Hypernociceptive responses following the intratibial inoculation of RM1 prostate cancer cells in mice.

Abstract

Pain due to bone metastases of prostatic origin is a relevant clinical issue. We study here the nociceptive responses obtained in mice receiving the intratibial inoculation of RM1 prostate cancer cells. 10(2) -10(5) RM1 cells were inoculated to C57BL/6 mice and tumor development was analysed histologically and with luciferase-expressing RM1 cells. Spinal astroglial (GFAP) or microglial (Iba-1) expression was assessed with immunohistochemical methods and hypernociception was measured by the unilateral hot plate, the paw pressure and the von Frey tests. The analgesic effect of morphine, zoledronic acid or the CCR2 antagonist RS504393 was measured. Levels of the chemokines CCL2, CCL3, and CCL5 were determined by ELISA. The inoculation of 10(3) RM1 cells induced tumoral growth in bone with a mixed osteoclastic/osteoblastic pattern and evoked astroglial, but not microglial, activation in the spinal cord. Hyperalgesia and allodynia were already established four days after inoculation and dose-dependently inhibited by the s.c. administration of morphine (1-5 mg/kg) or zoledronic acid (1-3 mg/kg). CCL2 and CCL5, but not CCL3, were released by RM1 cells in culture whereas only an increased presence of CCL2 was found in bone tumor homogenates. The administration of the CCR2 antagonist RS504393 (0.3-3 mg/kg) inhibited RM1 induced thermal hyperalgesia without modifying mechanical allodynia. The intratibial inoculation of RM1 cells in immunocompetent mice induces hypernociceptive responses and can be useful to perform studies of bone cancer induced pain related to androgen-independent prostate cancer. The antinociceptive role derived from the blockade of the CCR2 chemokine receptors is further envisaged.