alvocidib and Colonic-Neoplasms

To review preclinical and clinical information on flavopiridol, an inhibitor of cyclin-dependent kinases (CDKs), tested as an antitumor agent.. Primary and review articles were identified by MEDLINE search (1990-June 2001). Abstracts from recent meetings were also used as source materials.. Flavopiridol was reviewed with regard to its mechanisms, preclinical and clinical results, pharmacokinetics, and metabolism.. Flavopiridol is an inhibitor of several CDKs and displays unique anticancer properties. In addition to direct CDK inhibition, flavopiridol also exhibited other features such as inducing apoptosis in many cancer cell lines, decreasing cyclin D1 concentration, and inhibiting angiogenesis. Preclinical xenograft models showed significant antitumor activity for flavopiridol. The regimen using 72-hour continuous infusion every 2 weeks has been most extensively applied in clinical trials, with a 1-hour infusion currently being explored to achieve higher peak concentrations. Several Phase I and II trials have been reported, with some evidence of antitumor activity noted. Further Phase I and II trials using flavopiridol as a single agent and in combination with standard chemotherapeutic regimens and various tumor types are ongoing.. Flavopiridol is the first CDK inhibitor to enter clinical trials. Several Phase I and Phase II clinical trials with different regimens (72-h or 1-h infusion) have been completed. Initial clinical trials have been intriguing, but many questions remain: What is the best regimen (< or =72-h infusion)? Does optimal future development of this drug depend on the combination with other chemotherapy? What is the best combination of flavopiridol with other chemotherapy?

Topics: Antineoplastic Agents; Clinical Trials, Phase I as Topic; Clinical Trials, Phase II as Topic; Colonic Neoplasms; Cyclin-Dependent Kinases; Diarrhea; Drug Evaluation, Preclinical; Drug Therapy, Combination; Fatigue; Flavonoids; Humans; Infusion Pumps; Kidney Neoplasms; Lymphoma, Non-Hodgkin; Neoplasms; Neutropenia; Piperidines

The results of a phase I clinical trial of the topoisomerase I (Topo I) poison CPT-11 followed by the cyclin-dependent kinase inhibitor flavopiridol in patients with advanced solid tumors indicate that patients whose tumors were wild-type, but not mutant, for p53 obtained the most clinical benefit from this combination therapy. We elected to elucidate the mechanistic basis for this effect in isogenic-paired HCT116 colon cancer cells that were either wild-type (+/+) or null (-/-) for p53. With the combination therapy of SN-38 (the active metabolite of CPT-11) followed by flavopiridol, the induction of apoptosis was 5-fold greater in the p53+/+ cells compared with the p53-/- cells. This sequential treatment induced phosphorylation of p53 at Ser(15), which interacted with Rad51, a DNA repair protein involved in homologous recombination. Rad51 bound to p53-Ser(15) within the first 5 hours of combination therapy, and then was transcriptionally suppressed at 24 hours by flavopiridol only in p53+/+ cells. Microarray analysis also revealed suppression of Rad51 in a p53-dependent manner. Depletion of Rad51 by small interfering RNA (siRNA) sensitized both p53+/+ and p53-/- cells to SN-38-induced apoptosis with increase of gamma H2AX, a marker of DNA damage. Conversely, overexpression of Rad51 rescued p53+/+ cells from SN-->F-induced apoptosis. Because flavopiridol inhibits Cdk9, we found that inhibition of Cdk9 by DRB or by siRNA could recapitulate the flavopiridol effects, with suppression of Rad51 and induction of apoptosis only in p53+/+ cells. In conclusion, after DNA damage by Topo I poisons, flavopiridol targets homologous recombination through a p53-dependent down-regulation of Rad51, resulting in enhancement of apoptosis.

