Integration of fingerprint-based similarity searching and kernel-based partial least squares analysis to predict inhibitory activity against CSK, HER2, JAK1, JAK2, and JAK3.

Fingerprint-based similarity searching is an important strategy for virtual screening in drug discovery. In the present study, we carried out a systematic virtual screening study, followed by the establishment of kernel-based partial least square (KPLS) analysis prediction models for five tyrosine kinase drug targets, C-terminal SRC kinase (CSK), human epidermal growth factor 2 (HER2), and Janus kinases 1, 2, and 3 (JAK1, JAK2, and JAK3), using a dataset of 3688 compounds. These kinases are important drug discovery targets, particularly as HER2 has been validated for the treatment of metastatic breast cancer, JAK inhibitors have been validated for the clinical management of arthritis and autoimmune diseases, and CSK has been found to play an important role in bone remodeling in arthritis. We conducted similarity screenings with the most active molecule for each target in the dataset as a query using eight (8) types of two-dimensional (2D) molecular fingerprints, comprising seven Hashed fingerprints, Linear, Dendritic, Radial, Pairwise, Triplet, Torsion, and MOLSPRINT2D, and one Structural keys fingerprint, MACCS. The top ranked 1% of compounds from each target's similarity screening results was used to set up kernel-based partial least square (KPLS) prediction models, with q2 values up to 0.8. The best KPLS model for each target was selected based on its predictive ability and boot strapping results and used for prediction. This integrated study approach combining similarity screening with KPLS analysis has a high potential to enhance the accuracy and efficiency of virtual screening and thus improve the drug discovery process.

SS-4 is a highly selective small molecule inhibitor of STAT3 tyrosine phosphorylation that potently inhibits GBM tumorigenesis in vitro and in vivo.

Glioblastoma (GBM) is a highly aggressive cancer with a dismal prognosis. Constitutively active STAT3 has a causal role in GBM progression and is associated with poor patient survival. We rationally designed a novel small molecule, SS-4, by computational modeling to specifically interact with STAT3. SS-4 strongly and selectively inhibited STAT3 tyrosine (Y)-705 phosphorylation in MT330 and LN229 GBM cells and inhibited their proliferation and induced apoptosis with an IC50 of ∼100 nM. The antiproliferative and apoptotic actions of SS-4 were Y-705 phosphorylation dependent, as evidenced by its lack of effects on STAT3 knockout (STAT3KO) cells or STAT3KO cells that overexpressed a phospho-Y705 deficient (STAT3Y705F) mutant, and the recovery of effects when wild-type STAT3 or a phospho-serine (S)727 deficient mutant was expressed in STAT3KO cells. SS-4 increased the expression of STAT3 repressed genes, while decreasing the expression of STAT3 promoted genes. Importantly, SS-4 markedly reduced the growth of GBM intracranial tumor xenografts. These data together identify SS-4 as a potent STAT3 inhibitor that selectively blocks Y705-phosphorylation, induces apoptosis, and inhibits growth of human GBM models in vitro and in vivo.

Targeting MDM2 for Neuroblastoma Therapy: In Vitro and In Vivo Anticancer Activity and Mechanism of Action.

BACKGROUND: Neuroblastoma is an aggressive pediatric solid tumor with an overall survival rate of <50% for patients with high-risk disease. The majority (>98%) of pathologically-diagnosed neuroblastomas have wild-type p53 with intact functional activity. However, the mouse double minute 2 (MDM2) homolog, an E3 ubiquitin ligase, is overexpressed in neuroblastoma and leads to inhibition of p53. MDM2 also exerts p53-independent oncogenic functions. Thus, MDM2 seems to be an attractive target for the reactivation of p53 and attenuation of oncogenic activity in neuroblastoma. METHODS: In this study, we evaluated the anticancer activities and underlying mechanisms of action of SP141, a first-in-class MDM2 inhibitor, in neuroblastoma cell lines with different p53 backgrounds. The findings were confirmed in mouse xenograft models of neuroblastoma. RESULTS: We demonstrate that SP141 reduces neuroblastoma cell viability, induces apoptosis, arrests cells at the G2/M phase, and prevents cell migration, independent of p53. In addition, in neuroblastoma xenograft models, SP141 inhibited MDM2 expression and suppressed tumor growth without any host toxicity at the effective dose. CONCLUSIONS: MDM2 inhibition by SP141 results in the inhibition of neuroblastoma growth and metastasis, regardless of the p53 status of the cells and tumors. These findings provide proof-of-concept that SP141 represents a novel treatment option for both p53 wild-type and p53 null neuroblastoma.

