Novel SN38 conjugate-forming nanoparticles as anticancer prodrug: In vitro and in vivo studies

SN-38-indoximod conjugate: carrier free nano-prodrug for cancer therapy

BACKGROUND

The integration of immunotherapy alongside chemotherapy represents a crucial approach in the treatment of cancer. Herein we report the SN-38-indoximod conjugate nano-prodrug to address the difficulties encountered by individuals. In this prodrug, SN-38 is connected to indoximod through a specific disulfide linker, which enables the release of the components in response to the tumor microenvironment characterized by elevated levels of glutathione, thereby facilitating programmed chemoimmunotherapy.

RESULTS

SN-38-indoximod conjugate was synthesized and fabricated to nano-prodrug by reprecipitation method. It showed comparable anti-cancer activity against A549 cells than SN-38 (IC50 = 0.24 ± 0.01 µM) with IC50 value 0.32 ± 0.04 µM. It inhibited 90% A549 cell at very lower concentration (IC90 = 6.07 ± 0.41 µM) as compared with SN-38 (IC90 = 24.60 ± 1.24 µM) and mixture of SN-38: indoximod (1:1, IC90 >30 µM). The nano-prodrug showed better size distribution profile and dispersion stability contains nanoparticles in effective size range (80-160 nm) required for the EPR effect.

CONCLUSION

This research offers valuable insights into the advancement of conjugate nano-prodrugs exhibiting synergistic pharmacological effects, while also presenting novel opportunities for the design of prodrug molecules capable of releasing drugs in response to diverse triggers.

Research Progress of SN38 Drug Delivery System in Cancer Treatment

The active metabolite of irinotecan (CPT-11), 7-ethyl-10-hydroxycamptothecin (SN38), is 100-1000 times more active than CPT-11 and has shown inhibitory effects on a range of cancer cells, including those from the rectal, small cell lung, breast, esophageal, uterine, and ovarian malignancies. Despite SN38's potent anticancer properties, its hydrophobicity and pH instability have caused substantial side effects and anticancer activity loss, which make it difficult to use in clinical settings. To solve the above problems, the construction of SN38-based drug delivery systems is one of the most feasible methods to improve drug solubility, enhance drug stability, increase drug targeting ability, improve drug bioavailability, enhance therapeutic efficacy and reduce adverse drug reactions. Therefore, based on the targeting mechanism of drug delivery systems, this paper reviews SN38 drug delivery systems, including polymeric micelles, liposomal nanoparticles, polymeric nanoparticles, protein nanoparticles, conjugated drug delivery systems targeted by aptamers and ligands, antibody-drug couplings, magnetic targeting, photosensitive targeting, redox-sensitive and multi-stimulus-responsive drug delivery systems, and co-loaded drug delivery systems. The focus of this review is on nanocarrier-based SN38 drug delivery systems. We hope to provide a reference for the clinical translation and application of novel SN38 medications.

A ROS-response hyaluronic acid-coated/chitosan polymer prodrug for enhanced tumor targeting efficacy of SN38

Ethyl-10-hydroxycamptothecin (SN38) is a camptothecin derivative with significant anti-tumor therapeutic potential, while the clinical application of SN38 was limited by its poor water solubility and low stability. Herein, a core-shell polymer prodrug hyaluronic acid @chitosan-S-SN38 (HA@CS-S-SN38) was designed by CS-S-SN38 as the core and the HA as the shell, which aims to overcome the limitations of the clinical application of SN38, while realizing the high tumor targeting of polymer prodrug and the controllable release of drug in tumor cells. HA@CS-S-SN38 showed the high responsiveness of the tumor microenvironment and the safe stability of blood circulation. Furthermore, HA@CS-S-SN38 exhibited the begin uptake efficiency and favorable apoptosis in the 4T1 cells. More importantly, compared with irinotecan hydrochloride trihydrate (CPT-11), HA@CS-S-SN38 significantly improved the conversion efficiency of the prodrug to SN38, and showed excellent tumor targeting and retention in vivo by combining passive and active targeting strategies. In tumor-bearing mice treatment, HA@CS-S-SN38 showed the perfect anti-tumor effect and therapeutic safety. These results indicated that the polymer prodrug designed by ROS-response/HA-modification strategy is a safe and efficient drug delivery system, which provides a new idea for clinical utilization of SN38 and warrants further evaluation.

Preparation and Cytotoxicity Evaluation of Folic Acid-Modified YF8-OA Self-Assembled Lipid Prodrug Nanoparticles

This study aimed to improve the use of YF8, a matrine derivative obtained through chemical transformation of matrine extracted from Sophora alopecuroides. YF8 has demonstrated improved cytotoxicity compared to matrine, but its hydrophobic nature hinders its application. To overcome this, the lipid prodrug YF8-OA was synthesized by linking oleic acid (OA) to YF8 through an ester bond. Although YF8-OA could self-assemble into unique nanostructures in water, it was not sufficiently stable. To enhance the stability of YF8-OA lipid prodrug nanoparticles (LPs), we employed the strategy of PEGylation using DSPE-mPEG₂₀₀₀ or DSPE-mPEG₂₀₀₀ conjugated with folic acid (FA). This resulted in the formation of uniform spherical nanoparticles with greatly improved stability and a maximum drug load capacity upto 58.63%. Cytotoxicity was evaluated in A549, HeLa, and HepG2 cell lines. The results showed that in HeLa cells, the IC₅₀ value of YF8-OA/LPs with FA-modified PEGylation was significantly lower than that of YF8-OA/LPs modified by PEGylation alone. However, no significant enhancement was observed in A549 and HepG2 cells. In conclusion, the lipid prodrug YF8-OA can form nanoparticles in aqueous solution to address its poor water solubility. Modification with FA resulted in further enhanced cytotoxicity, providing a potential avenue for exerting the antitumor activity of matrine analogs.

