Will MDR-1/P-gp modulators provide clinical benefit in hematologic malignancies?
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ATP Binding Cassette Transporter, Subfamily B, Mem↗
Biomedical subjects
Daruka Mahadevan
Publications and source records attributed to Daruka Mahadevan.
Transcriptosome and serum cytokine profiling of an atypical case of myelodysplastic syndrome with progression to acute myelogenous leukemia.
A Native American-Indian female presenting with anemia and thrombocytosis was diagnosed with myelodysplastic syndrome (MDS, refractory anemia). Over the course of 5 years she developed cytopenias and periods of leukocytosis with normal bone marrow (BM) blast counts, features of an unclassifiable MDS/MPS syndrome. The patient ultimately progressed to acute myelogenous leukemia (AML, FAB M2) and had a normal karyotype throughout her course. The episodes of leukocytosis were associated with infectious complications. Transformation to AML was characterized by a BM blast percentage of 49%. Peripheral blood and BM samples were obtained for serum protein analysis and gene expression profiling (GEP) to elucidate her disease process. An ELISA assay of the serum analyzed approximately 80 cytokines, which demonstrated that hepatocyte growth factor/scatter factor and insulin-like growth factor binding protein 1 were markedly elevated compared to normal. GEP demonstrated a unique "tumor molecular profile," which included overexpression of oncogenes (HOXA9, N-MYC, KOC1), proliferative genes (PAWR, DLG5, AKR1C3), invasion/metastatic genes (FN1, N-CAM-1, ITGB5), pro-angiogenesis genes (c-Kit), and down regulation of tumor suppressor genes (SUI1, BARD1) and anti-apoptotic genes (PGLYRP, SERPINB2, MPO). Hence, a biomics approach has provided insight into elucidating disease mechanisms, molecular prognostic factors, and discovery of novel targets for therapeutic intervention.
Aged↗
Identification of a lead small-molecule inhibitor of the Aurora kinases using a structure-assisted, fragment-based approach.
Aurora A and Aurora B are potential targets for anticancer drug development due to their roles in tumorigenesis and disease progression. To identify small-molecule inhibitors of the Aurora kinases, we undertook a structure-based design approach that used three-dimensional structural models of the Aurora A kinase and molecular docking simulations of chemical entities. Based on these computational methods, a new generation of inhibitors derived from quinazoline and pyrimidine-based tricyclic scaffolds were synthesized and evaluated for Aurora A kinase inhibitory activity, which led to the identification of 4-(6,7-dimethoxy-9H-1,3,9-triaza-fluoren-4-yl)-piperazine-1-carbothioic acid [4-(pyrimidin-2-ylsulfamoyl)-phenyl]-amide. The lead compound showed selectivity for the Aurora kinases when it was evaluated against a panel of diverse kinases. Additionally, the compound was evaluated in cell-based assays, showing a dose-dependent decrease in phospho-histone H3 levels and an arrest of the cell cycle in the G(2)-M fraction. Although biological effects were observed only at relatively high concentrations, this chemical series provides an excellent starting point for drug optimization and further development.
Antineoplastic Agents↗
Amino acid changes in Drosophila alphaPS2betaPS integrins that affect ligand affinity.
We developed a ligand-mimetic antibody Fab fragment specific for Drosophila alphaPS2betaPS integrins to probe the ligand binding affinities of these invertebrate receptors. TWOW-1 was constructed by inserting a fragment of the extracellular matrix protein Tiggrin into the H-CDR3 of the alphavbeta3 ligand-mimetic antibody WOW-1. The specificity of alphaPS2betaPS binding to TWOW-1 was demonstrated by numerous tests used for other integrin-ligand interactions. Binding was decreased in the presence of EDTA or RGD peptides and by mutation of the TWOW-1 RGD sequence or the betaPS metal ion-dependent adhesion site (MIDAS) motif. TWOW-1 binding was increased by mutations in the alphaPS2 membrane-proximal cytoplasmic GFFNR sequence or by exposure to Mn2+. Although Mn2+ is sometimes assumed to promote maximal integrin activity, TWOW-1 binding in Mn2+ could be increased further by the alphaPS2 GFFNR --> GFANA mutation. A mutation in the betaPS I domain (betaPS-b58; V409D) greatly increased ligand binding affinity, explaining the increased cell spreading mediated by alphaPS2betaPS-b58. Further mutagenesis of this residue suggested that Val-409 normally stabilizes the closed head conformation. Mutations that potentially reduce interaction of the integrin beta subunit plexin-semaphorin-integrin (PSI) and stalk domains have been shown to have activating properties. We found that complete deletion of the betaPS PSI domain enhanced TWOW-1 binding. Moreover the PSI domain is dispensable for at least some other integrin functions because betaPS-DeltaPSI displayed an enhanced ability to mediate cell spreading. These studies establish a means to evaluate mechanisms and consequences of integrin affinity modulation in a tractable model genetic system.
