Development of 'DFG-out' inhibitors of gatekeeper mutant kinases

HG-7-85-01(22) and HG-7-86-01(26) are thiazolo[5,4-b]pyridine containing type II tyrosine kinase inhibitors with potent cellular activity against both wild-type and 'gatekeeper' mutant T315I- Bcr-Abl. Here we report on the 'hybrid design' concept and subsequent structure activity guided optimization efforts that resulted in the development of these inhibitors.

An amino-indazole scaffold with spectrum selective kinase inhibition of FLT3, PDGFRα and kit

Here we describe the synthesis and characterization of a number of 3-amino-1H-indazol-6-yl-benzamides that were designed to target the 'DFG-out' conformation of the kinase activation loop. Several compounds such as 4 and 11 exhibit single-digit nanomolar EC(50)s against FLT3, c-Kit and the gatekeeper T674M mutant of PDGFRα.

Inhibition of CXCR4 in CML cells disrupts their interaction with the bone marrow microenvironment and sensitizes them to nilotinib

Drug resistance is a growing area of concern. It has been shown that a small, residual pool of leukemic CD34+ progenitor cells can survive in the marrow microenvironment of chronic myeloid leukemia (CML) patients after years of kinase inhibitor treatment. Bone marrow (BM) stroma has been implicated in the long-term survival of leukemic cells, and contributes to the expansion and proliferation of both transformed and normal hematopoietic cells. Mechanistically, we found that CML cells expressed CXCR4, and that plerixafor diminished BCR-ABL-positive cell migration and reduced adhesion of these cells to extra cellular-matrix components and to BM stromal cells in vitro. Moreover, plerixafor decreased the drug resistance of CML cells induced by co-culture with BM stromal cells in vitro. Using a functional mouse model of progressive and residual disease, we demonstrated the ability of the CXCR4 inhibitor, plerixafor, to mobilize leukemic cells in vivo, such that a plerixafor-nilotinib combination reduced the leukemia burden in mice significantly below the baseline level suppression exhibited by a moderate-to-high dose of nilotinib as single agent. These results support the idea of using CXCR4 inhibition in conjunction with targeted tyrosine kinase inhibition to override drug resistance in CML and suppress or eradicate residual disease.

Antileukemic Effects of Novel First- and Second-Generation FLT3 Inhibitors: Structure-Affinity Comparison

Constitutively activated mutant FLT3 has emerged as a promising target for therapy for the subpopulation of acute myeloid leukemia (AML) patients who harbor it. The small molecule inhibitor, PKC412, targets mutant FLT3 and is currently in late-stage clinical trials. However, the identification of PKC412-resistant leukemic blast cells in the bone marrow of AML patients has propelled the development of novel and structurally distinct FLT3 inhibitors that have the potential to override drug resistance and more efficiently prevent disease progression or recurrence. Here, we present the novel first-generation "type II" FLT3 inhibitors, AFG206, AFG210, and AHL196, and the second-generation "type II" derivatives and AST487 analogs, AUZ454 and ATH686. All agents potently and selectively target mutant FLT3 protein kinase activity and inhibit the proliferation of cells harboring FLT3 mutants via induction of apoptosis and cell cycle inhibition. Cross-resistance between "type I" inhibitors, PKC412 and AAE871, was demonstrated. While cross-resistance was also observed between "type I" and first-generation "type II" FLT3 inhibitors, the high potency of the second-generation "type II" inhibitors was sufficient to potently kill "type I" inhibitor-resistant mutant FLT3-expressing cells. The increased potency observed for the second-generation "type II" inhibitors was observed to be due to an improved interaction with the ATP pocket of FLT3, specifically associated with introduction of a piperazine moiety and placement of an amino group in position 2 of the pyrimidine ring. Thus, we present 2 structurally novel classes of FLT3 inhibitors characterized by high selectivity and potency toward mutant FLT3 as a molecular target. In addition, presentation of the antileukemic effects of "type II" inhibitors, such as AUZ454 and ATH686, highlights a new class of highly potent FLT3 inhibitors able to override drug resistance that less potent "type I" inhibitors and "type II" first-generation FLT3 inhibitors cannot.