Recent advances in SN-38 drug delivery system

DNA topoisomerase I plays a key role in lubricatingthe wheels of DNA replication or RNA transcription through breaking and reconnecting DNA single-strand. It is widely known that camptothecin and its derivatives (CPTs) have inhibitory effects on topoisomerases I, and have obtained some clinical benefits in cancer treatment. The potent cytotoxicity makes 7-ethyl-10-hydroxycamptothecin (SN-38) become a brilliant star among these derivatives. However, some undesirable physical and chemical properties of this compound, including poor solubility and stability, seriously hinder its effective delivery to tumor sites. In recent years, strategies to alleviate these defects have aroused extensive research interest. By focusing on the loading mechanism, basic nanodrug delivery systems with SN-38 loaded, like nanoparticles, liposomes and micelles, are demonstrated here. Additionally, functionalized nanodrug delivery systems of SN-38 including prodrug and active targeted nanodrug delivery systems and delivery systems designed to overcome drug resistance are also reviewed. At last, challenges for future research in formulation development and clinical translation of SN-38 drug delivery system are discussed.

Gold nanorods-loaded chitosan-based nanomedicine platform enabling an effective tumor regression in vivo

The clinical utility of 7-ethyl-10-hydroxycamptothecin (SN-38) is hampered by its low water solubility and reduced bioactivity at neutral or alkaline conditions. The rational design of an effective drug delivery system that can significantly enhance the therapeutic index of SN-38 and achieve complete tumor regression still remains a challenge. Herein, chitosan-based hybrid nanoparticles system co-loading with chemotherapeutic drug SN-38 and gold nanorods (AuNRs) was engineered for effective combinational photothermal-chemotherapy. To increase the solubility of SN-38, soluble polymeric prodrug poly (l-glutamic acid)-SN38 (l-PGA-SN38) was firstly synthesized and then complexed with chitosan to form stable nanomedicine via a mild and facile way without using any organic solvent or surfactant. Upon introducing AuNRs into chitosan-based nanomedicine by coordination interaction between the amine group of chitosan and AuNRs, the hybrid nanoparticles exhibited distinct synergistic therapeutic effect compared with single chemotherapy or photothermal treatment in vitro and in vivo. Almost complete tumor regression was achieved after 21-day treatment of the developed hybrid nanoparticles and showed no recurrence for at least 60 days.

Improving cellular uptake and bioavailability of periplocymarin-linoleic acid prodrug by combining PEGylated liposome

Periplocymarin (PPM), a cardiac glycoside isolated from Cortex periplocae, has a strong anti-tumor effect against various cancer cells. However, cardiotoxicity and rapid metabolism hinder its clinical applications. In this study, small molecule prodrug was integrated into PEGylated liposome to improve the efficiency of periplocymarin in vivo. The periplocymarin-linoleic acid (PL) prodrug was constructed by conjugating the linoleic acid with PPM via esterification, which was further facilitated to form PEGylated liposome (PL-Lip) through film dispersion. Compared with PL self-assembling nano-prodrug (PL-SNP), PL-Lip showed better colloid stability, sustained drug release kinetics, and enhanced cellular uptake by tumor cells. Notably, PL-Lip performed better than PPM and PL-SNP in terms of tumor distribution and pharmacokinetics, which include bioavailability and half-life. Altogether, the prodrug PEGylated liposome represents a good strategy and method for long-circulating and tumor-targeting delivery of periplocymarin with enhanced clinical application prospect.

A nanotherapeutic strategy to overcome chemoresistance to irinotecan/7-ethyl-10-hydroxy-camptothecin in colorectal cancer

Clinical development of 7-ethyl-10‑hydroxy-camptothecin (SN38), the active metabolite of irinotecan (CPT-11), is hindered by its insolubility and poor stability. Another obstacle is that tumors could become resistant to SN38/CPT-11 through multiple mechanisms involving breast cancer resistance protein (BCRP). Herein one of the most potent and selective BCRP inhibitors, Ko143, is encapsulated into a recently constructed prodrug PEG-S-S-SN38 displaying a high and fixed drug loading, multiple intratumoral stimuli (oxidative stress, GSH and esterase)-responsive drug release and significant in vitro and in vivo superiorities over CPT-11. The obtained "combo" for simultaneous delivery of SN38 and Ko143, named as BI@PEG-SN38, has a high SN38 loading efficacy (14.85 wt.%) and a good Ko143 encapsulation efficacy (3.79%). Through generating panels of human colorectal cancer models expressing altered levels of BCRP via lentiviral transfection and CRISPR-Cas9, characteristics of different drug formulations are carefully evaluated. Impressively, BI@PEG-SN38 nanoparticles effectively reverse chemoresistance to CPT-11 (resistance index dropping from ∼274.00-456.00 to ∼1.70-4.68) and PEG-S-S-SN38 (resistance index dropping from ∼5.83-14.00 to ∼1.70-4.68) in three BCRP-overexpressing cancer cell lines. More importantly, reversal of BCRP-mediated chemoresistance to CPT-11 (P values lower than 0.001-0.0001) and PEG-S-S-SN38 (P values lower than 0.01-0.001) by BI@PEG-SN38 nanoparticles are further confirmed with two panels of colorectal cancer xenograft models in vivo. As the first nano-formulation of Ko143 and the first systemic co-delivery vehicle of SN38/CPT-11 and a BCRP inhibitor, BI@PEG-SN38 provides a new approach for resolving the bottlenecks for clinical translation of SN38 and numerous "chemosensitizers" like Ko143, and exhibits promising applicability in precision cancer medicine. STATEMENT OF SIGNIFICANCE: To resolve the bottlenecks in clinical application of anticancer agents SN38/CPT-11 and the most potent breast cancer resistant protein (BCRP) inhibitor Ko143, a "combo" nanotherapeutic simultaneously delivering SN38 and Ko143 was constructed and named as BI@PEG-SN38. By generating panels of colorectal cancer models, we demonstrate that BI@PEG-SN38 nanoparticles effectively and selectively reversed BCRP-mediated tumor resistance to SN38/CPT-11 in vitro and in vivo. As the first nano-formulation of Ko143 and the first systemic co-delivery vehicle of SN38/CPT-11 and a BCRP inhibitor, BI@PEG-SN38 provides a new strategy for clinical development of SN38 and numerous "chemosensitizers", and exhibits promising applicability in precision cancer medicine. Panels of cancer cell lines established here provides a useful platform for BCRP- and cancer-related research and technology development.

