Phase II trial of echinomycin in patients with advanced or recurrent colorectal cancer

Synthesis and biological evaluation of echinomycin analogues as potential colon cancer agent

Colorectal cancer is the third most commonly diagnosed cancer and the second leading cause of cancer-related death, thus a novel chemotherapeutic agent for colon cancer therapy is needed. In this study, analogues of echinomycin, a cyclic peptide natural product with potent toxicity to several human cancer cell lines, were synthesized, and their biological activities against human colon cancer cells were investigated. Analogue 3 as well as 1 inhibit HIF-1α-mediated transcription. Notably, transcriptome analysis indicated that the cell cycle and its regulation were involved in the effects on cells treated with 3. Analogue 3 exhibited superior in vivo efficacy to echinomycin without significant toxicity in mouse xenograft model. The low dose of 3 needed to be efficacious in vivo is also noteworthy and our data suggest that 3 is an attractive and potentially novel agent for the treatment of colon cancer.

Structure-Activity Relationships of Bis-Intercalating Peptides and Their Application as Antibody-Drug Conjugate Payloads

Synthetic analogs based on the DNA bis-intercalating natural product peptides sandramycin and quinaldopeptin were investigated as antibody drug conjugate (ADC) payloads. Synthesis, biophysical characterization, and in vitro potency of 34 new analogs are described. Conjugation of an initial drug-linker derived from a novel bis-intercalating peptide produced an ADC that was hydrophobic and prone to aggregation. Two strategies were employed to improve ADC physiochemical properties: addition of a solubilizing group in the linker and the use of an enzymatically cleavable hydrophilic mask on the payload itself. All ADCs showed potent in vitro cytotoxicity in high antigen expressing cells; however, masked ADCs were less potent than payload matched unmasked ADCs in lower antigen expressing cell lines. Two pilot in vivo studies were conducted using stochastically conjugated DAR4 anti-FRα ADCs, which showed toxicity even at low doses, and site-specific conjugated (THIOMAB) DAR2 anti-cMet ADCs that were well tolerated and highly efficacious.

Synergistic binding of actinomycin D and echinomycin to DNA mismatch sites and their combined anti-tumour effects

Combination cancer chemotherapy is one of the most useful treatment methods to achieve a synergistic effect and reduce the toxicity of dosing with a single drug. Here, we use a combination of two well-established anticancer DNA intercalators, actinomycin D (ActD) and echinomycin (Echi), to screen their binding capabilities with DNA duplexes containing different mismatches embedded within Watson-Crick base-pairs. We have found that combining ActD and Echi preferentially stabilised thymine-related T:T mismatches. The enhanced stability of the DNA duplex-drug complexes is mainly due to the cooperative binding of the two drugs to the mismatch duplex, with many stacking interactions between the two different drug molecules. Since the repair of thymine-related mismatches is less efficient in mismatch repair (MMR)-deficient cancer cells, we have also demonstrated that the combination of ActD and Echi exhibits enhanced synergistic effects against MMR-deficient HCT116 cells and synergy is maintained in a MMR-related MLH1 gene knockdown in SW620 cells. We further accessed the clinical potential of the two-drug combination approach with a xenograft mouse model of a colorectal MMR-deficient cancer, which has resulted in a significant synergistic anti-tumour effect. The current study provides a novel approach for the development of combination chemotherapy for the treatment of cancers related to DNA-mismatches.

Antitumor effect of the selective hypoxia-inducible factor-1 inhibitors echinomycin and PX-478 on uterine fibroids

OBJECTIVE

To investigate the antitumor effects of the selective hypoxia-inducible factor-1 (HIF-1) inhibitors echinomycin and PX-478 on uterine fibroids.

DESIGN

Experimental study using in vitro primary culture systems and an in vivo mouse xenograft model.

SETTING

Academic university center.

PATIENT(S)

Women with uterine fibroids who underwent hysterectomy or myomectomy.

INTERVENTION(S)

Administration of the selective HIF-1 inhibitors echinomycin and PX-478 to the media of the primary cultured uterine fibroid cells and to nonobese diabetic/severe combined immunodeficient mice bearing fibroid xenografts consisting of the primary cultured fibroid cells and type Ⅰ collagen gels beneath the kidney capsule.

