Neural stem cell-mediated enzyme/prodrug therapy for glioma: preclinical studies

High-grade gliomas are extremely difficult to treat because they are invasive and therefore not curable by surgical resection; the toxicity of current chemo- and radiation therapies limits the doses that can be used. Neural stem cells (NSCs) have inherent tumor-tropic properties that enable their use as delivery vehicles to target enzyme/prodrug therapy selectively to tumors. We used a cytosine deaminase (CD)-expressing clonal human NSC line, HB1.F3.CD, to home to gliomas in mice and locally convert the prodrug 5-fluorocytosine to the active chemotherapeutic 5-fluorouracil. In vitro studies confirmed that the NSCs have normal karyotype, tumor tropism, and CD expression, and are genetically and functionally stable. In vivo biodistribution studies demonstrated NSC retention of tumor tropism, even in mice pretreated with radiation or dexamethasone to mimic clinically relevant adjuvant therapies. We evaluated safety and toxicity after intracerebral administration of the NSCs in non-tumor-bearing and orthotopic glioma-bearing immunocompetent and immunodeficient mice. We detected no difference in toxicity associated with conversion of 5-fluorocytosine to 5-fluorouracil, no NSCs outside the brain, and no histological evidence of pathology or tumorigenesis attributable to the NSCs. The average tumor volume in mice that received HB1.F3.CD NSCs and 5-fluorocytosine was about one-third that of the average volume in control mice. On the basis of these results, we conclude that combination therapy with HB1.F3.CD NSCs and 5-fluorocytosine is safe, nontoxic, and effective in mice. These data have led to approval of a first-in-human study of an allogeneic NSC-mediated enzyme/prodrug-targeted cancer therapy in patients with recurrent high-grade glioma.

Neural stem cells improve intracranial nanoparticle retention and tumor-selective distribution

AIM

The purpose of this work is to determine if tumor-tropic neural stem cells (NSCs) can improve the tumor-selective distribution and retention of nanoparticles (NPs) within invasive brain tumors.

MATERIALS & METHODS

Streptavidin-conjugated, polystyrene NPs are surface-coupled to biotinylated human NSCs. These NPs are large (798 nm), yet when conjugated to tropic cells, they are too large to passively diffuse through brain tissue or cross the blood-tumor barrier. NP distribution and retention was quantified 4 days after injections located either adjacent to an intracerebral glioma, in the contralateral hemisphere, or intravenously.

RESULTS & CONCLUSION

In all three in vivo injection paradigms, NSC-coupled NPs exhibited significantly improved tumor-selective distribution and retention over free-NP suspensions. These results provide proof-of-principle that NSCs can facilitate the tumor-selective distribution of NPs, a platform useful for improving intracranial drug delivery.

Intraperitoneal Administration of Neural Stem Cell-Nanoparticle Conjugates Targets Chemotherapy to Ovarian Tumors

Ovarian cancer is particularly aggressive once it has metastasized to the abdominal cavity (stage III). Intraperitoneal (IP) as compared to intravenous (IV) administration of chemotherapy improves survival for stage III ovarian cancer, demonstrating that concentrating chemotherapy at tumor sites has therapeutic benefit; unfortunately, IP therapy also increases toxic side effects, thus preventing its completion in many patients. The ability to target chemotherapy selectively to ovarian tumors while sparing normal tissue would improve efficacy and decrease toxicities. We have previously shown that tumor-tropic neural stem cells (NSCs) dramatically improve the intratumoral distribution of nanoparticles (NPs) when given intracerebrally near an orthotopic brain tumor or into a flank xenograft tumor. Here, we show that NPs either conjugated to the surface of NSCs or loaded within the cells are selectively delivered to and distributed within ovarian tumors in the abdominal cavity following IP injection, with no evidence of localization to normal tissue. IP administration is significantly more effective than IV administration, and NPs carried by NSCs show substantially deeper penetration into tumors than free NPs. The NSCs and NPs target and localize to ovarian tumors within 1 h of administration. Pt-loaded silica NPs (SiNP[Pt]) were developed that can be transported in NSCs, and it was found that the NSC delivery of SiNP[Pt] (NSC-SiNP[Pt]) results in higher levels of Pt in tumors as compared to free drug or SiNP[Pt]. To the best of our knowledge, this work represents the first demonstration that cells given IP can target the delivery of drug-loaded NPs.

