The Ca-MOv18 molecule, a cell-surface marker of human ovarian carcinomas, is anchored to the cell membrane by phosphatidylinositol

Peptide-Based Cancer Vaccine Strategies and Clinical Results

Active cancer immunotherapy is an exciting and developing field in oncology research. Peptide vaccines, the use of isolated immunogenic tumor-associated antigen (TAA) epitopes to generate an anticancer immune response, are an attractive option as they are easily produced and administered with minimal toxicity. Multiple TAA-derived peptides have been identified and evaluated with various vaccine strategies currently in clinical testing. Research suggests that utilizing vaccines in patients with minimal-residual disease may be a more effective strategy compared to targeting patients with widely metastatic disease as it avoids the immune suppression and tolerance associated with higher volumes of more established disease. Clinical trials also suggest that vaccines may need to be tailored and administered to specific cancer subtypes to achieve maximum efficacy. Additionally, numerous immunomodulators now in research and development show potential synergy with peptide vaccines. Our group has focused on a simpler, single-peptide strategy largely from the HER2/neu protein. We will discuss our experience thus far as well as review other peptide vaccine strategies that have shown clinical efficacy.

Conversion of murine antibodies to human antibodies and their optimization for ovarian cancer therapy targeted to the folate receptor

We previously developed murine and chimeric antibodies against a specific epithelial ovarian carcinoma (EOC) marker, named folate receptor (FR), and promising results were obtained in phase II trials. More recently, we successfully generated a completely human Fab fragment, C4, by conversion of one of the murine anti-FR antibodies to human antibody using phage display and guided selection. However, subsequent efforts to obtain C4 in a dimer format, which seems especially desirable for EOC locoregional treatment, resulted in a highly heterogeneous product upon natural dimerization and in a very poor production yield upon chemical dimerization by a non-hydrolyzable linker to a di-Fab-maleimide (DFM). We therefore designed, constructed and characterized a large Fab dual combinatorial human antibody phage display library obtained from EOC patients and potentially biased toward an anti-tumor response in an effort to obtain new anti-FR human antibodies suitable for therapy. Using this library and guiding the selection on FR-expressing cells with murine/human antibody chains, we generated four new human anti-FR antibody (AFRA) Fab fragments, one of which was genetically and chemically manipulated to obtain a chemical dimer, designated AFRA-DFM5.3, with high yield production and the capability for purification scaled-up to clinical grade. Overall affinity of AFRA-DFM5.3 was in the 2-digit nanomolar range, and immunohistochemistry indicated that the reagent recognized the FR expressed on EOC samples. (131)I-AFRA-DFM5.3 showed high immunoreactivity, in vitro stability and integrity, and specifically accumulated only in FR-expressing tumors in subcutaneous preclinical in vivo models. Overall, our studies demonstrate the successful conversion of murine to completely human anti-FR antibodies through the combined use of antibody phage display libraries biased toward an anti-tumor response, guided selection and chain shuffling, and point to the suitability of AFRA5.3 for future clinical application in ovarian cancer.

Complement Activated by Chimeric Anti–Folate Receptor Antibodies Is an Efficient Effector System to Control Ovarian Carcinoma

Two chimeric monoclonal antibodies (mAb), cMOV18 and cMOV19, recognizing distinct epitopes of folate receptor highly expressed on epithelial ovarian cancer (EOC) cells were analyzed for their ability to activate complement (C) as a means to enhance their antitumor activity. The individual cMOVs failed to activate C on six EOC cell lines as documented by the marginal deposition of C components and the negligible C-dependent cytotoxicity (CDC). Conversely, the mixture of cMOVs was more effective, although the percentage of cell killing did not exceed 25%. Fluorescence-activated cell sorting analysis of EOC cells for surface expression of the membrane C regulatory proteins (mCRP) revealed high levels of CD46, variable expression of CD59, and absence of CD55. This finding was confirmed in tumor tissue specimens obtained from advanced-stage EOC patients and analyzed for the expression of mCRPs mRNA using a cDNA microarray and for the presence of proteins by immunohistochemistry. Incubation of EOC cells with neutralizing mAbs to CD46 and CD59 led to a significant increase in the CDC from 10%-20% to 45%-50%. The relative contribution of antibody-dependent cell cytoxicity (ADCC) and C-dependent killing of two EOC cell lines induced by the mixture of cMOV18 and cMOV19 was about 15% and 25%-35%, respectively, bringing the total killing to about 40%-50%. This value increased to 60%-70% after neutralization of CD46 and CD59 without an appreciable change of ADCC. These results suggest that C is the major contributor to the killing of EOC cells induced by the mixture of cMOV18 and cMOV19.

