Thermodynamic Studies and Loading of 7-Ethyl-10-hydroxycamptothecin into Mesoporous Silica Particles MCM-41 in Strongly Acidic Solutions

Sacituzumab Govitecan Demonstrates Efficacy across Tumor Trop-2 Expression Levels in Patients with Advanced Urothelial Cancer

PURPOSE

Human trophoblast cell surface antigen 2 (Trop-2) is a protein highly expressed in urothelial cancer (UC). Sacituzumab govitecan (SG) is a Trop-2-directed antibody drug conjugate with a hydrolysable linker and a potent SN-38 payload. This study explored Trop-2 expression in tumors treated with SG in cohorts 1 to 3 (C1-3) from the TROPHY-U-01 study and evaluated whether efficacy was associated with Trop-2 expression.

PATIENTS AND METHODS

TROPHY-U-01 (NCT03547973) is an open-label phase II study that assessed the efficacy and safety of SG (alone or in combinations) in patients with unresectable locally advanced or metastatic UC (mUC). Archival tumor samples collected at enrollment for C1-3 were analyzed for Trop-2 membrane expression by considering histological scores (H-scores; scale 0-300) and the percentage of membrane positive tumor cells at low magnification (4×). The association of Trop-2 with clinical endpoints [objective response rate (ORR), progression-free survival (PFS), and overall survival (OS)] was evaluated.

RESULTS

In C1-3, tissue was collected from 158 (82%) of 192 treated patients, and 146 (76%) had evaluable Trop-2 data. Trop-2 was highly expressed in tumor samples. The median [interquartile range (IQR)] Trop-2 H-score was 215 (180-246), and the median (IQR) percentage of membrane positive tumor cells was 91% (80-98). Trop-2 expression at any level was observed in 98% of patients. Furthermore, ORR, PFS, and OS benefits were observed across all Trop-2 expression levels.

CONCLUSIONS

Trop-2 protein is highly expressed in UC, as confirmed by examining tumors from patients enrolled in the TROPHY-U-01 trial. The results indicate that SG demonstrates efficacy in mUC across Trop-2 expression levels.

Modification of Poly(Glycerol Adipate) with Tocopherol and Cholesterol Modulating Nanoparticle Self-Assemblies and Cellular Responses of Triple-Negative Breast Cancer Cells to SN-38 Delivery

This study aimed to fabricate new variations of glycerol-based polyesters by grafting poly(glycerol adipate) (PGA) with hydrophobic bioactive moieties, tocopherol (TOC), and cholesterol (CHO). Their effects on nanoparticle (NP) formation, drug release, and cellular responses in cancer and normal cells were evaluated. CHO and TOC were successfully grafted onto PGA backbones with 30% and 50% mole grafting. Increasing the percentage of mole grafting in both molecules increased the glass transition temperature and water contact angle of the final polymers but decreased the critical micelle concentration of the formulated particles. PGA-TOC NPs reduced the proliferation of MDA-MB-231 cancer cells. However, they enhanced the proliferation of primary dermal fibroblasts within a specific concentration range. PGA-CHO NPs minimally affected the growth of cancer and normal cells. Both types of NPs did not affect apoptosis or the cell cycle of cancer cells. PGA-CHO and PGA-TOC NPs were able to entrap SN-38, a hydrophobic anticancer drug, with a particle size <200 nm. PGA-CHO NPs had a higher drug loading capacity and a greater drug release than PGA-TOC NPs. However, SN-38-loaded PGA-TOC NPs showed higher toxicity than SN-38 and SN-38-loaded PGA-CHO NPs due to the combined effects of antiproliferation and higher cellular uptake. Compared with SN-38, the drug-loaded NPs more profoundly induced sub-G1 in the cell cycle analysis and apoptosis of cancer cells in a similar pattern. Therefore, PGA-CHO and PGA-TOC polymers have potential applications as delivery systems for anticancer drugs.

