Molecular mechanism of inhibitory effects of C-phycocyanin combined with all-trans-retinoic acid on the growth of HeLa cells in vitro.

We studied the effects of all-trans-retinoic acid (ATRA), C-phycocyanin (C-PC), or ATRA+C-PC on the growth of cervical cells (HeLa cells), cell cycle distribution, and apoptosis. The anticancer mechanism of the drug combination was revealed. MTT assay was adopted to determine the effects of C-PC and ATRA on the growth of HeLa cells. The expression quantities of cyclin-dependent kinase (CDK) 4, cyclin D1, Bcl-2, caspase-3, and CD59 were determined by in situ hybridization, immunofluorescence, immunohistochemistry staining, Western blot, and RT-PCR. TUNEL assay was adopted to determine the cellular apoptosis levels. Both C-PC and ATRA could inhibit the growth of HeLa cells, and the combination of ATRA+C-PC functioned cooperatively to induce apoptosis in HeLa cells. The dosage of ATRA was reduced when it cooperated with C-PC to reduce the toxicity. ATRA treated with C-PC could induce more cell cycle arrests than the single drug used by decrease in cyclin D1 and CDK4 expression. The combination of the two drugs could upregulate caspase-3 and downregulate the Bcl-2 gene and induce cell apoptosis. Moreover, the combination therapy has an important immunological significance in decreased expression of the CD59 protein. Singly, C-PC or ATRA could inhibit the growth of HeLa cells, and the effects of treatment were further enhanced in the combination group. In combination with C-PC, the dosage of ATRA was effectively reduced. The C-PC + ATRA combination might take effect by inhibiting the progress of the cell cycle, inducing cell apoptosis and promoting complement-mediated cytolysis.