In vitro study of farnesyltransferase inhibitor SCH 66336, in combination with chemotherapy and radiation, in non-small cell lung cancer cell lines

K-ras alterations have been reported in 20-30% of non-small cell lung cancer (NSCLC) and represent a suitable target for the development of novel anticancer agents, such as Farnesyl transferase inhibitors (FTi), a new class of agents inhibiting the post-translational modification of the K-ras proteins. The effectiveness of FTi SCH66336 in inhibiting cell proliferation and deranging cell cycle of NSCLC cell lines as well as its interaction with chemotherapy or radiation have been evaluated. The activity of FTi SCH66336, alone or in combination with paclitaxel, gemcitabine, and radiotherapy, was examined in 3 cell lines, A-549, LX-1 and CaLu-6, by colorimetric MTT assay. Cell cycle perturbation and apoptosis were also assessed by cytofluorimetric analysis. The activity of SCH 66336 was found to be concentration- and time-dependent. The effect of SCH 66336, as demonstrated by cell growth recovery experiments, resulted cytostatic and it was superimposable in both cell lines bearing 2 different K-ras mutations (A-549 and LX-1) and in K-ras wild-type Ca-Lu-6. In all cell lines the combination of SCH 66336 and paclitaxel resulted in a synergism of action when SCH 66336 followed paclitaxel treatment, whereas, antagonism was found when SCH 66336 preceded paclitaxel treatment. No significant synergism or addition with SCH 66336 followed by radiation treatment was noted. Different cell cycle phase blocks at various drug concentrations were observed. In conclusion, SCH 66336 displays concentration-dependent cytostatic antitumour activity and schedule-dependent synergy with 2 commonly used anticancer agents in NSCLC cell lines. Further clinical testing of these combinations is warranted.     

Activity of SCH 66336, a tricyclic farnesyltransferase inhibitor, against human tumor colony-forming units

Background: The ras gene product regulates transduction of growth-proliferative signals from the membrane to the nucleus. Mutationally-activated Ras is the oncogene most frequently found in human tumors. In order to perform its function in cell signaling, Ras must be farnesylated on the CAAX motif present on the carboxyl terminus of the ras protein. This reaction is catalysed by farnesyl protein transferase. In the present study, SCH 66336, an orally bioavailable nonpeptide tricyclic farnesyltransferase inhibitor, was tested against a large variety of human tumors to define its preclinical activity profile, utilizing the human tumor cloning assay.Materials and methods: A soft agar cloning assay was used to determine the in vitro effects of SCH 66336 against primary human tumor specimens taken directly from patients. A total of 70 evaluable specimens were exposed to SCH 66336 for 14-day continuous exposure at concentrations ranging from 0.1 to 2.5 µM. In vitro responses were defined as an inhibition 50% of human tumor colony forming units at a given concentration.Results: There was a positive relationship between concentration and response to SCH 66336. With the highest concentration (2.5 µM), response was demonstrated in 50% (three of six) of breast tumors, 40% (6 of 15) of ovarian tumors, and 38% (5 of 13) of non-small-cell lung tumor colony forming units. Among the 69 specimens tested at the concentration of 2.5 µM, SCH 66336 had activity in 27% of tumor specimens that were resistant to doxorubicin, 38% of tumor specimens resistant to cisplatin, 33% of tumor specimens resistant to paclitaxel, and 27% of tumor specimens resistant to etoposide.Conclusions: The broad spectrum of soft agar growth inhibition by SCH 66336 in the human tumor cloning assay, and its efficacy at physiologically relevant concentrations in animal models, suggest that SCH 66336 may deserve future clinical trials in patients with ovarian, breast and non-small-cell lung cancer.     

Combination therapy with the farnesyl protein transferase inhibitor SCH66336 and SCH58500 (p53 adenovirus) in preclinical cancer models

SCH66336 is a p.o.-active, farnesyl protein transferase inhibitor. SCH66336 inhibits farnesylation of RAS and other proteins in tumor cells and suppresses tumor growth in human xenograft and transgenic mouse cancer models in vivo. SCH58500 is a replication-deficient, recombinant adenovirus, which expresses the human p53 tumor suppressor. In preclinical models, SCH58500 has therapeutic efficacy against a wide range of human tumor types containing nonfunctional p53 and enhanced activity in combination with many chemotherapeutic drugs. Here we report that combination therapy with SCH66336 and SCH58500 has synergistic or additive antiproliferative effects on a panel of tumor cells lines in vitro. The efficacy of the three-drug combination of SCH66336, SCH58500, and paclitaxel was also examined in vitro. Each two-drug interaction displayed such marked synergy, the addition of a third drug to the statistical model could only yield additivity. Greater combined efficacy for SCH66336 and SCH58500 was also observed in vivo in the DU-145 human prostate and wap-ras/F transgenic mouse cancer models.     

