A spontaneous acinar cell carcinoma model for monitoring progression of pancreatic lesions and response to treatment through noninvasive bioluminescence imaging

RNAi-Based Approaches for Pancreatic Cancer Therapy

Pancreatic cancer is one of the most lethal forms of cancer, predicted to be the second leading cause of cancer-associated death by 2025. Despite intensive research for effective treatment strategies and novel anticancer drugs over the past decade, the overall patient survival rate remains low. RNA interference (RNAi) is capable of interfering with expression of specific genes and has emerged as a promising approach for pancreatic cancer because genetic aberrations and dysregulated signaling are the drivers for tumor formation and the stromal barrier to conventional therapy. Despite its therapeutic potential, RNA-based drugs have remaining hurdles such as poor tumor delivery and susceptibility to serum degradation, which could be overcome with the incorporation of nanocarriers for clinical applications. Here we summarize the use of small interfering RNA (siRNA) and microRNA (miRNA) in pancreatic cancer therapy in preclinical reports with approaches for targeting either the tumor or tumor microenvironment (TME) using various types of nanocarriers. In these studies, inhibition of oncogene expression and induction of a tumor suppressive response in cancer cells and surrounding immune cells in TME exhibited a strong anticancer effect in pancreatic cancer models. The review discusses the remaining challenges and prospective strategies suggesting the potential of RNAi-based therapeutics for pancreatic cancer.

Nanoprobe-Based Magnetic Resonance Imaging of Hypoxia Predicts Responses to Radiotherapy, Immunotherapy, and Sensitizing Treatments in Pancreatic Tumors

Accurate diagnosis of tumors and predicting the therapeutic responses are highly demanded in the clinic to improve the treatment efficacy and survival rates. Since hypoxia develops in the progression of tumors and inversely correlates with prognosis and promotes resistance to radiotherapies and immunotherapies, it is a potential marker for therapeutic prediction. Therefore, effective discrimination of tumor hypoxia for predicting therapeutic outcomes is critical. Here, a magnetic resonance imaging (MRI)-based diagnosis strategy using contrast-amplifying nanoprobes that sense tumor acidosis and real-time observation of hypoxic conditions in tumors has been developed, aiming at accurate detection of pancreatic tumors and prediction of therapeutic effects. Our approach selectively probed xenograft, allograft, and transgenic spontaneous models of intractable pancreatic cancer, which lacks standardized predictive markers to identify patients who benefit most from treatments, and effectively discriminated the intratumoral hypoxia levels. By stratification of pancreatic tumors based on quantitative MR imaging of hypoxia, it enabled prediction of the responses to radiotherapy and immune checkpoint inhibitors. Moreover, the nanoprobe-based MRI could monitor hypoxia reduction by tumor normalization treatments, which permits visualizing pancreatic tumors that will respond to immune checkpoint blockade therapy, enhancing the response rate. The results demonstrate the potential of our strategy for accurate tumor diagnosis, patient stratification, and effective therapy.

Illuminating Epigenetics and Inheritance in the Immune System with Bioluminescence

The remarkable process of light emission by living organisms has fascinated mankind for thousands of years. A recent expansion in the repertoire of catalytic luciferase enzymes, coupled with the discovery of the genes and pathways that encode different luciferin substrates, means that bioluminescence imaging (BLI) is set to revolutionize longitudinal and dynamic studies of gene control within biomedicine, including the regulation of immune responses. In this review article, we summarize recent advances in bioluminescence-based imaging approaches that promise to enlighten our understanding of in vivo gene and epigenetic control within the immune system.

