Leiomyosarcomas can develop in the uterus, blood vessels, gastrointestinal tract and soft tissues. When the disease becomes unresectable or metastatic, treatment options are limited, and doxorubicin remains one of the established chemotherapy drugs used in advanced disease. Although it can damage cancer cells by interfering with DNA replication and repair, its activity is often constrained by drug resistance, tumor heterogeneity and the ability of malignant tissue to suppress immune attack. The combination explored in this study is intended to confront the tumor on both fronts: direct chemotherapy and immune-system activation.

Ontorpacept is a recombinant fusion protein engineered to block signaling through signal regulatory protein alpha, or SIRPα. The molecule contains a modified form of SIRPα linked to a human antibody fragment. This design allows it to bind CD47, a surface protein frequently displayed at high levels by cancer cells, while preventing CD47 from engaging SIRPα on immune cells. The CD47–SIRPα pathway is commonly described as a “don’t eat me” signal because it can stop macrophages, a type of immune cell, from engulfing abnormal cells.

Under normal conditions, CD47–SIRPα signaling helps protect healthy cells from accidental destruction. Cancer can exploit the same system by increasing CD47 expression or using the pathway to avoid immune surveillance. When ontorpacept interrupts the interaction, macrophages may become more capable of recognizing tumor cells as targets for phagocytosis, the process by which they surround, ingest and digest cellular material. This mechanism does not depend solely on the cancer cell’s ability to divide rapidly, giving the approach a potentially different profile from conventional cytotoxic chemotherapy.

The scientific rationale for combining ontorpacept with doxorubicin is based on the possibility that chemotherapy can make tumors more visible to the immune system. Doxorubicin damages DNA through several complementary mechanisms, including inhibition of topoisomerase II and generation of molecular stress that can injure or kill malignant cells. As tumor cells die, they may release antigens and danger signals that alert immune cells. Blocking CD47–SIRPα signaling at the same time could help macrophages respond to that altered tumor environment and remove cancer cells that would otherwise remain protected.

The trial’s Phase 1/2 structure reflects the two-stage priorities of early cancer-drug development. Phase 1 generally examines safety, tolerability, dose selection and the identification of treatment-related toxicities, while Phase 2 explores preliminary signals of antitumor activity in a defined patient population. In a combination study, investigators must also determine whether the new agent changes the safety profile of chemotherapy or introduces immune-related complications. Particular attention is typically given to blood counts, infusion reactions, infections, organ function and other adverse events relevant to both agents.

This distinction is important because a biologically compelling mechanism does not automatically translate into clinical benefit. Tumors can resist macrophage-mediated clearance through other immune checkpoints, physical barriers in the tumor microenvironment or changes in antigen presentation. Leiomyosarcoma is also genetically and biologically diverse, meaning that CD47 expression, macrophage activity and sensitivity to doxorubicin may vary considerably from one patient to another. The Phase 1/2 investigation is therefore intended not only to test the combination, but also to clarify how it behaves in the complex environment of advanced human cancer.

The study adds to a broader effort to develop therapies that engage the innate immune system. Much recent immuno-oncology research has focused on T cells and checkpoint proteins such as PD-1 and PD-L1. Macrophages, however, are abundant in many solid tumors and can either attack cancer or support its growth, depending on the signals they receive. By targeting CD47–SIRPα communication, ontorpacept is designed to shift macrophage behavior toward tumor-cell removal. The approach may be especially relevant in cancers where immune suppression and dense stromal tissue limit the reach of T-cell-based therapies.

For patients with unresectable or metastatic high-grade leiomyosarcoma, new treatment strategies are urgently needed because advanced disease can progress despite surgery, chemotherapy and other systemic treatments. The combination examined in this trial represents a coordinated attempt to intensify therapy without relying on chemotherapy alone. Its ultimate value will depend on the balance between tumor control, treatment tolerability and the durability of any responses. Results from carefully monitored clinical follow-up will be essential for determining whether disrupting the CD47–SIRPα “don’t eat me” signal can become a meaningful addition to the therapeutic options for this rare and difficult cancer.