Reversible resistance induced by FLT3 inhibition: a novel resistance mechanism in mutant FLT3-expressing cells

Objectives

Clinical responses achieved with FLT3 kinase inhibitors in acute myeloid leukemia (AML) are typically transient and partial. Thus, there is a need for identification of molecular mechanisms of clinical resistance to these drugs. In response, we characterized MOLM13 AML cell lines made resistant to two structurally-independent FLT3 inhibitors.

Methods

MOLM13 cells were made drug resistant via prolonged exposure to midostaurin and HG-7-85-01, respectively. Cell proliferation was determined by Trypan blue exclusion. Protein expression was assessed by immunoblotting, immunoprecipitation, and flow cytometry. Cycloheximide was used to determine protein half-life. RT-PCR was performed to determine FLT3 mRNA levels, and FISH analysis was performed to determine FLT3 gene expression.

Results and Conclusions

We found that MOLM13 cells readily developed cross-resistance when exposed to either midostaurin or HG-7-85-01. Resistance in both lines was associated with dramatically elevated levels of cell surface FLT3 and elevated levels of phosphor-MAPK, but not phospho-STAT5. The increase in FLT3-ITD expression was at least in part due to reduced turnover of the receptor, with prolonged half-life. Importantly, the drug-resistant phenotype could be rapidly reversed upon withdrawal of either inhibitor. Consistent with this phenotype, no significant evidence of FLT3 gene amplification, kinase domain mutations, or elevated levels of mRNA was observed, suggesting that protein turnover may be part of an auto-regulatory pathway initiated by FLT3 kinase activity. Interestingly, FLT3 inhibitor resistance also correlated with resistance to cytosine arabinoside. Over-expression of FLT3 protein in response to kinase inhibitors may be part of a novel mechanism that could contribute to clinical resistance.

The JAK2V617F oncogene requires expression of inducible phosphofructokinase/fructose-bisphosphatase 3 for cell growth and increased metabolic activity

Myeloproliferative neoplasms are characterized by overproduction of myeloid lineage cells with frequent acquisition of oncogenic JAK2V617F kinase mutations. The molecular mechanisms that regulate energy requirements in these diseases are poorly understood. Transformed cells tend to rely on fermentation instead of more efficient oxidative phosphorylation for energy production. Our data in JAK2V617F-transformed cells show that growth and metabolic activity were strictly dependent on the presence of glucose. Uptake of glucose and cell surface expression of the glucose transporter Glut1 required the oncogenic tyrosine kinase. Importantly, JAK2V617F as well as active STAT5 increased the expression of the inducible rate-limiting enzyme 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 3 (PFKFB3), which controls glycolytic flux through 6-phosphofructo-1-kinase. PFKFB3 was required for JAK2V617F-dependent lactate production, oxidative metabolic activity and glucose uptake. Targeted knockdown of PFKFB3 also limited cell growth under normoxic and hypoxic conditions and blocked in vivo tumor formation in mice. Overall, these data suggest that inducible PFKFB3 is required for increased growth, metabolic activity and is regulated through active JAK2 and STAT5. Novel therapies that specifically block PFKFB3 activity or expression would, therefore, be expected to inhibit JAK2/STAT5-dependent malignancies and related cancers.

Smac mimetics: implications for enhancement of targeted therapies in leukemia

Drug resistance is a growing concern with clinical use of tyrosine kinase inhibitors. Utilizing in vitro models of intrinsic drug resistance and stromal-mediated chemoresistance, as well as functional mouse models of progressive and residual disease, we attempted to develop a potential therapeutic approach designed to suppress leukemia recurrence following treatment with selective kinase inhibitors. The novel IAP inhibitor, LCL161, [corrected] was observed to potentiate the effects of tyrosine kinase inhibition against leukemic disease both in the absence and presence of a stromal-protected [corrected] environment. LCL161 enhanced the proapoptotic effects of nilotinib and PKC412, against leukemic disease in vitro and potentiated the activity of both kinase inhibitors against leukemic disease in vivo. In addition, LCL161 synergized in vivo with nilotinib to reduce leukemia burden significantly below the baseline level suppression exhibited by a moderate-to-high dose of nilotinib. Finally, LCL161 displayed antiproliferative effects against cells characterized by intrinsic resistance to tyrosine kinase inhibitors as a result of expression of point mutations in the protein targets of drug inhibition. These results support the idea of using IAP inhibitors in conjunction with targeted tyrosine kinase inhibition to override drug resistance and suppress or eradicate residual disease.

