Long-circulating siRNA nanoparticles for validating Prohibitin1-targeted non-small cell lung cancer treatment.

RNA interference (RNAi) represents a promising strategy for identification and validation of putative therapeutic targets and for treatment of a myriad of important human diseases including cancer. However, the effective systemic in vivo delivery of small interfering RNA (siRNA) to tumors remains a formidable challenge. Using a robust self-assembly strategy, we develop a unique nanoparticle (NP) platform composed of a solid polymer/cationic lipid hybrid core and a lipid-poly(ethylene glycol) (lipid-PEG) shell for systemic siRNA delivery. The new generation lipid-polymer hybrid NPs are small and uniform, and can efficiently encapsulate siRNA and control its sustained release. They exhibit long blood circulation (t1/2 ∼ 8 h), high tumor accumulation, effective gene silencing, and negligible in vivo side effects. With this RNAi NP, we delineate and validate the therapeutic role of Prohibitin1 (PHB1), a target protein that has not been systemically evaluated in vivo due to the lack of specific and effective inhibitors, in treating non-small cell lung cancer (NSCLC) as evidenced by the drastic inhibition of tumor growth upon PHB1 silencing. Human tissue microarray analysis also reveals that high PHB1 tumor expression is associated with poorer overall survival in patients with NSCLC, further suggesting PHB1 as a therapeutic target. We expect this long-circulating RNAi NP platform to be of high interest for validating potential cancer targets in vivo and for the development of new cancer therapies.

Identification of genes regulating migration and invasion using a new model of metastatic prostate cancer.

BACKGROUND: Understanding the complex, multistep process of metastasis remains a major challenge in cancer research. Metastasis models can reveal insights in tumor development and progression and provide tools to test new intervention strategies. METHODS: To develop a new cancer metastasis model, we used DU145 human prostate cancer cells and performed repeated rounds of orthotopic prostate injection and selection of subsequent lymph node metastases. Tumor growth, metastasis, cell migration and invasion were analyzed. Microarray analysis was used to identify cell migration- and cancer-related genes correlating with metastasis. Selected genes were silenced using siRNA, and their roles in cell migration and invasion were determined in transwell migration and Matrigel invasion assays. RESULTS: Our in vivo cycling strategy created cell lines with dramatically increased tumorigenesis and increased ability to colonize lymph nodes (DU145LN1-LN4). Prostate tumor xenografts displayed increased vascularization, enlarged podoplanin-positive lymphatic vessels and invasive margins. Microarray analysis revealed gene expression profiles that correlated with metastatic potential. Using gene network analysis we selected 3 significantly upregulated cell movement and cancer related genes for further analysis: EPCAM (epithelial cell adhesion molecule), ITGB4 (integrin ß4) and PLAU (urokinase-type plasminogen activator (uPA)). These genes all showed increased protein expression in the more metastatic DU145-LN4 cells compared to the parental DU145. SiRNA knockdown of EpCAM, integrin-ß4 or uPA all significantly reduced cell migration in DU145-LN4 cells. In contrast, only uPA siRNA inhibited cell invasion into Matrigel. This role of uPA in cell invasion was confirmed using the uPA inhibitors, amiloride and UK122. CONCLUSIONS: Our approach has identified genes required for the migration and invasion of metastatic tumor cells, and we propose that our new in vivo model system will be a powerful tool to interrogate the metastatic cascade in prostate cancer.

Hybrid lipid-polymer nanoparticles for sustained siRNA delivery and gene silencing.

