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1. WO1990014595 - COMPOSITION AND METHOD TO DETECT SENSITIVITY TO ALPHA INTERFERON THERAPY

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COMPOSITION AND METHODS TO
DETECT SENSITIVITY TO ALPHA INTERFERON THERAPY

This application is a continuation-in-part of application U.S. Serial No. 357,075, filed May 25, 1989, the contents of which are hereby incorporated by reference into the present application.

Background of the Invention

Throughout this application various publication are referenced by arabic numerals within parentheses. Full citations for these publications may be found at the end of the specification immediately preceding the claims. The disclosures of these publication in their entireties are hereby incorporated by reference into this application in order to more fully describe the state of the art to which this invention pertains.

Renal cell carcinoma (RC) is the most common neoplasm of the adult kidney, with over 20,000 new cases each year in the

U.S. (1, 2). Approximately 30-40% of patients with renal cancer present with locally advanced or metastatic disease (3) , while another 30% relapse following nephrectomy for early stage disease (4) .

Chemotherapeutic agents are ineffective in renal cancer patients. In 1983, uesada et al., reported the clinical efficacy of the biological response modifier (BRM) human leukocyte interferon alpha (IFN-α) in metastatic renal cancer (5, 6) . Subsequently, numerous clinical trials with purified and recombinant IFN-α reported major responses.

i.e. from five to 29% of patients treated, with a median duration of response ranging from three to 16 months (7, 8) .

The cumulative clinical experience with IFN-α indicates that a subset of renal cancer patients are sensitive to this therapy. However, it has been impossible to predict which patients will respond to IFN-α. Previous studies have demonstrated that cultured and non-cultured renal cancers can be subclassified by virtue of differing expression of a series of kidney associated differentiation antigens to which monoclonal antibodies ( Abs) have been generated (9-13) . As a consequence, it is speculated that differential expression of one or more of these kidney antigens may be useful in identifying renal cancers with different biological and clinical characteristics (12, 14), for example, IFN-α sensitivity.

It is an object of this invention to provide a method and composition useful therein to determine which patients may be effectively treated with alpha interferon therapy.

Bιιmma γ of the Invention

This invention provides the hybridoma designated F 33 (ATCC No. HB 10155) and the monoclonal antibody produced by it. This invention also provides a method of detecting the sensitivity of a malignant cell or tissue to alpha interferon therapy which comprises contacting a sample of the malignant cell or tissue with a monoclonal antibody which recognizes an epitope of a gp 160 cell surface antigen under conditions such that an antibody-antigen complex is formed between the monoclonal antibody and the gp 160 cell surface antigen, if the antigen is present in the sample; and detecting any complex so formed, the absence of complex indicating that the malignant cell or tissue is sensitive to alpha interferon therapy.

This invention further provides a method of treating patients having tumors which do not express gp 160 cell surface antigen. This method comprises administering to the patient an effective amount of alpha interferon, effective to inhibit the growth of the tumor.

Further provided by this invention is a method of determining whether the growth of malignant cells or tissue will be inhibited by contacting the malignant cells or tissue with alpha interferon, which comprises contacting a sample of the malignant cell or tissue with a monoclonal antibody which recognizes an epitope of a gp 160 cell surface antigen under conditions such that an antibody-antigen complex is formed between the monoclonal antibody and the gp 160 cell surface antigen, if the antigen is present in the sample; and detecting any complex so formed, the absence of complex indicating that the growth of the malignant cell or tissue will be inhibited by contact with alpha interferon.

A method of detecting the sensitivity of a malignant cell or tissue to alpha interferon therapy is further provided which comprises contacting a sample of the malignant cell or tissue with a monoclonal antibody which recognizes an epitope of gp 160 cell surface antigen under conditions such that an antibody-antigen complex is formed between the monoclonal antibody and the gp 160 cell surface antigen, if the antigen is present in the sample; and detecting any complex so formed, the presence of complex indicating that the malignant cell or tissue is resistant to alpha interferon therapy.

