The cyclin dependent kinase (CDK)-retinoblastoma (RB)-E2F pathway plays a critical role in the control of cell cycle in estrogen receptor-positive (ER
) breast cancer. Small-molecule inhibitors of ...CDK4/6 have shown promise in this tumor type in combination with hormonal therapies, reflecting the particular dependence of this subtype of cancer on cyclin D1 and E2F transcription factors. mTOR inhibitors have also shown potential in clinical trials in this disease setting. Recent data have suggested cooperation between the PI3K/mTOR pathway and CDK4/6 inhibition in preventing early adaptation and eliciting growth arrest, but the mechanisms of the interplay between these pathways have not been fully elucidated. Here we show that profound and durable inhibition of ER
breast cancer growth is likely to require multiple hits on E2F-mediated transcription. We demonstrate that inhibition of mTORC1/2 does not affect ER function directly, but does cause a decrease in cyclin D1 protein, RB phosphorylation, and E2F-mediated transcription. Combination of an mTORC1/2 inhibitor with a CDK4/6 inhibitor results in more profound effects on E2F-dependent transcription, which translates into more durable growth arrest and a delay in the onset of resistance. Combined inhibition of mTORC1/2, CDK4/6, and ER delivers even more profound and durable regressions in breast cancer cell lines and xenografts. Furthermore, we show that CDK4/6 inhibitor-resistant cell lines reactivate the CDK-RB-E2F pathway, but remain sensitive to mTORC1/2 inhibition, suggesting that mTORC1/2 inhibitors may represent an option for patients that have relapsed on CDK4/6 therapy.
.
Targeting the estrogen receptor alpha (ERα) pathway is validated in the clinic as an effective means to treat ER+ breast cancers. Here we present the development of a VHL-targeting and orally ...bioavailable proteolysis-targeting chimera (PROTAC) degrader of ERα. In vitro studies with this PROTAC demonstrate excellent ERα degradation and ER antagonism in ER+ breast cancer cell lines. However, upon dosing the compound in vivo we observe an in vitro-in vivo disconnect. ERα degradation is lower in vivo than expected based on the in vitro data. Investigation into potential causes for the reduced maximal degradation reveals that metabolic instability of the PROTAC linker generates metabolites that compete for binding to ERα with the full PROTAC, limiting degradation. This observation highlights the requirement for metabolically stable PROTACs to ensure maximal efficacy and thus optimisation of the linker should be a key consideration when designing PROTACs.
Abstract
Background: Trastuzumab deruxtecan (T-DXd) is an antibody-drug conjugate composed of an anti-HER2 antibody, a cleavable tetrapeptide-based linker, and a cytotoxic topoisomerase I inhibitor ...approved for HER2+ metastatic breast and gastric cancer. Clinically, T-DXd has demonstrated significant antitumor activity in both HER2+ and HER2-low (IHC 1+ & 2+/ISH-) breast cancer patients. The PI3K/AKT pathway is frequently activated in breast cancer, and mediates signals downstream of HER2. T-DXd has been shown to inhibit downstream AKT signaling driven by HER2. Capivasertib, a potent, selective inhibitor of all three AKT isoforms (AKT1/2/3) has shown clinical activity in breast cancer trials. Given the clinical activity of both agents, the anti-tumor activity of combined treatment with T-DXd with capivasertib, was explored preclinically in HER2+ and HER2-low models. Methods: The antiproliferative activity of the combination of T-DXd with capivasertib was assessed in a panel of 27 breast cancer cell lines using a 7 day viability assay. To determine whether the combination also translates in vivo, T-DXd (3 and 10mg/kg Q3W) and capivasertib (130mg/kg BID 4 days on/3 days off) were tested in KPL4 (HER2+). To determine whether the combination of T-DXd and capivasertib has a negative impact on normal tissue integrity, we further evaluated the combination in a human 2D in vitro bone marrow progenitor assay. Results: The combination treatment was more effective than each single agent in 6/27 of the models tested in vitro, resulting in increased cell kill in the viability assay. Two of these positive cell lines, HCC1569 (HER2+) and AU565 (HER2+) were PTEN altered, KPL4 (HER2+) and EFM19 (ER+) were mutant in PIK3CA, and HCC1419 (HER2+) and ZR-75-30 (ER+/HER2+) were neither PTEN or PIK3CA altered. In KPL4 xenografts, the combination of T-DXd and capivasertib showed modest increased activity over monotherapy T-DXd or capivasertib at 28d (Tumor Growth Inhibition (TGI) of T-DXd = 76%, capivasertib = 25%, and T-DXd+Capivasertib = 83%; p=0.3 combo vs. mono T-DXd) and more markedly at 46d (TGI of the combination vs T-DXd monotherapy was 65%). Importantly, the combination showed enhanced durability of response (stasis) in 100% mice while 38% (3/8) mice in the T-DXd mono therapy treatment group were actively re-growing at 46d. In the in vitro bone marrow assay, the combination demonstrated no increased interaction over monotherapy activity (average Loewe Synergy Score of -0.2). Conclusions: These results suggest combining T-DXd with capivasertib has potential to be active in breast cancer patients, with activity likely to be enriched in tumours with mutations in PIK3CA and PTEN, but also in tumours with no PI3K pathway activating mutations.
