AUTOTAC Degraders ATB‑238 and ATB‑239 Target AR and AR‑v7 in Advanced Prostate Cancer

AUTOTACs (Autophagy‑Targeting Chimeras), are molecules designed to force cancer cells to “clean up” and destroy the androgen receptor (AR), a key driver of prostate cancer growth and progression.
The latest research on two second‑generation AR‑targeting AUTOTACs, ATB‑238 and ATB‑239, shows that these compounds can effectively degrade not only the normal AR but also its troublesome splice variants, such as AR‑v7, which are often responsible for treatment resistance in castration‑resistant prostate cancer (CRPC).

In previous work, the research team described ATC‑324, the first AR‑targeting AUTOTAC. It uses enzalutamide, a well‑known AR inhibitor, as a “target‑binding ligand” that latches onto the receptor, while a second “autophagy‑targeting ligand” redirects the AR into the cell’s autophagy–lysosomal machinery for destruction. The new compounds ATB‑238 and ATB‑239 are improved versions of this approach, engineered to be more potent and stable, with a sharper ability to remove AR and its variants from the cancer cell. Researchers tested these molecules in several prostate cancer models, including AR‑null cells (PC3), hormone‑sensitive lines (LNCaP and LAPC4), and CRPC models (CWR‑R1 and 22Rv1), which are known to express AR‑v7 and other resistance‑associated isoforms.

The results showed that both ATB‑238 and ATB‑239 significantly reduced the levels of multiple AR isoforms and strongly suppressed AR‑driven gene transcription, including the activity driven by AR‑v7. This is important because many men with CRPC eventually stop responding to enzalutamide and similar drugs when AR‑v7 or other splice variants take over control of the cell. In functional assays, ATB‑238 killed AR‑positive prostate cancer cells (LAPC4, CWR‑R1, and 22Rv1) but had little effect on AR‑null PC3 cells, supporting the idea that its cytotoxicity is specifically tied to AR degradation rather than off‑target toxic effects.

To assess how these molecules might behave in the bone, the most common site of lethal metastasis in prostate cancer, the team used a bone‑in‑culture array (BICA) system containing 22Rv1 micrometastases embedded in a bone‑like microenvironment. In this model, both ATB‑238 and ATB‑239 showed high potency against the tumor lesions, indicating that they remain effective even in the complex setting of bone‑associated disease. The study also explored combinations with docetaxel, a standard‑of‑care chemotherapy for advanced prostate cancer. ATB‑238 demonstrated synergistic killing of LNCaP and CWR‑R1 cells when combined with docetaxel, raising the possibility that AUTOTAC‑based AR degradation could be integrated into existing treatment strategies rather than simply replacing them.

Ongoing intra‑iliac‑artery xenograft experiments are now focused on evaluating whether these AUTOTACs can actually inhibit the establishment or growth of bone metastases in vivo, a major unmet need in the clinic.

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