Oligonucleotide treatment of ras-induced tumors in nude mice

Indoloquinoline-Mediated Targeted Downregulation of KRAS through Selective Stabilization of the Mid-Promoter G-Quadruplex Structure

KRAS is a well-validated anti-cancer therapeutic target, whose transcriptional downregulation has been demonstrated to be lethal to tumor cells with aberrant KRAS signaling. G-quadruplexes (G4s) are non-canonical nucleic acid structures that mediate central dogmatic events, such as DNA repair, telomere elongation, transcription and splicing events. G4s are attractive drug targets, as they are more globular than B-DNA, enabling more selective gene interactions. Moreover, their genomic prevalence is increased in oncogenic promoters, their formation is increased in human cancers, and they can be modulated with small molecules or targeted nucleic acids. The putative formation of multiple G4s has been described in the literature, but compounds with selectivity among these structures have not yet been able to distinguish between the biological contribution of the predominant structures. Using cell free screening techniques, synthesis of novel indoloquinoline compounds and cellular models of KRAS-dependent cancer cells, we describe compounds that choose between KRAS promoter G4_near and G4_mid, correlate compound cytotoxic activity with KRAS regulation, and highlight G4_mid as the lead molecular non-canonical structure for further targeting efforts.

Targeting KRAS Regulation with PolyPurine Reverse Hoogsteen Oligonucleotides

KRAS is a GTPase involved in the proliferation signaling of several growth factors. The KRAS gene is GC-rich, containing regions with known and putative G-quadruplex (G4) forming regions. Within the middle of the G-rich proximal promoter, stabilization of the physiologically active G4mid structure downregulates transcription of KRAS; the function and formation of other G4s within the gene are unknown. Herein we identify three putative G4-forming sequences (G4FS) within the KRAS gene, explore their G4 formation, and develop oligonucleotides targeting these three regions and the G4mid forming sequence. We tested Polypurine Reverse Hoogsteen hairpins (PPRHs) for their effects on KRAS regulation via enhancing G4 formation or displacing G-rich DNA strands, downregulating KRAS transcription and mediating an anti-proliferative effect. Five PPRH were designed, two against the KRAS promoter G4mid and three others against putative G4FS in the distal promoter, intron 1 and exon 5. PPRH binding was confirmed by gel electrophoresis. The effect on KRAS transcription was examined by luciferase, FRET Melt2, qRT-PCR. Cytotoxicity was evaluated in pancreatic and ovarian cancer cells. PPRHs decreased activity of a luciferase construct driven by the KRAS promoter. PPRH selectively suppressed proliferation in KRAS dependent cancer cells. PPRH demonstrated synergistic activity with a KRAS promoter selective G4-stabilizing compound, NSC 317605, in KRAS-dependent pancreatic cells. PPRHs selectively stabilize G4 formation within the KRAS mid promoter region and represent an innovative approach to both G4-stabilization and to KRAS modulation with potential for development into novel therapeutics.

Identification and characterization of a new G-quadruplex forming region within the kRAS promoter as a transcriptional regulator

kRAS is one of the most prevalent oncogenic aberrations. It is either upregulated or mutationally activated in a multitude of cancers, including pancreatic, lung, and colon cancers. While a significant effort has been made to develop drugs that target kRAS, their clinical activity has been disappointing due to a variety of mechanistic hurdles. The presented works describe a novel mechanism and molecular target to downregulate kRAS expression--a previously undescribed G-quadruplex (G4) secondary structure within the proximal promoter acting as a transcriptional silencer. There are three distinct guanine-rich regions within the core kRAS promoter, including a previously examined region (G4near). Of these regions, the most distal region does not form an inducible and stable structure, whereas the two more proximal regions (termed near and mid) do form strong G4s. G4near is predominantly a tri-stacked structure with a discontinuous guanine run incorporated; G4mid consists of seven distinct runs of continuous guanines and forms numerous competing isoforms, including a stable three-tetrad stacked mixed parallel and antiparallel loop structures with longer loops of up to 10 nucleotides. Comprehensive analysis of the regulation of transcription by higher order structures has revealed that the guanine-rich region in the middle of the core promoter, termed G4mid, is a stronger repressor of promoter activity than G4near. Using the extensive guanine-rich region of the kRAS core promoter, and particularly the G4mid structure, as the primary target, future drug discovery programs will have potential to develop a potent, specifically targeted small molecule to be used in the treatment of pancreatic, ovarian, lung, and colon cancers.

Immuno- and gene-therapeutic strategies targeted against cancer (mainly focusing on pancreatic cancer)

Current treatment modalities of surgical resection and chemotherapy against cancers have improved survival. However, mortality from tumor recurrence remains high. Immunotherapy and gene therapy are potential additions to the treatment arsenal in the care of cancer patients. These novel therapeutic approaches need further investigation in in vitro and in vivo models as they are developed for potential use in humans. Here we reviewed immunotherapies and gene therapies that included clinical trials against cancers (mainly focusing on pancreatic cancer) suggesting the strong possibility of using these novel approaches.

