Investigate the mode of action ofInvestigate the mode of action of beta-carboline derivative Harmine on increasing MHC-I expression and potentiating the Immune Checkpoint Blockade cancer immunotherapy

Project Information

INCEPTOR

Grant agreement ID: 101109424

DOI

10.3030/101109424

Project closed

EC signature date 20 April 2023

Start date 1 April 2024

End date 31 March 2026

Funded under

• Marie Skłodowska-Curie Actions (MSCA)

Total cost

No data

EU contribution

€ 191 760,00

Coordinated by

LUXEMBOURG INSTITUTE OF HEALTH
Luxembourg

Periodic Reporting for period 1 - INCEPTOR (Investigate the mode of action ofInvestigate the mode of action of beta-carboline derivative Harmine on increasing MHC-I expression and potentiating the Immune Checkpoint Blockade cancer immunotherapy)

Reporting period: 2024-04-01 to 2026-03-31

Summary of the context and overall objectives of the project

Colorectal cancer (CRC) is a malignant tumor that forms in the tissues of the colon (large intestine) or rectum (the digestive system's final part). In 2020, the European Cancer Information System (ECIS) estimated that CRC made up 12.7% of new cancer diagnoses (150,366 in women and 191,053 in men). It also accounted for 12.4% of all cancer deaths (https://ecis.jrc.ec.europa.eu accessed 15/01/2021). CRC risk increases with age, and most cases occur in people over 50 years. In the EU-27, the estimated lifetime risk (ages 0-74) is 1 in 35 for women, and 1 in 22 for men. In the 70+ age group, 195,667 cases were recorded. Treating CRC remains particularly difficult in advanced stages. The outlook for patients is poor, and options for therapy are limited.
In the past decade, immune checkpoint inhibitors (ICIs) have transformed cancer care. These treatments reawaken the body's immune system to fight tumors. However, they help only a small fraction of CRC patients—roughly 15–20%—whose tumors have specific genetic features (high microsatellite instability, MSI-H). The other 80–85% have tumors classified as microsatellite-stable (MSS). These are largely invisible to the immune system and unresponsive to immunotherapy. Research has studied why CRC-MSS tumors evade immune attack. A key mechanism of the immune evasion is a failure of tumor antigen presentation. For the immune system to recognize and destroy a cancer cell, the cell must display fragments of abnormal proteins on its surface via molecules of the major histocompatibility complex class I (MHC-I). In MSS cancers, this display system often shuts down. Without MHC-I signals, the immune system's killer cells (CD8⁺ cytotoxic T lymphocytes) cannot identify or attack the tumor. Modifying these silent tumors so the immune system can detect and destroy them is a major priority in cancer research.
The INCEPTOR project aimed to address this challenge by studying ACB1801, a harmine derivative and naturally occurring beta-carboline alkaloid. Previous work by the research group suggested harmine increases MHC-I expression on tumor cells. This could make tumors visible to immune cells. The fellowship's main aim was to clarify how ACB1801 reprogrammed the tumor microenvironment. This environment is a complex network of immune and non-immune cells surrounding a tumor. The project also tested, in preclinical models, whether combining ACB1801 with an anti-PD-1 ICB could create a stronger anti-tumor response than either treatment alone.
The project pursued three connected objectives. First, map the molecular mechanisms by which ACB1801 boosts antigen processing and presentation in CRC cells. Second, assess the drug's effects on immune cell populations in the tumor microenvironment using mouse models of MSS colorectal cancer. Third, generate proof-of-concept data on whether harmine can enhance the efficacy of dendritic cell vaccination. In this approach, the patient's antigen-presenting cells are loaded with tumor proteins and reinfused to trigger a targeted immune response.
This project sits at the intersection of cancer immunology, molecular biology, and translational medicine. Its relevance is high: MSS colorectal cancer affects hundreds of thousands of patients each year in Europe. No effective immunotherapy exists for this group. The INCEPTOR fellowship took place at the Luxembourg Institute of Health (LIH). It was supported by the Marie Skłodowska-Curie Actions Postdoctoral Fellowship program. The project involved a collaboration with AC BioScience (Switzerland) and scientific partners in France and Luxembourg.

