Enhancing SN38 prodrug delivery using a self-immolative linker and endogenous albumin transport.

Enhancing the delivery and release efficiency of hydroxyl agents, constrained by high pKa values and issues of release rate or unstable linkage, is a critical challenge. To address this, a self-immolative linker, composed of a modifiable p-hydroxybenzyl ether and a fast cyclization adapter (N-(ortho-hydroxyphenyl)-N-methylcarbamate) was strategically designed, for the synthesis of prodrugs. The innovative linker not only provides a side chain modification but also facilitates the rapid release of the active payloads, thereby enabling precise drug delivery. Particularly, five prodrug model compounds (J1, J2, J3, J5 and J6) were synthesized to evaluate the release rates by using ß-glucuronic acid as trigger and five hydroxyl compounds as model payloads. Significantly, all prodrug model compounds could efficiently release the hydroxyl payloads under the action of ß-glucuronidase, validating the robustness of the linker. And then, to assess the drug delivery and release efficiency using endogenous albumin as a transport vehicle, J1148, a SN38 prodrug modified with maleimide side chain was synthesized. Results demonstrated that J1148 covalently bound to plasma albumin through in situ Michael addition, effectively targeting the tumor microenvironment. Activated by ß-glucuronidase, J1148 underwent a classical 1, 6-elimination, followed by rapid cyclization of the adapter, thereby releasing SN38. Impressively, J1148 showed excellent therapeutic efficacy against human colonic cancer xenograft model, leading to a significant reduction or even disappearance of tumors (3/6 of mice cured). These findings underscore the potential of the designed linker in the delivery system of hydroxyl agents, positioning it at the forefront of advancements in drug delivery technology.

Design, synthesis, and biological evaluation of cathepsin B cleavage albumin-binding SN38 prodrug in breast cancer.

Here, we introduce a novel and effective approach utilizing a cathepsin B cleavage albumin-binding SN38 prodrug specifically designed for the treatment of metastatic breast cancer. Termed Mal-va-mac-SN38, our prodrug exhibits a unique ability to rapidly and covalently bind with endogenous albumin, resulting in the formation of HSA-va-mac-SN38. This prodrug demonstrates exceptional stability in human plasma. Importantly, HSA-va-mac-SN38 showcases an impressive enhancement in cellular uptake by 4T1 breast cancer cells, primarily facilitated through caveolin-mediated endocytosis. Intriguingly, the release of the active SN38, is triggered by the enzymatic activity of cathepsin B within the lysosomal environment. In vivo studies employing a lung metastasis 4T1 breast cancer model underscore the potency of HSA-va-mac-SN38. Histological immunohistochemical analyses further illuminate the multifaceted impact of our prodrug, showcasing elevated levels of apoptosis, downregulated expression of matrix metalloproteinases, and inhibition of angiogenesis, all critical factors contributing to the anti-metastatic effect observed. Biodistribution studies elucidate the capacity of Mal-va-mac-SN38 to augment tumor accumulation through covalent binding to serum albumin, presenting a potential avenue for targeted therapeutic interventions. Collectively, our findings propose a promising therapeutic avenue for metastatic breast cancer, through the utilization of a cathepsin B-cleavable albumin-binding prodrug.

Synthesis and biological evaluation of novel quaternary ammonium antibody drug conjugates based on camptothecin derivatives.

Antibody drug conjugates (ADCs) have emerged as a highly promising class of cancer therapeutics, comprising antibodies, effector molecules, and linkers. Among them, DS-8201a with DXd as the effector molecule, has shown remarkable anti-tumor efficacy against solid tumors, sparking a surge of interest in ADCs with camptothecin derivatives as ADC effector molecules. In this study, we introduced and successfully constructed quaternary ammonium ADCs utilizing camptothecin derivatives WL-14 and CPTS-1 for the first time. All four ADCs displayed excellent stability under physiological conditions and in plasma, facilitating their prolonged circulation in vivo. Moreover, the four ADCs, employing Val-Cit or Val-Ala dipeptide linkers effectively achieved complete release of the effector molecules via cathepsin B. Although, the in vitro antitumor activity of these ADCs was comparatively limited, the development of quaternary ammonium ADCs based on novel camptothecin derivatives as effector molecules is still a viable and promising strategy. Significantly, our study provides valuable insights into the crucial role of linker optimization in ADCs design.