Topics: Antineoplastic Combined Chemotherapy Protocols; Apoptosis; Camptothecin; Colonic Neoplasms; Cyclin-Dependent Kinase 9; Down-Regulation; Drug Synergism; Flavonoids; HCT116 Cells; Humans; Irinotecan; Phosphorylation; Piperidines; Protein Kinase Inhibitors; Rad51 Recombinase; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Topoisomerase I Inhibitors; Tumor Suppressor Protein p53

Clinical treatment of solid tumors with docetaxel, flavopiridol, or 5-fluorouracil (5-FU) often encounters undesirable side effects and drug resistance. This study aims to evaluate the potential role of combination therapy with docetaxel, flavopiridol, or 5-FU in modulating chemosensitivity and better understand how they might be used clinically.. HCT116 colon cancer cells were treated with docetaxel, flavopiridol, and 5-FU in several different administrative schedules in vitro, either sequentially or simultaneously. Cell survival was measured by MTT assay. The activity of caspase-3 was determined by caspase-3 assays and the soft agar colony assay was used to test the colony formation of HCT116 cells in soft agar. We also established xenograft models to extend in vitro observations to an in vivo system.. The maximum cytotoxicity was found when human colon cancer HCT116 cells were treated with docetaxel for 1 h followed by flavopiridol for 24 h and 5-FU for another 24 h. This sequential combination therapy not only inhibits tumor cell growth more strongly compared to other combination therapies but also significantly reduces colony formation in soft agar and augments apoptosis of HCT116 cells. Sequencing of docetaxel followed 1 h later by flavopiridol, followed 24 h later by 5-FU in xenograft models, also resulted in delayed tumor growth and higher survival rate.. These results highlight the importance of an administrative schedule when combining docetaxel with flavopiridol and 5-FU, providing a rationale explanation for its development in clinical trials.

Topics: Adenocarcinoma; Animals; Antineoplastic Combined Chemotherapy Protocols; Apoptosis; Cell Proliferation; Colonic Neoplasms; Docetaxel; Female; Flavonoids; Fluorouracil; HCT116 Cells; Humans; Mice; Mice, Nude; Neoplasm Transplantation; Piperidines; Taxoids

Flavopiridol is one of the first cyclin-dependent kinase inhibitors undergoing clinical tests. We found that the combination treatment of flavopiridol (100-500 nM) with tumor necrosis factor (TNF)-alpha (10 ng/ml) induced a rapid and eminent apoptosis, 20 +/- 5% in 6-h treatment, in a human non-small cell lung carcinoma cell line, A549, as determined by the increase of sub-G(1) fraction in flow cytometry. A similar observation was also made in human colon cancer cell lines, HCT-116 and HCT-15, but not in Rat2, a rat fibroblast cell line. In A549 cells, the cytotoxic synergy by the combination treatment involved the activation of caspase-1, caspase-3, and caspase-8 and generated huge chromosomal degradation. The treatment schedules were so important that only the treatments of flavopiridol concomitantly with or followed by TNF-alpha showed the pronounced apoptosis in A549 cells. Prior treatment of TNF-alpha inhibited the apoptosis by the following combination treatment, leading to little cell death. Yet, such inhibition was reversed when 100 microM of 5,6-dichloro-1-beta-D-ribofuranosyl-benzimidazole, a transcription inhibitor, was present during the TNF-alpha pretreatment, suggesting that the inhibitory pretreatment of TNF-alpha might involve antiapoptotic gene expression at the transcriptional level. TNF-alpha treatment resulted in nuclear factor (NF)-kappa B activation, revealed by NF-kappa B activity reporter assay. In contrast, flavopiridol was found to inhibit the NF-kappa B-dependent gene transcription, which might give an explanation for the synergistic effect of flavopiridol with TNF-alpha. TNF-related apoptosis-inducing ligand (TRAIL; 100 ng/ml) also caused a rapid and strong cytotoxic synergy with flavopiridol. In contrast to TNF-alpha, however, all of the treatment sequences supported the synergy by TRAIL and flavopiridol. The combination of flavopiridol with TNF-alpha or TRAIL may be of use for the development in cancer therapy.

Topics: Animals; Antineoplastic Combined Chemotherapy Protocols; Apoptosis; Apoptosis Regulatory Proteins; Carcinoma, Small Cell; Caspase Inhibitors; Caspases; Colonic Neoplasms; Drug Screening Assays, Antitumor; Drug Synergism; Enzyme Activation; Fibroblasts; Flavonoids; Humans; Lung Neoplasms; Membrane Glycoproteins; NF-kappa B; Piperidines; Rats; Recombinant Proteins; TNF-Related Apoptosis-Inducing Ligand; Transcriptional Activation; Tumor Cells, Cultured; Tumor Necrosis Factor-alpha

