18F-FDG Dedicated Breast PET Complementary to Breast MRI for Evaluating Early Response to Neoadjuvant Chemotherapy

Purpose To compare quantitative measures of tumor metabolism and perfusion using fluorine 18 (18F) fluorodeoxyglucose (FDG) dedicated breast PET (dbPET) and breast dynamic contrast-enhanced (DCE) MRI during early treatment with neoadjuvant chemotherapy (NAC). Materials and Methods Prospectively collected DCE MRI and 18F-FDG dbPET examinations were analyzed at baseline (T0) and after 3 weeks (T1) of NAC in 20 participants with 22 invasive breast cancers. FDG dbPET-derived standardized uptake value (SUV), metabolic tumor volume, and total lesion glycolysis (TLG) and MRI-derived percent enhancement (PE), signal enhancement ratio (SER), and functional tumor volume (FTV) were calculated at both time points. Differences between FDG dbPET and MRI parameters were evaluated after stratifying by receptor status, Ki-67 index, and residual cancer burden. Parameters were compared using Wilcoxon signed rank and Mann-Whitney U tests. Results High Ki-67 tumors had higher baseline SUVmean (difference, 5.1; P = .01) and SUVpeak (difference, 5.5; P = .04). At T1, decreases were observed in FDG dbPET measures (pseudo-median difference T0 minus T1 value [95% CI]) of SUVmax (-6.2 [-10.2, -2.6]; P < .001), SUVmean (-2.6 [-4.9, -1.3]; P < .001), SUVpeak (-4.2 [-6.9, -2.3]; P < .001), and TLG (-29.1 mL3 [-71.4, -6.8]; P = .005) and MRI measures of SERpeak (-1.0 [-1.3, -0.2]; P = .02) and FTV (-11.6 mL3 [-22.2, -1.7]; P = .009). Relative to nonresponsive tumors, responsive tumors showed a difference (95% CI) in percent change in SUVmax of -34.3% (-55.9%, 1.5%; P = .06) and in PEpeak of -42.4% (95% CI: -110.5%, 8.5%; P = .08). Conclusion 18F-FDG dbPET was sensitive to early changes during NAC and provided complementary information to DCE MRI that may be useful for treatment response evaluation. Keywords: Breast, PET, Dynamic Contrast-enhanced MRI Clinical trial registration no. NCT01042379 Supplemental material is available for this article. © RSNA, 2024.

Quantifying hormone receptor status in lobular breast cancer in an institutional series: the relationship between estrogen and progesterone receptor status and outcomes

PURPOSE

Recent guidelines defined a new reporting category of ER-low-positive breast cancer based on immunohistochemistry (IHC). While low positivity of either hormone receptor is uncommon in invasive lobular carcinoma (ILC), we sought to investigate whether relatively low hormone receptor positivity was associated with tumor characteristics and patient outcomes in a single institutional cohort.

METHODS

We searched an institutional database for cases of stage I-III ILC with available IHC reports. Based on prior published categories in ILC, ER was classified as low, medium, or high as defined by ER staining of 10-69%, 70-89%, and ≥ 90% respectively. PR low and high tumors were defined by < 20%, or ≥ 20% staining respectively. We used chi-squared tests, t-tests, and Cox proportional hazards models to evaluate associations between ER/PR categories and tumor characteristics or disease-free survival (DFS).

RESULTS

The cohort consisted of 707 ILC cases, with 11% of cases categorized as ER low, 15.1% as medium, and 73.8% as high. The majority (67.6%) were PR high. Patients with ER low/medium expression were significantly younger, and more likely to also have PR low and/or HER2 positive tumors compared to those that were ER high. In a Cox proportional hazards model adjusting for age, stage, grade, pleomorphic histology, and treatment, ER category was not prognostic for DFS, but PR negative and PR low status each had significantly worse DFS compared to PR high status (HR 3.5, 95% CI 1.8-6.7, p < 0.001; and HR 2.0, 95% CI 1.1-3.5, p = 0.015, respectively).

CONCLUSION

These findings highlight the relevance of quantifying ER and PR within ILC.

Area Deprivation Index in Patients with Invasive Lobular Carcinoma of the Breast: Associations with Tumor Characteristics and Outcomes

BACKGROUND

Although investigators have shown associations between socioeconomic status (SES) and outcomes in breast cancer, there is a paucity of such data for invasive lobular carcinoma (ILC), the second most common type of breast cancer. Herein we evaluated the relationship between SES with tumor features and outcomes in stage I to III patients with ILC.

METHODS

We analyzed a prospectively maintained institutional ILC database and utilized the area deprivation index (ADI) to determine neighborhood adversity, an indicator of SES. We used Cox proportional hazards models in Stata 17.0 to evaluate relationships between ADI quintile (Q), race, body mass index (BMI), clinicopathologic features, treatment type, and event-free survival (EFS).

RESULTS

Of 804 patients with ILC, 21.4% lived in neighborhoods classified as ADI Q1 (least resource-deprived) and 19.7% in Q5 (most resource-deprived). Higher deprivation was significantly associated with larger tumor size (3.6 cm in Q5 vs. 3.1 cm in Q1), increased presence of lymphovascular invasion (8.9% in Q5 vs. 6.7% in Q1), and decreased use of adjuvant endocrine therapy (67.1% in Q5 vs. 73.6% in Q1). On multivariable analysis, tumor size, receptor subtypes, and omission of adjuvant endocrine therapy were associated with reduced EFS.

CONCLUSIONS

These data show that patients with ILC and higher ADI experience more aggressive tumors and differences in treatment. More data evaluating the complex relationships between these factors is needed to optimize outcomes for patients with ILC, regardless of SES.

IMPACT

ADI is associated with differences in patients with ILC.

HER-2 low status in early-stage invasive lobular carcinoma of the breast: associated factors and outcomes in an institutional series

PURPOSE

HER2 overexpression has a central role in breast cancer carcinogenesis and is associated with poor prognosis if untreated. Lately, identification of HER2-low breast cancer has been proposed to select patients for novel HER2-directed chemotherapy and includes cancers with immunohistochemistry 1 + or 2 + with negative FISH, encompassing approximately 55-60% of all breast carcinomas. In early-stage breast cancer, the prognostic significance of HER2 low-disease is less well understood, with a particular paucity of data evaluating the prevalence and implications of HER2-low status in invasive lobular carcinoma (ILC).

