We have synthesized a set of bombesin derivatives with the aim of exploring their tumor targeting properties to deliver metal-based chemotherapeutics into cancer cells. Peptide QRLGNQWAVGHLL-NH₂ (BN3) was selected based on its high internalization in gastrin-releasing peptide receptor (GRPR)-overexpressing PC-3 cells. Three metallopeptides were prepared by incorporating the terpyridine Pt(II) complex [PtCl(cptpy)]Cl (1) (cptpy = 4′-(4-carboxyphenyl)-2,2′:6,2″-terpyridine) at the N-terminus of BN3 or at the N^Ɛ- or N^α-amino group of an additional Lys residue (1-BN3, Lys-1-BN3 and 1-Lys-BN3, respectively). 1-Lys-BN3 displayed the best cytotoxic activity (IC₅₀: 19.2 ± 1.7 μM) and similar ability to intercalate into DNA than complex 1. Moreover, the polypyridine Ru(II) complex [Ru(bpy)₂)(cmbpy)](PF₆)₂ (2) (bpy = 2,2′-bipyridine; cmbpy = 4-methyl-2,2′-bipyridine-4′-carboxylic acid), with proven activity as photosensitizer, was coupled to BN3 leading to metallopeptide 2-Lys-BN3. Upon photoactivation, 2-Lys-BN3 displayed 2.5-fold higher cytotoxicity against PC-3 cells (IC₅₀: 7.6 ± 1.0 μM) than complex 2. To enhance the accumulation of the drugs into the cell nucleus, the nuclear localization signal (NLS) PKKKRKV was incorporated at the N-terminus of BN3. NLS-BN3 displayed higher cellular internalization along with nuclear biodistribution. Accordingly, metallopeptides 1-NLS-BN3 and 2-NLS-BN3 showed increased cytotoxicity (IC₅₀: 12.0 ± 1.1 μM and 2.3 ± 1.1 μM). Interestingly, the phototoxic index of 2-NLS-BN3 was 8-fold higher than that of complex 2. Next, the selectivity towards cancer cells was explored using 1BR3.G fibroblasts. Higher selectivity indexes were obtained for 1-NLS-BN3 and 2-NLS-BN3 than for the unconjugated complexes. These results prove NLS-BN3 effective for targeted delivery of metallodrugs to GRPR-overexpressing cells and for enhancing the cytotoxic efficacy of metal-based photosensitizers.

我们合成了一组铃蟾肽衍生物，旨在探索它们的肿瘤靶向特性，以将基于金属的化疗药物输送到癌细胞中。选择肽 QRLGNQWAVGHLL-NH ₂ ( BN3 ) 是基于其在胃泌素释放肽受体 (GRPR) 过表达的 PC-3 细胞中的高度内化。三个metallopeptides分别通过将三联吡啶制备的Pt（II）络合物[氯铂酸（cptpy）]氯（1）（cptpy = 4' - （4-羧基苯基）-2,2'：6,2“ -三联吡啶）在N -末端的BN3或在ñ ^ɛ -或ñ ^α -氨基基团的附加Lys残基的（1-BN3，赖氨酸-1- BN3和1-赖氨酸BN3， 分别）。1-Lys-BN3显示出最好的细胞毒活性 (IC ₅₀ : 19.2 ± 1.7 μM) 和与复合物1相比类似的嵌入 DNA 的能力。此外，多吡啶Ru(II)配合物[Ru(bpy) ₂ )(cmbpy)](PF ₆ ) ₂ ( 2 ) (bpy = 2,2'-联吡啶；cmbpy = 4-甲基-2,2'-联吡啶-4'-羧酸），具有作为光敏剂的证明活性，与BN3偶联产生金属肽2-Lys-BN3。光活化后，2-Lys-BN3对 PC-3 细胞的细胞毒性比复合物2高 2.5 倍（IC ₅₀：7.6 ± 1.0 μM）. 为了增强药物在细胞核中的积累，核定位信号 (NLS) PKKKRKV 被纳入BN3的 N 端。NLS-BN3显示出更高的细胞内化以及核生物分布。因此，金属肽1-NLS-BN3和2-NLS-BN3显示出增加的细胞毒性（IC ₅₀：12.0 ± 1.1 μM 和 2.3 ± 1.1 μM）。有趣的是，2-NLS-BN3的光毒性指数是复合物2 的8 倍。接下来，使用 1BR3.G 成纤维细胞探索了对癌细胞的选择性。1-NLS-BN3和2-NLS-BN3获得了更高的选择性指数而不是非共轭配合物。这些结果证明NLS-BN3 可有效地将金属药物靶向递送至 GRPR 过表达细胞并增强基于金属的光敏剂的细胞毒性功效。