Salutaxel, a Conjugate of Docetaxel and a Muramyl Dipeptide (MDP) Analogue, Acts as Multifunctional Prodrug That Inhibits Tumor Growth and Metastasis

Muramyl Dipeptide-Presenting Polymersomes as Artificial Nanobacteria to Boost Systemic Antitumor Immunity

The clinical efficacy of cancer vaccines is closely related to immunoadjuvants that play a crucial role in magnifying and prolonging the immune response. Muramyl dipeptide (MDP), a minimal and conserved peptidoglycan found in almost all bacteria, can trigger robust immune activation by uniquely antagonizing the nucleotide-binding oligomerization domain 2 (NOD2) pathway. However, its effectiveness has been hindered by limited solubility, poor membrane penetration, and rapid clearance from the body. Here, we introduce MDP-presenting polymersomes as artificial nanobacteria (NBA) to boost the antitumor immune response. The NBA, featuring abundant MDP molecules, induces superior stimulation of immune cells including macrophages and bone marrow-derived dendritic cells (BMDCs) compared to free MDP, likely via facilitating immune cell uptake and cooperatively stimulating systemic NOD2 signaling. Importantly, systemic administration of NBA significantly enhances the chemo-immunotherapy of B16-F10 melanoma-bearing mice pretreated with doxorubicin by reversing the immunosuppressive tumor microenvironment. Furthermore, NBA carrying ovalbumin and B16-F10 cell lysates induces robust OVA-IgG antibody production and effectively inhibit tumor growth, respectively. The artificial nanobacteria hold great promise as a potent systemic immunoadjuvant for cancer immunotherapy.

PTX-RPPR, a conjugate of paclitaxel and NRP-1 peptide inhibitor to prevent tumor growth and metastasis

Paclitaxel, a potent anti-tumor drug widely recognized for its therapeutic efficacy, has faced limitations in clinical application due to its poor solubility. The use of Cremophor EL (CrEL) as a cosolvent in paclitaxel injections has been associated with hypersensitivity reactions in some patients. To overcome these challenges, we have developed a novel conjugate by linking a neuropilin-1 targeting peptide, RPPR, to paclitaxel, resulting in PTX-RPPR. This innovative approach has significantly enhanced the solubility of paclitaxel, achieving a 3.8 mg/mL concentration, a remarkable 90-fold increase over the native drug. PTX-RPPR has shown potent anti-tumor activity, inhibiting tumor cell proliferation with an IC50 ranging from 0.26 to 1.64 μM and effectively suppressing migration, invasion, and angiogenesis at a concentration of 75 nM. Notably, in a 4T1 mammary carcinoma model, PTX-RPPR administered at a dose of 0.7 μmol/kg exhibited tumor growth inhibition comparable to that of paclitaxel at a higher dose of 3.5 μmol/kg, with superior efficacy in preventing lung metastasis. Furthermore, PTX-RPPR effectively reduced NRP-1 expression in both tumors and lungs post-treatment. In contrast to paclitaxel formulated with CrEL, PTX-RPPR did not induce IL-6 expression, suggesting a safer profile in terms of immunological response. Characterized by a particle size of 200 nm and a zeta potential of +30 mV, the nano-formulation of PTX-RPPR demonstrated remarkable stability over seven days. This study introduced PTX-RPPR as a promising peptide-drug conjugate that addresses the solubility and hypersensitivity issues associated with paclitaxel, offering a safer therapeutic strategy for cancer treatment.

Muropeptides and muropeptide transporters impact on host immune response

In bacteria, the cell envelope is the key element surrounding and protecting the bacterial content from mechanical or osmotic damages. It allows the selective interchanges of solutes, ions, cellular debris, and drugs between the cellular compartments and the external environment, thanks to the presence of transmembrane proteins called transporters. The major component of the cell envelope is the peptidoglycan, consisting of long linear glycan strands cross-linked by short peptide stems. During cell growth or under stress conditions, peptidoglycan fragments, the muropeptides, are released by bacteria and recognized by the host Pattern Recognition Receptor, promoting the activation of their innate defense mechanisms. The review sums up the salient aspects of microbiota-host interaction with a focus on the NOD-dependent immune response to bacterial peptidoglycan and on the accountability of muropeptide transporters in the crosstalk with the host and in antibiotic resistance. Furthermore, it retraces the discoveries and applications of microorganisms-derived components such as vaccines or vaccine adjuvants.

