Towards prevention of cancer relapse: Major strides from Japanese scientists

Cancer relapse after chemotherapy remains a major cause of cancer-related deaths. However, the exact mechanism of cancer reoccurrence has so far remained unclear. In this study, researchers from Japan developed a live imaging system and revealed that yes-associated protein (YAP) promotes the relapse of human colorectal cancer. Their study sheds light on the therapeutic potential of YAP inhibition in preventing cancer relapse among patients undergoing chemotherapy.

Recent developments in medical science have greatly improved the effectiveness and outcomes of cancer therapies. However, cancer relapse or the recurrence of cancer after chemotherapy remains a challenge and leads to many cancer-related deaths worldwide. Understanding how relapse occurs could hold the key to preventing it.

New evidence indicates that resident cancer stem cells (CSCs) that persevere and survive through chemotherapy may be the main culprits behind cancer recurrence. Unfortunately, current experimental systems are insufficient for testing this hypothesis, preventing targeted interventions against cancer recurrence.

To solve this problem, a group of scientists from Japan, led by Prof. Toshiro Sato of Keio University School of Medicine, developed a novel live imaging system. Using this system, they monitored human colorectal cancer (CRC) organoids—3D assemblies of cancer cells that mimic tumors—in real time. More specifically, they looked at the dynamics of specific cancer cells during and after chemotherapy. Their findings, first published online on 7 July 2022 in the journal Nature, have been published in an article in the August 25, 2022 print issue of the journal. These findings shed light on the mechanisms that cause dormant cancer cells to reawaken and trigger cancer relapse after chemotherapy.

Prof. Sato explains, “Cancerous tumors are made up of different types of cells. Each group of cells expresses a specific gene, which acts as a unique identifier and can be used to trace their lineage. Based on this principle, we traced the growth and proliferation of specific cancer cell types over time, before and after chemotherapy.” Through this analysis, the researchers identified a group of cells marked by the gene LGR5, which remain dormant before chemotherapy. Interestingly, they found that LGR5-expressing cells that also express p27—a key regulator of cell proliferation—can remain “asleep” or dormant and even tolerate chemotherapy. However, after chemotherapy, these cells “reawaken” and undergo rapid proliferation, leading to regrowth of the tumor and cancer relapse.

Encouraged by these findings, Prof. Sato and his team, which also comprised researcher Yuki Ohta and assistant professor Masayuki Fujii, both from Keio University School of Medicine, asked another important question: how do these cells remain dormant and tolerate chemotherapy? To answer this question, they performed a large-scale analysis of gene expression in this specific group of cells. To their surprise, they found that these cells show an unusually high expression of the collagen protein COL17A1, which allows the cells to sleep through chemotherapy and survive. More intriguingly, chemotherapy disrupts COL17A1, reawakening these cells and causing them to proliferate. This leads to the recurrence of CRC.

“Chemotherapy is widely believed to kill cancer cells. However, we found that chemotherapy has the opposite effect on some dormant cancer cells and instead allows them to proliferate and make new tumors. This knowledge is very valuable for developing better anticancer treatments,” comments Prof. Sato.

To enable more specific interventions against cancer relapse, the research team went on to examine how chemotherapy disrupts dormancy in cells with COL17A1. Through their investigations, they narrowed down on a special network of molecules called the FAK-YAP signaling pathway. When this YAP signally was inhibited, the dormant cells found it difficult to reawaken. As a result, tumor regrowth after chemotherapy—i.e., CRC relapse—was delayed.

Hailing these results, Prof. Sato says, “The networks controlling cancer are very intricate. Our findings offer a new piece of the puzzle, providing novel insights into what causes dormant cells to reawaken and make more tumors. They show that YAP inhibition could offer an effective treatment option for preventing cancer relapse.” 

The findings by Prof. Sato and his team bring us one step closer to solving the major problem of cancer relapse.