Abstract P4-10-17: Baseline and pharmacodynamic changes of circulating exosomal microRNAs predict early versus late progression to palbociclib plus endocrine therapy in patients with metastatic breast cancer. A sub-analysis of the PARSIFAL-1 trial

BACKGROUND: Palbociclib in combination with endocrine therapy (ET) is the first- or second-line standard of care for patients (pts) with hormone receptor (HR)-positive (+)/human epidermal growth factor receptor 2 (HER2)-negative (-) metastatic breast cancer (MBC). No clinically validated markers of long-term benefit from palbociclib have been established and the clinically relevant resistance mechanisms to cyclin-dependent kinases 4 and 6 inhibitors remain undefined. In the present study, we explored candidate circulating exosomal microRNAs (miRNAs) as putative predictors of benefit and/or resistance to palbociclib in combination with ET in pts included in the PARSIFAL-1 trial (ClinicalTrials.gov identifier: NCT02491983). MATERIALS AND METHODS: PARSIFAL-1 was a randomized, open-label, phase II trial aimed at evaluating the efficacy and safety of palbociclib plus either fulvestrant or letrozole in HR+/HER2- MBC pts. For the study of exosomal miRNAs, forty-five consenting pts were selected based on primary endocrine resistance according to the ABC-4 criteria. Nine pts who progressed within the first six months after treatment initiation in the absence of an objective response were considered Resistant and thirty-six pts who progressed more than six months after starting therapy were classified as Sensitive. Exosomes were isolated from plasma samples collected at study entry (baseline) and after 12 weeks of treatment initiation. Differences in miRNA expression between Resistant and Sensitive pts as well as miRNA pharmacodynamic changes between baseline and 12-week samples were assessed. Ribonucleic acid (RNA) was isolated using the miRNeasy plasma kit and the library preparation was done using the QIAseq miRNA library kit according to manufacturer’s instructions. All experiments were conducted at QIAGEN Genomic Services in Germany. Differential expression of miRNA between different conditions was studied using EdgeR statistical software package from Bioconductor. Estimated p-values for significantly differentially expressed miRNAs were adjusted using Benjamini-Hochberg’s False Discovery Rate (FDR). Differences in expression of miRNA with an FDR below 0.05 were considered significant. RESULTS: Sequencing of exosomal RNA and preparation of miRNA libraries were successful for all included samples, with good technical performance. On average, 2.8 million Unique Molecular Index-corrected reads were obtained for each sample and the average percentage of mappable reads was 34.5%. Overall, expression of miRNAs was higher in Resistant compared with Sensitive pts. Eight miRNAs were called as differentially expressed between the two groups. Four miRNAs (miR-1246; miR-375; miR-193a-5p; miR-181d-5p) were differentially expressed at baseline, three (miR-196a-5p, miR-200a-3p, miR-320d) were differentially expressed at 12 weeks, and expression of one miRNA (miR-141-3p) was consistently higher across both time points in Resistant pts. Significant pharmacodynamic changes in miRNA expression were observed both in Resistant and Sensitive pts. Seven miRNAs (miR-224-5p, miR-16-5p, let-7a-5p, miR-381-3p, miR-200c-3p, miR-493-3p, let-7b-5p) in Sensitive pts and three miRNAs (miR-223-3p, miR-126-3p, miR-320b) in Resistant pts were differentially expressed between baseline and 12-week samples. CONCLUSIONS: Circulating exosomal miRNA profiling is feasible in liquid biopsies from MBC pts. Differential expression of selected miRNAs at baseline or their pharmacodynamic modulation may predict benefit from palbociclib combined with ET in pts with HR+/HER2- MBC. Validation of the most promising miRNAs by custom quantitative PCR is warranted. Citation Format: David Casadevall, Joan Albanell Mestres, Federico Rojo, Beatriz Bellosillo, Abel Gonzalez, Violeta Serra, Meritxell Bellet, Miguel Angel Gil, Miquel Angel Pujana, Angelo Gamez, Enrique Espinosa, Peter Schmid, Joseph Gligorov, Frederik Marme, Carlos L. Arteaga, Leonardo Mina, Andrea Malfettone, Miguel Sampayo, Jose Manuel Perez-Garcia, Javier Cortes, Antonio Llombart-Cussac. Baseline and pharmacodynamic changes of circulating exosomal microRNAs predict early versus late progression to palbociclib plus endocrine therapy in patients with metastatic breast cancer. A sub-analysis of the PARSIFAL-1 trial [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P4-10-17.