Citation Format: Azadeh Cheraghchi Bashi, Theresa Proia, Suzanne Randle, Mark Anderton, Zeshaan Rasheed, J. Elizabeth Pease, Simon Barry, Danielle Carroll, Jerome Mettetal. Activity and tolerability of combination of trastuzumab deruxtecan with the pan-AKT inhibitor capivasertib in preclinical HER2+ and HER2-low breast cancer models abstract. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P2-13-23.
Abstract
Background: Trastuzumab deruxtecan (T-DXd) is an antibody-drug conjugate composed of an anti-HER2 antibody, a cleavable tetrapeptide-based linker, and a cytotoxic topoisomerase I inhibitor ...approved for HER2+ metastatic breast and gastric cancer. Clinically, T-DXd has demonstrated antitumor activity in both HER2+ and HER2-low cancers. PARP performs a key role as a mediator in the resolution of topoisomerase1 cleavage complexes (TOP1cc) through recruitment of tyrosyl-DNA phosphodiesterase 1 (TDP1). We hypothesized that combination of T-DXd with the PARP1/2 inhibitor olaparib, will halt the resolution of TOP1cc and enhance the activity of T-DXd. Methods: To test the hypothesis, we evaluated the antiproliferative ability of the combination of T-DXd with olaparib in a panel of 27 breast cancer cell lines in an in vitro 7-day viability assay. The combination was also evaluated in vivo in two non-HRD models, a HER2+ (KPL4) and HER2-low (JIMT1) cell line xenograft at 3mg/kg and 10mg/kg Q3W for T-DXd, as well as 100mg/kg BID of olaparib. To evaluate the specificity of the combination activity in tumor cells (vs normal tissue), we further evaluated the combination in a human 2D in vitro bone marrow progenitor assay. Results: We found that the combination had enhanced in vitro cell killing activity over single agents in 8/27 of the models tested. The benefit was present in both Homologous Repair Deficient (HRD) as well as wild-type models, suggesting it does not depend on HRD (as defined by mutations in DNA damage repair genes). In vivo, the combination was more active than monotherapy of either compound in both KPL4 (28d TGI of 76% with T-DXd, olaparib 17% TGI, and T-DXd + olaparib 94.4% TGI; p=0.009) and JIMT1 (28d TGI of 80.8% with T-DXd, olaparib 52%, and T-DXd + Olaparib 88.1%; p=0.03). In the in vitro human bone marrow assay, the combination demonstrated modest enhancement over monotherapy activity (average Loewe Synergy Score of 2.5). To explore the ability to optimize therapeutic index, we tested alternative doses and schedules of the combination in vivo. Specifically, we tested whether lower doses of T-DXd or delayed administration of olaparib would provide greater activity. We found that combination of 3mg/kg of T-DXd with olaparib provided greater activity in KPL4 xenograft model than 3mg/kg T-DXd alone (69% TGI for combination vs. 35% TGI for monotherapy on d28), but this was no greater than high dose 10mg/kg monotherapy T-DXd (76% TGI on d28; p=0.19). Interestingly, 7-day delay of olaparib in combination with 10mg/kg T-DXd provided greater activity (91% TGI on d28) than monotherapy T-DXd or olaparib alone (76% TGI and 17% TGI on d28, respectively). Conclusions: These results suggest that T-DXd combined with olaparib is a potentially active combination in breast cancer, with preclinical activity demonstrated in HRD and non-HRD models.
