Bombesin receptor antagonists. 3. Irreversible alkylating analogues: melphalan derivatives

Area of Science:

• Oncology
• Molecular Pharmacology

Background:

• Bombesin (BN)-like peptides, including gastrin-releasing peptide (GRP), function as autocrine growth factors in small cell lung carcinoma (SCLC).
• Targeting BN receptors offers a potential therapeutic strategy for SCLC treatment.

Purpose of the Study:

• To investigate a novel class of bombesin analogues functionalized with nitrogen mustard at the N-terminus.
• To evaluate their mechanism of action and efficacy in blocking BN receptor-mediated signaling.

Main Methods:

• Synthesis of N-terminal nitrogen mustard-modified bombesin analogues.
• Assessment of [125I]GRP binding inhibition in Swiss 3T3 fibroblasts.
• Evaluation of [3H]thymidine incorporation and p115 phosphorylation in response to analogues and GRP.
• Competition experiments to determine the timing and nature of receptor blockade.

Main Results:

• The novel analogues exhibit irreversible binding to BN receptors, inhibiting mitogenic effects.
• Inhibition of [125I]GRP binding occurred in the nanomolar/micromolar range.
• Alkylating 'antagonists' selectively inhibited BN-induced thymidine incorporation when administered simultaneously or 24 hours prior to GRP.
• Alkylating 'agonists' demonstrated antagonistic effects only in sequential treatment protocols.

Conclusions:

• N-terminal nitrogen mustard modification yields bombesin analogues with irreversible BN receptor antagonism.
• These compounds effectively block BN receptor-driven proliferation in SCLC models.
• The distinct activity profiles of alkylating 'agonists' and 'antagonists' provide insights into receptor modulation strategies.