From oncogene to drug: development of small molecule tyrosine kinase inhibitors as anti-tumor and anti-angiogenic agents.

The confluence of two distinct but related activities in the past 10 years has dramatically accelerated efforts towards the discovery and development of novel drugs to treat cancer. The first is a rapidly emerging understanding that a number of distinct tyrosine kinases play roles in diverse but fundamentally important aspects of tumor progression (growth, survival, metastasis and angiogenesis). The second is the discovery that small molecule compounds have the capacity to potently and selectively inhibit the biochemical function of tyrosine kinases by competing for ATP binding at the enzyme catalytic site. These observations have been conjoined in major efforts to bring forward into clinical development novel cancer drugs with the potential to provide both clinical efficacy and improved tolerability. The focus of this review is on the development of small molecule tyrosine kinase inhibitors, and does not extend to other approaches that could be applied to disrupt the same pathways in clinical tumors (receptor and/or ligand-competitive antibodies, intrabodies, antisense ribonucleotides, ribozymes, phosphatase inhibitors or SH2/SH3-directed agents). Selected tyrosine kinase inhibitors, known or believed to be in development in cancer treatment trials, are summarized as are some of the key issues that must be addressed if these compounds are to be developed into clinically useful cancer chemotherapeutic agents.     

Biologic agents as modifiers of chemotherapeutic effects.

Recent papers dealing with the effect of biologic response modifiers on the therapeutic activity of anticancer drugs are reviewed. Preclinical findings indicate that both interferons and tumor necrosis factor-alpha are able to synergize with different cytotoxic drugs in increasing both tumor cytotoxicity or cytostasis in vitro and the therapeutic effect in animal models in vivo. The mechanism of such a synergy, however, has not been definitively worked out. Several clinical phase I and II trials have assessed the interactions of biologic response modifiers (mainly interferons and interleukin-2) with anticancer drugs, particularly in melanoma and renal cancer patients. Evidence of a therapeutic synergism is limited with most of the studies, indicating a lack of synergic or additive effects of the combination compared with single agents. Few phase III studies provided conflicting results. It is concluded that further studies on the combination of biologic response modifiers and chemotherapy both at preclinical and clinical levels are necessary to establish the possible synergistic or additive therapeutic effect of such a therapeutic approach.     

No cross-resistance of taxotere and taxol to conventional chemotherapeutic agents against gastric cancers as detected by MTT assay

To evaluate the clinical usefulness of taxanes as antitumor agents, we compared the antitumor spectrum of taxanes with those of conventional antitumor agents against 88 fresh gastric cancer specimens by MTT assay. At cut-off concentrations of 100 micrograms/ml for taxotere (Docetaxel, DOC) and 300 micrograms/ml for taxol (Paclitaxel, PAC), both agents showed a higher efficacy rate than mitomycin C (MMC), cisplatin (CDDP) and 5-fluorouracil (5-FU) against the gastric cancer specimens. The patterns of antitumor activity of DOC and PAC were independent from those of the conventional agents, while the patterns of antitumor activity of the taxanes significantly correlated with each other. Conventional agent antitumor activity patterns tended to correlate with the patterns of other conventional agents. In conclusion, taxanes may be useful for clinical application against gastric cancer due to their different antitumor spectrum as compared to conventional agents.     

Biologic agents as biochemical modulators: pharmacologic basis for the interaction of cytotoxic chemotherapeutic drugs and interferon