"Open Sesame" to the complexity of pattern recognition receptors of myeloid-derived suppressor cells in cancer

Pattern recognition receptors are primitive sensors that arouse a preconfigured immune response to broad stimuli, including nonself pathogen-associated and autologous damage-associated molecular pattern molecules. These receptors are mainly expressed by innate myeloid cells, including granulocytes, monocytes, macrophages, and dendritic cells. Recent investigations have revealed new insights into these receptors as key players not only in triggering inflammation processes against pathogen invasion but also in mediating immune suppression in specific pathological states, including cancer. Myeloid-derived suppressor cells are preferentially expanded in many pathological conditions. This heterogeneous cell population includes immunosuppressive myeloid cells that are thought to be associated with poor prognosis and impaired response to immune therapies in various cancers. Identification of pattern recognition receptors and their ligands increases the understanding of immune-activating and immune-suppressive myeloid cell functions and sheds light on myeloid-derived suppressor cell differences from cognate granulocytes and monocytes in healthy conditions. This review summarizes the different expression, ligand recognition, signaling pathways, and cancer relations and identifies Toll-like receptors as potential new targets on myeloid-derived suppressor cells in cancer, which might help us to decipher the instruction codes for reverting suppressive myeloid cells toward an antitumor phenotype.

Muramyl dipeptide-based analogs as potential anticancer compounds: Strategies to improve selectivity, biocompatibility, and efficiency

According to the WHO, cancer is the second leading cause of death in the world. This is an important global problem and a major challenge for researchers who have been trying to find an effective anticancer therapy. A large number of newly discovered compounds do not exert selective cytotoxic activity against tumorigenic cells and have too many side effects. Therefore, research on muramyl dipeptide (MDP) analogs has attracted interest due to the urgency for finding more efficient and safe treatments for oncological patients. MDP is a ligand of the cytosolic nucleotide-binding oligomerization domain 2 receptor (NOD2). This molecule is basic structural unit that is responsible for the immune activity of peptidoglycans and exhibits many features that are important for modern medicine. NOD2 is a component of the innate immune system and represents a promising target for enhancing the innate immune response as well as the immune response against cancer cells. For this reason, MDP and its analogs have been widely used for many years not only in the treatment of immunodeficiency diseases but also as adjuvants to support improved vaccine delivery, including for cancer treatment. Unfortunately, in most cases, both the MDP molecule and its synthesized analogs prove to be too pyrogenic and cause serious side effects during their use, which consequently exclude them from direct clinical application. Therefore, intensive research is underway to find analogs of the MDP molecule that will have better biocompatibility and greater effectiveness as anticancer agents and for adjuvant therapy. In this paper, we review the MDP analogs discovered in the last 10 years that show promise for antitumor therapy. The first part of the paper compiles the achievements in the field of anticancer vaccine adjuvant research, which is followed by a description of MDP analogs that exhibit promising anticancer and antiproliferative activity and their structural changes compared to the original MDP molecule.

Docetaxel enhances the therapeutic efficacy of PSMA-specific CAR-T cells against prostate cancer models by suppressing MDSCs

PURPOSE

Prostate cancer can undergo curative effects by radical prostatectomy or radical radiotherapy. However, the best treatment for more aggressive high-risk prostate cancer remains controversial. Insufficient infiltration capacity and dysfunction are commonly occurrences in engineered T lymphocytes expressing chimeric antigen receptor (CAR-T), characterizing cancer immunotherapy failure. We conducted this study to investigate whether the combinative application of docetaxel and PSMA-CAR-T cells could be a more effective treatment to prostate cancer.

METHODS

Expressions of prostate specific membrane antigen (PSMA) on prostate cancer cells were examined by Flow cytometry. The efficaciousness of PSMA-CAR-T was evaluated in vitro using ELISA and RTCA. The effect of intermixed therapy was assessed in vivo utilizing a human prostate cancer liver metastasis mouse model and a human prostate cancer cell xenograft mouse model.

RESULTS

The outcome of cytokine discharge and cell killing assays demonstrated that PSMA-CAR-T cells have characteristic effector capacity against PSMA⁺ prostate cancer cells in vitro. Additionally, collaborative treatment of PSMA-CAR-T cells and docetaxel have cooperative efficacy in a mouse model of human prostate cancer. The merged strategy could be seen as an undeveloped avenue to augmenting adoptive CAR-T cell immunotherapy and mitigating the adverse side effects of chemotherapy.

CONCLUSIONS

Cooperation of PSMA-specific CAR-T cells and the chemotherapy drug docetaxel can impressively ameliorate antitumor effectiveness against an installed metastatic human prostate cancer model in NPG mice.

