Clinical Use of PPARgamma Ligands in Cancer

PPARγ activation modulates the balance of peritoneal macrophage populations to suppress ovarian tumor growth and tumor-induced immunosuppression

BACKGROUND

Ovarian adenocarcinoma (OVAD) frequently metastasizes to the peritoneal cavity and manifests by the formation of ascites, which constitutes a tumor-promoting microenvironment. In the peritoneal cavity, two developmentally, phenotypically and functionally distinct macrophage subsets, immunocompetent large peritoneal macrophages (LPM) and immunosuppressive small peritoneal macrophages (SPM), coexist. Because peroxisome proliferator-activated receptor γ (PPARγ) is a critical factor participating in macrophage differentiation and cooperates with CCAAT/enhancer binding protein β (C/EBPβ), a transcription factor essential for SPM-to-LPM differentiation, PPARγ could be also involved in the regulation of SPM/LPM balance and could be a promising therapeutic target.

METHODS

To evaluate the 15(S)-hydroxyeicosatetraenoic acid (HETE), a PPARγ endogenous ligand, impact on ovarian tumor growth, we intraperitoneally injected 15(S)-HETE into a murine ovarian cancer model. This experimental model consists in the intraperitoneally injection of ID8 cells expressing luciferase into syngeneic C57BL/6 female mice. This ID8 orthotopic mouse model is a well-established experimental model of end-stage epithelial OVAD. Tumor progression was monitored using an in vivo imaging system. Peritoneal immune cells in ascites were analyzed by flow cytometry and cell sorting. To determine whether the impact of 15(S)-HETE in tumor development is mediated through the macrophages, these cells were depleted by injection of liposomal clodronate. To further dissect how 15(S)-HETE mediated its antitumor effect, we assessed the tumor burden in tumor-bearing mice in which the PPARγ gene was selectively disrupted in myeloid-derived cells and in mice deficient of the recombination-activating gene Rag2. Finally, to validate our data in humans, we isolated and treated macrophages from ascites of individuals with OVAD.

RESULTS

Here we show, in the murine experimental model of OVAD, that 15(S)-HETE treatment significantly suppresses the tumor growth, which is associated with the differentiation of SPM into LPM and the LPM residency in the peritoneal cavity. We demonstrate that C/EBPβ and GATA6 play a central role in SPM-to-LPM differentiation and in LPM peritoneal residence through PPARγ activation during OVAD. Moreover, this SPM-to-LPM switch is associated with the increase of the effector/regulatory T-cell ratio. Finally, we report that 15(S)-HETE attenuates immunosuppressive properties of human ovarian tumor-associated macrophages from ascites.

CONCLUSION

Altogether, these results promote PPARγ as a potential therapeutic target to restrain OVAD development and strengthen the use of PPARγ agonists in anticancer therapy.

Engaging plasticity: Differentiation therapy in solid tumors

Cancer is a systemic heterogeneous disease that can undergo several rounds of latency and activation. Tumor progression evolves by increasing diversity, adaptation to signals from the microenvironment and escape mechanisms from therapy. These dynamic processes indicate necessity for cell plasticity. Epithelial-mesenchymal transition (EMT) plays a major role in facilitating cell plasticity in solid tumors by inducing dedifferentiation and cell type transitions. These two practices, plasticity and dedifferentiation enhance tumor heterogeneity creating a key challenge in cancer treatment. In this review we will explore cancer cell plasticity and elaborate treatment modalities that aspire to overcome such dynamic processes in solid tumors. We will further discuss the therapeutic potential of utilizing enhanced cell plasticity for differentiation therapy.