Biochemical modulation of cytotoxic cancer chemotherapeutic agents is one means of enhancing the activity and selectivity of antitumor drugs. Traditionally this approach has utilized detailed information regarding a particular enzymatic reaction or biochemical pathway to develop potential modulating agents. In contrast, the reported clinical therapeutic activity of IFN in combination with cytotoxic agents has prompted a reexamination of the biochemical actions of the cytokine. Interferon elicits a number of cellular actions that might contribute to its pharmacologic activity, including both direct antitumor effects and host-mediated actions. The best understood are those related to the cytotoxicity of the fluoropyrimidine antimetabolites and include enzymatic reactions involved in fluoropyrimidine metabolic activation, catabolism, and interaction with its target enzyme. However, even in this instance, a mechanistic association of a specific pharmacologic action with therapeutic activity remains to be determined. These studies demonstrate that cytokines and other biologic agents may exert specific biochemical modulations that augment (or potentially attenuate) the activity of the cytotoxic chemotherapeutic agents.Supported in part by grant CA54422 from the National Cancer Institute and by an educational grant from Schering Corporation. The views expressed in this paper are those of the authors and do not necessarily reflect those of the supporters     

Potentiation of chemotherapeutic drugs by energy metabolism inhibitors 2-deoxyglucose and etomoxir

Inhibition of energy production as a strategy for potentiation of anticancer chemotherapy was investigated using 1 glycolysis inhibitor and 1 fatty acid beta-oxidation inhibitor-2-deoxyglucose and etomoxir, respectively, both known to be clinically well tolerated. Eighteen anticancer drugs were screened for potentiation by these inhibitors. 2-deoxyglucose potentiated acute apoptosis (24 hr) induced mainly by some, but not all, genotoxic drugs, whereas etomoxir had effect only on cisplatin. By contrast, etomoxir did potentiate the overall, 48 hr effects of some genotoxic drugs, and was in addition more efficient than deoxyglucose in potentiating the overall effects of several non-genotoxic drugs. Both types of potentiation were largely lost in the absence of p53. Because cisplatin was potentiated by both energy inhibitors in both types of assay, it was investigated at additional concentrations and over longer time. Both energy inhibitors strongly potentiated non-apoptotic concentrations of cisplatin in p53-wildtype as well as in p53-deficient, cisplatin-resistant HCT-116 colon carcinoma cells. Reduced ATP levels correlated with, but were not sole determinants, the antiproliferative effects. We conclude that the long-term effects of cisplatin potentiation are important and either p53-independent or improved by a lack of p53. We also conclude that although the potentiated drugs as yet have no obvious mechanistic factor in common, the strategy holds promise with genotoxic as well non-genotoxic anticancer drugs.     

Intracellular signal transduction pathway proteins as targets for cancer therapy.

Circulating cytokines, hormones, and growth factors control all aspects of cell proliferation, differentiation, angiogenesis, apoptosis, and senescence. These chemical signals are propagated from the cell surface to intracellular processes via sequential kinase signaling, arranged in modules that exhibit redundancy and cross talk. This signal transduction system comprising growth factors, transmembrane receptor proteins, and cytoplasmic secondary messengers is often exploited to optimize tumor growth and metastasis in malignancies. Thus, it represents an attractive target for cancer therapy. This review will summarize current knowledge of selected intracellular signaling networks and their role in cancer therapy. The focus will be on pathways for which inhibitory agents are currently undergoing clinical testing. Original data for inclusion in this review were identified through a MEDLINE search of the literature. All papers from 1966 through March 2005 were identified by the following search terms: "signal transduction," "intracellular signaling," "kinases," "proliferation," "growth factors," and "cancer therapy." All original research and review papers related to the role of intracellular signaling in oncogenesis and therapeutic interventions relating to abnormal cell signaling were identified. This search was supplemented by a manual search of the Proceedings of the Annual Meetings of the American Association for Cancer Research, American Society of Clinical Oncology, and the American Association for Cancer Research (AARC)--European Organisation for Research and Treatment of Cancer (EORTC)--National Cancer Institute (NCI) Symposium on New Anticancer Drugs.     

Sequential therapy with chemotherapeutic drugs and liposome-encapsulated muramyl tripeptide: determination of potential interactions between these agents.

