TUB-040, an investigational drug being developed by Tubulis, represents a significant advancement in the field of antibody-drug conjugates (ADCs), offering a targeted therapeutic approach for the treatment of platinum-resistant ovarian cancer (PROC) and non-small cell lung adenocarcinoma (NSCLC).
TUB-040 is engineered to maximize tumor-specific delivery and minimize off-target effects, addressing longstanding challenges in ADC design.
NaPi2b, or sodium-dependent phosphate transport protein 2b, is a cell surface receptor highly overexpressed in high-grade epithelial ovarian cancers and adenocarcinoma subtypes of NSCLC. Immunohistochemical analyses confirm that more than 90% of ovarian cancer samples and up to 70% of lung adenocarcinomas exhibit considerable NaPi2b expression. In contrast, its expression is minimal in most healthy tissues, primarily limited to specific cells in the lung, testis, breast, and kidney. This restricted expression profile makes NaPi2b an ideal target for selective cancer therapy.
Innovative ADC Engineering
TUB-040 is based on a humanized IgG1 monoclonal antibody that specifically binds the second extracellular loop of NaPi2b. The antibody incorporates LALA mutations to silence Fc effector function, reducing the risk of immune-related side effects such as thrombocytopenia and pulmonary toxicity.
The unique aspect of TUB-040 lies in its conjugation technology. Using Tubulis’ proprietary Tubutecan* linker-payload system and ethynylphosphonamidate (P5) chemistry, TUB-040 achieves an unprecedented drug-to-antibody ratio (DAR) of 8. Each antibody is site-specifically conjugated to the cytotoxic payload exatecan—a potent, water-soluble, synthetic camptothecin analog that acts as a topoisomerase I inhibitor—via a cleavable linker that ensures stable, controlled release only within the tumor environment. The hydrophilic and highly homogeneous design of TUB-040 translates into superior biophysical properties, including high purity, low aggregation, and excellent serum stability.
Preclinical Efficacy and Safety
In vitro, TUB-040 demonstrates high-affinity binding and rapid internalization in NaPi2b-positive cancer cells, triggering efficient and antigen-specific cytotoxicity. Notably, the exatecan payload confers a strong bystander effect, capable of killing neighboring tumor cells regardless of their NaPi2b status—a key advantage in heterogeneous tumors.
Animal studies reinforce TUB-040’s therapeutic promise. In both cell line-derived and patient-derived xenograft (PDX) models of ovarian cancer and NSCLC, single intravenous doses of TUB-040 induce robust and durable tumor regressions—even in models with low NaPi2b expression. Complete remissions are observed at doses as low as 1 mg/kg in the OVCAR-3 ovarian cancer model**, and the agent remains effective across a range of tumor types and antigen expression levels.
Pharmacokinetic analyses in rats reveal dose-proportionality, low free payload levels, and stable exatecan delivery to tumor sites. Importantly, repeated-dose toxicity studies show that TUB-040 is well tolerated, with no evidence of lung toxicity or thrombocytopenia—side effects that have limited the development of earlier NaPi2b-directed ADCs.
Mechanistic Insights
TUB-040’s anti-tumor activity is rooted in its ability to deliver exatecan directly to NaPi2b-expressing cells. Once internalized, exatecan induces DNA damage, cell cycle arrest, and apoptosis. Additionally, TUB-040 triggers immunogenic cell death, characterized by the release of damage-associated molecular patterns (DAMPs) such as ATP and HMGB1, potentially enhancing anti-tumor immune responses.
Previous ADCs targeting NaPi2b, particularly those using tubulin inhibitors and maleimide-based linkers, have shown limited efficacy or unacceptable toxicity. For example, lifastuzumab vedotin, an investigational ADC designed to treat cancers expressing the NaPi2b protein, combines a humanized anti-NaPi2b antibody with the cytotoxic agent MMAE, and Upifitamab rilsodotin (XMT-1536), another NaPi2b-targeting investigational ADC designed to maximize antitumor activity while managing toxicities by using Mersana Therapeutics Dolaflexin platform, demonstrated clinical activity but were hampered by short response durations or pulmonary toxicity. TUB-040 overcomes these challenges with its stable, hydrophilic linker-payload system, Fc silencing, and use of a topoisomerase I inhibitor payload with proven bystander effect.
Clinical Development and Early Results
In June 2024, TUB-040 received Fast Track designation from the U.S. Food and Drug Administration (FDA) for the treatment of platinum-resistant ovarian cancer. It is currently under evaluation in a multicenter, open-label Phase 1/2a trial (NAPISTAR 1-01, NCT06303505) enrolling patients with heavily pre-treated PROC or relapsed/refractory adenocarcinoma of the NSCLC. The study comprises a dose-escalation phase to define the maximum tolerated dose, followed by dose optimization to determine the optimal therapeutic regimen. Patients receive TUB-040 intravenously every three weeks until disease progression or intolerable side effects.
Initial clinical data presented at the ESMO Congress in October 2025 indicate that TUB-040 exhibits robust anti-tumor activity and a favorable safety profile, even in biomarker-unselected and heavily pre-treated PROC patients.
Future direction
TUB-040 exemplifies the next generation of ADCs, combining tumor-specific targeting, potent delivery of a cytotoxic payload, and an optimized safety profile. Its preclinical and emerging clinical data suggest that TUB-040 could set a new standard for treating ovarian cancer and NSCLC, especially for patients with limited options after standard therapies. As clinical development advances, TUB-040 has the potential to deliver durable responses and improved outcomes for patients with these challenging cancers.
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Note: Tubutecan is a proprietary linker-payload technology developed by Tubulis that combines a topoisomerase 1 inhibitor (exatecan) with a stable, hydrophilic P5 conjugation system. Designed for antibody-drug conjugates (ADCs), it minimizes systemic toxicity and increases tumor-targeting stability.
** Isolated in 1982 from malignant ascites of a patient with progressive adenocarcinoma of the ovary after chemotherapy, OVCAR-3 is a widely used human ovarian adenocarcinoma cell line model for high-grade serous ovarian cancer (HGSOC). It represents a clinically relevant model for studying drug resistance, particularly to platinum-based therapies, and typically exhibits high-grade epithelial morphology, TP53 mutation, and hormone receptor expression (ER/PR)
Clinical trials
FiH Study to Investigate Safety, PK and Efficacy of the NaPi2b ADC TUB-040 in Patients With PROC or r/r Adenocarcinoma NSCLC (NAPISTAR1-01)
ClinicalTrials.gov ID NCT06303505
Reference
[1] Vogl AM, Schmitt S, Mai I, Machui P, Herterich S, Leonardi N, Cyprys P, Hauswald D, Ochtrop P, Kozlowska I, Kitowski A, Gerlach M, Waldmann F, Marcq O, Trail PA, Schumacher D, Fingerle-Rowson GR, Hock B, Kasper MA, Helma J. TUB-040, a Homogeneous and Hydrophilic NaPi2b-Targeting ADC with Stably Linked Exatecan, Exhibits Long-lasting Antitumor Activity and a Well-Tolerated Safety Profile. Mol Cancer Ther. 2025 Nov 3;24(11):1685-1700. doi: 10.1158/1535-7163.MCT-25-0254. PMID: 40667801; PMCID: PMC12580765.
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DOI: 10.14229/jadc.2026.04.01.015
