Oligonucleotide N3' --> P5' thio-phosphoramidate telomerase template antagonists as potential anticancer agents

From Crypts to Cancer: A Holistic Perspective on Colorectal Carcinogenesis and Therapeutic Strategies

Colorectal cancer (CRC) represents a significant global health burden, with high incidence and mortality rates worldwide. Recent progress in research highlights the distinct clinical and molecular characteristics of colon versus rectal cancers, underscoring tumor location's importance in treatment approaches. This article provides a comprehensive review of our current understanding of CRC epidemiology, risk factors, molecular pathogenesis, and management strategies. We also present the intricate cellular architecture of colonic crypts and their roles in intestinal homeostasis. Colorectal carcinogenesis multistep processes are also described, covering the conventional adenoma-carcinoma sequence, alternative serrated pathways, and the influential Vogelstein model, which proposes sequential APC, KRAS, and TP53 alterations as drivers. The consensus molecular CRC subtypes (CMS1-CMS4) are examined, shedding light on disease heterogeneity and personalized therapy implications.

Oligonucleotide inhibitors of telomerase: prospects for anticancer therapy and diagnostics

The activity of telomerase allows eukaryotic cells to have unlimited division potential. On its functioning, telomerase synthesizes short DNA repeats at the 3'-end of DNA within chromosomes that ensures genome stability during cell division. Telomerase is active in the majority of cancer cell types and is virtually absent in somatic cells with rare exceptions. This difference allows us to consider inhibition of telomerase activity as a possible approach to antitumor therapy. Telomerase is a nucleoprotein composed of two main components: the reverse transcriptase (hTERT), which is a catalytic subunit, and telomerase RNA (hTR), which encodes a template for synthesis of repeats. The biogenesis and features of telomerase seem very promising for its inhibition due to complementary interactions. In this review, we analyze putative pathways of oligonucleotide influence on telomerase and consider the known native and modified oligonucleotide inhibitors of telomerase, as well as possible mechanisms of their action. We also discuss the application of telomerase-targeted oligonucleotide conjugates for in vivo imaging of tumor cells.

The role of telomere biology in cancer

Telomere biology plays a critical and complex role in the initiation and progression of cancer. Although telomere dysfunction resulting from replicative attrition constrains tumor growth by engaging DNA-damage signaling pathways, it can also promote tumorigenesis by causing oncogenic chromosomal rearrangements. Expression of the telomerase enzyme enables telomere-length homeostasis and allows tumor cells to escape the antiproliferative barrier posed by short telomeres. Telomeres and telomerase also function independently of one another. Recent work has suggested that telomerase promotes cell growth through pathways unrelated to telomere maintenance, and a subset of tumors elongate telomeres through telomerase-independent mechanisms. In an effort to exploit the integral link between telomere biology and cancer growth, investigators have developed several telomerase-based therapeutic strategies, which are currently in clinical trials. Here, we broadly review the state of the field with a particular focus on recent developments of interest.

Twenty years of cell-penetrating peptides: from molecular mechanisms to therapeutics

The recent discovery of new potent therapeutic molecules that do not reach the clinic due to poor delivery and low bioavailability have made of delivery a key stone in therapeutic development. Several technologies have been designed to improve cellular uptake of therapeutic molecules, including cell-penetrating peptides (CPPs). CPPs were first discovered based on the potency of several proteins to enter cells. Numerous CPPs have been described so far, which can be grouped into two major classes, the first requiring chemical linkage with the drug for cellular internalization and the second involving formation of stable, non-covalent complexes with drugs. Nowadays, CPPs constitute very promising tools for non-invasive cellular import of cargo and have been successfully applied for in vitro and in vivo delivery of therapeutic molecules varying from small chemical molecule, nucleic acids, proteins, peptides, liposomes and particles. This review will focus on the structure/function and cellular uptake mechanism of CPPs in the general context of drug delivery. We will also highlight the application of peptide carriers for the delivery of therapeutic molecules and provide an update of their clinical evaluation.

