Bioengineered PBGD variant improves the therapeutic index of gene therapy vectors for acute intermittent porphyria.

A first-in-human gene therapy trial using a recombinant adeno-associated viral (rAAV) vector for acute intermittent porphyria (AIP) reveals that higher doses would be required to reach therapeutic levels of the porphobilinogen deaminase (PBGD) transgene. We developed a hyperfunctional PBGD protein to improve the therapeutic index without increasing vector dose. A consensus protein sequence from 12 mammal species was compared to the human PBGD sequence, and eight amino acids were selected. I291M and N340S variants showed the highest increase in enzymatic activity when expressed in prokaryotic and eukaryotic systems. In silico analysis indicates that isoleucine 291 to methionine and asparagine 340 to serine variants did not affect the active site of the enzyme. In vitro analysis indicated a synergistic interaction between these two substitutions that improve kinetic stability. Finally, full protection against a phenobarbital-induced attack was achieved in AIP mice after the administration of 1 × 1011 gc/kg of rAAV2/8-PBGD-I291M/N340S vector; three times lower than the dose required to achieve full protection with the control rAAV2/8-hPBGD vector. In conclusion, we have developed and characterized a hyperfunctional PBGD protein. The inclusion of this variant sequence in a rAAV2/8 vector allows the effective dose to be lowered in AIP mice.

Computational disease model of phenobarbital-induced acute attacks in an acute intermittent porphyria mouse model.

INTRODUCTION: Acute intermittent porphyria (AIP) is characterized by hepatic over-production of the heme precursors when aminolevulinic acid (ALA)-synthase 1 is induced by endogenous or environmental factors. The aim of this study was to develop a semi-mechanistic computational model to characterize urine accumulation of heme precursors during acute attacks based on experimental pharmacodynamics data and support the development of new therapeutic strategies. METHODS: Male AIP mice received recurrent phenobarbital challenge starting on days 1, 9, 16 and 30. 24-h urine excretion of ALA, porphobilinogen (PBG) and porphyrins from challenges D1, D9 and D30 constituted the training data set to build the mechanistic model using the population approach. In a second study, porphyrin and porphyrin precursor excretion from challenge D16 were used as a validation data set. RESULTS: The computational model presented the following features: (i) urinary excretion of ALA, PBG and porphyrins was governed by unmeasured circulating heme precursor amounts, (ii) the circulating amounts of ALA and PBG were the precursors of circulating amounts of PBG and porphyrins, respectively, and (iii) the phenobarbital effect linearly increased the synthesis of circulating ALA and PBG levels. The model displayed good parameter precision (coefficient of variation below 32% in all parameters), and adequately described the experimental data. Finally, a theoretical hemin effect was implemented to illustrate the applicability of the model to dosage optimization in drug therapies. CONCLUSIONS: A semi-mechanistic disease model was successfully developed to describe the temporal evolution of urinary heme precursor excretion during recurrent biochemical-induced acute attacks in AIP mice. This model represents the first computational approach to explore and optimize current and new therapies.

Glucose metabolism during fasting is altered in experimental porphobilinogen deaminase deficiency.

Porphobilinogen deaminase (PBGD) haploinsufficiency (acute intermittent porphyria, AIP) is characterized by neurovisceral attacks when hepatic heme synthesis is activated by endogenous or environmental factors including fasting. While the molecular mechanisms underlying the nutritional regulation of hepatic heme synthesis have been described, glucose homeostasis during fasting is poorly understood in porphyria. Our study aimed to analyse glucose homeostasis and hepatic carbohydrate metabolism during fasting in PBGD-deficient mice. To determine the contribution of hepatic PBGD deficiency to carbohydrate metabolism, AIP mice injected with a PBGD-liver gene delivery vector were included. After a 14 h fasting period, serum and liver metabolomics analyses showed that wild-type mice stimulated hepatic glycogen degradation to maintain glucose homeostasis while AIP livers activated gluconeogenesis and ketogenesis due to their inability to use stored glycogen. The serum of fasted AIP mice showed increased concentrations of insulin and reduced glucagon levels. Specific over-expression of the PBGD protein in the liver tended to normalize circulating insulin and glucagon levels, stimulated hepatic glycogen catabolism and blocked ketone body production. Reduced glucose uptake was observed in the primary somatosensorial brain cortex of fasted AIP mice, which could be reversed by PBGD-liver gene delivery. In conclusion, AIP mice showed a different response to fasting as measured by altered carbohydrate metabolism in the liver and modified glucose consumption in the brain cortex. Glucose homeostasis in fasted AIP mice was efficiently normalized after restoration of PBGD gene expression in the liver.

Radiotherapy protocols for mouse cancer model.

