Image-aided Suicide Gene Therapy Utilizing Multifunctional hTERT-targeting Adenovirus for Clinical Translation in Hepatocellular Carcinoma

Types of RNA therapeutics

RNA therapy is one of the new treatments using small RNA molecules to target and regulate gene expression. It involves the application of synthetic or modified RNA molecules to inhibit the expression of disease-causing genes specifically. In other words, it silences genes and suppresses the transcription process. The main theory behind RNA therapy is that RNA molecules can prevent the translation into proteins by binding to specific messenger RNA (mRNA) molecules. By targeting disease-related mRNA molecules, RNA therapy can effectively silence or reduce the development of harmful proteins. There are different types of RNA molecules used in therapy, including small interfering RNAs (siRNAs), microRNAs (miRNAs), aptamer, ribozyme, and antisense oligonucleotides (ASOs). These molecules are designed to complement specific mRNA sequences, allowing them to bind and degrade the targeted mRNA or prevent its translation into protein. Nanotechnology is also highlighted to increase the efficacy of RNA-based drugs. In this chapter, while examining various methods of RNA therapy, we discuss the advantages and challenges of each.

Nanomaterial-based CT contrast agents and their applications in image-guided therapy

Computed tomography (CT), a diagnostic tool with clinical application, comprehensive coverage, and low cost, is used in hospitals worldwide. However, CT imaging fails to distinguish soft tissues from normal organs and tumors because their mass attenuation coefficients are similar. Various CT contrast agents have been developed in recent years to improve the sensitivity and contrast of imaging. Here, we review the progress of nanomaterial-based CT contrast agents and their applications in image-guided therapy. The CT contrast agents are classified according to their components; gold (Au)-based, bismuth (Bi)-based, lanthanide (Ln)-based, and transition metal (TM)-based nanomaterials are discussed. CT image-guided therapy of diseases, including photothermal therapy (PPT), photodynamic therapy (PDT), chemotherapy, radiotherapy (RT), gas therapy, sonodynamic therapy (SDT), immunotherapy, starvation therapy, gene therapy (GT), and microwave thermal therapy (MWTT), are reviewed. Finally, the perspectives on the CT contrast agents and their biomedical applications are discussed.

miRNA Pathway Alteration in Response to Non-Coding RNA Delivery in Viral Vector-Based Gene Therapy

Gene therapy is widely used to treat incurable disorders and has become a routine procedure in clinical practice. Since viruses can exhibit specific tropisms, effectively penetrate the cell, and are easy to use, most gene therapy approaches are based on viral delivery of genetic material. However, viral vectors have some disadvantages, such as immune response and cytotoxicity induced by a disturbance of cell metabolism, including miRNA pathways that are an important part of transcription regulation. Therefore, any viral-based gene therapy approach involves the evaluation of side effects and safety. It is possible for such effects to be caused either by the viral vectors themselves or by the delivered genetic material. Many gene therapy techniques use non-coding RNA delivery as an effective agent for gene expression regulation, with the risk of cellular miRNA pathways being affected due to the nature of the non-coding RNAs. This review describes the effect of viral vector entry and non-coding RNA delivery by these vectors on miRNA signaling pathways.

Emerging Therapies for Hepatocellular Carcinoma (HCC)

Hepatocellular carcinoma (HCC) arises from hepatocytes and accounts for 90% of primary liver cancer. According to Global Cancer Incidence, Mortality and Prevalence (GLOBOCAN) 2020, globally HCC is the sixth most common cancer and the third most common cause of cancer-related deaths. Reasons for HCC prognosis remaining dismal are that HCC is asymptomatic in its early stages, leading to late diagnosis, and it is markedly resistant to conventional chemo- and radiotherapy. Liver transplantation is the treatment of choice in early stages, while surgical resection, radiofrequency ablation (RFA) and trans arterial chemoembolization (TACE) are Food and Drug Administration (FDA)-approved treatments for advanced HCC. Additional first line therapy for advanced HCC includes broad-spectrum tyrosine kinase inhibitors (TKIs), such as sorafenib and lenvatinib, as well as a combination of immunotherapy and anti-angiogenesis therapy, namely atezolizumab and bevacizumab. However, these strategies provide nominal extension in the survival curve, cause broad spectrum toxic side effects, and patients eventually develop therapy resistance. Some common mutations in HCC, such as in telomerase reverse transcriptase (TERT), catenin beta 1 (CTNNB1) and tumor protein p53 (TP53) genes, are still considered to be undruggable. In this context, identification of appropriate gene targets and specific gene delivery approaches create the potential of gene- and immune-based therapies for the safe and effective treatment of HCC. This review elaborates on the current status of HCC treatment by focusing on potential gene targets and advanced techniques, such as oncolytic viral vectors, nanoparticles, chimeric antigen receptor (CAR)-T cells, immunotherapy, and clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 9 (CRISPR/Cas9), and describes future prospects in HCC treatment.

