Abstract P5-13-20: Identifying a metabolite signature that correlates with tumor proliferation in early-stage breast cancer patients treated with CDK4/6 inhibitors from matched plasma and serum samples

Background: Cyclin-dependent kinase 4/6 inhibitors (CKD4/6i) have demonstrated clinical utility extending progression-free survival (PFS) and overall survival (OS) for advanced hormone receptor positive and HER2 negative (HR+/HER2-) breast cancer patients. The efficacy in early-stage breast cancer (eBC) is unclear, with conflicting results from adjuvant CDK4/6i trials on invasive disease-free survival. Thus, there is a critical need to identify biomarkers of response (BoR) to determine which, if any, eBC patients could benefit from this treatment. This BoR could also stratify advanced BC patients for likelihood to respond to CDK4/6i. Metabolism is influenced by both genome and environment, and changes in the metabolome can be correlated with drug responsiveness. Thus, metabolite BoRs may serve to identify eBC patients for which CDK4/6i would offer a therapeutic benefit.Methods: Plasma and serum samples from 50 early-stage ER+/HER2- breast cancer patients, treated with neoadjuvant CDK4/6 inhibitor palbociclib (palbo) and aromatase inhibitor (AI) anastrozole on NeoPalAna trial (ClinicalTrials.gov identifier NCT01723774), were collected from treatment-naïve patients (BL) and 3 consecutive time points: anastrozole,1 mg daily for 4 weeks (C1D1), anastrozole plus palbo,125 mg daily, for 15 days (C1D15), and for 4-5 months before surgery (SURG). Metabolites were extracted from all samples via methanol and chloroform precipitation and quantified using an unbiased, non-destructive, nuclear magnetic resonance (NMR)-based profiling platform (Olaris®, Inc., Waltham, MA). Statistical analysis and machine learning was used to identify differential metabolites and generate predictive models. A separate validation set of samples was collected from a subset of patients (N=6) who received an additional cycle of palbo treatment prior to surgery to assess model accuracy. Results: Non-parametric differential expression analysis of BL/C1D1, BL/C1D15, and C1D1/C1D15 identified 53 ,97, and 90 differential NMR resonances in plasma (p<0.05) and 36, 34, and 25 differential NMR resonances in serum (p<0.05), respectively. Based on the proliferative marker Ki67 levels at C1D15, 37 patients were classified as responders (Ki67≤2.7%) and 6 patients as non-responders (Ki67>2.7%). Analysis of the responder (R) and non-responder (NR) groups identified that 13 plasma and 14 serum resonances (21 unique resonances and 6 overlapping) were differentially expressed (p<0.05) at C1D1. Many of the differential resonances could be mapped back to amino acid metabolites including several branched chain amino acids such as leucine, valine, and isoleucine, and positively charged amino acids such as lysine. A Olaris® BoR score was generated using 5 differential resonances that had an AUC of 0.931 (training set) and 100% accuracy when predicting palbo-response in a blinded test set (N=6).Conclusion: The differential metabolites identified from matching plasma and serum samples suggest that, compared to serum, plasma has a better representation of the metabolic changes associated with palbo treatment-response. While comparing samples from R and NR patients, amino acids were found to be consistently altered in both serum and plasma before palbo treatment. In addition, a BoR model based on select metabolites could precisely stratify palbo-response in a blinded dataset. A larger independent validation cohort is ongoing.

Citation Format: Chen Dong, Shana Thomas, Chandrashekhar Honrao, Leonardo O. Rodrigues, Nathalie Tessier, Bo Zhang, Souzan Sanati, Kiran Vij, Brenda J. Ernst, Karen S. Anderson, Mateusz Opyrchal, Foluso Ademuyiwa, Lindsay L. Peterson, Matthew P. Goetz, Donald Northfelt, Elizabeth O'Day, Cynthia Ma. Identifying a metabolite signature that correlates with tumor proliferation in early-stage breast cancer patients treated with CDK4/6 inhibitors from matched plasma and serum samples [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 P5-13-20.

Abstract P5-13-22: Serum thymidine kinase 1 activity (TKa) levels and progression-free survival (PFS) in patients (pts) with hormone receptor positive (HR+) HER2-negative metastatic breast cancer (MBC) on palbociclib (Pb) and endocrine therapy (ET)

Background: Cyclin dependent 4/6 kinase inhibitors (CDK4/6i) and endocrine therapy (ET) have improved progression-free survival (PFS) and overall survival in HR+ MBC, but progression of disease ultimately occurs. Apart from HR+ status, there are no clinically available biomarkers that enable oncologists to determine prognosis and predict response to CDK4/6i. An emerging biomarker is serum thymidine kinase 1 (TK1), a secreted marker of proliferation that is prognostic in pts with HR+ HER2- MBC. High levels of TKa are associated with inferior PFS, whereas pts with low TKa levels pretreatment, or TKa levels that decrease on ET and a CDK4/6i, have superior PFS. Notably, TKa levels rebound ≥ 5 days off Pb, with resumption of cell cycling. PROMISE (NCT0281902) is a prospective study that enrolled women with HR+ MBC starting Pb + letrozole (L) in the 1st line [FL] or Pb + fulvestrant in the 2nd line [SL] setting. The trial includes a comprehensive “omic” assessment of blood, tumor, urine and the fecal microbiome to identify novel genomic variants and pathways associated with an early decline in TKa (measured after 2 months or end of cycle [C]2) and PFS. Here, we report the association between i) pre-treatment TKa (pre-TKa) levels and PFS (i.e. from registration to the 1st disease event) and ii) TKa levels at the end of C2 (C2-TKa) and PFS-2 (i.e. from the start of C3 to the 1st disease event).Methods: TKa testing was performed using the DiviTum assay (Biovica). TKa+ disease was defined as ≥ 200 Du/L and TKa- disease as below limit of detection to 200 Du/L. Log-rank test and univariate Cox modeling were used to assess the association between pre-TKa levels and PFS and between end of C2-TKa levels and PFS-2. The database was locked on June 28, 2021. Results: Of 68 pts enrolled, 4 were ineligible and pre-TKa data was unavailable for 4. Of the remaining 60 pts (45 FL, 15 SL), the percentage of pts with pre-TKa+ disease was 33.3% in FL (15/45, 95% CI: 20.0-49.0%), and 46.7% (7/15, 95% CI: 21.4-71.9%) in the SL. The median follow-up time for pts on study was 24 months (range: 2-42 months). There were 22 disease events (13 in FL, 9 in SL). In the FL setting, PFS was significantly shorter for preTKa+ pts compared to preTKa- pts (HR: 4.15, 95% CI:1.35-12.74; p=0.007), but not for SL pts (HR: 1.11, 95% CI: 0.30-4.18, p=0.875). End of C2 TKa data was obtained for pts while on Pb (n=5), or after stopping Pb as follows: 1-4 days (n=9), 5-8 days (n=28) and 9-36 days (n=11). PFS-2 was not associated with C2-TKa in the FL (p=0.834) or SL (p=0.454) settings. An analysis of TKa levels by metastatic site will be presented at the meeting.Conclusions: A secreted biomarker of proliferation (TK1) obtained prior to initiating CDK4/6i and ET for the treatment of HR+ MBC is associated with PFS in pts receiving 1st line Pb + L, but not in those receiving 2nd line Pb + fulvestrant. While the end of C2 TKa levels were not associated with PFS, the interpretability of these data are limited, given treatment delays (0-36 days) prior to starting C3 that may result in TKa rebound. Future studies evaluating the predictive nature of TKa and Pb response should focus on earlier timepoints while on drug.

