Novel Non-Cyclooxygenase Inhibitory Derivative of Sulindac Inhibits Breast Cancer Cell Growth In Vitro and Reduces Mammary Tumorigenesis in Rats.

The nonsteroidal anti-inflammatory drug (NSAID) sulindac demonstrates attractive anticancer activity, but the toxicity resulting from cyclooxygenase (COX) inhibition and the suppression of physiologically important prostaglandins precludes its long-term, high dose use in the clinic for cancer prevention or treatment. While inflammation is a known tumorigenic driver, evidence suggests that sulindac's antineoplastic activity is partially or fully independent of its COX inhibitory activity. One COX-independent target proposed for sulindac is cyclic guanosine monophosphate phosphodiesterase (cGMP PDE) isozymes. Sulindac metabolites, i.e., sulfide and sulfone, inhibit cGMP PDE enzymatic activity at concentrations comparable with those associated with cancer cell growth inhibitory activity. Additionally, the cGMP PDE isozymes PDE5 and PDE10 are overexpressed during the early stages of carcinogenesis and appear essential for cancer cell proliferation and survival based on gene silencing experiments. Here, we describe a novel amide derivative of sulindac, sulindac sulfide amide (SSA), which was rationally designed to eliminate COX-inhibitory activity while enhancing cGMP PDE inhibitory activity. SSA was 68-fold and 10-fold less potent than sulindac sulfide (SS) in inhibiting COX-1 and COX-2, respectively, but 10-fold more potent in inhibiting growth and inducing apoptosis in breast cancer cells. The pro-apoptotic activity of SSA was associated with inhibition of cGMP PDE activity, elevation of intracellular cGMP levels, and activation of cGMP-dependent protein kinase (PKG) signaling, as well as the inhibition of ß-catenin/Tcf transcriptional activity. SSA displayed promising in vivo anticancer activity, resulting in a 57% reduction in the incidence and a 62% reduction in the multiplicity of tumors in the N-methyl-N-nitrosourea (MNU)-induced model of breast carcinogenesis. These findings provide strong evidence for cGMP/PKG signaling as a target for breast cancer prevention or treatment and the COX-independent anticancer properties of sulindac. Furthermore, this study validates the approach of optimizing off-target effects by reducing the COX-inhibitory activity of sulindac for future targeted drug discovery efforts to enhance both safety and efficacy.

Conformationally Defined Rexinoids for the Prevention of Inflammation and Nonmelanoma Skin Cancers.

Compound 1 is a potent rexinoid that is highly effective in cancer chemoprevention but elevates serum triglycerides. In an effort to separate the lipid toxicity from the anticancer activity of 1, we synthesized four new analogs of rexinoid 1, of which three rexinoids did not elevate serum triglycerides. Rexinoids 3 and 4 are twice as potent as rexinoid 1 in binding to Retinoid X receptor (RXR). All-trans retinoic acid (ATRA) plays a key role in maintaining skin homeostasis, and rexinoids 3-6 are highly effective in upregulating the genes responsible for the biosynthesis of ATRA. Inflammation plays a key role in skin cancer, and rexinoids 3 and 4 are highly effective in diminishing LPS-induced inflammation. Rexinoids 3 and 4 are highly effective in preventing UVB-induced nonmelanoma skin cancer (NMSC) without displaying any overt toxicities. Biophysical studies of rexinoids 3 and 5 bound to hRXRα-ligand binding domain (LBD) reveal important conformational and dynamical differences in the ligand binding domain.

Effects of High-Fructose Diet vs. Teklad Diet in the MNU-Induced Rat Mammary Cancer Model: Altered Tumorigenesis, Metabolomics and Tumor RNA Expression.

