Proteolysis Targeting Chimera Degraders Research Articles

Structure-Based Discovery of SD-36 as a Potent, Selective, and Efficacious PROTAC Degrader of STAT3 Protein.

Signal transducer and activator of transcription 3 (STAT3) is a transcription factor and an attractive therapeutic target for cancer and other human diseases. Despite 20 years of persistent research efforts, targeting STAT3 has been very challenging. We report herein the structure-based discovery of potent small-molecule STAT3 degraders based upon the proteolysis targeting chimera (PROTAC) concept. We first designed SI-109 as a potent, small-molecule inhibitor of the STAT3 SH2 domain. Employing ligands for cereblon/cullin 4A E3 ligase and SI-109, we obtained a series of potent PROTAC STAT3 degraders, exemplified by SD-36. SD-36 induces rapid STAT3 degradation at low nanomolar concentrations in cells and fails to degrade other STAT proteins. SD-36 achieves nanomolar cell growth inhibitory activity in leukemia and lymphoma cell lines with high levels of phosphorylated STAT3. A single dose of SD-36 results in complete STAT3 protein degradation in xenograft tumor tissue and normal mouse tissues. SD-36 achieves complete and long-lasting tumor regression in the Molm-16 xenograft tumor model at well-tolerated dose-schedules. SD-36 is a potent, selective, and efficacious STAT3 degrader.

Simple Structural Modifications Converting a Bona fide MDM2 PROTAC Degrader into a Molecular Glue Molecule: A Cautionary Tale in the Design of PROTAC Degraders.

Inducing protein degradation by proteolysis targeting chimeras (PROTACs) has gained tremendous momentum for its promise to discover and develop new therapies. Based upon our previously reported PROTAC MDM2 degraders, we have designed and synthesized additional analogues. Surprisingly, we found that simple structural modifications of MD-222, a bona fide MDM2 PROTAC degrader, converts it into a "molecular glue", as exemplified by MG-277. MG-277 induces only moderate MDM2 degradation and fails to activate wild-type p53 but is highly potent in inhibition of tumor cell growth in a p53-independent manner. Our mechanistic investigation established that MG-277 is not a PROTAC MDM2 degrader but instead works as a molecular glue, inducing degradation of a translation termination factor, GSPT1 to achieve its potent anticancer activity. Our study provides the first example that simple structural modifications can convert a bona fide PROTAC degrader into a molecular glue compound, which has a completely different mechanism of action.

Potent and Preferential Degradation of CDK6 via Proteolysis Targeting Chimera Degraders

A focused PROTAC library hijacking cancer therapeutic target CDK6 was developed. A design principle as "match/mismatch" was proposed for understanding the degradation profile differences in these PROTACs. Notably, potent PROTACs with specific and remarkable CDK6 degradation potential were generated by linking CDK6 inhibitor palbociclib and E3 ligase CRBN recruiter pomalidomide. The PROTAC strongly inhibited proliferation of hematopoietic cancer cells including multiple myeloma and robustly degraded copy-amplified/mutated forms of CDK6, indicating future potential clinical applications.

ARV-110: An oral androgen receptor PROTAC degrader for prostate cancer.