Reversion of transformed phenotype in ovarian cancer cells by intracellular expression of anti folate receptor antibodies

The alpha-folate receptor (FR) is selectively overexpressed in 90% of nonmucinous ovarian carcinomas, whereas no expression is detectable in normal ovarian surface epithelium (OSE). Indirect evidence suggests that FR expression is associated with tumor progression and affects cell proliferation. To evaluate better the role of FR, we developed an approach based on intracellular expression of single-chain (sc) antibodies (intrabody) to downmodulate membrane expression of FR in ovary cancer cells. IGROV-1 and SKOV3 ovarian carcinoma cell lines were transfected with an anti-FR intrabody. Transfectants and parental cells were tested for FR, integrins and anti-FR intrabody expression by fluorescence-activated cell sorting (FACS), reverse transcription and polymerase chain reaction (RT-PCR) and/or immunoblotting. Cell growth characteristics and adhesion properties were evaluated in liquid, semisolid and organotypic cultures. The anti-FR scFv inhibited FR expression from 60 to 99%. At physiological concentrations of folate, proliferation varied directly as a function of FR expression. FR downmodulation was accompanied by reduced colony-forming ability in soft agar, morphological change of the cells, significant enhanced adhesion to laminin or Matrigel, a two- to three-fold increase in alpha6beta4 integrin expression, and a marked reduction in laminin production. In three-dimensional organotypic cultures, anti-FR intrabody-transfected IGROV1 cells grew as a single-ordered layer, reminiscent of normal OSE growth in vivo. In conclusion, the anti-FR intrabody reverses the transformed phenotype in ovary cancer cells and may provide an efficient means to inhibit selectively the growth of these cells.

Downmodulation of caveolin-1 expression in human ovarian carcinoma is directly related to alpha-folate receptor overexpression

Caveolin (cav-1) and the GPI-anchored alpha-folate receptor (alphaFR) are membrane proteins both found associated to caveolar structures. Several studies in tumor cells independently reported cav-1 downregulation and alphaFR overexpression. Here we analysed the expression of the two molecules in normal and tumor ovarian samples derived from fresh specimens and from cultured cell lines. Whereas normal ovary surface epithelial cells displayed only cav-1 expression, ovarian tumor surgical samples and cell lines (COR, IGROV1, OVCAR3 and OVCA432) displayed high alphaFR and low-level or no cav-1 expression, except those cell lines (SKOV3 and SW626) with the lower alphaFR expression. SKOV3, but not two alphaFR-negative non-ovarian cell lines, exhibited down-regulation of cav-1 expression following stable alphaFR cDNA transfection. Conversely, cav-1 transfection in IGROV1 cells led to downregulated alphaFR expression, together with formation of caveolar structures and reduction of growth capability. Moreover, cav-1 expression was induced in IGROV1 cells by transfection with intracellular anti-alphaFR antibodies to downmodulate alphaFR expression. In cav-1 transfected cells, transcriptional activity of the alphaFR-specific promoter P1 was reduced by 70% and an additional specific DNA-protein complex was identified by gel-shift assay, indicating that cav-1 expression influences alphaFR gene transcription. Together these results support the notion that alphaFR and cav-1 protein expression is reciprocally regulated in ovary cancer cells.