Differential Effects of Cancer-Associated Mutations Enriched in Helix H3 of PPARγ

Peroxisome proliferator-activated receptor gamma (PPARγ) has recently been revealed to regulate tumor microenvironments. In particular, genetic alterations of PPARγ found in various cancers have been reported to play important roles in tumorigenesis by affecting PPARγ transactivation. In this study, we found that helix H3 of the PPARγ ligand-binding domain (LBD) has a number of sites that are mutated in cancers. To uncover underlying molecular mechanisms between helix H3 mutations and tumorigenesis, we performed structure‒function studies on the PPARγ LBDs containing helix H3 mutations found in cancers. Interestingly, PPARγ Q286E found in bladder cancer induces a constitutively active conformation of PPARγ LBD and thus abnormal activation of PPARγ/RXRα pathway, which suggests tumorigenic roles of PPARγ in bladder cancer. In contrast, other helix H3 mutations found in various cancers impair ligand binding essential for transcriptional activity of PPARγ. These data indicate that cancer-associated mutations clustered in helix H3 of PPARγ LBD exhibit differential effects in PPARγ-mediated tumorigenesis and provide a basis for the development of new biomarkers targeting tumor microenvironments.

Association between pioglitazone use and head and neck cancer: Population-based case-control study

BACKGROUND

This study aimed to evaluate the association between pioglitazone use and the occurrence of head and neck cancer.

METHODS

Data for this case-control study were retrieved from the Taiwan National Health Insurance Research Database. A total of 21 464 diabetic patients newly diagnosed with head and neck cancers were identified. We used propensity score matching to select 64 392 comparison patients (3:1 ratio). Multiple logistic regression modeling was used to examine the association of head and neck cancer with pioglitazone use in the 5 years preceding the cancer diagnosis.

RESULTS

Bivariate analysis showed a significant difference in the prevalence of prior using pioglitazone between cases and controls (19.3% vs 18.5%, P < .001) was observed. Multiple regression analysis showed adjusted odds of pioglitazone use of 1.06 (95% CI: 1.02-1.10) among cases relative to controls.

CONCLUSIONS

Prior pioglitazone use was associated with oral cavity cancer.

Challenges in the management of people with diabetes and cancer

Although micro- and macrovascular complications of diabetes are the most important cause of mortality and morbidity in people with diabetes, it is increasingly recognized that diabetes increases the risk of developing cancer. Diabetes and cancer commonly co-exist, and outcomes in people with both conditions are poorer than in those who have cancer but no diabetes. There is no randomized trial evidence that treating hyperglycaemia in people with cancer improves outcomes, but therapeutic nihilism should be avoided, and a personalized approach to managing hyperglycaemia in people with cancer is needed. This review aims to outline the link between diabetes therapies and cancer, and discuss the reasons why glucose should be actively managed people with both. In addition, we discuss clinical challenges in the management of hyperglycaemia in cancer, specifically in relation to glucocorticoids, enteral feeding and end-of-life care.

The PPARγ Agonist Rosiglitazone Suppresses Syngeneic Mouse SCC (Squamous Cell Carcinoma) Tumor Growth through an Immune-Mediated Mechanism

Recent evidence suggests that PPARγ agonists may promote anti-tumor immunity. We show that immunogenic PDV cutaneous squamous cell carcinoma (CSCC) tumors are rejected when injected intradermally at a low cell number (1 × 106) into immune competent syngeneic hosts, but not immune deficient mice. At higher cell numbers (5 × 106 PDV cells), progressively growing tumors were established in 14 of 15 vehicle treated mice while treatment of mice with the PPARγ agonist rosiglitazone resulted in increased tumor rejection (5 of 14 tumors), a significant decrease in PDV tumor size, and a significant decrease in tumor cell Ki67 labeling. Rosiglitazone treatment had no effect on tumor rejection, tumor volume or PDV tumor cell proliferation in immune deficient NOD.CB17-PrkdcSCID/J mice. Rosiglitazone treatment also promoted an increase in tumor infiltrating CD3+ T-cells at both early and late time points. In contrast, rosiglitazone treatment had no significant effect on myeloid cells expressing either CD11b or Gr-1 but suppressed a late accumulation of myeloid cells expressing both CD11b and Gr-1, suggesting a potential role for CD11b+Gr-1+ myeloid cells in the late anti-tumor immune response. Overall, our data provides evidence that the PPARγ agonist rosiglitazone promotes immune-mediated anti-neoplastic activity against tumors derived from this immunogenic CSCC cell line.

