Microbot Drug Delivery

1
Microbot Drug Delivery

• Which model organism?
• Mark Fang, Stanford iGEM

2
Microbots Overview

• Microbot drug delivery involves attaching drugs
  to the exterior of microscopic biological
  chasses, such as bacteria and viruses, so that
  when the chasses are phagocytosed by their target
  cells they bring inside with them the drugs.
• Choosing the chassis is thus an important design
  parameter, since the chassis will be responsible
  for which cells are targetted and how it will
  travel to those cells.
• In order to get the chassis to localize to the
  desired targets, we will need to make several
  considerations

3
Selecting a chassis

• The chassis that will transport the drug should
  be
• Highly specific
• Immune response
• Genetically well characterized
• Pathogenically well characterized

4
Bactofection vs. Virofection

• Two broad chassis classes
• Bacteria
• Viruses

• SEM micrograph of Escherichia coli

Vesicular Somatitis Virus
5
Highly Specific

• As with all drug delivery methods, the more
  specific, the fewer
• the side effects.
• The chassis can be engineered to be specific
• Quorum sensing
• Hypoxia
• Inducible control
• The chassis can also be naturally specific
• Listeria monocytogenes
• Vesicular somatitis virus rp34a

6
Immune response

• The patients immune response can be a hindrance
  or
• a mechanism for inducing localization of the
  chassis.

Macrophage engulfing bacteria. The chassis will
need to avoid being engulfed by immune cells to
prevent incidentally compromising the
immune system.
7
Genetically/structurally well characterized

• Bacteria many strains have entire genome
  sequenced. Ex. E. coli has been used extensively
  in genetic engineering.
• Virus more difficult to engineer. Virus may
  also be too small for example, lambda phages
  can only hold genomes between 75 and 105 the
  size of the normal genome.

8
Pathogenically well characterized

• Non-pathogenic
• The virulence of certain bacteria species can be
  attenuated through knock out mutants.

• The rate and extent of bacterial expansion can
  also be controlled.

9
Advantages vs. Disadvantages

• Viruses
• More difficult to engineer
• May be too small
• Can cause undesirable mutations during
  integration of viral genome into host genome
• Can be naturally specific
• Bacteria
• Easier to manipulate, virulence shown to be
  pliable, some are also naturally localized in body

10
Choosing a chassis

• Listeria monocytogenes with the view of
  targeted drug delivery to cancer cells
• Has been show to localize to tumor cells and
  metastases
• Has been engineered to exhibit attenuated
  virulence
• Expansion can be controlled
• Riboswitches naturally extant in certain Listeria
  species

11
Testing the chassis

• HeLa cancer cells can conduct in vitro test for
  general invasion of human cancer cells
• Human glioma cells - to establish possibility for
  chassis to invade brain cancer cells. Further
  tests in animals may show whether the chassis is
  able to penetrate the blood brain barrier.
• For a listing of 60 human cancer cell lines
  http//dtp.nci.nih.gov/docs/misc/common_files/cell
  _list.html