Activity of TER286 against human tumor colony-forming units

Drug Repurposing of the Anthelmintic Niclosamide to Treat Multidrug-Resistant Leukemia

Multidrug resistance, a major problem that leads to failure of anticancer chemotherapy, requires the development of new drugs. Repurposing of established drugs is a promising approach for overcoming this problem. An example of such drugs is niclosamide, a known anthelmintic that is now known to be cytotoxic and cytostatic against cancer cells. In this study, niclosamide showed varying activity against different cancer cell lines. It revealed better activity against hematological cancer cell lines CCRF-CEM, CEM/ADR5000, and RPMI-8226 compared to the solid tumor cell lines MDA-MB-231, A549, and HT-29. The multidrug resistant CEM/ADR5000 cells were similar sensitive as their sensitive counterpart CCRF-CEM (resistance ration: 1.24). Furthermore, niclosamide caused elevations in reactive oxygen species and glutathione (GSH) levels in leukemia cells. GSH synthetase (GS) was predicted as a target of niclosamide. Molecular docking showed that niclosamide probably binds to the ATP-binding site of GS with a binding energy of -9.40 kcal/mol. Using microscale thermophoresis, the binding affinity between niclosamide and recombinant human GS was measured (binding constant: 5.64 μM). COMPARE analyses of the NCI microarray database for 60 cell lines showed that several genes, including those involved in lipid metabolism, correlated with cellular responsiveness to niclosamide. Hierarchical cluster analysis showed five major branches with significant differences between sensitive and resistant cell lines (p = 8.66 × 10⁵). Niclosamide significantly decreased nuclear factor of activated T-cells (NFAT) activity as predicted by promoter binding motif analysis. In conclusion, niclosamide was more active against hematological malignancies compared to solid tumors. The drug was particularly active against the multidrug-resistant CEM/ADR5000 leukemia cells. Inhibition of GSH synthesis and NFAT signaling were identified as relevant mechanisms for the anticancer activity of niclosamide. Gene expression profiling predicted the sensitivity or resistance of cancer cells to niclosamide.

Cytoprotective and regulatory functions of glutathione S-transferases in cancer cell proliferation and cell death

PURPOSE

Glutathione S-transferases (GSTs) family of enzymes is best known for their cytoprotective role and their involvement in the development of anticancer drug resistance. Recently, emergence of non-detoxifying properties of GSTs has provided them with significant biological importance. Addressing the complex interactions of GSTs with regulatory kinases will help in understanding its precise role in tumor pathophysiology and in designing GST-centered anticancer strategies.

METHODS

We reviewed all published literature addressing the detoxification and regulatory roles of GSTs in the altered biology of cancer and evaluating novel agents targeting GSTs for cancer therapy.

RESULTS

The role of GSTs, especially glutathione S-transferase P1 isoform in tumoral drug resistance, has been the cause of intense debate. GSTs have been demonstrated to interact with different protein partners and modulate signaling pathways that control cell proliferation, differentiation and apoptosis. These specific functions of GSTs could lead to the development of new therapeutic approaches and to the identification of some interesting candidates for preclinical and clinical development. This review focuses on the crucial role played by GSTs in the development of resistance to anticancer agents and the major findings regarding the different modes of action of GSTs to regulate cell signaling.

Phase 2 study of canfosfamide in combination with pegylated liposomal doxorubicin in platinum and paclitaxel refractory or resistant epithelial ovarian cancer

Background

Canfosfamide is a novel glutathione analog activated by glutathione S-transferase P1-1. This study evaluated the safety and efficacy of canfosfamide in combination with pegylated liposomal doxorubicin (PLD) in patients with platinum resistant ovarian cancer. Patients with platinum resistant ovarian carcinoma and measurable disease received canfosfamide at 960 mg/m² in combination with PLD at 50 mg/m², intravenously day 1 in every 28 day cycles until tumor progression or unacceptable toxicities. The primary endpoints were objective response rate (ORR) and progression-free survival (PFS).

