Synthesis and biological evaluation of bis and monocarbonate prodrugs of 10-hydroxycamptothecins

Supramolecular assembly of isomeric SN-38 prodrugs regulated by conjugation sites

Supramolecular polymers (SPs) are an emerging class of drug transporters employed to improve drug therapy. Through the rational design of self-assembling monomers, one can optimize the properties of the resulting supramolecular nanostructures, such as size, shape, surface chemistry, release, and, therefore, biological fates. This study highlights the design of isomeric SN38 prodrugs through the conjugation of hydrophilic oligo(ethylene glycol) (OEG) with hydroxyls at positions 10 and 20 on hydrophobic SN-38. Self-assembling prodrug (SAPD) isomers 10-OEG-SN38 and 20-OEG-SN38 can self-assemble into giant nanotubes and filamentous assemblies, respectively, via aromatic associations that dominate self-assembly. Our study reveales the influence of modification sites on the assembly behavior and ability of the SN38 SAPDs, as well as drug release and subsequent in vitro and in vivo antitumor effects. The SAPD modified at position 20 exhibits stronger π-π interactions among SN38 units, leading to more compact packing and enhanced assembly capability, whereas OEG at position 10 poses steric hindrance for aromatic associations. Importantly, owing to its higher chemical and supramolecular stability, 20-OEG-SN38 outperforms 10-OEG-SN38 and irinotecan, a clinically used prodrug of SN38, in a CT26 tumor model, demonstrating enhanced tumor growth inhibition and prolonged animal survival. This study presents a new strategy of using interactions among drug molecules as dominating features to create supramolecular assemblies. It also brings some insights into creating effective supramolecular drug assemblies via the engineering of self-assembling building blocks, which could contribute to the optimization of design principles for supramolecular drug delivery systems.

Stimulus-cleavable chemistry in the field of controlled drug delivery

This review comprehensively summarises stimulus-cleavable linkers from various research areas and their cleavage mechanisms, thus provides an insightful guideline to extend their potential applications to controlled drug release from nanomaterials.

Application and design of esterase-responsive nanoparticles for cancer therapy

Nanoparticles have been developed for tumor treatment due to the enhanced permeability and retention effects. However, lack of specific cancer cells selectivity results in low delivery efficiency and undesired side effects. In that case, the stimuli-responsive nanoparticles system designed for the specific structure and physicochemical properties of tumors have attracted more and more attention of researchers. Esterase-responsive nanoparticle system is widely used due to the overexpressed esterase in tumor cells. For a rational designed esterase-responsive nanoparticle, ester bonds and nanoparticle structures are the key characters. In this review, we overviewed the design of esterase-responsive nanoparticles, including ester bonds design and nano-structure design, and analyzed the fitness of each design for different application. In the end, the outlook of esterase-responsive nanoparticle is looking forward.

Enhanced Liver Targeting of Camptothecin via Conjugation with Deoxycholic Acid

Camptothecin (CPT) shows potent anticancer activity through inhibition of topoisomerase I. However, its water insolubility and severe toxicity limit its clinical application. Coupling with bile acid moieties is a promising method for liver-targeted drug delivery, which takes advantage of the bile acid receptors on hepatocytes. In this study, we evaluated the potential liver targeting and stability of a deoxycholic acid-CPT conjugate (G2). The competitive inhibition of antitumor activity experiment based on bile acid transporters was performed using the MTT method. The effects of deoxycholic acid on uptake of G2 and CPT were assessed in 2D and 3D HepG2 cell models. The stability of G2 and CPT was evaluated in vitro (in simulated gastric fluid, simulated intestinal fluid, and fresh rat plasma). Finally, biodistribution of G2 and CPT was investigated in Kunming mice following oral administration. The results showed that deoxycholic acid pretreatment could significantly reduce the antitumor activity and cellular uptake of G2 in HepG2 cells, but had no distinct effects on CPT. Meanwhile, G2 exhibited better stability compared with CPT. More importantly, biodistribution study in mice demonstrated that the liver targeting index of G2 increased 1.67-fold than that of CPT. Overall, the study suggests that conjugation with deoxycholic acid is a feasible method to achieve liver targeting delivery of CPT.