Discovery and characterization of novel mutant FLT3 kinase inhibitors

For a subpopulation of acute myeloid leukemia (AML) patients, the constitutively activated tyrosine kinase, mutant FLT3, has emerged as a promising target for therapy. The development of drug resistance, however, is a growing concern for mutant FLT3 inhibitors, such as PKC412. Potential therapeutic benefit can arise from the combination of two structurally diverse inhibitors that target-but bind differently to-the same protein or from two inhibitors with completely different mechanisms of action. Thus, there is a need for identification and development of novel FLT3 inhibitors that have the ability to positively combine with PKC412 or standard chemotherapeutic agents used to treat AML as a way to suppress the development of drug resistance and consequently prolong disease remission. Here, we report the effects of the novel type II ATP-competitive inhibitors, HG-7-85-01 and HG-7-86-01, which potently and selectively target mutant FLT3 protein kinase activity and inhibit the proliferation of cells harboring FLT3-ITD or FLT3 kinase domain point mutants via induction of apoptosis and cell cycle inhibition. Antileukemic activity of HG-7-85-01 was shown in vivo to be comparable with that observed with PKC412 in a bioluminescence assay using NCr nude mice harboring Ba/F3-FLT3-ITD-luc+ cells. HG-7-85-01 was also observed to override PKC412 resistance. Finally, HG-7-85-01 and HG-7-86-01 synergized with PKC412 and standard chemotherapeutic agents against mutant PKC412-sensitive and some PKC412-resistant, FLT3-positive cells. Thus, we present a structurally novel class of FLT3 inhibitors that warrants consideration for clinical testing against drug-resistant disease in AML patients.

Combining the FLT3 inhibitor PKC412 and the triterpenoid CDDO-Me synergistically induces apoptosis in acute myeloid leukemia with the internal tandem duplication mutation

Mutations of the FLT3 receptor tyrosine kinase consisting of internal tandem duplications (ITD) have been detected in blasts from 20% to 30% of patients with acute myeloid leukemia (AML) and are associated with a poor prognosis. FLT3/ITD results in constitutive autophosphorylation of the receptor and factor-independent survival in leukemia cell lines. The C-28 methyl ester of the oleane triterpenoid (CDDO-Me) is a multifunctional molecule that induces apoptosis of human myeloid leukemia cells. Here, we report that CDDO-Me blocks targeting of NFkappaB to the nucleus by inhibiting IkappaB kinase beta-mediated phosphorylation of IkappaBalpha. Moreover, CDDO-Me blocked constitutive activation of the signal transducer and activator of transcription 3. We report the potent and selective antiproliferative effects of CDDO-Me on FLT3/ITD-positive myeloid leukemia cell lines and primary AML cells. The present studies show that CDDO-Me treatment results in caspase-3-mediated induction of apoptosis of FLT3/ITD-expressing cells and its antiproliferative effects are synergistic with PKC412, a FLT3-tyrosine kinase inhibitor currently in clinical trials. Taken together, our studies indicate that CDDO-Me greatly enhanced the efficacy of the FLT3 inhibitor PKC412, suggesting that combining two separate pathway inhibitors might be a viable therapeutic strategy for AML associated with a FLT3/ITD mutation.