Results

Canfosfamide plus PLD combination therapy was administered at 960/50 mg/m², respectively. Thirty-nine patients received a median number of 4 cycles (range 1.0-18.0). The ORR was 27.8% (95% CI, 14.2-45.2) with a disease stabilization rate of 80.6% (95% CI, 64.0-91.8) in the evaluable population. The CA-125 marker responses correlated with the radiological findings of complete response or partial response. The median PFS was 6.0 months (95% CI, 4.2-7.9) and median survival was 17.8 months. The combination was well tolerated. Myelosuppression was managed with dose reductions and growth factor support. Grade 3 febrile neutropenia was observed in 2 patients (5.1%). Non-hematologic adverse events occurred at the expected frequency and grade for each drug alone, with no unexpected or cumulative toxicities.

Conclusions

Canfosfamide in combination with PLD is well tolerated and active in platinum and paclitaxel refractory or resistant ovarian cancer. A randomized phase 3 study was conducted based on this supportive phase 2 study.

Trial Registration

This study was registered at www.clinicaltrials.gov: NCT00052065.

Multi-institutional phase 2 study of TLK286 (TELCYTA, a glutathione S-transferase P1-1 activated glutathione analog prodrug) in patients with platinum and paclitaxel refractory or resistant ovarian cancer

The purpose of this study was to determine the safety and efficacy of TLK286 (TELCYTA(TM)), a glutathione analog prodrug, in patients with platinum and paclitaxel refractory or resistant ovarian carcinoma. Thirty-six patients with measurable disease were enrolled. TLK286 was administered at 1000 mg/m2 intravenously every 3 weeks. The endpoints were objective response rate assessed by Response Evaluation Criteria in Solid Tumors (RECIST) and survival. Adverse events were graded using the National Cancer Institute Common Toxicity Criteria. Thirty-four platinum refractory or resistant patients (94%) were evaluable for objective tumor response. Five patients (15%) had objective tumor responses, including one durable complete response (CR) of greater than 3 years and continuing. The disease stabilization rate was 50%, including one CR (3%), four partial responses (12%), and 12 durable disease stabilizations (35%). Responses were accompanied by improvement in clinical symptoms and Eastern Cooperative Oncology Group Performance Status (ECOG PS) and decline in CA125 levels. Median survival was 423 days with survival of 60% at 1 year and 40% at 18 months. TLK286 was well tolerated in this population. TLK286 is an active agent in chemotherapy-resistant ovarian cancer. Further studies of TLK286 in platinum and paclitaxel refractory or resistant ovarian cancer are in progress.

Novel agents in epithelial ovarian cancer

The gold standard chemotherapy for previously untreated patients with ovarian cancer is currently a combination of taxane and platinum. However, most patients still suffer relapse, and less than 20% of the patients with stage III or IV disease survive long term. With more advanced technology, newer cytotoxic agents have been identified and are currently being tested in patients with ovarian cancer. Recent advances in the understanding of ovarian cancer biology have also led to the identification of multiple molecular targets that may soon change the standard treatment of ovarian cancer. Several of these targeted agents have entered clinical trials. Small molecular-weight inhibitors, monoclonal antibodies, antisense therapy, and gene therapy are all being evaluated alone and in combination with cytotoxic chemotherapy. Several of these cytotoxic and targeted therapies are reviewed here. Ultimately, the success of ovarian cancer therapy lies not just in the availability of new agents but in the ability to identify patients with biomarkers that may predict their response to these agents.

Phase 1 Study of TLK286 (Telcyta) Administered Weekly in Advanced Malignancies

PURPOSE

To determine the dose-limiting toxicities, maximum tolerated dose, and pharmacokinetics of TLK286, a novel cancer prodrug, administered weekly.

PATIENTS AND METHODS

Patients with advanced malignancies were treated with TLK286 administered weekly by i.v. infusion over 30 min in escalating doses 60-960 mg/m(2). A treatment cycle was defined as 3 weekly treatments. Patients underwent tumor assessments on day 43, and those patients receiving clinical benefit continued on treatment until disease progression or unacceptable toxicity. Safety was assessed by the WHO criteria.

RESULTS

Thirty-seven patients received 111 cycles of TLK286 at eight dose levels (median, 3 cycles; range, 1-16 cycles). In this study, TLK286 given weekly at 960 mg/m(2) was well tolerated without dose-limiting toxicities. TLK286-related toxicities included grade 1-2 nausea and vomiting, fatigue and anemia. Nine of 31 evaluable patients continued therapy beyond day 43 and received a median of 5 cycles (range of 3-16 cycles) and experienced durable stable disease or minor tumor regression. Pharmacokinetic characteristics of TLK286 are described by an optimized two-compartment model. Mild to moderate renal or hepatic organ dysfunction did not impact the elimination of TLK286.

