Novel pyrrolopyrimidines as Mps1/TTK kinase inhibitors for breast cancer.

New targeted therapy approaches for certain subtypes of breast cancer, such as triple-negative breast cancers and other aggressive phenotypes, are desired. High levels of the mitotic checkpoint kinase Mps1/TTK have correlated with high histologic grade in breast cancer, suggesting a potential new therapeutic target for aggressive breast cancers (BC). Novel small molecules targeting Mps1 were designed by computer assisted docking analyses, and several candidate compounds were synthesized. These compounds were evaluated in anti-proliferative assays of a panel of 15 breast cancer cell lines and further examined for their ability to inhibit a variety of Mps1-dependent biological functions. The results indicate that the lead compounds have strong anti-proliferative potential through Mps1/TTK inhibition in both basal and luminal BC cell lines, exhibiting IC50 values ranging from 0.05 to 1.0µM. In addition, the lead compounds 1 and 13 inhibit Mps1 kinase enzymatic activity with IC50 values from 0.356µM to 0.809µM, and inhibited Mps1-associated cellular functions such as centrosome duplication and the spindle checkpoint in triple negative breast cancer cells. The most promising analog, compound 13, significantly decreased tumor growth in nude mice containing Cal-51 triple negative breast cancer cell xenografts. Using drug discovery technologies, computational modeling, medicinal chemistry, cell culture and in vivo assays, novel small molecule Mps1/TTK inhibitors have been identified as potential targeted therapies for breast cancers.

Rapamycin-loaded Immunoliposomes Functionalized with Trastuzumab: A Strategy to Enhance Cytotoxicity to HER2-positive Breast Cancer Cells.

BACKGROUND: Liposomes have been employed to improve pharmacokinetics and reduce side effects of drugs. They can be functionalized with antibodies for targeted delivery. While the monoclonal antibody trastuzumab has been employed in the therapy of HER2-positive breast cancer, the resistance developed during treatment has been reported. Rapamycin could be used in combination with trastuzumab for improved therapeutic response. OBJECTIVE: In this study, we aimed to develop rapamycin-loaded liposomes and immunoliposomes with trastuzumab, characterize them and evaluate their in vitro cytotoxicity. METHOD: Formulations were prepared by the thin film hydration method and immunoliposome was conjugated to antibody by covalent bond. Characterization involved particle size, polydispersity, zeta potential, encapsulation efficiency, functionalization efficiency, DSC and FTIR assays. Cell studies were conducted through the MTT assay. RESULTS: SPC:Chol:DSPE-PEG formulation prepared at 1:10 drug to lipid ratio presented high encapsulation efficiency, appropriate particle size, low polydispersity, negative zeta potential and colloidal stability. Rapamycin exhibited intermolecular interactions with lipids and underwent crystallinity reduction. Rapamycin-loaded immunoliposomes were prepared with high trastuzumab functionalization efficiency and antibody stability. Cytotoxicity studies showed that the HER2-positive SK-BR-3 cell line was sensitive to trastuzumab, either as free drug or in the context of immunoliposomes, and is more sensitive to rapamycin than the triple negative MDA-MB-231 cells. For MDA-MB-231, the liposomal rapamycin was more cytotoxic than the free drug. Furthermore, the immunoliposomes showed potent cytotoxicity against SK-BR-3 cells. Finally, rapamycin and trastuzumab exhibited in vitro synergistic effect, particularly through immunoliposomes. CONCLUSION: The formulation developed herein has potential for in vivo evaluation.

Oncolytic potential of a novel KGFR tyrosine kinase inhibitor using a KGFR-selective breast cancer xenograft model.

BACKGROUND: Keratinocyte growth factor (KGF)/KGF receptor (KGFR) signaling produces a rapid increase in the progression of breast cancer. Molecular modeling was used to create a group of KGFR-selective kinase inhibitors (TKI). Compound L-27 is a potent and selective KGFR TKI. The present study examined the oncolytic potential of L-27 using a breast cancer xenograft model. MATERIALS AND METHODS: An orthotopic xenograft model was developed with KGF-transfected MCF-7 cells to examine the influence of L-27 upon KGFR-mediated tumor progression. RESULTS: L-27 was found to produce a dose-related reduction in the growth and metastasis of mouse xenograft tumors. Furthermore, L-27 treatment did not produce any signs of gross toxicity. CONCLUSION: L-27 was found to reduce the growth and metastasis of MCF-7 tumor xenografts with elevated expression of KGF. Thus, KGFR TKI may provide a new therapeutic approach for the treatment of breast and other types of cancer.

