The role of cancer vaccines following autologous stem cell rescue in breast and ovarian cancer patients: experience with the STn-KLH vaccine (Theratope)

Efficacy of cancer vaccines in selected gynaecological breast and ovarian cancers: A 20-year systematic review and meta-analysis

BACKGROUND

Therapeutic cancer vaccination is an area of interest, even though promising efficacy has not been demonstrated so far.

DESIGN

A systematic review and meta-analysis was conducted to evaluate vaccines' efficacy on breast cancer (BC) and ovarian cancer (OC) patients. Our search was based on the PubMed electronic database, from 1st January 2000 to 4th February 2020.

OBJECTIVE

response rate (ORR) was the primary end-point of interest, while progression-free survival (PFS), overall survival (OS) and toxicity were secondary end-points. Analysis was performed separately for BC and OC patients. Pooled ORRs were estimated by fixed or random effects models, depending on the detected degree of heterogeneity, for all studies with more than five patients. Subgroup analyses by vaccine type and treatment schema as well as sensitivity analyses, were implemented.

RESULTS

Among 315 articles initially identified, 67 were eligible for our meta-analysis (BC: 46, 1698 patients; OC: 32, 426 patients; where both BC/OC in 11). Dendritic-cell and peptide vaccines were found in more studies, 6/10 BC and 10/13 OC studies, respectively. In our primary BC analysis (21 studies; 428 patients), the pooled ORR estimate was 9% (95%CI[5%,13%]). The primary OC analysis (12 studies; 182 patients), yielded pooled ORR estimate of 4% (95%CI[1%,7%]). Similar were the results derived in sensitivity analyses. No statistically significant differences were detected by vaccine type or treatment schema. Median PFS was 2.6 months (95% confidence interval (CI)[1.9,2.9]) and 13.0 months (95%CI[8.5,16.3]) for BC and OC respectively, while corresponding median OS was 24.8 months (95%CI[15.0,46.0]) and 39.0 months (95%CI[31.0,49.0]). In almost all cases, the observed toxicity was only moderate.

CONCLUSION

Despite their modest results in terms of ORR, therapeutic vaccines in the last 20 years display relatively long survival rates and low toxicity. Since a plethora of different approaches have been tested, a better understanding of the underlying mechanisms is needed in order to further improve vaccine efficacy.

Development of Therapeutic Vaccines for Ovarian Cancer

Ovarian cancer remains the deadliest of all gynecologic malignancies. Our expanding knowledge of ovarian cancer immunology has allowed the development of therapies that generate systemic anti-tumor immune responses. Current immunotherapeutic strategies include immune checkpoint blockade, cellular therapies, and cancer vaccines. Vaccine-based therapies are designed to induce both adaptive and innate immune responses directed against ovarian cancer associated antigens. Tumor-specific effector cells, in particular cytotoxic T cells, are activated to recognize and eliminate ovarian cancer cells. Vaccines for ovarian cancer have been studied in various clinical trials over the last three decades. Despite evidence of vaccine-induced humoral and cellular immune responses, the majority of vaccines have not shown significant anti-tumor efficacy. Recently, improved vaccine development using dendritic cells or synthetic platforms for antigen presentation have shown promising clinical benefits in patients with ovarian cancer. In this review, we provide an overview of therapeutic vaccine development in ovarian cancer, discuss proposed mechanisms of action, and summarize the current clinical experience.

Therapeutic potential of toll-like receptors in treatment of gynecological cancers

Toll-like receptors (TLRs) play an important role in the innate and adaptive immune system. They are expressed in various regions of the female reproductive tract, and their regulation may be involved in the pathogenesis of gynecological lesions. There is growing evidence that ligands for several TLRs are potentially anticancer agents, some of which have already been approved by the FDA, and these compounds are now undergoing clinical evaluation. There is a rationale for using these ligands as adjuvants in the treatment or prevention of gynecological cancer. Some TLR agonists that are of potential interest in the treatment of gynecological lesions include imiquimod, motolimod, cervarix, and CpG-oligodeoxynucleotides (ODNs). In this review, we outline the different functions of TLRs in gynecological cancer with particular emphasis on the value of TLR agonists as a potential therapeutic target in the treatment of gynecological cancer. © 2019 IUBMB Life, 71(5):549-564, 2019.

