Preclinical Evaluation of Bavdegalutamide (ARV-110), a Novel PROteolysis TArgeting Chimera Androgen Receptor Degrader

Abstract

Androgen receptor (AR) signaling is the principal driver of prostate cancer, and drugs that target this pathway (e.g., abiraterone and enzalutamide) are standard treatments for metastatic hormone-sensitive prostate cancer and metastatic castration-resistant prostate cancer. However, continual evolution during prostate cancer progression can result in AR alterations (e.g., mutation, amplification, and splicing) that can cause tumors to become resistant to these therapies. Bavdegalutamide (ARV-110) is a PROteolysis TArgeting Chimera (PROTAC) protein degrader that recruits the cereblon-containing E3 ubiquitin ligase to direct the polyubiquitination and subsequent proteasomal degradation of AR. Bavdegalutamide selectively degrades wild-type AR and most clinically relevant mutants with low nanomolar potency. The advantages of the degradation mechanism of action are demonstrated by the higher activity of bavdegalutamide relative to the AR antagonist enzalutamide in cell-based systems that assess effects on PSA synthesis, proliferation of prostate cancer cells, and induction of apoptosis. In an AR-expressing patient-derived xenograft mouse model, bavdegalutamide showed substantial AR degradation and greater tumor growth inhibition compared with enzalutamide. Bavdegalutamide also showed robust tumor growth inhibition in enzalutamide- and abiraterone-resistant prostate cancer animal models and enhanced activity in combination with abiraterone. These promising preclinical data supported the clinical development of bavdegalutamide as a potential treatment for patients with prostate cancer. Bavdegalutamide was the first PROTAC protein degrader to enter human clinical trials, specifically in patients with metastatic castration-resistant prostate cancer in a phase I/II study (NCT03888612).

Graphical abstract

Figure 1.

Bavdegalutamide degrades AR via the ubiquitin–proteasome pathway. A, Bavdegalutamide structure and MOA. B, Binding affinity of bavdegalutamide vs. enzalutamide for AR. The data shown are representative of two independent experiments; mean and SEM are plotted. C, Dose-dependent degradation of AR by bavdegalutamide in VCaP and LNCaP cells at 24 hours (representative of two independent experiments). D, Time course of AR degradation with 10 nmol/L bavdegalutamide in VCaP cells. E, Polyubiquitination of AR with 10 nmol/L bavdegalutamide. F, E3 ligase–dependent and proteasome-dependent degradation of AR by bavdegalutamide. FL, full length; hMito, human mitochondria; Ub, ubiquitin.

Figure 2.

Bavdegalutamide-induced AR degradation is CRBN dependent. A, AR degradation with increasing concentrations of bavdegalutamide in LNCaP parental cells (left) and LNCaP KO clone with doxycycline (dox)-inducible CRBN (right). CRBN expression is induced with 32–0.5 ng/mL (twofold dilutions) dox. Representative western blots from two independent experiments are shown. B, AR degradation with increasing concentrations of bavdegalutamide in 22Rv1 parental cells (left) and 22Rv1 KO clone with dox-inducible CRBN (right). CRBN expression is induced with 20–1.3 ng/mL (twofold dilutions) dox. Representative western blots from two independent experiments are shown.

Figure 3.

Bavdegalutamide selectively degrades AR and targets WT AR and clinically relevant mutants. A, Degradation of AR but not GR at 30, 100, or 300 nmol/L bavdegalutamide in MCF-7 cells. B, Selective degradation of AR among nearly 4,000 proteins measured by mass spectrometry following treatment of VCaP cells with 10 nmol/L bavdegalutamide for 8 hours (representative of four experiments). C, Degradation of stably expressed WT AR and clinically relevant mutants of AR in T-REx-293 cells treated with up to 100 nmol/L of bavdegalutamide. (representative of five independent experiments; mean and SEM are plotted). D, Degradation of stably expressed WT AR and AR^L702H in T-REx-293 cells and endogenously expressed AR^T878A/L702H in MDA PCa 2B cells (representative of three independent experiments). hMito, human mitochondria.