Subject of Research: Ontorpacept (TTI-621) combined with doxorubicin for patients with unresectable or metastatic high-grade leiomyosarcoma.

Article Title: A Phase 1/2 study of ontorpacept (TTI-621) in combination with doxorubicin in patients with unresectable or metastatic high-grade leiomyosarcoma.

Article References: Movva, S., Allgood, V., Chugh, R. et al. “A Phase 1/2 study of ontorpacept (TTI-621) in combination with doxorubicin in patients with unresectable or metastatic high-grade leiomyosarcoma.” British Journal of Cancer (2026). https://doi.org/10.1038/s41416-026-03574-z

Image Credits: AI Generated

DOI: https://doi.org/10.1038/s41416-026-03574-z

Keywords: ontorpacept, TTI-621, SIRPα, CD47, doxorubicin, leiomyosarcoma, sarcoma, cancer immunotherapy, macrophages, Phase 1/2 clinical trial

The PI3K signaling pathway is critical for numerous cellular functions, including growth, survival, and metabolism. Dysregulation and hyperactivation of this pathway, often through mutations or overexpression, are common in many cancers, including breast tumors. Among the Class I PI3K isoforms, p110δ has traditionally been associated with hematological malignancies and immune cell function. However, emerging evidence has suggested a more nuanced role for p110δ in solid tumors, such as breast cancer. The study led by Goulielmaki and colleagues delves deeply into this less explored territory, revealing that targeting p110δ with IOA-244 can effectively disrupt tumor cell survival and proliferation mechanisms.

The research hinges on the molecular specificity of IOA-244, which distinguishes it from other PI3K inhibitors by exhibiting a profound selectivity for the p110δ isoform. Previous pan-PI3K inhibitors often suffered from off-target effects and dose-limiting toxicities due to the inhibition of multiple PI3K isoforms involved in normal physiological processes. IOA-244’s precision promises a better therapeutic window, minimizing side effects while maximizing antitumor activity. Mechanistic studies demonstrated that upon administration, IOA-244 effectively blocks p110δ-mediated signaling cascades, leading to apoptosis and autophagy in breast cancer cells—salient processes that undermine tumor viability.

In vitro studies revealed that breast cancer cell lines treated with IOA-244 experienced significant growth inhibition. The inhibitor was shown to selectively impair the phosphorylation of downstream effectors such as AKT and mTOR, key nodes in the PI3K signaling pathway responsible for cell cycle progression and survival. These biochemical hallmarks corroborate the hypothesis that p110δ plays a previously underappreciated role in sustaining breast cancer cell growth and that its inhibition with IOA-244 cripples the tumor cells’ proliferative capacity.

Moving beyond cell culture, the team evaluated IOA-244 in vivo using murine models harboring human breast tumor xenografts. Treatment with the inhibitor resulted in a pronounced reduction in tumor volume compared to untreated controls. Notably, IOA-244 exhibited robust anti-tumor activity without eliciting overt toxicity, affirming its safety profile. The authors stressed that this aspect of the drug is especially vital since long-term tolerability is a crucial concern when developing therapies intended for sustained use in chronic cancer management.

An intriguing facet of this study is the dual utility of IOA-244—not only as a monotherapy but also in synergy with established therapeutic agents such as chemotherapy and immune checkpoint inhibitors. Combination regimens enhanced the therapeutic efficacy markedly, underscoring the potential of IOA-244 to integrate seamlessly into existing treatment paradigms. The co-administration of IOA-244 alongside immune modulators appeared to amplify antitumor immunity, possibly through modulation of the tumor microenvironment, which is often immunosuppressive in breast cancers.

