Annamycin MIRACLE Trial: High-Stakes Interim Catalyst With No Disclosed Efficacy Data to Anchor It

Moleculin Highlights Interim MIRACLE Trial Results at Conference

Moleculin Biotech, Inc. announced its participation in the Virtual Investor “Why Now” on-demand conference, where CEO Walter Klemp highlighted the company's clinical progress. He discussed encouraging interim results from the pivotal Phase 2/3 MIRACLE trial, evaluating Annamycin for relapsed or refractory acute myeloid leukemia (AML). The presentation also covered Annamycin's differentiated clinical profile, ongoing enrollment, expanding commercial opportunities, and the upcoming 90-patient interim analysis, which is a key catalyst for potential registration.

• Moleculin Biotech's CEO, Walter Klemp, presented at the Virtual Investor “Why Now” on-demand conference, focusing on the company's clinical advancements and future prospects. The presentation specifically highlighted the encouraging interim data from the pivotal Phase 2/3 MIRACLE trial, which is investigating Annamycin for relapsed or refractory acute myeloid leukemia (AML).
• The MIRACLE trial (MB-108) is an adaptive design, multi-center, randomized, double-blind, placebo-controlled Phase 2/3 study. It evaluates Annamycin in combination with cytarabine (AnnAraC) for relapsed or refractory AML. The company believes the development pathway for Annamycin in AML is substantially de-risked following a successful Phase 1B/2 study and FDA input.
• Annamycin, also known as naxtarubicin, is an anthracycline designed to overcome multidrug resistance mechanisms and avoid the cardiotoxicity often associated with other anthracyclines. Beyond AML, Annamycin is also in development for soft tissue sarcoma (STS) lung metastases, showcasing its potential broad applicability in hard-to-treat tumors.

The Unmet Need in Relapsed or Refractory AML

Relapsed or refractory (R/R) AML continues to represent one of the most therapeutically intractable settings in oncology, with outcomes remaining dismal despite recent advances. A Danish nationwide study reported a median overall survival of just 9.3 months and an estimated 1-year overall survival of 34% across R/R AML patients, underscoring the substantial unmet need that persists even in the era of targeted therapies.

• Limited durability of salvage regimens: Conventional chemotherapy offers marginal survival benefit in the R/R setting, and even venetoclax-based salvage approaches — despite producing high initial response rates — yield responses of limited duration for most patients, failing to translate into sustained disease control.

• Venetoclax resistance driven by molecular and phenotypic features: Resistance to venetoclax is multifactorial, encompassing mutations in BCL-2 or pro-apoptotic proteins, increased MCL-1 dependency, and metabolic reprogramming toward glycolysis and fatty acid oxidation. Clinically, decreased venetoclax sensitivity is associated with FLT3-ITD, TP53, K/NRAS, and PTPN11 mutations, as well as a monocytic AML phenotype and prior hypomethylating agent exposure.

• Emergent resistance to FLT3 inhibition: Gilteritinib is not curative, and progression is frequently driven by treatment-emergent mutations activating RAS/MAPK signaling — most commonly in NRAS or KRAS — as well as secondary FLT3-F691L gatekeeper mutations or BCR-ABL1 fusions. Notably, the F691L gatekeeper mutation confers universal resistance to all currently approved FLT3 inhibitors.

• TP53-mutated AML remains refractory to available strategies: TP53-mutant AML is characterized by high rates of primary and acquired resistance to venetoclax-based combinations, with the addition of venetoclax to azacitidine providing no overall survival benefit in this genetically defined subgroup — reflecting the profound treatment resistance conferred by loss of p53 function.

• Post-transplant relapse carries an especially poor prognosis: Relapse following allogeneic hematopoietic stem cell transplantation (allo-HSCT) — including rare extramedullary manifestations that frequently precede systemic relapse — represents a major clinical challenge, as the feasibility of further therapeutic intervention is severely constrained in this setting, resulting in very poor outcomes.

Annamycin's Differentiated Safety Profile and MDR Avoidance

Published safety and tolerability data for annamycin derive primarily from a phase I/II multicenter, open-label study conducted in adult patients with relapsed/refractory acute lymphoblastic leukemia (ALL). Across 31 enrolled patients, the maximum tolerated dose (MTD) was established at 150 mg/m²/day administered over 3 consecutive days. The MTD-determining toxicity was mucositis, with 3 cases of grade 3 severity observed at this threshold. Additional grade 3 adverse events included isolated cases of diarrhea, typhlitis, and nausea, along with tumor lysis syndrome — a pharmacodynamically expected event in this heavily pretreated hematologic malignancy population.

Overall, single-agent nanomolecular liposomal annamycin was characterized as well tolerated at therapeutic dose levels. The adverse event profile, defined principally by manageable gastrointestinal and mucosal toxicities rather than dose-limiting cardiotoxicity, is notably relevant given the class-effect cardiotoxicity concerns associated with conventional anthracyclines. This tolerability signal supports the continued clinical development of annamycin in patient populations where anthracycline re-exposure would otherwise be constrained by cumulative cardiac risk.

The tolerability data are further contextualized by meaningful clinical activity observed in the phase IIA portion of the study. Among 10 patients enrolled, 8 completed at least one cycle at the MTD, and 5 of these (62%) demonstrated efficacy signals including complete clearance of circulating peripheral blasts. Three of these patients additionally achieved clearance of bone marrow blasts, with one proceeding to successful stem cell transplantation — underscoring that clinically relevant responses were achieved within a tolerable dosing framework as a single agent in refractory adult ALL.

Unpacking the Pivotal MIRACLE Trial Design and Endpoints

The pivotal trials in relapsed or refractory (R/R) AML have employed distinct design paradigms — ranging from randomized controlled comparisons to single-arm cohort studies — reflecting both the heterogeneity of the patient population and the targeted nature of the agents investigated. Across FLT3- and IDH1-mutated R/R AML, trial endpoints have consistently centered on composite remission rates, response durability, transfusion independence, and overall survival.