In vivo rendezvous of small nucleic acid drugs with charge-matched block catiomers to target cancers

Stabilisation of fragile oligonucleotides, typically small interfering RNA (siRNA), is one of the most critical issues for oligonucleotide therapeutics. Many previous studies encapsulated oligonucleotides into ~100-nm nanoparticles. However, such nanoparticles inevitably accumulate in liver and spleen. Further, some intractable cancers, e.g., tumours in pancreas and brain, have inherent barrier characteristics preventing the penetration of such nanoparticles into tumour microenvironments. Herein, we report an alternative approach to cancer-targeted oligonucleotide delivery using a Y-shaped block catiomer (YBC) with precisely regulated chain length. Notably, the number of positive charges in YBC is adjusted to match that of negative charges in each oligonucleotide strand (i.e., 20). The YBC rendezvouses with a single oligonucleotide in the bloodstream to generate a dynamic ion-pair, termed unit polyion complex (uPIC). Owing to both significant longevity in the bloodstream and appreciably small size (~18 nm), the uPIC efficiently delivers oligonucleotides into pancreatic tumour and brain tumour models, exerting significant antitumour activity.

In Vivo Molecular Bioluminescence Imaging: New Tools and Applications

in vivo bioluminescence imaging (BLi) is an optical molecular imaging technique used to visualize molecular and cellular processes in health and diseases and to follow the fate of cells with high sensitivity using luciferase-based gene reporters. The high sensitivity of this technique arises from efficient photon production, followed by the reaction between luciferase enzymes and luciferin substrates. Novel discoveries and developments of luciferase reporters, substrates, and gene-editing techniques, and emerging fields of applications, promise a new era of deeper and more sensitive molecular imaging.

Novel patient-derived xenograft mouse model for pancreatic acinar cell carcinoma demonstrates single agent activity of oxaliplatin

BACKGROUND

Pancreatic acinar cell carcinoma (PACC) is a rare malignancy, accounting for <1 % of all pancreatic neoplasms. Very few retrospective studies are available to help guide management. We previously reported the case of a patient with metastatic PACC who achieved prolonged survival following doxorubicin treatment. Personalized treatment was based on molecular and in vitro data collected from primary cells developed from their liver metastasis. We now report the characterization of a patient derived tumor xenograft (PDTX) mouse model that originated from this patient's PACC liver metastasis.

METHODS

Fragments of biopsy tissue (5 mm(3)) from PACC liver metastasis were implanted into athymic nude mice. Tumors were grown and passaged from the host mice into new mice to be tested for therapeutic response. Immuno-histochemical (IHC) biomarkers were used to confirm that the PDTX model represents human PACC. The antitumor activities of multiple drugs (5-FU, irinotecan, oxaliplatin, gemcitabine, bevacizumab, erlotinib, doxorubicin and imatinib) were tested. Tumor size was measured over 74 days or until they reached an endpoint volume of ~800 mm(3). Tests to measure serum lipase levels and histological analyses of tumor tissues were also conducted to assess PACC progression and re-differentiation.

RESULTS

The model presented here expresses the same IHC markers found in human PACC. In the chemotherapy study, oxaliplatin produced a prolonged durable growth response associated with increased apoptosis, decreased serum lipase levels and increased healthy acinar cells. Bevacizumab also produced a significant growth response, but the effect was not prolonged as demonstrated by oxaliplatin treatment. The other chemotherapies had moderate to little effect, particularly after treatment ceased. Mutations in DNA repair genes are common in PACC and increase tumor susceptibility to oxaliplatin. To explore this we performed IHC and found no nuclear expression of BRCA2 in our model, indicating a mutation affecting nuclear localization. Gene sequencing confirms BRCA2 has a homozygous gene deletion on Exon 10, which frequently causes a protein truncation.

CONCLUSIONS

In summary, we report the development and characterization of the first and only preclinical PACC PDTX model. Here we show sustained anti-tumor activity of single agent oxaliplatin, a compound that is more effective in tumors that harbor mutations in DNA repair genes. Our data shows that BRCA2 is mutated in our PACC model, which could contribute to the oxaliplatin sensitivity observed. Further studies on this rare PACC model can serve to elucidate other novel therapies, biomarkers, and molecular mechanisms of signaling and drug resistance.

