Genetic Analysis of Triple-Negative Breast Cancer and Pineoblastoma

Metastatic triple-negative breast cancer (TNBC) is a devastating disease affecting relatively young women. The tumor suppressor genes TP53 and RB1 are commonly lost together in a subset of TNBC with exceedingly poor prognosis. The identification of oncogenic drivers that cooperate with p53/Rb-loss in TNBC may uncover novel therapeutic modalities. Here, I employed sleeping beauty (SB) mutagenesis screens to identify oncogenic drivers that cooperate with p53- versus p53 plus Rb-deletion to promote primary mammary tumors and lung metastases, using a WAP-Cre deleter line to induce transposon mobilization. SB mutagenesis accelerated tumorigenesis in the absence of functional p53 or p53 plus Rb. 66.7% of metastases formed in p53/Rb-deficient mice had transposon insertions in genes involved in the Ras pathway (Hras1 and Sos2) or cell motility/migration (Rock2, Fam19a5, and Ntn1). In accordance, bioinformatic analysis revealed that the Ras pathway is enriched in TNBC samples and cell lines. Inhibition of ERK1/2 via ulixertinib suppressed growth of TNBC cell lines with high Ras activity; suppression was more pronounced in cells with stable RB1 knocked-down relative to parental RB1 wild-type cells. These results suggest that alterations in genes involved in Ras pathway activation and motility promote metastatic p53/Rb-deficient TNBC, and point to ERK1/2 inhibitors as potential therapeutic intervention for this subgroup of metastatic TNBC patients. I also used WAP-Cre to generate a mouse model for Pineoblastoma (PB), a lethal pediatric brain cancer. Germline mutations in RB1 and DICER1 have been implicated in the etiology of PB, and deletion of Rb and p53 via WAP-Cre has been shown to induce pineal tumors that resemble human PB with 100% penetrance. Here, I inactivated Dicer1 plus p53 or Dicer1 plus Rb and p53 in the pineal gland via WAP-Cre. Dicer1/p53 and Dicer1/Rb/p53-deficient mice developed PB with 33.3% and 93.8% penetrance, respectively. These tumors clustered close to human PB, and exhibited sensitivity to the tricyclic antidepressant drug nortriptyline in vitro. This study describes the first mouse model for Dicer1-deficient pineoblastoma, demonstrates that WAP-Cre can be used to target the cell-of-origin of distinct PB subtypes, and identifies nortriptyline as a potential new therapeutic for children with DICER1-deficient pineoblastoma.Ph.D

Targeting Hedgehog Signalling as a Drug Therapy in Aggressive Fibromatosis

Aggressive fibromatosis is a benign fibroproliferative tumour that can occur as a sporadic lesion or a manifestation in patients with familial syndromes, such as familial adenomatous polyposis. Tumours are characterized by the stabilization of β-catenin and the activation of β-catenin-mediated transcription. Current treatment results are far from ideal, and recurrence rates are high. As a result, there remains a need for more effective therapeutic strategies. In this work, we demonstrate the effect of hedgehog signalling inhibition on aggressive fibromatosis tumour development and β-catenin modulation. We found that hedgehog inhibition decreased cell viability and proliferation as well as total β-catenin levels in human aggressive fibromatosis tumour cells in vitro. Furthermore, following hedgehog inhibition in Apc+/Apc1638N aggressive fibromatosis mouse model, the number and volume of the tumours formed was reduced. Together, this work suggests that hedgehog signalling inhibitor agents are potential candidates to effectively manage aggressive fibromatosis.MAS

CDC25 as a common therapeutic target for triple-negative breast cancer - the challenges ahead

The dual phosphatase CDC25 has recently been identified as a target for diverse triple-negative breast cancers including RB1/PTEN/P53-deficient tumors. Moreover, CDC25 inhibitors effectively synergize with PI3K inhibitors to suppress tumor growth. We discuss these findings and the challenges that lie ahead in bringing CDC25 inhibitors to the clinic

Thinking (Metastasis) outside the (Primary Tumor) Box

The metastasis of tumor cells into vital organs is a major cause of death from diverse types of malignancies [...

Distinct shared and compartment-enriched oncogenic networks drive primary versus metastatic breast cancer

Abstract Metastatic breast-cancer is a major cause of death in women worldwide, yet the relationship between oncogenic drivers that promote metastatic versus primary cancer is still contentious. To elucidate this relationship in treatment-naive animals, we hereby describe mammary-specific transposon-mutagenesis screens in female mice together with loss-of-function Rb, which is frequently inactivated in breast-cancer. We report gene-centric common insertion-sites (gCIS) that are enriched in primary-tumors, in metastases or shared by both compartments. Shared-gCIS comprise a major MET-RAS network, whereas metastasis-gCIS form three additional hubs: Rho-signaling, Ubiquitination and RNA-processing. Pathway analysis of four clinical cohorts with paired primary-tumors and metastases reveals similar organization in human breast-cancer with subtype-specific shared-drivers (e.g. RB1-loss, TP53-loss, high MET, RAS, ER), primary-enriched (EGFR, TGFβ and STAT3) and metastasis-enriched (RHO, PI3K) oncogenic signaling. Inhibitors of RB1-deficiency or MET plus RHO-signaling cooperate to block cell migration and drive tumor cell-death. Thus, targeting shared- and metastasis- but not primary-enriched derivers offers a rational avenue to prevent metastatic breast-cancer