Abstract PO3-25-02: Circadian Rhythm Disruption Accelerates Aggressive Mammary Tumorigenesis by Altering Tumor Microenvironment
Authors: Ogunlusi Olajumoke , Sarkar Mrinmoy , Nguyen Tristan , Boland Devon , Cai James , Chakrabarti Arhit , Mallick Bani , Keene Alex , Sarkar Tapasree Roy 
Published: May 2024

Abstract
\Breast cancer is the most common cancer in women worldwide, leading to over 650,000 deaths worldwide. The circadian rhythm is a 24-hour biological rhythm that controls most cellular, hormonal, and behavioral processes in living organisms, which is why perturbation of these rhythms is linked to several devastating diseases such as cardiovascular diseases, diabetes, and cancer. In the mammary gland, circadian clocks regulate the rhythmic expression of numerous genes. Circadian rhythm disruption (CRD), which has been termed a "carcinogen" by the International Agency for Research in Cancer, is caused by different factors, one of them being shift work. Several epidemiological studies have revealed that women who work night shifts are predisposed to breast cancer. The aim of this study is to investigate the effect of circadian rhythm disruption on aggressive mammary tumorigenesis. To do this, we used genetically engineered mouse models of mammary tumors (HER2-tumor and triple-negative breast tumor, or TNBC). Chronic jetlag, which mimics shift work in mice and is known to cause CRD, was introduced in one group of mice by perturbing the normal light and dark cycles with an 8-hour advance every three days. Wheel-running, which is represented by an actogram, was used to confirm the circadian disruption in the CRD mice. CRD was found to accelerate tumor initiation with a significant increase in weight in the CRD group of mice. CRD enhanced tumor burden significantly compared to LD mice. Our results also showed high metastatic foci in the lungs of CRD mice compared to LD mice. A flow cytometry study showed a higher cancer stem cell population in CRD tumors. Mammosphere assays with tumor-derived cells showed that CRD increased the number and size of the mammospheres compared to the control tumors. The tumor cells were analyzed using single-cell RNA sequencing, which showed that CRD alters the tumor microenvironment by developing more immunosuppressive and "cold" tumors. The tumor-derived organoids (tumoroid) showed resistance to chemotherapeutics. Finally, bioinformatics analysis using single-cell RNA seq data from human breast tumors (TNBC, ER/PR, and HER2) showed that the malignant cells in TNBC tumors had a significantly higher circadian rhythm disrupted score (CRD score) compared to ER/PR tumors. Taken together, our data showed how circadian rhythm disruption affects TNBC tumorigenesis and drug response by altering the tumor microenvironment.
Citation Format: Olajumoke Ogunlusi, Mrinmoy Sarkar, Tristan Nguyen, Devon Boland, James Cai, Arhit Chakrabarti, Bani Mallick, Alex Keene, Tapasree Roy Sarkar. Circadian Rhythm Disruption Accelerates Aggressive Mammary Tumorigenesis by Altering Tumor Microenvironment [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-25-02.