NVC-422 Does Not Generate Resistance in MRSA, Staphylococcus aureus, Pseudomonas aeruginosa and Escherichia coli after Multiple Serial Passages at Sub-Inhibitory Concentrations 5980 Horton Street, Suite 550 L. D’Lima, L. Friedman, P. Xu, L. Wang, M. Anderson, D. Debabov Emeryville, CA 94608 NovaBay Pharmaceuticals, Inc., Emeryville, CA 2011 ICAAC, Chicago; September 17-20 Phone (510) 899-8800 FAX (510) 280-8730 E-135 [email protected] Abstract Results Background: NVC-422 (N,N-dichloro-2,2-dimethyltaurine) is a potent, broad-spectrum, fast-acting antimicrobial agent with a novel mechanism of action. This study evaluated the potential of NVC-422 and comparator antibiotics ciprofloxacin, mupirocin, fusidic acid and retapamulin to generate drug resistance in Gram-negative and Gram-positive Figure 1: Serial passage of S. aureus ATCC 29213 against NVC-422 (blue) and Ciprofloxacin (red). Figure 3: Serial passage of E. coli ATCC 25922 against NVC-422 (blue) and Ciprofloxacin (red). Figure 5: Serial passage of MRSA ATCC 33591 against NVC-422 (blue) and Retapamulin (yellow). strains in a multiple serial passage study.
Methods: Serial passages using CLSI MIC methodology were used to study evolution of resistance at 0.5 MIC as 70.0 70.0 determined by the previous passage. The strains used were: Escherichia coli ATCC 25922, Pseudomonas aeruginosa 260.0 PAO1, Staphylococcus aureus ATCC 29213 and MRSA ATCC 33591. Stability of compounds in cation adjusted 240.0 60.0 NVC-422: 60.0 Mueller Hinton broth (CAMHB) and M9 minimal medium was studied using HPLC/UV. From our stability studies of Ciprofloxacin 220.0 NVC-422 in media and the ability of microbes to grow in a minimal M9 medium, we selected M9 medium for P. 200.0 50.0 NO RESISTANCE 50.0 180.0 aeruginosa and E. coli and CAMHB for S. aureus and MRSA. 160.0 40.0 140.0 Results: MIC of ciprofloxacin increased by 256 fold in E. coli, and 32 fold in P. aeruginosa and S. aureus. Mupirocin, 40.0 120.0 30.0 fusidic acid and retapamulin MICs against MRSA increased by 64, 256 and 16 fold respectively. In contrast, no MIC in
100.0 MIC in change Fold Fold change in MIC in change Fold
increase in MIC was observed for NVC-422 in any of the 19 independent bacterial cultures tested. At 37°C the half-life 30.0 changeFold in MIC 80.0 20.0 increase of NVC-422 is 30 minutes in CAMHB, and >24 hrs in M9 media. 60.0 Fold 40.0 20.0 10.0
Conclusions: NVC-422 is a potent, broad-spectrum antimicrobial agent. This study shows that NVC-422 did not MIC in change Fold 20.0 0.0 0.0 generate drug resistance in Gram-negative or Gram-positive pathogens, while comparator antibiotics ciprofloxacin, 10.0 0 0 2 mupirocin, fusidic acid and retapamulin showed a dramatic 16-256 fold increase in MIC after repeated sub-lethal 1 4 2 6 3 8 exposure over 25 to 50 passages. NVC-422 is currently in Phase II clinical trials for the treatment of impetigo and for 4 10 0.00 5 12 1 6 2 14 the prevention of urinary catheter blockage and encrustation (UCBE). 3 7 16 4 8 18 5 9 20 6 10 22 7 11 24 8 12 26 9 13 28 Introduction 10 14 30 11 32 12 15 34 13 16 36
In healthcare facilities around the world, bacterial pathogens that express multiple resistance mechanisms are becoming 14 17 38
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common, complicating treatment and increasing human morbidity and mortality. The development of resistance to one 16 19 42 422
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or multiple drugs results from medical and agricultural use and overuse of antimicrobials that promote transfer of 19 NVC
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resistance by both vertical and horizontal mechanisms. As a consequence, there is an urgent, unmet medical need Retapamulin
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for safe, novel antimicrobial agents that are effective against existing resistant pathogens and that carry a low potential NVC
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NVC-422 is a rapidly bactericidal antimicrobial agent that is active against a broad range of Gram-positive and Gram- NO RESISTANCE UnexposedRetapamulin -
negative species, including drug resistant pathogens. NVC-422 is cidal to pathogens by the oxidative modification of NO RESISTANCE 422 - sulfur-containing amino acids, such as methionine and cysteine, resulting in protein inactivation. Pathogens die within 422 minutes after exposure to lethal concentrations of NVC-422 as measured by our time-kill assays. This novel mechanism Conclusions differentiates chlorotaurines from traditional antibiotics by attacking multiple specific targets on the surface of bacteria; therefore, making it virtually impossible for pathogens to develop resistance. NVC-422: No resistance was observed for any of the 19 cultures passaged independently. (Figs.1-5). Figure 4: Serial passage of MRSA ATCC 33591 against NVC-422 (blue), Mupirocin (orange) and Fusidic acid We evaluated the propensity to select for resistance in vitro through multiple serial passages in the presence of sub- Furthermore no cross-resistance was observed with mupirocin, fusidic acid or retapamulin resistant strains when Figure 2: Serial passage of P. aeruginosa PAO1 against NVC-422 (blue) and Ciprofloxacin (red). (green). inhibitory concentrations of NVC-422, ciprofloxacin, mupirocin, fusidic acid and retapamulin. Twenty-five serial passages tested against NVC-422 (data not shown). of two E. coli ATCC 25922, five P. aeruginosa PAO1 and five S. aureus ATCC 29213 independent cultures and up to 50 serial passages with seven methicillin resistant S. aureus (MRSA) ATCC 33591 independent cultures were used to Ciprofloxacin: Resistance was generated with MIC increasing by 32-fold against S. aureus (Fig.1) and P. 600 study evolution of resistance to NVC-422 and other antibiotic drugs. 80.0 aeruginosa (Fig.2) and 256-fold against E. coli (Fig.3) over 25 passages.