Drug delivery strategy in hepatocellular carcinoma therapy

Hepatocellular carcinoma (HCC) is one of the most common malignant tumors worldwide, with high rates of recurrence and death. Surgical resection and ablation therapy have limited efficacy for patients with advanced HCC and poor liver function, so pharmacotherapy is the first-line option for those patients. Traditional antitumor drugs have the disadvantages of poor biological distribution and pharmacokinetics, poor target selectivity, high resistance, and high toxicity to nontargeted tissues. Recently, the development of nanotechnology has significantly improved drug delivery to tumor sites by changing the physical and biological characteristics of drugs and nanocarriers to improve their pharmacokinetics and biological distribution and to selectively accumulate cytotoxic agents at tumor sites. Here, we systematically review the tumor microenvironment of HCC and the recent application of nanotechnology in HCC.

Non-Canonical Splicing and Its Implications in Brain Physiology and Cancer

The advance of experimental and computational techniques has allowed us to highlight the existence of numerous different mechanisms of RNA maturation, which have been so far unknown. Besides canonical splicing, consisting of the removal of introns from pre-mRNA molecules, non-canonical splicing events may occur to further increase the regulatory and coding potential of the human genome. Among these, splicing of microexons, recursive splicing and biogenesis of circular and chimeric RNAs through back-splicing and trans-splicing processes, respectively, all contribute to expanding the repertoire of RNA transcripts with newly acquired regulatory functions. Interestingly, these non-canonical splicing events seem to occur more frequently in the central nervous system, affecting neuronal development and differentiation programs with important implications on brain physiology. Coherently, dysregulation of non-canonical RNA processing events is associated with brain disorders, including brain tumours. Herein, we summarize the current knowledge on molecular and regulatory mechanisms underlying canonical and non-canonical splicing events with particular emphasis on cis-acting elements and trans-acting factors that all together orchestrate splicing catalysis reactions and decisions. Lastly, we review the impact of non-canonical splicing on brain physiology and pathology and how unconventional splicing mechanisms may be targeted or exploited for novel therapeutic strategies in cancer.

Dendrimer-modified gold nanorods as a platform for combinational gene therapy and photothermal therapy of tumors

Background

The exploitation of novel nanomaterials combining diagnostic and therapeutic functionalities within one single nanoplatform is challenging for tumor theranostics.

Methods

We synthesized dendrimer-modified gold nanorods for combinational gene therapy and photothermal therapy (PTT) of colon cancer. Poly(amidoamine) dendrimers (PAMAM, G3) grafted gold nanorods were modified with GX1 peptide (a cyclic 7-mer peptide, CGNSNPKSC). The obtained Au NR@PAMAM-GX1 are proposed as a gene delivery vector to gene (FAM172A, regulates the proliferation and apoptosis of colon cancer cells) for the combination of photothermal therapy (PTT) and gene therapy of Colon cancer cells (HCT-8 cells). In addition, the CT imaging function of Au NR can provide imaging evidence for the diagnosis of colon cancer.

Results

The results display that Au NR@PAMAM-GX1 can specifically deliver FAM172A to cancer cells with excellent transfection efficiency. The HCT-8 cells treated with the Au NR@PAMAM-GX1/FAM172A under laser irradiation have a viability of 20.45%, which is much lower than the survival rate of other single-mode PTT treatment or single-mode gene therapy. Furthermore, animal experiment results confirm that Au NR@PAMAM-GX1/FAM172A complexes can achieve tumor thermal imaging, targeted CT imaging, PTT and gene therapy after tail vein injection.

Conclusion

Our findings demonstrate that the synthesized Au NR@PAMAM-GX1 offer a facile platform to exert antitumor and improve the diagnostic level of tumor.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-021-02105-3.

