You are hereJuly 9, 2020
Gene Edited and Engineered Cell-based Therapeutics for Cancer
Discussion of stem cells and cancer cell-based therapeutics that have been tested in mouse models of cancer in recent years and are quickly moving toward translation.
Co-Chairs and Speakers
Massimo Dominici - Engineering MSCs Against Tumors
Massimo Dominici began his talk with a discussion of his work regarding using mesenchymal stem cells (MSCs) as autologous anti-tumor agents, given the inherent ability of MSCs to target tumors after administration. The sampling of MSCs from patients followed by their modification with anti-cancer agent encoding genes and their subsequent expansion provides a treatment option for patients suffering from cancers such as sarcomas, pancreatic cancer, or glioblastoma. The choice to focus on pancreatic ductal adenocarcinoma (PDAC) came from the resistance of this tumor type to conventional treatments, its low 5-year survival rate, and a lack of significant improvements over the last 30 years.
The gene modification of choice, in this case, was designed to induce the expression of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) from MSCs; the TRAIL protein functions as a ligand for death receptors DR4 and 5, which activate caspases to induce apoptosis. The first iteration of TRAIL-modified MSCs as an anti-cancer agent employed a membrane-bound TRAIL form that required cell-cell contact for apoptosis; however, the subsequent development of MSCs secreting a soluble form of TRAIL (sTRAIL) allowed this therapeutic approach to impact both the PDAC tumor cells and the tumor microenvironment. In vitro and in vivo mouse model analyses provided evidence for the improved anti-tumor efficacy of this MSC-based approach, which the authors again significantly improved by combining this strategy with exposure to a common chemotherapeutic (gemcitabine).
The next step involved the analysis of TRAIL-resistance PDAC cells, which highlighted the potential of paclitaxel as part of an improved combination therapy thanks to its ability to reverse TRAIL resistance. As this reversion included the significant repression of high levels of NF-kB expression observed in PDAC, the authors also developed another effective combination therapy using DHMEQ, an NF-kB inhibitor, in combination with TRAIL-secreting MSCs. Moving their combination approaches in vivo, the team discovered that the treatment of mice with TRAIL-secreting MSCs and a nanoparticle albumin form of paclitaxel (Abraxane) led to a significant reduction in tumor size when compared with single therapy treatments. To further analyze the ability of TRAIL-secreting MSCs and chemotherapeutics to efficiently treat PDAC, the authors evaluated the treatment of PDAC cells within a three-dimensional bioreactor that aims to recreate tumor tissue. Chemotherapeutic treatment followed a day later by the application of TRAIL-secreting MSCs led to an almost perfect cell targeting efficiency in both TRAIL-resistant and non-resistant PDAC cells.
Massimo Dominici has employed this robust preclinical evidence to plan clinical trials in the hope of developing an approach that will allow for early systemic and targeted treatment, effective local treatment, and faster and radical surgical removal in PDAC patients.
Moving to another cell-based anti-tumor strategy, Massimo Dominici next described their work regarding the development of chimeric antigen receptor T cells (CAR-T cells) that target the GD2-antigen, which has low expression in healthy tissues but is highly overexpressed in some pediatric and adult solid tumors (neuroectoderm-derived tumors, sarcomas, and triple-negative breast cancer).
Their initial in vitro analysis using neuroblastoma cells demonstrated that GD2 CAR-T cells prompted enormous amounts of cell lysis and a massive increase in IFN gamma and TRAIL release. Their subsequent in vivo mouse model-based analysis established the near-complete destruction of a neuroblastoma tumor following GD2 CAR-T cell treatment, and, encouragingly, the team has been able to expand these findings to the treatment of glioblastoma (in cell-based assays). Furthermore, they are now isolating patient-derived glioblastoma cells to analyze the effectiveness of this approach
Finally, the speaker set out to synthesize the two separate parts of the talk by asking, “Can we put CARs on TRAIL?” Specifically, the team set out to generate bifunctional MSCs modified to express membrane-bound or sTRAIL that also carry GD2 CARs. Encouragingly, this approach has seen success in targeting glioblastoma cells, and they are now moving to assess the efficacy in the treatment of Ewing sarcoma lung metastases.
Khalid Shah - Gene Edited and Engineered Edited Cell Therapies for Solid Tumors
Following on from Massimo Dominici’s presentation, Khalid Shah next shared his vision “Translating Biological Therapies into Clinical Care” via the presentation of his team’s research concerning stem cell and cancer cell-based tumor therapies. The presentation began with a discussion of two studies from his laboratory, spanning nearly a decade, showing that engineered human adult MSCs and cancer stem cells both home to tumors in the brain. He highlighted that recent technological advancements, such as CRISPR and improved vectors, have improved the applicability of such approaches to patients.