The development of controlled-release nanoparticle (NP) technologies has great potential to further improve the therapeutic efficacy of RNA interference (RNAi), by prolonging the release of small interfering RNA (siRNA) for sustained, long-term gene silencing. Herein, we present an NP platform with sustained siRNA-release properties, which can be self-assembled using biodegradable and biocompatible polymers and lipids. The hybrid lipid-polymer NPs showed excellent silencing efficacy, and the temporal release of siRNA from the NPs continued for over one month. When tested on luciferase-expressed HeLa cells and A549 lung carcinoma cells after short-term transfection, the siRNA NPs showed greater sustained silencing activity than lipofectamine 2000-siRNA complexes. More importantly, the NP-mediated sustained silencing of prohibitin 1 (PHB1) generates more effective tumor cell growth inhibition in vitro and in vivo than the lipofectamine complexes. We expect that this sustained-release siRNA NP platform could be of interest in both fundamental biological studies and clinical applications. FROM THE CLINICAL EDITOR: Emerging gene silencing applications could be greatly enhanced by prolonging the release of siRNA for sustained gene silencing. This team of scientists presents a hybrid lipid-polymer nanoparticle platform that successfully accomplishes this goal, paving the way to future research studies and potential clinical applications.

Rescue of paclitaxel sensitivity by repression of Prohibitin1 in drug-resistant cancer cells.

Paclitaxel has emerged as a front line treatment for aggressive malignancies of the breast, lung, and ovary. Successful therapy of cancer is frequently undermined by the development of paclitaxel resistance. There is a growing need to find other therapeutic targets to facilitate treatment of drug-resistant cancers. Using a proteomics approach, elevated levels of Prohibitin1 (PHB1) and GSTpi were found associated with paclitaxel resistance in discrete subcellular fractions of two drug-resistant sublines relative to their sensitive sublines. Immunofluorescence staining and fractionation studies revealed increased levels of PHB1 on the surface of resistant cell lines. Transiently silencing either PHB1 or GSTpi gene expression using siRNA in the paclitaxel-resistant cancer cell sublines partially sensitized these cells toward paclitaxel. Intriguingly, silencing PHB1 but not GSTpi resulted in activation of the intrinsic apoptosis pathway in response to paclitaxel. Similarly, stably silencing either PHB1 or GSTpi significantly improved paclitaxel sensitivity in A549TR cells both in vitro and in vivo. Our results indicate that PHB1 is a mediator of paclitaxel resistance and that this resistance may depend on the cellular localization of the protein. We suggest PHB1 as a potential target for therapeutic strategies for the treatment of drug-resistant tumors.

Regenerative protein thymosin beta-4 is a novel regulator of purinergic signaling.

By an unknown mechanism, ß-thymosins are extracellular modulators of angiogenesis, inflammation, wound healing, and development. We were interested in identifying ß-thymosin interactors and determining their importance in ß-thymosins signaling in human vein endothelial cells (HUVECs). We performed pulldown experiments with biotinylated thymosin ß-4 (Tß4) in comparison to neutravidin beads alone and used mass spectrometric analysis to identify differentially interacting proteins. By this method, we identified F1-F0 ATP synthase, a known target of antiangiogenic angiostatin. By surface plasmon resonance, we determined for Tß4 binding to the ß subunit of ATP synthase a K(D) of 12 nM. Blocking antibodies and antagonists (oligomycin, IC(50) ∼1.8 µM; piceatannol, IC(50) ∼1.05 µM; and angiostatin, IC(50) ∼2.9 µg/ml) of ATP synthase inhibited the Tß4-induced increase in cell surface ATP levels, as measured by luciferase assay, and the Tß4-induced increase in HUVEC migration, as measured by transwell migration assay. Silencing of the ATP-responsive purinergic receptor P2X4 with siRNA also blocked Tß4-induced HUVEC migration in a transwell assay. Furthermore, in silico we identified common amphiphilic α-helical structural similarities between ß-thymosins and the inhibitory factor 1 (IF1), an inhibitor of ATP synthase hydrolysis. In summary, we have identified an extracellular signaling pathway where Tß4 increases cell surface ATP levels via ATP synthase and have shown further that ATP-responsive P2X4 receptor is required for Tß4-induced HUVEC migration.

Knockdown of antizyme inhibitor decreases prostate tumor growth in vivo.

