Analyses of Tumor Burden In Vivo and Metastasis Ex Vivo Using Luciferase-Expressing Cancer Cells in an Orthotopic Mouse Model of Neuroblastoma

KPC-luciferase-expressing cells elicit an anti-tumor immune response in a mouse model of pancreatic cancer

Mouse models for the study of pancreatic ductal adenocarcinoma (PDAC) are well-established and representative of many key features observed in human PDAC. To monitor tumor growth, cancer cells that are implanted in mice are often transfected with reporter genes, such as firefly luciferase (Luc), enabling in vivo optical imaging over time. Since Luc can induce an immune response, we aimed to evaluate whether the expression of Luc could affect the growth of KPC tumors in mice by inducing immunogenicity. Although both cell lines, KPC and Luc transduced KPC (KPC-Luc), had the same proliferation rate, KPC-Luc tumors had significantly smaller sizes or were absent 13 days after orthotopic cell implantation, compared to KPC tumors. This coincided with the loss of bioluminescence signal over the tumor region. Immunophenotyping of blood and spleen from KPC-Luc tumor-bearing mice showed a decreased number of macrophages and CD4+ T cells, and an increased accumulation of natural killer (NK) cells in comparison to KPC tumor mice. Higher infiltration of CD8+ T cells was found in KPC-Luc tumors than in their controls. Moreover, the immune response against Luc peptide was stronger in splenocytes from mice implanted with KPC-Luc cells compared to those isolated from KPC wild-type mice, indicating increased immunogenicity elicited by the presence of Luc in the PDAC tumor cells. These results must be considered when evaluating the efficacy of anti-cancer therapies including immunotherapies in immunocompetent PDAC or other cancer mouse models that use Luc as a reporter for bioluminescence imaging.

Poloxamer-linked prodrug of a topoisomerase I inhibitor SN22 shows efficacy in models of high-risk neuroblastoma with primary and acquired chemoresistance

High‐risk solid tumors continue to pose a tremendous therapeutic challenge due to multidrug resistance. Biological mechanisms driving chemoresistance in high‐risk primary and recurrent disease are distinct: in newly diagnosed patients, non‐response to therapy is often associated with a higher level of tumor “stemness” paralleled by overexpression of the ABCG2 drug efflux pump, whereas in tumors relapsing after non‐curative therapy, poor drug sensitivity is most commonly linked to the dysfunction of the tumor suppressor protein, p53. In this study, we used preclinical models of aggressive neuroblastoma featuring these characteristic mechanisms of primary and acquired drug resistance to experimentally evaluate a macromolecular prodrug of a structurally enhanced camptothecin analog, SN22, resisting ABCG2‐mediated export, and glucuronidation. Together with extended tumor exposure to therapeutically effective drug levels via reversible conjugation to Pluronic F‐108 (PF108), these features translated into rapid tumor regression and long‐term survival in models of both ABCG2‐overexpressing and p53‐mutant high‐risk neuroblastomas, in contrast to a marginal effect of the clinically used camptothecin derivative, irinotecan. Our results demonstrate that pharmacophore enhancement, increased tumor uptake, and optimally stable carrier‐drug association integrated into the design of the hydrolytically activatable PF108‐[SN22]₂ have the potential to effectively combat multiple mechanisms governing chemoresistance in newly diagnosed (chemo‐naïve) and recurrent forms of aggressive malignancies. As a macromolecular carrier‐based delivery system exhibiting remarkable efficacy against two particularly challenging forms of high‐risk neuroblastoma, PF108‐[SN22]₂ can pave the way to a robust and clinically viable therapeutic strategy urgently needed for patients with multidrug‐resistant disease presently lacking effective treatment options.

Nanocarrier-Based Delivery of SN22 as a Tocopheryl Oxamate Prodrug Achieves Rapid Tumor Regression and Extends Survival in High-Risk Neuroblastoma Models

Despite the use of intensive multimodality therapy, the majority of high-risk neuroblastoma (NB) patients do not survive. Without significant improvements in delivery strategies, anticancer agents used as a first-line treatment for high-risk tumors often fail to provide clinically meaningful results in the settings of disseminated, recurrent, or refractory disease. By enhancing pharmacological selectivity, favorably shifting biodistribution, strengthening tumor cell killing potency, and overcoming drug resistance, nanocarrier-mediated delivery of topoisomerase I inhibitors of the camptothecin family has the potential to dramatically improve treatment efficacy and minimize side effects. In this study, a structurally enhanced camptothecin analog, SN22, reversibly coupled with a redox-silent tocol derivative (tocopheryl oxamate) to allow its optimally stable encapsulation and controlled release from PEGylated sub-100 nm nanoparticles (NP), exhibited strong NB cell growth inhibitory activity, translating into rapid regression and durably suppressed regrowth of orthotopic, MYCN-amplified NB tumors. The robust antitumor effects and markedly extended survival achieved in preclinical models recapitulating different phases of high-risk disease (at diagnosis vs. at relapse with an acquired loss of p53 function after intensive multiagent chemotherapy) demonstrate remarkable potential of SN22 delivered in the form of a hydrolytically cleavable superhydrophobic prodrug encapsulated in biodegradable nanocarriers as an experimental strategy for treating refractory solid tumors in high-risk cancer patients.

