Hemolytic uremic syndrome (HUS) Generally
HUS is classified as typical versus atypical, and most cases are assocaited with acute kidney injruy. Typical HUS is caused by Shiga toxin producing organisms (most commoly E. coli and Shigella dysenteriae). The mianstay of therapy is supportive care. Atypical HUS (aHUS) is most commonly caused by defects in the regulation of the alternative pathway of complement. (Brodsky, US 2018/0246082).
HUS most frequently occurs in children under the age of 5, with an annual incidence of 6.1 cases per 100k children. The presentation is generally heralded by diarrhea, which is often bloodly. Most cases (including more than 90% of those in children, are secondary to infection with Escherichia coli serotypes (see below). (Noris, “Ayptical Hemolytic-Uremic syndrome” New England J. Medicine, 2009, 361, 1676-87. )
HUS is characterized by thrombocytopenia, microangiopathic hemolytic anemia, and acute renal failure. Thrombocytopenia can be diagnosed as having one or more of (i) a platelet count that is less than 150k mm3 (e.g., less than 60k mm3), (ii) a reduction in platelet survival time, reflecting enhanced platelet disruption in the circulation and (iii) giant platelets observed in a peripheral smear, which is consistent with secondary activaiton of thrombocytopoiesis. Microangiopathic hemolytic anemia can be diagnosed as having one or more of (i hemoglobin concentrations that are less than 10 mg/dL (e.g., less than 6.5 mg/dL), (ii) increased serum lactate dehydrogenase (LDH) concentrations (e.g., greater than 460 U/L), (iii) hyperbilirubienia, reticulocytosis, circulating free hemoglobin and low or undetectable haptoglobin concetnrations and (iv) the detection of fragmented red blood cells (shistocytes) with the typical aspect of burr or helmet cells in the peripheral smear together with a negative Coombs test (Kaplan (1992), ISBN 0824786637, Informa Health Care and Zipfel, Springer (2005), ISBN 3764371668.
Various Types
HUS is classified into three primary types: (1) HUS due to infections, often associated with diarrhea (D+HUS), with the rare exception of HUS due to a severe disseminated infection caused by Streptococcus; (2) HUS related to complement abnormalities or related to factor-ADAMTS13 deficit, such HUS is also known as “atypical HUS” and is not diarrhea associated (D-HUS); and (3) HUS of unknown etiology that usually occurs in the course of systemic diseases or physiopathologic conditions such as pregnancy, after transplantation or after drug assumption. (Bertoni, World J. Nephrol. 2013 Aug 6; 2(3): 56–76.
Hemolytic uremic syndrome (HUS) is characterized by actue onset of non-immune hemolytic anemia, thrombocytopenia and acute renal failure. Two groups of cases have been defined, typical D+ (or epidemic) and atypical D- (or sporadic). Typical HUS (D+) usually follows a well defined prodromal illness that is often a gastroenteritis and tends to have a good outcome. Atypical D-HUS is characterized by the absence of antecedent diarrhea, insidious onset, tendency to relapste and, in most studies a poor outcome. (Al-Eisa, Pediatr Nephrol (2001) 16: 1093-1098.
D+HUS (Stx-Associated HUS)
Diarrheal-associated HUS ( D+HUS) is the most common form of HUS, accounting for more than 90% of cases and is caused by a preceding illness with a shiga-like toxin producing bacterium, e.g., E. coli 0157:H7.
