Francesca Liccardo

Acute myeloid leukemia with mutations in TP53 (TP53 ^mut AML) is fatal with a median survival of 6 months. RNA sequencing on purified AML patient samples showed that TP53 ^mut AML had higher expression of mevalonate pathway genes. Using novel, isogenic TP53 ^mut AML cell lines and primary samples, we determined that TP53 ^mut AML resistance to AML chemotherapy cytarabine (AraC) correlated with increased mevalonate pathway activity, a lower induction of reactive oxygen species (ROS), and a mitochondrial response with increased mitochondrial mass and oxidative phosphorylation. Pretreatment with the statin class of mevalonate pathway inhibitors reversed these effects and chemosensitized TP53 ^mut AML. The geranylgeranyl pyrophosphate (GGPP) branch of the mevalonate pathway was required for TP53 ^mut AML chemoresistance. In addition to its role in mitochondria biogenesis, we identified a novel function of GGPP in regulating glutathione for management of AraC-induced ROS. However, statins alone were inadequate to fully reverse chemoresistance in vivo and in a retrospective study of 364 TP53 ^mut AML patients who received chemotherapy concurrently with a statin. Finally, we identified clinical settings and strategies to successfully target the mevalonate pathway, particularly to address the unmet need of TP53 ^mut AML.

Phosphodiesterase 2A (Pde2A) is a dual-specific PDE that breaks down both cAMP and cGMP cyclic nucleotides. We recently highlighted a direct relationship between Pde2A impairment, a consequent increase of cAMP, and the appearance of mouse congenital heart defects (CHDs). Here we aimed to characterize the pathways involved in the development of CHDs and in their prevention by pharmacological approaches targeting cAMP and cGMP signaling. Transcriptome analysis revealed a modulation of more than 500 genes affecting biological processes involved in the immune system, cardiomyocyte development and contractility, angiogenesis, transcription, and oxidative stress in hearts from Pde2A^−/− embryos. Metoprolol and H89 pharmacological administration prevented heart dilatation and hypertabeculation in Pde2A^−/− embryos. Metoprolol was also able to partially impede heart septum defect and oxidative stress at tissue and molecular levels. Amelioration of cardiac defects was also observed by using the antioxidant NAC, indicating oxidative stress as one of the molecular mechanisms underpinning the CHDs. In addition, Sildenafil treatment recovered cardiac defects suggesting the requirement of cAMP/cGMP nucleotides balance for the correct heart development.

Background: Phosphodiesterases (PDEs) are the enzymes that hydrolyze cyclic nucleotides (cAMP and cGMP) playing a key role in the homeostasis of these two second messengers. PDE2A is a dual-specific PDE that breaks down both cAMP and cGMP and can be activated by cGMP. It appears peculiar that the Pde2A-deficient ( Pde2A ^-/- ) mouse model is embryonically lethal, likely due to a strongly reduced size of liver and to a severe anemia. In addition, the heart of Pde2A ^-/- embryos shows ventricular and atrial septum defects, hypertrabeculation, heart dilatation and non-compaction defects. We recently highlighted a direct relationship between Pde2A impairment, consequent increase of cAMP and the onset of mouse congenital heart defects (CHDs), however the molecular mechanisms underlining the heart defects remain unknown. Methods: Transcriptome analysis of Pde2A ^-/- embryonic heart was performed by RNA sequencing and the most altered genes were also analyzed by quantitative real time PCR. In vivo treatment with drugs acting on cAMP signaling (Metoprolol and H89) and oxidative stress (N-Acetyl-Cysteine, NAC) were carried out on pregnant Pde2A ^+/- female. Histological, biochemical, and molecular analyses were then performed on embryonic hearts. Results: We found a significant modulation of more than 500 genes affecting biological processes involved in the immune system, cardiomyocyte development and contractility, angiogenesis, control of gene transcription and oxidative stress in hearts from Pde2A ^-/- embryos. Metoprolol and H89 administration were able to prevent heart dilatation and hypertabeculation in Pde2A ^-/- embryos. Metoprolol was also able to partially impede heart septum defect and oxidative stress at tissue and molecular levels. Partial rescue of cardiac defects was observed by using the antioxidant NAC, indicating oxidative stress like one of the molecular mechanisms underpinning the CHDs. Conclusions: We identified specific biological processes, molecules and cell signaling that can be targeted by selected drugs with consequent beneficial effects for cAMP-dependent CHDs. Novelty and Significance: What is Known?: Congenital Heart Defects are the most frequent heart birth defects including septal defects, hypertrabeculation and non-compacted myocardium. Pde2A hydrolyses the cAMP and cGMP second messengers. Pde2A -deficient mice are embryonic lethal and show cAMP-dependent Congenital Heart Defects. What New Information Does This Article Contribute?: We identified several novel pathways altered in hearts of Pde2A ^-/- embryos. We demonstrated that drugs lowering cAMP levels rescued specific CHDs in Pde2A ^-/- embryos. We discovered that antioxidants are beneficial for CHDs in Pde2A ^-/- embryos. The significance of this work relay in molecular discoveries and pharmacological approaches to treat CHDs by using a mouse model that recapitulate the major congenital heart defects. Among the pathways involved in specific defects associated with CHDs, the transcriptome analysis revealed an impairment of genes of the immune system, cardiomyocyte development and contractility, angiogenesis, control of gene transcription and oxidative stress in Pde2A ^-/- hearts. The scientific community will have open access to the RNA-seq data that can be utilized to further understand the congenital cardiac pathology and clarify the molecular implication in selected defects such as septal and ventricular wall defects. Up to date CHDs, when possible and if identified in time, are mostly treated trough surgery. The identification of drugs blunting the cAMP signaling response or reducing oxidative stress pathways will be useful for setting therapeutic approaches to alleviate CHDs.

Acute myeloid leukemia (AML) is a hematological malignancy originating from defective hematopoietic stem cells in the bone marrow. In spite of the recent approval of several molecular targeted therapies for AML treatment, disease recurrence remains an issue. Interestingly, increasing evidence has pointed out the relevance of bone marrow (BM) niche remodeling during leukemia onset and progression. Complex crosstalk between AML cells and microenvironment components shapes the leukemic BM niche, consequently affecting therapy responsiveness. Notably, circular RNAs are a new class of RNAs found to be relevant in AML progression and chemoresistance. In this review, we provided an overview of AML-driven niche remodeling. In particular, we analyzed the role of circRNAs and their possible contribution to cell–cell communication within the leukemic BM microenvironment. Understanding these mechanisms will help develop a more effective treatment for AML.