Therapeutic applications of trans-splicing

BACKGROUND

RNA trans-splicing joins exons from different pre-mRNA transcripts to generate a chimeric product. Trans-splicing can also occur at the protein level, with split inteins mediating the ligation of separate gene products to generate a mature protein.

SOURCES OF DATA

Comprehensive literature search of published research papers and reviews using Pubmed.

AREAS OF AGREEMENT

Trans-splicing techniques have been used to target a wide range of diseases in both in vitro and in vivo models, resulting in RNA, protein and functional correction.

AREAS OF CONTROVERSY

Off-target effects can lead to therapeutically undesirable consequences. In vivo efficacy is typically low, and delivery issues remain a challenge.

GROWING POINTS

Trans-splicing provides a promising avenue for developing novel therapeutic approaches. However, much more research needs to be done before developing towards preclinical studies.

AREAS TIMELY FOR DEVELOPING RESEARCH

Increasing trans-splicing efficacy and specificity by rational design, screening and competitive inhibition of endogenous cis-splicing.

Targeted suicide gene therapy for liver cancer based on ribozyme-mediated RNA replacement through post-transcriptional regulation

Hepatocellular carcinoma (HCC) has high fatality rate and limited therapeutic options. Here, we propose a new anti-HCC approach with high cancer-selectivity and efficient anticancer effects, based on adenovirus-mediated Tetrahymena group I trans-splicing ribozymes specifically inducing targeted suicide gene activity through HCC-specific replacement of telomerase reverse transcriptase (TERT) RNA. To confer potent anti-HCC effects and minimize hepatotoxicity, we constructed post-transcriptionally enhanced ribozyme constructs coupled with splicing donor and acceptor site and woodchuck hepatitis virus post-transcriptional regulatory element under the control of microRNA-122a (miR-122a). Adenovirus encoding post-transcriptionally enhanced ribozyme improved trans-splicing reaction and decreased human TERT (hTERT) RNA level, efficiently and selectively retarding hTERT-positive liver cancers. Adenovirus encoding miR-122a-regulated ribozyme caused selective liver cancer cytotoxicity, the efficiency of which depended on ribozyme expression level relative to miR-122a level. Systemic administration of adenovirus encoding the post-transcriptionally enhanced and miR-regulated ribozyme caused efficient anti-cancer effects at a single dose of low titers and least hepatotoxicity in intrahepatic multifocal HCC mouse xenografts. Minimal liver toxicity, tissue distribution, and clearance pattern of the recombinant adenovirus were observed in normal animals administered either systemically or via the hepatic artery. Post-transcriptionally regulated RNA replacement strategy mediated by a cancer-specific ribozyme provides a clinically relevant, safe, and efficient strategy for HCC treatment.

Oncolytic Adenoviruses: Strategies for Improved Targeting and Specificity

Cancer is a major health problem. Most of the treatments exhibit systemic toxicity, as they are not targeted or specific to cancerous cells and tumors. Adenoviruses are very promising gene delivery vectors and have immense potential to deliver targeted therapy. Here, we review a wide range of strategies that have been tried, tested, and demonstrated to enhance the specificity of oncolytic viruses towards specific cancer cells. A combination of these strategies and other conventional therapies may be more effective than any of those strategies alone.

Stem Cell Therapy for Hepatocellular Carcinoma: Future Perspectives

Hepatocellular carcinoma (HCC) is one of the most common types of cancer and results in a high mortality rate worldwide. Unfortunately, most cases of HCC are diagnosed in an advanced stage, resulting in a poor prognosis and ineffective treatment. HCC is often resistant to both radiotherapy and chemotherapy, resulting in a high recurrence rate. Although the use of stem cells is evolving into a potentially effective approach for the treatment of cancer, few studies on stem cell therapy in HCC have been published. The administration of stem cells from bone marrow, adipose tissue, the amnion, and the umbilical cord to experimental animal models of HCC has not yielded consistent responses. However, it is possible to induce the apoptosis of cancer cells, repress angiogenesis, and cause tumor regression by administration of genetically modified stem cells. New alternative approaches to cancer therapy, such as the use of stem cell derivatives, exosomes or stem cell extracts, have been proposed. In this review, we highlight these experimental approaches for the use of stem cells as a vehicle for local drug delivery.

