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Sitting on a metal bed in a bleak hospital ward in central London is
Jim. Jim is sick. He has pneumonia, and when he breathes he wheezes like
a steam train. For the first time in many years, Jim’s prognosis is not
certain. In April a woman patient at Guy’s Hospital in London died from
pneumonia caused by an antibiotic-resistant strain of Streptococcus pneumoniae
that defeated every one of the doctors’ antibiotic weapons.

Increasingly, the medical columns of newspapers and magazines have been
busy documenting the rise of strains of bacteria that no longer succumb
to antibiotics. First there was drug-resistant Mycobacterium tuberculosis.
TB now accounts for one in seven new cases in the US and five per cent of
these patients are expected to die. In Britain, the number of hospitals
that sent the Central Public Health Laboratory’s Antibiotic Reference Unit
samples of penicillin-resistant S. pneumoniae rose from around 25 in 1987
to over 130 in 1993. And in 1992, 13 300 hospital patients in the US died
from bacterial infections that refused to respond to antibiotic treatment.

Fading magic

The message seems clear: antibiotics are losing their magic touch after
decades of incautious prescription, improper use and the inevitable spread
of bacterial genes that confer drug resistance. ‘We have always assumed
we will have another antibiotic saviour up our sleeves,’ said Alexander
Tomasz, professor of microbiology at Rockefeller University in New York,
when speaking at the American Association for the Advancement of Science
meeting in February. ‘We can’t make that assumption any more.’

In the 1980s, many drugs companies and researchers gave up trying to
develop new approaches to antibiotics, believing that existing drugs (or
modified versions of them) could keep pace with infectious bacteria. ‘It
seemed that we had everything we needed, and there was a greater medical
need for drugs to treat ailments such as high blood pressure,’ says Mike
Marriott, head of chemotherapy for Glaxo Group Research. Now the quest
for antibacterial drugs and therapies has become hot science as laboratories
move away from research based solely on penicillin-style compounds.

In the old days scientists looked for antibiotic substances mainly in
organisms from soil. But today researchers are broadening their search to
include creatures as diverse as frogs and sharks. In some laboratories,
the break with tradition is even greater. Instead of focusing on drugs that
block bacterial growth, researchers are trying to develop carbohydrate or
protein molecules that can boost people’s natural defences against bacteria.
In the end, say advocates of this immunological approach, it might be the
only way to deal with the small pockets of resistant bacteria that survive
antibiotic treatments.

New wave agents

Most of these ‘new wave’ antibacterial agents have yet to make it into
clinical trials, and the researchers behind them are keeping the molecular
structures close to their chests. Leading the way are small American companies
with names like Alpha-Beta Technology (Worcester, Massachusetts), Microcide
Pharmaceuticals (Silicon Valley) and Magainin Pharmaceuticals (Plymouth
Meeting in Pennsylvania). But competition from mainstream companies, such
as Glaxo, is gradually building up. It is hard for anyone to be indifferent
when people are once again dying from TB, pneumonia and meningitis, and
the traditional antibiotics such as the penicillins, cephalosporins and
quinolones are beginning to fail.

These drugs work by blocking bacterial cell division. Some species of
bacterium can produce between ten and twenty million offspring in a day.
Penicillins, the oldest class of antibiotics, stop bacteria making the peptidoglycans
needed to build the polysaccharide wall that surrounds all bacteria. Cephalosporins
work in a similar way, while quinolones act by blocking DNA synthesis.

Once antibiotics have halted the growth of a bacterial colony, any survivors
must be dealt with by the immune system. But bacteria are no slouches. If
the immune system fails to eradicate all drug-resistant survivors, these
bacteria will begin to pass their genes to other bacteria in the host. And
that can spell disaster, for a single gene can make all the difference between
a bacteria being vulnerable or resistant to a drug. Some strains of M. tuberculosis,
for example, owe their resistance to the drug isoniazid to the lack of a
gene encoding an enzyme, catalase, which plays a part in activating the
drug.

Alternatively, resistant bacteria can be transferred from person to
person, or animal to animal simply by direct contact or non-sterile instruments.
In hospitals, the threat of resistant bacteria running amok has never been
greater, with more and more patients suffering from impaired immunity –
not just people with HIV, but transplant patients, the elderly and people
undergoing chemotherapy.

