Opioid inhibition of the growth of the transplantable androgen-responsive (AR) Shionogi mouse mammary carcinoma (SC115)
We investigated the effects of steroid hormones, growth factors, and anti-growth factor antibodies on the growth of cells in primary culture from the transplantable androgen-responsive(AR) Shionogi mouse mammary carcinoma (SC115). In addition, the effects of opioid agonists and antagonists on the growth of SC115tumor cells in primary culture were examined. The possible role of opioids in mediating the differential tumor growth rates of mice exposed to experimental housing groups was also examined.SC115 tumor cells were cultured at 5 x 104 cells/cm2 onto collagen-coated 96-well microtiter tissue culture plates. The cells were incubated in medium containing 5% fetal bovine serum(FBS), 2% dextran charcoal-treated FBS (DCTFBS), or seurm-free medium, with or without different concentrations of dihydrotestosterone (DHT), hydrocortisone (HC), 178-estradiol(E2), basic fibroblast growth factor (bFGF), epidermal growth factor (EGF), anti-bFGF antibody with either DHT or bFGF, or anti-EGF antibody with either E2 or EGF. After 48 h, some of the cultures were exposed to 10-14-10-7 M of either 8-endorphin (5-EP), which binds to the 8 opioid receptor, cyclazocine (CZ),which binds to the k receptor, or morphine sulfate (MS), which binds to the g receptor. These opioids were added daily for 3 d. In some experiments, 10-8 and 10-6 M of naloxone, an opioid receptor antagonist, were added with the opioids. On day 5, the cultures were terminated and cell numbers determined by the tetrazolium dye reduction assay. The results show that AR SC115 tumor cells in serum-containing medium were significantly stimulated to grow in a dose-dependent manner with DHT ranging from 3.5 x 10-1° - 3•5 x10-6 M and bFGF ranging from 1-100 ng/ml and in serum-free medium were significantly stimulated to grow by bFGF at all concentrations examined (1-500 ng/ml). HC ranging from 10-9-10-5M also significantly stimulated SC115 tumor cell growth. In contrast, E2 (10-9-10-6 M) and EGF (1-100 ng/ml) at all concentrations examined significantly inhibited SC115 tumor cell growth in serum-containing medium, whereas EGF had no effect onSC115 tumor cell growth in serum-free medium at any of these concentrations. Anti-bFGF antibody had a significant inhibitory effect on the DHT- or bFGF-stimulated SC115 tumor cell growth in serum-free medium. Anti-EGF antibody also significantly inhibitedSC115 tumor cell growth with or without E2 or EGF in serum-free medium. All 3 opioids at concentrations higher than 10-12 M significantly inhibited S0115 tumor cell growth (up to 40%) in medium that maximally stimulated these cells (DHT at 3.5 x 10-8M, HC at 10-6 M, or 5% FBS), although inhibition also occured, albeit to a lesser degree, in steroid hormone-free medium. 8-EPat concentrations of 10-10-10-7 M also inhibited SC115 tumor cell growth when added to medium containing DCTFBS and 10 ng/ml bFGF. When naloxone was added with 8-EP or MS, the inhibitory effects of the opioids were partially or totally blocked. Both 8-EP andCZ also significantly inhibited growth of SC115 tumor cells from mice exposed to different social housing conditions. Overall, 5-EP inhibited growth of SC115 tumor cells from IG mice (smaller tumors) to a greater degree than SC115 tumor cells from GI mice(larger tumors) in 2% DCTFBS-containing and HC-containing media, whereas the result was reversed in DHT-containing medium. CZ inhibited growth of SC115 tumor cells from GI mice to a greater degree than cells from IG mice in 2% DCTFBS-containing and DHT-containing media, whereas the result was the same in HC-containing medium. The results suggest that the growth of AR SC115 tumor cell is sensitive to different steroid hormones and growth factors in primary culture. Opioid peptides may be involved in regulating endocrine control of growth of the AR SC115 carcinoma and the inhibitory effects of opioids may be mediated by multiple opioid receptors. In our animal-tumor model, opioids may also play a role in the differential tumor growth rates of mice exposed to the experimental housing groups.
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