Suppression of ABCE1-Mediated mRNA Translation Limits N-MYC-Driven Cancer Progression

The ability of the N-MYC transcription factor to drive cancer progression is well demonstrated in neuroblastoma, the most common extracranial pediatric solid tumor, where MYCN amplification heralds a poor prognosis, with only 11% of high-risk patients surviving past 5 years. However, decades of attempts of direct inhibition of N-MYC or its paralogues has led to the conclusion that this protein is "undruggable." Therefore, targeting pathways upregulated by N-MYC signaling presents an alternative therapeutic approach. Here, we show that MYCN-amplified neuroblastomas are characterized by elevated rates of protein synthesis and that high expression of ABCE1, a translation factor directly upregulated by N-MYC, is itself a strong predictor of poor clinical outcome. Despite the potent ability of N-MYC in heightening protein synthesis and malignant characteristics in cancer cells, suppression of ABCE1 alone selectively negated this effect, returning the rate of translation to baseline levels and significantly reducing the growth, motility, and invasiveness of MYCN-amplified neuroblastoma cells and patient-derived xenograft tumors in vivo. The growth of nonmalignant cells or MYCN-nonamplified neuroblastoma cells remained unaffected by reduced ABCE1, supporting a therapeutic window associated with targeting ABCE1. Neuroblastoma cells with c-MYC overexpression also required ABCE1 to maintain cell proliferation and translation. Taken together, ABCE1-mediated translation constitutes a critical process in the progression of N-MYC-driven and c-MYC-driven cancers that warrants investigations into methods of its therapeutic inhibition. SIGNIFICANCE: These findings demonstrate that N-MYC-driven cancers are reliant on elevated rates of protein synthesis driven by heightened expression of ABCE1, a vulnerability that can be exploited through suppression of ABCE1.

Accelerating development of high-risk neuroblastoma patient-derived xenograft models for preclinical testing and personalised therapy

Background

Predictive preclinical models play an important role in the assessment of new treatment strategies and as avatar models for personalised medicine; however, reliable and timely model generation is challenging. We investigated the feasibility of establishing patient-derived xenograft (PDX) models of high-risk neuroblastoma from a range of tumour-bearing patient materials and assessed approaches to improve engraftment efficiency.

Methods

PDX model development was attempted in NSG mice by using tumour materials from 12 patients, including primary and metastatic solid tumour samples, bone marrow, pleural fluid and residual cells from cytogenetic analysis. Subcutaneous, intramuscular and orthotopic engraftment were directly compared for three patients.

Results

PDX models were established for 44% (4/9) of patients at diagnosis and 100% (5/5) at relapse. In one case, attempted engraftment from pleural fluid resulted in an EBV-associated atypical lymphoid proliferation. Xenogeneic graft versus host disease was observed with attempted engraftment from lymph node and bone marrow tumour samples but could be prevented by T-cell depletion. Orthotopic engraftment was more efficient than subcutaneous or intramuscular engraftment.

Conclusions

High-risk neuroblastoma PDX models can be reliably established from diverse sample types. Orthotopic implantation allows more rapid model development, increasing the likelihood of developing an avatar model within a clinically useful timeframe.

Pre-Conditioning the Airways of Mice with Bleomycin Increases the Efficiency of Orthotopic Lung Cancer Cell Engraftment

Lung cancer is a deadly treatment refractory disease that is biologically heterogeneous. To understand and effectively treat the full clinical spectrum of thoracic malignancies, additional animal models that can recapitulate diverse human lung cancer subtypes and stages are needed. Allograft or xenograft models are versatile and enable the quantification of tumorigenic capacity in vivo, using malignant cells of either murine or human origin. However, previously described methods of lung cancer cell engraftment have been performed in non-physiological sites, such as the flank of mice, due to the inefficiency of orthotopic transplantation of cells into the lungs. In this study, we describe a method to enhance orthotopic lung cancer cell engraftment by pre-conditioning the airways of mice with the fibrosis inducing agent bleomycin. As a proof-of-concept experiment, we applied this approach to engraft tumor cells of the lung adenocarcinoma subtype, obtained from either mouse or human sources, into various strains of mice. We demonstrate that injuring the airways with bleomycin prior to tumor cell injection increases the engraftment of tumor cells from 0-17% to 71-100%. Significantly, this method enhanced lung tumor incidence and subsequent outgrowth using different models and mouse strains. In addition, engrafted lung cancer cells disseminate from the lungs into relevant distant organs. Thus, we provide a protocol that can be used to establish and maintain new orthotopic models of lung cancer with limiting amounts of cells or biospecimen and to quantitatively assess the tumorigenic capacity of lung cancer cells in physiologically relevant settings.

