There is increasing evidence that basal-like triple negative breast cancer (TNBC) originates from luminal mammary epithelial cells. Specific gene signatures have already been experimentally proven to serve as genetic lineage switches that, when overexpressed, transform pre-malignant luminal cells to oncogenic cells with basal, stem-like characteristics. Conversely, depletion of these genes in oncogenic cells with basal, stem-like characteristics leads to luminal differentiation. These studies suggest that during the earliest steps of neoplastic transformation, specific gene sets can alter cell fate decisions and differentiation status in mammary epithelial cells, which ultimately contributes to the heterogeneity of breast tumors.

Our lab has identified a novel Wnt/β-Catenin target gene, Limb bud and heart (LBH) that is majorly overexpressed in TNBC. LBH is a regulator of the basal mammary stem cell lineage and repressor of luminal differentiation via induction of ΔNp63 and repression of estrogen receptor alpha. LBH is required for the self-renewal and maintenance of adult basal mammary stem cells, which tend to be enriched in TNBC. Knockout studies in mice have shown that genetic ablation of LBH does not impair embryogenesis or normal adult organ function, making it a possible therapeutic target.

Using crosses between MMTV-Wnt-1 transgenic mice and K14Cre LBHloxP knockout mice, we are studying the effect of LBH ablation in the basal cells of the mammary epithelium downstream of ectopic Wnt expression in the mammary gland. We postulated that LBH may be an effector of Wnt-driven TNBC, therefore its inhibition would lead to decreased Wnt-induced mammary gland hyperplasia and tumor formation. In our model, LBH ablation in the basal mammary epithelium of female Wnt transgenic mice reduces mammary gland hyperplasia and delays tumor onset. MMTV-Wnt-1 driven, LBH-null tumors also exhibit histopathological differences indicative of a luminal to basal conversion.

There is an urgent need to elucidate mechanisms underlying TNBC development and progression and find reliable avenues for treatment. Our data indicates a role for Lbh as a novel effector for Wnt-driven TNBC and further studies may prove antagonism of Lbh to be a novel method to control TNBC progression.

Citation Format: Kilan C. Ashad-Bishop, Karoline Briegel. Loss of the stem cell and basal lineage regulator LBH delays onset of basal-like triple negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2876. doi:10.1158/1538-7445.AM2017-2876