Targeted Brain Tumor Therapy by Inhibiting the MDM2 Oncogene: In Vitro and In Vivo Antitumor Activity and Mechanism of Action.

There is a desperate need for novel and efficacious chemotherapeutic strategies for human brain cancers. There are abundant molecular alterations along the p53 and MDM2 pathways in human glioma, which play critical roles in drug resistance. The present study was designed to evaluate the in vitro and in vivo antitumor activity of a novel brain-penetrating small molecule MDM2 degrader, termed SP-141. In a panel of nine human glioblastoma and medulloblastoma cell lines, SP-141, as a single agent, potently killed the brain tumor-derived cell lines with IC50 values ranging from 35.8 to 688.8 nM. Treatment with SP-141 resulted in diminished MDM2 and increased p53 and p21cip1 levels, G2/M cell cycle arrest, and marked apoptosis. In intracranial xenograft models of U87MG glioblastoma (wt p53) and DAOY medulloblastoma (mutant p53) expressing luciferase, treatment with SP-141 caused a significant 4- to 9-fold decrease in tumor growth in the absence of discernible toxicity. Further, combination treatment with a low dose of SP-141 (IC20) and temozolomide, a standard anti-glioma drug, led to synergistic cell killing (1.3- to 31-fold) in glioma cell lines, suggesting a novel means for overcoming temozolomide resistance. Considering that SP-141 can be taken up by the brain without the need for any special delivery, our results suggest that SP-141 should be further explored for the treatment of tumors of the central nervous system, regardless of the p53 status of the tumor.

A novel RNA variant of human concentrative nucleoside transporter 1 (hCNT1) that is a potential cancer biomarker.

BACKGROUND: The human concentrative nucleoside transporter 1 (hCNT1) a product of the SLC28A1 gene is one of the three concentrative nucleoside transporters, with a substrate specificity for physiological pyrimidine nucleosides. It has recently been implicated in tumor suppression. We have unraveled a splice variant RNA transcript that is overexpressed in some tumor tissues and some cancer cells. This study established  that observation. METHODS: We examined several clones of hCNT1 generated from RT-PCR of total RNA from human kidney tissue purchased from Ambion. The resulting cDNA clones were then sequenced, and a variant that retained intron 4, and skipped some exons fully or partly, specifically exons 5 and 13 were completely missed and only part of exon 6 was spliced. Tissue expression analysis by PCR indicated a similar distribution of expression of RNA of the splice variant hCNT1-IR as that of the dominant variant hCNT1, particularly in the small intestine, kidney and liver. Further, analysis of various tumor samples with PCR primers designed from this novel hCNT1 splice variant (hCNT1-IR) revealed interestingly that it is overexpressed in some cancer tissues relative to normal tissues, particularly kidney, liver and pancreatic cancers. CONCLUSION: We have identified a novel intron retaining and exon skipping splice variant of the hCNT1 nucleoside transporter, and designated it hCNT1-IR, which has a similar tissue expression distribution as the normal hCNT1 variant, but unlike the normal transcript, hCNT1-IR is overexpressed in some cancers and may serve as a potential cancer biomarker.

Inhibiting ß-Catenin by ß-Carboline-Type MDM2 Inhibitor for Pancreatic Cancer Therapy.