CD133+ cancer stem-like cells promote migration and invasion of salivary adenoid cystic carcinoma by inducing vasculogenic mimicry formation

Cancer stem cells (CSCs) have gained much attention due to their roles in the invasion and metastasis of numerous kinds of human cancers. Here, we showed that the positive expression of CD133, the stemness marker, was positively associated with vasculogenic mimicry (VM) formation, local regional recurrence, distant metastasis and poorer prognosis in salivary adenoid cystic carcinoma (ACC) specimens. Compared with CD133⁻ ACC cells, CD133⁺ cancer stem-like cells had more migration and invasion capabilities, as well as more VM formation. The levels of endothelial cell marker VE-cadherin, MMP-2 and MMP-9 expression in CD133⁺ cancer stem-like cells and xenograft tumors of nude mice injected with CD133⁺ cells were significantly higher than those with CD133⁻ cells. The data indicated that CD133⁺ cancer stem-like cells might contribute to the migration and invasion of ACC through inducing VM formation.

Cancer Vaccines in Ovarian Cancer: How Can We Improve?

Epithelial ovarian cancer (EOC) is one important cause of gynecologic cancer-related death. Currently, the mainstay of ovarian cancer treatment consists of cytoreductive surgery and platinum-based chemotherapy (introduced 30 years ago) but, as the disease is usually diagnosed at an advanced stage, its prognosis remains very poor. Clearly, there is a critical need for new treatment options, and immunotherapy is one attractive alternative. Prophylactic vaccines for prevention of infectious diseases have led to major achievements, yet therapeutic cancer vaccines have shown consistently low efficacy in the past. However, as they are associated with minimal side effects or invasive procedures, efforts directed to improve their efficacy are being deployed, with Dendritic Cell (DC) vaccination strategies standing as one of the more promising options. On the other hand, recent advances in our understanding of immunological mechanisms have led to the development of successful strategies for the treatment of different cancers, such as immune checkpoint blockade strategies. Combining these strategies with DC vaccination approaches and introducing novel combinatorial designs must also be considered and evaluated. In this review, we will analyze past vaccination methods used in ovarian cancer, and we will provide different suggestions aiming to improve their efficacy in future trials.

Survival Advantage in Patients with Metastatic Breast Cancer Receiving Endocrine Therapy plus Sialyl Tn-KLH Vaccine: Post Hoc Analysis of a Large Randomized Trial

Background: A multicenter, double blinded, randomized phase III trial of the therapeutic cancer vaccine sialy1-Tn (STn) conjugated to keyhole-limpet Hemocyanin (KLH) was completed in an international cohort of 1,028 women with metastatic breast cancer who had nonprogressive disease or no evidence of disease after first-line chemotherapy (ClinicalTrials.gov, (NCT00003638). STn-KLH was safe and relatively well tolerated but did not affect time to progression (TTP) or overall survival (OS) duration. The purpose of this post hoc analysis was to explore whether patients who received concurrent endocrine therapy and STn-KLH had a TTP or OS benefit.

Methods: A retrospective, blinded review of the data from the phase III trial of STn-KLH was performed to ensure that strata assignments were appropriate. We then studied the effect of concomitant endocrine therapy and STn-KLH or KLH on TTP and OS in the cohort described above. We also assessed the TTP and OS by antibody responses in patients who received endocrine therapy.

Results: The women treated with concomitant endocrine therapy, a pre-stratified subset comprising approximately one-third of the original study population, and STn-KLH had longer TTP and OS than the control group of women who received KLH alone. Moreover, of the women who received endocrine therapy, those who had a median or greater antibody response (titer >1:320 toward ovine sub maxillary mucin) to the STn-KLH vaccine had significantly longer median OS than those who had a below-median antibody response.

Conclusion: Adding STn-KLH to endocrine therapy may improve clinical outcomes with few adverse effects for women with metastatic breast cancer.

Management of breast cancer by vaccine: fact or fiction

Breast cancer (BC) is the most common malignancy (75–80%) among women. Options for management of BC are multivariate. Available modalities include surgery, radiotherapy, chemotherapy and hormone therapy. Despite availability of improved therapeutic adjuncts, mortality from BC is 40%. Vaccination strategies against BC are emerging as a viable alternative. This review highlights the available results of this emerging therapeutic strategy.