Epidemiology, clinical and experimental animal studies suggest high fructose diets are detrimental to metabolic status and may contribute to tumor development. This due to increased obesity and metabolic syndrome, known risk factors for many types of cancer. We compared tumor development in N-methyl-N-nitrosourea (MNU)-treated rats fed either a high (60%)-fructose diet (HFD) or a standard diet (SD). Female Sprague-Dawley rats at 43 days of age (DOA) were fed a SD or HFD followed by administration of MNU at 50 DOA. Rats were palpated weekly and sacrificed at 190 DOA. MNU-treated rats on HFD exhibited decreased tumor latency and roughly a two-fold increase in tumor multiplicity. RNA-Seq on frozen tumors (SD vs. HFD rats) showed altered expression of approximately 10% of genes (P < 0.05). When examined by Ingenuity Pathway Analysis, multiple highly significant pathways were identified including A) mechanisms of cancer, B) Wnt pathway, C) immune response (e.g., "Th1 and Th2 activation" and "antigen presentation") and D) LXR/RXR nuclear receptor. These generalized pathways were indirectly confirmed by alterations of various interrelated disease pathways (epithelial cancers, T cell numbers and apoptosis). In a second study, serum was collected from rats on the HFD or SD pre-MNU and at the time of sacrifice. Metabolomics revealed that the HFD yielded: A) increased levels of fructose, B) increases of various monoglycerols, C) reduced levels of various diacylglycerols and oxygenated inflammatory lipids (9 and 13 HODE and 12,13 DHOME) and D) increased levels of secondary bile acids (hyodeoxycholate and 6-oxolithocholate), which may reflect microbiome changes. These metabolomic changes, which are distinct from those on a high-fat diet, may prove relevant when examining individuals who consume higher levels of fructose.

Combination of Erlotinib and Naproxen Employing Pulsatile or Intermittent Dosing Profoundly Inhibits Urinary Bladder Cancers.

Daily dosing of either NSAIDs or EGFR inhibitors has been shown to prevent bladder cancer development in a N-butyl-(4-hydroxybutyl)nitrosamine (OH-BBN)-induced rat model. However, these inhibitors cause gastrointestinal ulceration and acneiform rash, respectively, limiting their continuous use in a clinical prevention setting. We studied chemopreventive efficacy of pulsatile dosing of EGFR inhibitor erlotinib (42 mg/kg BW, once/week) combined with intermittent or continuous low doses of the NSAID naproxen (30 mg/kg BW/day, 3 weeks on/off or 128 ppm daily in diet) in the OH-BBN induced rat bladder cancer model. The interventions were started either at 1 or 4 weeks (early intervention) or 3 months (delayed intervention) after the last OH-BBN treatment, by which time the rats had developed microscopic bladder lesions. All combination regimens tested as early versus late intervention led to the reduction of the average bladder tumor weights (54%-82%; P < 0.01 to P < 0.0001), a decrease in tumor multiplicity (65%-85%; P < 0.01 to P < 0.0001), and a decrease in the number of rats with large palpable tumors (>200 mg; 83%-90%; P < 0.01 to P < 0.0001). Levels of signal transduction markers, Ki-67, cyclin D1, IL1ß, pSTAT3, and pERK, were significantly (P < 0.05 to P < 0.001) reduced in the treated tumors, demonstrating their potential utility as predictive markers for efficacy. These findings demonstrate that significant chemopreventive efficacy could be achieved with alternative intervention regimens designed to reduce the toxicity of agents, and that starting erlotinib and/or naproxen treatments at the time microscopic tumors were present still conferred the efficacy.

Use of Biomarker Modulation in Normal Mammary Epithelium as a Correlate for Efficacy of Chemopreventive Agents Against Chemically Induced Cancers.

