Timothy J. O’Brien

The CA 125 Gene: An Extracellular Superstructure Dominated by Repeat Sequences

CA 125 has long presented problems to both clinicians and investigators because there was no definitive information on its structure and function. Here, we describe our work on cloning the CA 125 gene with the anticipation that such information will provide the basis for understanding its structure and its physiologic role in both normal and malignant tissues. The CA 125 protein core is composed of a short cytoplasmic tail, a transmembrane domain and an extraordinarily large glycosylated extracellular structure. This structure is dominated by a repeat domain composed of 156 amino acid repeat units which encompass the epitope binding sites. The molecule also includes an amino terminal domain of serine/threonine-rich sequences which would account for most of the O-glycosylation known to be present in CA 125. CA 125 is an unusually large transmembrane glycoprotein. Its release from the surface of the cell is most probably dependent on cytoplasmic phosphorylation followed by proteolytic cleavage. The extracellular domain is characterized by a large number of repeat units (probably 60+) which encompass an interactive disulfide bridged cysteine-loop and the site of OC125 and M11 binding. Sequencing the gene provides us with the ability to initiate the quest to understand the biological function of CA 125.

A Mutation in SNAP29, Coding for a SNARE Protein Involved in Intracellular Trafficking, Causes a Novel Neurocutaneous Syndrome Characterized by Cerebral Dysgenesis, Neuropathy, Ichthyosis, and Palmoplantar Keratoderma

Neurocutaneous syndromes represent a vast, largely heterogeneous group of disorders characterized by neurological and dermatological manifestations, reflecting the common embryonic origin of epidermal and neural tissues. In the present report, we describe a novel neurocutaneous syndrome characterized by cerebral dysgenesis, neuropathy, ichthyosis, and keratoderma (CEDNIK syndrome). Using homozygosity mapping in two large families, we localized the disease gene to 22q11.2 and identified, in all patients, a 1-bp deletion in SNAP29, which codes for a SNARE protein involved in vesicle fusion. SNAP29 expression was decreased in the skin of the patients, resulting in abnormal maturation of lamellar granules and, as a consequence, in mislocation of epidermal lipids and proteases. These data underscore the importance of vesicle trafficking regulatory mechanisms for proper neuroectodermal differentiation.

Specificity and Affinity of 26 Monoclonal Antibodies against the CA 125 Antigen: First Report from the ISOBM TD-1 Workshop

The specificity of 26 monoclonal antibodies against the CA 125 antigen was investigated in two phases of the ISOBM TD-1 workshop. The binding specificity was studied using CA 125 immunoextracted by specific antibodies immobilized on various solid phases, or on the surface of human cell lines. Immunometric assays using all possible antibody combinations were used to study the topography of antibody binding sites on the antigen. We conclude that the CA 125 antigen carries only two major antigenic domains, which classifies the antibodies as OC125-like (group A) or M11-like (group B). One antibody, OV 197, showed binding specificity related to some of the OC125-like antibodies, but was classified into a separate group C. The OC125-like group of antibodies has four subgroups with different binding specificities. These are A1 = OC 125 and K 95, A2 = K 93, A3 = B43.13, and A4 = ZS 33, B27.1 and CCD 247. Binding of nonlabelled OC 125 or K 95 to CA 125 caused a marked increase in binding of labelled OV 197 to the complex. This conformational change was not observed with any other antibody combinations. Antibody B43.13 could form immunometric assay combinations particularly with antibodies of subgroup A4, indicating that the B43.13 epitope is in the periphery of the binding area of OC125-like antibodies. The M11-like group of antibodies is more homogenous with strong cross-inhibition between most antibodies. Only one antibody, ZR 38, would form an immunoassay combination with other M11-like antibodies and thus represents a distinct subgroup. The main group of M11-like antibodies are M 11, ZR 45, MA602-6, K 91, OV 185, K 101, K 90, K 96, K 97, K 102, CCD 242, 145-9, and 130-22. Antibody OV 197 binds to a domain designated C and is unique, as stated above. Antibody pairs from any two of the three groups may be used in immunometric assays. Three antibodies were not studied by complete cross-inhibition due to low affinity (OV 198 and K 100) or lack of material (MA602-1). OV 198 and K 100 are most likely OC125-like and MA602-1 is M11-like. Antibody affinity was estimated with labelled antigen in solution or with antigen absorbed on microtiter wells. Western blot analysis showed staining both in the stacking gel and corresponding to a molecule of 200 kDa. There was a marked difference between the antibodies in their ability to bind to CA 125 immobilized on a membrane. Strongest binding was observed with the M11-like antibodies, particularly M 11, K 96, K 97, MA602-6, 145-9. Antibodies belonging to the subgroup A4 were the only OC 125-like antibodies which reacted well with CA 125 in Western analysis. Digestion of CA 125 with proteolytic enzymes showed it to be particularly sensitive to trypsin cleavage. However, no low molecular weight fragments with preserved immunoreactivity were found.

