An antimetabolite and a chlorine derivative of the intracellular secondary messenger, cyclic adenosine 3,5-monophosphate (cAMP), with potential antineoplastic activity. Tocladesine appears to be converted to 8-chloro-adenosine by phosphodiesterases and subsequently phosphorylated to 8-chloro-ATP, which functions as a purine analogue and competes with ATP in transcription. In addition, generation of 8-chloro-ATP depletes endogenous ATP pool that is essential for many biological reactions in intracellular energy transfer. As a result, this agent causes RNA synthesis inhibition, blocks cellular proliferation, and induces apoptosis.