Sialidase Fusion Protein Research Articles

Cold Weather Viruses.

1. Asif Noor, MD* 2. Theresa Fiorito, MD* 3. Leonard R. Krilov, MD*,† 1. *Department of Pediatrics, Children's Medical Center, NYU Winthrop Hospital, Mineola, NY 2. †Department of Pediatrics, State University of New York, Stony Brook School of Medicine, Stony Brook, NY * Abbreviations: AAP: : American Academy of Pediatrics Adv: : adenovirus CDC: : Centers for Disease Control and Prevention FDA: : Food and Drug Administration hMPV: : human metapneumovirus PCR: : polymerase chain reaction PIV: : parainfluenza virus RSV: : respiratory syncytial virus RV: : rhinovirus Clinicians must learn to identify viral infections in children during the winter months and must practice caution with the use of unnecessary medications in such cases. Recognition of the clinical pattern of viral infection (eg, bronchiolitis) in conjunction with judicious use of viral tests (either office-based immunoassays or newer molecular tests) may assist in epidemiological monitoring, cohorting patients in the hospital, withholding unnecessary therapies, and providing a definitive diagnosis. After completing this article, readers should be able to: 1. Review the epidemiological aspects and clinical signs and symptoms of common cold weather viruses. 2. Recognize situations in which viral testing is indicated. 3. Recognize situations in which treatment is indicated. In early November you are evaluating a 9-month-old boy born at 33 weeks of gestation. The infant presents with 2 days of fevers (101°F–102°F [38.3°C–38.8°C]), copious rhinorrhea, and 1 day of coughing with difficulty breathing. He is otherwise feeding well and has had adequate urination. His 4-year-older sister has an upper respiratory tract infection. On physical examination, the infant has a respiratory rate of 45 breaths/min without chest wall retractions. On auscultation there is good air entry with scattered rhonchi bilaterally. What is the most appropriate next step in management? 1. Obtain respiratory syncytial virus (RSV) and influenza antigen testing. 2. Obtain a chest radiograph to look for focal infiltrate. 3. Provide supportive care with nasal …

A Post-Hoc Analysis of the Randomized, Double-Blind, Placebo-Controlled Multicenter Phase 2 Trial to Examine the Effects of DAS181 in Hematopoeitic Cell Transplant (HCT) Recipients with Parainfluenza Virus (PIV) Lower Respiratory Tract Infection (LRTI) on Supplemental Oxygen (SO)

Background PIV infections are an important cause of morbidity and mortality in HCT recipients. DAS181, a sialidase fusion protein, has demonstrated activity in pre-clinical and clinical studies. Methods Adult immunocompromised patients (IC), including HCT recipients, diagnosed with PIV LRTI on chest imaging and required SO ≥ 2L/min were randomized 2:1 (stratified by mechanical ventilation [MV] at baseline) to nebulized DAS181 (4.5 mg in 3.5mL/day) or matching placebo for up to 10 consecutive days. The primary endpoint was the proportion of patients reaching clinical stability survival (CSS, defined as alive, resolution of SO requirement, and normalization of vital signs) by Day 45. An exploratory end point of proportion to return to room air (RTRA) was analyzed. Results Out of the 110 patients randomized, 64 HCT recipients received study drug (43 DAS181 and 21 placebo). Median age was 53 years (range, 19-77), half were male (50%), white (84%), and had received an allogeneic HCT (86%). A post-hoc analysis of the HCT recipients on SO showed that day 45 CSS was achieved by 46.5% of DAS181-treated patients compared to 33.3% of placebo (p = 0.23). In addition, when compared to placebo, HCT recipients on SO who received DAS181 within 1 year from transplant were more likely to achieve CSS at day 45 (48.4% vs. 12.5%; p = 0.071), were more likely to RTRA at day 28 and day 45 (53.3% vs. 12.5%; p = 0.04 and 60% vs. 25%; p = 0.086, respectively), more likely to be discharged from the hospital by day 45 (64.5% vs. 12.5%; p = 0.011), and had a trend for lower mortality at day 45 (25.8% vs. 62.5%, p = 0.064). The rate of adverse events was similar in both treatment groups. Conclusion DAS181 was well tolerated and a post-hoc analysis in HCT recipients with PIV LRTI on SO within 1 year of transplant, DAS181 was effective (RTRA) and showed a trend towards lower mortality by day 45. DAS181 was granted Breakthrough Therapy Designation for the treatment of PIV LRTI in IC patients and a phase 3 trial is being planned.