Ovarian tumor cells express a novel multi-domain cell surface serine protease

Serine proteases serve many functions in normal biological processes. These functions are often usurped by cancer cells to allow progression of tumors by increasing the growth and metastatic potential of the neoplasia. Here, we have used a polymerase chain reaction (PCR)-based strategy to clone Tumor Associated Differentially-expressed Gene-12 (TADG-12), a new serine protease from ovarian carcinoma. This technique also revealed a variant splicing form of TADG-12 that could lead to a truncated protein product. Semi-quantitative PCR showed that TADG-12 is overexpressed in 41 of 55 ovarian cancer specimens relative to normal expression, and the variant form, TADG-12V is found at increased levels in 8 of 22 carcinomas examined. Northern blot revealed three transcripts, the largest of which is approximately 2.4 kb. An ovarian tumor cDNA library was screened, and the entire cDNA of TADG-12 has been identified. This sequence encodes a putative protein of 454 amino acids which includes a potential transmembrane domain, an LDL receptor-like domain, a scavenger receptor cysteine-rich domain, and a serine protease domain. These features imply that TADG-12 will be at the cell surface, and it may be useful as a molecular target for therapy or a diagnostic marker.

Current treatment options for endometrial cancer

In North America, endometrial cancer is the most prevalent cancer of the female genital tract. On the basis of clinical and histologic variables, two main types of endometrial cancer have been described: Type I tumors, which are usually well differentiated and endometrioid in histology and account for the majority of cases; and Type II, which are poorly differentiated tumors, often with serous papillary or clear cell histology. Due to the early declaration of the disease by vaginal bleeding, approximately 80% of endometrial cancers are diagnosed at an early stage. Total abdominal hysterectomy and bilateral salpingo-oophorectomy with or without lymph node dissection remains the cornerstone of treatment. Tumor stage, histologic grade and depth of myometrial invasion are the most important prognostic factors. If myometrial invasion to 50% or more of the myometrial width and/or grade 2 or 3 histology is present, pelvic radiotherapy is indicated to reduce the risk of pelvic recurrence. Postoperative radiation therapy may improve local control but does not affect survival for Stage I endometrial cancer patients. Systemic chemotherapy is typically reserved for women with disseminated primary disease or extrapelvic recurrence. Although the combination of cisplatin plus doxorubicin is commonly used, carboplatin plus paclitaxel represents an efficacious, low-toxicity regimen for managing advanced or recurrent endometrial cancer. Recently, a significant percentage of Type II uterine tumors have been found to overexpress the epidermal growth factor Type II receptor. Anti-HER-2/neu-targeted therapy might be a novel and attractive therapeutic strategy in patients harboring this biologically aggressive variant of endometrial cancer.

Epitopes on CA 125 from Cervical Mucus and Ascites Fluid and Characterization of Six New Antibodies

CA 125 is found in body fluids in a variety of molecular weight forms. The largest species are found in normal abdominal fluid and cervical mucus. The present study therefore incorporated CA 125 derived from these sources as well as ascites fluid to investigate if the source of CA 125 influenced epitope characterization. Ascites-derived CA 125 varied in size from about 190 to about 2,700 kD. Cervical mucus-derived CA 125 treated with ultrasound changed its apparent size from more than 20,000 to 700 kD. Epitope mapping of antibodies was not grossly influenced by the size or source of CA 125 used as target. However, low-molecular-weight CA 125, i.e. ascites fractions CA 17/E, CA 17/F and CA 10/7, did show differences in certain assay combinations and cross-inhibition patterns which probably can be explained by steric effects due to the smaller size compared with the most abundant forms of CA 125 present in serum and other body fluids. The specificity of six new monoclonal antibodies to CA 125 was tested by cross-inhibition and immunometric assay combinations and compared to reference antibodies. One antibody, X306, belonged to the OC125-like antibodies. Four antibodies, X52, X75, X325 and VK8, were M11-like. The sixth antibody, 7C12, reacted with an epitope which was difficult to define. This antibody was inhibited by M11-like antibodies and OV197. However, used as an inhibitor, 7C12 inhibited only itself. We grouped it as an OV197-like antibody, but clearly different from OV197. The topography of epitopes was studied by analyzing all antibody pairs in immunoradiometric assays. These results confirmed the grouping of antibodies described above and are in accordance with previous findings that the highest signal is obtained using an OC125-like antibody or OV197 on the solid phase and an M11-like antibody as tracer. The composition of the sample in terms of high- and low-molecular-weight species of CA 125 was measured, with different responses depending on the antibody pair used. This might be one reason for discrepancies between assay results for CA 125 using different assays.