259 Background: The Androgen Receptor (AR) remains the principal driver of castration-resistant prostate cancer during the transition from a localized to metastatic disease. Most patients initially respond to inhibitors of the AR pathway, but the response is often relatively short-lived. The majority of patients progressing on enzalutamide or abiraterone exhibit genetic alterations in the AR locus, either in the form of amplifications or point mutations in the AR gene. Given these mechanisms of resistance, our goal is to eliminate the AR protein using the PROteolysis TArgeting Chimera (PROTAC) technology. Methods: Here we report an orally bioavailable small molecule AR PROTAC degrader, ARV-110, that promotes ubiquitination and degradation of AR. This molecule has been characterized in in vitro degradation and functional assays, and DMPK, toxicology and preclinical efficacy studies. Results: ARV-110 robustly degrades AR in all cell lines tested, with an observed half-maximal degradation concentration (DC50) of ~1 nM. ARV-110 treatment leads to highly selective AR degradation, as demonstrated by proteomic studies. In VCaP cells, PROTAC-mediated AR degradation suppresses the expression of the AR-target gene PSA, inhibits AR-dependent cell proliferation, and induces apoptosis at low nanomolar concentrations. Further, ARV-110 degrades clinically relevant mutant AR proteins and retains activity in a high androgen environment. In mouse xenograft studies, greater than 90% AR degradation is observed at a 1 mg/kg PO QD dose. Significant inhibition of tumor growth and AR signaling has been achieved in LNCaP, VCaP and prostate cancer patient derived xenograft (PDX) models. Notably, ARV-110 demonstrates in vivo efficacy and reduction of AR-target gene expression in a long term, castrate, enzalutamide-resistant VCaP tumor model. Conclusions: In summary, we report preclinical data on an orally bioavailable AR PROTAC degrader, ARV-110, that demonstrates efficacy in multiple prostate cancer models. ARV-110 has completed IND-enabling studies and FIH studies are planned for 1Q2019.

Abstract 5236: ARV-110: An androgen receptor PROTAC degrader for prostate cancer

Abstract The Androgen Receptor (AR) remains the principal driver of castration-resistant prostate cancer during the transition from a localized to metastatic disease. Most patients initially respond to inhibitors of the AR pathway, but the response is often short-lived. The majority of patients progressing on enzalutamide or abiraterone exhibit genetic alterations in the AR locus, either in the form of amplifications or point mutations in the AR gene. Given these mechanisms of resistance, our goal is to eliminate the AR protein using the PROteolysis TArgeting Chimera (PROTAC) technology. Here we report an orally bioavailable small molecule ARV-110 that leads to ubiquitination and degradation of AR. ARV-110 completely degrades AR in all cell lines tested, with an observed 50% degradation concentration (DC50) < 1 nM. PROTAC-mediated AR degradation suppresses the expression of the AR-target genes PSA and FKBP5, inhibits AR-dependent cell proliferation, and induces potent apoptosis in VCaP cells. ARV-110 degrades clinically relevant mutant AR proteins and retains activity in a high androgen environment. In mouse xenograft studies, greater than 90% AR degradation is observed at a 1 mg/kg PO QD dose. Significant inhibition of tumor growth and AR signaling can be achieved in both an intact and castrate setting. Further, ARV-110 demonstrates in vivo efficacy and reduction of oncogenic Erg protein in a long term, castrate, enzalutamide-resistant VCaP tumor model. DMPK and exploratory toxicology studies show robust oral, dose proportional drug exposure in rodent and non-rodent species. In summary, we report preclinical data on ARV-110, an orally bioavailable androgen receptor PROTAC degrader that demonstrates efficacy in enzalutamide-resistant prostate cancer. Citation Format: Taavi Neklesa, Lawrence B. Snyder, Ryan R. Willard, Nicholas Vitale, Kanak Raina, Jennifer Pizzano, Deborah Gordon, Mark Bookbinder, Jennifer Macaluso, Hanqing Dong, Zheng Liu, Caterina Ferraro, Gan Wang, Jing Wang, Craig M. Crews, John Houston, Andrew P. Crew, Ian Taylor. ARV-110: An androgen receptor PROTAC degrader for prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5236.

An oral androgen receptor PROTAC degrader for prostate cancer.