Brief Description of the Figures

Figures 1A and IB show the effects of interferon-α on renal carcinoma cell proliferation. Sixteen (16) renal cancer cell lines and two short term cultures of normal proximal tubule cells were plated at 1 x 10s cells in 25 cm2 flasks (Day 0) and refed with medium containing recombinant IFN-α at 100 units/ml, 300 units/ml, 1000 units/ml and 3000 units/ml (Day 1) . Control cultures were refed with medium without IFN-α. On day seven, the cells were harvested by trypsinization and counted. The ratios of the cell number on day 7 to that on day 0 in IFN-treated cultures were expressed as a percentage of the ratio in untreated control cultures. Values represent an average of at least two separate experiments on each cell line. The designation SK-RC denotes renal cancer cell lines established at Sloan-Kettering Institute; PT denotes short term cultures of normal proximal tubule cells.

Panel A: Resistant Cells: SK-RC-26,["] ; SK-RC-28, φ SK-RC-35, D ; SK-RC-45, < ; SK-RC-4, ■
SK-RC-12, Q ; SK-RC-1, A ; SK-RC-38,
PT-1, g ; PT-2, —j

Panel B: Sensitive Cells: SK-RC-29, [ϊ] ; SK-RC-2, SK-RC-17, Q ; SK-RC-39, ; SK-RC-42, g

SK-RC- 1, Q ; SK-RC-49, A ; SK-RC- 4, ^

Figure 2 shows the results of immunoprecipitation of the gpl60 protein. Autoradiograms of immunoprecipitates obtained with mAb F 33 (anti-gpl60) and extracts of [35S] methionine-labeled SK-RC-45 (gpl60+) and SK-RC-44 (gpl60") as analyzed by SDS-PAGE. (Lane A) SK-RC-45; (Lane B) SK-RC-44. Arrow shows gpl60 protein.

Detailed Description of the Invention

This invention provides the hybridoma designated F 33 (ATCC No. HB 10155) and the monoclonal antibody produced by the hybridoma F 33. The hybridoma F 33 has been deposited pursuant to the Budapest Treaty On The International

Recognition OF The Deposit Of Microorganisms For The

Purposes Of Patent Procedure with the Patent Culture

Depository of the American Type Culture Collection (ATCC) ,

12301 Parklawn Drive, Rockville, Maryland, 20852 U.S.A. under ATCC Accession No. HB 10155.

This invention provides an antigen, the expression of which is associated with the nonresponsiveness of a malignant cell or tumor to alpha interferon therapy, the antigen being characterized by its specific binding to the monoclonal antibody produced by the hybridoma F 33.

This invention also provides a method of detecting the sensitivity of a malignant cell or tissue to alpha interferon therapy which comprises contacting a sample of the malignant cell or tissue with a monoclonal antibody which recognizes an epitope of a gp 160 cell surface antigen under conditions such that an antibody-antigen complex is formed between the monoclonal antibody and the gp 160 cell surface antigen, if the antigen is present in the sample; and detecting any complex so formed, the absence of complex indicating that the malignant cell or tissue is sensitive to alpha interferon therapy. As used herein, the alpha interferon therapy for which the methods of this invention are useful comprises any alpha interferon therapy which uses an alpha interferon molecule or derivative thereof which has an anti-proliferative effect on malignant cells, i.e. natural or recombinant alpha interferon molecules or derivatives thereof. The monoclonal antibody which may be useful in the practice of this invention is any monoclonal antibody which recognizes an epitope of the gp 160 cell surface antigen, such as the monoclonal produced by the hybridoma designated F 33. Other monoclonal antibodies which also recognize the same antigen which is recognized by the monoclonal antibody produced by the hybridoma F 33 are also useful in the practice of this invention.

Malignant cells or tissue useful in the practice of this invention comprise all malignant cells or tissue, and shall include, but is not limited to human and animal carcinoma cells or tissue, such as renal carcinoma cells or tissue and more specifically human renal carcinoma cells or tissue.