Quantitative Evaluation of Intraventricular Delivery of Therapeutic Neural Stem Cells to Orthotopic Glioma

Neural stem cells (NSCs) are inherently tumor-tropic, which allows them to migrate through normal tissue and selectively localize to invasive tumor sites in the brain. We have engineered a clonal, immortalized allogeneic NSC line (HB1.F3.CD21; CD-NSCs) that maintains its stem-like properties, a normal karyotype and is HLA Class II negative. It is genetically and functionally stable over time and multiple passages, and has demonstrated safety in phase I glioma trials. These properties enable the production of an "off-the-shelf" therapy that can be readily available for patient treatment. There are multiple factors contributing to stem cell tumor-tropism, and much remains to be elucidated. The route of NSC delivery and the distribution of NSCs at tumor sites are key factors in the development of effective cell-based therapies. Stem cells can be engineered to deliver and/or produce many different therapeutic agents, including prodrug activating enzymes (which locally convert systemically administered prodrugs to active chemotherapeutic agents); oncolytic viruses; tumor-targeted antibodies; therapeutic nanoparticles; and extracellular vesicles that contain therapeutic oligonucleotides. By targeting these therapeutics selectively to tumor foci, we aim to minimize toxicity to normal tissues and maximize therapeutic benefits. In this manuscript, we demonstrate that NSCs administered via intracerebral/ventricular (IVEN) routes can migrate efficiently toward single or multiple tumor foci. IVEN delivery will enable repeat administrations for patients through an Ommaya reservoir, potentially resulting in improved therapeutic outcomes. In our preclinical studies using various glioma lines, we have quantified NSC migration and distribution in mouse brains and have found robust migration of our clinically relevant HB1.F3.CD21 NSC line toward invasive tumor foci, irrespective of their origin. These results establish proof-of-concept and demonstrate the potential of developing a multitude of therapeutic options using modified NSCs.

Human Neural Stem Cell Biodistribution and Predicted Tumor Coverage by a Diffusible Therapeutic in a Mouse Glioma Model

Engineered neural stem cells (NSCs) intrinsically migrating to brain tumors offer a promising mechanism for local therapeutic delivery. However, difficulties in quantitative assessments of NSC migration and in estimates of tumor coverage by diffusible therapeutics have impeded development and refinement of NSC-based therapies. To address this need, we developed techniques by which conventional serial-sectioned formalin-fixed paraffin-embedded (FFPE) brains can be analyzed in their entirety across multiple test animals. We considered a conventional human glioblastoma model: U251 glioma cells orthotopically engrafted in immunodeficient mice receiving intracerebral (i.c.) or intravenous (i.v.) administrations of NSCs expressing a diffusible enzyme to locally catalyze chemotherapeutic formation. NSC migration to tumor sites was dose-dependent, reaching 50%-60% of total administered NSCs for the i.c route and 1.5% for the i.v. route. Curiously, the most efficient NSC homing was seen with smaller NSC doses, implying existence of rate-limiting process active during administration and/or migration. Predicted tumor exposure to a diffusing therapeutic (assuming a 50 µm radius of action) could reach greater than 50% of the entire tumor volume for i.c. and 25% for i.v. administration. Within individual sections, coverage of tumor area could be as high as 100% for i.c. and 70% for i.v. routes. Greater estimated therapeutic coverage was observed for larger tumors and for larger tumor regions in individual sections. Overall, we have demonstrated a framework within which investigators may rationally evaluate NSC migration to, and integration into, brain tumors, and therefore enhance understanding of mechanisms that both promote and limit this therapeutic modality. Stem Cells Translational Medicine 2017;6:1522-1532.

