Characterization of monoclonal antibody PAM4 reactive with a pancreatic cancer mucin

Advances in MUC1 resistance to chemotherapy in pancreatic cancer

The incidence of pancreatic cancer (PC), a highly fatal malignancy, is increasing every year. Chemotherapy is an important treatment for it in addition to surgery, yet most patients become resistant to chemotherapeutic agents within a few weeks of treatment initiation.​ MUC1 is a highly glycosylated transmembrane protein, and studies have shown that aberrantly glycosylated overexpression of MUC1 is involved in regulating the biology of chemoresistance in cancer cells. This article summarizes the mechanism of MUC1 in PC chemoresistance and reviews MUC1-based targeted therapies.

Predictive Value of MUC5AC Signature in Pancreatic Ductal Adenocarcinoma: A Hypothesis Based on Preclinical Evidence

Mucin 5AC (MUC5AC) glycoprotein plays a crucial role in carcinogenesis and drug sensitivity in pancreatic ductal adenocarcinoma (PDAC), both individually and in combination with other mucins. Its function and localization are glycoform-specific. The immature isoform (detected by the CLH2 monoclonal antibody, or mab) is usually in the perinuclear (cytoplasmic) region, while the mature (45 M1, 2-11, Nd2) variants are in apical and extracellular regions. There is preclinical evidence suggesting that mature MUC5AC has prognostic and predictive (response to treatment) value. However, these findings were not validated in clinical studies. We propose a MUC5AC signature with three components of MUC5AC-localization, variant composition, and intensity-suggesting a reliable marker in combination of variants than with individual MUC5AC variants alone. We also postulate a theory to explain the occurrence of different MUC5AC variants in abnormal pancreatic lesions (benign, precancerous, and cancerous). We also analyzed the effect of mature MUC5AC on sensitivity to drugs often used in PDAC management, such as gemcitabine, 5-fluorouracil, oxaliplatin, irinotecan, cisplatin, and paclitaxel. We found preliminary evidence of its predictive value, but there is a need for large-scale studies to validate them.

Understanding the Clinical Significance of MUC5AC in Biliary Tract Cancers

Biliary tract cancers (BTC) arise from biliary epithelium and include cholangiocarcinomas or CCA (including intrahepatic (ICC) and extrahepatic (ECC)) and gallbladder cancers (GBC). They often have poor outcomes owing to limited treatment options, advanced presentations, frequent recurrence, and poor response to available systemic therapy. Mucin 5AC (MUC5AC) is rarely expressed in normal biliary epithelium, but can be upregulated in tissues of benign biliary disease, premalignant conditions (e.g., biliary intraepithelial neoplasia), and BTCs. This mucin's numerous glycoforms can be divided into less-glycosylated immature and heavily-glycosylated mature forms. Reported MUC5AC tissue expression in BTC varies widely, with some associations based on cancer location (e.g., perihilar vs. peripheral ICC). Study methods were variable regarding cancer subtypes, expression positivity thresholds, and MUC5AC glycoforms. MUC5AC can be detected in serum of BTC patients at high concentrations. The hesitancy in developing MUC5AC into a clinically useful biomarker in BTC management is due to variable evidence on the diagnostic and prognostic value. Concrete conclusions on tissue MUC5AC are difficult, but serum detection might be relevant for diagnosis and is associated with poor prognosis. Future studies are needed to further the understanding of the potential clinical value of MUC5AC in BTC, especially regarding predictive and therapeutic value.

Antibody-Based Approaches to Target Pancreatic Tumours

Pancreatic cancer is an aggressive cancer with a dismal prognosis. This is due to the difficulty to detect the disease at an early and curable stage. In addition, only limited treatment options are available, and they are confronted by mechanisms of resistance. Monoclonal antibody (mAb) molecules are highly specific biologics that can be directly used as a blocking agent or modified to deliver a drug payload depending on the desired outcome. They are widely used to target extracellular proteins, but they can also be employed to inhibit intracellular proteins, such as oncoproteins. While mAbs are a class of therapeutics that have been successfully employed to treat many cancers, they have shown only limited efficacy in pancreatic cancer as a monotherapy so far. In this review, we will discuss the challenges, opportunities and hopes to use mAbs for pancreatic cancer treatment, diagnostics and imagery.

Molecular Targeted Positron Emission Tomography Imaging and Radionuclide Therapy of Pancreatic Ductal Adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) has an inauspicious prognosis, mainly due to difficulty in early detection of the disease by the current imaging modalities. The upcoming development of tumour-specific tracers provides an alternative solution for more accurate diagnostic imaging techniques for staging and therapy response monitoring. The future goal to strive for, in a patient with PDAC, should definitely be first to receive a diagnostic dose of an antibody labelled with a radionuclide and to subsequently receive a therapeutic dose of the same labelled antibody with curative intent. In the first part of this paper, we summarise the available evidence on tumour-targeted diagnostic tracers for molecular positron emission tomography (PET) imaging that have been tested in humans, together with their clinical indications. Tracers such as radiolabelled prostate-specific membrane antigen (PSMA)-in particular, 18F-labelled PSMA-already validated and successfully implemented in clinical practice for prostate cancer, also seem promising for PDAC. In the second part, we discuss the theranostic applications of these tumour-specific tracers. Although targeted radionuclide therapy is still in its infancy, lessons can already be learned from early publications focusing on dose fractioning and adding a radiosensitiser, such as gemcitabine.

An Immunohistochemical Evaluation of Tumor-Associated Glycans and Mucins as Targets for Molecular Imaging of Pancreatic Ductal Adenocarcinoma

Simple Summary

Distinguishing pancreatic cancer from healthy tissue before and during surgery can be enhanced by using molecular tracers directed at molecules on tumor cells allowing high-contrast visualization of tumor tissue, eventually improving diagnosis and surgical removal. Albeit sugar molecules and proteins carrying a large amount of sugars-mucins- have gained significant interest as tumor-specific targets, their relative presence on structures surrounding tumor tissues and lymph node metastases is unknown. The current study shows that the presence of several, but not all, investigated sugar molecules and mucins on pancreatic cancer cells is higher compared to surrounding tissues. Moreover, given their abundance on tumor cells in lymph nodes and their absence on normal lymph nodes, all investigated targets are high-potential targets for visualization of lymph node metastases. This study paves the way for the development of molecular tracers against the targets evaluated herein to allow improvement of pancreatic cancer treatment.

Abstract

Targeted molecular imaging may overcome current challenges in the preoperative and intraoperative delineation of pancreatic ductal adenocarcinoma (PDAC). Tumor-associated glycans Le^a/c/x, sdi-Le^a, sLe^a, sLe^x, sTn as well as mucin-1 (MUC1) and mucin-5AC (MU5AC) have gained significant interest as targets for PDAC imaging. To evaluate their PDAC molecular imaging potential, biomarker expression was determined using immunohistochemistry on PDAC, (surrounding) chronic pancreatitis (CP), healthy pancreatic, duodenum, positive (LN⁺) and negative lymph node (LN⁻) tissues, and quantified using a semi-automated digital image analysis workflow. Positive expression on PDAC tissues was found on 83% for Le^a/c/x, 94% for sdi-Le^a, 98% for sLe^a, 90% for sLe^x, 88% for sTn, 96% for MUC1 and 67% for MUC5AC, where all were not affected by the application of neoadjuvant therapy. Compared to PDAC, all biomarkers were significantly lower expressed on CP, healthy pancreatic and duodenal tissues, except for sTn and MUC1, which showed a strong expression on duodenum (sTn tumor:duodenum ratio: 0.6, p < 0.0001) and healthy pancreatic tissues (MUC1 tumor:pancreas ratio: 1.0, p > 0.9999), respectively. All biomarkers are suitable targets for correct identification of LN⁺, as well as the distinction of LN⁺ from LN⁻ tissues. To conclude, this study paves the way for the development and evaluation of Le^a/c/x-, sdi-Le^a-, sLe^a-, sLe^x- and MUC5AC-specific tracers for molecular imaging of PDAC imaging and their subsequent introduction into the clinic.

Biomarkers in the diagnosis of pancreatic cancer: Are we closer to finding the golden ticket?