Image-guided thermosensitive liposomes for focused ultrasound enhanced co-delivery of carboplatin and SN-38 against triple negative breast cancer in mice

Triggerable nanocarriers have the potential to significantly improve the therapeutic index of existing anticancer agents. They allow for highly localised delivery and release of therapeutic cargos, reducing off-target toxicity and increasing anti-tumour activity. Liposomes may be engineered to respond to an externally applied stimulus such as focused ultrasound (FUS). Here, we report the first co-delivery of SN-38 (irinotecan's super-active metabolite) and carboplatin, using an MRI-visible thermosensitive liposome (iTSL). MR contrast enhancement was achieved by the incorporation of a gadolinium lipid conjugate in the liposome bilayer along with a dye-labelled lipid for near infrared fluorescence bioimaging. The resulting iTSL were successfully loaded with SN-38 in the lipid bilayer and carboplatin in the aqueous core - allowing co-delivery of both. The iTSL demonstrated both thermosensitivity and MR-imageability. In addition, they showed effective local targeted co-delivery of carboplatin and SN-38 after triggered release with brief FUS treatments. A single dosage induced significant improvement of anti-tumour activity (over either the free drugs or the iTSL without FUS-activation) in triple negative breast cancer xenografts tumours in mice.

Liposomal codelivery of an SN38 prodrug and a survivin siRNA for tumor therapy

Purpose

A liposome-based siRNA–drug combination was evaluated as a potential therapeutic strategy to improve the curative effect.

Methods

A topoisomerase inhibitor SN38 prodrug was combined with a survivin siRNA through codelivery using transferrin (Tf)-L-SN38/P/siRNA. In this combination, SN38 was conjugated to the cell penetrating peptide TAT through a polyethylene glycol (PEG) linker to synthesize TAT-PEG-SN38. The amphiphilic TAT-PEG-SN38 was used as an ingredient of liposomes to improve the cellular uptake. Protamine was added to form an electrostatic complex with siRNA in the core of the liposomes. Tf was introduced to enable tumor cell targeting of liposomes (Tf-L-SN38/P/siRNA).

Results

Tf-L-SN38/P/siRNA exhibited a particle size of 148 nm and a ζ-potential of +7.8 mV. The cellular uptake and antitumor activity were dependent on Tf receptor targeting, TAT-PEG-SN38, and siRNA codelivery. Tf-L-SN38/P/siRNA was shown to be considerably more effective than liposomes carrying individual components. This combination induced potent tumor inhibition (76.8%) in HeLa cell xenograft tumor-bearing nude mice.

Conclusion

These data indicated that Tf-L-SN38/P/siRNA was an effective system for codelivery of SN38 and a survivin siRNA and that its therapeutic potential deserved further evaluation.

SN38-loaded <100 nm targeted liposomes for improving poor solubility and minimizing burst release and toxicity: in vitro and in vivo study

Background

SN38 (7-ethyl-10-hydroxycamptothecin) is a camptothecin derivative acts against various tumors. However, SN38 is hydrolyzed in the physiological environment (pH 7.4), and this instability interferes with its potential therapeutic effect. Our objective was to investigate SN38-loaded liposomes to overcome the poor solubility of SN38 and its biodistribution, which further diminish its toxicity.

Materials and methods

The sub-100 nm targeted liposomes was employed to deliver SN-38 and evaluate the characterization, release behaviors, cytotoxicity, in vivo pharmacokinetics and biochemical assay.

Results

The SN38-loaded targeted liposomes consisted of small (100.49 nm) spherical nanoparticles with negative charge (−37.93 mV) and high entrapment efficiency (92.47%). The release behavior of the SN38-loaded targeted liposomes was fitted with Higuchi kinetics (R²=0.9860). Free SN38 presented initial burst release. The IC₅₀ for the SN38-loaded targeted liposomes (0.11 μM) was significantly lower than for the SN38 solution (0.37 μM) in the MCF7 cell line (P<0.01). Confocal laser scanning microscopy also confirmed highly efficient accumulation in the MCF7 cells. Pharmacokinetics demonstrated that the SN38-loaded targeted liposomes had a slightly increased half-life and mean residence time and decreased area under the concentration–time curve and maximum concentration. The results suggested that retention was achieved while the exposure of SN38 was significantly decreased. A noninvasive in vivo imaging system also showed that the targeted liposomes selectively targeted MCF7 tumors. In vivo toxicity data demonstrated that the decrease in platelets was significantly improved by SN38-loaded targeted liposomes, and diarrhea was not observed in BALB/c mice.

Conclusion

In summary, SN38-loaded targeted liposomes could be a good candidate for application in human breast cancer.