Radiotherapy is a crucial treatment modality for cancer patients, with approximately 60% of individuals undergoing ionizing radiation as part of their disease management. In recent years, there has been a growing trend toward minimizing irradiation fields through the use of image-guided dosimetry and innovative technologies. These advancements allow for selective irradiation, delivering higher local doses while reducing the number of treatment sessions. Consequently, computer-assisted methods have significantly enhanced the effectiveness of radiotherapy in the curative and palliative treatment of various cancers. Although radiation therapy alone can effectively achieve local control in some cancer types, it may not be sufficient for others. As a result, further preclinical research is necessary to explore novel approaches including new schedules of radiotherapy treatments. Unfortunately, there is a concerning lack of correlation between clinical outcomes and experiments conducted on mouse models. We hypothesize that this disparity arises from the differences in irradiation strategies employed in preclinical studies compared to those used in clinical practice, which ultimately affects the translatability of findings to patients. In this study, we present two comprehensive radiotherapy protocols for the treatment of orthotopic melanoma and glioblastoma tumors. These protocols utilize a small animal radiation research platform, which is an ideal radiation device for delivering localized and precise X-ray doses to the tumor mass. By employing these platforms, we aim to limit the side effects associated with irradiating healthy surrounding tissues. Our detailed protocols offer a valuable framework for conducting preclinical studies that closely mimic clinical radiotherapy techniques, bridging the gap between experimental results and patient outcomes.

Flow cytometry-assisted quantification of immune cells infiltrating irradiated tumors in mice.

The immunomodulatory properties of local hypofractionated radiotherapy are known to promote the generation of anti-tumor immune responses. Such responses are largely due to the infiltration of cytotoxic lymphocytes (TILs) into the tumors that are able to destroy malignant lesions. In this context, characterizing the tumor immune microenvironment following radiotherapy is crucial for the study of its mechanism of action. Flow cytometry-based analyses are frequently used to elucidate changes in the tumor immune microenvironment. The use of a fluorochrome-conjugated antibody panel is currently a standard technique to assess the number and phenotype of immune cell populations infiltrating the tumors. Here, we describe a method to isolate and quantify TILs based on flow-cytometry in mammary carcinoma-bearing mice that undergo a local hypofractionated radiotherapy regimen consisting of 3 consecutive doses of 8 Gy. With some adaptations, this protocol can be successfully applied to a diverse range of transplantable and inducible solid mouse tumors of different origins.

Methods to assess radiation induced abscopal responses in mice.

Radiotherapy (RT) can work together with the immune system to eliminate cancer. It can cause immunogenic cell death and facilitate tumor neoantigen presentation and thereby the cross-priming of tumor-specific T-lymphocytes, turning irradiated tumors into in-situ vaccines. Accumulating preclinical and clinical evidence indicates that RT in conjunction with ICB leads to systemic anti-tumor immune responses, thus stimulating interest in using ICB to overcome primary and acquired cancer resistance to radiotherapy. However, the systemic effects (abscopal effects) obtained to date are far from being acceptable for clinical translation. In this context, multiple preclinical mouse models have demonstrated that a variety of immunotherapy agents can be delivered locally to enhance antitumor immunity both in a local and systemic fashion. Using two slightly asynchronous and anatomically distant subcutaneous B16OVA tumors in syngeneic immunocompetent hosts (C57BL/6), we describe the feasibility of a local immunotherapy treatment given in combination with external beam irradiation, which exerts immune-mediated antitumor effects in mice and humans upon intratumoral delivery. With minor variations, the same technique can be easily applied to a variety of mouse transplantable tumors.

A simple method to assess clonogenic survival of irradiated cancer cells.

The clonogenic assay is an in vitro method based on the ability of a single cell to proliferate indefinitely into a colony. This assay is the gold standard method to analyze cell viability and quantify reproductive cell survival fraction after treatment with ionizing radiation and other cytotoxic agents in vitro. After the cytotoxic effect, only some cells retain their ability to grow from one cell and form colonies. The colony is defined to consist of at least 50 cells. The radiosensitivity of each cell line may vary. Thus, characterizing cell sensitivity following radiation is crucial to choose the optimum radiotherapy dose. Here, we describe a method to test the in vitro capability of cell lines to form colonies following radiation treatment. This assay allows to analyze the efficacy of specific treatments on the cell reproductivity of cell lines With some adaptations, this protocol can be essentially applied to analyze the cell proliferation rate after different doses of irradiation on many different cell lines.

Intratumoral BO-112 in combination with radiotherapy synergizes to achieve CD8 T-cell-mediated local tumor control.

