Treatment of IEM Where are we and where are we going

Treatment of IEM Where are we and where are we going November 18, 2008 John Mitchell Introduction  Lecture I    What is screening and how it can be applied Newborn screening  Past, present and future Examples TSD, Sickle cell Ethics Heterozygote screening    Personal genomics Lecture II  Treatment of genetic disease How are we doing?  What are different modalities of restoring homeostasis  Treatment of Metabolic diseases  Background History  Progress  Outlines  Types of therapy  Specific examples  Phenylketonuria  Lysosomal storage diseases  Urea cycle defects  Goal of Therapy     The goal of treatment is to restore normal homeostasis Homeostasis reflects the central tendency of a complex trait value Since the 1800s, it has been recognized that maintenance of a steady state is a universal feature of living systems All too often, our treatments are not sufficient to restore homeostasis Diabetes, Type I     Before the discovery of insulin, children used to die Studies of this simple hormone replacement have shown that we are far from a cure and restoring homeostasis This has pushed us to investigate other treatment options (pancreatic islet cell transplant) However, the main thrust of therapy is still intensive insulin management with multiple injections or pump How are we doing now? A review of inborn errors of metabolism Evaluation of Therapy     In 1985, Charles Scriver conducted a study in which they scored 351 diseases from MIM on the significance of their impact Found 25% presented at birth and 90% by end of puberty Life span reduced in 57% Although each disease was individually rare, they had a significant cumulative impact on childhood health Treatment of IEM      A subset of the 351 diseases that involved IEM were scored on success of treatment Complete relief in 12% Partial response in 40% No response in 48% Gave a good database to score subsequently (10 and 25 years later) Response to treatment 35 30 Number of conditions No response Partial<10 Partial≥10 Full response 25 20 15 10 5 0 1983 1993 2006 Mechanisms of Restoring Homeostasis 0% Restrict substrate Replace product Toxin removal Supplement enzyme cofactor Enzyme replacement therapy Inhibit toxin production or effect Liver transplantation Bone marrow transplantation Kidney transplantation 6% 3% 11% 11% 8% 12% 24% 18% 10% 20% 30% 40% 37% MMBID p180 What explains the improvement?  Availability of new technology? Understanding of pathophysiology?  Campeau et, al, 2008 60 PHENOTYPE GENOTYPE No of conditions 50 40 30 20 10 0 1880 1900 1920 1940 1960 1980 2000 PKU PKU Phenylalanine Phenylalanine Hydroxylase Tyrosine Success of Therapy for PKU      In the broadest sense, PKU is a genuine success story However, treatment still results in individuals who have an IQ 1/2 standard deviation below normal Specific holes Compliance with diet is poor What can we do to improve this? Types of Therapy 11 Chaperone PKU  SRT Diet  Neutral amino acid transport     Chaperone ERT Gene therapy Treatment via substrate reduction   Limit of phe intake Low protein food Treatment by Low-Phe Diet   Mainstay of treatment Optimal treatment requirements: Early onset (within 1 month of birth)  Continuous treatment throughout childhood and adolescence  Severe restriction of Phenylalanine intake while ensuring adequate protein for growth and development  Response to Early Treatment     Ameliorating the clinical impact of PKU Early treated children’s IQ scores approx. half SD lower than scores for their unaffected sibs and corresponding population High proportion of early-treated subjects exhibit some degree of intellectual impairment Most children function within the broad normal range of ability Subtle Deficits in Outcome     Impairment in problem solving, abstract reasoning, and executive functions More extrovert behaviour along with negative task orientation Increased frequency of neurotic and emotional disorders DISORDERED FUNCTION OF PREFRONTAL CORTEX Response to Termination of Treatment      Significant fall in the IQ score Abnormal neurologic features in later life Deviant EEG findings Decreased levels of NT metabolites Abnormal brain white matter on MRI The Modalities for Dietary Treatment: Implications     Alter body composition PKU patients incur low levels of trace minerals and cholesterol Absence of preformed arachidonic acid and C22:6 fatty acid Other? Summary  ADVANTAGES Near reversal of key biochemical abN  Improved neuropsychological performance  Prevention of neurologic deterioration   DISADVANTAGES Difficulty in obtaining full compliance  Need for complex social support  Risks of nutrient imbalance and deficiency  Large Neutral Amino Acids (LNAA)          