Preclinical development of new nucleoside-based drug against leukemia

Project Information

leuCAB

Grant agreement ID: 101188113

DOI

10.3030/101188113

Project closed

EC signature date 6 August 2024

Start date 1 September 2024

End date 28 February 2026

Funded under

• European Research Council (ERC)

Total cost

No data

EU contribution

€ 150 000,00

Coordinated by

LUDWIG-MAXIMILIANS-UNIVERSITAET MUENCHEN
Germany

Periodic Reporting for period 1 - leuCAB (Preclinical development of new nucleoside-based drug against leukemia)

Reporting period: 2024-09-01 to 2026-02-28

Summary of the context and overall objectives of the project

Blood cancers, particularly acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS), affect over 470,000 patients annually worldwide. Outcomes remain poor, above all for so-called high-risk (HR) patients, who account for approximately 40% of all AML/MDS cases. This group consists predominantly of elderly individuals with multiple co-morbidities, who face one-year survival rates below 10% for AML and approximately 35% for MDS. Intensive chemotherapy and modern immunotherapies are frequently unsuitable for these patients due to excessive toxicity, leaving hypomethylating agents (HMAs) such as decitabine (DEC) and azacitidine (AZA) as the primary and often only treatment option.

HMAs aim to change the genetic expression pattern of cancerous cells, in order to allows activation of previously silenced tumour suppressor genes, rather than killing the cell by toxic interference.

The clinical utility of current HMAs is, however, fundamentally constrained by their intrinsic chemical and enzymatic instability. This limits achievable therapeutic concentrations, necessitates frequent dosing, and results in modest response rates of only 20–30% with median response durations of 8–12 months. Treatment consequently remains largely palliative rather than curative, and there is a clear, unmet medical need for a more effective and better tolerated alternative.

The leuCAB project addresses this need by advancing Carbacitabine (CAB), a novel carbocyclic HMA developed at LMU Munich. CAB is structurally derived from DEC through a single targeted molecular modification: the replacement of the deoxyribose ring oxygen with a methylene group (CH2). This carbocyclic modification confers markedly enhanced resistance to both hydrolytic degradation and enzymatic inactivation, while fully preserving the established mechanism of action — inhibition of DNA methyltransferases (DNMTs) and reactivation of silenced tumor suppressor genes. In preclinical studies, CAB demonstrated up to 100-fold reduced hematotoxicity compared to DEC, alongside superior anti-leukemic efficacy in patient-derived xenograft (PDX) mouse models, including the capacity to overcome resistance mechanisms that render current HMAs ineffective. leuCAB was designed to consolidate this preclinical promise into a validated, commercially viable drug candidate by optimizing the lead structure, advancing synthesis scalability, establishing a regulatory roadmap, and securing the intellectual property and business development foundations required for clinical advancement.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

Lead compound optimization: A series of CAB derivatives was synthesized through structural modification of the lead compound, including phenylalanine-, isobutyl-, and PEG-chain conjugates, and assessed in vitro in AML cell lines. None of the derivatives showed meaningfully reduced activity compared to CAB, but none demonstrated a superior therapeutic profile either. The most promising candidate, a PEG-conjugate, was subsequently evaluated in a mouse toxicology study, a mouse pharmacokinetic study, and an AML-PDX efficacy trial. Results confirmed comparable but not superior performance relative to unmodified CAB, most likely because the PEG modification is rapidly cleaved in vivo. Based on these findings, unmodified CAB was confirmed as the optimal lead structure, eliminating the need for further derivative development cycles prior to clinical advancement.

Synthesis scale-up: Synthesis optimization was conducted at laboratory scale to identify and improve critical process steps, followed by engagement with a specialized contract research organization (CRO) for industrial scale-up. Key synthetic steps were significantly optimized in the process, and production capacity was successfully increased from the initial 1–5 g laboratory scale to approximately 50 g. All planned activities were completed, and the groundwork for finalizing the synthesis at industrial scale has been firmly established.

Regulatory strategy: A comprehensive regulatory roadmap for CAB's clinical development was established in collaboration with a specialized regulatory consultancy, resulting in a detailed preclinical development plan defining the studies required prior to a Clinical Trial Application (CTA). Building on this foundation, subsequent work supported by additional funding led to a successful Scientific Advice interaction with the relevant regulatory authority, which validated the proposed preclinical development approach and confirmed that CAB is on a well-defined path toward first-in-human studies.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

leuCAB positions CAB as a structurally and functionally differentiated next-generation HMA. Previous attempts to improve upon DEC, most notably guadecitabine (SGI-110), pursued a purely pharmacokinetic strategy by slowing DEC's release from a prodrug formulation. CAB's carbocyclic modification targets the fundamental source of DEC's limitations at the molecular level, conferring intrinsic chemical stability without altering the established pharmacological mechanism.

The project has delivered three interconnected results with direct translational impact.

Preclinically, CAB demonstrated consistently superior anti-leukemic efficacy across multiple genetically diverse AML-PDX models, including complete remission in approximately 50% of animals, alongside up to 100-fold reduced hematotoxicity compared to DEC and resistance-breaking activity in patient-derived AML cell lines. No derivative tested showed superiority over unmodified CAB, confirming it as the optimal lead structure. Further structural exploration may be pursued in basic research settings, but is not a prerequisite for clinical advancement.

On the synthesis side, critical process steps were significantly optimized and production capacity was scaled from gram- to 50 g-scale, demonstrating that CAB's chemical synthesis is scalable to industrial quantities. The originally targeted batch size of ≥500 g was not achieved within the project period, but was subsequently not considered necessary either: ongoing CDMO negotiations are targeting a demonstration batch of approximately 200 g to supply the planned preclinical studies, which will then serve as the direct basis for full GMP batch production for the clinical trial.

Regulatory interaction conducted on the basis of work initiated in leuCAB confirmed the proposed preclinical development strategy. This provides a precise and actionable roadmap of the remaining steps required before a first-in-human study can begin — a result with substantial impact on the efficiency and cost of the further development program.

The key needs to ensure further success are access to finance for the remaining preclinical package and the planned Phase I/IIa clinical trial, finalization of GMP-scale synthesis via a CDMO partner, and establishment of the EpiCure spin-off to enable out-licensing to a pharmaceutical partner following clinical proof of concept. IP protection is secured across key markets. The regulatory pathway is clearly defined. CAB is ready to advance toward first-in-human studies in high-risk AML and MDS patients who currently lack adequate treatment options.