Liposome-loaded thermo-sensitive hydrogel for stabilization of SN-38 via intratumoral injection: optimization, characterization, and antitumor activity

Main challenges of the clinical use of 7-ethyl-10-hydroxycamptothecin (SN-38) are its facile transition between the active lactone form (SN-38 A) and the inactive carboxylate form (SN-38I) under physiological conditions and its low solubility. The purpose of this study was to develop a thermo-sensitive hydrogel system with acidic SN-38 liposomes (SN-38-Lip-Gel) for local chemotherapy to solve these problems and to evaluate its antitumor activity and tissue distribution in tumor-bearing mice. A study of structural conversion between SN-38I and SN-38 A under various pH conditions indicated that acidic solution could inhibit the conversion. Namely, a preparation with low pH was essential to stabilize lactone form of SN-38. SN-38-Lip-Gel had an appropriate gelation time (GT) at 25/37 °C. The particle size of SN-38-Lip-Gel was similar to that of SN-38-Lip. SN-38-Lip-Gel showed a slower release than SN-38-Lip in vitro. SN-38-Lip-Gel suggested pH-dependent stability, the percentage of SN-38 A remaining decreased along with the increasing pH. In vivo studies SN-38-Lip-Gel showed better antitumor efficacy and lower systemic toxicity compared with other groups at the same drug dose. In conclusion, SN-38-Lip-Gel could improve the effective use of SN-38 by stabilizing the lactone form, extending the drug release, providing a high local drug concentration, and reducing systemic toxicity.

In vitro and in vivo evaluation of SN-38 nanocrystals with different particle sizes

7-Ethyl-10-hydroxycamptothecin (SN-38) is a potent broad-spectrum antitumor drug derived from irinotecan hydrochloride (CPT-11). Due to its poor solubility and instability of the active lactone ring, its clinical use is significantly limited. As one of the most promising formulations for poorly water-soluble drugs, nanocrystals have attracted increasing attention. In order to solve these problems and evaluate the antitumor effect of SN-38 in vitro and in vivo, two nanocrystals with markedly different particle sizes were prepared. Dynamic light scattering and transmission electron microscopy were used to investigate the two nanocrystals. The particle sizes of SN-38 nanocrystals A (SN-38/NCs-A) and SN-38 nanocrystals B (SN-38/NCs-B) were 229.5±1.99 and 799.2±14.44 nm, respectively. X-ray powder diffraction analysis showed that the crystalline state of SN-38 did not change in the size reduction process. An accelerated dissolution velocity of SN-38 was achieved by nanocrystals, and release rate of SN-38/NCs-A was significantly faster than that of SN-38/NCs-B. Cellular uptake, cellular cytotoxicity, pharmacokinetics, animal antitumor efficacy, and tissue distribution were subsequently examined. As a result, enhanced intracellular accumulation in HT1080 cells and cytotoxicity on different tumor cells were observed for SN-38/NCs-A compared to that for SN-38/NCs-B and solution. Besides, compared to the SN-38 solution, SN-38/NCs-A had a higher bioavailability after intravenous injection; while the bioavailability of SN-38/NCs-B was even lower than that of the SN-38 solution. SN-38/NCs-A exhibited a significant inhibition of tumor growth compared to SN-38 solution and SN-38/NCs-B in vivo. The antitumor effect of SN-38/NCs-B was stronger than SN-38 solution. The tissue distribution study in tumor-bearing mice showed that nanocrystals could markedly improve the drug accumulation in tumor tissue by the enhanced permeability and retention effect compared to SN-38 solution, and the amount of SN-38 in tumors of SN-38/NCs-A group was much more than that of SN-38/NCs-B group. In conclusion, nanocrystals dramatically enhanced the anticancer efficacy of SN-38 in vitro and in vivo, and the particle size had a significant influence on the dissolution behavior, pharmacokinetic properties, and tumor inhibition of nanocrystals.