Interaction of folate receptor with signaling molecules lyn and G(alpha)(i-3) in detergent-resistant complexes from the ovary carcinoma cell line IGROV1

Using as a model the ovary carcinoma cell line IGROV1, we analyzed the partitioning of the glycosyl-phosphatidylinositol-anchored folate receptor into lipid rafts based on its relative detergent insolubility, with a focus on physically and functionally associated signaling molecules. A variable amount (40-60%) of folate receptor was found in low-density Triton X-100 insoluble complexes together with subunits of heterotrimeric G-proteins and the src-family non-receptor tyrosine kinases p53-56 lyn. In the same fraction the structural component of caveolae, caveolin, was not detected at the protein level, although the corresponding mRNA was detected in trace amounts. Comodulation of folate receptor and signalling molecules was observed in the detergent-insoluble complexes during cell proliferation or induced by phosphatidylinositol-specific phospholipase C treatment or by interaction with anti-folate receptor monoclonal antibodies. Moreover, complexes of folate receptor, lyn and the G(α)(i-3) subunit were immunoprecipitated using either anti-folate receptor or anti-lyn antibodies. In vitro kinase assay of the immunoprecipitates revealed stimulation of phosphorylation of common and specific proteins. In particular, the p53 form of lyn appeared to be enriched and phosphorylated in the anti-folate receptor MOv19 monoclonal antibody immunoprecipitate, whereas a 40 kDa band common to anti-folate receptor and anti-lyn immunoprecipitates was the phosphorylated form of the G(α)(i-3) subunit. These findings point to the functional interaction between folate receptor and associated signaling molecules.

Comparison of IgE and IgG antibody-dependent cytotoxicity in vitro and in a SCID mouse xenograft model of ovarian carcinoma

Allergic reactions are mediated by IgE antibodies bound to high-affinity receptors on mast cells in peripheral tissues and are characterized by their immediacy and hypersensitivity. These properties could also be advantageous in immunotherapy against cancer growth in peripheral tissues. We have constructed chimeric IgE and IgG1 antibodies with murine V regions and human C regions corresponding to the MOv18 monoclonal antibody against the human ovarian tumor-associated antigen, folate binding protein. The antibodies exhibited the expected binding affinities for antigen and Fc receptors, and effector activities with human basophils and platelets in vitro. The protective activities of MOv18-IgE and MOv18-IgG1 were compared in a SCID mouse xenograft model of ovarian carcinoma. The beneficial effects of MOv18-IgE were greater and of longer duration than those of MOv18-IgG1. Our results suggest that the allergic reaction could be harnessed for the suppression of ovarian tumors.

Ovarian cancer-associated lymphocyte recognition of folate binding protein peptides

BACKGROUND

Tumor-associated lymphocytes (TAL) isolated from ovarian cancer patients contain cytotoxic T lymphocytes (CTL) capable of recognizing specific HLA/peptide complexes on tumor cells leading to tumor cell lysis. Currently, HER2/neu, overexpressed in only 30% of breast and ovarian cancers, is the only known source of CTL-recognized peptides in epithelial cancers. Therefore, we have investigated peptides derived from folate binding protein (FBP), which is over-expressed in more than 90% of ovarian cancers and in the majority of other epithelial tumors.

METHODS

TAL were isolated from the malignant ascites of four consecutive HLA-A2+ ovarian cancer patients and incubated in IL-2. Initial chromium-release assays were performed within 1 week. T2 cells, incubated with peptide, were used to reconstitute T cell epitopes. The FBP sequence was interrogated for HLA-A2 binding peptides, and five were synthesized (E37-41).

RESULTS

Freshly cultured, unstimulated ovarian TAL recognize peptides derived from FBP. These peptides are presented in the context of HLA-A2, and are specifically recognized in a HLA class I-restricted fashion. TAL recognition of these reconstituted T cell epitopes is concentration dependent. Furthermore, the FBP peptides are shown by cold target inhibition studies to be naturally processed and presented antigens.

