Immunoselection of Breast and Ovarian Cancer Cells with Trastuzumab and Natural Killer Cells: Selective Escape of CD44high/CD24low/HER2low Breast Cancer Stem Cells

Abstract

Although trastuzumab (Herceptin) has substantially improved the overall survival of patients with mammary carcinomas, even initially well-responding tumors often become resistant. Because natural killer (NK) cell-mediated antibody-dependent cell-mediated cytotoxicity (ADCC) is thought to contribute to the therapeutic effects of trastuzumab, we have established a cell culture system to select for ADCC-resistant SK-OV-3 ovarian cancer and MCF7 mammary carcinoma cells. Ovarian cancer cells down-regulated HER2 expression, resulting in a more resistant phenotype. MCF7 breast cancer cells, however, failed to develop resistance in vitro. Instead, treatment with trastuzumab and polyclonal NK cells resulted in the preferential survival of individual sphere-forming cells that displayed a CD44 high CD24 low ''cancer stem cell-like'' phenotype and expressed significantly less HER2 compared with non-stem cells. Likewise, the CD44 high CD24 low population was also found to be more immunoresistant in SK-BR3, MDA-MB231, and BT474 breast cancer cell lines. When immunoselected MCF7 cells were then re-expanded, they mostly lost the observed phenotype to regenerate a tumor cell culture that displayed the initial HER2 surface expression and ADCCsusceptibility, but was enriched in CD44 high CD24 low cancer stem cells. This translated into increased clonogenicity in vitro and tumorigenicity in vivo. Thus, we provide evidence that the induction of ADCC by trastuzumab and NK cells may spare the actual tumor-initiating cells, which could explain clinical relapse and progress. Moreover, our observation that the ''relapsed'' in vitro cultures show practically identical HER2 surface expression and susceptibility toward ADCC suggests that the administration of trastuzumab beyond relapse might be considered, especially when combined with an immunestimulatory treatment that targets the escape variants. [Cancer Res 2009;69(20):8058-66]

Understanding cancer stem cell heterogeneity and plasticity

“…Most current anti-cancer therapeutics primarily target either differentiated or proliferating cancer cells, and, conceivably, will not be effective against undifferentiated cells that are mostly quiescent. Indeed, multiple lines of evidence have demonstrated that CSCs are more resistant to chemotherapeutics, radiation, and immunotherapy [124,144,145] and are endowed with enhanced ability to metastasize [146]. Moreover, many anti-cancer therapies may enrich CSCs [124,147], perhaps partially by inducing dedifferentiation ( Figure 5D).…”

Oncogenes and Tumor Suppressor Genes

“…The CD29 hi CD24 med cancer stem cells in tumors developed in WAPCre c Brca1 D11 p53 D5&6 mice expanded in cisplatin-refractory tumors (Shafee et al 2008). In several breast cancer cell lines, expansion of CD44 hi CD24 med cells was associated with herceptin resistance (Reim et al 2009). Strategies to target specific pathways required for the maintenance of cancer stem cells are being developed.…”

Cancer Cells with Stem Cell-Like Phenotypes and Liver Metastasis from Colon Carcinoma

“…These variant isoforms are expressed in many different organs and have been strongly linked to tumor progression behaviors in various cancers [41][42][43]. Expression of CD44 is widely identified in cancer stem cells in various organs, such as breast, colon, and pancreas [44][45][46]. Among these SCLC markers, CD133 and CD44, already validated as informative markers of stem cells in both primary tumors and xenografts, [24,25] have been identified in gene expression signatures whose genes have been shown to enhance cell migration and invasion activity from colon cancer to liver metastasis [47].…”