Citation Format: Theresa Proia, Yann Wallez, Azadeh Cheraghchi Bashi, Zena Wilson, Suzanne Randle, Mark Anderton, Danielle Carroll, Zeshaan Rasheed, J. Elizabeth Pease, Elisabetta Leo, Jerome Mettetal. Activity and tolerability of combination of trastuzumab deruxtecan with olaparib in preclinical HER2+ and HER2-low breast cancer models abstract. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P2-13-18.
Oral selective estrogen receptor degraders (SERD) could become the backbone of endocrine therapy (ET) for estrogen receptor-positive (ER+) breast cancer, as they achieve greater inhibition of ...ER-driven cancers than current ETs and overcome key resistance mechanisms. In this study, we evaluated the preclinical pharmacology and efficacy of the next-generation oral SERD camizestrant (AZD9833) and assessed ER-co-targeting strategies by combining camizestrant with CDK4/6 inhibitors (CDK4/6i) and PI3K/AKT/mTOR-targeted therapy in models of progression on CDK4/6i and/or ET. Camizestrant demonstrated robust and selective ER degradation, modulated ER-regulated gene expression, and induced complete ER antagonism and significant antiproliferation activity in ESR1 wild-type (ESR1wt) and mutant (ESR1m) breast cancer cell lines and patient-derived xenograft (PDX) models. Camizestrant also delivered strong antitumor activity in fulvestrant-resistant ESR1wt and ESR1m PDX models. Evaluation of camizestrant in combination with CDK4/6i (palbociclib or abemaciclib) in CDK4/6-naive and -resistant models, as well as in combination with PI3Kαi (alpelisib), mTORi (everolimus), or AKTi (capivasertib), indicated that camizestrant was active with CDK4/6i or PI3K/AKT/mTORi and that antitumor activity was further increased by the triple combination. The response was observed independently of PI3K pathway mutation status. Overall, camizestrant shows strong and broad antitumor activity in ER+ breast cancer as a monotherapy and when combined with CDK4/6i and PI3K/AKT/mTORi.
Camizestrant, a next-generation oral SERD, shows promise in preclinical models of ER+ breast cancer alone and in combination with CDK4/6 and PI3K/AKT/mTOR inhibitors to address endocrine resistance, a current barrier to treatment.
Abstract
Diffuse large B-cell lymphoma (DLBCL) is an aggressive type of non-Hodgkin lymphoma (NHL) and the most common form of adult lymphoma. Despite efforts to develop new therapies, the standard ...of care for DLBCL remains chemotherapy based. The current standard of care is comprised of a regimen of 4 drugs (cyclophosphamide, doxorubicin, vincristine, and prednisone) combined with immunotherapy using a chimeric mAb against the protein CD20 (rituximab), R-CHOP. Unfortunately only 50 to 60% of patients with DLBCL achieve and maintain complete remission after first-line therapy and 40 to 50 % relapse or have refractory disease. In addition, the average age at the time of diagnosis for DLBCL is 64 which makes intensive chemotherapy challenging. Therefore, the development of new treatment options is critical. We explored preclinical activity of AZD2811 nanoparticle, a potent and selective inhibitor of Aurora B kinase combined with venetoclax, an inhibitor of BCL2 currently used as standard of care in treatment of Haematological cancers, in B-Cell non-Hodgkin lymphoma models. Twenty five B-cell NHL cell lines including 11 Diffuse Large B-cell Lymphoma (DLBCL) cell lines were exposed to a 7 x 7 matrix of AZD2811 and venetoclax for 72 hrs. Cell viability was assessed using Celltiter-glo. Strong combination activity (HSA > 0.1 and combination Emax > 0.5) was observed in 6 cell lines including 2 DLBCL cell lines (WSU-DLCL2 and KARPAS_422). Moreover, pre-treatment with pan caspase inhibitor Q-VD-OPH, increased cell viability in cells treated with the combination. Next we explored the significant gene expression and mutation biomarkers (effect size > 1, p < 0.05) for this combination associated with Bliss and combination Emax in B-cell NHL cell lines. We found downregulation of 4 genes (FLT4, TIE1, PRKN) and mutations in 2 genes (EP300 and PTEN) to be associated with Bliss score and upregulation of one gene (FGR) associated with combination Emax. In vivo, antitumor activity of AZD2811 combined with venetoclax was assessed in mice bearing WSU-DLCL2luc xenografts. Once weekly intravenous administration of 25 mg/kg AZD2811 resulted in a statistically significant tumor growth inhibition (TGI) of 74%, while daily oral gavage of 100 mg/kg venetoclax resulted in 49% TGI but failed to reach statistical significance. While both monotherapies were unable to prevent progressive tumor growth, a combination dosing regimen of AZD2811 and venetoclax drove progressive tumor regression resulting in statistically significant complete regression (98% regression) by the third week of dosing. These results suggest combining AZD2811 with venetoclax has potential to be active in DLBCL patients.
