Dual PROTACs Close In on Two Disease Proteins at Once

Targeted protein degradation has been one of the most disruptive ideas in modern drug discovery. Instead of blocking the activity of a disease-causing protein, proteolysis-targeting chimeras, or PROTACs, recruit it to the cell’s waste-disposal machinery and destroy it outright. A PROTAC molecule is built from two warheads joined by a chemical linker: one end grips the protein of interest, the other grips an E3 ubiquitin ligase, an enzyme that stamps its targets with ubiquitin tags that mark them for destruction by the proteasome. Crucially, PROTACs act catalytically; a single molecule can eliminate many copies of its target, so the effect persists far beyond what ordinary inhibitors achieve. Now a comprehensive review published in the journal Molecular Diversity argues that the field’s next leap forward is happening at the level of pairs: molecules engineered to wipe out two pathogenic proteins simultaneously.

The new review, authored by Shun-Ran Li, Meng-Qian Yu, and colleagues at Hangzhou Normal University and collaborating institutions, systematically surveys the explosion of dual- and multi-target degraders reported between 2023 and 2026. Its central premise is that complex diseases rarely depend on a single molecular culprit. Cancer and neurodegenerative disorders are governed by redundant and compensatory signaling networks, so when one driver protein is eliminated, others rush to fill the gap. Conventional single-target PROTACs, however powerful, can be undermined by this biological backup system. Dual PROTACs attempt to solve the problem in a single chemical entity, collapsing what would otherwise be a combination of two drugs into one compound with one set of pharmacokinetics.

The authors organize the growing catalog of dual degraders into two broad design classes. The first targets homologous proteins within the same family, where structural similarity can be exploited by a single warhead that binds both. Cyclin-dependent kinases have been a particular focus, with dual degraders reported for CDK4/6, CDK2/5, and CDK12/13, the latter exemplified by the orally bioavailable triple-negative breast cancer candidate DN1679. The BCL-2 family of apoptosis regulators has yielded dual BCL-2/BCL-xL degraders with improved anti-leukemic activity, and the field has now seen first-in-class degraders for the bromodomain proteins BAZ2A and BAZ2B as well as dual histone deacetylase degraders, including HDAC3/HDAC8 molecules that revealed new roles for histone acetylation in gene regulation.

The second, and pharmacologically more ambitious, class targets two distinct proteins sitting on different but interconnected disease pathways. Here the review catalogues an impressive roster: ERα/aromatase degraders designed to overcome endocrine-resistant breast cancer by hitting both the receptor and the enzyme that produces its activating estrogen; α-synuclein/tau degraders aimed at the protein aggregates that define Parkinson’s and Alzheimer’s disease; BET/HDAC and CBP/BRD4 degraders that combine epigenetic readers and erasers in one molecule; PI3K/mTOR degraders that suppress the entire eponymous survival pathway; and FLT3/CHK1 degraders that pair an oncogenic kinase with a checkpoint kinase to attack acute myeloid leukemia from two directions.

The technical heart of the review lies in its dissection of structure-activity relationships. Linker chemistry is where dual PROTACs live or die. Because a single molecule must accommodate two target-binding events, the linker length, attachment point, and flexibility determine not only potency but the ternary geometry between target, PROTAC, and E3 ligase that licenses ubiquitin transfer. Several case studies illustrate the point. Dual BCL-xL/BCL-w degraders were built by exploiting the bis(sulfonyl)benzene ring of the clinical inhibitor ABT-263 as a linkage vector, showing how careful warhead decoration can convert a blocker into a degrader. In the FLT3/CHK1 program, systematic linker scans revealed how marginal changes in length flipped degradation selectivity between the two kinases. The authors emphasize that hook effects, hook-like concentration dependence in which excess PROTAC saturates both binding sites separately and aborts the ternary complex, remain a persistent design trap requiring careful dose-response characterization.

