Incubation of 50 μm rosmarinic acid with B16 melanoma cells for 48 h resulted in a significant increase in melanin content and tyrosinase protein expression, the mechanism being that rosmarinic acid induces melanin synthesis by activating the PKA/CREB signaling pathway via phosphorylation (Shomirzoeva et al., 2019). Here, CREB1 is linked to melanoma.