Towards principled design of cancer nanomedicine to accelerate clinical translation

Nanotechnology in medical applications, especially in oncology as drug delivery systems, has recently shown promising results. However, although these advances have been promising in the pre-clinical stages, the clinical translation of this technology is challenging. To create drug delivery systems with increased treatment efficacy for clinical translation, the physicochemical characteristics of nanoparticles such as size, shape, elasticity (flexibility/rigidity), surface chemistry, and surface charge can be specified to optimize efficiency for a given application. Consequently, interdisciplinary researchers have focused on producing biocompatible materials, production technologies, or new formulations for efficient loading, and high stability. The effects of design parameters can be studied in vitro, in vivo, or using computational models, with the goal of understanding how they affect nanoparticle biophysics and their interactions with cells. The present review summarizes the advances and technologies in the production and design of cancer nanomedicines to achieve clinical translation and commercialization. We also highlight existing challenges and opportunities in the field.

Nanomedicine from amphiphilizedprodrugs: Concept and clinical translation

Nanomedicines generally consisting of carrier materials with small fractions of active pharmaceutical ingredients (API) have long been used to improve the pharmacokinetics and biodistributions, augment the therapeutic efficacies and mitigate the side effects. Amphiphilizing hydrophobic/hydrophilic drugs to prodrugs capable of self-assembly into well-defined nanostructures has emerged as a facile approach to fabricating nanomedicines because this amphiphilized prodrug (APD) strategy presents many advantages, including minimized use of inert carrier materials, well-characterized prodrug structures, fixed and high drug loading contents, 100% loading efficiency, and burst-free but controlled drug release. This review comprehensively summarizes recent advances in APDs and their nanomedicines, from the rationale and the stimuli-responsive linker chemistry for on-demand drug release to their progress to the clinics, clinical performance of APDs, as well as the challenges and perspective on future development.

Small-Molecule Prodrug Nanoassemblies: An Emerging Nanoplatform for Anticancer Drug Delivery

The antitumor efficiency and clinical translation of traditional nanomedicines is mainly restricted by low drug loading, complex preparation technology, and potential toxicity caused by the overused carrier materials. In recent decades, small-molecule prodrug nanoassemblies (SMP-NAs), which are formed by the self-assembly of prodrugs themselves, have been widely investigated with distinct advantages of ultrahigh drug-loading and negligible excipients-trigged adverse reaction. Benefited from the simple preparation process, SMP-NAs are widely used for chemotherapy, phototherapy, immunotherapy, and tumor diagnosis. In addition, combination therapy based on the accurate co-delivery behavior of SMP-NAs can effectively address the challenges of tumor heterogeneity and multidrug resistance. Recent trends in SMP-NAs are outlined, and the corresponding self-assembly mechanisms are discussed in detail. Besides, the smart stimuli-responsive SMP-NAs and the combination therapy based on SMP-NAs are summarized, with special emphasis on the structure-function relationships. Finally, the outlooks and potential challenges of SMP-NAs in cancer therapy are highlighted.

A biocompatible superparamagnetic chitosan-based nanoplatform enabling targeted SN-38 delivery for colorectal cancer therapy

7-Ethyl-10-hydroxycamptothecin (SN-38) as a potent anti-tumor candidate, suffers the constraints from its poor water solubility, pH-dependent lactone ring stability and the lack of efficient delivery system without losing its activity. Herein, biocompatible superparamagnetic chitosan-based nanocomplexes complexing with water-soluble polymeric prodrug poly(L-glutamic acid)-SN-38 (PGA-SN-38) was engineered for efficient delivery of SN-38. The manufacturing process of colloidal complexes was green, expeditious and facile, with one-shot addition of PGA-SN-38 into chitosan solution without using any organic solvent or surfactant. Upon introducing ultra-small-size superparamagnetic nanoparticles (~10 nm), the developed magnetic nanocomplexes exhibited significantly boosted tumor-targeted accumulation and efficient cellular internalization under a local magnetic field. Notably, the magnetic nanocomplexes achieved distinctly superior targeting and anti-tumor efficacy in the established xenograft colorectal cancer model of mice, with high tumor suppression rate up to 81%. Therefore, this superparamagnetic chitosan-based nanocomplex system could provide a promising platform for the targeted delivery of SN-38 in colorectal cancer therapy.

Repurposing of camptothecin: An esterase-activatable prodrug delivered by a self-emulsifying formulation that improves efficacy in colorectal cancer

The global burden of colorectal cancer (CRC), the third most commonly diagnosed malignancy, continues to rise. Therefore, more effective and less toxic therapies are needed for CRC. CPT-11 (also called irinotecan), the standard-of-care treatment for CRC, has only had limited effects on survival outcomes. In vivo, CPT-11 must be converted to an active metabolite, SN38, to exert antitumor activity in the presence of carboxylesterases, but the conversion rate is extremely low (usually less than 8%). To fully harness the active SN38 compound, we showed here that esterification of SN38 using α-linolenic acid (LNA) generated a prodrug (termed LSN38), which can be formulated in pharmaceutically acceptable surfactants, such as polysorbate 80. Upon blending with an aqueous ethanolic solution, the mixture of LSN38/polysorbate 80 formed self-emulsifying nanomicelles (termed LSN38 NMs), enabling systemic injection. Unlike the insufficient release of active SN38 from CPT-11, drug activation from the LSN38 prodrug was quantitative and relied on esterase, which is abundant in cancerous cells. Pharmacokinetics studies revealed that polysorbate 80-based nanomicelles stably constrained the prodrug in the reservoir and prolonged blood circulation compared to CPT-11. Furthermore, LSN38 NMs showed superior therapeutic efficacy against a colorectal xenograft-bearing mouse model that failed to be treated with clinically approved CPT-11. Overall, these studies highlight the feasibility of converting a chemotherapeutic agent that is not miscible or compatible with pharmaceutical surfactants into an injectable self-emulsifying formulation. This approach could be applied to rescue other drugs or drug candidates that are abandoned in the preclinical stages due to pharmaceutical challenges.