METHODS

We evaluated 666 stage I-III ILC tumors from a prospectively maintained institutional database, comparing clinicopathologic features and disease-free survival (DFS) using a multivariable Cox proportional hazards model.

RESULTS

HER2-low status was common in this cohort of patients with ILC, but most clinicopathologic features did not differ between HER2-low and HER2-negative cases. However, when adjusting for tumor size, number of positive nodes, ER/PR status, and local therapy received, patients with HER2-low status had worse disease-free survival (DFS) than those with HER2-negative tumors (hazard ratio 2.0, 95% confidence interval 1.0-4.1, p = 0.05).

CONCLUSION

This difference in DFS supports the notion that HER2-low and HER2-negative early stage ILC may differ clinically, despite similar clinicopathologic features. Further investigation into the potential benefit of HER2 targeted therapy in HER2-low early-stage breast cancer, and specifically lobular cancer, is warranted to ensure optimal outcomes in this distinct tumor subtype.

Abstract P5-07-03: The Association Between Symptom Severity and Physical Function among Participants in I-SPY2

Background. Patient-reported outcomes (PROs) are increasingly recognized as a valuable component to understand treatment tolerability and toxicity among patients on clinical trials. We have implemented a system for monitoring patient reported outcomes (PROs), symptoms, and quality of life (QOL) using electronic PRO (ePRO) instruments for patients enrolled in the I-SPY2 trial. I-SPY2 is a phase II multi-site clinical trial evaluating the effect of novel neoadjuvant therapies for locally advanced breast cancer. We correlated patient demographic factors with symptoms, investigated the trajectory of symptoms throughout treatment, and sought to characterize symptoms associated with decline in physical function (PF). Methods. Our study population included 259 I-SPY2 patients that completed surveys on one of 9 study arms (including novel oral taxane/immunotherapy combinations, IV paclitaxel, checkpoint inhibitor+/- LAG3 inhibitor, and control IV paclitaxel +/- trastuzumab/pertuzumab). After the 12 week period of investigational agents, most patients received standard adriamycin and cyclophosphamide (AC). Symptom severity, frequency, and interference was assessed weekly using 33 items from the PRO-CTCAE item bank. PF was assessed using the NIH PROMIS instrument and was evaluated at baseline, inter-regimen (after 12 weeks of treatment), pre-surgery, and 1 and 6 months at follow-up. An odds ratio was used to assess univariate associations between age and race, and symptoms. Regularized multi-variate regression was used to evaluate early symptoms (prior to week 6) predictive of a clinically significant (&gt;5 point T-score) decline in PF from baseline to post-treatment follow-up among all races and age groups. Results. Of 259 patients (mean age (SD) = 46.8 (13.6)), 160 (58%) were White, 13 (5%) were Asian, 26 (10%) were African American (AA), 25 (9.3%) were Hispanic, and 35 (13.5%) self-reported “Other”. At baseline, AA patients had a higher severity of joint pain than White patients (OR = 14.9, P &lt; 0.05). During study treatment with paclitaxel and/or novel agent within the first 12 weeks of treatment, AA patients and non-white (NW) patients were more likely to report severe vomiting than White patients (OR =13.22 and 12.72, P&lt; 0.05 and P&lt; 0.03 respectively). During treatment with AC, NW patients were more likely to report higher severity of neuropathy than White patients (OR = 5.43, P&lt; 0.03). Among all patients, in analysis of early symptoms predictive of a clinically significant decline in PF between baseline and 1 month post treatment, predictors included high frequency of diarrhea, severity of itching, and severity of joint pain. Further analysis of symptom trajectories revealed that frequency of diarrhea reported rose sharply between baseline and Cycle 2 with 9 patients (7%) reporting occasional or frequent diarrhea to 39 patients (28%) reporting occasional to almost constant diarrhea and remained stable at that proportion for the remainder of treatment. Frequency of diarrhea declined slightly during AC (17%) and dropped to baseline levels by follow-up. In contrast, severity of joint pain persisted post-treatment, rising consistently from baseline through follow- up with 3 patients (2%) reporting moderate to severe joint pain at baseline to 18 patients (35%) reporting moderate to severe joint pain at follow-up. Conclusion. Among I-SPY2 participants, when higher grade of diarrhea is persistent (or uncontrolled), it impacts physical function even after end of therapy. In some cases, race was also a determinant in symptom trajectory, although a higher enrollment of AA and NW patients will enable more robust estimates to be computed. While some of these early symptom predictors are transient and resolve by the time of follow-up, others persist long-term and contribute more directly towards impaired physical function at follow-up.

Citation Format: Amrita Basu, Saumya Umashankar, Kaylee Blevins, Anna Northrop, Anika Christofferson, Ebunoluwa Olunuga, Jaeyoon Cha, Ananya Mittal, Julissa Molina-Vega, Laura Sit, Thelma Brown, Bev Parker, Diane Heditsian, Susie Brain, Carol Simmons, Alessandra Taboada, Tina J. Hieken, Kathryn Ruddy, Carolina Salvador, Candace Mainor, Anosheh Afghahi, Sarah Tevis, Anne Blaes, Irene M. Kang, Jane Perlmutter, Hope Rugo, Sai Kanaparthi, Garry Peterson, Lisa T. Weiss, Adam Asare, Laura J. Esserman, Michelle Melisko, Dawn Hershman. The Association Between Symptom Severity and Physical Function among Participants in I-SPY2 [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P5-07-03.

Abstract HER2-14: HER2-14 HER-2 low status in early stage invasive lobular carcinoma of the breast: associated factors and outcomes in an institutional series

