Proportion of Tumor Initiating Cells Contributes to Chemotherapeutic Resistance of Breast Cancers.

Abstract

Abstract Background: The mechanisms determining chemotherapeutic resistance of breast cancers are rather complicated with a variety of molecules involved. While targeting one single molecule or one signaling pathway are not sufficient to reverse chemo-resistance. Therefore, it is more important to identify and eliminate the subpopulations of tumor cells that are resistant to chemotherapy. Recently, accumulating evidence demonstrates that a wide variety of malignancies may be driven by a small subset of “tumor-initiating cells (T-ICs) displays a variety of drug-resisting mechanisms. Nevertheless, it remains obscure whether the proportion of breast tumor initiating cells (BT-ICs) correlates with chemotherapeutic sensitivity of breast cancers, and whether targeting BT-ICs may help to reverse chemo-resistance in the malignancy.Material and Methods: Using immunohistochemistry, we tested the expression level of ALDH1 in 192 human breast cancer samples before underwent neoadjuvant chemotherapy and analyzed the relationship between the ALDH1 level and clinical pathological features including clinical response and disease free survival (DFS). We tested the proportion of CD44+/CD24-, ALDH1+ and side population in primary cancer cells, wide type MCF7 and Adriamycin resistant (AdrR) MCF-7 by FACS. Compared the mammosphere formations in suspension culture. We further tested the drug sensitivity after treated with 1UM Lapatinib in AdrR MCF-7 mammospheric cells by MTT and AnnexinV staining. Results: In all 192 cases, there were 19.79% (38 of 192) cases with high ALDH1 expression (>20% positive cancer cells) compared to 80.21% (154 of 192) cases with low expression (≤20% positives cells). The clinical response (PR and cCR) was only 52.63%% (20 of 38) in patients with high ALDH1 expression compared with 81.17% (125 of 154) in patients with low ALDH1 expression (x2=15.926; P=0.000). Patients with low ALDH1expression survived significantly longer than those with high ALDH1 expression (P = 0.006). In primary cancer cells, the percentage of ALDH1+ and CD44+/CD24-cells were up to 8.72% ±3.73% and 36% ±7.9% in the PD samples respectively, whereas only 1.42%±1.63% and 3.17 ±0.45% in PR samples (p=0.037 and 0.018). Moreover, mammosphere formation of primary human breast cancer cells was 10-20 fold higher in PD samples than in PR samples (p=0.01). Then we compared the proportion of BT-ICs between two breast cancer cell lines. The mammoshpere formation rate of the AdrR MCF-7 increased to 9.1%±1.01% compared with 1.03%±0.15% in the parent MCF-7 breast cancer cell (p=0.0046), meanwhile, the percentage of CD44+/CD24- cells was much higher in the AdrR MCF-7 cells(64.85%±1.3% vs than 1.3%±0.1%,p=0.01), the proportion of ALDH1+ cells was 15.9%±1.5% to 2.7%±0.3% (p=0.01),as well as the percentage of side population was 10.8%±1.4% to.0.25%±0.05% (p=0.001).After treated with Lapatinib, the sensitivity of passaged mammospheric AdrR MCF-7 cells to chemotherapy increased in the cell viability assay, while the dead cells increased from 50% ±2.8% to 75%±6.5% tested by FACS under chemotherapy pressure (p=012).Conclusion: Proportion of tumor initiating cells contributes to chemotherapeutic resistance of breast cancers. Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 503.