Citation Format: Azadeh Cheraghchi-Bashi, Brandon Willis, Kevin. Mongeon, Jacob Gordon, Krishna Bulusu, Elizabeth Coker, Patricia Jaaks, Mathew Garnett, Jerome Mettetal. Activity and tolerability of combination of venetoclax with the Aurora kinase B Inhibitor AZD2811 in preclinical diffuse large B-cell lymphoma models abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 6303.
Abstract
Mitogen-activated protein kinase (MAPK) pathway alterations comprise some of the most frequent mutations in newly diagnosed acute myeloid leukemia (AML). Moreover, MAPK pathway alterations ...are also emerging as potential mechanisms of resistance to targeted therapy in AML including FLT3 inhibitors and venetoclax. In an ex vivo pharmacologic analysis of primary AML samples, sensitivity to the MEK inhibitor selumetinib (ARRY-142886) was enriched in patient samples resistant to venetoclax. Clinical activity of MAPK pathway inhibitors such as selumetinib has been explored in AML but monotherapy responses were modest. Another MEK inhibitor, cobimetinib, is currently being tested in combination with venetoclax in AML. We sought to understand whether combining selumetinib with BH3 mimetics such as venetoclax would improve efficacy in AML models. We evaluated combination activity of selumetinib plus venetoclax or the MCL1 inhibitor AZD5991 in a panel of AML cell lines. Cells were exposed to a 6x6 matrix of both agents for 72hrs and then viability assessed using CellTiter-Glo. Combination benefit was assessed using highest single agent (HSA) analysis. Selumetinib+AZD5991 demonstrated strong combination benefit (HSA score >0.1, Emax >0.5) in 4/19 AML cell lines. Selumetinib+venetoclax showed strong combination activity in 6/19 lines. Three lines showed benefit with both combinations. Many of these cell lines harbor MAPK pathway mutations including OCI-AML5 (SOS1N233Y, NF1K1385R), ML-2 (KRASA146T), HL-60 (NRASQ61L), and Nomo-1 (KRASG13D). Selumetinib treatment also led to robust BIM induction in vitro. Nomo-1 xenografts were evaluated for in vivo sensitivity to venetoclax (100 mg/kg qd PO), 5-azacytidine (1mg/kg BID q8h 3days on/4days off IP), AZD5991 (30mpk bid q2h qw IV), selumetinib (10 mg/kg bid q8h PO), as well as combinations of venetoclax+5-aza, AZD5991+selumetinib, and venetoclax+selumetinib. Venetoclax and venetoclax+5-aza treatment were ineffective. Selumetinib monotherapy led to 63% tumor growth inhibition (TGI) but tumors eventually grew out through treatment. The combination of selumetinib+venetoclax slightly improved efficacy (81% TGI) but markedly delayed tumor outgrowth (selumetinib monotherapy arm reached mean tumor volume >1000 mm3 on day 17, selumetinib+venetoclax reached average of ~966 mm3 on day 28). Reducing venetoclax dose (30mg/kg qd) or frequency (100mg/kg 3days on/4days off) maintained most of the combination efficacy. Selumetinb+AZD5991 also strongly improved efficacy compared to either monotherapy (88% TGI, mean tumor volume did not exceed ~400mm3 by day 28). Together these data suggest potential for combining MEK inhibitors with BH3 mimetics in AML. Work is ongoing to further understand how scheduling impacts combination efficacy, evaluate the triple combination of selumetinib+BH3 mimetic+azacytidine, and assess efficacy in disseminated models.
