Efungumab – Mycograb, heat shock protein 90 (HSP90) monoclonal antibody, recombinant
Status: rejected by EU; development halted in fall 2010
Organizations involved:
NeuTec Pharma plc. – R&D; Tech.
Novartis AG – World mark.; Parent
BioReliance GmbH – Manuf.
CMC Biopharmaceuticals A/S – Manuf.
University of Manchester –R&D; Tech.
Cross ref.: See Monoclonal Antibodies (entry #300)
Description: Mycograb is a lyophilized (freeze-dreed) formulation of efungumab, a recombinant polyhistidine-tagged human monoclonal antibody fragment (termed a ‘grab’ by its developer, NeuTec) with specificity for yeast (fungal) heat shock protein-90 (NKILKVIRKNIVKK epitope of HSP90), expressed by transformed Escherichia coli (E. coli) bacteria. Efungumab was derived from HSP90 antibody cDNA from patients recently recovered from invasive candidiasis, and was developed for treatment of systemic candidiais (infection with Candida species fungi). It consists of the antigen-binding variable domains of antibody heavy and light chains linked, and does not have an Fc component. Mycograb powder is dissolved in sterile water to make a solution 2 mg/mL for injection.
Mycograb had been on track to become the first human recombinant antibody fragment to be used in fungal infections.
Nomenclature: heat shock protein Mab, rDNA [BIO]; efungumab [INN]; immunoglobulin scFv fragment, anti-(heat shock protein 90 homolog from Candida albicans (yeast)), methionylalanyl-[human monoclonal HSP90 mab VH domain (120 residues)]-tris[(tetraglycyl)seryl]-[human monoclonal HSP90 mab V-KAPPA domain (107 residues)]-[arginyl- trialanyl-leucyl-glutamyl]-hexahistidine [CAS]; heat shock protein 90 monoclonal antibody, recombinant [SY]; HSP90 Mab [SY]
Biological.: Heat shock protein 90 (hsp90) is a tumor marker expressed on the surface of certain tumor cells and fungi. Antibodies to HSP90 are closely associated with recovery in patients with invasive candidiasis who are receiving amphotericin B. HSP90 is needed for tumor cell survival. The growth of tumor cells is particularly sensitive to hsp90 inhibition. This anti-cancer activity has been demonstrated in a series of vitro studies in various human tumor cell lines. Human/tumor and fungal HSP90 have a high degree of conserved sequences, and antibodies to human and fungal HSP90 often cross-react.
In fungal infections, and especially deep-seated systemic infections, HSP90 plays a crucial role and is essential for the viability of the yeast. Total soluble protein extracts from exponentially growing C. albicans or Saccharomyces cerevisiae yield not only full-length HSP90 but also subfragments of 72-76 kDa and 47 kDa, which are the result of partial degradation within viable yeast cells. Numerous studies examining antibody responses to C. albicans in infected patients and animal models of the infection have shown immunodominant antigens in the size range 45-52 kDa. One of these antigens, at 48 kDa, was identified as enolase and is used as the basis of a diagnostic test.
An antigen at 47 kDa has been identified as the carboxy fragment of C. albicans heat shock protein 90 (HSP90). This is more abundant than, and clearly distinct from enolase, and is immunodominant in patients with AIDS and chronic mucocutaneous candidiasis. An antibody response to this antigen is significantly more common in patients with deep-seated candidiasis than those with superficial candidiasis, and has been associated with abdominal sepsis in intensive care patients. In patients with deep-seated, invasive candidiasis, a sustained antibody response to this antigen correlates closely with a good prognosis, while lack of or falling levels of antibody are associated with fatality. Dissecting this potentially protective antibody response to the level of individual epitopes showed that it was primarily directed against the epitope NKILKVIRKNIVKK, the epitiope to which efungumab is directed. Patient sera containing such an antibody and a mouse monoclonal antibody and human recombinant antibodies against this epitope have been shown to be therapeutically active in murine models of invasive candidiasis .