Objectives: The concept of human epidermal growth factor receptor 2 (HER2)-low status has been proposed as a potential treatment target for breast cancers previously considered to be HER2-negative. Defined by an immunohistochemistry (IHC) score of 1+ or 2+ and negative fluorescent in situ hybridization (FISH) for HER2, HER2-low status predicts significant clinical benefit from novel therapeutic compounds in recent clinical trials. The prevalence and clinical implications of HER2-low status in patients with early stage invasive lobular carcinoma (ILC) has not been described. We aimed to describe the clinicopathologic features and prevalence of HER2-low status in ILC, and identify any potential differences in clinical outcome. Methods: We evaluated stage I-III ILC tumors from a prospectively maintained institutional database of patients where both IHC and FISH testing for HER2 status was performed as standard clinical care. Tumors were classified as HER2 negative (IHC=0), HER2-low (IHC=1+ or 2+ and negative FISH), or HER2 positive (IHC=3+ or FISH ratio ⇒2). Data were analyzed in Stata 16.1 using chi-squared tests, t-tests, and Cox proportional hazards models for disease free survival (DFS). Results: 666 ILC tumors with available HER2 status were available for analysis. The mean age at diagnosis was 59.8 years (range 21-91). The majority of patients had stage I disease (63.1%) with an average follow up time of 6.7 years (standard deviation [5.4]). Overall, 184 (27.6%) tumors were HER2 negative, 434 (65.1%) were HER2-low, and 48 (7.2%) were HER2 positive. There were no associations between HER2 status and age, menopausal status, body mass index, tumor stage, grade, presence of lymphovascular invasion, or molecular assay results. Hormone receptor status was significantly associated with HER2 status, with HER2 positive tumors significantly less likely to be estrogen receptor (ER) positive than both HER2 negative and HER2-low tumors (89.6% versus 97.3% and 96.8% respectively, p=0.03). HER2-low tumors were also significantly more likely to have progesterone receptor (PR) positivity (86.6% compared to 79.9% of HER2 negative and 72.9% of HER2 positive tumors, p = 0.01). This difference remained significant when comparing just HER2-low to HER2 negative cases (p=0.034). While there were no differences in use of neoadjuvant or adjuvant chemotherapy by HER2 status, HER2-low patients were significantly more likely to undergo mastectomy versus lumpectomy when compared to HER2 negative and HER2 positive patients (53.7% versus 38.0% and 43.8% respectively, p= 0.001). In a multivariable Cox proportional hazards model adjusting for tumor size, number of positive nodes, ER/PR status, and local therapy received, patients with HER2-low status had worse DFS than those with HER2 negative tumors (hazard ratio 2.0, 95% confidence interval 1.0 - 4.1, p=0.05). Conclusions: In this analysis of 666 early stage ILC cases, we found that most tumors were HER2-low, and that those with HER2-low disease were significantly more likely to have PR positive tumors and to undergo mastectomy. When adjusting for these variables, we identified a difference in DFS between HER2 negative and HER2-low early stage ILC. These findings support the contention that HER2-low and HER2 negative disease represent two different clinical entities. Further investigation of the potential benefit of HER2 targeted therapy in ILC, which predominately lacks HER2-amplified disease, is needed to ensure optimal outcomes in this understudied tumor type.

Citation Format: Harriet T. Rothschild, Elle Clelland, Anne Patterson, Julissa Molina-Vega, Mandeep Kaur, Mary Kathryn Abel, W. Fraser Symmans, Christopher J. Schwartz, Rita Mukhtar. HER2-14 HER-2 low status in early stage invasive lobular carcinoma of the breast: associated factors and outcomes in an institutional series [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr HER2-14.

Abstract P3-09-01: Characterization of residual disease after neoadjuvant selective estrogen receptor degrader (SERD) therapy using tumor organoids in the I-SPY Endocrine Optimization Protocol (EOP)

Background: Treatment of estrogen receptor (ER)-positive breast cancer with selective estrogen receptor degraders (SERDs) frequently results in the loss or reduction of ER expression. Whether these changes are due to on-target effects of SERDs degrading ER or arise as a mechanism of tumor resistance with associated changes in cellular phenotypes remains unknown. It is critical to distinguish between these possibilities to accurately assess treatment response and determine the most appropriate subsequent therapy. To this end, we created and conducted molecular analyses on patient-derived organoid cultures from post-treatment tissue in patients receiving neoadjuvant SERD therapy for early-stage ER+ breast cancer in the I-SPY2 Endocrine Optimization Protocol (EOP). Methods: The I-SPY2 EOP study is a prospective, randomized substudy within the I-SPY TRIAL testing the oral SERD amcenestrant alone or in combination with letrozole or abemaciclib in stage 2/3 ER+ Her2-negative breast cancer. Enrollment is ongoing, with patients receiving amcenestrant neoadjuvantly for 6 months until the day before surgery. Tumor tissue is collected at baseline, 3 weeks, and at surgery. Organoids were generated from post-treatment surgical samples. Organoid cultures were optimized based on established methods (Dekkers et al., Nature Protocols, 2021) to assess ER levels and activity. Pre- and post-treatment tissue samples were also assessed for ER, PR, Ki67, and GATA3, a luminal marker and transcription factor that is functionally linked with ER, via immunohistochemistry. Results: In 7 patients with both pre- and post-treatment tissue samples including fresh surgical samples for organoid generation, the ER in baseline tumor tissue was &gt;=90% in all patients, PR ranged from 40-90%, and Ki67 ranged from 5-30%. In post-treatment surgical tissue from these cases, ER ranged from 0-30%, PR from 0-50%, Ki67 from &lt; 1%-10%, and GATA3 was positive in 5 of 5 cases tested to-date. The creation of organoids from residual disease at surgery was attempted for these 7 patients, with organoids successfully propagated in 5 cases thus far. 3 of 5 organoid cultures were ready for analysis and in all cases strong ER and PR expression in organoids was observed after culture for &gt; 1 month in the absence of amcenestrant. Detailed gene expression profiling (including Mammaprint/Blueprint) and gene set enrichment analyses (GSEA) to assess for intrinsic breast cancer subtype and ER activity in each sample and corresponding organoid culture are in progress and will be reported with the full dataset. Conclusion: Patient-derived organoid culturing of residual disease after neoadjuvant endocrine therapy is feasible. Neoadjuvant treatment with a SERD can render ER and PR low or absent at the time of surgical resection, which does not necessarily imply the presence of endocrine therapy resistant disease. The use of organoids and additional IHC markers (GATA3) demonstrate that receptor negativity may be an indicator of the drug hitting its target, suggesting ER signaling is still intact. In general, patient-derived tumor organoid cultures modeling residual disease states can be a useful adjunct to existing methods used to monitor the effects of neoadjuvant endocrine therapy and is being explored in the I-SPY EOP trial.

Citation Format: Jennifer Rosenbluth, Christopher J. Schwartz, Tam Binh Bui, Shruti Warhadpande, Pravin Phadatare, Sigal Eini, Michael Bruck, Julissa Molina-Vega, Kami Pullakhandam, Nicole Schindler, Lamorna A. Brown Swigart, Christina Yau, Gillian Hirst, Rita Mukhtar, Karthik V. Giridhar, Olufunmilayo I. Olopade, Kevin Kalinsky, Cheryl A. Ewing, Jasmine M. Wong, Michael D. Alvarado, Laura Van’t Veer, Laura J. Esserman, Jo Chien. Characterization of residual disease after neoadjuvant selective estrogen receptor degrader (SERD) therapy using tumor organoids in the I-SPY Endocrine Optimization Protocol (EOP) [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P3-09-01.