Advances in delivery vectors for gene therapy in liver cancer

Hepatocellular carcinoma (HCC) is the third most common cause of cancer death globally, mainly due to lack of effective treatments – a problem that gene therapy is poised to solve. Successful gene therapy requires safe and efficient delivery vectors, and recent advances in both viral and nonviral vectors have made an important impact on HCC gene therapy delivery. This review explores how adenoviral, retroviral and adeno-associated viral vectors have been modified to increase safety and delivery capacity, highlighting studies and clinical trials using these vectors for HCC gene therapy. Nanoparticles, liposomes, exosomes and virosomes are also featured in their roles as HCC gene delivery vectors. Finally, new discoveries in gene editing technology and their impacts on HCC gene therapy are discussed.

Small Animal PET Imaging of hTERT RNA-Targeted HSV1-tk Gene Expression with Trans-Splicing Ribozyme

Background: Trans-splicing ribozymes (TSR) are useful anticancer agents targeting cancer-specific transcripts and replacing the RNA to induce anticancer gene expression specifically and selectively in cancer cells. Similar to other gene therapy methods, it is also important to evaluate the transgene expression for target specificity and ribozyme activity. Materials and Methods: In this study, the authors performed in vivo small animal positron emission tomography (PET) imaging and biodistribution assay to evaluate human telomerase reverse transcriptase (hTERT) RNA-targeting-specific TSR, which directs the expression of herpes simplex virus type 1 thymidine kinase (HSV1-tk) gene selectively in hTERT-positive tumors through targeted RNA replacement of the hTERT transcript. Results: The hTERT RNA-targeted HSV1-tk expression with TSR was monitored by PET imaging with ¹²⁴I labeled 2'-fluoro-2'-deoxy-1-β-D-arabinofuranosyl-5-iodouracil, which is one of the thymidine derivatives acting as substrates for HSV1-tk, in hTERT-positive tumor-bearing mice. Conclusions: Imaging of hTERT RNA-targeted HSV1-tk expression by TSR could be used in the development of advanced gene therapy using tumor-specific TSR.

Oncolytic Adenovirus-A Nova for Gene-Targeted Oncolytic Viral Therapy in HCC

Hepatocellular carcinoma (HCC) is one of the most frequent cancers worldwide, particularly in China. Despite the development of HCC treatment strategies, the survival rate remains unpleasant. Gene-targeted oncolytic viral therapy (GTOVT) is an emerging treatment modality-a kind of cancer-targeted therapy-which creates viral vectors armed with anti-cancer genes. The adenovirus is a promising agent for GAOVT due to its many advantages. In spite of the oncolytic adenovirus itself, the host immune response is the determining factor for the anti-cancer efficacy. In this review, we have summarized recent developments in oncolytic adenovirus engineering and the development of novel therapeutic genes utilized in HCC treatment. Furthermore, the diversified roles the immune response plays in oncolytic adenovirus therapy and recent attempts to modulate immune responses to enhance the anti-cancer efficacy of oncolytic adenovirus have been discussed.

Golgi membrane protein GP73 modified-liposome mediates the antitumor effect of survivin promoter-driven HSVtk in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most common types of cancer worldwide, and there is currently no effective therapeutic strategy in clinical practice. Gene therapy has great potential for decreasing tumor-induced mortality but has been clinically limited because of the lack of tumor-specific targets and insufficient gene transfer. The study of targeted transport of therapeutic genes in HCC treatment seems to be very important. In this study, we evaluated a gene therapy approach targeting HCC using the herpes simplex virus thymidine kinase/ganciclovir (HSVtk/GCV) suicide gene system in HCC cell lines and in an in vivo human HCC xenograft mouse model. GP73-modified liposomes targeted gene delivery to the tumor tissue, and the survivin promoter drove HSVtk expression in the HCC cells. Our results showed that the survivin promoter was specifically activated in tumor cells and HSVtk was expressed selectively in tumor cells. Combined with GCV treatment, HSVtk expression resulted in suppression of HCC cell proliferation via enhancing apoptosis. Moreover, tail vein injection of GP73-HSVtk significantly suppressed the growth of xenograft tumors through an apoptosis-dependent pathway and extended the survival of tumor-bearing mice without damaging the mice liver functions. Taken together, this study demonstrates an effective cancer-specific gene therapy strategy using the herpes simplex virus thymidine kinase/ganciclovir (HSVtk/GCV) suicide gene system for HCC that can be further developed for future clinical trials.