MAIN OUTCOME MEASURE(S)

Cell proliferation was measured by Cell Counting Kit-8 assay. Apoptosis was evaluated by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assay and by measuring caspase 3 and 7 activities. The xenografts were evaluated by gross appearance, surface area, and histology. The Ki-67 index was measured to evaluate proliferation of the xenografts.

RESULT(S)

Both echinomycin and PX-478 inhibited cell proliferation and induced apoptosis in fibroid cells cultured under hypoxia and normoxia. Enlargement of the fibroid xenografts was significantly attenuated. The Ki-67 index significantly decreased after the administration of the HIF-1 inhibitors in the xenograft model. Eight of 27 xenografts treated with the HIF-1 inhibitors contained calcification and hyalinizing components from 3 days after the grafting to 2 weeks, suggesting that the HIF-inhibitors induce degeneration of the fibroid xenografts.

CONCLUSION(S)

The selective HIF-1 inhibitors echinomycin and PX-478 show antitumor effects against uterine fibroids both in vitro and in vivo. These findings support the potential use of HIF-1 inhibitors for the treatment of uterine fibroids.

Advances in heterocycles as DNA intercalating cancer drugs

The insertion of a molecule between the bases of DNA is known as intercalation. A molecule is able to interact with DNA in different ways. DNA intercalators are generally aromatic, planar, and polycyclic. In chemotherapeutic treatment, to suppress DNA replication in cancer cells, intercalators are used. In this article, we discuss the anticancer activity of 10 intensively studied DNA intercalators as drugs. The list includes proflavine, ethidium bromide, doxorubicin, dactinomycin, bleomycin, epirubicin, mitoxantrone, ellipticine, elinafide, and echinomycin. Considerable structural diversities are seen in these molecules. Besides, some examples of the metallo-intercalators are presented at the end of the chapter. These molecules have other crucial properties that are also useful in the treatment of cancers. The successes and limitations of these molecules are also presented.

Characterization of Streptomyces sp. LS462 with high productivity of echinomycin, a potent antituberculosis and synergistic antifungal antibiotic

A biologically active microbial strain, designated as "LS462," was isolated from a soil sample collected from Yaoli Virgin Forest of Jiangxi Province, China. The strain was able to produce a high yield of echinomycin (172 mg/l) even under nonoptimized culture conditions and is proposed to serve as a promising source of echinomycin. In this study, echinomycin exhibited strong anti-Mycobacterium tuberculosis H37Rv activity and synergistic antifungal effect with a greatly reduced dosage of posaconazole on Candida albicans SC5314. The strain belongs to the genus Streptomyces according to its morphological and 16S rDNA phylogenetic analysis. The 16S rDNA was found to have the highest sequence identity with Streptomyces fuscichromogenes (99.37% similarity). Extensive nuclear magnetic resonance and mass spectroscopic data were used to determine the structure of echinomycin. The strain S. fuscichromogenes has not been previously reported to produce echinomycin. Strain LS462 may be exploited as a new potential source for the commercial production of echinomycin. Also, this work is the first to report the new synergistic antifungal activity of echinomycin and further study of the synergistic mechanism will be helpful to guide the development of antifungal agents.

Quinomycin A reduces cyst progression in polycystic kidney disease

Polycystic kidney disease (PKD) is a genetic disorder characterized by aberrant renal epithelial cell proliferation and formation and progressive growth of numerous fluid-filled cysts within the kidneys. Previously, we showed that there is elevated Notch signaling compared to normal renal epithelial cells and that Notch signaling contributes to the proliferation of cystic cells. Quinomycin A, a bis-intercalator peptide, has previously been shown to target the Notch signaling pathway and inhibit tumor growth in cancer. Here, we show that Quinomycin A decreased cell proliferation and cyst growth of human ADPKD cyst epithelial cells cultured within a 3D collagen gel. Treatment with Quinomycin A reduced kidney weight to body weight ratio and decreased renal cystic area and fibrosis in Pkd1^RC/RC ; Pkd2^+/- mice, an orthologous PKD mouse model. This was accompanied by reduced expression of Notch pathway proteins, RBPjk and HeyL and cell proliferation in kidneys of PKD mice. Quinomycin A treatments also normalized cilia length of cyst epithelial cells derived from the collecting ducts. This is the first study to demonstrate that Quinomycin A effectively inhibits PKD progression and suggests that Quinomycin A has potential therapeutic value for PKD patients.