1715. A Randomized, Double-Blind, Placebo-Controlled Multicenter Phase 2 Trial to Examine the Effects of DAS181 in Immunocompromised (IC) Patients With Parainfluenza Virus (PIV) Lower Respiratory Tract Infection (LRTI) on Supplemental Oxygen (SO)

BackgroundPIV infections are an important cause of morbidity and mortality in IC patients. DAS181, a sialidase fusion protein, has demonstrated activity in preclinical and clinical studies.MethodsAdult IC patients diagnosed with PIV LRTI on chest imaging and required SO ≥ 2 L/minute were randomized 2:1 (stratified by mechanical ventilation [MV] at baseline) to nebulized DAS181 (4.5 mg in 3.5 mL/day) or matching placebo for up to 10 days. The primary endpoint was the proportion of patients reaching clinical stability survival (CSS, defined as alive, resolution of SO requirement, and normalization of vital signs) by Day 45.ResultsFrom 2014 to 2016, 110 patients were randomized and received study drug (74 DAS181 and 36 placebo). Median age was 57 years (range, 18–85). The majority were hematopoietic cell transplant (HCT) recipients (74), followed by hematological malignancy/solid tumor patients on chemotherapy (29), and lung transplant recipients (7). Day 45 CSS was achieved by 39.2% of DAS181-treated patients compared with 31.4% of placebo (P = 0.29), while the proportion among non-MV patients was 45.0% vs. 31.0% (difference −14.0%, P = 0.15), respectively. Time to CSS in the non-MV stratum was shorter in DAS181-treated patients (figure). Median change in nasopharyngeal PIV viral load by Day 10 and median hospitalization days were −1.44 vs. −0.68 log10 (P = 0.51) and 13.5 vs. 21 days (P = 0.10) for DAS181 and placebo, respectively. Mean absolute increase from baseline FEV1% predicted was 16.82 for DAS181 vs. 2.02 for placebo (P = 0.001). Post-hoc analysis on the probability to return to room air (RTRA) suggested that DAS181 reduced SO need in the non-MV stratum after Day 21 (P = 0.09). HCT recipients within 360 days from transplant had a 40.8% treatment effect on RTRA at Day 28 (P = 0.04) and 36.7% on mortality at Day 45 when compared with placebo (P = 0.06). The rate of adverse events was similar in both treatment groups. Day 45 all-cause mortality was comparable in both groups (32.4% DAS181 vs. 31.4% placebo).ConclusionDAS181 was well tolerated and showed a signal for clinical efficacy in IC patients with PIV LRTI. DAS181 was granted Breakthrough Therapy Designation for the treatment of PIV LRTI in IC patients and a phase 3 trial is being planned. Disclosures R. F. Chemaly, Ansun Biopharma: Consultant and Investigator, Consulting fee and Research grant. R. Moss, Ansun Biopharma: Employee, Salary. F. M. Marty, Ansun Biopharma: Investigator, Research grant. C. R. Wolfe, Ansun Biopharma: Investigator, Research grant. S. J. Lawrence, Ansun Biopharma: Investigator, Research grant. S. Dadwal, Ansun Biopharma: Investigator, Research grant. R. Soave, Ansun Biopharma: Investigator, Research grant. J. Hwang, Ansun Biopharma: Employee, Salary. S. Hawley, Ansun Biopharma: Employee, Salary. R. Routh, Ansun Biopharma: Employee, Salary. J. Ho, Ansun Biopharma: Employee, Salary. G. Wang, Ansun Biopharma: Employee, Salary. N. Chang, Ansun Biopharma: Employee, Salary. M. Boeckh, Ansun Biopharma: Consultant and Investigator, Consulting fee and Research support.

