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

Pharmacodynamics of Cyclin D1 Degradation in Ovarian Cancer Xenografts with Repeated Oral SHetA2 Dosing

SHetA2 is a promising, orally active small molecule with anticancer properties that target heat shock proteins. In this study, we aimed to investigate the pharmacodynamic (PD) effects of SHetA2 using preclinical in vitro and in vivo models of ovarian cancer and establish a physiologically based pharmacokinetic (PBPK)/PD model to describe their relationships with SHetA2 concentrations in mice. We found that daily oral administration of 60 mg/kg SHetA2 for 7 days resulted in consistent plasma PK and tissue distribution, achieving tumor drug concentrations required for growth inhibition in ovarian cancer cell lines. SHetA2 effectively induced cyclin D1 degradation in cancer cells in a dose-dependent manner, with up to 70% reduction observed and an IC50 of 4~5 µM. We identified cyclin D1 as a potential PD marker for SHetA2, based on a well-correlated time profile with SHetA2 PK. Additionally, we examined circulating levels of ccK18 as a non-invasive PD marker for SHetA2-induced apoptotic activity and found it unsuitable due to high variability. Using a PBPK/PD model, we depicted SHetA2 levels and their promoting effects on cyclin D1 degradation in tumors following multiple oral doses. The model suggested that twice-daily dosing regimens would be effective for sustained reduction in cyclin D1 protein. Our study provides valuable insights into the PK/PD of SHetA2, facilitating future clinical trial designs and dosing schedules.

Distinct mechanism of cervical cancer cell death caused by the investigational new drug SHetA2

Drug-targetable vulnerabilities of cancer cells include their dependence on heat shock proteins (HSPs) to support elevated mitochondrial metabolism and counteract cell death factors. The investigational new drug SHetA2 targets these vulnerabilities in ovarian and endometrial cancer cells by disrupting complexes of the mortalin HSP with its client proteins (mitochondrial support proteins, metabolic enzymes, p53) leading to mitochondrial leakage of cytochrome c and apoptosis-inducing factor (AIF), and caspase-dependent apoptosis. Our objective was to evaluate the roles of mitochondrial damage and another SHetA2-target HSP protein, cytoplasmic heat shock cognate 70 (hsc70), in the mechanism of SHetA2 killing of cervical cancer cells. Cervical cancer cells responded to SHetA2 with excessive mitophagy that did not deter AIF leakage into the cytoplasm. Then, hsc70 was unable to prevent cytoplasmic AIF nuclear translocation and promotion of DNA damage and cell death, because SHetA2 disrupted hsc70/AIF complexes. The Cancer Genome Atlas analysis found that overexpression of hsc70, but not mortalin, was associated with worse cervical cancer patient survival. Use of specific inhibitors documented that AIF and mitophagy, but not caspases, contributed to the mechanism of SHetA2-induced cell death in cervical cancer cells. As validation, excessive mitophagy and lack of caspase activation were observed in SHetA2-inhibited xenograft tumors.

SHetA2 Attack on Mortalin and Colleagues in Cancer Therapy and Prevention

Heat Shock Proteins of the 70-kDa family (HSP70s) do not cause cancer by themselves, but instead protect cells as they transform into cancer. These molecular chaperones bind numerous client proteins and utilize ATP hydrolysis to facilitate proper protein folding, formation of functional complexes and cellular localizations, or degradation of irreparably damaged proteins. Their transient upregulation by stressful situations avoids induction of programmed cell death. Continued upregulation of the mortalin, heat shock cognate (hsc70) and glucose regulated protein 78 (Grp78) support cancer development and progression by supporting pro-proliferative and metabolic functions and repressing pro-death functions of oncoproteins and tumor suppressor proteins. This review describes the discovery and development of a lead anti-cancer compound, sulfur heteroarotinoid A2 (SHetA2, NSC726189), which was originally developed to bind retinoic acid receptors, but was subsequently found to work independently of these receptors. The discovery and validation of mortalin, hsc70 and Grp78 as SHetA2 target proteins is summarized. The documented and hypothesized roles of these HSP70 proteins and their clients in the mechanism of SHetA2 inhibition of cancer without toxicity are discussed. Use of this mechanistic data to evaluate drug action in a cancer clinical trial and develop synergistic drug combinations is explained. Knowledge needed to optimize SHetA2 analogs for use in cancer therapy and prevention is proposed as future directions.

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.