Tumor cell-specific bioluminescence platform to identify stroma-induced changes to anticancer drug activity

Conventional anticancer drug screening is typically performed in the absence of accessory cells of the tumor microenvironment, which can profoundly alter antitumor drug activity. To address this limitation, we developed the tumor cell-specific in vitro bioluminescence imaging (CS-BLI) assay. Tumor cells (for example, myeloma, leukemia and solid tumors) stably expressing luciferase are cultured with nonmalignant accessory cells (for example, stromal cells) for selective quantification of tumor cell viability, in presence versus absence of stromal cells or drug treatment. CS-BLI is high-throughput scalable and identifies stroma-induced chemoresistance in diverse malignancies, including imatinib resistance in leukemic cells. A stroma-induced signature in tumor cells correlates with adverse clinical prognosis and includes signatures for activated Akt, Ras, NF-kappaB, HIF-1alpha, myc, hTERT and IRF4; for biological aggressiveness; and for self-renewal. Unlike conventional screening, CS-BLI can also identify agents with increased activity against tumor cells interacting with stroma. One such compound, reversine, shows more potent activity in an orthotopic model of diffuse myeloma bone lesions than in conventional subcutaneous xenografts. Use of CS-BLI, therefore, enables refined screening of candidate anticancer agents to enrich preclinical pipelines with potential therapeutics that overcome stroma-mediated drug resistance and can act in a synthetic lethal manner in the context of tumor-stroma interactions.

Endometrial and vaginal effects of low-dose estradiol delivered by vaginal ring or vaginal tablet

AIMS

The major aims of the study were to compare the safety of a continuous low-dose estradiol-releasing vaginal ring (ESTring) to that of a vaginal estradiol tablet (Vagifem) on the endometrium and the relief of subjective symptoms and signs of urogenital estrogen deficiency. Quality of life and acceptability of treatment delivery were also assessed.

STUDY DESIGN

A prospective, randomized study in which women were assigned in a 2:1 ratio to ESTring and Vagifem and followed for 12 months. The primary endpoint was endometrial safety, based on the results of ultrasound measurement of endometrial thickness and a progestogen challenge test at baseline and week 48. Efficacy was determined by subjective assessment of urogenital estrogen deficiency symptoms at baseline and weeks 3, 12, 24, 36 and 48 and assessment of signs of vaginal epithelial atrophy by the clinician at baseline, 12 and 48 weeks. In addition, pelvic floor strength, vaginal cytological evaluation and pH, bacteruria and patient acceptability were assessed. Quality of life was assessed using a menopause-specific quality-of-life questionnaire and a 2-day bladder diary at baseline and 12 and 48 weeks. The comparability of the two groups was assessed using ANOVA, chi2 or Fisher's exact tests.

RESULTS

A total of 126 women were randomized to ESTring and 59 to Vagifem. There was no statistical difference between the groups in the alleviation of symptoms and signs of urogenital estrogen deficiency. Maturation indices increased in both groups, from generally atrophic at baseline to proliferative or highly proliferative at 48 weeks. After 48 weeks of treatment, there was no statistically significant difference in endometrial thickness between the two groups. A statistically smaller proportion of bleeding/spotting occurred in the ESTring group (n = 0) compared to the Vagifem users (n = 4). Estradiol and total estrone serum levels increased during treatment in both groups but remained within the normal postmenopausal range. General health status in both groups was unchanged but the urogenital component of health burden was significantly improved in both groups. Bladder diary variables showed no differences between treatment groups.

CONCLUSION

Equivalent endometrial safety and efficacy in the relief of the symptoms and signs of urogenital estrogen deficiency were demonstrated for the 12 months' use of a low-dose estradiol-releasing vaginal ring and a vaginal estradiol tablet.

FLT3 inhibition and mechanisms of drug resistance in mutant FLT3-positive AML

An appealing therapeutic target in AML is constitutively activated, mutant FLT3, which is expressed in a subpopulation of AML patients and is generally a poor prognostic indicator in patients under the age of 65. There are currently several FLT3 inhibitors that are undergoing clinical investigation. However, the discovery of drug-resistant leukemic blast cells in FLT3 inhibitor-treated AML patients has prompted the search for novel, structurally diverse FLT3 inhibitors that could be alternatively used to circumvent drug resistance. Here, we provide an overview of FLT3 inhibitors under preclinical and clinical investigation, and we discuss mechanisms whereby AML cells develop resistance to FLT3 inhibitors, and the ways in which combination therapy could potentially be utilized to override drug resistance. We discuss how the cross-talk between major downstream signaling pathways, such as PI3K/PTEN/Akt/mTOR, RAS/Raf/MEK/ERK, and Jak/STAT, can be exploited for therapeutic purposes by targeting key signaling molecules with selective inhibitors, such as mTOR inhibitors, HSP90 inhibitors, or farnesyltransferase inhibitors, and identifying those agents with the ability to positively combine with inhibitors of FLT3, such as PKC412 and sunitinib. With the widespread onset of drug resistance associated with tyrosine kinase inhibitors, due to mechanisms involving development of point mutations or gene amplification of target proteins, the use of a multi-targeted therapeutic approach is of potential clinical benefit.

