If you are searching for "cracked" PSP ISOs, you likely already have Custom Firmware (CFW) installed. While you cannot play GTA 4, the PSP modding scene gave us something arguably more impressive:
: Rockstar Games only released GTA 4 for PC, PlayStation 3, and Xbox 360. The only GTA titles officially on PSP are Liberty City Stories Vice City Stories Chinatown Wars Security Risks psp iso club gta 4 cracked