NeuTec investigators sequenced the carboxy-end of the Candidal HSP90 stress protein and raised an antibody (efungumab) against the epitope LKVIRKNIVKKMIE that recognised both the 47 and 92 Kda Candidal stress proteins in sera from patients suffering from systemic Candidal infection. In pre-clinical studies, efungumab was found to be highly effective when used in combination with amphotericin-B, and showed significant antifungal activity against all five species of Candida -- C. albicans, C. krusei, C. tropicalis, C. parapsilosis, and C. glabrata. However, when combined with fluconazole, it did not increase the response rate in fluconazole-resistant species, but did increase the clearance of fluconazole-sensitive species of Candida. Mycograb shows therapeutic synergy in combination with the oral azole antifungal agents itraconazole, and voriconazole. Surprisingly, it was found that the efficacy of amphotericin B against a wide variety of pathologically important fungal strains (e.g., Candida species) is significantly enhanced in the presence of efungumab.
The mechanisms by which Mycograb achieves efficacy against candidiasis in vivo may not depend solely on inhibition of fungal HSP90 alone. The epitope targeted by Mycograb is conserved among yeast, murine, and human homologues of HSP90. HSP90 has been shown to bind to endothelial nitric oxide synthase. leading to the release of nitric oxide (NO), which is important in regulating cardiovascular hemodynamics. When administered, HSP90 causes large vessel vasodilation, the proliferation of vascular smooth muscle cells, leukocyte adhesion, platelet aggregation, and, in a human volunteer study, activation of the microcirculation. HSP90 has also been shown to catalyze the activation of the prekallikrein-kininogen complex, in the absence of Factor XII, leading to release of bradykinin. This zinc dependent activation was inhibited by a polyclonal antibody against HSP90. Bradykinin is a major mediator of swelling in C1 inhibitor deficiency and is responsible for the angioedema seen with ACE inhibitors. It is released from mast cells during asthma attacks and it is a gastrointestinal vasodilator. Inhibition of pathways such as these by an HSP90 inhibitor would occur at physiological rather than pharmacological levels, and could contribute towards the benefit of Mycograb in candidiasis at relatively low serum levels.
Antibody to human HSP90 is part of the natural human antibody repertoire. The lack of detectable antibody to HSP90 in patients succumbing to invasive candidiasis could reflect the patient’s inability to produce the antibody (because they are immunosuppressed, for example) or that the antibody is being produced but rapidly forms complexes with an excess of HSP90 antigen. This imbalance between HSP90 and the natural antibody can be corrected by adminstration of Mycograb.
NeuTec’s ‘grab’ or FabTec technology involves identifies those antibodies produced by patients who recover from infectious disease and then replicating them as recombinant monoclonal antibody fragments (‘grabs’). NeuTec identifies key antigens and associated antibodies by characterising the antibody responses produced by patients who recover from an infection and then comparing them with those in patients who die from the infection. The resulting “grabs” are of high specificity, affinity and potency against their microbial target. Mycograb has intrinsic antifungal activity; synergistic activity with amphotericin B, with the combined use giving greater activity than either agent alone; and a broad spectrum of activity against all Candida species examined, including fluconazole-resistant Candida albicans and Candida krusei.
Companies.: Efungumab, Mycograb and “grab” technology were developed by NeuTec Pharma plc, which originally spun off from the Infectious Diseases Research Unit, University of Manchester. Intellectual property rights were transferred from the University to the new company in 1997. The company was founded by Univ. of Manchester Professors James Burnie and Ruth Matthew (married).
NeuTec has contracted with two companies for manufacture of Mycograb. BioReliance GmbH was the original contractor, and manufactured supplies used in clinical trials. CMC Biopharmaceuticals A/S will also commercially manufacture Mycograb.
In June 2006, Novartis AG acquired NeuTec for around $575 million. Novartis stated that Mycograb (and also Aurograb, which was abandoned in 2008) was the primary reason for the acquisition. Novartis now has full worldwide rights.