381 Background: The Androgen Receptor (AR) remains the principal driver of castration-resistant prostate cancer during the transition from a localized to metastatic disease. Most patients initially respond to inhibitors of the AR pathway, but the response is often short-lived. The majority of patients progressing on enzalutamide or abiraterone exhibit genetic alterations in the AR locus, either in the form of amplifications or point mutations in the AR gene. Given these mechanisms of resistance, our goal is to eliminate the AR protein using the PROteolysis TArgeting Chimera (PROTAC) technology. Methods: Here we report an orally bioavailable small molecule AR PROTAC that leads to ubiquitination and degradation of AR. This molecule has been characterized in in vitro degradation and functional assays, DMPK, toxicology and preclinical efficacy studies. Results: This AR PROTAC completely degrades AR in all cell lines tested, with an observed 50% degradation concentration (DC50) < 1 nM. PROTAC-mediated AR degradation suppresses the expression of the AR-target gene PSA, inhibits AR-dependent cell proliferation, and induces potent apoptosis in VCaP cells. The AR PROTAC degrades all clinically relevant mutant AR proteins and retains activity in a high androgen environment. In mouse xenograft studies, greater than 90% AR degradation is observed at a 1 mg/kg PO QD dose. Significant inhibition of tumor growth and AR signaling can be achieved in both an intact and castrate setting. Further, the AR PROTAC demonstrates in vivo efficacy and reduction of oncogenic Erg protein in a long term, castrate, enzalutamide-resistant VCaP tumor model. DMPK and exploratory toxicology studies show robust oral, dose proportional drug exposure in rodent and non-rodent species. Conclusions: In summary, we report preclinical data on an orally bioavailable AR PROTAC degrader that demonstrates efficacy in enzalutamide-resistant prostate cancer.

Abstract 5637: An oral Androgen Receptor PROTAC degrader for prostate cancer

Abstract The Androgen Receptor (AR) remains the principal driver of castration-resistant prostate cancer during the transition from a localized to metastatic disease. Most patients initially respond to inhibitors of the AR pathway, but the response is often short-lived. The majority of patients progressing on enzalutamide or abiraterone exhibit genetic alterations in the AR locus, either in the form of amplifications or point mutations in the AR gene. Given these mechanisms of resistance, our goal is to eliminate the AR protein using the PROteolysis TArgeting Chimera (PROTAC) technology. Further, we sought to make an orally bioavailable AR PROTAC. Medicinal chemistry efforts yielded a small molecule AR PROTAC that simultaneously binds E3-ubiquitin ligase and AR, thus leading to ubiquitination and degradation of AR. This molecule has been characterized in in vitro and in vivo preclinical studies. Our lead oral AR PROTAC degrades approximately 98% of total AR in all cell lines tested, with 50% degradation concentration (DC50) < 1 nM. AR degradation suppresses the expression of AR-target gene PSA, inhibits cell proliferation, and induces potent apoptosis in VCaP cells. No activity is observed in AR-null cell lines, such as PC-3. While enzalutamide loses its activity in the presence of elevated androgens, AR PROTAC maintains its antiproliferative activity. Further, AR PROTAC is able to degrade all clinically relevant mutant AR proteins. A robust oral bioavailability is observed across multiple species and overall ADME properties are encouraging. Approximately 95% AR degradation is observed in AR-amplified VCaP xenografts at doses as low as 10 mg/kg. Congruent with AR degradation, a dose responsive tumor growth inhibition is observed in AR-dependent xenograft studies. In summary, we report the first orally bioavailable AR PROTAC that robustly degrades AR in vitro and in vivo. Citation Format: Taavi K. Neklesa, Lawrence B. Snyder, Mark Bookbinder, Xin Chen, Andrew P. Crew, Craig M. Crews, Hanqing Dong, Deborah Gordon, Jennifer Macaluso, Kanak Raina, AnnMarie Rossi, Ian Taylor, Nicholas Vitale, Jing Wang, Ryan R. Willard, Kurt Zimmermann. An oral Androgen Receptor PROTAC degrader for prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5637. doi:10.1158/1538-7445.AM2017-5637

An oral androgen receptor PROTAC degrader for prostate cancer.