The beginning of the end for conventional RECIST - novel therapies require novel imaging approaches

Owing to improvements in our understanding of the biological principles of tumour initiation and progression, a wide variety of novel targeted therapies have been developed. Developments in biomedical imaging, however, have not kept pace with these improvements and are still mainly designed to determine lesion size alone, which is reflected in the Response Evaluation Criteria in Solid Tumors (RECIST). Imaging approaches currently used for the evaluation of treatment responses in patients with solid tumours, therefore, often fail to detect successful responses to novel targeted agents and might even falsely suggest disease progression, a scenario known as pseudoprogression. The ability to differentiate between responders and nonresponders early in the course of treatment is essential to allowing the early adjustment of treatment regimens. Various imaging approaches targeting a single dedicated tumour feature, as described in the hallmarks of cancer, have been successful in preclinical investigations, and some have been evaluated in pilot clinical trials. However, these approaches have largely not been implemented in clinical practice. In this Review, we describe current biomedical imaging approaches used to monitor responses to treatment in patients receiving novel targeted therapies, including a summary of the most promising future approaches and how these might improve clinical practice.

BPTF promotes hepatocellular carcinoma growth by modulating hTERT signaling and cancer stem cell traits

Bromodomain PHD finger transcription factor (BPTF), a core subunit of nucleosome-remodeling factor (NURF) complex, plays an important role in chromatin remodeling. However, its precise function and molecular mechanism involved in hepatocellular carcinoma (HCC) growth are still poorly defined. Here, we demonstrated the tumor-promoting role of BPTF in HCC progression. BPTF was highly expressed in HCC cells and tumor tissues of HCC patients compared with normal liver cells and tissues. Knockdown of BPTF inhibited cell proliferation, colony formation and stem cell-like traits in HCC cells. In addition, BPTF knockdown effectively sensitized the anti-tumor effect of chemotherapeutic drugs and induced more apoptosis in HCC cells. Consistently, knockdown of BPTF in a xenograft mouse model also suppressed tumor growth and metastasis accompanied by the suppression of cancer stem cells (CSC)-related protein markers. Moreover, the mechanism study showed that the tumor-promoting role of BPTF in HCC was realized by transcriptionally regulating the expression of human telomerase reverse transcriptase (hTERT). Furthermore, we found that HCC patients with high BPTF expression displayed high hTERT expression, and high BPTF or hTERT expression level was positively correlated with advanced malignancy and poor prognosis in HCC patients. Collectively, our results demonstrate that BPTF promotes HCC growth by targeting hTERT and suggest that the BPTF-hTERT axis maybe a novel and potential therapeutic target in HCC.

Group I Intron-Based Therapeutics Through Trans-Splicing Reaction

In 1982, the Cech group discovered that an intron structure in an rRNA precursor of Tetrahymena thermophila is sufficient to complete splicing without assistance from proteins. This was the first moment that scientists recognized RNAs can have catalytic activities derived from their own unique three-dimensional structures and thus play more various roles in biological processes than thought before. Several additional catalytic RNAs, called ribozymes, were subsequently identified in nature followed by intense studies to reveal their mechanisms of action and to engineer them for use in fields such as molecular cell biology, therapeutics, imaging, etc. Naturally occurring RNA-targeting ribozymes can be broadly classified into two categories by their abilities: Self-cleavage and self-splicing. Since ribozymes use base-pairing to recognize cleavage sites, identification of the catalytic center of naturally occurring ribozymes enables to engineer from "self" to "trans" acting ones which has accelerated to design and use ribozyme as valuable tools in gene therapy fields. Especially, group I intron-based trans-splicing ribozyme has unique property to use as a gene therapeutic agent. It can destroy and simultaneously repair (and/or reprogram) target RNAs to yield the desired therapeutic RNAs, maintaining endogenous spatial and temporal gene regulation of target RNAs. There have been progressive improvements in trans-splicing ribozymes and successful applications of these elements in gene therapy and molecular imaging approaches for various pathogenic conditions. In this chapter, current status of trans-splicing ribozyme therapeutics, focusing on Tetrahymena group I intron-based ribozymes, and their future prospects will be discussed.