In both estrogen receptor/progesterone receptor-positive (ER+/PR+) human breast cancer and in ER+/PR+ cancers in the methylnitrosourea (MNU)-induced rat model, short-term modulation of proliferation in early cancers predicts preventive/therapeutic efficacy. We determined the effects of known effective/ineffective chemopreventive agents on proliferative index (PI) in both rat mammary epithelium and small cancers. Female Sprague-Dawley rats were treated with MNU at 50 days of age. Five days later, the rats were treated with the individual compounds for a period of 14 days. At that time, normal mammary tissue from the inguinal gland area was surgically removed. After removal, the rats remained on the agents for an additional 5 months. This cancer prevention study confirmed our prior results of striking efficacy with tamoxifen, vorozole, Targretin, and gefitinib, and no efficacy with metformin, naproxen, and Lipitor. Employing a separate group of rats, the effects of short-term (7 days) drug exposure on small palpable cancers were examined. The PI in both small mammary cancers and in normal epithelium from control rats was >12%. In agreement with the cancer multiplicity data, tamoxifen, vorozole, gefitinib, and Targretin all strongly inhibited proliferation (>65%; P < 0.025) in the normal mammary epithelium. The ineffective agents metformin, naproxen, and Lipitor minimally affected PI. In the small cancers, tamoxifen, vorozole, and Targretin all reduced the PI, while metformin and Lipitor failed to do so. Thus, short-term changes in the PI in either normal mammary epithelium or small cancers correlated with long-term preventive efficacy in the MNU-induced rat model.

A Randomized, Placebo-Controlled, Double-Blind, Dose Escalation, Single Dose, and Steady-State Pharmacokinetic Study of 9cUAB30 in Healthy Volunteers.

9cUAB30 is a synthetic analogue of 9-cis retinoic acid with chemoprevention activity in cell lines and animal models. The purpose of this phase I placebo-controlled, double-blinded, dose escalation study of 9cUAB30 was to evaluate its safety, pharmacokinetics, and determine a dose for future phase II studies. Participants received a single dose of study drug (placebo or 9cUAB30) on day 1 followed by a 6-day drug-free period and then 28 days of continuous daily dosing starting on day 8. Fifty-three healthy volunteers were enrolled into five dose cohorts (20, 40, 80, 160, and 240 mg). Participants were randomized within each dose level to receive either 9cUAB30 (n = 8) or placebo (n = 2). 9cUAB30 was well tolerated, with no dose limiting toxicities reported and no evidence of persistent elevations in serum triglycerides or cholesterol. Treatment-emergent grade 3 hypertension occurred in 1 of 8 participants at the 20 mg dose level and in 2 of 8 at the 240 mg dose level, all considered unlikely related to study agent; no other grade 3 adverse events were observed. The AUC increased, as expected, between day 1 (single dose) and day 36 (steady state). Pharmacokinetics were linear in dose escalation through 160 mg. 9cUAB30 administered by daily oral dosing has a favorable safety and pharmacokinetic profile. On the basis of the observed safety profile and lack of linearity in pharmacokinetics at doses greater than 160 mg, the recommended phase II dose with the current formulation is 160 mg once daily.

Pharmacometabolomic Pathway Response of Effective Anticancer Agents on Different Diets in Rats with Induced Mammary Tumors.

Metabolomics is an effective approach to characterize the metabotype which can reflect the influence of genetics, physiological status, and environmental factors such as drug intakes, diet. Diet may change the chemopreventive efficacy of given agents due to the altered physiological status of the subject. Here, metabolomics response to a chemopreventive agent targretin or tamoxifen, in rats with methylnitrosourea-induced tumors on a standard diet (4% fat, CD) or a high fat diet (21% fat, HFD) was evaluated, and found that (1) the metabolome was substantially affected by diet and/or drug treatment; (2) multiple metabolites were identified as potential pharmacodynamic biomarkers related to targretin or tamoxifen regardless of diet and time; and (3) the primary bile acid pathway was significantly affected by targretin treatment in rats on both diets, and the lysolipid pathway was significantly affected by tamoxifen treatment in rats on the high fat diet.

Evaluation of the STAT3 inhibitor GLG­302 for the prevention of estrogen receptor­positive and ­negative mammary cancers.

