Heteroarotinoids with anti-cancer activity against ovarian cancer cells

Tetrahydroquinoline units in flexible heteroarotinoids (Flex-Hets) convey anti-cancer properties in A2780 ovarian cancer cells

SHetA2 (NSC 721689), our lead Flex-Het anti-cancer agent, consists of a thiochroman (Ring A) and a 4-nitrophenyl (Ring B) linked by a thiourea bridge. In this work, several series of new analogs having a tetrahydroquinoline (THQ, Ring A) unit connected by a urea or thiourea linker to a 4-substituted phenyl (Ring B) have been prepared and evaluated relative to SHetA2 in terms of binding affinity with mortalin and inhibition of A2780 ovarian cancer cells. Six of the derivatives equaled or exceeded the efficacy shown by SHetA2. Compounds 1a-d (series 1), lacking a methyl on the Ring A nitrogen and the gem-dimethyls on the adjacent carbon, showed only weak activity. Salt 2, the quaternized N,N-dimethyl iodide salt analog of 1a, also possessed very modest growth inhibition in the cell line studied. Series 3 compounds, which had a C3 ketone and an N-methyl replacing the sulfur in Ring A, were most successful. Compound 3a [Ring A = 1,2,2,4,4-pentamethyl-3-oxo-1,2,3,4-tetrahydroquinolin-6-yl; urea linker; Ring B = 4-nitrophenyl] had slightly lower potency (IC₅₀ 3.8 μM), but better efficacy (94.8%) than SHetA2 (IC₅₀ 3.17 μM, efficacy 84.3%). In addition, 3c and 3d [urea and thiourea linkers, respectively; Ring B = 4-(trifluoromethyl)phenyl] and 3e and 3f [urea and thiourea linkers, respectively; Ring B = 4-(trifluoromethoxy)phenyl] were also evaluated since these agents possessed electron-withdrawing groups with H-bonding capability. All displayed good activity. Compounds 3c and 3e showed improvement in both potency and efficacy compared to SHetA2. In general, when the linker group between Rings A and B was a urea, efficacy values slightly exceeded those with a thiourea linker in the carbonyl-containing THQ systems 3a-g. In contrast, when Ring A possessed the 1,2,2,4,4-pentamethyl-3-hydroxytetrahydroquinolin-6-yl unit (4a-f, series 4), very modest potency and efficacy was observed. Model compound 5, an exact N-methyl THQ analog of SHetA2, demonstrated less potency (IC₅₀ 4.5 μM), but improved efficacy (91.7%). Modeling studies were performed to rationalize the observed results.

Dione-thiophene conjugate inhibits proliferation and metastasis of nasopharyngeal carcinoma cells through calcium binding protein-P down-regulation

In the present study a series of dione-thiophenol conjugates was prepared and evaluated against nasopharyngeal carcinoma (NPC) cells. MTT assay showed that compound 4a reduced proliferation of C666-1 and CNE-1 cells to 26 and 24%, respectively at 10 μmol/l concentration. Flow cytometry revealed that increasing the concentration of compound 4a from 2 to 10 μmol/l increased the proportion of early apoptotic C666-1 cells from 2.76 to 69.43%. A significant (P < 0.001) decrease in the expression of S100P was caused by compound 4a. In compound 4a treated C666-1 cells the expression of RAGE, EGFR, CD44, MMP2 and MMP9 was markedly decreased. In summary, compound 4a inhibits nasopharyngeal cancer cell proliferation and induces apoptosis through down-regulation of S100P. Moreover, compound 4a also decreases MMP-2, MMP-9, EGFR, CD44 and RAGE expression in nasopharyngeal cancer cells. Thus, compound 4a can be investigated further as a drug candidate for the treatment of nasopharyngeal cancer.

