For the combination experiments, when cells treated with All-trans retinoic acid (ATRA) combined with C-phycocyanin, the IC ₅₀ value is lower than that in ATRA group. But under the same IC ₅₀ , the more C-phycocyanin is used, the less ATRA is needed. Results demonstrate that C-phycocyanin combined with ATRA can significantly decrease CDK-4 mRNA level (P<0.05). The combination index (CI) value of the C-phycocyanin+ATRA combination group is 0.852 which is less than 1, indicating that the two drugs are synergetic under the action concentration (88 μg/L C-phycocyanin+0.102 mM ATRA). Compare with control group, the Integrated optical density (IOD) in C-phycocyanin or ATRA treated group is increased, and the differences are statistically significant (P<0.05) and the differences are further exaggerated in combination group (P<0.01). The expression of caspase-3 in C-phycocyanin group is more than that in the control group but is similar to that in ATRA group, whereas the expression in combination group is maximum.

Compare with control group, the average tumor weights of mice in solely C-phycocyanin or ATRA treatment groups are significantly decreased, and further reduced in C-phycocyanin+ATRA synergy group. Results show that single C-phycocyanin can increase the spleen weight of mice but the effects of ATRA are just opposite. C-phycocyanin can also promote the growth of immune organs in mice and increase the body's immune function. C-phycocyanin and ATRA alone can significantly inhibit Cyclin D1 expression, and when being combined, the inhibitory effect is more obvious.