Human serum albumin-coated lipid nanoparticles for delivery of siRNA to breast cancer.

Human serum albumin (HSA)-coated lipid nanoparticles (HSA-LNPs) loaded with phrGFP-targeted siRNA (HSA-LNPs-siRNA) were prepared and evaluated for gene downregulation effect in phrGFP-transfected breast cancer cells and the corresponding xenograft tumor model. HSA-LNPs-siRNA were successfully prepared with a particle size of 79.5±5.5 nm. In phrGFP-transfected MCF-7 cells, HSA-LNPs-siRNA significantly decreased cell fluorescence even in the presence of fetal bovine serum (FBS). Moreover, cell fluorescence and phrGFP mRNA expression were significantly downregulated by HSA-LNPs-siRNA in phrGFP-transfected MCF-7, MDA-MB-231, and SK-BR-3 cells in comparison with control or HSA-LNPs-siRNA (scrambled). In phrGFP-transfected MCF-7 xenograft tumor model, tumor fluorescence was significantly decreased after three IV administrations of HSA-LNPs-siRNA at a dose of 3 mg/kg in comparison with siRNA alone. HSA-LNPs-siRNA demonstrated a superior pharmacokinetic profile in comparison with siRNA at a dose of 1mg/kg. These results show that the novel nonviral carrier, HSA-LNPs, may be used for the delivery of siRNA to breast cancer cells. FROM THE CLINICAL EDITOR: Targeted delivery of siRNA to cancer cells may be a viable anti-cancer strategy with low toxicity. In this study the novel nonviral carrier, human serum albumin-coated lipid nanoparticles (HSA-LNP) were demonstrated as an efficient delivery agent of siRNA to breast cancer cells.

Highly efficient cationic ethylphosphatidylcholine siRNA carrier for GFP suppression in modified breast cancer cells.

AIM: Cationic ethylphosphatidylcholines (ePCs) were evaluated for the delivery of siRNA in modified breast cancer cells. MATERIALS AND METHODS: Dimyristoleoyl-ePC (C14), dioleoyl-ePC (C18), and dilauroyl-ePC (C12) nanoparticles were complexed with siRNA for green fluorescent protein (GFP) suppression in modified MCF-7 breast cancer cells. The kinetics of GFP suppression were followed over the course of 72 hours. RESULTS: C14, which has been previously found to be particularly effective in gene transfection into primary human umbilical artery endothelial cells, was also remarkably effective as siRNA carrier, with an efficacy exceeding that of Lipofectamine RNAiMAX. The C14 toxicity remained comparable to that of RNAiMAX. The efficacy of the other tested cationic ePC formulations was less than that of C14 and RNAiMAX. CONCLUSION: The cationic lipid C14 is a highly efficient siRNA carrier that could be used for the development of new formulations for siRNA delivery into cancer cells. A valuable advantage of the C14 formulations is the fact that they are simple, and do not require adjuvants or complex preparation procedures.

Differential efficacy of DOTAP enantiomers for siRNA delivery in vitro.

DOTAP, as a racemic mixture, is a cationic lipid and a widely used transfection reagent. In this study, the effect of DOTAP's stereochemical structure on transfection efficiency was evaluated in vitro. Racemic and enantiomerically pure DOTAP were used in lipoplex formulations to deliver siRNA to MCF-7 cells, targeting the aromatase enzyme. At the 50 nM siRNA concentration and lipid-to-RNA charge ratios of 4 and 5, the R enantiomer of DOTAP was found to perform better than either the S- or the racemic agent. In addition, at 10 nM siRNA concentration and a charge ratio of 3, the R- lipoplex formulation silenced aromatase by ∼50% whereas the S and racemic formulations caused no significant target downregulation. Differences in lipid packing were modeled using membrane simulations. The results showed that, when combined with cholesterol, pure R-DOTAP and S-DOTAP enantiomers had 105% and 115% of lipid density relative to racemic DOTAP, respectively. These findings suggest an important role of lipid chirality in future development of lipid based siRNA delivery systems.