Monophosphoryl lipid A (MPL) as an adjuvant for anti-cancer vaccines: clinical results

As technological advances allow for the identification of tumor-associated antigens (TAAs) against which adaptive immune responses can be raised, efforts to develop vaccines for the treatment of cancer continue to gain momentum. Some of these vaccines target differentiation antigens that are expressed by tumors derived from one particular tissue (e. g., Melan-A/ MART-1, tyrosinase, gp 100). Some target antigens are specifically expressed in tumors of different types but not in normal tissues (e. g., MAGE-3), while other possible targets are antigens that are expressed at low level in normal tissues and are over-expressed in tumors of different types (e. g., HER2, Muc 1). Oncogenes (HER2/neu, Ras, E7 HPV 16), tumor suppressor genes (pS3) or tumor-specific post-translational modified proteins (under glycosylated Muc 1) can also be used as cancer vaccine candidates. In either case, these antigens tend to be poorly inmmunogenic by themselves and vaccines containing them generally require the inclusion of potent immunological adjuvants in order to generate robust anti-tumor immune responses in humans. Many adjuvants currently under evaluation for use in cancer vaccines activate relevant antigen presenting cells, such as dendritic cells and macrophages, via toll-like receptors (TLRs) and promote effective uptake, processing and presentation of antigen to T-cells in draining lymph nodes.Lipid A, the biologically active portion of the gram-negative bacterial cell wall constituent lipopolysaccharide (LPS), is known to possess strong immunostimulatory properties and has been evaluated for more than two decades as an adjuvant for promoting immune responses to minimally immunogenic antigens, including TAAs. The relatively recent discovery of TLRs and the identification of TLR4 as the signaling receptor for lipid A have allowed for a better understanding of how this immunostimulant functions with regard to induction of innate and adaptive immune responses.Although several lipid A species, including LPS and synthetic analogs, have been developed and tested as monotherapeutics for the treatment of cancer,1-8 only 3-O-desacyl-4'-monophosphoryl lipid A (MPL) has been evaluated as a cancer vaccine adjuvant in published human clinical trials. MPL comprises the lipid A portion of Salmonella minnesota LPS from which the (R)-3-hydroxytetrade canoyl group and the l-phosphare have been removed by successive acid and base hydrolysis.9 LPS and MPL induce similar cytokine profiles, but MPLis at least 1OO-fold less toxic.9,10 lOMPL has been administered to more than 300, 000 human subjects in studies of next-generation vaccines.11 In this chapter, published clinical trials conducted to evaluate the safety and/or efficacy of various cancer vaccines containing MPL, either alone or combined with other immunostimulants, Such as cell wall skeleton (CWS) of Mycobacterium phlei in the adjuvant Detox; Biomira, Inc.), the saponin QS-21 (in the adjuvants AS01B and AS02B; GSK Biologicals) or with QS-21 and CpG oligonucleotides (in the adjuvant AS15; GSK Biologicals) will be summarized. Combining MPL with other immunostimulants has been demonstrated to be advantageous in many cases and may be required to elicit the full complement of activities necessary to achieve an effective immune response and overcome the ability of tumors to evade attack by the immune system. In this chapter, information relating to vaccines targeting specific cancers will be presented in the first section, while information relating to vaccines targeting multiple tumor types by the induction of immune responses to shared TAAs is presented in the second section.

Toll-like receptor agonists in cancer therapy

Toll-like receptors (TLRs) are pattern-recognition receptors related to the Drosophila Toll protein. TLR activation alerts the immune system to microbial products and initiates innate and adaptive immune responses. The naturally powerful immunostimulatory property of TLR agonists can be exploited for active immunotherapy against cancer. Antitumor activity has been demonstrated in several cancers, and TLR agonists are now undergoing extensive clinical investigation. This review discusses recent advances in the field and highlights potential opportunities for the clinical development of TLR agonists as single agent immunomodulators, vaccine adjuvants and in combination with conventional cancer therapies.

MUC1-based recombinant Bacillus Calmette-Guerin vaccines as candidates for breast cancer immunotherapy

IMPORTANCE OF THE FIELD

The challenge in breast cancer vaccine development is to find the best combination of antigen, adjuvant and delivery system to produce a strong and long-lasting immune response. Mucin 1 (MUC1) is a potential candidate target for breast cancer immunotherapy. Bacillus Calmette-Guerin (BCG) is used widely in human vaccines. Furthermore, it can potentially offer unique advantages for developing a safe and effective multi-vaccine vehicle. Due to these properties, the development of MUC1 based recombinant BCG (rBCG) vaccines for breast cancer immunotherapy has gained great momentum in recent years.