Phenylalanine (Phe) Leucine Isoleucine Valine Tyrosine Tryptophan Methionine Histidine Threonine LAT1 & LAT2    LAT1 involved in transport of LNAA across BBB LAT2 is expressed primarily in kidneys and intestine Share many of same properties Characteristics of LATs    Specificity is broad Carrier is saturable, sterospecific and independent of sodium and energy System has trans-stimulation such that elevation of one LNAA results in exchange of other LNAA on the other side of the membrane LAT2     LNAA and cationic amino acids share an intestinal transporter Km of this transporter is 2 orders of magnitude higher than LAT1 By overloading this system with other LNAA, may prevent absorption of phe in intestine and therefore lead to lower blood phenylalanine Again a form of substrate inhibition Summary of Double Blind Study 1800 1600 1400 1200 1000 800 600 400 200 0 zero 1 week On Neo Phe 2 week Placebo E280K/E280K F299C/IVS12ntg1>a F299C/I65T/R408W micromol/L 11 Chaperone Mechanisms of IEM Co-Factor Deficiency BH4 Synthesis BH4 Phenylalanine PAH Tyrosine PKU and Cofactor Therapy    In 1999, it was discovered that giving high doses of BH4 to PKU patients resulted in improved phenylalanine levels Up to 60% of patients respond to a therapeutic dose of BH4 by a decrease of at least 30% of phe blood levels May act as a chaperone in high concentration 11 Chaperone NEJM 353;14 1489 What are Chaperones?     Chaperones assist a polypeptide chain to obtain its functional conformation and then to assist in the arrival at the site where it acts Stress to a cell can cause protein denaturation. The protein will lose its natural configuration and it will start to unfold Chaperones assist the damaged molecule to regain its functional conformation Disruption of the chaperone mechanism contributes to ageing and disease Am. J. Med. Genet. Vol.146A, 22 Pages: 2851-2859 BH4 and PKU     Will not work on most null mutations (these are the patients who need it most) Long term efficacy? Often still require diet but gives more flexibility Expense!! Identification of pharmacological chaperones    High-throughput ligand screen of over 1000 randomly selected pharmacological agents (J. Clin. Invest. Angel L. Pey, et al. 118:2858) Compared t 0.5 value of PAH in absence or presence of compounds Identified 4 compounds that enhanced thermal stability of PAH Figure 1 Four hit compounds found to stabilize PAH in the HTS and further detailed fluorescence analyses. (A) Representative thermal denaturation profiles of WT-PAH in the absence (black) or presence of 100 μM of the hit compounds I (red), II (green), III (light blue), and IV (dark blue), resulting from the HTS procedure as monitored by ANS fluorescence. (B) Chemical structures of compounds I, II, III, and IV. J. Clin. Invest. Angel L. Pey, et al. 118:2858 Enzyme Therapy   Enzyme Replacement  Heterologous partial transplantation of normal liver Enzyme Substitution  plant phenylalanine ammonia-lyase (PAL) converts phenylalanine to nontoxic t-cinnamic acid  The problems of this potential enzyme therapy have been the low stability in the circulation and the antigenicity of the plant enzyme Phe Degradation with PAL PAL Phenylalanine Ammonia Trans-cinnamic acid Tyrosine Phe Degradation with PAL Sarkissian et al Prc Natl Acad Sci 1999      3 prior concepts  AA are in equilibrium between various compartments of body fluids  PAL placed in the intestinal lumen affect all body pools  PAL placed in the intestinal lumen will act on both dietary Phe and endogenous run out of free Phe from bound pools used a chemically induced rat model PAL lowered intestinal, plasma, and tissue Phe Provided proof of both pharmacologic and physiological principle DISADVANTAGE: very high cost Peg-ylation     SC injection of PAL work very well to decrease Phe level However, SC injection of PAL is degraded PEG (polyethylene glycol) can be added to protect, prolong half-life and reduce immunogenicity in vivo. Works very well on mice…. Preclinical Studies of PEG-PAL   The PEG-PAL Phase II trial is expected to begin in the first half of 2009 and it is hoped that positive preclinical data showing sustained decreases in blood Phe levels in PKU mice will be replicated in humans. If proven safe and effective, PEG-PAL has tremendous potential to treat the entire spectrum of PKU patients by bringing their Phe levels down to normal levels. Gene Therapy  SOMATIC GENE THERAPY Cloned PAH cDNA  Recombinant adenoviral vector  Integration of gene into nuclear genome  Expression and transmission to daughter cells  Orthologous (PKU) mouse model  Clinical genetics, Harding, 2008, 74 iss:2 pg:97 -104   A group of over 40 genetic disorders Due to a deficiency of a lysosomal enzyme resulting in the accumulation