Citation Format: Ciara C O'Sullivan, Jun He, Jason Sinnwell, Vera J Suman, Krishna R Kalari, Peter T Vedell, Ann M Moyer, Xiaojia Tang, Kevin J Thompson, Abe Eyman Casey, Alvaro Moreno-Aspitia, Donald W Northfelt, Minetta C Liu, Tufia C Haddad, Saranya Chumsri, Brendan McMenomy, Prema Peethambaram, Kathryn J Ruddy, Karthik V Giridhar, Roberto A Leon-Ferre, Mattias Bergqvist, Adrian Nordmark, Richard M Weinshilboum, Liewei Wang, Matthew P Goetz. Serum thymidine kinase 1 activity (TKa) levels and progression-free survival (PFS) in patients (pts) with hormone receptor positive (HR+) HER2-negative metastatic breast cancer (MBC) on palbociclib (Pb) and endocrine therapy (ET) [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 P5-13-22.

Abstract P4-01-03: Multiomics data reveal novel biomarkers for CDK4/6 resistance

Background: Cyclin-dependent 4/6 kinase inhibitors (CDK4/6i) and endocrine therapy (ET) have improved progression-free survival (PFS) and overall survival in hormone-receptor-positive (HR+) metastatic breast cancer (MBC), but endocrine resistance is a major challenge. PROMISE [NCT0281902; n=63] is a multicenter study that enrolled women with HR+ HER2- MBC commencing palbociclib (Pb) with letrozole (1st line [1L]) or fulvestrant (2nd line [2L]), and was designed to perform a comprehensive “omic” assessment of prospectively collected biospecimens (pre-treatment (M1), at 2 months (M2), and at disease progression). The goal is to identify novel genomic variants and pathways associated with resistance to CDK4/6i and ET and PFS outcomes. Here we report the association between the proteomic, metabolomics, and lipidomics data generated from pre-Pb and 2-month serum samples and PFS. Methods: Untargeted mass spectrometry data was generated from Metabolon, assaying 1308 metabolites and 831 lipids. Additionally, 1436 proteins were assayed on the Olink platform. Cox proportional hazard models were used to evaluate the univariate hazard ratio (HR) for all features with respect to PFS. The analyses were performed on samples from 45 patients (N=33 1Lwith 9 progression events and 12 2L with 8 progression events), obtained from M1 and M2 timepoints on Pb + ET. Enrichment analysis p-values are calculated using Fisher’s exact test. Results: Proteomics: In the M1 timepoint, 93 and 43 proteins were associated with PFS in the 1L and 2L settings, respectively; inflammation genes were enriched among the 1L setting (p= 0.034); 33 proteins presented HRs ranging between 0.026 and 0.56. The FABP9 protein (HR of 1.98, 95% CI 1.02-3.83) was associated with worse PFS. Conversely, inflammation genes were not observed to be enriched in 2L. In the M2 timepoint, we observed 60 and 21 proteins significantly associated with PFS, but no biological function was enriched in 1L and 2L. Metabolites: In the M1 timepoint, metabolism of the sulfur-containing amino acids (methionine, cysteine, SAM and taurine) were enriched in the 1L setting (p= 0.035, HR range 0.15-0.33); and the branched-chain amino acids (leucine, isoleucine, and valine) were significantly associated with PFS in the 2L setting (p= 0.028, HR range 0.013-0.33). At the M2 timepoint, the amino acids were no longer enriched, but fatty acid metabolism was significantly enriched for both 1L and 2L (p= 0.048 and 0.067, respectively). Pathways involving lipids, amino acids, and xenobiotics were enriched in metabolites related to PFS (p <0.05) for both treatment lines at M1 and M2. Lipidomics: In the M1 timepoint, 10 and 19 lipids were associated with PFS for 1L and 2L, respectively. The most notable lipid associated with worse PFS in the 1L was an 18 carbon phosphatidylinositol, PI(18:1/18:2), (HR 7.34 (CI 1.27-42.50); 8 triglycerides were associated with improved PFS (HR range 0.39 and 0.55). In 2L, the 19 lipids associated with PFS included 12 phosphatidylcholines (enrichment p = 5.6X10-8). In the M2 timepoint, 15 and 8 lipids were significantly associated with PFS for 1L and 2L. An enrichment of phosphatidylinositols was observed in 1L (p= 1.2X10-5); none were observed in the 2L.Future Directions: Networks are being constructed using the proximity scores of the proteins, lipids, and metabolites associated with PFS in M1 and M2 for 1L and 2L. Network similarities and analyses will be conducted.Conclusion: Distinct multi-omic changes identified in serum samples obtained from PROMISE participants M1 and M2 on Pb correlate with disease progression in both 1L and 2L settings. Additionally, validation studies will determine the significance of these findings.

Citation Format: Krishna R. Kalari, Kevin J. Thompson, Jason Sinnwell, Xiaojia Tang, Vera J. Suman, Jun He, Seul Kee Byeon, Akhilesh Pandey, Abe Eyman Casey, Peter T. Vedell, Ann M. Moyer, Alvaro Moreno-Aspitia, Donald W. Northfelt, Minetta C. Liu, Tufia C. Haddad, Saranya Chumsri, Prema Peethambaram, Kathryn J. Ruddy, Karthik V. Giridhar, Roberto A. Leon-Ferre, Richard M. Weinshilboum, Liewei Wang, Ciara C. O’ Sullivan, Matthew P. Goetz. Multiomics data reveal novel biomarkers for CDK4/6 resistance [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 P4-01-03.

Abstract OT2-11-06: SERENA-4: A Phase III comparison of AZD9833 (camizestrant) plus palbociclib, versus anastrozole plus palbociclib, for patients with ER-positive/HER2-negative advanced breast cancer who have not previously received systemic treatment for advanced disease

