R115777 is a nonpeptidomimetic enzymespecific inhibitor of farnesyl protein transferase (FT) that was developed as a potential inhibitor of Ras protein signaling, with antitumor activity in preclinical models. This study was a phase 1 trial of orally administered R115777 in 35 adults with poor-risk acute leukemias. Cohorts of patients received R115777 at doses ranging from 100 mg twice daily (bid) to 1200 mg bid for up to 21 days. Dose-limiting toxicity occurred at 1200 mg bid, with central neurotoxicity evidenced by ataxia, confusion, and dysarthria. Non-dose-limiting toxicities included reversible nausea, renal insufficiency, polydipsia, paresthesias, and myelosuppression. R115777 inhibited FT activity at 300 mg bid and farnesylation of FT substrates lamin A and HDJ-2 at 600 mg bid. Extracellular signal-regulated kinase (ERK), an effector enzyme of Ras-mediated signaling, was detected in its phosphorylated (acti- vated IntroductionAdult acute leukemias remain formidable therapeutic challenge. Only 70% of adults with newly diagnosed acute myelogenous leukemias (AMLs) achieve complete remission (CR) after cytotoxic induction chemotherapy. Although these CRs may be prolonged in 35% to 40% of younger adults (age Ͻ 60), 1-5 the remainder have a relapse and die. Certain subgroups, including older adults, 3,5,6 patients with AMLs linked to environmental or occupational exposures (including therapy-induced AMLs), and patients with previous myelodysplasia (MDS) or other antecedent hematologic disorders, 7,8 have extremely poor outcomes, with CR rates of 40% or less, CR durations less than 12 months, and cure rates less than 10% to 15%. 3,5,6 The overall outlook for adult acute lymphoblastic leukemias (ALLs) is similar, 9-11 with a particularly poor prognosis in Philadelphia chromosome (Ph ϩ ) disease. 9,12 Thus, new approaches are needed to improve the outcome for adults with refractory leukemias.Improved understanding of signal transduction pathways has resulted in identification of a panoply of potential therapeutic targets. [13][14][15][16] Among these are the membrane-associated G proteins encoded by the ras family of proto-oncogenes. Ras proteins are activated downstream of protein tyrosine kinases (PTKs, eg, growth factor receptors) and, in turn, trigger a cascade of phosphorylation events through sequential activation of Raf, MEK-1, and ERKs (extracellular signal-related kinases). These events are critical to survival of hematopoietic cells. [16][17][18][19] The Ras proteins are synthesized as cytosolic precursors that must attach to the cell membrane to transmit signals. Membrane attachment depends on the addition of a 15-carbon farnesyl group to Ras, a reaction that is catalyzed by the enzyme farnesyltransferase (FT). [20][21][22] FT inhibitors (FTIs) were developed on the premise that FT inhibition would prevent Ras processing and, therefore, transduction of proliferative signals. [22][23][24] Subsequent studies, however, have suggested that the cytotoxic actions of FTIs might also involve other farnesylated ...

PC12 cells, which differentiate morphologically and biochemically into sympathetic neuronlike cells in response to nerve growth factor, also respond to epidermal growth factor . The response to epidermal growth factor is similar in certain respects to the response to nerve growth factor . Both peptides produce rapid increases in cellular adhesion and 2-deoxyglucose uptake and both induce ornithine decarboxylase . But nerve growth factor causes a decreased cell proliferation and a marked hypertrophy of the cells. In contrast, epidermal growth factor enhances cell proliferation and does not cause hypertrophy . Nerve growth factor induces the formation of neurites ; epidermal growth factor does not.When both factors are presented simultaneously, the cells form neurites . Furthermore, the biological response to epidermal growth factor, as exemplified by the induction of ornithine decarboxylase, is attenuated by prior treatment of the cells with nerve growth factor . PC12 cells have epidermal growth factor receptors. The binding of epidermal growth factor to these receptors is rapid and specific, and exhibits an equilibrium constant of 1 .9 x 10 -9 M. Approximately 80,000 receptors are present per cell, and this number is independent of cell density.Treatment of the cells with nerve growth factor reduces the amount of epidermal growth factor binding by at least 809'0. The decrease in receptor binding begins after -12-18 h of nerve growth factor treatment and is complete within 3 d . Scatchard plots indicate that the number of binding sites decreases, not the affinity of the binding sites for epidermal growth factor .The rat pheochromocytoma clone PC 12 has been used extensively as a model of neuronal differentiation . This clone, developed from an adrenal tumor by Greene and his colleagues (12, 18-20, 22, 45), is of adrenergic neural crest derivation . The cells grow readily under standard conditions and exhibit many of the properties of adrenal medullary chromaffin cells . In the presence of nerve growth factor in nanogram or even subnanogram amounts, the cells differentiate into a phenotype resembling sympathetic neurons . The changes occur within a few days and include process formation, electrical excitability, amine uptake and storage, and a cessation of cell division . The cells contain increased levels of certain transmitter-synthesizing enzymes (13,20,41) and will make synapses with appropriate target tissues (41). The differentiation appears to be reversible, but except for this, it resembles, as far as has been explored, the changes occurring in normal cells differentiating into sympathetic neurons .