Abstract P2-03-16: Quantifying estrogen and progesterone receptor status in early-stage invasive lobular carcinoma of the breast: associated factors and outcomes in an institutional series

Background: Recent guidelines regarding estrogen (ER) and progesterone (PR) receptor testing from the American Society of Clinical Oncology and College of American Pathologists defined a new reporting category of ER-low positive breast cancer for tumors with 1-10% ER expression by immunohistochemistry (IHC). The clinical implications of ER-low positivity are incompletely understood, especially in invasive lobular carcinoma (ILC), the second most common type of breast cancer. Given the rarity of low-ER positivity in ILC, we evaluated tumor features and outcomes associated with a spectrum of ER/PR positivity in a monoinstitutional ILC cohort. Methods: We analyzed cases of stage I-III ILC with available IHC reports. Based on prior published categories in ILC, we classified ER as low, medium, or high as defined by ER staining of 10–69%, 70–89%, and ≥90% respectively. PR negative, low, and high tumors were defined by 0%, &lt; 20%, or ≥20% staining respectively. We used chi-squared tests, t-tests, and Cox proportional hazards models in Stata 16.1 to evaluate associations between ER/PR categories including clinicopathologic variables and event-free survival (EFS). Results: Of 744 cases, 24 (3.2%) were ER negative and 10 (1.3%) were ER-low positive as defined by 1-10% positive staining. 713 remaining cases had ER positivity ≥ 10% and comprised the cohort categories of ER low, medium, and high for this study (11.2%, 15.0%, and 73.8% respectively). In 751 cases with PR data, 122 (16.2%) were PR negative, 145 (19.4%) were PR low and 483 (64.3%) were PR high. ER high status was significantly associated with older age (mean 56.7, 56.7, and 60.6 years in ER low, medium, and high respectively, p=0.0005). ER low was associated with PR negative and low status (42.3% were PR neg/low and ER low, versus 37.4% with ER medium and 29.9% in ER high, p=0.045), and more likely to have overexpression of HER2 (9.7%, 9.0%, and 2.9% ER low, medium, high, respectively, p=0.002). ER low tumors were more likely to be grade 1 than ER medium or high (41.8%, 29.8% and 24.5% respectively, p=0.025), and have positive surgical margins (39.4%, 35.9% and 23.9% respectively, p=0.002). ER status was not associated with Ki67, stage, body mass index (BMI), lymphovascular invasion, lobular carcinoma in situ (LCIS), pleomorphic histology, local therapy, or chemotherapy use. In contrast, PR high was significantly associated with younger age (57.6 versus 63.5 years in PR low, p&lt; 0.0001). PR low was associated with HER2 overexpression (8.6% versus 3.2% in PR high, p=0.002). PR low cases were more likely to present at higher stages (15.8% stage III versus 10.1% stage III in PR high, p=0.032), to be pleomorphic (16.8% versus 8.2%, p&lt; 0.001), and to receive chemotherapy (30.8% versus 23.1%, p=0.022) but were less likely to have associated LCIS (64.0 versus 74.2%, p=0.004). PR status was not associated with Ki67, BMI, lymphovascular invasion, local therapy, or surgical margins. In a Cox proportional hazards model adjusting for age, stage, grade, pleomorphic histology, and chemotherapy use, ER category was not associated with EFS but both PR negative and PR low status each had significantly worse EFS compared to PR ≥20% (HR 3.5, 95% CI 1.8-6.7, p&lt; 0.001 for PR negative, and HR 2.0, 95% CI 1.1-3.5, p=0.015 for PR low). The estimated cumulative 5-year EFS for patients with ER low, medium, and high tumors was 87.1%, 93.4%, and 90.1% respectively. The estimated cumulative 5-year EFS for patients with PR negative, low, and high tumors was 78.9%, 90.2%, and 92.7% respectively. Conclusions: Using ILC-specific categories for ER expression, we found associations between ER category and clinicopathologic variables but not with EFS. In contrast, PR negative and low status was associated with worse EFS. These findings highlight the importance of exploring the spectrum of ER/PR activity within ILC, a classically strongly hormone receptor-positive tumor type, using more quantitative methods.

Citation Format: Elle Clelland, Harriet T. Rothschild, Anne Patterson, Julissa Molina-Vega, Mandeep Kaur, Mary Kathryn Abel, W. Fraser Symmans, Jo Chien, Christopher J. Schwartz, Rita Mukhtar. Quantifying estrogen and progesterone receptor status in early-stage invasive lobular carcinoma of the breast: associated factors and outcomes in an institutional series [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P2-03-16.

Abstract LB564: (±) 14,15-epoxyeicosatrienoic acid induces hallmark ER and MYC gene expression and associated ER and c-Myc nuclear translocation in ER+/HER2- breast cancer cells