Liposomal formulation of HIF-1α inhibitor echinomycin eliminates established metastases of triple-negative breast cancer

Hypoxia-inducible factor 1α (HIF-1α) is recognized as a prime molecular target for metastatic cancer. However, no specific HIF-1α inhibitor has been approved for clinical use. Here, we demonstrated that in vivo efficacy of echinomycin in solid tumors with HIF-1α overexpression is formulation-dependent. Compared to previously-used Cremophor-formulated echinomycin, which was toxic and ineffective in clinical trials, liposomal-echinomycin provides significantly more inhibition of primary tumor growth and only liposome-formulated echinomycin can eliminate established triple-negative breast cancer (TNBC) metastases, which are the leading cause of death from breast cancer, as available therapies remain minimally effective at this stage. Pharmacodynamic analyses reveal liposomal-echinomycin more potently inhibits HIF-1α transcriptional activity in primary and metastasized TNBC cells in vivo, the latter of which are HIF-1α enriched. The data suggest that nanoliposomal-echinomycin can provide safe and effective therapeutic HIF-1α inhibition and could represent the most potent HIF-1α inhibitor in prospective trials for metastatic cancer.

Encapsulation of echinomycin in cyclodextrin inclusion complexes into liposomes: in vitro anti-proliferative and anti-invasive activity in glioblastoma

Echinomycin, a DNA bis-intercalator peptide antibiotic, was complexed with γCD and loaded into PEGylated liposomes. The liposomes encapsulating echinomycin showed potent anti-proliferative and anti-invasive effect against U-87 MG glioblastoma cells.

Quinomycin A targets Notch signaling pathway in pancreatic cancer stem cells

Cancer stem cells (CSCs) appear to explain many aspects of the neoplastic evolution of tumors and likely account for enhanced therapeutic resistance following treatment. Dysregulated Notch signaling, which affects CSCs plays an important role in pancreatic cancer progression. We have determined the ability of Quinomycin to inhibit CSCs and the Notch signaling pathway. Quinomycin treatment resulted in significant inhibition of proliferation and colony formation in pancreatic cancer cell lines, but not in normal pancreatic epithelial cells. Moreover, Quinomycin affected pancreatosphere formation. The compound also decreased the expression of CSC marker proteins DCLK1, CD44, CD24 and EPCAM. In addition, flow cytometry studies demonstrated that Quinomycin reduced the number of DCLK1+ cells. Furthermore, levels of Notch 1–4 receptors, their ligands Jagged1, Jagged2, DLL1, DLL3, DLL4 and the downstream target protein Hes-1 were reduced. The γ-secretase complex proteins, Presenilin 1, Nicastrin, Pen2, and APH-1, required for Notch activation also exhibited decreased expression. Ectopic expression of the Notch Intracellular Domain (NICD) partially rescued the cells from Quinomycin mediated growth suppression. To determine the effect of Quinomycin on tumor growth in vivo, nude mice carrying tumor xenografts were administered Quinomycin intraperitoneally every day for 21 days. Treatment with the compound significantly inhibited tumor xenograft growth, coupled with significant reduction in the expression of CSC markers and Notch signaling proteins. Together, these data suggest that Quinomycin is a potent inhibitor of pancreatic cancer that targets the stem cells by inhibiting Notch signaling proteins.

