Novel serpentine transmembrane antigens expressed in human cancers and uses thereof

Abstract

Described is a novel family of cell surface serpentine transmembrane antigens. Two of the proteins in this family are exclusively or predominantly expressed in the prostate, as well as in prostate cancer, and thus members of this family have been termed “STEAP” (Six Transmembrane Epithelial Antigen of the Prostate). Four particular human STEAPs are described and characterized herein. The human STEAPs exhibit a high degree of structural conservation among them but show no significant structural homology to any known human proteins. The prototype member of the STEAP family, STEAP-1, appears to be a type IIIa membrane protein expressed predominantly in prostate cells in normal human tissues. Structurally, STEAP-1 is a 339 amino acid protein characterized by a molecular topology of six transmembrane domains and intracellular N- and C-termini, suggesting that it folds in a “serpentine” manner into three extracellular and two intracellular loops. STEAP-1 protein expression is maintained at high levels across various stages of prostate cancer. Moreover, STEAP-1 is highly over-expressed in certain other human cancers.

1 . An isolated STEAP-2 protein having the amino acid sequence shown in  FIG. 9  (SEQ ID NO:6).  
     
     
         2 . An isolated polypeptide of at least 8 contiguous amino acids of an amino acid sequence selected from the group consisting of amino acids 1-205, 100-108, 227-235, 229-254, 278-303, 306-314, or 307-315 of the protein of  claim 1 .  
     
     
         3 . An isolated polypeptide comprising an amino acid sequence which is at least 90% identical to the amino acid sequence shown in  FIG. 9  over its entire length.  
     
     
         4 . An isolated polynucleotide selected from the group consisting of (a) a polynucleotide having the sequence as shown in  FIG. 9 , wherein T can also be U; (b) a polynucleotide encoding a STEAP-2 polypeptide whose sequence is encoded by the cDNA contained in plasmid 98P4B6-GTD3 as deposited with American Type Culture Collection as Accession No. PTA-311; and (c) a polynucleotide encoding the STEAP-2 protein of  claim 1 .  
     
     
         5 . An isolated polynucleotide which selectively hybridizes under stringent conditions to a polynucleotide according to  claim 4  or its complement.  
     
     
         6 . An isolated fragment of a polynucleotide according to  claim 4  which is at least 20 nucleotide bases in length.  
     
     
         7 . An isolated polynucleotide which is fully complementary to a polynucleotide according to  claim 4 .  
     
     
         8 . An isolated fragment of a polynucleotide according to  claim 7  which is at least 20 nucleotide bases in length.  
     
     
         9 . A recombinant expression vector which contains a polynucleotide according to  claim 4 .  
     
     
         10 . A host cell which contains an expression vector according to  claim 9 .  
     
     
         11 . An isolated polynucleotide according to  claim 5  which is labeled with a detectable marker.  
     
     
         12 . A process for producing a STEAP-2 protein comprising culturing a host cell of  claim 10  under conditions sufficient for the production of the polypeptide and recovering the STEAP-2 protein from the culture.  
     
     
         13 . An antibody or fragment thereof which specifically binds to an epitope within amino acids 1-205, 100-108, 227-235, 229-254, 278-303, 306-314, or 307-315 of the STEAP-2 protein of  claim 1 .  
     
     
         14 . A monoclonal antibody according to  claim 13 .  
     
     
         15 . The monoclonal antibody of  claim 14  which is labeled with a detectable marker.  
     
     
         16 . The monoclonal antibody of  claim 14  which is conjugated to a toxin.  
     
     
         17 . The monoclonal antibody of  claim 14  which is conjugated to a therapeutic agent.  
     
     
         18 . An assay for detecting the presence of a STEAP-2 protein in a biological sample comprising contacting the sample with an antibody of  claim 15 , and detecting the binding of STEAP-2 protein in the sample thereto.  
     