R115777 is bioavailable after oral administration and has an acceptable toxicity profile. Based upon pharmacokinetic data, the recommended dose for phase II trials is 500 mg orally bid (total daily dose, 1, 000 mg) for 5 consecutive days followed by 9 days of rest. Studies of continuous dosing and studies of R115777 in combination with chemotherapy are ongoing.

Oral tipifarnib is well tolerated in children receiving the drug twice daily for 21 days and a continuous dosing schedule at 200 mg/m2/dose, which is equivalent to the MTD in adults. The pharmacokinetic profile of tipifarnib in children is similar to that in adults, and at the MTD, FTase is inhibited in PBMC in vivo.

We investigated for the first time the ability of farnesyltransferase inhibitors (FTI) to radiosensitize human glioma. For this, human glioma cell lines were treated with the specific FTI, R115777, 48 hr prior to a 2Gy irradiation. The treatment with R115777 decreased by 45% the SF2 value of the more radioresistant glioma cell lines (SF763 and U87) without any significant effect on the radioresistance of the radiosensitive ones (SF767 and U251-MG). This radiosensitizer effect was due to the induction of post-mitotic necrotic cell death. We then tested the hypothesis that wild-type Ras or RhoB, which has been proposed as potential FTI target, could control the glioma radioresistance. For this, we expressed inducible dominant negative forms of Ras (RasN17) and RhoB (RhoBN19) in radioresistant U87 glioma cell line and analyzed the survival after irradiation of the obtained clones. While blocking Ras pathways by expression of RasN17 did not affect the SF2 value of the U87 glioma cell line, the expression of RhoBN19 dramatically reduced the cell survival after irradiation of these cells. Taken together, these data demonstrated that RhoB, but not Ras, is implicated in glioma radioresistance. Furthermore, the R115777 differential radiosensitizer effect underlines the potential therapeutic interest of using this drug as a radiosensitizer of human glioma.

Farnesyltransferase inhibitors represent a new class of agents that target signal transduction pathways responsible for the proliferation and survival of diverse malignant cell types. Although these agents were developed to prevent a processing step necessary for membrane attachment and maturation of Ras proteins, recent studies suggest that farnesyltransferase inhibitors block the farnesylation of additional cellular polypeptides, thereby exerting antitumor effects independent of the presence of activating ras gene mutations. Clinical trials of two farnesyltransferase inhibitors--the tricyclic SCH66336 and the methylquinolone R115777--as single agents have demonstrated disease stabilization or objective responses in 10 to 15% of patients with refractory malignancies. Combinations of farnesyltransferase inhibitors with cytotoxic chemotherapies are yielding complete and partial responses in patients with advanced solid tumors. A phase I trial of R115777 in refractory and relapsed acute leukemias induced responses in 8 (32%) of 25 patients with acute myelogenous leukemia (including two complete remissions) and in two of three with chronic myelogenous leukemia in blast crisis. In patients with solid tumors, accessible normal tissues such as peripheral blood lymphocytes or, perhaps more germane to epithelial malignancies, buccal mucosa have provided surrogate tissues that allow confirmation that farnesyltransferase is inhibited in vivo at clinically achievable drug doses. In conjunction with the R115777 acute leukemia trial, serial measurements provided evidence of farnesyltransferase enzyme inhibition, interference with farnesyltransferase function ( ie, protein processing), and blockade of signal transduction pathways in leukemic bone marrow cells. Preclinical studies of farnesyltransferase inhibitor resistance and clinical trials of farnesyltransferase inhibitors in combination with other agents currently are in progress.

R115777 (R)-6-amino[(4-chlorophenyl)(1-methyl-1H-imidazol-5-yl)methyl]-4-(3-chlorophenyl)-1-methyl-2(1H)-quinolinone is a potent and selective inhibitor of farnesyl protein transferase with significant antitumor effects in vivo subsequent to oral administration in mice. Taking its roots into Janssen's ketoconazole and retinoic acid catabolism programs, our interest into Ras prenylation process led us stepwise to identify the key structural features of R115777. Methodology, structure activity relationships, and pharmacology will be presented. R115777 is currently in phase III clinical evaluation.

The discovery that post‐translational farnesylation of Ras oncoprotein was an essential step in exercising its biological effect led to the design of farnesyl protein transferase inhibitors (FTIs) in order to control growth of tumors bearing Ras mutations. Pre‐clinical studies on murine models have confirmed their inhibitory effect on tumor growth and enabled clinical development. R115777 (ZARNESTRATM) is currently undergoing clinical evaluation and recent studies have confirmed its antitumor potential and low toxicity. We wish to describe here the chemical synthesis routes that our group have developed to access ZARNESTRATM. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)