L-MYC Expression Maintains Self-Renewal and Prolongs Multipotency of Primary Human Neural Stem Cells

Pre-clinical studies indicate that neural stem cells (NSCs) can limit or reverse CNS damage through direct cell replacement, promotion of regeneration, or delivery of therapeutic agents. Immortalized NSC lines are in growing demand due to the inherent limitations of adult patient-derived NSCs, including availability, expandability, potential for genetic modifications, and costs. Here, we describe the generation and characterization of a new human fetal NSC line, immortalized by transduction with L-MYC (LM-NSC008) that in vitro displays both self-renewal and multipotent differentiation into neurons, oligodendrocytes, and astrocytes. These LM-NSC008 cells were non-tumorigenic in vivo, and migrated to orthotopic glioma xenografts in immunodeficient mice. When administered intranasally, LM-NSC008 distributed specifically to sites of traumatic brain injury (TBI). These data support the therapeutic development of immortalized LM-NSC008 cells for allogeneic use in TBI and other CNS diseases.

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The generation of a new human fetal L-MYC-immortalized NSC line is described

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These NSCs display self-renewal and can differentiate into neurons and glia

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The NSCs can target glioma xenografts and sites of traumatic brain injury in mice

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This NSC line may become applicable in therapy of various CNS diseases

Bcl-2 Overexpression Improves Survival and Efficacy of Neural Stem Cell-Mediated Enzyme Prodrug Therapy

Tumor-tropic neural stem cells (NSCs) can be engineered to localize gene therapies to invasive brain tumors. However, like other stem cell-based therapies, survival of therapeutic NSCs after transplantation is currently suboptimal. One approach to prolonging cell survival is to transiently overexpress an antiapoptotic protein within the cells prior to transplantation. Here, we investigate the utility and safety of this approach using a clinically tested, v-myc immortalized, human NSC line engineered to contain the suicide gene, cytosine deaminase (CD-NSCs). We demonstrate that both adenoviral- and minicircle-driven expression of the antiapoptotic protein Bcl-2 can partially rescue CD-NSCs from transplant-associated insults. We further demonstrate that the improved CD-NSC survival afforded by transient Bcl-2 overexpression results in decreased tumor burden in an orthotopic xenograft glioma mouse model following administrations of intracerebral CD-NSCs and systemic prodrug. Importantly, no evidence of CD-NSC transformation was observed upon transient overexpression of Bcl-2. This research highlights a critical need to develop clinically relevant strategies to improve survival of therapeutic stem cell posttransplantation. We demonstrate for the first time in this disease setting that improving CD-NSC survival using Bcl-2 overexpression can significantly improve therapeutic outcomes.

Intrinsic suppression of type I interferon production underlies the therapeutic efficacy of IL-15-producing natural killer cells in B-cell acute lymphoblastic leukemia

BACKGROUND

Type I interferons (IFN-Is), secreted by hematopoietic cells, drive immune surveillance of solid tumors. However, the mechanisms of suppression of IFN-I-driven immune responses in hematopoietic malignancies including B-cell acute lymphoblastic leukemia (B-ALL) are unknown.

METHODS

Using high-dimensional cytometry, we delineate the defects in IFN-I production and IFN-I-driven immune responses in high-grade primary human and mouse B-ALLs. We develop natural killer (NK) cells as therapies to counter the intrinsic suppression of IFN-I production in B-ALL.

RESULTS

We find that high expression of IFN-I signaling genes predicts favorable clinical outcome in patients with B-ALL, underscoring the importance of the IFN-I pathway in this malignancy. We show that human and mouse B-ALL microenvironments harbor an intrinsic defect in paracrine (plasmacytoid dendritic cell) and/or autocrine (B-cell) IFN-I production and IFN-I-driven immune responses. Reduced IFN-I production is sufficient for suppressing the immune system and promoting leukemia development in mice prone to MYC-driven B-ALL. Among anti-leukemia immune subsets, suppression of IFN-I production most markedly lowers the transcription of IL-15 and reduces NK-cell number and effector maturation in B-ALL microenvironments. Adoptive transfer of healthy NK cells significantly prolongs survival of overt ALL-bearing transgenic mice. Administration of IFN-Is to B-ALL-prone mice reduces leukemia progression and increases the frequencies of total NK and NK-cell effectors in circulation. Ex vivo treatment of malignant and non-malignant immune cells in primary mouse B-ALL microenvironments with IFN-Is fully restores proximal IFN-I signaling and partially restores IL-15 production. In B-ALL patients, the suppression of IL-15 is the most severe in difficult-to-treat subtypes with MYC overexpression. MYC overexpression promotes sensitivity of B-ALL to NK cell-mediated killing. To counter the suppressed IFN-I-induced IL-15 production in MYC^high human B-ALL, we CRISPRa-engineered a novel human NK-cell line that secretes IL-15. CRISPRa IL-15-secreting human NK cells kill high-grade human B-ALL in vitro and block leukemia progression in vivo more effectively than NK cells that do not produce IL-15.