This article is part of a themed section on Vector Design and Drug Delivery. For a list of all articles in this section see the end of this paper, or visit: http://www3.interscience.wiley.com/journal/121548564/issueyear?year=2009

Cell-penetrating peptides: from molecular mechanisms to therapeutics

The recent discovery of new potent therapeutic molecules which do not reach the clinic due to poor delivery and low bioavailability have made the delivery of molecules a keystone in therapeutic development. Several technologies have been designed to improve cellular uptake of therapeutic molecules, including CPPs (cell-penetrating peptides), which represent a new and innovative concept to bypass the problem of bioavailability of drugs. CPPs constitute very promising tools and have been successfully applied for in vivo. Two CPP strategies have been described to date; the first one requires chemical linkage between the drug and the carrier for cellular drug internalization, and the second is based on the formation of stable complexes with drugs, depending on their chemical nature. The Pep and MPG families are short amphipathic peptides, which form stable nanoparticles with proteins and nucleic acids respectively. MPG- and Pep-based nanoparticles enter cells independently of the endosomal pathway and efficiently deliver cargoes, in a fully biologically active form, into a large variety of cell lines, as well as in animal models. This review focuses on the structure-function relationship of non-covalent MPG and Pep-1 strategies, and their requirement for cellular uptake of biomolecules and applications in cultured cells and animal models.

Delivery of proteins and nucleic acids using a non-covalent peptide-based strategy

The recent discovery of new potent therapeutic molecules which do not reach the clinic due to poor delivery and low bioavailability have made of delivery a key stone in therapeutic development. Several technologies have been designed to improve cellular uptake of therapeutic molecules, including cell-penetrating peptides (CPPs), which have been successfully applied for in vivo delivery of biomolecules and constitute very promising tools. Distinct families of CPPs have been described; some require chemical linkage between the drug and the carrier for cellular drug internalization while others like Pep-and MPG-families, form stable complexes with drugs depending on their chemical nature. Pep and MPG are short amphipathic peptides, which form stable nanoparticles with proteins and nucleic acids respectively. MPG and Pep based nanoparticles enter cells independently of the endosomal pathway and efficiently deliver cargoes in a fully biologically active form into a large variety of cell lines as well as in animal models. This review will focus on the mechanisms of non-covalent MPG and Pep-1 strategies and their applications in cultured cells and animal models.

Telomerase template antagonist GRN163L disrupts telomere maintenance, tumor growth, and metastasis of breast cancer

PURPOSE

Maintenance of telomeres by telomerase is critical for the continuing proliferation of most advanced cancer cells. Telomerase activity has been detected in the vast majority of cancer cells but not most normal cells, making the enzyme an attractive target for anticancer therapy. The aim of this study was to address the breast cancer translational potential of the novel telomerase inhibitor, GRN163L.

EXPERIMENTAL DESIGN

In the present study, we investigated the effects of GRN163L treatment on a panel of breast cancer cells representing different tumor subtypes with varying genetic backgrounds, including ER+, ER-, HER2+, BRCA1 mutant breast tumor cells as well as doxorubicin-resistant cancer cells. To investigate the in vivo effects of GRN163L, we employed a breast cancer xenograft and metastasis model that simulates a clinical situation in which a patient arrives with a primary tumor that may be then treated or surgically removed.

RESULTS

GRN163L effectively inhibited telomerase activity in a dose-dependent fashion in all breast cancer cell lines resulting in progressive telomere shortening. A mismatch control oligonucleotide showed no effect on telomerase activity and GRN163L did not significantly affect telomere shortening in normal human mammary epithelial cells or in endothelial cells. Breast cancer cells that exhibited telomerase inhibition also exhibited significant reduction in colony formation and tumorigenicity. Furthermore, GRN163L suppressed tumor growth and lung metastases (P = 0.017) of MDA-MB-231 cells in vivo after 4 weeks of treatment.

CONCLUSIONS

These results show in vivo effectiveness of GRN163L in breast cancer and support its promising clinical potential for breast cancer treatment.

Interactions of amphipathic CPPs with model membranes

We have investigated the interactions between two carrier peptides and model membrane systems as well as the conformational consequences of these interactions. Studies performed with lipid monolayers at the air-water interface have enabled identification of the nature of the lipid-peptide interactions and characterization of the influence of phospholipids on the ability of these peptides to penetrate into lipidic media. Penetration experiments reveal that both peptides interact strongly with phospholipids. Conformational investigations indicate that the lipid-peptide interaction govern the conformational state of the peptides. Based on the ability of both peptides to promote ion permeabilization of both natural and artificial membranes, we propose a model illustrating the translocation process. For MPG, it is based on the formation of a beta-barrel pore-like structure, while for Pep-1, it is based on association of helices.

