Targeting the Sugar Coat: Oncofetal Chondroitin Sulfate Emerges as a Precision ADC Target in AML

Highlights

• Oncofetal chondroitin sulfate (ofCS) is highly expressed on the surface of AML cells and patient-derived xenografts (PDXs) but remains nearly undetectable in healthy adult bone marrow tissues.
• Anti-ofCS antibody-drug conjugates (ADCs) demonstrate potent and selective cytotoxicity against AML cells in vitro and significantly prolong survival in PDX models.
• The unique expression profile of ofCS offers a broader therapeutic window compared to current targets like CD33, potentially reducing dose-limiting hematotoxicity.
• This study identifies ofCS as the first glycosaminoglycan-based druggable target for the development of effective antibody-based therapies in acute myeloid leukemia.

The Therapeutic Paradox in Acute Myeloid Leukemia

Acute myeloid leukemia (AML) remains a significant clinical challenge, characterized by the rapid proliferation of immature myeloid cells and a high rate of relapse. While the advent of targeted therapies, particularly antibody-drug conjugates (ADCs), promised a shift away from the systemic toxicity of traditional induction chemotherapy, clinical success has been hampered by a lack of truly tumor-specific targets. The most notable ADC currently in the AML landscape, Gemtuzumab ozogamicin, targets CD33. However, CD33 is also expressed on healthy hematopoietic stem and progenitor cells (HSPCs) and myeloid lineage cells. This overlapping expression leads to severe myelosuppression and hepatotoxicity, restricting the use of such agents to younger, fitter patients who can withstand these off-target effects. For the elderly or those with significant comorbidities, the therapeutic window remains prohibitively narrow.

Oncofetal Chondroitin Sulfate: A Novel Glycan Target

In a landmark study published in Blood, Mujollari and colleagues explored a paradigm shift by targeting the cancer-specific glycan landscape rather than surface proteins. Glycosaminoglycans (GAGs) are complex carbohydrates that decorate proteoglycans on the cell surface. Oncofetal chondroitin sulfate (ofCS) is a specific carbohydrate modification typically associated with placental development and various solid malignancies. Crucially, ofCS is largely absent from normal adult tissues. The research team hypothesized that if ofCS was present in AML, it could serve as an ideal target for ADCs, offering high tumor specificity while sparing healthy bone marrow components.

Study Design and Translational Methodology

The study utilized a multi-faceted approach to validate ofCS as a therapeutic target. The researchers first characterized ofCS expression across a broad spectrum of clinical samples, including bone marrow cells from patients with AML and healthy donors. To further evaluate the target in a clinically relevant environment, patient-derived xenograft (PDX) models were established. The therapeutic intervention involved the development of a recombinant anti-ofCS antibody conjugated to a potent cytotoxic payload. The team assessed the binding affinity, internalization kinetics, and in vitro killing efficiency of the anti-ofCS ADC. Finally, the efficacy and safety profiles were tested in vivo, comparing the survival rates of AML-bearing mice treated with the anti-ofCS ADC against those receiving control treatments.

Key Findings: Specificity, Efficacy, and Survival

High Expression Specificity

The researchers found that ofCS was abundantly expressed on the surface of bone marrow cells from a significant majority of AML patients. In stark contrast, bone marrow cells from healthy individuals showed low to undetectable levels of ofCS. This disparity is critical, as it suggests that an ADC targeting ofCS would have minimal interaction with the healthy myeloid compartment, addressing the primary limitation of current AML-targeted therapies.

Rapid Internalization and Cytotoxicity

For an ADC to be effective, the antibody must not only bind to the target but also be internalized by the cell to release its cytotoxic payload. The study demonstrated that the anti-ofCS antibody was rapidly internalized into AML cells. In vitro assays revealed that anti-ofCS ADCs effectively killed AML cell lines and primary patient cells with high potency, confirming that the ofCS-proteoglycan complex is a functional gateway for intracellular drug delivery.

Superior Survival in PDX Models

In vivo experiments provided the most compelling evidence for clinical potential. Treatment with anti-ofCS ADCs significantly prolonged the survival of AML PDXs compared to control groups. Importantly, this therapeutic effect was achieved with low overall toxicity, as evidenced by stable body weights and minimal impact on the remaining healthy hematopoietic indices in the animal models.

Expert Commentary: A New Class of Targets

The identification of ofCS as a druggable target in AML represents a significant departure from traditional protein-centric drug development. While most ADCs target lineage-specific proteins (which are often shared by healthy cells), targeting a post-translational modification like ofCS allows for a degree of cancer-selectivity that was previously difficult to achieve. This glycan-based approach could potentially bypass the issue of ‘target-mediated drug disposition’ where the drug is sequestered by healthy tissues before it can reach the tumor.

However, limitations must be considered. As with any glycosylated target, the heterogeneity of ofCS expression across different AML subtypes needs further characterization. Furthermore, while the murine models showed low toxicity, the true safety profile regarding human placental-like tissues or rare adult cell populations must be rigorously evaluated in Phase I clinical trials. The integration of ofCS-targeted therapy into current treatment algorithms—whether as a monotherapy or in combination with venetoclax or hypomethylating agents—will be a key area of future research.

Conclusion

The study by Mujollari et al. provides a robust proof-of-concept for the use of anti-ofCS ADCs in the treatment of acute myeloid leukemia. By exploiting the unique oncofetal glycan signature of AML cells, this approach offers a promising strategy to expand the therapeutic window of ADCs, potentially providing a life-extending option for patients who are currently ineligible for intensive chemotherapy. As the first study to demonstrate that a glycosaminoglycan-like ofCS is a viable target in hematological malignancies, it opens a new frontier in the development of precision antibody-based therapies.

References

1. Mujollari J, Estruch M, Khadgawat P, et al. The glycosaminoglycan oncofetal chondroitin sulfate is a novel target for antibody-drug conjugate therapy for AML. Blood. 2026;147(11):1229-1236. PMID: 41405498.
2. Sievars S, et al. The landscape of antibody-drug conjugates in acute myeloid leukemia. Blood Reviews. 2023.
3. Salanti A, et al. Targeting human cancer by a glycosaminoglycan binding malaria protein. Cancer Cell. 2015;28(4):500-514.