The endogenous protein antizyme inhibitor (AZI) is a potential oncogene which promotes cell growth by both inhibiting antizyme (AZ) activity and releasing ornithine decarboxylase (ODC) from AZ-mediated degradation. High levels of ODC and polyamines are associated with numerous types of neoplastic transformation, and the genomic region including AZI is frequently amplified in tumors of the ovary and prostate. To determine whether AZI functionally promotes prostate tumor growth, we made PC3M-LN4 (human) and AT6.1 (rat) cancer cell lines stably expressing shRNA to knockdown antizyme inhibitor 1 (AZI). AZI knockdown was confirmed by western blot, quantitative real-time PCR, and immunofluorescence. To examine the ability of these cells to form tumors in vivo, 1 × 10(6) cells were injected subcutaneously into nude mice either with (PC3M-LN4) or without (AT6.1) Matrigel. Tumor growth was measured two times per week by caliper. We found that cells in which AZI levels had been knocked down by shRNA formed significantly smaller tumors in vivo in both human and rat prostate cancer cell lines. These results suggest that not only does AZI promote tumor growth, but also that AZI may be a valid therapeutic target for cancer treatment.

AZIN1 RNA editing alters protein interactions, leading to nuclear translocation and worse outcomes in prostate cancer.

The transcript encoding Antizyme Inhibitor 1 (AZIN1) is frequently edited in various cancers, and this editing is associated with enhanced tumor aggressiveness. After comparison of wild-type AZIN1 (wtAZIN1) and edited AZIN1 (edAZIN1, which contains a Ser367Gly substitution), we report differential binding of edAZIN1 to a small set of proteins; specifically, edAZIN1 binds to alpha-smooth muscle actin (ACTA2), gamma actin 1 (ACTG1), and myosin9, whereas wtAZIN1 does not. This binding enables nuclear translocation of edAZIN1. In contrast to overexpression of edAZIN1 and, to a lesser extent, (editable) wtAZIN1, overexpression of an uneditable AZIN1 allele does not promote a cellular phenotype associated with increased tumorigenicity. In patients, both editing and nuclear localization of AZIN1 are common and are associated with tumor aggressiveness, i.e., a higher Gleason score, higher genomic instability, and a shorter progression-free survival time. In conclusion, the data indicate that binding of edAZIN1 to the actin/myosin9 complex supports its nuclear translocation, leading to enhanced cellular aggressiveness, and is associated with worse prostate cancer outcomes.

Adjuvant-pulsed mRNA vaccine nanoparticle for immunoprophylactic and therapeutic tumor suppression in mice.

Synthetic mRNA represents an exciting cancer vaccine technology for the implementation of effective cancer immunotherapy. However, inefficient in vivo mRNA delivery along with a requirement for immune co-stimulation present major hurdles to achieving anti-tumor therapeutic efficacy. Here, we demonstrate a proof-of-concept adjuvant-pulsed mRNA vaccine nanoparticle (NP) that is composed of an ovalbumin-coded mRNA and a palmitic acid-modified TLR7/8 agonist R848 (C16-R848), coated with a lipid-polyethylene glycol (lipid-PEG) shell. This mRNA vaccine NP formulation retained the adjuvant activity of encapsulated C16-R848 and markedly improved the transfection efficacy of the mRNA (>95%) and subsequent MHC class I presentation of OVA mRNA derived antigen in antigen-presenting cells. The C16-R848 adjuvant-pulsed mRNA vaccine NP approach induced an effective adaptive immune response by significantly improving the expansion of OVA-specific CD8+ T cells and infiltration of these cells into the tumor bed in vivo, relative to the mRNA vaccine NP without adjuvant. The approach led to an effective anti-tumor immunity against OVA expressing syngeneic allograft mouse models of lymphoma and prostate cancer, resulting in a significant prevention of tumor growth when the vaccine was given before tumor engraftment (84% reduction vs. control) and suppression of tumor growth when given post engraftment (60% reduction vs. control). Our findings indicate that C16-R848 adjuvant pulsation to mRNA vaccine NP is a rational design strategy to increase the effectiveness of synthetic mRNA vaccines for cancer immunotherapy.