Pancreatic cancer (PC) is a leading cause of cancer related mortality on a global scale. The disease itself is associated with a dismal prognosis, partly due to its silent nature resulting in patients presenting with advanced disease at the time of diagnosis. To combat this, there has been an explosion in the last decade of potential candidate biomarkers in the research setting in the hope that a diagnostic biomarker may provide a glimmer of hope in what is otherwise quite a substantial clinical dilemma. Currently, serum carbohydrate antigen 19-9 is utilized in the diagnostic work-up of patients diagnosed with PC however this biomarker lacks the sensitivity and specificity associated with a gold-standard marker. In the search for a biomarker that is both sensitive and specific for the diagnosis of PC, there has been a paradigm shift towards a focus on liquid biopsy and the use of diagnostic panels which has subsequently proved to have efficacy in the diagnosis of PC. Currently, promising developments in the field of early detection on PC using diagnostic biomarkers include the detection of microRNA (miRNA) in serum and circulating tumour cells. Both these modalities, although in their infancy and yet to be widely accepted into routine clinical practice, possess merit in the early detection of PC. We reviewed over 300 biomarkers with the aim to provide an in-depth summary of the current state-of-play regarding diagnostic biomarkers in PC (serum, urinary, salivary, faecal, pancreatic juice and biliary fluid).

Understanding the Clinical Impact of MUC5AC Expression on Pancreatic Ductal Adenocarcinoma

Simple Summary

Management of pancreatic cancer is challenging as there are limited treatment options, and most cases are diagnosed at advanced stages. In addition, there are no dependable tests available to predict bad outcomes or treatment responses in current clinical practice. Here, we shed light on the available evidence on mucin, MUC5AC in predicting the outcome of pancreatic cancers. We also discuss variants of MUC5AC believed to have a role in the malignant transformation of pancreatic tissues.

Abstract

Mucin-5AC (MUC5AC) is a heavily glycosylated gel-forming secreted mucin with a reliable prognostic value when detected in multiple malignancies. It is highly prevalent (70%) in PDA and is nonexistent in normal pancreatic tissues. Retrospective studies on PDA tumor tissue (detected by immunohistochemistry or IHC)) have investigated the prognostic value of MUC5AC expression but were equivocal. Some studies associated it with poor outcomes (survival or pathological features such as lymph node disease, vascular/neural invasion in resected tumors), while others have concluded that it is a good prognostic marker. The examination of expression level threshold (5%, 10%, or 25%) and the detected region (apical vs. cytoplasmic) were variable among the studies. The maturation stage and glycoform of MUC5AC detected also differed with the Monoclonal antibody (Mab) employed for IHC. CLH2 detects less mature/less glycosylated versions while 45M1 or 21-1 detect mature/more glycosylated forms. Interestingly, aberrantly glycosylated variants of MUC5AC were detected using lectin assays (Wheat Germ Agglutinin-MUC5AC), and Mabs such as NPC-1C and PAM4 have are more specific to malignant pancreatic tissues. NPC-1C and PAM4 antibody reactive epitopes on MUC5AC are immunogenic and could represent specific changes on the native MUC5AC glycoprotein linked to carcinogenesis. It was never studied to predict treatment response.

Targeting Glycans and Heavily Glycosylated Proteins for Tumor Imaging

Simple Summary

Distinguishing malignancy from healthy tissue is essential for oncologic surgery. Targeted imaging during an operation aids the surgeon to operate better. The present tracers for detecting cancer are directed against proteins that are overexpressed on the membrane of tumor cells. This review evaluates the use of tumor-associated sugar molecules as an alternative for proteins to image cancer tissue. These sugar molecules are present as glycans on glycosylated membrane proteins and glycolipids. Due to their location and large numbers per cell, these sugar molecules might be better targets for tumor imaging than proteins.

Abstract

Real-time tumor imaging techniques are increasingly used in oncological surgery, but still need to be supplemented with novel targeted tracers, providing specific tumor tissue detection based on intra-tumoral processes or protein expression. To maximize tumor/non-tumor contrast, targets should be highly and homogenously expressed on tumor tissue only, preferably from the earliest developmental stage onward. Unfortunately, most evaluated tumor-associated proteins appear not to meet all of these criteria. Thus, the quest for ideal targets continues. Aberrant glycosylation of proteins and lipids is a fundamental hallmark of almost all cancer types and contributes to tumor progression. Additionally, overexpression of glycoproteins that carry aberrant glycans, such as mucins and proteoglycans, is observed. Selected tumor-associated glyco-antigens are abundantly expressed and could, thus, be ideal candidates for targeted tumor imaging. Nevertheless, glycan-based tumor imaging is still in its infancy. In this review, we highlight the potential of glycans, and heavily glycosylated proteoglycans and mucins as targets for multimodal tumor imaging by discussing the preclinical and clinical accomplishments within this field. Additionally, we describe the major advantages and limitations of targeting glycans compared to cancer-associated proteins. Lastly, by providing a brief overview of the most attractive tumor-associated glycans and glycosylated proteins in association with their respective tumor types, we set out the way for implementing glycan-based imaging in a clinical practice.

Recent Discoveries of Diagnostic, Prognostic and Predictive Biomarkers for Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive disease with a dismal prognosis that is frequently diagnosed at an advanced stage. Although less common than other malignant diseases, it currently ranks as the fourth most common cause of cancer-related death in the European Union with a five-year survival rate of below 9%. Surgical resection, followed by adjuvant chemotherapy, remains the only potentially curative treatment but only a minority of patients is diagnosed with locally resectable, non-metastatic disease. Patients with advanced disease are treated with chemotherapy but high rates of treatment resistance and unfavorable side-effect profiles of some of the used regimens remain major challenges. Biomarkers reflect pathophysiological or physiological processes linked to a disease and can be used as diagnostic, prognostic and predictive tools. Thus, accurate biomarkers can allow for better patient stratification and guide therapy choices. Currently, the only broadly used biomarker for PDAC, CA 19-9, has multiple limitations and the need for novel biomarkers is urgent. In this review, we highlight the current situation, recent discoveries and developments in the field of biomarkers of PDAC and their potential clinical applications.

MUC1 antibody-based therapeutics: the promise of cancer immunotherapy

Antibody-based targeted therapies have been able to target cancers with enhanced specificity and high efficacy. In this regard, identifying cancer markers (antigens) that are only present (tumor-specific antigens) or have an increased expression (tumor-associated antigen) on the surface of cancer cells is a crucial step for targeted cancer treatment. Various cancer antigens have already been used for therapeutic and diagnostic purposes. MUC1 is one of the most important tumor markers with high levels of expression in various solid tumors which makes it as a potential target for antibody-based therapies. This review discusses preclinical and clinical results from various platforms based on monoclonal antibodies, nanobodies as well as bispecific antibodies against MUC1. We also highlight unmet challenges that must be overcome to generate more effective cancer immunotherapy strategies.

Inducing a humoral immune response to pancreatic cancer antigen

BACKGROUND

Patients with pancreatic carcinoma have a grim prognosis. Here, we examine the induction of an in vitro antibody response of human B cells to pancreatic carcinoma antigens.

MATERIAL AND METHODS

Cells of five cultured pancreatic ductal adenocarcinoma lines were lysed and their plasma membrane fragments isolated in an aqueous two-phase-system. The plasma membrane fragments were then added to cultures of isolated peripheral blood mononuclear cells from healthy volunteers for 14 days to act as a tumor antigen. Also, we added combinations of IL-2, IL-4, IL-21, anti-CD40 mAb and varying protein concentrations of the plasma membrane fragments to these cultures. We then tested characteristics and binding of resulting IgG and IgM against aforementioned tumor plasma membrane fragments and their respective cells using ELISAs.

RESULTS

The combination of IL-2, IL-4 and anti-CD40 mAb elicited IgM production showing significant binding (p<0.05) to plasma membrane fragments. PANC-1 antigen and the combination of IL-4, IL-21 and anti-CD40 mAb was able to produce a significant and specific IgG formation against PANC-1 plasma membrane fragments (p<0.05). Tumor antigen, interleukins and anti-CD40 mAb had a significant impact on the binding capacity of these antibodies (p<0.05). IgG binding pancreatic carcinoma cells was observed when the tumor antigen concentration was increased during stimulation (p<0.05). BxPC3 plasma membrane fragments showed inhibitory effects on IgG binding BxPC3 antigens (p<0.05).