of substrate in the cells Lysosomal Storage Disorders normal   Jointly affect an estimated 1:7,700 newborns Usually displaying progressive disease pattern, with wide spectrum of symptoms, signs and severity. affected LSD subdivision Sphingolipidoses Failure to degrade glycosphingolipids containing three or less carbohydrate residues. Fabry, Gaucher, ASM deficiency (Niemann Pick A,B), Metachromatic Leukodystrophy, Krabbe,…. Oligosaccharidoses Failure to degrade oligosaccharides Mucopolysaccharidoses Failure to degrade glycosaminoglycans MPS I (Hurler, Hurler Scheie, Scheie), Hunter, San Filippo, Morquio, Maroteaux-Lamy, … Others Fucosidosis, Mannosidosis, Sialidosis, Galactosialidosis,… Pompe, Mucolipidosis, Ceroid lipofuscinosis, … For reference, please see notes Pathogenesis of LSD     Lysosomal GSL may act to disrupt cell signaling inducing cell death Storage of lipids may be directly cytotoxic May also cause dysfunction by proinflammatory cascade Illustrates the effects of one block and how this will affect many other pathways MPS I Multi-systemic -L-iduronidase deficiency Lysosomal storage of GAG in multiple tissues • • • • • • • • • • • Central Nervous System Ears/Nose/Throat Eyes Teeth Airways Cardiovascular system Gastrointestinal system Joints Skeleton Peripheral Nervous System Other GAG Degradation Hurler MPS I - Spectrum of disease severity MOST SEVERE Mental retardation +++++ ATTENUATED - Communicating hydrocephalus Spinal cord compression Hearing loss Corneal clouding Skeletal abnormalities Joint restrictions Obstructive airway disease Cardiac (valvular) disease Carpal tunnel syndrome Dysostosis multiplex Inguinal or umbilical hernia +++ +++ +++ +++ +++++ +++++ +++++ +++++ +++++ +++++ +++ +/+++ ++ +++ ++++ ++++ +++ ++++ ++++ +++ ++ ++ +/+++ ++ +++ +/+++ +++ +/+ Neufeld EF, Muenzer J. The mucopolysaccharidoses. In: Scriver CR, Beaudet AL, Sly W, Valle D, eds. The Metabolic & Molecular Bases MPS I Mucopolysaccharidosis type I A disease with many faces Targeting the cause    Enzymes involved are secretory proteins synthesized in ER and post translationally modified with N-glycosylation and phosphorylation of mannose residues Newly synthesized enzyme may be secreted and taken up by neighboring cells Easy target because of uptake mechanism (M-6-P) and fact that need small amount for correction ERT Neurologic Clinics Volume 20 • Number 3 • August 2002 MPS-I ERT        Liver and size of spleen reduced Range of shoulder motion and elbow extension increased Increased rate of growth and reduction of GAGs in urine Increased FVC and six meter walk test Reduction urinary gags Some have reduced sleep apnea Difficult to answer efficacy questions now Side Effects in ERT    Infusion reactions treated with antihistamines or steroids Develop antibodies (IgG) Long term immune response is not known CNS disease in MPS I • • • • • Developmental decline (most severe only) Abnormal increase in head circumference Hydrocephalus Headaches Spinal cord compression Hydrocephalus, white matter abnormalities, subarachnoid cysts Enzyme Replacement Therapy     Does not pass blood brain barrier and hence does not influence the neurological component of the disease So how do we treat these children? Intrathecal therapy? Modified enzyme that can pass BBB? * SmPC of Aldurazyme® #G.M. Pastores, poster presentation ASHG 2003, The clinical benefit of Laronidase for the treatment of MPS I BMT in MPS I   Used in children with most severe MPS I Outcomes improved:     with normal or near normal developmental quotient (DQ>70 - motor scores always poor) when transplant was done in patients less than 2 years of age without significant CNS white matter involvement – hydrocephalus is not a contraindication without other significant major organ dysfunction Neurologic Clinics Volume 20 • Number 3 • August 2002 BMT     For MPS 1 positively influence rate of cognitive decline Positively influences most systemic functions, however bone disease is usually not beneficially affected and requires careful orthopedic management Still a big deal to do a BMT ERT as an adjunct to BMT Questions with ERT and BMT    It may be necessary to initiate ERT early in life to prevent irreversible organ and tissue damage How early is early (studies with Krabbe have shown that only BMT prior to onset of disease is effective) How do you deal with lack of effectiveness in different organs (ie reduction of gb3 in Fabry podocytes may require distinct isoform of the enzyme) Signs and symptoms of Type 1 Gaucher disease     Generalized fatigue Hepatosplenomegaly Loss of appetite Intestinal complaints   Increased bleeding tendency Subnormal levels of    blood platelets red blood cells white blood cells acid phosphatase plasma