The prodrugs are very different as far as MoA. The are similar in the fact they use a well accepted chemo agent as the active drug (alkylator) Telcyta was a flop because of the toxicity of the drug to tissue that wasnt a tumor. Telcyta was activated by glutathione S-transferase which is present in enough healthy tissue to have caused the problems with toxicity in the phase 3 trials for TELK. So it was the MoA rather then the active drug that was the issue for TELK. It killed cancer - just killed everything else around it too.
So the problem with TELK's drug Telcyta wasn't the payload it was the guidance system. The just needed a MoA that was more selective. Now you can possibly argue that HAP as far as a MoA is garbage - but the problem won't be with the prodrug as much as the delivery method to tissue that is a tumor.
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