Signal transducer and activator of transcription 3 (STAT3) plays a key role in the transformation of normal cells to cancerous cells. Although inhibitors of STAT3 have been shown to suppress the growth of multiple cancer types in vitro and in vivo, such agents are of particular interest for the prevention of breast cancer, which affects over 200,000 women and claims more than 40,000 lives in the United States each year. In the present study, we employed the MMTV/Neu transgenic mouse model, which develops estrogen receptor (ER)­negative, Neu­overexpressing tumors, and the Sprague­Dawley (SD) rat model, which develops ER­positive tumors upon exposure to the carcinogen 7,12­dimethylbenz[a]anthracene (DMBA), to test the efficacy of the STAT3 inhibitor GLG­302 in the prevention of mammary cancer. Orally administered GLG­302 and its trizma salt derivative reduced mammary cancer incidence, multiplicity, and tumor weights in female MMTV/Neu mice, and GLG­302 reduced tumor multiplicity and weights in female DMBA­treated rats. Consistent with the mechanism of action of STAT3 inhibitors, the reductions in mammary tumors were correlated with decreases in STAT3 phosphorylation and cell proliferation. These data suggest that GLG­302 is a novel agent with potential for prevention of mammary cancer and support the further development of STAT3 inhibitors for this cause.

[Corrigendum] Daily or weekly dosing with EGFR inhibitors, gefitinib and lapatinib, and AKT inhibitor MK2206 in mammary cancer models.

The AKT inhibitor employed in this article was identified as MK 2206 (8­[4­(1­aminocyclobutyl) phenyl]­9­phenyl­1,2,4­ triazolo[3,4­f][1,6]naphthyridin­3(2H)­one hydrochloride (1:2). However, another AKT inhibitor was actually used, which is typically identified as Akt I­1,2 (HC,I. IPA (2­[4­(3­phenylquinoxalin­2­yl)phenyl]propan­2­amine hydrochloride isopropanol (1:1:1). Therefore, all references to MK 2206 in the paper should have been made to Akt I­1.2. Based on the experience of the present authors with a range of targeted inhibitors, it is expected that both inhibitors would have given rise to similar results; therefore, the results obtained in the paper are not likely to have been greatly affected as a consequence of the use of the alternative inhibitor. The authors regret that this error was not identified sooner, prior to the publication of the article, and regret any inconvenience that has been caused. [the original article was published in Oncology Reports 40: 1545­1553, 2018; DOI: 110.3892/or.2018.6313].

Comparison of Effects of Diet on Mammary Cancer: Efficacy of Various Preventive Agents and Metabolomic Changes of Different Diets and Agents.

To determine the effects of diet, rats were placed on a standard diet (4% fat) or on a modified Western (high-fat diet, HFD) diet (21% fat) at 43 days of age (DOA) and administered methylnitrosourea (MNU) at 50 DOA. Rats were administered effective (tamoxifen, vorozole, and Targretin) or ineffective (metformin and Lipitor) chemopreventive agents either by daily gavage or in the diet beginning at 57 DOA and continuing until sacrifice (190 DOA). Latency period of the tumors was determined by palpation, and multiplicity and cancer weights per rat were determined at final sacrifice. Rats on the HFD versus standard diet had: (i) a 6% increase in final body weights; (ii) significant decreases in tumor latency; and (iii) significant increases in final tumor multiplicity and average tumor weight. Tamoxifen, vorozole, and Targretin were highly effective preventive agents, whereas Lipitor and metformin were ineffective in rats on either diet. Serum was collected at 78 DOA and at sacrifice (190 DOA), and metabolomics were determined to identify the metabolite changes due to diets and effective agents. Rats given the HFD had increased levels of saturated free fatty acids (including myristate) and decreased levels of 2-aminooctanoate. Furthermore, rats on the HFD diet had increased levels of 2-aminobutyrate and decreases in glycine markers previously identified as indicators of prediabetes. Targretin increased long-chain glycophospholipids (e.g., oleyl-linoleoyl-glycerophosphocholine) and decreased primary bile acids (e.g., taurocholate). Tamoxifen increased palmitoyl-linoleoyl-glycophosphocholine and decreased stearoyl-arachidonyl glycophosphocholine. Finally, increased levels of methylated nucleotides (5-methylcytidine) and decreased levels of urea cycle metabolites (N-acetylcitrulline) were associated with the presence of mammary cancers.

