CRISPR editing to mimic porphyria combined with light: A new preclinical approach for prostate cancer.

Thanks to its very high genome-editing efficiency, CRISPR-Cas9 technology could be a promising anticancer weapon. Clinical trials using CRISPR-Cas9 nuclease to ex vivo edit and alter immune cells are ongoing. However, to date, this strategy still has not been applied in clinical practice to directly target cancer cells. Targeting a canonical metabolic pathway essential to good functioning of cells without potential escape would represent an attractive strategy. We propose to mimic a genetic metabolic disorder in cancer cells to weaken cancer cells, independent of their genomic abnormalities. Mutations affecting the heme biosynthesis pathway are responsible for porphyria, and most of them are characterized by an accumulation of toxic photoreactive porphyrins. This study aimed to mimic porphyria by using CRISPR-Cas9 to inactivate UROS, leading to porphyrin accumulation in a prostate cancer model. Prostate cancer is the leading cancer in men and has a high mortality rate despite therapeutic progress, with a primary tumor accessible to light. By combining light with gene therapy, we obtained high efficiency in vitro and in vivo, with considerable improvement in the survival of mice. Finally, we achieved the preclinical proof-of-principle of performing cancer CRISPR gene therapy.

An Orthotopic Model of Glioblastoma Is Resistant to Radiodynamic Therapy with 5-AminoLevulinic Acid.

Radiosensitization of glioblastoma is a major ambition to increase the survival of this incurable cancer. The 5-aminolevulinic acid (5-ALA) is metabolized by the heme biosynthesis pathway. 5-ALA overload leads to the accumulation of the intermediate fluorescent metabolite protoporphyrin IX (PpIX) with a radiosensitization potential, never tested in a relevant model of glioblastoma. We used a patient-derived tumor cell line grafted orthotopically to create a brain tumor model. We evaluated tumor growth and tumor burden after different regimens of encephalic multifractionated radiation therapy with or without 5-ALA. A fractionation scheme of 5 × 2 Gy three times a week resulted in intermediate survival [48-62 days] compared to 0 Gy (15-24 days), 3 × 2 Gy (41-47 days) and, 5 × 3 Gy (73-83 days). Survival was correlated to tumor growth. Tumor growth and survival were similar after 5 × 2 Gy irradiations, regardless of 5-ALA treatment (RT group (53-67 days), RT+5-ALA group (40-74 days), HR = 1.57, p = 0.24). Spheroid growth and survival were diminished by radiotherapy in vitro, unchanged by 5-ALA pre-treatment, confirming the in vivo results. The analysis of two additional stem-like patient-derived cell lines confirmed the absence of radiosensitization by 5-ALA. Our study shows for the first time that in a preclinical tumor model relevant to human glioblastoma, treated as in clinical routine, 5-ALA administration, although leading to important accumulation of PpIX, does not potentiate radiotherapy.

Mutation-Specific Guide RNA for Compound Heterozygous Porphyria On-target Scarless Correction by CRISPR/Cas9 in Stem Cells.

CRISPR/Cas9 is a promising technology for gene correction. However, the edition is often biallelic, and uncontrolled small insertions and deletions (indels) concomitant to precise correction are created. Mutation-specific guide RNAs were recently tested to correct dominant inherited diseases, sparing the wild-type allele. We tested an original approach to correct compound heterozygous recessive mutations. We compared editing efficiency and genotoxicity by biallelic guide RNA versus mutant allele-specific guide RNA in iPSCs derived from a congenital erythropoietic porphyria patient carrying compound heterozygous mutations resulting in UROS gene invalidation. We obtained UROS function rescue and metabolic correction with both guides with the potential of use for porphyria clinical intervention. However, unlike the biallelic one, the mutant allele-specific guide was free of on-target collateral damage. We recommend this design to avoid genotoxicity and to obtain on-target scarless gene correction for recessive disease with frequent cases of compound heterozygous mutations.

Iron chelation rescues hemolytic anemia and skin photosensitivity in congenital erythropoietic porphyria.

