On the article "Findings questioning the involvement of Sigma-1 receptor in the uptake of anisamide-decorated particles" [J. Control. Release 224 (2016) 229-238]: Letter to the Editor 1 (September 14, 2016)

Rapid Microwave-Assisted Synthesis of pH-Sensitive Carbon-Based Nanoparticles for the Controlled Release of Doxorubicin to Cancer Cells

Carbon-based nanoparticles (CNPs) are a new type of interesting nanomaterials applied in various pharmaceutical fields due to their outstanding biocompatible properties. Novel pH-sensitive CNPs were rapidly synthesized within 1 min by microwave-assisted technique for doxorubicin (DOX) delivery into five cancer cell lines, including breast cancer (BT-474 and MDA-MB-231 cell lines), colon cancer (HCT and HT29 cell lines), and cervical cancer (HeLa cell lines). CNPs and DOX-loaded CNPs (CNPs-DOX) had nano-size of 11.66 ± 2.32 nm and 43.24 ± 13.25 nm, respectively. DOX could be self-assembled with CNPs in phosphate buffer solution at pH 7.4 through electrostatic interaction, exhibiting high loading efficiency at 85.82%. The release of DOX from CNPs-DOX at pH 5.0, often observed in the tumor, was nearly two times greater than the release at physiological condition pH 7.4. Furthermore, the anticancer activity of CNPs-DOX was significantly enhanced compared to free DOX in five cancer cell lines. CNPs-DOX could induce cell death through apoptosis induction in MDA-MB-231 cells. The findings revealed that CNPs-DOX exhibited a promising pH-sensitive nano-system as a drug delivery carrier for cancer treatment.

Strategies targeting tumor immune and stromal microenvironment and their clinical relevance

The critical role of tumor microenvironment (TME) in tumor initiation and development has been well-recognized after more than a century of studies. Numerous therapeutic approaches targeting TME are rapidly developed including those leveraging nanotechnology, which have been further accelerated since the emergence of immune checkpoint blockade therapies in the past decade. While there are many reviews focusing on TME remodeling therapies via drug delivery and engineering strategies in animal models, state-of-the-art evaluation of clinical development states of TME-targeted therapeutics is rarely found. Here, we illustrate opportunities for integrating nano-delivery system for the development of TME-specific therapeutic regimen, followed by a comprehensive summary of the most up to date approved or clinically evaluated therapeutics targeting cellular and extracellular components within tumor immune and stromal microenvironment, including small molecule and monoclonal antibody drugs as well as nanomedicines. In the end, we also discuss challenges and possible solutions for clinical translation of TME-targeted nanomedicines.

Magnolol-loaded Cholesteryl Biguanide Conjugate Hydrochloride Nanoparticles for Triple-negative Breast Cancer Therapy

The potential of combination therapy using nanoparticle delivery systems in improving triple-negative breast cancer treatment efficacy remains to be explored. Here, we report a novel nanoparticle system using a cholesterol biguanide conjugate hydrochloride (CBH) as both a drug and carrier to load magnolol (MAG). Poly(ethylene glycol)-poly(lactic-co-glycolic acid) (mPEG-PLGA) and aminoethyl anisamide-poly(ethylene glycol)-poly(lactic-co-glycolic acid) (AEAA-PEG-PLGA) were added to form nanoparticles. Nanoparticles accumulated most in tumor tissues when the weight ratio of AEAA-PEG-PLGA to mPEG-PLGA was 4:1. MAG and CBH exerted a synergistic inhibitory effect on 4T1 cells. An in vitro study showed that nanoparticles displayed the highest tumor cell uptake rate, highest apoptosis rate, and strongest inhibitory effect on tumor cell migration and monoclonal formation. CBH might promote nanoparticle uptake by cells and lysosomal escape. After intravenous administration to mice with 4T1 breast tumors in situ, the nanoparticles inhibited tumor growth without obvious toxicity. Western blot results showed that nanoparticles altered the levels of p53, p-AKT, and p-AMPK in the tumor tissue. Moreover, cell apoptosis was found in the same area of H&E-stained and TUNEL-stained tumors treated with the nanoparticles. Collectively, this nanoparticle system provides a novel combination drug delivery strategy for treating triple-negative breast cancer.

Tumor-targeted delivery of silibinin and IPI-549 synergistically inhibit breast cancer by remodeling the microenvironment

We induced changes in the tumor microenvironment (TME) through the synergistic actions of two drugs used in breast cancer therapy. The anti-fibrotic drug silibinin (SLB) targets tumor-associated fibroblasts and exerts immune-mediated anti-cancer effects. IPI-549, an efficient and highly selective phosphoinositide-3-kinase-gamma (PI3Kγ) inhibitor, was applied to alter the balance of immunosuppressive cells by inhibiting PI3Kγ molecules; it also promotes anti-tumor immunity. We developed nanoparticle formulations to encapsulate both drugs into the targeting carrier aminoethyl anisamide-polyethylene glycol-polycaprolactone (AEAA-PEG-PCL) respectively. The drugs were intravenously delivered in mice and resulted in an increase in anti-tumor efficacy and apoptotic tumor tissue compared with either IPI-549 or SLB alone in 4T1 breast cancer cell-derived tumors. Furthermore, a significant reduction in regulatory T (Treg) cells and myeloid suppressor cells (MDSCs) was observed. A normalized TME structure was also observed, including angiogenesis suppression, antifibrotic effects and the inhibition of collagen formation in the tumor tissue, significantly enhancing the anti-tumor effects. In summary, this combination strategy may offer an alternative treatment for breast cancer.