A multiplicity of anti-invasive effects of farnesyl transferase inhibitor SCH66336 in human head and neck cancer

Metastasis is a critical event in the progression of head and neck squamous cell carcinoma (HNSCC) and closely correlates with clinical outcome. We previously showed that the farnesyl transferase inhibitor SCH66336 has antitumor activities in HNSCC by inducing the secretion of insulin-like growth factor binding protein 3 (IGFBP-3), which in turn inhibits tumor growth and angiogenesis. In our study, we found that SCH66336 at a sublethal dose for HNSCC inhibited the migration and invasion of HNSCC cells. The inhibitory effect of SCH66336 was associated with the blockade of the IGF-1 receptor (IGF-1R) pathway via suppressing IGF-1R itself and Akt expression. Consistent with previous work, induction of IGFBP-3 by SCH66336 also contributed in part to the anti-invasive effect. SCH66336 treatment also reduced the expression and activity of the urokinase-type plasminogen activator (uPA) and matrix metalloproteinase 2 (MMP-2), both important regulators of tumor metastasis. The effect of SCH66336 on uPA activity was inhibited partly by knockdown of IGFBP-3 using small interfering RNA. The inhibitory effect of SCH66336 on migration or invasion was attenuated partly or completely by knockdown of IGFBP-3, Akt or IGF-1R expression, respectively. Our results demonstrate that the IGF-1R pathway plays a major role in the proliferation, migration and invasion of HNSCC cells, suggesting that therapeutic obstruction of the IGF-1R pathway would be a useful approach to treating patients with HNSCC.     

Farnesyl transferase inhibitor SCH66336 is cytostatic,pro-apoptotic and enhances chemosensitivity to cisplatin in melanoma cells

The constitutive activity of a number of growth and cell survival pathways are thought to contribute to the inherent resistance of melanoma to chemotherapy and radiotherapy. Many of these pathways are driven through the small GTPase Ras. Novel drugs such as the farnesyl transferase inhibitors (FTIs) and farnesyl thiosalicylic acid (FTS) interfere with the signaling of oncogenic Ras. The aim of our study was to assess the anti-tumour activity of the FTI SCH66336 in melanoma and to assess whether SCH66336 and FTS could modulate chemoresistance in melanoma cells. SCH66336 had marked anti-proliferative activity in both human and mouse melanoma cell lines, but not in non-transformed NIH 3T3 cells. The anti-proliferative activity of SCH66336 was due to G1-phase cell cycle arrest and retinoblastoma protein inactivation, followed by apoptosis. Cisplatin, when administered alone, induced little apoptosis. In combination with cisplatin, both FTS and SCH66336 markedly enhanced the level of cisplatin-induced apoptosis, an effect that was associated with enhanced G2/M cell cycle arrest. Pharmacological inhibitors of either ERK or PI-3 kinase/Akt did not mimic the chemosensitising activity of either SCH66336 or FTS. In summary, our study demonstrates that SCH66336 has good in vitro anti-tumour activity in both human and mouse melanoma cell lines, and suggests that Ras antagonists could be useful in overcoming chemoresistance to cisplatin in melanoma.     

Phase I and pharmacological study of the oral farnesyltransferase inhibitor SCH 66336 given once daily to patients with advanced solid tumours

