAb-B43.13, the patients generated anti-CA125 antibodies that were directed against various epitopes on the antigen and were not restricted to the specific epitope recognized by MAb-B43.13. The generation of CA125-specific B and T cell responses after MAb-B43.13 injection correlated with improved survival. The influence of circulating CA125 for the induction of CA125-specific immune responses and the multi-epitopic nature of the human anti-CA125 antibodies suggest that the majority of these antibodies were not induced via the idiotypic network but by the autologous antigen itself. Since antibody and T cell responses to CA125 were not present before injection of MAb-B43.13, it is hypothesized that complex formation of MAb-B43.13 with circulating antigen triggers the induction of CA125-specific immune responses.

Development and characterization of a bispecific single-chain antibody directed against T cells and ovarian carcinoma

Bispecific antibodies with specificity for tumor antigen and CD3 have been shown to redirect the cytotoxicity of T cells against relevant tumor. Our objective was to generate single-chain bispecific antibodies (bsSCA) that could retarget mouse cytotoxic T lymphocytes (CTL) to destroy human ovarian carcinoma in a xenogeneic setting. A bsSCA, 2C11 x B43.13, was constructed by genetic engineering and expressed in mammalian cells. Molecular characteristics, binding properties, and ability to retarget CTL were studied. Western blot analysis showed that the product is a 65-kDa protein. Purification of antibodies could be done by single-step affinity chromatography using protein L-agarose with an unoptimized yield of 200 microg/L. BsSCA 2C11 x B43.13 was capable of binding to mouse CD3 and human CA125 as detected by FACS analysis of EL4 and OVCAR Nu3H2 cells, respectively. It could also bridge activated splenic T cells and human ovarian carcinoma as demonstrated by a bridge FACS assay. Redirected mouse CTL could mediate human target cell lysis in a 20-h 51Cr release assay despite that they are xenogeneic. Prolonged incubation of redirected CTL and tumor targets resulted in a dramatic reduction in tumor cell number. CD28 co-stimulation enhanced redirected CTL function in both types of assays. BsSCA 2C11 x B43.13 thus can be used as a preclinical immunotherapeutic model for human ovarian cancer in a xenogeneic setting.

Immunotherapy of human ovarian carcinoma with OvaRex MAb-B43.13 in a human-PBL-SCID/BG mouse model

The monoclonal antibody (MAb) B43.13, binding to the ovarian cancer-associated antigen CA125, has been injected into more than 200 patients with ovarian cancer to detect recurrence of the disease. The follow-up of the patients revealed surprisingly long survival spans for several patients despite high CA125 levels. To investigate the therapeutic effectiveness of OvaRex MAb-B43.13 (AltaRex, Edmonton, Canada) under well-controlled conditions, the antibody was tested in a human-PBL-SCID/BG mouse model with CA125 positive human ovarian cancer cells. Mice were reconstituted with human peripheral blood lymphocytes (PBL, normal donors) by intraperitoneal (IP) injection of 2 to 3 x 10(7) PBL/mouse. OvaRex MAb-B43.13 was administered at 100 microg/mouse in phosphate buffered saline (PBS), in three different experimental set-ups. An isotype-matched control antibody (MOPC21 or MAb-170) and PBS injection served as controls. The ovarian cancer cell line NIH:OVCAR-NU-3 was injected IP at 1 x 10(6) cells/mouse or subcutaneously (SC) at 4 x 10(6) cells/mouse. Human-PBL-SCID/BG mice were either immunized before injection of tumor cells, along with tumor cells or after small tumors were established (2 weeks after transplantation). Antibody injections were repeated twice in 2-week intervals. Functional and cellular characterization of serum and PBL from these mice demonstrated the successful engraftment of a human immune system in those mice. All three experiments showed that OvaRex MAb-B43.13 treatment could (a) delay or prevent development of tumors; (b) reduce the size of small established tumors (SC tumor injection) or suppress ascites formation; (c) delay tumor growth when injected prior to tumor implantation; and (d) prolong the survival of the mice (i.p. tumor injection).

Generation of Human Monoclonal Anti-idiotypic Antibodies with Specificity to the Murine Monoclonal Anti-CA 125 Antibody B43.13

Two human monoclonal antibodies, HID-7E7 and ROB-6F2, were produced by EBV transformation of peripheral blood lymphocytes (PBL). PBL were obtained from a patient with ovarian cancer who had been exposed several times to a Tc-99m labeled murine monoclonal anti-CA 125 antibody (B43.13, Biomira, Edmonton) for immunoscintigraphy. The HID-7E7 and ROB-6F2 producing B-cells were cloned with a limiting dilution technique and have shown stable immunoglobulin secretion within a period of three years. The human monoclonal antibodies HID-7E7 and ROB-6F2 are of the IgG isotype, and bind with significant affinity to the murine monoclonal antibody B43.13, which was used for immunoscintigraphy. Binding affinity of ROB-6F2 to other murine antibodies could not be detected. Cross reactivity of HID-7E7 to a murine anti-CEA monoclonal antibody was observed. In order to verify the anti-idiotypic character of the generated human antibodies, the ability of HID-7E7 and ROB-6F2, respectively, to inhibit the formation of the CA125/B43.13 complex is demonstrated via an enzyme-linked immunosorbent assay. These human anti-idiotypic antibodies are possible candidates for immunotherapy of ovarian cancer in patients with a small tumor burden following surgery and/or chemotherapy.

Antiidiotype induction therapy: evidence for the induction of immune response through the idiotype network in patients with ovarian cancer after administration of anti-CA125 murine monoclonal antibody B43.13

The immune status of ovarian cancer patients receiving anti-CA125 murine monoclonal antibody B43.13 was evaluated by measuring antiidiotypic antibodies (Ab2), antiantiidiotypic antibodies (Ab3), antiisotypic human antimouse antibodies (HAMA), interferon-gamma, and CA125 levels in the serum. A specific assay was developed for the determination of Ab2 antibodies using chimeric MAb B43.13. Of the 50 patients studied, 26 had elevated levels of Ab2. Eleven of these 26 patients also had high titer of antiantiidiotypic (Ab3) antibodies. Eight of the 22 patients analyzed had increased interferon-gamma levels. A tentative correlation was found between survival of these patients' antiidiotype induction.