Overexpression of miR-155 in the liver of transgenic mice alters the expression profiling of hepatic genes associated with lipid metabolism

Hepatic expression profiling has revealed miRNA changes in liver diseases, while hepatic miR-155 expression was increased in murine non-alcoholic fatty liver disease, suggesting that miR-155 might regulate the biological process of lipid metabolism. To illustrate the effects of miR-155 gain of function in transgenic mouse liver on lipid metabolism, transgenic mice (i.e., Rm155LG mice) for the conditional overexpression of mouse miR-155 transgene mediated by Cre/lox P system were firstly generated around the world in this study. Rm155LG mice were further crossed to Alb-Cre mice to realize the liver-specific overexpression of miR-155 transgene in Rm155LG/Alb-Cre double transgenic mice which showed the unaltered body weight, liver weight, epididymal fat pad weight and gross morphology and appearance of liver. Furthermore, liver-specific overexpression of miR-155 transgene resulted in significantly reduced levels of serum total cholesterol, triglycerides (TG) and high-density lipoprotein (HDL), as well as remarkably decreased contents of hepatic lipid, TG, HDL and free fatty acid in Rm155LG/Alb-Cre transgenic mice. More importantly, microarray data revealed a general downward trend in the expression profile of hepatic genes with functions typically associated with fatty acid, cholesterol and triglyceride metabolism, which is likely at least partially responsible for serum cholesterol and triglyceride lowering observed in Rm155LG/Alb-Cre mice. In this study, we demonstrated that hepatic overexpression of miR-155 alleviated nonalcoholic fatty liver induced by a high-fat diet. Additionally, carboxylesterase 3/triacylglycerol hydrolase (Ces3/TGH) was identified as a direct miR-155 target gene that is potentially responsible for the partial liver phenotypes observed in Rm155LG/Alb-Cre mice. Taken together, these data from miR-155 gain of function study suggest, for what we believe is the first time, the altered lipid metabolism and provide new insights into the metabolic state of the liver in Rm155LG/Alb-Cre mice.

Opening up the optical imaging window using nano-luciferin

PURPOSE

The objective of this study was to formulate nanoparticles of D-luciferin (Nano-Luc), DiR (Nano-DiR) and dual functional nanoparticles with DiR and luciferin (Nano-LucDiR) for in-vivo imaging as well as tracking of the nanoparticles in tumors.

METHODS

Nano-Luc and Nano-LucDiR were prepared using different lipids, and subsequently characterized for loading and entrapment efficiency, physical properties, release profile, toxicity and stability. We utilized Response Surface Methodology (RSM) to optimize the nanoparticles using design of experiment (DOE Vr.8.0). Nano-Luc was evaluated against free luciferin to establish its pharmacokinetic parameters in mice. In-vivo imaging of tumors and tracking of nanoparticles was carried out with an IVIS® Spectrum-CT (Caliper) using xenograft, orthotopic and metastatic tumor models in BALB/c nude mice with different cell lines and different routes of nanoparticle administration (subcutaneous, intraperitoneal and intravenous).

RESULTS

Particle size of both Nano-Luc and Nano-LucDiR were found to be <200 nm. Nano-Luc formulation showed a slow and controlled release upto 72 h (90%) in vitro. The optimized Nano-Luc had loading efficiency of 5.0 mg/ml with 99% encapsulation efficiency. Nano-Luc and Nano-LucDiR formulations had good shelf stability. Nano-Luc and Nano-LucDiR enhanced plasma half-life of luciferin compared to free luciferin thus providing longer circulation of luciferin in plasma enabling imaging of tumors for more than 24 h. Nano-LucDiR allowed simultaneous bioluminescent and fluorescent imaging to be conducted, with three-dimensional reconstruct of tumors without losing either signal during the acquisition time.

CONCLUSION

Nano-Luc and Nano-LucDiR allowed prolonged reproducible in-vivo imaging of tumors, especially during multimodality 3D imaging.