This is why there is such interest in developing antibacterial therapies
that work by boosting immunity. One such compound is Betafectin, a carbohydrate
polymer based on glucan, a substance found in yeast cell walls. Alpha-Beta
Technology is developing Betafectin as a way of stimulating the body’s
natural defences against infection by enhancing the efficiency of white
blood cells called macrophages and neutrophils, explains Spiros Jamas, chief
executive officer of Alpha-Beta.

These cells are the body’s first defence against invading bacteria and
other pathogens. Their job is to destroy the invading organisms before the
body produces antibodies against the foreign proteins. Betafectin is thought
to work by mimicking a bacterial attack. When a bacterium comes into contact
with a white blood cell, it stimulates an antenna-like molecule found on
the cell’s surface known as the B glucan receptor. This in turn triggers
a series of biochemical messages which increase the antibacterial activity
of the white cells, at the site of infection as well as attracting more
macrophages and neutrophils to the area and in some instances increasing
the number of white cells in the blood. The result is an improved immune
response.

Betafectin seems able to act as a sentinel for the immune system, locking
on to the B glucan receptor to raise the alarm. This type of stimulation
could offer great benefits to people with impaired immune systems, says
Jamas. He points out that healthy people have few problems ‘mopping-up’
the bacteria left over after antibiotic treatment. But people with damaged
immunity may never eradicate all the pathogenic bacteria, so providing a
breeding ground for antibiotic-resistant bacteria. In these circumstances
Betafectin may give the immune system the boost it needs to destroy the
residual bacteria.

Immune response

Alpha-Beta did its first clinical trials on healthy volunteers in 1992.
The trials showed that a single intravenous dose of Betafectin increased
the number of macrophages and neutrophils in the volunteers’ blood and improved
their killing capacity. The increased immune response could be related to
the amount of the drug given. A trial of Betafectin began in late 1992 when
the drug was given to 17 patients undergoing major surgery. These patients
are often given a cocktail of antibiotics as a prophylactic. This has several
unwelcome side effects. The first is that the antibiotics will kill off
harmless as well as harmful bacteria. It also gives drug-resistant bacteria
a chance to swap genetic material, so encouraging the growth of bacteria
which are resistant to many drugs.

In the Betafectin trial, the patients given the drug spent on average
five days less in hospital, and three days less in intensive care than the
13 control patients who were given a placebo. If Betafectin proves effective
enough to win approval from the US Food and Drug Administration, it is most
likely to be used alongside traditional antibiotics, rather than as a replacement.
But Alpha-Beta hopes that the drug will enable doctors to reduce the number
of antibiotics used before major surgery. The company believes Betafectin
may be useful for patients suffering from severe burns who are prone to
bacterial infections and it could help patients with AIDS fend off opportunistic
bacterial and fungal invasions. Betafectin is unlikely to face the problems
of resistance seen with antibiotics, says Jamas, because the drug is stimulating
a natural immune response.

Other companies have looked at boosting the immune systems, but Alpha-Beta
is the first to use a genetically engineered carbohydrate. Jamas began his
research into Betafectin in the early 1980s at the Massachusetts Institute
of Technology. At that time it was becoming clear that the vast numbers
of complex carbohydrate molecules found on the surfaces of cells act like
distinctive chemical signatures, allowing cells to recognise each other
and deliver biochemical signals. In 1985 Joyce Czop, associate professor
of medicine at Harvard Medical School discovered the B glucan receptor.

Czop worked with Alpha-Beta on the structure of this receptor and on
screening glucans to find the carbohydrate that elicited the best immune
response. Once the glucan structure had been identified, Alpha-Beta engineered
a strain of yeast that could produce this optimised carbohydrate in usable
quantities. As part of this process, the company identified the genes involved
in the synthesis of the optimised B glucan, and it is now in the process
of cloning these genes.

Another start-up company in the US is also investigating the therapeutic
potential of carbohydrates. In Pennsylvania, Neose is considering using
a carbohydrate as an antibacterial agent. But its aim is to make the carbohydrate
compete with bacteria for the protein receptor sites on epithelial cells.
It is known, for example, that a carbohydrate on the surface of Helicobacter
pylori – which his associated with ulcers – attaches to protein receptor
sites on epithelial cells. Neose believes it can reduce the impact of infection
by giving a patient a large amount of carbohydrate structurally similar
to the one on the bacteria.