Screening of Chemopreventive Agents in Animal Models: Results on Reproducibility, Agents of a Given Class, and Agents Tested During Tumor Progression.

Because of the importance of testing reproducibility of results, we present our findings regarding screening agents in preclinical chemoprevention studies in rodent models performed by the Chemopreventive Agent Development Research Group (CADRG) of the Division of Cancer Prevention of the NCI. These studies were performed via contracts to various commercial and academic laboratories. Primarily, results with positive agents are reported because positive agents may progress to the clinics. In testing reproducibility, a limited number of direct repeats of our standard screening assays were performed; which entailed initiating treatment shortly after carcinogen administration or in young transgenic mice and continuing treatment until the end of the study. However, three additional protocols were employed relating to reproducibility: (i) testing agents at lower doses to determine efficacy and reduced toxicity; (ii) testing agents later in tumor progression when microscopic lesions existed and, (iii) testing multiple agents of the same mechanistic class. Data with six models that were routinely employed are presented: MNU-induced ER-positive mammary cancer in rats; MMTV-Neu ER-negative mammary cancers in transgenic mice; AOM-induced colon tumors in rats; intestinal adenomas in Min mice; OH-BBN-induced invasive rat urinary bladder cancers in rats; and UV-induced skin squamous carcinomas in mice. It was found that strongly positive results were highly reproducible in the preclinical models evaluated. Cancer Prev Res; 11(10); 595-606. ©2018 AACR.

A novel retinoid X receptor agonist, UAB30, inhibits rhabdomyosarcoma cells in vitro.

BACKGROUND: While patients with early-stage rhabdomyosarcoma (RMS) have seen steady improvement in prognosis over the last 50 y, those with advanced-stage or high-grade disease continue to have a dismal prognosis. Retinoids have been shown to cause growth suppression and terminal differentiation in RMS cells, but the toxicities associated with retinoic acid limit its use. Rexinoids provide an alternative treatment approach to retinoic acid. Rexinoids primarily bind the retinoid X receptor with minimal retinoic acid receptor binding, the entity responsible for many of the toxicities of retinoid therapies. UAB30 is a novel rexinoid with limited toxicities. We hypothesized that UAB30 would lead to decreased cell survival in RMS. MATERIALS AND METHODS: Two RMS cell lines, one embryonal (RD) subtype and one alveolar (St. Jude Cancer Research Hospital 30) subtype, were used. Cells were treated with UAB30, and cytotoxicity, proliferation, mobility, and apoptosis were evaluated. RESULTS: UAB30 significantly decreased RMS tumor cell viability and proliferation. Invasion, migration, and attachment-independent growth were reduced following UAB30 treatment. UAB30 also resulted in apoptosis and G1 cell cycle arrest. UAB30 affected both the alveolar and embryonal RMS cell lines in a similar fashion. CONCLUSIONS: The results of these studies suggest a potential therapeutic role for the low-toxicity synthetic retinoid X receptor selective agonist, UAB30, in RMS treatment.

Daily or weekly dosing with EGFR inhibitors, gefitinib and lapatinib, and AKt inhibitor MK2206 in mammary cancer models.