A randomized controlled trial of treatment options for troublesome uterine bleeding in Implanon users

BACKGROUND

Pilot data have indicated that both doxycycline alone and mifepristone combined with ethinyl estradiol (EE) are effective in stopping episodes of bleeding in Implanon users with troublesome bleeding. We compared four treatments against a placebo in Implanon users and tested whether repeated treatment improved subsequent bleeding patterns.

METHOD

Implanon users aged 18-45 years were randomized to treatment with (i) mifepristone 25 mg given twice on day 1 followed by 4 days of EE 20 microg; (ii) doxycycline 100 mg twice daily for 5 days; (iii) mifepristone 25 mg given twice on day 1 plus doxycycline 100 mg twice daily for 5 days; (iv) doxycycline 100 mg twice daily with EE 20 microg daily; and (v) placebo twice daily for 5 days. The primary end-point was the number of days of bleeding/spotting immediately following initiation of the first 5-day course of each therapy, compared with placebo.

RESULTS

There were 204 women assigned to treatment. Mifepristone in combination with either EE or doxycycline was significantly more effective in stopping an episode of bleeding (mean 4.0 days (CI 3.5-4.6) and 4.4 days (CI 3.8-5.2), respectively) than doxycycline alone or in combination with EE, or placebo (6.4 days (CI 4.4-9.2), 6.4 days (CI 4.8-8.6) and 6.4 days (CL 5.1-8.0), respectively).

CONCLUSION

Mifepristone combined with either EE or doxycycline was significantly more effective than placebo in terminating an episode of bleeding in Implanon users. However there was no improvement in subsequent bleeding patterns.

TRIAL REGISTRATION NUMBER

ACTR # 012605000206628.

Stromal-mediated protection of tyrosine kinase inhibitor-treated BCR-ABL-expressing leukemia cells

Clinical studies of patients with chronic myeloid leukemia revealed that a common pattern of response is a dramatic fall in the circulating population of blast cells, with a minimal or delayed decrease in marrow blasts, suggesting a protective environment. These observations suggest that a greater understanding of the interaction of stromal cells with leukemic cells is essential. Here, we present an in vivo system for monitoring relative tumor accumulation in leukemic mice and residual disease in leukemic mice treated with a tyrosine kinase inhibitor and an in vitro system for identifying integral factors involved in stromal-mediated cytoprotection. Using the in vivo model, we observed high tumor burden/residual disease in tissues characterized as significant sources of hematopoiesis-promoting stroma, with bone marrow stroma most frequently showing the highest accumulation of leukemia in untreated and nilotinib-treated mice as well as partial protection of leukemic cells from the inhibitory effects of nilotinib. These studies, which showed a pattern of leukemia distribution consistent with what is observed in imatinib- and nilotinib-treated chronic myeloid leukemia patients, were followed by a more in-depth analysis of stroma-leukemia cell interactions that lead to protection of leukemia cells from nilotinib-induced cytotoxicity. For the latter, we used the human BCR-ABL-positive cell line, KU812F, and the human bone marrow stroma cell line, HS-5, to more closely approximate the bone marrow-associated cytoprotection observed in drug-treated leukemia patients. This in vitro system helped to elucidate stromal-secreted viability factors that may play a role in stromal-mediated cytoprotection of tyrosine kinase inhibitor-treated leukemia cells.