There are, however, limitations with carbohydrate drugs. One of the
main criticisms levelled against Betafectin, for example, is that acids
in a patient’s stomach break down the carbohydrate so that the drug can
only be injected or given by an intravenous drip.

Small is practical

That is why other companies are more interested in making antibacterial
drugs based on smaller molecules. Abingdon-based Oxford Glycosystems, for
example, have identified carbohydrates that play a part in the immune response,
and these are being used as lead compounds. They hope to use their knowledge
of the carbohydrates to produce molecules that look like these carbohydrates.
Glaxo Group Research is also interested in small molecule drugs. And it
is in the process of developing a new range of penicillin-related drugs
using this technique. The company also hopes to make small molecule drugs
that are specific for a particular strain of bacteria such as M. tuberculosis.

Interest in developing these specialised killers is high. Microcide
Pharmaceuticals (MPI) was founded in 1992 with the aim of developing novel
antibacterial agents to treat infections, including antibiotic resistant
infections acquired in hospitals and nursing homes. Michael Sterns, director
of operations and business development for MPI says that the company’s approach
is to understand the genetic regulation of bacterial infections. From this
work MPI hopes to identify new target processes for antibacterial agents
to attack. The next stage is to identify small molecule lead compounds that
can be screened for their ability to attack these targets using a variety
of chemical and computer-based molecular modelling techniques. The most
successful will be refined for clinical use.

But not all the research into future antibiotics is so specific. There
are still some companies who are looking beyond the laboratory for their
inspiration. One example is Magainin Pharmaceuticals. Michael Zasloff, Magainin’s
executive vice president, shot to fame in the late 1980s when he publicised
his discovery that African clawed frogs (Xenopus laevis) contained a chemical
in their skin that helped them fight infection. He called this chemical
‘magainin’, the Hebrew word for shield.

Magainin was found to be a small peptide (around 20 amino acids long)
that was stored in the frogs’ nerve endings, called granular glands. The
chemical not only killed bacteria, it also appeared to be effective against
fungi, parasites and even some tumour cells. Since the initial discovery
in 1986, Zasloff has found another magainin in frogs, as well as similar
substances in humans and insects. He also recently found a new antibiotic
substance in dog fish sharks. This chemical (squalamine) is a steroid found
in the blood and tissue of the fish.

Zasloff believes all these natural antibiotics work in a similar way:
by attaching themselves to the foreign cell’s membrane, and then creating
holes so that the unwanted organism becomes leaky and dies. In the case
of magainin, the peptide is thought to identify bacteria and fungi by their
negatively charged surface.

Magainin Pharmaceuticals has synthesised antibiotics based on the magainins.
The first US clinical trials of a drug based on frog magainin did not produce
a significant result, but Zasloff is still confident that the chemical has
useful antibacterial activity. He is also excited by the potential of squalamine:
‘We’ve produced its structure. It’s an extremely potent, broad-spectrum
agent that could be used in many types of diseases. It acts against many
types of fungi, protozoa and bacteria,’ says Zasloff.

Excitement over discoveries such as magainin and squalamine has prompted
other researchers to go back and look at other naturally occurring substances
that have antibacterial function. Researchers have known for over ten years
that a lipid produced by the fat glands in human skin has antibiotic potential.
And last year Raza Aly, adjunct professor of dermatology, microbiology and
immunology at the University of California at San Francisco, showed that
this lipid called sphingosine could kill common bacteria such as staphyloccus
and streptococcus.

Further discoveries of this type are likely, says Zasloff. ‘We’ve only
begun to touch on the diversity of antibiotics from animals and marine
creatures. Most traditional drugs come from sifting soil. The real future
has to do with antibiotics animals make in their gut and wet epithelial
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But regardless of whether the next antibiotic is going to come from
the natural world or the artificial world of computer modelling, one thing
that all researchers agree on is that some-thing must be done soon. The
laissez faire days of the 1980s are over, and without new antibacterial
treatments the doors of the TB wards and isolation units may need to be
reopened.

Lori Valigra is a freelance writer based in Boston.