Three syngeneic murine tumor models were used to determine potential interactions between chemotherapeutic drugs and the synthetic liposome-encapsulated macrophage activator, muramyl tripeptide phosphatidylethanolamine (MLV-19835). Experiments were designed to maximize any additive toxicity of the simultaneous administration of MLV-19835 on the known myelosuppressive effects of doxorubicin, ifosfamide, and cisplatin. Treatment with these drugs resulted in diminished blood leukocyte counts, altered leukocyte differentials, and decreased hematocrits, but the systemic administration of MLV-19835 produced no additional deleterious effects. Myelosuppression normally observed at 2 weeks following treatment of mice with doxorubicin was prevented by combination treatment with MLV-19835. In addition, there was no interference of the antitumor activity of ifosfamide or doxorubicin against subcutaneous, kidney, and spleen tumors. These studies and the recent demonstration of the biological activity of MLV-19835 in phase II trials of osteosarcoma recommend clinical testing of these combined modalities.     

The rapamycin-sensitive signal transduction pathway as a target for cancer therapy.

The high frequency of mutations in cancer cells which result in altered cell cycle regulation and growth signal transduction, conferring a proliferative advantage, indicates that many of these aberrant mechanisms may be strategic targets for cancer therapy. The macrolide fungicide rapamycin, a natural product with potent antimicrobial, immunosuppressant, and anti-tumor properties, inhibits the translation of key mRNAs of proteins required for cell cycle progression from G1 to S phase. Rapamycin binds intracellularly to the immunophilin FK506 binding protein 12 (FKBP12), and the resultant complex inhibits the protein kinase activity of a protein kinase termed mammalian target of rapamycin (mTOR). The inhibition of mTOR, in turn, blocks signals to two separate downstream pathways which control the translation of specific mRNAs required for cell cycle traverse from G1 to S phase. Blocking mTOR affects the activity of the 40S ribosomal protein S6 kinase (p70s6k) and the function of the eukaryotic initiation factor 4E-binding protein-1 (4E-BP1), leading to growth arrest in the the G1 phase of the cell cycle. In addition to its actions on p70s6k and 4E-BP1, rapamycin prevents cyclin-dependent kinase activation, inhibits retinoblastoma protein (pRb) phosphorylation, and accelerates the turnover of cyclin D1 that leads to a deficiency of active cdk4/cyclin D1 complexes, all of which can inhibit cell cycle traverse at the G1/S phase transition. Both rapamycin and CCI-779, an ester analog of rapamycin with improved pharmaceutical properties and aqueous solubility, have demonstrated impressive activity against a broad range of human cancers growing in tissue culture and in human tumor xenograft models, which has supported the development of compounds targeting rapamycin-sensitive signal-transduction pathways. CCI-779 has completed several phase I clinical evaluations and is currently undergoing broad disease-directed efficacy studies. The agent appears to be well tolerated at doses that have resulted in impressive anti-tumor activity in several types of refractory neoplasms. Important challenges during clinical development include the definition of a recommended dose range associated with optimal biological activity and maximal therapeutic indices, as well as the ability to predict which tumors will be sensitive or resistant to CCI-779.     

Retrovirus-mediated transduction of TRAIL and chemotherapeutic agents co-operatively induce apoptotic cell death in both sarcoma and myeloma cells

BACKGROUND: Resistance to multiple chemotherapeutic agents results from a variety of factors including a lack of apoptosis in tumor cells. To induce apoptosis in two types of tumor cells, RPMI-8226 and MG-63, a combination of chemotherapeutic agents and retroviral transduction of TRAIL was employed. MATERIALS AND METHODS: Both TRAIL-sensitive 8226 and -resistant MG-63 cells were pretreated with the anti-tumor agent doxorubicin or cisplatin for 24 hours, washed and then exposed to retroviral transduction with TRAIL for a further 24 hours, followed by assay for cell survival using a WST-8 kit. RESULTS: Doxorubicin or cisplatin sensitized both RPMI-8226 and MG-63 cells to TRAIL-induced death in a synergistic manner. This combined treatment was also effective in the MG-63 cells overexpressing Bcl-xL, which are resistant to multiple chemotherapeutic agents. CONCLUSION: A retroviral transduction of TRAIL in conjunction with anti-tumor agents could provide a new treatment modality for the treatment of patients with multiple-drug resistance.     

