Sclerotium rolfsii Lectin Induces Stronger Inhibition of Proliferation in Human Breast Cancer Cells than Normal Human Mammary Epithelial Cells by Induction of Cell Apoptosis

Sclerotium rolfsii lectin (SRL) isolated from the phytopathogenic fungus Sclerotium rolfsii has exquisite binding specificity towards O-linked, Thomsen-Freidenreich (Galβ1-3GalNAcα1-Ser/Thr, TF) associated glycans. This study investigated the influence of SRL on proliferation of human breast cancer cells (MCF-7 and ZR-75), non-tumorigenic breast epithelial cells (MCF-10A) and normal mammary epithelial cells (HMECs). SRL caused marked, dose-dependent, inhibition of proliferation of MCF-7 and ZR-75 cells but only weak inhibition of proliferation of non-tumorigenic MCF-10A and HMEC cells. The inhibitory effect of SRL on cancer cell proliferation was shown to be a consequence of SRL cell surface binding and subsequent induction of cellular apoptosis, an effect that was largely prevented by the presence of inhibitors against caspases -3, -8, or -9. Lectin histochemistry using biotin-labelled SRL showed little binding of SRL to normal human breast tissue but intense binding to cancerous tissues. In conclusion, SRL inhibits the growth of human breast cancer cells via induction of cell apoptosis but has substantially less effect on normal epithelial cells. As a lectin that binds specifically to a cancer-associated glycan, has potential to be developed as an anti-cancer agent

SRL histochemistry to normal and cancerous human breast tissues.

<p>SRL histochemistry was performed in human breast (normal, primary cancer and metastatic) tissue samples. SRL shows weak binding to normal human breast tissues but strong binding to primary cancer and metastatic breast tissues. All the images were obtained with 100X magnification. Arrows point to SRL binding to apical surface of the secretory gland epithelia. Representative images of both Haematoxylin-Eosin and Biotin-SRL staining are shown. SRL binding was evaluated through optical analysis by measuring the mean area of stained cells scored arbitrarily as intense (+++), moderate (++), light (+) and no staining (−).</p

Effect of SRL on proliferation of non-tumorigenic and normal human breast epithelial cells.

<p>(<b>A and B</b>) Non-tumorigenic MCF-10A and normal HMECs were incubated with different concentrations of SRL in serum free media for different time intervals (24, 48 and 72 h for MCF-10A) and 48 h (HMECs). Cell proliferation was measured using Calcein AM and MTT for MCF-10A and HMEC respectively. The experiments were carried out in triplicate, and the data were expressed as Mean ± SD percentage of control. *p<0.05; ***p<0.001.</p

SRL inhibits proliferation of human breast cancer cells.

<p>(<b>A</b>). SRL causes dose-dependent inhibition of human breast cancer MCF-7 and ZR-75 cell proliferation. The cells were incubated with or without different concentrations of SRL for 72 h. SRL-mediated cell growth inhibition is prevented by the presence of TF-expressing glycoprotein: MCF-7and ZR-75 cells were incubated with or without 20 µg/ml SRL in the presence of 100 µg/ml asialo bovine submaxillarymucin (aBSM) for 72 h. SRL caused time-dependent inhibition of MCF-7 cell proliferation. (<b>B</b>). The MCF-7 cells were incubated with or without different concentrations of SRL, BSA (40 µg/ml) and TBS for 24, 48 and 72 h before cell proliferation was assessed. Data represent Mean ±SD of triplicate determinations from three different assessments. *p<0.05; ***p<0.001.</p