Radiolabelled antimicrobial peptides for infection detection

1
Radiolabelled antimicrobial peptides for
infection detection

• Antonella Lupetti, Mick M Welling, Ernest K J
  Pauwels, and Peter H Nibbering
• THE LANCET Infectious Diseases Vol 3 April 2003
• ??? ???? ???

2
Introduction

• The identification of infection at an early stage
  of its disease is critical for favorable outcome.
• More than 85 patients referred to a hospital are
  febrile due to an infection.

3
Introduction

• However, in patients who have serious underlying
  diseases, fewer than a half have an infectious
  cause.
• The clinical manifestations of infection are
  often subtle, non typical, non existent in
  critically ill patients.
• It is crucial to identify the infection source at
  give compatible treatment ASAP.

4
Introduction

• Methods to distinguish infection from
• inflammation
• Medical history
• Physical examination
• Laboratory tests
• Image studies
• Nuclear medicine

5
Introduction

• Current radiolabelled pharmacueticals
• 1. gallium-67-citrate (67Ga), indium-111 or
  technetium-99m -labelled polyclonal human
  immunoglobulins, and autologous leucocytes
• These agents accumulate in both infected
  and non-infected areas due to non-specific
  mechnism.

6
Introduction

• 2. Other agents interact with receptors or
  domains on infiltrating leucocytes, such as
• 99mTc-labelled antigranulocyte monoclonal
  antibodies and 99mTc-labelled chemotactic
  peptides or interleukins

7
Introduction to anti-microbial peptides

• Antimicrobial peptides often display preferential
  binding to microorganisms than host cells.
• Promising radiopharmaceuticals for discriminating
  infections from inflammations may be recruited
  from the array of human antimicrobial
  peptides/proteins.

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Antimicrobial peptides

• The first report on antimicrobial proteinsie,
  lactoferrin and histonesdates back to 1930
• Antimicrobial peptides usually contain less than
  50 aminoacids with a net positive charge due to
  an excess of basic residues, such as lysine and
  arginine, and approximately 50 hydrophobic
  aminoacids.

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Antimicrobial peptides

• They can be categorized to 3 main structural
  classes
• Linear peptides adopting an amphipathic -helical
  structure
• cecropin, magainins, bee mellitin, and
  human ubiquicidin and histatins

10
Antimicrobial peptides

• 2. peptides with disulphide bridges (14) may
  adopt a loop or a beta-sheet structure, or
  combines helical regions and beta-sheet
  structures connected by two of the three
  disulphide bridges, forming a cysteine-stabilised
  motif
• defensins

11
Antimicrobial peptides

• 3. Peptides that are particularly rich in one
  aminoacid (besides lysine and arginine) such as
• tryptophan-rich indolicidin of bovine
  neutrophils proline-arginine-rich peptide PR39 of
  pig neutrophils

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Antimicrobial peptides

• Mechanisms

13
Antimicrobial peptides
14
Selection of Tc-99 Ubiquicidin29-41

• Preferential binding to microorganisms than to
  host cells.
• Rapidly cleared via the kidneys (half life 3060
  mins) and low activity in the liver with no
  deposits in the bowels.
• Accumulated rapidly (within the first hour) in
  the target tissues (12 of the injected dose)

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99mTc-UBI 2941

• Biodistribution

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99mTc-UBI 2941
17
99mTc-UBI 2941
Figure 4. Accumulation of 99mTc- defensins (HNP
13 blue bars), 99mTc-UBI 2941 (yellow bars),
and 99mTc-IgG (red bars) in thigh muscles of mice
nfected with S aureus, Klebsiella pneumoniae, or
C albicans or inflamed with lipopolysaccharide or
heat-killed microorganisms. 99mTc-IgG was
included as positive tracer for both infection
and inflammation.11 Briefly, mice were infected
with 1107 bacteria or yeast or injected with 100
g of lipopolysaccharide or 2108 heat-killed
microorganisms 18 h before administration of the
tracer. Accumulation of 99mTc-labelled tracers at
sites of infection or inflammation is expressed
as the ratio between the amount of radioactivity
in the infected or inflamed (target) and the
non-infected or non-inflamed (non-target) thighs,
which is further referred to as target-tonon-
target (T/NT) ratio. Results are means (SEM) T/NT
ratio of at least four animals in two independent
experiments. plt005 compared with the values for
mice with an inflammatory process according to
Student t test.
18
99mTc-UBI 2941

• The composition and sequence of peptides are key
  to their ability to accumulate at sites of
  infection
• The charge of the radiolabelled peptides
  contributes significantly to their accumulation
  at the site of infection.

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99mTc-UBI 2941
Together, both the sequence and charge of
peptides are important for their accumulation at
the site of infection.
20
99mTc-UBI 2941

• Monitoring of antimicrobial therapy

21
99mTc-UBI 2941

• Limitations
• 1. Not able to distinguish between two different
  infectious sources.
• 2. Not able to detect intra-cellular infectious
  sources.
• 3. Anti-viral peptides still under research.

22
99mTc-UBI 2941

• Considerations for the future
• Investigations regarding toxicology,
  pharmaceuticokinetics, adverse effects,
  antimicrobial activity must be done before human
  usage.
• Search for specific anti-microbial peptides for
  different microorganisms.
• Search for intra-cellular peptides for
  intracellular infection detection.

23
99mTc-UBI 2941

• Conclusion
• 99mTc-UBI 2941 can discriminated between
  infectious and inflammation processes.
• They rapidly detect Gram(), Gram(-) infetions as
  well as fungal.
• The amount of anti-microbial peptides accumulated
  at the infectious site correlates with the number
  of microorganisms. Thus we can follow up the
  efficacy of anti-microbial therapy.

24
99mTc-UBI 2941

• 4. Further studies of radiolabelled antimicrobial
  peptides must be done before clinical use.
• 5. The search for more specific and intracellular
  peptides

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• Thank you very much for your attention.

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Reference

• THE LANCET Infectious Diseases Vol 3 April 2003
• ???? ?????