A dual role for SAMHD1 in regulating HBV cccDNA and RT-dependent particle genesis

Chronic hepatitis B is one of the world's unconquered diseases with more than 240 million infected subjects at risk of developing liver disease and hepatocellular carcinoma. Hepatitis B virus reverse transcribes pre-genomic RNA to relaxed circular DNA (rcDNA) that comprises the infectious particle. To establish infection of a naïve target cell, the newly imported rcDNA is repaired by host enzymes to generate covalently closed circular DNA (cccDNA), which forms the transcriptional template for viral replication. SAMHD1 is a component of the innate immune system that regulates deoxyribonucleoside triphosphate levels required for host and viral DNA synthesis. Here, we show a positive role for SAMHD1 in regulating cccDNA formation, where KO of SAMHD1 significantly reduces cccDNA levels that was reversed by expressing wild-type but not a mutated SAMHD1 lacking the nuclear localization signal. The limited pool of cccDNA in infected Samhd1 KO cells is transcriptionally active, and we observed a 10-fold increase in newly synthesized rcDNA-containing particles, demonstrating a dual role for SAMHD1 to both facilitate cccDNA genesis and to restrict reverse transcriptase-dependent particle genesis

Characterisation of SAMHD1's ancestral function

Deoxynucleoside triphosphates (dNTPs) are the building blocks of DNA. DNA synthesis requires dNTPs for replication and subsequent cell division. Therefore, nucleotide metabolism in cells is tightly regulated and failure of this regulation results in damage, toxicity and cell death. SAMHD1 is a highly conserved protein that degrades dNTPs and restricts HIV-1 through dNTP starvation. SAMHD1 is mutated in Aicardi-Goutières syndrome, a disease characterised by the chronic production of type I interferon. SAMHD1 is also involved in DNA repair and is mutated in cancer. SAMHD1 evolved before lentiviruses, suggesting that SAMHD1’s main function is not to restrict viruses. This project aimed to identify and characterise SAMHD1’s ancestral function. I show that addition of deoxynucleosides (dNs) to the culture medium resulted in the death of SAMHD1-deficient cells but not of WT cells. dNs were taken up by the cells and converted into dNTPs through the nucleotide salvage pathway. Cell death was most pronounced upon feeding with deoxyguanosine (dG) alone, suggesting that dGTP overload is particularly toxic to cells. In this model SAMHD1 tunes dNTP levels and protects cells against apoptosis triggered by dNTP overload or imbalances in the dNTP pools. Characterisation of this mechanism shed light on the mechanism of action of forodesine, an anti-cancer agent that inhibits purine nucleoside phosphorylase. Forodesine induces the accumulation of dGTP and subsequent cell death. Nevertheless, forodesine showed efficacy only in a minority of leukaemic patients, for unknown reasons. PBMCs from CLL patients with SAMHD1 loss-of-function mutations showed a significant reduction of CLL B-cells upon treatment with forodesine and dG compared with the control group. Therefore, I propose a model where SAMHD1 limits the efficacy of the PNP inhibitor forodesine which predict that patients with SAMHD1 mutations respond well to forodesine treatment. Forodesine could be used as a precision medicine. This new important role of SAMHD1 in dealing with dNTP overload and unbalances may be SAMHD1’s ancestral function. This mechanism can be exploited physiologically where dNTP accumulation is required for toxicity, such as forodesine treatment.</p

Characterisation of SAMHD1's ancestral function: Investigation of SAMHD1's role in nucleotide metabolism and cancer

