The PROTAC Era: From VEPPANU’s Landmark Approval to the Next Generation of CRBN-Targeted Therapies
On May 1, 2026, the U.S. Food and Drug Administration (FDA) approved VEPPANU (vepdegestrant), an oral PROteolysis TArgeting Chimera (PROTAC) developed by Arvinas in collaboration with Pfizer, for adults with estrogen receptor-positive (ER+), HER2-negative, ESR1-mutated advanced or metastatic breast cancer who have progressed after at least one line of endocrine therapy[1]. This marks not only the first approved therapy specifically for ESR1-mutant disease in this setting but, more profoundly, the first-ever regulatory approval of a heterobifunctional PROTAC protein degrader. It ushers in what many in the biotech industry are calling the “PROTAC Era.” However, the journey from targeted protein degradation (TPD) concept to an FDA-approved oral therapy is fraught with translational bottlenecks.Within this landmark protein degradation mechanism, CRBN (Cereblon) serves as the indispensable core engine. To replicate VEPPANU’s success, researchers urgently need in vivo tools that can faithfully bridge the gap between human target engagement and preclinical validation.
1. FDA Approval of VEPPANU (Vepdegestrant): A Milestone for PROTAC Therapeutics
VEPPANU works by recruiting the E3 ubiquitin ligase cereblon (CRBN) to the estrogen receptor (ER), marking it for proteasomal degradation. Unlike traditional small-molecule inhibitors that merely block ER signaling, this catalytic mechanism eliminates the protein entirely. It overcomes resistance mechanisms common in ESR1-mutated tumors. In the pivotal Phase 3 VERITAC-2 trial, VEPPANU demonstrated a 43% reduction in the risk of disease progression or death versus fulvestrant in the ESR1-mutant subgroup. It extended median progression-free survival to 5.0 months from 2.1 months[2].
Figure 1. VEPPANU (vepdegestrant) Mechanism of Action[3].
For the preclinical development sector, this approval is a watershed validation of the entire PROTAC platform. For over a decade, PROTACs have promised a paradigm shift in drug discovery: harnessing the cell’s own ubiquitin-proteasome system to degrade “undruggable” or resistant proteins with exquisite specificity and sub-stoichiometric potency. Skeptics long questioned whether these large, bifunctional molecules could achieve sufficient oral bioavailability, tissue penetration, and therapeutic index in humans. VEPPANU’s success, delivered as a once-daily oral tablet, silences those doubts. It proves that PROTACs can translate from bench to bedside, delivering meaningful clinical benefit where conventional modalities fall short. The FDA’s accelerated review and approval ahead of the June 5, 2026 PDUFA date further underscore regulatory confidence in the platform’s safety and efficacy profile[4].
This milestone has immediate ripple effects across oncology and beyond. The portfolios of industry titans are now supercharged; Bristol Myers Squibb is advancing next-generation CRBN-based molecular glues like Iberdomide, Mezigdomide and Golcadomide for hematologic malignancies, while Amgen and Merck are aggressively scaling programs against elusive targets like PRMT5 and other solid tumor drivers. The reach of this technology even extends into the central nervous system, where major MNC-backed collaborations are now targeting the underlying proteins of neurodegeneration. This approval effectively de-risks the modality, likely unlocking a flood of investor capital, accelerating trial enrollment, and emboldening more ambitious combination strategies. In short, VEPPANU is not just a new breast cancer drug; it is the definitive proof-of-concept that targeted protein degradation has graduated from a biotech curiosity to a clinically validated, heavyweight therapeutic class.
Figure 2. Preclinical studies, clinical trials and reviews in pubmed[5].
2. Humanized CRBN Mice: Overcoming Translation Barriers in PROTAC R&D
As a bifunctional molecule, the PROTAC mechanism relies on a ligand at one end to specifically capture the CRBN protein inside the cell. This interaction pulls the disease-causing protein into a degradation pathway. Because of this, the quality of the bond between the ligand and CRBN directly dictates how well the PROTAC functions. While human and mouse CRBN proteins share about 95% of the same amino acid sequence, there are critical differences in their binding domains. The most important distinction is at a specific site where humans have valine while mice have isoleucine. The larger isoleucine in mice creates physical clutter that prevents new target proteins from being recruited into the complex. Interestingly, while the initial drug binding to CRBN is similar across species, other structural differences further disrupt how these molecules interact in mice compared to humans[6].