A method of detecting the sensitivity of a malignant cell or tissue to alpha interferon therapy is further provided which comprises contacting a sample of the malignant cell or tissue with a monoclonal antibody which recognizes an epitope of gp 160 cell surface antigen under conditions such that an antibody-antigen complex is formed between the monoclonal antibody and the gp 160 cell surface antigen, if the antigen is present in the sample; and detecting any complex so formed, the presence of complex indicating that the malignant cell or tissue is resistant to alpha interferon therapy. One such monoclonal antibody useful in the practice of this invention is the monoclonal antibody produced by the hybridoma designated F 33 (ATCC No. HB 10155) , but any monoclonal antibody which recognizes the same antigen which is recognized by the monoclonal antibody produced by the hybridoma F 33 is also useful in the practice of this invention.

Suitable samples of the malignant cell or tissue may comprise, but is not limited to human malignant cells or tissue, for example, carcinoma cells or tissue, such as renal carcinoma cells or tissue. However, in the preferred embodiment of this invention, the renal carcinoma cells or tissue are human renal carcinoma cells or tissue.

A method of treating patients having tumors which do not express gp 160 cell surface antigen is also provided by this invention. This method comprises administering to the patient an effective amount of alpha interferon, effective to inhibit the growth of the tumor. The effective amount of alpha interferon will vary with the type of tumor and the number of lesions to be treated. The gp 160 antigen which is useful in the practice of this invention is an antigen which has an epitope which is recognized by the monoclonal antibody produced by the hybridoma designated F 33 (HB 10155) . As used herein, the tumor maybe, but is not limited to, tumors which have contained therein carcinoma cells or tissue, for example, renal carcinoma cells or tissue.

Further provided by this invention is a method of determining whether the growth of malignant cells or tissue will be inhibited by contacting the malignant cells or tissue with alpha interferon which comprises contacting a sample of the malignant cell or tissue with a monoclonal antibody which recognizes an epitope of gp 160 cell surface antigen under conditions such that an antibody-antigen complex is formed between the monoclonal antibody and the gp 160 cell surface antigen, if the antigen is present in the sample; and detecting any complex so formed, the absence of complex indicating that the growth of the malignant cell or tissue will be inhibited by alpha interferon. One monoclonal antibody which is useful in the practice of this invention is the monoclonal antibody produced by the hybridoma designated F 33 (ATCC No. HB 10155) , although any monoclonal antibody which recognized the antigen which is recognized by the monoclonal antibody produced by the hybridoma designated F 33 may also be used to practice this invention.

Malignant cells or tissue useful in the practice of this method comprise animal and human malignant cells or tissue such as carcinoma cells or tissue, e.g. renal carcinoma cells or tissue.

Materials and Methods

Cell Lines and Tissue Culture

Short-term cultures of normal proximal tubule cells (PT1, PT2) , and renal cancer cell lines were derived as previously described (15) . Renal cancer cell lines were from either primary (SK-RC-1, 4, 35, 44, 49) or metastatic (SK-RC-2, 12, 17, 26, 28, 29, 38, 39, 41, 42, 45; adrenal 3, lung 3, bone 2, soft tissue 2, brain 1) renal cancers. Cultures were maintained in Eagle's minimal essential media (MEM) supplemented with 2 mM glutamine, 1% nonessential amino acids, 1000 U/ml streptomycin, 100 U/ml penicillin, and 7.5% fetal bovine serum (FBS) .

Sβroloqjcal Reaσents

The mouse mAbs used are summarized in TABLE 1 below.

TABLE 1
Monoclonal Antibodies

Designation Mr Of Site of
(lg Subclass) Antigen Expression1 Reference

MabF33 (7l) 160,000 Glom, PT
mAbS22 (7l) 115,000 RC only (10) mAbS23 (7l) 120,000 PT, LH (10) mAbT43 (7l) 85,000 PTC (26) mAbF23 (7l) 140,000 PT (10) mAbF31 (lgm) glycolipid PTS (13)

1Glom = Glomerulus; Ptc = Pars convoluta of the proximal tubule;
Pts = Pars recta of the proximal tubule; LH = Loop of Henie.