Citation Format: Courtney L. Andersen, Azadeh Cheraghchi-Bashi, Patricia Jaaks, Elizabeth A. Coker, Kathleen Burke, Justin Cidado, Paul Smith, Corinne Reimer, Raoul Tibes, Mathew Garnett, Jerome Mettetal. Combining selumetinib with BH3 mimetics enhances activity in MAPK-activated acute myeloid leukemia abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 4024.
Abstract
Anti-hormonal therapy has been the mainstay treatment for estrogen receptor (ER) +ve breast cancer for >40 years. The selective ER degrader (SERD) fulvestrant has demonstrated clinical ...benefit over aromatase inhibitors and the selective ER modulator tamoxifen. However, fulvestrant's efficacy may be limited by the intramuscular route of administration. To overcome this, AstraZeneca has developed orally bioavailable SERDs, the first generation compound AZD9496 and the next generation oral SERD AZD9833. Here we report the preclinical comparison of fulvestrant, AZD9496 and AZD9833. All three compounds induced equal ERα degradation in the ER+ breast cancer cell line MCF7. Importantly, analysis of other ER+ cell lines revealed AZD9833 phenocopied ERα degradation induced by fulvestrant, while AZD9496 only reduced ERα levels to 54% of that achieved by fulvestrant. Activity in the endometrial Ishikawa cell line demonstrated induction of progesterone receptor, an ER target gene, by AZD9496 but not AZD9833. RNAseq analysis of ER+ breast cancer cell lines treated with the three agents with and without estradiol did not reveal differences between the compounds; all estradiol-induced gene expression changes were completely reversed by the SERDs and no ER agonism was detected. By contrast, AZD9833 and fulvestrant produced an equivalent maximal anti-proliferative effect in MCF-7 and CAMA-1 cells, while AZD9496 induced a significantly inferior anti-proliferative effect. The pure anti-estrogen nature of AZD9833 and the partial agonist potential of AZD9496 was confirmed in vivo in a juvenile rat uterine assay. Like fulvestrant, AZD9833 caused a significant reduction in uterine weight and endometrial thickness, while AZD9496 produced a significant increase in both parameters. In MCF7 xenografts, both oral SERDs caused equivalent anti-tumour and pharmacodynamic effects to a supraclinical exposure of fulvestrant. However, in the patient derived xenograft CTC174 harbouring an ESR1 D538G mutation, AZD9833 caused equivalent anti-tumour and ERα degradation effects to supraclinical fulvestrant. By contrast, AZD9496 produced significantly poorer maximal anti-tumour and pharmacodynamic effects in this model compared to fulvestrant. These data demonstrate that AZD9833 phenocopied fulvestrant preclinically, as a SERD and pure anti-estrogen. It is, therefore, a suitable candidate to test the hypothesis that increasing the exposure of a SERD above what is achieved with fulvestrant can provide additional patient benefit. AZD9496, on the other hand, demonstrated inferior ERα degradation in several ER+ breast cancer cell lines and partial agonism. This may explain the result of the clinical window of opportunity study, comparing AZD9496 to fulvestrant, in which AZD9496 failed to demonstrate superior degradation of ERα, downregulation of PR expression and reduction in Ki67 positivity.
Citation Format: Mandy Lawson, Natalie Cureton, Michelle DuPont, Oona Delpuech, Dawn Trueman, Pei Zhang, Azadeh Cheraghchi-Bashi-Astaneh, Sladjana Gagrica, Gareth Maglennon, Daniel Sutton, Bairu Zhang, Jonathan Cairns, Jamie Scott, Teresa Klinowska, Christopher J. Morrow. Not all selective estrogen receptor degraders are equal - Preclinical comparison of AZD9833, AZD9496 and fulvestrant abstract. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4379.