BACKGROUND: Radioimmunotherapy combines irradiation of tumor lesions with immunotherapy to achieve local and abscopal control of cancer. Most immunotherapy agents are given systemically, but strategies for delivering immunotherapy locally are under clinical scrutiny to maximize efficacy and avoid toxicity. Local immunotherapy, by injecting various pathogen-associated molecular patterns, has shown efficacy both preclinically and clinically. BO-112 is a viral mimetic based on nanoplexed double-stranded RNA (poly I:C) which exerts immune-mediated antitumor effects in mice and humans on intratumoral delivery. BO-112 and focal irradiation were used to make the proof-of-concept for local immunotherapy plus radiation therapy combinations. METHODS: Murine transplantable tumor cell lines (TS/A, MC38 and B16-OVA) were used to show increased immunogenic features under irradiation, as well as in bilateral tumor models in which only one of the lesions was irradiated or/and injected with BO-112. Flow cytometry and multiplex tissue immunofluorescence were used to determine the effects on antitumor immunity. Depletions of immune cell populations and knockout mice for the IFNAR and BATF-3 genes were used to delineate the immune system requirements for efficacy. RESULTS: In cultures of TS/A breast cancer cells, the combination of irradiation and BO-112 showed more prominent features of immunogenic tumor cell death in terms of calreticulin exposure. Injection of BO-112 into the tumor lesion receiving radiation achieved excellent control of the treated tumor and modest delays in contralateral tumor progression. Local effects were associated with more prominent infiltrates of antitumor cytotoxic tumor lymphocytes (CTLs). Importantly, local irradiation plus BO-112 in one of the tumor lesions that enhanced the therapeutic effects of radiotherapy on distant irradiated lesions that were not injected with BO-112. Hence, this beneficial effect of local irradiation plus BO-112 on a tumor lesion enhanced the therapeutic response to radiotherapy on distant non-injected lesions. CONCLUSION: This study demonstrates that local BO-112 immunotherapy and focal irradiation may act in synergy to achieve local tumor control. Irradiation plus BO-112 in one of the tumor lesions enhanced the therapeutic effects on distant irradiated lesions that were not injected with BO-112, suggesting strategies to treat oligometastatic patients with lesions susceptible to radiotherapy and with at least one tumor accessible for repeated BO-112 intratumoral injections.

Assessment of hypoxia by pimonidazole staining following radiotherapy.

The rapid proliferation of cancer cells and the aberrant vasculature present in most solid tumors frequently result in the lack of oxygen generating a hypoxic tumor microenvironment. Low levels of oxygen not only affect the tumor cell biology and tumorigenesis, but also the other components of the tumor microenvironment such as the tumor stroma and the immune infiltrate, promoting a more suppressive environment. In addition, tumor hypoxia has been associated with reduced sensitivity to chemotherapy (CH) and radiotherapy (RT), leading to poor outcomes in cancer patients. Therefore, the evaluation of tumor oxygen status has become clinically relevant. Tumor hypoxia can be assessed by different methods that include the analysis of the oxygen concentration or the expression of endogenous markers directly related to hypoxia. In this paper, we focus on the use of the hypoxia-specific marker pimonidazole as a straightforward way to measure tumor hypoxia following radiotherapy in a preclinical melanoma model.

Recombinant porphobilinogen deaminase targeted to the liver corrects enzymopenia in a mouse model of acute intermittent porphyria.

Correction of enzymatic deficits in hepatocytes by systemic administration of a recombinant protein is a desired therapeutic goal for hepatic enzymopenic disorders such as acute intermittent porphyria (AIP), an inherited porphobilinogen deaminase (PBGD) deficiency. Apolipoprotein A-I (ApoAI) is internalized into hepatocytes during the centripetal transport of cholesterol. Here, we generated a recombinant protein formed by linking ApoAI to the amino terminus of human PBGD (rhApoAI-PBGD) in an attempt to transfer PBGD into liver cells. In vivo experiments showed that, after intravenous injection, rhApoAI-PBGD circulates in blood incorporated into high-density lipoprotein (HDL), penetrates into hepatocytes, and crosses the blood-brain barrier, increasing PBGD activity in both the liver and brain. Consistently, the intravenous administration of rhApoAI-PBGD or the hyperfunctional rApoAI-PBGD-I129M/N340S (rApoAI-PBGDms) variant efficiently prevented and abrogated phenobarbital-induced acute attacks in a mouse model of AIP. One month after a single intravenous dose of rApoAI-PBGDms, the protein was still detectable in the liver, and hepatic PBGD activity remained increased above control values. A long-lasting therapeutic effect of rApoAI-PBGDms was observed after either intravenous or subcutaneous administration. These data describe a method to deliver PBGD to hepatocytes with resulting enhanced hepatic enzymatic activity and protection against AIP attacks in rodent models, suggesting that the approach might be an effective therapy for AIP.

Consolidating Radiotherapy with Immunotherapy.