Congenital erythropoietic porphyria (CEP) is an inborn error of heme synthesis resulting from uroporphyrinogen III synthase (UROS) deficiency and the accumulation of nonphysiological porphyrin isomer I metabolites. Clinical features are heterogeneous among patients with CEP but usually combine skin photosensitivity and chronic hemolytic anemia, the severity of which is related to porphyrin overload. Therapeutic options include symptomatic strategies only and are unsatisfactory. One promising approach to treating CEP is to reduce the erythroid production of porphyrins through substrate reduction therapy by inhibiting 5-aminolevulinate synthase 2 (ALAS2), the first and rate-limiting enzyme in the heme biosynthetic pathway. We efficiently reduced porphyrin accumulation after RNA interference-mediated downregulation of ALAS2 in human erythroid cellular models of CEP disease. Taking advantage of the physiological iron-dependent posttranscriptional regulation of ALAS2, we evaluated whether iron chelation with deferiprone could decrease ALAS2 expression and subsequent porphyrin production in vitro and in vivo in a CEP murine model. Treatment with deferiprone of UROS-deficient erythroid cell lines and peripheral blood CD34+-derived erythroid cultures from a patient with CEP inhibited iron-dependent protein ALAS2 and iron-responsive element-binding protein 2 expression and reduced porphyrin production. Furthermore, porphyrin accumulation progressively decreased in red blood cells and urine, and skin photosensitivity in CEP mice treated with deferiprone (1 or 3 mg/mL in drinking water) for 26 weeks was reversed. Hemolysis and iron overload improved upon iron chelation with full correction of anemia in CEP mice treated at the highest dose of deferiprone. Our findings highlight, in both mouse and human models, the therapeutic potential of iron restriction to modulate the phenotype in CEP.

Genetic background influences hepcidin response to iron imbalance in a mouse model of hemolytic anemia (Congenital erythropoietic porphyria).

Clinical severity is heterogeneous among patients suffering from congenital erythropoietic porphyria (CEP) suggesting a modulation of the disease (UROS deficiency) by environmental factors and modifier genes. A KI model of CEP due to a missense mutation of UROS gene present in human has been developed on 3 congenic mouse strains (BALB/c, C57BL/6, and 129/Sv) in order to study the impact of genetic background on disease severity. To detect putative modifiers of disease expression in congenic mice, hematologic data, iron parameters, porphyrin content and tissue samples were collected. Regenerative hemolytic anemia, a consequence of porphyrin excess in RBCs, had various expressions: 129/Sv mice were more hemolytic, BALB/c had more regenerative response to anemia, C57BL/6 were less affected. Iron status and hemolysis level were directly related: C57BL/6 and BALB/c had moderate hemolysis and active erythropoiesis able to reduce iron overload in the liver, while, 129/Sv showed an imbalance between iron release due to hemolysis and erythroid use. The negative control of hepcidin on the ferroportin iron exporter appeared strain specific in the CEP mice models tested. Full repression of hepcidin was observed in BALB/c and 129/Sv mice, favoring parenchymal iron overload in the liver. Unchanged hepcidin levels in C57BL/6 resulted in retention of iron predominantly in reticuloendothelial tissues. These findings open the field for potential therapeutic applications in the human disease, of hepcidin agonists and iron depletion in chronic hemolytic anemia.

Targeted gene therapy in human-induced pluripotent stem cells from a patient with primary hyperoxaluria type 1 using CRISPR/Cas9 technology.

Primary hyperoxaluria type 1 (PH1) is an inherited metabolic disorder caused by a deficiency of the peroxisomal enzyme alanine-glyoxylate aminotransferase (AGT), which leads to overproduction of oxalate by the liver and results in urolithiasis, nephrocalcinosis and renal failure. The only curative treatment for PH1 is combined liver and kidney transplantation, which is limited by the lack of suitable organs, significant complications, and the life-long requirement for immunosuppressive agents to maintain organ tolerance. Hepatocyte-like cells (HLCs) generated from CRISPR/Cas9 genome-edited human-induced pluripotent stem cells would offer an attractive unlimited source of autologous gene-corrected liver cells as an alternative to orthotopic liver transplantation (OLT). Here we report the CRISPR/Cas9 nuclease-mediated gene targeting of a single-copy AGXT therapeutic minigene into the safe harbour AAVS1 locus in PH1-induced pluripotent stem cells (PH1-iPSCs) without off-target inserts. We obtained a robust expression of a codon-optimized AGT in HLCs derived from AAVS1 locus-edited PH1-iPSCs. Our study provides the proof of concept that CRISPR/Cas9-mediated integration of an AGXT minigene into the AAVS1 safe harbour locus in patient-specific iPSCs is an efficient strategy to generate functionally corrected hepatocytes, which in the future may serve as a source for an autologous cell-based gene therapy for the treatment of PH1.

