Moleculin's Annamycin hits 3x control CR rate in R/R AML interim
Moleculin Biotech has reported encouraging interim efficacy data from Part A of its pivotal Phase 2/3 MIRACLE trial, showing that both Annamycin dose arms substantially outperformed the control arm in patients with relapsed or refractory acute myeloid leukaemia (R/R AML).
The interim analysis, conducted across the first 45 patients enrolled and assessed on a full intent-to-treat basis, found complete remission (CR) rates of 43% and 36% for the 190 mg/m² and 230 mg/m² Annamycin plus high-dose cytarabine (HiDAC) cohorts respectively, against 12% for the HiDAC control arm. Composite complete remission rates reached 50% and 57% in the two Annamycin arms, versus 29% for control. All responses were assessed after a single treatment cycle, as required by the MIRACLE protocol design.
Trial context and caveats
The Independent Data Monitoring Committee (iDMC) conducted the interim review and unanimously recommended continuing the trial, noting a strong numeric trend in favour of both Annamycin arms. However, it also confirmed that formal statistical significance was not achieved at this stage. Moleculin was clear that this was expected: the trial uses an O'Brien-Fleming group-sequential spending function that deliberately reserves the bulk of its statistical budget for the planned final analysis in approximately 282 subjects. The trial retains 80% power to detect a difference in CR rates of 20% in the control arm versus 35% in the test arm at final readout.
The iDMC also declined to drop either Annamycin dose arm, citing insufficient differentiation between the two cohorts. Part A, which is designed to identify the optimal dose before the pivotal Part B begins, has enrolled 67 of a targeted 90 patients. Walter Klemp, chairman and chief executive of Moleculin, described the data as "the strongest clinical validation of Annamycin we have seen to date" and noted that achieving meaningful remission rates in venetoclax-pretreated patients, who comprised 31% of the cohort, is particularly difficult in this setting.
Moleculin cautioned that cross-trial comparisons should be made carefully. Frequently cited historical benchmarks such as the MIRROS and CLASSIC I studies permitted multiple treatment cycles, whereas MIRACLE specifies a single-cycle assessment for this interim look. The company argues the most meaningful comparison is therefore the relative performance of Annamycin versus the concurrent randomised control arm evaluated under identical conditions.
Competitive landscape and regulatory path
R/R AML remains one of haematology's most challenging indications, with a high proportion of patients who relapse after or are refractory to standard induction regimens. Several agents have received regulatory approval in this setting, including gilteritinib for FLT3-mutant disease, enasidenib and ivosidenib for IDH-mutated patients, and venetoclax-based combinations in the frontline. Most approved second-line options serve genetically defined subpopulations, leaving a gap for broadly applicable salvage regimens in unselected R/R AML.
Annamycin is an anthracycline reformulated to avoid multidrug resistance mechanisms and, the company says, to lack the cardiotoxicity associated with standard anthracyclines such as daunorubicin and idarubicin. If that profile holds at scale, it could offer a meaningful differentiator, since cardiac toxicity limits cumulative anthracycline exposure in many AML patients. Moleculin says the development pathway has been substantially shaped by prior FDA input following its Phase 1b/2 MB-106 study.
The company now needs to complete Part A enrolment, select the optimal dose, and carry Part A efficacy data forward into the Part B pivotal analysis. Moleculin disclosed in the release that it will require significant additional financing to complete the programme and has no committed funding in place, a material risk that investors will weigh against the encouraging interim signal.