Oral Ribavirin Treatment Failure for Severe Parainfluenza Type 1 Infection in a Patient with End Stage Interstitial Lung Disease Successfully Treated with DAS181

Parainfluenza virus (PIV) infections can cause serious respiratory infections and death in immunocompromised patients. No antiviral drugs have proven efficacy against PIV. DAS181, a sialidase fusion protein has been shown to inhibit infection with PIV strains both in vitro and in animal model. The clinical course of immunocompromised patients with PIV-1 infection is described. After being diagnosed with PIV infection, patient was treated for 18 days with oral Ribavirin (RBV) but failed to respond clinically and no virus clearance was obtained. However, patient tested negative for PIV after a 10-days DAS181 treatment course. This case exemplifies failure of oral RBV treatment of severe Parainfluenza virus infection and subsequent viral clearance associated with administration of inhaled DAS181. Large scale randomized trials are warranted to determine the therapeutic efficacy of DAS181 against PIV related lung disease.

DAS181 Treatment of Severe Parainfluenza Virus 3 Pneumonia in Allogeneic Hematopoietic Stem Cell Transplant Recipients Requiring Mechanical Ventilation.

Parainfluenza virus (PIV) may cause life-threatening pneumonia in allogeneic hematopoietic stem cell transplant (HSCT) recipients. Currently, there are no proven effective therapies. We report the use of inhaled DAS181, a novel sialidase fusion protein, for treatment of PIV type 3 pneumonia in two allogeneic hematopoietic SCT recipients with respiratory failure.

Effect of sialidase fusion protein (DAS 181) on human metapneumovirus infection of Hep-2 cells.

Hep-2 cells were preincubated with DAS181 or control DAS185 (a mutated sialidase) prior to inoculation with human metapneumovirus strains. Infectivity was assessed by a cell-based ELISA quantitating human metapneumovirus matrix protein. The effect of DAS181 on binding of recombinant G attachment protein was also determined. DAS181 blocked infection of human metapneumovirus strains A2, B1, and B2 at low concentrations. No effect of DAS185 was observed. Binding of MPV G protein to Hep-2 cells was also markedly inhibited by preincubation of cells with DAS181. These results suggest that human metapneumovirus may utilize sialic acids as an entry cofactor. DAS181 may thus represent a new therapeutic agent useful for the treatment of human metapneumovirus.

DAS181 treatment of severe parainfluenza type 3 pneumonia in a lung transplant recipient

Parainfluenza virus (PIV) may cause life‐threatening pneumonia in lung transplant patients and there are no proven effective therapies. We report the use of inhaled DAS181, a novel sialidase fusion protein, to treat severe PIV type 3 pneumonia in a lung transplant patient. Treatment was well tolerated and associated with improvement in oxygenation and symptoms, along with rapid clearance of PIV. DAS181 should be systematically evaluated for treatment of PIV infection in transplant recipients.

Clinical potential of DAS181 for treatment of parainfluenza‐3 infections in transplant recipients

Parainfluenza virus (PIV) infections can cause serious respiratory infections and death in immunocompromised patients. No antiviral agents have proven efficacy against PIV, and therapy generally consists of supportive care. DAS181, a novel sialidase fusion protein that temporarily disables airway epithelial PIV receptors by enzymatic removal of sialic acid moieties, has been shown to inhibit infection with PIV strains in vitro and in an animal model. We describe here the clinical course of 2 immunocompromised patients with PIV-3 infection, one with a history of lung transplantation and the other neutropenic after autologous hematopoietic stem cell transplantation for multiple myeloma. Both patients had substantial clinical improvement in respiratory and systemic symptoms after a 5-day DAS181 treatment course, although the clinical improvement in the autologous stem cell transplantation patient also paralleled neutrophil engraftment.

A safety evaluation of DAS181, a sialidase fusion protein, in rodents.