SHetA2 interference with mortalin binding to p66shc and p53 identified using drug-conjugated magnetic microspheres

SHetA2 is a small molecule flexible heteroarotinoid (Flex-Het) with promising cancer prevention and therapeutic activity. Extensive preclinical testing documented lack of SHetA2 toxicity at doses 25 to 150 fold above effective doses. Knowledge of the SHetA2 molecular target(s) that mediate(s) the mechanism of SHetA2 action is critical to appropriate design of clinical trials and improved analogs. The aim of this study was to develop a method to identify SHetA2 binding proteins in cancer cells. A known metabolite of SHetA2 that has a hydroxyl group available for attachment was synthesized and conjugated to a linker for attachment to a magnetic microsphere. SHetA2-conjugated magnetic microspheres and unconjugated magnetic microspheres were separately incubated with aliquots of a whole cell protein extract from the A2780 human ovarian cancer cell line. After washing away non-specifically bound proteins with the protein extraction buffer, SHetA2-binding proteins were eluted with an excess of free SHetA2. In two independent experiments, an SDS gel band of about 72 kDa was present at differential levels in wells of eluent from SHetA2-microspheres in comparison to wells of eluent from unconjugated microspheres. Mass spectrometry analysis of the bands (QStar) and straight eluents (Orbitrap) identified mortalin (HSPA9) to be present in the eluent from SHetA2-microspheres and not in eluent from unconjugated microspheres. Co-immunoprecipitation experiments demonstrated that SHetA2 interfered with mortalin binding to p53 and p66 Src homologous-collagen homologue (p66shc) inside cancer cells. Mortalin and SHetA2 conflictingly regulate the same molecules involved in mitochondria-mediated intrinsic apoptosis. The results validate the power of this protocol for revealing drug targets.

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.

Membrane expression of the death ligand trail receptors DR4 and DR5 in the normal endometrium, endometrial atypical hyperplasia and endometrioid endometrial cancer

To assess membrane expression of DR4 and DR5 in the normal endometrium (NE), endometrial atypical hyperplasia (EAH) and endometrioid endometrial cancer (EEC), the study examined 101 patients: 20 NE, 14 EAH and 67 EEC. The expression of DR4 and DR5 was examined and presented as the total score (TS). DR4 expression was seen in 18 NE, 11 EAH and 10 EEC. DR5 expression was seen in 20 NE, 13 EAH and 21 EEC. A strong correlation between type of endometrial tissue and TS of both receptors was identified. In EEC TS of DR4 and DR5 was not related to grading, staging or survival. Malignant transformation in the endometrium is related to reduction of membrane DR4 and DR5 expression. The level of membrane staining of the receptors in EEC is not dependent on grading and staging, and is not sufficient to predict survival in EEC patients.

Membrane expression of TRAIL receptors DR4, DR5, DcR1 and DcR2 in the normal endometrium, atypical endometrial hyperplasia and endometrioid adenocarcinoma: a tissue microarray study

Purpose

To evaluate the membrane expression of DR4, DR5, DcR1 and DcR2 in the normal endometrium (NE), atypical endometrial hyperplasia (AEH) and endometrioid adenocarcinoma (EAC).

Methods

The study comprised 197 patients: 20 NE, 18 AEH and 159 EAC. Tissue microarrays were constructed. Membrane expression of DR4, DR5, DcR1 and DcR2 was examined and presented as total score (TS).

Results

In EAC, the membrane expression of DR4, DR5 and DcR2 was less common compared to NE (p < 0.001; p < 0.001; p = 0.018) and AEH (p < 0.001; p < 0.001; p = 0.004). In EAC the membrane expression of DcR1 did not differ when compared to NE (p = 0.055) and AEH (p = 0.173). A strong correlation was found between the type of endometrial tissue (NE/AEH/EAC) and the TS of DR4 (p < 0.001), DR5 (p < 0.001), DcR1 (p = 0.033) and DcR2 (p < 0.001). In EAC, the TS of DR4, DR5, DcR1 and DcR2 was not related to grading and staging. In EAC, the membrane expression of DR5, but not DR4, DcR1 and DcR2, was related to better disease-free survival (DFS). The overall survival (OS) was not related to membrane TRAIL receptors expression.

Conclusions

The membrane expression of the receptors for TRAIL DR4, DR5, DcR1 and DcR2 is greater in NE than EAC. The level of membrane staining of the receptors in EAC is not dependent on grading and staging. In EAC patients, membrane expression of DR4, DR5, DcR1 and DcR2 are not independent predictors of survival.

The use of retinoids in ovarian cancer: a review of the literature

Ovarian cancer is the deadliest of all gynecologic malignancies. The search for novel treatment modalities to augment traditional chemotherapy and improve quality of life is ongoing. Retinoids, a class of compounds composed of vitamin A, its natural derivatives, and synthetic analogs, have been studied extensively in both the prevention and treatment of gynecologic malignancies. In this article, we reviewed preclinical studies and clinical trials conducted using retinoids in ovarian cancer.

