101P - Patient-derived organoids to optimize CDK4/6 inhibitor-based treatment selection in early breast cancer

Background

The proven success of combined CDK4/6 inhibitor (CDK4/6i) and endocrine therapy in estrogen receptor-positive (ER+) metastatic breast cancer has prompted evaluation of this therapeutic approach in patients with early-stage disease. Notably, the CDK4/6i abemaciclib and ribociclib, but not palbociclib, improved invasive disease-free survival in the adjuvant setting in clinical trials. These data suggest that complex assessment of breast tumor genomic, clinical and pathological characteristics, and CDK4/6i efficacy and toxicity profiles, will be required for a better refinement of indication for specific CDK4/6i in the early-stage setting. In the present study, we aimed to identify and characterize the early breast cancer patient population that will benefit the most from each CDK4/6i by using patient-derived breast cancer organoids.

Methods

We developed a repository of patient-derived organoids (PDOs) from ER+ primary breast tumor resections. RNA, DNA, and protein were purified from PDOs and paired fresh frozen tissue, for validation of organoids characteristics compared to the original tumor. To fully characterize our PDOs, we performed RNA sequencing (RNAseq), single nucleotide polymorphism/copy number variation (SNP/CNV) array, live-cell imaging, quantitative real-time PCR, and drug testing. Efficacy of CDK4/6i on selected PDOs was evaluated by viability and cytotoxicity assays, and gene expression profile in sensitive vs. resistant PDOs was compared by RNAseq.

Results

We found that various PDOs retained the main alterations of the original tumor, by SNP/CNV arrays. Furthermore, we were able to rank the organoids based on the response (IC₅₀) to abemaciclib. By RNAseq and RT-qPCR we identified specific genes that might be linked with differential responses to CDK4/6i. Among these, we found concomitant CDK6 overexpression and, surprisingly, cyclin D1 downregulation in PDOs with higher IC₅₀ towards CDK4/6i in both innate and acquired resistance models.

Conclusions

Our data suggest that high-CDK6 and low-cyclin D1 expression might be a biomarker for selection of patients with poor response to CDK4/6i abemaciclib in the adjuvant setting.

Editorial acknowledgement

Clinical trial identification

Legal entity responsible for the study

Ethics Committee of the Region of Southern Denmark and Copenhagen and Frederiksberg Counties; Danish Data Protection Agency and the Danish Breast Cancer Cooperative Group.

Funding

Danish Cancer Society; Sygeforsikring Danmark; Danmarks 3R-Center.

Disclosure

All authors have declared no conflicts of interest.