PPARγ Contributes to Immunity Induced by Cancer Cell Vaccines That Secrete GM-CSF

Peroxisome proliferator activated receptor-γ (PPARγ) is a lipid-activated nuclear receptor that promotes immune tolerance through effects on macrophages, dendritic cells (DCs), and regulatory T cells (Tregs). Granulocyte-macrophage colony stimulating factor (GM-CSF) induces PPARγ expression in multiple myeloid cell types. GM-CSF contributes to both immune tolerance and protection, but the role of PPARγ in these pathways is poorly understood. Here, we reveal an unexpected stimulatory role for PPARγ in the generation of antitumor immunity with irradiated, GM-CSF-secreting tumor-cell vaccines (GVAX). Mice harboring a deletion of pparg in lysozyme M (LysM)-expressing myeloid cells (KO) showed a decreased ratio of CD8⁺ T effectors to Tregs and impaired tumor rejection with GVAX. Diminished tumor protection was associated with altered DC responses and increased production of the Treg attracting chemokines CCL17 and CLL22. Correspondingly, the systemic administration of PPARγ agonists to vaccinated mice elevated the CD8⁺ T effector to Treg ratio through effects on myeloid cells and intensified the antitumor activity of GVAX combined with cytotoxic T lymphocyte-associated antigen-4 antibody blockade. PPARγ agonists similarly attenuated Treg induction and decreased CCL17 and CCL22 levels in cultures of human peripheral blood mononuclear cells with GM-CSF-secreting tumor cells. Together, these results highlight a key role for myeloid cell PPARγ in GM-CSF-stimulated antitumor immunity and suggest that PPARγ agonists might be useful in cancer immunotherapy. Cancer Immunol Res; 6(6); 723-32. ©2018 AACR.

Rosiglitazone reduces breast cancer risk in Taiwanese female patients with type 2 diabetes mellitus

This study investigated whether rosiglitazone may affect breast cancer risk in female patients with type 2 diabetes mellitus in Taiwan. The reimbursement database of all female patients with type 2 diabetes mellitus under oral antidiabetic agents or insulin from 1996 to 2009 was retrieved from the National Health Insurance. An entry date was set on 1 January 2006 and a total of 431447 patients were followed up for breast cancer incidence till the end of 2009. Incidences for ever users, never users and subgroups of rosiglitazone dose-response parameters (tertile cutoffs of cumulative duration and cumulative dose) were calculated and hazard ratios estimated by Cox regression. There were 53029 ever users and 378418 never users, respective numbers of incident breast cancer 410 (0.77%) and 3292 (0.87%), and respective incidence 217.53 and 249.12 per 100000 person-years. The overall hazard ratio was 0.889 (95% confidence interval: 0.797−0.992) in the fully adjusted model. Significantly lower risk was observed for the third tertiles of cumulative duration (> 14 months) and cumulative dose (> 1792 mg) while compared to never users, with respective adjusted hazard ratio of 0.815 (95% confidence interval: 0.682−0.973) and 0.815 (95% confidence interval: 0.682−0.974). Additionally, a significant interaction between metformin and rosiglitazone was observed. The lowest risk was seen in patients who used both drugs (hazard ratio 0.812, 95% confidence interval: 0.705−0.934). In conclusion, rosiglitazone reduces breast cancer risk in female patients with type 2 diabetes mellitus, which shows a significant interaction with metformin.

