Disclaimer: This newsletter is for educational and informational purposes only and does not constitute medical, investment, or financial advice, nor does it establish a provider-patient relationship. Content may include forward-looking statements and discussions of investigational therapeutic candidates that are not FDA/EMA approved; their safety and efficacy remain unestablished and clinical outcomes are unpredictable. While we strive for accuracy, all information is provided as is without guarantees. This newsletter is independent, and the author holds no financial positions in the companies mentioned nor receives third-party compensation for this coverage. Please find a complete version of our disclaimers at the bottom of this article.

On April 7, 2026, Gilead Sciences announced that it had entered into a definitive agreement to acquire Tubulis GmbH for $3.15 billion in upfront cash consideration and up to $1.85 billion in contingent milestone payments. Evotec, a major shareholder in Tubulis, expects to receive about $100 million upfront from this deal. The proposed acquisition expands Gilead’s antibody-drug conjugate (ADC) capabilities by adding next-generation ADCs to their growing oncology pipeline; however, the ultimate commercial value of the deal remains contingent upon successful clinical transitions of the lead assets. Gilead leadership specifically highlighted their two clinical-stage programs:

Here, we expand on the history of antibody-drug conjugates (ADCs), what differentiates Tubulis’ ADC platform, and the clinical data they have shown to date.

Dr. Paul Ehrlich (1854–1915) is widely considered the father of modern precision medicine for introducing the concept of molecular specificity. His work was the first to bridge chemistry and biology by proposing that drugs must bind to specific “receptors” to be effective, a principle summarized by his famous maxim: Corpora non agunt nisi fixata (“Substances do not act unless they are bound”). Ehrlich’s early work centered around infectious disease but, in those cases, the target is an external parasite (ex. Treponema pallidum bacterium in syphilis). In 1901, Ehrlich shifted his focus to cancer research, but he immediately hit a wall: The Similarity Problem. Unlike bacteria, a cancer cell is the body’s own tissue gone wrong. It shares almost all the same receptors, proteins, and metabolic pathways as healthy cells. Ehrlich realized that the lock and key for cancer would have to be far more sophisticated than for infectious disease applications. He needed a carrier that could distinguish between a healthy epithelial cell and a malignant one based on subtle molecular differences.

Early chemotherapy discovered in the 1940s was effective, but it has long been viewed as a systemic ‘sledgehammer’. It killed rapidly dividing cells indiscriminately, leading to the severe side effects we associate with cancer treatment (hair loss, nausea, immune suppression). While these agents are potent, they lack molecular discrimination, attacking any rapidly dividing cell and leading to narrow therapeutic windows. The emergence of Antibody-Drug Conjugates (ADCs) represents a pivot toward a potential molecular ‘scalpel’ that Ehrlich imagined, designed to deliver cytotoxic payloads with higher precision. ADCs consist of three component parts:

Ehrlich’s vision of molecular specificity in cancer remained a fantasy until two major breakthroughs brought it closer to reality:

While the antibodies and the toxic payloads (the medicine) are important, the most significant leaps across generations have been in the linker chemistry and the conjugation site (where the drug attaches to the antibody). Targeted delivery aims to widen the therapeutic window by increasing the concentration of the drug at the tumor site relative to systemic exposure. By designing the chemical bond to tether the ‘poison’ to the antibody until internalization, next-generation ADCs aim to minimize damage to healthy tissues while allowing for higher, more effective doses at the tumor site.

Despite this promise, 1st generation ADCs have struggled with leaky chemistry. In the early 2000s, the goal was simply to prove that an antibody could carry a toxin. However, the technology was blunt. Researchers used random conjugation. Imagine an antibody as a Y-shaped tree; the drugs were mixed with it and stuck wherever they landed. This led to a mix of antibodies with 0, 2, or 8 drugs attached. The chemical bonds were often acid-labile and unstable in human blood. The toxic payload would often fall off while the drug was still circulating, leading to systemic toxicity, poisoning the patient rather than the tumor. Mylotarg (CD33 ADC for AML), the first FDA approved ADC, was first approved in 2000, voluntarily withdrawn in 2010 due to safety concerns, then re-approved at a lower dose and different dosing schedule in 2017 with an expanded indication in 2020.