Quantitative proteomics analysis reveals molecular networks regulated by epidermal growth factor receptor level in head and neck cancer.

Epidermal growth factor receptor (EGFR) is overexpressed in up to 90% of head and neck cancer (HNC), where increased expression levels of EGFR correlate with poor prognosis. To date, EGFR expression levels have not predicted the clinical response to the EGFR-targeting therapies. Elucidation of the molecular mechanisms underlying anti-EGFR-induced antitumor effects may shed some light on the mechanisms of HNC resistance to EGFR-targeting therapeutics and provide novel targets for improving the treatment of HNC. Here, we conducted a quantitative proteomics analysis to determine the molecular networks regulated by EGFR levels in HNC by specifically knocking-down EGFR and employing stable isotope labeling with amino acids in cell culture (SILAC). Following data normalization to minimize systematic errors and Western blotting validation, 12 proteins (e.g., p21, stratifin, and maspin) and 24 proteins (e.g., cdc2 and MTA2) were found to be significantly upregulated or downregulated by EGFR knockdown, respectively. Bioinformatic analysis revealed that these proteins were mainly involved in long-chain fatty acid biosynthesis and beta-oxidation, cholesterol biosynthesis, cell proliferation, DNA replication, and apoptosis. Cell cycle analysis confirmed that G(2)/M phase progression was significantly inhibited by EGFR knockdown, a hypothesis generated from network modeling. Further investigation of these molecular networks may not only enhance our understanding of the antitumor mechanisms of EGFR targeting but also improve patient selection and provide novel targets for better therapeutics.

Inhibition of endothelial cell migration by thrombospondin-1 type-1 repeats is mediated by beta1 integrins.

The anti-angiogenic effect of thrombospondin-1 has been shown to be mediated through binding of the type-1 repeat (TSR) domain to the CD36 transmembrane receptor. We now report that the TSR domain can inhibit VEGF-induced migration in human umbilical vein endothelial cells (HUVEC), cells that lack CD36. Moreover, we identified beta1 integrins as a critical receptor in TSR-mediated inhibition of migration in HUVEC. Using pharmacological inhibitors of downstream VEGF receptor effectors, we found that phosphoinositide 3-kinase (PI3k) was essential for TSR-mediated inhibition of HUVEC migration, but that neither PLCgamma nor Akt was necessary for this response. Furthermore, beta1 integrins were critical for TSR-mediated inhibition of microvascular endothelial cells, cells that express CD36. Together, our results indicate that beta1 integrins mediate the anti-migratory effects of TSR through a PI3k-dependent mechanism.

Cystatin B as a tissue and urinary biomarker of bladder cancer recurrence and disease progression.

PURPOSE: Using proteomic techniques, we sought to identify novel protein biomarkers in tissue and urine from patients with transitional cell carcinoma (TCC). EXPERIMENTAL DESIGN: Urinary and tissue proteomes were analyzed and differentially expressed proteins were identified by mass spectrometry. One of the proteins, cystatin B, was further analyzed in TCC tissue by immunohistochemistry and in urine by semiquantitative Western blot analysis. RESULTS: Cystatin B tissue staining intensity significantly increased concordantly with TCC grade (P = 0.0008). Elevated urinary cystatin B levels correlated with increasing tumor grade (P = 0.062) and stage (P = 0.0047). Patients with elevated levels of cystatin B had a shorter mean +/- SE time to disease recurrence (12 +/- 1.82 months) compared with patients who had low levels (28.8 +/- 2.26 months; P = 0.0047). Similarly, patients with elevated cystatin B levels had a shorter time to grade/stage progression compared with patients with low urinary cystatin B (P = 0.0007). By multivariate Cox regression analysis, an elevated cystatin B level was the most significant variable predicting disease recurrence (hazard ratio, 3.8; 95% confidence interval, 1.5-9.5; P = 0.0049) and grade/stage progression (hazard ratio, 10.4; 95% confidence interval, 1.6-201.5; P = 0.0104). CONCLUSIONS: Cystatin B is elevated in tissue and urine of bladder cancer patients. Cystatin B urine levels are positively correlated with tumor grade, stage, and shorter time to disease recurrence and progression. Consequently, cystatin B may be useful as a novel predictive biomarker in TCC of the bladder.

