The differentiation status of luminal-type breast cancer–derived organoids can be altered in vitro through the activation of NOTCH signaling

Abstract Background Drug therapy of luminal-type breast cancer has advanced remarkably; however, its effectiveness continues to be limited by primary and acquired treatment resistance. To identify the means of overcoming such resistance, in vitro disease models that faithfully reproduce the characteristics of original patient tumors must be developed. Although the three-dimensional culturing of breast cancer cells has been improved, the changes in differentiation status and underlying mechanisms require further elucidation. Methods The organoids from 33 luminal-type breast cancers were prepared using a method developed by us. Using immunohistochemistry and gene expression profiling, the levels and time courses of estrogen receptor, progesterone receptor, Ki67, and differentiation marker expression were monitored during culture as well as the variation among the patients and individual organoids. Furthermore, we examined the effect of NOTCH inhibitor treatment on differentiation status. Results We successfully prepared organoids from samples obtained from 33 patients with luminal-type breast cancer and studied their ER expression. The expression status was well maintained in primary organoids, whereas it decreased after passaging in most of the cases. In fact, the studied organoid lines were classified into those that retained a high level of ER expression (9%), those that completely lost it (9%), and those that repressed it to varying degrees (82%). In some cases, the ER expression was suddenly and drastically decreased after passaging. Marker protein immunohistochemistry revealed that after passaging, the differentiation status shifted from a luminal- to a basal-like status. Differentially expressed genes suggested the activation of NOTCH signaling in the passaged organoids, wherein a NOTCH inhibitor was able to substantially rescue the decreased ER expression and alter the differentiation status. Conclusions Our findings suggest that the differentiation status of luminal-type cancer cells is quite flexible, and that by inhibiting the NOTCH signaling we can preserve the differentiation status of luminal-type breast cancer organoids.