A single-agent dose-escalating phase I study on the farnesyl transferase inhibitor SCH 66336 was performed to determine the safety profile and recommended dose for phase II studies. Plasma pharmacokinetics were determined as well as the SCH 66336-induced inhibition of farnesyl protein transferase in vivo. SCH 66336 was given orally once daily (OD) without interruption to patients with histologically-confirmed solid tumours. Routine antiemetics were not prescribed. 12 patients were enrolled into the study. Dose levels studied were 300 mg (6 patients) and 400 mg (6 patients) OD. Pharmacokinetic sampling was performed on days 1 and 15. Although at 400 mg OD only 1 patient had a grade 3 diarrhoea, 3 out of 6 patients interrupted treatment early due to a combination of various grade 1-3 toxicities (diarrhoea, uremiacreatinine, asthenia, vomiting, weight loss) indicating that this dose was not tolerable for a prolonged period of time. At 300 mg OD, the same pattern of toxicities was observed, but all were grade 1-2. Therefore, this dose can be recommended for phase II studies. Pharmacokinetic analysis showed that peak plasma concentrations as well as the AUCs were dose-related, with increased parameters at day 15 compared with day 1, indicating some accumulation upon multiple dosing. Plasma half-life ranged from 5 to 9 h and appeared to increase with increasing dose. Steady state plasma concentrations were attained by day 14. A large volume of distribution at steady state suggested extensive distribution outside the plasma compartment. There is evidence of inhibition of protein prenylation in some patients after OD oral administration of SCH 66336. SCH 66336 can be safely administered using a continuous oral OD dosing regimen. The recommended dose for phase II studies using this regimen is 300 mg OD.     

The farnesyl protein transferase inhibitor SCH66336 is a potent inhibitor of MDR1 product P-glycoprotein

P-glycoprotein (Pgp)-mediated drug efflux is a major factor contributing to the variance of absorption and distribution of many drugs, particularly cancer chemotherapeutics. Multidrug resistance (MDR) is caused largely by the efflux of therapeutics out of the tumor cell by Pgp, resulting in reduced efficacy of chemotherapy. SCH66336, a farnesyl transferase inhibitor in development for cancer therapy, was examined in the present study for its ability to inhibit Pgp. In a test system consisting of a NIH-G185 cell line presenting an overexpressed amount of the human transporter Pgp, known Pgp inhibitors, such as cyclosporin A, paclitaxel, verapamil, tamoxifen, and vinblastine, were demonstrated to inhibit the Pgp-mediated efflux of daunorubicin. SCH66336 significantly inhibited daunorubicin transport with an IC50 of about 3 microM and similarly affected the transport of rhodamine 123 with a potency similar to cyclosporin A. Additionally, by an ATP-hydrolysis assay, SCH66336 was shown to decrease Pgp-mediated ATP hydrolysis by >70% with a Km of 3 microM. This observation indicates that SCH66336 directly interacts with the substrate binding site of Pgp, a quality unique to SCH66336 and its analogues, although not inherent to farnesyl transferase inhibitors in general. Moreover, low concentrations of SCH66336 exhibit synergy with the Pgp substrate/inhibitors paclitaxel, tamoxifen, and vinblastine respectively by significantly potentiating their inhibition of Pgp. Treatment with SCH66336 would be predicted to be synergistic with coadministered cancer therapeutics that are substrates of Pgp. A further benefit of coadministration of SCH66336 could be reduced chemotherapy dosage, hence, lower exposure to normal cells and, therefore, less undesired toxicity.     

Effect of lung resistance-related protein on the resistance to cisplatin in human ovarian cancer cell lines

The mechanisms of drug-resistance in human ovarian cancer cells have not been entirely clarified. The purpose of this study was to investigate whether LRP is involved in the resistance of ovarian cancer cell lines to cisplatin and its molecular mechanism. Human ovarian cisplatin-resistant cancer cell lines (A2780/DDP and COC1/DDP) and their parental cisplatin-sensitive cell lines (A2780 and COC1), alone or transfected with antisense LRP-specific oligonucleotides (ODN) or sense ODN, were treated with cisplatin to induce differentiation. Expression of LRP was examined by RT-PCR and Western blot analysis. The sensitivities of cells to cisplatin were assessed using sulforhodamine B (SRB) assay and flow cytometry, and the accumulation and efflux of cisplatin in the cells and isolated nuclei were examined by high performance liquid chromatographic (HPLC) assay. The expressions of LRP in A2780/DDP and COC1/DDP cells were higher than those in A2780 and COC1 cells and conferred resistance to cisplatin. Transfection of LRP AsODN into A2780/DDP and COC1/DDP cells down-regulated LRP expression and reversed the resistance phenotype. Levels of cisplatin accumulating in cells were increased by LRP-specific AsODN and anti-LRP monoclonal antibody. Isolated nuclei from A2780 and COC1 cells or A2780/DDP and COC1/DDP cells incubated with anti-LRP antibody contained more cisplatin than the nuclei of A2780/DDP and COC1/DDP cells not treated with anti-LRP antibody. Efflux of cisplatin was greater from the nuclei of A2780/DDP and COC1/DDP cells than those of A2780 and COC1 cells, and was inhibited by anti-LRP monoclonal antibody. Thus, LRP was involved in the resistance of ovarian cancer cells to cisplatin and has an important role in the transport of cisplatin both in exocytotic vesicles and between the nucleus and cytoplasm.     