Combined treatment of cholangiocarcinoma with interventional radiofrequency hyperthermia and heat shock protein promoter-mediated HSV-TK gene therapy

Cholangiocarcinoma is a most lethal malignancy frequently resistant to chemotherapy. Herpes simplex virus thymidine kinase/Ganciclovir (HSV-TK/GCV) suicide gene therapy is a promising approach to treat different cancers, including cholangiocarcinoma. However drawbacks including low therapeutic gene expression and lack of precise targeted gene delivery limit the wide clinical utilization of the suicide gene therapy. We attempted to overcome these obstacles. We established the "proof-of-principle" of this concept via serial in-vitro experiments using human cholangiocarcinoma cells and then validated the new interventional oncology technique in vivo using mice harboring the same patient derived cholangiocarcinomas. Curative effects were evaluated by magnetic resonance imaging and confirmed by pathology and laboratory examinations. Intratumoral radiofrequency hyperthermia (RFH) significantly elevated the targeted expression of HSV-TK gene and further enhanced the therapeutic effects of direct intratumoral HSV-TK/GCV gene therapy, evident as the least number of survival tumor cells, smallest tumor size, and the highest apoptosis index in the combination treatment of HSV-TK plus RFH, compared to other control treatments. The novel combination of image-guided interventional oncology, RFH technology, and direct gene therapy may be valuable for the effective treatment of cholangiocarcinoma.

RNA Trans-Splicing Modulation via Antisense Molecule Interference

In recent years, RNA trans-splicing has emerged as a suitable RNA editing tool for the specific replacement of mutated gene regions at the pre-mRNA level. Although the technology has been successfully applied for the restoration of protein function in various genetic diseases, a higher trans-splicing efficiency is still desired to facilitate its clinical application. Here, we describe a modified, easily applicable, fluorescence-based screening system for the generation and analysis of antisense molecules specifically capable of improving the RNA reprogramming efficiency of a selected KRT14-specific RNA trans-splicing molecule. Using this screening procedure, we identified several antisense RNAs and short rationally designed oligonucleotides, which are able to increase the trans-splicing efficiency. Thus, we assume that besides the RNA trans-splicing molecule, short antisense molecules can act as splicing modulators, thereby increasing the trans-splicing efficiency to a level that may be sufficient to overcome the effects of certain genetic predispositions, particularly those associated with dominantly inherited diseases.

Therapeutic applications of group I intron-based trans-splicing ribozymes

Since the breakthrough discovery of catalytic RNAs (ribozymes) in the early 1980s, valuable ribozyme-based gene therapies have been developed for incurable diseases ranging from genetic disorders to viral infections and cancers. Ribozymes can be engineered and used to downregulate or repair pathogenic genes via RNA cleavage mediated by trans-cleaving ribozymes or repair and reprograming mediated by trans-splicing ribozymes, respectively. Uniquely, trans-splicing ribozymes can edit target RNAs via simultaneous destruction and repair (and/or reprograming) to yield the desired therapeutic RNAs, thus selectively inducing therapeutic gene activity in cells expressing the target RNAs. In contrast to traditional gene therapy approaches, such as simple addition of therapeutic transgenes or inhibition of disease-causing genes, the selective repair and/or reprograming abilities of trans-splicing ribozymes in target RNA-expressing cells facilitates the maintenance of endogenous spatial and temporal gene regulation and reduction of disease-associated transcript expression. In molecular imaging technologies, trans-splicing ribozymes can be used to reprogram specific RNAs in living cells and organisms by the 3'-tagging of reporter RNAs. The past two decades have seen progressive improvements in trans-splicing ribozymes and the successful application of these elements in gene therapy and molecular imaging approaches for various pathogenic conditions, such as genetic, infectious, and malignant disease. This review provides an overview of the current status of trans-splicing ribozyme therapeutics, focusing on Tetrahymena group I intron-based ribozymes, and their future prospects. This article is categorized under: RNA in Disease and Development > RNA in Disease.

