Cell-Penetrating, Guanidinium-Rich Oligophosphoesters: Effective and Versatile Molecular Transporters for Drug and Probe Delivery

Abstract

The design, synthesis, and biological evaluation of a new family of highly effective cell-penetrating molecular transporters, guanidinium-rich oligophosphoesters, are described. These unique transporters are synthesized in two steps, irrespective of oligomer length, by the organocatalytic ring-opening polymerization (OROP) of 5-membered cyclic phospholane monomers followed by oligomer deprotection. Varying the initiating alcohol results in a wide variety of cargo attachment strategies for releasable or nonreleasable transporter applications. Initiation of oligomerization with a fluorescent probe produces, upon deprotection, a transporter-probe conjugate that is shown to readily enter multiple cell lines in a dose-dependent manner. These new transporters are superior in cell uptake to previously studied guanidinium-rich oligocarbonates and oligoarginines, showing over 2-fold higher uptake than the former and 6-fold higher uptake than the latter. Initiation with a protected thiol gives, upon deprotection, thiol-terminated transporters which can be thiol-click conjugated to a variety of probes, drugs and other cargos as exemplified by the conjugation and delivery of the model probe fluorescein-maleimide and the medicinal agent paclitaxel (PTX) into cells. Of particular significance given that drug resistance is a major cause of chemotherapy failure, the PTX-transporter conjugate, designed to evade Pgp export and release free PTX after cell entry, shows efficacy against PTX-resistant ovarian cancer cells. Collectively this study introduces a new and highly effective class of guanidinium-rich cell-penetrating transporters and methodology for their single-step conjugation to drugs and probes, and demonstrates that the resulting drug/probe-conjugates readily enter cells, outperforming previously reported guanidinium-rich oligocarbonates and peptide transporters.

Ribbon‐like Foldamers for Cellular Uptake and Drug Delivery

“…Although the exact uptake mechanism of these short cationic and/or amphipathic peptides remains controversial, the crucial first step of internalization is an interaction between the positively charged residues of the CPP and the anionic groups of the phospholipid bilayer . Thus, arginine (Arg) represents a key residue for efficient internalization, as highlighted by the development of diverse guanidinium‐rich compounds, including synthetic oligoarginine sequences; peptoids; aminoproline‐derived peptides; oligocarbamates, oligocarbonates, or oligophosphoesters; and disulfide‐containing polymers . The efficiency and mode of cellular uptake were shown to be influenced by the content of Arg residues, and by the distance between them, which could be controlled by introducing spacers or through the cyclization of CPPs .…”

ROMP‐ and RAFT‐Based Guanidinium‐Containing Polymers as Scaffolds for Protein Mimic Synthesis

“…This platform has been extended to allow for the synthesis of block polymers with varying functionality. [30] Other examples of CPPMs include aguanidine bearing oligocarbonate [28] and oligophosphoester [31] scaffold developed by Wender and co-workers through ring opening polymerization,a sw ell as ag uanidine containing polymethacrylamide system developed by McCormick and co-workers. [32] These systemsa lso demonstrate cellular internalization, reinforcing the critical importance of guanidiniumi ncorporation.I t is important to note that polymeric guanindium methacrylates similart os ome molecules studied in this reporth ave also been synthesized by Locock et al,a nd examined as highly effectivea ntimicrobials.…”

A Carbon Nanotube Optical Sensor Reports Nuclear Entry via a Noncanonical Pathway

“…6–8 Guanidine, the functional side chain in arginine, is a small moiety that allows integration into molecular probes with minimal structural perturbations and has been widely incorporated in synthetic drugs and drug-carriers, including polymers and nanoparticles, to improve cell uptake. 9 Guanidine-functionalized oligomers and small polymers have been found to translocate to the cell nucleus in cultured cells, 10 making guanidine a potential class of non-canonical nuclear localization signals to facilitate nuclear delivery. Non-canonical NLSs may enhance stability; obviate problems with the in vivo use of peptide-based targeting moieties, which are susceptible to enzymatic degradation and immunogenic responses.…”