Design and synthesis of multivalent drug delivery system with CA IX inhibitors as ligands.

A multivalent ligand delivery system holds tremendous potential in the field of tumor-targeted drug delivery. It addresses the challenges posed by the low affinity between small molecule ligand receptors and the rapid metabolism of small molecule drug conjugates (SMDCs) in vivo. Notably, existing multivalent ligand systems have demonstrated significant anti-tumor activity in various tumor models. In this study, we have developed a novel multivalent ligand delivery system for SN38, utilizing acetazolamide, a carbonic anhydrase IX (CA IX) inhibitor, as the target ligand. Our multivalent ligand delivery systems exhibited superior metabolic stability and enhanced targeting specificity compared to SMDC molecules. Furthermore, they demonstrated improved anti-proliferation activity, addressing the existing challenges associated with the low receptor affinity and rapid metabolism of SMDCs.

Synthesis, and biological evaluation of EGFR/HER2-NAMPT conjugates for tumor treatment.

Throughout the reported applications of EGFR inhibitors, it is usually employed with HDAC or other targets to design multi-target inhibitors for cancer treatment. In this paper, we designed a drug conjugate that targeted EGFR&HER2 and had inhibitory activity of NAMPT simultaneously. Compound 20c significantly inhibited the EGFR&HER2 and NAMPT enzyme activities, and had comparable or even higher anti-proliferative activity than lapatinib in various cancer cells with over-expressed EGFR and HER2. Importantly, 20c was expected to increase sensitivity to EGFR inhibitor-resistant cells. In Osimertinib-resistant cells (NCI-1975 cells with the L858R/T790M/C797S triple mutation and Ba/F3 cells with the Del19/T790M/C797S triple mutation), the anti-proliferative activity of compound 20c was increased by more than twofold compared with Osimertinib, so as to obtain better curative effect. This strategy is a promising method of embedding multiple pharmacophores into a single molecule, which lays a good foundation for the design and synthesis of small molecule drug conjugates with strong targeting ability and high cytotoxicity.

Development of HSP90 inhibitors-SN38 conjugates for cancer treatment.

Presently, chemotherapy remains to be one of the most important therapeutic approaches for malignant tumors. Ligands based drug conjugates are showing considerable promise as potential therapeutic agents delivery systems for cancer. Here, a series of HSP90 inhibitors-SN38 conjugates were developed through cleavable linkers for tumor-specific delivery of SN38 and reducing its side effects. In vitro assays showed that these conjugates exhibited acceptable stability in PBS and plasma, appreciable HSP90 binding affinity, and potent cytotoxic abilities. Cellular uptake behaviors also indicated that these conjugates could selectively target cancer cells in a time-dependent manner via HSP90. Among them, compound 10b with a glycine linkage exhibits appreciable in vitro and in vivo pharmacokinetic profiles, and excellent in vivo antitumor activity in Capan-1 xenograft models, demonstrating the selective targeting and accumulation of the active payload at tumor sites. Above all, these results suggest that compound 10b has the potential as a potent anticancer drug, meriting further evaluation in the future.

Monitoring the in vivo siRNA release from lipid nanoparticles based on the fluorescence resonance energy transfer principle.

The siRNA-loaded lipid nanoparticles have attracted much attention due to its significant gene silencing effect and successful marketization. However, the in vivo distribution and release of siRNA still cannot be effectively monitored. In this study, based on the fluorescence resonance energy transfer (FRET) principle, a fluorescence dye Cy5-modified survivin siRNA was conjugated to nanogolds (Au-DR-siRNA), which were then wrapped with lipid nanoparticles (LNPs) for monitoring the release behaviour of siRNA in vivo. The results showed that once Au-DR-siRNA was released from the LNPs and cleaved by the Dicer enzyme to produce free siRNA in cells, the fluorescence of Cy5 would change from quenched state to activated state, showing the location and time of siRNA release. Besides, the LNPs showed a significant antitumor effect by silencing the survivin gene and a CT imaging function superior to iohexol by nanogolds. Therefore, this work provided not only an effective method for monitoring the pharmacokinetic behaviour of LNP-based siRNA, but also a siRNA delivery system for treating and diagnosing tumors.

