EHA 2025 | The ongoing Phase I/IIa trial investigating HDP-101, a novel antibody-drug conjugate, in myeloma

I’m very excited about this poster. It is a first in human drug. It’s a novel antibody-drug conjugate targeting BCMA in multiple myeloma cells. It is linked to a synthetic payload, amanitin, so it’s a different payload from the other ADCs. It’s a Phase I/IIa looking at this particular drug and its safety, tolerability, and of course efficacy in multiple myeloma, and so primarily we’re focused on finding the maximum tolerated dose or the recommended Phase II dose for this drug. 

We’ve been through the first several cohorts, the earlier dose levels, which have been shown to be quite safe. Activity levels have been at the higher doses, so starting at 90 micrograms per kilogram, we’re actually seeing activity. Cohort 5 was a dose of 100 micrograms per kilogram, we actually had a 50% response rate on that, and there was one patient who currently continues to remain on therapy at 19 months plus of therapy with stringent complete remission, so we’re very excited about the activity that we are seeing. 

What we did notice was at these higher dose levels, there was significant thrombocytopenia and some liver function test abnormalities. So the subsequent cohorts are now testing either split dosing or dosing with pre-medication. And we’re finding that both of these maneuvers have been effective in mitigating the toxicity. We are now testing higher dose levels with these strategies of pre-medication and split-level dosing. And we are at cohort 8, which is currently enrolling at 140 micrograms per kilogram.

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