CONCLUSIONS

A human anti-tumor antibody formation can be induced in vitro using PANC-1 antigens and B cell stimulating agents. This response has the potential to generate antibodies specific to PANC-1 antigens. PRéCIS: The concept presented is novel and a promising approach to eliciting a specific B cell response to tumor antigen. The method may prove useful in understanding and developing anti-tumor immunity.

Identification of PAM4 (clivatuzumab)-reactive epitope on MUC5AC: a promising biomarker and therapeutic target for pancreatic cancer

PAM4 is a monoclonal antibody showing high specificity for pancreatic ductal adenocarcinoma (PDAC). Humanized PAM4 labeled with ⁹⁰Y in combination with low-dose gemcitabine has shown promising therapeutic activity, and is being evaluated in a phase III clinical trial. Prior efforts have suggested that PAM4 potentially reacts with MUC5AC, a secretory mucin expressed de novo in early pancreatic neoplasia and retained throughout disease progression. In present study, we provide further evidence validating MUC5AC as the PAM4 antigen, and locate PAM4-reactive epitope within the N-terminal cysteine-rich subdomain 2 (Cys2), thus differentiating PAM4 from most anti-MUC5AC antibodies known to-date. Specifically, we show (i) PAM4-antigen and MUC5AC were co-localized in multiple human cancer cell lines, including Capan-1, BxPC-3, and CFPAC-1; (ii) MUC5AC-specific siRNA prominently reduced the expression of both MUC5AC and PAM4-antigen in CFPAC-1 cells; (iii) PAM4 preferentially binds to the void-volume fractions from Sepharose-CL2B chromatography of Capan-1 culture supernatants, which were revealed by Western blot to display the ladder pattern characteristic of oligomeric MUC5AC; and (iv) the N-terminal Cys2 within several recombinant MUC5AC fragments is essential for binding to PAM4. These findings shed light on the mechanism of PAM4-based diagnosis and treatment for pancreatic cancer, and guide further exploration of its clinical utility.

Novel agents for advanced pancreatic cancer

Pancreatic cancer is relatively insensitive to conventional chemotherapy. Therefore, novel agents targeting dysregulated pathways (MAPK/ERK, EGFR, TGF-β, HEDGEHOG, NOTCH, IGF, PARP, PI3K/AKT, RAS, and Src) are being explored in clinical trials as monotherapy or in combination with cytotoxic chemotherapy. This review summarizes the most recent advances with the targeted therapies in the treatment of patients with advanced pancreatic cancer.

(90)Y-clivatuzumab tetraxetan with or without low-dose gemcitabine: A phase Ib study in patients with metastatic pancreatic cancer after two or more prior therapies

BACKGROUND

For patients with metastatic pancreatic adenocarcinoma, there are no approved or established treatments beyond the 2nd line. A Phase Ib study of fractionated radioimmunotherapy was undertaken in this setting, administering (90)Y-clivatuzumab tetraxetan (yttrium-90-radiolabelled humanised antibody targeting pancreatic adenocarcinoma mucin) with or without low radiosensitising doses of gemcitabine.

METHODS

Fifty-eight patients with three (2-7) median prior treatments were treated on Arm A (N=29, (90)Y-clivatuzumab tetraxetan, weekly 6.5 mCi/m(2)doses×3, plus gemcitabine, weekly 200 mg/m(2) doses×4 starting 1 week earlier) or Arm B (N=29, (90)Y-clivatuzumab tetraxetan alone, weekly 6.5 mCi/m(2)doses×3), repeating cycles after 4-week delays. Safety was the primary endpoint; efficacy was also evaluated.

RESULTS

Cytopaenias (predominantly transient thrombocytopenia) were the only significant toxicities. Fifty-three patients (27 Arm A, 26 Arm B, 91% overall) completed ⩾1 full treatment cycles, with 23 (12 Arm A, 11 Arm B; 40%) receiving multiple cycles, including seven (6 Arm A, 1 Arm B; 12%) given 3-9 cycles. Two patients in Arm A had partial responses by RECIST criteria. Kaplan-Meier overall survival (OS) appeared improved in Arm A versus B (hazard ratio [HR] 0.55, 95% CI: 0.29-0.86; P=0.017, log-rank) and the median OS for Arm A versus Arm B increased to 7.9 versus 3.4 months with multiple cycles (HR 0.32, P=0.004), including three patients in Arm A surviving >1 year.

CONCLUSIONS

Clinical studies of (90)Y-clivatuzumab tetraxetan combined with low-dose gemcitabine appear feasible in metastatic pancreatic cancer patients beyond 2nd line and a Phase III trial of this combination is now underway in this setting.

Radioimmunotherapy--a potential novel tool for pancreatic cancer therapy?

Pancreatic cancer is one of the most severe cancers and is predicted to rise up to the number two cancer killer by 2030. The ineffective treatment options available and that the cancer is silent until very late in its course are the main reasons for the poor outcome of the disease. Surgery is the only curative option but only available for 10-15 % of the patients, but even then many relapse due to metastases. Many new treatments are under way, and one of the promising ones is radioimmunotherapy (RIT). This review includes clinical trials with RIT in pancreatic cancer as well as a review of adverse events observed during treatment of other solid tumors. Additionally, preclinical studies are reviewed with emphasis on effect, adverse events, the tumor targeting as well as isotope function. Four clinical trials with pancreatic cancer have been conducted with positive results, and one phase III trial is underway. The use of RIT in patients with solid tumors has proven to be well tolerated, and the adverse effects are almost exclusively hematological. Multiple targets and isotopes have been evaluated preclinically, alone, or in combination with existing drug options. Smaller tumors have in several studies completely regressed, while larger ones have stabilized or progressed more slowly. Pancreatic cancer is one of the solid tumors where RIT have reached the longest. The tumor heterogeneity will most likely leave room for more than one treatment option, and several aspiring therapies are under way. RIT may become part of multimodality tumor-directed therapy for pancreatic cancer.

Biomarkers for early diagnosis of pancreatic cancer

Pancreatic ductal adenocarcinoma is an aggressive malignancy with a 5-year survival rate of approximately 5%. The lack of established strategies for early detection contributes to this poor prognosis. Although several novel candidate biomarkers have been proposed for earlier diagnosis, none have been adopted into routine clinical use. In this review, the authors examine the challenges associated with finding new pancreatic cancer diagnostic biomarkers and explore why translation of biomarker research for patient benefit has thus far failed. The authors also review recent progress and highlight advances in the understanding of the biology of pancreatic cancer that may lead to improvements in biomarker detection and implementation.

Early diagnosis of pancreatic cancer

Pancreatic cancer is a common malignancy of the pancreas, with about 90% originating in the glandular epithelium. As a highly malignant gastrointestinal tumor, pancreatic cancer is difficult to diagnose and treat. The silent nature of the clinical manifestations and the difficulty of early diagnosis lead to a poor prognosis. In recent years, the incidence rate and mortality rate have increased significantly, with the 5-year survival rate being less than 1%. It is evident that early diagnosis is an effective strategy to improve the prognosis and therefore has become a hotspot of research. This article reviews the progress in early diagnosis of pancreatic cancer in terms of imageological diagnosis, serological examinations and genomic testing as well as the screening of high-risk populations.

The role of PAM4 in the management of pancreatic cancer: diagnosis, radioimmunodetection, and radioimmunotherapy

PAM4, a new monoclonal antibody (MAb) known as clivatuzumab, is highly reactive with pancreatic cancer and precursor lesions. It is absent from the normal tissues and has limited reactivity with nonpancreatic cancer. The detailed characteristic of the PAM4 epitope is unknown but recent studies have shown that it is dependent on MUC1 glycosylation status. The limited PAM4 expression pattern makes it an attractive candidate for management of pancreatic adenocarcinoma. In addition, PAM4 is a serum biomarker for diagnosis of pancreatic cancer. Several different radiolabeled immunodiagnostic and immunotherapeutic agents of PAM4 have been developed and some are being evaluated in preclinical and/or clinical studies. The review will focus on PAM4 and its potential utility for the diagnosis, radioimmunodetection, and radioimmunotherapy of pancreatic cancer.