Deoxynucleoside triphosphates (dNTPs) are the building blocks of DNA. DNA synthesis requires dNTPs for replication and subsequent cell division. Therefore, nucleotide metabolism in cells is tightly regulated and failure of this regulation results in damage, toxicity and cell death. SAMHD1 is a highly conserved protein that degrades dNTPs and restricts HIV-1 through dNTP starvation. SAMHD1 is mutated in Aicardi-Goutières syndrome, a disease characterised by the chronic production of type I interferon. SAMHD1 is also involved in DNA repair and is mutated in cancer. SAMHD1 evolved before lentiviruses, suggesting that SAMHD1’s main function is not to restrict viruses. This project aimed to identify and characterise SAMHD1’s ancestral function. I show that addition of deoxynucleosides (dNs) to the culture medium resulted in the death of SAMHD1-deficient cells but not of WT cells. dNs were taken up by the cells and converted into dNTPs through the nucleotide salvage pathway. Cell death was most pronounced upon feeding with deoxyguanosine (dG) alone, suggesting that dGTP overload is particularly toxic to cells. In this model SAMHD1 tunes dNTP levels and protects cells against apoptosis triggered by dNTP overload or imbalances in the dNTP pools. Characterisation of this mechanism shed light on the mechanism of action of forodesine, an anti-cancer agent that inhibits purine nucleoside phosphorylase. Forodesine induces the accumulation of dGTP and subsequent cell death. Nevertheless, forodesine showed efficacy only in a minority of leukaemic patients, for unknown reasons. PBMCs from CLL patients with SAMHD1 loss-of-function mutations showed a significant reduction of CLL B-cells upon treatment with forodesine and dG compared with the control group. Therefore, I propose a model where SAMHD1 limits the efficacy of the PNP inhibitor forodesine which predict that patients with SAMHD1 mutations respond well to forodesine treatment. Forodesine could be used as a precision medicine. This new important role of SAMHD1 in dealing with dNTP overload and unbalances may be SAMHD1’s ancestral function. This mechanism can be exploited physiologically where dNTP accumulation is required for toxicity, such as forodesine treatment

PNP inhibitors selectively kill cancer cells lacking SAMHD1

Purine nucleoside phosphorylase inhibitors (PNP-Is) were developed to ablate transformed lymphocytes. However, only some patients with leukemia benefit from PNP-Is. We provide a molecular explanation: the deoxyribonucleoside triphosphate (dNTP) hydrolase SAM and HD domain-containing protein 1 (SAMHD1) prevents the accumulation of toxic dNTP levels during purine nucleoside phosphorylase inhibition. We propose PNP-Is for targeted therapy of patients with acquired SAMHD1 mutations

Characterisation of SAMHD1's ancestral function

Deoxynucleoside triphosphates (dNTPs) are the building blocks of DNA. DNA synthesis requires dNTPs for replication and subsequent cell division. Therefore, nucleotide metabolism in cells is tightly regulated and failure of this regulation results in damage, toxicity and cell death. SAMHD1 is a highly conserved protein that degrades dNTPs and restricts HIV-1 through dNTP starvation. SAMHD1 is mutated in Aicardi-Goutières syndrome, a disease characterised by the chronic production of type I interferon. SAMHD1 is also involved in DNA repair and is mutated in cancer. SAMHD1 evolved before lentiviruses, suggesting that SAMHD1âs main function is not to restrict viruses. This project aimed to identify and characterise SAMHD1âs ancestral function. I show that addition of deoxynucleosides (dNs) to the culture medium resulted in the death of SAMHD1-deficient cells but not of WT cells. dNs were taken up by the cells and converted into dNTPs through the nucleotide salvage pathway. Cell death was most pronounced upon feeding with deoxyguanosine (dG) alone, suggesting that dGTP overload is particularly toxic to cells. In this model SAMHD1 tunes dNTP levels and protects cells against apoptosis triggered by dNTP overload or imbalances in the dNTP pools. Characterisation of this mechanism shed light on the mechanism of action of forodesine, an anti-cancer agent that inhibits purine nucleoside phosphorylase. Forodesine induces the accumulation of dGTP and subsequent cell death. Nevertheless, forodesine showed efficacy only in a minority of leukaemic patients, for unknown reasons. PBMCs from CLL patients with SAMHD1 loss-of-function mutations showed a significant reduction of CLL B-cells upon treatment with forodesine and dG compared with the control group. Therefore, I propose a model where SAMHD1 limits the efficacy of the PNP inhibitor forodesine which predict that patients with SAMHD1 mutations respond well to forodesine treatment. Forodesine could be used as a precision medicine. This new important role of SAMHD1 in dealing with dNTP overload and unbalances may be SAMHD1âs ancestral function. This mechanism can be exploited physiologically where dNTP accumulation is required for toxicity, such as forodesine treatment.</p

Evaluation of Tumour Exposure following the Administration of an Innovative Cisplatin Dry Powder for Inhalation at Different Dose Levels and Regimens

info:eu-repo/semantics/nonPublishe

Evaluation of Tumour Exposure following the Administration of an Innovative Cisplatin Dry Powder for Inhalation at Different Dose Levels and Regimens

info:eu-repo/semantics/inPres

Inhaled cisplatin dry powder combined with anti-PD1 induces anti-tumour immune-response in lung cancer

info:eu-repo/semantics/publishe