The ß-catenin and MDM2 oncoproteins are overexpressed and constitutively activated in human pancreatic cancer and contribute to its initiation, progression, and metastasis. The Wnt/ß-catenin signaling pathway strongly interacts with the MDM2-p53 signaling pathway, accelerating the tumorigenesis and its development. Therefore, therapies inhibiting both ß-catenin and MDM2 are suggested to be ideal treatments for patients with advanced pancreatic cancer. We have recently identified a novel class of ß-carboline compounds as the specific and potent MDM2 inhibitors, including a lead compound SP141. In the present study, we utilized SP141 as an exemplary ß-carboline compound to characterize ß-catenin as a molecular target of the ß-carboline compounds and to demonstrate an important role of ß-catenin in the anticancer activity of ß-carboline. We found that the silencing of either ß-catenin or MDM2 largely reduced the anticancer activity of SP141 while the double silencing of both genes almost completely blocked SP141's activity. SP141 directly bound to ß-catenin and inhibited its expression and activity in pancreatic cancer cells in vitro and in vivo. The inhibitory effects of SP141 on ß-catenin were mediated by the ubiquitin-proteasome system in an MDM2-independent manner. In conclusion, these results suggest that SP141 exerts its anticancer activity by dually inhibiting ß-catenin and MDM2. We envision that ß-carboline derivatives can be developed as promising dual inhibitors of ß-catenin and MDM2 for the treatment of advanced pancreatic cancer.

QSAR Studies of New Pyrido[3,4-b]indole Derivatives as Inhibitors of Colon and Pancreatic Cancer Cell Proliferation.

We have discovered a new class of pyrido[b]bindole derivatives that show potent and broad spectrum anticancer activity with IC50 values down to submicromolar levels. Structure-activity relationship data acquired with the compounds as antiproliferative agents against several cancer cell lines, i.e. human HCT116 colon cancer cell line, and HPAC, Mia-PaCa2 and Panc-1 pancreatic cancer cell lines, were subjected to two different QSAR modeling methods. A kernel-based partial least squares (KPLS) regression analysis with chemical 2D fingerprint descriptors, and a PHASE pharmacophore alignment with 3D-QSAR study. The KPLS method afforded successful predictive QSAR models for antiproliferative activity of the HCT116 colon cell line and on two of the pancreatic cancer cell lines HPAC and Mia-PaCa2, with the following statistics: R 2s of 0.99, 0.99 and 0.98, for training set coefficients of determination, and external test set predictive r 2s of 0.70, 0.58 and 0.70, respectively. The best 2D fingerprint descriptor for both the HCT116 and HPAC data out of the eight finger prints utilized was the atom triplet fingerprint; whereas the one that worked best for the Mia-PaCa2 data was the linear fingerprint descriptor. The PHASE pharmacophore based 3D-QSAR study afforded a four-point pharmacophore model comprising one hydrogen bond donor (D) and three ring (R) elements, which yielded a successful 3D-QSAR model only with the HCT116 cell line data with training set R 2 of 0.683, and an external test set predictive r 2 of 0.562. With the PHASE 3D-QSAR, the influence of electronic effects and hydrophobicity were visualized, and were in agreement with the observed SAR of substitutions, while the KPLS method the relative extent of contribution of each atom in a compound to the activity. These models will foster the lead optimization process for this potent series of anticancer pyrido [3,4-b]indole compounds.

Homology Modeling of Human Concentrative Nucleoside Transporters (hCNTs) and Validation by Virtual Screening and Experimental Testing to Identify Novel hCNT1 Inhibitors.