Serolocrical Assays

The protein-A and anti-mouse immunoglobulin hemadsorption assays were performed as described (16) . Indicator cells were prepared by conjugating the immunoglobulin fraction of rabbit anti-mouse heavy chain (DAKO Corp., Santa Barbara, CA) to human 0+ erythrocytes with 0.01% chromium chloride. Assays were performed in Falcon 3040 microtest plates (Falcon Labware, Oxnard, CA) . Target cells (plated 1-2 days previously) and serial antibody dilution were incubated for 1 hour at room temperature, then washed and human erythrocyte indicator cells were added for 45 minutes. Target cells were washed again to remove non-adherent indicator cells. Titers were defined as the antibody dilution showing 20% positive (rosetted) target cells as evaluated by light microscopy.

Immunoprecipitation Analysis

Cells were radiolabeled by metabolic incorporation of [35S]methionine (1,000 Ci/m ol; New England Nuclear, Boston, MA) using 250 uCi in 10 ml of methionine-free MEM obtaining 1% FBS for 16 hours. Labeled cells were extracted as described (17) . Immunoprecipitation was carried out by mixing a portion of the cell extract (10 x 106 cpm) with 1 ul of undiluted ascites fluid of mAb F33 (anti-gpl60) . Immune complexes were isolated with protein A-Sepharose-C14B (Pharmacia, Inc., Piscataway, NJ) and the labeled components were detected by SDS-polyacrylamide gel electrophoresis and fluorography as described (17) .

Interferon Effect on Proliferation

Cell lines were plated at 1 x 10s cells/25 cm2 flask in Eagle's MEM with FBS. After one day the cells were refed with MEM with FBS containing recombinant IFN-Alpha (r-metHulFN-Con1) , a consensus analogue of the most frequent a ino acid residues known to occur in subspecies of alpha interferons (A gen, Inc., Thousand Oaks, CA) (18) at 100 units/ml, 300 units/ml, 1000 units/ml and 3000 units/ml. A unit of alpha interferon is defined as the amount which is necessary to inhibit replication of Vesicular stomatitis virus in a cell culture by 50%. Control cultures were refed with MEM with FBS and without IFN-α. On day 7, cells were washed once with PBS and harvested by trypsinization for 5 minutes at 37 *C. Cell counts were performed on a Coulter counter (Coulter Electronics, Hialeah, FL) . The ratios of the cell number on day 7 to that on day 0 in IFN-α-treated cultures were expressed as a percentage of the same ratio (day 7/day 0) in untreated control cultures.

Renal Cancer Xenoαrafts

The renal cancer cell lines used above were assayed for their ability to form tumors following inoculation of 1 x 106 cells into the flank of 4-6 week old Swiss female nu/nu mice. Cell lines that were tumorigenic were then used to determine the effect of IFN-α on renal cancer xenografts in vivo. For each cell line tested, eight to ten mice were inoculated subcutaneously in the right flank with a single cell suspension of 1 x 106 cells in 0.2 ml of MEM without FBS. Subsequently, one half of the mice in each group received one million units of recombinant IFN-Alpha (r-metHulFN-Con_,) in 0.5 ml of MEM without FBS intraperitoneally. IFN-α therapy was initiated at the time of injection of renal cancer cells and continued on a thrice weekly schedule. One half of the mice in each experiment (the control group) received no IFN-α therapy. All mice were examined for tumor formation three times a week. Individual mice in each trial with a different renal cancer cell line were terminated when (i) the tumors reached a diameter of 1 cm; (ii) the tumors became ulcerated; (iii) no tumor had formed after 150 days; or (iv) the mice developed an opportunistic infection (bacterial or fungal) unrelated to the treatment. Serum levels of IFN-α were not monitored.

RESULTS

Growth Inhibition Assays

The effects of IFN-α on the proliferation of two normal proximal tubule cell cultures (PT1, PT2) , and 16 renal cancer cell lines were analyzed at increasing concentrations ranging from 100 to 3000 units iFN-α/ml. Both normal proximal tubule cultures, and 8 renal cancer cell lines were found to be relatively resistant to the anti-proliferation effect of IFN-α. These cell lines showed <20% inhibition of growth with IFN-α concentrations as high as 3000 units/ml (Figure 1A) . In contrast, 7 other renal cancer cell lines showed >50% growth inhibition with IFN-α concentrations of < 1000 units/ml when compared to untreated cultures (Figure IB) . A 50% inhibition of cell proliferation was also demonstrated in an eighth renal cancer cell line (SK-RC-29) , but this cell line required an IFN-α concentration of 3000 units/ml. Cytotoxicity at high concentrations of IFN-α (> 1,000 units/ml) was noted in several highly sensitive cell lines (SK-RC-2, 41, 42, 44, and 49).

