CD44hiCD24lo mammosphere-forming cells from primary breast cancer display resistance to multiple chemotherapeutic drugs.

It has been widely suggested that mammosphere-forming cells from tumor cell lines or primary tumors represent the population of cancer stem cells (CSCs), which is supposed to lead to the failure of routine chemotherapy and the recurrence of the disease. However, it is still difficult to obtain CSCs from primary breast cancer for further investigation. We performed a modified culture system to generate mammosphere-forming cells derived from freshly isolated human breast cancer samples and the breast cancer cell line MCF-7. Cancer stem cell-like phenotypes such as CD44 and CD24 were measured by flow cytometry while alkaline phosphatase (AP) and mammaglobin (MGB1) expression was evaluated immunohistochemically. The expression levels of Klf4, Nanog, Oct4, Sox2 and mdr1 genes were analyzed by quantitative real­time PCR. Resistance to chemotherapeutic drugs was detected through the apoptosis assay upon drug treatments together with the detection of drug-resistant gene mdr1. The results revealed that we successfully obtained mammosphere­forming cells from the primary breast cancer in conditioned medium after 14 days of culture. Mammosphere-forming cells from primary breast cancer displayed a CD44hiCD24lo phenotype as well as positive AP and MGB1 reactivity. Stem cell-related genes such as Klf4, Nanog and Oct4 were detectably expressed in these cells. These cells formed tumor-like structures in the lymph nodes of nude mice, which were morphologically and histologically similar to breast cancer. Compared to the breast cancer cell line MCF-7 or mammosphere-forming cells from MCF-7 cells, the mammosphere-forming cells from the primary breast cancer exhibited resistance to three of four first-line chemotherapeutic drugs investigated through the induction of apoptosis, which was largely associated with the increased expression of drug-resistant gene mdr1 upon drug treatment. In conclusion, mammosphere-forming cells generated from the primary breast cancer exhibit CSC-like properties together with multiple drug resistance. Determination of the sensitivity of these primary cancer-derived mammosphere-forming cells to chemotherapeutic drugs may thus provide useful instructions for individualized therapy against the recurrence of breast cancer in the future.