Human endogenous retrovirus type K antibodies and mRNA as serum biomarkers of early-stage breast cancer.

A simple and accurate test to detect early-stage breast cancer has not been developed. Previous studies indicate that the level of human endogenous retrovirus type K (group HERV-K(HML-2)) transcription may be increased in human breast tumors. We hypothesized that HERV-K(HML-2) reactivation can serve as a biomarker for early detection of breast cancer. Serum samples were collected from women without cancer (controls) and patients with ductal carcinoma in situ (DCIS) and invasive breast cancer. ELISA assays were used to detect serum anti-HERV-K(HML-2) antibody titers. RNA was extracted from sera and analyzed by real-time RT-PCR to quantitate the level of HERV-K(HML-2) mRNA. We measured significantly higher serum mRNA and serum antibody titers against HERV-K(HML-2) proteins in women with DCIS and stage I disease than in women without cancer. At optimized cutoffs for the antibody titers, the assay produced an area under the receiver operating characteristic curve (AUC) of 0.89 (95% confidence interval 0.77-1.00) for DCIS and of 0.95 (95% confidence interval 0.89-1.00) for invasive breast cancer. These AUCs are comparable to those observed for mammograms. We also found that serum HERV-K(HML-2) mRNA tended to be higher in breast cancer patients with a primary tumor who later on developed the metastatic disease than in patients who did not develop cancer metastasis. Our results show that HERV-K(HML-2) antibodies and mRNA are already elevated in the blood at an early stage of breast cancer, and further increase in patients who are at risk of developing a metastatic disease.

Immunotherapeutic potential of anti-human endogenous retrovirus-K envelope protein antibodies in targeting breast tumors.

BACKGROUND: The envelope (env) protein of the human endogenous retrovirus type K (HERV-K) family is commonly expressed on the surface of breast cancer cells. We assessed whether HERV-K env is a potential target for antibody-based immunotherapy of breast cancer. METHODS: We examined the expression of HERV-K env protein in various malignant (MDA-MB-231, MCF-7, SKBR3, MDA-MB-453, T47D, and ZR-75-1) and nonmalignant (MCF-10A and MCF-10AT) human breast cell lines by immunoblot, enzyme-linked immunosorbent assay, immunofluorescence staining, and flow cytometry. Anti-HERV-K env monoclonal antibodies (mAbs; 6H5, 4D1, 4E11, 6E11, and 4E6) were used to target expression of HERV-K, and antitumor effects were assessed by quantifying growth and apoptosis of breast cancer cells in vitro, and tumor growth in vivo in mice (n = 5 per group) bearing xenograft tumors. The mechanisms responsible for 6H5 mAb-mediated effects were investigated by microarray assays, flow cytometry, immunoblot, and immunofluorescence staining. The expression of HERV-K env protein was assessed in primary breast tumors (n = 223) by immunohistochemistry. All statistical tests were two-sided. RESULTS: The expression of HERV-K env protein in malignant breast cancer cell lines was substantially higher than nonmalignant breast cells. Anti-HERV-K-specific mAbs inhibited growth and induced apoptosis of breast cancer cells in vitro. Mice treated with 6H5 mAb showed statistically significantly reduced growth of xenograft tumors compared with mice treated with control immunoglobulin (control [mIgG] vs 6H5 mAb, for tumors originating from MDA-MB-231 cells, mean size = 1448.33 vs 475.44 mm(3); difference = 972.89 mm(3), 95% CI = 470.17 to 1475.61 mm(3); P < .001). Several proteins involved in the apoptotic signaling pathways were overexpressed in vitro in 6H5 mAb-treated malignant breast cells compared with mIgG-treated control. HERV-K expression was detected in 148 (66%) of 223 primary breast tumors, and a higher rate of lymph node metastasis was associated with HERV-K-positive compared with HERV-K-negative tumors (43% vs 23%, P = .003). CONCLUSION: Monoclonal antibodies against HERV-K env protein show potential as novel immunotherapeutic agents for breast cancer therapy.