Versatile and enhanced tumour modelling in mice via somatic cell transduction

Genetically engineered mouse (GEM) models of cancer currently comprise the most accurate way to experimentally recapitulate the human disease in the laboratory. Given recent advances in genomics and genetic screens, however, as well as an increasing urgency for the translation of effective preclinical treatments into the clinic, there is a pressing need to make these models easier and more efficient to work with. Accordingly, we have developed a versatile lentivirus-based approach to induce tumours from somatic cells of GEMs, add or subtract gene expression and render the tumours imageable from a simple breeding stock. The vectors deliver a tamoxifen-inducible and self-inactivating Cre recombinase, conditional bioluminescent and fluorescent proteins and an shRNA component. Following the transduction of somatic cells, tumours are initiated by Cre-mediated recombination of the inherited floxed alleles. Self-inactivation of Cre expression switches on the expression of luciferase, thereby rendering the recombined cells and resulting tumours bioluminescent. We demonstrate proof of concept of this approach by inducing bioluminescent lung tumours in conditional Kras and p53 mice. We also show that a variant vector expressing shRNA alters tumour growth dynamics and the histological grade associated with the inherited genotype. This approach comprises a versatile means to induce imageable and spontaneous tumour burden in mice. The vectors can be readily customized at the bench to modify reporter readout or tumour phenotype without additional transgenic strain development or breeding. They should also be useful for inducing imageable tumours in organs other than the lung, provided that the inherited conditional genotype is sufficiently penetrant.

Bioluminescent imaging of HPV-positive oral tumor growth and its response to image-guided radiotherapy

The treatment paradigms for head and neck squamous cell cancer (HNSCC) are changing due to the emergence of human papillomavirus (HPV)-associated tumors possessing distinct molecular profiles and responses to therapy. Although patients with HNSCCs are often treated with radiotherapy, preclinical models are limited by the ability to deliver precise radiation to orthotopic tumors and to monitor treatment responses accordingly. To better model this clinical scenario, we developed a novel autochthonous HPV-positive oral tumor model to track responses to small molecules and image-guided radiation. We used a tamoxifen-regulated Cre recombinase system to conditionally express the HPV oncogenes E6 and E7 as well as a luciferase reporter (iHPV-Luc) in the epithelial cells of transgenic mice. In the presence of activated Cre recombinase, luciferase activity, and by proxy, HPV oncogenes were induced to 11-fold higher levels. In triple transgenic mice containing the iHPV-Luc, K14-CreER(tam), and LSL-Kras transgenes, tamoxifen treatment resulted in oral tumor development with increased bioluminescent activity within 6 days that reached a maximum of 74.8-fold higher bioluminescence compared with uninduced mice. Oral tumors expressed p16 and MCM7, two biomarkers associated with HPV-positive tumors. After treatment with rapamycin or image-guided radiotherapy, tumors regressed and possessed decreased bioluminescence. Thus, this novel system enables us to rapidly visualize HPV-positive tumor growth to model existing and new interventions using clinically relevant drugs and radiotherapy techniques.

Generation of Rm21LG transgenic mice: a powerful tool to generate conditional overexpression of miR-21 that is involved in oncogenesis

miR-21 is highly expressed in a variety of cancers, suggesting that it might play a role in the process of oncogenesis, as supported by it directly causing pre-B cell lymphomas in transgenic mice. Rm21LG transgenic mice for the conditional co-expression of miR-21 and luciferase (Luc) mediated by Cre/lox P system were generated. The homozygous Rm21LG transgenic mice were visually and readily characterized immediately after birth by whole-body fluorescence imaging. More importantly, miR-21 and Luc were successfully activated in the liver of Rm21LG/Alb-Cre double-transgenic mice, demonstrating that Rm21LG conditional transgenic system could work in a Cre-dependent manner. The combined use of this conditional miR-21 transgenic mouse line, various cell/tissue-specific Cre mouse lines and bioluminescence imaging will be a valuable tool in vivo to uncover the functions of miR-21 as oncomiR in initiating tumors.

