Molecular mechanism of action of the flavanone pinostrobin from Cajanus cajan leaves in cancer cells

We have earlier reported the in-vitro cytotoxic effect of the methanol extract of Cajanus cajan (L.) Millsp. (Leguminosae) and three of its constituents on some solid tumour cell lines.¹ Pinostrobin, one of these constituents, is now reported to show significant inhibition in a cell proliferation assay using human CCRF-CEM leukaemia cells. The IC₅₀ value obtained in an XTT assay was 5.0µM. Additionally, the compound was tested against the multi-drug resistant subline, CEM/ADR5000, where we observed a cross-resistance with the MDR cells. It arrested the migration of cells into the G₁ phase of the cell cycle which could be demonstrated in a flow cytometry study. The compound also generated reactive oxygen species (ROS) in the ROS assay. The damage of the mitochondria membrane has been known to play a key role in apoptosis, hence we measured the effect of pinostrobin on its membrane potential (ΔΨm): it was intact. We further confirmed the mechanism behind the observed massive apoptosis by measuring its impact on the Fas receptors (Apo 1 or CD95), an important molecule of the extrinsic pathway of apoptosis. There was significant dose-dependent upregulation of the Fas receptors which explained the observed apoptosis. Significant accumulation of the compound in the cytosol after 2h incubation when assessed by auto-fluorescence assay was also found. Our findings lend support to the local use of C. cajan in prevention and therapy of cancer. An in-vivo study of pinostrobin in leukaemia subjects is suggested.

Acknowledgements: JSA thanks the Commonwealth Scholarship Commission and King's College London, United Kingdom for their financial support.

Reference: 1. Ashidi J.S. et al. (2006), Planta Med. 72:P016.