PAGR1 and melanoma: To evaluate the effects of PKG activation on melanoma cell viability we tested three monomeric cGMP analogues that acted as PKG activators, i.e. PA1 (8-pCPT-cGMP) [9], PA2 (8-Br-PET-cGMP) [9] and PA3 (8-Br-(2-N)-ET-cGMP) [26].