Emerging Nanotherapeutic Approaches to Overcome Drug Resistance in Cancers with Update on Clinical Trials

A key issue with modern cancer treatments is the emergence of resistance to conventional chemotherapy and molecularly targeted medicines. Cancer nanotherapeutics were created in order to overcome the inherent limitations of traditional chemotherapeutics. Over the last few decades, cancer nanotherapeutics provided unparalleled opportunities to understand and overcome drug resistance through clinical assessment of rationally designed nanoparticulate delivery systems. In this context, various design strategies such as passive targeting, active targeting, nano-drug, and multimodal nano-drug combination therapy provided effective cancer treatment. Even though cancer nanotherapy has made great technological progress, tumor biology complexity and heterogeneity and a lack of comprehensive knowledge of nano-bio interactions remain important roadblocks to future clinical translation and commercialization. The current developments and advancements in cancer nanotherapeutics employing a wide variety of nanomaterial-based platforms to overcome cancer treatment resistance are discussed in this article. There is also a review of various nanotherapeutics-based approaches to cancer therapy, including targeting strategies for the tumor microenvironment and its components, advanced delivery systems for specific targeting of cancer stem cells (CSC), as well as exosomes for delivery strategies, and an update on clinical trials. Finally, challenges and the future perspective of the cancer nanotherapeutics to reverse cancer drug resistance are discussed.

Amphiphilic desmuramyl peptides for the rational design of new vaccine adjuvants: Synthesis, in vitro modulation of inflammatory response and molecular docking studies

Nucleotide-binding oligomerization domain 2 (NOD2) is cytosolic surveillance receptor of the innate immune system capable of recognizing the bacterial and viral infections. Muramyl dipeptide (MDP) is the minimal immunoreactive unit of murein. NOD2 perceives MDP as pathogen-associated molecular pattern, thereby triggering an immune response with undesirable side-effects. Beneficial properties of MDP, such as pro-inflammatory characteristics for the rational design of new vaccine adjuvants, can be harnessed by strategically re-designing the molecule. In this work, a new class of amphiphilic desmuramylpeptides (DMPs) were synthesized by replacing the carbohydrate moiety (muramic acid) of the parent molecule with hydrophilic arenes. A lipophilic chain was also introduced at the C-terminus of dipeptide moiety (alanine-isoglutamine), while conserving its L-D configuration. These novel DMPs were found to set off the release of higher levels of tumour necrosis factor alpha (TNF-α) than Murabutide, which is a well-known NOD2 agonist. Molecular docking studies indicate that all these DMPs bind well to NOD2 receptor with similar dock scores (binding energy) through a number of hydrogen bonding and hydrophobic/π interactions with several crucial residues of the receptor. More studies are needed to further assess their immunomodulatory therapeutic potential, as well as the possible involvement of NOD2 activation.

Nonpeptidic quinazolinone derivatives as dual nucleotide-binding oligomerization domain-like receptor 1/2 antagonists for adjuvant cancer chemotherapy

Nucleotide-binding oligomerization domain-containing protein 1 and 2 (NOD1/2) receptors are potential immune checkpoints. In this article, a quinazolinone derivative (36b) as a NOD1/2 dual antagonist was identified that significantly sensitizes B16 tumor-bearing mice to paclitaxel treatment by inhibiting both nuclear factor κB (NF-κB) and mitogen-activated protein kinase inflammatory signaling that mediated by NOD1/2.

Identification of benzofused five-membered sultams, potent dual NOD1/NOD2 antagonists in vitro and in vivo

Nucleotide-binding oligomerization domain-containing proteins 1 and 2 play important roles in immune system activation. Recently, a shift has occurred due to the emerging knowledge that preventing nucleotide-binding oligomerization domains (NODs) signaling could facilitate the treatment of some cancers, which warrants the search for dual antagonists of NOD1 and NOD2. Herein, we undertook the synthesis and identification of a new class of derivatives of dual NOD1/NOD2 antagonists with novel benzofused five-membered sultams. Compound 14k was finally demonstrated to be the most potent molecule that inhibits both NOD1-and NOD2-stimulated NF-κB and MAPK signaling in vitro and in vivo.

Self-assembling prodrug nanotherapeutics for synergistic tumor targeted drug delivery

Self-assembling prodrugs represents a robust and effective nanotherapeutic approach for delivering poorly soluble anticancer drugs. With numerous intrinsic advantages, self-assembling prodrugs possess the maximum drug loading capacity, controlled drug release kinetics, prolonged blood circulation, and preferential tumor accumulation based on the enhanced permeability and retention (EPR) effect. These prodrug conjugates allow for efficient self-assembly into nanodrugs with the potential of encapsulating other therapeutic agents that have different molecular targets, enabling simultaneous temporal-spatial release of drugs for synergistic antitumor efficacy with reduced systemic side effects. The aim of this review is to summarize the recent progress of self-assembling prodrug cancer nanotherapeutics that are made through conjugating therapeutically active agents to Polyethylene glycol, Vitamin E, or drugs with different physicochemical properties via rational design, for synergistic tumor targeted drug delivery.

