Frances L. Byrne

Acid-Labile Core Cross-Linked Micelles for pH-Triggered Release of Antitumor Drugs

Micelles of a model amphiphilic block copolymer, poly(hydroxyethyl acrylate)-block-poly(n-butyl acrylate) (PHEA-b-PBA), synthesized via the RAFT polymerization were cross-linked by copolymerization of a degradable cross-linker from the living RAFT-end groups of PBA chains, yielding a cross-linked core without affecting significantly the original micelle size. The cross-linker incorporation into the micelles was evidenced via physicochemical analysis of the copolymer unimers formed upon acidic cleavage of the cross-linked micelles. High doxorubicin loading capacities (60 wt %) were obtained. Hydrolysis of less than half of the cross-links in the core was found to be sufficient to release doxorubicin faster at acidic pH compared to neutral pH. The system represents the first example of core-cross-linked micelles that can be destabilized (potentially both above and below CMC) by the pH-dependent cleavage of the cross-links and the subsequent polarity change in the core to enable the release of hydrophobic drugs entrapped inside the micelle.

Erk2 Phosphorylation of Drp1 Promotes Mitochondrial Fission and MAPK-Driven Tumor Growth

Ras is mutated in up to 30% of cancers, including 90% of pancreatic ductal adenocarcinomas, causing it to be constitutively GTP-bound, and leading to activation of downstream effectors that promote a tumorigenic phenotype. As targeting Ras directly is difficult, there is a significant effort to understand the downstream biological processes that underlie its protumorigenic activity. Here, we show that expression of oncogenic Ras or direct activation of the MAPK pathway leads to increased mitochondrial fragmentation and that blocking this phenotype, through knockdown of the mitochondrial fission-mediating GTPase Drp1, inhibits tumor growth. This fission is driven by Erk2-mediated phosphorylation of Drp1 on Serine 616, and both this phosphorylation and mitochondrial fragmentation are increased in human pancreatic cancer. Finally, this phosphorylation is required for Ras-associated mitochondrial fission, and its inhibition is sufficient to block xenograft growth. Collectively, these data suggest mitochondrial fission may be a target for treating MAPK-driven malignancies.

Genetic inhibition of hepatic acetyl-CoA carboxylase activity increases liver fat and alters global protein acetylation

Lipid deposition in the liver is associated with metabolic disorders including fatty liver disease, type II diabetes, and hepatocellular cancer. The enzymes acetyl-CoA carboxylase 1 (ACC1) and ACC2 are powerful regulators of hepatic fat storage; therefore, their inhibition is expected to prevent the development of fatty liver. In this study we generated liver-specific ACC1 and ACC2 double knockout (LDKO) mice to determine how the loss of ACC activity affects liver fat metabolism and whole-body physiology. Characterization of LDKO mice revealed unexpected phenotypes of increased hepatic triglyceride and decreased fat oxidation. We also observed that chronic ACC inhibition led to hyper-acetylation of proteins in the extra-mitochondrial space. In sum, these data reveal the existence of a compensatory pathway that protects hepatic fat stores when ACC enzymes are inhibited. Furthermore, we identified an important role for ACC enzymes in the regulation of protein acetylation in the extra-mitochondrial space.

RNAi-mediated stathmin suppression reduces lung metastasis in an orthotopic neuroblastoma mouse model