In Oct. 2010, Novartis reported it was abandoning further development of Mycograb. Novartis took a $360 million loss in relation to the Mycograb program.
Manufacture: The DNA sequence of the efungumab antibody was genetically modified by codon optimization for expression in Escherichia coli (obtained from Operon Technologies Inc.) and inserted into an E. coli expression vector. The amino acid sequence of efungumab includes the heavy, light and spacer domains. See “Cloning of a DNA sequence encoding a major fragment of the 47 kilodalton stress protein homologue of Candida albicans” FEMS Microbiol. Lett.. 60:25-30. Efungumab expressed by E. coli was purified by affinity chromatography using an imidazole exchange column using standard protocols.
Status: A MAA was submitted for European Union (EU) approval in March 2005 for Mycograb (2 mg/mL powder for solution for injection) in adult patients in combination with amphotericin B or a lipid formulation of amphotericin B for treatment of invasive candidiasis . Mycograb has orphan status in the EU and U.S. NeuTec initiated a compassionate use program for Mycograb in Jan. 2005.
On Nov. 16, 2006, the Committee for Medicinal Products for Human Use (CHMP), EMEA, EU, adopted a negative opinion, recommending the refusal of the marketing authorisation for Mycograb (i.e., the application was rejected). The CHMP was concerned about some manufacturing-associated aspects, including the way the molecules of efungumab may fold or aggregate in solution for injection and the level of some substances present (perhaps, HSP80 fragments) that could stimulate an immune response in patients. It also had concerns about the safety of Mycograb, which has been associated with ‘cytokine release syndrome’, a condition that can cause nausea, vomiting, pain and also hypertension (high blood pressure). The reason for this is not clear. Too few patients were found to have received Mycograb for its safety to be sufficiently assessed. The committee concluded that the benefits of Mycograb in the treatment of invasive candidiasis did not outweigh its risks.
After the EU rejection, Novartis stated it plans to provide additional manufacturing and safety data to support the safety profile of the drug, but has not disclosed a timeframe for securing approval.
An BLA for U.S. approval is expected to be filed in 2009 (by Novartis, reported at the time of the EU rejection).
Tech. transfer: NeuTec’s founders discovered that stress proteins from both bacteria and fungi, e.g., Candida albicans, comprise an immunodominant conserved antigen. Patents assigned to NeuTec covering aspects of Mycograb include U.S. 5,777,083 (and EP0861892), “Stress protein epitopes,” claiming human HSP90 epitopes; and EP1737488, “Treatment of Fungal Infections,” concerning therapeutic use of HSP90 antibodies with Claim 1, “A composition comprising an antibody or an antigen binding fragment thereof specific for at least one epitope of hsp90 from an organism of the Aspergillus genus, and at least one antifungal agent selected from the group consisting of: itraconazole and voriconazole.” This was based on the inventors finding “that despite the prior finding that azole antifungal agents displayed little or no synergy with the Mycograb antibody disclosed in WO01/76627 in the treatment of infections due to Aspergillus or Candida strains, there is a therapeutic synergy between the oral azole antifungal agents itraconazole, and voriconazole, in combination with Mycograb antibody.”
Trials: Phase I trials began in Dec. 2000.
The pivotal Phase III study for invasive (systemic) candidiasis involved 139 patients in 10 European countries and the U.S., about half of whom received Mycograb plus liposomal amphotericin B, and half placebo plus liposomal amphotericin B. The primary endpoint was comparison of the frequency with which patients showed a complete clinical and mycological response by Day 10 compared to the placebo group. In this respect, there was a highly statistically significant difference (p < 0.001) between the two groups. Those receiving Mycograb.had a complete overall (clinical and mycological) response in 84% of cases vs. 48% in the placebo group. The frequency of deaths due to the Candidal infection under treatment was as high as 18% in the placebo group and 4% in the Mycograb group (p < 0.025). The rate of culture-confirmed eradication of the infection showed a highly statistically significant difference between the two groups (p < 0.001), with the median time to last positive culture being 3 days for the test group vs. 23 days for the placebo group (Kaplan-Meier). A candidemia sub-group analysis of the most severely ill patients with positive blood cultures showed that the number of Mycograb patients in the test group with negative cultures and clinical response at day 10 was 30 out of 34 (88%) vs. 15 out of 33 (45%) in the placebo group (p < 0.0002).