AREAS COVERED IN THIS REVIEW

Our aim is to discuss the recent progress in MUC1-based breast cancer immunotherapy and to highlight the advantages of MUC1-based rBCG vaccines as the new breast cancer vaccines.

WHAT THE READER WILL GAIN

Several promising MUC1-based rBCG vaccines have been shown to induce MUC1-specific antitumor immune responses in pre-clinical studies. This review updates and evaluates this very important and rapidly developing field, and provides a critical perspective and information source for its potential clinical applications.

TAKE HOME MESSAGE

MUC1-based rBCG vaccines have been shown to elicit an effective anti-tumor immune response in vivo demonstrating its potential utility in breast cancer treatment.

ST3Gal.I sialyltransferase relevance in bladder cancer tissues and cell lines

BACKGROUND

The T antigen is a tumor-associated structure whose sialylated form (the sialyl-T antigen) involves the altered expression of sialyltransferases and has been related with worse prognosis. Since little or no information is available on this subject, we investigated the regulation of the sialyltransferases, able to sialylate the T antigen, in bladder cancer progression.

METHODS

Matched samples of urothelium and tumor tissue, and four bladder cancer cell lines were screened for: ST3Gal.I, ST3Gal.II and ST3Gal.IV mRNA level by real-time PCR. Sialyl-T antigen was detected by dot blot and flow cytometry using peanut lectin. Sialyltransferase activity was measured against the T antigen in the cell lines.

RESULTS

In nonmuscle-invasive bladder cancers, ST3Gal.I mRNA levels were significantly higher than corresponding urothelium (p < 0.001) and this increase was twice more pronounced in cancers with tendency for recurrence. In muscle-invasive cancers and matching urothelium, ST3Gal.I mRNA levels were as elevated as nonmuscle-invasive cancers. Both non-malignant bladder tumors and corresponding urothelium showed ST3Gal.I mRNA levels lower than all the other specimen groups. A good correlation was observed in bladder cancer cell lines between the ST3Gal.I mRNA level, the ST activity (r = 0.99; p = 0.001) and sialyl-T antigen expression, demonstrating that sialylation of T antigen is attributable to ST3Gal.I. The expression of sialyl-T antigens was found in patients' bladder tumors and urothelium, although without a marked relationship with mRNA level. The two ST3Gal.I transcript variants were also equally expressed, independently of cell phenotype or malignancy.

CONCLUSION

ST3Gal.I plays the major role in the sialylation of the T antigen in bladder cancer. The overexpression of ST3Gal.I seems to be part of the initial oncogenic transformation of bladder and can be considered when predicting cancer progression and recurrence.

Mucin-type O-glycosylation and its potential use in drug and vaccine development

Mucin-type O-glycans are found on mucins as well as many other glycoproteins. The initiation step in synthesis is catalyzed by a large family of polypeptide GalNAc-transferases attaching the first carbohydrate residue, GalNAc, to selected serine and threonine residues in proteins. During the last decade an increasing number of GalNAc-transferase isoforms have been cloned and their substrate-specificities partly characterized. These differences in substrate specificities have been exploited for in vitro site-directed O-glycosylation. In GlycoPEGylation, polyehylene glycol (PEG) is transferred to recombinant therapeutics to specific acceptor sites directed by GalNAc-transferases. GalNAc-transferases have also been used to control density of glycosylation in the development of glycopeptide-based cancer vaccines. The membrane-associated mucin-1 (MUC1) has long been considered a target for immunotherapeutic and immunodiagnostic measures, since it is highly overexpressed and aberrantly O-glycosylated in most adenocarcinomas, including breast, ovarian, and pancreatic cancers. By using vaccines mimicking the glycosylation pattern of cancer-cells, it is possible to overcome tolerance in transgenic animals expressing the human MUC1 protein as a self-antigen providing important clues for an improved MUC1 vaccine design. The present review will highlight some of the potential applications of site-directed O-glycosylation.