Generation of induced pluripotent stem cells-derived hepatocyte-like cells for ex vivo gene therapy of primary hyperoxaluria type 1.

Primary hyperoxaluria type 1 (PH1) is a rare autosomal recessive disorder of the liver metabolism due to functional deficiency of the peroxisomal enzyme alanine:glyoxylate aminotransferase (AGT). AGT deficiency results in overproduction of oxalate which complexes with calcium to form insoluble calcium-oxalate salts in urinary tracts, ultimately leading to end-stage renal disease. Currently, the only curative treatment for PH1 is combined liver-kidney transplantation, which is limited by donor organ shortage and lifelong requirement for immunosuppression. Transplantation of genetically modified autologous hepatocytes is an attractive therapeutic option for PH1. However, the use of fresh primary hepatocytes suffers from limitations such as organ availability, insufficient cell proliferation, loss of function, and the risk of immune rejection. We developed patient-specific induced pluripotent stem cells (PH1-iPSCs) free of reprogramming factors as a source of renewable and genetically defined autologous PH1-hepatocytes. We then investigated additive gene therapy using a lentiviral vector encoding wild-type AGT under the control of the liver-specific transthyretin promoter. Genetically modified PH1-iPSCs successfully provided hepatocyte-like cells (HLCs) that exhibited significant AGT expression at both RNA and protein levels after liver-specific differentiation process. These results pave the way for cell-based therapy of PH1 by transplantation of genetically modified autologous HLCs derived from patient-specific iPSCs.

CRISPR-Cas9 genome editing induces megabase-scale chromosomal truncations.

CRISPR-Cas9 is a promising technology for genome editing. Here we use Cas9 nuclease-induced double-strand break DNA (DSB) at the UROS locus to model and correct congenital erythropoietic porphyria. We demonstrate that homology-directed repair is rare compared with NHEJ pathway leading to on-target indels and causing unwanted dysfunctional protein. Moreover, we describe unexpected chromosomal truncations resulting from only one Cas9 nuclease-induced DSB in cell lines and primary cells by a p53-dependent mechanism. Altogether, these side effects may limit the promising perspectives of the CRISPR-Cas9 nuclease system for disease modeling and gene therapy. We show that the single nickase approach could be safer since it prevents on- and off-target indels and chromosomal truncations. These results demonstrate that the single nickase and not the nuclease approach is preferable, not only for modeling disease but also and more importantly for the safe management of future CRISPR-Cas9-mediated gene therapies.

Missense UROS mutations causing congenital erythropoietic porphyria reduce UROS homeostasis that can be rescued by proteasome inhibition.

Congenital erythropoietic porphyria (CEP) is an inborn error of heme biosynthesis characterized by uroporphyrinogen III synthase (UROS) deficiency resulting in deleterious porphyrin accumulation in blood cells responsible for hemolytic anemia and cutaneous photosensitivity. We analyzed here the molecular basis of UROS impairment associated with twenty nine UROS missense mutations actually described in CEP patients. Using a computational and biophysical joint approach we predicted that most disease-causing mutations would affect UROS folding and stability. Through the analysis of enhanced green fluorescent protein-tagged versions of UROS enzyme we experimentally confirmed these data and showed that thermodynamic instability and premature protein degradation is a major mechanism accounting for the enzymatic deficiency associated with twenty UROS mutants in human cells. Since the intracellular loss in protein homeostasis is in excellent agreement with the in vitro destabilization, we used molecular dynamic simulation to rely structural 3D modification with UROS disability. We found that destabilizing mutations could be clustered within three types of mechanism according to side chain rearrangements or contact alterations within the pathogenic UROS enzyme so that the severity degree correlated with cellular protein instability. Furthermore, proteasome inhibition using bortezomib, a clinically available drug, significantly enhanced proteostasis of each unstable UROS mutant. Finally, we show evidence that abnormal protein homeostasis is a prevalent mechanism responsible for UROS deficiency and that modulators of UROS proteolysis such as proteasome inhibitors or chemical chaperones may represent an attractive therapeutic option to reduce porphyrin accumulation and prevent skin photosensitivity in CEP patients when the genotype includes a missense variant.