Amino Acid Motifs↗
Actin microfilament aggregation induced by withaferin A is mediated by annexin II.
The actin cytoskeleton supports diverse cellular processes such as endocytosis, oriented growth, adhesion and migration. The dynamic nature of the cytoskeleton, however, has made it difficult to define the roles of the many accessory molecules that modulate actin organization, especially the multifunctional adapter protein annexin II. We now report that the compound withaferin A (1) can alter cytoskeletal architecture in a previously unknown manner by covalently binding annexin II and stimulating its basal F-actin cross-linking activity. Drug-mediated disruption of F-actin organization is dependent on annexin II expression by cells and markedly limits their migratory and invasive capabilities at subcytotoxic concentrations. Given the extensive ethnobotanical history of withaferin-containing plant preparations in the treatment of cancer and inflammatory and neurological disorders, we suggest that annexin II represents a feasible, previously unexploited target for therapeutic intervention by small-molecule drugs.
Actin Cytoskeleton↗
A conserved glutamate residue in transmembrane helix 10 influences substrate specificity of rabbit OCT2 (SLC22A2).
OCT1 and OCT2 are involved in renal secretion of cationic drugs. Although they have similar selectivity for some substrates (e.g. tetraethylammonium (TEA)), they have distinct selectivities for others (e.g. cimetidine). We postulated that "homolog-specific residues," i.e. the 24 residues that are conserved in OCT1 orthologs as one amino acid and in OCT2 as a different one, influence homolog-specific selectivity and examined the influence on substrate binding of three of these conserved residues that are found in the C-terminal half of the rabbit orthologs of OCT1/2. The N353L and R403I substitutions (OCT2 to OCT1) did not significantly change the properties of OCT2. However, the E447Q replacement shifted substrate selectivity toward an OCT1-like phenotype. Substitution of glutamate with cationic amino acids (E447K and E447R) abolished transport activity, and the E447L mutant displayed markedly reduced transport of TEA and cimetidine while retaining transport of 1-methyl-4-phenylpyridinium. In a novel homology model of the three-dimensional structure of OCT2, Glu(447) was found in a putative docking region within a hydrophilic cleft of the protein. In addition, six residues identified in separate studies as exerting significant effects on OCT binding were also found within the putative cleft region. There was a significant correlation (r(2) = 0.82) between the IC(50) values for inhibition of TEA transport by 14 different compounds and their calculated K(D) values for binding to the model of rabbit OCT2. The results suggest that homology modeling offers an opportunity to direct future site-directed studies of OCT/substrate interaction.
1-Methyl-4-phenylpyridinium↗
Efficacy of lenalidomide in myelodysplastic syndromes.
BACKGROUND: Ineffective erythropoiesis is the hallmark of myelodysplastic syndromes. Management of the anemia caused by ineffective erythropoiesis is difficult. In patients with myelodysplastic syndromes and symptomatic anemia, we evaluated the safety and hematologic activity of lenalidomide, a novel analogue of thalidomide. METHODS: Forty-three patients with transfusion-dependent or symptomatic anemia received lenalidomide at doses of 25 or 10 mg per day or of 10 mg per day for 21 days of every 28-day cycle. All patients either had had no response to recombinant erythropoietin or had a high endogenous erythropoietin level with a low probability of benefit from such therapy. The response to treatment was assessed after 16 weeks. RESULTS: Neutropenia and thrombocytopenia, the most common adverse events, with respective frequencies of 65 percent and 74 percent, necessitated the interruption of treatment or a dose reduction in 25 patients (58 percent). Other adverse events were mild and infrequent. Twenty-four patients had a response (56 percent): 20 had sustained independence from transfusion, 1 had an increase in the hemoglobin level of more than 2 g per deciliter, and 3 had more than a 50 percent reduction in the need for transfusions. The response rate was highest among patients with a clonal interstitial deletion involving chromosome 5q31.1 (83 percent, as compared with 57 percent among those with a normal karyotype and 12 percent among those with other karyotypic abnormalities; P=0.007) and patients with lower prognostic risk. Of 20 patients with karyotypic abnormalities, 11 had at least a 50 percent reduction in abnormal cells in metaphase, including 10 (50 percent) with a complete cytogenetic remission. After a median follow-up of 81 weeks, the median duration of transfusion independence had not been reached and the median hemoglobin level was 13.2 g per deciliter (range, 11.5 to 15.8). CONCLUSIONS: Lenalidomide has hematologic activity in patients with low-risk myelodysplastic syndromes who have no response to erythropoietin or who are unlikely to benefit from conventional therapy.