Targeting transcription factors by small compounds--Current strategies and future implications

Transcription factors are central regulators of gene expression and critically steer development, differentiation and death. Except for ligand-activated nuclear receptors, direct modulation of transcription factor function by small molecules is still widely regarded as "impossible". This "un-druggability" of non-ligand transcription factors is due to the fact that the interacting surface between transcription factor and DNA is huge and subject to significant changes during DNA-binding. Besides some "success studies" with compounds that directly interfere with DNA binding, drug targeting approaches mostly address protein-protein interfaces with essential co-factors, transcription factor dimerization partners, chaperone proteins or proteins that regulate subcellular shuttling. An alternative strategy represent DNA-intercalating, alkylating or DNA-groove-binding compounds that either block transcription factor-binding or change the 3D-conformation of the consensus DNA-strand. Recently, much interest has been focused on chromatin reader proteins that steer the recruitment and activity of transcription factors to a gene transcription start site. Several small compounds demonstrate that these epigenetic reader proteins are exciting new drug targets for inhibiting lineage-specific transcription in cancer therapy. In this research update we will discuss recent advances in targeting transcription factors with small compounds, the challenges that are related to the complex function and regulation of these proteins and also the possible future directions and applications of transcription factor drug targeting.

Echinomycin protects mice against relapsed acute myeloid leukemia without adverse effect on hematopoietic stem cells

Acute myeloid leukemia (AML) often relapses following chemotherapy-induced remission and is generally chemo-resistant. Given the potential role for cancer stem cells in relapse, targeting of the leukemia-initiating cell (LIC) in AML may provide improved outcome following remission induction. However, due to overlap in their self-renewal program with normal hematopoietic stem cells (HSCs), therapeutic targeting of the LIC may have an adverse effect on long-term hematopoietic recovery. Here we used a mouse model of relapsed AML to explore whether the hypoxia-inducible factor (HIF)1α inhibitor echinomycin can be used to treat relapsed AML without affecting host HSCs. We show that echinomycin cured 40% to 60% of mice transplanted with relapsed AML. Bone marrow cells from the cured mice displayed normal composition of HSCs and their progenitors and were as competent as those isolated from nonleukemic mice in competitive repopulation assays. Importantly, in mice with complete remission, echinomycin appeared to completely eliminate LICs because no leukemia could be propagated in vivo following serial transplantation. Taken together, our data demonstrate that in a mouse model of relapsed AML, low-dose echinomycin selectively targets LICs and spares normal hematopoiesis.

Acute myelogenous leukemia stem cells: from Bench to Bedside

Despite reaching remission with traditional chemotherapy, most adult patients with acute myeloid leukemia (AML) will relapse and die of their disease. Numerous studies have identified a rare subset of leukemia cells that evade traditional chemotherapy and are capable of self-renewal and initiating leukemia. These cells are thought to be responsible for relapse and are termed leukemia stem cells (LSCs). This article will review the current LSC translational research and focus on new approaches to detect LSC burden and its prognostic implications, as well as the identification and development of therapeutic agents active against LSCs.

Patterns of tumor oxygenation and their influence on the cellular hypoxic response and hypoxia-directed therapies

Deficiencies in the oxygenation of solid tumors are associated with poor patient prognosis due to changes in cell metabolism, angiogenesis, invasiveness and resistance to therapy. Work over the past 10 years has defined several distinct oxygen sensing pathways that together determine the cellular response to hypoxia. These include both a transcriptional response initiated by oxygen-dependent stabilisation of the HIF-1 transcription factor and an mRNA translational response characterized by activation of the unfolded protein response (UPR) and inhibition of mTOR signalling. Laboratory experiments have established the importance of these hypoxic response pathways for tumor growth and resistance to treatment. This has led to the development of agents aimed at targeting hypoxic response pathways in tumors, several of which are in clinical trials. However, several important features of the tumor microenvironment that may affect the success of these new therapies have not been thoroughly evaluated. Oxygenation patterns in human tumors have proven to be highly complex, leading to a large degree of heterogeneity with respect to the severity and duration of hypoxic exposure. Because both of these properties strongly influence the known cellular responses to hypoxia, this heterogeneity is expected to be a strong determinant of the fate of hypoxic cells and the success of new hypoxia-directed therapies. Here we summarize the important oxygen response pathways that currently serve as targets for therapy and their dependence on the specific oxygenation patterns that are expected in human tumors.