Self-assembly delivery system based on small-molecule camptothecin prodrug for treatment of colorectal carcinoma

The aim of this study was to prepare small-molecule camptothecin (CPT) prodrugs and evaluate their effectiveness in colorectal carcinoma therapy. Prodrug nanoparticles (NPs) were physicochemically characterized and evaluated for their cytotoxicity in human colon cancer (HCT116) cell lines. The antitumor efficacy of the NPs was evaluated in HCT116 tumor-bearing mice. The prepared NPs exhibited high drug loading capacity (32% of CPT w/w) and also kept a high active lactone fraction of CPT (>85%) during circulation. The NPs were internalized into tumor cells efficiently compared with free drug and significantly enhanced the drug's therapeutic efficacy. The developed small-molecule CPT prodrug NPs could be a promising strategy in the clinical therapy of colorectal carcinoma.

Macrophages as a Double-Edged Weapon: The Use of Macrophages in Cancer Immunotherapy and Understanding the Cross-Talk Between Macrophages and Cancer

Macrophages (Mϕs) play an essential role in maintaining body homeostasis. They perform dual functions produced by different subtypes. Mϕs not only fight against pathogens and foreign bodies such as bacteria or cancer cells but also participate in healing and repairing damaged tissue since they maintain both proinflammatory and anti-inflammatory effects sequentially. Tumors possess the ability to polarize Mϕs from proinflammatory M1 subtype to anti-inflammatory M2-like Mϕs called tumor-associated macrophages, which, in turn, help the tumors to acquire cancer hallmarks. Consequently, this polarization allows tumors to grow and spread. In this light, Mϕs have been a subject of intense study, and researchers have developed protocols to derive different Mϕs subtypes either as a new state-of-the-art therapeutic approach or to understand the cross-talk between cancer and Mϕs. In this review, we present the use of primary Mϕs in adoptive immunotherapy for cancer, illustrate the reciprocating interplay between cancer and Mϕs, and the resulting structural and functional change on both cell types. Furthermore, we summarize the recent cutting-edge approaches of using Mϕs in cancer immunotherapy.

In situ activation of STING pathway with polymeric SN38 for cancer chemoimmunotherapy

STING (stimulator of interferon genes) signaling pathway has attracted considerable attention in cancer immunotherapy due to its capacity to boost vigorous antitumor immunity. However, the shortage of effective STING agonists limits the promotion of STING pathway in cancer treatment. Herein, we present an approach for in situ activation of STING pathway with nanoparticles delivered DNA-targeting chemo agents, based on the understanding that cytosol DNA is a pre-requisite for STING pathway activation. Through in vitro screening among several DNA-targeting chemo agents, we identified 7-ethyl-10-hydroxycamptothecin (SN38) as the most potent drug for stimulating interferon (IFN)-β secretion and proved that this process is mediated by the passage of DNA-containing exosomes from treated tumor cells to bone marrow-derived dendritic cells (BMDCs) and subsequent activation of the STING pathway. Furthermore, we designed a polymeric-SN38 conjugate that could self-assemble into nanoparticles (SN38-NPs) for in vivo application. The SN38-NPs formulation reduced toxicity of free SN38, effectively stimulated the activation of STING pathway in E0771 tumors, and resulted in a tumor suppression rate (TSR%) of 82.6%. Our results revealed a new mechanism of SN38 in cancer treatment and should inspire using more DNA-targeting agents, especially in nanoformulation, for activating STING pathway and cancer chemoimmunotherapy.

Polyphenol-cisplatin complexation forming core-shell nanoparticles with improved tumor accumulation and dual-responsive drug release for enhanced cancer chemotherapy

Cisplatin (CDDP) is a potent first-line antitumor drug but suffers severe side effects and poor pharmacokinetics. Its complexation with polycarboxylic acids, such as polyglutamic acids, is generally used to fabricate nanoformulations for CDDP delivery; however, the multiple strong complexations makes intracellular drug release slow. Herein, we report a novel polyphenol-metal coordination method to fabricate CDDP-incorporated core-shell nanoparticles, which are stable in blood circulation but dissociate in the tumor. Methoxyl-PEG terminated with one or two gallic acids (PEG-GA or PEG-GA2) complexed CDDP and produced well-defined nanoparticles (PEG-GAx/Pt) with CDDP loading contents as high as 17.7% to 29.8%. The PEG-GAx/Pt nanoparticles were very stable in the physiological conditions and had slow blood clearance and efficient tumor accumulation, but dissociated quickly and released CDDP in response to the tumor acidity or elevated levels of reactive oxygen species (ROS). PEG-GAx/Pt nanoparticles exhibited improved antitumor efficiency against 4 T1 breast cancer and A549 lung carcinoma with much-reduced toxicity compared to free CDDP. The work demonstrates a new strategy of cisplatin-polyphenol coordination for developing platinum drugs' nanomedicines.