CONCLUSIONS

FBP peptides are recognized by freshly isolated TAL from ovarian cancer patients, suggesting in vivo expression and sensitization. Because FBP is over-expressed 20-fold in most adenocarcinomas, these peptides may be used in a widely applicable peptide-based vaccine for epithelial tumors.

Shedding of the 67-kD laminin receptor by human cancer cells

The 67-kD laminin receptor (67LR) is a cell membrane-associated molecule exhibiting high affinity for the basement membrane glycoprotein, laminin. While export of the 67LR toward the extracellular matrix has been recently suggested by electron microscopy studies, there is to date no evidence of shedding of the 67LR from cells. Using two monoclonal antibodies directed against the 67LR, we developed a double-determinant radioimmunoassay that demonstrates that the 67LR is released from cancer cells into the culture medium. The shed molecule exhibited the same apparent molecular weight as that of the membrane-associated 67LR, suggesting that no proteolytic cleavage is involved in the process. Furthermore, we demonstrate that the 67LR is not anchored to the membrane through a glycolsyl-phosphatidylinositol bridge. However, the observation that lactose increased the release of 67LR suggests that a lectin-type interaction is involved in the cell membrane association of this laminin binding protein and the cell surface. Interestingly, the released 67LR recovered after HPLC gel filtration was found free as well as associated to high molecular weight complexes. The free 67LR retained its ability to bind to the cell surface. Our study is the first demonstration that the 67LR is effectively shed by cancer cells. The released free 67LR could play an important role in modulating interactions between cancer cells and laminin during tumor invasion and metastasis.

Endocytosis of GPI-linked membrane folate receptor-alpha

GPI-linked membrane folate receptors (MFRs) have been implicated in the receptor-mediated uptake of reduced folate cofactors and folate-based chemotherapeutic drugs. We have studied the biosynthetic transport to and internalization of MFR isoform alpha in KB-cells. MFR-alpha was synthesized as a 32-kD protein and converted in a maturely glycosylated 36-38-kD protein 1 h after synthesis. 32-kD MFR-alpha was completely soluble in Triton X-100 at 0 degree C. In contrast, only 33% of the 36-38-kD species could be solubilized at these conditions whereas complete solubilization was obtained in Triton X-100 at 37 degrees C or in the presence of saponin at 0 degree C. Similar solubilization characteristics were found when MFR-alpha at the plasma membrane was labeled with a crosslinkable 125I-labeled photoaffinity-analog of folic acid as a ligand. Triton X-100-insoluble membrane domains containing MFR-alpha could be separated from soluble MFR-alpha on sucrose flotation gradients. Only Triton X-100 soluble MFR-alpha was internalized from the plasma membrane. The reduced-folate-carrier, an integral membrane protein capable of translocating (anti-)folates across membranes, was completely excluded from the Triton X-100-resistant membrane domains. Internalized MFR-alpha recycled slowly to the cell surface during which it remained soluble in Triton X-100 at 0 degree C. Using immunoelectron microscopy, we found MFR-alpha along the entire endocytic pathway: in clathrin-coated buds and vesicles, and in small and large endosomal vacuoles. In conclusion, our data indicate that a large fraction, if not all, of internalizing MFR-alpha bypasses caveolae.