Epidermal PPARγ influences subcutaneous tumor growth and acts through TNF-α to regulate contact hypersensitivity and the acute photoresponse

It is known that ultraviolet B (UVB) induces PPARγ ligand formation while loss of murine epidermal PPARγ (Pparg-/-^epi) promotes UVB-induced apoptosis, inflammation, and carcinogenesis. PPARγ is known to suppress tumor necrosis factor-α (TNF-α) production. TNF-α is also known to promote UVB-induced inflammation, apoptosis, and immunosuppression. We show that Pparg-/-^epi mice exhibit increased baseline TNF-α expression. Neutralizing Abs to TNF-α block the increased photo-inflammation and photo-toxicity that is observed in Pparg-/-^epi mouse skin. Interestingly, the increase in UVB-induced apoptosis in Pparg-/-^epi mice is not accompanied by a change in cyclobutane pyrimidine dimer clearance or in mutation burden. This suggests that loss of epidermal PPARγ does not result in a significant alteration in DNA repair capacity. However, loss of epidermal PPARγ results in marked immunosuppression using a contact hypersensitivity (CHS) model. This impaired CHS response was significantly alleviated using neutralizing TNF-α antibodies or loss of germline Tnf. In addition, the PPARγ agonist rosiglitazone reversed UVB-induced systemic immunosuppression (UV-IS) as well as UV-induced growth of B16F10 melanoma tumor cells in syngeneic mice. Finally, increased B16F10 tumor growth was observed when injected subcutaneously into Pparg-/-^epi mice. Thus, we provide novel evidence that epidermal PPARγ is important for cutaneous immune function and the acute photoresponse.

Effects of Ranolazine on Astrocytes and Neurons in Primary Culture

Ranolazine (Rn) is an antianginal agent used for the treatment of chronic angina pectoris when angina is not adequately controlled by other drugs. Rn also acts in the central nervous system and it has been proposed for the treatment of pain and epileptic disorders. Under the hypothesis that ranolazine could act as a neuroprotective drug, we studied its effects on astrocytes and neurons in primary culture. We incubated rat astrocytes and neurons in primary cultures for 24 hours with Rn (10-7, 10-6 and 10-5 M). Cell viability and proliferation were measured using trypan blue exclusion assay, MTT conversion assay and LDH release assay. Apoptosis was determined by Caspase 3 activity assay. The effects of Rn on pro-inflammatory mediators IL-β and TNF-α was determined by ELISA technique, and protein expression levels of Smac/Diablo, PPAR-γ, Mn-SOD and Cu/Zn-SOD by western blot technique. In cultured astrocytes, Rn significantly increased cell viability and proliferation at any concentration tested, and decreased LDH leakage, Smac/Diablo expression and Caspase 3 activity indicating less cell death. Rn also increased anti-inflammatory PPAR-γ protein expression and reduced pro-inflammatory proteins IL-1 β and TNFα levels. Furthermore, antioxidant proteins Cu/Zn-SOD and Mn-SOD significantly increased after Rn addition in cultured astrocytes. Conversely, Rn did not exert any effect on cultured neurons. In conclusion, Rn could act as a neuroprotective drug in the central nervous system by promoting astrocyte viability, preventing necrosis and apoptosis, inhibiting inflammatory phenomena and inducing anti-inflammatory and antioxidant agents.

Cancer and bone fractures in observational follow-up of the RECORD study

AIMS

The RECORD study evaluated the effects of rosiglitazone on cardiovascular outcomes. A 4-year observational follow-up was added to the study to monitor the occurrence of cancer and bone fractures. We present the cancer and bone fracture data aggregated across the main study and its observational follow-up.

METHODS

RECORD was a multicentre, open-label trial in people with type 2 diabetes on metformin or sulfonylurea monotherapy randomly assigned to addition of rosiglitazone (n = 2,220) or to a combination of metformin and sulfonylurea (n = 2,227). At the end of the main study, patients stopped study drug and were invited to enter the observational follow-up during which glucose-lowering treatment was selected by the patient's physician. Serious adverse events of cancer and serious and non-serious events of bone fracture were recorded. The study is registered with ClinicalTrials.gov, number NCT00379769.

