Caygill, Katie

1087 Background: EP is a unique topoisomerase 1 inhibitor that provides continuous exposure to SN38. EP demonstrated a 29% overall response rate in patients with mBC, leading to a phase III global BEACON study in patients with mBC. CTCs in patient blood samples provide a minimally invasive approach to detect PD markers of drug activity. We developed quantitative multiplex immunofluorescent assays to measure target-specific PD biomarkers for EP in CTCs isolated pre- and post-treatment. Methods: Assays for Top1, Top2, g-H2Ax, Rad51, ABCG2, and Ki-67 were developed using control (0.1% DMSO) and drug-treated (SN38, 10 uM) tumor cell lines (HCT116, MCF7, A549, SKBr3) and PBMCs from healthy donors. The optimal antibody for each biomarker was then multiplexed in a panel with antibodies against cytokeratin, CD45 and DAPI for phenotypic identification of CTCs. For analysis of BEACON pts, serial 7.5 mL whole blood samples were drawn and shipped ambient to Apocell (Houston, TX) for further processing. PBMCs were separated and CTCs were isolated using ApoStream technology. CTCs were stained for PD markers and analyzed using an iCys laser scanning cytometer equipped with image analysis software. Results: Antibodies bound to tumor cells showed staining confined to the nucleus (Top1, Top2, g-H2AX, Ki-67) or membrane (ABCG2), exhibited defined peak separation from their isotype controls, and signal strength correlated with cellular expression of high and low levels of markers. To date, ~ 80% of BEACON pts consent to participate in the CTC sub-study. As of 30 Oct 2012, data from 167 pre-dose blood samples from BEACON pts were available. 99% of blood samples were successfully processed. 93% had detectable CTCs, yielding a median of 216 CTCs (range: 7.5-14816). Staining was positive for Top1, Top2, g-H2Ax, Rad51, ABCG2, and Ki-67 in 82%, 89%, 16%, 53%, 31%, 52% of samples, respectively. Conclusions: EP target-specific pharmacodynamic biomarkers can be reliably measured in CTCs isolated from patients participating in BEACON. Sample collection and analysis of pre- and post-treatment samples is ongoing. Clinical trial information: NCT01492101.

Abstract Purpose: Preplanned exploratory analyses were performed to identify biomarkers in circulating tumor cells (CTC) predictive of response to the topoisomerase 1 inhibitor etirinotecan pegol (EP). Experimental Design: The BEACON trial treated patients with metastatic breast cancer (MBC) with EP or treatment of physician's choice (TPC). Blood from 656 of 852 patients (77%) was processed with ApoStream to enrich for CTCs. A multiplex immunofluorescence assay measured expression of candidate response biomarkers [topoisomerase 1 (Top1), topoisomerase 2 (Top2), Ki67, RAD51, ABCG2, γH2AX, and terminal deoxynucleotidyl transferase–mediated dUTP nick end labeling (TUNEL)] in CTCs. Patients were classified as Top1 low (Top1Lo) or Top1 high (Top1Hi) based on median CTC Top1 expression. Correlation of CTC biomarker expression at baseline, cycle 2 day 1 (C2D1), and cycle 4 day 1 with overall survival (OS) was investigated using Cox regression and Kaplan–Meier analyses. Results: Overall, 98% of samples were successfully processed, of which 97% had detectable CTCs (median, 47–63 CTCs/mL; range, 0–2,020 CTCs/mL). Top1, Top2, and TUNEL expression was detected in 52% to 90% of samples; no significant associations with OS were observed in pretreatment samples for either group. EP-treated patients with low C2D1Top1+ CTCs had improved OS compared with those with higher positivity (14.1 months vs. 11.0 months, respectively; HR, 0.7; P = 0.02); this difference was not seen in TPC-treated patients (HR, 1.12; P = 0.48). Patients whose CTCs decreased from Top1Hi to Top1Lo at C2D1 had the greatest OS benefit from EP (HR, 0.57; P = 0.01). Conclusions: CTC Top1 expression following EP treatment may identify patients with MBC most likely to have an OS benefit. Clin Cancer Res; 24(14); 3348–57. ©2018 AACR.