Statement of Significance

All current FDA-approved nanomedicines use inert biomaterials as drug delivery carriers. These biomaterials lack any therapeutic potential, contributing not only to the cost, but may also elicit severe unfavorable adverse effects. Despite the reduction in toxicity associated with the payload, these nanotherapeutics have been met with limited clinical success, likely due to the monotherapy regimen. The self-assembling prodrug (SAP) has been emerging as a powerful platform for enhancing efficacy through co-delivering other therapeutic modalities with distinct molecular targets. Herein, we opportunely present a comprehensive review article summarizing three unique approaches of making SAP for synergistic drug delivery: pegylation, vitamin E-derivatization, and drug-drug conjugation. These SAPs may inevitably pave the way for developing more efficacious, clinically translatable, combination cancer nanotherapies.

NOD2 inhibits tumorigenesis and increases chemosensitivity of hepatocellular carcinoma by targeting AMPK pathway

Nucleotide binding oligomerization domain 2 (NOD2) is a recognized innate immune sensor which can initiate potent immune response against pathogens. Many innate immune sensors have been reported to be of great importance in carcinogenesis. However, the role of NOD2 in cancer is not well understood. Here we investigated the role of NOD2 in the development of hepatocellular carcinoma (HCC). We demonstrated that NOD2 deficiency promoted hepatocarcinogenesis in N-nitrosodiethylamine (DEN)/carbon tetrachloride (CCl₄) induced HCC mice model and xenograft tumor model. In vitro investigation showed that NOD2 acted as a tumor suppressor and inhibited proliferation, colony formation and invasion of HCC cells. Clinical investigation showed that NOD2 expression was completely lost or significantly downregulated in clinical HCC tissues, and loss of NOD2 expression was significantly correlated with advanced disease stages. Further investigation showed that NOD2 exerted its anti-tumor effect through activating adenosine 5'-monophosphate (AMP) -activated protein kinase (AMPK) signaling pathway, and NOD2 significantly enhanced the sensitivity of HCC cells to sorafenib, lenvatinib and 5-FU treatment through activating AMPK pathway induced apoptosis. Moreover, we demonstrated that NOD2 activated AMPK pathway by directly binding with AMPKα-LKB1 complex, which led to autophagy-mediated apoptosis of HCC cells. Altogether, this study showed that NOD2 acted as a tumor suppressor as well as a chemotherapeutic regulator in HCC cells by directly activating AMPK pathway, which indicated a potential therapeutic strategy for HCC treatment by upregulating NOD2-AMPK signaling axis.

Harnessing the untapped potential of nucleotide-binding oligomerization domain ligands for cancer immunotherapy

In the last decade, cancer immunotherapy has emerged as an effective alternative to traditional therapies such as chemotherapy and radiation. In contrast to the latter, cancer immunotherapy has the potential to distinguish between cancer and healthy cells, and thus to avoid severe and intolerable side‐effects, since the cancer cells are effectively eliminated by stimulated immune cells. The cytosolic nucleotide‐binding oligomerization domains 1 and 2 receptors (NOD1 and NOD2) are important components of the innate immune system and constitute interesting targets in terms of strengthening the immune response against cancer cells. Many NOD ligands have been synthesized, in particular NOD2 agonists that exhibit favorable immunostimulatory and anticancer activity. Among them, mifamurtide has already been approved in Europe by the European Medicine Agency for treating patients with osteosarcoma in combination with chemotherapy after complete surgical removal of the primary tumor. This review is focused on NOD receptors as promising targets in cancer immunotherapy as well as summarizing current knowledge of the various NOD ligands exhibiting antitumor and even antimetastatic activity in vitro and in vivo.

Preparation, characterization and in vitro activity of a docetaxel-albumin conjugate

Docetaxel is one of the most effective anticancer drugs. However, the current formulation of docetaxel contains Tween 80 and ethanol as the solvent, which can cause severe side effects. Consequently, the development of new type of formulation of docetaxel with high efficiency and low side effects is a very important issue. In this study, we explored the covalent linking of docetaxel and albumin via one organic linker. 6-Maleimidocaproic acid was applied to link the C2' hydroxyl group of docetaxel with the cysteine-34 of albumin to obtain 1:1 docetaxel-albumin conjugate. The synthesized conjugate can control the release of docetaxel in the bovine serum. Furthermore, in vitro cell cytotoxicity experiments indicated that the docetaxel-albumin conjugate have high activities for human prostate cancer cell line PC3 and human breast cancer cell line MCF-7. The present study provides a valuable strategy for further development of a new type of docetaxel-albumin prodrug.