The use of surfactants to enhance the solubility and stability of the water-insoluble anticancer drug SN38 into liquid crystalline phase nanoparticles

Cubosomes were used to increase the aqueous solubility of the water insoluble anticancer drug SN38. The results showed that the use of a common cubosome formulation consisting of phytantriol (PHYT) as the matrix amphiphile (PHYT-cubosome) led to a 6-fold increase in the solubility of SN38. However, mean hydrodynamic diameter (D_H) and polydispersity index (PDI) of these PHYT-cubosome particles were 345±49nm and 0.37±0.05, respectively, making them unsuitable for intravenous applications. Several additives were investigated to increase the solubility of SN38 and reduce the D_H and PDI values of the resulting particles. Charged additives such as didodecyldimethyl ammonium bromide (DDAB) and sodium dodecyl sulfate (SDS) led to improvements in the physiochemical properties of the cubosomes. Notably, the PHYT-DDAB and PHT-SDS cubosomes led to 15- and 14-fold increases in the aqueous solubility of SN38, respectively. Moreover, the SN38 loaded into the PHYT-DDAB and PHYT-SDS cubosomes was found to be highly stable, with very little hydrolysis to its inactive acid form. In summary, the addition of DDAB and SDS to PHYT-cubosome nanoparticle drug delivery systems not only led to considerable improvements in their physiochemical properties, but also enhanced the aqueous solubility of SN38 and increased its chemical stability.

The antitumour drug 7-ethyl-10-hydroxycamptothecin monohydrate and its solid-state hydrolysis mechanism on heating

7-Ethyl-10-hydroxycamptothecin [systematic name: (4S)-4,11-diethyl-4,9-dihydroxy-1H-pyrano[3',4':6,7]indolizino[1,2-b]quinoline-3,14(4H,12H)-dione, SN-38] is an antitumour drug which exerts activity through the inhibition of topoisomerase I. The crystal structure of SN-38 as the monohydrate, C₂₂H₂₀N₂O₅·H₂O, reveals that it is a monoclinic crystal, with one SN-38 molecule and one water molecule in the asymmetric unit. When the crystal is heated to 473 K, approximately 30% of SN-38 is hydrolyzed at its lactone ring, resulting in the formation of the inactive carboxylate form. The molecular arrangement around the water molecule and the lactone ring of SN-38 in the crystal structure suggests that SN-38 is hydrolyzed by the water molecule at (x, y, z) nucleophilically attacking the carbonyl C atom of the lactone ring at (x - 1, y, z - 1). Hydrogen bonding around the water molecules and the lactone ring appears to promote this hydrolysis reaction: two carbonyl O atoms, which are hydrogen bonded as hydrogen-bond acceptors to the water molecule at (x, y, z), might enhance the nucleophilicity of this water molecule, while the water molecule at (-x, y + 1/2, -z), which is hydrogen bonded as a hydrogen-bond donor to the carbonyl O atom at (x - 1, y, z - 1), might enhance the electrophilicity of the carbonyl C atom.

Supramolecular Crafting of Self-Assembling Camptothecin Prodrugs with Enhanced Efficacy against Primary Cancer Cells

Chemical modification of small molecule hydrophobic drugs is a clinically proven strategy to devise prodrugs with enhanced treatment efficacy. While this prodrug strategy improves the parent drug's water solubility and pharmacokinetic profile, it typically compromises the drug's potency against cancer cells due to the retarded drug release rate and reduced cellular uptake efficiency. Here we report on the supramolecular design of self-assembling prodrugs (SAPD) with much improved water solubility while maintaining high potency against cancer cells. We found that camptothecin (CPT) prodrugs created by conjugating two CPT molecules onto a hydrophilic segment can associate into filamentous nanostructures in water. Our results suggest that these SAPD exhibit much greater efficacy against primary brain cancer cells relative to that of irinotecan, a clinically used CPT prodrug. We believe these findings open a new avenue for rational design of supramolecular prodrugs for cancer treatment.

SN-38 active loading in poly(lactic-co-glycolic acid) nanoparticles and assessment of their anticancer properties on COLO-205 human colon adenocarcinoma cells

SN-38 is a highly effective drug against many cancers. The development of an optimal delivery system for SN-38 is extremely challenging due to its low solubility and labile lactone ring. Herein, SN-38 encapsulated in poly(D,L-lactide-co-glycolide) nanoparticles (NPs) is introduced to enhance its solubility, stability and cellular uptake. SN-38-loaded NPs prepared by spontaneous emulsification solvent diffusion (SESD) method had an average diameter of 310 nm, a zeta potential of -9.69 mV and a loading efficiency of 71%. They were able to protect the active lactone ring of SN-38 against inactivation under physiological condition. A colorectal adenocarcinoma cell line (COLO-205) was used to assess the NPs effects on cytotoxicity and cellular uptake. Result showed a significant decreased cell proliferation and cell apoptosis. These results suggest that these SN-38-loaded NPs can be an effective delivery system for the treatment of colon cancer and potentially for other types of cancers.