Lessons from randomized phase III studies with active cancer immunotherapies--outcomes from the 2006 meeting of the Cancer Vaccine Consortium (CVC)

After years of effort to develop active cancer immunotherapies, seven candidate products achieved promising results in phase I/II studies that triggered phase III randomized studies. One candidate to date has received an approvable letter from the United States Food and Drug Administration (FDA), defining a clear path to licensure for sipuleucel-T (Provenge, Dendreon) within the next couple of years. The other phase III studies failed to achieve statistical criteria for some or all of the critical endpoints. Yet, there is widespread recognition that using a patient's own immune system to target and destroy cancer cells may offer an effective biological therapy with less toxicity than presently available anti-cancer therapies, and several candidates are still being evaluated in clinical studies. This review summarizes the lessons learned from these case studies, evaluates scientific, study design, and business factors that can affect study outcomes, identifies common challenges faced by sponsors developing these innovative therapies, and provides considerations for future study designs that may increase the likelihood of success.

Preclinical pharmacokinetics, tissue distribution, and antitumor activity of a folate-hapten conjugate-targeted immunotherapy in hapten-immunized mice

Folic acid (pteroylglutamic acid) represents a useful ligand for targeted cancer therapies because it binds to a common epithelial tumor antigen known as the folate receptor. We previously devised an immunotherapy strategy that uses a bispecific ligand, a folate-hapten (FITC) conjugate, to redirect endogenously induced anti-FITC antibodies to folate receptor-positive tumor cells following parenteral administration. Here, we present results from preclinical pharmacokinetic and tissue biodistribution studies using a radioactive folate-FITC conjugate and results from dose optimization studies done in tumor-bearing animals. Folate-FITC was found to be rapidly eliminated in non-immunized mice; however, in immunized hosts, folate-FITC was shown to form immune complexes with FITC-specific antibodies, the consequence of which was a approximately 173-fold increase in drug exposure (i.e., area under the curve). Using a newly developed ELISA assay, the extent of circulating anti-FITC antibodies occupied by parenterally given folate-FITC was determined to be proportional to the given dose. Furthermore, high doses of folate-FITC were found to promote the cosaturation of tumor cell surface folate receptors and circulating FITC-specific antibodies, blocking the immune recognition of tumor cells and thereby reducing antitumor activity. Nonetheless, by extending the duration of treatment and administering subsaturating doses of folate-FITC, enhanced antitumor response was observed in mice bearing established folate receptor-positive M109 tumors. Overall, results from the present study may help to guide clinicians through on-going clinical investigations of folate-targeted immunotherapy.

Expression of MUC1 in primary and metastatic human epithelial ovarian cancer and its therapeutic significance

BACKGROUND

MUC1 is associated with cellular transformation and tumorigenicity and is considered as an important tumor-associated antigen (TAA) for cancer therapy. The objective of this study was to evaluate the patterns of MUC1 expression in primary tumors and metastatic lesions in the advanced stages of epithelial ovarian cancers (EOCs) and correlate the expression with clinicopathological features.

METHODS

The expression of MUC1 was examined on frozen tissue sections from primary EOC (n=42), the matched metastatic lesions (n=30) and paraffin-embedded tissue sections from primary EOC (n=60), normal ovarian tissues (n=20) using immunohistochemistry (IHC) by monoclonal antibody (MAb) C595.

RESULTS

The expression of MUC1 was found in 92% (39/42) of EOC and 90% (27/30) of the matched metastatic lesions in frozen tissue sections respectively while the expression of MUC1 was found in 95% (57/60) of EOC and 5% (1/20) of normal ovarian tissues in paraffin-embedded sections respectively. Most of the tumors showed moderate to strong intensity staining while normal ovarian tissues only showed weak intensity staining. The overexpression of MUC1 was significantly associated with various progression parameters such as tumor stage, grade, residual disease status and presence of ascites (P<0.05).

CONCLUSIONS

MUC1 is overexpressed in above 90% of late stage of EOC and of metastatic lesions but not in normal ovarian tissues, and the high expression of MUC1 is correlated with EOC progression. MUC1 antigen may be a useful therapeutic target to prevent the development of incurable, recurrent metastatic EOC.

