AB065. EP4 antagonist suppresses bone metastasis in prostate cancer

Background: Bone metastasis is one of the most common complications in clinical intractable castration-resistant prostate cancer (CRPC) and advanced prostate cancer period. The invasion ability of cancer cells was thought to have important relationship with the potential of cancer metastasis. EP4 receptor is overexpressed in several cancers, and enhanced EP4 receptor signaling has been previously shown to correlate with the invasion of several different cancer types. In present study, we found that EP4 antagonist can in vitro suppress the invasion phenotype abilities of CRPC PC3 cells, LNCaP cells with EP4 overexpressed which have the tendency to castration-resistance and in vivo suppress the CRPC bone metastasis animal models.

Methods: RNA interference was used to stably transfected EP4 to LNCaP with the pcDNA3.1-EP4, so as to be the LNCaP with vector control (LNCaP-mock) and LNCaP with EP4 overexpressed (LNCaP/EP4+) as described in our previous article. Effect on cell proliferation was determined firstly by the MTT assay. Transwell invasion assay was used to in vitro examine the metastasis abilities of PC3 cells, LNCaP cells, LNCaP/EP4+ and all after EP4 antagonist affected. Cells with ONO-AE3-208 at the final concentration of 0.1, 1 and 10 µmol/L were administrated to be the experimental group. To observe the effect of EP4 antagonist on the bone metastasis of prostate cancer in vivo, PC3/Luc cells were inoculated into the left cardiac ventricle of 5-week-old male nude mice. The mice developed osteolytic lesions with a mean endpoint at 52±7 days. To assess whether EP4 antagonist suppresses bone metastasis, ONO-AE3-208 (10 mg/kg/d) was given to the animals 5 days a week i.p. which the same volume of DDW was given as the control. To detect PC3 cell dissemination, bioluminescent imaging (BLI) was applied using a cooled CCD camera. We evaluated the efficacy of ONO-AE3-208 by measuring the photon counts of the metastatic lesions in the mandible and both hip joints in a blinded manner.

Results: The invasion assay showed that ONO-AE3-208 can inhibit the invasive abilities of both PC3 and LNCaP/EP4+ in a dose-dependent manner (P<0.01). In animal experiment, metastatic bone lesions in the control group progressed while the photon emission was significantly suppressed in the ONO-AE3-208 treatment group during the observation period from day 28 every 7 days (P<0.01).

Conclusions: We demonstrated that EP4 antagonist can in vitro inhibit the invasive abilities of CRPC PC3 and LNCaP/EP4+ cells. The administration of it can also suppress the bone metastasis of CRPC in vivo.

Keywords: EP4; prostate cancer; bone metastasis