D+HUS is the form characterized by a preceding infection with a Shiga toxin secreting pathogen, typically E. coli O157:H7. This pathogen causes painful and typically bloody diarrhea and about 10% of those affected subsequently develop D+ HUS. This subtype is the most common (about 95%) with a reported incidence of 2 cases per 100k persons per year. Renal function recovers in the majority of patients. (Kavanagh, Annul. Rev. Med. 2008: 59: 293-309)
In children, the disease is most commonly triggered by Shiga-like toxin (Stx) producing E. coli and manifests with diarrhea (D*HUS), often boody. Cases of Stx-E. coli HUS, aobut 25%, which, hoever do not present with diarrhea, have also been reported. Acute renal failure manifests in 55-70% of cases, however, renal funciton recovers in most of them. (Noris “Hemolytic uremic syndrome” Am Soc Nephrol 16: 1035-1050, 2005)
Transmission:
Stx-producing E. coli colonize in healthy cattle intestine but also have been isolated from deer, sheep, goats, horses, dogs, birds and flies. They are found in manure and water troughs in farms, which epxlains the increased risk for infection in people who live in rural areas. Humans become infected form contaminted milk, meat and water (water born outbreaks have occured as a result of drinking and swimming in unchlorinated water). (Noris “Hemolytic uremic syndrome” Am Soc Nephrol 16: 1035-1050, 2005)
Diagnosis/Symptoms:
The disease is characterized by prodromal diarrhea followed by acute renal failure. The average interval between E. coli expousre and illness is 3 days. Illness typically begins with abdorminal cramps, and nonbloody diarrhea. Diarrhea may become hemorrhagic in 70% of cases usually within 1-2 d. Vomiting occurs in 30-60% of cases, and fever coccurs in 30%. Leukocyte count is usually elevated. Stx-HUS is not a benign disease. 70% of patietns who develop HUS require red blood cell transfusion, 50% need dialysis and 25% have neurologic involvement, including storke, seizure and coma. After infection Stx-E. coli may be shed in the stools for several weeks after the symptoms are resolved, paritculalry in children. Diagnosis rests on detect of Stx-E. coli in stool cultures. (Noris “HemolytiTrc uremic syndrome” Am Soc Nephrol 16: 1035-1050, 2005)
Treatment:
There is no treatmetn of proven value, and care during the acute phase of the illness is still merely supportive. There is no clear consensus on wehter antiotics should be adminsitered to treat Stx-E. coli infection. (Noris “Hemolytic uremic syndrome” Am Soc Nephrol 16: 1035-1050, 2005)
(non-Siga toxin-associated HUS (non-Stx-HUS))
Non-Shiga toxin-associated HUS (non-Stx-HUS) includes a heterogenous gorup of patients in whom an infection by Stx-producing bacteria could be excluded as cause of the disease. It can be sporadic or familial (i.e., more than one member of a family affected by the disease and exposure to Stx-E. coli excluded). Collectively, non-Stx-HUS forms have a poor outcome. Up to 50% of cases progress to ESRD or have irreversible brain damage, and 25% may die during the acute phase of the disease. Genetic studies have documented that the familial form is associated with genetic abnormalities of the complement regulatory proteins. (Noris “Hemolytic uremic syndrome” Am Soc Nephrol 16: 1035-1050, 2005).
Causes:
A wide vareity of triggers for sporadic non-Stx-HUS have been dientified, including various nonepteric infections, viruses, drugs, amlignancies, transplantation, rpegnancy and other underlying medical conditions scuh as lupus. Infections caused by Streptococcus pneumoniae accounts for 40% of non-Stx-HUS and 4.7% of all causes of HUS in children in the US. Neuroamimidase produced by S. pneumoniae, by removing sialic acids form the cell membranes, exposes Thomsen-Friedenreich antigen to preformed ciruclaitng IgM antibodies, which bind to this neoantigen on platelet and endothelial cells and cause platelet aggregateion and endothelial damage. Categories of drugs that have been most frequently reported to induce non-Stx-HUS include anticancer molecules (mitomycin, cisplatin, beomycin and gemcitabine), immunotherapeutic (cyclosporine, tacrolimus, OKT2, IFN and quinidine) and antiplatelet (ticlopidiene and clopidogrel) agents. Teh resik for developing HUS after mitomycin is 2-10%. (Noris “Hemolytic uremic syndrome” Am Soc Nephrol 16: 1035-1050, 2005)
Treatment:
The discovery of mutations in three different coplement regulatory genes provides enough evidence of the involvement of complement activaiton in the pathogenesis of non-Stx-HUS and indicates that complement inhibition could represent a therapeutic target in these patients. Pexelizumab and eculizumab, two humanized mAbs directed agaisnt C5 have been developed and adminsiteration of eculizumab to patietns with paroxymsal noctururnal hemooglobinuria, a disease characterized by a genetic deficiency of surface rpoteins that protect hematopoietic cells against the attack by the complement system, reduced intravascular hemolysis, hemoglobinuria and the need for transfusions. (Noris “Hemolytic uremic syndrome” Am Soc Nephrol 16: 1035-1050, 2005)
Atypical hemolytic uremic syndrome (aHUS) :
aHUS is a genetic, life-threatening, chronic disease of complement mediated thrombotic microangiopathy, often characterized by microangiopathic haemolytic anaemia with high lactate dehydrogenase (LDH) levels and reduced or undetectable haptoglobin levels, throbocytopenia and acute renal fialure. It affects both paediatric patientsa and adults. Although rare, aHUS has a poor prognosis and is associated with high morbidity and mortality. In one study, progression to end stage renal disease was seen in 56% of adults with aHUS within the first year. (Keating, Drugs, 73: 2013, pp. 2053-2066).
