Syntheses and in vitro antitumor activities of ferrocene-conjugated Arg-Gly-Asp peptides

Ferrocene (Fc) and its conjugates have attracted considerable attention in recent years due to their unique electrochemical behavior and significant biological activities such as antitumor, antimalarial, and antifungal. Arg-Gly-Asp (RGD)-containing peptides, because of their selective binding to integrins which are highly expressed in tumor-induced angiogenesis, play a key role in cancer targeted therapy. In this study, Fc–RGD and Fc–Am–RGD (Fc: ferrocenoyl; Am: 6-aminohexanoic acid) conjugates were synthesized, and the antitumor activities in vitro were investigated. The cell uptake of the conjugates by B16 murine melanoma cells was measured using HPLC-electrochemical method. The antitumor activities of the conjugates were also evaluated by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) and flow cytometric measurements. The experimental results revealed that Fc–RGD and Fc–Am–RGD exhibit more effective antitumor activities than their parent compounds RGD and Fc-COOH. Moreover, it is found that Fc–Am–RGD yields the lowest IC50 values of 5.2±1.4μM toward B16 cells. The HPLC-electrochemical studies confirmed that the insertion of flexible alkyl spacer Am between Fc and RGD significantly increases the cell uptake toward B16 cells and consequently improves the antitumor activity. Our results suggest that Fc–RGD and Fc–Am–RGD conjugates are potential candidates for cancer treatment. The ferrocene-conjugated Arg-Gly-Asp peptides were synthesized in solution. The cell uptake of the ferrocenoyl conjugates was tested by HPLC-electrochemical method. Fc–Am–RGD shows higher cell uptake and antitumor activity than its parent compound Fc-COOH due to the attachment of RGD and insertion of flexible alkyl spacer between ferrocene and RGD. [Display omitted] ► Ferrocene-conjugated Arg-Gly-Asp peptides were synthesized in solution. ► Cell uptake of the ferrocenoyl conjugates was tested by HPLC-electrochemical method. ► Fc–Am–RGD shows much higher antitumor activity than Fc-COOH. ► The flexible alkyl spacer between ferrocene and RGD enhances the cell uptake.