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Scott H Kaufmann

Publications and source records attributed to Scott H Kaufmann.

At least 55 records · Page 3Linked to original sources
PubMed2003

Caspase-7 gene disruption reveals an involvement of the enzyme during the early stages of apoptosis.

Caspases play a key role during apoptotic execution. In an attempt to elucidate the specific role of caspase-7 we generated a chicken DT40 cell line in which both alleles of the gene were disrupted. Viability assays showed that caspase-7-/- clones are more resistant to the common apoptosis-inducing drugs etoposide and staurosporine. Caspase-7-/- cells show a delay in phosphatidylserine externalization and DNA fragmentation as well as cleavage of the caspase substrates poly(ADP-ribose) polymerase 1 and lamins B1 and B2. Caspase affinity labeling and activity assays indicated that deficient cells exhibit a delay in caspase activation compared with wild type DT40 cells, providing an explanation for the differences in apoptotic execution between caspase-7 null and wild type DT40 cells. These results strongly suggest that caspase-7 is involved earlier than other effector caspases in the apoptotic execution process in DT40 B lymphocytes.

Animals↗
PubMed2003

Alterations in the apoptotic machinery and their potential role in anticancer drug resistance.

Anticancer drugs can potentially kill cells in two fundamentally different ways, by interfering with cellular processes that are essential for maintenance of viability or by triggering an endogenous physiological cell death mechanism. Apoptosis is a form of physiological cell death mediated by caspases, a unique family of intracellular cysteine proteases. Zymogen forms of these proteases are found in virtually all somatic cells, but remain latent until their activation is induced by ligation of specific cell surface receptors (the so-called "death receptors"), by mitochondrial alterations that allow release of cytochrome c and other intermembrane components, or possibly by other mechanisms. Most anticancer drugs activate the mitochondrial pathway. This apoptotic pathway is regulated by pro- and antiapoptotic members of the Bcl-2 family of proteins. Once activated, certain caspases might also be controlled by the inhibitor of apoptosis (IAP) proteins. Alterations in apoptotic pathway components or their regulators have been detected in a variety of cancers, suggesting that loss of the ability of cells to undergo apoptosis might contribute to carcinogenesis. Because cancer therapies such as radiation, glucocorticoids, and chemotherapeutic drugs exert their beneficial effects, at least in part, by inducing apoptosis of cancer cells, the same alterations in apoptotic pathways would be predicted to contribute to resistance. A key issue is whether the direct toxic activity of these treatments is of benefit when neoplastic cells contain changes that diminish their ability to undergo apoptosis.

Animals↗
PubMed2003

Central role of Fas-associated death domain protein in apoptosis induction by the mitogen-activated protein kinase kinase inhibitor CI-1040 (PD184352) in acute lymphocytic leukemia cells in vitro.

Because the MAPK pathway plays important roles in cell proliferation and inhibition of apoptosis, this pathway has emerged as a potential therapeutic target for solid tumors and leukemia. At the present time there is little information about activation of this pathway and the consequences of its inhibition in acute lymphocytic leukemia cells (ALL). In the present study, constitutive MAPK pathway activation, as evidenced by phosphorylation of ERK1 and ERK2, was observed in 8 of 8 human lymphoid cell lines and 33% (8:24) of pretreatment ALL bone marrows. Inhibition of this pathway by the MEK inhibitors CI-1040 and PD098059 induced apoptosis through a unique pathway involving dephosphorylation and aggregation of Fas-associated death domain protein followed by death receptor-independent caspase-8 activation. Jurkat cell variants lacking Fas-associated death domain protein or procaspase-8 were resistant to CI-1040-induced apoptosis, as were Jurkat or Molt3 cells treated with the O-methyl ester of the caspase-8 inhibitor N-(Nalpha-benzyloxycarbonylisoleucylglutamyl) aspartate fluoromethyl ketone. In contrast, CI-1040-induced apoptosis was unaffected by blocking anti-Fas antibody, soluble tumor necrosis factor-alpha-related apoptosis-inducing ligand decoy receptor, or transfection with cDNA encoding the anti-apoptotic Bcl-2 family member Mcl-1 or dominant negative caspase-9. Collectively, these results identify the MAPK pathway as a potential therapeutic target in ALL and delineate a mechanism by which MEK inhibition triggers apoptosis in ALL cells.

Adaptor Proteins, Signal Transducing↗
PubMed2003

Involvement of reactive oxygen species in adaphostin-induced cytotoxicity in human leukemia cells.