A multifunctional SN38-conjugated nanosystem for defeating myelosuppression and diarrhea induced by irinotecan in esophageal cancer

A combination of chemotherapy and phototherapy has been proposed as a promising treatment for esophageal cancer (EC). Irinotecan as a first-line treatment option is widely prescribed for metastatic EC, however, its clinical application is extremely restricted by the low conversion rate to SN38, severe myelosuppression and diarrhea. As a more potent active metabolite of irinotecan, SN38 is a better substitution for irinotecan, but the poor water solubility and the difficulty of encapsulation hindered its medical application. Herein, a multifunctional SN38-conjugated nanosystem (FA-PDA@PZM/SN38@BSA-MnO2, denoted as FA-PPSM) is designed for overcoming the above-mentioned drawbacks and achieving collaborative chemotherapy, photodynamic therapy (PDT) and photothermal therapy (PTT). The tumor acidic microenvironment induces decomposition of BSA-MnO2 nanoparticles into O2 and Mn2+, thus enhancing oxygen-dependent PDT efficacy; meanwhile, Mn2+ can be employed as a magnetic resonance imaging (MRI) contrast agent. Under 650 and 808 nm laser irradiation, the FA-PPSM nanocomposites exhibit superior antitumor efficacy in Eca-109-tumor bearing mice. Notably, there is low gastrointestinal toxicity and myelosuppression in the FA-PPSM treated mice compared with those treated with irinotecan (alone). Taken together, this work highlights the great potential of the FA-PPSM nanocomposites for MRI-guided chemotherapy in combination with endoscopic light therapy for esophageal cancer.

Developments of Smart Drug-Delivery Systems Based on Magnetic Molecularly Imprinted Polymers for Targeted Cancer Therapy: A Short Review

Cancer therapy is still a huge challenge, as especially chemotherapy shows several drawbacks like low specificity to tumor cells, rapid elimination of drugs, high toxicity and lack of aqueous solubility. The combination of molecular imprinting technology with magnetic nanoparticles provides a new class of smart hybrids, i.e., magnetic molecularly imprinted polymers (MMIPs) to overcome limitations in current cancer therapy. The application of these complexes is gaining more interest in therapy, due to their favorable properties, namely, the ability to be guided and to generate slight hyperthermia with an appropriate external magnetic field, alongside the high selectivity and loading capacity of imprinted polymers toward a template molecule. In cancer therapy, using the MMIPs as smart-drug-delivery robots can be a promising alternative to conventional direct administered chemotherapy, aiming to enhance drug accumulation/penetration into the tumors while fewer side effects on the other organs. Overview: In this review, we state the necessity of further studies to translate the anticancer drug-delivery systems into clinical applications with high efficiency. This work relates to the latest state of MMIPs as smart-drug-delivery systems aiming to be used in chemotherapy. The application of computational modeling toward selecting the optimum imprinting interaction partners is stated. The preparation methods employed in these works are summarized and their attainment in drug-loading capacity, release behavior and cytotoxicity toward cancer cells in the manner of in vitro and in vivo studies are stated. As an essential issue toward the development of a body-friendly system, the biocompatibility and toxicity of the developed drug-delivery systems are discussed. We conclude with the promising perspectives in this emerging field. Areas covered: Last ten years of publications (till June 2020) in magnetic molecularly imprinted polymeric nanoparticles for application as smart-drug-delivery systems in chemotherapy.

Development of High-Drug-Loading Nanoparticles

Formulating drugs into nanoparticles offers many attractive advantages over free drugs including improved bioavailability, minimized toxic side effects, enhanced drug delivery, feasibility of incorporating other functions such as controlled release, imaging agents for imaging, targeting delivery, and loading more than one drug for combination therapies. One of the key parameters is drug loading, which is defined as the mass ratio of drug to drug-loaded nanoparticles. Currently, most nanoparticle systems have relatively low drug loading (<10 wt%), and developing methods to increase drug loading remains a challenge. This Minireview presents an overview of recent research on developing nanoparticles with high drug loading (>10 wt%) from the perspective of synthesis strategies, including post-loading, co-loading, and pre-loading. Based on these three different strategies, various nanoparticle systems with different materials and drugs are summarized and discussed in terms of their synthesis methods, drug loadings, encapsulation efficiencies, release profiles, stabilities, and their applications in drug delivery. The advantages and disadvantages of these strategies are presented with an objective of providing useful design rules for future development of high-drug-loading nanoparticles.

Supramolecular self-assembled drug delivery system (SADDs) of vancomycin and tocopherol succinate as an antibacterial agent: in vitro, in silico and in vivo evaluations

In this study self-assembled drug delivery system (SADDs) composed of a hydrophobic d-α-tocopherol succinate (TS) and a hydrophilic vancomycin (VCM) were formulated, and its potential for enhancing the antibacterial activity of VCM against Staphylococcus aureus (SA) and Methicillin-resistant Staphylococcus aureus (MRSA) were explored. The SADDs were synthesized via supramolecular complexation, then characterized for in silico, in vitro and in vivo studies. In silico studies confirmed the self-assembly of VCM/TS into NPs. The size, surface charge and drug loading of the SADDs was ˂100 nm, -27 mV and 68%, respectively. The SADDs were non-hemolytic and biosafe. A sustained release of VCM from SADDs was noted, with 52.2% release after 48 hr. The in vitro antibacterial test showed a twofold decrease in Minimum inhibitory concentration (MIC) against SA and MRSA, and a significantly higher reduction in MRSA biofilms compared to bare VCM. Further, in silico studies confirmed strong and stable binding of TS to MRSA efflux pumps. The in vivo study using mice skin infection models showed a 9.5-fold reduction in bacterial load after treatment with SADDs, in comparison with bare VCM. These findings affirmed that VCM/TS NPs as a promising novel nano-delivery for treating bacterial infections.