Vaccination with Theratope (STn-KLH) as treatment for breast cancer

Cancer vaccines have demonstrated that they can stimulate antibody and cell-mediated immune responses against tumor-associated antigens in the laboratory. However, few clinical studies with cancer vaccines have demonstrated convincing clinical responses. Sialyl-Tn is a carbohydrate associated with MUC1. It is a unique tumor-associated antigen, present on many adenocarcinomas including breast, ovarian, colorectal, gastric and pancreatic. Consequently, Sialyl-TN is an ideal candidate for boosting the patient's immune system specifically against a unique tumor-associated antigen. The cancer vaccine Theratope was developed by Biomira, Inc. using a synthetic Sialyl-Tn antigen that emulates the unique carbohydrate on human cancer. Clinical trials have predominantly been carried out in breast cancer patients and these trials are outlined in this profile.

Biological significance of cancer-associated sialyl-Tn antigen: modulation of malignant phenotype in gastric carcinoma cells

The activation of an abnormal glycosylation pathway in cancer cells leads to the formation of the sialyl-Tn antigen, blocking regular carbohydrate chain elongation. Sialyl-Tn antigen is rarely expressed in normal tissues but is aberrantly expressed in a variety of carcinomas, where it constitutes a marker of poor prognosis. Although the clinical significance of sialyl-Tn is well characterized, a functional role for this glycan and its contribution to cancer progression remain to be elucidated. This study evaluates the capability of sialyl-Tn to modify processes like cell cycle, apoptosis, actin cytoskeleton dynamics, adhesion and motility on ECM components, cell-cell aggregation and invasion. De-novo expression of sialyl-Tn leads to major morphological and cell behavior alterations in gastric carcinoma cells which were reverted by specific antibody blockage. Sialyl-Tn antigen is able to modulate a malignant phenotype inducing a more aggressive cell behavior, such as decreased cell-cell aggregation and increased ECM adhesion, migration and invasion.

The sweet and sour of cancer: glycans as novel therapeutic targets

A growing body of evidence supports crucial roles for glycans at various pathophysiological steps of tumour progression. Glycans regulate tumour proliferation, invasion, haematogenous metastasis and angiogenesis, and increased understanding of these roles sets the stage for developing pharmaceutical agents that target these molecules. Such novel agents might be used alone or in combination with operative and/or chemoradiation strategies for treating cancer.

Role of the human ST6GalNAc-I and ST6GalNAc-II in the synthesis of the cancer-associated sialyl-Tn antigen

The Sialyl-Tn antigen (Neu5Acalpha2-6GalNAc-O-Ser/Thr) is highly expressed in several human carcinomas and is associated with carcinoma aggressiveness and poor prognosis. We characterized two human sialyltransferases, CMP-Neu5Ac:GalNAc-R alpha2,6-sialyltransferase (ST6GalNAc)-I and ST6GalNAc-II, that are candidate enzymes for Sialyl-Tn synthases. We expressed soluble recombinant hST6GalNAc-I and hST6GalNAc-II and characterized the substrate specificity of both enzymes toward a panel of glycopeptides, glycoproteins, and other synthetic glycoconjugates. The recombinant ST6GalNAc-I and ST6GalNAc-II showed similar substrate specificity toward glycoproteins and GalNAcalpha-O-Ser/Thr glycopeptides, such as glycopeptides derived from the MUC2 mucin and the HIVgp120. We also observed that the amino acid sequence of the acceptor glycopeptide contributes to the in vitro substrate specificity of both enzymes. We additionally established a gastric cell line, MKN45, stably transfected with the full length of either ST6GalNAc-I or ST6GalNAc-II and evaluated the carbohydrate antigens expression profile induced by each enzyme. MKN45 transfected with ST6GalNAc-I showed high expression of Sialyl-Tn, whereas MKN45 transfected with ST6GalNAc-II showed the biosynthesis of the Sialyl-6T structure [Galbeta1-3 (Neu5Acalpha2-6)GalNAc-O-Ser/Thr]. In conclusion, although both enzymes show similar in vitro activities when Tn antigen alone is available, whenever both Tn and T antigens are present, ST6GalNAc-I acts preferentially on Tn antigen, whereas the ST6GalNAc-II acts preferentially on T antigen. Our results show that ST6GalNAc-I is the major Sialyl-Tn synthase and strongly support the hypothesis that the expression of the Sialyl-Tn antigen in cancer cells is due to ST6GalNAc-I activity.

Immunological treatment of ovarian cancer

PURPOSE OF REVIEW

Development of immunological treatments for ovarian cancer has not been a conspicuous success story over the past few years. Only a handful of clinical trials have reported immunological responses, and correlation with clinical benefit has been elusive. Several recent studies presented in this review, however, point to a revival of optimism for the development of novel immunotherapeutic strategies.