Background: More than two thirds of patients with advanced breast cancer (ABC) have estrogen receptor-positive (ER+), human epidermal growth factor receptor 2-negative (HER2−) tumors. In most countries, current standard-of-care first-line treatments include an aromatase inhibitor or fulvestrant, a selective ER degrader, combined with cyclin-dependent kinase 4/6 inhibitors. Concurrent use of luteinizing hormone-releasing hormone agonists is recommended for men and premenopausal women with ABC. Nevertheless, almost all ABCs eventually become resistant to endocrine therapy and the disease is incurable in these cases. New therapies are needed to combat endocrine therapy resistance, maintain patient health-related quality-of-life, and delay the need for chemotherapy. AZD9833 (camizestrant) is a highly potent, next-generation selective ER degrader and pure ER antagonist that has demonstrated anticancer properties across a range of preclinical models, including those with ER-activating mutations (Scott et al, AACR 2020). A Phase I dose-escalation and expansion study (SERENA-1) has demonstrated that AZD9833 is well tolerated and has a promising antitumor activity when administered alone or in combination with the cyclin-dependent kinase 4/6 inhibitor palbociclib (Baird et al, SABCS 2020). SERENA-4 (NCT04711252) is a randomized, multicenter, double-blind, Phase III trial to evaluate the safety and efficacy of AZD9833 in combination with palbociclib for patients with ER+/HER2− ABC who have not received systemic treatment in the advanced disease setting. Methods: SERENA-4 will enroll 1342 patients with de novo or recurrent ER+/HER2− ABC who have not previously received systemic treatment for their locoregionally recurrent or metastatic disease. Patients with recurrent disease must have received adjuvant aromatase inhibitor or tamoxifen therapy for at least 24 months without relapse. Patients will be randomized 1:1 to receive oral treatment with either (a) AZD9833 75 mg once daily, palbociclib 125 mg once daily for 21 days followed by 7 days off treatment and a placebo for anastrozole 1 mg once daily or (b) anastrozole 1 mg once daily, palbociclib (same as active arm) and a placebo for AZD9833 75 mg once daily. Men and premenopausal women will also receive a luteinizing hormone-releasing hormone agonist. The primary endpoint is progression-free survival (PFS; up to 5 years). Secondary endpoints include overall survival (up to 8 years), second PFS, time to chemotherapy, objective response rate, and changes in health-related quality-of-life measures. Enrollment began in January 2021. As of 02 July 2021, the number of open sites is 57 across 15 countries. Acknowledgments: We thank Julia Mawer, PhD, of Oxford PharmaGenesis, Oxford, UK, for providing medical writing support funded by AstraZeneca Funding: The SERENA-4 trial is funded and overseen by AstraZeneca. © 2021 American Society of Clinical Oncology, Inc. Reused with permission. This abstract was accepted and previously presented at the 2021 ASCO Annual Meeting. All rights reserved.

Citation Format: Fabrice André, Seock-Ah Im, Patrick Neven, Richard D Baird, Johannes Ettl, Matthew P Goetz, Erika Hamilton, Hiroji Iwata, Zefei Jiang, Anil Abraham Joy, Vincent Haddad, Andrew Walding, Manuel Selvi Miralles, Cynthia Huang Bartlett, Antonio Llombart-Cussac. SERENA-4: A Phase III comparison of AZD9833 (camizestrant) plus palbociclib, versus anastrozole plus palbociclib, for patients with ER-positive/HER2-negative advanced breast cancer who have not previously received systemic treatment for advanced disease [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 OT2-11-06.

Abstract P1-18-21: Abemaciclib plus fulvestrant or nonsteroidal aromatase inhibitor in participants with HR+, HER2- breast cancer - A pooled analysis of the endocrine therapy-naïve participants with measurable disease in MONARCH 2 and MONARCH 3

Background: Abemaciclib is an oral selective cyclin dependent kinases 4 & 6 inhibitor (CDK4 & 6i), administered on a continuous schedule. Abemaciclib demonstrated significant overall survival (OS) and progression-free survival (PFS) benefit in women with hormone receptor positive (HR+), human epidermal growth factor receptor 2-negative (HER2-) advanced breast cancer (ABC) in combination with fulvestrant in MONARCH 2 (M2). Similarly, abemaciclib demonstrated a PFS benefit in women with HR+, HER2- ABC in combination with nonsteroidal aromatase inhibitors (NSAI) in MONARCH 3 (M3). Here, we present the objective response rate (ORR) from the pooled cohort of endocrine-naïve (EN) participants with measurable disease enrolled in M2 and M3 that received abemaciclib. Methods: M2 (NCT02107703) and M3 (NCT02246621) were double-blind, Phase 3 studies in women with HR+, HER2- ABC. In M2, all patients received fulvestrant (500 mg, per label) and were randomized to receive either abemaciclib (150 mg or 200 mg BID) or placebo. 20 EN participants with measurable disease at baseline were enrolled to the abemaciclib arm. A M2 single arm addendum enrolled 90 additional EN participants with measurable disease to abemaciclib. EN M2 participants had received no previous endocrine therapy (ET) in any setting nor prior chemotherapy in the metastatic setting. In M3, all participants received NSAI (anastrozole 1 mg or letrozole 2.5 mg daily) and were randomized to receive abemaciclib (150 mg BID) or placebo based on stratification factors including prior neoadjuvant or adjuvant ET (NSAI, no ET or other) with 142 M3 EN participants with measurable disease randomized to abemaciclib. The population for analysis consisted of a pooled EN cohort from M2 and M3 with measurable disease that received abemaciclib (N=252). The primary endpoint was investigator-assessed ORR (percentage of participants with best response of complete [CR] or partial response [PR]). The secondary endpoints included PFS, clinical benefit rate (CBR = CR + PR + stable disease persistent for ≥6 months), disease control rate (DCR = CR + PR + SD), duration of response (DoR), and safety. Results: 252 EN participants with measurable disease (43.7% M2, 56.3% M3) from 21 countries were included in the analysis population. Median participant age was 59.0 years. Most patients (n=167 [66.3%]) had ≥3 metastatic organ sites involved. In the pooled EN cohort, confirmed ORR was 57.5% (95% CI 51.4-63.6). CBR was 78.6% (95% CI 73.5-83.6) and DCR was 92.9% (95% CI 89.7-96.0). PFS and DoR data for the M2 EN addendum are not yet mature. No new safety signals were observed. The safety profile was consistent with the previously reported M2 and M3 populations. Conclusion: Primary analysis of confirmed ORR in M2 and M3 EN participants with measurable disease compares favorably with previously reported ORR for fulvestrant monotherapy (FALCON study: 46% unconfirmed; FIRST study: 36% unconfirmed) or NSAI (PALOMA-2 study: 44.8% confirmed; MONALEESA-2: 34% unconfirmed) in participants with a similar disease state. The safety profile is similar to that reported in the primary M2 and M3 main studies.

Citation Format: Matthew P. Goetz, Jose Luis Gonzalez Trujillo, Masakazu Toi, Jens Huober, Antonio Llombart-Cussac, Wei Zhang, Holly Knoderer, Nadine Haddad, Gertjan Van Hal, George W. Sledge, Jr. Abemaciclib plus fulvestrant or nonsteroidal aromatase inhibitor in participants with HR+, HER2- breast cancer - A pooled analysis of the endocrine therapy-naïve participants with measurable disease in MONARCH 2 and MONARCH 3 [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 P1-18-21.