While epoxyeicosatrienoic acids (EETs) have been implicated in breast cancer growth and progression, less is known about their effects on oncogene transcription. We have previously found that the oncogenic regioisomer (±)14,15-EET drives mitochondrial respiration, ATP synthesis, and proliferation of ER+/HER2- breast cancer cells [Cell Chem Biol. 2017 Oct 19;24(10):1259-1275]. RNAseq analysis was performed (5 replicates per condition) on serum starved (16 hours) MCF-7 cells which were then treated with (±)14,15-EET or vehicle (2 hours; serum and phenol red free medium without estradiol). Using gene set enrichment analysis (GSEA), we found that (±)14,15-EET activated an estrogen receptor alpha (ER) hallmark early response gene set and synchronously activated a MYC hallmark gene set. With activation of the MYC hallmark gene set, c-Myc gene expression was also induced at 2 hours (3.99-fold; P=2.3 x 10-17; FDR=2.8 x 10-14). These data suggest an alternative pathway for activation of estrogen and MYC regulated genes in the absence of estradiol. The 15 genes most transcriptionally activated by (±)14,15-EET at 2 hours were: VMP1, ZFP36, JUNB, FOS, IER3, EGR1, IER5L, ELF3, JUN, NR4A1, HES1, DUSP1, MYC, TOB1, and CITED2 [fold change range: 3.25 (CITED2) to 90.5 (FOS); all P&lt; 2.86 x 10-17; all FDR &lt; 3.03 x 10-14]. The ER regulated genes most transcriptionally activated (&gt;1.5 fold) were: IER3, TOB1, AREG, CISH, KCNMB3, and PDK4 (fold change range: 1.77 to 4.35; P= 1.74 x 10-18 to 1.35 x 10-5; FDR=5.54 x 10-15 to 6.4 x 10-4). The MYC regulated genes most transcriptionally activated (&gt; 1.5-fold change) were EIF4A1 (fold change= 2.37; P=1.0 x 10-7; FDR=1.33 x 10-5), IRF9 (fold change=1.58; P=0.0044; FDR= 0.026), and FOSL1 (fold change=1.51; P=0.008; FDR=0.04). Supporting the hypothesis of (±)14,15-EET activation of ER-regulated transcription, (±)14,15-EET promoted nuclear translocation of ER at 1 hour measured by DAPI normalized immunofluorescence [MCF-7 nuclear ER increase of 1.66-fold (P=0.031); ZR75-1 nuclear ER increase of 1.77-fold (P=0.015)]. Supporting the hypothesis of (±)14,15-EET activation of MYC-regulated transcription, (±)14,15-EET treatment promoted nuclear translocation of c-Myc with MCF-7 cells exhibiting a 1.22-fold increase at 2 hours (P=0.002). (±)14,15-EET also promoted nuclear translocation of FITC-70 kDa dextran with MCF-7 cells exhibiting an increase of 1.35-fold at 1 hour (P=0.029). These data suggest that (±)14,15-EET can induce an estradiol-like immediate early gene response in ER+/HER2- breast cancer cells correlating with c-Myc activation. In summary, while the effect of (±)14,15-EET on nuclear translocation may be partially cargo agnostic, (±)14,15-EET promotes ER and c-Myc nuclear translocation and associated transcription, mimicking a tandem hormonal and growth factor response.

Citation Format: Jianxun Lei, Zhijun Guo, Julissa Molina-Vega, Paloma Cervantes, Swaathi Jayaraman, John R. Hawse, Carlos Perez, Juan Abrahante, Xiaojia Tang, Krishna Kalari, Jinhua Wang, John R. Falck, Carol Lange, Matthew P. Goetz, David Potter. (±) 14,15-epoxyeicosatrienoic acid induces hallmark ER and MYC gene expression and associated ER and c-Myc nuclear translocation in ER+/HER2- breast cancer cells [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 LB564.

Abstract OT1-10-02: I-SPY2 endocrine optimization protocol (EOP): A pilot neoadjuvant endocrine therapy study with amcenestrant as monotherapy or in combination with abemacicilib or letrozole in molecularly selected HR+/HER2- clinical stage 2/3 breast cancer

Background: There is no clinical equipoise on the best upfront management of patients with early-stage hormone receptor-positive (HR+)/HER2-negative (HER2-) breast cancer (BC) that is high-risk by clinicopathologic criteria, and low-risk based on molecular profiling. These patients are unlikely to respond to chemotherapy. However, these patients still have risk, often risk of late recurrence, despite standard adjuvant endocrine therapy. Novel endocrine-based strategies that are more effective and tolerable than current standard therapies are needed for this population. Next-generation orally-bioavailable selective estrogen receptor degraders (oSERDs) with improved pharmacokinetic (PK) properties are promising potential therapies for HR+ BC. The oSERD amcenestrant has demonstrated a favorable safety profile and encouraging efficacy in a phase I/II dose escalation and expansion trial for heavily pre-treated patients with HR+ metastatic BC and is an attractive agent for assessment in the neoadjuvant BC setting. The neoadjuvant setting offers a unique opportunity to study novel agents and to assess early biological endpoints. However, one of the challenges in studying endocrine-based strategies in the neoadjuvant setting is the lack of a robust surrogate endpoint to reliably predict response and benefit. The I-SPY2 Endocrine Optimization Protocol (EOP) is a pilot sub-study within the main I-SPY2 TRIAL that will test amcenestrant alone or in combination with abemaciclib or letrozole. EOP will test the feasibility of using the I-SPY2 platform to test novel endocrine-based strategies in the neoadjuvant setting in patients with clinical high-risk, molecular low-risk, HR+/HER2- tumors, and will generate a rich database of imaging, molecular, and pathologic correlative endpoints that may potentially inform the improved assessment of response to neoadjuvant endocrine therapy. Trial Design/Eligibility/Accrual: The I-SPY2 EOP is a prospective, randomized, open-label trial specifically for patients with HR+/HER2-negative MammaPrint (MP) low-risk tumors that are at least 2.5 cm in size. Eligible patients are identified during the screening process for the parent I-SPY2 trial. The planned total accrual for the EOP is 120 patients. Patients are randomized 1:1:1 to one of 3 oral treatment arms: 1) amcenestrant 200 mg daily; 2) amcenestrant 200 mg daily + abemaciclib 150 mg bid; 3) amcenestrant 200 mg daily + letrozole 2.5 mg daily. Patients are treated for 6 months prior to surgery. Premenopausal women must receive concomitant monthly ovarian suppression. Serial breast MRIs, breast biopsies, blood, and patient reported outcomes (PROs) are being collected, and patients will be followed for 10 years for recurrence and survival. Serial dedicated breast PET (dbPET) scans and PKs will be assessed in a subset of patients. Objectives/Statistics: The primary objective of the EOP is to investigate the feasibility of enrolling and treating molecularly-selected patients with early stage HR+/HER2- MP low-risk BC in a randomized neoadjuvant trial using an oral-SERD backbone. Treatment will be determined to be feasible if ≥75% of enrolled patients complete ≥75% of assigned study therapy. Secondary objectives include the safety, tolerability, PROs, and PKs related to amcenestrant +/- abemacilcib and letrozole, as well as the assessment of imaging, pathologic, and molecular correlative endpoints as potential biomarkers of response to neoadjuvant endocrine therapy. Status: This study opened in May 2021. Accrual is ongoing.