CONCLUSIONS

TLK286 administered weekly at doses up to 960 mg/m(2) were well tolerated. The safety and antitumor activity observed in a broad range of cancer types supports Phase 2 disease-specific investigations of TLK286 given weekly at 960 mg/m(2).

TLK 286

TLK 286 [TELCYTA] is an antitumour agent in clinical development with Telik. It was developed through the application of Telik's proprietary TRAP chemogenomics technology. TLK 286 works by targeting tumours that overexpress glutathione S-transferase (GST) P1-1, an enzyme that has been implicated in drug resistance and poor prognosis, and is elevated in solid tumours such as head and neck, breast, gastrointestinal, lung and ovarian tumours. TLK 286 is activated by GST P1-1 and, subsequently, initiates apoptosis in targeted tumour cells. Telik owns worldwide rights to TLK 286 and intends to commercialise it in the North American market. The company plans to select a collaborator in other territories with capabilities in manufacturing, sales and marketing. Telik was previously collaborating with Taiho, Japan, on development of TLK 286, but this agreement appears to have been terminated. Telik announced in October 2002 that it had begun the first of a series of planned clinical trials of TLK 286 in combination with docetaxel in patients with non-small cell lung cancer. A phase II trial was initiated in May 2001 in patients with ovarian cancer. Two additional combination trials were initated in ovarian cancer patients in December 2002. One of the trials will evaluate the combination of TLK 286 with Doxil in patients who have failed platinum-based chemotherapy. The second trial will evaluate TLK 286 in combination with carboplatin in patients who have recurrent, platinum-sensitive ovarian cancer. Telik held a successful phase III meeting with the US FDA to discuss plans for the first registration trial of TLK 286, and in March 2003 it was announced that a phase III registration trial of TLK 286 as monotherapy had been initiated in platinum-refractory ovarian cancer patients. The multinational trial has been designated the ASSIST-1 (Assessment of Survival in Solid Tumours-1) trial. Telik plans to enrol approximately 440 women who will be assigned to either TLK 286 treatment or a control (doxorubicin liposomal or topotecan).

Anticancer therapy targeting the apoptotic pathway

Apoptosis, or programmed cell death, has an essential role in controlling cell number in many developmental and physiological settings and in chemotherapy-induced tumour-cell killing. It is a genetically regulated biological process, guided by the ratio of proapoptotic and antiapoptotic proteins. Recently, inducers of apoptosis have been used in cancer therapy. Several studies have attempted to induce apoptosis by triggering the tumour-necrosis-factor-related apoptosis-inducing ligand receptor and the BCL2 family of proteins, and others have targeted the caspases, and proteins that inhibit apoptosis. Most of these therapies are still in preclinical development because of their low efficacy and susceptibility to drug resistance, but some of them have shown promising results. In this article, we review the development and clinical efficacy of proapoptotic drugs that have shown promise.

The role of glutathione-S-transferase in anti-cancer drug resistance

Glutathione-S-transferases (GSTs) are a family of Phase II detoxification enzymes that catalyse the conjugation of glutathione (GSH) to a wide variety of endogenous and exogenous electrophilic compounds. GSTs are divided into two distinct super-family members: the membrane-bound microsomal and cytosolic family members. Microsomal GSTs are structurally distinct from the cytosolic in that they homo- and heterotrimerize rather than dimerize to form a single active site. Microsomal GSTs play a key role in the endogenous metabolism of leukotrienes and prostaglandins. Human cytosolic GSTs are highly polymorphic and can be divided into six classes: alpha, mu, omega, pi, theta, and zeta. The pi and mu classes of GSTs play a regulatory role in the mitogen-activated protein (MAP) kinase pathway that participates in cellular survival and death signals via protein : protein interactions with c-Jun N-terminal kinase 1 (JNK1) and ASK1 (apoptosis signal-regulating kinase). JNK and ASK1 are activated in response to cellular stress. GSTs have been implicated in the development of resistance toward chemotherapy agents. It is plausible that GSTs serve two distinct roles in the development of drug resistance via direct detoxification as well as acting as an inhibitor of the MAP kinase pathway. The link between GSTs and the MAP kinase pathway provides a rationale as to why in many cases the drugs used to select for resistance are neither subject to conjugation with GSH, nor substrates for GSTs. GSTs have emerged as a promising therapeutic target because specific isozymes are overexpressed in a wide variety of tumors and may play a role in the etiology of other diseases, including neurodegenerative diseases, multiple sclerosis, and asthma. Some of the therapeutic strategies so far employed are described in this review.