Abstract P5-13-09: Identifying homologous recombination deficiency in breast cancer: Genomic instability score thresholds differ in breast cancer subtypes

Background: Patients with homologous recombin ation (HR) deficient tumors may benefit from treatment with DNA damaging agents. Markers of genomic instability can be used to identify HR deficiency, including a 3-biomarker Genomic Instability Score (GIS). For patients with ovarian cancer (OC), the FDA-approved GIS threshold for identifying HR deficiency is 42, set as the 5th percentile for BRCA deficient tumors. Recently, a lower 1st percentile cutoff of 33 was explored in OC; this threshold was significantly associated with improved outcome after platinum-based treatment.1,2 Determining an optimal GIS threshold for different types of tumors is crucial, as the GIS distribution may vary between different cancers and even between different cancer subtypes. We propose GIS thresholds for breast cancer separately for triple-negative breast cancer (TNBC) and estrogen receptor-positive (ER+) breast cancer, using the exploratory threshold of 33 for OC as a comparator. Methods: GISs in BRCA deficient tumors were determined for patients newly diagnosed with varying stages of OC, TNBC, or ER+ breast cancer across 5 cohorts (Timms et al,3 TCGA,4 Abkevich et al,5 TBCRC008,6 the OlympiaD trial7). GIS was determined as a combination of loss of heterozygosity, telomeric-allelic imbalance, and large-scale state transitions. BRCA deficiency was defined by loss of function resulting from a pathogenic variant in BRCA1 or BRCA2 or by methylation of the BRCA1 promoter region, with loss of heterozygosity in the affected gene. GIS distributions in different cancer types and subtypes were compared using the Kolmogorov-Smirnov test. A normal distribution was fit to GISs in BRCA deficient ER+ breast tumors. The 1st percentile of the fitted distribution was chosen as the threshold. Results: A total of 561 OC tumors (190 BRCA deficient), 99 TNBC tumors (44 BRCA deficient), and 406 ER+ breast tumors (76 BRCA deficient) were included across the 5 cohorts. When score distributions were evaluated for BRCA deficient tumors, the GIS distribution within ER+ breast cancer was significantly different than for OC (p=9.6x10-5) and TNBC (p=3.2x10-4). This indicates that different GIS thresholds are appropriate for breast cancer subtypes and that the GIS threshold developed for OC is not appropriate for ER+ breast cancer. The 1st percentile of a normal distribution fit in BRCA deficient ER+ breast cancer tumors yields a threshold of 24. Using this threshold, 45.1% (183/406; 75 BRCA deficient, 108 BRCA intact) of ER+ breast tumors were HR deficient. In contrast, the GIS distribution for TNBC was not significantly different than for OC (p=0.77). Using the exploratory threshold of 33, 63.6% (63/99; 44 BRCA deficient, 19 BRCA intact) of TNBC tumors were HR deficient. Conclusions: When compared to OC, the distribution of GIS in BRCA deficient tumors was different for ER+ breast cancer, but not for TNBC. These findings are consistent with the fact that OC and TNBC are known to have similar molecular signatures.8 Exploratory thresholds of 24 for ER+ breast cancer, and 33 for TNBC and OC could be examined to determine if these cutoffs are associated with a benefit from treatment with DNA targeting agents. Clinical validity and utility of these more inclusive 1% thresholds would require demonstration of correlation with clinical outcomes. The threshold difference observed between these cancer subtypes also suggests that cancer or cancer subtype specific thresholds may be needed as evaluations of HR deficiency expands beyond OC to identify candidates for PARP inhibitors. References: 1 Mol Cancer Res. 2018;16(7):1103-11. 2 Cancers. 2021;13(5):946. 3 Br J Cancer. 2012;107(10):1776-82. 4 Nature. 2012;490(7418):61-70. 5 Breast Cancer Res. 2014;16(145):1-9. 6 J Nucl Med. 2015;56(1):31-7. 7 NEJM. 2017;377(17):1700. 8 Int J Mol Sci. 2016;17(5):759.

Citation Format: Kirsten M Timms, Lauren Lenz, Chris Neff, Cara Solimeno, Darl Flake, Judy C Boughey, Matthew P Goetz, Andrea Richardson, Anna Maria Storniolo, Alexander Gutin, Roisin M Connolly, Vered Stearns, Jerry S Lanchbury. Identifying homologous recombination deficiency in breast cancer: Genomic instability score thresholds differ in breast cancer subtypes [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 P5-13-09.

Mapping molecular subtype specific alterations in breast cancer brain metastases identifies clinically relevant vulnerabilities

The molecular events and transcriptional plasticity driving brain metastasis in clinically relevant breast tumor subtypes has not been determined. Here we comprehensively dissect genomic, transcriptomic and clinical data in patient-matched longitudinal tumor samples, and unravel distinct transcriptional programs enriched in brain metastasis. We report on subtype specific hub genes and functional processes, central to disease-affected networks in brain metastasis. Importantly, in luminal brain metastases we identify homologous recombination deficiency operative in transcriptomic and genomic data with recurrent breast mutational signatures A, F and K, associated with mismatch repair defects, TP53 mutations and homologous recombination deficiency (HRD) respectively. Utilizing PARP inhibition in patient-derived brain metastatic tumor explants we functionally validate HRD as a key vulnerability. Here, we demonstrate a functionally relevant HRD evident at genomic and transcriptomic levels pointing to genomic instability in breast cancer brain metastasis which is of potential translational significance.

The phase II MutHER study of neratinib alone and in combination with fulvestrant in HER2 mutated, non-amplified metastatic breast cancer

PURPOSE

HER2 mutations (HER2^mut) induce endocrine resistance in estrogen receptor positive (ER+) breast cancer.

EXPERIMENTAL DESIGN

In this single arm multi-cohort phase II trial, we evaluated the efficacy of neratinib plus fulvestrant in patients with ER+/HER2^mut, HER2-non-amplified metastatic breast cancer (MBC) in the fulvestrant-treated (n=24) or fulvestrant-naïve cohort (n=11). Patients with ER-negative/HER2^mut MBC received neratinib monotherapy in an exploratory ER- cohort (n=5).

RESULTS

The clinical benefit rate (CBR: 95% CI) was 38% (18-62%), 30% (7-65%), and 25% (1-81%) in the fulvestrant-treated, fulvestrant-naïve, and ER- cohort, respectively. Adding trastuzumab at progression in 5 patients resulted in 3 partial responses and 1 stable disease {greater than or equal to}24 weeks. CBR appeared positively associated with lobular histology and negatively associated with HER2 L755 alterations. Acquired HER2^mut were detected in 5 of 23 patients at progression.

CONCLUSION

Neratinib and fulvestrant is active for ER+/HER2^mut MBC. Our data supports further evaluation of dual HER2 blockade for the treatment of HER2^mut MBC.

Anastrozole Regulates Fatty Acid Synthase in Breast Cancer

Our previous matched case-control study of postmenopausal women with resected early-stage breast cancer revealed that only anastrozole, but not exemestane or letrozole, showed a significant association between the 6-month estrogen concentrations and risk of breast cancer. Anastrozole, but not exemestane or letrozole, is a ligand for estrogen receptor α. The mechanisms of endocrine resistance are heterogenous and with the new mechanism of anastrozole, we have found that treatment of anastrozole maintains fatty acid synthase (FASN) protein level by limiting the ubiquitin-mediated FASN degradation, leading to increased breast cancer cell growth. Mechanistically, anastrozole decreases the guided entry of tail-anchored proteins factor 4 (GET4) expression, resulting in decreased BCL2-associated athanogene cochaperone 6 (BAG6) complex activity, which in turn, prevents RNF126-mediated degradation of FASN. Increased FASN protein level can induce a negative feedback loop mediated by the MAPK pathway. High levels of FASN are associated with poor outcome only in patients with anastrozole-treated breast cancer, but not in patients treated with exemestane or letrozole. Repressing FASN causes regression of breast cancer cell growth. The anastrozole-FASN signaling pathway is eminently targetable in endocrine-resistant breast cancer.