The role of dietary folate in modulation of folate receptor expression, folylpolyglutamate synthetase activity and the efficacy and toxicity of lometrexol

We have studied the molecular effects of a LFD in a murine model in order to better define the biochemical changes associated with folate deficiency. In addition, we have demonstrated the effect of a LFD on the pharmacokinetic profile and therapeutic activity and toxicity of lometrexol. These studies showed increased density of FR in tumors implanted in LFD mice and a decrease in the affinity of these receptors for folic acid. The results suggest that tumors can compensate for low folate bioavailability by up-regulation of a second FR with slightly lower affinity for folic acid. The higher density of this FR would provide greater capacity for garnering serum folate. FPGS activity increased in several tumors and liver and kidney of LFD mice. The increase in this enzyme activity would result in enhanced polyglutamation of folates and classical antifolates and thus increased cellular retention. Consistent with these changes in liver FPGS, mice injected i.v. with a single dose of lometrexol accumulated significantly more drug in liver and tumors of LFD animals compared to SD mice. Also, higher liver concentrations of lometrexol persisted longer in LFD mice. Polyglutamate analysis showed that longer polyglutamate forms appeared earlier in liver of LFD mice. After 7 days, longer polyglutamyl forms were recovered from liver of LFD mice (octa- and hepta-glutamyl lometrexol) compared to those on SD. A comparison of the efficacy and toxicity of lometrexol in C3H mammary tumor-bearing mice showed that in mice on LFD, lometrexol treatment produced a delayed toxicity with an LD50 of 0.1-0.3 mg/kg, a 3000-fold increase in lethality compared to SD mice. Supplementation of mice with folic acid restored anti-tumor activity and increased the therapeutic dose-range over which efficacy could be assessed. These studies support the use of folic acid supplementation for cancer patients treated with antifolate therapy in order to prevent the biochemical changes in FR and FPGS associated with folate deficiency, prevent delayed toxicity to GARFT inhibitors and enhance the therapeutic potential of this class of drugs.

Growth of ovarian-carcinoma cell lines at physiological folate concentration: effect on folate-binding protein expression in vitro and in vivo

Ovarian-carcinoma cell lines (OVCAR3, IGROVI, OVCA432, SW626 and SKOV3), grown in standard medium containing supra-physiological (2.3 microM) folate concentration, display different levels of reactivity with the anti-folate-binding-protein (FBP) monoclonal antibody MOv18, which recognizes the alpha-isoform of the protein. Gel-filtration and absorption experiments indicated that on IGROVI cells this molecule accounts for all folic-acid binding at nanomolar concentrations. The aim of the study was to investigate the effect of extracellular folate levels on cells adapted to grow in medium containing physiological folate concentration (20 nM). By the ternary complex assay, all cell lines showed a marked depletion of intracellular reduced folates, compared with those in standard folate medium. The monitoring of FBP by MOv18 showed on IGROVI cells a transient up-regulation of the protein, whereas on the other cell lines, except SKOV3, no changes were detected. These data suggest that in these cells further over-expression of the molecule cannot generally be induced by lowering the extracellular folate concentration. On SKOV3, Scatchard analysis of 125I-MOv18 binding, as well as the evaluation of total folate binding capacity, showed a 2- to 3-fold stable increase of FBP expression after long-term growth in low-folate medium. Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis indicated in these cells a 1.5-fold increase in alpha-FBP mRNA. SKOV3 cells, maintained in vitro in medium containing supraphysiological and physiological (i.e., low-folate) concentrations were injected into nude mice. Weight differences, though not statistically significant, were observed in favour of low-folate-derived tumors. Immunohistochemical and immunochemical analysis of the tumor samples showed that in SKOV3 cells the receptor modulation can also be induced by restoring the physiological folate concentration in vivo.

Folate binding protein distribution in normal tissues and biological fluids from ovarian carcinoma patients as detected by the monoclonal antibodies MOv18 and MOv19