Adaphostin (NSC 680410), an analog of the tyrphostin AG957, was previously shown to induce Bcr/abl down-regulation followed by loss of clonogenic survival in chronic myelogenous leukemia (CML) cell lines and clinical samples. Adaphostin demonstrated selectivity for CML myeloid progenitors in vitro and remained active in K562 cells selected for imatinib mesylate resistance. In the present study, the mechanism of action of adaphostin was investigated in greater detail in vitro. Initial studies demonstrated that adaphostin induced apoptosis in a variety of Bcr/abl- cells, including acute myelogenous leukemia (AML) blasts and cell lines as well as chronic lymphocytic leukemia (CLL) samples. Further study demonstrated that adaphostin caused intracellular peroxide production followed by DNA strand breaks and, in cells containing wild-type p53, a typical DNA damage response consisting of p53 phosphorylation and up-regulation. Importantly, the antioxidant N-acetylcysteine (NAC) blunted these events, whereas glutathione depletion with buthionine sulfoximine (BSO) augmented them. Collectively, these results not only outline a mechanism by which adaphostin can damage both myeloid and lymphoid leukemia cells, but also indicate that this novel agent might have a broader spectrum of activity than originally envisioned.

Acetylcysteine↗
PubMed2003

Irinotecan in the treatment of glioma patients: current and future studies of the North Central Cancer Treatment Group.

Other than nitrosoureas (carmustine and lomustine) and temozolomide, no agents have consistently demonstrated clinically meaningful benefits for patients with gliomas. The active metabolite of irinotecan, 7-ethyl-10-hydroxy camptothecin (SN-38), exhibited promising antitumor effects in preclinical glioma models. Clinical trials using weekly or every 3 weeks dosing of irinotecan have been completed. Toxicity consisted primarily of mild to moderate neutropenia and diarrhea with both schedules, with occasional severe toxicity including one death from neutropenia and infection. Preliminary analyses have suggested imaging responses in 10-15% of patients. Preclinical models and our understanding of the mechanism of action suggest that irinotecan may sensitize glioma cells to the cytotoxic actions of radiation therapy and alkylating agents; clinical trials designed to assess the therapeutic benefit of combination therapy currently are in progress. There is substantial clinical evidence that the concurrent administration of irinotecan with certain anticonvulsants produces reduced exposure to SN-38. In the absence of anticonvulsants, there is also substantial interpatient variability in drug exposure, perhaps reflecting inherited differences in drug metabolism. Finally several mechanisms of tumor cell resistance to irinotecan have been hypothesized, but the clinical significance of these observations has not been confirmed. Correlative studies to address these pharmacokinetic, pharmacogenetic, and drug resistance questions are ongoing.

Antineoplastic Agents, Phytogenic↗
PubMed2003

Phase II study of the farnesyl transferase inhibitor R115777 in patients with advanced non-small-cell lung cancer.

PURPOSE: This phase II study was undertaken to define the efficacy and pharmacodynamics of R115777, a farnesyl transferase inhibitor, in the first-line treatment of patients with advanced non-small-cell lung cancer. PATIENTS AND METHODS: Forty-four patients with measurable stage IIIB (pleural effusion) or stage IV disease received 193 courses of treatment (median, 2.0; range, 1 to 22) with R115777 300 mg administered orally twice daily for 21 of every 28 days. Buccal mucosa samples and peripheral blood mononuclear cells (PBMCs) were collected before and after 8 days of treatment to evaluate inhibition of farnesyl transferase in vivo. RESULTS: No objective complete or partial responses were documented. Seven patients (16%; 95% confidence interval [CI], 8% to 31%) had disease stabilization for greater than 6 months. Median survival was 7.7 months (95% CI, 6.5 to 10.5) and time to progression was 2.7 months (95% CI, 1.9 to 3.1). The most severe toxicity was neutropenia (9% grade 3, 7% grade 4) and the most common toxicities were anemia (50% grade 1 or 2, 5% grade 3) and anorexia (50% grade 1 or 2, 2% grade 3). Mild peripheral neuropathy occurred in 25% of patients. Evidence of farnesyl transferase inhibition was documented in 83% of patients. CONCLUSION: Single-agent R115777 was well tolerated in patients with advanced NSCLC, but demonstrated minimal clinical activity. Inhibition of farnesylation in vivo was consistently documented. On the basis of promising results of farnesyl transferase inhibitor combinations with standard chemotherapy agents, future studies of this agent in NSCLC should be in combination with systemic chemotherapy.

