We learned from the human studies that the duration of adequate levels of exposure of DT-216 was much shorter than expected. While we knew that the drug was short-lived in plasma. Human studies showed by muscle biopsy that it was also short-lived in tissue and that what you observe in plasma is predictive of what is observed in tissue.
The tissue levels from human muscle biopsies were approximately only eight to 10 nanomolar at day two, and the drug was almost gone with levels of one nanomolar by day seven. Well, despite that, there was a clear increase in frataxin expression observed in treated patients in a dose dependent fashion with one patient frataxin level, going to clinically normal carrier levels as shown in the right. However, the effect was transient because the drug exposure was transient, so we needed to develop a new drug product that could sustain this drug exposure. While the drug was generally well tolerated, there were injection site thrombophlebitis events observed, which limited the frequency and levels of dosing with the prior product candidate. Nonclinical studies showed that these reactions were attributable to the formulation excipients in the drug product.
We have now conducted new non GLP animal studies with DT-216P2, which lead us to believe that these issues have now been solved and we can progress to confirmatory GLP studies to get back into the clinic. Furthermore, this new drug product appears suitable for IV administration, compatible with injections or infusions, peripheral or central, and also appears suitable for a subcutaneous route of administration. As we showed in the beginning, the new drug product, DT-216P2 has a much more sustained exposure profile as seen in the single dose ID PK curve from non-human primates.
