C-Phycocyanin (C-PC), the major light harvesting biliprotein from Spirulina 
platensis is of greater importance because of its various biological and 
pharmacological properties. It is a water soluble, non-toxic fluorescent protein 
pigment with potent anti-oxidant, anti-inflammatory and anti-cancer properties. 
In the present study the effect of highly purified C-PC was tested on growth and 
multiplication of human chronic myeloid leukemia cell line (K562). The results 
indicate significant decrease (49%) in the proliferation of K562 cells treated 
with 50 microM C-PC up to 48 h. Further studies involving fluorescence and 
electron microscope revealed characteristic apoptotic features like cell 
shrinkage, membrane blebbing and nuclear condensation. Agarose electrophoresis 
of genomic DNA of cells treated with C-PC showed fragmentation pattern typical 
for apoptotic cells. Flow cytometric analysis of cells treated with 25 and 50 
microM C-PC for 48 h showed 14.11 and 20.93% cells in sub-G0/G1 phase, 
respectively. C-PC treatment of K562 cells also resulted in release of 
cytochrome c into the cytosol and poly(ADP) ribose polymerase (PARP) cleavage. 
These studies also showed down regulation of anti-apoptotic Bcl-2 but without 
any changes in pro-apoptotic Bax and thereby tilting the Bcl-2/Bax ratio towards 
apoptosis. These effects of C-PC appear to be mediated through entry of C-PC 
into the cytosol by an unknown mechanism. The present study thus demonstrates 
that C-PC induces apoptosis in K562 cells by cytochrome c release from 
mitochondria into the cytosol, PARP cleavage and down regulation of Bcl-2.