Book of abstract 2008

Kallikrein-related peptidases: novel therapeutic target molecules
Manfred Schmitt and Viktor Magdolen
Clinical Research Unit, Dept. Obstetrics and Gynecology, Klinikum rechts der Isar, Technical University
of Munich, Munich, Germany
The novel tumor-associated biomarkers, the kallikrein-related peptidases (tissue kallikreins,
KLK) KLK4-15 have the potential to serve as novel prognostic and even predictive markers
for patients afflicted with solid malignant tumors. Tissue kallikreins are a subgroup of the
serine protease enzyme family. Until the mid of the 1990s, it was thought that the human
tissue kallikrein gene family contained only three members: (1) tissue kallikrein [KLK1],
(2) glandular kallikrein-1 [KLK2], and (3) prostate-specific antigen [PSA/KLK3]. In
the past years, the expansion of the human tissue kallikrein gene family from 3 to now
15 members, all of which co-localize to chromosome 19q13.3-13.4 was reported. With
the identification and characterization of all members of the tissue kallikrein gene family,
accumulating reports have indicated that in addition to the established tissue kallikreins
KLK1, KLK2, and KLK3, the novel tissue kallikreins KLK4 to KLK15 might also be
related to hormonally regulated malignancies such as that of the prostate, testis, breast,
and ovary.
Growing evidence suggests that certain KLKs are involved in cancer progression; several
may even serve as novel cancer biomarkers for tumor staging and prediction of therapy
response, associated with the course of disease of cancer patients. While KLKs are
expressed in a variety of normal tissues, such as prostate, ovary, breast, testis, the central
nervous system, and skin, their expression or downregulation in tumor tissues have only
partially been revealed by immunohistochemical approaches although expression of KLKs
have been investigated in malignant tissue extracts by PCR (mRNA) or ELISA (protein).
Therefore, we have generated/selected a panel of highly specific antibodies to various
KLKs which allow localization and assessment of protein expression in tumor tissues.
Recent advances in our laboratory allowed recombinant protein production of all of the
15 KLKs in bacteria in their pro-forms and conversion into their enzymatically active
l43
forms. For some of the KLKs, protein crystals were obtained (KLK4, KLK5, KLK6,
KLK7) and the structures of these kallikrein-related peptidases solved by crystallography.
Furthermore, extended substrate specificity profiling for the nonprime side and further
enzyme kinetic studies have been performed. The shape and polarity of the specificity
pockets of the investigated KLKs explain very well the substrate preferences of KLK4, 5,
6, and 7. KLK4 and KLK5 exhibit a trypsin-like specificity with a strong preference for
P1-Arg, while KLK6 is less stringent for arginine in P1, but prefers this residue also in P2
whereas KLK7 displays a unique chymotrypsin-like specificity for tyrosine both in P1 and
P2 position. Comparison of structure and substrate specificity may support the discovery
of natural substrates as well as the design of efficient inhibitory compounds for targeting
these KLKs in vivo as a novel approach of tumor therapy.
59