Blacksmith Forges New Path in Cancer Therapy by Targeting 'Undruggable' Enzymes

SAN DIEGO, CA – April 16, 2026 – San Diego-based Blacksmith Medicines is set to pull back the curtain on its pioneering oncology program at the American Association for Cancer Research (AACR) Annual Meeting this week, revealing preclinical data on a novel drug candidate that targets a historically challenging class of enzymes. The company will present findings on BSM-1516, a small-molecule inhibitor designed to attack cancer by disabling a critical DNA repair enzyme known as flap endonuclease 1 (FEN1).

The presentation marks a significant milestone for Blacksmith, a biopharmaceutical firm dedicated to drugging metalloenzymes—a vast and vital class of proteins long considered beyond the reach of conventional drug discovery. The data not only highlights a potential new weapon in the fight against cancer but also serves as a powerful validation of the company's unique platform, which aims to systematically unlock this difficult-to-drug target space.

Cracking the Code of Metalloenzymes

Metalloenzymes are the unsung workhorses of biology. Representing over 30% of all known enzymes, they rely on metal ions like magnesium, zinc, and iron within their active sites to perform a staggering array of critical functions, from metabolism to DNA replication. Despite their prevalence and importance in disease, they have remained a formidable challenge for medicinal chemists. The very metal ions that make them effective catalysts also make them difficult to target with the precision required for safe and effective medicines, often leading to issues with potency and selectivity.

Blacksmith Medicines was founded to solve this very problem. The company has built a purpose-built drug discovery engine that integrates multiple cutting-edge technologies. At its core is a proprietary fragment library of metal-binding pharmacophores (MBPs)—specially designed chemical building blocks that can precisely engage the metal ions in an enzyme's active site. This library is coupled with a comprehensive database mapping metalloenzyme functions and disease associations, a unique metallo-CRISPR screening library to validate targets, and an advanced computational toolkit for structure-based drug design.

This integrated approach allows Blacksmith to move beyond the trial-and-error methods of the past. By rationally designing inhibitors that bind to the metal cofactor, the company aims to rapidly and predictably develop potent and selective drugs for this underserved target class, potentially opening up entirely new therapeutic avenues.

FEN1: A Strategic Vulnerability in Cancer's Armor

The company’s lead oncology program targeting FEN1 exemplifies the power of this strategy. FEN1 is a di-magnesium metallonuclease that acts as a molecular scissors during DNA replication, specifically in a process called Okazaki fragment maturation. It ensures that newly copied DNA strands are stitched together seamlessly. Because cancer cells replicate rapidly and often have defects in their DNA repair machinery, they become heavily reliant on enzymes like FEN1 to maintain genomic stability and survive.

This reliance creates a strategic vulnerability. FEN1 is overexpressed in numerous tumor types, and its inhibition can be particularly devastating to cancer cells that already have defects in other DNA repair pathways, such as those with BRCA gene mutations. This concept, known as synthetic lethality, is a cornerstone of modern precision oncology. By inhibiting FEN1, BSM-1516 is designed to deliver a one-two punch that kills cancer cells while largely sparing healthy ones. Research has already shown that BSM-1516 is especially effective in BRCA2-deficient cancer cells.

Furthermore, the data to be presented at AACR indicates that BSM-1516 works synergistically with several other classes of DNA Damage Response (DDR) inhibitors, including PARP inhibitors like olaparib and ATR inhibitors. This suggests a significant potential for BSM-1516 to be used in combination therapies, enhancing the efficacy of existing treatments and overcoming resistance mechanisms in hard-to-treat cancers.

Identifying a Signature of Success

The upcoming poster presentation, titled "Proteomic profiling of FEN1 inhibition by BSM-1516 reveals chromatin-associated biomarkers for preclinical pharmacodynamic evaluation," delves into the molecular mechanics of how the drug works. A critical step in developing any new drug is proving that it is engaging its intended target within a living system. Blacksmith's research focused on identifying these so-called pharmacodynamic (PD) biomarkers.

Using a sophisticated technique known as iPOND (isolation of Proteins On Nascent DNA) coupled with mass spectrometry, researchers were able to identify a distinct "proteomic signature" that appears when FEN1 is inhibited by BSM-1516. They observed that inhibiting FEN1 caused a build-up of other DNA repair proteins—including FEN1 itself, PARP1/2, and LIG3—at the site of DNA replication. This signature provides a clear, measurable signal that the drug is having its intended biological effect.

These findings are crucial as the program advances. The identified biomarkers can now be used in ongoing and future preclinical animal studies to confirm target engagement and optimize dosing. Ultimately, they could become essential tools in future human clinical trials to monitor treatment response and select patients most likely to benefit, accelerating the path from the lab to the clinic.

Forging Alliances and Building Momentum

The progress with the FEN1 program is underpinned by Blacksmith's strong foundation of strategic support and partnerships. The company has attracted a roster of high-profile collaborators from the pharmaceutical and biotechnology industries, including Eli Lilly and Company, Hoffmann-La Roche, Basilea Pharmaceutica, Cyteir Therapeutics, and Zoetis. These alliances provide not only significant financial resources but also deep domain expertise and external validation of the platform's potential.

This industry confidence is mirrored by a robust investor base that includes Lilly, Evotec A.G., MP Healthcare Partners, MagnaSci Ventures, and Alexandria Venture Investments. Beyond private investment, Blacksmith has also secured prestigious non-dilutive funding from government and non-profit organizations like CARB-X and the National Institute of Allergy and Infectious Diseases (NIH/NIAID) for other programs, signaling the broad scientific importance of its work on metalloenzymes.

As Blacksmith Medicines prepares to share its latest progress with the global oncology community, the AACR presentation represents more than just a scientific update. It is a demonstration of a powerful new engine for drug discovery beginning to yield tangible results. The insights into FEN1 inhibition offer a promising new direction for cancer therapy and provide a compelling proof-of-concept that the vast, challenging world of metalloenzymes is finally being brought within the grasp of modern medicine.