70.0 Ciprofloxacin Fusidic acid Mupirocin: Resistance was generated with a 64-fold increase in MIC against MRSA over 25 passages (Fig.4). Materials and Methods 70 60.0 Fusidic acid: Similarly, resistance was generated with a 256-fold increase in MIC against MRSA (Fig.4). 6 NVC-422 preparation: The synthesis of NVC-422 has been described previously. The purity of NVC-422 powder was 50.0 60 determined to be 99.83% using an HPLC method. Retapamulin: Resistance was generated against MRSA with MIC increasing by 16-fold over 50 passages 40.0 Stability testing: Stock solutions of NVC-422 were prepared by dissolving NVC-422 powder in media. Stabilities of (Fig.5). 50
NVC-422 (100 mg/mL) in cation adjusted Mueller Hinton broth (CAMHB) and minimal M9 medium were tested at 37°C 30.0 Fold change in in MIC change Fold using Agilent HPLC-1200 equipped with diode array UV detector over a period of 24 hours. MIC in change Fold 20.0 40 References Bacterial cultures: E. coli 25922, S. aureus 29213 and MRSA 33591 were purchased from the American Type Culture 10.0 Collection (ATCC) while P. aeruginosa PAO1 was obtained from Queens University. All strains were grown on Tryptic MIC in change Fold 1. Tenover, F. C. 2006. Mechanisms of Antimicrobial Resistance in Bacteria. The American Journal of Medicine, 119: S3–S10. o 30 Soy Agar at 37 C overnight for Day 0. MIC in change Fold 0.0 2. Gilbert, D. N., S.J. Kohlhepp, K.A. Slama, G. Grunkemeier, G. Lewis, R.J. Dworkin, S.E. Slaughter, J.E. Leggett. 2001. Phenotypic 01 2 resistance of S. aureus, selected Enterobacteriaceae and P. aeruginosa after single and multiple in vitro exposures to ciprofloxacin, 3 4 Antimicrobial agents and MIC testing: MICs were tested by the Clinical and Laboratory Standards Institute (CLSI) 5 6 levofloxacin and trovafloxacin Antimicrob Agents Chemother, 45: 883-891. 20 7 7 8 broth microdilution method using CAMHB or M9 minimal medium. 9 3. Goossens, H., M. Ferech, R. Vander Stichele, M. Elseviers. 2005. Outpatient antibiotic use in Europe and association with resistance: a 10 11 12 cross-national database study. Lancet, 365: 579–87. 13 Multiple passage resistance selection studies: On Day 0, a single colony of the organism was inoculated in 5 ml of 14 4. Levy, S. B. 2000. Antibiotic and antiseptic resistance: impact on public health. Pediatr Infect Dis J, 19: S120–2. 10 15 5 16 CAMHB or M9 medium and grown for 2-3 hours. The culture was diluted with broth to obtain a final inoculum of 1 x 10 17 5. Shawar, R., N. Scangarella-Oman, M. Dalessandro, J. Breton, M. Twynholm, G. Li, H. Garges. 2009 Topical retapamulin in the 18 6 19 management of infected traumatic skin lesions, Therapeutics and Clinical Risk Management, 5: 41–49.
cfu/mL to 1 x 10 cfu/mL. One hundred eighty µL inoculum was added to each well of the 96 well plate. Twenty µl of 20 Fusidicacid Fusidic acidFusidic
21 acidFusidic Fusidic acidFusidic 6. Wang, L., B. Khosrovi, and R. Najafi 2008. N-Chloro-2,2-dimethyltaurines: stable homologues of N-chlorotaurines. Tetrahedron Lett, 49:
0 22 Fusidicacid
Fusidic acidFusidic Mupirocin drug dilutions in water were added to the well. Plates were incubated at 37°C for 16-20 hours and subsequently read acid Fusidic
23 422 Mupirocin
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spectrophotometrically at O.D . Readings >0.05 units are considered growth. For day 1 and each subsequent 6 7 422
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600nm 8 422 7. Clinical Laboratory Standards Institute. 2003. Methods for Dilution Antimicrobial Susceptibility Tests for Bacteria that Grow Aerobically;
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passage, inoculum was prepared from the well in the 96-well MIC plate with the highest concentration of the compound 15 16 422 Approved Standard M7-A6. Clinical Laboratory Standards Institute, Wayne, P - 17 NVC-422: NVC 18 19 20 NVC 21 22 that supported growth. Multiple independent cultures for each organism were prepared at day 1 and passaged 23 24 separately to maximize the chance of resistance development. Serial passages were performed in CAMHB for S. NO RESISTANCE Mupirocin aureus 29213 and MRSA 33591 and in M9 for E. coli 25922 and P. aeruginosa PAO1. Fifty passages were completed
UnexposedNVC Acknowledgements UnexposedMupirocin for retapamulin and NVC-422 against MRSA, while 25 passages were completed for other control antibiotics and NVC- UnexposedFusidic acid 422 against the other test organisms. A control strain previously unexposed to any antimicrobial was tested for each The authors would like to thank K. Poole of Queens University for providing the PAO1 strain. drug in every passage.