Moreover, molecular profiling of treated tumors exhibited a decrease in regulatory T cells (Tregs) and myeloid-derived suppressor cells (MDSCs), both of which contribute to immune evasion and cancer progression. IOA-244’s ability to recalibrate the immune milieu offers a compelling rationale for its combination with immunotherapies that rely on reactivating the patient’s immune response against cancer cells. This property could be particularly transformative for patients with tumors that are refractory to conventional treatments or those exhibiting resistance to immune checkpoint blockade.

The research team employed advanced transcriptomic and proteomic approaches to dissect the broader impact of IOA-244 on tumor biology. They identified that IOA-244 treatment downregulated genes involved in cell adhesion and metastasis pathways, potentially curtailing the invasive and metastatic potential of breast cancer cells. This multi-pronged assault on tumor progression reaffirms IOA-244 as a formidable candidate in the oncologist’s arsenal, not just for tumor eradication but also for preventing disease dissemination and relapse.

A particularly compelling insight from the study is the inhibitor’s impact on cancer stem cell populations within breast tumors. These cells are notorious for their role in therapy resistance and tumor recurrence. IOA-244 diminished markers associated with stemness and self-renewal, implying that it might effectively target the ‘root’ of tumor persistence. Targeting these resilient cell populations could improve long-term outcomes and reduce relapse rates, a significant hurdle in breast cancer therapeutics.

The specificity of IOA-244 also paves the way for biomarker-driven patient selection. Identifying patients whose tumors demonstrate p110δ dependency or overexpression could refine treatment protocols, ensuring maximum benefit from IOA-244 while sparing others from ineffective therapy. Biomarker development is pivotal in ushering personalized medicine approaches in oncology, where treatments are tailored to individual tumor profiles.

While this study lays a solid preclinical foundation, the translation of IOA-244 into clinical settings remains an exciting and anticipated next step. Phase I trials are warranted to assess pharmacokinetics, optimal dosing, and initial efficacy in humans. Given the favorable safety and potent antitumoral effects observed in preclinical models, IOA-244 is well poised to progress through clinical development swiftly.

The significance of this advancement cannot be overstated. Breast cancer treatment has largely revolved around estrogen receptor targeting, HER2 inhibition, and cytotoxic chemotherapy. However, many patients eventually develop resistance or suffer from side effects, underscoring the urgent need for novel, more targeted agents. IOA-244 promises to fill this therapeutic void by attacking a hitherto underexploited pathway that plays a critical role in tumor survival.

Furthermore, the versatility of IOA-244 in combination therapies heralds a broader application spectrum that may extend beyond breast cancer. Given the involvement of PI3K signaling in diverse tumor types, this inhibitor’s platform could be adapted or combined with other agents for multifactorial attack strategies in oncology.

In summary, the study by Goulielmaki et al. has brought IOA-244 from conceptualization to compelling proof-of-concept validation, illustrating that selective p110δ inhibition is a viable and potent strategy to curb breast tumor progression. Its dual capability to act alone or synergistically offers oncologists a flexible, precision medicine tool against an often intractable disease. This research invites a paradigm shift, advocating for deep dives into isoform-specific targeting within the PI3K pathway as a cornerstone for next-generation cancer therapies.

As breast cancer continues to challenge medical science with its heterogeneity and adaptive resistance, IOA-244 shines as a beacon of hope that holds the potential to transform patient outcomes through precision molecular intervention. The oncology community eagerly anticipates further clinical insights into this promising compound, which could soon redefine the standards of breast cancer treatment in the years ahead.

Subject of Research: Targeting the p110δ isoform of PI3K in breast cancer using the novel inhibitor IOA-244

Article Title: IOA-244, a novel p110δ PI3K inhibitor, blocks breast tumour progression on either mono- or combined-therapy

Article References:
Goulielmaki, E., Tsapara, A., Xenou, L. et al. IOA-244, a novel p110δ PI3K inhibitor, blocks breast tumour progression on either mono- or combined-therapy. Cell Death Discov. (2026). https://doi.org/10.1038/s41420-026-03073-3

Image Credits: AI Generated

DOI: https://doi.org/10.1038/s41420-026-03073-3