OBJECTIVE: The nucleoside transporter family is an emerging target for cancer, viral and cardiovascular diseases. Due to the difficulty in the expression, isolation and crystallization of membrane proteins, there is a lack of structural information on any of the mammalian and for that matter the human proteins. Thus the objective of this study was to build homology models for the three cloned concentrative nucleoside transporters hCNT1, hCNT2 and hCNT3 and validate them for screening towards the discovery of much needed inhibitors and probes. METHODS: The recently reported crystal structure of the Vibrio cholerae concentrative nucleoside transporter (vcCNT), has satisfactory similarity to the human CNT orthologues and was thus used as a template to build homology models of all three hCNTs. The Schrödinger modeling suite was used for the exercise. External validation of the homology models was carried out by docking a set of recently reported known hCNT1 nucleoside class inhibitors at the putative binding site using induced fit docking (IDF) methodology with the Glide docking program. Then, the hCNT1 homology model was subsequently used to conduct a virtual screening of a 360,000 compound library, and 172 compounds were obtained and biologically evaluated for hCNT 1, 2 and 3 inhibitory potency and selectivity. RESULTS: Good quality homology models were obtained for all three hCNTs as indicated by interrogation for various structural parameters and also external validated by docking of known inhibitors. The IDF docking results showed good correlations between IDF scores and inhibitory activities; particularly for hCNT1. From the top 0.1% of compounds ranked by virtual screening with the hCNT1 homology model, 172 compounds selected and tested for against hCNT1, hCNT2 and hCNT3, yielded 14 new inhibitors (hits) of (i.e., 8% success rate). The most active compound exhibited an IC50 of 9.05 µM, which shows a greater than 25-fold higher potency than phlorizin the standard CNT inhibitor (IC50 of 250 µM). CONCLUSION: We successfully undertook homology modeling and validation for all human concentrative nucleoside transporters (hCNT 1, 2 and 3). The proof-of-concept that these models are promising for virtual screening to identify potent and selective inhibitors was also obtained using the hCNT1 model. Thus we identified a novel potent hCNT1 inhibitor that is more potent and more selective than the standard inhibitor phlorizin. The other hCNT1 hits also mostly exhibited selectivity. These homology models should be useful for virtual screening to identify novel hCNT inhibitors, as well as for optimization of hCNT inhibitors.

Synthesis, Biological Evaluation and Modeling Studies of New Pyrido[3,4-b]indole Derivatives as Broad-Spectrum Potent Anticancer Agents.

OBJECTIVE: There is an urgent need drugs against particularly difficult to treat solid tumors such as pancreatic, triple negative breast, lung, colon, metastatic prostate cancers and melanoma. Thus, the objective of this study was to synthesize compounds based computational modeling that indicated the pyrido[3,4-b]indole class bind to MDM2, a new cancer target for which there are still no drug on the market. METHODS: Compounds were synthesized by established methods and tested for antiproliferative activity against a broad range of human cancer cell lines, comprising HCT116 colon, HPAC, MIA PaCa-2 and Panc-1 pancreatic, MCF-7 and MDA-MB-468 breast, A375 and WM164 melanoma, A549 lung, and LNCaP, DU145 and PC3 prostate cancer lines. Computational docking was also undertaken. RESULTS: The novel pyrido[3,4-b]indoles synthesized exhibited a clear SAR with regards to antiproliferative activity, with potent broad-spectrum anticancer activity with IC50s down to 80, 130, 130 and 200 nM for breast, colon, melanoma and pancreatic cancer cells, respectively. 1-Naphthyl at C1 combined with methoxy at C6 provided the best antiproliferative activity. Thus, compound 11 (1-naphthyl-6-methoxy-9H-pyrido[3,4-b]indole) showed the highest potency. A mechanistic feature of the compounds as a group is a strongly selective G2/M cell cycle phase arrest. Docking at on MDM2 suggested a hydrogen bond interaction between the 6-methoxy Tyr106, hydrophobic interaction with Val93, pi-pi stacking interactions with Tyr100 and His96 and hydrophobic interactions with Leu54 and Ile99. An N9-methyl group disrupted binding interactions, such as H-bond interactions involving the N9 hydrogen. CONCLUSION: We have identified a novel series of pyrido[3,4-b]indoles with potent broad spectrum anticancer activity towards the most aggressive and difficult to treat cancers including metastatic pancreatic cancer, non-small cell lung cancer, triple negative breast cancers, and BRAFV600E mutant melanoma, as well as metastatic colon and prostate cancers. There was also evidence of selectivity towards cancer cells relative to normal cells. These compounds will serve as new leads from which novel therapeutics and molecular tools can be developed for a wide variety of cancers.