Potentiation of antileukemic therapies by Smac mimetic, LBW242: effects on mutant FLT3-expressing cells

Members of the inhibitor of apoptosis protein (IAP) family play a role in mediating apoptosis. Studies suggest that these proteins may be a viable target in leukemia because they have been found to be variably expressed in acute leukemias and are associated with chemosensitivity, chemoresistance, disease progression, remission, and patient survival. Another promising therapeutic target, FLT3, is mutated in about one third of acute myelogenous leukemia (AML) patients; promising results have recently been achieved in clinical trials investigating the effects of the protein tyrosine kinase inhibitor PKC412 on AML patients harboring mutations in the FLT3 protein. Of growing concern, however, is the development of drug resistance resulting from the emergence of point mutations in targeted tyrosine kinases used for treatment of acute leukemia patients. One approach to overriding resistance is to combine structurally unrelated inhibitors and/or inhibitors of different signaling pathways. The proapoptotic IAP inhibitor, LBW242, was shown in proliferation studies done in vitro to enhance the killing of PKC412-sensitive and PKC412-resistant cell lines expressing mutant FLT3 when combined with either PKC412 or standard cytotoxic agents (doxorubicin and Ara-c). In addition, in an in vivo imaging assay using bioluminescence as a measure of tumor burden, a total of 12 male NCr-nude mice were treated for 10 days with p.o. administration of vehicle, LBW242 (50 mg/kg/day), PKC412 (40 mg/kg/day), or a combination of LBW242 and PKC412; the lowest tumor burden was observed in the drug combination group. Finally, the combination of LBW242 and PKC412 was sufficient to override stromal-mediated viability signaling conferring resistance to PKC412.

Second generation inhibitors of BCR-ABL for the treatment of imatinib-resistant chronic myeloid leukaemia

Imatinib, a small-molecule ABL kinase inhibitor, is a highly effective therapy for early-phase chronic myeloid leukaemia (CML), which has constitutively active ABL kinase activity owing to the expression of the BCR-ABL fusion protein. However, there is a high relapse rate among advanced- and blast-crisis-phase patients owing to the development of mutations in the ABL kinase domain that cause drug resistance. Several second-generation ABL kinase inhibitors have been or are being developed for the treatment of imatinib-resistant CML. Here, we describe the mechanism of action of imatinib in CML, the structural basis of imatinib resistance, and the potential of second-generation BCR-ABL inhibitors to circumvent resistance.

Effects of PKC412, nilotinib, and imatinib against GIST-associated PDGFRA mutants with differential imatinib sensitivity

BACKGROUND & AIMS

Activating mutations in platelet-derived growth factor receptor alpha (PDGFRA) have been reported in a subset of gastrointestinal stromal tumor (GIST) patients who do not express the mutant stem cell factor receptor c-kit. The responsiveness of mutant PDGFRA-positive GIST to imatinib depends on the location of the PDGFRA mutation; for example, the V561D juxtamembrane domain mutation is more sensitive to imatinib than the D842V kinase domain mutation. In this study, we compare the effects of 3 tyrosine kinase inhibitors, PKC412 and nilotinib, and imatinib, on 2 GIST-related PDGFRA mutants, V561D and D842V, which possess differential sensitivity to imatinib.

METHODS

The effects of PKC412, nilotinib, and imatinib, alone and in combination, were evaluated via in vitro proliferation studies performed with V561D- or D842V-PDGFRA mutants. The effects of nilotinib and PKC412, alone and combined, were investigated in vivo.

RESULTS

PKC412 potently inhibited the V561D-PDGFRA mutant in vitro and the D842V-PDGFRA mutant in vitro and in vivo. Both imatinib and nilotinib displayed potent activity in vitro against the V561D-PDGFRA mutant but were significantly less efficacious against D842V-PDGFRA. However, when combined with either imatinib or PKC412, nilotinib showed no evidence for antagonism and acted in a cooperative fashion against D842V-PDGFRA.

CONCLUSIONS

Our findings support the clinical testing of PKC412 for treatment of mutant PDGFRA-GIST. The data also support the use of nilotinib as a treatment option for V561D-PDGFRA-associated GIST, although the reduced sensitivity of D842V-PDGFRA probably limits the potential of nilotinib monotherapy for D842V-PDGFRA-associated GIST.