RESULTS

Of the 4,447 patients comprising the intent-to-treat population, 2,546 entered the observational follow-up (1,288 rosiglitazone, 1,258 metformin/sulfonylurea) and added 9,336 patient-years experience to the main RECORD study, making an aggregate of 33,744 patient-years. Based on the totality of follow-up, malignancies were reported in 179 of 2,220 patients (8.1 %) in the group originally randomised to rosiglitazone and in 195 of 2,227 patients (8.8 %) in the group allocated metformin/sulfonylurea [relative risk, RR, 0.92 (95 % CI 0.76-1.12)]. More patients reported bone fractures in the rosiglitazone group (238, 10.7 %) than in the metformin/sulfonylurea control [151, 6.8 %; RR 1.58 (1.30-1.92)]. For women, the corresponding figures were rosiglitazone 156 (14.5 %), metformin/sulfonylurea 91 (8.5 %), RR 1.71 (1.34-2.18), and for men, the corresponding figures were rosiglitazone 82 (7.2 %), metformin/sulfonylurea 60 (5.2 %), RR 1.37 (0.99-1.90). Potentially high-morbidity fractures (hip, pelvis, femur, and spine) occurred in the same number of patients (31, 1.4 %) in the two treatment groups.

CONCLUSIONS

We conclude that data from a 4-year observational follow-up, combined with the main RECORD study data, do not suggest an increased risk of cancer in patients randomised to rosiglitazone combination use compared with those randomised to metformin/sulfonylurea. Consistent with the main study, rosiglitazone is associated with an increased risk of peripheral bone fracture in women, and probably in men, but the combined data do not suggest an increase in potentially high-morbidity (hip, pelvis, femur, and spine) fractures.

Involvement of insulin-like growth factor binding protein-3 in peroxisome proliferator-activated receptor gamma-mediated inhibition of breast cancer cell growth

We have previously reported that insulin-like growth factor binding protein-3 (IGFBP-3), a protein with dichotomous effects on both cell proliferation and cell survival, interacts with peroxisome proliferator-activated receptor gamma (PPARγ) and inhibits adipogenic PPARγ signaling. We now show that IGFBP-3 and PPARγ interact in breast cancer cells, through amino- and carboxyl-terminal residues of IGFBP-3. IGFBP-3 and the PPARγ ligands, rosiglitazone or 15-deoxy-Δ(12,14)-prostaglandin J2, separately inhibited the proliferation of MCF-7, MDA-MB-231 and MDA-MB-468 breast cancer cells. However, growth inhibition by IGFBP-3 and PPARγ ligand combined was greater than by either alone. Two IGFBP-3 mutants with reduced PPARγ binding caused no growth inhibition when used alone and abolished the inhibitory effect of rosiglitazone when used in combination with PPARγ ligand. Cell growth inhibition by PPARγ ligands was substantially blocked by IGFBP-3 siRNA and restored by exogenous IGFBP-3. We conclude that the interaction between IGFBP-3 and PPARγ is important for the growth-inhibitory effect of PPARγ ligands in human breast cancer cells, suggesting that IGFBP-3 expression by breast tumors may regulate their sensitivity toward PPARγ ligands.

Inverse association of colorectal cancer prevalence to serum levels of perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) in a large Appalachian population

Background

Perfluorooctanoate (PFOA) and perfluorooctane sulfonate (PFOS) are persistent environmental contaminants that affect metabolic regulation, inflammation, and other factors implicated in the development and progression of colorectal cancer (CRC). However, the link between these compounds and CRC remains unknown. In this cross-sectional study, we investigated the association of CRC diagnosis to PFOA and PFOS blood levels in a large Appalachian population.

Methods

Participants were 47,359 adults ≥ 21 years of age and residing in six PFOA-contaminated water districts in the mid-Ohio Valley (N = 47,151 cancer-free adults, 208 cases of primary CRC). All participants completed a comprehensive health survey between 2005 and 2006; serum levels of PFOA, PFOS, and a range of other blood markers were also measured. Medical history was assessed via self report and cancer diagnosis confirmed via chart review.

