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

Membrane-Fusing Vehicles for Re-Sensitizing Transporter-Mediated Multiple-Drug Resistance in Cancer

Reversing the multiple drug resistance (MDR) arising from the overexpression of the efflux transporters often fails mainly due to the high toxicity or the poor water solubility of the inhibitors of these transporters. Here, we demonstrate the delivery of an inhibitor targeting three ABC transporters (ABCB1, ABCC1 and ABCG2) directly to the cell membrane using membrane-fusing vehicles (MFVs). Three different transfected MDCK II cell lines, along with parental cells, were used to investigate the inhibitory effect of cyclosporine A (CsA) in solution versus direct delivery to the cell membrane. CsA-loaded MFVs successfully reversed MDR for all three investigated efflux transporters at significantly lower concentrations compared with CsA in solution. Results showed a 15-fold decrease in the IC50 value for ABCB1, a 7-fold decrease for ABCC1 and an 11-fold decrease for ABCG2. We observed binding site specificity for ABCB1 and ABCG2 transporters. Lower concentrations of empty MFVs along with CsA contribute to the inhibition of Hoechst 33342 efflux. However, higher concentrations of CsA along with the high amount of MFVs activated transport via the H-binding site. This supports the conclusion that MFVs can be useful beyond their role as delivery systems and also help to elucidate differences between these transporters and their binding sites.

Hindering the unlimited proliferation of tumor cells synergizes with destroying tumor blood vessels for effective cancer treatment

The rational combination of chemotherapy drugs can improve the curative effect of cancer treatment. As two early recognized tumor hallmarks, the limitless replicative potential of tumor cells is essential for the development of their malignant growth state, and sustained angiogenesis is a prerequisite to the rapid growth of tumors. Based on this, we propose a combination therapy that hinders the unlimited proliferation of tumor cells and destroys tumor blood vessels. Herein, 7-ethyl-10-hydroxycamptothecin (SN38), a typical topoisomerase I inhibitor, was bonded to poly(L-glutamic acid) (PLG) to prepare the nanodrug SN38-NPs, which hinders the unlimited proliferation of tumor cells. A poly(L-glutamic acid)-combretastatin A4 conjugate (CA4-NPs), a representative vascular disrupting agent (VDA), was used to selectively disrupt the tumor blood vessels, cutting off the necessary nutrients and oxygen for the proliferation of tumor cells. In the 4T1 tumor model with an initial volume of about 400 mm3, the combined treatment of SN38-NPs and CA4-NPs showed an excellent cancer treatment effect with a tumor suppression rate of 94.3% and a synergistic interaction (Q = 1.25). Our study provides a new combination therapy approach for chemotherapy, with the hope of further improving the curative effect of anti-cancer therapy.

Development of a Targeted SN-38-Conjugate for the Treatment of Glioblastoma

Glioblastoma (GBM) is the most aggressive and fatal brain tumor, with approximately 10,000 people diagnosed every year in the United States alone. The typical survival period for individuals with glioblastoma ranges from 12 to 18 months, with significant recurrence rates. Common therapeutic modalities for brain tumors are chemotherapy and radiotherapy. The main challenges with chemotherapy for the treatment of glioblastoma are high toxicity, poor selectivity, and limited accumulation of therapeutic anticancer agents in brain tumors as a result of the presence of the blood-brain barrier. To overcome these challenges, researchers have explored strategies involving the combination of targeting peptides possessing a specific affinity for overexpressed cell-surface receptors with conventional chemotherapy agents via the prodrug approach. This approach results in the creation of peptide drug conjugates (PDCs), which facilitate traversal across the blood-brain barrier (BBB), enable preferential accumulation of chemotherapy within the neoplastic microenvironment, and selectively target cancerous cells. This approach increases accumulation in tumors, thereby improving therapeutic efficiency and minimizing toxicity. Leveraging the affinity of the HAIYPRH (T7) peptide for the transferrin receptor (TfR) overexpressed on the blood-brain barrier and glioma cells, a novel T7-SN-38 peptide drug conjugate was developed. The T7-SN-38 peptide drug conjugate demonstrates about a 2-fold reduction in glide score (binding affinity) compared to T7 while maintaining a comparable orientation within the TfR target site using Schrödinger-2022-3 Maestro 13.3 for ligand preparation and Glide SP-Peptide docking. Additionally, SN-38 extends into a solvent-accessible region, enhancing its susceptibility to protease hydrolysis at the cathepsin B (Cat B) cleavable site. The SN-38-ether-peptide drug conjugate displayed high stability in buffer at physiological pH, and cleavage of the conjugate to release free cytotoxic SN-38 was observed in the presence of exogenous cathepsin B. The synthesized peptide drug conjugate exhibited potent cytotoxic activities in cellular models of glioblastoma in vitro. In addition, blocking transferrin receptors using the free T7 peptide resulted in a notable inhibition of cytotoxicity of the conjugate, which was reversed when exogenous cathepsin B was added to cells. This work demonstrates the potential for targeted drug delivery to the brain in the treatment of glioblastoma using the transferrin receptor-targeted T7-SN-38 conjugate.