Development and validation of a rapid HPLC method for quantitation of SP-141, a novel pyrido[b]indole anticancer agent, and an initial pharmacokinetic study in mice.

There is an increasing interest in targeting the MDM2 oncogene for cancer therapy. SP-141, a novel designed small molecule MDM2 inhibitor, exerts excellent in vitro and in vivo anticancer activity. To facilitate the preclinical development of this candidate anticancer agent, we have developed an HPLC method for the quantitative analysis of SP-141. The method was validated to be precise, accurate, and specific, with a linear range of 16.2-32,400 ng/mL in plasma, 16.2-6480 ng/mL in homogenates of brain, heart, liver, kidneys, lungs, muscle and tumor, and 32.4-6480 ng/mL in spleen homogenates. The lower limit of quantification was 16.2 ng/mL in plasma and all the tissue homogenates, except for spleen homogenates, where it was 32.4 ng/mL. The intra- and inter-assay precisions (coefficient of variation) were between 0.86 and 13.39%, and accuracies (relative errors) ranged from -8.50 to 13.92%. The relative recoveries were 85.6-113.38%. SP-141 was stable in mouse plasma, modestly plasma bound and metabolized by S9 microsomal enzymes. We performed an initial pharmacokinetic study in tumor-bearing nude mice, demonstrating that SP-141 has a short half-life in plasma and wide tissue distribution. In summary, this HPLC method can be used in future preclinical and clinical investigations of SP-141.

Dilazep analogues for the study of equilibrative nucleoside transporters 1 and 2 (ENT1 and ENT2).

As ENT inhibitors including dilazep have shown efficacy improving oHSV1 targeted oncolytic cancer therapy, a series of dilazep analogues was synthesized and biologically evaluated to examine both ENT1 and ENT2 inhibition. The central diamine core, alkyl chains, ester linkage and substituents on the phenyl ring were all varied. Compounds were screened against ENT1 and ENT2 using a radio-ligand cell-based assay. Dilazep and analogues with minor structural changes are potent and selective ENT1 inhibitors. No selective ENT2 inhibitors were found, although some analogues were more potent against ENT2 than the parent dilazep.

The pyrido[b]indole MDM2 inhibitor SP-141 exerts potent therapeutic effects in breast cancer models.

A requirement for Mouse Double Minute 2 (MDM2) oncogene activation has been suggested to be associated with cancer progression and metastasis, including breast cancer. To date, most MDM2 inhibitors have been designed to block the MDM2-p53-binding interphase, and have low or no efficacy against advanced breast cancer with mutant or deficient p53. Here we use a high-throughput screening and computer-aided, structure-based rational drug design, and identify a lead compound, SP-141, which can directly bind to MDM2, inhibit MDM2 expression and induce its autoubiquitination and proteasomal degradation. SP-141 has strong in vitro and in vivo antibreast cancer activity, with no apparent host toxicity. While further investigation is needed, our data indicate that SP-141 is a novel targeted therapeutic agent that may especially benefit patients with advanced disease.

A quantitative LC-MS/MS method for determination of SP-141, a novel pyrido[b]indole anticancer agent, and its application to a mouse PK study.