Optimal construction and pharmacokinetic study of CZ48-loaded poly (lactic acid) microbubbles for controlled drug delivery

CZ48, a prodrug of camptothecin (CPT) with derivative resistant to lactone hydrolysis, suffers from limited application for cancer treatment due to poor water-solubility, thus causing its low bioavailability and absorption in vivo. To echo this problem, CZ48 was incorporated into poly (lactic acid) (PLA) microbubbles via a double emulsion technique (W/O/W), and the successful loading was confirmed by X-ray diffraction (XRD) patterns and confocal laser scanning microscope (CLSM). The obtained CZ48-loaded microbubbles had a diameter ranging from 0.5 to 6.7 μm, and the encapsulation efficiency and drug-loading content were as high as 85.73 ± 2.41% and 26.07 ± 0.76%, respectively. The in vitro drug release demonstrated that only about 55% of CZ48 was released for CZ48-loaded PLA microbubbles in 48 h. In contrast, over 90% of CZ48 was released for free CZ48 crystals sample in only 5 h. Besides, in vivo pharmacokinetic studies further revealed that the availability of both CZ48 and its metabolite CPT were obviously enhanced after the incorporation of CZ48 into PLA microbubbles. To be noted, the value of AUC_0-∞ of the CZ48-loaded microbubbles was about 5-fold higher than that of free CZ48 suspension, implying a much higher anticancer effect of the CZ48-loaded microbubbles. The half-life time (T_1/2) of both CZ48 and CPT of the CZ48-loaded microbubbles were also significantly longer than that of the free CZ48, indicating a delayed release time for the microbubbles. Hence, this work promotes a promising drug carrier system for the controlled release of CZ48 as well as other drugs with poor water-solubility.

Facile Fabrication of 10-Hydroxycamptothecin-Backboned Amphiphilic Polyprodrug with Precisely Tailored Drug Loading Content for Controlled Release

Polymeric prodrugs with precisely controlled drug loading content (DLC) and rapid intracellular destabilization generally require complicated chemistry that hinders large-scale manufacture. For this purpose, we reported in this study a facile construction of reduction-sensitive amphiphilic polyprodrugs with an anticancer drug, 10-hydroxycamptothecin (HCPT), and a hydrophilic poly(ethylene oxide) (PEG) moiety as the alternating building blocks of the multiblock copolymer using Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAc) click coupling between azide-SS-HCPT-SS-azide and alkyne-PEG-alkyne. Adoption of PEGs with two different molecular weights (MWs) of 400 and 1450 Da (PEG400 and PEG1450) afforded two polyprodrugs with different DLCs. Both formulations can self-assemble into spherical micelles with hydrodynamic diameter smaller than 200 nm, and exhibit glutathione (GSH)-triggered degradation for promoted drug release. A further comparison study revealed that the PEG1450-based polyprodrug is a better formulation than the analogue constructed from PEG400 in terms of in vitro drug release behaviors, and cytotoxicity. This work thus provides a facile yet efficient strategy toward polymeric prodrugs with precisely controlled DLC and reduction-triggered degradation for enhanced anticancer drug delivery.

Synthesis and Biological Evaluation of Paclitaxel and Camptothecin Prodrugs on the Basis of 2-Nitroimidazole

Due to the low esterase activity in human plasma, many ester and carbonate prodrugs tested in humans may be less effective than that in preclinical animals. In this letter, PTX and SN-38 were attached to the N-1 position of 2-nitroimidazole via a carbonate linker. Presumably, 2-aminoimidazole may help promote the intramolecular hydrolysis of the carbonate bond. The prodrugs exhibited a considerable stability in buffers at different pH values as well as in human plasma. Furthermore, a rapid reduction was exhibited in the presence of nitroreductase. An in vitro cytotoxicity assay demonstrated that hypoxic conditions could increase the toxicity of prodrugs. Potentially, the compound species may form a new class of promising antitumor agents.

10-Hydroxycamptothecin (HCPT) nanosuspensions stabilized by mPEG1000-HCPT conjugate: high stabilizing efficiency and improved antitumor efficacy

In this study, polyethylene glycol (PEG)ylated 10-hydroxycamptothecin (mPEG₁₀₀₀-HCPT) was synthesized and used as a stabilizer to prepare 10-hydroxycamptothecin (HCPT) nanosuspensions for their in vitro and in vivo antitumor investigation. The resultant HCPT nanosuspensions (HCPT-NSps) had a very high drug payload of 94.90% (w/w) and a mean particle size of 92.90±0.20 nm with narrow size distribution (polydispersity index of 0.16±0.01). HCPT-NSps could be lyophilized without the need of the addition of any cryoprotectant and then be reconstituted into nanosuspensions of a similar size by direct resuspension in water. HCPT was in crystalline form in HCPT-NSps. Using mPEG₁₀₀₀-HCPT as stabilizer, insoluble camptothecin and 7-ethyl-10-hydroxycamptothecin could also be easily made into nanosuspensions with similar features such as high drug payload, small particle size, and cryoprotectant-free freeze drying. The 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide assay indicated that the HCPT-NSps had a significantly higher cytotoxicity than HCPT injections, with 3.77 times lower IC₅₀ value against HepG2 cells and 14.1 times lower IC₅₀ value against MCF-7 cells. An in vivo study in H22 tumor-bearing mice after intravenous injection of HCPT-NSps demonstrated that HCPT-NSps significantly improved the antitumor efficacy compared to the commercially available HCPT injections (86.38% vs 34.97%) at the same dose of 5 mg/kg. Even at 1/4 of the dose, HCPT-NSps could also achieve a similar antitumor efficacy to that of HCPT injections. mPEG₁₀₀₀-HCPT may be a highly efficient stabilizer able to provide camptothecin-based drugs, and probably other antitumor agents containing aromatic structure, with unique nanosuspensions or nanocrystals for improved in vivo therapeutic efficacy.