Hypoxia inducible factor-1: a novel target for cancer therapy

Hypoxia develops in the majority of solid tumors due to the inability of the existing vascular system to supply the growing tumor mass with adequate amounts of oxygen. A large body of clinical evidence suggests that intratumoral hypoxia correlates with the elevated aggressive behavior of cancer cells and their resistance to therapy, leading to poor patient prognoses. A heterodimeric transcription factor, hypoxia inducible factor-1 (HIF-1), has been shown to orchestrate a large number of molecular events required for the adaptation of tumor cells to hypoxia. Therefore, HIF-1 has become an attractive target for the development of anti-cancer drugs. Here, we highlight some of the recently developed small-molecule inhibitors of HIF-1 function. These drugs disrupt the HIF-1 signaling pathway through a variety of mechanisms, including the inhibition of HIF-1alpha protein synthesis, stabilization, nuclear translocation and HIF-1 transactivation of target genes.

Echinomycin, a small-molecule inhibitor of hypoxia-inducible factor-1 DNA-binding activity

The identification of small molecules that inhibit the sequence-specific binding of transcription factors to DNA is an attractive approach for regulation of gene expression. Hypoxia-inducible factor-1 (HIF-1) is a transcription factor that controls genes involved in glycolysis, angiogenesis, migration, and invasion, all of which are important for tumor progression and metastasis. To identify inhibitors of HIF-1 DNA-binding activity, we expressed truncated HIF-1alpha and HIF-1beta proteins containing the basic-helix-loop-helix and PAS domains. Expressed recombinant HIF-1alpha and HIF-1beta proteins induced a specific DNA-binding activity to a double-stranded oligonucleotide containing a canonical hypoxia-responsive element (HRE). One hundred twenty-eight compounds previously identified in a HIF-1-targeted cell-based high-throughput screen of the National Cancer Institute 140,000 small-molecule library were tested in a 96-well plate ELISA for inhibition of HIF-1 DNA-binding activity. One of the most potent compounds identified, echinomycin (NSC-13502), a small-molecule known to bind DNA in a sequence-specific fashion, was further investigated. Electrophoretic mobility shift assay experiments showed that NSC-13502 inhibited binding of HIF-1alpha and HIF-1beta proteins to a HRE sequence but not binding of the corresponding proteins to activator protein-1 (AP-1) or nuclear factor-kappaB (NF-kappaB) consensus sequences. Interestingly, chromatin immunoprecipitation experiments showed that NSC-13502 specifically inhibited binding of HIF-1 to the HRE sequence contained in the vascular endothelial growth factor (VEGF) promoter but not binding of AP-1 or NF-kappaB to promoter regions of corresponding target genes. Accordingly, NSC-13502 inhibited hypoxic induction of luciferase in U251-HRE cells and VEGF mRNA expression in U251 cells. Our results indicate that it is possible to identify small molecules that inhibit HIF-1 DNA binding to endogenous promoters.

QSAR analysis of substituted bis[(acridine-4-carboxamide)propyl]methylamines using optimized block-wise variable combination by particle swarm optimization for partial least squares modeling

In the current work, we employed optimized block-wise variable combination (OBVC) by particle swarm optimization (PSO) based on partial least squares (PLS) modeling for variable combination and compared it to the traditional methods. It has been demonstrated that the modified PSO is a useful tool for searching optimized variable combination. Quantitative structure-activity relationship (QSAR) model has been formulated for a set of DNA binding topoisomerase (topo) (substituted bis[(acridine-4-carboxamide)propyl]methylamines) on murine Lewis lung carcinoma (LL(c)) cells. The spatial descriptors especially Jurs descriptors play important roles in predicting the compound's inhibitory activity to murine LL(c) cells, and polar interactions are the principal binding strength between compounds and murine LL(c) cells. In addition, rotatable bonds in molecules and molar refractivity of the compounds will markedly affect the compounds' inhibitory activity.

Peptides with anticancer use or potential

This review is an attempt to illustrate the diversity of peptides reported for a potential or an established use in cancer therapy. With 612 references, this work aims at covering the patents and publications up to year 2000 with many inroads in years 2001-2002. The peptides are classed according to four categories of effective (or plausible) biological mechanisms of action: receptor-interacting compounds; inhibitors of protein-protein interaction; enzymes inhibitors; nucleic acid-interacting compounds. The fifth group is made of the peptides for which no mechanism of action has been found yet. Incidentally this work provides an overview of many of the modern targets of anticancer research.

