Heidelberg Pharma has reported further clinical activity from its Phase 1/2a study evaluating HDP-101 (pamlectabart tismanitin) in patients with relapsed or refractory multiple myeloma, with evidence of stringent complete remissions observed in Cohort 8.

The company said two patients achieved stringent complete remission (sCR) at a dose of 140 µg/kg, with no tumour cells detectable in blood or bone marrow. Across the cohort of seven evaluable patients, HDP-101 continued to show a favourable safety and tolerability profile, with no dose-limiting toxicities reported.

Four patients showed signs of biological activity, including one partial response, one very good partial response and two stringent complete remissions. The findings mark the strongest clinical activity seen so far in the study and follow an earlier complete remission observed in Cohort 5.

Dr András Strassz, chief medical officer at Heidelberg Pharma, said: “We are very delighted by the data seen so far. Several patients across different cohorts have shown objective responses and promising anti-tumour activity. Observing two stringent complete remissions is an encouraging validation of our therapeutic approach. We have previously seen complete remission in one patient from Cohort 5, but in Cohort 8 onset of the response was more rapid.”

He added that the results “further strengthen our confidence in the therapeutic potential of HDP-101 in heavily pretreated patients with relapsed or refractory multiple myeloma” as the company advances to Cohort 9 with an escalated dose of 175 µg/kg.

The ongoing open-label, dose-escalation trial is evaluating the safety, tolerability, pharmacokinetics and preliminary efficacy of HDP-101 in patients with relapsed or refractory multiple myeloma or other BCMA-expressing plasma cell disorders.