Differentiation of pancreatic ductal adenocarcinoma from chronic pancreatitis by PAM4 immunohistochemistry

CONTEXT

PAM4 is a monoclonal antibody that shows high specificity for pancreatic ductal adenocarcinoma (PDAC) and its neoplastic precursor lesions. A PAM4-based serum immunoassay is able to detect 71% of early-stage patients and 91% with advanced disease. However, approximately 20% of patients diagnosed with chronic pancreatitis (CP) are also positive for circulating PAM4 antigen. The specificity of the PAM4 antibody is critical to the interpretation of the serum-based and immunohistochemical assays for detection of PDAC.

OBJECTIVE

To determine whether PAM4 can differentiate PDAC from nonneoplastic lesions of the pancreas.

DESIGN

Tissue microarrays of PDAC (N = 43) and surgical specimens from CP (N = 32) and benign cystic lesions (N = 19) were evaluated for expression of the PAM4 biomarker, MUC1, MUC4, CEACAM5/6, and CA19-9.

RESULTS

PAM4 and monoclonal antibodies (MAbs) to MUC1, MUC4, CEACAM5/6, and CA19-9 were each reactive with the majority of PDAC cases; however, PAM4 was the only monoclonal antibody not to react with adjacent, nonneoplastic parenchyma. Although PAM4 labeled 19% (6 of 32) of CP specimens, reactivity was restricted to pancreatic intraepithelial neoplasia associated with CP; inflamed tissues were negative in all cases. In contrast, MUC1, MUC4, CEACAM5/6, and CA19-9 were detected in 90%, 78%, 97%, and 100% of CP, respectively, with reactivity also present in nonneoplastic inflamed tissue.

CONCLUSIONS

PAM4 was the only monoclonal antibody able to differentiate PDAC (and pancreatic intraepithelial neoplasia precursor lesions) from benign, nonneoplastic tissues of the pancreas. These results suggest the use of PAM4 for evaluation of tissue specimens, and support its role as an immunoassay for detection of PDAC.

MUC1: a multifaceted oncoprotein with a key role in cancer progression

The transmembrane glycoprotein Mucin 1 (MUC1) is aberrantly glycosylated and overexpressed in a variety of epithelial cancers, and plays a crucial role in progression of the disease. Tumor-associated MUC1 differs from the MUC1 expressed in normal cells with regard to its biochemical features, cellular distribution, and function. In cancer cells, MUC1 participates in intracellular signal transduction pathways and regulates the expression of its target genes at both the transcriptional and post-transcriptional levels. This review highlights the structural and functional differences that exist between normal and tumor-associated MUC1. We also discuss the recent advances made in the use of MUC1 as a biomarker and therapeutic target for cancer.

Mapping PAM4 (clivatuzumab), a monoclonal antibody in clinical trials for early detection and therapy of pancreatic ductal adenocarcinoma, to MUC5AC mucin

BACKGROUND

PAM4, an antibody that has high specificity for pancreatic ductal adenocarcinoma (PDAC), compared to normal pancreas, benign lesions of the pancreas, and cancers originating from other tissues, is being investigated as a biomarker for early detection, as well as antibody-targeted imaging and therapy. Therefore, the identity of the antigen bound by this monoclonal antibody (MAb) can provide information leading to improved use of the antibody. Prior results suggested the antigen is a mucin-type glycoprotein rich in cysteine disulfide bridges that provide stable conformation for the PAM4-epitope.

METHODS

Indirect and sandwich enzyme immunoassays (EIA) were performed to compare and contrast the reactivity of PAM4 with several anti-mucin antibodies having known reactivity to specific mucin species (e.g., MUC1, MUC4, MUC5AC, etc.). Studies designed to block reactivity of PAM4 with its specific antigen also were performed.

RESULTS

We demonstrate that MAbs 2-11 M1 and 45 M1, each reactive with MUC5AC, are able to provide signal in a heterologous sandwich immunoassay where PAM4 is the capture antibody. Further, we identify MAbs 21 M1, 62 M1, and 463 M1, each reactive with MUC5AC, as inhibiting the reaction of PAM4 with its specific epitope. MAbs directed to MUC1, MUC3, MUC4, MUC16 and CEACAM6 are not reactive with PAM4-captured antigen, nor are they able to block the reaction of PAM4 with its antigen.

CONCLUSIONS

These data implicate MUC5AC as a specific mucin species to which PAM4 is reactive. Furthermore, this realization may allow for the improvement of the current PAM4 serum-based immunoassay for detection of early-stage PDAC by the application of anti-MUC5AC MAbs as probes in this sandwich EIA.

Mucin-based targeted pancreatic cancer therapy

The prognosis of pancreatic cancer (PC) patients is very poor with a five-year survival of less than 5%. One of the major challenges in developing new therapies for PC is the lack of expression of specific markers by pancreatic tumor cells. Mucins are heavily Oglycosylated proteins characterized by the presence of short stretches of amino acid sequences repeated several times in tandem. The expression of several mucins including MUC1, MUC4, MUC5AC, and MUC16 is strongly upregulated in PC. Recent studies have also demonstrated a link between the aberrant expression and differential overexpression of mucin glycoproteins to the initiation, progression, and poor prognosis of the disease. These studies have led to increasing recognition of mucins as potential diagnostic markers and therapeutic targets in PC. In this focused review we present an overview of the therapies targeting mucins in PC, including immunotherapy (i.e. vaccines, antibodies, and radioimmunoconjugates), gene therapy, and other novel therapeutic strategies.

PAM4 enzyme immunoassay alone and in combination with CA 19-9 for the detection of pancreatic adenocarcinoma

BACKGROUND

The monoclonal antibody PAM4 has high specificity for pancreatic ductal adenocarcinoma (PDAC), as well as its precursor lesions, but has not been found to be reactive with normal and benign pancreatic tissues. The objective of the current study was to evaluate a PAM4-based serum enzyme immunoassay alone and in combination with the carbohydrate antigen (CA) 19-9 assay for the detection of PDAC, with particular attention to early stage disease.

METHODS

Sera from patients with confirmed PDAC (N = 298), other cancers (N = 99), benign disease of the pancreas (N = 120), and healthy adults (N = 79) were evaluated by a specific enzyme immunoassay for the concentration of PAM4 and CA 19-9 antigen levels by blinded analyses. All tests for statistical significance were 2-sided.

RESULTS

The overall sensitivity for PAM4 detection of PDAC was 76%, with 64% of patients with stage I disease also identified. The detection rate was considerably higher (85%) for patients with advanced disease. The assay demonstrated high specificity compared with benign pancreatic disease (85%), with a positive likelihood ratio of 4.93. CA 19-9 provided an overall sensitivity of 77%, and was positive in 58% of patients with stage I disease; however, the specificity was significantly lower for CA 19-9 (68%), with a positive likelihood ratio of 2.85 (P = .026 compared with PAM4). It is important to note that a combined PAM4 and CA 19-9 biomarker serum assay demonstrated an improved sensitivity (84%) for the overall detection of PDAC without a significant loss of specificity (82%) compared with either arm alone.

CONCLUSIONS

The PAM4 enzyme immunoassay identified approximately two-thirds of patients with stage I PDAC with high discriminatory power with respect to benign, nonneoplastic pancreatic disease. These results provide a rationale for testing patient groups considered to be at high risk for PDAC with a combined PAM4 and CA 19-9 biomarker serum assay for the detection of early stage PDAC.

Relationship of pancreatic mass size and diagnostic yield of endoscopic ultrasound-guided fine needle aspiration

BACKGROUND

Endoscopic ultrasound-guided fine needle aspiration (EUS-FNA) is central to discerning the diagnosis of solid pancreatic tumors through tissue acquisition. Test performance is affected by a number of factors including location of mass within the pancreas, presence of onsite cytology technologist, and number of passes with the needle. The influence of tumor size has not been well studied.

AIM

The objective of the current study was to determine whether the size of mass affects the diagnostic accuracy for solid pancreatic lesions aspirated under EUS guidance.