In the present study, a specific and sensitive liquid chromatography-triple quadrupole mass spectrometry method was developed and validated for the determination of SP-141, a novel pyrido[b]indole anticancer agent. After a liquid-liquid extraction with n-hexane-dichloromethane-2-propanol (20:10:1, v/v/v) mixture, the analyte was separated on a Kinetex C18 column (50×2.1mm, 2.6µm) with mobile phases comprising of water (0.1% formic acid, v/v) and acetonitrile (0.1% formic acid, v/v) at a flow rate of 0.4mL/min. The test compound (SP-141) and the internal standard (SP-157) were analyzed in the multiple reaction-monitoring mode using the mass transitions m/z 325.1 → 282.0. The method was linear in the concentration range of 0.648-162ng/mL with coefficients of determination (R(2)) of 0.999 in mouse plasma. The lower limit of quantification was 0.648ng/mL. The intra- and inter-day assay precisions (coefficient of variation, %CV) were less than 4.2% and accuracies (relative error, %RE) ranged from -6.1% to 2.1%. The extraction recoveries were between 97.1 and 103.1% and the relative matrix effect was minimal. In addition, SP-141 was found to be stable in the plasma after three freeze-thaw cycles, at 37°C and 4°C for 24h, and at -80°C for 4 weeks. It was also stable in the stock solution at room temperature for 24h and after preparation in the autosampler for 36h. The validated method was successfully applied to an initial pharmacokinetic study of SP-141 in CD-1 mice following intraperitoneal and intravenous administrations.

Identification of a new class of MDM2 inhibitor that inhibits growth of orthotopic pancreatic tumors in mice.

BACKGROUND & AIMS: The oncogene MDM2, which encodes an E3 ubiquitin ligase, is overexpressed in pancreatic cancers and is therefore a therapeutic target. Current inhibitors of MDM2 target the interaction between MDM2 and P53; these would have no effect on cancer cells that do not express full-length P53, including many pancreatic cancer cells. We searched for a compound that specifically inhibits MDM2 itself. METHODS: We performed a virtual screen and structure-based design to identify specific inhibitors of MDM2. We tested the activities of compounds identified on viability, proliferation, and protein levels of HPAC, Panc-1, AsPC-1, and Mia-Paca-2 pancreatic cancer cell lines. We tested whether intraperitoneal injections of one of the compounds identified affected growth of xenograft tumors from Panc-1 cells, or orthotopic tumors from Panc-1 and AsPC-1 cells (injected into pancreata), in nude mice. RESULTS: We identified a compound, called SP141, which bound directly to MDM2, promoting its auto-ubiquitination and degradation by the proteasome. The compound reduced levels of MDM2 in pancreatic cancer cell lines, as well as their proliferation, with 50% inhibitory concentrations <0.5 µM (0.38-0.50 µM). Increasing concentrations of SP141 induced increasing levels of apoptosis and G2-M-phase arrest of pancreatic cancer cell lines, whether or not they expressed functional P53. Injection of nude mice with SP141 (40 mg/kg/d) inhibited growth of xenograft tumors (by 75% compared with control mice), and led to regression of orthotopic tumors. CONCLUSIONS: In a screen for specific inhibitors of MDM2, we identified a compound called SP141 that reduces levels of MDM2 in pancreatic cancer cell lines, as well as their proliferation and ability to form tumors in nude mice. SP141 is a new class of MDM2 inhibitor that promotes MDM2 auto-ubiquitination and degradation. It might be further developed as a therapeutic agent for pancreatic cancer.

Impact of resistance mutations on inhibitor binding to HIV-1 integrase.

