Anti-Cancer Agents in Medicinal Chemistry (Formerly Current Medicinal Chemistry - Anti-Cancer Agents) - Volume 10, Issue 9, 2010

FK506 binding proteins (FKBPs) are the intracellular ligands of FK506 and rapamycin, two natural compounds with powerful and clinically efficient immunosuppressive activity. In recent decades, a relevant role for immunosuppressants as anticancer agents has emerged. Especially, rapamycin and its derivatives are used, with successful results, across a variety of tumors. Of note, rapamycin and FK506 bind to FKBP12, and the resulting complexes interfere with distinct intracellular signaling pathways driven, respectively, by the mammalian target of rapamycin and calcineurin phosphatase. These pathways are related to T-cell activation and growth. Hyperactivation of the mammalian target of rapamycin (mTOR), particularly in cancers that have lost the tumor suppressor gene PTEN, plays an important pathogenetic role in tumor transformation and growth. The signaling pathway involving calcineurin and nuclear factors of activated T-lymphocytes is also involved in the pathogenesis of different cancer types and in tumor metastasis, providing a rationale for use of FK506 in anticancer therapy. Recent studies have focused on FKBPs in apoptosis regulation: Targeting of FKBP12 promotes apoptosis in chronic lymphocytic leukemia, FKBP38 knockdown sensitizes hepatoma cells to apoptosis, and FKBP51 silencing overcomes resistance to apoptosis in acute lymphoblastic leukemia, prostate cancer, melanoma, and glioma. Interestingly, derivatives of FK506 that have the same FKBP12-binding properties as FK506 but lack functional immunosuppressant activity, exert the same apoptotic effect as FK506 in chronic lymphocytic leukemia. These findings suggest that a direct FKBP inhibition represents a further mechanism of immunosuppressants' anticancer activity. In this review, we focus on the role of FKBP members in apoptosis control and summarize the data on the antitumor effect of selective targeting of FKBP.

British developed Bisdioxopiperazine compound (Biz compounds) {ICRF-159 or ICRF-187 (razoxane, Raz)} which was the first agent ever to be observed inhibiting and controlling the spontaneous pulmonary metastases of murine Lewis Lung Carcinoma (LLC) tumor model worldwide. Since 1980, two new Biz compounds {probimane (Pro, AT-2153, MST-2) and MST-16} have been synthesized at the Shanghai Institute of Materia Medica, Chinese Academy of Sciences, PR China, based on structural modifications from British developed Biz compounds. Despite some similarities and differences of structural and pharmacological activities observed between Raz, Pro and MST-16, the systematic comparisons of their pharmacological activities and mechanisms, especially on neoplasm metastases, are still much needed. This work demonstrates that Biz compounds may inhibit tumor cell migration in vitro through a Matrigel-Coated Transwell plate assay and a wound-healing assay by using three human mammary tumor cell lines (MDA-MB-231, MDA-MB-435 and MDA-MB-468). Pro, ICRF-187 and MST-16 affect the network of actin assembly. We conclude that Biz compounds might inhibit neoplasm metastases via affecting a cascade of GTPases, cell skeleton polarizations and cell movements.

Metastatic melanoma is a very aggressive cancer. Dacarbazine has been considered as the standard therapy for decades. Due to a better understanding of melanoma cells signalling and immunological response, new targeted therapies are now proposed. The efficency of these new drugs needs to be confirmed by on larger clinical trials. Ipilimumab (anti-CTLA4 monoclonal antibody) and V600-E- B-raf inhibitor have shown encouraging results, while c-KIT and MEK inhibitors are currently under evaluation. These recently published data shed the light on melanoma management. We review here the latest development of these molecules and the current perspectives in the treatment of metastatic melanoma.

Chronic lymphocytic leukemia (CLL) is the most frequent type of hematological cancer in the Western World. An accumulation of leukemic cells in peripheral blood of patients is a result of apoptosis disturbances as well as an increase in germinal centers CLL cell proliferation. The differences between CLL patients in the course and response to therapy reflects personal variability between patients in their genetic material. It was documented that many sufferers from CLL are over 60 years old, and because of many countries' population obsolescence this type of leukemia could become more frequent in the future. CLL remains incurable, and the therapy regimens available at present could induce even complete remissions, but finally a relapse of the disease. The etiology of this disease is still not known, but our understanding of the processes running in CLL cells has significantly increased. A number of new agents with potential of CLL cell elimination by apoptosis or autophagy were characterized. Some of them reflect potential in cell sensitization to standard therapy. The major challenge for the future is to develop targeted anti-cancer therapy and design the optimal personalized manner of CLL treatment. A special interest is focused on anti-cancer agents - natural substances of plant origin. This paper reviews chosen new antileukemic agents belonging to different drug-classes (new monoclonal antibodies or apoptosis-, BCR signaling- and cell cycle-related inhibitors, substances of plant origin) which are under intense investigation in preclinical studies and early clinical trials.

High grade primary CNS gliomas hold some of the worst prognoses of any malignancy, with the vast majority of patients dying within two years of diagnosis, even with aggressive modern treatments. Surgical resection and radiotherapy are cornerstones of treatment when possible. In spite of many years of research, only recently has management with chemotherapy been able to prolong survival in patients with high grade gliomas, albeit only modestly at best. Topoisomerase I (TOP1) inhibitors target an enzyme critical for DNA replication and cell-cycle progression; they cross the blood-brain barrier and have antitumor activity against glioblastoma cells in vitro. The most frequently associated toxicities are neutropenia and diarrhea, but are often manageable. The two most used agents are irinotecan and topotecan. Due to enhanced cytochrome CY3A4/5 enzyme activity, irinotecan dose must be adjusted with concomitant enzyme- inducing antiepileptic drug usage; the data is less clear regarding the effects on topotecan. Clinical trials in patients with recurrent malignant glioma have evaluated TOP1 inhibitors as monotherapy and in combination with other agents. There is evidence for using topotecan with radiotherapy. Irinotecan has limited efficacy as monotherapy, but shows promise in combination with other agents, particularly temozolomide and bevacizumab. Newer generation TOP1 inhibitors are currently being evaluated in phase I trials. TOP1 inhibitors show promising activity in patients with primary CNS malignancies and warrant further study.

Current cancer chemotherapy relies heavily on cytotoxic agents, such as the taxanes and Vinca alkaloids, that interfere with the cellular machinery required for cell division and divert the cell down a pathway of programmed cell death. These antimitotic agents, or spindle poisons, target the mitotic spindle by binding to tubulin, a protein required not only for mitosis but also for structural integrity and proper function of healthy, terminally differentiated cells. To avoid side effects attributed to this nonselective mechanism of action, new targets in the mitotic pathway that act only in dividing cells were sought and a leading candidate to emerge from these efforts was kinesin spindle protein (KSP or HsEg5). KSP is a molecular motor protein that is expressed only during mitosis and controls the formation of a functional mitotic spindle. Inhibition of KSP causes mitotic arrest followed by cell death in malignant cells and thus has the potential to become a novel chemotherapeutic strategy with the potential for reduced toxicity. This article summarizes efforts carried out at Merck to discover potent, selective and water soluble KSP inhibitors that culminated in the discovery of MK-0731, the second KSP inhibitor to enter clinical trials. Of special focus in this article is how an HTS lead was optimized in apparently divergent directions, but these disparate leads converged in the design of compounds that overcame P-glycoprotein efflux and hERG channel activity, two issues that required considerable optimization within our program.