Combination therapy of hTERTR and FAM96A for hepatocellular carcinoma through enhancing apoptosis sensitivity

Avoidance of apoptosis induced by anticancer drugs is an essential factor of carcinogenesis and a hallmark of resistance to cancer therapy. Human telomerase reverse transcriptase receptor (hTERTR) is a potential anti-cancer agent for inhibiting tumor growth. Family with sequence similarity 96 member A (FAM96A) is a ubiquitous, conserved protein and possesses apoptosome-activating and pro-apoptotic tumor suppressor potential in hepatocellular carcinoma (HCC). In the present study, hTERTR and FAM96A were identified as efficient anti-cancer agents for activating apoptosomes and reducing tumor growth. The potential tumor suppressor function of combination treatment with hTERTR and FAM96A in HCC was also investigated. hTERTR and FAM96A proteins were expressed by genetic engineering and their anti-cancer function was explored in vitro and in vivo. Effects of hTERTR and FAM96A on improvement of apoptotic sensitivity and inhibition of migration and invasion were examined in cancer cells and in a mouse model. The present results demonstrated that the therapeutic effects of hTERTR and FAM96A were effective for inhibiting tumor growth and inducing apoptosis of HCC cells in H22-bearing nude mice compared with single agent treatment. hTERTR and FAM96A were found to bind with apoptotic protease activating factor 1 and human telomerase reverse transcriptase, which enhanced the apoptosis of tumor cells and apoptosis sensitivity. In addition, hTERTR and FAM96A therapy enhanced cytotoxic effects by cytotoxic T lymphocyte responses, interferon-γ release, T lymphocytes infiltration and apoptosis on tumor cells. Furthermore, hTERTR and FAM96A protein inhibited tumor growth in HCC mice. In conclusion, the present findings suggested that combination therapy with hTERTR and FAM96A may serve as novel tumor suppressor agents.

RBFOX3 Promotes Tumor Growth and Progression via hTERT Signaling and Predicts a Poor Prognosis in Hepatocellular Carcinoma

Activation of the telomere maintenance mechanism is a key hallmark of cancer. Human telomerase reverse transcriptase (hTERT) is the catalytic subunit of telomerase, which is highly expressed in more than 80% of tumors, including hepatocellular carcinoma (HCC). However, the exact mechanisms by which hTERT is up-regulated in HCCs and promotes tumor growth and progression is not fully understood. The aim of this study was to discover the novel molecular targets that modulate hTERT signaling and HCC growth. In this study, we pulled down and identified RBFOX3 (RNA binding protein fox-1 homolog 3) as a novel hTERT promoter-binding protein in HCC cells using biotin-streptavidin-agarose pull-down and proteomics approach, and validated it as a regulatory factor for hTERT signaling and tumor growth in HCCs. Knockdown of RBFOX3 suppressed the promoter activity and expression of hTERT and consequently inhibited the growth and progression of HCC cells in vitro and in vivo. The suppression of HCC growth mediated by RBFOX3 knockdown could be rescued by hTERT overexpression. Conversely, exogenous overexpression of RBFOX3 activated the promoter activity and expression of hTERT and promoted the growth and progression of HCC cells. Moreover, we found that RBFOX3 interacted with AP-2β to regulate the expression of hTERT. Furthermore, we demonstrated that RBFOX3 expression was higher in the tumor tissues of HCC patients compared to the corresponding paracancer tissues, and was positively correlated with hTERT expression. Kaplan-Meier analysis showed that the HCC patients with high levels of RBFOX3 and hTERT had poor prognosis. Collectively, our data indicate that RBFOX3 promotes HCC growth and progression and predicts a poor prognosis by activating the hTERT signaling, and suggest that the RBFOX3/hTERT pathway may be a potential therapeutic target for HCC patients.

Specific and Efficient Regression of Cancers Harboring KRAS Mutation by Targeted RNA Replacement

Mutations in the KRAS gene, which persistently activate RAS function, are most frequently found in many types of human cancers. Here, we proposed and verified a new approach against cancers harboring the KRAS mutation with high cancer selectivity and efficient anti-cancer effects based on targeted RNA replacement. To this end, trans-splicing ribozymes from Tetrahymena group I intron were developed, which can specifically target and reprogram the mutant KRAS G12V transcript to induce therapeutic gene activity in cells. Adenoviral vectors containing the specific ribozymes with downstream suicide gene were constructed and then infection with the adenoviruses specifically downregulated KRAS G12V expression and killed KRAS G12V-harboring cancer cells additively upon pro-drug treatment, but it did not affect the growth of wild-type KRAS-expressing cells. Minimal liver toxicity was noted when the adenoviruses were administered systemically in vivo. Importantly, intratumoral injection of the adenoviruses with pro-drug treatment specifically and significantly impeded the growth of xenografted tumors harboring KRAS G12V through a trans-splicing reaction with the target RNA. In contrast, xenografted tumors harboring wild-type KRAS were not affected by the adenoviruses. Therefore, RNA replacement with a mutant KRAS-targeting trans-splicing ribozyme is a potentially useful therapeutic strategy to combat tumors harboring KRAS mutation.