RECENT FINDINGS

The cloning and sequencing of CA125, coupled with novel structural and functional insights, undoubtedly represent important steps forward. The possibility that CA125 could play a role in evasion of immunity by ovarian tumors may represent a new challenge, but does not detract from its potential as a therapeutic target. Of the recent clinical trial reports, the most intriguing results were seen from immunotherapy with a conventional mouse monoclonal antibody specific for CA125, in which human anti-mouse antibody responses correlated significantly with improved survival of patients with advanced stage ovarian cancer and clinical evidence of recurrent disease at the time of treatment.

SUMMARY

There is little doubt that CA125 will undergo a renaissance as an important target antigen for development of novel immunological treatments, particularly with regard to cellular therapies. Identification of other novel ovarian tumor antigens will also accelerate research focused on stimulation of T-cell immunity. Current research trends suggest a paradigm shift in emphasis from vaccines designed to elicit antibody responses to strategies such as dendritic cell vaccination that are designed to induce broader immunity, including ovarian tumor antigen-specific helper T-lymphocyte and cytotoxic T-lymphocyte responses.

Clinical development of the STn-KLH vaccine (Theratope)

The development of active specific immunotherapy depends on the identification of altered cancer cell-specific molecules or epitopes that are immunogenic. Many cancer-specific peptide or glycoprotein target antigens have been identified. Tumors carrying aberrant epitopes as a result of underglycosylation of mucins are associated with poor prognosis in many epithelial cancers. The aberrant mucin sialyl-Tn (STn) epitope, in addition to being a predictor of poor prognosis when expressed in tumors, is associated with increased aggressiveness and metastatic potential, making it a promising target for immunotherapy. The STn-keyhole limpet hemocyanin (KLH) vaccine (Theratope) is an investigational active specific immunotherapy consisting of a synthetic STn epitope conjugated to a high molecular weight protein carrier, KLH. The immune response generated by the STn-KLH vaccine is both humoral and cellular. More than 1000 breast cancer patients with metastatic disease are currently enrolled in a phase III clinical trial to assess the safety and efficacy of the STn-KLH vaccine. Interim analysis from a current phase III trial has confirmed the safety of the STn-KLH vaccine, and the clinical outcome awaits the final analysis expected in 2003.

Rationale for the clinical development of STn-KLH (Theratope) and anti-MUC-1 vaccines in breast cancer

Mucin-1 (MUC-1) is a high-molecular-weight glycoprotein rich in serine and threonine residues that are O-glycosylated. Expression of MUC-1 is increased in breast, ovarian, and other adenocarcinomas, and altered glycosylation results in exposure of novel peptide epitopes and the expression of tumor-associated carbohydrate residues, such as Thomsen-Freidenreich and sialyl-Tn (STn) antigens. Preclinical studies suggested that induction of immune response to tumor-associated carbohydrate moieties results in inhibition of tumor growth. A synthetic STn-keyhole limpet hemocyanin (KLH) vaccine (Theratope) is currently being evaluated in clinical trials as active specific immunotherapy in the treatment of advanced breast cancer. Two phase II trials in 50 breast cancer patients compared the STn-KLH vaccine with and without a single low-dose infusion of cyclophosphamide used as an immunomodulator prior to initiation of treatment. Humoral immune responses were higher in patients who had received low-dose cyclophosphamide intravenously (I.V.) compared with patients who had received no cyclophosphamide or oral cyclophosphamide. There was a statistically significant survival difference between all patients treated with the STn-KLH vaccine (overall median survival, 19.1 months; n = 50) and the retrospective control patients (overall median survival, 9.2 months; n = 104). Furthermore, patients who received cyclophosphamide I.V. prior to the STn-KLH vaccine had median survival rates close to 3 times that of patients in a retrospective, frequency-matched, control group who received conventional therapies (cyclophosphamide-I.V. group, 26.5 months vs. 9.2 months, control group). The trials reported minimal toxicity profile with local reactions in the injection site and some flu-like symptoms. On the basis of the phase II trial results, a phase III clinical trial of the STn-KLH vaccine is underway. The trial was closed to enrollment in March 2001 with the accrual of 1030 women. The final analysis is event driven and is expected to commence mid 2003.