Folate-binding proteins (FBP), which are molecules relevant in folate metabolism, are overexpressed in ovarian carcinomas, as detected by the monoclonal antibodies (MAb) MOv18 and MOv19, which recognise two different epitopes of the gp38/FBP. In this paper, features of the FBP such as the distribution on normal tissues and the release in biological fluids of normal and tumour origin have been investigated. Immunohistochemical analyses on frozen sections of normal tissues showed the presence of the gp38/FBP on some epithelia. The reactivity of both the MAb on Fallopian tubes was intense and comparable to that observed on ovary carcinoma sections. The kidney, bronchial glands, alveolar epithelium of the lung, oesophagus, stomach, pancreas, breast and thyroid showed different levels of staining. By MOv18/MOv19 double-determinant immunoradiometric assay (DDIRMA), the gp38/FBP was found in soluble form in ascitic fluid, serum and urine of nude mice in which the human ovary carcinoma cell line IGROV1 grew as ascitic carcinomatosis. In human biological fluids, the gp38/FBP was detected in ascites of 60% of ovarian carcinoma patients, and in 29% of those with other carcinomas, but not in patients with non-epithelial tumours or with other non-tumoral pathologies. The mean serum arbitrary units (a.u.)/ml values of ovary carcinoma patients were significantly different to those of healthy donors or patients with endometriosis (P < 0.005 and P < 0.01, respectively), but not when compared to the sera of lung carcinoma patients. In addition, the sensitivity of DDIRMA was poor, since only 24% of the ovary carcinoma patients were positive with this assay. When a restricted number of cases selected for the presence of tumour cells in the ascites was examined, the percentage of DDIRMA-positive sera and ascites rose to 41 and 94%, respectively. In the urine, a strong reactivity was observed in the samples of both normal and tumour origin.

The folate receptor in central nervous system malignancies of childhood

The folate receptor is a membrane linked glycoprotein that participates in the cellular accumulation of 5-methyltetrahydrofolic acid, methotrexate and 5,10-dideazatetrahydrofolic acid. Relative receptor overexpression has been observed in several malignant cell lines and tissues. In this study we determined receptor expression using western blot analysis in primary pediatric malignancies involving the central nervous system. This study suggests that ependymoma tumors have a high frequency of receptor expression which may reflect a specific cytogenetic abnormality or the cellular origin of these tumors. The potential role in developing selective chemotherapy mediated by the folate receptor is also discussed.

Effect of hydrostatic pressure and cholesterol depletion on the expression of a tumor-associated antigen

The molecular events related to the expression of three tumor-associated epitopes, Ca-MOv17, Ca-MOv18 and Ca-MOv19 have been addressed. The epitopes are carried by a 38-kDa glycoprotein (gp38), recently cloned and identified as a human folate-binding protein. They were found to be coexpressed on the surface of the ovarian carcinoma cell line OVCA432, while they are not coordinately expressed on other adenocarcinoma cell lines (IGROV1, HT-29). This lack of coexpression was investigated from a molecular point of view. We studied three carcinoma cell lines, characterized by a different reactivity with the three relevant monoclonal antibodies MOv17, MOv18 and MOv19. The epitope expression was examined after modifying the membrane properties by using hydrostatic pressure and/or the variation of cholesterol content. Measurement of the expression after cell labelling by mAbs was performed by indirect immunofluorescence, using both fluorescence microscopy and flow cytometry. At variance with HT-29 cells, treatment of ovarian carcinoma IGROV1 cells with hydrostatic pressure failed to exert any effect. On IGROV1, instead, cholesterol depletion affected the expression Ca-MOv17, increasing, in the indirect immunofluorescence tests, the proportion of positive cells from 0 to 66 +/- 9%. Moreover, restoring the cholesterol content of the plasma membrane did not reverse the induced epitope expression. In parallel, immunoprecipitation experiments confirmed that, on IGROV1 surface, gp38 was recognized by all three mAbs. The data presented suggest that in IGROV1 cells the selective lacking of the epitope expression is related to the physical state of the plasma membrane. An explanation is provided by the model of membrane microdomains in which epitope expression may be influenced by the cholesterol level of different plasma membrane regions.