Physicochemical characterization of 9-aminocamptothecin in aqueous solutions

The present manuscript provides a detailed physicochemical and thermodynamic characterization of 9-aminocamptothecin (9AC) which can be used as a tool to develop novel formulation strategies for optimum pharmacological activity. The pKa of 9AC was determined to be 2.43 at 37°C, while the basicity of quinoline nitrogen of 9AC was found to decrease with increasing temperature due to a positive enthalpy of deprotonation of 10.36 kJ mol(-1). The equilibrium solubility as well as the intrinsic solubility of the drug was found to increase with increasing temperature and decreasing pH. The enthalpies of solution of unionized and ionized forms of 9AC obtained from isothermal and iso-pH equilibrium solubility measurements were found to be 36.01 and 24.72 kJ mol(-1), respectively. Equilibrium hydrolysis studies revealed the hydrolytic susceptibility of 9AC with only 14% of active lactone species remaining at physiological pH 7.4. The intrinsic partition coefficient log P of the free base, 9AC-lactone, was estimated to be 1.28 (a characteristic of molecules suitable for oral absorption). The estimated pKa and log P values of 9AC, combined with its increased solubility at lower pH, are features that can be utilized to develop novel drug delivery systems to optimize the antitumor activity of 9AC.

Prodrug and nanomedicine approaches for the delivery of the camptothecin analogue SN38

SN38 (7-ethyl-10-hydroxy camptothecin) is a prominent and efficacious anticancer agent. It is poorly soluble in both water and pharmaceutically approved solvents; therefore, the direct formulation of SN38 in solution form is limited. Currently, the water soluble prodrug of SN38, irinotecan (CPT-11), is formulated as a low pH solution and is approved for chemotherapy. However, CPT-11, along with most other water-soluble prodrugs shows unpredictable inter-patient conversion to SN38 in vivo, instability in the physiological environment and variable dose-related toxicities. More recently, macromolecular prodrugs (i.e. EZN-2208, IMMU-130) and nanomedicine formulations (i.e. nanoemulsions, polymeric micelles, lipid nanocapsule/nanoparticle, and liposomes) of SN38 have been investigated for improved delivery to cancer cells and tissues. Specifically, these carriers can take advantage of the EPR effect to direct drug preferentially to tumour tissues, thereby substantially improving efficacy and minimising side effects. Furthermore, oral delivery has been shown to be possible in preclinical results using nanomedicine formulations (i.e. dendrimers, lipid nanocapsules, polymeric micelles). This review summarizes the recent advances for the delivery of SN38 with a focus on macromolecular prodrugs and nanomedicines.

SN-38 loaded polymeric micelles to enhance cancer therapy

7-Ethyl-10-hydroxycamptothecin (SN-38) loaded poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (Pluronic F-108) and poly(ethylene glycol)-block-poly(ε-caprolactone) (PEG-b-PCL) nanoparticles were successfully prepared by a modified film hydration method and characterized by scanning electric microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM) and dynamic light scattering (DLS). Satisfactory drug loading of 20.73 ± 0.66% and a high encapsulation efficiency of 83.83 ± 1.32% were achieved. The SN-38 nanoparticles (SN-38 NPs) can completely disperse into a phosphate buffered saline (PBS) medium to produce a clear aqueous suspension that remains stable for up to three days. Total drug releases were 67.91% and 91.09% after 24 h in a PBS or fetal bovine serum (FBS) medium. Half maximal inhibitory concentration (IC(50)) tests of SN-38 and SN-38 NPs on A549 lung cells produced results of 200.0 ± 14.9 ng ml(-1) and 80.0 ± 4.6 ng ml(-1), respectively. Similarly, IC(50) tests of SN-38 and SN-38 NPs on MCF-7 breast cells yielded results of 16.0 ± 0.7 ng ml(-1) and 8.0 ± 0.5 ng ml(-1), respectively. These in vitro IC(50) studies show significant (p < 0.01) enhancement of the SN-38 NP drug efficiency in killing cancer cells in comparison to the free drug SN-38 control. All the materials used for this nanoformulation are approved by the US FDA, with the virtue of extremely low toxicity to normal cells.