A new article from The Lancet reports the synthesis of an antibiotic that not only kills all drug-resistant bacteria that have been tested (in vitro or in vivo in mice), but also seems impervious to being rendered ineffective by the evolution of bacteria. If this works out in humans, it would be a terrific advance in medicine: an antibiotic that can be used on people whose infections aren’t treatable because the bacteria are drug-resistant (this is common in TB, for instance), but also an antibiotic that seems to be impervious to the evolution of bacterial resistance. It’s also easy to synthesize using organic chemistry, and can be easily tweaked in its structure just in case some bacteria eventually do develop resistance.
Click on the screenshot below to read the original article, or download the pdf here. The researchers hail mostly from UC Santa Barbara, but also come from UC Davis, Singapore, and Australia.
I found the link from reader Jeannie, who sent me a short piece on kottke.org calling attention to the results. That linked to the original paper (above), but added this:
The discovery was serendipitous. The U.S. Army had a pressing need to charge cell phones while in the field — essential for soldier survival. Because bacteria are miniature power plants, compounds were designed by Bazan’s group to harness bacterial energy as a “‘microbial”’ battery. Later the idea arose to re-purpose these compounds as potential antibiotics.
“When asked to determine if the chemical compounds could serve as antibiotics, we thought they would be highly toxic to human cells similar to bleach,” said Mahan, the project lead investigator. “Most were toxic — but one was not — and it could kill every bacterial pathogen we tested.”
Such are the totally unexpected side effects of research, and although this was applied research, it’s also a justification for pure research. Remember: the whole apparatus for sequencing DNA, and then the CRISPR technique, gene editing, and so on, began with the simple observation that some bacteria live in hot springs near the boiling point, and some curious scientists who asked “I wonder how they do it.”
Back to the paper. My take will be short as it’s complicated and, to be sure, parts of it are beyond me. The compound they found was COE2-2hexyl, and below is the structure. It can be synthesized without much difficulty using standard methods of organic chemistry, so you don’t have to get it from massive quantities of fungi or other organisms. Captions are from the paper.
Asyou see, it consists of two aromatic central chains with four long carbon tails, each of which has a nitrogen atom in it:

It works, as implied in the caption above, by attacking the cell membranes of bacteria, disrupting essential functions of the membrane. These include the ability of the bacterium to absorb and emit cell contents, to help the bacterium metabolize, and also, critically, to divide. Here’s how COE2-2hexyl looks when it gets into the bacterial membrane and disrupts it. Other similar compounds, called COEs, have the same shape and do the same thing:

This compound was tested on 17 bacterial isolates taken from people with drug-resistant infections:
You’ll recognize some of these as bacteria that cause gonorrhea, tuberculosis, pneumonia, dysentery (Shigella flexneri) Acinetobacter baumannii, which causes bad infections associated with hospitals, and so on. All of these were isolates taken from humans who had shown antibiotic resistance. The drugs were tested in vitro, using mouse cell cultures that were infected with bacterial isolates from humans, and also in vivo, in mice that had been infected (there were of course controls that had been mock-treated). (I have to add that I feel sorry for the mice in the control group.)
As the authors note (my emphasis):
Expanded antibacterial activity analyses revealed that COE2-2hexyl exhibited broad antibacterial activity against all 17 clinical bacterial isolates tested (Table 1). Notably, methicillin-resistant S. aureus (MRSA, MT3302) and CRE K. pneumoniae (MT3325) were derived from sepsis patients with refractory bacteremia, whereby the CRE organism was resistant to 20/22 antibiotics determined by clinical VITEK testing (bioMerieux, Inc.) and 19/24 antibiotics determined by broth microdilution.
Note that it worked when nearly all antibiotics had failed. The authors also made two derivatives of this compound, adding one cabon atom to two of the four chains; these two compounds also showed antibacterial activity against 9 drug-resistant bacterial isolates tested.
Of course you’re wondering “well, this is great, but is it safe?” It was, even in higher doses, and in the doses that killed bacteria. But of course it was safe in mice but may not be in humans. Clinical testing will be in order, and that might take a long time before we see if this and its derivatives are truly “wonder drugs”.
Finally, testing the compound for relatively long periods against bacteria showed that the bacteria did NOT develop immunity to the drug (that’s via natural selection, of course), which is really good news, since few antibiotics have not been overcome by mutations that render bacteria immune to them. (I believe that the Streptococcus bacterium that causes “strep throat” has never evolved resistance to penicillin, nor has the polio virus evolved immunity to polio vaccines, but such cases are rare.) Now, as Orgel’s Second Rule states, “evolution is cleverer than you are,” and eventually, if COE2-2hexyl is used for long enough, bacteria might find a way around it. But right now, things look promising.
Finally why are bacteria unable to evolve resistance to COE2-2hexyl? The clue is in this sentence in the paper:
COE2-2hexyl had specific effects on multiple membrane-associated functions that may act together to disrupt bacterial cell viability and the evolution of drug-resistance through a mechanism of action distinct from most membrane disrupting antimicrobials or detergents which destabilize.
The compound, it seems, disrupts many different functions of the bacterial membrane, and while one disruption might be fixed by one or more mutations in the bacteria, something that screws up your system big time, and in multiple ways, may be impossible to repair, as bacterial mutations that overcome one disruption may make it harder to fix the other disruptions. The more ways a drug can screw up a bug, the less likely it is that the bug can evolve resistance. But remember—bacteria are clever.
I’ll end with the authors’ final paragraph about what’s good about this compound and what needs to be done (mostly efficacy and safety testint in humans). But if this thing works out, it will be a medical advance of almost unparalleled value (bolding is mine):
The ease of molecular design and modular nature of COEs offer many advantages over conventional antimicrobials due to their intermediate molecular size, sufficient aqueous solubility to achieve efficacy, and the absence of complex chemical structures/chiral centers, making synthesis simple, scalable and affordable. The COE refinement workflow potentially accelerates lead-compound optimization by more rapid screening of novel compounds for the iterative directed-design process. It also reduces the time and cost of subsequent biophysical characterization, medicinal chemistry and bioassays, ultimately facilitating the discovery of novel compounds with improved pharmacological properties. Additionally, COEs provide an approach to gain new insights into microbial physiology, including membrane structure/function and mechanism of drug action/resistance, while also generating a suite of tools that enable the modulation of bacterial and mammalian membranes for scientific or manufacturing uses. Notably, further COE safety and efficacy studies will need to be conducted on a larger scale to ensure adequate understanding of the clinical benefits and risks to assure clinical efficacy and toxicity before COEs can be added to the therapeutic armamentarium. Despite these limitations, the modular design of COEs enables the construction of a spectrum of compounds with the potential as a new versatile therapy for the emergence and rapid global spread of pathogens that are resistant to all, or nearly all, existing antimicrobial medicines.
h/t: Jeannie