cφ!60 Expression and IFN-α Sensitivity

The antigenic phenotype of each cell used above was determined by immunorosetting assays and a panel of monoclonal antibodies generated to 6 distinct and unrelated kidney associated differentiation antigens (see Table 1) . This panel of antigens, consisting of 5 surface glycoproteins and 1 surface glycolipid, represents a range of kidney specific markers that are expressed universally in normal proximal tubule cells (except for S22 which is only expressed in renal cancers) , and variably in cultured and non-cultured renal cancers. As shown in Table 2, the expression of this set of antigens was correlated with the biological phenotype of resistance or sensitivity to the anti-proliferative action of IFN-α. There was no demonstrable correlation with 5 of the 6 antigens. However, one antigen, a surface glycoprotein of 160 kilodaltons (gpl60) defined by mAb F33, did correlate with IFN-α effect. The PT1, PT2, and 7 renal cancer cell lines that were resistant to IFN-α expressed high levels of gpl60 (Figure iA, Table 2) . In contrast, 8/9 other renal cancer cell lines that did not show detectable expression of gpl60 were markedly sensitive to the anti-proliferative effects of IFN-α (Figure IB and Table 2) . These data suggested that the lack of gpl60 expression by renal cancer cell lines is predictive for sensitivity to the anti-proliferative effect of recombinant IFN-α, and, conversely, that resistance correlates with the expression of gpl60.

TABLE 2
Expression of Kidney Differentiation Antigens and
Interferon-α Effect1

ANTIBODIES CELL LINES S22 S23 T43 F23 F31 F33 IFN-α2

PT1 D ■ D B R
PT2 α ■ ■ D B R
SK-RC-1 ■ B ■ D B R
SK-RC-4 B D o B R
SK-RC-12 n.d.3 o o ■ R
SK-RC-26 o D D B R
SK-RC-28 o o D B R
SK-RC-38 n. d. ■ ■ ■ B R
SK-RC-45 ■ ■ D B R
SK-RC-35 n.d. o D o R

SK-RC-2 S ■ D o S
SK-RC-17 n.d. ■ ■ o S
SK-RC-29 o ■ α o S
SK-RC-39 n.d. ■ α o S
SK-RC-41 n.d. D R o S
SK-RC-42 o K K D o S
SK-RC-44 n. d. D B o S
SK-RC- 9 n. d. ■ B o S 1Expression of surface glycoproteins was determined by erythrocyte rosetting assays, o indicates no reactivity; D indicates a reactive mAb titer of < 1/10,000; B indicates a reactive mAb titer of > 1/100,000.

2IFN-α effect determined by growth inhibition assays (see

Methods) .
(S) indicates a >50% inhibition of cell growth as compared to untreated control cultures at an IFN-α concentration < 1000 units/ml (except for SK-RC-29, where 50% inhibition occurred at 3000 units/ml) .
(R) indicates <20% inhibition of cell growth as compared to untreated control cultures at an IFN-α concentration up to 3000 units/ml.

n.d., not determined.

gpl60 Expression bv Immunoprecipitation

In order to confirm the presence or absence of gpl60, renal cancer cell lines were radiolabeled with 35S-methionine and cell lysates were subjected to immunoprecipitation with mAb F33. Figure 2 (above) shows representative immunoprecipitation results. In confirmation of the immunorosetting analysis, a protein of 160 kD was present on gpl60* renal cancer cell lines and not detectable in gpl60* renal cancer cell lines.

