1. A Novel Application of Radiomimetic Compounds as Antibiotic Drugs
Christina Andros1, Aaron Chen2, Dawn Holmes2 and Daniel R. Kennedy1
1College of Pharmacy and 2College of Arts & Sciences
Western New England University, Springfield MA 01119
Introduction
Results
Conclusions
Protein-Chromophore enediynes were much more effective against gram positive organisms, perhaps due their size
The glycopeptides were the most effective drugs against gram negative organisms.
Overall, the non-protein chromophore enediyne (Cali) was the most broad spectrum agent but similar to the other enediynes, was more effective aginst gram positive bacteria.
All compounds showed effectiveness against S. aureus specifically, requiring no more than 0.10 mM of drug for an LD90. begin killing
All of the compounds induced antibiotic effects within 1 hour, with C-1027 doing so as quickly as 5 minutes.
Radiomimetics show potential as an option of last resort against a wide variety of bacteria strains. .
The present study investigated the antimicrobial properties of radiomimetic compounds, compounds that mimic the effect of ionizing radiation and directly induce DNA double stranded breaks. These compounds were originally isolated over 60 years ago as antibiotics, but as a result of their low therapeutic window, the clinical utility of radiomimetics has generally been reserved for cancer treatment (1). However, with the rapid increase of multi-drug resistant bacteria and significant advances in the specificity of radiomimetic targeting (2), the potential use of these compounds as antibiotics warrants further examination.
In this study, representative radiomimetics from each of the 3 major categories was examined; C-1027 and neocarzinostatin (NCS) from the protein-chromophore enediyne family; calicheamicin (Cali) from the non-protein chromophore enediyne family and bleomycin (Bleo) and tallysomycin S10b (Tally) from the glycopeptide family (1).
C Cali
NCS Bleo
Tally
Gram positive
Bleo (mm)
Tally (mm)
S. aureus
12.5± 3.5
S. pneumoniae
5.5± 7.8
9.5± 2.1
S. epidermis
18.5± 0.7
17.5± 0.7
E. faecalis
M. luteus
21± 0
20± 0
B.subtilis
25± 0
26.5± 1.4
Gram negative
K. pneumoniae
27.5± 2.1
26± 1.4
S. marcescens
22.5± 0.7
25.5± 0.7
P. vulgarus
19± 0
P. aeruginosa
13± 2.8
N. sicca
9.5± 0.7
9± 0
E. coli
23± 0
26± 0
Figure 1: Bleo and Tally on gram negative and gram positive organisms.
Figure 4: Overall average effectiveness of drugs on gram positive vs. negative organisms.
Gram positive
C-1027 (mm)
NCS (mm)
S. aureus
19.5± 6.4
11± 1.4
S. pneumoniae
13.5± 2.1
20.5± 0.7
S. epidermis
14.5± 2.1
14± 0
E. faecalis
11± 0
17.5± 0.7
M. luteus
15± 1.4
20.5± 2.1
B. subtilis
13± 1.4
14± 2.8
Gram negative
K. pneumoniae
S. marcescens
P. vulgarus
P. aeruginosa
9.5± 0.7
N. sicca
9±0
14.5± 0.7
E. coli
7± 0
Methods
Chemicals: C-1027, neocarzinostatin (NCS), bleomycin (Bleo) Tallysomycin S10B (Tally), and Calicheamicin (Cali)were generous gifts from Dr. Terry Beerman. C-1027, NCS, Bleo, and Tally were dissolved in water, while Cali was dissolved in DMSO.10 ml of each drug was used in each experiment. C-1027, NCS, and Cali were used at 10 mM, while Bleo and Tally were used at 1 mM.
Bacteria Strains: All bacteria strains were purchased from Carolina Biotechnologies (Burlington NC.) B. Subtilis, E. Coli, K. pneumoniae and E. faecalis were cultured on nutrient agar; S. marcescens, P. vulgaris and M. luteus were cultured on tryptic soy agar; while S. epidermidis, N. sicca S. Aureus and S. pneumoniae were cultured on brain heart infused agar.
Growth Inhibition Assays: All bacterial species were grown on solid agar medium with filter paper discs saturated with 10 mM of the compounds. Sensitivity to these compounds was determined by the size of zones of inhibition surrounding the discs on bacterial lawns.
Timed Plate Assays: S. Aureus was diluted in BHI and mixed with 10µM of each compound. Each mixture was spun down in a centrifuge and the supernantant was removed. The remaining mixture was plated at five, fifteen, and sixty minutes and placed in an incubator at 37°C overnight to grow.
Xi Z, Goldberg IH. DNA-Damaging Enediyne Compounds. In: Barton DHR, Nakanishi, K., and Meth-Cohn, O., editor. Comprehensive Natural Products Chemistry. Oxford, U.K.: Elsevier Science; p
2. Stasi R. Gemtuzumab ozogamicin: an anti-CD33 immunoconjugate for the
treatment of acute myeloid leukaemia. Expert Opinion on Biological Therapy, Vol 8 (4) p
C-1027
Cali
NCS
Bleo
Figure 2: C-1027 and NCS on gram negative and gram positive organisms.
Figure 5: Minimum inhibitory concentrations of each compound with S. aureus.
Radiomimetic compounds have some unique properties that would be very advantageous as antibiotic therapies. For example, radiomimetic compounds are generally very potent as anti-tumor agents, a property that would be expected to translate to their antimicrobial activity. Additionally,
Gram positive
Cali (mm)
S. aureus
17.5± 3.5
S. pneumoniae
43± 4.2
S. epidermis
27.5± 0.7
E. faecalis
21.5± 0.7
M. luteus
32.35± 0.4
B. subtilis
27± 0
Gram negative
K. pneumoniae
15.25± 0.4
S. marcescens
P. vulgarus
15± 0
P. aeruginosa
24± 0
N. sicca
18.5± 0.7
E. coli
17± 0
References
radiomimetics are very fast acting compounds, with a demonstrated induction of damage in as little as ten minutes. In this study, we have examined the activity of representative members of each of the radiomimetic families against a variety of gram positive and gram negative organisms. We then further determined the actual potency of the compounds. Finally, the time required for each of the radiomimetics to kill the bacteria was determined.
Figure 3: Cali on gram negative and gram positive organisms.
Figure 6: Time of action
Presentation for the 114th General Meeting of the American Society of Microbiology, Boston MA, May 2014