Lysis of ovarian cancer cells by human lymphocytes redirected with a chimeric gene composed of an antibody variable region and the Fc receptor gamma chain

To expand the spectrum of recognition of effector lymphocytes and to redirect them towards predefined targets, we have altered the specificity of human tumor-infiltrating lymphocytes (TIL) through stable modification with chimeric receptor genes consisting of single-chain antibody variable regions linked to the gamma subunit common to the immunoglobulin (Ig)G and IgE Fc receptors. Using either hapten or ovarian carcinoma-specific monoclonal antibodies, we constructed chimeric receptor genes and retrovirally introduced them into CD8+ TIL. Redirected TIL specifically lysed trinitrophenyl-labeled Daudi or a human ovarian carcinoma cell line (IGROV-1), and secreted granulocyte/macrophage colony-stimulating factor upon stimulation with the appropriate antigen. This strategy may allow new approaches towards the adoptive immunotherapy of cancer in humans.

Isolation and biochemical characterization of the soluble and membrane forms of folate binding protein expressed in the ovarian carcinoma cell line IGROV1

The human ovarian carcinoma cell line, IGROV1, produces two forms of folate binding protein (FBP), the membrane form that is anchored to the cell surface by a glycosylphosphatidylinositol tail and the soluble form that is shed into the tissue culture medium. Both forms are recognized by the monoclonal antibodies MOv18 and MOv19. Here we describe their purification and biochemical characterization. The purified soluble protein appeared as a single band with an apparent Mr of 36 kDa after SDS-PAGE, whereas the membrane form appeared as a single band with an apparent Mr of 38 kDa. The size difference between the two forms of FBP was confirmed by gel filtration of both the native and the N-glycanase-treated proteins. Both purified proteins had equal capacity to bind folic acid. The immunological cross-reactivity and the folic acid binding capability of the FBPs extracted from IGROV1 gave more evidence of the possible existence of a precursor-product relationship between them.

Genomic organization of the human folate receptor genes on chromosome 11q13

There has been interest in the high affinity folate receptor (FOLR) recently because of its high expression in the majority of ovarian tumors. The FOLR genes are part of a family that includes an adult gene, a fetal gene, and one or more pseudogenes, which have been localized to chromosome 11. As a step toward understanding why the adult FOLR gene product is expressed on tumors, we have determined the organization of all the human FOLR-related genes. YAC clones were isolated using the adult FOLR probe. The organization of the locus was determined by PFGE of YAC DNA and by YAC fragmentation. Four FOLR-related genes were found within 140 kb. The adult and fetal genes are not more than 23 kb apart, with the 3' end of the adult gene facing the 5' of the fetal gene. A physical map of over 900 kb of the surrounding region was also constructed. The chromosomal assignment of the FOLR locus was refined to 11q13.3-q13.5 telomeric of the FGF3 locus using fluorescence in situ hybridization.

Biochemical characterization of Trop-2, a cell surface molecule expressed by human carcinomas: formal proof that the monoclonal antibodies T16 and MOv-16 recognize Trop-2

Trop-2 is a cell surface structure recognized by the 162-46.2 mAb and expressed by most human carcinomas. Since the 162-46.2 mAb works poorly in immunoprecipitation, to characterize the structure of Trop-2 we searched for other mAbs directed against this molecule. Selection of candidates was performed by analyzing the characteristics of mAbs directed against epithelial cells and by comparing the staining pattern of each mAb with the one of the 162-46.2 on frozen sections of human epidermis. Two mAbs, T16 and MOv-16, were selected for further analysis. Formal proof that candidate mAbs reacted with Trop-2 was obtained by comparing their binding patterns to mouse L cells transfected with the Trop-2 gene by genomic DNA transfection and selected by FACS using the FITC-162-46.2 mAb. In immunofluorescence FACS analysis the FITC-T16 and FITC-MOv-16 mAbs specifically stained Trop-2 transfectants. The specificity of binding was confirmed by selective blocking of the staining by the respective unconjugated mAb. Interestingly, cross-blocking studies indicated that the 162-46.2, T16 and MOv-16 mAbs recognize the same epitope or closely spaced ones on the Trop-2 molecule. T16 and MOv-16 efficiently immunoprecipitate Trop-2 from Trop-2 transfectants and from the human cell line OVCA-432, indicating that it is a cell surface glycoprotein, with an apparent molecular weight of 57 kD in non-reducing conditions. A weaker band of 38 kD is often co-precipitated with the 57 kD form in an apparently specific manner.(ABSTRACT TRUNCATED AT 250 WORDS)