Targeted therapy of spontaneous murine pancreatic tumors by polymeric micelles prolongs survival and prevents peritoneal metastasis

Nanoscaled drug-loaded carriers are of particular interest for efficient tumor therapy as numerous studies have shown improved targeting and efficacy. Nevertheless, most of these studies have been performed against allograft and xenograft tumor models, which have altered microenvironment features affecting the accumulation and penetration of nanocarriers. Conversely, the evaluation of nanocarriers on genetically engineered mice, which can gradually develop clinically relevant tumors, permits the validation of their design under normal processes of immunity, angiogenesis, and inflammation. Therefore, considering the poor prognosis of pancreatic cancer, we used the elastase 1-promoted luciferase and Simian virus 40 T and t antigens transgenic mice, which develop spontaneous bioluminescent pancreatic carcinoma, and showed that long circulating micellar nanocarriers, incorporating the parent complex of oxaliplatin, inhibited the tumor growth as a result of their efficient accumulation and penetration in the tumors. The reduction of the photon flux from the endogenous tumor by the micelles correlated with the decrease of serum carbohydrate-associated antigen 19-9 marker. Micelles also reduced the incidence of metastasis and ascites, extending the survival of the transgenic mice.

Analysis of LKB1 mutations and other molecular alterations in pancreatic acinar cell carcinoma

Acinar cell carcinoma is a rare non-ductal neoplasm of the pancreas with poorly defined molecular genetic features. Recently, biallelic inactivation of LKB1 was described in an acinar cell carcinoma of a Peutz-Jeghers patient carrying a heterozygous germline LKB1 mutation, and inhibition of mTOR signaling resulted in partial remission of the tumor. To explore the potential of mTOR inhibitors in sporadic acinar cell carcinoma, the LKB1 gene was investigated in five sporadic acinar cell carcinomas by sequence analysis, methylation analysis and mRNA expression. In addition, microsatellite instability and methylation of a number of tumor suppressor genes were investigated and KRAS, TP53, CDKN1A, SMAD4 and CTNNB1 were studied by mutation analysis and immunohistochemistry. No mutations, deletions or promoter hypermethylation of LKB1 were found in any of the sporadic acinar cell carcinomas, and mRNA expression of LKB1 was not altered. Amplifications at chromosome 20q and 19p were found in 100 and 80% of the cases, respectively. In addition, hypermethylation of one or more tumor suppressor genes was found in 80% of cases. One case harbored a TP53 mutation, and expression of SMAD4 and CTNNB1 was altered in one case each. No KRAS mutations or microsatellite instability were found. To conclude, no evidence for a role for LKB1 in tumorigenesis of sporadic pancreatic acinar cell carcinoma was found. However, copy number variations and hypermethylation were found in a majority of cases. Molecular pathways involved in acinar cell carcinoma-tumorigenesis differ from those involved in ductal pancreatic neoplasms. Further studies are needed to increase our understanding of molecular pathogenesis of acinar cell carcinoma, which may eventually result in development of new therapeutic targets.

The ARF tumor suppressor inhibits tumor cell colonization independent of p53 in a novel mouse model of pancreatic ductal adenocarcinoma metastasis

Pancreatic ductal adenocarcinoma (PDAC) is an incurable, highly metastatic disease that is largely resistant to existing treatments. A better understanding of the genetic basis of PDAC metastasis should facilitate development of improved therapies. To that end, we developed a novel mouse xenograft model of PDAC metastasis to expedite testing of candidate genes associated with the disease. Human PDAC cell lines BxPC-3, MiaPaCa-2, and Panc-1 stably expressing luciferase were generated and introduced by intracardiac injections into immunodeficient mice to model hematogenous dissemination of cancer cells. Tumor development was monitored by bioluminescence imaging. Bioluminescent MiaPaCa-2 cells most effectively recapitulated PDAC tumor development and metastatic distribution in vivo. Tumors formed in nearly 90% of mice and in multiple tissues, including normal sites of PDAC metastasis. Effects of p14ARF, a known suppressor of PDAC, were tested to validate the model. In vitro, p14ARF acted through a CtBP2-dependent, p53-independent pathway to inhibit MiaPaCa-2-invasive phenotypes, which correlated with reduced tumor cell colonization in vivo. These findings establish a new bioluminescent mouse tumor model for rapidly assessing the biological significance of suspected PDAC metastasis genes. This system may also provide a valuable platform for testing innovative therapies.