SPANosomes as delivery vehicles for small interfering RNA (siRNA).

Nonionic surfactant vesicles, or SPANosomes (SPs), comprised of cationic lipid and sorbitan monooleate (Span 80) were synthesized and evaluated as small interfering RNA (siRNA) vectors. The SPs had a mean diameter of less than 100 nm and exhibited excellent colloidal stability. The SP/siRNA complexes possessed a slightly positive zeta potential of 12 mV and demonstrated a high siRNA incorporation efficiency of greater than 80%. Cryogenic transmission electron microscopy (cryo-TEM) imaging of the SP/siRNA indicated a predominantly core-shell structure. The SP/siRNA complexes were shown to efficiently and specifically silence expression of both green fluorescent protein (GFP) (66% knockdown) and aromatase (77% knockdown) genes in breast cancer cell lines. In addition, the cellular trafficking pathway of the SP/siRNA was investigated by confocal microscopy using molecular beacons as probes for cytosolic delivery. The results showed efficient endosomal escape and cytosolic delivery of the siRNA cargo following internalization of the SP/siRNA complexes. In conclusion, Span 80 is a potent helper lipid, and the SPs are promising vehicles for siRNA delivery.

Comparison of increased aromatase versus ERα in the generation of mammary hyperplasia and cancer.

Factors associated with increased estrogen synthesis increase breast cancer risk. Increased aromatase and estrogen receptor α (ERα) in both normal epithelium and ductal carcinoma in situ lesions are found in conjunction with breast cancer, leading to the idea that altered estrogen signaling pathways predispose the mammary gland to cancer development. Here, we developed a transgenic mouse that conditionally expresses aromatase in the mammary gland, and used it along with a deregulated ERα expression model to investigate the molecular pathways involved in the development of mammary gland preneoplasia and carcinoma. Both increased ERα and aromatase expression led to the development of preneoplasia, but increased preneoplasia, in addition to carcinoma, was found in aromatase overexpressing mice. Increased prevalence of mammary pathologic changes in mice expressing aromatase correlated with increased cyclin E and cyclin-dependent kinase 2 expression. Gain of both ERα and aromatase increased expression of ERα and progesterone receptor, but aromatase produced a higher increase than ERα, accompanied by higher levels of downstream target genes Ccnd1, Myc, and Tnfsf11. In summary, whereas gain of both ERα and aromatase activate abnormal growth pathways in the mammary gland, aromatase induced a wider range of abnormalities that was associated with a higher prevalence of mammary preneoplasia and cancer progression.

Phase II trial of neoadjuvant exemestane in combination with celecoxib in postmenopausal women who have breast cancer.

PURPOSE: Within breast tissue, aromatase expression and activity is increased by prostaglandin E2, providing a rationale for combining the COX-2 inhibitor celecoxib with an aromatase inhibitor. To evaluate the effect of these drugs on aromatase and other biomarkers, a phase II trial of neoadjuvant exemestane followed sequentially by celecoxib plus exemestane was performed. METHODS: Postmenopausal women with estrogen receptor (ER) and/or progesterone (PR) positive stages II-III breast cancers received 8 weeks of exemestane 25 mg daily, followed by 8 weeks of exemestane 25 mg daily and celecoxib 400 mg twice daily. Core biopsies were collected pretreatment, after 8 weeks of exemestane, and at definitive breast cancer surgery. A tissue microarray was constructed and immunohistochemistry (IHC) for aromatase, ER, PR, HER-2, Ki-67, and COX-2 was performed. RESULTS: Twenty-two women were enrolled. Celecoxib was discontinued in 4 (18%) women for toxicity (all grade 1 and 2) and 2 (9%) developed serious cardiac events occurring at 1 and 4 months after completing treatment. By US, there were 8 (36%)-partial responses and 12 (55%)-stable disease. There were no pathological complete responses (pCR). There were statistically significant decreases in ER (P = .003), PR (P = .002), Ki-67 (P < .001), and COX-2 (P = .004) expression. No significant differences in aromatase or HER-2 expression were observed (P = .13 and P = .39, respectively). CONCLUSION: The addition of celecoxib to exemestane was tolerated by the majority of women and anti-tumor response was observed. Additional studies, including gene expression, are required to more fully understand the basis for the decreased expression of ER, PR, Ki-67, and COX-2.