Daily vs. weekly dosing with EGFR inhibitors (gefitinib and lapatinib) and an AKT inhibitor (MK2206) were compared in two rodent breast cancer models. Female Sprague-Dawley rats were administered methylnitrosourea (MNU) at 50 days of age, and gefitinib (daily/weekly dosing at 10/70 mg/kg BW) or lapatinib (daily/weekly dosing at 75/525 mg/kg BW) were administered by gavage beginning 5 days after MNU. For the prevention studies, weekly or daily dosing with gefitinib or lapatinib reduced cancer multiplicity >75%, and all treatments reduced tumor weights by >90%. For the therapeutic studies, MNU-treated rats were followed until small palpable mammary cancers developed. The rats were then treated daily or weekly as above for 6 weeks. Either daily or weekly dosing with lapatinib or gefitinib caused regression in >50% of the tumors. Immunohistochemistry biomarker studies in palpable mammary cancers following a weekly dose of gefitinib showed that 1 day (but not 7 days) after treatment, the levels of phosphorylated EGFR1 were significantly decreased. In an ER-negative (ER-) Neu-overexpressing model employing MMTV-Neu/P53KO mice, daily (100 mg/kg BW/day, 5 days each week), or weekly dosing (500 or 250 mg/kg BW) with gefitinib reduced tumor multiplicity 65, 85 and 75%, respectively. In the MNU prevention model, daily dosing (100 mg/kg BW/day) with the allosteric AKT inhibitor MK2206 was ineffective, while weekly dosing (700 mg/kg BW) reduced the final tumor weight >70%. Combining weekly MK2206 with the aromatase inhibitor vorozole (0.12 mg/kg BW/day) showed that each compound alone reduced tumor multiplicity 40-50%. The combination reduced cancer multiplicity ~70%. These studies demonstrate the efficacy of weekly dosing with various protein kinase inhibitors; raising the possibility of employing these agents in a breast cancer preventive setting.

The retinoid X receptor agonist, 9-cis UAB30, inhibits cutaneous T-cell lymphoma proliferation through the SKP2-p27kip1 axis.

BACKGROUND: Bexarotene (Targretin®) is currently the only FDA approved retinoid X receptor (RXR) -selective agonist for the treatment of cutaneous T-cell lymphomas (CTCLs). The main side effects of bexarotene are hypothyroidism and elevation of serum triglycerides (TGs). The novel RXR ligand, 9-cis UAB30 (UAB30) does not elevate serum TGs or induce hypothyroidism in normal subjects. OBJECTIVES: To assess preclinical efficacy and mechanism of action of UAB30 in the treatment of CTCLs and compare its action with bexarotene. METHODS: With patient-derived CTCL cell lines, we evaluated UAB30 function in regulating growth, apoptosis, cell cycle check points, and cell cycle-related markers. RESULTS: Compared to bexarotene, UAB30 had lower half maximal inhibitory concentration (IC50) values and was more effective in inhibiting the G1 cell cycle checkpoint. Both rexinoids increased the stability of the cell cycle inhibitor, p27kip1 protein, in part, through targeting components involved in the ubiquitination-proteasome system: 1) decreasing SKP2, a F-box protein that binds and targets p27kip1 for degradation by 26S proteasome and 2) suppressing 20S proteasome activity (cell line-dependent) through downregulation of PSMA7, a component of the 20S proteolytic complex in 26S proteasome. CONCLUSIONS: UAB30 and bexarotene induce both early cell apoptosis and suppress cell proliferation. Inhibition of the G1 to S cell cycle transition by rexinoids is mediated, in part, through downregulation of SKP2 and/or 20S proteasome activity, leading to increased p27kip1 protein stability. Because UAB30 has minimal effect in elevating serum TGs and inducing hypothyroidism, it is potentially a better alternative to bexarotene for the treatment of CTCLs.

Lack of chemopreventive efficacy of metformin in rodent models of urinary bladder, head and neck, and colon/intestine cancer.

Metformin is a biguanide employed in treating type II diabetes. Its potential efficacy for treating cancer has been demonstrated epidemiologically (lower cancer incidence in metformin users compared with users of sulfonylureas or insulin) and mechanistically, primarily in cell culture. Metformin decreases the levels of insulin-like growth factor 1 and secondarily inhibits the mammalian target of rapamycin pathway to exhibit anticancer effects. The current study examined its cancer preventive efficacy in multiple standard in situ arising cancer models. Metformin was administered orally by gavage or in the diet, at human equivalent doses, in numerous cancer models. In the hydroxybutyl(butyl)nitrosamine-induced model of invasive urinary bladder cancer, metformin (50 or 150 mg/kg body weight/day, intragastric) was ineffective despite high urinary concentrations of metformin. Metformin (250 or 500 ppm in diet) failed to decrease the incidence or invasiveness of squamous cell cancer of the tongue in a 4-nitroquinoline-1-(4NQO)-induced model. Finally, in the Min mouse model of gastrointestinal cancer, metformin (400 or 1,200 ppm in diet) was ineffective. Notably, a slight increase in intestinal tumor multiplicity was observed at the higher dose. Therefore, metformin lacked efficacy in multiple standard cancer models in non-diabetic rodents. This lack of efficacy may discourage any large phase clinical cancer trials in non-diabetic individuals in the absence of clear phase-II studies.