The impact of novel retinoids in combination with platinum chemotherapy on ovarian cancer stem cells

OBJECTIVE

Retinoids are important modulators of cell growth, differentiation, and proliferation. 9cUAB30, 9cUAB124, and 9cUAB130 are three novel retinoid compounds that show cytotoxic effects in other malignancies. We evaluated these novel retinoids in combination with chemotherapy against ovarian cancer stem cells (CSCs) in vitro and in an ex vivo model.

METHODS

A2780 cells were plated in 96-well plates and treated with retinoid, carboplatin, or combination therapy. Cell viability was evaluated using ATPLite assay. The A2780 cell line was also analyzed for CSCs by evaluating ALDH activity using flow cytometry. A2780 cells treated ex vivo with retinoids and chemotherapy were injected into the flank of athymic nude mice in order to evaluate subsequent tumor initiating capacity.

RESULTS

A2780 cells were sensitive to treatment with retinoids and carboplatin. The best treatment resulted from the combination of retinoid 9cUAB130 and carboplatin. Untreated A2780 cells demonstrated ALDH activity in 3.3% of the cell population. Carboplatin treatment enriched ALDH activity to 27.3%, while 9cUAB130±carboplatin maintained the ALDH positive levels similar to untreated controls (2.3% and 6.7%, respectively). Similar results were found in tumorsphere-forming conditions. Flank injections of ex vivo treated A2780 cells resulted in 4/4 mice developing tumors at 40 days in the untreated group, while 0/4 tumors developed in the 9cUAB130 and carboplatin treated group.

CONCLUSION

Combination treatment with carboplatin and retinoids reduced cell-viability, reduced CSC marker expression, and inhibited tumorigenicity, making it a more effective treatment when compared with carboplatin alone.

Novel HTS strategy identifies TRAIL-sensitizing compounds acting specifically through the caspase-8 apoptotic axis

Tumor Necrosis Factor-Related Apoptosis-Inducing Ligand (TRAIL) is potentially a very important therapeutic as it shows selectivity for inducing apoptosis in cancer cells whilst normal cells are refractory. TRAIL binding to its cognate receptors, Death Receptors-4 and -5, leads to recruitment of caspase-8 and classical activation of downstream effector caspases, leading to apoptosis. As with many drugs however, TRAIL's usefulness is limited by resistance, either innate or acquired. We describe here the development of a novel 384-well high-throughput screening (HTS) strategy for identifying potential TRAIL-sensitizing agents that act solely in a caspase-8 dependent manner. By utilizing a TRAIL resistant cell line lacking caspase-8 (NB7) compared to the same cells reconstituted with the wild-type protein, or with a catalytically inactive point mutant of caspase-8, we are able to identify compounds that act specifically through the caspase-8 axis, rather than through general toxicity. In addition, false positive hits can easily be "weeded out" in this assay due to their activity in cells lacking caspase-8-inducible activity. Screening of the library of pharmacologically active compounds (LOPAC) was performed as both proof-of-concept and to discover potential unknown TRAIL sensitizers whose mechanism is caspase-8 mediated. We identified known TRAIL sensitizers from the library and identified new compounds that appear to sensitize specifically through caspase-8. In sum, we demonstrate proof-of-concept and discovery of novel compounds with a screening strategy optimized for the detection of caspase-8 pathway-specific TRAIL sensitizers. This screen was performed in the 384-well format, but could easily be further miniaturized, allows easy identification of artifactual false positives, and is highly scalable to accommodate diverse libraries.

NF-kappaB is involved in SHetA2 circumvention of TNF-alpha resistance, but not induction of intrinsic apoptosis

Treatment of cancer with tumor necrosis factor-alpha (TNF-alpha) is hindered by resistance and toxicity. The flexible heteroarotinoid, SHetA2, sensitizes resistant ovarian cancer cells to TNF-alpha-induced extrinsic apoptosis, and also induces intrinsic apoptosis as a single agent. This study tested the hypothesis that nuclear factor-kappaB (NF-kappaB) is involved in SHetA2-regulated intrinsic and extrinsic apoptosis. SHetA2 inhibited basal and TNF-alpha-induced or hydrogen peroxide-induced NF-kappaB activity through counter-regulation of upstream kinase (IkappaB kinase) activity, inhibitor protein (IkappaB-alpha) phosphorylation, and p-65 NF-kappaB subunit nuclear translocation, but independently of reactive oxygen species generation. Ectopic over-expression of p-65, or treatment with TNF-alpha receptor 1 (TNFR1) small interfering RNA or a caspase-8 inhibitor, each attenuated synergistic apoptosis by SHetA2 and TNF-alpha, but did not affect intrinsic apoptosis caused by SHetA2. In conclusion, NF-kappaB repression is involved in SHetA2 circumvention of resistance to TNF-alpha-induced extrinsic apoptosis, but not in SHetA2 induction of intrinsic apoptosis.