Figure 4.

Bavdegalutamide inhibits PSA synthesis, blocks prostate cancer cell proliferation in the absence and presence of elevated androgen levels, and induces apoptosis. A, PSA levels with increasing concentrations of bavdegalutamide or enzalutamide in LNCaP/AR cells. The data shown are representative of two independent experiments. B, Proliferation of VCaP cells with increasing concentrations of bavdegalutamide or enzalutamide (representative of nine independent experiments; mean and SEM are plotted). C, Proliferation of VCaP cells with 300 nmol/L bavdegalutamide or 1,000 nmol/L enzalutamide and co-treatment with increasing concentrations of R1881 for 5 days. D, Apoptosis, measured by the activity of caspase-3 and caspase-7 and PARP cleavage, with increasing concentrations of bavdegalutamide or enzalutamide in VCaP cells. (representative of three independent experiments; mean and SEM are plotted). A825 is a BET degrader used as a positive control for apoptosis. BET, bromodomain and extra terminal; hMito, human mitochondria; MitoC, mitochondria control; RLU, relative light unit.

Figure 5.

Oral doses of bavdegalutamide every day result in substantial degradation of AR in xenografts, provide TGI in prostate cancer mouse models, and induce rat prostate involution. A, AR degradation with increasing doses (every day × 3) of bavdegalutamide in a castrated VCaP xenograft model (16 hours after last dose, mean and SD are denoted. The data shown are representative of at least 10 similar studies that were conducted. B, TGI with bavdegalutamide vs. enzalutamide in a castrated VCaP xenograft model. Mean tumor volume and SEM are plotted. The data shown are representative of at least 10 similar studies that were conducted. C, TGI (mean tumor volume and SEM are plotted) and AR degradation (16 hours after the last dose; mean and SD are denoted) with increasing doses of bavdegalutamide vs. enzalutamide in an intact (noncastrated) VCaP xenograft model. The data shown are representative of four independent studies that were conducted. D, TGI (mean tumor volume and SEM are plotted) and PSA reduction (16 hours after the last dose, mean and SD are denoted) with bavdegalutamide vs. enzalutamide in an AR-expressing patient-derived xenograft model. The data shown are representative of the two independent studies that were conducted. E, Rat prostate involution with bavdegalutamide vs. enzalutamide. Intact male adult rats were treated orally for 10 days, after which prostates were isolated and weighed (24 hours after the last dose, mean and SD are denoted). One-way ANOVA with the Tukey multiple comparison test was used to compare treatments. The data shown are representative of three independent studies conducted. hMito, human mitochondria.

Figure 6.

Bavdegalutamide shows activity in enzalutamide- and abiraterone-resistant xenograft models. A, TGI (mean tumor volume and SEM are plotted), animal body weight (mean and SEM are plotted), AR degradation (mean and SD are denoted), and downstream signaling inhibition (ERG protein levels; mean and SD are denoted) with 10 or 3 mg/kg bavdegalutamide orally every day vs. 20 mg/kg enzalutamide in an enzalutamide-resistant VCaP model. VCaP cells harbor the TMPRSS2–ERG fusion, putting ERG under the transcriptional control of AR. Tumors were harvested 16 hours after the last dose. The data shown are representative of four independent studies conducted. B, TGI with oral, 3 mg/kg bavdegalutamide every day, 100 mg/kg abiraterone, or combination treatment in a VCaP xenograft model (phase I) and with 10 mg/kg bavdegalutamide or 100 mg/kg abiraterone (phase III) after emergence of abiraterone resistance (phase II; mean tumor volume and SEM are plotted). AR degradation with 3 mg/kg bavdegalutamide vs. 3 mg/kg bavdegalutamide in combination with 100 mg/kg abiraterone in the VCaP xenografts in phase I of the model. Tumors were harvested 16 hours after the last dose. The data shown are representative of two independent studies conducted. ERG, ETS-related gene; hMito, human mitochondria.