Translation of a Tissue-Selective Rexinoid, UAB30, to the Clinic for Breast Cancer Prevention.

This review focuses on our efforts to translate a low-toxicity retinoid X receptor-selective agonist, UAB30, to the clinic for the prevention of breast cancers. The review is divided into several sections. First, the current status of breast cancer prevention is discussed. Next, preclinical studies are presented that support translation of rexinoids to the clinic for cancer prevention. While current FDAapproved retinoids and rexinoids demonstrate profound effects in treating cancers, they lack sufficient safety for long term use in the high risk population that is otherwise disease free. The review stresses the need to identify cancer preventive drugs that are effective and safe in order to gain wide use in the clinic. Due to the heterogeneity of the disease, UAB30 is evaluated for the prevention of ER-positive and ER-negative mammary cancers. Since selective estrogen receptor modulators and aromatase inhibitors are used clinically to prevent and treat ER-positive breast cancers, preclinical studies also must demonstrate efficacy of UAB30 in combination with existing drugs under use in the clinic. To support an Investigational New Drug Application to the FDA, data on pharmacology and toxicity as well as mutagenicity is gathered prior to human trials. The review concludes with a discussion of the outcomes of human Phase 0/1 clinical trials that determine the safety and pharmacology of UAB30. These studies are essential before this agent is evaluated for efficacy in phase 2 trials. Success in phase 2 evaluation is critical before long-term and costly phase 3 trials are undertaken. The lack of surrogate biomarkers as endpoints for phase 2 evaluation of rexinoid preventive agents is discussed.

5MeCDDO Blocks Metabolic Activation but not Progression of Breast, Intestine, and Tongue Cancers. Is Antioxidant Response Element a Prevention Target?

The preventive efficacy of the triterpenoid 5MeCDDO was tested in two models of mammary cancer, the Min model of intestinal cancer, and a chemically induced model of head and neck cancer. In one model of mammary cancer, female Sprague-Dawley rats were administered MNU at 50 days of age, and 5MeCDDO (27 ppm) was administered in the diet beginning 5 days later for the duration of the study; 5MeCDDO was ineffective. In contrast, in a model examining initiation of mammary cancers by the procarcinogen dimethyl-benzanthracene, 5, 6-benzoflavone (500 ppm, an Ah receptor agonist) or 5MeCDDO (27 or 2.7 ppm) decreased tumor multiplicity by 90%, 80%, and 50%, respectively. This anti-initiating effect which is presumably mediated by altered metabolic activation parallels our observation that 5MeCDDO induced proteins of various antioxidant response element (ARE)-related phase II drug-metabolizing enzymes [e.g., GST Pi, AKR 7A3 (aflatoxicol), epoxide hydrolase, and quinone reductase] in the liver. 5MeCDDO tested in the 4-nitroquinoline-l-oxide (4-NQO) head and neck cancer model failed to decrease tumor incidence or invasiveness. In the Min mouse model of intestinal cancer, a high dose of 5MeCDDO (80 ppm) was weakly effective in reducing adenoma multiplicity [∼30% (P < 0.05)]; however, a lower dose was totally ineffective. These findings question whether measuring increased levels of certain ARE-related genes (e.g., quinone reductase, GST Pi), indicating decreased carcinogen activation are sufficient to imply general chemopreventive efficacy of a given agent or mixture. Cancer Prev Res; 9(7); 616-23. ©2016 AACR.

Preclinical Evaluation of UAB30 in Pediatric Renal and Hepatic Malignancies.