Khalid Shah also noted that while many cell-based approaches exist, allogenic off-the-shelf therapies are likely to be the way forward—specifically, receptor-targeted therapies for tumors that induce apoptosis or block proliferation in diseases such as glioblastoma. Of note, bottlenecks to the translation of cell-based therapies into a patient-based setting include concerns regarding translatable preclinical models, delivery, safety, and patient stratification, which we need to address in parallel to boost clinical translation. Subsequent research from the Shah laboratory had these bottlenecks in mind while developing advanced therapeutics for glioblastoma, and the team developed a mouse model of glioblastoma resection model that mimicked the clinical scenario of tumor debulking.
Using this model, the team found that MSC administration to the tumor cavity associated with the washout of therapeutic cells; however, the administration of extracellular matrix-encapsulated TRAIL-secreting MSCs led to higher levels of surviving MSCs in the resected tumor cavity and significantly increased mouse survival rates. The team’s next advance in this area was to create bimodal MSCs that expressed both TRAIL and the herpes simplex virus type I thymidine kinase (HSV-TK), whose activity selectively sensitizes cells to ganciclovir and can be in positron emission tomography (PET) using a fluorine-18-labeled acycloguanosine derivative substrate. Furthermore, HSV-TK can function as a safety switch by allowing the removal of MSCs after the fact.
The next question, as was also posed in the previous presentation, was how to deal with TRAIL-resistant tumors. Patient stratification would allow us to know which patients would respond to MSC-based therapies, but based on what? The DR5 receptor can be detected on circulating tumor cells in glioblastoma patients and may, therefore, function as a biomarker. Potential treatments for TRAIL-insensitive tumors include a bivalent EGFR nanobody linked to TRAIL, which binds to DR4/DR5 and EGFR to induce apoptosis via AKT/EGFR signaling-mediated upregulation of DR4/DR5 to allow apoptotic induction.
The final part of this section of the presentation discussed how such approaches could be applied to the treatment of brain micrometastases in conditions such as melanoma and triple-negative breast cancer. The Shah laboratory has now created three important models systems and has tested various MSC-based therapeutics; this research has shown that stem cells home to tumors, release the relevant molecule, and destroy tumors efficiently.
The next section of the presentation dealt with immuno-oncological concerns when targeting glioblastoma. Unfortunately, this tumor type is immunologically quiet, or cold, with the lowest degree of T cell infiltration and the highest number of myeloid-derived suppressor cells (MDSCs) present. Using immunocompetent mouse models, the team discovered that surgical resection of glioblastoma reduces the levels of MDSCs and increases dendritic cells and T cells in the glioblastoma tumor microenvironment, which supported the administration of encapsulated MSCs expressing interferon-beta (pro-apoptotic and immunomodulatory) to diminish leftover tumor cell growth and increase the survival of mice bearing resected glioblastoma. To this end, Khalid Shah hopes to present important data for the next meeting.
The concluding section concerned the use of cancer cells as anti-cancer therapeutics; tumor cells can home to tumors, so why not take advantage of this ability? An autologous approach can use cells derived from a primary tumor surgery to treat a recurrent tumor or even metastasis and involves the creation of a therapy-resistant cancer cell that expresses a pro-apoptotic ligand to induce cell death of other tumor cells after encapsulation and administration and a kill switch to destroy the engineered tumor cell after the fact. The speaker described how encapsulated gene-edited cancer cells have therapeutic efficacy in mouse models of glioblastoma resection, and, again, he hopes to present significant data for the next meeting.
In summary, cell-based receptor-targeted therapies have an enormous potential to be translated into clinical settings, and understanding the mechanisms behind the functioning of therapeutic cells is essential in developing meaningful cell-based therapies. Developing tumor models that mimic the clinical setting of tumor growth will foster the development of cancer therapeutics, while understanding the current treatment regimen for each cancer type is necessary for translating novel therapies into a clinical setting.
The discussion of these talks included the critical factors in TRAIL resistance, one of which is the lack of TRAIL receptors on the target cell. This may be overcome by upregulating receptors through the administration of temozolomide or the downregulated phosphorylation of AKT and EGFR. However, other resistance mechanisms are mediated by caspase 8, which we currently do not have a solution for.
A subsequent question dealt with the clinical translation of glioblastoma therapies; an allogenic approach seems the best choice for two main reasons: an off-the-shelf treatment is better, and enough time does not exist to take glioblastoma patient-derived cells and modify them for autologous anti-cancer therapies before the patient would succumb to the disease.
Finally, what does one need to do at the GMP level to make a treatment happen? The first apparent answers are money and time, but the development of this approach also requires people who know the product and can jump into the industrial side of things, including manufacturing and regulatory steps. Everything must be scaled up, including the culture of the humans in the laboratory, to move from animal models to patients; however, as this process is occurring in numerous labs across the world, collaborations and synergism will help in the battle against cancer.
More from the Speakers
STEM CELLS Translational Medicine - Safety Profile of Good Manufacturing Practice Manufactured Interferon γ‐Primed Mesenchymal Stem/Stromal Cells for Clinical Trials
STEM CELLS Translational Medicine - Challenges in Clinical Development of Mesenchymal Stromal/Stem Cells: Concise Review