MRI Radiomics for Assessment of Molecular Subtype, Pathological Complete Response, and Residual Cancer Burden in Breast Cancer Patients Treated With Neoadjuvant Chemotherapy

RATIONALE AND OBJECTIVES

There are limited data on pretreatment imaging features that can predict response to neoadjuvant chemotherapy (NAC). To extract volumetric pretreatment MRI radiomics features and assess corresponding associations with breast cancer molecular subtypes, pathological complete response (pCR), and residual cancer burden (RCB) in patients treated with NAC.

MATERIALS AND METHODS

In this IRB-approved study, clinical and pretreatment MRI data from patients with biopsy-proven breast cancer who received NAC between September 2009 and July 2016 were retrospectively analyzed. Tumors were manually identified and semi-automatically segmented on first postcontrast images. Morphological and three-dimensional textural features were computed, including unfiltered and filtered image data, with spatial scaling factors (SSF) of 2, 4, and 6 mm. Wilcoxon rank-sum tests and area under the receiver operating characteristic curve were used for statistical analysis.

RESULTS

Two hundred and fifty nine patients with unilateral breast cancer, including 73 (28.2%) HER2+, 112 (43.2%) luminal, and 74 (28.6%) triple negative breast cancers (TNBC), were included. There was a significant difference in the median volume (p = 0.008), median longest axial tumor diameter (p = 0.009), and median longest volumetric diameter (p = 0.01) among tumor subtypes. There was also a significant difference in minimum signal intensity and entropy among the tumor subtypes with SSF = 4 mm (p = 0.009 and p = 0.02 respectively) and SSF = 6 mm (p = 0.007 and p < 0.001 respectively). Additionally, sphericity (p = 0.04) in HER2+ tumors and entropy with SSF = 2, 4, 6 mm (p = 0.004, 0.02, 0.047 respectively) in luminal tumors were significantly associated with pCR. Multiple features demonstrated significant association (p < 0.05) with pCR in TNBC and with RCB in luminal tumors and TNBC, with standard deviation of intensity with SSF = 6 mm achieving the highest AUC (AUC = 0.734) for pCR in TNBC.

CONCLUSION

MRI radiomics features are associated with different molecular subtypes of breast cancer, pCR, and RCB. These features may be noninvasive imaging biomarkers to identify cancer subtype and predict response to NAC.

Residual cancer burden after neoadjuvant chemotherapy and long-term survival outcomes in breast cancer: a multicentre pooled analysis of 5161 patients

BACKGROUND

Previous studies have independently validated the prognostic relevance of residual cancer burden (RCB) after neoadjuvant chemotherapy. We used results from several independent cohorts in a pooled patient-level analysis to evaluate the relationship of RCB with long-term prognosis across different phenotypic subtypes of breast cancer, to assess generalisability in a broad range of practice settings.

METHODS

In this pooled analysis, 12 institutes and trials in Europe and the USA were identified by personal communications with site investigators. We obtained participant-level RCB results, and data on clinical and pathological stage, tumour subtype and grade, and treatment and follow-up in November, 2019, from patients (aged ≥18 years) with primary stage I-III breast cancer treated with neoadjuvant chemotherapy followed by surgery. We assessed the association between the continuous RCB score and the primary study outcome, event-free survival, using mixed-effects Cox models with the incorporation of random RCB and cohort effects to account for between-study heterogeneity, and stratification to account for differences in baseline hazard across cancer subtypes defined by hormone receptor status and HER2 status. The association was further evaluated within each breast cancer subtype in multivariable analyses incorporating random RCB and cohort effects and adjustments for age and pretreatment clinical T category, nodal status, and tumour grade. Kaplan-Meier estimates of event-free survival at 3, 5, and 10 years were computed for each RCB class within each subtype.

FINDINGS

We analysed participant-level data from 5161 patients treated with neoadjuvant chemotherapy between Sept 12, 1994, and Feb 11, 2019. Median age was 49 years (IQR 20-80). 1164 event-free survival events occurred during follow-up (median follow-up 56 months [IQR 0-186]). RCB score was prognostic within each breast cancer subtype, with higher RCB score significantly associated with worse event-free survival. The univariable hazard ratio (HR) associated with one unit increase in RCB ranged from 1·55 (95% CI 1·41-1·71) for hormone receptor-positive, HER2-negative patients to 2·16 (1·79-2·61) for the hormone receptor-negative, HER2-positive group (with or without HER2-targeted therapy; p<0·0001 for all subtypes). RCB score remained prognostic for event-free survival in multivariable models adjusted for age, grade, T category, and nodal status at baseline: the adjusted HR ranged from 1·52 (1·36-1·69) in the hormone receptor-positive, HER2-negative group to 2·09 (1·73-2·53) in the hormone receptor-negative, HER2-positive group (p<0·0001 for all subtypes).

INTERPRETATION

RCB score and class were independently prognostic in all subtypes of breast cancer, and generalisable to multiple practice settings. Although variability in hormone receptor subtype definitions and treatment across patients are likely to affect prognostic performance, the association we observed between RCB and a patient's residual risk suggests that prospective evaluation of RCB could be considered to become part of standard pathology reporting after neoadjuvant therapy.

FUNDING

National Cancer Institute at the US National Institutes of Health.

Endoxifen, an Estrogen Receptor Targeted Therapy: From Bench to Bedside

The selective estrogen receptor (ER) modulator, tamoxifen, is the only endocrine agent with approvals for both the prevention and treatment of premenopausal and postmenopausal estrogen-receptor positive breast cancer as well as for the treatment of male breast cancer. Endoxifen, a secondary metabolite resulting from CYP2D6-dependent biotransformation of the primary tamoxifen metabolite, N-desmethyltamoxifen (NDT), is a more potent antiestrogen than either NDT or the parent drug, tamoxifen. However, endoxifen's antitumor effects may be related to additional molecular mechanisms of action, apart from its effects on ER. In phase 1/2 clinical studies, the efficacy of Z-endoxifen, the active isomer of endoxifen, was evaluated in patients with endocrine-refractory metastatic breast cancer as well as in patients with gynecologic, desmoid, and hormone-receptor positive solid tumors, and demonstrated substantial oral bioavailability and promising antitumor activity. Apart from its potent anticancer effects, Z-endoxifen appears to result in similar or even greater bone agonistic effects while resulting in little or no endometrial proliferative effects compared with tamoxifen. In this review, we summarize the preclinical and clinical studies evaluating endoxifen in the context of breast and other solid tumors, the potential benefits of endoxifen in bone, as well as its emerging role as an antimanic agent in bipolar disorder. In total, the summarized body of literature provides compelling arguments for the ongoing development of Z-endoxifen as a novel drug for multiple indications.