Development of a dietary formulation of the SHetA2 chemoprevention drug for mice

Development of cancer chemoprevention compounds requires enhanced consideration for toxicity and route of administration because the target population is healthy. The small molecule drug, SHetA2 (NSC 726189), exhibited in vivo chemoprevention activity and lack of toxicity when administered by oral gavage. Our objective was to determine if a dietary formulation of SHetA2 could achieve effective tissue drug levels without toxicity. C57bl/6 J mice were monitored on modified American Institute of Nutrition (AIN)76A diet mixed with SHetA2 in a 3:1 ratio with Kolliphor HS15, a self-emulsifying drug delivery system (SEDDS) to deliver 37.5, 62.5, 125, 187 or 250 mg SHetA2/kg/day. Blood and tissues were evaluated after 1, 3 and 6 weeks. The 187 mg/kg/day dose was identified as optimal based on achievement of maximum blood and tissue drug levels in the effective micromolar range without evidence of toxicity. The 250 mg/kg/day group exhibited lower drug levels and the highest intestinal drug content suggesting that an upper limit of intestinal absorption had been surpassed. Only this highest dose resulted in liver and kidney function tests that were outside of the normal range, and significant reduction of cyclin D1 protein in normal cervical tissue. SHetA2 reduced cyclin D1 to greater extents in cancer compared to non-cancer cell cultures. Given this differential effect, optimal chemoprevention without toxicity would be expected to occur at doses that reduced cyclin D1 in neoplastic, but not in normal tissues. These findings support further development of SHetA2 as a chemoprevention agent and potential food additive.

Bioanalytical method development and validation of HPLCUV assay for the quantification of SHetA2 in mouse and human plasma: Application to pharmacokinetics study

Background

SHetA2 is an oral anticancer agent being investigated for cancer treatment and prevention. The aim of this study was to develop and validate a simple, cost-effective, and sensitive HPLC-UV method for the quantification of SHetA2 in biological samples and to apply the method to pharmacokinetic studies of the drug.

Methods

Sample preparation for mouse and human plasmas involved liquid-liquid precipitation and extraction using chilled acetonitrile with 2, 3-Diphenylquinoxaline as an internal standard. The separation of SHetA2 and internal standard was achieved via Waters XBridge™ BEH 130 C18 (3.5 μm, 2.1×150 mm) column coupled with a Waters XBridge™ C-18 (3.5 μm, 2.1×10 mm) guard column using 65% v/v acetonitrile: distilled water as a mobile phase in an isocratic mode with a flow rate of 0.18 ml/min. The analytes were eluted at a detection wavelength of 341 nm at a column temperature of 25°C.

Results

The method was validated across a range of 5-1000 ng/ml for SHetA2 in plasma, with a lower limit of quantification of 5 ng/ml. The method showed high recovery in human (79.9-81.8%) and mouse (95.4-109.2%) plasma with no matrix effect. The intra- and inter-day accuracy and precision studies demonstrated that the method was specific, sensitive, and reliable. Stability studies showed that SHetA2 is stable for 20 h postoperatively in the auto sampler, and for six weeks at -80°C in plasma. Repetitive freezing and thawing may be avoided by preparing the aliquots and storing them at -80°C. The developed method was successfully applied to study the plasma pharmacokinetics of SHetA2 in tumor-bearing nude mice after intravenous and oral administration.

Conclusion

A novel method for quantifying SHetA2 in mouse and human plasmas has been validated and is being applied for pharmacokinetic evaluation of SHetA2 in tumor-bearing mice. The developed method will be utilized for the quantification of SHetA2 in clinical studies.

Chemoprevention of colon and small intestinal tumorigenesis in APC(min/+) mice by SHetA2 (NSC721689) without toxicity

The occurrence of intestinal polyps in people at high risk for developing colorectal cancer provides an opportunity to test the efficacy of chemoprevention agents. In this situation of treating otherwise healthy people, the potential for toxicity must be minimal. The small-molecule flexible heteroarotinoid (Flex-Het), called SHetA2, has chemoprevention activity in organotypic cultures in vitro and lack of toxicity at doses capable of inhibiting xenograft tumor growth in vivo. The objective of this study was to evaluate SHetA2 chemoprevention activity and toxicity in the APC(min/+) murine model. Oral administration of SHetA2 at 30 and 60 mg/kg five days per week for 12 weeks significantly reduced development of intestinal polyps by 40% to 60% depending on the dose and sex of the treatment group. Immunohistochemical and Western blot analysis of polyps showed reduced levels of cyclin D1 and proliferating cell nuclear antigen in both SHetA2 treatment groups. Western blot analysis also showed SHetA2 induction of E-cadherin, Bax, and caspase-3 cleavage along with reduction in Bcl-2, COX-2, and VEGF, consistent with SHetA2 regulation of apoptosis, inflammation, and angiogenesis. Neither dose caused weight loss nor gross toxicity in APC(min/+) or wild-type littermates. Magnetic resonance imaging (MRI) of cardiac function showed no evidence of SHetA2 toxicity. SHetA2 did not alter left ventricular wall thickness. In summary, SHetA2 exerts chemoprevention activity without overt or cardiac toxicity in the APC(min/+) model. SHetA2 modulation of biomarkers in colon polyps identifies potential pharmacodynamic endpoints for SHetA2 clinical trials.