Results

CRC showed a strong inverse, dose–response association with PFOS serum levels (odds ratio (OR) adjusted for potential confounders = 0.2, 95% confidence interval (CI) 0.2,0.3) for highest vs. lowest quartile of PFOS, P-trend < 0.00001) and a significant, but more modest inverse association with PFOA (adjusted OR = 0.6 (CI 0.4, 0.9) for highest vs. lowest quartile, P-trend = 0.001). These inverse associations were stronger in those diagnosed within the previous 6 years and resident in the same water district for a minimum of 10–15 years preceding assessment. The relationship between PFOA and CRC was also more pronounced in men and leaner adults, and showed a stronger linear trend at lower exposure levels.

Conclusions

In this large cross-sectional study, we found a strong, inverse association between PFOS and likelihood of CRC diagnosis and a significant, although more modest inverse association between PFOA and CRC. If confirmed in prospective investigations, these findings may aid in identifying new strategies for CRC prevention and treatment and inform future studies regarding mechanisms underlying CRC pathogenesis.

Pioglitazone and oral cancer risk in patients with type 2 diabetes

BACKGROUND

Pioglitazone has shown an inhibitory effect on the growth of cell lines derived from human salivary gland and human oral squamous cell carcinoma. However, whether this effect can be applied to patients with type 2 diabetes mellitus who use pioglitazone for glycemic control remains unanswered.

METHODS

The reimbursement records of all Taiwanese diabetic patients under treatment with oral anti-diabetic agents or insulin from 1996 to 2009 were retrieved from the National Health Insurance database. The entry date was set at 1 January 2006 and a total of 1,093,391 patients with type 2 diabetes were followed up for oral cancer incidence till the end of 2009. Incidences for ever-users, never-users and subgroups of pioglitazone dose-responsive exposure (using the parameters of time since starting pioglitazone, duration of therapy and cumulative dose) were calculated and hazard ratios estimated by Cox regression.

RESULTS

There were 58,238 ever-users and 1,035,153 never-users, with respective numbers of incident oral cancer of 201 (0.35%) and 4168 (0.40%), and respective incidences of 94.26 and 114.24 per 100,000 person-years. The overall hazard ratios (95% confidence intervals) did show a significantly lower risk in unadjusted [0.832 (0.722-0.958)] and age-sex-adjusted [0.866 (0.752-0.998)] models. However, the multivariable-adjusted hazard ratio (95% confidence interval) was not significant: 0.992 (0.857-1.148). Although significant P-trends for the dose-response parameters could be observed in some of the unadjusted and age-sex-adjusted models, none was significant in the multivariable-adjusted models.

CONCLUSIONS

Pioglitazone has a null association with oral cancer after adjustment for potential confounders.

PPARγ agonists target aromatase via both PGE2 and BRCA1

Obesity is a well-recognized risk factor for postmenopausal breast cancer. Although the underlying mechanisms are not clearly defined, aromatase is thought to play a pivotal role in connecting obesity-associated inflammation with postmenopausal breast cancer. It has been well established that both the proinflammatory prostaglandin E(2) (PGE(2)) and the BRCA1 tumor-suppressor gene regulate aromatase expression. In this issue of the journal (beginning on p. 1183), Subbaramaiah and colleagues improve our understanding of the molecular mechanisms by which PPARγ inhibits aromatase expression. They found that pioglitazone, a PPARγ agonist, inhibited aromatase expression by inhibition of PGE(2) signaling and upregulation of BRCA1. Their findings provide potential targets for preventing or treating obesity-related breast cancer.

Targeting PPARγ Signaling Cascade for the Prevention and Treatment of Prostate Cancer