     
         19 . An assay for detecting the presence of a STEAP-2 polynucleotide in a biological sample, comprising 
 (a) contacting the sample with a polynucleotide probe which specifically hybridizes to a polynucleotide of  claim 4  or its complement; and    (b) detecting the presence of a hybridization complex formed by the hybridization of the probe with STEAP-2 polynucleotide in the sample, wherein the presence of the hybridization complex indicates the presence of STEAP-2 polynucleotide within the sample.    
     
     
         20 . An assay for detecting the presence of STEAP-2 mRNA in a biological sample comprising: 
 (a) producing cDNA from the sample by reverse transcription using at least one primer;    (b) amplifying the cDNA so produced using STEAP-2 polynucleotides as sense and antisense primers to amplify STEAP-2 cDNAs therein;    (c) detecting the presence of the amplified STEAP-2 cDNA,    wherein the STEAP-2 polynucleotides used as the sense and antisense primers are capable of amplifying the polynucleotide shown in  FIG. 9  or a fragment thereof.    
     
     
         21 . A composition for the treatment of prostate cancer comprising an antibody according to  claim 14 ,  16  or  17 , wherein the antibody binds to an extracellular domain of STEAP-2.  
     
     
         22 . A vaccine composition for the treatment of a cancer expressing a STEAP-2 protein comprising a STEAP-2 protein according to  claim 1  and a physiologically acceptable carrier.  
     
     
         23 . A vaccine composition for the treatment of a cancer expressing a STEAP-2 protein comprising an immunogenic portion of a STEAP-2 protein according to  claim 2  and a physiologically acceptable carrier.  
     
     
         24 . A method of delivering a cytotoxic agent, a therapeutic agent or a diagnostic agent to a cell that expresses a STEAP-2 protein (SEQ ID NO:6), comprising: 
 providing a cytotoxic agent, a therapeutic agent or a diagnostic agent conjugated to an antibody or fragment thereof comprising an antigen binding site that binds specifically to SEQ ID NO:6 or a protein comprising an extracellular domain of SEQ ID NO:6, to form an antibody-agent or fragment-agent conjugate; and,    exposing the cell to the antibody-agent or fragment-agent conjugate.    
     
     
         25 . A method of inhibiting the growth of a cancer cell that expresses a STEAP-2 protein (SEQ ID NO:6), comprising: 
 providing a cytotoxic agent or a therapeutic agent conjugated to an antibody or fragment thereof comprising an antigen binding site that binds specifically to SEQ ID NO:6 or a protein comprising an extracellular domain of SEQ ID NO:6, to form an antibody-agent or fragment-agent conjugate; and,    exposing the cell to the antibody-agent or fragment-agent conjugate.    
     
     
         26 . The method of  claim 24 , wherein the diagnostic agent comprises a detectable marker.  
     
     
         27 . The method of  claim 25 , wherein the cytotoxic agent comprises a toxin.  
     
     
         28 . The method of  claim 26 , wherein the detectable marker is a radioisotope, a fluorescent compound, a bioluminescent compound, a chemiluminescent compound, a metal chelator or an enzyme.  
     
     
         29 . The method of  claim 25 , wherein the therapeutic agent comprises paclitaxel, an androgen blocker, or an immune modulator.  
     
     
         30 . The method of  claim 25 , wherein the antibody is administered in conjunction with radiation or chemotherapy.  
     
     
         31 . The method of  claim 25  wherein the antibody or antibody fragment is administered to a human patient who has received one or more rounds of chemotherapy prior to the administration of said antibody or antibody fragment.  
     
     
         32 . The method of  claim 25  wherein the antibody or antibody fragment is a humanized antibody.  
     
     
         33 . The method of  claim 25  wherein the antibody or antibody fragment is a human antibody.  
     
     
         34 . The method of  claim 25  wherein the antibody is a bispecific antibody or a homodimeric antibody.  
     
     
         35 . The method of  claim 25  further comprising administering a therapeutic agent.  
     
     
         36 . The method of  claim 35  wherein the therapeutic agent is a chemotherapeutic agent, an androgen blocker, or an immune modulator.  
     