METHODS

Data were collected retrospectively on all patients with solid pancreatic masses undergoing EUS-FNA from June 2003 to August 2010. The cytology samples were reported as positive, suspicious for malignancy, atypical, negative, or nondiagnostic. The gold standard for a cytological diagnosis was histological confirmation or clinical follow-up of more than 6 months with repeat imaging. Patients were divided into five groups based upon lesion size as follows: (a) less than 1 cm, (b) 1-2 cm, (c) 2-3 cm, (d) 3-4 cm, and (e) greater than 4 cm. Performance characteristics of EUS-FNA including sensitivity, specificity, and accuracy were compared for each group. Accuracy was defined as the ratio of the sum of true-positive and true-negative values divided by the number of lesions.

RESULTS

We identified 583 patients with solid pancreatic lesions in which EUS-FNA was performed and adequate cellularity was obtained (47% men, mean age 65 ± 1.4 (SE) years). Overall, 486 (83%) of lesions were pancreatic adenocarcinoma, 18 (3%) were neuroendocrine tumors, 12 (2%) were lymphomas, and 67 (12%) were benign lesions. The median size of the mass was 3 cm (range, 0.5-7 cm). A mean of 4.9 passes (range, 1-9 passes) was needed to obtain adequate samples from lesions. The overall yield of obtaining adequate samples for diagnosis was 85%. When stratified by size, the EUS-FNA sensitivity for lesions with size <1, 1-2, 2-3, 3-4, and >4 cm was 40, 75.9, 86.9, 93.2, and 91.6%, respectively; EUS-FNA sensitivity strongly correlate with tumor size (p < 0.001). Similarly, the accuracy of EUS-FNA increased as lesion size increased, ranging from 47% for tumors less than 1 cm to 88% for tumors greater than 4 cm (p < 0.05). Location of tumor and number of needle passes did not significantly influence EUS-FNA performance characteristics.

CONCLUSIONS

The sensitivity and diagnostic accuracy of EUS-FNA for solid pancreatic lesions is strongly correlated with tumor size. Sensitivity and accuracy decrease significantly for tumors that are smaller than 1 cm.

False-positive EUS-guided FNA cytology for solid pancreatic lesions

BACKGROUND

The currently accepted paradigm is that the false-positive (FP) rate for EUS-guided fine-needle aspiration (EUS-FNA) cytologic analysis of a pancreatic lesion is less than 1%.

OBJECTIVE

To assess the FP rate of EUS-FNA in patients who underwent surgical resection for presumed pancreatic cancer.

DESIGN

Retrospective study.

SETTING

Tertiary-care referral center.

PATIENTS

This study involved 367 patients with solid pancreatic lesions in whom EUS-FNA cytology results were interpreted as positive or suspicious for malignancy, which resulted in subsequent surgical resection.

INTERVENTION

Surgical resection.

MAIN OUTCOME MEASUREMENTS

The FP diagnosis was defined as EUS-FNA cytology specimens being reported as "positive" or "suspicious for malignancy" but that were later proven to be benign on surgical pathology.

RESULTS

The FP rate for EUS-FNA was 4 of 367 (1.1%) when only "positive" cytology findings were interpreted as malignant and 14 of 367 (3.8%) when both suspicious and positive cytology findings were interpreted as malignant. Among the 4 cases falsely interpreted as positive, 1 was falsely diagnosed cytologically as a neuroendocrine tumor and 3 as adenocarcinomas. All FP specimens showed chronic pancreatitis on surgical pathology. The incidence of discordance between cytology and surgical pathology did not change over time (2000-2006: 8/188 [4.3%] vs 2007-2010: 6/179 [3.4%]; P = .79).

LIMITATIONS

Retrospective study at a single center.

CONCLUSION

In a retrospective cohort trial, the FP rate for EUS-FNA of solid pancreatic lesions was 1.1%. Findings of the current study are in line with previous studies that have evaluated the FP cytology rates with EUS-FNA of solid lesions. FP cases transpired primarily as a result of cytologic misinterpretation in the setting of chronic pancreatitis.

Treatment of advanced pancreatic carcinoma with 90Y-Clivatuzumab Tetraxetan: a phase I single-dose escalation trial

PURPOSE

Humanized antibody hPAM4 specifically binds a mucin glycoprotein expressed in pancreatic adenocarcinomas. This phase I study evaluated a single dose of (90)Y-clivatuzumab tetraxetan ((90)Y-labeled hPAM4) in patients with advanced pancreatic cancer.

EXPERIMENTAL DESIGN

Twenty-one patients (4 stage III; 17 stage IV) received (111)In-hPAM4 for imaging and serum sampling before (90)Y-hPAM4. Study procedures evaluated adverse events, safety laboratories, computed tomography (CT) scans, biomarkers, pharmacokinetics, radiation dosimetry, and immunogenicity (HAHA).

RESULTS

(111)In-hPAM4 showed normal biodistribution with radiation dose estimates to red marrow and solid organs acceptable for radioimmunotherapy and with tumor targeting in 12 patients. One patient withdrew before (90)Y-hPAM4; otherwise, 20 patients received (90)Y doses of 15 (n = 7), 20 (n = 9), and 25 mCi/m(2) (n = 4). Treatment was well tolerated; the only significant drug-related toxicities were (NCI CTC v.3) grade 3 to 4 neutropenia and thrombocytopenia increasing with (90)Y dose. There were no bleeding events or serious infections, and most cytopenias recovered to grade 1 within 12 weeks. Three patients at 25 mCi/m(2) encountered dose-limiting toxicity with grade 4 cytopenias more than 7 days, establishing 20 mCi/m(2) as the maximal tolerated (90)Y dose. Two patients developed HAHA of uncertain clinical significance. Most patients progressed rapidly and with CA19-9 levels increasing within 1 month of therapy, but 7 remained progression-free by CT for 1.5 to 5.6 months, including 3 achieving transient partial responses (32%-52% tumor diameter shrinkage).

CONCLUSION

(90)Y-Clivatuzumab tetraxetan was well tolerated with manageable hematologic toxicity at the maximal tolerated (90)Y dose, and is a potential new therapeutic for advanced pancreatic cancer.

Carbohydrate markers of pancreatic cancer

Pancreatic cancer is the fourth most common cause of death from cancer in the world and the sixth in Europe. Pancreatic cancer is more frequent in males than females. Worldwide, following diagnosis of pancreatic cancer, <2% of patients survive for 5 years, 8% survive for 2 years and <50% survive for only approx. 3 months. The biggest risk factor in pancreatic cancer is age, with a peak of morbidity at 65 years. Difficulty in the diagnosis of pancreatic cancer causes a delay in its detection. It is one of the most difficult cancers to diagnose and therefore to treat successfully. Additional detection of carbohydrate markers may offer a better diagnosis of pancreatic cancer. Carbohydrate markers of cancer may be produced by the cancer itself or by the body in response to cancer, whose presence in body fluids suggests the presence and growth of the cancer. The most widely used, and best-recognized, carbohydrate marker of pancreatic cancer is CA 19-9 [CA (carbohydrate antigen) 19-9]. However, the relatively non-specific nature of CA 19-9 limits its routine use in the early diagnosis of pancreatic cancer, but it may be useful in monitoring treatment of pancreatic cancer (e.g. the effectiveness of chemotherapy), as a complement to other diagnostic methods. Some other carbohydrate markers of pancreatic cancer may be considered, such as CEA (carcinoembryonic antigen), CA 50 and CA 242, and the mucins MUC1, MUC2 and MUC5AC, but enzymes involved in the processing of glycoconjugates could also be involved. Our preliminary research shows that the activity of lysosomal exoglycosidases, including HEX (N-acetyl-β-D-hexosaminidase), GAL (β-D-galactosidase), FUC (α-L-fucosidase) and MAN (α-D-mannosidase), in serum and urine may be used in the diagnosis of pancreatic cancer.

Detection of early-stage pancreatic adenocarcinoma

BACKGROUND

Pancreatic adenocarcinoma is an almost universally lethal disease, in large part, due to our inability to detect early-stage disease. Monoclonal antibody PAM4 is reactive with a unique biomarker expressed by >85% of pancreatic adenocarcinomas. In this report, we examined the ability of a PAM4-based immunoassay to detect early-stage disease.