Citation Format: A. Jo Chien, Kevin M Kalinsky, Julissa Molina-Vega, Rita Mukhtar, Karthik Giridhar, Olufunmilayo I Olopade, Amrita Basu, Smita M Asare, Paul Henderson, Gillian Hirst, Ruixiao Lu, Ella Jones, Nola Hylton, Lamorna Brown-Swigart, Laura J van 't Veer, Douglas Yee, Ingrid Mayer, Laura J Esserman. I-SPY2 endocrine optimization protocol (EOP): A pilot neoadjuvant endocrine therapy study with amcenestrant as monotherapy or in combination with abemacicilib or letrozole in molecularly selected HR+/HER2- clinical stage 2/3 breast cancer [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 OT1-10-02.

Abstract P3-02-02: FES-dedicated breast PET uptake in early-stage ER+ breast cancers

BACKGROUND: Patients with ER+ breast cancer may have a recurrence risk of aggressive disease. While clinical evidence suggests that ER+ tumors are responsive to endocrine therapy, up to one-third of patients with early-stage ER+ disease may not respond to endocrine therapy. Tumor biologic factors such as ER functionality, cell proliferation, and molecular traits may influence endocrine treatment responsiveness and long-term recurrence risk. More comprehensive tools are needed to depict the primary breast tumor. [18F]fluoroestradiol (FES) is a radiotracer developed for positron emission tomography (PET) imaging of ER status. We used FES with a high-resolution dedicated breast PET (dbPET) to quantify ER expression in primary ER+ tumors and assessed the relationship between FES uptake and tumor characteristics. METHODS: With IRB approval, patients with biopsy-proven ER+/HER2- breast cancer were imaged using dbPET with 5 mCi of FES before treatment. FES uptake (SUVmax, SUVmean, and SUVpeak), background parenchymal uptake (BPU), tumor uptake volume (TUV), and tumor to background ratio (TBR) were calculated. Background values (SUVbkg) were obtained from the normal region of the ipsilateral breast. Lesions with background-corrected SUVmax 2 times higher than SUVbkg were considered FES avid. Tumor size (longest diameter) was measured by MRI. The histologic subtype, ER expression, tumor grade, and Ki67 were obtained from core biopsies before treatment. Ki67 was dichotomized to low and high using a 20% cutoff. Spearman’s rank correlation was used to assess the correlation between FES uptake and tumor size. Differences between FES uptake, histologic subtype, and Ki67 were compared using a Wilcoxon rank-sum test. RESULTS: 19 treatment-naïve patients were included in this analysis as part of an ongoing study. Patient and tumor characteristics are listed in Table 1. While all patients had ER positivity &gt;90% by immunohistochemistry (IHC), we observed varying FES avidity in ER+ breast cancers, with 14 FES avid and 5 non-FES avid lesions. There was a statistically significant difference between FES avid vs. non-avid lesions measured by all uptake metrics except BPU. FES uptake in invasive ductal carcinoma was similar to invasive lobular carcinoma. FES uptake correlated with tumor size, with the highest correlation ρ = 0.58, 95% CI (0.17, 0.84), p=0.012, detected in TUV. FES uptake was associated with Ki67, with all uptake metrics except BPU showing a statistically significant difference between high and low Ki67 expression (Table 2). CONCLUSION: We found that not all lesions that were highly ER+ by IHC were FES avid. FES-dbPET captures information from the entire tumor, providing a more comprehensive assessment of functional ER status than IHC of a limited tumor sample. Moreover, FES uptake correlates with tumor size and cell proliferation. This is an ongoing study; additional data may help to guide endocrine therapy decisions. Future studies with a larger cohort are planned to assess the relationship between FES uptake and tumor grade and molecular risk profiles.

Table 1.Patient and tumor characteristicsCharacteristicsNo. of patientsTotal N=19Age (median (IQR))56.0 (21.5)Pre-menopausal7Post-menopausal12Histologic subtypeInvasive ductal carcinoma (IDC)6Invasive lobular carcinoma (ILC)13Tumor size (N=18) (MRI LD (cm), median (IQR))3.2 (4.1)Tumor grade1421332Ki67Low12High6Unknown1FESNon-avid5Avid14

Table 2.Summary of baseline FES uptake valuesTumor Size (cm)FES AvidityHistologic SubtypeKi67Spearman CorrelationAvid vs. Non-avidILC vs. IDCHigh vs. Lowρ (95%CI)P-valueMedian Diff (95%CI)P-valueMedian Diff (95%CI)P-valueMedian Diff (95%CI)P-valueSUVmax0.51 (0.054, 0.79)0.0318.02 (3.55, 11.9)0.0010.187 (-8.04, 6.32)0.976.38 (2.36, 11.6)0.017SUVmean0.31 (-0.18, 0.68)0.2042.42 (1.47, 3.49)0.001-0.477 (-1.96, 1.37)0.571.61 (0.81, 2.77)0.028SUVpeak0.46 (-0.0053, 0.76)0.0533.16 (1.42, 5.2)0.003-0.583 (-3.76, 2.61)0.633.16 (1.32, 4.66)0.013BPU-0.09 (-0.53, 0.39)0.723-0.33 (-1.25, 0.46)0.3790.226 (-0.58, 1.19)0.40-0.49 (-1.49, 0.28)0.122TUV (cm3)0.58 (0.15, 0.82)0.0125.45 (1.09, 12.5)0.005-2.82 (-12.5, 4.06)0.405.9 (0.98, 12.66)0.021TBR0.5 (0.047, 0.79)0.0333.48 (2.2, 13.5)0.001-0.295 (-11.9, 7.42)0.9010.2 (1.47, 13.49)0.028

Citation Format: Ella F. Jones, Deep K. Hathi, Julissa Molina-Vega, David C. Newitt, Courtney Lawhn-Heath, Kimberly M. Ray, Bonnie N. Joe, Diane Heditsian, Susie Brain, Rita A. Mukhtar, A. Jo Chien, Hope S. Rugo, I-SPY 2 TRIAL Consortium, I-SPY 2 TRIAL Imaging Working Group, Laura J. Esserman, Nola M. Hylton. FES-dedicated breast PET uptake in early-stage ER+ breast cancers [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 P3-02-02.