Development of (G3-C12)-mediated camptothecin polymeric prodrug targeting to Galectin-3 receptor against androgen-independent prostate cancer

The development of small molecule anticancer drugs, with low water solubility and high toxicity, into polymeric prodrugs has developed into a promising strategy in clinical application. In this study, we synthesized a novel G3-C12-mediated esterase-sensitive tumor-targeting polymeric prodrug of camptothecin (CPT), P(OEGMA-co-CPT-co-G3-C12), and explored its anticancer activity against androgen-independent prostate cancer in vitro and in vivo. Compared to free CPT, the multifunctional polymeric prodrug demonstrated improved water solubility and stability, higher intracellular uptake, and enhanced cytotoxicity in DU145 cells in vitro. Furthermore, it displayed an improved accumulation in the tumor and an enhanced anticancer activity in vivo. Hence, P(OEGMA-co-CPT-co-G3-C12) could be a promising drug in the treatment of androgen-independent prostate cancer.

Synergistic action of doxorubicin and 7-Ethyl-10-hydroxycamptothecin polyphosphorylcholine polymer prodrug

There are opportunities for improvements to the efficiency and toxicity of widely used cancer chemotherapy agents such as doxorubicin (DOX·HCl) and 7-Ethyl-10-hydroxycamptothecin (SN38). We developed a safe and effective combination therapy by encapsulating DOX into micelles of a zwitterionic polymer prodrug, SN38 conjugate of poly (α-azide caprolactone-co-caprolactone)-b-poly (2-methacryloyloxyethyl phosphorylcholine [P(CL/CL-g-SN38)-b-PMPC)] which was described in our previous work. The polymer prodrug micelles displayed a higher loading capacity of DOX due to the π-π stacking effect between DOX and SN38 in comparison with the micelles self-assembled by prodrug's precursor, poly(α-azide caprolactone-co-caprolactone)-b-poly(2-methacryloyloxyethyl phosphorylcholine (P(ACL/CL)-b-PMPC). The DOX loaded prodrug micelles decelerated the release of DOX, and also prolonged its circulation. The micelles showed favorable cellular internalization by 4T1 cells. DOX loaded SN38 prodrug micelles displayed good in vitro anticancer effects owing to the synergistic action of doxorubicin and SN38 and were as effective as DOX·HCl, but with lower toxicity than DOX·HCl. Given the synergetic effects of free drug and polymer prodrug, this nanomedicine may offer a safe and effective drug delivery methodology for conventional drug formations.

Novel lipophilic SN38 prodrug forming stable liposomes for colorectal carcinoma therapy

Background: SN38 (7-ethyl-10-hydroxy camptothecin), as a potent metabolite of irinotecan, is highly efficacious in cancer treatment. However, the clinical utility of SN38 has been greatly limited due to its undesirable properties, such as poor solubility and low stability.

Materials and methods: In order to overcome these weaknesses, moeixitecan, a lipophilic SN38 prodrug containing a SN-38, a trolox, a succinic acid linker, and a hexadecanol chain, was loaded into liposomal nanoparticles by ethanol injection method.

Results: Experiments showed that the moeixitecan-loaded liposomal nanoparticles (MLP) with a diameter of 105.10±1.49 nm have a satisfactory drug loading rate (90.54±0.41%), high solubility and stability, and showed sustained release of SN38. Notably, MLP exhibited better antitumor activity against human colon adenocarcinoma cells than irinotecan, a FDA-approved drug for the treatment of advanced colorectal cancer. Furthermore, xenograft model results showed that MLP outperformed irinotecan in terms of pharmacokinetics, in vivo therapeutic efficacy and safety. Finally, we used molecular dynamic simulations to explore the association between the structure of MLP and the physical and functional properties of MLP, moeixitecan molecules in MLP folded themselves inside the hydrocarbon chain of the lipid bilayer, which led an increased acyl chain order of the lipid bilayer, and therefore enhanced the lactone ring stability protecting it from hydrolysis.

Conclusion: Our MLP constructing strategy by liposome engineering technology may serve a promising universal approach for the effective and safe delivery of lipophilic prodrug.

Hydrophobized SN38 to redox-hypersensitive nanorods for cancer therapy

Redox-hypersensitive hydrophobized SN38 self-assembled into rod-shaped nanoaggregates with uncompromised in vitro cytotoxicity and potent in vivo antitumor effects.

Novel SN38 derivative-based liposome as anticancer prodrug: an in vitro and in vivo study

Background

Many novel drug delivery systems have been extensively studied to exploit the full therapeutic potential of SN38, which is one of the most potent antitumor analogs of camptothecins (CPTs), whose clinical application is seriously hindered by poor water solubility, low plasmatic stability, and severe toxicity, but results are always unsatisfactory.

Methods

In this study, combining the advantages of prodrug and nanotechnology, a lipophilic prodrug of SN38, SN38-PA, was developed by conjugating palmitic acid to SN38 via ester bond at C₁₀ position, and then the lipophilic prodrug was encapsulated into a long-circulating liposomal carrier by film dispersion method.

Results

The SN38-PA liposomes were characterized as follows: an average particle size of 80.13 nm, an average zeta potential of -33.53 mv, and the entrapment efficiency of 99%. Compared with CPT-11, SN38-PA liposome was more stable in close lactone form, more efficient in conversion rate to SN38, and more potent in cytotoxicity against tumor cells. Pharmacokinetic study showed that SN38-PA liposome had significantly enhanced plasma half-life (t_1/2) value of SN38 and increased area under the curve (AUC) of SN38, which was 7.5-fold higher than that of CPT-11. Biodistribution study showed that SN38-PA liposome had more active metabolite SN38 in each tissue. Finally, the pharmacodynamic study showed that SN38-PA liposome had higher antitumor effect with the antitumor inhibition rate of 1.61 times than that of CPT-11.

Conclusion

These encouraging data merit further investigation on this novel SN38-PA liposome.