DAS181 is a novel inhaled drug candidate blocking influenza virus (IFV) and parainfluenza virus (PIV) infections through removal of sialic acid receptors from epithelial surface of the respiratory tract. To support clinical development, a 28-day Good Laboratory Practices inhalation toxicology study was conducted in Sprague-Dawley rats. In this study, achieved average daily doses based on exposure concentrations were 0.47, 0.90, 1.55, and 3.00 mg/kg/day of DAS181 in a dry powder formulation. DAS181 was well tolerated at all dose levels, and there were no significant toxicological findings. DAS181 administration did not affect animal body weight, food consumption, clinical signs, ophthalmology, respiratory parameters, or organ weight. Gross pathology evaluations were unremarkable. Histological examination of the lungs was devoid of pulmonary tissue damage, and findings were limited to mild and transient changes indicative of exposure and clearance of a foreign protein. DAS181 did not show any cytotoxic effects on human and animal primary cells, including hepatocytes, skeletal muscle cells, osteoblasts, or respiratory epithelial cells. DAS181 did not cause direct or indirect hemolysis. A laboratory abnormality observed in the 28-day toxicology study was mild and transient anemia in male rats at the 3.00 mg/kg dose, which is an expected outcome of enhanced clearance of desialylated red blood cells resulting from systemic exposure with DAS181. Another laboratory observation was a transient dose-dependent elevation in alkaline phosphatase (ALP), which can be attributed to reduced ALP clearance resulting from increased protein desialylation due to DAS181 systemic exposure. These laboratory parameters returned to normal at the end of the recovery period.

Phenotypic and genotypic characterization of influenza virus mutants selected with the sialidase fusion protein DAS181

influenza viruses (IFVs) frequently achieve resistance to antiviral drugs, necessitating the development of compounds with novel mechanisms of action. DAS181 (Fludase), a sialidase fusion protein, may have a reduced potential for generating drug resistance due to its novel host-targeting mechanism of action. IFV strains B/Maryland/1/59 and A/Victoria/3/75 (H3N2) were subjected to >30 passages under increasing selective pressure with DAS181. The DAS181-selected IFV isolates were characterized in vitro and in mice. despite extensive passaging, DAS181-selected viruses exhibited a very low level of resistance to DAS181, which ranged between 3- and 18-fold increase in EC(50). DAS181-selected viruses displayed an attenuated phenotype in vitro, as exhibited by slower growth, smaller plaque size and increased particle to pfu ratios relative to wild-type virus. Further, the DAS181 resistance phenotype was unstable and was substantially reversed over time upon DAS181 withdrawal. In mice, the DAS181-selected viruses exhibited no greater virulence than their wild-type counterparts. Genotypic and phenotypic analysis of DAS181-selected viruses revealed mutations in the haemagglutinin (HA) and neuraminidase (NA) molecules and also changes in HA and NA function. results indicate that resistance to DAS181 is minimal and unstable. The DAS181-selected IFV isolates exhibit reduced fitness in vitro, likely due to altered HA and NA functions.

Antiviral strategies for pandemic and seasonal influenza.

While vaccines are the primary public health response to seasonal and pandemic flu, short of a universal vaccine there are inherent limitations to this approach. Antiviral drugs provide valuable alternative options for treatment and prophylaxis of influenza. Here, we will review drugs and drug candidates against influenza with an emphasis on the recent progress of a host-targeting entry-blocker drug candidate, DAS181, a sialidase fusion protein.

Sialidase‐Based Anti–Influenza Virus Therapy Protects against Secondary Pneumococcal Infection

DAS181 (Fludase) is a sialidase fusion protein in clinical development as a broad-spectrum anti-influenza virus (IFV) therapeutic agent. Previous reports by other investigators have raised the concern that desialylation of airway epithelium might increase susceptibility to Streptococcus pneumoniae infection. To address whether DAS181 would lead to an increased risk of pneumococcal infection, we tested S. pneumoniae colonization after DAS181 treatment of human A549 cells, healthy mice, and mice challenged with a lethal dose of IFV A/PR/8/34 (H1N1) or A/Victoria/3/75 (H3N2), followed by 10(4) cfu of S. pneumoniae (D39) on day 3 or day 7. DAS181 treatment was given 24-48 h after IFV challenge. DAS181 treatment did not increase S. pneumoniae colonization in vitro or in vivo in healthy animals. In IFV-infected mice, DAS181 prevented pneumonia and significantly prolonged survival and inhibited the IFV titer by > or = 3 logs. None of the treated animals showed enhanced S. pneumoniae colonization of the lung. In addition, opportunistic infections with Citrobacter species or Klebsiella species occurred only in mice receiving vehicle, not in animals treated with DAS181. These data indicate that DAS181 treatment does not exacerbate secondary bacterial infection in mice. DAS181 may reduce the risk of secondary bacterial infection by inhibiting IFV.