Statin drugs and dietary isoprenoids as antithrombotic agents

Statin drugs and various isoprenoids from plant origins inhibit mevalonic acids, cholesterol, and other isoprenoid products. Among these, reduction of farnesyl and geranylgeranyl prenylated proteins impedes signal transduction at the cellular level. The authors envision that limiting such prenylated proteins downregulates thrombin-stimulated events, including decreasing the expression and availability of protease-activated receptor-1 mitigating thrombin stimulation of cells, tissue factor preventing additional thrombin generation, and plasminogen activator inhibitor-1 allowing thrombosis. Additional processes may enhance nitric oxide production and induce other processes. Downregulation of thrombin-stimulated events should promote hypothrombotic or quiescent conditions that reduce cardiovascular disease, thus contributing to longevity.     

Treatment of advanced soft tissue sarcoma: conventional agents and promising new drugs

Effective treatment of advanced soft tissue sarcomas remains challenging, despite more than 30 years of clinical trials with conventional chemotherapy. Although some agents display modest efficacy against soft tissue sarcomas, modifications in the doses and combinations of therapies have not consistently led to significant improvements in response rates or concomitant increase in overall survival. Novel therapies designed to inhibit defined molecular alterations, as exemplified by the use of imatinib in gastrointestinal stromal tumors, have revolutionized the approach to the treatment of sarcomas. As more underlying genetic mechanisms are uncovered, new agents designed to target these lesions will lead to more specific, less toxic, and more effective therapies.     

PUMA sensitizes lung cancer cells to chemotherapeutic agents and irradiation.

PURPOSE: Lung cancer, the leading cause of cancer mortality worldwide, is often diagnosed at late stages and responds poorly to conventional therapies, including chemotherapy and irradiation. A great majority of lung tumors are defective in the p53 pathway, which plays an important role in regulating apoptotic response to anticancer agents. PUMA was recently identified as an essential mediator of DNA damage-induced and p53-dependent apoptosis. In this study, we investigated whether the regulation of PUMA by anticancer agents is abrogated in lung cancer cells and whether PUMA expression suppresses growth of lung cancer cells and/or sensitizes lung cancer cells to chemotherapeutic agents and irradiation through induction of apoptosis. EXPERIMENTAL DESIGNS: The expression of PUMA was examined in lung cancer cells with different p53 status treated with chemotherapeutic agents. An adenovirus expressing PUMA (Ad-PUMA), alone or in combination with chemotherapeutic agents or gamma-irradiation, was used to treat lung cancer cells. The growth inhibitory and apoptotic effects of PUMA in vitro and in vivo were examined. The mechanisms of PUMA-mediated growth suppression and apoptosis were investigated through analysis of caspase activation and release of mitochondrial apoptogenic proteins. The cytotoxicities of PUMA on cancer and normal/nontransformed cells were compared. The efficacy of PUMA and p53 in suppressing the growth of lung cancer cells was also compared. RESULTS: We showed that the induction of PUMA by chemotherapeutic agents is abolished in p53-deficient lung cancer cells. PUMA expression resulted in potent growth suppression of lung cancer cells and suppressed xenograft tumor growth in vivo through induction of apoptosis. Low dose of Ad-PUMA significantly sensitized lung cancer cells to chemotherapeutic agents and gamma-irradiation through induction of apoptosis. The effects of PUMA are mediated by enhanced caspase activation and release of cytochrome c and apoptosis-inducing factor into the cytosol. Furthermore, PUMA seems to be selectively toxic to cancer cells and more efficient than p53 in suppressing lung cancer cell growth. CONCLUSIONS: Our findings indicate that PUMA is an important modulator of therapeutic responses of lung cancer cells and is potentially useful as a sensitizer in lung cancer therapy.