Design, synthesis, and biological evaluation of 4-(1H-1,2,3-triazol-1-yl)benzamides as HSP90 inhibitors.

Heat shock protein 90 (HSP90) is a promising anticancer drug target, which could be employed to construct HSP90 inhibitors-based drug conjugates for selective tumor therapy. Herein, a series of 4-(1H-1,2,3-triazol-1-yl)benzamides were rationally designed, synthesized as HSP90 inhibitors, and their structures were characterized by 1H NMR, 13C NMR, and HR-MS. Preliminary HSP90 binding assay showed that compounds 6b, 6l, 6m, 6n, 6t, and 6u exhibited significant HSP90α binding affinity. Among these selected compounds, 6u displayed the most potent anti-proliferative activities and particularly in Capan-1 cell line. Molecular modeling studies also confirmed possible mode of interaction between 6u and the binding sites of HSP90 by hydrogen bond and hydrophobic interactions. Above all, these encouraging data indicated that 6u could be used as a HSP90 inhibitor for further study and helped the recognition of the 4-(1H-1,2,3-triazol-1-yl)benzamide motif as a new scaffold for HSP90 inhibitors.

Design, synthesis, and biological evaluation of BRD4 degraders.

Epigenetic proteins are one of the important targets in the current research fields of cancer therapy. A family of bromodomain-containing (BRD) and extra terminal domain (BET) proteins act as epigenetic readers to regulate the expression of key oncogenes and anti-apoptotic proteins. Recently, although BET degraders based on PROTAC technology have achieved significant antitumor effects, the lack of selectivity for BET protein degradation has not been fully addressed. Herein, a series of small molecule BRD4 PROTACs were designed and synthesized. Most of the degraders were effective in inhibiting MM.1S and MV-4-11 cell lines, especially in MV-4-11. Among them, degrader 8b could induce the degradation of BRD4 and exhibited a time- and concentration-dependent depletion manner and there was a significant depletion of BRD4, laying a foundation for effectively treating leukemia and multiple myeloma. Moreover, 8b could also effectively prevent the activation of MRC5 cells by inducing the degradation of BRD4 protein, which preliminarily proves that the BRD4 degrader based on the PROTAC concept has great potential for the treatment of pulmonary fibrosis. Taken together, these findings laid a foundation for BRD4 degraders as an effective strategy for treating related diseases.

Design, synthesis, and biological evaluation of Wee1 kinase degraders.

Proteolysis targeting chimera (PROTAC) technology has received widespread attention in recent years as a promising strategy for drug development. Herein, we report a series of novel Wee1 degraders, which were designed and synthesized based on PROTAC technology by linking AZD1775 with CRBN ligands through linkers of different lengths and types. All degraders could effectively and completely degrade cellular Wee1 protein in MV-4-11 cell line at IC50 concentrations. Preliminary assessments identified 42a as the most active degrader, which possessed potent antiproliferative activity and induced CRBN- and proteasome-dependent degradation of Wee1. Moreover, 42a also exhibited a time- and concentration-dependent depletion manner and inducing cell cycle arrest in G0/G1 phase and cancer cell apoptosis. More importantly, 42a showed acceptable in vitro and in vivo pharmacokinetic properties and displayed rapid and sustained Wee1 degradation ability in vivo. Taken together, these findings contribute to understanding the development of PROTACs and demonstrate that our Wee1-targeting PROTAC strategy has potential novel applications in cancer therapy.

Hypoxia-Activated Albumin-Binding Exatecan Prodrug for Cancer Therapy.

