Anthracycline/taxane-based chemotherapy is frequently used to treat breast cancer. However, not all patients respond to chemotherapy due to naturalor acquired chemo-resistance. Glutathione S-transferase P1(GSTP1), which belongs to the family of phase II metabolic enzymes, has been reported to function in detoxifying several anti-cancer drugs by conjugating them with glutathione.
We identified GSTP1 as a drug-resistance-related factor by microarray. Then, we used cell apoptosis and immunofluorescence staining to confirm the ability of GSTP1-containing exosomes in conferring drug resistance. And the knockdown of GSTP1 gene was performed to found the influence of drug-resistance. Furthermore, the role of GSTP1 and its relationship with exosomes was proved by analysed 40 pairs of breast cancer tissues by IHC. Then, the levels of GSTP1 in serum exosomes were detected in 28 patients treated with neoadjuvant chemotherapy(NAC).
By microarray data, we found that GSTP1, which located in extracellular exosome, is higher in Adriamycin(ADR)-resistant cell line compared with its parental cell line. Then, we also confirmed a higher expression of GSTP1 protein in ADR-resistant cells by immunofluorescence staining and western blot. Moreover, the addition of GSTP1-containing exosomes can increase the resistance to ADR in sensitive cells. Also, we found that a higher expression GSTP1 in the PD/SD group than in the PR/CR group in 40 paired samples collected before and after chemotherapy. Similar results were obtained for the exosomal marker tumor susceptibility gene 101 protein (TSG101), which also increased in the cytoplasm after chemotherapy. We further explored the levels of GSTP1 in serum exosomes of 28 patients treated with anthracycline/taxane-based NAC, and discovered that the levels of GSTP1 in exosomes from patients in the PD/SD group were higher than those in the PR/CR group.
GSTP1-containing exosomes appeared to be essential in conferring resistance to anti-cancer drugs. We explored the predictive role of GSTP1 in circulating exosomes as a biomarker for chemo-sensitivity in patients treated with anthracycline/taxane-based chemotherapy.
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All authors have declared no conflicts of interest.