Hereditable forms of aHUS can be associated with mutations in a number of human complement components including complement factor H (CFH), membrane cofactor protein (MCP), complement factor I, C4b-binding protein, complement fact B and complement ocmponent 3.
Although onset of aHUS may occur at any age, 40% of patients develop aHUS by 18 years of age. (Greenbaum, “Eculizumab is a safe and effective treatment in pediatric patients with atypical hemolytic uremic syndrome” Kidney International 2016, 89, 701-711).
Signs & Symptoms: Symptoms of aHUS include fatigue and microagniopathic anemia. The pathologic hallmark of HUS is the thrombotic microangiopathy (TMA) that can be seen on renal biopsy. The clincial signs of aHUS overlap with those of TTP which is primarily an autoimmune disorder.
aHUS is a very rare life-threatning disease. It is characterized by the triad of microangiopathic hemolytic anemia, thrombocytopenia, and renal filaure. It is differentiated from hemolytic uremic syndrome (HUS) by the absence of diarrhea and Singa toxin-induced infection. (Turk J. Ophthalmol 47; 6: 2017)
Diagnosis and Treatment Monitoring:
A subject can be identified as having aHUS by evaluating blood concentrations of C3 and C4 as a measure of complement activaiton or dysregulation. In addition, a subject can be identified as haivng a genetic aHUS by identifying the subject as harboring one or more mutations in a gene assocaited with aHUS such as CFI, CFB, CFH or MCP.
–Changes in Biomarker levels:
A change in the concentraiton or activity level of certain biomarker proteins such as TNFR1, C5b-9 and C5a have been shown to be assocaited with aHUS. (mcKnight US 2016/0154009).
aHUS assocaited biomarker proteins also include proteolytic fragments of complement component factor B (e.g Ba or Bb), coluble C5b9, thrombomodulin, VCAM-1 von Willebrand Factor (vWF), soluble CD40 ligan, prothrombin fragment F1_2, D-dimer, CXCL10, MCP-1, TNFR1, IFNgamma, ICAM-1, IL-1 beta, IL-12p70. aHUS assocaited biomarkers can be assessessed for monitoring and evaluating the status of aHUS in a patient. (WO 2015021166).
–Particular Assays:
Brodsky, (US 2018/0246082) discloses an assay to distingguish aHUS from other microangiopathic hemolytic anemias. The mtehtod includes incubating serum obtained form a patient suspected of aHUS with a plurality of GPI-AP deficient cells and performing a cell viability assay on the cells. IN an embodiment, the mtethod also includes the step of diagnosing based on a statistically significant increased difference of non-viable cells from the pateint serum as compared to a control.
Causes/Mechanisms of Action: aHUS is usually caused by uncontrolled activation of the complement system. A missing or significantly reduced function of Factor H, either due to missing or reduced protein levels or gene mutation(s) has been demonstrated as important in this disease. Since the glomerular membrane lacks endogenous regulators, continuous cleaveg of C3 occurs at this site, resulting in deposition of complement activation products.
Among about 200 children with the disease, 50% had mutations of the complement regulatory proteins factor H, MCP or facto I. (Pediatr Nephrol (2008) 23: 1957-1972
Treatment:
Renal transplantation is the treatment of choice. A problem, however, is recurrence of HUS in the allograft. (Taheri, Archives of Iranian Medicine, 9(2), 2006, 170-172.
Treatment options for patients with aHUS are limited and generally involve plasma infusion or plasma exchange. Other treatments include.e.g, use of anti-latelet agents, prostacyclin, heparin, fibrinolytic agents and/or steroid. (Ruggeenenti, Kidney Int. 60, 2001 pp. 831-46). In some cases, aHUS patietns undergo uni-or biolateral nephrectomy or renal transplation (Artz, Transplantation, 76, 2003; pp. 821-826. However, recurrence of the disease in treated patients is common.
(i) Anti-Complement Treatment:
–Administration of Complement Regulators:
––Factor H: Chtourou (US2008/0318841) teaches using factor H for producing a drug for treating Uremic Haemolytic Syndrome (UHS).
–Administration of Antibodies against Complement Componen:
—Antibodies to C5 (eculizumab, Ravulizumab, etc):
A humanized anti-C5 antibody, eculizumab has been reported as promising in patients with aHUS (Noris, “Ayptical Hemolytic-Uremic syndrome” New England J. Medicine, 2009, 361, 1676-87. ).
The FDA approved eculizumab for aHUS in September of 2011.