Nano-puerarin regulates tumor microenvironment and facilitates chemo- and immunotherapy in murine triple negative breast cancer model

Tumor associated fibroblasts (TAFs) are key stromal cells mediating the desmoplastic reaction and being partially responsible for the drug-resistance and immunosuppressive microenvironment formation in solid tumors. Delivery of genotoxic drugs off-targetedly to kill TAFs results in production of Wnt16 which renders the neighboring tumor cells drug resistant as shown in our previous study (PMC4623876). Our current approach looks for means to deactivate, rather than kill, TAFs. Reactive oxygen species (ROS) are the central hub of multiple profibrogenic pathways and indispensable for TAFs activation. Herein, puerarin was identified to effectively downregulate ROS production in the activated myofibroblast. In this study, a novel puerarin nanoemulsion (nanoPue) was developed to improve the solubility and bioavailability of puerarin. NanoPue significantly deactivated the stromal microenvironment (e.g., ~6-fold reduction of TAFs in nanoPue treated mice compared with the PBS control, p < 0.0001) and facilitated chemotherapy effect of nano-paclitaxel in the desmoplastic triple-negative breast cancer (TNBC) model. Moreover, the removal of the physical barrier increased intra-tumoral infiltration of cytotoxic T cell by 2-fold. This activated immune microenvironment allowed nanoPue to synergize PD-L1 blockade therapy in TNBC model.

Inhibiting PI3 kinase-γ in both myeloid and plasma cells remodels the suppressive tumor microenvironment in desmoplastic tumors

Phosphoinositide-3-kinases (PI3Ks) are part of signal transducing enzymes that mediate key cellular functions in cancer and immunity. PI3K-γ is crucial for cellular activation and migration in response to certain chemokines. PI3K-γ is highly expressed in myeloid cells and promotes their migration and the production of inflammatory mediators. We found that PI3K-γ was also highly expressed in tumor-associated B cells. IPI-549, the only PI3K-γ inhibitor in clinical development, offers a unique approach to enhance the anti-tumor immune response. We encapsulated IPI-549 in targeted polymeric nanoparticles (NP) and tested its activity in both murine pancreatic cancer and melanoma models. IPI-549 NP significantly decreased tumor growth and prolonged host survival in both models. Importantly, IPI-549 NP treatment reduced the suppressive tumor microenvironment by decreasing both suppressive myeloid and plasma cells in the tumor. We concluded that IPI-549 NP delivery could be a promising method for treating pancreatic cancer and other immune-suppressive tumors.

Relaxin gene delivery mitigates liver metastasis and synergizes with check point therapy

Activated hepatic stellate cell (aHSC)-mediated liver fibrosis is essential to the development of liver metastasis. Here, we discover intra-hepatic scale-up of relaxin (RLN, an anti-fibrotic peptide) in response to fibrosis along with the upregulation of its primary receptor (RXFP1) on aHSCs. The elevated expression of RLN serves as a natural regulator to deactivate aHSCs and resolve liver fibrosis. Therefore, we hypothesize this endogenous liver fibrosis repair mechanism can be leveraged for liver metastasis treatment via enforced RLN expression. To validate the therapeutic potential, we utilize aminoethyl anisamide-conjugated lipid-calcium-phosphate nanoparticles to deliver plasmid DNA encoding RLN. The nanoparticles preferentially target metastatic tumor cells and aHSCs within the metastatic lesion and convert them as an in situ RLN depot. Expressed RLN reverses the stromal microenvironment, which makes it unfavorable for established liver metastasis to grow. In colorectal, pancreatic, and breast cancer liver metastasis models, we confirm the RLN gene therapy results in significant inhibition of metastatic progression and prolongs survival. In addition, enforced RLN expression reactivates intra-metastasis immune milieu. The combination of the RLN gene therapy with PD-L1 blockade immunotherapy further produces a synergistic anti-metastatic efficacy. Collectively, the targeted RLN gene therapy represents a highly efficient, safe, and versatile anti-metastatic modality, and is promising for clinical translation.