DAS181, a sialidase fusion protein, protects human airway epithelium against influenza virus infection: an in vitro pharmacodynamic analysis

The influenza virus (IFV) infection models commonly used to evaluate antiviral agents (e.g. MDCK cell line and mice) are limited by physiological differences from the human respiratory tract in vivo. Here we report the pharmacodynamics of DAS181, a sialidase fusion protein that inhibits influenza infection, in the model systems of well-defined human airway epithelium (HAE) culture and ex vivo culture of fresh human bronchial tissue, both of which are close mimics of the human respiratory tract in vivo. HAE culture and ex vivo human bronchi were used to evaluate the sialic acid removal and regeneration efficiency and IFV inhibition after various DAS181 treatment levels and regimens. DAS181 effectively desialylates HAE cultures and ex vivo bronchi tissues and therefore potently inhibits replication of different IFV strains. The treatment effect of DAS181 occurs immediately upon application to the epithelial surface and is unaffected by the respiratory mucus. In both HAE and human bronchial tissue, the inhibitory effect of DAS181 treatment lasts for at least 2 days. Approximately 80% epithelial surface desialylation and significant anti-IFV efficacy can be achieved at topical concentrations of DAS181 in the range of 5-10 microg/cm(2) when applied once daily. An additional treatment or a higher loading dose of DAS181 on the first day provides significant additional treatment benefit. Comparing the effect of DAS181 versus its two analogues, DAS180 and DAS185, has confirmed that sialidase function is critical for DAS181, and the cell-binding domain (amphiregulin tag) prolongs DAS181 retention and potentiates its function. These results provide valuable insights into DAS181 treatment dose and potential regimens in the clinical setting.

Novel pandemic influenza A(H1N1) viruses are potently inhibited by DAS181, a sialidase fusion protein.

BackgroundThe recent emergence of a novel pandemic influenza A(H1N1) strain in humans exemplifies the rapid and unpredictable nature of influenza virus evolution and the need for effective therapeutics and vaccines to control such outbreaks. However, resistance to antivirals can be a formidable problem as evidenced by the currently widespread oseltamivir- and adamantane-resistant seasonal influenza A viruses (IFV). Additional antiviral approaches with novel mechanisms of action are needed to combat novel and resistant influenza strains. DAS181 (Fludase™) is a sialidase fusion protein in early clinical development with in vitro and in vivo preclinical activity against a variety of seasonal influenza strains and highly pathogenic avian influenza strains (A/H5N1). Here, we use in vitro, ex vivo, and in vivo models to evaluate the activity of DAS181 against several pandemic influenza A(H1N1) viruses.Methods and FindingsThe activity of DAS181 against several pandemic influenza A(H1N1) virus isolates was examined in MDCK cells, differentiated primary human respiratory tract culture, ex-vivo human bronchi tissue and mice. DAS181 efficiently inhibited viral replication in each of these models and against all tested pandemic influenza A(H1N1) strains. DAS181 treatment also protected mice from pandemic influenza A(H1N1)-induced pathogenesis. Furthermore, DAS181 antiviral activity against pandemic influenza A(H1N1) strains was comparable to that observed against seasonal influenza virus including the H274Y oseltamivir-resistant influenza virus.ConclusionsThe sialidase fusion protein DAS181 exhibits potent inhibitory activity against pandemic influenza A(H1N1) viruses. As inhibition was also observed with oseltamivir-resistant IFV (H274Y), DAS181 may be active against the antigenically novel pandemic influenza A(H1N1) virus should it acquire the H274Y mutation. Based on these and previous results demonstrating DAS181 broad-spectrum anti-IFV activity, DAS181 represents a potential therapeutic agent for prevention and treatment of infections by both emerging and seasonal strains of IFV.