Interactions of amphipathic carrier peptides with membrane components in relation with their ability to deliver therapeutics

To identify rules for the design of efficient CPPs that can deliver therapeutic agents such as nucleic acids (DNAs, siRNAs) or proteins and PNAs into subcellular compartments, we compared the properties of several primary and secondary amphipathic CPPs. Studies performed with lipid monolayers at the air-water interface have enabled identification of the nature of the lipid-peptide interactions and characterization of the influence of phospholipids on the ability of these peptides to penetrate into lipidic media. Penetration and compression experiments reveal that both peptides interact strongly with phospholipids, and observations on Langmuir-Blodgett transfers indicate that they can modify the lipid organization. Conformational investigations indicate that the lipid-peptide interactions govern the conformational state(s) of the peptides. On the basis of the ability of both peptides to promote ion permeation through both natural and artificial membranes, models illustrating the translocation processes have been proposed. One is based on the formation of a beta-barrel pore-like structure while another is based on the association of helices.

Telomerase inhibition in cancer therapeutics: molecular-based approaches

Current standard cancer therapies (chemotherapy and radiation) often cause serious adverse off-target effects. Drug design strategies are therefore being developed that will more precisely target cancer cells for destruction while leaving surrounding normal cells relatively unaffected. Telomerase, widely expressed in most human cancers but almost undetectable in normal somatic cells, provides an exciting drug target. This review focuses on recent pharmacogenomic approaches to telomerase inhibition. Antisense oligonucleotides, RNA interference, ribozymes, mutant expression, and the exploitation of differential telomerase expression as a strategy for targeted oncolysis are discussed here in the context of cancer therapeutics. Reports of synergism between telomerase inhibitors and traditional cancer therapeutic agents are also analyzed.

In vivo inhibition of lung cancer by GRN163L: a novel human telomerase inhibitor

Differential regulation of telomerase activity in normal and tumor cells provides a rationale for the design of new classes of telomerase inhibitors. The telomerase enzyme complex presents multiple potential sites for the development of inhibitors. GRN163L, a telomerase enzyme antagonist, is a lipid-modified 13-mer oligonucleotide N3' --> P5'-thio-phosphoramidate, complementary to the template region of telomerase RNA (hTR). We evaluated both the in vitro and in vivo effects of GRN163L using A549-luciferase (A549-Luc) human lung cancer cells expressing a luciferase reporter. GRN163L (1 micromol/L) effectively inhibits telomerase activity of A549-Luc cells, resulting in progressive telomere shortening. GRN163L treatment also reduces colony formation in soft agar assays. Surprisingly, after only 1 week of treatment with GRN163L, A549-Luc cells were unable to form robust colonies in the clonal efficiency assay, whereas the mismatch control compound had no effect. Finally, we show that in vivo treatment with GRN163L is effective in preventing lung metastases in xenograft animal models. These in vitro and in vivo data support the development of GRN163L as a therapeutic for the treatment of cancer.

Telomerase antagonists GRN163 and GRN163L inhibit tumor growth and increase chemosensitivity of human hepatoma

Most cancer cells have an immortal growth capacity as a consequence of telomerase reactivation. Inhibition of this enzyme leads to increased telomere dysfunction, which limits the proliferative capacity of tumor cells; thus, telomerase inhibition represents a potentially safe and universal target for cancer treatment. We evaluated the potential of two thio-phosphoramidate oligonucleotide inhibitors of telomerase, GRN163 and GRN163L, as drug candidates for the treatment of human hepatoma. GRN163 and GRN163L were tested in preclinical studies using systemic administration to treat flank xenografts of different human hepatoma cell lines (Hep3B and Huh7) in nude mice. The studies showed that both GRN163 and GRN163L inhibited telomerase activity and tumor cell growth in a dose-dependent manner in vitro and in vivo. The potency and efficacy of the lipid-conjugated antagonist, GRN163L, was superior to the nonlipidated parent compound, GRN163. Impaired tumor growth in vivo was associated with critical telomere shortening, induction of telomere dysfunction, reduced rate of cell proliferation, and increased apoptosis in the treatment groups. In vitro, GRN163L administration led to higher prevalence of chromosomal telomere-free ends and DNA damage foci in both hepatoma cell lines. In addition, in vitro chemosensitivity assay showed that pretreatment with GRN163L increased doxorubicin sensitivity of Hep3B. In conclusion, our data support the development of GRN163L, a novel lipidated conjugate of the telomerase inhibitor GRN163, for systemic treatment of human hepatoma. In addition to limiting the proliferative capacity of hepatoma, GRN163L might also increase the sensitivity of this tumor type to conventional chemotherapy.