Renal Cancer Xenoσrafts

To assess the potential applicability of this finding to patient therapy, an in vivo mouse model was used to determine (i) whether in vitro sensitivity to the anti-proliferative action of IFN-α correlated with anti-tumor effects of IFN-α in vivo, and (ii) whether the correlation of resistance to IFN-α and expression of gpl60 seen in vitro was valid in vivo in a mouse model. The experiment was designed to simulate the clinical application of IFN-α in the treatment of renal cancers, in which patients receive IFN-α systemically and not directly to the tumor mass. Therefore, unlike the in vitro experiments discussed above in which IFN-α was added directly to the renal cancer cells, here the effects of systemically administered IFN-α on the growth of subcutaneous human renal cancer xenografts was determined. Since not all renal cancer cell lines are tumorigenic in nu/nu mice, the ability of gpl60+ and gpl60' renal cancer cell lines to form subcutaneous tumors was first assessed in athymic mice (see methods) . Upon injection of 1 x 106 renal cancer cells, 8/16 renal cancer cell lines were consistently tumorigenic, forming a 0.2-0.5 cm3 tumor within six weeks; the remaining 8 showed negligible growth under similar conditions. Of these eight tumorigenic renal cancer cell lines, 2 were gpl60+ and 6 were gpl60", and 7 of these were used for mouse experiments (see Table 3 below) . Tumors appeared at the sites of inoculation in all mice injected with gpl60* renal cancer cells within 10-15 days (median values, range 10-25 days), regardless of whether they were treated or untreated with IFN-α. Mice injected with gpl60" renal cancer cells, but not receiving IFN-α, also formed tumors. In contrast, IFN-α exhibited a marked anti-tumor effect in the mice injected with gpl60* renal cancer cells; the mice in this group manifested either no tumor formation or substantially delayed tumor formation. These data indicate that similar to previous experience in clinical trials with renal cancer patients, a subset of renal cancers is sensitive to IFN-α therapy. More importantly, these results show that each of the gpl60" renal cancer are sensitive to IFN-α in an in vivo setting.

TABLE 3
Anti-Proliferative Effect of Interferon-α on
Renal Cancer Xenografts

gpl60 Median Days to Tumor formation

Cell Line Expression2 IFN-α +IFN-α3

SK-RC-01 + 14 15
SK-RC-45 + 10 10
SK-RC-17 6 > 77*

SK-RC-39 30 > 735

SK-RC- 2 40 NTF6 SK-RC-44 7 NTF7

SK-RC- 9 5 NTF8

1Tumor formation assessed as the initial presentation of a subcutaneous nodule >.2mm which continued to enlarge. 2gpl60 expression determined by immunorosetting assays. (+) indicates detectable expression at mAb titers of
>1:100,000. (-) indicates no detectable expression
(see Table 2) .
3IFN-α = treatment with 1 million units of recombinant IFN-α

(r-metHuIFN-Con1) intraperitoneally on a M- -F schedule.
4In this group of 4 mice, tumors were detected at dl9, d59, and 2 mice were sacrificed at d98 with no evidence of tumor formation (NTF) .
5In this group 3 mice, tumors were detected at d66, d73, and

1 mouse was sacrificed at d82 with NTF.
^his entire group of 4 mice was sacrificed at dl50 with
NTF.
7This group of 5 mice was sacrificed at d33, 94, 122, 122, 122 with NTF.
^his group of 4 mice was sacrificed atd49, 86, 86, 86 with NTF.

Experimental Discussion

IFN-α is an effective form of therapy in the treatment of a subset of metastatic renal cell carcinomas with the proportion of patients responding in clinical trials of IFN-α in renal cancer averaging approximately 15% [range of 5-29%] (7, 8). However, the majority of renal cancers are unresponsive to the anti-tumor effects of IFN-α. Whether the biological basis for this differential sensitivity to IFN-α is a function of the individual renal cancer or of the host is obscure. The mode of action of IFN-α is presumed to involve both direct cytotoxic and anti-proliferative effects on tumor cells as well as indirect effects that facilitate immune detection by the host (e.g., increased NK cell and monocyte activity, induction of tumor cell surface antigens, etc.) (19). Clearly, an ability to discriminate and define cellular as well as host mechanisms involved in the anti-proliferative effects of IFN would be valuable. Moreover, identification of the subset of renal cancers that would be inhibited by IFN-α would provide, not only a model system with which to study the mechanism of the anti-tumor action of IFN-α, but potentially a diagnostic procedure allowing a more precise tailoring of treatment for individual patients. In the present study, it was shown that (i) IFN-α has direct anti-proliferative and anti-tumorigenic effects on cultured renal cancers; (ii) renal cancers can be subsetted into those that are sensitive to the effects of IFN and those that are resistant; and (iii) that the phenotype of resistance or sensitivity can be correlated with the expression of one cell surface glycoprotein of 160 kilodaltons.