A Guanosine-Derived Antitumor Supramolecular Prodrug

The prodrug strategy for its potential to enhance the pharmacokinetic and/or pharmacodynamic properties of drugs, especially chemotherapeutic agents, has been widely recognized as an important means to improve therapeutic efficiency. Irinotecan's active metabolite, 7-ethyl-10-hydroxycamptothecin (SN38), a borate derivative, was incorporated into a G-quadruplex hydrogel (GB-SN38) by the ingenious and simple approach. Drug release does not depend on carboxylesterase, thus bypassing the side effects caused by ineffective activation, but specifically responds to the ROS-overexpressed tumor microenvironment by oxidative hydrolysis of borate ester that reduces serious systemic toxicity from nonspecific biodistribution of SN38. Comprehensive spectroscopy was used to define the structural and physicochemical characteristics of the drug-loaded hydrogel. The GB-SN38 hydrogel's high level of biosafety and notable tumor-suppressive properties were proven in in vitro and in vivo tests.

Camptothecin-based prodrug nanomedicines for cancer therapy

Camptothecin (CPT) is a cytotoxic alkaloid that attenuates the replication of cancer cells via blocking DNA topoisomerase 1. Despite its encouraging and wide-spectrum antitumour activity, its application is significantly restricted owing to its instability, low solubility, significant toxicity, and acquired tumour cell resistance. This has resulted in the development of many CPT-based therapeutic agents, especially CPT-based nanomedicines, with improved pharmacokinetic and pharmacodynamic profiles. Specifically, smart CPT-based prodrug nanomedicines with stimuli-responsive release capacity have been extensively explored owing to the advantages such as high drug loading, improved stability, and decreased potential toxicity caused by the carrier materials in comparison with normal nanodrugs and traditional delivery systems. In this review, the potential strategies and applications of CPT-based nanoprodrugs for enhanced CPT delivery toward cancer cells are summarized. We appraise in detail the chemical structures and release mechanisms of these nanoprodrugs and guide materials chemists to develop more powerful nanomedicines that have real clinical therapeutic capacities.

Progress in the treatment of drug-loaded nanomaterials in renal cell carcinoma

Renal cell carcinoma (RCC) is a common urinary tract tumor that arises from the highly heterogeneous epithelium of the renal tubules. The incidence of kidney cancer is second only to the incidence of bladder cancer, and has shown an upward trend over time. Although surgery is the preferred treatment for localized RCC, treatment decisions should be customized to individual patients considering their overall health status and the risk of developing or worsening chronic kidney disease postoperatively. Anticancer drugs are preferred to prevent perioperative and long-term postoperative complications; however, resistance to chemotherapy remains a considerable problem during the treatment process. To overcome this challenge, nanocarriers have emerged as a promising strategy for targeted drug delivery for cancer treatment. Nanocarriers can transport anticancer agents, achieving several-fold higher cytotoxic concentrations in tumors and minimizing toxicity to the remaining parts of the body. This article reviews the use of nanomaterials, such as liposomes, polymeric nanoparticles, nanocomposites, carbon nanomaterials, nanobubbles, nanomicelles, and mesoporous silica nanoparticles, for RCC treatment, and discusses their advantages and disadvantages.

Full-profile pharmacokinetics, anticancer activity and toxicity of an extended release trivalent PEGylated irinotecan prodrug

Irinotecan is an anticancer topoisomerase I inhibitor that acts as a prodrug of the active metabolite, SN-38. Unfortunately, the limited utility of irinotecan is attributed to its pH-dependent stability, short half-life and dose-limiting toxicity. To address this problem, a novel trivalent PEGylated prodrug (PEG-[Irinotecan]3) has been synthesized and its full-profile pharmacokinetics, antitumor activity and toxicity compared with those of irinotecan. The results show that after intravenous administration to rats, PEG-[Irinotecan]3 undergoes stepwise loss of irinotecan to form PEG-[Irinotecan]3‒x (x = 1,2) and PEG-[linker] during which time the released irinotecan undergoes conversion to SN-38. As compared with conventional irinotecan, PEG-[Irinotecan]3 displays extended release of irinotecan and efficient formation of SN-38 with significantly improved AUC and half-life. In a colorectal cancer-bearing model in nude mice, the tumor concentrations of irinotecan and SN-38 produced by PEG-[Irinotecan]3 were respectively 86.2 and 2293 times higher at 48 h than produced by irinotecan. In summary, PEG-[Irinotecan]3 displays superior pharmacokinetic characteristics and antitumor activity with lower toxicity than irinotecan. This supports the view that PEG-[Irinotecan]3 is a superior anticancer drug to irinotecan and it has entered the phase II trial stage.