Andrien (US 2017/0298123) discloses that BNJ441 (“Ravulizumab”) relative to exulizumab contains four amino acid substitutions in the H chain, Tyr-27-His, Ser-57-His, Met-429-Leu and Asn-435 Ser (note that positions 429 and 435 of BNJ441 correspond to positions 428 and 434 uner the EU nubmewing system). These mutations were engineered to enable an extended dosing interval verus exulizumab by increasing the circulating half-life by reducing antibody clearnce and increasing the eficiency o f the FcRn-medaited antiboy recylcing. Adrian teaches taht the antibodies are useful for treating a variety of complement associated disorders such as aHUS, PNH and myasthenia gravis.
Chatelet (American J. Transplantation, 2009, 9, 2644-2645) discloses that chronic blockage of complement C5 with eculizumab in a patient with aHUS previously dependent on frequent plasmapheresis is safe, and leads to maintained rental function, reduced need for blood transfusions and control of TMA and hemolysis in the absence of plasmapheresis.
Chatelet (Am J Transplant, “Safety and long-term efficacy of eculizumab in a renal transplant patient with recurrent atypical hemolytic-uremic syndrom” Am J Transplant 2009 (Nov; 9(11): 2644-5; Epub 2009, Sep 22) discloses efficacy of eculizumab in a patient who presented a recurrence of atypical hemolytic syndrome 3 eyars after renal transplantation. Based upon the dose regimen determeind for PNH, the patient received 4 doses of eculizumab, 900 mg IV every 7 days, followed by a maintenance dose of 1200 mg every 14 days. After 7 months of treatment and without concomitant plasmapheresis, schistocytes decreased to 0.5%, haptoglobin increased to within normal limits, creatinine levels stabilized and no further episodes of diarrhea were reported.
Mache (“complement inhibitor Eculizumab in atypical hemolytic uremic syndrome” Clin J Am Soc Nephrol 4: 1312-1316, 2009) discloses that a single dose of eculizumab (60 mg, using a 40 min intravenous infusion) resulted in normalization of platelet counts within 3 days and haptoglobin levels within 5 days in a 17.8 year old boy with HUS. ubsequently, renal function improved again and about 2 weeks after recovery of complement hemolytic activity, aHUS replapsed and PCr increased. Repetive doses of eculizumab again led to a normalization of haptoglobin levels within 6 days. Only minor renal recovery (PCr 9.2 mg/dL) ensured and severe hypervolemic hypertension required ehmodialysis again.
Rother (US Patent Application, published as US 2020/007191) discloses a method of treating myasthenia gravis (MG) in an anti-AChR antibody positive patient which includes admionstiering eculizumab at 600 mg once per week for the first four weeks followed by a minatenance dose of at least 900 mg of eculizumab every two weeks
——Dose Based on age/sex/weight:
Greenbaum, (“Eculizumab is a safe and effective treatment in pediatric patients with atypical hemolytic uremic syndrome” Kidney International 2016, 89, 701-711) discloses a clinical trail in paitents with aHUS aged less than 18 years. Greenbaum teahes a schedule of eculizumab does administraiton based on the patient weight. For example, for a patient over 40 kg, 900 mg weekly x 4 and a 1200 mg maintenance dose at week 5 and then 1200 mg q2 week. Overall, the approved pediatric dosing resulted in eculizmab concentraiotn of 50 to 700 ug/ml for all age cohorts.
Gruppo (N Engl J Med 360: 5 (January 29, 2009) discloses hematologic and renal improvement within 48 hours after initiation of eculizumab and a remission occurred within 10 days. An eculizumab dosing regimen of 600 mg every 2 weeks continued for 4 months, to date, with sustained clinical remission.
McNight (WO 2015/021166) discloses treating aHUS with a suitalbe dose of an anti-C5 antibody that can depend on a variety of factors such as the age, sex and weight of a subject to be treated. McNight discloses various administration schedules depending on the body weight of the subject such as a body weight less than 40 but greater than or equal to 30 kg, or less than 30 but greater than or equal to 20 kg or less than 20 but greater than or equal to 10 kg. For example, in the case of a subject who is less than 20 but greater than or equal to 10 kg, the antiobdy is adminsitered for at least 4 weeks under the folloiwng schedule: at least 500 mg once a week for one week; at least 200 mg of the antibody oncde durin gthe second week; at at least 200 mg of the anitbody bi-weekly therfater.