Consequently, wild-type rodent models present a profound translation barrier for CRBN-recruiting degraders. These compounds often show powerful activity in human cell cultures but fail during studies in wild-type rodents. In these models, researchers frequently see poor target binding, inefficient complex formation, and issues with stability or oral absorption. This species mismatch has historically derailed CRBN-based pipelines, making reliable pharmacokinetic and pharmacodynamic (PK/PD) profiling nearly impossible in conventional models[7].
CRBN humanized mice solve this mismatch by expressing the human version of the protein. This allows the model to accurately mirror the drug recruitment and protein degradation processes that occur in the human body. As a result, researchers can gain much more reliable data on how a drug is distributed through tissues, its overall effectiveness, and its potential toxicity within a complete living system.
Figure 3. Mice are resistant to IMiDs due to non-conserved amino-acids in CRBN[8].
The clinical success of VEPPANU has drawn significant attention to the importance of preclinical development, which often relies on patient-derived xenogeneic transplantation (PDX) models[9]. Humanized CRBN mouse models have become an essential supplement to these methods. By overcoming long-standing translation hurdles, these models are helping expand the PROTAC pipeline beyond cancer into fields like neurology, immunology, and rare diseases.
To overcome these persistent translational hurdles, Cyagen has engineered next-generation CRBN humanized mouse models. These include the B6 background strain hCRBN (Product No.: C001683) and the BALB/c background strain hCRBN(BALB/c) (Product No.: C001724).
By fully expressing the human CRBN protein, our models eliminate the species barrier, allowing for accurate mapping of in vivo drug distribution, potent target degradation, and comprehensive safety profiling.
Featured Validation Showcase：
● hCRBN(BALB/c) (Product ID：C001724)
Figure 4. In vivo detection of human and mouse CRBN gene and protein expression in hCRBN(BALB/c) humanized mice. (6 weeks old, homozygous, n=3)
CC-885 is a CRBN molecular glue compound that exhibits potent anti-tumor activity by inducing the degradation of key proteins such as GSPT1. Although mouse and human CRBN share >98% sequence homology, several nucleotide differences exist in the immunomodulatory drug-binding region. These differences prevent the compound from promoting substrate degradation through mouse wild-type CRBN, which is sufficient to abolish the anti-tumor efficacy and toxicity of CC-885 in mice in vivo.
They were treated with 5 mg/kg CC-885 (Catalog No. HY-101488) or vehicle control via intraperitoneal injection for 7 consecutive days. (A) Percentage of mouse survival rate; (B) Body weight of mice during the treatment period.
CC-885 exhibits significant toxicity only in CRBN humanized mice.
Figure 5. In vivo toxicity analysis of CC-885 in wild-type mice and homozygous hCRBN(BALB/c) mice. (Female, 8–9 weeks old, n=5)
CC-885 induces GSPT1 degradation in hCRBN(BALB/c) humanized mice, but this effect is not observed in wild-type mice.
Figure 6. Western blot analysis of CRBN, GSPT1, and CK1ε protein levels in the heart and spleen tissues of wild-type mice and homozygous hCRBN(BALB/c) mice after CC-885 treatment.
3. Looking Ahead: A Maturing Pipeline and Broader Therapeutic Horizons
VEPPANU’s approval marks an important first step. With the technology now proven and the supporting tools in place, the next generation of CRBN-targeted PROTACs is ready to tackle tougher targets and reach more patients.
Arvinas and its partners are already looking at new uses, while other companies push forward with their own degraders that offer better potency, selectivity, and safety.
There are still hurdles to clear, such as improving delivery to specific tissues, avoiding unwanted protein breakdown, and scaling up manufacturing. Even so, the forward momentum is clear.
For the biotech world, VEPPANU helps establish targeted protein degradation as a major new approach in modern medicine. The PROTAC era has undeniably begun. As pipelines expand toward elusive CNS and solid tumor targets, robust predictive tools will separate the winners from the rest. With Cyagen’s humanized CRBN models and end-to-end preclinical evaluation platforms, biopharma innovators now have the foundational support required to turn today's early clinical promise into tomorrow's blockbuster therapies.