Influence of novel KGFR tyrosine kinase inhibitors on KGF-mediated proliferation of breast cancer.

BACKGROUND: Keratinocyte growth factor (KGF) acts at the KGF receptor (KGFR) to produce a rapid stimulation of breast cancer cell proliferation and motility which is mediated via the Erk signaling pathway. Enhancement of KGF/KGFR signal transduction may be an early step in the metastatic progression of breast cancer. Receptor modeling of KGFR was used to identify selective KGFR tyrosine kinase (TK) inhibitor molecules that have the potential to bind selectively to the KGFR. The present study evaluated the biological activity of 57 of these KGFR TK inhibitor compounds on breast cancer cells. MATERIALS AND METHODS: These compounds were tested for their ability to inhibit KGF-mediated breast cancer cell proliferation in MCF-7 breast cancer cells. Furthermore, the effects of the most effective proliferation inhibitors were examined on Erk signaling and on the relative density of cell membrane KGFR. RESULTS: It was observed that 27 of the 57 compounds tested produced a 20% or greater reduction in KGF-mediated proliferation; while five compounds produced greater than 50% inhibition. In addition, the most potent inhibitors also reduced Erk signaling and cell membrane density of the KGFR. CONCLUSION: The compounds examined appear to be selective KGFR inhibitors which inhibit KGF-mediated activity and reduce the expression of KGFR on cancer cells. These results may lead to the development of a novel class of anticancer agents for the prevention of metastatic cancer progression.

Transferrin-conjugated lipid-coated PLGA nanoparticles for targeted delivery of aromatase inhibitor 7alpha-APTADD to breast cancer cells.

Transferrin (Tf)-conjugated lipid-coated poly(d,l-lactide-co-glycolide) (PLGA) nanoparticles carrying the aromatase inhibitor, 7alpha-(4'-amino)phenylthio-1,4-androstadiene-3,17-dione (7alpha-APTADD), were synthesized by a solvent injection method. Formulation parameters including PLGA-to-lipid, egg PC-to-TPGS, and drug-to-PLGA ratios and aqueous-to-organic phase ratio at the point of synthesis were optimized to obtain nanoparticles with desired sizes and drug loading efficiency. The optimal formulation had a drug loading efficiency of 36.3+/-3.4%, mean diameter of 170.3+/-7.6nm and zeta potential of -18.9+/-1.5mV. The aromatase inhibition activity of the nanoparticles was evaluated in SKBR-3 breast cancer cells. IC(50) value of the Tf-nanoparticles was ranging from 0.77 to 1.21nM, and IC(50) value of the nanoparticles was ranging from 1.90 to 3.41nM (n=3). The former is significantly lower than the latter (p<0.05). These results suggested that the aromatase inhibition activity of the Tf-nanoparticles was enhanced relative to that of the non-targeted nanoparticles, which was attributable to Tf receptor (TfR) mediated uptake. In conclusion, Tf-conjugated lipid-coated PLGA nanoparticles are potential vehicles for improving the efficiency and specificity of therapeutic delivery of aromatase inhibitors.

Selective regulation of aromatase expression for drug discovery.