Flavopiridol is a broad-spectrum inhibitor of cyclin-dependent kinases and of global transcription via the inhibition of positive transcription elongation factor b (P-TEFb). Although flavopiridol is currently undergoing phase II clinical trials, acquired cellular resistance to the compound during treatment is a potential problem, as it is with almost all current anticancer agents. A HCT116 human colon carcinoma cell line with an acquired 8-fold resistance to flavopiridol has been established. We report here that there are changes in these resistant cells in terms of telomere length and telomerase activity, whereas no change in the expression of the P-TEFb subunits CDK9, cyclin T1, cyclin T2a, or cyclin T2b was observed. The level of mRNA expression for the telomerase catalytic subunit hTERT was increased over 2-fold in the resistant cells, and mean telomere length was found to be 2 kb longer than the parental length, although telomerase activity was unchanged. The level of mRNA expression for the telomeric binding protein Pot1 was also increased. We also report that treatment of HCT116 cells with a combination of the G-quadruplex interacting telomerase inhibitor BRACO-19 and flavopiridol results in a 3-fold decrease in population doubling and prevents recovery from treatment with either compound alone. Treatment of flavopiridol-resistant cells with BRACO-19 alone also led to rapid inhibition of cell growth, which is not observed in the parental line. The finding that only the resistant line, with up-regulated telomerase, responds to this G-quadruplex inhibitor is consistent with the hypothesis that the mechanism of BRACO-19 down-regulation of cell growth directly involves the targeting of telomeres and telomerase.

Topics: Acridines; Antineoplastic Agents; Catalytic Domain; Colonic Neoplasms; Cyclin D1; Cyclin T; Cyclin-Dependent Kinase 9; Cyclin-Dependent Kinase Inhibitor p21; Cyclins; DNA-Binding Proteins; Drug Combinations; Drug Resistance, Neoplasm; Enzyme Inhibitors; Flavonoids; Humans; Piperidines; Telomerase; Telomere; Tumor Cells, Cultured; Tumor Suppressor Protein p53; Up-Regulation

Flavopiridol is a cyclin-dependent kinase inhibitor currently under development by the National Cancer Institute both as a single agent and in combination with chemotherapy. There have been numerous reports that flavopiridol potently enhances the induction of apoptosis by chemotherapy. However, the effect of flavopiridol on radiotherapy (RT)-induced apoptosis has been largely untested. RT has become the cornerstone of adjuvant treatment of colorectal and gastric cancer. In view of this, we elected to evaluate the effect of flavopiridol on potentiating RT-induced apoptosis in the human colon cancer cell line HCT-116 and the gastric cancer cell line MKN-74.. The efficacy of combination of gamma-irradiation and flavopiridol was tested in vitro in MKN-74 and HCT-116 cells and correlated to changes in p21 expression. HCT-116 cells were also established as tumors in nude mice and treated with gamma-irradiation and flavopiridol either as single agents or in sequential combinations such that flavopiridol was either given 7 h before, concomitantly, or 3 and 7 h after gamma-irradiation.. Flavopiridol significantly enhanced the induction of apoptosis by gamma-irradiation in both cell lines as measured by quantitative fluorescent microscopy, caspase-3 activation, poly(ADP-ribose) polymerase cleavage, and cytochrome c release. To achieve the best effect, it was important to expose the tumor cells to gamma-irradiation before the flavopiridol. This sequence dependence was confirmed in vivo. When gamma-irradiation was administered 7 h before flavopiridol, 42% of the tumor-bearing animals were rendered disease free, compared with no animals treated with either gamma-irradiation or flavopiridol alone. Examination of the p21 status of HCT-116 and MKN-74 cells, after treatment with sequential gamma-irradiation and flavopiridol, indicated a loss of p21 protein expression. Loss of p21 was mainly due to cleavage by caspases. HCT-116 cells that lack p21 (p21(-/-)) also exhibited sensitization to gamma-irradiation and showed an even greater enhancement of gamma-irradiation-induced apoptosis by flavopiridol when compared with the parental HCT-116 cells.. These studies indicate that gamma-irradiation followed by flavopiridol enhances apoptosis and yields significantly increased tumor regressions and cures that are not achievable with radiation alone. These results indicate that flavopiridol can potently enhance the effect of gamma-radiation both in vitro and in vivo and may provide a new means to treat patients with locally advanced gastrointestinal cancers.

