Targeting cathepsin K diminishes prostate cancer establishment and growth in murine bone

Abstract

Background The processes of prostate cancer (PCa) invasion and metastasis are facilitated by proteolytic cascade involving multiple proteases, such as matrix metalloproteinases, serine proteases and cysteine proteases including cathepsin K (CatK). CatK is predominantly secreted by osteoclasts and specifically degrades collagen I leading to bone destruction. PCa and breast cancer preferentially metastasize to the bone. Importantly, CatK expression level is greater in PCa bone metastatic sites compared to primary tumor and normal prostate tissues. However, the underlying mechanism of CatK during PCa metastases into the bone remains to be elucidated. We investigated the functional role of CatK during the PCa establishment and growth process in the murine bone. Methods CatK mRNA expression was validated by RT-PCR, protein expression by immunoblotting in PCa LNCaP, C4-2B, and PC3 cells as well as in PCa tissues. Its protein production was measured using ELISA assay. The effect of both knockdowns via siRNA and CatK inhibitor was compared in regard to PCa cell invasion. We further studied the dose-dependent CatK inhibitor effect on conditioned media-induced bone resorption. In setting up an animal model, C4-2B cells were injected into the tibiae of SCID mice. The animals treated with either vehicle or CatK inhibitor for 8 weeks at the time of tumor cell injection (tumor establishment model; protocol I) or 4 weeks after tumor cell injection (tumor progression model; protocol II) were applied to histological and histomorphometric analyses. Results We confirmed CatK expression in PCa LNCaP, C4-2B, and PC3 cells as well as in PCa tissues. Furthermore, we observed the inhibitory effects of a selective CatK inhibitor on PCa cell invasion. The CatK inhibitor dose-dependently inhibited PCa-conditioned media-induced bone resorption. Upon injection of C4-2B cells into the tibiae of SCID mice, the selective CatK inhibitor significantly prevented the tumor establishment in protocol I, and reduced the tumor growth in bone in protocol II. It also decreased serum PSA levels in both animal models. The inhibitory effects of the CatK inhibitor were enhanced in combination with zoledronic acid (ZA). Conclusion The selective CatK inhibitor may prevent the establishment and progression of PCa in bone, thus making it a novel therapeutic approach for advanced PCa.

Key Matrix Remodeling Enzymes: Functions and Targeting in Cancer

“…Furthermore, CTSK has been found poorly expressed in normal prostate and in the prostate epithelial cells, whereas the expression was higher in the non-metastatic LNCaP cells and even greater in C4-2B and PC3 cells, and in skeletal metastatic tumor as revealed by tissue microarray. To this extent, CTSK affirmed as a key factor specific in PCa skeletal metastasis and PCa-induced bone lesions in vivo [ 165 ]. In a study by Yu et al, the role of cathepsins in a multistage epithelial carcinogenesis was examined using K14-HPV16 transgenic mice.…”

Potential Role of Cathepsin K in Regulation of Micro Tumor Environment, Onset and Progression of Cancers in Human- A Review

“…novel but yet a standardized and a reliable, precise therapeutic in order to be used to treat prostate cancers, eventually by facilitating complete recovery from even at the secondary stage of the prostate cancer (Liang et al, 2019).…”

The Role of Cathepsins in the Growth of Primary and Secondary Neoplasia in the Bone

“…CatK secretion from PCa cell lines (LNCaP, DU145) and macrophages participates in local invasion by mediating extracellular degradation [109,177]. Liang et al [178] reported that CatK expression occurs both in PCa cell lines (LNCaP, C4-2B, and PC3) and in PCa tissues. CatK protein and enzymatic activity has been detected in the human PCa cell lines by Western blot and a fluorogenic assay, respectively [109].…”

“…In the same tumor model, twice daily treatment with the CatK inhibitor CKI (50 mg/kg) resulted in osteolytic lesions that were 79% smaller than those of tumor-bearing mice treated with the drug vehicle, and in a 62% reduction in the skeletal tumor burden [204]. More recently, this inhibitor was used to treat C4-2B prostate cancer cells in the tibiae of SCID mice; it significantly inhibited the tumor establishment, reduced the tumor growth in the bone, and decreased the serum prostate-specific antigen, likely due to the noted inhibition of bone resorption demonstrated in vitro with the CKI treatment [178]. Interestingly, the inhibitory effects of the CatK inhibitor were enhanced when it was administered in combination with ZOL [178].…”

“…More recently, this inhibitor was used to treat C4-2B prostate cancer cells in the tibiae of SCID mice; it significantly inhibited the tumor establishment, reduced the tumor growth in the bone, and decreased the serum prostate-specific antigen, likely due to the noted inhibition of bone resorption demonstrated in vitro with the CKI treatment [178]. Interestingly, the inhibitory effects of the CatK inhibitor were enhanced when it was administered in combination with ZOL [178]. As shown by confocal microscopy, phalloidin-stained osteoclasts treated with the vehicle (panels i and ii) or AFG-495 (panels iii and iv) attach to the bone matrix and exhibit a typical sealing zone (white arrow), irrespective of the treatment.…”