273 Background: The Androgen Receptor (AR) remains the principal driver of castration-resistant prostate cancer during the transition from a localized to metastatic disease. Most patients initially respond to inhibitors of the AR pathway, but the response is often short-lived. The majority of patients progressing on enzalutamide or abiraterone exhibit genetic alterations in the AR locus, either in the form of amplifications or point mutations in the AR gene. Given these mechanisms of resistance, our goal is to eliminate the AR protein using the PROteolysis TArgeting Chimera (PROTAC) technology. Further, we sought to make an orally bioavailable AR PROTAC. Methods: Medicinal chemistry efforts yielded a small molecule AR PROTAC that simultaneously binds E3-ubiquitin ligase and AR, thus leading to ubiquitination and degradation of AR. This molecule has been characterized in in vitro and in vivo preclinical studies. Results: Our lead oral AR PROTAC degrades 92-98% of total AR in all cell lines tested, with 50% degradation concentration (DC50) < 1 nM. AR degradation suppresses the expression of AR-target gene PSA, inhibits cell proliferation, and induces potent apoptosis in VCaP cells. No activity is observed in AR-null cell lines, such as PC-3. While enzalutamide loses its activity in the presence of elevated androgens, AR PROTAC maintains its antiproliferative activity. Further, AR PROTAC is able to degrade all clinically relevant mutant AR proteins. A robust oral bioavailability is observed across multiple species and overall ADME properties are encouraging. Approximately 95% AR degradation is observed in AR-amplified VCaP xenografts at doses as low as 10 mg/kg. Congruent with AR degradation, a dose responsive tumor growth inhibition is observed in AR-dependent xenograft studies. Conclusions: In summary, we report the first orally bioavailable AR PROTAC that robustly degrades AR in vitro and in vivo.

ARV-330: Androgen receptor PROTAC degrader for prostate cancer.

267 Background: The transition from localized prostate cancer to metastatic disease often involves modulation of the Androgen Receptor (AR). During the disease progression, patients progressing on enzalutamide or abiraterone therapy exhibit amplified AR, increased intra-tumoral androgen production or AR mutations leading to promiscuity to other ligands. Therefore, AR is still the principal driver of the disease. Methods: A novel approach to block AR signaling is to specifically target AR for degradation. To this end, we have developed the PROteolysis TArgeting Chimera (PROTAC) technology that employs hetero-bifunctional small molecules that simultaneously bind VHL E3 ubiquitin ligase and a target of interest (e.g. AR). Due to induced proximity between VHL and AR, an AR PROTAC leads to ubiquitination and subsequent degradation of AR. Results: Our lead AR PROTAC, ARV-330, degrades 92-98% of total AR in all cell lines tested, with 50% degradation concentrations (DC50) < 1nM. AR degradation suppresses the AR-target gene PSA expression, inhibits proliferation, and induces potent apoptosis in VCaP cells with maximal apoptosis observed at 20 nM. While enzalutamide loses its activity in the presence of > 0.5 nM R1881, ARV-330 maintains its activity. In cells containing the ARF876L mutation, enzalutamide is an agonist; however, ARV-330 remains effective. In fact, ARV-330 is able to degrade all clinically relevant AR mutations. ARV-330 exhibits good pharmacokinetic properties, with t1/2 values of several hours and bioavailability of > 80% after sc injection. Treatment of mice with ARV-330, at doses ranging from 0.3 to 10 mg/kg, results in reduction of AR protein levels. The in vitro potency translates into in vivo efficacy, as ARV-330 demonstrates prostate involution in intact mice. In castrated mice implanted with VCaP tumors, ARV-330 shows robust reduction of plasma PSA and blockade of tumor growth. Conclusions: In summary, the AR PROTAC ARV-330 removes AR from prostate cancer cells in a potent manner and produces therapeutic effects as a result. This cellular efficacy has translated into biomarker activity and efficacy in animal models, and ARV-330 is now in preclinical development.