Rare tumors of solid organs remain some of the most difficult pediatric cancers to cure. These difficult tumors include rare pediatric renal malignancies, such as malignant rhabdoid kidney tumors (MRKT) and non-osseous renal Ewing sarcoma, and hepatoblastoma, a pediatric liver tumor that arises from immature liver cells. There are data in adult renal and hepatic malignancies demonstrating the efficacy of retinoid therapy. The investigation of retinoic acid therapy in cancer is not a new strategy, but the widespread adoption of this therapy has been hindered by toxicities. Our laboratory has been investigating a novel synthetic rexinoid, UAB30, which exhibits a more favorable side-effect profile. In this study, we hypothesized that UAB30 would diminish the growth of tumor cells from both rare renal and liver tumors in vitro and in vivo We successfully demonstrated decreased cellular proliferation, invasion and migration, cell-cycle arrest, and increased apoptosis after treatment with UAB30. Additionally, in in vivo murine models of human hepatoblastoma or rare human renal tumors, there were significantly decreased tumor xenograft growth and increased animal survival after UAB30 treatment. UAB30 should be further investigated as a developing therapeutic in these rare and difficult-to-treat pediatric solid organ tumors. Mol Cancer Ther; 15(5); 911-21. ©2016 AACR.

Conformationally Defined Rexinoids and Their Efficacy in the Prevention of Mammary Cancers.

(2E,4E,6Z,8Z)-8-(3',4'-Dihydro-1'(2H)-naphthalen-1'-ylidene)-3,7-dimethyl-2,3,6-octatrienoinic acid (UAB30) is currently undergoing clinical evaluation as a novel cancer prevention agent. In efforts to develop even more highly potent rexinoids that prevent breast cancer without toxicity, we further explore here the structure-activity relationship of two separate classes of rexinoids. UAB30 belongs to the class II rexinoids and possesses a 9Z-tetraenoic acid chain bonded to a tetralone ring, whereas the class I rexinoids contain the same 9Z-tetraenoic acid chain bonded to a disubstituted cyclohexenyl ring. Among the 12 class I and class II rexinoids evaluated, the class I rexinoid 11 is most effective in preventing breast cancers in an in vivo rat model alone or in combination with tamoxifen. Rexinoid 11 also reduces the size of established tumors and exhibits a therapeutic effect. However, 11 induces hypertriglyceridemia at its effective dose. On the other hand rexinoid 10 does not increase triglyceride levels while being effective in the in vivo chemoprevention assay. X-ray studies of four rexinoids bound to the ligand binding domain of the retinoid X receptor reveal key structural aspects that enhance potency as well as those that enhance the synthesis of lipids.

Preclinical Evaluation of a Novel RXR Agonist for the Treatment of Neuroblastoma.

Neuroblastoma remains a common cause of pediatric cancer deaths, especially for children who present with advanced stage or recurrent disease. Currently, retinoic acid therapy is used as maintenance treatment to induce differentiation and reduce tumor recurrence following induction therapy for neuroblastoma, but unavoidable side effects are seen. A novel retinoid, UAB30, has been shown to generate negligible toxicities. In the current study, we hypothesized that UAB30 would have a significant impact on multiple neuroblastoma cell lines in vitro and in vivo. Cellular survival, cell-cycle analysis, migration, and invasion were studied using AlamarBlue assays, FACS, and Transwell assays, respectively, in multiple cell lines following treatment with UAB30. In addition, an in vivo murine model of human neuroblastoma was utilized to study the effects of UAB30 upon tumor xenograft growth and animal survival. We successfully demonstrated decreased cellular survival, invasion, and migration, cell-cycle arrest, and increased apoptosis after treatment with UAB30. Furthermore, inhibition of tumor growth and increased survival was observed in a murine neuroblastoma xenograft model. The results of these in vitro and in vivo studies suggest a potential therapeutic role for the low toxicity synthetic retinoid X receptor selective agonist, UAB30, in neuroblastoma treatment.