Administration, Oral↗
PubMed2003

Loss of HSulf-1 up-regulates heparin-binding growth factor signaling in cancer.

Emerging data suggest that signaling by heparin-binding growth factors is influenced by the sulfation state of N-acetylglucosamine residues of heparan sulfate proteoglycans (HSPGs). Here we report that the recently identified protein HSulf-1, a heparin-degrading endosulfatase, encodes a cell surface-associated enzyme that diminishes sulfation of cell surface HSPGs. The message encoding this enzyme is readily detectable in a variety of normal tissues, including normal ovarian surface epithelial cells, but is undetectable in 5 of 7 ovarian carcinoma cell lines and markedly diminished or undetectable in approximately 75% of ovarian cancers. Similar down-regulation is also observed in breast, pancreatic, renal cells, and hepatocellular carcinoma lines. Re-expression of HSulf-1 in ovarian cancer cell lines resulted in diminished HSPG sulfation, diminished phosphorylation of receptor tyrosine kinases that require sulfated HSPGs as co-receptors for their cognate ligands, and diminished downstream signaling through the extracellular signal-regulated kinase pathway after treatment with fibroblast growth factor-2 or heparin-binding epidermal growth factor. Consistent with these changes, HSulf-1 re-expression resulted in reduced proliferation as well as sensitivity to induction of apoptosis by the broad spectrum kinase inhibitor staurosporine and the chemotherapeutic agent cisplatin. Collectively, these observations provide evidence that HSulf-1 modulates signaling by heparin-binding growth factors, and HSulf-1 down-regulation represents a novel mechanism by which cancer cells can enhance growth factor signaling.

5' Untranslated Regions↗
PubMed2003

Heterogeneous role of caspase-8 in fenretinide-induced apoptosis in epithelial ovarian carcinoma cell lines.

The mechanism of action of fenretinide, a synthetic retinoid currently undergoing testing as a chemopreventive and chemotherapeutic agent, is incompletely understood. In the present study, fenretinide caused apoptotic changes, including DNA fragmentation and cleavage of caspase substrates, in six low-passage ovarian cancer cell lines. However, the caspase activation pathway used by this agent varied. Transient transfection of cDNA-encoding cytokine response modifier A (CrmA), a caspase-8 inhibitor, diminished fenretinide-induced death in OV177 cells. Likewise, IETD(OMe)-fluoromethylketone (fmk) inhibited fenretinide-induced apoptosis by >80% in OV177 or OV266 cells and by approximately 50% in OV17, OV167, or OV207 cells. Further analysis demonstrated that inhibition of Fas ligand, tumor necrosis factor-alpha, or TRAIL signaling with blocking reagents did not affect fenretinide-induced apoptosis, raising the possibility that fenretinide activates caspase-8 in a death receptor-independent manner. In contrast, CrmA transfection or IETD(OMe)-fmk treatment did not inhibit fenretinide-induced apoptosis in OV202 cells. These divergent behaviors did not correlate with increased levels of procaspase-10, which is relatively resistant to CrmA and IETD(OMe)-fmk, nor with the expression of procaspase-8 and -9, apoptotic protease activating factor-1, or cellular FLICE-like inhibitory protein. Similarly, fenretinide treatment increased ceramide levels equally in cells that do (OV177) and do not (OV202) rely on caspase-8 to initiate apoptosis. These results indicate that synthetic retinoids can use caspase-8 as an initiating caspase, but they also indicate unexpected heterogeneity in caspase activation pathways among closely related cell lines.

Apoptosis↗
PubMed2003

A Phase I trial of the farnesyl protein transferase inhibitor R115777 in combination with gemcitabine and cisplatin in patients with advanced cancer.