Adult↗
Transcript profiling in peripheral T-cell lymphoma, not otherwise specified, and diffuse large B-cell lymphoma identifies distinct tumor profile signatures.
To glean biological differences and similarities of peripheral T-cell lymphoma-not otherwise specified [PTCL-NOS] to diffuse large B-cell lymphoma (DLBCL), a transcriptosome analysis was done on five PTCL-NOS and four DLBCL patients and validated by quantitative real-time reverse transcription-PCR on 10 selected genes. Normal peripheral blood T cells, peripheral blood B cells, and lymph node were used as controls. The resultant gene expression profile delineated distinct "tumor profile signatures" for PTCL-NOS and DLBCL. Several highly overexpressed genes in both PTCL-NOS and DLBCL involve the immune network, stroma, angiogenesis, and cell survival cascades that make important contributions to lymphomagenesis. Inflammatory chemokines and their receptors likely play a central role in these complex interrelated pathways: CCL2 and CXCR4 in PTCL-NOS and CCL5 and CCR1 in DLBCL. Highly overexpressed oncogenes unique to PTCL-NOS are SPI1, STK6, alpha-PDGFR, and SH2D1A, whereas in DLBCL they are PIM1, PIM2, LYN, BCL2A1, and RAB13. Oncogenes common to both lymphomas are MAFB, MET, NF-kappaB2, LCK, and LYN. Several tumor suppressors are also down-regulated (TPTE, MGC154, PTCH, ST5, and SUI1). This study illustrates the relevance of tumor-stroma immune trafficking and identified potential novel prognostic markers and targets for therapeutic intervention.
Base Sequence↗
Strategies for targeting the multidrug resistance-1 (MDR1)/P-gp transporter in human malignancies.
ATP-binding cassette (ABC) transporters are a super family of channel proteins that include multi-drug resistance 1 (MDR1/P-gp) and multi-drug resistance related proteins (MRPs) whose functions include the efflux of ions, nutrients, lipids, amino acids, peptides, proteins and drugs. The three-dimensional structures of bacterial and human ABC transporters demonstrate that these proteins are ATP-dependent molecular machines that scan the inner membrane leaflet for lipids/drugs and flip them to the outer membrane leaflet. In many human cancers, the level of expression of MDR1 is an important independent prognostic factor that determines response to combination chemotherapy. Intrinsic and acquired resistance to chemotherapy exposure are due to a high level of MDR1 expression that enhances drug efflux, with associated poor clinical outcome and lower complete remission (CR) rates. Recent clinical trials in hematological and solid malignancies have shown promise for a prolonged remission and improved overall survival when the MDR1 P-gp is inhibited when combined with chemotherapy. Structure-based homology modeling of these ABC transporters may help design novel drug candidates to both the membrane-spanning domain (MSD) and the nucleotide-binding domain (NBD) located within the cytoplasm. This review will highlight advances in the utilization of homology modeling in the drug discovery process and how this will impact on fundamental insights to the development of novel therapeutics that could alter and/or inhibit their functions.
ATP Binding Cassette Transporter, Subfamily B, Mem↗
Thioredoxin-1 binds to the C2 domain of PTEN inhibiting PTEN's lipid phosphatase activity and membrane binding: a mechanism for the functional loss of PTEN's tumor suppressor activity.
