Khalid Shah talks with StemBook about stem cell-based therapeutics for brain tumors
Khalid Shah heads the Molecular Neurotherapy and Imaging Laboratory at Massachusetts General Hospital where he is also Director of the Stem Cell Therapeutics and Imaging Program. In addition, he is an Associate Professor at Harvard Medical School and Harvard Stem Cell Institute Principal Faculty member. Khalid’s laboratory focuses on creating stem cell-based therapeutics for primary and metastatic brain tumors. StemBook editor, Lisa Girard, spoke with Khalid recently about recent progress in his lab.
Can you tell us about some of the projects that are going on in your lab?
The overall goal of my laboratory is to develop and test novel targeted therapies for cancer. Current projects in my laboratory are focused on engineering different stem cell types (embryonic, adult and induced pluripotent cells) with 1) bi-modal diagnostic proteins to study their tumor homing properties in mouse models of brain tumors; and 2) therapeutic (pro-apoptotic TRAIL, anti-angiogenic TSP-1, anti-proliferative IL-24 and IL-13 targeted pseudomonas exotoxin proteins, immunoconjugates: EGFR nanobody-TRAIL and oncolytic herpes simplex viruses) to study the mechanism based therapeutic effect in different mouse brain tumor (glioblastoma) models that mimic the clinical scenario of tumor aggressiveness, resistance, invasion and metastasis. We are also investigating a new approach to brain tumor treatment using therapeutic stem cells encapsulated in biodegradable, synthetic extracellular matrix (sECM) in mouse models of human brain tumor resection. Inherent to our stem cell therapeutics, we integrate bimodal fluorescent, bioluminescent and PET imaging markers and imaging modalities to study delivery and fate of stem cells and tumors and also pharmacokinetics of therapeutic proteins in real time in vivo.
Those are the same techniques by which you have determined how long they live in the mouse brain?
Yes, the techniques are similar to what we have used before but we are now utilizing different stem cell types that we engineer with therapeutics which specifically target receptors on the surface of both the tumor cells and tumor associated endothelial cells. Based on the molecular profile of the tumor, we then test the therapeutic efficacy of these engineered stem cells in mouse models of brain tumors that mimic the clinical scenario of tumor aggression and resection.
Are some of these methodologies particularly amenable to glioblastomas because of challenges related to delivering traditional therapeutics across the blood brain barrier?
The tumor profile based receptor targeted therapeutic stem cells that we have developed could be utilized to treat any type of cancer cells. However, the techniques we have used to deliver them in mouse models of resected tumors are more amenable to brain tumors. Current treatment for glioblastomas is maximal surgical tumor resection followed by radiation therapy, with concomitant and adjuvant chemotherapy. Despite many preclinical studies, most in vivo glioblastoma models do not mimic the clinical scenario of surgical debulking and instead focus on treating solid intact intracranial tumors. In a recent study we have developed a mouse resection model of glioblastoma which simulates the clinical scenario of glioblastoma resection. We have shown that the release of tumor-selective S-TRAIL from sECM-encapsulated stem cells in the resection cavity eradicates residual tumor cells and significantly increases survival of mice. We have obtained similar data on breast and melanoma tumor cells that metastasize to brain and they do respond to the stem cell-based treatment in a similar way as glioblastoma lines do.
These stem cells that are modified with TRAIL, interferon, etc., presumably have some kind of imaging tag as well? If so, once it transitions into clinical use, how does the FDA approval go, in terms of assaying for effectiveness without the imaging tag?
We’ve developed therapeutic stem cells with and without imaging tags. For pre-clinical studies, as it is necessary to assess the fate of stem cells and their therapeutic efficacy most of our published studies are with stem cells that have imaging tags. For studies that are submitted for IND approval from FDA, we utilize the stem cells without imaging tags and assess their fate and efficacy with conventional imaging methods and immunohistochemistry.
And you are able to get that approval without visualizing the cells?
Most likely we will, we haven’t gotten one yet.
What is it about mesenchymal cells that make them particularly useful? What distinguishes them from other types of stem cells?
MSC migrate to tumors, are non-immunogenic and do not proliferate in the brain or in any other organs. They can also be efficiently transduced with lentiviral vectors to create lines and once transduced, they express proteins at high levels compared to, for example, neural stem cells. I think the biggest advantage of using MSC for cancer therapy is that they can be obtained from the same patient and expanded in culture after their modification.
Is it understood why mesenchymal stem cells migrate toward rapidly proliferating cells?
Extensive studies have shown that migration involves cytokines secreted by MSC that cooperate with G-protein coupled receptor (GPCR) and growth factor receptors on tumor cells. Different cytokine/receptor pairs SDF-1/CXCR4, SCF-c-Kit, HGF/c-Met, VEGF/VEGFR, PDGF/PDGFR, MCP-1/CCR2, and HMGB1/RAGE have been identified. Among these stromal cell-derived factor SDF-1 and its receptor CXC chemokine receptor-4 (CXCR4) are important mediators of stem cell recruitment to tumors. Recently, matrix metalloproteases have been shown to be involved in MSC migration. In our laboratory, we are trying to enhance the migration of MSC by engineering MSC to express CXCR4.
Can you talk a little bit about stem cell encapsulation in cancer therapies?
Cell encapsulation technology refers to immobilization of cells within biocompatible, semipermeable membranes such as hyaluronic acid, alginate, agarose and other polymers. The encapsulation of therapeutic stem cells releasing tumor specific proteins is an important prospect for the treatment of glioblastomas. The recurrence rates of glioblastoma and associated patient mortality are nearly 100%, which is largely attributed to inefficient delivery of many therapeutic molecules to brain tumor cells, due to the blood brain barrier (BBB) and vascular dysfunction in the tumor. One of the approaches to overcoming drug delivery problems to intracranial tumors is to develop on-site means to deliver novel tumor-specific agents. However, in order to effectively deliver such therapeutic agents, methods must be developed to introduce stem cells into the resection cavity while preventing the rapid “wash- out” of a significant number of cells by cerebrospinal fluid (CSF). Additionally, it is critical to allow efficient secretion of anti-glioblastoma therapies and retain the ability of stem cells to migrate from the resection cavity into the parenchyma towards invasive tumor deposits. In our recent study, we investigated a new approach to glioblastoma treatment using NSC and human MSC encapsulated in hyaluronic acid-based biocompatible gel. We found that gel encapsulation of MSC and NSC increased their retention in the tumor resection cavity, permitted tumor-selective migration and release of therapeutic protein TRAIL in clinically relevant mouse tumor model of resection. As the gel is biocompatible and degrades over time, the therapeutic stem cells are free to migrate to tumor deposits that are distant from the primary tumor site. As around 75% of glioblastoma patients undergo tumor resection, this study has enormous implications for developing effective therapies for glioblastomas.We have also encapsulated virus-loaded stem cells and tested their fate in culture and in mouse glioblastoma models.
You also mentioned that you are using viral vectors?
Oncolytic viruses have shown great potential in treating tumors in preclinical studies and among them oncolytic Herpes Simplex Virus (oHSV) is inherently neurotropic and one of the most promising candidates for glioblastoma the. In an ongoing study, we show that MSC loaded oHSV effectively produce oHSV progeny which results in killing of glioblastomas in vitro and in vivo mediated by a dynamic process of oHSV-infection and tumor destruction. We also show that gel encapsulated MSC-loaded oHSV and its pro-apoptotic variant oHSV-TRAIL results in significantly increased anti-glioma efficacy compared to direct injection of purified oHSV in a pre-clinical model of glioblastoma resection.
Thank you for your time, Khalid.