Induction of death receptor ligand-mediated apoptosis in epithelial ovarian carcinoma: The search for sensitizing agents

OBJECTIVE

To assess the abilities of cisplatin, paclitaxel, and flexible heteroarotinoid (Flex-Het) compound (SHetA2) to sensitize ovarian cancer cells to induction of the extrinsic apoptosis pathway by death receptor ligands, tumor necrosis factor alpha (TNFalpha), and TNF-related apoptosis-inducing ligand (TRAIL).

STUDY DESIGN

The effects of various combinations of TNFalpha, TRAIL, cisplatin, paclitaxel, and SHetA2 on viability and apoptosis in two established ovarian cancer cell lines, A2780 and SK-OV-3, and normal human primary endometrial cultures were measured with a cytotoxicity assay, flow cytometric analysis of annexin-V, and propidium iodide staining and Western blot analysis of caspase 8 and 3 activation.

RESULTS

Ovarian cancer and normal cells were resistant to TNFalpha and TRAIL. Cisplatin and paclitaxel did not increase sensitivity to these agents in either cell type. In contrast, combination of SHetA2 with TNFalpha or TRAIL induced a synergistic induction of apoptosis in cancer cells that involved activation of the extrinsic pathway caspase 8 and executioner caspase 3. The TRAIL combination was more potent than the TNFalpha combination. SHetA2 did not harm the viability of normal cells as a single agent or in combination with the death receptor ligands.

CONCLUSIONS

SHetA2, but not cisplatin or paclitaxel, can overcome resistance of ovarian cancer cells to TNFalpha and TRAIL without increasing sensitivity of normal cells to these death receptor ligands.

Development of flexible-heteroarotinoids for kidney cancer

Potential chemopreventive and therapeutic value of the lead Flexible Heteroarotinoid (Flex-Het), SHetA2, was indicated by growth inhibition of multiple cancer cell lines. The objective of this study was to evaluate the SHetA2 mechanism and in vivo activity in kidney cancer. SHetA2 induced apoptosis in the Caki-1 kidney cancer cell line through reduction of Bcl-2 protein and induction of PARP-1 and caspase 3 cleavages, whereas normal kidney epithelial cells exhibited resistance. Both normal and cancerous cells underwent G(1) arrest and loss of Cyclin D1. Tubule differentiation was induced in organotypic cultures and xenograft tumors in association with increases in E-Cadherin mRNA and protein expression. SHetA2 repressed activity of nuclear factor-κB, a transcription factor that regulates apoptosis, Bcl-2, growth, Cyclin D1, differentiation, and E-Cadherin in the opposite manner as SHetA2. Glutathione binding and generation of reactive oxygen species were not required for these activities. Oral SHetA2 inhibited growth in one of two renal cancer xenograft models without causing mortality or weight loss. Structure function analysis of related Flex-Hets for potential improvement of SHetA2 pharmaceutical properties showed that compounds with increased hydrophilicity slightly reduced the growth inhibition efficacy, but retained the differential effect on cancer over normal cells. Flex-Hets and metabolites were not mutagenic in the Ames test. In conclusion, SHetA2 regulates growth, differentiation, and apoptosis in kidney cancer cells through multiple molecular events downstream of nuclear factor-κB repression. Increasing the hydrophilicity of Flex-Hets does not attenuate the differential effect on cancer cells over normal cells, thus offering alternatives for improvement of therapeutic value.