4. Reference
[1] FDA approves vepdegestrant for ER-positive, HER2-negative, ESR1-mutated advanced or metastatic breast cancer [Internet]. Silver Spring (MD): U.S. Food and Drug Administration; 2026 May 1 [cited 2026 May 7]. Available from: https://www.fda.gov/drugs/resources-information-approved-drugs/fda-approves-vepdegestrant-er-positive-her2-negative-esr1-mutated-advanced-or-metastatic-breast.
[2] Campone M, De Laurentiis M, Jhaveri K, Hu X, Ladoire S, Patsouris A, Zamagni C, Cui J, Cazzaniga M, Cil T, Jerzak KJ, Fuentes C, Yoshinami T, Rodriguez-Lescure A, Sezer A, Fontana A, Guarneri V, Molckovsky A, Mouret-Reynier MA, Demirci U, Zhang Y, Valota O, Lu DR, Martignoni M, Parameswaran J, Zhi X, Hamilton EP; VERITAC-2 Study Group. Vepdegestrant, a PROTAC Estrogen Receptor Degrader, in Advanced Breast Cancer. N Engl J Med. 2025 Aug 7;393(6):556-568. doi: 10.1056/NEJMoa2505725. Epub 2025 May 31. PMID: 40454645.
[3] Vepdegestrant (ARV-471) [Internet]. Pfizer Oncology Development Website. New York (NY): Pfizer; [updated 2026 Feb 27; cited 2026 May 7]. Available from: https://www.pfizeroncologydevelopment.com/molecule/protac-estrogen-receptor-degrader
[4] Arvinas. Arvinas Announces FDA Approval of VEPPANU (vepdegestrant) for the Treatment of ESR1m, ER+/HER2- Advanced Breast Cancer [Internet]. New Haven (CT): Arvinas; 2026 May 1 [cited 2026 May 7]. Available from: https://ir.arvinas.com/news-releases/news-release-details/arvinas-announces-fda-approval-veppanu-vepdegestrant-treatment
[5] Gentile G, D'Aguanno S, Di Martile M, Petricca A, Valentini E, Scalera S, Del Bufalo D. PROTAC-based protein degradation: a window of opportunity for melanoma therapy. J Biomed Sci. 2026 Feb 27;33(1):23. doi: 10.1186/s12929-026-01225-2. PMID: 41761284; PMCID: PMC12949513.
[6] Gemechu Y, Millrine D, Hashimoto S, Prakash J, Sanchenkova K, Metwally H, Gyanu P, Kang S, Kishimoto T. Humanized cereblon mice revealed two distinct therapeutic pathways of immunomodulatory drugs. Proc Natl Acad Sci U S A. 2018 Nov 13;115(46):11802-11807. doi: 10.1073/pnas.1814446115. Epub 2018 Oct 29. PMID: 30373817; PMCID: PMC6243262.
[7] Yamamoto J, Ito T, Yamaguchi Y, Handa H. Discovery of CRBN as a target of thalidomide: a breakthrough for progress in the development of protein degraders. Chem Soc Rev. 2022 Aug 1;51(15):6234-6250. doi: 10.1039/d2cs00116k. PMID: 35796627.
[8] Lindner S, Krönke J. The molecular mechanism of thalidomide analogs in hematologic malignancies. J Mol Med (Berl). 2016 Dec;94(12):1327-1334. doi: 10.1007/s00109-016-1450-z. Epub 2016 Aug 5. PMID: 27492707.
[9] Gough SM, Flanagan JJ, Teh J, Andreoli M, Rousseau E, Pannone M, Bookbinder M, Willard R, Davenport K, Bortolon E, Cadelina G, Gordon D, Pizzano J, Macaluso J, Soto L, Corradi J, Digianantonio K, Drulyte I, Morgan A, Quinn C, Békés M, Ferraro C, Chen X, Wang G, Dong H, Wang J, Langley DR, Houston J, Gedrich R, Taylor IC. Oral Estrogen Receptor PROTAC Vepdegestrant (ARV-471) Is Highly Efficacious as Monotherapy and in Combination with CDK4/6 or PI3K/mTOR Pathway Inhibitors in Preclinical ER+ Breast Cancer Models. Clin Cancer Res. 2024 Aug 15;30(16):3549-3563. doi: 10.1158/1078-0432.CCR-23-3465. PMID: 38819400; PMCID: PMC11325148.