Differential regulation of human thymosin beta 15 isoforms by transforming growth factor beta 1.

We recently identified an additional isoform of human thymosin beta 15 (also known as NB-thymosin beta, gene name TMSB15A) transcribed from an independent gene, and designated TMSB15B. The purpose of this study was to investigate whether these isoforms were differentially expressed and functional. Our data show that the TMSB15A and TMSB15B isoforms have distinct expression patterns in different tumor cell lines and tissues. TMSB15A was expressed at higher levels in HCT116, DU145, LNCaP, and LNCaP-LN3 cancer cells. In MCF-7, SKOV-3, HT1080, and PC-3MLN4 cells, TMSB15A and TMSB15B showed approximately equivalent levels of expression, while TMSB15B was the predominant isoform expressed in PC-3, MDA-MB-231, NCI-H322, and Caco-2 cancer cells. In normal human prostate and prostate cancer tissues, TMSB15A was the predominant isoform expressed. In contrast, normal colon and colon cancer tissue expressed predominantly TMSB15B. The two gene isoforms are also subject to different transcriptional regulation. Treatment of MCF-7 breast cancer cells with transforming growth factor beta 1 repressed TMSB15A expression but had no effect on TMSB15B. siRNA specific to the TMSB15B isoform suppressed cell migration of prostate cancer cells to epidermal growth factor, suggesting a functional role for this second isoform. In summary, our data reveal different expression patterns and regulation of a new thymosin beta 15 gene paralog. This may have important consequences in both tumor and neuronal cell motility.

Lipidation Approaches Potentiate Adjuvant-Pulsed Immune Surveillance: A Design Rationale for Cancer Nanovaccine.

Adjuvant-pulsed peptide vaccines hold great promise for the prevention and treatment of different diseases including cancer. However, it has been difficult to maximize vaccine efficacy due to numerous obstacles including the unfavorable tolerability profile of adjuvants, instability of peptide antigens, limited cellular uptake, and fast diffusion from the injection site, as well as systemic adverse effects. Here we describe a robust lipidation approach for effective nanoparticle co-delivery of low-molecular weight immunomodulators (TLR7/8 agonists) and peptides (SIINFEKL) with a potent in vivo prophylactic effect. The lipidation approaches (C16-R848 and C16-SIINFEKL) increased their hydrophobicity that is intended not only to improve drug encapsulation efficiency but also to facilitate the membrane association, intracellular trafficking, and subcellular localization. The polymer-lipid hybrid nanoparticles (PLNs) are designed to sustain antigen/adjuvant levels with less systemic exposure. Our results demonstrated that a lipidated nanovaccine can induce effective immunity by enhancing the expansion and activation of antigen-specific CD8+ T cells. This adaptive immune response led to substantial tumor suppression with improved overall survival in a prophylactic setting. Our new methodology enhances the potential of nanovaccines for anti-tumor therapy.

Unbiased Phenotype-Based Screen Identifies Therapeutic Agents Selective for Metastatic Prostate Cancer.