HIV-1 integrase (IN) is essential for HIV-1 replication, catalyzing two key reaction steps termed 3' processing and strand transfer. Therefore, IN has become an important target for antiviral drug discovery. However, mutants have emerged, such as E92Q/N155H and G140S/Q148H, which confer resistance to raltegravir (RAL), the first IN strand transfer inhibitor (INSTI) approved by the FDA, and to the recently approved elvitegravir (EVG). To gain insights into the molecular mechanisms of ligand binding and drug resistance, we performed molecular dynamics (MD) simulations of homology models of the HIV-1 IN and four relevant mutants complexed with viral DNA and RAL. The results show that the structure and dynamics of the 140s' loop, comprising residues 140 to 149, are strongly influenced by the IN mutations. In the simulation of the G140S/Q148H double mutant, we observe spontaneous dissociation of RAL from the active site, followed by an intrahelical swing-back of the 3'-OH group of nucleotide A17, consistent with the experimental observation that the G140S/Q148H mutant exhibits the highest resistance to RAL compared to other IN mutants. An important hydrogen bond between residues 145 and 148 is present in the wild-type IN but not in the G140S/Q148H mutant, accounting for the structural and dynamical differences of the 140s' loop and ultimately impairing RAL binding in the double mutant. End-point free energy calculations that broadly capture the experimentally known RAL binding profiles elucidate the contributions of the 140s' loop to RAL binding free energies and suggest possible approaches to overcoming drug resistance.

Synthesis, docking, and biological studies of phenanthrene ß-diketo acids as novel HIV-1 integrase inhibitors.

In the present study we report the synthesis of halogen-substituted phenanthrene ß-diketo acids as new HIV-1 integrase inhibitors. The target phenanthrenes were obtained using both standard thermal- and microwave-assisted synthesis. 4-(6-Chlorophenanthren-2-yl)-2,4-dioxobutanoic acid (18) was the most active compound of the series, inhibiting both 3'-end processing (3'-P) and strand transfer (ST) with IC50 values of 5 and 1.3 µM, respectively. Docking studies revealed two predominant binding modes that were distinct from the binding modes of raltegravir and elvitegravir, and suggest a novel binding region in the IN active site. Moreover, these compounds are predicted not to interact significantly with some of the key amino acids (Q148 and N155) implicated in viral resistance. Therefore, this series of compounds can further be investigated for a possible chemotype to circumvent resistance to clinical HIV-1 IN inhibitors.

Dipyridamole analogs as pharmacological inhibitors of equilibrative nucleoside transporters. Identification of novel potent and selective inhibitors of the adenosine transporter function of human equilibrative nucleoside transporter 4 (hENT4).

To identify needed human equilibrative nucleoside transporter 4 (hENT4) inhibitors, we cloned and stably expressed the recombinant protein in PK15NTD (nucleoside transporter deficient) cells, and, investigated its interaction with a series of dipyridamole analogs synthesized in our laboratory. Compounds were tested in this newly established hENT4 expressing system as well in previous stably expressed hENT1 and hENT2 expressing systems. Of the dipyridamole analogs evaluated, about one fourth of the compounds inhibited hENT4 with higher potencies than dipyridamole. The most potent of them, Compound 30 displayed an IC50 of 74.4 nM, making it about 38 times more potent than dipyridamole (IC50=2.8 µM), and selectivities of about 80-fold and 20-fold relative to ENT1 and ENT2, respectively. Structure-activity relationship showed nitrogen-containing monocyclic rings and noncyclic substituents at the 4- and 8-positions of the pyrimido[5,4-d]pyrimidine were important for the inhibitory activity against hENT4. The most potent and selective hENT4 inhibitors tended to have a 2,6-di(N-monohydroxyethyl) substitution on the pyrimidopyrimidine ring system. The inhibitors of hENT4 identified in this study are the most selective and potent inhibitors of hENT4 adenosine transporter function to date, and should serve as useful pharmacological/biochemical tools and/or potential leads for ENT4-based therapeutics. Also, the new hENT4-expressing PK15 cell line established will serve as a useful screening tool for the discovery and design of hENT4 ligands.

Chemoprevention activity of dipyridamole in the MMTV-PyMT transgenic mouse model of breast cancer.