Metastatic neuroblastoma is an aggressive childhood cancer of neural crest origin. Stathmin, a microtubule destabilizing protein, is highly expressed in neuroblastoma although its functional role in this malignancy has not been addressed. Herein, we investigate stathmin’s contribution to neuroblastoma tumor growth and metastasis. Small interfering RNA (siRNA)-mediated stathmin suppression in two independent neuroblastoma cell lines, BE(2)-C and SH-SY5Y, did not markedly influence cell proliferation, viability or anchorage-independent growth. In contrast, stathmin suppression significantly reduced cell migration and invasion in both the neuroblastoma cell lines. Stathmin suppression altered neuroblastoma cell morphology and this was associated with changes in the cytoskeleton, including increased tubulin polymer levels. Stathmin suppression also modulated phosphorylation of the actin-regulatory proteins, cofilin and myosin light chain (MLC). Treatment of stathmin-suppressed neuroblastoma cells with the ROCKI and ROCKII inhibitor, Y-27632, ablated MLC phosphorylation and returned the level of cofilin phosphorylation and cell invasion back to that of untreated control cells. ROCKII inhibition (H-1152) and siRNA suppression also reduced cofilin phosphorylation in stathmin-suppressed cells, indicating that ROCKII mediates stathmin’s regulation of cofilin phosphorylation. This data demonstrates a link between stathmin and the regulation of cofilin and MLC phosphorylation via ROCK. To examine stathmin’s role in neuroblastoma metastasis, stathmin short hairpin RNA (shRNA)\luciferase-expressing neuroblastoma cells were injected orthotopically into severe combined immunodeficiency-Beige mice, and tumor growth monitored by bioluminescent imaging. Stathmin suppression did not influence neuroblastoma cell engraftment or tumor growth. In contrast, stathmin suppression significantly reduced neuroblastoma lung metastases by 71% (P<0.008) compared with control. This is the first study to confirm a role for stathmin in hematogenous spread using a clinically relevant orthotopic cancer model, and has identified stathmin as an important contributor of cell invasion and metastasis in neuroblastoma.

Specific β-Tubulin Isotypes Can Functionally Enhance or Diminish Epothilone B Sensitivity in Non-Small Cell Lung Cancer Cells

Epothilones are a new class of microtubule stabilizing agents with promising preclinical and clinical activity. Their cellular target is β-tubulin and factors influencing intrinsic sensitivity to epothilones are not well understood. In this study, the functional significance of specific β-tubulin isotypes in intrinsic sensitivity to epothilone B was investigated using siRNA gene knockdown against βII-, βIII- or βIVb-tubulins in two independent non-small cell lung cancer (NSCLC) cell lines, NCI-H460 and Calu-6. Drug-treated clonogenic assays showed that sensitivity to epothilone B was not altered following knockdown of βII-tubulin in both NSCLC cell lines. In contrast, knockdown of βIII-tubulin significantly increased sensitivity to epothilone B. Interestingly, βIVb-tubulin knockdowns were significantly less sensitive to epothilone B, compared to mock- and control siRNA cells. Cell cycle analysis of βIII-tubulin knockdown cells showed a higher percentage of cell death with epothilone B concentrations as low as 0.5 nM. In contrast, βIVb-tubulin knockdown cells displayed a decrease in epothilone B-induced G2-M cell cycle accumulation compared to control siRNA cells. Importantly, βIII-tubulin knockdowns displayed a significant dose-dependent increase in the percentage of apoptotic cells upon treatment with epothilone B, as detected using caspase 3/7 activity and Annexin-V staining. Higher concentrations of epothilone B were required to induce apoptosis in the βIVb-tubulin knockdowns compared to control siRNA, highlighting a potential mechanism underlying decreased sensitivity to this agent. This study demonstrates that specific β-tubulin isotypes can influence sensitivity to epothilone B and may influence differential sensitivity to this promising new agent.

TUBB3/βIII-tubulin acts through the PTEN/AKT signaling axis to promote tumorigenesis and anoikis resistance in non-small cell lung cancer.

βIII-tubulin (encoded by TUBB3) expression is associated with therapeutic resistance and aggressive disease in non-small cell lung cancer (NSCLC), but the basis for its pathogenic influence is not understood. Functional and differential proteomics revealed that βIII-tubulin regulates expression of proteins associated with malignant growth and metastases. In particular, the adhesion-associated tumor suppressor maspin was differentially regulated by βIII-tubulin. Functionally, βIII-tubulin suppression altered cell morphology, reduced tumor spheroid outgrowth, and increased sensitivity to anoikis. Mechanistically, the PTEN/AKT signaling axis was defined as a critical pathway regulated by βIII-tubulin in NSCLC cells. βIII-Tubulin blockage in vivo reduced tumor incidence and growth. Overall, our findings revealed how βIII-tubulin influences tumor growth in NSCLC, defining new biologic functions and mechanism of action of βIII-tubulin in tumorigenesis.