Therapeutic potential of proteasome inhibitors in congenital erythropoietic porphyria.

Congenital erythropoietic porphyria (CEP) is a rare autosomal recessive disorder characterized by uroporphyrinogen III synthase (UROS) deficiency resulting in massive porphyrin accumulation in blood cells, which is responsible for hemolytic anemia and skin photosensitivity. Among the missense mutations actually described up to now in CEP patients, the C73R and the P248Q mutations lead to a profound UROS deficiency and are usually associated with a severe clinical phenotype. We previously demonstrated that the UROS(C73R) mutant protein conserves intrinsic enzymatic activity but triggers premature degradation in cellular systems that could be prevented by proteasome inhibitors. We show evidence that the reduced kinetic stability of the UROS(P248Q) mutant is also responsible for increased protein turnover in human erythroid cells. Through the analysis of EGFP-tagged versions of UROS enzyme, we demonstrate that both UROS(C73R) and UROS(P248Q) are equally destabilized in mammalian cells and targeted to the proteasomal pathway for degradation. We show that a treatment with proteasomal inhibitors, but not with lysosomal inhibitors, could rescue the expression of both EGFP-UROS mutants. Finally, in CEP mice (Uros(P248Q/P248Q)) treated with bortezomib (Velcade), a clinically approved proteasome inhibitor, we observed reduced porphyrin accumulation in circulating RBCs and urine, as well as reversion of skin photosensitivity on bortezomib treatment. These results of medical importance pave the way for pharmacologic treatment of CEP disease by preventing certain enzymatically active UROS mutants from early degradation by using proteasome inhibitors or chemical chaperones.

Metabolic correction of congenital erythropoietic porphyria with iPSCs free of reprogramming factors.

Congenital erythropoietic porphyria (CEP) is due to a deficiency in the enzymatic activity of uroporphyrinogen III synthase (UROS); such a deficiency leads to porphyrin accumulation and results in skin lesions and hemolytic anemia. CEP is a candidate for retrolentivirus-mediated gene therapy, but recent reports of insertional leukemogenesis underscore the need for safer methods. The discovery of induced pluripotent stem cells (iPSCs) has opened up new horizons in gene therapy because it might overcome the difficulty of obtaining sufficient amounts of autologous hematopoietic stem cells for transplantation and the risk of genotoxicity. In this study, we isolated keratinocytes from a CEP-affected individual and generated iPSCs with two excisable lentiviral vectors. Gene correction of CEP-derived iPSCs was obtained by lentiviral transduction of a therapeutic vector containing UROS cDNA under the control of an erythroid-specific promoter shielded by insulators. One iPSC clone, free of reprogramming genes, was obtained with a single proviral integration of the therapeutic vector in a genomic safe region. Metabolic correction of erythroblasts derived from iPSC clones was demonstrated by the disappearance of fluorocytes. This study reports the feasibility of porphyria gene therapy with the use of iPSCs.

Neonatal bone marrow transplantation prevents liver disease in a murine model of erythropoietic protoporphyria.

