A First‑in‑Class Dual AR‑V7/AR Molecular Glue Degrader for Metastatic Castration‑Resistant Prostate Cancer

Most prostate cancer treatments today target the part of the AR protein that binds hormones, known as the ligand‑binding domain or LBD. At first these drugs like enzalutamide and abiraterone can shrink tumors or slow progression, but over time the cancer adapts and becomes resistant. This adaptation is a major reason why men with mCRPC eventually die from the disease.

One powerful way the cancer escapes treatment is by producing a shorter form of the AR protein called AR‑V7, which is a splice variant that lacks the LBD but still activates the same growth and survival programs as the full‑length receptor. Because AR‑V7 does not need hormones to turn on, drugs that only block the LBD cannot stop it. AR‑V7 is now known to be present in more than three‑quarters of men with mCRPC, and its expression is strongly linked to resistance to all AR‑pathway inhibitors, yet there are no approved drugs specifically designed to target it. This creates a big unmet need: clinicians can block the full‑length AR, but they have no way to shut down AR‑V7 once it appears.

To tackle this problem, scientists recently ran a very large drug screen testing more than 170,000 small molecules on prostate cancer cells that depend on AR and AR‑V7 for survival. From this screen they found a new type of compound that works in a completely different way from existing AR drugs. Instead of blocking a pocket on the receptor, this new molecule acts as a “molecular glue” that causes both the full‑length AR and AR‑V7 to be destroyed by the cell’s own garbage disposal system, the ubiquitin‑proteasome pathway. It is the first example of a small molecule that can simultaneously degrade both forms of the receptor in a single treatment, and it does so with a chemical structure that has never been seen before in prostate cancer drugs.

In animal experiments, the best‑optimized compounds were tested in a model where human prostate cancer cells known to be resistant to enzalutamide grow as tumors in mice (the 22Rv1 xenograft model). In these resistant tumors, the new compounds strongly suppressed tumor growth, reversed the resistance to enzalutamide, and showed superior efficacy compared with ARV‑110, which is currently the only full‑length AR‑targeting PROTAC degrader being tested in clinical trials. In fact, the potency advantage over ARV‑110 was larger than ten‑fold, yet the animals did not lose weight or show obvious signs of sickness, suggesting a good safety margin. Detailed pharmacokinetic studies showed that the drug reaches the tumor at effective levels and stays around long enough to keep the receptors turned over continuously.

Inside the tumor tissue, the researchers could see that AR and AR‑V7 protein levels dropped to very low levels within 24 hours after the last dose, and this near‑complete degradation went hand‑in‑hand with rapid tumor‑growth inhibition. This tight correlation between protein loss and effect on the tumor is exactly what one would expect from a true degrader rather than a simple inhibitor. Additional safety studies in animals treated at different doses and schedules did not reveal any major organ damage under the microscope, which supports the idea that this class of drugs may be tolerable enough to move into human trials.

To understand how selective the drug really is, the team ran global proteomics experiments that measured the abundance of nearly 10,000 proteins in treated cells. In this broad view, AR and AR‑V7 ranked among the top 1% of all proteins that were significantly reduced, while almost everything else stayed the same. Importantly, other major nuclear receptors such as the estrogen receptor, progesterone receptor, and glucocorticoid receptor were largely unaffected, which is a big advantage because messing with these receptors can cause serious side effects. This high degree of selectivity suggests that the new degraders might avoid some of the off‑target problems seen with earlier AR‑targeting strategies.

Another key breakthrough lies in where the drug binds on the AR protein. Instead of targeting the LBD, which is the usual target of current AR drugs, the compounds attach to the intrinsically disordered N‑terminal domain, or NTD, which sticks out like an unstructured tail at the beginning of the receptor. Because the NTD is upstream of the LBD, hitting it allows the drug to bypass almost all known LBD mutations that cause resistance to enzalutamide, abiraterone, and similar agents. The lead compounds were able to inhibit cancer cell growth driven by multiple clinically validated AR‑pathway‑inhibitor–resistant isoforms, including common LBD mutations and AR‑V7 itself. This means that the new degraders are not just a solution for AR‑V7‑mediated resistance; they also represent a broader “resistance‑proof” strategy that targets several relevant AR variants at the same time.

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