Radiotherapy and immunotherapy can be concomitantly or sequentially combined seeking synergistic effects in terms of control of irradiated tumors and abscopal effects on nonirradiated lesions. Clinical-trial testing of such combinations faces several obstacles to demonstrate efficacy and needs improvements in trial design, patient selection, evaluation of results and biomarker discovery.See related article by Foster et al., p. 5510.

An Inducible Promoter Responsive to Different Porphyrinogenic Stimuli Improves Gene Therapy Vectors for Acute Intermittent Porphyria.

Porphobilinogen deaminase (PBGD) gene therapy represents a promising therapeutic option for acute intermittent porphyria (AIP) patients suffering recurrent acute attacks. A first-in-human Phase I clinical trial confirmed the safety and tolerability of adeno-associated virus (AAV)-AAT-PBGD gene therapy, but higher doses and/or more efficient vectors are needed to achieve therapeutic expression of the transgene. This study assayed the insertion into the promoter of a short enhancer element able to induce transgene expression during exposure to endogenous and exogenous stimuli related to the pathology of the disease. The inclusion in tandem of two elements of the minimal functional sequence of human δ-aminolevulinic acid synthase drug-responsive enhancing sequence (ADRES) positioned upstream of the promoter strongly induced transgene expression in the presence of estrogens, starvation, and certain drugs known to trigger attacks in porphyria patients. The inclusion of two ADRES motives in an AAV vector improved therapeutic efficacy, reducing 10-fold the effective dose in AIP mice. In conclusion, the inclusion of specific enhancer elements in the promoter of gene therapy vectors for AIP was able to overexpress the therapeutic transgene when it is most needed, at the time when porphyrinogenic factors increase the demand for hepatic heme and precipitate acute porphyria attacks.

Vitamin D-binding protein as a biomarker of active disease in acute intermittent porphyria.

UNLABELLED: Acute intermittent porphyria (AIP) is an autosomal dominant metabolic disorder caused by a deficiency of hepatic porphobilinogen deaminase (PBGD). The disease is characterized by life threatening acute neurovisceral attacks. The aim of this study was to identify metabolites secreted by the hepatocytes that reflect differential metabolic status in the liver and that may predict response to the acute attack treatment. Plasma vitamin D binding protein (VDBP) from a mouse model of AIP displayed an abnormal migration in 2D-electrophoresis that is efficiently recovered upon gene therapy leading to liver specific over-expression of the PBGD protein. The change in VDBP mobility results from a differential isoelectric point suggesting a post-translational modification that takes place preferably in the liver. Liquid chromatography-mass spectrometry (LC-MS) analysis of human samples before and after glycosidase treatment revealed glycosylated plasma VDBP specifically in patients with recurrent attacks of AIP. Glycosylated VDBP recovered normal values in three severely afflicted AIP patients submitted to therapeutic liver transplantation. Our findings suggest that post-translational modification of VDBP might be considered as a promising biomarker to study and monitor the liver metabolic status in patients with AIP. SIGNIFICANCE: We describe an increased glycosylation of VDBP in porphyric livers. Normal glycosylation was recovered upon liver gene therapy in a mouse model of porphyria or after liver transplantation in severely afflicted patients with AIP. Moreover, quantification of glycosylated VDBP by our ELISA immunoassay or LC-MS protocol in patients undergoing PBGD-gene therapy (www.aipgene.org) may be used as a marker indicating improvement or normalization of the patient's hepatic metabolism. This article is part of a Special Issue entitled: HUPO 2014.

Innate functions of immunoglobulin M lessen liver gene transfer with helper-dependent adenovirus.

The immune system poses obstacles to viral vectors, even in the first administration to preimmunized hosts. We have observed that the livers of B cell-deficient mice were more effectively transduced by a helper-dependent adenovirus serotype-5 (HDA) vector than those of WT mice. This effect was T-cell independent as shown in athymic mice. Passive transfer of the serum from adenovirus-naïve WT to Rag1KO mice resulted in a reduction in gene transfer that was traced to IgM purified from serum of adenovirus-naïve mice. To ascribe the gene transfer inhibition activity to either adenoviral antigen-specific or antigen-unspecific functions of IgM, we used a monoclonal IgM antibody of unrelated specificity. Both the polyclonal and the irrelevant monoclonal IgM inhibited gene transfer by the HDA vector to either cultured hepatocellular carcinoma cells or to the liver of mice in vivo. Adsorption of polyclonal or monoclonal IgMs to viral capsids was revealed by ELISAs on adenovirus-coated plates. These observations indicate the existence of an inborn IgM mechanism deployed against a prevalent virus to reduce early post-infection viremia. In conclusion, innate IgM binding to adenovirus serotype-5 capsids restrains gene-transfer and offers a mechanism to be targeted for optimization of vector dosage in gene therapy with HDA vectors.