BACKGROUND & AIMS: Erythropoietic protoporphyria (EPP) is an inherited disorder of heme biosynthesis caused by partial ferrochelatase deficiency, resulting in protoporphyrin IX (PPIX) accumulation in erythrocytes, responsible for skin photosensitivity. In some EPP patients, the development of cholestatic liver injury due to PPIX accumulation can lead to hepatic failure. In adult EPP mice, bone marrow transplantation (BMT) leads to skin photosensitivity correction but fails to reverse liver damages, probably because of the irreversible nature of liver fibrosis. Our aim was to determine the time course of liver disease progression in EPP mice and to evaluate the protective effect of BMT into neonates. METHODS: We studied the development of liver disease from birth in EPP mice, in relation with erythroid and hepatic PPIX accumulation. To prevent the development of liver disease, BMT was performed into newborn mice using a novel busulfan-mediated preconditioning assay. RESULTS: We showed that hepatic PPIX accumulates during the first 2 weeks and correlates with the onset of a progressive liver fibrosis in 12-day-old EPP mice. Transplantation of normal congenic hematopoietic stem cells into EPP neonates led to long-term donor hematopoiesis recovery. A full correction of erythroid PPIX accumulation and skin photosensitivity was obtained. Furthermore, five months after neonatal BMT, liver damage was almost completely prevented. CONCLUSIONS: We demonstrated for the first time that BMT could be successfully used to prevent liver disease in EPP mice and suggested that BMT would be an attractive therapeutic option to prevent severe liver dysfunction in EPP patients.

Modeling of congenital erythropoietic porphyria by RNA interference: a new tool for preclinical gene therapy evaluation.

BACKGROUND: Congenital erythropoietic porphyria (CEP) is a severe autosomal recessive disorder characterized by a deficiency in uroporphyrinogen III synthase (UROS), the fourth enzyme of the heme biosynthetic pathway. We recently demonstrated the definitive cure of a murine model of CEP by lentiviral vector-mediated hematopoietic stem cell (HSC) gene therapy. In the perspective of a gene therapy clinical trial, human cellular models are required to evaluate the therapeutic potential of lentiviral vectors in UROS-deficient cells. However, the rare incidence of the disease makes difficult the availability of HSCs derived from patients. METHODS: RNA interference (RNAi) has been used to develop a new human model of the disease from normal cord blood HSCs. Lentivectors were developed for this purpose. RESULTS: We were able to down-regulate the level of human UROS in human cell lines and primary hematopoietic cells. A 97% reduction of UROS activity led to spontaneous uroporphyrin accumulation in human erythroid bone marrow cells of transplanted immune-deficient mice, recapitulating the phenotype of cells derived from patients. A strong RNAi-induced UROS inhibition allowed us to test the efficiency of different lentiviral vectors with the aim of selecting a safer vector. Restoration of UROS activity in these small hairpin RNA-transduced CD34(+) cord blood cells by therapeutic lentivectors led to a partial correction of the phenotype in vivo. CONCLUSIONS: The RNAi strategy is an interesting new tool for preclinical gene therapy evaluation.

Effective gene therapy of mice with congenital erythropoietic porphyria is facilitated by a survival advantage of corrected erythroid cells.

Achieving long-term expression of a therapeutic gene in a given hematopoietic lineage remains an important goal of gene therapy. Congenital erythropoietic porphyria (CEP) is a severe autosomal-recessive disorder characterized by a deficiency in uroporphyrinogen III synthase (UROS), the fourth enzyme of the heme biosynthetic pathway. We used a recently obtained murine model to check the feasibility of gene therapy in this disease. Lentivirus-mediated transfer of the human UROS cDNA into hematopoietic stem cells (HSCs) from Uros(mut248) mice resulted in a complete and long-term enzymatic, metabolic, and phenotypic correction of the disease, favored by a survival advantage of corrected red blood cells. These results demonstrate that the cure of this mouse model of CEP at a moderate transduction level supports the proof of concept of a gene therapy in this disease by transplantation of genetically modified hematopoietic stem cells.

Congenital erythropoietic porphyria: report of a novel mutation with absence of clinical manifestations in a homozygous mutant sibling.

In a Palestinian family, four siblings were shown to express typical and severe congenital erythropoietic porphyria (CEP). A new mutation of the uroporphyrinogen III synthase (UROS) gene was evidenced by systematic sequencing of the UROS gene: the substitution of serine by proline at the amino acid residue 47 (S47P) was present at the homozygous state in the four patients. The mother was heterozygous, the father was not examined. Surprisingly, in one unaffected sister, UROS activity was markedly deficient and UROS gene analysis showed a homozygous mutant profile. The deleterious role of the mutant S47P protein on UROS activity was demonstrated by prokaryotic expression. This observation is the first report of a healthy status associated with homozygosity for a mutation of UROS gene in a severely affected family. We then draw hypotheses to explain the protective phenotype in the homozygous healthy subject.