By the 2010s, scientists moved toward more stable linkers and “humanized” antibodies, which the body’s immune system was less likely to reject. Because 1st-generation drugs weren’t potent enough, the 2nd generation introduced extremely powerful toxins like DM1 or MMAE. These are thousands of times more toxic than standard chemotherapy. Better maleimide linkers were used, which stayed attached in the bloodstream much longer, aimed to enhance the amount of the drug that actually reached the tumor. While better, they still used random conjugation. If an antibody carried too many drugs (a high DAR or Drug-to-Antibody Ratio), it became “greasy” and was cleared by the liver too quickly, reducing its effectiveness.

We are currently in the era of 3rd generation of ADCs (2020–2026), where the focus has shifted to site-specific conjugation. Scientists can now place the drug at an exact spot on the antibody. This creates a uniform drug (nearly every molecule is identical), which makes the medicine much more predictable and safer. Modern payloads are designed to pass through cell membranes. Once the ADC kills the primary cancer cell, the toxin can drift into neighboring cancer cells that might not even have the target protein. This is crucial because tumors are heterogeneous; messy mixtures where not every cell looks the same. Furthermore, scientists can now load more toxic payloads onto a single antibody without making the ADC toxic to the rest of the body or unstable in the blood.

Tubulis and companies like them have been working on solving the 3rd Generation problem of linker stability and site-specific conjugation. By using site-specific chemistry, they can do a better job of making sure the toxin stays attached to the antibody until it is inside the cancer cell, allowing for higher doses that kill the tumor while aiming to spare healthy tissue and reduce systemic toxicity.

The transition from systemic toxins to stabilized conjugates is best understood through the lens of serum stability and drug-to-antibody ratio (DAR) homogeneity. Early ADCs often failed because their chemical bonds were susceptible to retro-Michael additions or thiol exchange with endogenous proteins like albumin, causing premature payload release. Tubulis has addressed this by developing the P5 and Alco5 platforms.

Tubulis’s proprietary technologies represent a paradigm shift in bioconjugation chemistry, moving beyond “one-size-fits-all” linkers to provide optimized, tailor-made solutions for specific payloads. Their strategy centers on two proprietary platforms:

As of April 7, 2026, Tubulis has presented primary clinical data for its lead candidate, TUB-040, a NaPi2b-targeted ADC, with preclinical data in mouse models noted for its second candidate, TUB-030.

At the ESMO 2025 Congress, Tubulis reported positive interim Phase 1b/2 results for TUB-040 (NaPi2b targeted TOPO1i ADC) in patients with platinum-resistant high-grade serous ovarian cancer (PROC-HGSOC). The study evaluated heavily pre-treated, biomarker-unselected patients who had received a median of four prior lines of therapy. In the focus dose cohorts, TUB-040 achieved an unconfirmed ORR of 59% (n=13/22) and a confirmed ORR of 50% (n=11/22) among heavily pre-treated patients. While cross-trial comparisons are limited due to differences in study design and patient populations, this signal is notable when viewed against historical benchmarks of chemotherapy, which typically yield an ORR of only 10-15%. It also showed a confirmed DCR of 96% and approximately 81% of patients in the focus group exhibited a CA-125 response, an established prognostic marker in ovarian cancer. Responses occurred as early as treatment cycle 2 and deepened over time. Efficacy was observed even in patients who had previously failed treatments like Elahere. TUB-040 was generally well tolerated, with the majority of treatment-emergent adverse events (TEAEs) being Grade 1 or 2, although the most common Grade 3 TEAEs included neutropenia (22%), anemia (9%), and low rates (4%) of thrombocytopenia and nausea. There were no fatal TEAEs and no patient discontinuations due to adverse events within the reported cohorts. Notably, the clinical profile showed no reports of clinically relevant pneumonitis, ocular toxicity, stomatitis, or neuropathy, which are often associated with other topoisomerase-I ADCs.