MATERIALS AND METHODS

The PAM4-based immunoassay was used to quantitate antigen in the serum of healthy volunteers (n = 19), patients with known pancreatic adenocarcinoma (n = 68), and patients with a primary diagnosis of chronic pancreatitis (n = 29).

RESULTS

Sensitivity for detection of pancreatic adenocarcinoma was 82%, with a false-positive rate of 5% for healthy controls. Patients with advanced disease had significantly higher antigen levels than those with early-stage disease (P < 0.01), with a diagnostic sensitivity of 91%, 86%, and 62% for stage 3/stage 4 advanced disease, stage 2, and stage 1, respectively. We also evaluated chronic pancreatitis sera, finding 38% positive for antigen; however, this was discordant with immunohistochemical findings that suggest the PAM4 antigen is not produced by inflamed pancreatic tissue. Furthermore, several of the serum-positive pancreatitis patients, for whom tissue specimens were available for pathologic interpretation, had evidence of neoplastic precursor lesions.

CONCLUSIONS

These results suggest the use of the PAM4 serum assay to detect early-stage pancreatic adenocarcinoma and that positive levels of PAM4 antigen are not derived from inflamed pancreatic tissues but rather may provide evidence of subclinical pancreatic neoplasia. EFFECT: The ability to detect pancreatic adenocarcinoma at an early stage could provide for early therapeutic intervention with potentially improved patient outcomes.

Pretargeted radioimmunotherapy for hematologic and other malignancies

Radioimmunotherapy (RIT) has emerged as one of the most promising treatment options, particularly for hematologic malignancies. However, this approach has generally been limited by a suboptimal therapeutic index (target-to-nontarget ratio) and an inability to deliver sufficient radiation doses to tumors selectively. Pretargeted RIT (PRIT) circumvents these limitations by separating the targeting vehicle from the subsequently administered therapeutic radioisotope, which binds to the tumor-localized antibody or is quickly excreted if unbound. A growing number of preclinical proof-of-principle studies demonstrate that PRIT is feasible and safe and provides improved directed radionuclide delivery to malignant cells compared with conventional RIT while sparing normal cells from nonspecific radiotoxicity. Early phase clinical studies corroborate these preclinical findings and suggest better efficacy and lesser toxicities in patients with hematologic and other malignancies. With continued research, PRIT-based treatment strategies promise to become cornerstones to improved outcomes for cancer patients despite their complexities.

Pretargeted radioimmunotherapy of pancreatic cancer xenografts: TF10-90Y-IMP-288 alone and combined with gemcitabine

Pancreatic cancer is a silent disease that most commonly presents in an already metastatic form. Current treatment options provide little survival benefit. Radiolabeled PAM4 IgG, a monoclonal antibody that recognizes a unique epitope associated with a mucin found almost exclusively in pancreatic cancer, has shown encouraging therapeutic effects in animal models and in early clinical testing ((90)Y-humanized PAM4 IgG, (90)Y-clivatuzumab tetraxetan). The studies reported herein examine a new pretargeting procedure for delivering therapeutic radionuclides.

METHODS

We prepared a humanized, recombinant tri-Fab bispecific monoclonal antibody (bsmAb) (TF10) using specificity for targeting pancreatic cancer of PAM4 and another Fab binding to a hapten (histamine-succinyl-glycine [HSG]) and tested this in a pretargeting setting with a (90)Y-1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid-di-HSG-peptide (pretargeted radioimmunotherapy [PT-RAIT]). Nude mice bearing established Capan-1 human pancreatic cancer xenografts were given TF10 and then received the (90)Y peptide as a single bolus dose 19 h later, or the therapy cycle was fractionated weekly. Other studies examined different combinations with gemcitabine.

RESULTS

PT-RAIT of 18.5 MBq ( approximately 50% of its maximum tolerated dose [MTD]) was as effective as the MTD of (90)Y-PAM4 IgG (5.55 MBq). Three monthly doses of 9.25 MBq of PT-RAIT combined with a monthly cycle of gemcitabine (3 weekly, 6-mg doses) significantly enhanced survival, compared with PT-RAIT alone. Adding gemcitabine as a radiosensitizer to 9.25 MBq of PT-RAIT enhanced objective responses. Weekly fractionation of the PT-RAIT, as compared with a single treatment, improved responses.

CONCLUSION

PAM4-based PT-RAIT with (90)Y hapten peptide is an effective treatment for pancreatic cancer, with less toxicity than (90)Y-PAM4 IgG, in this model. Combinations with gemcitabine and dose fractionation of the PT-RAIT enhanced therapeutic responses.

A novel bispecific, trivalent antibody construct for targeting pancreatic carcinoma

Preclinical and clinical studies have demonstrated the application of radiolabeled mAb-PAM4 for nuclear imaging and radioimmunotherapy of pancreatic carcinoma. We have now examined the ability of a novel PAM4-based, bispecific monoclonal antibody (mAb) construct, TF10, to pretarget a radiolabeled peptide for improved imaging and therapy. TF10 is a humanized, bispecific mAb, divalent for mAb-PAM4 and monovalent for mAb-679, reactive against the histamine-succinyl-glycine hapten. Biodistribution studies and nuclear imaging of the radiolabeled TF10 and/or TF10-pretargeted hapten-peptide (IMP-288) were conducted in nude mice bearing CaPan1 human pancreatic cancer xenografts. (125)I-TF10 cleared rapidly from the blood, with levels decreasing to <1% injected dose per gram (ID/g) by 16 hours. Tumor uptake was 3.47 +/- 0.66% ID/g at this time point with no accumulation in any normal tissue. To show the utility of the pretargeting approach, (111)In-IMP-288 was administered 16 hours after TF10. At 3 hours postadministration of radiolabeled peptide, imaging showed intense uptake within the tumors and no evidence of accretion in any normal tissue. No targeting was observed in animals given only the (111)In-peptide. Tumor uptake of the TF10-pretargeted (111)In-IMP-288 was 24.3 +/- 1.7% ID/g, whereas for (111)In-IMP-288 alone it was only 0.12 +/- 0.002% ID/g at 16 hours. Tumor/blood ratios were significantly greater for the pretargeting group ( approximately 1,000:1 at 3 hours) compared with (111)In-PAM4-IgG ( approximately 5:1 at 24 hours; P < 0.0003). Radiation dose estimates suggested that TF10/(90)Y-peptide pretargeting would provide a greater antitumor effect than (90)Y-PAM4-IgG. Thus, the results suggest that TF10 pretargeting may provide improved imaging for early detection, diagnosis, and treatment of pancreatic cancer as compared with directly radiolabeled PAM4-IgG.

Is there a role for advanced radiation therapy technologies in the treatment of pancreatic adenocarcinoma?

Pancreatic cancer remains a highly challenging problem in oncology. Oncologists continue to search for therapies that are more effective than those currently available to improve on the existing poor treatment results. Persistence of both systemic and local disease causes high rates of morbidity and mortality for patients. Radiation continues to play a role in the treatment of pancreatic cancer, in both the adjuvant and locally advanced settings. Efforts to improve on the results of radiotherapy have led to the use of new and improved technologies. This review discusses a variety of these technological improvements and their current and potential future roles in the clinic.

PAM4-reactive MUC1 is a biomarker for early pancreatic adenocarcinoma

PURPOSE

The anti-MUC1 monoclonal antibody (MAb), PAM4, has a high specificity for pancreatic adenocarcinoma compared with other cancers, normal tissues, or pancreatitis. In order to assess its role in early pancreatic cancer development, we examined the expression of the PAM4-reactive MUC1 in the noninvasive precursor lesions, pancreatic intraepithelial neoplasia (PanIN) and intraductal papillary mucinous neoplasia (IPMN).

EXPERIMENTAL DESIGN

Tissue microarrays prepared from formalin-fixed, paraffin-embedded specimens were assessed by immunohistology for expression of the PAM4-reactive, non-variable number of tandem repeats (VNTR), MUC1 epitope, and the VNTR epitope bound by the MA5 MAb.