Aromatase is a particularly attractive drug target in the treatment of hormone-responsive breast cancer, and aromatase activity in breast cancer patients is greater in or near the tumor tissue compared with the normal breast tissue. Complex regulation of aromatase expression in human tissues involves alternative promoter sites that provide tissue-specific control. Previous studies in our laboratories suggested a strong association between aromatase (CYP19) gene expression and the expression of cyclooxygenase (COX) genes. Additionally, COX selective inhibitors can suppress CYP19 gene expression and decrease aromatase activity. Our current hypothesis is that pharmacological regulation of aromatase can act locally to decrease the biosynthesis of estrogen and may provide additional therapy options for patients with hormone-dependent breast cancer. Two pharmacological approaches are being developed, one approach utilizing small molecule drug design and the second approach involving mRNA silencing technology. The small molecule drug design approach focuses on the synthesis and biological evaluation of a novel series of sulfonanilide analogs derived from COX-2 selective inhibitors. Combinatorial chemistry approaches were used to generate diversely substituted novel sulfonanilides. The compounds suppress aromatase enzyme activity in SK-BR-3 breast cancer cells in a dose and time dependent manner, and structure activity analysis does not find a correlation between aromatase suppression and COX inhibition. Real-time PCR analysis demonstrates that the sulfonanilide analogs decrease aromatase gene transcription in breast cells. Furthermore, the sulfonanilide compounds selectively decrease aromatase gene expression in several breast cancer cells, without exhibiting cytotoxic or apoptotic effects at low micromole concentrations. A ligand-based pharmacophore model for selective aromatase modulation (SAM) by the novel sulfonanilides identified an aromatic ring, two hydrogen bond acceptors, and a hydrophobic function as four key chemical features. In the second approach, short interfering RNAs (siRNA) were designed targeting human aromatase mRNA. Treatment of breast cancer cells with siRNAs targeting aromatase (siAROMs) completely masked the aromatase enzyme activity and resulted in suppression of CYP19 mRNA. Thus, these results suggest that the novel sulfonanilides and the siRNAs targeting aromatase expression may be valuable tools for selective regulation of aromatase in breast cancer.

Isolation and Characterization of Aromatase Inhibitors from Brassaiopsis glomerulata (Araliaceae).

The hexane- and ethyl acetate-soluble extracts of the leaves of Brassaiopsis glomerulata (Blume) Regel (Araliaceae), collected in Indonesia, were found to inhibit aromatase, the rate-limiting enzyme in the production of estrogens from androgens, in both enzyme- and cell-based aromatase inhibition (AI) assays. Bioassay-guided fractionation led to the isolation of six known compounds of the steroid and triterpenoid classes (1-6) from the hexane extract, of which 6ß-hydroxystimasta-4-en-3-one (5), was moderately active in the cell-based AI assay. Fractionation of the ethyl acetate extract afforded seven pure isolates (7-13) of the modified peptide, fatty acid, monoterpenoid, and benzenoid types, including six known compounds and the new natural product, N-benzoyl-L-phenylalanine methyl ester (9). The absolute stereochemistry of 9 and the other two peptides, 7 and 8, was determined by Marfey's analysis. Linoleic acid (10) was found to be active in the enzyme-based AI assay, while 9 and (-)-dehydrololiolide (12) showed activity in the cell-based AI assay.

Aromatase inhibitors: are there differences between steroidal and nonsteroidal aromatase inhibitors and do they matter?

Aromatase inhibitors (AIs) are approved for use in both early- and advanced-stage breast cancer in postmenopausal women. Although the currently approved "third-generation" AIs all powerfully inhibit estrogen synthesis, they may be subdivided into steroidal and nonsteroidal inhibitors, which interact with the aromatase enzyme differently. Nonsteroidal AIs bind noncovalently and reversibly to the aromatase protein, whereas steroidal AIs may bind covalently and irreversibly to the aromatase enzyme. The steroidal AI exemestane may exert androgenic effects, but the clinical relevance of this has yet to be determined. Switching between steroidal and nonsteroidal AIs produces modest additional clinical benefits, suggesting partial noncrossresistance between the classes of inhibitor. In these circumstances, the response rates to the second AI have generally been low; additional research is needed regarding the optimal sequence of AIs. To date, clinical studies suggest that combining an estrogen-receptor blocker with a nonsteroidal AI does not improve efficacy, while combination with a steroidal AI has not been evaluated. Results from head-to-head trials comparing steroidal and nonsteroidal AIs will determine whether meaningful clinical differences in efficacy or adverse events exist between the classes of AI. This review summarizes the available evidence regarding known differences and evaluates their potential clinical impact.

Natural products as aromatase inhibitors.

With the clinical success of several synthetic aromatase inhibitors (AIs) in the treatment of postmenopausal estrogen receptor-positive breast cancer, researchers have also been investigating the potential of natural products as AIs. Natural products from terrestrial and marine organisms provide a chemically diverse array of compounds not always available through current synthetic chemistry techniques. Natural products that have been used traditionally for nutritional or medicinal purposes (e.g., botanical dietary supplements) may also afford AIs with reduced side effects. A thorough review of the literature regarding natural product extracts and secondary metabolites of plant, microbial, and marine origin that have been shown to exhibit aromatase inhibitory activity is presented herein.