Schedule-dependent antagonism of gemcitabine and cisplatin in human anaplastic thyroid cancer cell lines.

Anaplastic thyroid carcinoma (ATC) affects primarily elderly patients, with a median survival of 4-12 months after diagnosis. Presently, under clinical investigation the combination of cisplatin (CDDP) and gemcitabine (GEM) has promising activity in several of human tumor types. To develop new approaches for therapy of ATC, we evaluated the antineoplastic activity of GEM and CDDP alone (1-h and 24-h drug exposure) or in combination in the ATC cell lines SW1736, 8505C, C643, and HTh74. IC50 values were determined by the sulforhodamine B assay, activity was evaluated by the relative antitumor activity (RAA) and drug interaction assessed by isobologram analysis. GEM seemed to be active in ATC, with RAA ranging from 12-114 and CDDP only modestly active (RAA, 0.24-1.4). In four different drug schedules tested, the drug combination was additive when GEM preceded CDDP exposure (combination index, approximately 1), whereas when CDDP preceded GEM exposure the combination was significantly antagonistic (combination index, >1). In SW1736 and 8505C cells, we observed a strong S phase arrest and DNA synthesis inhibition 24 h after a 1-h exposure to an IC50 of CDDP. On the basis of molecular drug targets, cell cycle arrest points, and DNA synthesis inhibition, a model was developed to explain the interaction observed for the combination of GEM and CDDP. In conclusion, GEM shows promising cytostatic activity in ATC. Interaction of GEM and CDDP was schedule and dose dependent, favoring a regime in which GEM is followed by CDDP. Additionally, our model system suggests that DNA-synthesis inhibition and S phase arrest may be important determinants for the drug interaction between GEM and CDDP.     

The farnesyl protein transferase inhibitor SCH66336 synergizes with taxanes in vitro and enhances their antitumor activity in vivo

Purpose: SCH66336 is an orally active, farnesyl protein transferase inhibitor. SCH66336 inhibits ras farnesylation in tumor cells and suppresses tumor growth in human xenograft and transgenic mouse cancer models in vivo. The taxanes, paclitaxel (Taxol) and docetaxel (Taxotere) block cell mitosis by enhancing polymerization of tubulin monomers into stabilized microtubule bundles, resulting in apoptosis. We hypothesized that anticancer combination therapy with SCH66336 and taxanes would be more efficacious than single drug therapy. Methods: We tested the efficacy of SCH66336 and taxanes when used in combination against tumor cell proliferation in vitro, against NCI-H460 human lung tumor xenografts in nude mice, and against mammary tumors in wap-ras transgenic mice. Results: SCH66336 synergized with paclitaxel in 10 out of 11 tumor cells lines originating from breast, colon, lung, ovary, prostate, and pancreas. SCH66336 also synergized with docetaxel in four out of five cell lines tested. In the NCI-H460 lung cancer xenograft model, oral SCH66336 (20 mg/kg twice daily for 14 days) and intraperitoneal paclitaxel (5 mg/kg once daily for 4 days) caused a tumor growth inhibition of 56% by day 7 and 65% by day 14 compared to paclitaxel alone. Male transgenic mice of the wap-ras/F substrain [FVB/N-TgN(WapHRAS)69LlnYSJL] spontaneously develop mammary tumors at 6–9 weeks of age which have been previously shown to be resistant to paclitaxel. Paclitaxel resistance was confirmed in the present study, while SCH66336 inhibited growth of these tumors. Most importantly, SCH66336 was able to sensitize wap-ras/F mammary tumors to paclitaxel chemotherapy. Conclusion: Clinical investigation of combination therapy using SCH66336 and taxanes in cancer patients is warranted. Further, SCH66336 may be useful for sensitizing paclitaxel-resistant tumors to taxane treatment. Received: 30 November 1999 / Accepted: 10 May 2000     

Tamoxifen delays the development of resistance to cisplatin in human melanoma and ovarian cancer cell lines.

