302
W. Li et al.
FXIa cleavage of tripeptide chromogenic substrate S-2366 and FXIa-catalyzed FIX
activation. Aptamer 12.7 significantly prolonged the APTT clotting time in normal
human plasma. RNA aptamers could recognize distinct sites on the FXIa catalytic
domain and non-competitively inhibited FXIa activity toward FIX with different
levels of potency. The authors suggested that aptamers can be further developed for
therapeutic antagonists [96].
Previous reports showed that antisense oligonucleotide downregulated FXI
production and thus prevented venous thrombosis in knee replacement therapy [94].
However, it took several weeks to take effect, which is not suitable for clinical settings
requiring rapid anticoagulation. Aptamer inhibitors can rapidly inactivate FXI/XIa
with a rapid antithrombotic strategy. Small molecular weight makes aptamers be
rapidly cleared by the kidney. Importantly, aptamer antidotes can neutralize aptamerinduced bleeding and lead to rapid reversal or control of anticoagulation level, and
thus increase the safety of aptamer drugs [96].
10.7 Aptamers Against FXII
FXII is a glycoprotein consisting of an enzymatic light chain and a heavy chain
with several conserved domains that mediate binding to anionic surfaces and other
proteins [97]. Many compounds can mediate the binding of FXII and anionic surface
to autoactivate FXII by binding FXII heavy chain to an anionic surface and induce
a conformational change to form activated FXII (FXIIa) [98]. Activated FXII then
triggers the intrinsic coagulation pathway of blood coagulation through the activation of FXI. Since the extrinsic coagulation pathway is thought to initiate thrombin
formation at the site of vascular injury, it may mediate continued thrombin generation
to stabilize a thrombus [99]. So FXII is another attractive drug target of thrombosis.
A nuclease-resistant, 80-mer 2
-fluoropyrimidine modified RNA aptamer,
R4cXII-1, bound to a region on the heavy chain of FXII (FXIIa) implicated in anionic
and FXI binding and inhibited FXII coagulant function. In coagulation tests of APTT
and TF-activated thrombin generation assay (TGA), R4cXII-1 dose-dependently
prolonged ellagic acid initiated APTT activation and increased the lag time, as well
as decreased thrombin generation, the endogenous thrombin potential (ETP), and the
rate of ellagic acid initiated thrombin generation. These data suggest that R4cXII1 can specifically inhibit FXII function, reduce FXIa formation, effectively turn off
intrinsic pathway activation, and decrease continued thrombin generation to stabilize
a thrombus. Animal models of thrombosis demonstrated that FXII deficiencies can
avoid occlusive thrombus formation after arterial injury and stroke without interruption of normal hemostatic events. The authors suggested that R4cXII-1 can act as an
attractive alternative of anticoagulant to prevent pathological thrombus formation,
especially in thrombosis, while minimizing hemorrhagic risk. The clinical evaluation
of R4cXII-1 is eagerly awaited [100].
Paul et al. applied different concentrations of aptamers in fresh human whole blood
to evaluate the hemostatic system involved in coagulation, platelets, complement, and
W. Li et al.
FXIa cleavage of tripeptide chromogenic substrate S-2366 and FXIa-catalyzed FIX
activation. Aptamer 12.7 significantly prolonged the APTT clotting time in normal
human plasma. RNA aptamers could recognize distinct sites on the FXIa catalytic
domain and non-competitively inhibited FXIa activity toward FIX with different
levels of potency. The authors suggested that aptamers can be further developed for
therapeutic antagonists [96].
Previous reports showed that antisense oligonucleotide downregulated FXI
production and thus prevented venous thrombosis in knee replacement therapy [94].
However, it took several weeks to take effect, which is not suitable for clinical settings
requiring rapid anticoagulation. Aptamer inhibitors can rapidly inactivate FXI/XIa
with a rapid antithrombotic strategy. Small molecular weight makes aptamers be
rapidly cleared by the kidney. Importantly, aptamer antidotes can neutralize aptamerinduced bleeding and lead to rapid reversal or control of anticoagulation level, and
thus increase the safety of aptamer drugs [96].
10.7 Aptamers Against FXII
FXII is a glycoprotein consisting of an enzymatic light chain and a heavy chain
with several conserved domains that mediate binding to anionic surfaces and other
proteins [97]. Many compounds can mediate the binding of FXII and anionic surface
to autoactivate FXII by binding FXII heavy chain to an anionic surface and induce
a conformational change to form activated FXII (FXIIa) [98]. Activated FXII then
triggers the intrinsic coagulation pathway of blood coagulation through the activation of FXI. Since the extrinsic coagulation pathway is thought to initiate thrombin
formation at the site of vascular injury, it may mediate continued thrombin generation
to stabilize a thrombus [99]. So FXII is another attractive drug target of thrombosis.
A nuclease-resistant, 80-mer 2
-fluoropyrimidine modified RNA aptamer,
R4cXII-1, bound to a region on the heavy chain of FXII (FXIIa) implicated in anionic
and FXI binding and inhibited FXII coagulant function. In coagulation tests of APTT
and TF-activated thrombin generation assay (TGA), R4cXII-1 dose-dependently
prolonged ellagic acid initiated APTT activation and increased the lag time, as well
as decreased thrombin generation, the endogenous thrombin potential (ETP), and the
rate of ellagic acid initiated thrombin generation. These data suggest that R4cXII1 can specifically inhibit FXII function, reduce FXIa formation, effectively turn off
intrinsic pathway activation, and decrease continued thrombin generation to stabilize
a thrombus. Animal models of thrombosis demonstrated that FXII deficiencies can
avoid occlusive thrombus formation after arterial injury and stroke without interruption of normal hemostatic events. The authors suggested that R4cXII-1 can act as an
attractive alternative of anticoagulant to prevent pathological thrombus formation,
especially in thrombosis, while minimizing hemorrhagic risk. The clinical evaluation
of R4cXII-1 is eagerly awaited [100].
Paul et al. applied different concentrations of aptamers in fresh human whole blood
to evaluate the hemostatic system involved in coagulation, platelets, complement, and