Abstract 15259: Breast Cancer and Heritable Pah Due to Bmpr2 Mutation: An Unexpected Discovery

Abstract

Introduction: BMPR2 mutation is reported in 80% of familial PAH and 20% of idiopathic cases. Recently, a rat model of hereditary Pulmonary Arterial Hypertension with a BMPR2 loss-of-function mutation has been generated. Similarly to human, only around 20% of the rats spontaneously developed mild PAH. Unexpectedly, we observed that 20% (95%CI:12-28) of the 82 Bmpr2+/Δ71 rats (93% of females) versus 4% (95%CI:0-9)of the 84 age-matched wild type littermates spontaneously developed mammary masses requiring euthanasia. Interestingly, rats with tumor had elevated PA and clearly exhibit PAH signs. Hypothesis: We hypothesized that mammary tumor exacerbates the penetrance of PAH in the BMPR2 mutated female rats. Methods/Results: BMPR2 mutated and wild-type female young rats were treated with the breast cancer inducer 7, 12- diméthylbenz(a)anthracene (DMBA) or Vehicle. DMBA causes on average more tumors development in BMPR2 mutated rats versus WT rats (6,2 vs. 4) P=0,0275. Compare to both vehicle-treated and DMBA rats (without tumor) BMPR2 mutated rats with DMBA-induced tumors had a significant increase in mean PA pressure (p<0,0001); total pulmonary resistance (p<0,0001) and a significant decrease in cardiac output (P=0,0293). Histologically, these changes were associated with an increase of pulmonary artery remodelling assessed by immunofluorescence. Mechanistically, development of PAH in the BMPR2 mutated rats with tumor was associated with a significant upregulation of BRD4 (western blot) (p=0,0149); IL-1β (P=0,0052), BRD3 (P=0,0791) and BIRC5 (P=0,0166) mRNA expression levels. Co-culture experiments with breast cancer cells and PASMC from both WT and BMPR2 mutated rats are ongoing to identify whether cancer cells are realising factors responsible for BRD4 activation and thus PASMC proliferation and resistance to apoptosis. Conclusions: We demonstrated for the first time that breast cancer exacerbates PAH development in BMPR2 mutated rats. Increased BRDs driven pro-inflammatory signalling is associated with PAH development in BMPR2 mutated rats. We are currently exploring whether BMPR2 mutated patients are more prone to breast cancer development or not and whether PAH development occurs more frequently in breast cancer patients.