PURPOSE: This Phase I study was undertaken to define the toxicity, pharmacodynamics, and maximum tolerated dose of the combination of R115777, a farnesyl transferase inhibitor, with gemcitabine and cisplatin in patients with advanced solid tumors. PATIENTS AND METHODS: Thirty patients with solid tumors received a median of 2.5 cycles (range 1-30+) through five dose levels. R115777 was administered p.o. twice daily for 14 days. Gemcitabine was infused 15 min after the ingestion of R115777 on days 1 and 8. Cisplatin was administered starting 30 min after completion of the gemcitabine infusion on day 1. Cycles were repeated every 21 days. Toxicities were graded by the National Cancer Institute Common Toxicity Criteria and recorded as maximum grade per patient for each treatment cycle. At the maximum tolerated dose, accumulation of prelamin A in buccal mucosa cells of patients was evaluated as a marker of farnesyl transferase inhibition by R115777. RESULTS: Neutropenia and thrombocytopenia were the most common toxicities. Dose-limiting toxicity in cycle 1 was myelosuppression with thrombocytopenia alone (4 patients), neutropenia alone (1 patient), or a combination of both (3 patients). Common nonhematologic toxicities were anorexia, rash, nausea, vomiting, and fatigue, none of which was dose limiting in the first cycle. At the maximum tolerated dose, defined as R115777 300 mg twice daily p.o., 1000 mg/m(2) gemcitabine, and 75 mg/m(2) cisplatin, inhibition of prelamin A farnesylation in buccal mucosa cells of patients was demonstrated, confirming that R115777 inhibits protein farnesylation in vivo. Nine objective responses (one complete response and eight partial responses) were documented in 27 evaluable patients. CONCLUSION: The combination of R115777 with gemcitabine and cisplatin was well tolerated and showed evidence of antitumor activity. The maximum tolerated dose of R115777 successfully inhibits farnesyltransferase in patients in vivo. This combination warrants further evaluation in a number of tumor types.

Adult↗
PubMed2002

A phase 2 trial of combination low-dose thalidomide and prednisone for the treatment of myelofibrosis with myeloid metaplasia.

Single-agent thalidomide (THAL) at "conventional" doses (> 100 mg/d) has been evaluated in myelofibrosis with myeloid metaplasia (MMM) based on its antiangiogenic properties and the prominent neoangiogenesis that occurs in MMM. THAL monotherapy at such doses produces approximately a 20% response rate in anemia but is poorly tolerated (an adverse dropout rate of > 50% in 3 months). To improve efficacy and tolerability, we prospectively treated 21 symptomatic patients (hemoglobin level < 10 g/dL or symptomatic splenomegaly) with MMM with low-dose THAL (50 mg/d) along with a 3-month oral prednisone (PRED) taper (beginning at 0.5 mg/kg/d). THAL-PRED was well tolerated in all enrolled patients, with 20 patients (95%) able to complete 3 months of treatment. An objective clinical response was demonstrated in 13 (62%) patients, all improvements in anemia. Among 10 patients who were dependent on erythrocyte transfusions, 7 (70%) improved and 4 (40%) became transfusion independent. Among 8 patients with thrombocytopenia (platelet count < 100 x 10(9)/L), 6 (75%) experienced a 50% or higher increase in their platelet count. In 4 of 21 patients (19%), spleen size decreased by more than 50%. Responses observed were mostly durable after discontinuation of the PRED. The dose of THAL in this study (50 mg/d) was better tolerated than the higher doses used in previous studies. Adverse events associated with corticosteroid therapy were mild and transient. Clinical responses did not correlate with improvements in either intramedullary fibrosis or angiogenesis. THAL-PRED is well tolerated and preliminarily appears to be a promising drug regimen for treating cytopenias in patients with MMM.

Adrenal Cortex Hormones↗
PubMed2002

Bile acids inhibit Mcl-1 protein turnover via an epidermal growth factor receptor/Raf-1-dependent mechanism.

Bile acids have been implicated in biliary tract carcinogenesis, in part, by activating the epidermal growth factor receptor (EGFR). Overexpression of Mcl-1, a potent antiapoptotic protein of the Bcl-2 family, has also been reported in cholangiocarcinomas. Because receptor tyrosine kinases like EGFR may modulate antiapoptotic protein expression, we examined the hypothesis that bile acids modulate Mcl-1 expression levels via EGFR. Deoxycholate increased cellular Mcl-1 protein in a concentration-dependent manner. The deoxycholate-mediated increase of cellular Mcl-1 protein was blocked equally by EGFR tyrosine kinase inhibitors or an EGFR-neutralizing antibody. Although inhibition of mitogen-activated protein kinases did not attenuate the deoxycholate-associated increase in Mcl-1 protein, the Raf-1 inhibitor, BAY 37-9751, effectively blocked the cellular increase of this protein. Neither Mcl-1 transcriptional activity nor its mRNA stability was altered by deoxycholate treatment. However, Mcl-1 protein stability was increased by bile acid treatment, an effect duplicated by proteasome inhibition. Deoxycholate prolongation of Mcl-1 turnover was blocked by either EGFR inhibitors or the Raf-1 inhibitor. Whereas the deoxycholate-induced increase in Mcl-1 reduced Fas-mediated apoptosis, the Raf-1 inhibitor potentiated Fas apoptosis. Our results demonstrate that bile acids block Mcl-1 protein degradation via activation of an EGFR/Raf-1 cascade resulting in its cellular accumulation. Raf-1 inhibitors block this increase of Mcl-1 and render the cells more susceptible to apoptosis, a potential therapeutic strategy for cholangiocarcinomas.