Molecular consequences of silencing mutant K-ras in pancreatic cancer cells: justification for K-ras-directed therapy

Mutation of the K-ras gene is an early event in the development of pancreatic adenocarcinoma and, therefore, RNA interference (RNAi) directed toward mutant K-ras could represent a novel therapy. In this study, we examine the phenotypic and molecular consequences of exposure of pancreatic tumor cells to mutant-specific K-ras small interfering RNA. Specific reduction of activated K-ras via RNAi in Panc-1 and MiaPaca-2 cells resulted in cellular changes consistent with a reduced capacity to form malignant tumors. These changes occur through distinct mechanisms but likely reflect an addiction of each cell line to oncogene stimulation. Both cell lines show reduced proliferation after K-ras RNAi, but only MiaPaca-2 cells showed increased apoptosis. Both cell lines showed reduced migration after K-ras knockdown, but changes in integrin levels were not consistent between the cell lines. Both cell lines showed alteration of the level of GLUT-1, a metabolism-associated gene that is downstream of c-myc, with Panc-1 cells demonstrating decreased GLUT-1 levels, whereas MiaPaca-2 cells showed increased levels of expression after K-ras knockdown. Furthermore, after K-ras RNAi, there was a reduction in angiogenic potential of both Panc-1 and MiaPaca-2 cells. Panc-1 cells increased the level of expression of thrombospondin-1, an endogenous inhibitor of angiogenesis, whereas MiaPaca-2 cells decreased the production of vascular endothelial growth factor, a primary stimulant of angiogenesis in pancreatic tumors. We have found that silencing mutant K-ras through RNAi results in alteration of tumor cell behavior in vitro and suggests that targeting mutant K-ras specifically might be effective against pancreatic cancer in vivo.

Terminally modified oligodeoxynucleotides directed against p53 in an orthotopic xenograft model: a novel adjuvant treatment strategy for pancreatic ductal carcinoma

OBJECTIVES

Investigation of a terminally modified oligodeoxynucleotide (ODN) directed against p53 mRNA (p53-3' polyethylene glycol-5' tocopherol ODN as a novel drug for pancreatic ductal carcinoma therapy in vitro and in vivo.

METHODS

The impact of lipophilic modifications at the 5' end of p53-directed ODNs on cellular uptake was analyzed in vitro using proliferation assays, fluorescence-activated cell sorting analysis, and confocal laser scanning microscopy. The in vivo effects of p53-PT-ODN on the growth of orthotopically xenografted human pancreatic ductal carcinoma cells (PancTuI) were studied in SCID beige mice. Distribution was examined in vitro and in vivo using Cy3-labeled ODNs.

RESULTS

Terminally modified p53-PT-ODN showed excellent cellular uptake without using transfection reagents. Microscopically detectable levels of p53-PT-ODN were reached in vivo within 3 hours after intraperitoneal injection, even in extraperitoneal organs. At this time, Cy3-labeled p53-PT-ODN was found in solid tumor formations. We observed a significant inhibition of tumor growth (50%) in vivo at low doses of p53-PT-ODN, whereas at high doses, 2 of 9 animals had no detectable tumors at necropsy. When p53-PT-ODN was injected on the day of tumor cell inoculation, the growth inhibition of solid tumors was significantly stronger compared with that with delayed treatment.

CONCLUSIONS

p53-Directed modified ODNs might be of therapeutic value in pancreatic ductal carcinoma, particularly as adjuvant therapy after pancreatic tumor resection.

Signal transduction mediated by the Ras/Raf/MEK/ERK pathway from cytokine receptors to transcription factors: potential targeting for therapeutic intervention

The Ras/Raf/Mitogen-activated protein kinase/ERK kinase (MEK)/extracellular-signal-regulated kinase (ERK) cascade couples signals from cell surface receptors to transcription factors, which regulate gene expression. Depending upon the stimulus and cell type, this pathway can transmit signals, which result in the prevention or induction of apoptosis or cell cycle progression. Thus, it is an appropriate pathway to target for therapeutic intervention. This pathway becomes more complex daily, as there are multiple members of the kinase and transcription factor families, which can be activated or inactivated by protein phosphorylation. The diversity of signals transduced by this pathway is increased, as different family members heterodimerize to transmit different signals. Furthermore, additional signal transduction pathways interact with the Raf/MEK/ERK pathway to regulate positively or negatively its activity, or to alter the phosphorylation status of downstream targets. Abnormal activation of this pathway occurs in leukemia because of mutations at Ras as well as genes in other pathways (eg PI3K, PTEN, Akt), which serve to regulate its activity. Dysregulation of this pathway can result in autocrine transformation of hematopoietic cells since cytokine genes such as interleukin-3 and granulocyte/macrophage colony-stimulating factor contain the transacting binding sites for the transcription factors regulated by this pathway. Inhibitors of Ras, Raf, MEK and some downstream targets have been developed and many are currently in clinical trials. This review will summarize our current understanding of the Ras/Raf/MEK/ERK signal transduction pathway and the downstream transcription factors. The prospects of targeting this pathway for therapeutic intervention in leukemia and other cancers will be evaluated.

Targeting the Raf kinase cascade in cancer therapy--novel molecular targets and therapeutic strategies

The mitogen-activated protein kinases (MAPKs) are a group of signal transducers with oncogenic potential in an assortment of cell types. Dysregulated signalling from any of the members of this family has been shown to result in development of human malignancies. Consequently, the collective goal of the scientific community is to inhibit aberrant signalling initiated from these molecules whilst minimising toxicity associated with such inhibition. This review covers events responsible for MAPK activation in detail, with an emphasis placed upon possible points of pharmacological intervention. A discussion addressing numerous chemotherapeutic approaches that have been developed over the previous decade for MAPK inhibition is also included. In addition, emphasis is placed upon the various arrays of kinase inhibitors, small molecule inhibitors, competitive inhibitors, nucleic acid aptamers and other molecules which have been proven effective in prevention of MAPK signalling. Finally, the potential therapeutic promise of many of these compounds is addressed in a manner that encompasses the complexities of MAPK signal transduction, in addition to concerns surrounding the development of drug resistance.