Dynamic altruistic cooperation within breast tumors
Authors: Masroni Muhammad Sufyan Bin , Lee Kee Wah , Lee Victor Kwan Min , Ng Siok Bian , Law Chao Teng , Poon Kok Siong , Lee Bernett Teck-Kwong , Liu Zhehao , Tan Yuen Peng , Chng Wee Ling , Tucker Steven , Ngo Lynette Su-Mien , Yip George Wai Cheong , Nga Min En , Hue Susan Swee Shan , Putti Thomas Choudary , Bay Boon Huat , Lin Qingsong , Zhou Lihan , Hartman Mikael , Loh Tze Ping , Lakshmanan Manikandan , Lee Sook Yee , Tergaonkar Vinay , Chua Huiwen , Lee Adeline Voon Hui , Yeo Eric Yew Meng , Li Mo-Huang , Chang Chan Fong , Kee Zizheng , Tan Karen Mei-Ling , Tan Soo Yong , Koay Evelyn Siew-Chuan , Archetti Marco , Leong Sai Mun 
Published: December 2023

Abstract
Background
Social behaviors such as altruism, where one self-sacrifices for collective benefits, critically influence an organism’s survival and responses to the environment. Such behaviors are widely exemplified in nature but have been underexplored in cancer cells which are conventionally seen as selfish competitive players. This multidisciplinary study explores altruism and its mechanism in breast cancer cells and its contribution to chemoresistance.

Methods
MicroRNA profiling was performed on circulating tumor cells collected from the blood of treated breast cancer patients. Cancer cell lines ectopically expressing candidate miRNA were used in co-culture experiments and treated with docetaxel. Ecological parameters like relative survival and relative fitness were assessed using flow cytometry. Functional studies and characterization performed in vitro and in vivo include proliferation, iTRAQ-mass spectrometry, RNA sequencing, inhibition by small molecules and antibodies, siRNA knockdown, CRISPR/dCas9 inhibition and fluorescence imaging of promoter reporter-expressing cells. Mathematical modeling based on evolutionary game theory was performed to simulate spatial organization of cancer cells.

Results
Opposing cancer processes underlie altruism: an oncogenic process involving secretion of IGFBP2 and CCL28 by the altruists to induce survival benefits in neighboring cells under taxane exposure, and a self-sacrificial tumor suppressive process impeding proliferation of altruists via cell cycle arrest. Both processes are regulated concurrently in the altruists by miR-125b, via differential NF-κB signaling specifically through IKKβ. Altruistic cells persist in the tumor despite their self-sacrifice, as they can regenerate epigenetically from non-altruists via a KLF2/PCAF-mediated mechanism. The altruists maintain a sparse spatial organization by inhibiting surrounding cells from adopting the altruistic fate via a lateral inhibition mechanism involving a GAB1-PI3K-AKT-miR-125b signaling circuit.

Conclusions
Our data reveal molecular mechanisms underlying manifestation, persistence and spatial spread of cancer cell altruism. A minor population behave altruistically at a cost to itself producing a collective benefit for the tumor, suggesting tumors to be dynamic social systems governed by the same rules of cooperation in social organisms. Understanding cancer cell altruism may lead to more holistic models of tumor evolution and drug response, as well as therapeutic paradigms that account for social interactions. Cancer cells constitute tractable experimental models for fields beyond oncology, like evolutionary ecology and game theory.