Topics: Animals; Antineoplastic Agents; Apoptosis; Caspase 3; Caspases; Cell Division; Colonic Neoplasms; Cyclin-Dependent Kinase Inhibitor p21; Cyclin-Dependent Kinases; Cyclins; Cytochromes c; Enzyme Activation; Enzyme Inhibitors; Flavonoids; Gamma Rays; Male; Mice; Mice, Nude; Microscopy, Fluorescence; Piperidines; Poly(ADP-ribose) Polymerases; Stomach Neoplasms; Transplantation, Heterologous; Tumor Cells, Cultured

Treatment of the human colon cancer cells Hct116 with SN-38 (an active metabolite of CPT-11) resulted in G2 cell cycle arrest without induction of apoptosis. However, subsequent treatment of SN-38-treated Hct116 cells with flavopiridol induced apoptosis. One of the genes markedly up-regulated during cell cycle arrest by SN-38 and suppressed during apoptosis by SN-38 followed by flavopiridol in Hct116 cells is Drg1. We found that Drg1 had profound effects on SN-38 sensitivity. Inhibition of endogenous Drg1 expression in Hct116 cells by stable expression of an antisense (AS) Drg1 cDNA increased the sensitivity of cells to undergo apoptosis by SN-38. Clonogenic and apoptosis assays with AS Drg1-expressing cells showed a 2-fold decrease in the IC50 and a 4-5-fold increase in induction of apoptosis with SN-38. Conversely, the forced expression of Drg1 in SW620 cells increased the resistance of these cells to SN-38-induced apoptosis by 2-5-fold. Moreover, when xenografted in mice, AS Drg1-expressing Hct116 cells were 3-fold more sensitive to CPT-11 as compared with vector transfected Hct116 cells. Similarly, tumors established from Drg1 overexpressing SW620 cells were more resistant to CPT-11 as compared with tumors established from vector-transfected SW620 cells in mice. Taken together, our data suggest that Drg1 is a novel gene that plays a direct role in resistance to CPT-11. Inhibition of Drg1 may provide a new means to increase the sensitivity of colon cancer cells to CPT-11.

Topics: Animals; Antineoplastic Combined Chemotherapy Protocols; Apoptosis; Camptothecin; Colonic Neoplasms; DNA, Antisense; DNA, Complementary; Drug Synergism; Flavonoids; GTP-Binding Proteins; Humans; Irinotecan; Male; Mice; Mice, Nude; Piperidines; Prodrugs; Tumor Cells, Cultured; Xenograft Model Antitumor Assays

CPT-11, a DNA topoisomerase I inhibitor, has demonstrated clinical activity in colorectal cancer. Flavopiridol, a cyclin-dependent kinase inhibitor, is rapidly emerging as a chemotherapy modulator. To enhance the therapeutic index of CPT-11 in colon cancer, we studied the combination of these two drugs in relatively resistant human colon cancer cells, Hct116. Exposure of parental Hct116 cells to clinically achievable concentrations of SN-38 (the active metabolite of CPT-11) induces p21 and a G(2) arrest. However, these conditions fail to induce apoptosis. In contrast, Hct116 cells that are p21 deficient (p21-/- Hct116) readily undergo apoptosis after treatment with SN-38. In this study we show that the parental Hct116 cells can be sensitized to undergo apoptosis by the addition of flavopiridol after SN-38 treatment. The induction of apoptosis was greatest with sequential therapy consisting of SN-38 followed by flavopiridol. Clonogenic assays also showed greatest inhibition with this sequence. Sequential treatment with SN-38 followed by flavopiridol was associated with higher activation of caspase-3 and greater cleavage of both p21 and XIAP, an inhibitor of apoptosis, compared with other treatment schedules. CPT-11 induced some tumor regressions but no complete responses in the p21-intact Hct116 xenografts. CPT-11 with flavopiridol more than doubled tumor regression, compared with CPT-11 alone, and produced a 30% complete response rate. Our studies indicate that CPT-11 induces cell cycle arrest rather than cell death and that flavopiridol, by activating the caspase cascade, cleaves the inhibitors of apoptosis and sensitizes the cells to undergo cell death. Thus, flavopiridol combined with CPT-11 may provide a completely new therapeutic approach in the treatment of colon cancer.

Topics: Animals; Antineoplastic Agents; Antineoplastic Agents, Phytogenic; Antineoplastic Combined Chemotherapy Protocols; Apoptosis; Camptothecin; Colonic Neoplasms; Flavonoids; Humans; Irinotecan; Male; Mice; Mice, Nude; Piperidines; Transplantation, Heterologous; Tumor Cells, Cultured