     
         37 . The method of  claim 25  further comprising administering one or more additional antibodies that binds specifically to SEQ ID NO:6 or a protein comprising an extracellular domain of SEQ ID NO:6.  
     
     
         38 . The method of  claim 37  wherein the one or more additional antibodies specifically binds to a different epitope of SEQ ID NO:6.  
     
     
         39 . The method of  claim 37  wherein the one or more additional antibodies has a different effector mechanism.  
     
     
         40 . The method of  claim 25  wherein the cancer is metastatic.  
     
     
         41 . The method of  claim 25  wherein the cancer is prostate, bone, lymph node, lung, liver or brain cancer.  
     
     
         42 . An assay for determining an expression level for a STEAP-2 (SEQ ID NO:6) gene product, comprising: 
 providing a test sample obtained from a subject having or suspected of having a cancer cell expressing the STEAP-2 gene product, and a normal sample;    determining the expression level of the STEAP-2 gene product in the test sample and the normal sample; and    comparing the expression level of the STEAP-2 gene product detected in the test sample and the normal sample.    
     
     
         43 . The assay of  claim 42 , wherein the test sample and the normal sample are obtained from the same subject.  
     
     
         44 . The assay of  claim 42 , wherein the test sample is obtained from the subject and the normal sample is obtained from a normal subject.  
     
     
         45 . An immunoassay for determining an expression level for STEAP-2 in a test sample, comprising: 
 providing a test sample obtained from a subject having or suspected of having a cancer cell expressing the STEAP-2 gene product;    contacting the test sample and the normal sample with an antibody or fragment thereof the binds specifically to STEAP-2 (SEQ ID NO:6) or a polypeptide comprising an extracellular domain of SEQ ID NO:6;    quantifying an amount of STEAP-2 bound to said antibody or fragment thereof in the test sample and the normal sample; and    comparing the amount of STEAP-2 bound to said antibody or fragment thereof in the test sample and the normal sample, whereby expression levels of the STEAP-2 detected in the test sample and the normal sample are assessed.    
     
     
         46 . An method for diagnostic imaging of a tumor in a subject, comprising injecting into said subject an antibody or fragment thereof that specifically binds to an extracellular domain of STEAP-2 (SEQ ID NO:6), and detecting the level of the antibody or fragment thereof bound to STEAP-2 in said subject.  
     
     
         47 . The assay of  claim 18 , wherein the sample is from a human tissue  
     
     
         48 . The assay of  claim 47 , wherein the human tissue is prostate, bone, lymph node, lung, liver or brain.  
     
     
         49 . The method of  claim 47  wherein the binding of the antibody or fragment thereof to STEAP-2 in the sample is detected using a radioscintigraphic imaging apparatus.  
     
     
         50 . The assay of  claim 18 , wherein the sample is serum, semen, urine, bone, prostate, lymph node, lung, liver, brain, or a cell preparation.  
     
     
         51 . The method of  claim 50  wherein the binding of the antibody or fragment thereof to STEAP-2 in the sample is detected using fluorescence-activated cell sorting (FACS) or ELISA.  
     
     
         52 . An assay for determining the presence of cancer in a subject, comprising detecting a significant increase in STEAP-2 (SEQ ID NO:6) mRNA or protein expression in a test cell or tissue sample relative to expression levels in the corresponding normal cell or tissue.  
     
     
         53 . A method of predicting susceptibility to developing cancer in a subject comprising: detecting STEAP-2 mRNA or STEAP-2 protein in a tissue sample, wherein the degree of STEAP-2 mRNA or STEAP-2 protein expression present is proportional to the degree of susceptibility.  
     
     
         54 . A method of gauging tumor aggressiveness in a subject comprising: determining the level of STEAP-2 mRNA or STEAP-2 protein expressed by cells in a sample of the tumor; and comparing the level so determined to the level of STEAP-2 mRNA or STEAP-2 protein expressed in a corresponding normal tissue taken from the same individual or a normal tissue reference sample, wherein the degree of STEAP-2 mRNA or STEAP-2 protein expression in the tumor sample relative to the normal sample indicates the degree of aggressiveness.