RESULTS

The PAM4-reactive MUC1 epitope was not detected in normal pancreas but was expressed in 87% (48 of 55) of invasive pancreatic adenocarcinomas, including early stage 1 disease: PAM4 labeled 94% (44 of 47) of the earliest PanIN lesions, PanIN-1A and 1B, along with 91% (10 of 11) of PanIN-2, 40% (2 of 5) of PanIN-3, and 86% (31 of 36) of intraductal papillary mucinous neoplasia lesions. A mostly diffuse pattern of labeling was observed. A second, unrelated, anti-MUC1 MAb, MA5, showed considerably less sensitivity with early PanIN-1 lesions; only 61% (25 of 41) were positive and the labeling did not differentiate normal pancreas from PanINs.

CONCLUSIONS

The results suggest that expression of the PAM4-reactive antigen may represent an early event in the development of invasive pancreatic adenocarcinoma, and is unrelated to the VNTR peptide core epitopes of MUC1. Detection of this biomarker using immunohistology, in vitro immunoassays, and in vivo antibody-based imaging may provide new opportunities for the early detection and improved diagnosis of pancreatic cancer.

Mucin gene expression in human male urogenital tract epithelia

BACKGROUND

Mucins are large, hydrophilic glycoproteins that protect wet-surfaced epithelia from pathogen invasion as well as provide lubrication. At least 17 mucin genes have been cloned to date. This study sought to determine the mucin gene expression profile of the human male urogenital tract epithelia, to determine if mucins are present in seminal fluid and to assess the effect of androgens on mucin expression.

METHODS AND RESULTS

Testis, epididymis, vas deferens, seminal vesicle, prostate, bladder, urethra and foreskin were assessed for mucin expression by RT-PCR (for 14 mucin genes) and immunohistochemistry (nine antibodies for five mucins). Epithelia of the vas deferens, prostate and urethra expressed the greatest number of mucins, each with mRNA for between 5 and 8 mucins. Except for MUC20 in epididymis, mRNA for MUC1 and MUC20, both membrane-associated mucins, was detected in all tissues analysed. By comparison, MUC6 was more restricted in expression, being primarily detected in seminal vesicle. MUC1, MUC5B and MUC6 were detected in seminal fluid samples by immunoblot analysis. Androgens had no effect on mucin expression in cultured human prostatic epithelial cells.

CONCLUSIONS

Each region of urogenital tract epithelium expressed a unique mucin gene repertoire. Secretory mucins are present in seminal fluid, and androgens do not appear to regulate mucin gene expression in prostatic epithelial cells in culture.

New MUC1 serum immunoassay differentiates pancreatic cancer from pancreatitis

PURPOSE

To evaluate a new immunoassay for identification and quantitation of MUC1 in the sera of patients with pancreatic cancer or pancreatitis. The sensitivity and specificity of the assay are examined and compared to results from a CA19-9 immunoassay.

METHODS

An in vitro enzyme immunoassay was established with monoclonal antibody PAM4 as the capture reagent, and a polyclonal anti-MUC1 antibody as the probe. Patient sera were obtained from healthy, adult patients with acute and chronic pancreatitis, and those with pancreatic and other forms of cancer, and were measured for PAM4-reactive MUC1.

RESULTS

At a cutoff of 10.2 units/mL, 41 (77%) of 53 pancreatic cancer patients, none of the healthy individuals (n = 43), and only four (5%) of 87 patients with pancreatitis were positive above this value. Among nonpancreatic cancers investigated, colorectal cancers gave the highest percentage of positives (14%; five of 36). Overall, the sensitivity and specificity of the immunoassay for pancreatic cancer were 77% and 95%, respectively. Receiver operator characteristic analyses for discrimination of pancreatic cancer from pancreatitis provided an area under the curve of 0.89 (95% CI, 0.82 to 0.93), with a specificity of 95.4% and a positive likelihood ratio of 16.8. A direct pair-wise comparison of PAM4 and CA19-9 immunoassays for discrimination of pancreatic cancer and pancreatitis resulted in a significant difference (P < .003), with the PAM4 immunoassay demonstrating superior sensitivity and specificity. CONCLUSION The high sensitivity and specificity observed suggest that the PAM4-based immunoassay of circulating MUC1 may be useful in the diagnosis of pancreatic cancer.

Improved targeting of pancreatic cancer: experimental studies of a new bispecific antibody, pretargeting enhancement system for immunoscintigraphy

PURPOSE

The early detection and diagnosis of pancreatic cancer remains a major clinical challenge in which imaging procedures have a central role. The purpose of this study was to evaluate a pretargeting method with a bispecific PAM4 (bsPAM4; anti-MUC1) antibody for radioimmunoscintigraphy of experimental human pancreatic cancer.

EXPERIMENTAL DESIGN

A bispecific F(ab')(2) antibody was generated from chimeric PAM4 Fab' and murine 734 (anti-indium-diethylenetriaminepentaacetic acid) Fab' fragments and then used in conjunction with 2 peptide haptens ((111)In-IMP-156 and (99m)Tc-IMP-192). Biodistribution studies and radioimmunoscintigraphic imaging properties of the radiolabeled bsPAM4, and pretargeted, radiolabeled peptides were examined in the CaPan1 human pancreatic tumor grown as s.c. xenografts in athymic nude mice. Tumor uptake and tumor:nontumor ratios were compared with a nontargeting irrelevant anti-CD20, bispecific rituximab, radiolabeled peptides alone, and with directly labeled PAM4.

RESULTS

Biodistribution results indicated significantly greater tumor uptake of radiolabeled peptides at 3 h after injection when pretargeting was performed with bsPAM4 as compared with the bispecific rituximab [20.2 +/- 5.5 percentage of injected dose per gram of tissue (%ID/g) versus 0.9 +/- 0.1%ID/g, respectively, for (111)In-IMP-156, and 16.8 +/- 4.8%ID/g versus 1.1 +/- 0.2%ID/g, respectively, for (99m)Tc-IMP-192]. Similar results were obtained at the 24-h time point. Tumor:nontumor ratios were >30 for all of the tissues except the kidneys, where a ratio of 7.8 +/- 2.8 was observed. By immunoscintigraphy, tumors could be visualized as early as 30 min after injection of the radiolabeled peptide.

CONCLUSIONS

These studies demonstrate the feasibility of using the pretargeted, bispecific antibody technology for nuclear imaging of pancreatic cancer. The advantage of pretargeted bsPAM4 antibody as an imaging platform is the high specificity for pancreatic cancer as compared with the physicochemical parameters identified by current imaging technologies.

Combined 90Yttrium-DOTA-labeled PAM4 antibody radioimmunotherapy and gemcitabine radiosensitization for the treatment of a human pancreatic cancer xenograft

We have examined the application of (90)Y-DOTA-cPAM4, anti-MUC1 IgG, in combination with the front-line drug gemcitabine as a potential therapeutic for pancreatic cancer. Athymic nude mice bearing CaPan1 human pancreatic cancer xenografts were administered 2 mg of gemcitabine on days 0, 3, 6, 9 and 12 with concurrent (90)Y-DOTA-cPAM4 (100 microCi) provided on day 0. A second group of mice received a second cycle of treatment 5 weeks after the start of the first cycle. Control groups of mice included those that received either treatment arm alone, the combined modality treatment employing a nontargeting control antibody (hLL2, anti-B-cell lymphoma) and a final group that was left untreated. Gemcitabine administered as a single agent provided no antitumor effect. A single cycle of the combined (90)Y-DOTA-cPAM4 and gemcitabine treatment provided greater inhibition of tumor growth than was observed for any of the other treatment procedures. Tumor growth was delayed for a period of 7 weeks. Two cycles of gemcitabine with concomitant (90)Y-DOTA-cPAM4 yielded significant tumor regression and increased median survival to 21 weeks vs. 12 weeks for mice receiving a single cycle of therapy (p<0.024). Median tumor volume doubling-times were 18 weeks in mice treated with 2-cycles of therapy vs. 7 weeks in mice given only 1-cycle (p<0.001), and 3.5 weeks for the group that received 2-cycles of gemcitabine concomitant with equitoxic nontargeting (90)Y-DOTA-hLL2 (p<0.001). These data suggest that addition of (90)Y-DOTA-cPAM4 RAIT to a gemcitabine treatment regimen may provide enhanced antitumor efficacy for the treatment of pancreatic cancer.