Our identification of dysregulation of the AKT pathway in ovarian cancer as a platinum resistance specific event led to a comprehensive analysis of in vitro, in vivo and clinical behaviour of the AKT ...inhibitor GSK2141795. Proteomic biomarker signatures correlating with effects of GSK2141795 were developed using in vitro and in vivo models, well characterised for related molecular, phenotypic and imaging endpoints. Signatures were validated in temporally paired biopsies from patients treated with GSK2141795 in a clinical study. GSK2141795 caused growth-arrest as single agent in vitro, enhanced cisplatin-induced apoptosis in vitro and reduced tumour volume in combination with platinum in vivo. GSK2141795 treatment in vitro and in vivo resulted in ~50-90% decrease in phospho-PRAS40 and 20-80% decrease in fluoro-deoxyglucose (FDG) uptake. Proteomic analysis of GSK2141795 in vitro and in vivo identified a signature of pathway inhibition including changes in AKT and p38 phosphorylation and total Bim, IGF1R, AR and YB1 levels. In patient biopsies, prior to treatment with GSK2141795 in a phase 1 clinical trial, this signature was predictive of post-treatment changes in the response marker CA125. Development of this signature represents an opportunity to demonstrate the clinical importance of AKT inhibition for re-sensitisation of platinum resistant ovarian cancer to platinum.
Abstract
Anti-hormonal therapy has been the mainstay for the treatment of estrogen receptor (ER) positive breast cancer for over 40 years. The selective ER degrader (SERD) fulvestrant (Faslodex) has ...been shown to provide clinical benefit over aromatase inhibitors and selective ER modulators. However, delivery of its maximum possible efficacy may be limited by the intra muscular route of administration. To overcome this, AstraZeneca developed the orally bioavailable SERD AZD9496. Here we report further preclinical characterisation of AZD9496 with regards to its ability to induce ERα degradation, antagonise and agonise ER in vitro and the impact on tumour xenografts. AZD9496 caused equivalent ERα degradation to fulvestrant in the MCF7 ER+ cell line. Interestingly, in other ER+ cell lines (e.g. CAMA1 and T47D), the maximal level of ERα degradation induced by AZD9496 was 54% of that induced by fulvestrant. RNAseq analysis of cell lines treated with AZD9496 or fulvestrant in the presence of estradiol did not reveal any differences in ER antagonism. Furthermore, no ER agonism was detected in ER+ breast cancer cell lines treated with AZD9496 in the absence of estradiol. However, unlike fulvestrant, AZD9496 was able to induce PR protein expression in the Ishikawa ER+ endometrial cancer cell line, demonstrating a potential to agonise ER. Also, in proliferation assays, while there was little difference in MCF7 cells between the maximal antiproliferative effect of fulvestrant and AZD9496, in CAMA1 and T47D cells the maximal antiproliferative effect of AZD9496 was 75% and 82% respectively of that caused by fulvestrant. In vivo, AZD9496 increased the uterine weight and induced PR expression in the uterus of juvenile rats, consistent with AZD9496 being a partial ER agonist albeit less than tamoxifen. AZD9496, at a maximally efficacious dose, did not induce the same degree of ER degradation or anti-tumour effect as a supraclinical dose of fulvestrant in CTC174, a patient derived xenograft that harbours a D538G ESR1 mutation and grows in the absence of supplemental estradiol. Taken together, these data suggest that, while AZD9496 is equivalent to fulvestrant in terms of ERα degradation and anti-proliferative/anti-tumour effects in some preclinical models, this is not the case in all models. However, it is not clear which, if any, model accurately reflects the clinical setting and how AZD9496 would compare to fulvestrant at exposures achievable in the clinic. Thus, testing AZD9496 vs fulvestrant in ER+ breast cancer patients is crucial to determine potential clinical benefit.
Citation Format: Mandy Lawson, Natalie Cureton, Oona Delpuech, Pei Zhang, Azadeh Cheraghchi-Bashi-Astaneh, Sladjana Gagrica, Dawn Trueman, Gareth Maglennon, Daniel Sutton, Bairu Zhang, Jonathan Cairns, Teresa Klinowska, Christopher J Morrow. Oral selective estrogen receptor degrader AZD9496 demonstrated preclinical model specific differences to fulvestrant in estrogen receptor degradation, agonism and anti-tumour effects abstract. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P6-04-15.