Safety has been well established at 3 times the dosages needed, 150 - 200 mg/m2. The data now shows and confirmed that the anticipated effective dose range, 200 mg/m2, can be safely administered multiple times per week.
The protocol first approved for Phase 1 with safety the primary outcome, began at 10 mg/m2 mainly because of precludes nical results across 3 species where dogs were the most sensitive to Kevetrin showing DLTs around 50 mg/m2 (equivalent). As per standard starting dose for a safety trial, the initiating dose was 1/5 the lowest safe dose administered across 3 species. At the onset of the trial, there was no way to determine whether or not the drug could reach the anticipated dose range, and in fact ran into side effect problems in the early cohorts, side effects that required treatment.
I suspect that the PK/PD data at doses above 500 mg/m2 suggest that multiple, long exposures to Kevetrin can be administered above 300 mg/m2 with highest efficacy, which is something they could not have confirmed until these last two dozen patients. Confirming data in safety trials is much more than seeing data repeated in two cohorts of 3 patients.