The development of resistance to cisplatin (DDP) occurs rapidly both in vitro and in vivo, and constitutes a major obstacle to effective therapy. We have previously demonstrated that there is a highly synergistic interaction between tamoxifen (TAM) and DDP against cell lines representative of three different human cancers: melanoma, ovarian carcinoma and small-cell lung cancer. The purpose of these studies was to determine if TAM interferes with the development of resistance to DDP. T-289 melanoma cells and 2008 ovarian cancer cells were cultured with increasing concentrations of DDP +/- TAM in an attempt to induce resistance to DDP. At various time points the cells were removed from culture and the degree of resistance to DDP was quantitated. Concurrent exposure to TAM and DDP decreased both the rate and the absolute magnitude of resistance to DDP in both melanoma and ovarian cancer cell lines. In the T-289 cell line the rate was decreased by a factor of 3.4 +/- 1.4 (P < 0.05), while in the 2008 cell line the rate was decreased by a factor of 2.4 (P < 0.01). TAM decreases the rate as well as the absolute magnitude of in vitro resistance to DDP in both melanoma and ovarian cancer cell lines. These data suggest that the concurrent administration of TAM and DDP may result in a delay in the development of resistance to DDP which may have important clinical implications in the design of DDP-containing regimens.     

Metallothionein content correlates with the sensitivity of human small cell lung cancer cell lines to cisplatin.

We have established cis-diamminedichloroplatinum(II) (cisplatin) resistant human small cell lung cancer cell lines, H69/CDDP0.2 and H69/CDDP, to investigate the mechanism of acquired resistance to cisplatin. H69/CDDP0.2 and H69/CDDP were 6- and 11-fold resistant to cisplatin compared with the H69 parental cell line. H69/CDDP was also resistant to cadmium chloride (2-fold), cis-diammine(glycolato)platinum (4-fold), 4-hydroperoxycyclophosphamide (3-fold) and 3-[(4-amino-2-methyl-5-pyrimidinyl)methyl]-1-(2-chloroethyl)-1-nitrosour ea (4-fold) if the drug concentrations that inhibit cell growth by 50% from growth inhibition assay were compared. There was no significant difference in the cisplatin accumulation among these cell lines. Although DNA interstrand cross-link formations, determined by filter elution assay in H69/CDDP0.2 and H69/CDDP, was decreased to 20 to 30% of that in H69 parental cells, the repair capacity of DNA interstrand cross-links was equivalent in all three cell lines. Intracellular glutathione content was equal in all cell lines. H69/CDDP had the highest glutathione S-transferase activity (H69, 11 nmol/min/mg protein, H69/CDDP0.2, 12 nmol/min/mg protein; H69/CDDP, 74 nmol/min/mg protein, respectively) and an overexpression of glutathione S-transferase pi mRNA. The drug concentrations that inhibit cell growth by 50% for cisplatin in all cell lines were decreased by treatment with ethacrynic acid, an inhibitor of glutathione S-transferase pi, but this did not alter the relative degree of resistance. Intracellular metallothionein content (H69, 14 pmol/mg protein, H69/CDDP0.2, 22 pmol/mg protein; H69/CDDP, 33 pmol/mg protein, respectively) and expression of metallothionein mRNA were correlated with the drug concentrations that inhibit cell growth by 50% of the three cell lines for cisplatin and cadmium chloride. The present study suggested the importance of metallothionein in the mechanisms of cisplatin resistance.     

Farnesyltransferase inhibitor SCH66336 induces rapid phosphorylation of eukaryotic translation elongation factor 2 in head and neck squamous cell carcinoma cells

Farnesyltransferase inhibitors (FTI) are a class of therapeutic agents designed to target tumors with mutations of the ras oncogene. However, the biological effect of FTIs is often independent of ras mutation status, which suggests the existence of additional mechanisms. In this study, we investigated the molecular effects of SCH66336, an FTI, in head and neck squamous cell carcinoma cells using proteomic approaches. We showed that SCH66336 induced phosphorylation (inactivation) of eukaryotic translation elongation factor 2 (eEF2), an important molecule for protein synthesis, as early as 3 hours after SCH66336 administration. Protein synthesis was subsequently reduced in the cells. Paradoxically, activation of eEF2 kinase (eEF2K), the only known kinase that regulates eEF2, was observed only at 12 hours after SCH66336 treatment. Consistent with this observation, the inhibition of phosphorylated-MEK and phosphorylated-p70S6K, the two key signaling molecules responsible for activation of eEF2K, also occurred at least 12 hours after SCH66336 administration. Our data suggest that inhibition of protein synthesis through inactivation of eEF2 is a novel mechanism of SCH66336-mediated growth inhibition and that this effect is independent of ras-MEK/p70S6K-eEF2K signaling cascades.     