The Transmembrane Protease Serine (TMPRSS3/TADG-12) D Variant: A Potential Candidate for Diagnosis and Therapeutic Intervention in Ovarian Cancer

The purpose of this study was to examine the expression of splice variants of the TADG-12 (TMPRSS3) gene in normal ovarian epithelial tissue and ovarian carcinoma and further to associate the expression of TADG-12 variant with clinicopathologic characteristics if such an association exists. TADG-12D variant expression was examined by semiquantitative PCR in 50 ovarian tumors [41 adenocarcinomas, 3 low malignant potential (LMP) tumors, and 6 adenomas] and 7 normal ovaries. In carcinomas as well as LMP tumors and adenomas, TADG-12D variant mRNA expression was significantly elevated compared to that in normal ovary samples. TADG-12 has several splice variants, one of which we originally identified and 3 others identified by Scott et al. [Nat Genet 2001;27:59–63]. We previously examined the expression of TADG-12V variant and here we confirm the overexpression of TADG-12D variant in ovarian carcinomas. Moreover, TADG-12D variant mRNA expression level in carcinomas was significantly elevated compared to that in adenomas and TADG-12D variant mRNA expression level in advanced clinical stage diseases was significantly higher than that in early stage diseases in ovarian carcinomas. With regard to histological type, TADG-12D variant mRNA expression level in mucinous adenocarcinomas was significantly higher than those in the other tissue subtypes. These features imply that TADG-12D variant expression may play an important role in ovarian cancer development and progression, and this variant may be useful both as a molecular target for therapy and/or a diagnostic marker.

Human Kallikrein Gene 11 (KLK11) mRNA Overexpression Is Associated with Poor Prognosis in Patients with Epithelial Ovarian Cancer

Purpose: The purpose of this study was to examine expression levels of the human tissue kallikrein 11 gene (KLK11) in epithelial ovarian tumors and to identify the relationship between KLK11 expression and patient survival. Experimental Design: KLK11 mRNA expression was examined by semiquantitative PCR in 64 epithelial ovarian tumors (7 adenomas, 6 low malignant potential tumors, and 51 adenocarcinomas) and in 10 normal ovaries. Semiquantitative PCR results were correlated with clinicopathologic variables and overall survival. cDNA from human normal tissues and tumor tissues was also analyzed. Results: KLK11 mRNA expression was detected in various human cancer tissues including breast, lung, colon, prostate, pancreas, and ovarian carcinoma. The mean value of relative KLK11 expression ratio was significantly higher in ovarian tumor samples than in normal ovary samples (compared with normal samples: adenoma, P = 0.0006; low malignant potential tumor, P = 0.0049; and carcinoma, P < 0.0001). No statistically significant associations between KLK11 mRNA expression level and clinical stage, histological type, or histological grade were observed. The log-rank test showed that high KLK11 mRNA expression and advanced clinical stage significantly correlated with poor patient survival (P = 0.0185 and P = 0.0043, respectively). High KLK11 mRNA expression and clinical stage remained significantly associated with overall survival (P = 0.0225 and P = 0.0202, respectively) after multivariate analysis. Conclusions: KLK11 expression may play an important role in ovarian cancer development and act as an independent prognostic marker in ovarian cancer patients.

Novel target antigens for dendritic cell-based immunotherapy against ovarian cancer.

Identification of tumor-specific target antigens has been a major hurdlefor the treatment of malignant disease by vaccination or immunotherapy. A second challenge has been the induction of therapeutically effective immune responses to these ‘self’ antigens. The recent recognition of dendritic cells as powerful antigen-presenting cells capable of inducing primary T-cell responses in vitro and in vivo – in combination with identification of tumor-specific antigens – has generated widespread interest in dendritic cell-based immunotherapy against a wide variety of tumors. In this review, a series of recently identified novel ovarian tumor antigens is discussed, and the potential for therapeutic dendritic cell vaccination targeted against these antigens is assessed.

Expression of Tumor-Associated Differentially Expressed Gene-14 (TADG-14/KLK8) and Its Protein hK8 in Uterine Endometria and Endometrial Carcinomas

To clarify the biological behavior of TADG-14/KLK8, we investigated TADG-14/KLK8 mRNA by semiquantitative RT-PCR and hK8 expression by immunohistochemistry using 37 normal endometria and 44 endometrial carcinoma tissues. TADG-14/KLK8 mRNA expression levels were significantly higher in proliferative compared to secretory phase endometria (p = 0.0143). Levels of TADG-14/KLK8 mRNA expression correlated with hK8 protein levels. hK8 was detected in 73.3% (11/15) of endometria with a significantly higher detection rate in the proliferative compared to secretory and atrophic phase endometria (p = 0.0002). High expression of hK8 was found in 61.4% of endometrial carcinomas compared to 35.1% of endometrial tissue samples (p = 0.0187). hK8 expression was significantly higher in stage I (p = 0.0433, 0.0038) and grade 1/2 (G1/2) of the tumors (p = 0.0195, 0.0044). We suggest that expression of TADG-14/KLK8may be regulated by sex steroid hormones in endometria. Our results indicate that elevated TADG-14/KLK8 expression is an early event in endometrial carcinogenesis, and may potentially serve as a useful early biomarker for the detection of endometrial carcinomas in menopausal women.