The peroxisome proliferator-activated receptor-gamma (PPARγ) is a member of the hormone-activated nuclear receptor superfamily. PPARγ can be activated by a diverse group of agents, such as endogenous polyunsaturated fatty acids, 15-deoxy-Δ^12,14-prostaglandin J₂ (15d-PGJ₂), and thiazolidinedione (TZD) drugs. PPARγ induces antiproliferative, antiangiogenic, and prodifferentiation pathways in several tissue types, thus making it a highly useful target for downregulation of carcinogenesis. These TZD-derived novel therapeutic agents, alone or in combination with other anticancer drugs, have translational relevance in fostering effective strategies for cancer treatment. TZDs have been proven for antitumor activity in a wide variety of experimental cancer models, both in vitro and in vivo, by affecting the cell cycle, inducing cell differentiation and apoptosis, as well as by inhibiting tumor angiogenesis. Angiogenesis inhibition mechanisms of TZDs include direct inhibition of endothelial cell proliferation and migration, as well as reduction in tumor cell vascular endothelial growth factor production. In prostate cancer, PPARγ ligands such as troglitazone and 15d-PGJ₂ have also shown to inhibit tumor growth. This paper will focus on current discoveries in PPARγ activation, targeting prostate carcinogenesis as well as the role of PPARγ as a possible anticancer therapeutic option. Here, we review PPARγ as an antitumor agent and summarize the antineoplastic effects of PPARγ agonists in prostate cancer.

PPARs: Interference with Warburg' Effect and Clinical Anticancer Trials

The metabolic/cell signaling basis of Warburg's effect ("aerobic glycolysis") and the general metabolic phenotype adopted by cancer cells are first reviewed. Several bypasses are adopted to provide a panoramic integrated view of tumoral metabolism, by attributing a central signaling role to hypoxia-induced factor (HIF-1) in the expression of aerobic glycolysis. The cancer metabolic phenotype also results from alterations of other routes involving ras, myc, p53, and Akt signaling and the propensity of cancer cells to develop signaling aberrances (notably aberrant surface receptor expression) which, when present, offer unique opportunities for therapeutic interventions. The rationale for various emerging strategies for cancer treatment is presented along with mechanisms by which PPAR ligands might interfere directly with tumoral metabolism and promote anticancer activity. Clinical trials using PPAR ligands are reviewed and followed by concluding remarks and perspectives for future studies. A therapeutic need to associate PPAR ligands with other anticancer agents is perhaps an important lesson to be learned from the results of the clinical trials conducted to date.

Do antidiabetic medications play a specific role in differentiated thyroid cancer compared to other cancer types?

The risk for differentiated thyroid cancer, like for many other types of cancer, is increased in obese individuals and people with intermediate hyperglycaemia. The incidence of all cancers, with the exception of thyroid cancer, is also increased in type 2 diabetes mellitus patients. The review compares the prevalence of thyroid carcinoma and other cancers in obese, people with intermediate hyperglycaemia and patients with diabetes and summarizes mode of action and anti-tumourigenic effect of common antidiabetic medications. The over-expression of dipeptidyl peptidase IV in the tumours, not seen in the other cancer types, is suggested as a potential reason for the unique situation in thyroid cancer.

Pioglitazone in chemically induced mammary carcinogenesis in rats

Data available from in-vitro and in-vivo studies suggest oncostatic properties of peroral antidiabetics, thiazolidinediones, in many types of cancer. This study is the first report on the chemopreventive effect of pioglitazone in mammary carcinogenesis in rats. Mammary carcinogenesis was induced by N-methyl-N-nitrosourea administered in two intraperitoneal doses per 50 mg/kg bodyweight on the 43rd and 50th postnatal days. Pioglitazone was administered in the diet at concentrations of 10 and 100 ppm, respectively, 12 days before the first carcinogen dose until the termination of the experiment. During the experiment, the animals were weighed weekly and palpated for the presence of mammary tumors, and the incidence, latency, tumor frequency, and tumor volume were recorded. The experiment was terminated 17 weeks after the first carcinogen dose; basic tumor growth parameters and metabolic and hormonal variables were evaluated. Pioglitazone at higher concentration decreased incidence and frequency per group from the 11th week of experiment when compared with the control group and a group receiving a lower dose. Pioglitazone at a higher dose decreased the final incidence by 38%, frequency per group by 63%, and extended latency period by 32% when compared with the control group. Our data suggest that pioglitazone and other glitazones should be further investigated for oncopreventive effects.

