Biomedical Engineering Reference
In-Depth Information
452-residue version with Asn at the N-termini (Asn- a
2
AP) (NQEQVSPLT . . .)
that exhibits increased cross-linking to fibrin making the fibrin resistant to
plasmin degradation.
28
During a proof of concept proteomics study aimed at
identifying candidate protease substrates in fractionated human plasma, the
cleaved pro-peptide of Asn-a
2
AP with methionine removed (EPLGRQLTSGP)
was identified as a potential DP4 substrate,
233
but the biological relevance of
this finding is as yet unknown. FAP has been previously demonstrated to cleave
gelatin and potentially collagen type I but not collagen IV, fibronectin, or
laminin.
91,234
Evidence suggests that FAP cleaves only collagen type I and III
that are partially degraded or denatured by the proteolytic activity of select
MMPs known to have collagenase activity and participating in ECM remo-
deling.
235
Thus, in the complex extracellular microenvironment of tumors or
sites of tissue remodeling, FAP may be working in concert with other proteases
that play important roles in ECM degradation, to participate in the degrada-
tion of ECM proteins and increase migratory abilities of tumors through
stroma. In turn, the increased activation of a2-AP leading to decreased
fibrinolysis of cross-linked fibrin might result in increased adhesion and
migration of tumors. In vitro cleavage of collagen by DP4 has been suggested,
but participation in ECM degradation is thought to occur via its non-enzymatic
protein-binding capabilities. Recently, Jost et al. used Wistar rats for an in vivo
protease inhibitor profiling approach coupled with endogenous blood pepti-
dome analysis, demonstrating that DP4 inhibition affects collagen alpha 1
metabolism in vivo and identified BRI (1-23) amyloid peptide as a novel sub-
strate of DP4.
236
Because of the intracellular localization of DP8/9, their direct
involvement in cleavage of ECM proteins is unlikely.
1.7 Therapeutic Targeting of the DPs
As illustrated, DP4 and FAP are involved in a wide range of pathophysiolo-
gical processes, and the importance of DP8/9 in human biology is only now
starting to emerge. This family is clearly of interest to Pharma with the
development of DP4 inhibitors for the treatment of type II diabetes and past
clinical investigations into the ecacy of targeting FAP in cancer or as a
potential biomarker. Because of the high degree of homology among the DP4
gene family members and their shared specificity with PEP and DP2, the spe-
cificity and selectivity of DP inhibitors must be ensured. Additionally, the issue
of inhibitor permeability must be addressed due to the intracellular localization
of DP8 and DP9. Both DP4 and FAP have a number of non-enzymatic
functions that appear to play important roles in cancer and fibrinolysis; hence,
therapeutic targeting to prevent protein-binding interaction may also prove to
be of use in future disease treatments. Here, we provide an overview of some
work that has already been carried out with regard to designing therapeutics
targeting the DPs with consideration given to enzymatic and non-enzymatic
approaches.