Alliance A011801 (compassHER2 RD): postneoadjuvant T-DM1 + tucatinib/placebo in patients with residual HER2-positive invasive breast cancer

This report describes the rationale, purpose and design of A011801 (CompassHER2 RD), an ongoing prospective, multicenter, Phase III randomized trial. Eligible patients in the United States (US) and Canada with high-risk (defined as ER-negative and/or node-positive) HER2-positive (HER2+) residual disease (RD) after a predefined course of neoadjuvant chemotherapy and HER2-directed treatment are randomized 1:1 to adjuvant T-DM1 and placebo, versus T-DM1 and tucatinib. Patients have also received adjuvant radiotherapy and/or endocrine therapy, if indicated per standard of care guidelines. The primary objective of the trial is to determine if the invasive disease-free survival (iDFS) with T-DM1 plus tucatinib is superior to iDFS with T-DM1 plus placebo; other outcomes of interest include overall survival (OS), breast cancer-free survival (BCFS), distant recurrence-free survival (DRFS), brain metastases-free survival (BMFS) and disease-free survival (DFS). Correlative biomarker, quality of life (QoL) and pharmacokinetic (PK) end points are also evaluated.

Adjuvant abemaciclib combined with endocrine therapy for high-risk early breast cancer: updated efficacy and Ki-67 analysis from the monarchE study

BACKGROUND

Adjuvant abemaciclib combined with endocrine therapy (ET) previously demonstrated clinically meaningful improvement in invasive disease-free survival (IDFS) and distant relapse-free survival (DRFS) in hormone receptor-positive, human epidermal growth factor receptor 2-negative, node-positive, high-risk early breast cancer at the second interim analysis, however follow-up was limited. Here, we present results of the prespecified primary outcome analysis and an additional follow-up analysis.

PATIENTS AND METHODS

This global, phase III, open-label trial randomized (1 : 1) 5637 patients to adjuvant ET for ≥5 years ± abemaciclib for 2 years. Cohort 1 enrolled patients with ≥4 positive axillary lymph nodes (ALNs), or 1-3 positive ALNs and either grade 3 disease or tumor ≥5 cm. Cohort 2 enrolled patients with 1-3 positive ALNs and centrally determined high Ki-67 index (≥20%). The primary endpoint was IDFS in the intent-to-treat population (cohorts 1 and 2). Secondary endpoints were IDFS in patients with high Ki-67, DRFS, overall survival, and safety.

RESULTS

At the primary outcome analysis, with 19 months median follow-up time, abemaciclib + ET resulted in a 29% reduction in the risk of developing an IDFS event [hazard ratio (HR) = 0.71, 95% confidence interval (CI) 0.58-0.87; nominal P = 0.0009]. At the additional follow-up analysis, with 27 months median follow-up and 90% of patients off treatment, IDFS (HR = 0.70, 95% CI 0.59-0.82; nominal P < 0.0001) and DRFS (HR = 0.69, 95% CI 0.57-0.83; nominal P < 0.0001) benefit was maintained. The absolute improvements in 3-year IDFS and DRFS rates were 5.4% and 4.2%, respectively. Whereas Ki-67 index was prognostic, abemaciclib benefit was consistent regardless of Ki-67 index. Safety data were consistent with the known abemaciclib risk profile.

CONCLUSION

Abemaciclib + ET significantly improved IDFS in patients with hormone receptor-positive, human epidermal growth factor receptor 2-negative, node-positive, high-risk early breast cancer, with an acceptable safety profile. Ki-67 index was prognostic, but abemaciclib benefit was observed regardless of Ki-67 index. Overall, the robust treatment benefit of abemaciclib extended beyond the 2-year treatment period.

Japanese subgroup analysis of the phase 3 MONARCH 3 study of abemaciclib as initial therapy for patients with hormone receptor-positive, human epidermal growth factor receptor 2-negative advanced breast cancer

Background

This was a Japanese subpopulation analysis of MONARCH 3, a randomized, double-blind, placebo-controlled phase 3 study of abemaciclib plus nonsteroidal aromatase inhibitors (NSAIs) for initial therapy for advanced breast cancer (ABC).

Methods

Eligibility included postmenopausal women with hormone receptor-positive, human epidermal growth factor receptor 2-negative ABC who had no prior systemic therapy in the advanced disease setting. Patients (N = 493) were randomized 2:1 to receive abemaciclib or placebo (150 mg) plus either 1 mg anastrozole or 2.5 mg letrozole (physician’s choice). The primary endpoint was progression-free survival (PFS). Secondary endpoints included objective response rate (ORR), pharmacokinetics (PK), safety, and health-related quality of life (HRQoL).

Results

In Japan, 53 patients were randomized (abemaciclib, n = 38; placebo, n = 15). At final PFS analysis (November 3, 2017), median PFS was 29.1 and 14.9 months in the abemaciclib and placebo groups, respectively (hazard ratio 0.537; 95% confidence interval 0.224–1.289). ORR in measurable disease was 62.1 and 50.0% in the abemaciclib and placebo groups, respectively. The Japanese PK profile was comparable to that of the overall population. Consistent with prior studies, the most frequent adverse events reported were diarrhea (abemaciclib: any grade, 94.7%; grade ≥ 3, 10.5%; placebo: any grade, 46.7%; grade ≥ 3, 0%) and neutropenia (abemaciclib: any grade, 68.4%; grade ≥ 3, 21.1%; placebo: any grade, 0%). HRQoL outcomes were generally similar between treatments except for the diarrhea score, which favored placebo.

Conclusions

Consistent with findings in the overall population, abemaciclib plus NSAI was an effective initial treatment in the Japanese subpopulation, with a manageable safety profile.

Clinical trial registration

NCT02246621; U.S. National Library of Medicine: https://clinicaltrials.gov/ct2/show/NCT02246621.

Supplementary information

The online version contains supplementary material available at 10.1007/s12282-021-01295-0.

Characteristics and Spatially Defined Immune (micro)landscapes of Early-stage PD-L1-positive Triple-negative Breast Cancer

PURPOSE

Programmed death ligand 1 [PD-(L)1]-targeted therapies have shown modest survival benefit in triple-negative breast cancer (TNBC). PD-L1+ microenvironments in TNBC are not well characterized and may inform combinatorial immune therapies. Herein, we characterized clinicopathologic features, RNA-based immune signatures, and spatially defined protein-based tumor-immune microenvironments (TIME) in early-stage PD-L1+ and PD-L1- TNBC.

EXPERIMENTAL DESIGN

From a large cohort of chemotherapy-naïve TNBC, clinicopathologic features, deconvoluted RNA immune signatures, and intraepithelial and stromal TIME (Nanostring GeoMX) were identified in subsets of PD-L1+ and PD-L1- TNBC, as defined by FDA-approved PD-L1 companion assays.

RESULTS

228 of 499 (46%) TNBC were PD-L1+ (SP142: ≥1% immune cells-positive). Using PD-L1 22C3, 46% had combined positive score (CPS) ≥ 1 and 16% had CPS ≥10. PD-L1+ TNBC were higher grade with higher tumor-infiltrating lymphocytes (TIL; P < 0.05). PD-L1 was not associated with improved survival following adjustment for TILs and other variables. RNA profiles of PD-L1+ TNBC had increased dendritic cell, macrophage, and T/B cell subset features; and decreased myeloid-derived suppressor cells. PD-L1+ stromal and intraepithelial TIMEs were highly enriched in IDO-1, HLA-DR, CD40, and CD163 compared with PD-L1-TIME, with spatially specific alterations in CTLA-4, Stimulator of Interferon Genes (STING), and fibronectin. Macrophage- and antigen presentation-related proteins correlated most strongly with PD-L1 protein.