Metabolic vulnerabilities in endometrial cancer

Women with metabolic disorders, including obesity and diabetes, have an increased risk of developing endometrial cancer. However, the metabolism of endometrial tumors themselves has been largely understudied. Comparing human endometrial tumors and cells with their nonmalignant counterparts, we found that upregulation of the glucose transporter GLUT6 was more closely associated with the cancer phenotype than other hallmark cancer genes, including hexokinase 2 and pyruvate kinase M2. Importantly, suppression of GLUT6 expression inhibited glycolysis and survival of endometrial cancer cells. Glycolysis and lipogenesis were also highly coupled with the cancer phenotype in patient samples and cells. To test whether targeting endometrial cancer metabolism could be exploited as a therapeutic strategy, we screened a panel of compounds known to target diverse metabolic pathways in endometrial cells. We identified that the glycolytic inhibitor, 3-bromopyruvate, is a powerful antagonist of lipogenesis through pyruvylation of CoA. We also provide evidence that 3-bromopyruvate promotes cell death via a necrotic mechanism that does not involve reactive oxygen species and that 3-bromopyruvate impaired the growth of endometrial cancer xenografts.

The emerging role of long non-coding RNAs in endometrial cancer.

The human genome is pervasively transcribed and approximately 98% of the genome is non-coding. Long non-coding RNAs (lncRNAs) are a heterogeneous group of RNA transcripts that are >200 nucleotides in length with minimal to no protein-coding potential. Similar to proteins, lncRNAs have important biological functions in both normal cells and disease states including many types of cancer. This review summarizes recent advances in our understanding of lncRNAs in cancer biology and highlights the potential for lncRNA as diagnostic biomarkers and therapeutics. Herein we focus on the poorly understood role of lncRNAs in endometrial cancer, the most common gynecologic malignancy in the developed world.

Stathmin mediates neuroblastoma metastasis in a tubulin-independent manner via RhoA/ROCK signaling and enhanced transendothelial migration

Neuroblastoma, the most common solid tumor of young children, frequently presents with aggressive metastatic disease and for these children the 5-year survival rates are dismal. Metastasis, the movement of cancer cells from one site to another, involves remodeling of the cytoskeleton including altered microtubule dynamics. The microtubule-destabilizing protein, stathmin, has recently been shown to mediate neuroblastoma metastasis although precise functions remain poorly defined. In this study we investigated stathmin’s contribution to the metastatic process and potential mechanism(s) by which it exerts these effects. Stathmin suppression significantly reduced neuroblastoma cell invasion of 3D tumor spheroids into an extracellular matrix. Moreover, inhibiting stathmin expression significantly reduced transendothelial migration in two different neuroblastoma cell lines in vitro. Inhibition of ROCK, a key regulator of cell migration, in neuroblastoma cells highlighted that stathmin regulates transendothelial migration through ROCK signaling. Reduced stathmin expression in neuroblastoma cells significantly increased the activation of the RhoA small GTPase. Notably, re-expression of either wild type or a phospho-mimetic stathmin mutant (4E) made defective in tubulin binding returned cell migration and transendothelial migration back to control levels, indicating that stathmin may influence these processes in neuroblastoma cells independent of tubulin binding. Finally, stathmin suppression in neuroblastoma cells significantly reduced whole body, lung, kidney and liver metastases in an experimental metastases mouse model. In conclusion, stathmin suppression interferes with the metastatic process via RhoA/ROCK signaling in neuroblastoma cells. These findings highlight the importance of stathmin to the metastatic process and its potential as a therapeutic target for the treatment of neuroblastoma.

Analysis of the circular RNA transcriptome in endometrial cancer

Circular RNAs (circRNAs) are a naturally occurring family of non-coding RNA that may regulate gene expression in mammals. circRNAs are more stable than messenger RNAs due to their resistance to RNA exonuclease. A growing body of evidence has shown that the expression of circRNAs is regulated during development in a tissue-specific manner. CircRNAs have been implicated in a number of cancers; however, their role in endometrial cancer (EC) is completely unknown. Here, we report the circular transcriptome specific for EC as determined by RNA sequencing. We found that the overall abundance of circRNAs is lower in EC than in normal endometrium. Further, there are numerous ‘hotspot’ genes from which circRNAs are transcribed that may account for alterations in circRNA expression between the normal and malignant endometrium. Most importantly, we have also identified circRNAs that are differentially expressed between malignant and normal endometrial tissue. The functional significance of these circRNAs in cancer remains to be determined, but they may serve as potential biomarkers for the diagnosis of EC or monitoring of EC progression.