Comparison of two self-assembled macromolecular prodrug micelles with different conjugate positions of SN38 for enhancing antitumor activity

7-Ethyl-10-hydroxycamptothecin (SN38), an active metabolite of irinotecan (CPT-11), is a remarkably potent antitumor agent. The clinical application of SN38 has been extremely restricted by its insolubility in water. In this study, we successfully synthesized two macromolecular prodrugs of SN38 with different conjugate positions (chitosan-(C₁₀-OH)SN38 and chitosan-(C₂₀-OH)SN38) to improve the water solubility and antitumor activity of SN38. These prodrugs can self-assemble into micelles in aqueous medium. The particle size, morphology, zeta potential, and in vitro drug release of SN38 and its derivatives, as well as their cytotoxicity, pharmacokinetics, and in vivo antitumor activity in a xenograft BALB/c mouse model were studied. In vitro, chitosan-(C₁₀-OH)SN38 (CS-(10s)SN38) and chitosan-(C₂₀-OH) SN38 (CS-(20s)SN38) were 13.3- and 25.9-fold more potent than CPT-11 in the murine colon adenocarcinoma cell line CT26, respectively. The area under the curve (AUC)_0–24 of SN38 after intravenously administering CS-(10s)SN38 and CS-(20s)SN38 to Sprague Dawley rats was greatly improved when compared with CPT-11 (both P<0.01). A larger AUC_0–24 of CS-(20s)SN38 was observed when compared to CS-(10s)SN38 (P<0.05). Both of the novel self-assembled chitosan-SN38 prodrugs demonstrated superior anticancer activity to CPT-11 in the CT26 xenograft BALB/c mouse model. We have also investigated the differences between these macromolecular prodrug micelles with regards to enhancing the antitumor activity of SN38. CS-(20s)SN38 exhibited better in vivo antitumor activity than CS-(10s)SN38 at a dose of 2.5 mg/kg (P<0.05). In conclusion, both macromolecular prodrug micelles improved the in vivo conversion rate and antitumor activity of SN38, but the prodrug in which C₂₀-OH was conjugated to macromolecular materials could be a more promising platform for SN38 delivery.

Camptothecin-20(s)-O-[N-(3'α,12'α-dihydroxy-24'-carbonyl-5'β-cholan)]-lysine, a novel camptothecin analogue, induces apoptosis towards hepatocellular carcinoma SMMC-7721 cells

Camptothecin-20(s)-O-[N-(3’α,12’α-dihydroxy-24’-carbonyl-5’β-cholan)]-lysine (B2) is a novel camptothecin analogue. Our previous study had shown that it displayed higher cytoxicity activity towards hepatocellular carcinoma SMMC-7721 cells than camptothecin (CPT) in vitro. In this paper, the underlying mechanism of anti-proliferation of B2 towards SMMC-7721 cells was further examined. Cell growth inhibition of B2 was determined using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay; morphological changes were observed under Laser Scanning Confocal Microscope (LSCM); cell cycle distribution, apoptotic population, changes in mitochondrial membrane potential, intracellular calcium concentration and reactive oxygen species (ROS) production were determined by flow cytometry (FCM). Activities of caspase-3 and caspase-9 were measured, and the expression level of Bcl-2 and Bax proteins were analyzed by Western blot. The results suggested that B2 inhibited SMMC-7721 cell growth by causing cell cycle arrest at the S and G2/M phases, and induced apoptosis involving a mitochondrial pathway. B2 appears to cause a high induction of apoptosis on SMMC-7721 cells in vitro, which suggests it might be a potential drug for cancer therapy.