CONCLUSIONS

In this early-stage TNBC cohort, nearly 50% were PD-L1+ (SP142 companion assay) while 16% were PD-L1+ with the 22C3 companion assay. PD-L1+ TNBC had specific myeloid-derived and lymphoid features. Spatially defined PD-L1+ TIME were enriched in several clinically actionable immune proteins. These data may inform future studies on combinatorial immunotherapies for patients with PD-L1+ TNBC.See related commentary by Symmans, p. 5446.

Interaction Between SNP Genotype and Efficacy of Anastrozole and Exemestane in Early-Stage Breast Cancer

Aromatase inhibitors (AIs) are the treatment of choice for hormone receptor-positive early breast cancer in postmenopausal women. None of the third-generation AIs are superior to the others in terms of efficacy. We attempted to identify genetic factors that could differentiate between the effectiveness of adjuvant anastrozole and exemestane by examining single-nucleotide polymorphism (SNP)-treatment interaction in 4,465 patients. A group of SNPs were found to be differentially associated between anastrozole and exemestane regarding outcomes. However, they showed no association with outcome in the combined analysis. We followed up common SNPs near LY75 and GPR160 that could differentiate anastrozole from exemestane efficacy. LY75 and GPR160 participate in epithelial-to-mesenchymal transition and growth pathways, in both cases with SNP-dependent variation in regulation. Collectively, these studies identified SNPs that differentiate the efficacy of anastrozole and exemestane and they suggest additional genetic biomarkers for possible use in selecting an AI for a given patient.

Quantitative Analysis of Tyrosine Phosphorylation from FFPE Tissues Reveals Patient-Specific Signaling Networks

Human tissue samples commonly preserved as formalin-fixed paraffin-embedded (FFPE) tissues after diagnostic or surgical procedures in the clinic represent an invaluable source of clinical specimens for in-depth characterization of signaling networks to assess therapeutic options. Tyrosine phosphorylation (pTyr) plays a fundamental role in cellular processes and is commonly dysregulated in cancer but has not been studied to date in FFPE samples. In addition, pTyr analysis that may otherwise inform therapeutic interventions for patients has been limited by the requirement for large amounts of frozen tissue. Here we describe a method for highly sensitive, quantitative analysis of pTyr signaling networks, with hundreds of sites quantified from one to two 10-μm sections of FFPE tissue specimens. A combination of optimized magnetic bead-based sample processing, optimized pTyr enrichment strategies, and tandem mass tag multiplexing enabled in-depth coverage of pTyr signaling networks from small amounts of input material. Phosphotyrosine profiles of flash-frozen and FFPE tissues derived from the same tumors suggested that FFPE tissues preserve pTyr signaling characteristics in patient-derived xenografts and archived clinical specimens. pTyr analysis of FFPE tissue sections from breast cancer tumors as well as lung cancer tumors highlighted patient-specific oncogenic driving kinases, indicating potential targeted therapies for each patient. These data suggest the capability for direct translational insight from pTyr analysis of small amounts of FFPE tumor tissue specimens. SIGNIFICANCE: This study reports a highly sensitive method utilizing FFPE tissues to identify dysregulated signaling networks in patient tumors, opening the door for direct translational insights from FFPE tumor tissue banks in hospitals.

FOXA1 overexpression suppresses interferon signaling and immune response in cancer

Androgen receptor-positive prostate cancer (PCa) and estrogen receptor-positive luminal breast cancer (BCa) are generally less responsive to immunotherapy compared with certain tumor types such as melanoma. However, the underlying mechanisms are not fully elucidated. In this study, we found that FOXA1 overexpression inversely correlated with interferon (IFN) signature and antigen presentation gene expression in PCa and BCa patients. FOXA1 bound the STAT2 DNA-binding domain and suppressed STAT2 DNA-binding activity, IFN signaling gene expression, and cancer immune response independently of the transactivation activity of FOXA1 and its mutations detected in PCa and BCa. Increased FOXA1 expression promoted cancer immuno- and chemotherapy resistance in mice and PCa and BCa patients. These findings were also validated in bladder cancer expressing high levels of FOXA1. FOXA1 overexpression could be a prognostic factor to predict therapy resistance and a viable target to sensitize luminal PCa, BCa, and bladder cancer to immuno- and chemotherapy.

Decreasing the Use of Sentinel Lymph Node Surgery in Women Older than 70 Years with Hormone Receptor-Positive Breast Cancer and the Impact on Adjuvant Radiation and Hormonal Therapy

BACKGROUND

In 2016, SSO Choosing Wisely guidelines recommended against routine sentinel lymph node (SLN) surgery in women ≥ 70 with HR+ cN0 breast cancer. Following this, we identified a group of women at low-risk of nodal positivity where SLN may be omitted (grade 1, cT1mi-T1c, or grade 2, cT1mi-T1b). This study evaluates the impact of these changes on our practice.

METHODS

Retrospective chart review of women aged ≥ 70 years with HR+ cN0 breast cancer at our institution from 2010 to 2020. We compared SLN use before (2010-2016)/after (2017-2020) guideline release according to clinical risk and the association with adjuvant therapy.

RESULTS

A total of 1015 breast cancers in 987 women identified. SLN surgery rate significantly decreased from 90.6% (2010-2016) to 62.8% in 2020 (p < 0.001). This was driven by breast-conserving surgery (BCS) with SLN rates of 88.2% (2010-2016) and 46.7% in 2020. During 2017-2020, SLN use varied by risk within BCS patients: 52.2% low-risk, 81.9% higher-risk, p < 0.001. In contrast, in mastectomy patients SLN was performed in ≥ 98% regardless of risk level. SLN positivity was 13.4% overall: 7.4% in low-risk and 20.8% in higher-risk, p < 0.001. After adjusting for age and clinical risk, SLN use was not associated with adjuvant radiation [odds ratio (OR) 1.61, p = 0.11] or endocrine therapy (OR 1.12, p = 0.71).

CONCLUSIONS

The Society of Surgical Oncology guideline release, followed by implementation of a clinical tool to stratify by nodal risk, was associated with decreased SLN use in women aged ≥ 70 years, in those with clinically low-risk HR+ disease surgically treated with BCS. Adjusting for confounders, omission of SLN surgery was not associated with use of subsequent adjuvant radiation or hormonal therapy.

Abstract LB078: Hexyl-(cuban-1-yl-methyl)-biguanide (HCB) inhibits hormone therapy resistant breast cancer cells, in part by Inhibiting CYP3A4 arachidonic acid epoxygenase activity

Introduction: Small molecule therapeutics of estrogen receptor-positive/HER2-negative breast cancer remains an area of active investigation where novel agents are greatly needed for treatment of hormone therapy resistant metastatic disease. The biguanide hexyl-benzyl-biguanide (HBB) is a potent inhibitor of CYP3A4 arachidonic acid (AA) epoxygenase activity and inhibits breast cancer cell proliferation and MCF-7 breast cancer tumor growth in nude mice. To explore the impact of bioisosteric substitution of the benzyl moiety of HBB with a cubane moiety, we synthesized hexyl-(cuban-1-yl-methyl)-biguanide (HCB) and tested its potency for the inhibition of the cognate CYP3A4 target AA epoxygenase activity as well as breast cancer cell proliferation of hormone therapy sensitive and resistant cell lines.

