Synergistic enhancement of beta-lactam antibiotics by modified tunicamycin analogs TunR1 and TunR2

Authors: Price, Neil; Jackson, Michael - Mike; SINGH, VINAYAK - University Of Cape Town; Hartman, Trina; Dowd, Patrick; Blackburn, Judith

Submitted to: Journal of Antibiotics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/8/2019
Publication Date: 8/16/2019
Citation: Price, N.J.P., Jackson, M.A., Singh, V., Hartman, T.M., Dowd, P.F., Blackburn, J.A. 2019. Synergistic enhancement of beta-lactam antibiotics by modified tunicamycin analogs TunR1 and TunR2. Journal of Antibiotics. 72(11):807-815. https://doi.org/10.1038/s41429-019-0220-x.
DOI: https://doi.org/10.1038/s41429-019-0220-x

Interpretive Summary: The penicillins, which represent a broad group of antibiotics, are the most important antimicrobial agents used in medicine and agriculture today. Over the years, the continual rise of antibiotic resistance has threatened the ability to rely on these important drugs to treat diseases and it has been estimated that at least 23,000 people die each year from antibiotic-resistant bacteria. A natural product called tunicamycin (TUN), which is produced by several Streptomyces bacteria has been shown to enhance the antibacterial activity of penicillins, it is also highly toxic to mammals. We have previously described methods to chemically modify TUN intoTunR1 and TunR2 that are significantly less toxic to mammals, but still enhance the activity of some of the more common penicillins. In this study, we tested the ability of TunR1 and TunR2 to enhance most of the remaining classes of penicillin antibiotics, including penems, cephems, and third generation penicillins. In a live animal model TunR2 was shown to be effectively non-toxic. The biggest improvements in activity we obtained were greater than 256-fold with aminothiazolidyl cephems, which include cefquinome - an antibiotic highly important to the animal farming industry. This new technology has the ability to significantly reduce antibiotic usage and ameliorate the impact of antibiotic resistance.

Technical Abstract: Antibiotics are routinely fed to livestock, fish, and poultry as growth promoters and to treat veterinary bacterial diseases. Nearly all dairy cows in the US, for example, receive prophylactic doses of antibiotics to control and prevent bovine mastitis, primarily with penicillins, cephalosporins, or other beta-lactam drugs. Besides the continuing problem of antibiotics- resistance development, there is also a significant threat to human health resulting from over-zealous antibiotic use in agriculture. Several compounds, including tunicamycin, greatly enhance the antibacterial activity of the ß-lactams, thereby lowering the MICs to the extent of overcoming resistance, although tunicamycin is also significantly toxic to mammalian cells. We have previously shown that selective hydrogenation of tunicamycin gives modified compounds (TunR1 and TunR2) with considerably reduced toxicity, but which retain the enhancement of ß-lactams. Here we show that TunR1 and TunR2 enhance the antibacterial activity of multiple ß-lactam family members, including penems, cephems, and third generation penicillins, to a similar extent as does the native tunicamycin. Eleven of the ß-lactams tested were enhanced 2- to >256-fold against Bacillus subtilis, with comparable results against a penicillin G-resistant strain. The most significant enhancements (>128 – 256 fold, FICI 0.14 – 0.19) were obtained with third generation aminothiazolidyl cephems, including cefotaxime, ceftazidime, and cefquinome - an antibiotic highly important to the animal farming industry. Our results support the potential of low toxicity tunicamycin analogs (TunR1 and TunR2) as clinically-valid, synergistic enhancers for the entire group of ß-lactam antibiotics.