Apoptosis↗
PubMed2002

Synthetic Smac/DIABLO peptides enhance the effects of chemotherapeutic agents by binding XIAP and cIAP1 in situ.

Inhibitor of apoptosis proteins (IAPs) interact with and inhibit caspases-3, -7, and -9. This interaction can be inhibited by Smac/DIABLO, a polypeptide released from mitochondria upon initiation of the apoptotic signaling process. Here we demonstrate that the first 4-8 N-terminal amino acids of Smac/DIABLO fused to the Drosophila antennapaedia penetratin sequence, a carrier peptide, enhance the induction of apoptosis and long term antiproliferative effects of diverse antineoplastic agents including paclitaxel, etoposide, 7-ethyl-10-hydroxycamptothecin (SN-38), and doxorubicin in MCF-7 breast cancer cells. Similar effects were observed in additional breast cancer and immortalized cholangiocyte cell lines. Further analysis demonstrated that the Smac-penetratin fusion peptide crossed the cellular membrane, bound XIAP and cIAP1, displaced caspase-3 from cytoplasmic aggregates, and enhanced drug-induced caspase action in situ. These studies demonstrate that inhibition of IAP proteins can modulate the efficacy of antineoplastic agents.

Amino Acid Sequence↗
PubMed2002

Calpain-mediated X-linked inhibitor of apoptosis degradation in neutrophil apoptosis and its impairment in chronic neutrophilic leukemia.

The number of neutrophils in the blood and tissues is controlled by constitutive apoptotic programmed cell death and clearance by phagocytes such as macrophages. Here, we found that calpains cleave the X-linked inhibitor of apoptosis (XIAP) in vitro, producing fragments that are unable to inhibit caspase-3. These fragments were detected in normal neutrophils but were unstable and rapidly degraded. Calpain inhibition delayed tumor necrosis factor-alpha-induced apoptosis of normal neutrophils, consistent with a role for calpains in regulating the onset of apoptosis. Interestingly, neutrophils from three patients with chronic neutrophilic leukemia, a rare syndrome characterized by accumulation of mature neutrophils, exhibited decreased mu-calpain expression, diminished calpain activity, and impaired XIAP degradation. Neutrophils from these patients displayed a delay in spontaneous, Fas-stimulated, and tumor necrosis factor-alpha-induced apoptosis. These observations suggest that calpain-mediated XIAP degradation contributes to initiation of apoptosis in normal neutrophils and dysfunction of this regulatory pathway can lead to pathological neutrophil accumulation.

Aged↗
PubMed2002

Phase 2 trial of imatinib mesylate in myelofibrosis with myeloid metaplasia.

In a phase 2 study, 23 patients with myelofibrosis with myeloid metaplasia were treated with imatinib mesylate at a constant dose of 400 mg/d. Treatment was held in 16 patients (70%), after 1 to 12 weeks, because of side effects (neutropenia, 6 patients; musculoskeletal pain, 5 patients; thrombocytosis, 4 patients; edema, 3 patients; diarrhea and hyperbilirubinemia, 1 patient). Including patients in whom retreatment at a reduced dose was possible, 11 patients (48%) were able to continue treatment beyond 3 months. None of the patients experienced a response in anemia, and only 2 had partial responses in splenomegaly. A greater than 50% increase in platelet count was documented in 11 (48%) patients, but not in those with baseline platelet counts of less than 100 x 10(9)/L. In vitro, imatinib mesylate caused variable degrees of growth suppression of myeloid and erythroid progenitors that unfortunately did not translate into clinical benefit.

Adult↗
PubMed2002

Caspase-6 gene disruption reveals a requirement for lamin A cleavage in apoptotic chromatin condensation.