Membrane association and shedding of the GPI-anchored Ca-MOv18 antigen in human ovary carcinoma cells

The antigen recognized by the MOv18 MAb (Ca-MOv18) was recently shown to be a glycosylphosphatidylinositol (GPI)-linked protein. In this report we show that GPI-anchorage is not limited to IGROVI cells nor to other ovary carcinoma cell lines, but Ca-MOv18 was also found to be sensitive to phosphatidylinositol-specific phospholipase C (PI-PLC) treatment on fresh ovarian cancer cells. Furthermore, we found a heterogeneous sensitivity of Ca-MOv18 to PI-PLC cleavage, not only among the different cells studied but also in different experiments performed on the same cell line, during extended periods of time in culture. Sensitivity to PI-PLC cleavage was determined by immunofluorescence on live cells and by double-determinant radioimmunoassay of the antigen released in the supernatant. The specificity of the PI-PLC cleavage was demonstrated as follows: (a) TX114 solubilized Ca-MOv18 shifts from the detergent to the aqueous phase after treatment with PI-PLC; (b) on membrane preparations, PI-PLC specifically released a fraction of the antigen, which is distinct from the weakly associated form released by high-salt treatment; (c) Ca-MOv18 from IGROVI expressed the cross-reacting determinant (CRD), which is characteristic of GPI-linked molecules. The absence of CRD expression on the spontaneously released protein and the possibility of artificially inducing antigen shedding during the resynthesis of Ca-MOv18 which follows bacterial PI-PLC treatment are interesting points which need to be further investigated in order to understand the physiology of the Ca-MOv18 tumor antigen.

Management of patients with ovarian cancer using monoclonal antibodies

We describe in detail the current trend using monoclonal antibodies to diagnose ovarian cancer either in vitro or in vivo. The approach with such powerful reagents allows to differentiate in vitro tumor histotypes and to detect in peritoneal washings the presence of a few neoplastic cells which characterize the minimal disease. The detection of elevated sera levels of ovarian cancer-associated antigens, such as CA-125 and TAG-72, allows the monitoring, follow-up of these patients and the response to therapy with great accuracy. We focused our attention on the role in vivo of labelled monoclonal antibodies, mainly for diagnostic purposes. Radioimmunoscintigraphy has been found to be more reliable than CT and US to detect foci of disease mainly in patients already treated by surgery, overcoming all the problems usually encountered with these two procedures.

Use of combination of monoclonal antibodies directed against three distinct epitopes of a tumor-associated antigen: analysis of cell binding and internalization

Three monoclonal antibodies (MAbs), MOv17, MOv18 and MOv19 with tumor-restricted specificity for human ovarian carcinoma, were tested alone or in double combination with the aim of analyzing their binding and internalization behavior on different in vitro cell lines. Biochemical studies indicated that the 3 MAbs were directed against 3 epitopes of the same 38 kDa surface molecule. By immuno-electron-microscopy they exhibited a different internalization behavior since MOv17 induced evident endocytosis through coated vesicles, whereas MOv18 gave rise to occasional uncoated vesicles and MOv19 was completely unable to promote internalization of the relevant molecule. When tested 2 by 2 there was a binding synergy in one of the 9 possible combinations (125I-labelled MOv18 and unlabelled MOv19), but no change in the internalization behavior. The binding synergy, which was highly reproducible, was temperature-dependent and was also evident on glutaraldehyde-fixed cells. A metabolism involvement is therefore unlikely. This could be attributed to an easier accessibility of the CaMOv18 due to a conformational change of the molecule after MOv19 MAb binding.