Structure-activity relationships for substituted bis(acridine-4-carboxamides): a new class of anticancer agents

A series of acridine-substituted bis(acridine-4-carboxamides) linked by a (CH2)3N(Me)(CH2)3 chain have been prepared by reaction of the isolated imidazolides of the substituted acridine-4-carboxylic acids with N,N-bis(3-aminopropyl)methylamine. These dimeric analogues of the mixed topoisomerase I/II inhibitor N-[2-(dimethylamino)ethyl]acridine-4-carboxamide (DACA), currently in clinical trial, show superior potencies to the corresponding monomeric DACA analogues in a panel of cell lines, including wild-type (JLC) and mutant (JLA and JLD) forms of human Jurkat leukemia. The latter mutant lines are resistant to topoisomerase II targeted agents because of lower levels of the enzyme. Analogues with small substituents (e.g., Me, Cl) at the acridine 5-position were clearly superior, with IC50's as low as 2 nM against the Lewis lung carcinoma and 11 nM against JLC. Larger substituents at any position caused a steady decrease in potency, likely due to lowering of DNA binding affinity. A small series of analogues of the most potent bis(5-methylDACA) compound, with second substituents (Me and Cl) in the 1- or 8- position had broadly similar potencies to the 5-Me compound, indicating that, while the 1- and 8-substituents are acceptable, they add little to the enhancing effect of the 5-methyl group. All of the compounds were at least equitoxic (some up to 4-fold more cytotoxic) against the mutant Jurkat lines than in the wild-type, consistent with a relatively greater effect on topoisomerase I compared with topoisomerase II. The bis(5-methylDACA) compound was found to inhibit the action of purified topoisomerase I in a cell-free assay. Compounds were on average 10-fold less cytotoxic in an MCF7 breast cancer line overexpressing P-glycoprotein than in the wild-type line and showed some selectivity for colon tumor lines in the NCI human tumor cell line panel. Several analogues produced significant growth delays in the relatively refractory subcutaneous colon 38 tumor model in vivo at substantially lower doses than DACA. The bis(acridine-4-carboxamides) represent a new and interesting class of potent topoisomerase inhibitors.

Current treatment modalities in advanced colorectal carcinoma

Several biochemical and immunological substances are currently being tested for their efficacy in the treatment of advanced colorectal cancer, the second-most malignant disease in the western world. Presently, a combination of 5-fluorouracil (FU) and the biochemical modulator folinic acid is considered to be the standard treatment for this malignancy, with a median response rate of 30%. A recent multi-analysis of phase III trials with methotrexate and FU versus FU alone has demonstrated a statistically significant doubling of the response rate as well as a significant survival advantage for the combination. So far, other biochemical or immunological modulators of FU have not shown a significant advantage regarding response or survival. Several new drugs such as tegafur, thymidilate synthase inhibitors, trimetrexate, or topoisomerase-I-inhibitors have been tested with promising results in preclinical and early clinical settings. While local treatment such as hepatic artery infusion has become safer, it is still more toxic than systemic treatment and showed a significant improvement of response but no survival advantage. Since all treatment strategies in advanced colorectal cancer are still palliative, quality of life is a more important endpoint in clinical trials.

A phase II clinical trial of echinomycin in metastatic soft tissue sarcoma. An Illinois Cancer Center Study

Echinomycin, a cyclic peptide in the family of quinoxaline antibiotics, was evaluated in patient with metastatic, soft tissue sarcoma not previously treated for metastatic disease. The starting dose of echinomycin was 1,200 mcg/m2 administered intravenously, once weekly x 4, followed by a two-week break. The protocol design called for dose escalation on subsequent cycles of therapy, but because of significant toxicity, dose escalation occurred in only 5 of 25 treatment cycles. Severe nausea and vomiting was the most common toxicity. No clinical responses were observed in the 12 evaluable patients. Echinomycin at this dose and schedule is inactive in metastatic soft tissue sarcoma.