Abstract Background: Etirinotecan pegol (EP) is a long-acting Top1 inhibitor providing sustained levels of active metabolite throughout the entire chemotherapy cycle. The phase 3 BEACON trial compared EP to treatment of physician's choice (TPC) in patients with advanced breast cancer, demonstrating a non-statistically significant 2.1 month difference in survival favoring EP in the intent to treat population. A novel aspect of the BEACON trial is to explore the utility of biomarkers measured in CTCs for predicting efficacy with EP. Pre- and post-treatment CTCs were isolated from blood of 77% of the 852 BEACON patients. Target-specific pharmacodynamic biomarkers for EP measured in CTCs were analyzed to identify patients most responsive to treatment with EP. Methods: Donation of blood samples for CTC analysis was voluntary. Participating BEACON patients had serial (baseline, Cycle 2 Day 1 [C2D1], Cycle 4 Day 1 [C4D1], End of Treatment) 7.5-mL whole blood samples drawn in EDTA tubes and shipped within 96 hours ambient to ApoCell (Houston, TX) for processing. PBMCs were separated by Ficoll® gradient, and CTCs were isolated using ApoStream® technology. Isolated cells were deposited on three slides and stained for DAPI, CD45, cytokeratin markers, as well as Top1, Top2, Ki67, γH2AX, Rad51, ABCG2, and TUNEL. Biomarkers were quantified by iCys® laser scanning cytometer equipped with image analysis software, and correlated with OS using Cox multiple regression and Kaplan-Meier analyses. Results: The CTC substudy yielded 611 pre-treatment, 519 C2D1, 268 C4D1, and 431 End of Treatment samples. Among the successfully processed blood samples, 98% had detectable CTCs, with a median of 63, 46, 51, and 57 CTCs/mL at baseline, C2D1, C4D1, and End of Treatment, respectively. Cox regression analyses of CTC number and percentage of Top1, Top2, Ki67, or TUNEL positive CTCs identified a correlation for post-treatment number of Top1-positive CTCs with OS in patients receiving EP. To assess the impact of Top1-positive CTCs, patients were classified as Top1-High (> median) or Top1-Low (≤ median) based on the percent of Top1-positive CTCs at baseline. Among the Top1-High patients at baseline, significantly improved OS (HR 0.54, p=0.007) was observed for those who converted to Top1-Low after their first treatment with EP (C2D1), but not TPC (HR 1.12, p=0.613). These results suggest that decreased number of Top1-positive CTCs may reflect EP target engagement with Top1, as these patients derived the most benefit from treatment. Conclusions: CTC collection and analysis was successfully incorporated into the phase 3 BEACON study, with 77% patient participation. CTC detection rate using ApoStream® was high, permitting evaluation of biomarkers at baseline and post-treatment. Significantly improved OS was observed in patients who had a decreased number of Top1-positive CTCs following cycle 1 of EP. Citation Format: Rugo HS, Cortes J, Awada A, O'Shaughnessy J, Twelves C, Im S-A, Hannah AL, Lu L, Sy S, Caygill K, Zajchowski D, Davis DW, Hoch U, Perez EA. Early change in topoisomerase 1 (Top1) positive circulating tumor cells (CTCs) is associated with overall survival (OS) in patients with advanced breast cancer after treatment with etirinotecan pegol. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P1-13-02.

Abstract Background: Etirinotecan pegol (EP) is the first long-acting topoisomerase 1-inhibitor providing sustained level of active metabolite that concentrate in the tumor for an entire chemotherapy cycle. In a Phase 2 study (Lancet Oncology 2013), EP demonstrated a 29% overall response rate in patients with metastatic breast cancer, leading to the Phase 3 global BEACON study in this population. Detection of circulating tumor cells (CTCs) using immunomagnetic EpCAM-based methods have been conceptually accepted as a "liquid tumor biopsy". To circumvent the limited recovery of CTCs these methods provide for molecular profiling applications, we isolated CTCs based on an antibody-independent, continuous flow dielectrophoresis (DEP) technology (ApoStream®). We developed quantitative multiplex immunofluorescent assays for target-specific pharmacodynamics (PD) biomarkers for EP in CTCs isolated pre- and post-treatment. Here we present the distribution of the PD biomarkers in CTC samples collected from BEACON patients. Methods: Donation of blood samples for CTC analysis was voluntary. BEACON patients participating in the substudy had serial (pre-dose, Cycle 2 Day 1, Cycle 4 Day 1, End of Treatment) 7.5-mL whole blood samples drawn in EDTA tubes and shipped ambient to ApoCell (Houston, TX) within 96 hrs for processing. PBMCs were separated by Ficoll® gradient, and CTCs were isolated using ApoStream® technology. Isolated cells were deposited on three slides and stained for DAPI, CD45, and cytokeratin markers, as well as 2-3 of the seven PD markers, and analyzed by iCys® laser scanning cytometer equipped with image analysis software. CTC count, mean fluorescence intensity (MFI) of PD biomarkers, and % marker-positive cells were analyzed for their distribution. Results: 75% of the 852 BEACON patients participated in the CTC substudy, yielding 649 pre-treatment CTC samples. As of Mar14, 538 Cycle 2 Day 1, 281 Cycle 4 Day 1, and 394 End of Treatment samples were collected. 98% of pre-treatment blood samples were successfully processed. 97% had detectable CTCs, with a median of 504 CTCs (interquartile range: 128-1432). PD markers could be analyzed in 83-92% of samples after implementing a minimum requirement of 10 CTCs analyzed. Staining was positive for Top1, Top2, μH2Ax, Rad51, ABCG2, Ki67, and TUNEL in 82%, 71%, 14%, 30%, 20%, 56%, and 94% of samples, respectively. Percent of marker-positive cells varied from 0.2-69%, with 6- to 37-fold interquartile ranges. Median MFI in these cells varied between 25x103 and 100x103, with 1.2- to 1.6-fold interquartile ranges. Conclusions: CTC collection was successfully incorporated into the BEACON study, with 75% patient participation. CTC detection rate using ApoStream® was high, permitting evaluation of biomarkers at baseline and over time. EP target-specific PD biomarkers can be measured in CTCs isolated from patients participating in BEACON and will be assessed for their potential to predict clinical response. Final BEACON efficacy and safety results are expected in early 2015, which will allow further analysis of CTCs with patient outcome (response, PFS, OS) and change in CTCs at time of progression. Citation Format: Edith A Perez, Katie Caygill, Alison L Hannah, Javier Cortes, Ahmad Awada, Joyce O'Shaughnessy, Christopher Twelves, Hope Rugo, Seock-Ah Im, Kenna Anderes, Darren W Davis, Ute Hoch. Etirinotecan pegol target-specific pharmacodynamic biomarkers in circulating tumor cells from patients with metastatic breast cancer in the phase 3 BEACON study [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P3-10-03.