Adenocarcinoma of the prostate gland is among the leading malignancies in men with high morbidity and mortality rates due to the development of skeletal metastases. PSP-94, one of the three predominant proteins produced by normal prostate gland, is absent in late stage prostate cancer which supports its potential tumor suppressor role. Previous studies carried out in our laboratory have shown the ability of PSP-94 and PCK3145 (amino acids 31–45 of PSP-94) to suppress prostate cancer growth and development of skeletal metastases. Recently, a phase IIa clinical trial carried out in patients with hormone refractory prostate cancer and treated with PCK3145 resulted in disease stabilization. Furthermore, treatment with PCK3145 caused either a stabilization or reduction of MMP-9 levels in these patients. In the current study we evaluated the possible mechanism(s) of action of PCK3145. For these studies, rat prostate cancer MatLyLu cells were treated with different concentrations of PCK3145. Total cellular RNA and conditioned media were collected. PCK3145 treatment resulted in a significant dose dependent reduction in MMP-9 mRNA and protein levels as analyzed by real time RT-PCR, Western blot analysis and zymography. No significant effect on MMP-2 production was seen. Furthermore, treatment of MatLyLu cells with different doses of PCK3145 resulted in a dose dependent reduction in the levels of p-Erk and p-Akt. For in vivo studies, male Copenhagen rats were inoculated either subcutaneously or via intracardiac injections with MatLyLu cells to develop primary tumor growth or experimental skeletal metastases, respectively. Animals were treated with different doses of PCK3145 (1.0–100.0μg/kg) and at the end of the study their tumors were excised and analyzed. PCK3145 caused a dose dependent reduction in tumor volume and a significant decrease in MMP-9 production and neovascularization as assessed by immunohistochemical analysis of primary tumors. These effects were due to the ability of PCK3145 to inhibit p-Erk and p-Akt production by primary tumors. Similarly PCK3145 treatment caused a significant reduction in skeletal tumor burden, delay in hind limb paralysis and inhibition of MMP-9 expression. Collectively, the results obtained from these studies show that the ability of PCK3145 to reduce tumor growth and delay the development of skeletal metastases is in part due to its ability to reduce the levels of MMP-9 and tumor angiogenesis, effects which are mediated through the reduction of active Akt kinase previously reported to modulate the expression of several genes including MMP-9. The results obtained from these studies provide evidence for the mechanism of action of PCK3145 which can be selectively targeted alone or in combination with other therapeutic agents for prostate cancer patients.
[Proc Amer Assoc Cancer Res, Volume 47, 2006]