NCT02949128 (Alexion, published 10/27/2016) discloses a single arm study of ALXN1210 in treatment of adolescent patients with aHUS. A single loading odse on Day 1 followed by regular maintenance dosing beinging on Day 15 was based on weight; 40 to less than 60 kg: 2400 mg, then 3000 mg every 8 weeks; 60 to less than 100 kg: 2700 mg loading, then 3300 mg every 8 weeks and greater than 100 kg: 3000 mg loading then 3600 mg every 8 weeks.
Payton (US Patent Applicaiton No: 16/757,512, published as US 20200254092) discloses a method for treating PNH or aHUS that includes adminstiering an anti-C5 antibody at 2400-3000 mg for a patient weighing 40-60kg, 2700-3300 mg for a patient weighting greater than 60 and less than 100 kg or 3000-36000 mg for a patient weighing more than 100 kg. Exemplary antibodies that can be administered include eculizumab (also known as Soliris), ravulizumab (also known as Ultomiris, ALXN1210 and BNJ441), 7086 antibody (described in US Patent Nos: 8,241,628 and 8,883,158), 305LO5 antibody (described in US 2016/0176954), the SKY59 antibody (described in Fukuzawa T., et al. Rep. 2017, Apr 24; 7(1): 1080) and REGN3918 antibody (alsko known as H4H12166PP and described in US 20170355757). The anti-C5 antibodies can also include substitutions that enhance the binding affinity of the antibody Fc constant region for FcRn such as the M252Y/S254T/T256E triple substitution (described by Dall’Acqua et al., 2006 J Biol Chem 281: 23514-23524), the M428L or T250Q/M428L substituions (described in Hinton (2004) J Biol Chem 279: 6213-6216 and Hinton (2006) J Immunol 176: 346-356) and the N434A or T307/E380A/N434A substitutions (described in Petkova (2006) Int Immunl 18(12): 1759-69).
Payton (US Patent Application No: 17/057,898, published as US2021/0332147) also discloses methods of treating aHUS in a pediatric patient (i.e., patient less than 18 years) by administrating an anti-C5 antibody such as ravulizumab (also known as ALXN1210 and BNJ441) according to a particular dosage schedule. In one embodiment, 300 mg of the anti-C5 antibody is administered to a pateint weighing greater than 4 but less than 9 kg, 600 mg if the patient weight greater than 9 but less than 20 kg, 900 or 2100 mg for a patient weight more than 19 but less than 30 kg, 1200 or 2700 mg for a patient weighng more than 29 but less than 40 kg and 2400-3000 mg for a patient weighing more than 39 but less than 59 kg.
—-Antibodies to C5 and Hemodialysis: Ayer discloses eculizumab added to hemodialysis and plasmaphoresis therapy for the treatment of aHUS (Turk J. Ophthalmol 47; 6: 2017)
–Antibodies against MASP2:
The anti-MASP2 monoclonal antibody, OMS721, which blocks the lectin pathway, has progressed to phase 3 in renal indications and has received ophan drug designation for aHUS and IgA nephropathy. In 2017, Omeros opened an open-label multi-centre phase 3 trail. (Ricklin, Molecular Immunogloy 102 (2018) 89-119
–RNAi:
—-RNAi of C5:
One strategy to overcome high target concentration is to target at the RNA or DNA level. Alnylam Pharmaceuticals have developed an RNAi, Cemdistran that is liver targeted (through GalNAc conjugation) and blocks hepatic production of C5. A phase 2 clinical trial of Cemdisiran in aHUS was launched in late 2017. Given that C5 blockage is required extremely rapidly when an individaul presents with acute episode of aHUS and it takes a nubmer of days for C5 to besuppressed with RNAi, it can be speculated that an additional therapeutic agent may need to be used in the initial stages of therapy to rescue renal funciton before C5 levels are subseqeuntly knocked down. (Ricklin, Molecular Immunogloy 102 (2018) 89-119
–-Small Molecule Antagonists:
—-against C5aR1:
While the blckade of C5 prevetns formation of both disease cuasing products, C5a and MAC, the specific interference with any of these effectors individually may provide further insight into disease mechanisms adn provide clinical benefits in some diseases. This is particularly true in the case of aHUS, for which it has not been resolved wither both C5a and MAC act as drivers of the conditions. Avacopan is an orally bioavailable small molecule antagnist of C5aR1, developed by ChemoCentryx (aquired by Amgen) which has progressed to phase 3 trials in AAV. The company obtained orphase disease designation for C3G in 2017. A phase 2 study in aHUS commenced in 2015. (Ricklin, Molecular Immunogloy 102 (2018) 89-119