Multifunctional Cargo-Free Nanomedicine for Cancer Therapy

Nanocarriers encapsulating multiple chemotherapeutics are a promising strategy to achieve combinational chemotherapy for cancer therapy; however, they generally use exotic new carriers without therapeutic effect, which usually suffer from carrier-related toxicity issues, as well as having to pass extensive clinical trials to be drug excipients before any clinical applications. Cargo-free nanomedicines, which are fabricated by drugs themselves without new excipients and possess nanoscale characteristics to realize favorable pharmacokinetics and intracellular delivery, have been rapidly developed and drawn much attention to cancer treatment. Herein, we discuss recent advances of cargo-free nanomedicines for cancer treatment. After a brief introduction to the major types of carrier-free nanomedicine, some representative applications of these cargo-free nanomedicines are discussed, including combination therapy, immunotherapy, as well as self-monitoring of drug release. More importantly, this review draws a brief conclusion and discusses the future challenges of cargo-free nanomedicines from our perspective.

Cargo-Free Nanomedicine with pH Sensitivity for Codelivery of DOX Conjugated Prodrug with SN38 To Synergistically Eradicate Breast Cancer Stem Cells

As a result of their ability to transform into bulk cancer cells and their resistance to radiotherapy and chemotherapy, cancer stem cells (CSCs) are currently considered as a major obstacle for cancer treatment. Application of multiple drugs using nanocarriers is a promising approach to simultaneously eliminate noncancer stem cells (non-CSCs) and CSCs. Herein, to employ the advantages of nanomedicine while avoiding new excipients, pH-responsive prodrug (PEG-CH═N-DOX) was employed as the surfactant to fabricate cargo-free nanomedicine for codelivery of DOX conjugated prodrug with SN38 to synergistically eradicate breast cancer stem cells (bCSCs) and non-bCSCs. Through the intermolecular interaction between DOX and SN38, PEG-CH═N-DOX and SN38 were assembled together to form a stable nanomedicine. This nanomedicine not only dramatically enhanced drug accumulation efficiency at the tumor site but also effectively eliminated bCSCs and non-bCSCs, which resulted in achieving a superior in vivo tumor inhibition activity. Additionally, the biosafety of this nanomedicine was systematically studied through immunohistochemistry, blood biochemistry assay, blood routine examination, and metabolomics. The results revealed that this nanomedicine significantly reduced the adverse effects of DOX and SN38. Therefore, this simple yet efficient nanomedicine provided a promising strategy for future clinical applications.

Functionalized Nanoparticles Efficiently Enhancing the Targeted Delivery, Tumor Penetration, and Anticancer Activity of 7-Ethyl-10-Hydroxycamptothecin

The enhanced permeability and retention (EPR) effect of tumors is much more complex than initially defined, and it alone is not sufficient for targeted delivery of nanosized agents. Meanwhile, poor tumor penetration is another major challenge for the treatment of solid tumors using nanoparticles. Development of delivery systems for SN38, the active metabolite of CPT-11 in human and a very potent anticancer molecule, has become an attractive research area. PEG_x -p(HEMASN38)_y (x and y are viable), a prodrug synthesized by using polyethylene glycol (PEG) as initiator and SN38 as monomer through atom transfer radical polymeration (ATRP) method, is previously reported. Using PEG_2.4K -p(HEMASN38)_3K as a model prodrug, herein an active-targeted strategy decorated with cys-arg-gly-asp-lys (CRGDK), a peptide specifically binds to neuropilin-1 overexpressed by tumor vessels and tumor cells, is successfully established to further improve the delivery and efficacy of SN38. CRGDK-functionalized PEG_2.4K -p(HEMASN38)_3K (C-SN38) nanoparticles and nonfunctionalized control (B-SN38) are prepared with two distinct sizes, 30 and 100 nm. Their physiochemical and biological characteristics are investigated in vitro and in vivo with multiple tumor models. It is demonstrated for the first time that CRGDK functionalization can be a promising strategy for efficient delivery of SN38, and C-SN38 is a potent drug candidate for the treatment of neuropilin-1 overexpressing tumors.

CD133-targeted delivery of self-assembled PEGylated carboxymethylcellulose-SN38 nanoparticles to colorectal cancer

Poor aqueous solubility of chemotherapeutics such as SN38 (7-ethyl-10-hydroxycamptothecin) and the associated systemic adverse effects are serious limitations of their clinical use. To improve the drug delivery efficiency of such compounds, they were covalently conjugated to hydrophilic macromolecular carriers that specifically deliver the drug moiety to the tumour cells. In the current study, we developed a PEGylated acetylated carboxymethylcellulose conjugate of SN38 which was covalently attached to an aptamer against a cancer stem cell marker, CD133. Then, the designed nanoplatform was used to specifically deliver SN38 to colorectal cancer cells. The results demonstrated that the synthesized conjugate was self-assembled to nanoparticles with 169 nm in size and poly dispersity index of 0.11. Besides, the targeted self-assembled nanoparticles could significantly enhance the cellular uptake by CD133-expressing HT29 cell line confirmed by fluorescent microscopy and flow cytometry. Moreover, our results revealed that the targeted self-assembled nanoconjugate exhibited significantly lower IC₅₀ in HT29 cells overexpressing CD133 compared to non-targeted self-assembled nanoconjugate. The promising data suggest that the prepared targeted self-assembled drug conjugate nanoparticles possess the potential to offer the desirable physicochemical properties thereby enhancing the solubility and the therapeutic index of poorly soluble cytotoxic agents.