TUB-030 (5T4 targeted ADC) is currently being evaluated in the Phase I/IIa 5-STAR 1-01 trial, a first-in-human dose-escalation and expansion study. Gilead and Tubulis leadership highlighted that TUB-030 has demonstrated “promising initial clinical data” across various solid tumor types, although very limited clinical data have been published as of April 7, 2026. Preclinical findings presented at the American Association of Cancer Research (AACR) 2025 medical meeting described that triple-negative breast cancer (TNBC) mouse models who were given with a single dose of TUB-030 demonstrated complete responses, suggesting potent activity in these specific models. In these same mice, data confirmed that TUB-030 can kill neighboring cancer cells that don’t express the 5T4 target antigen. This is notable because in these mouse models it showed that the medicine’s membrane-permeable exatecan payload demonstrated a bystander effect that killed neighboring 5T4-negative cells, a critical feature for overcoming tumor heterogeneity in colorectal and lung cancers.

For decades, Ehrlich’s dream of molecular specificity in cancer was held back by the limitations of chemistry. Today, through site-specific conjugation of tumor-specific antibodies and the expansion of the payload universe, the industry is exploring whether these platforms can translate theoretical precision into clinical outcomes. Gilead’s proposed acquisition of Tubulis and its bioconjugation platforms could help them move away from unstable maleimide chemistry and the “chemotherapy-like toxicities” that have plagued 1st generation ADC approvals. Furthermore, platforms like Alco5 allow for the delivery of novel payloads (like protein degraders or DHODH inhibitors), providing a vital toolset to combat acquired drug resistance.

Thank you for reading! Subscribe to Biotech Readout to receive new posts spotlighting biotech innovation every week.

To contact us, please email [email protected]

The therapeutic candidates discussed in this newsletter are currently in clinical development and have not been approved for commercial sale by the U.S. Food and Drug Administration (FDA), the European Medicines Agency (EMA), or other global regulatory authorities. Their safety and efficacy have not been established. References to pipeline products and ongoing clinical trials involve significant risks and uncertainties. Statements regarding the potential safety, potency, or efficacy of investigational drugs reflect current hypotheses and are not a guarantee of future performance or regulatory clearance. The outcome of clinical trials is inherently unpredictable, and clinical results from earlier stages may not be predictive of results in later, larger-scale trials.

This newsletter is for informational and educational purposes only. The content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or another qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read in this publication.

This newsletter contains “forward-looking statements” regarding future events, including clinical trial timing, regulatory milestones, and projected market performance. These statements are based on current expectations and assumptions that are subject to significant risks and uncertainties. Actual results may differ materially from those expressed or implied. We undertake no obligation to update these statements as a result of new information or future developments.

The information provided in this newsletter is for educational and analytical purposes only. Receipt of this information, or any interaction with this content, does not create a physician-patient, pharmacist-patient, or any other professional-provider relationship between you and the authors or publishers. This newsletter should not be used as a substitute for a personal consultation with a qualified healthcare professional.

This newsletter contains links to third-party websites, including clinical trial registries and corporate presentations. Biotech Readout does not endorse, guarantee, or assume responsibility for the accuracy or reliability of any information offered by third-party providers.

While we strive for technical accuracy, the information in this newsletter is provided on an “as is” basis with no guarantees of completeness, accuracy, or timeliness. Biotech Readout assumes no liability for any errors or omissions in the content of this publication.

Any reference to specific commercial products, processes, or services by trade name, trademark, or manufacturer does not constitute or imply an endorsement or recommendation by the author. All trademarks are the property of their respective owners.

This newsletter is for informational purposes only and does not constitute financial, investment, or legal advice. The author is not a registered investment advisor. You should consult with a professional financial advisor before making any investment decisions. The biotechnology sector is highly volatile; past performance is not indicative of future results.

The author of this newsletter maintains a position of independence. At the time of publication, the author holds no direct financial interest, equity, or options in any of the companies mentioned in this report. No compensation has been received from any third party to feature or analyze specific therapeutic candidates or corporate entities.