A bicistronic SIN-lentiviral vector containing G156A MGMT allows selection and metabolic correction of hematopoietic protoporphyric cell lines.

BACKGROUND: Erythropoietic protoporphyria (EPP) is an inherited disease characterised by a ferrochelatase (FECH) deficiency, the latest enzyme of the heme biosynthetic pathway, leading to the accumulation of toxic protoporphyrin in the liver, bone marrow and spleen. We have previously shown that a successful gene therapy of a murine model of the disease was possible with lentiviral vectors even in the absence of preselection of corrected cells, but lethal irradiation of the recipient was necessary to obtain an efficient bone marrow engraftment. To overcome a preconditioning regimen, a selective growth advantage has to be conferred to the corrected cells. METHODS: We have developed a novel bicistronic lentiviral vector that contains the human alkylating drug resistance mutant O(6)-methylguanine DNA methyltransferase (MGMT G156A) and FECH cDNAs. We tested their capacity to protect hematopoietic cell lines efficiently from alkylating drug toxicity and correct enzymatic deficiency. RESULTS: EPP lymphoblastoid (LB) cell lines, K562 and cord-blood-derived CD34(+) cells were transduced at a low multiplicity of infection (MOI) with the bicistronic constructs. Resistance to O(6)-benzylguanine (BG)/N,N'-bis(2-chloroethyl)-N-nitrosourea (BCNU) was clearly shown in transduced cells, leading to the survival and expansion of provirus-containing cells. Corrected EPP LB cells were selectively amplified, leading to complete restoration of enzymatic activity and the absence of protoporphyrin accumulation. CONCLUSIONS: This study demonstrates that a lentiviral vector including therapeutic and G156A MGMT genes followed by BG/BCNU exposure can lead to a full metabolic correction of deficient cells. This vector might form the basis of new EPP mouse gene therapy protocols without a preconditioning regimen followed by in vivo selection of corrected hematopoietic stem cells.

Highly efficient lentiviral gene transfer in CD34+ and CD34+/38-/lin- cells from mobilized peripheral blood after cytokine prestimulation.

Because mobilized peripheral blood (mPB) represents an attractive source of cells for gene therapy, we investigated lentiviral gene transfer in CD34(+) cells and the stem/progenitor-cell-enriched CD34(+)/38(-)/lin(-) cell subset isolated from mPB. In this study, we used an optimized third-generation self-inactivating lentiviral vector containing both the central polypurine tract and the woodchuck hepatitis posttranscriptional regulatory element sequences and encoding enhanced green fluorescent protein (EGFP) under the control of the elongation factor lalpha promoter. This lentivector was first used to compare multiplicity of infection (MOI)-dependent gene transfer efficiency in cord blood (CB) versus mPB CD34(+)-derived cells, colony-forming cells (CFCs), and long-term culture-initiating cells (LTC-ICs). Results showed a difference in the percentage of transduced cells particularly significant at low MOIs. A plateau was reached where 15% and 25% of CB and mPB cells, respectively, remained refractory to lentiviral trans-duction. Effects of a cytokine prestimulation period (18 hours) with interleukin-3, stem cell factor, Flt-3 ligand, and thrombopoietin were then analyzed in total cells, CFCs, and LTC-ICs derived from mPB CD34(+) cells. Transduction levels in those conditions demonstrated a two- and fourfold increase in CFCs and LTC-ICs, respectively, compared with unstimulated (<3 hours) control cells. Moreover, using the same transduction protocol, we were able to efficiently transduce CD34(+)/38(-)/lin(-) cells isolated from mPB, with up to >85% of colonies derived from LTC-ICs expressing EGFP and gene transfer levels remaining stable for 10 weeks in liquid culture. We therefore demonstrate a highly efficient gene transfer in this therapeutically relevant target cell population.