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
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 multidrug 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 nonprotein chromophore enediyne family and bleomycin (Bleo) and tallysomycin
S10b (Tally) from the glycopeptide family (1).
Gram positive
S. aureus
S. pneumoniae
S. epidermis
E. faecalis
M. luteus
B.subtilis
Gram negative
K. pneumoniae
S. marcescens
P. vulgarus
P. aeruginosa
N. sicca
E. coli
Bleo (mm)
12.5± 3.5
5.5± 7.8
18.5± 0.7
0
21± 0
25± 0
Tally (mm)
12.5± 3.5
9.5± 2.1
17.5± 0.7
0
20± 0
26.5± 1.4
27.5± 2.1
22.5± 0.7
19± 0
12.5± 3.5
9.5± 0.7
23± 0
26± 1.4
25.5± 0.7
25± 0
13± 2.8
9± 0
26± 0
Figure 1: Bleo and Tally on gram negative and gram positive organisms.
C-1027
C1027
NCS
NCS
Cali
Cali
Bleo
Gram positive
S. aureus
S. pneumoniae
S. epidermis
E. faecalis
M. luteus
B. subtilis
Gram negative
K. pneumoniae
S. marcescens
P. vulgarus
P. aeruginosa
N. sicca
E. coli
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
Tally
antimicrobial activity. Additionally,
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.
Gram positive
S. aureus
S. pneumoniae
S. epidermis
E. faecalis
M. luteus
B. subtilis
Gram negative
K. pneumoniae
S. marcescens
P. vulgarus
P. aeruginosa
N. sicca
E. coli
• Protein-Chromophore enediynes were much more effective against gram
positive organisms, perhaps due their size
Average Effect of Each Drug
30
• The glycopeptides were the most effective drugs against gram
negative organisms.
25
20
Gram +
15
Gram -
10
• 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
5
0
Bleo
Tally
Cali
C-1027
NCS
Figure 4: Overall average effectiveness of drugs on gram positive vs. negative organisms.
• 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.
C-1027 (mm)
19.5± 6.4
13.5± 2.1
14.5± 2.1
11± 0
15± 1.4
13± 1.4
NCS (mm)
11± 1.4
20.5± 0.7
14± 0
17.5± 0.7
20.5± 2.1
14± 2.8
.
0
0
0
9.5± 0.7
9±0
0
0
0
0
15± 1.4
14.5± 0.7
7± 0
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.
Figure 2: C-1027 and NCS on gram negative and gram positive organisms.
Bleo
Conclusions
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.
Figure 5: Minimum inhibitory concentrations of each compound with S. aureus.
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.
Cali (mm)
17.5± 3.5
43± 4.2
27.5± 0.7
21.5± 0.7
32.35± 0.4
27± 0
References
1. 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; 1999. p. 553-92.
15.25± 0.4
15.25± 0.4
15± 0
24± 0
18.5± 0.7
17± 0
Figure 3: Cali on gram negative and gram positive organisms.
Methods
2. Stasi R. Gemtuzumab ozogamicin: an anti-CD33 immunoconjugate for the
treatment of acute myeloid leukaemia. Expert Opinion on Biological Therapy,
Vol 8 (4) p527-40.
Figure 6: Time of action
Presentation for the 114th General Meeting of the American Society of Microbiology, Boston MA, May 2014