IFN-α markedly inhibited the growth of a sunset of renal cancer cell lines growing as monolayers in vitro. While IFN-α has direct anti-proliferative effects on these renal cancer cell lines, the specific types of biochemical derangements have not yet been defined. The concentrations of IFN-α that inhibited the growth of these renal cancer cell lines in vitro were within a range that is equivalent to mean serum concentrations achieved in patients with renal cancer after a standard IFN-α protocol (i.e., 100-1,000 units/ml) (20) . When the same set of renal cancer cell lines was grown, not in tissue culture, but as tumor xenografts in mice, their proliferation was also markedly inhibited by systemically administered (i.e., intraperitoneal) IFN-α. Therefore, regardless of whether IFN-α was added directly to tumor cells in vitro or indirectly to the tumor in vivo, the biological results, i.e., the inhibition of proliferation, were identical. While it is more difficult to define the precise effects of IFN-α given systemically to mice carrying a renal cancer xenograft, it would be reasonable to assume that IFN-α had a direct anti-proliferative effect which was sufficient to inhibit tumor formation by renal cancer cells.

I munological analysis indicated that IFN-α sensitive and resistant renal cancers expressed a similar panel of kidney associated antigens and, thus, have a common antigenic phenotype. However, there was one notable exception. Renal cancers that were resistant to IFN-α expressed a glycoprotein of 160 kilodaltons, gpl60, on their cell surfaces, while those renal cancers that were sensitive to IFN-α did not express gpl60 (Table 2) . The gpl60 molecule, which has been previously characterized (9, 10, 12) , is normally expressed on the cell surfaces of the glomerulus and proximal tubule cell of the human nephron, and on the cell surface of approximately 80% of cultured and non-cultured renal cancers (N.H. Bander, unpublished data, 21) .

A wide range of normal and neoplastic tissues of nonkidney origin do not express detectable amounts of gpl60 (10) . However, gpl60 can be detected on a subset of sarcomas (10) . Immunoprecipitation studies using radiolabeled cell lysates confirmed that gpl60" renal cancer cell lines did not have detectable amounts of this protein. Consequently, based on differential expression of one surface glycoprotein, a prediction could be made as to which renal cancers cell lines would respond to the anti-proliferative effects of IFN-α. This predictive correlation was shown to be valid

10 both in vitro and in vivo in a mouse model system.

The biochemical function of gpl60 is not yet known. Therefore, whether gpl60 is directly or indirectly involved in the resistance of renal cancer to IFN-α, or merely cophenotypes fortuitously with another gene(s) product which does convey resistance to IFN-α remains to be determined. The possibility that gpl60 is related to the multiple drug resistance (MDR) gene product was considered. This consideration was based on the facts that (i) the 170

Of)
kilodalton p-glycoprotein (pl70) is similar in molecular weight to gpl60 (22), (ii) pl70 is also expressed at high levels in renal tissues (23) , and (iii) expression of pl70 correlates with resistance of renal cancers to the cytotoxic effects of certain chemotherapeutic agents, e.g. , adriamycin 25 (24). Immunological analysis, however, showed a different pattern of expression of gpl60 and pl70 in renal cancer cell lines and renal tissues: gpl60 and pl70 were not . coordinately expressed in vitro in the renal cancers used in this study (data not shown) . Moreover, in vivo, glomerular 0 epithelium was gpl60* but 170" (9, 25) . Thus, it is unlikely that gpl60 and the MDR P170 are identical proteins.

The benefit of the present invention is that patients unlikely to derive therapeutic benefit from IFN could be 5 spared the toxicity of ΪFN-α treatment and could be offered alternative therapy without delay. Moreover, patients at high risk of failure (e.g., those with resected stage III disease) who have gpl60 tumors could be offered adjuvant therapy early, at a time when they are theoretically most likely to benefit.

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