As an effective drug delivery strategy for traditional antitumor drugs, the stimulus-responsive albumin-based prodrugs are getting more and more attention. These prodrugs only release drugs in specific tumor microenvironments, which can prevent premature release of the drug in the circulation. Tumor hypoxia is a fundamental feature of the solid tumor microenvironment. As a hypoxia-activated linker, the 5-position branched linker of 1-methyl-2-nitro-5-hydroxymethylimidazole can be a trigger for albumin-based prodrugs. In this study, we report the synthesis and biological evaluation of the hypoxia-activated albumin-binding prodrug Mal-azo-Exatecan. After intravenous administration, the maleimide on the side chain can rapidly bind to endogenous albumin, enabling the prodrugs to accumulate in tumors, where tumor-associated hypoxia microenvironments trigger the selective release of Exatecan. The 5-position branched linker of 1-methyl-2-nitro-5-hydroxymethylimidazole as a cleavable linker has high plasma stability and does not cause Exatecan release from HSA-azo-Exatecan during circulation in vivo, avoiding systemic side effects caused by Exatecan.

Design, Synthesis, and Biological Evaluation of HDAC Degraders with CRBN E3 Ligase Ligands.

Histone deacetylases (HDACs) play important roles in cell growth, cell differentiation, cell apoptosis, and many other cellular processes. The inhibition of different classes of HDACs has been shown to be closely related to the therapy of cancers and other diseases. In this study, a series of novel CRBN-recruiting HDAC PROTACs were designed and synthesized by linking hydroxamic acid and benzamide with lenalidomide, pomalidomide, and CC-220 through linkers of different lengths and types. One of these PROTACs, denoted 21a, with a new benzyl alcohol linker, exhibited comparably excellent HDAC inhibition activity on different HDAC classes, acceptable degradative activity, and even better in vitro anti-proliferative activities on the MM.1S cell line compared with SAHA. Moreover, we report for the first time the benzyl alcohol linker, which could also offer the potential to be used to develop more types of potent PROTACs for targeting more proteins of interest (POI).

Design, Synthesis, and Evaluation of Near-Infrared Fluorescent Molecules Based on 4H-1-Benzopyran Core.

A series of novel fluorescent 4H-1-benzopyrans was designed and developed as near-infrared fluorescent molecules with a compact donor-acceptor-donor architecture. Spectral intensity of the fluorescent molecules M-1, M-2, M-3 varied significantly with the increasing polarities of solvents, where M-3 showed high viscosity sensitivity in glycerol-ethanol system with a 3-fold increase in emission intensity. Increasing concentrations of compound M-3 to 5% BSA in PBS elicited a 4-fold increase in fluorescence intensity, exhibiting a superior environmental sensitivity. Furthermore, the in vitro cellular uptake behavior and CLSM assay of cancer cell lines demonstrated that M-3 could easily enter the cell nucleus and bind to proteins with low toxicity. Therefore, the synthesized near-infrared fluorescent molecules could provide a new direction for the development of optical imaging probes and potential further drugs.

A water-soluble probe with p-hydroxybenzyl quaternary ammonium linker for selective imaging in senescent cells.

A water-soluble probe with p-hydroxybenzyl quaternary ammonium linker, FR-2a, for selective imaging in senescent cells is reported. Probe FR-2a integrated water-soluble fluorophore (HT-4a) and ß-galactosidase (ß-gal) trigger into one entity by a p-hydroxybenzyl quaternary ammonium linker. HT-4a is a styryl-based push-pull benzothiazole fluorophore with attractive properties, including excellent water-solubility, intense fluorescence emission and a large Stokes shift (161 nm), characterized by an intramolecular charge transfer (ICT) excited state. The formation of quaternary ammonium deactivated the ICT state, resulting in fluorescence quenching of FR-2a. In the presence of ß-gal, the glycosidic bond was hydrolyzed and fluorophore HT-4a was released through self-immolative process, resulting in effective fluorescence recovery. FR-2a shows high affinity to ß-gal (Km = 1.33 µM), exhibiting good sensitivity, selectivity and stability for imaging in senescent cells.

Design, Synthesis, and Biological Evaluation of HSP90 Inhibitor-SN38 Conjugates for Targeted Drug Accumulation.