STA-8666, a novel HSP90 inhibitor/SN-38 drug conjugate, causes complete tumor regression in preclinical mouse models of pediatric sarcoma

Long-term survival in patients with metastatic, relapsed, or recurrent Ewing sarcoma and rhabdomyosarcoma is dismal. Irinotecan, a topoisomerase 1 inhibitor, has activity in these sarcomas, but due to poor bioavailability of its active metabolite (SN-38) has had limited clinical efficacy. In this study we have evaluated the efficacy and toxicity of STA-8666, a novel drug conjugate which uses an HSP90 inhibitor to facilitate intracellular, tumor-targeted delivery of the topoisomerase 1 inhibitor SN-38, thus preferentially delivering and concentrating SN-38 within tumor tissue. We present in vivo evidence from mouse xenograft models that STA-8666 results in more persistent inhibition of topoisomerase 1 and prolonged DNA damage compared to irinotecan. This translates into superior antitumor efficacy and survival in multiple aggressive models of both diseases in mouse xenografts, as well as in an irinotecan-resistant model of pediatric osteosarcoma, demonstrated by dramatic tumor shrinkage, durable remission and prolonged complete regressions following short-term treatment, compared to conventional irinotecan. Gene expression analysis performed on xenograft tumors treated with either irinotecan or STA-8666 showed that STA-8666 affected expression of DNA damage and repair genes more robustly than irinotecan. These results suggest that STA-8666 may be a promising new agent for patients with pediatric-type sarcoma.

SN-38 Conjugated Gold Nanoparticles Activated by Ewing Sarcoma Specific mRNAs Exhibit In Vitro and In Vivo Efficacy

The limited delivery of chemotherapy agents to cancer cells and the nonspecific action of these agents are significant challenges in oncology. We have previously developed a customizable drug delivery and activation system in which a nucleic acid functionalized gold nanoparticle (Au-NP) delivers a drug that is selectively activated within a cancer cell by the presence of an mRNA unique to the cancer cell. The amount of drug released from sequestration to the Au-NP is determined by both the presence and the abundance of the cancer cell specific mRNA in a cell. We have now developed this technology for the potent, but difficult to deliver, topoisomerase I inhibitor SN-38. Herein, we demonstrate both the efficient delivery and selective release of SN-38 from gold nanoparticles in Ewing sarcoma cells with resulting efficacy in vitro and in vivo. These results provide further preclinical validation for this novel cancer therapy and may be extendable to other cancers that exhibit sensitivity to topoisomerase I inhibitors.

Macrophages as an active tumour-targeting carrier of SN38-nanoparticles for cancer therapy

Taking advantage of their enhanced permeability and retention (EPR) effect, nanomedicines have been extensively studied for targeted drug delivery to tumour tissues. However, tumour heterogeneity restricts the EPR effect and drug penetration into tumours, and nanoformulations only generate a limited therapeutic improvement in clinical settings. Macrophages have the inherent ability of tumour homing, stealth in blood circulation, and phagocytosis of particles. In this study, we used peritoneal macrophages as carriers for the delivery of SN38 nanoparticles (SN38-NPs) for cancer treatment. SN38-NPs were internalised by macrophages without any obvious effect on viability and migration, and not only induced apoptosis of tumour cells in vitro, but also accumulated in tumour tissues in vivo. In addition, the macrophage-based delivery system for SN38-NPs showed improved therapeutic effect than an equivalent dose of CPT-11 in an A549 subcutaneous tumour model.

Construction of a Supramolecular Drug-Drug Delivery System for Non-Small-Cell Lung Cancer Therapy

Nanoscale drug delivery systems (DDSs) are generally considered to be an effective alternative to small molecular chemotherapeutics due to improved accumulation in the tumor site and enhanced retention in blood. Nevertheless, most DDSs have low loading efficiency or even pose a high threat to normal organs from severe side effects. Ideally, a supramolecular drug-drug delivery system (SDDDS) composed of pure drugs via supramolecular interaction provides a hopeful approach for cancer treatment. Herein we propose a facile method to construct SDDDS via coassembly of gefitinib (GEF) and tripeptide tyroservatide (YSV), two kinds of chemotherapeutic pharmaceuticals for non-small-cell lung cancer (NSCLC) via multiple intermolecular interactions, including hydrogen bonding and π-π stacking. As shown through transmission electron microscopy (TEM) and dynamic light scattering (DLS), GEF and YSV self-assemble into nanoparticles with regular morphology and uniform size, which facilitates the delivery of both drugs. In vitro studies demonstrate that the SDDDS is much more efficient in entering cancer cells and inhibiting the proliferation of cancer cells compared with single GEF, YSV, or GEF/YSV drug mixture. In vivo experiments show that the SDDDS can selectively accumulate in tumor tissue, resulting in much better drug efficacy without evident side effects. Considering the advantages of the SDDDS, we believe this strategy provides a promising route for enhanced anticancer therapy in nanomedicine.

Cancer Nanomedicines Stabilized by π-π Stacking between Heterodimeric Prodrugs Enable Exceptionally High Drug Loading Capacity and Safer Delivery of Drug Combinations

Combination therapy using distinct mode-of-action drugs has sparked a rapidly growing interest because this paradigm holds promise for improving the therapeutic efficacy of anticancer therapy. However, the current drug combination therapy refers to administering individual drugs together, which is far from a perfect regimen for cancer patients. The aim of this work was to demonstrate that synergistic delivery of two chemotherapeutic drugs in a single nanoparticle reservoir could be achieved through the rational chemical ligation of the drugs followed by supramolecular nano-assembly via blending of the drugs with a minimal amount of matrix. Choosing 7-ethyl-10-hydroxycamptothecin and taxanes, which are rich in aromatic structures, as model compounds, we show that the heterodimeric conjugates of the two agents are miscible with lipids to form systemically injectable nanomedicines. The compatibility between the prodrug conjugates and lipid carriers is substantially augmented by the intermolecular π-π stacking and alleviated polarity, thus enabling an exceptionally high drug loading (DL) capacity (~92%) and a gratifyingly long drug retention time within the micellar core. We further observed superior therapeutic outcomes in a mouse tumor model without detecting accompanying systemic toxicity. This structure-based, self-assembled cancer nanomedicine increased the potency and drug tolerability in animals and thus offers a robust strategy for simultaneously formulating two or more drugs in single nanovehicles.