In American men, prostate cancer is the second leading cause of cancer-related death. Dissemination of prostate cancer cells to distant organs significantly worsens patients' prognosis, and currently there are no effective treatment options that can cure advanced-stage prostate cancer. In an effort to identify compounds selective for metastatic prostate cancer cells over benign prostate cancer cells or normal prostate epithelial cells, we applied a phenotype-based in vitro drug screening method utilizing multiple prostate cancer cell lines to test 1,120 different compounds from a commercial drug library. Top drug candidates were then examined in multiple mouse xenograft models including subcutaneous tumor growth, experimental lung metastasis, and experimental bone metastasis assays. A subset of compounds including fenbendazole, fluspirilene, clofazimine, niclosamide, and suloctidil showed preferential cytotoxicity and apoptosis towards metastatic prostate cancer cells in vitro and in vivo. The bioavailability of the most discerning agents, especially fenbendazole and albendazole, was improved by formulating as micelles or nanoparticles. The enhanced forms of fenbendazole and albendazole significantly prolonged survival in mice bearing metastases, and albendazole-treated mice displayed significantly longer median survival times than paclitaxel-treated mice. Importantly, these drugs effectively targeted taxane-resistant tumors and bone metastases - two common clinical conditions in patients with aggressive prostate cancer. In summary, we find that metastatic prostate tumor cells differ from benign prostate tumor cells in their sensitivity to certain drug classes. Taken together, our results strongly suggest that albendazole, an anthelmintic medication, may represent a potential adjuvant or neoadjuvant to standard therapy in the treatment of disseminated prostate cancer.

Developing a novel FRET assay, targeting the binding between Antizyme-AZIN.

Antizyme inhibitor (AZIN) stimulates cell proliferation by binding to and sequestering the cell cycle suppressor antizyme. Despite the important role of the antizyme-AZIN protein-protein interaction (PPI) in cell cycle regulation, there are no assays for directly measuring the binding of AZIN to antizyme that are amenable to high throughput screening. To address this problem, we developed and validated a novel antizyme-AZIN intramolecular FRET sensor using clover and mRuby2 fluorescent proteins. By introducing alanine mutations in the AZIN protein, we used this sensor to probe the PPI for key residues governing the binding interaction. We found that like many PPIs, the energy of the antizyme-AZIN binding interaction is distributed across many amino acid residues; mutation of individual residues did not have a significant effect on disrupting the PPI. We also examined the interaction between Clover-AZIN and antizyme-mRuby2 in cells. Evidence of a direct interaction between Clover-AZIN and antizyme-mRuby2 was observed within cells, validating the use of this FRET sensor for probing intracellular antizyme-AZIN PPI. In conclusion, we have developed and optimized a FRET sensor which can be adapted for high throughput screening of either in vitro or intracellular activity.

Collagen XXIII expression is associated with prostate cancer recurrence and distant metastases.

PURPOSE: We had previously identified a new transmembrane collagen, type XXIII, in metastatic rat prostate carcinoma cells. The purpose of this study was to determine the expression of collagen XXIII in human prostate cancer and investigate its relationship with disease progression. EXPERIMENTAL DESIGN: We investigated collagen XXIII expression in prostate cancer tissue and did a retrospective analysis of association with prostate-specific antigen (PSA)-defined disease recurrence. The presence of collagen XXIII in prostate cancer patient urine was also assessed before and after prostatectomy. RESULTS: Collagen XXIII protein was detected at very low levels in benign prostate tissue and was significantly increased in prostate cancer. Distant metastases exhibited significantly higher collagen XXIII levels compared with either localized prostate cancer or regional (lymph node) metastases. Patients with high collagen XXIII levels had a 2.8-fold higher risk of PSA failure with median time to failure of 8.1 months, compared with low collagen XXIII patients with a median time to failure of 5 years. Multivariate Cox regression showed that the presence of collagen XXIII was significantly associated with time to PSA recurrence, independent of other clinical variables. Collagen XXIII was also detected in prostate cancer patient urine, with reduced levels after prostatectomy, indicating potential as a noninvasive fluid biomarker. CONCLUSIONS: We present the first report demonstrating increased collagen XXIII expression in prostate cancer tissue. We show that collagen XXIII level is a significant independent predictor of PSA-defined disease recurrence, suggesting a potential role as a molecular biomarker of prostate cancer progression and metastasis.

Synthesis and anticancer activity of novel water soluble benzimidazole carbamates.

