Amita Raj

 Introduction.  The cell cycle is an essential process consisting of 4 phases that lead to proliferation (S: DNA replication, G2: growth to double genome, M: mitosis, G1: growth before S)¹. Circadian clock proteins can regulate key phases, such as G1/S and G2/M transitions². The endogenous circadian clock produces ‘rhythms’ that are oscillating changes in physiology and behavior that developed as adaptations to the Earth’s rotation and persist without external signals³. Disruptions in the cell cycle are involved in the development of some cancers, suggesting that cell-cycle regulation and circadian clock proteins may be important targets for chemotherapy^1,2. Studies suggest that the response to chemotherapy varies with the time of day and status of circadian proteins^4,5. Chronotherapy (chemotherapy administered to coincide with relevant circadian rhythm) may reduce adverse effects of chemotherapy due to synchronization of tissue that undergoes renewal rapidly². A decrease in toxicity with chronotherapy can improve personalized medicine and lead to better responses to treatments. Methods.  6-phoshphofructo-2-kinase (PFKFB3 gene) is a metabolic regulator that promotes cell cycle progression and regulates cell cycle machinery⁶. PFKFB3 supports cancer cell survival by activating glycolysis and mediating circadian control of carcinogenesis⁷. Tissue samples from subjects with and without tongue cancers were collected; PFKFB3 expression was analyzed at both protein and mRNA levels. Subjects were matched for age and general biochemical parameters⁷. Since the clinical samples were collected at varying times of the day, the study also explored the rhythmicity of PFKFB3 and core clock genes (BMAL1, CLOCK) in synchronized cancer cells (SCC9) and control cells (KC cells)⁷. Luciferase reporter assays were performed on the SCC9 cells to investigate how clocks control PFKFB3 rhythmicity⁷.  Results.  PFKFB3 expression and protein levels are increased and exhibit circadian rhythmicity in cancerous cells, accompanied by dysregulation of clock gene expression in cancerous tissue. Tongue cancer samples showed an increase in inducible PFK2 levels compared to normal tongue tissues⁷. The SCC9 cells showed different PFKFB3 expression patterns compared to control cells and had peaks in CLOCK expression compared to peaks in BMAL1 expression in control cells. Therefore, cancer cells have distinct rhythmic expressions of PFKFB3 and clock genes compared to control cells. In synchronized cells, CLOCK drives PFKFB3 rhythmicity by stimulating transcriptional activity at the PFKFB3 promoter. Timed PFKFB3 inhibition results in different outcomes on cancer growth; inhibiting PFKFB3 at its peak expression time generates better efficacy at inhibiting proliferation and stimulating apoptosis of cancer cells⁷.

1. Masri S, Cervantes M, Sassone-Corsi P. The circadian clock and cell cycle: Interconnected biological circuits. Current opinion in cell biology. 2013;25(6):730-734.http://www.ncbi.nlm.nih.gov/pubmed/23969329.doi: 10.1016/j.ceb.2013.07.013.
2. Kelleher, Rao, Maguire. Circadian molecular clocks and cancer. Cancer Letters.2013;342:9-18.
3. Dierickx, Du Pré, Feyen, et al. Circadian rhythms in stem cell biology and function. In: Stem cells and cardiac regeneration. 2015:57-78. 10.1007/978-3-319-25427-2_5.
4. Kai Yang, Ningbo Zhao Dan Zhao, Dan Chen Yadong Li. The drug efficacy and adverse reactions in a mouse model of oral squamous cell carcinoma treated with oxaliplatin at different time points during a day. 2013;7:511-517. doi:10.2147/DDDT.S46323.
5. Zeng Z, Luo H, Yang J, et al. Overexpression of the circadian clock gene Bmal1increases sensitivity to oxaliplatin in colorectal cancer. Clinical cancer research: an official journal of the American Association for Cancer Research. 2014;20(4):1042-1052.http://www.ncbi.nlm.nih.gov/pubmed/24277452. doi: 10.1158/1078-0432.CCR-13-0171.
6. Roy D, Sheng GY, Herve S, et al. Interplay between cancer cell cycle and metabolism: Challenges, targets and therapeutic opportunities. Biomedicine & Pharmacotherapy. 2017;89:288-296. doi: 10.1016/j.biopha.2017.01.019.
7. Lili Chen, Jiajia Zhao, Qingming Tang, et al. PFKFB3 control of cancer growth by responding to circadian clock outputs. Scientific Reports. 2016;6:24324. http://www.ncbi.nlm.nih.gov/pubmed/27079271. doi: 10.1038/srep24324.