Inhibition of Neuraminidase Inhibitor-Resistant Influenza Virus by DAS181, a Novel Sialidase Fusion Protein

Antiviral drug resistance for influenza therapies remains a concern due to the high prevalence of H1N1 2009 seasonal influenza isolates which display H274Y associated oseltamivir-resistance. Furthermore, the emergence of novel H1N1 raises the potential that additional reassortments can occur, resulting in drug resistant virus. Thus, additional antiviral approaches are urgently needed. DAS181 (Fludase®), a sialidase fusion protein, has been shown to have inhibitory activity against a large number of seasonal influenza strains and a highly pathogenic avian influenza (HPAI) strain (H5N1). Here, we examine the in vitro activity of DAS181 against a panel of 2009 oseltamivir-resistant seasonal H1N1 clinical isolates. The activity of DAS181 against nine 2009, two 2007, and two 2004 clinical isolates of seasonal IFV H1N1 was examined using plaque number reduction assay on MDCK cells. DAS181 strongly inhibited all tested isolates. EC50 values remained constant against isolates from 2004, 2007, and 2009, suggesting that there was no change in DAS181 sensitivity over time. As expected, all 2007 and 2009 isolates were resistant to oseltamivir, consistent with the identification of the H274Y mutation in the NA gene of all these isolates. Interestingly, several of the 2007 and 2009 isolates also exhibited reduced sensitivity to zanamivir, and accompanying HA mutations near the sialic acid binding site were observed. DAS181 inhibits IFV that is resistant to NAIs. Thus, DAS181 may offer an alternative therapeutic option for seasonal or pandemic IFVs that become resistant to currently available antiviral drugs.

Sialidase Fusion Protein as Inhibitor of Infection by Influenza Virus

Malakhov et al. reported that sialidase fusion protein could be used as a novel broad-spectrum inhibitor of influenza virus infection (2). They showed a 90% effective concentration (nM) of 6.5 ± 86.8 in Table 1 as the concentration of DAS181 that gave rise to 90% cell protection from influenza virus A/Victoria/504/2000 infection (2). However, it is extremely unusual for three positive numbers with an average of 6.5 to have a standard deviation of 86.8, suggesting that the standard deviation may be a typographical error. The authors should explain this oddity. Malakhov et al. mentioned in the abstract of their paper that “mouse and ferret studies confirmed significant in vivo efficacy of the sialidase fusion in both prophylactic and treatment modes.” In my opinion, the ferret studies presented in Table 6 of the paper do not really support that statement. Comparing the mean values of virus titers (log10 50% tissue culture infective dose/ml) between vehicle-treated ferrets and sialidase fusion protein-treated ferrets on day 1 (4.4 versus 2.4), day 2 (4.7 versus 4.6), day 3 (2.7 versus 3.9), day 4 (3.7 versus 3.4), and day 5 (negative value versus 2.6) postinfection, it is hard for readers to understand how Malakhov et al. could make the conclusion that differences between these two groups are significant. Furthermore, Malakhov et al. ignored the fact that in the group treated with the sialidase fusion protein, 7 of 12 ferrets shed virus on days 2 and 3 postchallenge, and 6 of 12 ferrets shed virus on day 4 postchallenge. More importantly, 2 of 12 ferrets in the group treated with the sialidase fusion protein still shed virus on day 5 postchallenge, while none of the 8 ferrets in the vehicle-treated group shed virus. Malakhov et al. also didn't mention that nasal virus titers in the sialidase fusion protein-treated ferrets were about 15 times higher on day 3 and at least 200 times higher on day 5 postchallenge than those in the vehicle-treated ferrets. Malakhov et al. should explain why 2 of 12 sialidase fusion protein-treated ferrets shed virus on day 5 postchallenge while none of the 8 vehicle-treated ferrets did and repeat the ferret studies before making conclusive statements. Nevertheless, Malakhov et al. did realize and describe the limitations of the ferret study in the Discussion section. Additionally, Malakhov et al. omitted the chapter title, page numbers, and names of the editors for their reference 12, which makes it difficult for readers to find the cited reference. Therefore, I list here the complete information for that reference (1).