Results from the trial were reported in Clinical Infectious Diseases, April 2006. An accompanying commentary referred to the results as “remarkable” and “dramatic.”
Disease: Systemic fungal infections are estimated at 320,000 incidences per year worldwide. Most common is systemic candidiasis, representing ~70% of all such infections. At particular risk are low birth-weight babies, post surgical patients, patients whose immune systems have been compromised, such as by therapies for cancer, bone marrow transplant recipients or HIV-infection and patients on peritoneal dialysis.
Systemic infection, despite the availability of antifungal drugs, remains deadly. Mortality from Candida species systemic infection, even with treatment with amphotericin B, the current drug of choice, in the U.S. is about 35-40%, and mortality rates appear comparable in other parts of the world. The high mortality rate is attributed to non-Candida albicans Candida species and their growing resistance to commonly used antifungal drugs.
Fungal infections caused by Aspergillus and Candida species have traditionally been treated by the antifungal agent amphotericin B, regarded as the “gold standard” of systemic antifungal therapy. However, amphotericin B is itself highly toxic and has side effects including chills, fever, myalgia or thrombophlebitis. Other antifungal agents include the oral azole drugs (miconazole, ketoconazole, itraconazole, fluconazole, voriconazole) and 5-fluorocytosine. However, many fungal species are becoming resistant to fluconazole and other antifungals, and these species often occur in patients where this drug has been administered prophylactically. Despite the recent advances made in therapeutic drugs, such as fluconazole, itraconazole and systemic liposomal-based variants of amphotericin B, the need for effective agents for treatment of fungal infections remains acute.
Marketing: NeuTec had planned to make direct sales in Europe using a small focused sales team once market authorisation had been achieved.
Ongoing: Phase III trials are underway with Mycograb as adjunctive therapy for cryptococcal meningitis (Cryptococcus neoformans) in patients with AIDS in combination with generic amphotericin B and 5-flucytosine. In Sept. 2005 NeuTec initiated a Phase Ib, pharmacokinetic open label study to evaluate the safety and efficacy of Mycograb administered in combination with Docetaxel for treatment of metastatic or recurrent breast cancer.
Index Terms:
Companies involvement:
Full monograph
173 Heat shock protein Mab, rDNA
Nomenclature:
heat shock protein Mab, rDNA [BIO]
efungumab [INN]
immunoglobulin scFv fragment, anti-(heat shock protein 90 homolog from Candida albicans (yeast)), methionylalanyl-[human monoclonal HSP90mab VH domain (120 residues)]-tris[(tetraglycyl)seryl]-[human monoclonal HSP90mab V-KAPPA domain (107 residues)]-[arginyl-
trialanyl-leucyl-glutamyl]-hexahistidine [CAS]
heat shock protein 90 monoclonal antibody, recombinant [SY]
HSP-90 Mab [SY]
FDA Class: Biologic BLA
antibodies (see also immune globulins; monoclonal antibodies)
biopharmaceutical products
exempt from CBER lot release requirements
monoclonal antibodies, recombinant
Escherichia coli (E. coli)
Harvard strain, Clostridium tetani
hP67.6, monoclonal antibody
histidine
imidazole
polygeline
apheresis (hemapheresis)
apheresis (hemapheresis)
North American coral snake
North American coral snake
orphan status
EU031 EU application denied
UM999 Not Available/Not Marketed in US
US01 FDA application withdrawn or rejected
EM999 Not Available/Not Marketed in EU
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