Locally Trapping the C-C Chemokine Receptor Type 7 by Gene Delivery Nanoparticle Inhibits Lymphatic Metastasis Prior to Tumor Resection

Triple negative breast cancer (TNBC) is the most aggressive breast cancer subtype. Currently, no targeted treatment is available for TNBC, and the most common clinical therapy is tumor resection, which often promotes metastasis risks. Strong evidence suggests that the lymphatic metastasis is mediated by the C-C chemokine receptor type 7 (CCR7)/C-C motif chemokine ligand 21 crosstalk between tumor cells and the lymphatic system. It is hypothesized that CCR7 is a key immune modulator in the tumor microenvironment and the local blockade of CCR7 could effectively inhibit TNBC lymphatic metastasis. Accordingly, a plasmid encoding an antagonistic CCR7 affinity protein-CCR7 trap is delivered by tumor targeting nanoparticles in a highly metastatic 4T1 TNBC mouse model. Results show that CCR7 traps are transiently expressed, locally disrupt the signaling pathways in the tumor site, and efficiently inhibit TNBC lymphatic metastasis, without inducing immunosuppression as observed in systemic therapies using CCR7 monoclonal antibody. Significantly, upon applying CCR7 trap therapy prior to tumor resection, a 4T1 TNBC mouse model shows good prognosis without any further metastasis and relapse. In addition, CCR7 trap therapy efficiently inhibits the lymphatic metastasis in a B16F10 melanoma mouse model, indicating its great potential for various metastatic diseases treatment.

Nanocarrier-Mediated Chemo-Immunotherapy Arrested Cancer Progression and Induced Tumor Dormancy in Desmoplastic Melanoma

In desmoplastic melanoma, tumor cells and tumor-associated fibroblasts are the major dominators playing a critical role in the fibrosis morphology as well as the immunosuppressive tumor microenvironment (TME), compromising the efficacy of therapeutic options. To overcome this therapeutic hurdle, we developed an innovative chemo-immunostrategy based on targeted delivery of mitoxantrone (MIT) and celastrol (CEL), two potent medicines screened and selected with the best anticancer and antifibrosis potentials. Importantly, CEL worked in synergy with MIT to induce immunogenic tumor cell death. Here, we show that when effectively co-delivered to the tumor site at their optimal ratio by a TME-responsive nanocarrier, the 5:1 combination of MIT and CEL significantly triggered immunogenic tumor apoptosis and recovered tumor antigen recognition, thus eliciting overall antitumor immunity. Furthermore, the strong synergy benefitted the host in reduced drug exposure and side effects. Collectively, the nanocarrier-mediated chemo-immunotherapy successfully remodeled fibrotic and immunosuppressive TME, arrested cancer progression, and further inhibited tumor metastasis to major organs. The affected tumors remained dormant long after dosing stopped, resulting in a prolonged progression-free survival and sustained immune surveillance of the host bearing desmoplastic melanoma.

Nano-delivery of fraxinellone remodels tumor microenvironment and facilitates therapeutic vaccination in desmoplastic melanoma

Rationale: Tumor-associated fibroblasts (TAFs) play a critical role in the suppressive immune tumor microenvironment (TME), compromising the efficacy of immunotherapy. To overcome this therapeutic hurdle, we developed a nanoemulsion (NE) formulation to deliver fraxinellone (Frax), an anti-fibrotic medicine, to TAFs, as an approach to reverse immunosuppressive TME of desmoplastic melanoma. Methods: Frax NE was prepared by an ultrasonic emulsification method. The tumor inhibition effect was evaluated by immunofluorescence staining, masson trichrome staining and western blot analysis. Immune cell populations in tumor and LNs were detected by flow cytometry. Results: This Frax NE, with a particle size of around 145 nm, can efficiently accumulate in the tumor site after systemic administration and was taken up by TAFs and tumor cells. A significant decrease in TAFs and stroma deposition was observed after intravenous administration of Frax NE, and Frax NE treatment also remolded the tumor immune microenvironment, as was reflected by an increase of natural-killer cells, cytotoxic T cells (CTLs) as well as a decrease of regulatory B cells, and myeloid-derived suppressor cells in the TME. In addition, after treatment by Frax NEs, T helper 1 (Th1) cytokines of interferon gamma (IFN-γ), which effectively elicit anti-tumor immunity, were enhanced. Transforming growth factor-β (TGF-β), chemokine (C-C motif) ligand 2 (CCL2) and interleukin 6 (IL6), which inhibit the development of anti-tumor immunity, were reduced. Although Frax NE demonstrated an inhibitory effect on tumor growth, this mono-therapy could only achieve partial antitumor efficacy, and the tumor growth effect was not maintained long-term after dosing stopped. Therefore, a tumor-specific peptide vaccine was combined with Frax NEs. The combination led to enhanced tumor-specific T-cell infiltration, activated death receptors on the tumor cell surface, and induced increased apoptotic tumor cell death. Conclusion: Collectively, Frax NE combined with tumor-specific peptide vaccine might be an effective and safe strategy to remodel fibrotic TME, thereby enhancing immune response activation, resulting in a prolonged efficiency for advanced desmoplastic melanoma.