A pyrimido isoquinoline derivative represented by formula (I): wherein: R1 represents a 4-pyridine ring or a 4-pyrimidine ring; R2 represents a hydrogen atom; R3 represents a hydrogen atom; R4 represents: a hydrogen atom; a halogen atom; R7, R8, R9, R10 represent independently from each other a hydrogen atom, a halogen atom, a C 1-6 alkoxy group, a nitro, a hydroxyl or an amino; represents a single or a double bond, in form of a free base or of an addition salt with an acid. The compounds of formula (I) are GSK3 inhibitors which are useful in the treatment of various diseases such as cancer, neurodegenerative disorders or diabetes.