Synergistic inhibition of growth of lung carcinomas by antagonists of growth hormone-releasing hormone in combination with docetaxel

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Abstract
We investigated the effect of antagonists of growth hormone-releasing hormone (GHRH) MZ-J-7-138 and JV-1-92 on H460 human non-small cell lung carcinoma (NSCLC) xenografted orthotopically into nude mice. Treatment with MZ-J-7-138 or JV-1-92 inhibited orthotopic growth of H460 NSCLC by 52-65% (P < 0.001) and was associated with a significant decrease in protein expression of K-Ras, cyclooxygenase-2 (Cox-2) and phospho-Akt (pAkt). In other experiments, treatment with MZ-J-7-138 or docetaxel reduced tumor volume of s.c. xenografted H460 human NSCLC by 30-36% (P < 0.01). The combination of MZ-J-7-138 and docetaxel resulted in a synergistic growth inhibition of H460 NSCLC xenografts of 63%. MZ-J-7-138 alone or in combination with docetaxel significantly reduced protein levels of K-Ras, Cox-2, and pAkt by 56-63%. Docetaxel given singly diminished the protein levels only of Cox-2 and did not affect K-Ras and pAkt. High-affinity binding sites, mRNA, and protein expression of pituitary GHRH receptors and its splice variant (SV) 1 were found in H460. H460 NSCLC cells contained GHRH peptide, and its growth was significantly inhibited in vitro by 10 microM MZ-J-7-138 (P < 0.001). Serum insulin-like growth factor 1 (IGF1) was not reduced by either GHRH antagonists. These findings suggest that antiproliferative effects of GHRH antagonists in H460 NSCLC are associated with down-regulation of K-Ras, Cox-2, and pAkt. In conclusion, GHRH antagonists in combination with docetaxel synergistically inhibit growth of H460 NSCLC and the expression of K-ras, Cox-2, and pAkt, which might abrogate the signal transduction pathways for cell growth stimulation and therapeutic resistance.