Thioredoxin-1 (Trx-1) is a 12 kDa redox protein that is overexpressed in a large number of human tumors. Elevated Trx-1 is associated with increased tumor cell proliferation, inhibited apoptosis, aggressive tumor growth, and decreased patient survival. The molecular mechanisms for the promotion of tumorigenesis by Trx-1 are not known. PTEN is a major tumor suppressor of human cancer that acts by hydrolyzing membrane phosphatidylinositol (PtdIns)-3-phosphates, thus, preventing the activation of the survival signaling kinase Akt by PtdIns-3-kinase. We show that Trx-1 binds in a redox dependent manner to PTEN to inhibit its PtdIns-3-phosphatase activity which results in increased Akt activation in cells. Molecular docking and site-specific mutation studies show that the binding of Trx-1 to PTEN occurs through a disulfide bond between the active site Cys(32) of Trx-1 and Cys(212) of the C2 domain of PTEN leading to steric interference by bound Trx-1 of the catalytic site of PTEN and of the C2 lipid membrane-binding domain. The results of the study suggest that the increased levels of Trx-1 in human tumors could lead to functional inhibition of PTEN tumor suppressor activity providing an additional mechanism for tumorigenesis with loss of PTEN activity.
Animals↗
Targeting the multidrug resistance-1 transporter in AML: molecular regulation and therapeutic strategies.
The multidrug resistance-1 (MDR1) gene product, P-glycoprotein (P-gp), and the multidrug resistance-related proteins (MRPs) are members of the adenosine triphosphate (ATP)-binding cassette (ABC) transporter gene superfamily that regulates the trafficking of drugs, peptides, ions, and xenobiotics across cell membrane barriers. Three-dimensional modeling of human MDR1/P-gp indicates that these glycoproteins function as efficient, ATP-dependent gate-keepers, which scan the plasma membrane and its inner leaflet to flip lipophilic substrates to the outer membrane leaflet. Delineation of the adverse prognostic power of MDR1 in adult acute myeloid leukemia (AML) raised hopes that pharmacologic blockade of P-gp would improve the outcome of conventional cytotoxic therapy, perhaps more so than in any other human malignancy. Phase 3 clinical trials investigating first- and second-generation P-gp antagonists have yielded conflicting results, emphasizing the importance of applying preclinical principals to realistically appraise expectations for clinical benefit. Structure-based design strategies and the delineation of transcriptional regulators of survival gene cassettes promise to yield novel, more-effective strategies to overcome drug resistance. Lessons learned from investigations of these and other mechanisms of cellular defense hold promise for a renaissance in the development of targeted therapeutics in acute leukemia.
ATP Binding Cassette Transporter, Subfamily B↗
In vivo molecular pharmacology and antitumor activity of the targeted Akt inhibitor PX-316.
Akt, a serine/threonine kinase that promotes cell survival, is activated by binding of its pleckstrin homology (PH) domain to membrane phosphatidylinositol (PtdIns)-3-phosphates formed by PtdIns-3-kinase. D-3-Deoxy-phosphatidyl-myo-inositols that cannot be phosphorylated on the 3-position of the myo-inositol group are inhibitors of the Akt PH domain. The most active compound is D-3-deoxy-phosphatidyl-myo-inositol 1-[(R)-2-methoxy-3-octadecyloxypropyl hydrogen phosphate] (PX-316). PX-316 administered intraperitoneally to mice at 150 mg/kg inhibits Akt activation in HT-29 human tumor xenografts up to 78% at 10 h with recovery to 34% at 48 h. Phosphorylation of GSK-3beta, a downstream target of Akt, is also inhibited. There is no decrease in PtdIns(3,4,5)-trisphosphate levels by PX-316, showing it is not an inhibitor of PtdIns-3-K in vivo. Gene expression profiling of HT-29 tumor xenografts shows many similarities between the effects of PX-316 and the PtdIns-3-K inhibitor wortmannin, with downregulation of several ribosomal-related genes, while PX-316 uniquely increases the expression of a group of mitochondrial-related genes. PX-316 has antitumor activity against early human MCF-7 breast cancer and HT-29 colon cancer xenografts in mice. PX-316 formulated in 20% hydroxypropyl-beta-cyclodextrin for intravenous administration is well tolerated in mice and rats with no hemolysis and no hematological toxicity. Thus, PX-316 is the lead compound of a new class of potential agents that inhibit Akt survival signaling.
2-Hydroxypropyl-beta-cyclodextrin↗
Structure-based design of novel anti-cancer agents targeting aurora kinases.
