CHD1 loss sensitizes prostate cancer to DNA damaging therapy by promoting error-prone double-strand break repair.

BACKGROUND: Deletion of the chromatin remodeler chromodomain helicase DNA-binding protein 1 (CHD1) is a common genomic alteration found in human prostate cancers (PCas). CHD1 loss represents a distinct PCa subtype characterized by SPOP mutation and higher genomic instability. However, the role of CHD1 in PCa development in vivo and its clinical utility remain unclear. PATIENTS AND METHODS: To study the role of CHD1 in PCa development and its loss in clinical management, we generated a genetically engineered mouse model with prostate-specific deletion of murine Chd1 as well as isogenic CHD1 wild-type and homozygous deleted human benign and PCa lines. We also developed patient-derived organoid cultures and screened patients with metastatic PCa for CHD1 loss. RESULTS: We demonstrate that CHD1 loss sensitizes cells to DNA damage and causes a synthetic lethal response to DNA damaging therapy in vitro, in vivo, ex vivo, in patient-derived organoid cultures and in a patient with metastatic PCa. Mechanistically, CHD1 regulates 53BP1 stability and CHD1 loss leads to decreased error-free homologous recombination (HR) repair, which is compensated by increased error-prone non-homologous end joining (NHEJ) repair for DNA double-strand break (DSB) repair. CONCLUSIONS: Our study provides the first in vivo and in patient evidence supporting the role of CHD1 in DSB repair and in response to DNA damaging therapy. We uncover mechanistic insights that CHD1 modulates the choice between HR and NHEJ DSB repair and suggest that CHD1 loss may contribute to the genomic instability seen in this subset of PCas.

Spontaneous bone metastases in a preclinical orthotopic model of invasive lobular carcinoma; the effect of pharmacological targeting TGFß receptor I kinase.

Invasive ductal carcinoma (IDC) and invasive lobular carcinoma (ILC) are the most frequently occurring histological subtypes of breast cancer, accounting for 80-90% and 10-15% of the total cases, respectively. At the time of diagnosis and surgical resection of the primary tumour, most patients do not have clinical signs of metastases, but bone micrometastases may already be present. Our aim was to develop a novel preclinical ILC model of spontaneous bone micrometastasis. We used murine invasive lobular breast carcinoma cells (KEP) that were generated by targeted deletion of E-cadherin and p53 in a conditional K14cre;Cdh1((F/F));Trp53((F/F)) mouse model of de novo mammary tumour formation. After surgical resection of the growing orthotopically implanted KEP cells, distant metastases were formed. In contrast to other orthotopic breast cancer models, KEP cells readily formed skeletal metastases with minimal lung involvement. Continuous treatment with SD-208 (60 mg/kg per day), an orally available TGFß receptor I kinase inhibitor, increased the tumour growth at the primary site and increased the number of distant metastases. Furthermore, when SD-208 treatment was started after surgical resection of the orthotopic tumour, increased bone colonisation was also observed (versus vehicle). Both our in vitro and in vivo data show that SD-208 treatment reduced TGFß signalling, inhibited apoptosis, and increased proliferation. In conclusion, we have demonstrated that orthotopic implantation of murine ILC cells represent a new breast cancer model of minimal residual disease in vivo, which comprises key steps of the metastatic cascade. The cancer cells are sensitive to the anti-tumour effects of TGFß. Our in vivo model is ideally suited for functional studies and evaluation of new pharmacological intervention strategies that may target one or more steps along the metastatic cascade of events.

The APC/C activator FZR1 is essential for meiotic prophase I in mice.

Fizzy-related 1 (FZR1) is an activator of the Anaphase promoting complex/cyclosome (APC/C) and an important regulator of the mitotic cell division cycle. Using a germ-cell-specific conditional knockout model we examined its role in entry into meiosis and early meiotic events in both sexes. Loss of APC/C(FZR1) activity in the male germline led to both a mitotic and a meiotic testicular defect resulting in infertility due to the absence of mature spermatozoa. Spermatogonia in the prepubertal testes of such mice had abnormal proliferation and delayed entry into meiosis. Although early recombination events were initiated, male germ cells failed to progress beyond zygotene and underwent apoptosis. Loss of APC/C(FZR1) activity was associated with raised cyclin B1 levels, suggesting that CDK1 may trigger apoptosis. By contrast, female FZR1Δ mice were subfertile, with premature onset of ovarian failure by 5 months of age. Germ cell loss occurred embryonically in the ovary, around the time of the zygotene-pachytene transition, similar to that observed in males. In addition, the transition of primordial follicles into the growing follicle pool in the neonatal ovary was abnormal, such that the primordial follicles were prematurely depleted. We conclude that APC/C(FZR1) is an essential regulator of spermatogonial proliferation and early meiotic prophase I in both male and female germ cells and is therefore important in establishing the reproductive health of adult male and female mammals.

Loss of CDH1 and Pten accelerates cellular invasiveness and angiogenesis in the mouse uterus.

E-cadherin (CDH1) is a cell adhesion molecule that coordinates key morphogenetic processes regulating cell growth, cell proliferation, and apoptosis. Loss of CDH1 is a trademark of the cellular event epithelial to mesenchymal transition, which increases the metastatic potential of malignant cells. PTEN is a tumor-suppressor gene commonly mutated in many human cancers, including endometrial cancer. In the mouse uterus, ablation of Pten induces epithelial hyperplasia, leading to endometrial carcinomas. However, loss of Pten alone does not affect longevity until around 5 mo. Similarly, conditional ablation of Cdh1 alone does not predispose mice to cancer. In this study, we characterized the impact of dual Cdh1 and Pten ablation (Cdh1(d/d) Pten(d/d)) in the mouse uterus. We observed that Cdh1(d/d) Pten(d/d) mice died at Postnatal Days 15-19 with massive blood loss. Their uteri were abnormally structured with curly horns, disorganized epithelial structure, and increased cell proliferation. Co-immunostaining of KRT8 and ACTA2 showed invasion of epithelial cells into the myometrium. Further, the uteri of Cdh1(d/d) Pten(d/d) mice had prevalent vascularization in both the endometrium and myometrium. We also observed reduced expression of estrogen and progesterone receptors, loss of cell adherens, and tight junction molecules (CTNNB1 and claudin), as well as activation of AKT in the uteri of Cdh1(d/d) Pten(d/d) mice. However, complex hyperplasia was not found in the uteri of Cdh1(d/d) Pten(d/d) mice. Collectively, these findings suggest that ablation of Pten with Cdh1 in the uterus accelerates cellular invasiveness and angiogenesis and causes early death.