Advances in the detection of telomerase activity using isothermal amplification

Telomerase plays a significantly important role in keeping the telomere length of a chromosome. Telomerase overexpresses in nearly all tumor cells, suggesting that telomerase could be not only a promising biomarker but also a potential therapeutic target for cancers. Therefore, numerous efforts focusing on the detection of telomerase activity have been reported from polymerase chain reaction (PCR)-based telomeric repeat amplification protocol (TRAP) assays to PCR-free assays such as isothermal amplification in recent decade. In this review, we highlight the strategies for the detection of telomerase activity using isothermal amplification and discuss some of the challenges in designing future telomerase assays as well.

Design and Experimental Evolution of trans-Splicing Group I Intron Ribozymes

Group I intron ribozymes occur naturally as cis-splicing ribozymes, in the form of introns that do not require the spliceosome for their removal. Instead, they catalyze two consecutive trans-phosphorylation reactions to remove themselves from a primary transcript, and join the two flanking exons. Designed, trans-splicing variants of these ribozymes replace the 3′-portion of a substrate with the ribozyme’s 3′-exon, replace the 5′-portion with the ribozyme’s 5′-exon, or insert/remove an internal sequence of the substrate. Two of these designs have been evolved experimentally in cells, leading to variants of group I intron ribozymes that splice more efficiently, recruit a cellular protein to modify the substrate’s gene expression, or elucidate evolutionary pathways of ribozymes in cells. Some of the artificial, trans-splicing ribozymes are promising as tools in therapy, and as model systems for RNA evolution in cells. This review provides an overview of the different types of trans-splicing group I intron ribozymes that have been generated, and the experimental evolution systems that have been used to improve them.

From the RNA world to the clinic

The study of RNA has continually emphasized the structural and functional versatility of RNA molecules. This versatility has inspired translational and clinical researchers to explore the utility of RNA-based therapeutic agents for a wide variety of medical applications. Several RNA therapeutics, with diverse modes of action, are being evaluated in large late-stage clinical trials, and many more are in early clinical development. Hundreds of patients are enrolled in large trials testing messenger RNAs to combat cancer, small interfering RNAs to treat renal and hepatic disorders, and aptamers to combat ocular and cardiovascular disease. Results from these studies are generating considerable interest among the biomedical community and the public and will be important for the future development of this emerging class of therapeutic agents.

A new fluorescence/PET probe for targeting intracellular human telomerase reverse transcriptase (hTERT) using Tat peptide-conjugated IgM

Despite an increasing need for methods to visualize intracellular proteins in vivo, the majority of antibody-based imaging methods available can only detect membrane proteins. The human telomerase reverse transcriptase (hTERT) is an intracellular target of great interest because of its high expression in several types of cancer. In this study, we developed a new probe for hTERT using the Tat peptide. An hTERT antibody (IgG or IgM) was conjugated with the Tat peptide, a fluorescence dye and (64)Cu. HT29 (hTERT+) and U2OS (hTERT-) were used to visualize the intracellular hTERT. The hTERT was detected by RT-PCR and western blot. Fluorescence signals for hTERT were obtained by confocal microscopy, live cell imaging, and analyzed by Tissue-FAXS. In nude mice, tumors were visualized using the fluorescence imaging devices Maestro™ and PETBOX. In RT-PCR and western blot, the expression of hTERT was detected in HT29 cells, but not in U2OS cells. Fluorescence signals were clearly observed in HT29 cells and in U2OS cells after 1 h of treatment, but signals were only detected in HT29 cells after 24 h. Confocal microscopy showed that 9.65% of U2OS and 78.54% of HT29 cells had positive hTERT signals. 3D animation images showed that the probe could target intranuclear hTERT in the nucleus. In mice models, fluorescence and PET imaging showed that hTERT in HT29 tumors could be efficiently visualized. In summary, we developed a new method to visualize intracellular and intranuclear proteins both in vitro and in vivo.