Inhibition of proliferation of small intestinal and bronchopulmonary neuroendocrine cell lines by using peptide analogs targeting receptors.
BACKGROUND
Currently, no consistently effective therapy is available to inhibit cell proliferation or metastasis of neuroendocrine tumor (NET) disease. The effects of 4 novel peptides were analyzed: a targeted cytotoxic analog of luteinizing hormone-releasing hormone (LH-RH) analog (AN-152), a targeted cytotoxic analog of somatostatin (AN-238), and 2 antagonists of growth hormone-releasing hormone (GH-RH) on 3 NET (carcinoid) cell lines that expressed respective peptide receptors.


METHODS
The effects of the compounds were evaluated on cell proliferation in vitro using MTT uptake and Ki67 expression, apoptosis (caspase 3 expression and activity), and cell cycle parameters (DNA distribution).


RESULTS
Proliferation of the LH-RH receptor-expressing lung NET, NCI-H720 line, was inhibited 2-fold by AN-152 containing doxorubicin compared with the chemotherapy alone (IC50 of 9.1 nM vs 24 nM). This was associated with a reduction in Ki67 transcript and an increase in both caspase 3 mRNA levels and activity. Proliferation of the GH-RH receptor expressing lung NET, NCI-H727 line, was inhibited by both GH-RH antagonists, the effects being mediated through changes in Ki67 expression, but not in caspase 3-mediated apoptosis. The small intestinal NET, KRJ-I line, was 8x more sensitive to inhibition by AN-238 than to 2-pyrolino-doxorubicin, reflected by increased caspase 3 transcript as well as activity. AN-238-mediated growth inhibition culminated in complete G1 arrest.


CONCLUSIONS
The data demonstrate GH-RH antagonists or peptide-linked antineoplastic agents such as AN-152 and AN-238 are effective inhibitors of NET proliferation in vitro. Because peptide receptors such as those for GH-RH, LH-RH, and SST subtypes are commonly expressed by NETs, the development of antineoplastic agents targeted to specific tumor receptors may provide a more efficacious strategy than systemic chemotherapeutic agents currently in use.
Kidd
Mark
M
Gastrointestinal Pathobiology Research Group, Yale University School of Medicine, New Haven, Connecticut 06520-8062, USA.
Schally
Andrew V
AV
Pfragner
Roswitha
R
Malfertheiner
Maximillian V
MV
Modlin
Irvin M
IM
D017209:Apoptosis / Q000187:drug effects; D001984:Bronchial Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D002276:Carcinoid Tumor / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D053148:Caspase 3 / Q000378:metabolism; D002453:Cell Cycle / Q000187:drug effects; D049109:Cell Proliferation / Q000187:drug effects*; D003603:Cytotoxins / Q000494:pharmacology; D004317:Doxorubicin / Q000031:analogs & derivatives / Q000494:pharmacology; D005434:Flow Cytometry; D007987:Gonadotropin-Releasing Hormone / Q000031:analogs & derivatives / Q000037:antagonists & inhibitors / Q000494:pharmacology; D013007:Growth Hormone-Releasing Hormone / Q000037:antagonists & inhibitors*; D006801:Humans; D007414:Intestinal Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D007421:Intestine, Small / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D019394:Ki-67 Antigen / Q000235:genetics / Q000378:metabolism; D008175:Lung Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D011758:Pyrroles / Q000494:pharmacology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011966:Receptors, LHRH / Q000037:antagonists & inhibitors; D017481:Receptors, Somatostatin / Q000037:antagonists & inhibitors; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014407:Tumor Cells, Cultured
C110845:AN 238; D003603:Cytotoxins; D019394:Ki-67 Antigen; D011758:Pyrroles; D012333:RNA, Messenger; D011966:Receptors, LHRH; D017481:Receptors, Somatostatin; C080883:LHRH, lysine(6)-doxorubicin; D007987:Gonadotropin-Releasing Hormone; D004317:Doxorubicin; D013007:Growth Hormone-Releasing Hormone; D053148:Caspase 3