Cyclic GMP- 13 C, 15 N 2 is 13 C and 15 N labeled Cyclic GMP. Cyclic GMP (cGAMP) is an endogenous second messenger that triggers interferon production in response to cytoplasmic DNA. Cyclic GMP activates the stimulator of interferon genes ( STING ), activating a signaling cascade that leads to the production of type I interferons and other immune mediators.