AXTEX-4D: A Three-Dimensional Ex Vivo Platform for Preclinical Investigations of Immunotherapy Agents

The latest advancements in oncology are majorly focused on immuno-oncology (I-O) therapies. However, only ∼7% of drugs are being approved from the preclinical discovery phase to phase 1. The most challenging issues in I-O are the development of active and efficient drugs in an economically feasible way and in a comparatively short time for testing and validation. This mandates an urgent need for the upgradation of preclinical screening models that closely mimic the in vivo tumor microenvironment (TME). The established and most common methods for investigating the tumoricidal activity of I-O drugs are either two-dimensional systems or primary tumor cells in standard tissue culture vessels. Unfortunately, they do not mimic the TME. Consequently, the more in vivo-like three-dimensional (3D) multicellular tumor spheroids are quickly becoming the favored model to examine immune cell-mediated responses in reaction to the administration of I-O drugs. Despite many advantages of multicellular spheroids, challenges (e.g., incompatibility of quantitative assays with spheroid platforms) are still involved in the tedious procedures required for the spheroid culture that is holding back the biological community from adapting the well-recognized spheroid tissue models for studying drug delivery more widely. To this end, we have demonstrated the utility of the 3D ex vivo oncology model, developed on our novel AXTEX-4D^™ platform to assess therapeutic efficacies of I-O drugs by investigating immune cell proliferation, migration, infiltration, cytokine profiling, and cytotoxicity of tumor tissueoids. The platform eliminates the need for additional biomolecules such as hydrogels and instead relies on the cancer cells themselves to create their own gradients and microenvironmental factors. In effect, the more comprehensive and ex vivo-like immune-oncology model developed on AXTEX-4D platform can be utilized for high-throughput screening of immunotherapeutic drugs.

Tumor perfusion enhancement by ultrasound stimulated microbubbles potentiates PD-L1 blockade of MC38 colon cancer in mice

Cancer immunotherapy holds tremendous promise as a strategy for eradicating solid tumors, and its therapeutic effect highly relies on sufficient CD8⁺ T cells infiltration. Here, we demonstrate that ultrasound stimulated microbubble cavitation (USMC) promotes tumor perfusion, thereby increasing CD8⁺ T cells infiltration and anti-PD-L1 antibody delivery, then further enhancing the PD-L1 blockade of MC38 colon cancer in mice. Firstly, we optimized the mechanic index (MI) of ultrasound, and found that USMC with MI of 0.4 (equal to peak negative pressure of 0.8 MPa) significantly improved the peak intensity and area under curve of tumor contrast-enhanced ultrasound. Also, flow cytometry exhibited higher percentage of infiltrating CD8⁺ T cells in the USMC (MI = 0.4)-treated tumors than that of the control. We further explored the combination therapy of optimized USMC with anti-PD-L1 antibody. The combination therapy enhanced tumor perfusion and even led to the tumor vascular normalization. More importantly, flow cytometry showed that the combination not only increased the percentage and absolute number of tumor infiltrating CD8⁺ T cells, but also promoted the expression of Ki67 as well as the secretions of IFN γ and granzyme B, therefore, the combination therapy achieved greater tumor growth inhibition and longer survival than that of the monotherapies. These suggest that USMC is a promising therapeutic modality for combining immune checkpoint blockade against solid tumors.

In Vivo Environment-Adaptive Nanocomplex with Tumor Cell-Specific Cytotoxicity Enhances T Cells Infiltration and Improves Cancer Therapy

Drug delivery strategies possessing selectivity for cancer cells are eagerly needed in therapy of metastatic breast cancer. In this study, the chemotherapeutic agent, docetaxel (DTX), is conjugated onto heparan sulfate (HS). Aspirin (ASP), which has the activity of anti-metastasis and enhancing T cells infiltration in tumors, is encapsulated into the HS-DTX micelle. Then the cationic polyethyleneimine (PEI)-polyethylene glycol (PEG) copolymer binds to HS via electrostatic force, forming the ASP-loaded HS-DTX micelle (AHD)/PEI-PEG nanocomplex (PAHD). PAHD displays long circulation behavior in blood due to the PEG shell. Under the tumor microenvironment with weakly acidic pH, PEI-PEG separates from AHD, and the free cationic PEI-PEG facilitates the cellular uptake of AHD by increasing permeability of cell membranes. Then the overexpressed heparanase degrades HS, releasing ASP and DTX. PAHD shows specific toxicity toward tumor cells but not normal cells, with advanced activity of inhibiting tumor growth and lung metastasis in 4T1 tumor-bearing mice. The number of CD8⁺ T cells in tumor tissues is also increased. Therefore, PAHD can become an efficient drug delivery system for breast cancer treatment.