CONCLUSION

We find that restoration of the intrinsically suppressed IFN-I production in B-ALL underlies the therapeutic efficacy of IL-15-producing NK cells and that such NK cells represent an attractive therapeutic solution for the problem of drugging MYC in high-grade B-ALL.

Silica Coated Paclitaxel Nanocrystals Enable Neural Stem Cell Loading For Treatment of Ovarian Cancer

Ovarian cancer is commonly diagnosed only after it has metastasized to the abdominal cavity (stage III). While the current standard of care of intraperitoneal (IP) administration of cisplatin and paclitaxel (PTX) combination chemotherapy has benefit, patient 5-year survival rates are low and have not significantly improved in the past decade. The ability to target chemotherapy selectively to ovarian tumors while sparing normal tissue would improve efficacy and decrease toxicities. We have previously shown that cisplatin-loaded nanoparticles (NPs) loaded within neural stem cells (NSCs) are selectively delivered to ovarian tumors in the abdominal cavity following IP injection, with no evidence of localization to normal tissue. Here we extended the capabilities of this system to also include PTX delivery. NPs that will be loaded into NSCs must contain a high amount of drug by weight but constrain the release of the drug such that the NSCs are viable after loading and can successfully migrate to tumors. We developed silica coated PTX nanocrystals (Si[PTX-NC]) meeting these requirements. Si[PTX-NC] were more effective than uncoated PTX-NC or Abraxane for loading NSCs with PTX. NSCs loaded with Si[PTX-NC] maintained their migratory ability and, for low dose PTX, were more effective than free PTX-NC or Si[PTX-NC] at killing ovarian tumors in vivo. This work demonstrates that NSC/NP delivery is a platform technology amenable to delivering different therapeutics and enables the pursuit of NSC/NP targeted delivery of the entire preferred chemotherapy regimen for ovarian cancer. It also describes efficient silica coating chemistry for PTX nanocrystals that may have applications beyond our focus on NSC transport.

Isoform-specific knockdown of long and intermediate prolactin receptors interferes with evolution of B-cell neoplasms

Prolactin (PRL) is elevated in B-cell-mediated lymphoproliferative diseases and promotes B-cell survival. Whether PRL or PRL receptors drive the evolution of B-cell malignancies is unknown. We measure changes in B cells after knocking down the pro-proliferative, anti-apoptotic long isoform of the PRL receptor (LFPRLR) in vivo in systemic lupus erythematosus (SLE)- and B-cell lymphoma-prone mouse models, and the long plus intermediate isoforms (LF/IFPRLR) in human B-cell malignancies. To knockdown LF/IFPRLRs without suppressing expression of the counteractive short PRLR isoforms (SFPRLRs), we employ splice-modulating DNA oligomers. In SLE-prone mice, LFPRLR knockdown reduces numbers and proliferation of pathogenic B-cell subsets and lowers the risk of B-cell transformation by downregulating expression of activation-induced cytidine deaminase. LFPRLR knockdown in lymphoma-prone mice reduces B-cell numbers and their expression of BCL2 and TCL1. In overt human B-cell malignancies, LF/IFPRLR knockdown reduces B-cell viability and their MYC and BCL2 expression. Unlike normal B cells, human B-cell malignancies secrete autocrine PRL and often express no SFPRLRs. Neutralization of secreted PRL reduces the viability of B-cell malignancies. Knockdown of LF/IFPRLR reduces the growth of human B-cell malignancies in vitro and in vivo. Thus, LF/IFPRLR knockdown is a highly specific approach to block the evolution of B-cell neoplasms.