Synthesis and Antitumor Evaluation of Biotin-SN38-Valproic Acid Conjugates

Despite the strong anticancer activity of SN38 (7-ethyl-10-hydroxy-camptothecin), the severe side effects and loss of anticancer activity caused by the lack of selectivity to cancer cells and hydrolysis of ring E prevent its clinical application. To address the issue, herein a multifunctional SN38 derivative (compound 9) containing biotin (tumor-targeting group) and valproic acid (histone deacetylase inhibitor, HDACi) was synthesized via click chemistry and evaluated using MTT assay. The in vitro cytotoxicity study showed that compound 9 exhibited superior cytotoxicity than irinotecan against human cervical cancer HeLa cells, albeit it was inferior to SN38. More significantly, compound 9 significantly reduced toxicity in mouse embryonic fibroblast NIH3T3 cells, indicating that compound 9 had the capacity to enhance tumor targeting due to its cell selectivity. Further studies demonstrated that, compared with irinotecan, compound 9 induced similar apoptosis of cancer cells. Consequently, compound 9 can not only improve its tumor-targeting ability mediated by biotin but also exert potent anticancer activity through the effect of SN38 and valproic acid, indicating that the design concept is an effective strategy for the structural modification of SN38.

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.

Critical roles of linker length in determining the chemical and self-assembly stability of SN38 homodimeric nanoprodrugs

Homodimeric prodrug nanoassemblies (HDPNs) have been widely studied for efficient cancer therapy by virtue of their ultra-high drug loading and distinct nanostructure. However, the development of SN38 HDPNs is still a great challenge due to the rigid planar aromatic ring structure. Improving the structural flexibility of homodimeric prodrugs by increasing the linker length may be a potential strategy for constructing SN38 HDPNs. Herein, three SN38 homodimeric prodrugs with different linker lengths were synthesized. The number of carbon atoms from the disulfide bond to the adjacent ester bond is 1 (denoted as α-SN38-SS-SN38), 2 (β-SN38-SS-SN38), and 3 (γ-SN38-SS-SN38), respectively. Interestingly, we found that α-SN38-SS-SN38 exhibited extremely low yield and poor chemical stability. Additionally, β-SN38-SS-SN38 demonstrated suitable chemical stability but poor self-assembly stability. In comparison, γ-SN38-SS-SN38 possessed good chemical and self-assembly stability, thereby improving the tumor accumulation and antitumor efficacy of SN38. We developed the SN38 HDPNs for the first time and illustrated the underlying molecular mechanism of increasing the linker length to enhance the chemical and self-assembly stability of homodimeric prodrugs. These findings would provide new insights for the rational design of HDPNs with superior performance.

Disulfide Bond-Based SN38 Prodrug Nanoassemblies with High Drug Loading and Reduction-Triggered Drug Release for Pancreatic Cancer Therapy

Purpose

Chemotherapy is a significant and effective therapeutic strategy that is frequently utilized in the treatment of cancer. Small molecular prodrug-based nanoassemblies (SMPDNAs) combine the benefits of both prodrugs and nanomedicine into a single nanoassembly with high drug loading, increased stability, and improved biocompatibility.

Methods

In this study, a disulfide bond inserted 7-ethyl-10-hydroxycamptothecin (SN38) prodrug was rationally designed and then used to prepare nanoassemblies (SNSS NAs) that were selectively activated by rich glutathione (GSH) in the tumor site. The characterization of SNSS NAs and the in vitro and in vivo evaluation of their antitumor effect on a pancreatic cancer model were performed.

Results

In vitro findings demonstrated that SNSS NAs exhibited GSH-induced SN38 release and cytotoxicity. SNSS NAs have demonstrated a passive targeting effect on tumor tissues, a superior antitumor effect compared to irinotecan (CPT-11), and satisfactory biocompatibility with double dosage treatment.

Conclusion

The SNSS NAs developed in this study provide a new method for the preparation of SN38-based nano-delivery systems with improved antitumor effect and biosafety.

