3.4 Other Aptamer-Specific TPPs and Diagnostic
Applications
As antibody-based diagnostics continue to dominate the diagnostics market, it will
not be prudent to compete against them, unless aptamer-based diagnostics offer very
convincing competitive advantages over antibody assays. Some advantages of
nucleic acid aptamers and their in vitro generation that can be used for TPP
development are:
• Specificity: Aptamers can be developed to discriminate nearly identical targets
whether it be small molecules or macromolecules. The classic example of greater
aptamer specificity for a small molecule target comes from the work of Jenison
et al. who demonstrated a greater than 11,000-fold difference in dissociation
constants for an RNA aptamer that could distinguish the bronchodilator theophylline from caffeine which differ by only one methyl group in structure. Ingesting
a simple cup of coffee may interfere with a theophylline immunoassay result, but
the Jenison aptamer enabled improved analyte discrimination [25]. Likewise,
Cruz-Aguado and Penner developed aptamers capable of distinguishing
ochratoxin A and B for wheat testing and incorporated these aptamers into
successfully marketed diagnostic field tests for NeoVentures Biotechnology in
Canada [26]. Bruno et al. developed aptamers capable of discriminating natural
from recombinant human growth hormone (hGH) for the World Anti-Doping
Agency (WADA) [27]. Recombinant hGH does exhibit amino acid modifications
in about 2% of the recombinant proteins. More recently, Bruno’s group has
worked on chemically modified aptamers in an attempt to discriminate a variant
of prostate-specific antigen (PSA) which is impossible to detect via antibodies but
is indicative of aggressive cancer and demonstrated some degree of success
[28]. An improved aptamer-based PSA or other cancer biomarker diagnostic
test would be a fine example of a worthy aptamer TPP. This ability (specificity)
to discriminate between two very similar targets can be incorporated in the
TPP list.
• Scope of the Diagnostics: Aptamers can be developed against poorly immunogenic molecules, while it is difficult to generate antibodies against such targets.
Aptamer development in vitro typically will work against molecules which are
either too small (haptens), too short (peptides less than ~10 amino acids), or too
repetitive to be immunogenic in animals. Numerous examples of high-affinity
aptamers developed against the monomers of otherwise non-immunogenic polymers exist in the literature [8].
• Development of aptamers to bind and detect highly lethal toxins that might easily
kill a host animal if injected. Numerous examples of this TPP exist for bacterial
and marine toxins, as well as snake, insect, scorpion, spider venoms, etc. [29–
32]. This feature of aptamers allows to broaden the scope of the developed test to
places where antibodies have clear limitations.
206
H. Kaur et al.
Applications
As antibody-based diagnostics continue to dominate the diagnostics market, it will
not be prudent to compete against them, unless aptamer-based diagnostics offer very
convincing competitive advantages over antibody assays. Some advantages of
nucleic acid aptamers and their in vitro generation that can be used for TPP
development are:
• Specificity: Aptamers can be developed to discriminate nearly identical targets
whether it be small molecules or macromolecules. The classic example of greater
aptamer specificity for a small molecule target comes from the work of Jenison
et al. who demonstrated a greater than 11,000-fold difference in dissociation
constants for an RNA aptamer that could distinguish the bronchodilator theophylline from caffeine which differ by only one methyl group in structure. Ingesting
a simple cup of coffee may interfere with a theophylline immunoassay result, but
the Jenison aptamer enabled improved analyte discrimination [25]. Likewise,
Cruz-Aguado and Penner developed aptamers capable of distinguishing
ochratoxin A and B for wheat testing and incorporated these aptamers into
successfully marketed diagnostic field tests for NeoVentures Biotechnology in
Canada [26]. Bruno et al. developed aptamers capable of discriminating natural
from recombinant human growth hormone (hGH) for the World Anti-Doping
Agency (WADA) [27]. Recombinant hGH does exhibit amino acid modifications
in about 2% of the recombinant proteins. More recently, Bruno’s group has
worked on chemically modified aptamers in an attempt to discriminate a variant
of prostate-specific antigen (PSA) which is impossible to detect via antibodies but
is indicative of aggressive cancer and demonstrated some degree of success
[28]. An improved aptamer-based PSA or other cancer biomarker diagnostic
test would be a fine example of a worthy aptamer TPP. This ability (specificity)
to discriminate between two very similar targets can be incorporated in the
TPP list.
• Scope of the Diagnostics: Aptamers can be developed against poorly immunogenic molecules, while it is difficult to generate antibodies against such targets.
Aptamer development in vitro typically will work against molecules which are
either too small (haptens), too short (peptides less than ~10 amino acids), or too
repetitive to be immunogenic in animals. Numerous examples of high-affinity
aptamers developed against the monomers of otherwise non-immunogenic polymers exist in the literature [8].
• Development of aptamers to bind and detect highly lethal toxins that might easily
kill a host animal if injected. Numerous examples of this TPP exist for bacterial
and marine toxins, as well as snake, insect, scorpion, spider venoms, etc. [29–
32]. This feature of aptamers allows to broaden the scope of the developed test to
places where antibodies have clear limitations.
206
H. Kaur et al.