Aurora kinases are a family of mitotic serine-threonine kinases (S/T kinases), that functions as a class of novel oncogenes and are over-expressed in several solid tumors including breast, ovary, prostate, pancreas and colorectal cancer. To validate human ARK1 (Aurora2, STK15, HsAIRK1) as a drugable target in pancreatic cancer, we undertook a structure-based approach to design specific inhibitors utilizing homology modeling, affinity docking and an in vitro kinase assay in an iterative process. In this review, we discuss the biology, rationale for targeting and approaches taken to inhibit this family of protein kinases, implicated in dysregulated chromosome segregation and cytokinesis.
Animals↗
Targeting aurora2 kinase in oncogenesis: a structural bioinformatics approach to target validation and rational drug design.
The aurora kinases are a novel oncogenic family of mitotic serine/threonine kinases (S/T kinases) that are overexpressed in a number of solid tumors, including pancreas and colorectal cancer. A PSI-BLAST search [National Center for Biotechnology Information (NCBI)] with the sequence of the S/T kinase domain of human aurora1 kinase [also known as AUR1, ARK2, AIk2, AIM-1, and STK12] and human aurora2 kinase (also known as AUR2, ARK1, AIK, BTAK, and STK15) showed a high sequence similarity to the three-dimensional structures of bovine cAMP-dependent kinase [Brookhaven Protein Data Bank code 1CDK], murine cAMP-dependent kinase (1APM), and Caenorhabditis elegans twitchin kinase (1KOA). When the aurora1 or aurora2 sequence was input into the tertiary structure prediction programs THREADER and 3D-PSSM (three-dimensional position-sensitive scoring matrix), the top structural matches were 1CDK, 1APM, and 1KOA, confirming that these domains are structurally conserved. The structural models of aurora1 and aurora2 were built using 1CDK as the template structure. Molecular dynamics and docking simulations, targeting the ATP binding site of aurora2 with adenylyl imidodiphosphate (AMP-PNP), staurosporine, and six small molecular S/T kinase inhibitors, identified active-site residues that interact with these inhibitors differentially. The docked structures of the aurora2-AMP-PNP and aurora2-staurosporine complexes indicated that the adenine ring of AMP-PNP and the indolocarbazole moiety of staurosporine have similar positions and orientations and provided the basis for the docking of the other S/T kinase inhibitors. Inhibitors with isoquinoline and quinazoline moieties were recognized by aurora2 in which H-89 and 6,7-dimethoxyquinazoline compounds exhibited high binding energies compared with that of staurosporine. The calculated binding energies for the docked small-molecule inhibitors were qualitatively consistent with the IC(50) values generated using an in vitro kinase assay. The aurora2 structural model provides a rational basis for site-directed mutagenesis of the active site; design of novel H-89, staurosporine, and quinazoline analogues; and the screening of the available chemical database for the identification of other novel, small-molecular entities.
Amino Acid Sequence↗
Specific inhibition of the Akt1 pleckstrin homology domain by D-3-deoxy-phosphatidyl-myo-inositol analogues.
Activation of Akt (protein kinase B), a Ser/Thr protein kinase that promotes cell survival, has been linked to tumorigenesis. Akt is activated by phosphorylation after binding of its pleckstrin homology (PH) domain to plasma membrane phosphatidyl-myo-inositol-3-phosphates, formed by phosphoinositide-3-kinase. We report a novel strategy to inhibit Akt activation based on the use of D-3-deoxy-phosphatidyl-myo-inositols (DPIs) that cannot be phosphorylated on the 3-position of the myo-inositol ring. We have studied the DPIs, DPI 1-[(R)-2,3-bis(hexadecanoyloxy)propyl hydrogen phosphate], its ether lipid derivative DPI 1-[(R)-2-methoxy-3-octadecyloxypropyl hydrogen phosphate] (DPIEL), and its carbonate derivative DPI 1-[(R)-2-methoxy-3-octadecyloxypropyl carbonate]. We demonstrate in platelet-derived growth factor-stimulated mouse NIH3T3 cells that the DPIs bind to the PH domain of Akt, trapping it in the cytoplasm and thus preventing Akt activation. DPIEL did not inhibit myristylated-Akt, a constitutively active membrane-bound Akt expressed in NIH3T3 cells, and cell growth was not inhibited, unlike in wild-type NIH3T3 cells. Molecular modeling and docking studies show that DPIEL binds with much higher affinity to Akt's PH domain as compared with DPI and DPI 1-[(R)-2-methoxy-3-octadecyloxypropyl carbonate]. This study shows that the DPIs are a novel class of growth inhibitory agents with a novel mechanism of action through binding to the PH domain of Akt and inhibition of Akt activation.
Animals↗