Abstract P3-02-01: Initial experience of FES-dedicated breast PET imaging of early-stage ER+ invasive lobular carcinoma

BACKGROUND: Invasive lobular carcinoma (ILC) is the second most common histological subtype of breast cancer, representing 15% of all invasive breast cancers. Most ILC tumors are estrogen receptor-positive (ER+) and may respond to endocrine therapy. However, tumor biologic factors such as ER functionality, cell proliferation, and molecular traits may influence endocrine treatment response and long-term recurrence risk, thus necessitating a comprehensive approach to characterize the primary breast tumor. [18F]fluoroestradiol (FES) is a radiotracer developed for positron emission tomography (PET) imaging of ER status. For this work, we studied the utility of imaging FES uptake in early-stage primary ER+ ILC lesions, using high-resolution dedicated breast PET (dbPET) to assess the relationship between FES uptake and tumor characteristics. METHODS: With institutional review board approval, patients with biopsy-proven ER+/HER2- ILC were prospectively imaged using dbPET with 5 mCi of FES before treatment. FES uptake (SUVmax, SUVmean, and SUVpeak), tumor uptake volume (TUV), and background parenchymal uptake (BPU) values were calculated. Background values (SUVbkg) were obtained from the normal region of the ipsilateral breast. Lesions with background-corrected SUVmax 2 times higher than SUVbkg were considered FES-avid. Tumor grade, Ki67 cell proliferation index, and ER expression were obtained from core biopsies before treatment. Ki67 was dichotomized to low and high using a 20% cutoff1. Tumor size (longest diameter) was measured by magnetic resonance imaging (MRI). Spearman rank correlation was used to assess the relationship between FES uptake and tumor size. Differences between FES uptake at high and low Ki67 were compared using a Wilcoxon rank-sum test. RESULTS: 13 treatment-naïve ILC patients aged 32-82 years were included in this analysis (Table 1). Despite all lesions exhibiting strongly positive ER expression &gt;90% by immunohistochemistry (IHC), we observed varying FES avidity with 9 FES avid and 4 FES non-avid ILC lesions. SUVmax, TUV, and TBR had substantial median differences between Ki67 high and low lesions (5.9, 4.3, and 9.6, respectively), but the difference did not achieve statistical significance. FES tumor uptake also correlated with tumor size, with the highest correlation observed for SUVpeak (ρ = 0.71 (95% CI: 0.22, 0.91), p=0.010) (Table 2). CONCLUSION: We found that not all highly ER expressing ILC by IHC were FES-avid. As FES-dbPET captures information from the entire tumor, it provides a more comprehensive assessment of functional ER status than IHC of a limited tumor sample. FES uptake in ILC also relates to tumor size and Ki67. This is an ongoing study; additional data may help to guide endocrine therapy decisions. Future studies with a larger cohort are planned to assess the relationship between FES uptake and tumor grade and molecular risk profiles. 1. Acs, B. et al. Ki-67 as a controversial predictive and prognostic marker in breast cancer patients treated with neoadjuvant chemotherapy. Diagn Pathol 12, 20, doi:10.1186/s13000-017-0608-5 (2017).

Patient and tumor characteristicsCharacteristicsNumber of patients (Total N=13)Age (median (range))56.0 (32-80)Pre-menopausal3Post-menopausal10MRI tumor size (median (interquartile range)4.1 (2.4-6.8)Tumor grade132931Ki6712Low/High3/9FES13Avid/Non-avid9/4

Summary of FES uptake values and correlation coefficients.FES avidity (N=13)Ki67 (N=12)MRI tumor size (N=12)Avid vs Non-avidHigh vs LowSpearman rank correlationMedian Difference (95% CI)P-valueMedian Difference (95% CI)P-valueSpearman ρ (95% CI)P-valueSUVmax8.68 (2.86, 12)0.0075.9 (-19.5, 11.6)0.140.67 (0.16, 0.9)0.017SUVmean2.56 (1.43, 4.86)0.0071.34 (-4.14, 3.1)0.200.6 (0.042, 0.87)0.039SUVpeak2.86 (1.14, 4.59)0.0112.15 (-14.4, 3.72)0.190.71 (0.22, 0.91)0.01BPU-0.31 (-1.89, 1.02)0.82-0.73 (-2.34, 0.28)0.0960.01 (-0.57, 0.58)0.98TUV (cm3)5.45 (1.04, 10)0.014.3 (-185, 10)0.190.70 (0.21, 0.91)0.011TBR3.61 (2.2, 13)0.0079.57 (-19.6, 12.4)0.0640.66 (0.13, 0.89)0.02

Citation Format: Ella F Jones, Deep K Hathi, Natalia Konovalova, Julissa Molina-Vega, David C Newitt, Courtney Lawhn-Heath, Kimberly M Ray, Bonnie N Joe, Diane Heditsian, Susie Brain, I-SPY 2 TRIAL Imaging Working Group, I-SPY 2 TRIAL Consortium, A. Jo Chien, Laura J Esserman, Nola M Hylton, Rita A Mukhtar. Initial experience of FES-dedicated breast PET imaging of early-stage ER+ invasive lobular carcinoma [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 P3-02-01.

Abstract 4372: Metformin inhibits nuclear localization of estrogen receptor alpha in breast cancer cells, in part, by inhibition of CYP-mediated epoxyeicosatrienoic acid (EET) biosynthesis

Introduction: Cancer cell-intrinsic CYP monooxygenases promote tumor progression. In ER+HER2-, breast cancer cells, CYP3A4 promotes tumor growth, in part, through epoxyeicosatrienoic acid (EET) biosynthesis (1). The biguanide diabetes drug metformin is currently being studied in breast cancer clinical trials. We have discovered that metformin binds to the active site heme of CYP3A4, thereby inhibiting EET biosynthesis (1). Structure-based design led to the discovery of the 100-fold more potent metformin analog N1-hexyl-N5-benzyl-biguanide (HBB). HBB specifically inhibits CYP3A4 arachidonic acid (AA) epoxygenase activity in breast cancer cells, suppresses the growth of breast cancer cell lines (IC50=3-30 uM), and inhibits growth of the MCF-7 ER+ mammary tumor model, similar to CYP3A4 gene silencing. Although CYP3A4 synthesizes EETs, how EETs may promote tumor growth is unknown. Recently, we found that HBB inhibits nuclear transit of estrogen receptor alpha (ERα) and 70kD FITC-dextran, but the mechanism was unknown (2). Metformin was discovered to inhibit nuclear pore complex (NPC) function, but the mechanism was also unknown (3). We therefore hypothesized that CYP-derived EETs function as second messengers that regulate nuclear translocation of ERα in breast cancer by promoting permeability of the NPC. This hypothesis implies that biguanide drugs suppress nuclear translocation of the ERα through inhibition of CYP-derived EETs that serve as second messengers to open the NPC.

