Antagonist G-mediated targeting and cytotoxicity of liposomal doxorubicin in NCI-H82 variant small cell lung cancer.

J.N Moreira,R Gaspar

doi:10.1590/s0100-879x2004000800008

Abstract

The aim of the present study was to characterize the interactions of antagonist G (H-Arg-D-Trp-N(me)Phe-D-Trp-Leu-Met-NH 2)-targeted sterically stabilized liposomes with the human variant small cell lung cancer (SCLC) H82 cell line and to evaluate the antiproliferative activity of encapsulated doxorubicin against this cell line. Variant SCLC tumors are known to be more resistant to chemotherapy than classic SCLC tumors. The cellular association of antagonist G-targeted (radiolabeled) liposomes was 20-30-fold higher than that of non-targeted liposomes. Our data suggest that a maximum of 12,000 antagonist G-targeted liposomes were internalized/cell during 1-h incubation at 37 masculine C. Confocal microscopy experiments using pyranine-containing liposomes further confirmed that receptor-mediated endocytosis occurred, specifically in the case of targeted liposomes. In any of the previously mentioned experiments, the binding and endocytosis of non-targeted liposomes have revealed to be negligible. The improved cellular association of antagonist G-targeted liposomes, relative to non-targeted liposomes, resulted in an enhanced nuclear delivery (evaluated by fluorimetry) and cytotoxicity of encapsulated doxorubicin for incubation periods as short as 2 h. For an incubation of 2 h, we report IC50 values for targeted and non-targeted liposomes containing doxorubicin of 5.7 +/- 3.7 and higher than 200 micro M doxorubicin, respectively. Based on the present data, we may infer that receptors for antagonist G were present in H82 tumor cells and could mediate the internalization of antagonist G-targeted liposomes and the intracellular delivery of their content. Antagonist G covalently coupled to liposomal drugs may be promising for the treatment of this aggressive and highly heterogeneous disease.

Highlights

Small cell lung cancer (SCLC) is an aggressive form of lung cancer that is highly metastatic in humans (1)
The aim of the present study was to characterize the interactions of antagonist G (H-Arg-D-Trp-NmePhe-D-Trp-Leu-Met-NH2)-targeted sterically stabilized liposomes with the human variant small cell lung cancer (SCLC) H82 cell line and to evaluate the antiproliferative activity of encapsulated doxorubicin against this cell line
Small cell lung cancer proliferation is driven by multiple autocrine and paracrine growth loops involving, among others, several neuropeptides including vasopressin, bradykinin and gastrin-releasing peptide

Summary

Introduction

Small cell lung cancer (SCLC) is an aggressive form of lung cancer that is highly metastatic in humans (1). SCLC accounts for 25% of all pulmonary cancers and, despite an initial responsiveness to radiotherapy and chemotherapy, the patient 5-year survival rate is only 5% (2). SCLC cell proliferation is driven by multiple autocrine and paracrine growth loops, involving multiple mitogenic neuropeptides, which play an impor-. Substances that interrupt the mitogenic signals triggered by these neuropeptides provide a new way of treating SCLC. The hexapeptide, H-Arg-D-Trp-NmePhe-D-TrpLeu-Met-NH2, known as antagonist G, is one such substance. It works by blocking the action of multiple neuropeptides at the receptor level (5,6) and has been shown to inhibit the growth of SCLC cells both in vitro and in vivo (4,6)

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