Interferon-gamma upregulates MUC1 expression in haematopoietic and epithelial cancer cell lines, an effect associated with MUC1 mRNA induction

Epithelial mucin-1 (MUC1) is an important target antigen that it is overexpressed in both epithelial and haematological cancers including multiple myeloma (MM) and some lymphomas and leukaemias. MUC1 has adhesive and immunosuppressive properties, which may promote cancer progression. These studies evaluated the effect of IFNs on MUC1 expression, since these agents are widely used in clinical cancer therapy. MUC1 and interferon (IFN) receptor expression were measured by radioligand binding. Changes in MUC1 mRNA levels in response to IFN-gamma were assessed by semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR). IFN-gamma was found to be a more potent inducer of MUC1 expression than IFN-alpha. 125I-IFN binding studies indicated that both IFN receptors were expressed in most of the cell lines. With IFN-gamma treatment, there was upregulation of MUC1 mRNA. IFN-gamma has a more consistent and more potent effect upon MUC1 induction than IFN-alpha. The ability to upregulate MUC1 across a broad range of cancer types by a clinically available cytokine, IFN-gamma, has important implications for enhancing immunotherapeutic approaches targeting MUC1.

Monoclonal antibody G47 engineered to be reactive with colorectal tumor mucin

We have previously shown that the normal adult colon produces a sialomucin containing the core trisaccharide 1,3 N-acetylgalactosamine. This structure was shown to be the epitope for a polyclonal antiserum that demonstrated colon "specific" activity. Antiserum binding is dependent upon the presence of O-acetylated sialic acids present at high concentrations in normal adult colon tissue. However, O-acetylation of sialic acids is decreased in colorectal cancer. Indeed, approximately 50% of colorectal carcinomas are nonreactive with this antiserum. In the current work, we used a de-O-acetylated, normal colon mucin as immunogen to generate monoclonal antibody (MAb) G47. Untreated normal colon mucins having a high O-acetylated sialic acid content were essentially nonreactive with G47. Removal of O-acetyl groups by saponification generated a reactive mucin derivative while subsequent treatment with neuraminidase abolished reactivity. By immunoperoxidase procedures MAb-G47 was reactive with approximately 85% of colorectal tumors while exhibiting relatively low reactivity with normal colon tissue. Mucins isolated from normal colon had on average less than 10% of the specific epitope as compared with mucins derived from colorectal tumors (p < 0.01). Initial immunohistochemical studies on tumors of noncolonic origin revealed few positive cases. The potential of MAb-G47 to assist in the diagnosis and/or prognosis of colorectal cancer is now being studied.

Combined gemcitabine and radioimmunotherapy for the treatment of pancreatic cancer

MAb-PAM4 is an anti-MUC1 antibody that has been shown to be reactive with 85% of pancreatic adenocarcinomas with no reactivity with normal pancreas or other tissues. Initial clinical studies have shown excellent targeting with high tumor/nontumor ratios. Gemcitabine, an analog of deoxycytidine, is currently a frontline treatment for pancreatic cancer. Acting via a number of metabolic pathways, gemcitabine is also a powerful radiosensitizer. Combined-modality, chemo/radiosensitization with gemcitabine and low dose (131)I-PAM4 radioimmunotherapy was performed to determine if a more effective treatment procedure could be developed. Athymic nude mice bearing large (1 cm(3)) CaPan1 human pancreatic tumors were given a single treatment cycle consisting of gemcitabine, 333 mg/m(2) administered on Days 0, 3, 6, 9 and 12 by intraperitoneal injection, along with either 100 or 200 microCi, (131)I-PAM4 administered on Day 0 by intravenous injection. Gemcitabine did not interfere with the biodistribution of radiolabeled antibody. Specific tumor targeting was observed for (131)I-PAM4, with a tumor/blood radiation dose ratio of 2.6 over the first 14 days. Gemcitabine alone and low dose radioimmunotherapy alone, each had no affect upon tumor growth; no statistical differences were noted in comparison to the untreated group. When combined, however, a statistically significant (p = 0.0324), synergistic anti-tumor effect was observed. Median survival time doubled for the combined treatment regimen compared to single modality treatment groups. The combined treatment modality was well tolerated by the mice. Our data show that combined gemcitabine with radioimmunotherapy may provide an improved alternative for the treatment of pancreatic cancer, achieving successful anti-tumor effects with low toxicity.

Localization of pancreatic cancer with radiolabeled monoclonal antibody PAM4

Experimental animal studies were performed with (111)In-labeled PAM4 anti-MUC1 antibody along with (111)In-labeled control antibody. Tumor uptake of radiolabeled PAM4 was significantly higher than for the control antibody at all time points. When normalized to a blood dose of 1500 cGy as an estimate of myelotoxicity, (90)Y-labeled PAM4 would provide 5344 cGy to the tumor, whereas an equitoxic dose of (90)Y-labeled control antibody would provide only 862 cGy to the tumor. In addition to the animal studies, five patients with proven pancreatic cancer were administered either (131)I-PAM4 IgG (n=2) or 99mTc-PAM4 Fab' (n=3). Tumor targeting was observed in four out of five patients. By immunohistochemistry, PAM4 was non-reactive with tumor from the one patient not targeted. Dosimetry from the patients given (131)I-PAM4 predicted that tumors would receive 10-20 cGy/mCi with tumor/red marrow dose ratios ranging from 3 to 10. Based upon these results, we have established a phase-I (111)In-labeled PAM4 imaging and (90)Y-labeled PAM4 therapy trial.

Antibody constructs for radioimmunodiagnosis and treatment of human pancreatic cancer

Pancreatic cancer (PC) is a common disease that is seldom cured. Current approaches to the treatment of PC are not effective because the non-specific nature of both chemotherapy and external beam radiation results in toxicity to normal tissue. Monoclonal antibodies (MAbs) can be used as selective carriers for delivering radionuclides, toxins, or cytotoxic drugs to malignant cell populations. Therefore, MAb-technology has led to a significant amount of research in targeted therapy. Targeted therapy would generally allow the concentration of cytotoxic agents in tumors and would markedly lessen the toxicity to normal tissues, which limits the dosage and effectiveness of systemically administered drugs. A variety of MAbs are being pre-clinically evaluated for the diagnosis and treatment of PC. Novel recombinant antibody constructs hold a promising future in both the diagnosis and treatment of cancer. By genetic-engineering methods, several high affinity antibody fragments with optimum tumor targeting properties, such as higher functional affinity (divalent and multivalent scFvs) and blood residence time (good tumor localization with high radiolocalization index), have been generated. Animal models have permitted the in vivo assessment of these antibody-based reagents, therapeutic/diagnostic radionuclide, radiolabeling conditions, and efficacy of administration regimes. For PC, immunoscintigraphy using MAbs has taken new strides. The use of MAbs and their fragments for radioimmunoguided surgery and therapy of PC has shown encouraging results at preclinical levels and warrants further attention.

Review article: current practice and future perspectives in detection and diagnosis of pancreatic cancer

Pancreatic cancer is the tenth most prevalent malignancy and the fifth most common cause of cancer death in the developed world. Less than 10% of patients survive for more than 1 year following diagnosis and the 5-year survival rate (0.4%) is the lowest of any cancer. The poor prognosis associated with this diagnosis led in the past to therapeutic nihilism on the part of clinicians who were all too aware of the limitations of their available therapeutic strategies. Breaking this therapeutic impasse requires a significant expansion in the knowledge of clinicians concerning the pathogenesis and behaviour of pancreatic cancer. Recent advances in the scientific understanding of the aetiology of pancreatic cancer has facilitated progress towards the development of promising and innovative approaches to the early detection and diagnosis of pancreatic cancer. While acknowledging that pancreatic cancer will continue to present significant challenges to both scientists and clinicians in the foreseeable future, it is becoming increasingly clear that recent advances in our scientific knowledge base holds the potential to significantly improve prognosis for patients. The challenge facing both scientists and clinicians is how best to translate such promising scientific advances into survival and quality of life benefits to patients.