Methods: Breast cancer cells were serum-starved for 16 hours and then treated with metformin, HBB, the (±)-14,15-EET regioisomer, or EET agonists, for varying times (30 min to 6 hours). Cells were fixed, permeabilized, and incubated with antibodies specific for ERα. After incubation with fluorescent secondary antibodies and Hoechst 33342 dye, cell images were acquired with a confocal microscope and the nuclear ERα fluorescence signal was quantified relative to the Hoechst signal. Quantitative PCR was used to measure the expression of ERα regulated genes.

Results: (±) 14,15-EET (5 uM) treatment for 1 hour increased nuclear ERα by 66 ± 26% (n=9, p=0.031) in MCF-7 cells and 77 ± 24% (n=7, p=0.015) in ZR-75 cells. Treatment with EET agonists C22 (5 uM) and EET-A (5 uM) for 1 hour increased nuclear ERα by 32 ± 13% (n=7, p=0.047) and 39 ± 14% (n=7, p=0.02) in MCF-7 cells. Metformin (5 mM) treatment for 6 hours reduced nuclear ERα in MCF-7 by 35 ± 4.9 % (mean ± SEM, n=8, p=0.003). HBB (20 uM) treatment for 2 hours reduced the expression of three ERα regulated genes in MCF-7 cells: estrogen receptor alpha (ESR1) was reduced by 15 ± 1.7% (n=3, p=0.001), progesterone receptor (PGR) by 21 ± 0.6% (n=3, p=0.02) and L-type amino acid transporter 1 (SLC7A5) by 14 ± 0.2% (n=3, p=0.002).

Conclusion: CYP epoxygenase activity in ER+HER2- breast cancer cells produces EETs, which function as second messengers that promote nuclear transit of ERα. Metformin and HBB inhibit nuclear ERα translocation, in part, through inhibition of CYP3A4 AA epoxygenase activity and this inhibition reduces ERα mediated gene expression, providing a novel mechanism for ERα regulation.

1. Cell Chem Biol. 2017 Oct 19; 24(10) 1259 - 1275.

2. Abstract of 109th AACR meeting (#LB-023), April 2019

3. Cell. 2016 Dec 15;167(7):1705-1718

Citation Format: Zhijun Guo, Jianxun Lei, Shaoping Wu, Julissa Molina-Vega, Paloma Cervantes, Aline R. Rom'Mand, Dylan C. Castillejo Mijangos, John R. Falck, Carol Lange, Jinhua Wang, David A. Potter. Metformin inhibits nuclear localization of estrogen receptor alpha in breast cancer cells, in part, by inhibition of CYP-mediated epoxyeicosatrienoic acid (EET) biosynthesis [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 4372.

Abstract LB-023: CYP monooxygenases regulate nuclear localization of ERá and mTORC1 component RagC in ER+HER2- breast cancer cells

Introduction: Cancer cell-intrinsic CYP monooxygenases promote tumor progression. In ER+ breast cancer cells, CYP3A4 is required for tumor growth and localizes to mitochondria where it promotes electron transport chain and respiration, while suppressing autophagy, in part, through epoxyeicosatrienoic acid (EET) biosynthesis (1). The diabetes drug metformin inhibited CYP3A4-mediated EET biosynthesis and depleted cancer cell-intrinsic EETs. Metformin bound to the active site heme of CYP3A4 in a co-crystal structure, establishing CYP3A4 as a biguanide target. Structure-based design led to discovery of N1-hexyl-N5-benzyl-biguanide (HBB), which bound to the CYP3A4 heme with higher affinity than metformin. HBB potently and specifically inhibited CYP3A4 arachidonic acid epoxygenase activity, reduced oxygen consumption rates and suppressed growth of breast cancer cell lines (IC50=3-30 μM) and an established ER+ mammary tumor model. HBB inhibited activation of mTOR and suppressed S6Kinase phosphorylation. HBB also suppressed intratumoral mTOR. Recently, nuclear transit of RagC has been shown to promote mTORC1 function, a process sensitive to metformin (2), which inhibits the nuclear pore complex (NPC). Therefore, we hypothesized that HBB as a more potent biguanide may inhibit mTOR through reduction of nuclear RagC by regulating NPC. HBB may also regulate the localization of other nuclear proteins such as estrogen receptor alpha (ERα).

Method: ER+HER2- breast cancer cells (MCF-7 and T47D) were seeded on chamber slides and treated with vehicle or HBB for varied periods of time. Cells were fixed, permeabilized, and incubated with specific antibodies against RagC and ERα. After incubation with fluorescence tagged secondary antibody, slides were stained with DAPI and analyzed by confocal microscopy. Levels of nuclear proteins of interest were normalized against DAPI staining.

Results: CYP3A4 shRNA knockdown reduced nuclear RagC in MCF-7 cells by 61.2±12.3 % (n=3, p&lt;0.05) relative to a non-targeted shRNA control line. HBB treatment for 6 hours (20 μM) reduced nuclear RagC by 66.1±15.4% (n=4, p&lt;0.001) in MCF-7 cells and by 32.4±5.1% (n=3, p&lt;0.001) in T47D cells. HBB treatment for 6 hours (20 μM) also reduced nuclear ERα by 36.8±11.1% (n=6, p&lt;0.001) in MCF-7 cells and by 32.2±8.1% (n=3, p&lt;0.01) in T47D cells grown in complete media. HBB treatment for 1 hour (20 μM) reduced passive transport of 70 kDa FITC-dextran through the NPC into the nuclear compartment by 17.5±3.6% (n=3, p&lt;0.01) in MCF-7 cells and by 28.3±3.2% (n=3, p&lt;0.01) in T47D cells. Immunofluorescence study results of HBB-mediated reduction of nuclear RagC and ERα were confirmed by Western-blotting analysis of nuclear extraction of T47D cells treated with HBB.

Conclusion: These data suggest that the biguanide sensitive enzyme CYP3A4 may play a role in nuclear localization of ERα and RagC, which work in tandem to promote the growth of ER+HER2- breast cancer cells.

1. Cell Chemical Biology. 2017 Oct 19; 24(10) 1259 – 1275.

2. Cell. 2016 Dec 15;167(7):1705-1718

Citation Format: Zhijun Guo, Shaoping Wu, Julissa Molina-Vega, Rafael Castillo, Jaime Barrera, Veronica Johnson, Carol Lange, David Potter. CYP monooxygenases regulate nuclear localization of ERá and mTORC1 component RagC in ER+HER2- breast cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr LB-023.