Oxidative stimuli-responsive nanoprodrug of camptothecin kills glioblastoma cells

The purpose of this study was to prepare and characterize nanometer-sized prodrug (nanoprodrug) of camptothecin. The camptothecin prodrug was synthesized using tetraethylene glycol spacer linked via carbonate bond to camptothecin and via ester bond to alpha-lipoic acid. The nanoprodrug was prepared through the spontaneous emulsification mechanism using the mixture of camptothecin prodrug and alpha-tocopherol which served as a structural matrix. The nanoprodrug was activated readily by porcine liver esterase and, with a much slower rate, by hydrolytic degradation. Upon longterm storage, the alpha-lipoic acid moiety of the camptothecin prodrug gradually oxidized without loss of structural integrity and therapeutic efficacy. Interestingly, the hydrolytic activation was negligible before the oxidation, but was significantly accelerated after the oxidation of the alpha-lipoic acid moiety, suggesting an oxidative stimuli-responsive activation of the prodrug. The camptothecin nanoprodrug was found to possess significant inhibitory effect on the proliferation of U87-MG glioma cells with an IC(50) of 20 nM.

Preparation and pharmacodynamics of stearic acid and poly (lactic-co-glycolic acid) grafted chitosan oligosaccharide micelles for 10-hydroxycamptothecin

Stearic acid (SA) and poly (lactic-co-glycolic acid) (PLGA) grafted chitosan oligosaccharide (SA-CSO-PLGA SCP) tripolymer was synthesized via the reaction between the carboxyl group of SA or PLGA with carboxylic side group, and the amine group of CSO in the presence of 1-Ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC). The degrees of amino-substitution for SA and PLGA were assayed through 2, 4, 6-trinitrobenzene sulfonic acid (TNBS) test and (13)C NMR spectrum, which were 8.15% and 5.82%, respectively; the critical micelle concentrations of SCP in PBS (pH 7.4) and deionized water (DI water) were about 34.9 and 14.5 microg/ml, respectively. Using 10-hydroxycamptothecin (HCPT) as a model drug, the drug-loaded micelles showed above 86% encapsulation efficiency, which not only enhanced the solubility of HCPT in aqueous medium markedly, but also protected the lactone ring of HCPT. Cellular uptakes of SCP micelles against A549, MCF-7 and HepG-2 tumor cells showed a faster cellular internalization. Comparing to the commercial HCPT injection, HCPT-loaded micelles showed higher cytotoxicities against A549, MCF-7 and HepG-2 cells. The increased folds were 22, 18 and 15, respectively. These results suggested the SCP could be applied as a carrier for hydrophobic drugs.

Development of a chemically stable 10-hydroxycamptothecin nanosuspensions

The purpose of this study was to prepare and characterize nanosuspensions loading the active lactone form of 10-hydroxycamptothecin (10-HCPT). Nanosuspensions were prepared in terms of microprecipitation-high-pressure homogenization method. As for the preparation processes, three important parameters, i.e. the agitation rate of stabilizer solution, homogenization pressure and cycle numbers, were investigated and optimized, and the optimal values were 1000 rpm, 1000 bar and 20 times, respectively. The particle size and zeta potential of the 10-HCPT-nanosuspensions were 131 nm and -25.5 mV. The particle morphology was determined by transmission electron microscopy and the 10-HCPT nanoparticles were baculine or trabecular in shape. The solid state of 10-HCPT in nanoparticles was analyzed using X-ray powder diffraction (XRD) and differential scanning calorimetry (DSC). The XRD and the DSC results both indicated that 10-HCPT was present as an amorphous state in the lyophilized powders for nanosuspension. The chemical stability tests demonstrated that near 90% lactone form of 10-HCPT was present in the nanosuspensions but it was easily transferred to the carboxylate form in the solution at pH 7.0-8.0. In vitro dissolution tests showed the dissolution rate of nanosuspensions, compared with the coarse suspensions, had been significantly increased.

Antibody conjugates of 7-ethyl-10-hydroxycamptothecin (SN-38) for targeted cancer chemotherapy

CPT-11 is a clinically used cancer drug, and it is a prodrug of the potent topoisomerase I inhibitor, SN-38 (7-ethyl-10-hydroxycamptothecin). To bypass the need for the in vivo conversion of CPT-11 and increase the therapeutic index, bifunctional derivatives of SN-38 were prepared for use in antibody-based targeted therapy of cancer. The general synthetic scheme incorporated an acetylene-azide click cycloaddition step in the design, a short polyethylene glycol spacer for aqueous solubility, and a maleimide group for conjugation. Conjugates of a humanized anti-CEACAM5 monoclonal antibody, hMN-14, prepared using these SN-38 derivatives were evaluated in vitro for stability in buffer and human serum and for antigen-binding and cytotoxicity in a human colon adenocarcinoma cell line. Conjugates of hMN-14 and SN-38 derivatives 16 and 17 were found promising for further development.