Concerns of using sialidase fusion protein as an experimental drug to combat seasonal and pandemic influenza

Sialidase fusion protein is reported to have great potential to combat seasonal and pandemic influenza, because it may prevent influenza virus infection by removing all sialic acid receptors from host cells. Meanwhile, recent studies have demonstrated that absence of alpha2-6 sialic acid does not protect a cell from influenza infection, and influenza virus can infect desialylated cells, suggesting that accessible surface sialic acid is dispensable for influenza virus infection. In addition, studies using animal models have shown that neuraminidase promotes adherence and invasion of Streptococcus pneumoniae, because cleavage of sialic acid from host cells exposes cryptic receptors for S. pneumoniae. The purpose of this article is to comment on the benefits and potential risks of using sialidase fusion protein as an experimental drug to combat seasonal and pandemic influenza.

Comment on: Antimicrobial policies in the neonatal units of the United Kingdom and Republic of Ireland

1. Zhang H. Concerns of using sialidase fusion protein as an experimental drug to combat seasonal and pandemic influenza. J Antimicrob Chemother 2008; 62: 219–23. 2. Nicholls JM, Aschenbrenner LM, Paulson JC et al. Comment on: Concerns of using sialidase fusion protein as an experimental drug to combat seasonal and pandemic influenza. J Antimicrob Chemother 2008; 62: 426–8. 3. McCullers JA, Bartmess KC. Role of neuraminidase in lethal synergism between influenza virus and Streptococcus pneumoniae. J Infect Dis 2003; 187: 1000–9. 4. Peltola VT, Murti KG, McCullers JA. Influenza virus neuraminidase contributes to secondary bacterial pneumonia. J Infect Dis 2005; 192: 249–57. 5. LeVine AM, Koeningsknecht V, Stark JM. Decreased pulmonary clearance of S. pneumoniae following influenza A infection in mice. J Virol Methods 2001; 94: 173–86. 6. Braun LE, Sutter DE, Eichelberger MC et al. Co-infection of the cotton rat (Sigmodon hispidus) with Staphylococcus aureus and influenza A virus results in synergistic disease. Microb Pathog 2007; 43: 208–16. 7. Stray SJ, Cummings RD, Air GM. Influenza virus infection of desialylated cells. Glycobiology 2000; 10: 649–58.

Concerns of using sialidase fusion protein as an experimental drug to combat seasonal and pandemic influenza--author's response

Concerns of using sialidase fusion protein as an experimental drug to combat seasonal and pandemic influenza--author's response

Comment on: Concerns of using sialidase fusion protein as an experimental drug to combat seasonal and pandemic influenza

Sir, Zhang 1 questioned the validity of developing a sialidase fusion protein (DAS181) as an experimental drug against influenza. He raised two main concerns—first, that sialidase treatment would result in a greater chance of bacterial infection by exposing novel cryptic binding sites to bacterial pathogens and second, that influenza virus (IFV) receptors may be different from sialic acids (SA); thus, sialidase treatment may be ineffective. Although we agree with Zhang that the safety and efficacy of any novel therapeutic candidate, including DAS181, needs to be evaluated cautiously, statements made by him on sialidase treatment and the general view presented on the role of SA in IFV infection are either incomplete or incorrect. We thus offer the following corrections. It is known that IFV infection is associated with an increased risk of secondary infection by Streptococcus pneumoniae. 2 A clear distinction that needs to be made, however, is whether the secondary S. pneumoniae infection arises from viral neuraminidase (a sialidase) by itself or from the secondary effects of IFV infection. Scientific evidence clearly supports the latter, as influenza infection in the trachea and bronchus causes much deeper changes to the airway epithelium than could be caused by treatment of the epithelial cell surface with a sialidase. Influenza infection in humans results in extensive denudation of the ciliated epithelial cells down to the basal cells, or even to the