Targeted therapy for epithelial ovarian cancer: Current status and future prospects

Despite advances in surgery and chemotherapy, less than 20% of patients with stage III or IV ovarian cancer survive long-term. In the past, cytotoxic regimens have been developed empirically, combining active agents at maximally tolerated doses, often without a clear rationale for their interaction. Advances in understanding the biology of ovarian cancer have identified multiple molecular targets that differ in normal and malignant cells. Targets include cell cycle regulators, growth factor receptors, signal transduction pathways, molecules that confer drug resistance, and angiogenic mechanisms. A number of targeted agents have entered clinical trials. Small molecular weight inhibitors, monoclonal antibodies, and antisense and gene therapy are all being evaluated alone and in combination with cytotoxic drugs. In contrast to earlier studies, the impact of each agent on the designated target can be assessed and agents can be matched to the genotype and phenotype of malignant and normal cells. In the long run, this should facilitate individualization of more effective, less toxic therapy for women with ovarian cancer.

In vitro antitumor activity of the novel marine agent, ecteinascidin-743 (ET-743, NSC-648766) against human tumors explanted from patients

BACKGROUND

Ecteinascidin-743 (ET-743), a member of the ecteinascidin family selected for clinical development, is a tetrahydroisoquinolone alkaloid isolated from the marine ascidian, Ecteinascidia turbinata. This novel compound is a minor groove binding, guanine-specific alkylating agent which also interacts with the microtubule network and blocks cell cycle progression at late S/G2.

MATERIALS AND METHODS

A soft agar cloning assay was used to determine the in vitro effects of ET-743 against primary human tumor specimens taken directly from patients. A total of 93 evaluable specimens were exposed to ET-743 for one-hour (n = 25) and/or 14-day continuous exposure (n = 92) at concentrations ranging from 0.1 nM to 1 microM. In vitro responses were defined as an inhibition > or = 50% of human tumor colony forming units at a given concentration.

RESULTS

One-hour exposure to ET-743 at concentrations of 0.1 nM, 1 nM, 10 nM, 100 nM and 1 microM induced in vitro responses in 0% (0/17), 6% (1/17), 16% (4/25), 13% (1/8), and 25% (2/8) of specimens, respectively. Continuous exposure to ET-743 at concentrations of 0.1 nM, 1 nM, 10 nM, 100 nM and 1 microM, inhibited 0% (0/16), 13% (2/16), 49% (44/90), 62% (47/76), and 77% (58/75) of tumor specimens, respectively. Tumor-specific responses and concentration-dependent relationships were observed with a continuous exposure to ET-743. At 100 nM, the compound inhibited 79% (11/14) breast, 69% (9/13) non-small-cell lung, 58% (7/12) ovary, and 88% (7/8) melanoma specimens. At 1 microM, ET-743 inhibited 100% (14/14) breast specimens, 85% (11/13) non-small-cell lung, 67% (8/12) ovary and 86% (6/7) melanoma specimens. Activity of ET-743 at and above 10 nM was also observed against sarcoma and kidney tumors. At 10 nM concentration and continuous exposure ET-743 demonstrated incomplete cross-resistance with paclitaxel, alkylating agents, doxorubicin and cisplatin.

CONCLUSIONS

Our data from the cloning assay indicate that the duration of exposure to ET-743 is an important factor in human tumors. Therefore, long-term exposure to ET-743 may be preferred in future clinical trials. The activity of ET-743 in breast, non-small-cell lung, and ovarian cancers as well as in melanoma may deserve further clinical evaluations. The potential of ET-743 in sarcoma and renal tumors might also be considered. In addition, our data indicate that a plasma concentration of 100 nM of ET-743 must be considered as a target during the clinical development of the compound; also the concept of continuous/protracted exposure in clinical trials with ET-743 has to be taken into account.