E3 ligase selection emerges as another decisive variable. Most reported dual degraders recruit either the von Hippel-Lindau (VHL) ligase or cereblon (CRBN), reflecting the maturity of their ligand chemistries. CRBN-recruiting degraders derived from pomalidomide and related immunomodulatory drugs have proven especially productive for kinases and transcriptional regulators, while VHL ligands dominate among cytosolic and nuclear targets. But the review is blunt about the field’s narrow toolkit: the reliance on just two or three E3 ligases limits tissue selectivity, constrains the design space for dual targets, and contributes to off-target degradation of neo-substrates such as IKZF1 and IKZF3. Expanding the E3 ligase repertoire, including tumor-selective or tissue-specific ligases, is flagged as a priority for next-generation design.

Among the milestones the review highlights are the first dual degraders aimed at non-kinase epigenetic regulators and, strikingly, at protein aggregates themselves. Degraders capable of clearing α-synuclein and tau aggregates simultaneously represent a conceptual breakthrough for neurodegeneration, because both misfolded proteins cross-seed one another and together drive pathology in diseases such as dementia with Lewy bodies and Alzheimer’s. The authors note that these designs repurposed aggregation-binding scaffolds, such as thioflavin-derived amyloid ligands, as warheads, demonstrating that even supramolecular pathological assemblies can be brought into the reach of the ubiquitin-proteasome system. In parallel, dual GSPT1/BRD4 degraders exploit cereblon-mediated translational termination factor degradation alongside epigenetic transcriptional collapse to kill leukemia cells through mechanistically independent routes.

The translational horizon is coming into view. The first PROTAC, vepdegestrant, has moved targeted degradation into approved oncology practice, and clinically advanced single-target degraders have validated the modality’s core principles. Dual degraders now face the harder test of converting dual potency into dual efficacy with an acceptable safety profile. The review identifies pharmacokinetics as the chief obstacle: dual PROTACs are large, often exceeding the classic rule-of-five boundaries for oral absorption, and their high polarity and molecular weight challenge permeability, metabolic stability, and brain penetration. Off-target toxicity arising from polypharmacology is a second concern, since the same warhead promiscuity that enables dual engagement can degrade unintended proteins. Strategies such as introducing one-carbon bridges to lower lipophilicity, incorporating molecular glue features into PROTAC scaffolds, and exploiting CD36-mediated endocytosis to improve cellular uptake are among the emerging countermeasures surveyed.

What the review ultimately delivers is a map. By consolidating the 2023 to 2026 literature into a coherent framework of homologous versus cross-pathway dual targets, and by extracting transferable SAR lessons on warhead choice, linker optimization, and E3 ligase pairing, the authors have given medicinal chemists a practical playbook for the next round of design. If the remaining pharmacokinetic and selectivity problems can be tamed, dual PROTACs could compress combination therapy into a single pill, offering patients with complex, drug-resistant diseases a weapon that dismantles two pillars of pathology at once. For a field that has already taught medicine to delete proteins rather than merely inhibit them, degrading disease networks two nodes at a time may be the logical, and inevitable, next act.

Subject of Research: Development of dual PROTACs that simultaneously degrade two disease-related proteins for therapeutic applications in cancer and neurodegenerative disease.

Article Title: Recent advances of dual PROTACs for potential therapeutic applications

Article References: Li, S.-R., Yu, M.-Q., Du, B.-Q., Jin, K.-J., Chen, S.-X., Hui, Z., Zhang, H., Mao, N.-D., Gao, Y., & Ye, X.-Y. (2026). Recent advances of dual PROTACs for potential therapeutic applications. Molecular Diversity. https://doi.org/10.1007/s11030-026-11734-9

Image Credits: AI Generated

DOI: 10.1007/s11030-026-11734-9

Keywords: PROTACs, targeted protein degradation, dual degraders, ubiquitin-proteasome system, E3 ubiquitin ligase, cancer therapy, neurodegenerative disease, BCL-2, BRD4, CDK inhibitors, structure-activity relationships, drug discovery