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

The project was divided into 3 main working packages (WP):
WP1: Fully achieved - Study the molecular mechanisms underlying ACB1801 treatment in CRC models. In this object, it was proposed to conduct transcriptional studies across different tumor cell lines following in vitro treatment to identify the multi-omics variables involved in the process. Methods (RNA-seq pipeline, siRNA knockdown, cytotoxicity assay), key results ACB1801 triggers pSTAT1(Tyr701), which drives NLRC5, which coordinates the full MHC-I machinery (HLA-A/B/C, TAP, proteasome), producing tumour cells that display their peptide content and become killable that was functional validated (enhanced OT-I killing).
WP2: Fully achieved - To study the effects of ACB1801 on different subsets of immune and other cells of the tumor microenvironment. In vivo design (4 groups, n = 10, CT26/BALB/c), efficacy outcomes (tumour volume p < 0.05 tumour weight p < 0.05 survival log-rank p < 0.05) immune phenotyping (CD8⁺ infiltration, Tregs, CD8/Treg ratio, T cell exhaustion markers), GSEA of intratumoral immune cells, CXCL10 multiplex profiling both in vitro and in vivo, and the full integrative mechanistic model.
WP3: Partially achieved — Preclinical proof-of-concept on how ACB1801 can be used to increase the anti-tumor immune responses from the cytotoxic T lymphocytes (CTL/CD8+). Explanation of the deviation (compound discontinuation) and the use of commercial compound harmine. In human setting, on THP-1 model results showed an increase in maturation markers, phagocytosis, and T cell proliferation. Using human PBMC (peripheral blood mononuclear cells) expansion results, showed a cDC1/cDC2 shift, TEM phenotype, cytokine production. Mouse BMDC (bone marrow-derived dendritic cells) cross-presentation results showed an increase of co-stimulatory molecules (CD80 and CD86) and SIINFEKL–MHC I. T cells primed with CEA-loaded DCs treated with harmine showed the highest killing capacity compared with the other groups.

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)

This project establishes harmine (ACB1801) as a novel immuno-oncology candidate that addresses key limitations of current cancer immunotherapies: insufficient tumor immunogenicity. We demonstrated that this compound enhances dendritic (DC) function, including antigen presentation and cross-presentation, while simultaneously priming tumor cells through increase interferon (IFN) responsiveness, STAT1 activation, and MHC-I upregulation. Despite the success of anti PD 1/PD L1 (ICI) therapies, a large proportion of patients—particularly those with microsatellite stable (MSS) colorectal cancer—fail to respond due to low tumor immunogenicity (e.g. reduced MHC-I expression). This positions ACB1801 as a first-in-class combination partner for checkpoint inhibitors, with the potential to:
• Increase response rates in resistant tumors
• Improve durability of clinical benefit
• Expand immunotherapy eligibility to currently non-responsive patient populations
• Development of next-generation DC-based cancer vaccines.
Further Research
• Validation in vivo models with clinical relevance
• While the study identifies key pathways (STAT1, NLRC5, CXCL10, TRIB3, DUSP5), the direct molecular targets of harmine/ACB1801 remain unclear, including the potential role of DYRK1A inhibition. Additional work is required to define the precise signaling networks and causal mechanisms.
• Biomarker-driven patient stratification
• Although harmine efficacy has been demonstrated in tumor models (e.g. CT26), the specific contribution of dendritic cell modulation to vivo anti-tumor responses remain to be fully established. Further studies using DC-specific depletion or tracking approaches are required to confirm causality.
Overall, while the results provide strong mechanistic and translational insights, further in vivo validation, clinical translation, and optimization of treatment conditions are required to fully establish the therapeutic potential of harmine.