Generation of Luciferase-expressing Tumor Cell Lines

Murine tumor models have been critical to advances in our knowledge of tumor physiology and for the development of effective tumor therapies. Essential to these studies is the ability to both track tumor development and quantify tumor burden in vivo. For this purpose, the introduction of genes that confer tumors with bioluminescent properties has been a critical advance for oncologic studies in rodents. Methods of introducing bioluminescent genes, such as firefly luciferase, by viral transduction has allowed for the production of tumor cell lines that can be followed in vivo longitudinally over long periods of time. Here we describe methods for the production of stable luciferase expressing tumor cell lines by lentiviral transduction.

Targeted Doxorubicin-Loaded Bacterially Derived Nano-Cells for the Treatment of Neuroblastoma

Advanced stage neuroblastoma is an aggressive disease with limited treatment options for patients with drug-resistant tumors. Targeted delivery of chemotherapy for pediatric cancers offers promise to improve treatment efficacy and reduce toxicity associated with systemic chemotherapy. The EnGeneIC Dream Vector (EDV^TM) is a nanocell, which can package chemotherapeutic drugs and target tumors via attachment of bispecific proteins to the surface of the nanocell. Phase I trials in adults with refractory tumors have shown an acceptable safety profile. Herein we investigated the activity of EGFR-targeted and doxorubicin-loaded EDV^TM (^EGFREDV^TM_Dox) for the treatment of neuroblastoma. Two independent neuroblastoma cell lines with variable expression of EGFR protein [SK-N-BE(2), high; SH-SY-5Y, low] were used. ^EGFREDV^TM_Dox induced apoptosis in these cells compared to control, doxorubicin, or non-doxorubicin loaded ^EGFREDV^TM In three-dimensional tumor spheroids, imaging and fluorescence life-time microscopy revealed that ^EGFREDV^TM_Dox had a marked enhancement of doxorubicin penetration compared to doxorubicin alone, and improved penetration compared to non-EGFR-targeted EDV^TM_Dox, with enhanced spheroid penetration leading to increased apoptosis. In two independent orthotopic human neuroblastoma xenograft models, short-term studies (28 days) of tumor-bearing mice led to a significant decrease in tumor size in ^EGFREDV^TM_Dox-treated animals compared to control, doxorubicin, or non-EGFR EDV^TM_Dox There was increased TUNEL staining of tumors at day 28 compared to control, doxorubicin, or non-EGFR EDV^TM_Dox Moreover, overall survival was increased in neuroblastoma mice treated with ^EGFREDV^TM_Dox (P < 0007) compared to control. Drug-loaded bispecific-antibody targeted EDVs^TM offer a highly promising approach for the treatment of aggressive pediatric malignancies such as neuroblastoma. Mol Cancer Ther; 17(5); 1012-23. ©2018 AACR.

Nanoparticles for radiooncology: Mission, vision, challenges

Cancer is one of the leading non-communicable diseases with highest mortality rates worldwide. About half of all cancer patients receive radiation treatment in the course of their disease. However, treatment outcome and curative potential of radiotherapy is often impeded by genetically and/or environmentally driven mechanisms of tumor radioresistance and normal tissue radiotoxicity. While nanomedicine-based tools for imaging, dosimetry and treatment are potential keys to the improvement of therapeutic efficacy and reducing side effects, radiotherapy is an established technique to eradicate the tumor cells. In order to progress the introduction of nanoparticles in radiooncology, due to the highly interdisciplinary nature, expertise in chemistry, radiobiology and translational research is needed. In this report recent insights and promising policies to design nanotechnology-based therapeutics for tumor radiosensitization will be discussed. An attempt is made to cover the entire field from preclinical development to clinical studies. Hence, this report illustrates (1) the radio- and tumor-biological rationales for combining nanostructures with radiotherapy, (2) tumor-site targeting strategies and mechanisms of cellular uptake, (3) biological response hypotheses for new nanomaterials of interest, and (4) challenges to translate the research findings into clinical trials.