Herein, a series of HSP90 inhibitor-SN38 conjugates through ester and carbamate linkage in the 20-OH and 10-OH positions of SN38 were developed for improving the tumor-specific penetration and accumulation of SN38 via extracellular HSP90 (eHSP90)-mediated endocytosis. Mechanistic analyses confirmed that these novel conjugates could bind to eHSP90 and be selectively internalized into the tumor cells, which led to prolonged tumor regression in multiple models of cancer. Among all studied conjugates, compound 18b showed excellent in vitro activities, including acceptable HSP90α affinity and potent antitumor activity. Moreover, compound 18b exhibited superior antitumor activity and low toxicity in HCT116 and Capan-1 xenograft models. Pharmacokinetic analyses in HCT116 and Capan-1 xenografts further confirmed that compound 18b treatment could lead to effective cleavage and extended SN38 exposure at tumor sites. All these encouraging data indicate that this compound is a promising new candidate for cancer therapy and merits further chemical and biological evaluation.

Dynamic core crosslinked camptothecin prodrug micelles with reduction sensitivity and boronic acid-mediated enhanced endocytosis: An intelligent tumor-targeted delivery nanoplatform.

The physicochemical properties of camptothecin (CPT) limit its clinical application. To maximize drug efficacy, a novel intelligent prodrug delivery nanoplatform with a tumor microenvironment-cleavable core crosslinking strategy was proposed based on a phenylboronic acid (PBA) modified polyethylene glycol (PEG)-polyglutamic acid (PGlu) polymer with disulfide-bonded CPT, called PBA-PEG-P(Glu-co-GlussCPT). The fabricated nanoplatform was a spherical micelle that could withstand dilution and carry a large number of therapeutic molecules to the tumor tissues, thereby minimizing premature drug release. Moreover, the nanoplatform release 6.2 ± 0.62, 12.4 ± 1.8, 46.7 ± 0.33, and 79.2 ± 1.58% of CPT after incubation in 0.02, 1, 5, and 10 mM dithiothreitol for 24 h, respectively, exhibiting good reduction-sensitivity. Moreover, the nanoplatform exhibited significant antiproliferative activity against tumor cells. In addition, with PBA modification, the nanoplatform demonstrated enhanced endocytosis efficiency. This prodrug nanoplatform also exhibited significant in vivo antitumor efficacy on both murine and human hepatoma xenograft models, without showing significant systemic toxicity but demonstrating good biocompatibility. In other words, this novel intelligent prodrug delivery nanoplatform with tumor microenvironment-cleavable core crosslinking strategy and active targeting strategy based on prodrug polymer PBA-PEG-P(Glu-co-GlussCPT) demonstrated multiple functions and significant potential for antitumor drug delivery.

Optimized HSP90 mediated fluorescent probes for cancer-specific bioimaging.

Cancer-specific bioimaging has been correlated with fluorescence-guided tumor therapy, garnering extensive interest from researchers. Herein, a highly efficient tumor-targeting fluorescent probe (NP-001), which is integrated with 4-hydroxy-1,8-naphthalimide and NVP-AUY922, for tumor imaging has been established. 4-Hydroxy-1,8-naphthalimide is a fluorescent molecule with remarkable imaging compatibility. NVP-AUY922 is a heat shock protein 90 (HSP90) inhibitor with preferential tumor selectivity that is conjugated to 4-hydroxy-1,8-naphthalimide as a tumor-targeting ligand. NP-002, a resorcinol-blocked probe which prevented binding with an amino acid residue of the HSP90 ATP binding pocket, was also synthesized as a control. In vitro and ex vivo assays showed that NP-001 could arrest cell proliferation, induce apoptosis and accumulate to inhibit HSP90. Confocal laser scanning microscopy (CLSM) also confirmed that NP-001 could be selectively internalized by tumor cells for cancer-specific bioimaging. Moreover, pharmacokinetic studies and histological analysis also indicated that NP-001 had a relatively longer retention time and showed no major organ-related toxicities. Overall, these encouraging data suggest that NP-001 is a promising new candidate for the early diagnosis of metastatic disease as well as targeted tumor imaging.