Results: HCB selectively inhibited CYP3A4-mediated biosynthesis of (±)-14,15-EET with an IC50 of 4.7±0.2 uM vs. 64.8±6.5 uM for 8,9-EET and 26.5±1.9 uM for 11,12-EET. At 24 hours, HCB inhibited proliferation of MCF-7 (ER+HER2-), BT474 (ER+HER2+) and MDA-MB-231 (ER-HER2-) cells at IC50 of 8.4±1.2, 11±1.3 and 15±0.9 uM, respectively. At 48 hours, HCB inhibited proliferation of aromatase inhibitor and fulvestrant resistant (LR,FR), and cyclin dependent kinase inhibitor (CDKi) palbociclib resistant (LR,FR,PR) MCF-7 cell lines; LR,FR MCF-7AC1 (IC50 =1.34±0.1 uM) and LR,FR,PR MCF-7AC1 (IC50 =1.64±0.2 uM). Addition of 14,15-EET (1 uM) partially rescues MCF-7 cells from HCB-mediated inhibition of proliferation.

OXPHOS is promoted, in part, by EETs. HCB is a potent OXPHOS inhibitor and rapidly inhibits O2 consumption of the MCF-7 and ZR75 (ER+HER2-) cells in a dose-dependent fashion (P&lt;0.05). HCB treatment (10 uM) reduces mitochondrial membrane potential to 57.4±15.3% (P&lt;0.001) of vehicle control in MCF-7 cells. Treatment with HCB at 20 uM for 0.5 hour also causes mitochondrial swelling in MCF-7 cells. HCB (10 uM) activates AMPK within 0.5 hour and increases the level of phosphorylation from 2.4±0.3 to 25.1±6.0 folds in a time dependent fashion in MCF-7 cells from 0.5-24 hours.

Conclusion: These results show that HCB inhibits proliferation of ER+HER2- breast cancer cells, in part through inhibition of OXPHOS and suppression of the CYP product 14,15-EET. This inhibition is highly active in hormonal therapy and CDKi resistant ER+HER2- breast cancer cells. These results suggest that HCB is a novel and potent biguanide that has potential to be developed for inhibition of hormone therapy resistant and CDKi resistant breast cancer.

Citation Format: Zhijun Guo, Jianxun Lei, Kwon Ho Hong, Beverly Norris, Craig M. Flory, Swaathi Jayaraman, Connor McDermott, Elizabeth Ambrose, Irina Sevrioukova, Tom Poulos, Ilia Denisov, Stephen Sliga, Robert J. Schumacher, Gunda I. Georg, John R. Hawse, Matthew P. Goetz, David A. Potter. Hexyl-(cuban-1-yl-methyl)-biguanide (HCB) inhibits hormone therapy resistant breast cancer cells, in part by Inhibiting CYP3A4 arachidonic acid epoxygenase activity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr LB078.

Abemaciclib as initial therapy for advanced breast cancer: MONARCH 3 updated results in prognostic subgroups

In MONARCH 3, continuous dosing of abemaciclib with an aromatase inhibitor (AI) conferred significant clinical benefit to postmenopausal women with HR+, HER2- advanced breast cancer. We report data for clinically prognostic subgroups: liver metastases, progesterone receptor status, tumor grade, bone-only disease, ECOG performance status, and treatment-free interval (TFI) from an additional 12-month follow-up (after final progression-free survival [PFS] readout). In the intent-to-treat population, after median follow-up of approximately 39 months, the updated PFS was 28.2 versus 14.8 months (hazard ratio [HR], 0.525; 95% confidence interval, 0.415-0.665) in abemaciclib versus placebo arms, respectively. Time to chemotherapy (HR, 0.513), time to second disease progression (HR, 0.637), and duration of response (HR, 0.466) were also statistically significantly prolonged with the addition of abemaciclib to AI. Treatment benefit was observed across all subgroups, as evidenced by objective response rate change from the addition of abemaciclib to AI, with the largest effects observed in patients with liver metastases, progesterone receptor-negative tumors, high-grade tumors, or TFI < 36 months. Extended follow-up in the MONARCH 3 trial further confirmed that the addition of abemaciclib to AI conferred significant treatment benefit to all subgroups, including those with poorer prognosis.

Establishment and characterization of immortalized human breast cancer cell lines from breast cancer patient-derived xenografts (PDX)

The application of patient-derived xenografts (PDX) in drug screening and testing is a costly and time-consuming endeavor. While cell lines permit extensive mechanistic studies, many human breast cancer cell lines lack patient characteristics and clinical treatment information. Establishing cell lines that retain patient's genetic and drug response information would enable greater drug screening and mechanistic studies. Therefore, we utilized breast cancer PDX from the Mayo Breast Cancer Genome Guided Therapy Study (BEAUTY) to establish two immortalized, genomically unique breast cancer cell lines. Through extensive genetic and therapeutic testing, the cell lines were found to retain the same clinical subtype, major somatic alterations, and drug response phenotypes as their corresponding PDX and patient tumor. Our findings demonstrate PDX can be utilized to develop immortalized breast cancer cell lines and provide a valuable tool for understanding the molecular mechanism of drug resistance and exploring novel treatment strategies.

Inhibition of ATM Induces Hypersensitivity to Proton Irradiation by Upregulating Toxic End Joining

Proton Bragg peak irradiation has a higher ionizing density than conventional photon irradiation or the entrance of the proton beam profile. Whether targeting the DNA damage response (DDR) could enhance vulnerability to the distinct pattern of damage induced by proton Bragg peak irradiation is currently unknown. Here, we performed genetic or pharmacologic manipulation of key DDR elements and evaluated DNA damage signaling, DNA repair, and tumor control in cell lines and xenografts treated with the same physical dose across a radiotherapy linear energy transfer spectrum. Radiotherapy consisted of 6 MV photons and the entrance beam or Bragg peak of a 76.8 MeV spot scanning proton beam. More complex DNA double-strand breaks (DSB) induced by Bragg peak proton irradiation preferentially underwent resection and engaged homologous recombination (HR) machinery. Unexpectedly, the ataxia-telangiectasia mutated (ATM) inhibitor, AZD0156, but not an inhibitor of ATM and Rad3-related, rendered cells hypersensitive to more densely ionizing proton Bragg peak irradiation. ATM inhibition blocked resection and shunted more DSBs to processing by toxic ligation through nonhomologous end-joining, whereas loss of DNA ligation via XRCC4 or Lig4 knockdown rescued resection and abolished the enhanced Bragg peak cell killing. Proton Bragg peak monotherapy selectively sensitized cell lines and tumor xenografts with inherent HR defects, and the repair defect induced by ATM inhibitor coadministration showed enhanced efficacy in HR-proficient models. In summary, inherent defects in HR or administration of an ATM inhibitor in HR-proficient tumors selectively enhances the relative biological effectiveness of proton Bragg peak irradiation. SIGNIFICANCE: Coadministration of an ATM inhibitor rewires DNA repair machinery to render cancer cells uniquely hypersensitive to DNA damage induced by the proton Bragg peak, which is characterized by higher density ionization.See related commentary by Nickoloff, p. 3156.