Metastases account for more than 90% of all cancer deaths and respond poorly to most therapies. There remains an urgent need for new therapeutic modalities for the treatment of advanced metastatic cancers. The benzimidazole methylcarbamate drugs, commonly used as anti-helmitics, have been suggested to have anticancer activity, but progress has been stalled by their poor water solubility and poor suitability for systemic delivery to disseminated cancers. We synthesized and characterized the anticancer activity of novel benzimidazoles containing an oxetane or an amine group to enhance solubility. Among them, the novel oxetanyl substituted compound 18 demonstrated significant cytotoxicity toward a variety of cancer cell types including prostate, lung, and ovarian cancers with strong activity toward highly aggressive cancer lines (IC50: 0.9-3.8 µM). Compound 18 achieved aqueous solubility of 361 µM. In a mouse xenograft model of a highly metastatic human prostate cancer, compound 18 (30 mg/kg) significantly inhibited the growth of established tumors (T/C: 0.36) without noticeable toxicity.

Author Correction: Restoration of tumour-growth suppression in vivo via systemic nanoparticle-mediated delivery of PTEN mRNA.

The authors wish to add the following sentence into the 'Competing interests' section of this Article: "P.W.K. has investment interest in Context Therapeutics LLC, DRGT, Placon, Seer Biosciences and Tarveda Therapeutics, is a company board member for Context Therapeutics LLC, is a consultant and scientific advisory board member for BIND Biosciences, Inc., BN Immunotherapeutics, DRGT, GE Healthcare, Janssen, Metamark, New England Research Institutes, Inc., OncoCellMDX, Progenity, Sanofi, Seer Biosciences, Tarveda Therapeutics and Thermo Fisher, and serves on data safety monitoring boards for Genentech/Roche and Merck." This has now been included.

Restoration of tumour-growth suppression in vivo via systemic nanoparticle-mediated delivery of PTEN mRNA.

Phosphatase and tensin homologue deleted on chromosome 10 (PTEN) is a well-characterized tumour-suppressor gene that is lost or mutated in about half of metastatic castration-resistant prostate cancers and in many other human cancers. The restoration of functional PTEN as a treatment for prostate cancer has, however, proven difficult. Here, we show that PTEN messenger RNA (mRNA) can be reintroduced into PTEN-null prostate cancer cells in vitro and in vivo via its encapsulation in polymer-lipid hybrid nanoparticles coated with a polyethylene glycol shell. The nanoparticles are stable in serum, elicit low toxicity and enable high PTEN mRNA transfection in prostate cancer cells. Moreover, significant inhibition of tumour growth is achieved when delivered systemically in multiple mouse models of prostate cancer. We also show that the restoration of PTEN function in PTEN-null prostate cancer cells inhibits the phosphatidylinositol 3-kinase (PI3K)-AKT pathway and enhances apoptosis. Our findings provide proof-of-principle evidence of the restoration of mRNA-based tumour suppression in vivo.

Thymosin beta-NB is the human isoform of rat thymosin beta15.

Thymosin beta15 is a small actin-binding protein upregulated in highly metastatic rat prostate cancer cells, relative to low metastatic cells. We have previously established an important role for thymosin beta15 as a diagnostic marker in human prostate cancer, with potential as a prognostic indicator. We here review the data supporting increased thymosin beta15 expression in other cancer types, including breast, brain, and lung. Human NB thymosin beta is a beta-thymosin originally found in neuroblastoma. New data demonstrate that NB thymosin beta represents the human homolog of rat thymosin beta15; thus we suggest classification as human thymosin beta15. In addition to the previously described gene, thymosin beta15a, we report the discovery of a new isoform of human thymosin beta15, thymosin beta15b, which is transcribed from an independent gene on human chromosome X. The gene structure of thymosin beta15a and beta15b is conserved and the isoforms show 87% identity across the nucleotide sequence. Across the coding sequence the nucleotide differences are silent, resulting in identical proteins. Other thymosin family members have recently been shown to exert potent clinical effects. The functional data available for thymosin beta15, combined with the tumor expression pattern, suggest that thymosin beta15 may play an important role in tumor development and progression in addition to its value as a biomarker in prostate cancer.