PEGylation Effects on Amphiphilic Platinum(IV) Complexes: Influence on Uptake, Activation, and Cytotoxicity

Abstract

Background/Objectives: The utilization of amphiphilic Pt(IV) complexes as prodrugs offers a promising strategy to revolutionize Pt-based cancer therapy by enhancing drug delivery and activation. While PEGylation is widely used to optimize drug properties, its impact on the biological behavior of amphiphilic Pt(IV) complexes remains unclear. This study systematically investigates how the PEGylation of varying molecular weights influences their cytotoxicity, cellular uptake, and activation. Methods: Pt(IV) complexes were synthesized with PEG chains of different molecular weights using HATU-catalyzed amide bond formation and copper-free click chemistry. Their biological properties were assessed through cell-based analyses, focusing on cytotoxicity, cellular uptake, and activation by biological reductants. Results: Small PEG modifications retained the potent cytotoxicity of amphiphilic Pt(IV) prodrugs, whereas large PEG chains significantly reduced efficacy. The decrease in potency was linked to impaired cellular uptake and mitochondrial accumulation. Additionally, large PEG modifications slowed the reduction and activation of Pt(IV) prodrugs by biological reductants, further limiting their anticancer activities. Conclusions: These findings underscore the critical role of PEGylation in metallodrug design and provide key insights into optimizing PEGylation strategies for enhancing platinum-based cancer therapies.

Keywords: PEGylation; cisplatin; mitochondria; platinum(IV) prodrugs.

Figure 1

Structures of amphiphilic Pt(IV) complexes (AMPCs) with PEGylation ranging from a low to high molecular weight (M.W.).

Figure 2

Cytotoxicity profiles of amphiphilic Pt(IV) complexes with varying PEGylation: (a) Table summarizing IC₅₀ values of Pt compounds against human cancer cell lines. (b) Dose–response (killing) curves of compounds 1–6 in A2780cis cells over 48 h.

Figure 3

Impact of PEGylation on the cytotoxicity of amphiphilic Pt(IV) complexes: (a) Bar graph comparing IC₅₀ values of AMPCs (1–6) with varying PEG modifications in A2780cis cells. (b) Live/dead cell assay images of A2780cis cells treated with compounds 1, 2, 4, and 5 ([Pt] = 1 µM) for 48 h. Scale bar: 100 µm.

Figure 4

Impact of PEGylation on cellular uptake and mitochondrial accumulation of amphiphilic Pt(IV) complexes: (a) Schematic representation of the mechanism of action of AMPCs. (b) Cellular uptake and (c) mitochondrial accumulation of AMPCs (4, 5, 6) and cisplatin (CisPt) in A2780cis cells after 48 h. Statistical analysis was performed using a t-test, with p-values indicating significance (p < 0.01 (**), p < 0.001 (***)).

Figure 5

Impact of PEGylation on reduction in amphiphilic Pt(IV) complexes: (a) Stability curves of compounds 4–6 in ascorbic acid (200 µM). (b) Stability curves of compounds 4–6 in glutathione (1 mM).

Figure 6

Impact of PEGylation on cellular responses of amphiphilic Pt(IV) complexes: (a) Flow cytometric analysis of γH2AX in A2780cis cells treated with AMPCs (4 or 5) or cisplatin for 48 h. (b) Flow cytometric analysis of MitoSOX in A2780cis cells treated with AMPCs (4 or 5) or cisplatin for 48 h.