Abstract IA16: Creation and preliminary analyses of a full spectrum of breast cancers initiated de novo from normal human mammary cells
Authors: Tan Susanna , Pellacani Davide , Lefort Sylvain , El-Naggar Amal , Ding Shengsen , Sorensen Poul H , Hirst Martin , Eaves Connie 
Published: February 2024

Abstract
Human breast cancers (BCs) are well recognized for the diagnostic and treatment challenges posed by their extensive and continuously evolving genetic and biologic heterogeneity. Although much progress has been made in identifying features that may serve as new targets, most of these have not been found to be usefully applied to metastatic BCs characterized by a lack of cellular expression of ER, PR, HER2 and a high proliferative activity. Accordingly, these generally incurable BCs, thus identified as “triple-negative” (TNBCs) are in particular need of strategies to model their development in ways that could facilitate the design and testing of effective treatments. Given the drawbacks historically encountered in using cell lines, mouse models, and patient-derived xenografts for this purpose, we launched experiments to assess the potential of creating a useful human model of TNBC de novo. We first discovered that forced expression of KRASG12D (K) alone is sufficient to produce low grade, but persistent human tumors in transplanted immunodeficient NRG mice from 2 of the 3 cell types that constitute and maintain the normal adult human female mammary gland. Histologically, these YB-1-dependent K–induced tumors were classified as variably human ER-, PR- and HER2-positive, invasive ductal carcinomas, also able to produce derivative small tumors in secondary hosts. Subsequent experiments to test whether the indolent properties of these tumors can be modified (i.e., by additional forced expression of human hepatocyte growth factor, or maintenance of transplanted mice on an obesity-inducing diet) showed that neither of these treatments enhance the growth of the K-induced tumors. However, in sharp contrast, transplantation of female NRG mice with the same types of freshly isolated normal adult female mammary cells transduced with lentivirally-encoded BMI1, MYC and TP53R273C and K (KBMT) produced growths containing an increased frequency of Ki67+ cells within a week, and subsequently, produced still YB-1-elevated, but continuously expanding TNBCs. Interestingly, K was required in addition to all 3 of these oncogenes to obtain aggressively expanding TNBCs and, when any one of the BMI1, MYC, or TP53R273C oncogenes was omitted, variably diminished outputs were obtained. FACS analyses showed the surface marker phenotypes of the cells present in any of the more rapidly growing tumors to be remarkably homogeneous with features of normal basal cells. In addition, despite any gross evidence of metastatic capability, cells isolated from all KBMT-induced tumors tested could be expanded in vitro and generated fast growing tumors in transplanted secondary mice. Taken together, these findings demonstrate the feasibility of rapidly and reproducibly creating a model of human TNBC de novo from initially normal human mammary cells, thus offering a new and powerful platform for potentially developing novel prevention, diagnostic, as well as treatment approaches applicable to this disease.
Citation Format: Susanna Tan, Davide Pellacani, Sylvain Lefort, Amal El-Naggar, Shengsen Ding, Poul H Sorensen, Martin Hirst, Connie Eaves. Creation and preliminary analyses of a full spectrum of breast cancers initiated de novo from normal human mammary cells [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Breast Cancer Research; 2023 Oct 19-22; San Diego, California. Philadelphia (PA): AACR; Cancer Res 2024;84(3 Suppl_1):Abstract nr IA16.