Aggresome induction by proteasome inhibitor bortezomib and alpha-tubulin hyperacetylation by tubulin deacetylase (TDAC) inhibitor LBH589 are synergistic in myeloma cells

Histone deacetylase (HDAC) inhibitors have shown cytotoxicity as single agents in preclinical studies for multiple myeloma (MM) cells. LBH589 is a novel hydroxamic acid derivative that at low nanomolar concentrations induces apoptosis in MM cells resistant to conventional therapies via caspase activation and poly-(ADP-ribose) polymerase (PARP) cleavage. Significant synergistic cytotoxicity was observed with LBH589 in combination with bortezomib against MM cells that were sensitive and resistant to dexamethasone (Dex), as well as primary patient MM cells. LBH589 at low nanomolar concentrations also induced alpha-tubulin hyperacetylation. Aggresome formation was observed in the presence of bortezomib, and the combination of LBH589 plus bortezomib induced the formation of abnormal bundles of hyeracetylated alpha-tubulin but with diminished aggresome size and apoptotic nuclei. These data confirm the potential clinical benefit of combining HDAC inhibitors with proteasome inhibitors, and provide insight into the mechanisms of synergistic anti-MM activity of bortezomib in combination with LBH589.

Beneficial effects of combining nilotinib and imatinib in preclinical models of BCR-ABL+ leukemias

Drug resistance resulting from emergence of imatinib-resistant BCR-ABL point mutations is a significant problem in advanced-stage chronic myelogenous leukemia (CML). The BCR-ABL inhibitor, nilotinib (AMN107), is significantly more potent against BCR-ABL than imatinib, and is active against many imatinib-resistant BCR-ABL mutants. Phase 1/2 clinical trials show that nilotinib can induce remissions in patients who have previously failed imatinib, indicating that sequential therapy with these 2 agents has clinical value. However, simultaneous, rather than sequential, administration of 2 BCR-ABL kinase inhibitors is attractive for many reasons, including the theoretical possibility that this could reduce emergence of drug-resistant clones. Here, we show that exposure of a variety of BCR-ABL+ cell lines to imatinib and nilotinib results in additive or synergistic cytotoxicity, including testing of a large panel of cells expressing BCR-ABL point mutations causing resistance to imatinib in patients. Further, using a highly quantifiable bioluminescent in vivo model, drug combinations were at least additive in antileukemic activity, compared with each drug alone. These results suggest that despite binding to the same site in the same target kinase, the combination of imatinib and nilotinib is highly efficacious in these models, indicating that clinical testing of combinations of BCR-ABL kinase inhibitors is warranted.

Effectiveness of trichostatin A as a potential candidate for anticancer therapy in non-small-cell lung cancer

BACKGROUND

A well-known histone deacetylase inhibitor, trichostatin A, was applied to non-small-cell lung cancer cells to determine whether inhibition of histone deacetylase leads to the production of proteins that either arrest tumor cell growth or lead to tumor cell death.

METHODS

Trichostatin A (0.01 to 1.0 micromol/L) was applied to one normal lung fibroblast and four non-small-cell lung cancer lines, and its effect was determined by flow cytometry, annexin-V staining, immunoprecipitation, and Western blot analysis.

RESULTS

Trichostatin A demonstrated tenfold greater growth inhibition in all four non-small-cell lung cancer lines compared with normal controls, with a concentration producing 50% inhibition ranging from 0.01 to 0.04 micromol/L for the tumor cell lines and 0.7 micromol/L for the normal lung fibroblast line. Trichostatin A treatment reduced the percentage of cells in S phase (10% to 23%) and increased G1 populations (10% to 40%) as determined by flow cytometry. Both annexin-V binding assay and upregulation of the protein, gelsolin (threefold to tenfold), demonstrated that the tumor cells were apoptotic, whereas normal cells were predominantly in cell cycle arrest. Trichostatin A increased histone H4 acetylation and expression of p21 twofold to 15-fold without significant effect on p16, p27, CDK2, and cyclin D1.

CONCLUSIONS

Collectively, these data suggest that inhibition of histone deacetylation may provide a valuable approach for lung cancer treatment. We evaluated trichostatin A as a potential candidate for anticancer therapy in non-small-cell lung cancer.