Regardless of the arrival of various therapeutic modalities [1], [2], chemotherapy stays a cornerstone of most cancers remedy in scientific follow [3], [4]. Nonetheless, the scientific potential of chemotherapeutic medicine is drastically restricted by insufficient tumor-targeting effectivity and dose-limiting systemic toxicity [5]. SN38 is a potent topoisomerase I inhibitor, however its scientific growth is hindered by restricted solubility and extreme antagonistic results [6]. To beat these obstacles, a liposomal formulation of irinotecan (ONIVYDE®), the prodrug of SN38, has been developed and permitted. Its therapeutic efficacy, nonetheless, depends upon two sequential steps, together with the discharge of irinotecan from liposomes and its metabolic conversion to SN38 in vivo [7]. These twin rate-limiting steps markedly attenuate antitumor response. As well as, irinotecan itself possesses solely about 1% of the cytotoxic exercise of SN38, which additional constrains the scientific advantage of ONIVYDE®. One other SN38-based agent, the antibody-drug conjugate Trodelvy®, suffers from inefficient and delayed drug launch at tumor websites [8]. Reaching an acceptable equilibrium between plasma stability and intratumoral drug launch stays a serious problem for ADCs [9], [10]. These instances underscore the necessity for drug supply methods with excessive tumor selectivity and speedy intratumoral activation [11]. Disappointingly, clinically permitted nanomedicines haven’t achieved superior efficacy in contrast with typical formulations, largely as a result of persistent imbalance between drug supply effectivity and drug launch kinetics in early-generation carriers [12], [13]. Albumin-bound paclitaxel nanoparticles (Abraxane®) quickly destabilize upon intravenous injection, resulting in drug-carrier dissociation and minimal enchancment in pharmacokinetics [14]. Liposomal doxorubicin (Doxil®) considerably extends the systemic circulation and promotes tumor accumulation of doxorubicin, but drug crystallization throughout distant loading ends in overstabilized encapsulation and inadequate launch at tumor websites [15], [16]. Appreciable efforts have targeted on engineering tumor-targeting and stimuli-responsive methods to reconcile supply and launch [17], [18], [19], [20]. Nonetheless, the scientific translation of carrier-based nanomedicines stays difficult as a result of most service supplies are troublesome to be developed as intravenous excipients. Furthermore, the advanced manufacturing processes of most useful nanomedicines hinder large-scale fabrication and industrial implementation.
Service-free self-assembled nanomedicines constructed from small-molecule prodrugs characterize a promising technique that mixes prodrug chemistry with nanotechnology [21], [22], [23], [24]. Small-molecule prodrugs spontaneously combination into steady nanostructures with out the assistance of service supplies, thus reaching ultrahigh drug-loading capacities exceeding 50% [25], [18]. With the incorporation of tumor microenvironment-responsive linkers corresponding to disulfide bonds in prodrugs, prodrug nanoassemblies (NAs) may understand selective drug activation and launch at tumor websites [26], [27], [28]. The synergistic impact of tumor-specific prodrug activation and drug launch contribute to considerably decreased systemic toxicity [29], [30], [31]. Nevertheless, the foremost problem confronted is find out how to steadiness the steadiness of NAs with on-site speedy drug activation, which is crucial for manufacturing, storage, and systemic supply [26]. This fully depends upon the rational molecular design of the prodrug, which generally consists of three modules, particularly, the father or mother drug, a responsive linker, and a side-chain modifier [32]. Disulfide bond is extensively employed as a linker owing to wonderful biocompatibility and redox sensitivity [33], [34]. Furthermore, the dihedral angle of roughly 90° has been recognized as a key structural characteristic of disulfide bond that promotes self-assembly [35], [36]. The side-chain modifiers of prodrug play an equally vital position in balancing meeting stability and drug activation kinetics [37]. Hydrophobic interactions represent the first driving forces within the building of most nanomedicines corresponding to liposomes and micelles [25], [31]. A collection of hydrophobic prodrugs with lipophilic aspect chains have been designed to engineer prodrug-assembled nanomedicines [35], [37]. Though robust hydrophobicity remarkably enhances nanoassembly stability, overly lipophilic aspect chains are inclined to hinder prodrug activation, notably when hydrolysis is concerned [38], [39]. In contrast to hydrophobic interactions, π-π stacking interactions additionally present robust ordering forces that facilitate prodrug nanoassembly with out considerably altering the molecular hydrophobicity [40], [41], [42], [43], [44]. In gentle of this, we proposed that the introduction of conjugated fragrant teams with low hydrophobicity as aspect chains can be a possible technique to advertise steady prodrug nanoassembly by π-π interactions whereas reaching on-demand drug activation. To systematically validate this idea, we chosen a collection of consultant fragrant motifs, together with benzene, naphthalene, Fmoc, anthracene, and pyrene, which give progressively prolonged π-conjugation whereas sustaining comparatively comparable hydrophobicity. These constructions additionally differ in planarity, rigidity, and steric configuration, enabling stepwise modulation of π-π stacking energy and molecular packing conduct. Such a design permits us to decouple the contributions of π-π interactions, molecular flexibility, and steric results to nanoassembly stability and prodrug activation. This method was anticipated to supply a sensible resolution to the long-standing contradiction between meeting stability and drug activation in carrier-free self-assembled nanomedicines.
To check our speculation, we synthesized a collection of disulfide-bridged SN38 prodrugs with fragrant aspect chains of accelerating π-conjugation, together with benzene, naphthalene, Fmoc, anthracene, and pyrene, yielding Ben-S-S-SN38 (BS), Na-S-S-SN38 (NS), Fmoc-S-S-SN38 (FS), An-S-S-SN38 (AS), and Py-S-S-SN38 (PS). Though their hydrophobicity was comparable, these fragrant aspect chains profoundly influenced the nanoassembly behaviors, colloidal stability, and in vivo supply fates of SN38 prodrugs by modulating π-π stacking energy, molecular flexibility, and disulfide dihedral angles. Amongst them, AS, bearing an anthracene moiety, exhibited probably the most favorable self-assembly traits, forming steady NAs at excessive concentrations (1 mg/mL) and whereas retaining passable colloidal stability in PBS (pH 7.4) with none stabilizer. Molecular dynamics simulations revealed that AS had a dihedral angle of 88.14°, approximating 90°, together with the bottom meeting free power of -3401 kcal/mol. These structural options endowed it with wonderful nanoassembly capability. To our shock, fragrant conjugation additionally drastically influenced prodrug activation kinetics. The a number of π-conjugation decreased the HOMO-LUMO power hole and tailored molecular floor electrostatics, lastly facilitating disulfide bond cleavage in AS and PS. Below a reductive containing 5 mM DTT, each AS and PS launched greater than 60% of SN38 inside 1 h. Against this, the activation of the opposite three prodrugs was comparatively gradual beneath the identical circumstances. Regardless of favorable drug launch efficiency, the inflexible pyrene core of PS was unfavorable for steady nanoassembly, leading to poor stability. Amongst these fragrant prodrugs, AS achieved a fragile steadiness between formulation stability and drug launch. After floor PEGylation modification, AS NAs with lengthy blood circulation time and excessive tumor accumulation produced placing antitumor results and passable security consequence in each xenograft and orthotopic colon tumor-bearing mouse fashions (Fig. 1). This examine gives the primary systematic demonstration that fragrant π-conjugation concurrently regulates nanoassembly and disulfide cleavage dynamics, providing vital chemical and structural steerage for the rational design and scientific translation of carrier-free self-assembling prodrugs.