To study the role of caspase-6 during nuclear disassembly, we generated a chicken DT40 cell line in which both alleles of the caspase-6 gene were disrupted. No obvious morphological differences were observed in the apoptotic process in caspase-6- deficient cells compared with the wild type. However, examination of apoptosis in a cell-free system revealed a block in chromatin condensation and apoptotic body formation when nuclei from HeLa cells expressing lamin A or lamin A-transfected Jurkat cells were incubated in caspase-6-deficient apoptotic extracts. Transfection of exogenous caspase-6 into the clone reversed this phenotype. Lamins A and C, which are caspase-6-only substrates, were cleaved by the wild-type and heterozygous apoptotic extracts but not by the extracts lacking caspase-6. Furthermore, the caspase-6 inhibitor z-VEID-fmk mimicked the effects of caspase-6 deficiency and prevented the cleavage of lamin A. Taken together, these observations indicate that caspase-6 activity is essential for lamin A cleavage and that when lamin A is present it must be cleaved in order for the chromosomal DNA to undergo complete condensation during apoptotic execution.

Animals↗
PubMed2002

Resistance of leukemic cells to 2-chlorodeoxyadenosine is due to a lack of calcium-dependent cytochrome c release.

The purine nucleoside 2-chlorodeoxyadenosine (CdA) is often used in leukemia therapy. Its efficacy, however, is compromised by the emergence of resistant cells. In the present study, 3 CdA-resistant cell lines were generated and characterized. Their ability to accumulate 2-chloroadenosine triphosphate (CdATP) varied, reflecting differences in activities of deoxycytidine kinase (dCK) and deoxyguanosine kinase (dGK). Nonetheless, the selected lines were uniformly resistant to CdA-induced apoptosis, as assessed by caspase activation and DNA fragmentation. In contrast, cytosols from resistant cells were capable of robust caspase activation when incubated in the presence of cytochrome c and dATP. Moreover, replacement of dATP with CdATP also resulted in caspase activation in the parental and some of the resistant cell lines. Strikingly, CdA-induced decreases in mitochondrial transmembrane potential and release of cytochrome c from mitochondria were observed in the parental cells but not in any resistant lines. The lack of cytochrome c release correlated with an increased ability of mitochondria from resistant cells to sequester free Ca2+. Consistent with this enhanced Ca2+ buffering capacity, an early increase in cytosolic Ca2+ after CdA treatment of parental cells but not resistant cells was detected. Furthermore, CdA-resistant cells were selectively cross-resistant to thapsigargin but not to staurosporine- or Fas-induced apoptosis. In addition, CdA-induced caspase-3 activation and DNA fragmentation were inhibited by the Ca2+ chelator BAPTA-AM in sensitive cells. Taken together, the data indicate that the mechanism of resistance to CdA may be dictated by changes in Ca2+-sensitive mitochondrial events.

Adenosine Triphosphate↗
PubMed2002

Effects of the Bcr/abl kinase inhibitors STI571 and adaphostin (NSC 680410) on chronic myelogenous leukemia cells in vitro.

The adenosine triphosphate binding-site-directed agent STI571 and the tyrphostin adaphostin are undergoing evaluation as bcr/abl kinase inhibitors. The current study compared the effects of these agents on the survival of K562 cells, bcr/abl-transduced FDC-P1 cells, and myeloid progenitors from patients with chronic myelogenous leukemia (CML) compared with healthy donors. Treatment of K562 cells with 10 microM adaphostin resulted in decreased p210(bcr/abl) polypeptide levels in the first 6 hours, followed by caspase activation and accumulation of apoptotic cells in less than 12 hours. By 24 hours, 90% of the cells were apoptotic and unable to form colonies. In contrast, 20 microM STI571 caused rapid inhibition of bcr/abl autophosphorylation without p210(bcr/abl) degradation. Although this was followed by the inhibition of Stat5 phosphorylation and the down-regulation of Bcl-x(L) and Mcl-1, only 7% +/- 3% and 25% +/- 9% of cells were apoptotic at 16 and 24 hours, respectively. Instead, the cytotoxic effects of STI571 became more pronounced with prolonged exposure, with IC90 values greater than 20 microM and 1.0 +/- 0.6 microM after 24 and 48 hours, respectively. Consistent with these results, 24-hour adaphostin exposure inhibited CML granulocyte colony-forming units (CFU-G) (median IC50, 12 microM) but not normal CFU-G (median IC50, greater than 20 microM), whereas 24-hour STI571 treatment had no effect on CML or normal CFU-G. Additional experiments revealed that STI571-resistant K562 cells remained sensitive to adaphostin. Moreover, the combination of STI571 + adaphostin induced more cytotoxicity in K562 cells and in CML CFU-G than either agent alone did. Collectively, these results identify adaphostin as a mechanistically distinct CML-selective agent that retains activity in STI571-resistant cell lines.

Adamantane↗