proteins  Elevated levels of   Skeletal system         Growth retardation Pain and degeneration of joints Loss of bone density widening of bones along the knee joint curvature of the bones spontaneous fractures Acute bone infarctions - "bone crises" Bone necrosis (death of tissue) Enzyme Replacement Therapy  Gaucher 1974/75 First ERT  At this point isolated from placenta but too little for sustained  Later developed CHO production system  Approved by FDA in 1994  Effect of Gaucher ERT       Decreases liver and spleen size Reduces bone pain Reverses abnormal blood counts Improved quality of life Quite a success ?poorer effect on bone (structural) and lungs Problems With Gaucher ERT    13% of patients develop antibodies to enzyme IV infusion CNS 5% of Gaucher exhibit signs of brain involvement (Most Type 3)  Principal manifestation is vertical gaze palsy  Smaller number exhibit progressive myoclonic epilepsy  Enzyme does not get to the brain  Small Molecule Therapeutics For LSD (Substrate Reduction)   Iminosugars are structural mimics of monosaccharides (where a nitrogen ring replaces the ring oxygen) Many occur naturally and are found in plants and microorganisms SRT Evolution     Miglustat (NB-DNJ) originally developed as an anti-viral as it inhibits alpha glucosidase 1 and 2 Viruses use host cells to glycosylate their envelope proteins so blocking this would throw a wrench into the machinery Unfortunately could not obtain high enough levels in vivo as an anti viral Further study found that lipid levels were decreased SRT Evolution    Platt et al (1994) discovered certain imino sugars inhibited ceramide glycotransferase (ie deoxynojirimicin) Rate limiting step in synthesis of most glycosphingolipids Although not successful for HIV therapy, initial studies documented safety data allowing for clinical trials in LSD SRT on mouse models    Tay Sachs: Observed reduction of GM2 ganglioside in the brain in Miglustat treated group Documented ability of NB-DNJ to cross BBB This is quite an exciting idea! SRT initial trials    Preclinical and clinical data from HIV trail allowed assessment of NB-DJN for Gaucher Type I Results showed improved organ volumes and hematological values allowing approval for use in patients unable or unwilling to take ERT Studies looking at combined ERT/SRT Challenges with SRT    Next challenge is to see if effective in treating neuronopathic LSD Preliminary results on 29 NP-C subjects show improvement in swallowing, audition and eye movement (not statistically significant) but early May need to treat prior to damage (again need for early detection) So how does this relate to LSDs? Chaperone    Many LSDs caused by missense mutation that alter folding but still maintain some catalytic activity Only properly folded proteins are excreted and misfolded proteins are degraded Theoretical treatment approach is to use chemical chaperones to overcome the misfolding/mistrafficking problem Imino Sugars for CMT    Imino sugars may also bind to enzyme and prevent them from being misfolded or inactivated For CMT, entry into the ER is necessary and need adequate concentration This often needs high oral dose and may be complicated with side effects (DNJ may inhibit intestinal sucrase/isomaltase complex) Methods of Treating LSD       Symptomatic/supportive ERT BMT Gene Therapy SRT Chaperones Final Thoughts    Clear that the more we understand about how a disease happens, the more we will be able to direct our therapy towards it (ie Chaperones for specific mutations) Importance of mouse/animal models Importance of expression systems (can quickly generate CMT via this method) Final thoughts    Difficult to prove efficacy in controlled studies in diseases that are so rare Does this mean they should not be approved? 6/19 new drugs for rare diseases have been refused reimbursement Final Thoughts     Need incentives to generate therapies for these rare diseases Not enough companies showing interest because of small numbers and huge development costs Government initiatives? Patient/family initiatives? Cost of Carbaglu   10 kg baby $250 000/ year 12 year old $1 000 000/ year Cost per day Name DIN Strength Dosage Regimen 3 capsules 0.1875-0.75 vials 0.375-1.5 vials Cost per Unit $108.551 $2,440.00 2 Cost per Day Zavesca Cerezyme Cerezyme 0225051 9 0224175 1 0223069 4 100mg/capsul e 400IU/vial 200IU/vial $325.65 $457.50$1,830.00 $457.50$1,830.00 $1,220.00 2 1 AQPP, October 2004 2 Publicly available prices as per the Patented Medicines Regulations And finally   Just because they are expensive… Should Canadians be refused access to potentially new treatments for formally untreatable disease just because it is expensive? Acknowledgments   Charles Scriver Phillippe Campeau