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Keywords:

  • AN-152;
  • AN-238;
  • bronchopulmonary carcinoid;
  • carcinoid;
  • cytotoxic peptide analogs;
  • doxorubicin;
  • drug sensitivity;
  • H720;
  • H727;
  • KRJ-I;
  • MZ-5-156;
  • neuroendocrine tumor;
  • somatostatin

Abstract

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 8× 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. Cancer 2008. © 2008 American Cancer Society.