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Differential effects of somatostatin and angiopeptin on cell proliferation
F Alderton1, H Lauder, W Feniuk
1Glaxo Institute of Applied Pharmacology, University of Cambridge.
Abstract:
1. Somatostatin (SRIF) exerts antiproliferative effects, and angiopeptin (an sst2/sst5 receptor-selective analogue) has recently been evaluated in clinical trials for the prophylaxis of restenosis following coronary angioplasty. Using an in vitro model of cell growth we have examined the effects of SRIF and angiopeptin on cell proliferation in CHO-K1 cells stably transfected with the human or rat recombinant sst2 or sst5 receptor and compared these with their effects on rat aortic vascular smooth muscle cells (VSMC) expressing endogenous somatostatin receptors. 2. In CHO-KI cells, expressing either human or rat recombinant sst2 or sst5 receptors, or in rat aortic VSMC, SRIF and angiopeptin (0.1-1000 nM) had no effect on basal re-growth of cells into a denuded area of a previously confluent monolayer. In contrast, basic fibroblast growth factor (bFGF, 10 ng ml(-1)) stimulated re-growth of these cells. 3. SRIF (0.1-1000 nM) caused a concentration-dependent inhibition of the bFGF-stimulated re-growth in CHO-K1 cells expressing human sst2 (h sst2) or sst5 (h sst5) receptors (pIC50=8.05+/-0.03 and 8.56+/-0.12, respectively). In contrast, angiopeptin (0.1-1000 nM) acted as a partial agonist at the h sst2 receptor (44.6+/-2.7% inhibition of the bFGF-stimulated re-growth at 100 nM; pIC50=8.69+/-0.25) but was devoid of any agonist activity at the h sst5 receptor. 4. In CHO-K1 cells stably expressing rat recombinant sst2 (r sst2) or sst5 (r sst5) receptors, SRIF (0.1-1000 nM) was able to inhibit the bFGF-stimulated re-growth (pIC50=7.98+/-24 and 8.50+/-0.12, respectively). Angiopeptin (0.1-1000 nM) caused a concentration-dependent inhibition of bFGF-stimulated re-growth at the r sst2 receptor (pIC50=8.08+/-0.24) but acted as a partial agonist at the r sst5 receptor (maximum response= 57.7+/-3.6% inhibition of bFGF-stimulated re-growth at 100 nM; pIC50=8.60+/-0.16). 5. Although angiopeptin was inactive as an agonist at the h sst5 receptor, 100 nM angiopeptin potently antagonized the SRIF-induced inhibition of proliferation in CHO h sst5 (estimated pKB= 10.4+/-0.3). 5-Hydroxytryptamine (0.1 nM-10 microM) also inhibited bFGF-stimulated re-growth (pIC50=8.36+/-0.11) and angiopeptin had no effect on this response (pKB<7). 6. SRIF (0.1-1000 nM) caused a concentration-dependent (pIC50=8.04+/-0.08) inhibition of bFGF-stimulated re-growth in VSMC, whereas angiopeptin displayed weak agonist activity, only inhibiting bFGF-stimulated re-growth at concentrations greater than 100 nM. Angiopeptin (100 nM) caused a rightward displacement of the concentration-effect curve to SRIF with an estimated pKB value of 7.70+/-0.12. 7. These findings suggest that the low intrinsic activity of angiopeptin at the h sst2 receptor, combined with its lack of agonist activity at the h sst5 receptor, may explain the poor clinical efficacy of angiopeptin in trials for coronary artery restenosis, which contrasts with encouraging data found in equivalent in vivo animal studies.
Insights
Somatostatin (SRIF) and angiopeptin were tested for effects on cell proliferation. Angiopeptin showed limited efficacy due to low activity at somatostatin receptors, potentially explaining its poor clinical results in restenosis trials.
Area of Science:
- Pharmacology
- Cell Biology
- Cardiovascular Research
Background:
- Somatostatin (SRIF) has antiproliferative effects.
- Angiopeptin, an sst2/sst5 receptor-selective analogue, was evaluated for restenosis prophylaxis.
- Understanding SRIF and angiopeptin's receptor interactions is crucial for cardiovascular applications.
Purpose of the Study:
- To investigate the effects of SRIF and angiopeptin on cell proliferation in cells expressing somatostatin receptors.
- To compare the activity of SRIF and angiopeptin on human and rat somatostatin receptor subtypes.
- To elucidate the mechanism behind angiopeptin's efficacy in preclinical versus clinical studies.
Main Methods:
- Utilized an in vitro cell growth model with CHO-K1 cells transfected with human or rat sst2/sst5 receptors.
- Assessed basal and basic fibroblast growth factor (bFGF)-stimulated cell re-growth.
- Determined concentration-dependent effects, including pIC50 and pKB values, for SRIF and angiopeptin.
Main Results:
- SRIF inhibited bFGF-stimulated re-growth in cells expressing human and rat sst2/sst5 receptors.
- Angiopeptin acted as a partial agonist at human sst2 and rat sst5 receptors, with limited activity at other subtypes.
- Angiopeptin antagonized SRIF's effect at human sst5 receptors but showed weak agonist activity in vascular smooth muscle cells.
Conclusions:
- Angiopeptin's limited intrinsic activity at human sst2 and lack of activity at human sst5 receptors may explain its poor clinical efficacy in restenosis.
- Differences in receptor activity between human and rat models might account for discrepancies between preclinical and clinical findings.
- Further research into somatostatin receptor pharmacology is warranted for developing effective restenosis treatments.