A carboxylesterase-activatable near-infrared phototheranostic probe for tumor fluorescence imaging and photodynamic therapy

Phototheranostic probes have been proven to be a promising option for cancer diagnosis and treatment. However, near-infrared phototheranostic probes with specific tumor microenvironment responsiveness are still in demand. In this paper, a carboxylesterase (CES)-responsive near-infrared phototheranostic probe was developed by incorporating 6-acetamidohexanoic acid into a hemicyanine dye through an ester bond. The probe exhibits highly sensitive and selective fluorescence enhancement towards CES because CES-catalyzed cleavage of the ester bond leads to the release of the fluorophore. By virtue of its near-infrared analytical wavelengths and high sensitivity, the probe has been employed for endogenous CES activatable fluorescence imaging of tumor cells. Moreover, under 660 nm laser irradiation, the probe can generate toxic reactive oxygen species and efficiently kill tumor cells, with low cytotoxicity in dark. As far as we know, the probe was the first CES-responsive phototheranostic probe with both near-infrared analytical wavelengths and photosensitive capacity, which may be useful in the real-time and in situ imaging of CES as well as imaging-guided photodynamic therapy of tumors. Therefore, the proposed probe may have wide application prospect in cancer theranostics.

CD44-targeting hydrophobic phosphorylated gemcitabine prodrug nanotherapeutics augment lung cancer therapy

Gemcitabine (GEM) is among the most used chemotherapies for advanced malignancies including non-small cell lung cancer. The clinical efficacy of GEM is, however, downplayed by its poor bioavailability, short half-life, drug resistance, and dose-limiting toxicities (e.g. myelosuppression). In spite of many approaches exploited to improve the efficacy and safety of GEM, limited success was achieved. The short A6 peptide (sequence: Ac-KPSSPPEE-NH₂) is clinically validated for specific binding to CD44 on metastatic tumors. Here, we designed a robust and CD44-specific GEM nanotherapeutics by encapsulating hydrophobic phosphorylated gemcitabine prodrug (HPG) into the core of A6 peptide-functionalized disulfide-crosslinked micelles (A6-mHPG), which exhibited reduction-triggered HPG release and specific targetability to CD44 overexpressing tumor cells. Interestingly, A6 greatly enhanced the internalization and inhibitory activity of micellar HPG (mHPG) in CD44 positive A549 cells, and increased its accumulation in A549 cancerous lung, leading to potent repression of orthotopic tumor growth, depleted toxicity, and marked survival benefits compared to free HPG and mHPG (median survival time: 59 days versus 30 and 45 days, respectively). The targeted delivery of gemcitabine prodrug with disulfide-crosslinked biodegradable micelles appears to be a highly appealing strategy to boost gemcitabine therapy for advance tumors. STATEMENT OF SIGNIFICANCE: Gemcitabine (GEM) though widely used in clinics for treating advanced tumors is associated with poor bioavailability, short half-life and dose-limiting toxicities. Development of clinically translatable GEM formulations to improve its anti-tumor efficacy and safety is of great interest. Here, we report on CD44-targeting GEM nanotherapeutics obtained by encapsulating hydrophobic phosphorylated GEM prodrug (HPG), a single isomer of NUC-1031, into A6 peptide-functionalized disulfide-crosslinked micelles (A6-mHPG). A6-mHPG demonstrates stability against degradation, enhanced internalization and inhibition toward CD44⁺ cells, and increased accumulation in A549 lung tumor xenografts, leading to potent repression of orthotopic tumor growth, depleted toxicity and marked survival benefits. The targeted delivery of GEM prodrug using A6-mHPG is a highly appealing strategy to GEM cancer therapy.

Implication of Different Tumor Biomarkers in Drug Resistance and Invasiveness in Primary and Metastatic Colorectal Cancer Cell Lines

Protein expression profiles are directly related to the different properties of cells and are conditioned by the cellular niche. As an example, they are the cause of the characteristic cell plasticity, epithelium-mesenchymal transition (EMT), and drug resistance of cancer cells. This article characterizes ten biomarkers related to these features in three human colorectal cancer cell lines: SW-480, SW-620, and DLD-1, evaluated by flow cytometry; and in turn, resistance to oxaliplatin is studied through dose-response trials. The main biomarkers present in the three studied lines correspond to EpCAM, CD-133, and AC-133, with the latter two in low proportions in the DLD-1 line. The biomarker CD166 is present in greater amounts in SW-620 and DLD-1 compared to SW-480. Finally, DLD-1 shows high values of Trop2, which may explain the aggressiveness and resistance of these cells to oxaliplatin treatments, as EpCAM is also highly expressed. Exposure to oxaliplatin slows cell growth but also helps generate resistance to the treatment. In conclusion, the response of the cell lines is variable, due to their genetic variability, which will condition protein expression and cell growth. Further analyses in this area will provide important information for better understanding of patients' cellular response and how to prevent resistance.