Closely held Solu Therapeutics is pairing heterobifunctional small molecules with monoclonal antibodies to develop therapeutic agents that eliminate disease-driving cells in cancer, immunology, and other therapeutic areas.
“We are unlocking the impossible by advancing therapies that combine the target-binding capabilities of small molecules with the therapeutic power of biologics,” Philip J. Vickers, PhD, president and CEO of Solu, says in an interview with BioTuesdays.
“It’s not a combination therapy,” he clarifies. “It’s two components—an antibody and a small molecule—that, when linked together, form the active therapeutic modality.”
Solu is leveraging its CyTAC technology—or cytotoxicity targeting chimera—a novel drug discovery platform that enables the rapid creation of innovative, high-value medicines to transform the lives of specific patient populations in areas of high unmet medical need.
Dr. Vickers explains that by linking potent and selective small molecules to effector antibodies in a unique way, Solu can target cell surface proteins that are otherwise inaccessible using traditional therapeutic modalities. Using best-in-class small molecule binders, deep binding pockets in receptors—such as G protein-coupled receptors (GPCRs) and ion channels—can now be accessed.
“To date, the industry has been unsuccessful in binding therapeutic antibodies to certain drug discovery targets. To the best of my knowledge, there isn’t a single therapeutic antibody that binds to an ion channel. With our approach, we can now very rapidly open up these targets to antibody pharmacology.”
Solu is unlocking novel targets by engineering the binders into bifunctional small molecules. One arm engages the extracellular target, while the other arm utilizes a proprietary linker platform to connect with a proprietary antibody.
The company’s innovative linker technology enables the creation of an entirely new class of drugs, in which bifunctional small molecules adopt the pharmacokinetic properties and functions of their antibody counterparts. This unique capability allows Solu to develop medicines that were previously impossible to create.
“Our current oncology and immunology programs utilize engineered antibodies that direct immune cells to potentially kill pathogenic target cells—we’re killing tumors cells in oncology and depleting aberrant immune cells that cause disease,” he says.
The company has developed a range of proprietary engineered antibodies. For example, its lead program employs an Fc-engineered, ADCC-enhanced antibody for tumor cell killing. Solu also utilizes proprietary antibody-drug conjugates for cytotoxic payload delivery, and CD3-mediated bispecifics for T cell-directed killing. “What we do is tailor the type of effector antibody to the needs of the patient and the disease we are trying to treat,” he adds.
Dr. Vickers points out that covalently attaching proprietary linkers to readily available, clinical-quality small molecules enables Solu to progress from concept to development candidate generally in less than one year.
“The very low small molecule doses required in the Solu platform is designed to reduce safety risks, and the deep binding pockets of drug targets enhance the efficacy of effector antibodies,” he notes.
The company’s lead CyTAC program, STX-0712, is a potential first-in-class depletor of disease-driving monocytes in cancer. It targets GPCR chemokine receptor 2 (CCR2), a selective marker highly expressed on pathogenic monocytes. These CCR2-expressing monocytes are known to be key drivers in certain hematological malignancies. STX-0712 is designed to selectively eliminate these pathogenic monocytes.
Solu recently initiated a Phase 1 study of STX-0712 in patients with chronic myelomonocytic leukemia (CMML).
“We have dosed our first patient for potential proof-of-concept (POC) in our lead indication and have data supporting the potential de-risked expansion into acute myeloid leukemia (AML) and other high-value hematological malignancies,” Dr. Vickers says.
He emphasizes that CMML is an orphan cancer with high unmet medical need and significant, yet underappreciated, commercial potential. “We are among the very few companies developing drugs in this area. This indication represents a greater than one billion-dollar market that currently has no effective standard of care.”
By targeting CMML, Solu can conduct rapid blood draws following treatment to quickly observe monocyte levels and confirm target cell depletion.
Dr. Vickers adds that because only a very low small molecule dose is needed for potent efficacy, Solu projects dosing at small levels with reasonable frequency. “This brings the potential for numerous benefits—for example, smaller manufacturing requirements and reduced safety concerns.”
Solu anticipates determining by Q3 2025 whether the target cells of interest have been depleted in Phase 1, validating its drug discovery approach. With clinical POC expected in 2027, Solu plans to transition into a registrational study in CMML, followed by expansion into additional hematological malignancies with high unmet need and strong commercial prospects.
“We have a robust in vitro, in vivo, and ex vivo data package, and we believe STX-0712 has the potential to transform treatment for patients with various hematological malignancies,” Dr. Vickers says.
The company is also advancing preclinical programs that are nearing development candidate selection in immunology and inflammation, as well as pain.
STX-0812 is a CyTAC targeting pathogenic monocytes in inflammatory diseases, while STX-0640 targets mast cells—clinically validated drivers of several immunological and inflammatory disorders.
Dr. Vickers emphasizes that CyTAC is a modular platform, allowing effector antibodies to be reused across multiple programs, which supports rapid pipeline expansion. “In areas where we choose not to move forward, there is a multitude of potential partnership opportunities with various pharma companies,” he contends.
In area of pain, Solu is developing its TicTAC program—or therapeutic index control-targeting chimera—three distinct therapeutic programs for potent, long-acting antagonism of sodium ion channels.
“Our proprietary TicTAC molecules drive precise associations between potent and selective small molecule agonists or antagonists with an Fc-modified antibody, allowing the small molecule to adopt the pharmacokinetic profile of the antibody. This results in multiple advantage and a superior therapeutic profile,” Dr. Vickers explains. “We believe we have a potential best-in-class sodium ion channel antagonist and are in active conversations with potential partners in this area.”
Although Solu was only formed in 2023, Dr. Vickers points out that the company is in a strong financial position following the completion of its Series A financing. “We have enough cash on hand to drive to clinical POC in CMML and to continue building our deep pipeline of candidate-stage assets. Our current financing takes us through mid-2027.”
In conclusion, Dr. Vickers says it’s an exciting time for Solu, with progress exceeding expectations. “We have a very experienced leadership team, an exceptional board of directors, and engaged investors—all aligned in our mission to rapidly apply our platform to therapeutic areas where we believe it can transform the lives of patients.”