The in vitro effects of lonidamine combined with cisplatin in human small cell lung cancer cell lines.

Two human small cell lung cancer (SCLC) cell lines were used to evaluate the in vitro response to lonidamine and cisplatin exposure. The two cell lines both showed growth inhibition when exposed to lonidamine alone at concentrations greater than 50 micrograms/ml; however, one cell line (H69) was more sensitive. When cisplatin was combined with lonidamine a synergistic interaction was observed when cells were exposed to 10 microM cisplatin for 1 hour combined with lonidamine at concentrations of 50 micrograms/ml or greater. At a concentration of 25 micrograms/ml lonidamine combined exposure with cisplatin had no effect on cell growth or viability.     

RPR-115135, a farnesyltransferase inhibitor,increases 5-FU- cytotoxicity in ten human colon cancer cell lines: role of p53

A new non peptidic farnesyltransferase inhibitor, RPR-115135, in combination with 5-FU was studied in 10 human colon cancer cell lines (HCT-116, RKO, DLD-1, Colo-320, LoVo, SW-620, HT-29, HCT-15, Colo-205 and KM-12) carrying several mutations but well characterized for p53 and Ras status. We found that there was a slight tendency (not statistically significant) for the p53 inactivated cells to be less sensitive to 5-FU after 6 days continuous treatment. Simultaneous administration of RPR-115135 and 5-FU, at subtoxic concentrations, resulted in a synergistic enhancement of 5-FU cytotoxicity in the p53 wildtype cells (HCT-116, RKO, DLD-1, Colo-320, LoVo). In the p53 mutated cells (SW-620, HT-29, HCT-15, Colo-205, KM-12) the effect was very complicated. In HCT-15 the combination resulted in antagonism, in KM-12 in antagonism or in synergy (at different concentrations) and in SW-620, HT-29 and Colo-205 cells in synergy but only when 5-FU was administered at high concentrations. Growth inhibition could be accounted for on the basis of a specific cell cycle arrest phenotype (G2-M arrest), as assayed by flow cytometry, only in the p53 functioning cell lines. The combination RPR-115135 + 5-FU increases apoptotic events only in these cell lines. In the mutated cell lines no major alterations on cell cycle arrest phenotype and no induction of apoptosis was observed. Although RPR-115135 can potentiate the effect of 5-FU in cells in which p53 function is disrupted, these data suggest strongly that RPR-115135 significantly enhances the efficacy of 5-FU only when p53 is functioning.     

Cdk inhibitors, roscovitine and olomoucine, synergize with farnesyltransferase inhibitor (FTI) to induce efficient apoptosis of human cancer cell lines

Farnesyltransferase inhibitor (FTI) induces apoptosis of transformed cells. This involves changes in mitochondria, including decrease of mitochondrial membrane potential and the release of cytochrome c. The released cytochrome c then induces events leading to the activation of caspase-3. In this study, we report that purine derivative cyclin-dependent kinase (Cdk) inhibitors, roscovitine and olomoucine, dramatically enhance this FTI-induced apoptosis of human cancer cell lines. We noticed the synergy between Cdk inhibitors and FTI through our screen to identify compounds that enhance FTI-induced apoptosis of promyelocytic leukemic cell line HL-60. The Cdk inhibitors by themselves do not induce apoptosis at the concentrations used. Roscovitine synergizes with FTI to release cytochrome c from mitochondria. In addition, we detected synergistic effects of FTI and roscovitine to inhibit hyperphosphorylation of retinoblastoma protein. Enhancement of FTI-induced apoptosis by roscovitine is not unique to HL-60 cells, since similar synergy was observed with a leukemic cell line CEM and a prostate cancer cell line LNCaP. In LNCaP cells, in addition to roscovitine and olomoucine, phophatidylinositol 3-kinase (PI 3-kinase) inhibitor, LY294002, was effective in enhancing FTI-induced apoptosis. However, the effects of roscovitine appear to be distinct from those of LY294002, since roscovitine did not affect Akt activity while LY294002 significantly decreased the activity of Akt. Our finding of the synergy between FTI and Cdk inhibitor is significant for understanding the mechanism of action of FTI as well as for clinical use of FTI.