Dipyridamole (DPM) is widely used to prevent strokes and vascular thrombosis. Combination therapy of DPM and antimetabolites has shown synergistic anticancer activity. This study investigated the chemopreventive effects of DPM in the mouse mammary tumor virus promoter-driven polyoma middle T oncoprotein metastatic breast cancer model. We also investigated the effects of DPM on gene and miRNA expression. Chemopreventive activity was assessed by comparing the time to onset of palpable lesions, primary tumor growth kinetics, and the number of lung metastases in transgenic mice treated with DPM or vehicle. Gene expression and miRNA expression profiles of mammary tumor tissues were then analyzed using the Affymetrix GeneChip or miRNA 2.0 arrays. Real-time quantitative PCR was used to confirm changes in gene expression. Treatment with DPM beginning at the age of 4 weeks delayed the onset of palpable lesions, delayed tumor progression, and suppressed lung metastasis. Microarray gene expression analysis identified 253 genes differentially expressed between DPM-treated and control mammary tumors. miRNA expression analysis revealed that 53 miRNAs were altered by DPM treatment. The results indicate that DPM has chemoprevention activity against breast cancer tumorigenesis and metastasis in mice. The array analyses provide insights into potential mechanisms of DPM's chemopreventive effects, involving upregulation of several genes and miRNAs known to suppress cancer growth and/or metastasis and downregulation of genes known to promote cancer. Some of these genes have not been previously studied in breast cancer and may serve as novel molecular targets for breast cancer chemoprevention.

Inhibition of gastric tumor growth by a novel Hsp90 inhibitor.

Heat shock protein 90 (Hsp90) is a molecular chaperone engaging in multiple cellular signaling by stabilizing oncoproteins (e.g. Akt and c-Raf) in tumor cells. Whereas Hsp90 inhibitors such as 17-AAG exert promising antitumor effects in clinical trials, current efforts focus on developing agents targeting Hsp90 with improved efficacy and lower toxicity. Using a fluorescence polarization assay, we screened over a hundred of synthetic small molecules and identified a resorcinol derivative LD053 that bound the Hsp90 ATP-binding pocket. The binding of LD053 to Hsp90 dissociated the co-chaperone protein cdc37 from Hsp90, resulting in destabilization of Akt and c-Raf and subsequent inhibition of PI3K/Akt and c-Raf/Mek/Erk signaling in BGC823 gastric cancer cells. As a consequence, LD053 decreased cancer cell viability and induced apoptosis evidenced by increased subG0/G1 cell population and increased cleavage of caspase 3 and PARP. Interestingly, normal human cells appeared insensitive to LD053 treatments. Consistent with its in vitro anticancer activities, LD053 significantly inhibited growth of BGC823 xenografts in nude mice without apparent body weight loss. These results thus demonstrate that LD053 is a novel Hsp90 inhibitor and has potential to be used to treat gastric cancer.

JKA97, a novel benzylidene analog of harmine, exerts anti-cancer effects by inducing G1 arrest, apoptosis, and p53-independent up-regulation of p21.

JKA97, a benzylidene analog of harmine, has been found to be a promising drug candidate for human cancer therapy, although the underlying molecular mechanisms have not been fully demonstrated. In this study, we evaluated the effects of JKA97 on human breast cancer cells in vitro and in vivo. JKA97 inhibited the growth and proliferation of MCF7 (p53 wild-type), MCF7 (p53 knockdown), and MDA-MB-468 (p53 mutant) cells in a dose-dependent manner. Treatment with JKA97 arrested breast cancer cells in G1 phase and induced apoptosis. JKA97 also significantly suppressed the growth of MCF7 and MDA-MB-468 xenograft tumors. It regulated the expression levels of G1 phase regulators, such as p21, p27, cyclinE, and cylinD1. JKA97 activated p21 transcription, independent of p53, but had little effect on p21 protein stability/degradation. In summary, our results suggest that JKA97 inhibits human breast cancer cell growth through activating p21, independent of p53, which provides a basis for developing this compound as a novel drug for human breast cancer therapy.