Inhalation delivery of a novel diindolylmethane derivative for the treatment of lung cancer

The purpose of this study was to determine the anticancer efficacy of 1,1-bis (3'-indolyl)-1-(p-biphenyl) methane (DIM-C-pPhC₆H₅) by inhalation delivery alone and in combination with i.v. docetaxel in a murine model for lung cancer. An aqueous DIM-C-pPhC₆H₅ formulation was characterized for its aerodynamic properties. Tumor-bearing athymic nude mice were exposed to nebulized DIM-C-pPhC₆H₅, docetaxel, or combination (DIM-C-pPhC₆H₅ plus docetaxel) using a nose-only exposure technique. The aerodynamic properties included mass median aerodynamic diameter of 1.8 ± 0.3 μm and geometric SD of 2.31 ± 0.02. Lung weight reduction in mice treated with the drug combination was 64% compared with 40% and 47% in mice treated with DIM-C-pPhC₆H₅ aerosol and docetaxel alone, respectively. Combination treatment decreased expression of Akt, cyclin D1, survivin, Mcl-1, NF-κB, IκBα, phospho-IκBα, and vascular endothelial growth factor (VEGF) and increased expression of c-Jun NH₂-terminal kinase 2 and Bad compared with tumors collected from single-agent treatment and control groups. DNA fragmentation was also enhanced in mice treated with the drug combination compared with docetaxel or DIM-C-pPhC₆H₅ alone. Combination treatment decreased expressions of VEGF and CD31 compared with single-agent treated and control groups. These results suggest that DIM-C-pPhC₆H₅ aerosol enhanced the anticancer activity of docetaxel in a lung cancer model by activating multiple signaling pathways. The study provides evidence that DIM-C-pPhC₆H₅ can be used alone or in combination with other drugs for the treatment of lung cancer using the inhalation delivery approach.

Peroxisome proliferator-activated receptor gamma (PPARgamma): Is the genomic activity the only answer?

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a member of the nuclear hormone receptor superfamily of transcription factors, widely expressed in the organism, including adipose, vascular and immune cells. Besides the well-known role in lipid/glycidic homeostasis, PPARgamma has also recently emerged as a key regulator of inflammatory and immune responses. Besides the natural ligands, more potent synthetic agonists of PPARgamma have been developed, including thiazolidinediones (TZDs), currently used in type 2 diabetes treatment, which also exert anti-inflammatory and anti-neoplastic effects. PPARgamma mechanism of action has focused considerable attention over the years. This receptor was initially shown to act on gene expression through a direct transcription and an indirect transrepression activity, mainly associated with metabolic and anti-inflammatory effects. Different post-translational modifications of the receptor can modulate PPARgamma activity. More recently, rapid nongenomic activity of TZDs affecting post-translation modifications of extranuclear proteins involved in cell signaling, has been reported. In particular, PPARgamma can physically interact with protein kinases resulting in a compartment specific recruitment and activity modulation of these enzymes. Among them, ERK can be positively/negatively regulated by PPARgamma ligands, as in endothelial cells, where TZDs exert anti-inflammatory effects through a novel mechanism involving a rapid inhibition of ERK1/2 phosphorylation/activation. Finally, some of the TZD anti-tumor effects seem to be PPARgamma-independent, raising the possibility that alternative receptors can act through extranuclear nongenomic pathways. In conclusion, different mechanisms of action of PPARgamma seem to coexist in an interacting functional network in the cell, concurring in mediating both pharmacological and natural ligand effects.

Troglitazone is an estrogen-related receptor alpha and gamma inverse agonist

As a ligand for peroxisome proliferators-activated receptor gamma (PPAR gamma), troglitazone inhibits cell growth by mechanisms besides activating PPAR gamma. In this study, we found that troglitazone interfered with the interactions between estrogen-related receptor alpha and gamma (ERR alpha and ERR gamma) and their coactivator PPAR gamma coactivator-1 alpha (PGC-1 alpha) functioning as an inverse agonist. Additionally, troglitazone suppressed the expressions of PGC-1 alpha and its related member PGC-1 beta which are key regulators of mitochondrial function. Consequently, troglitazone reduced mitochondrial mass and suppressed the expressions of superoxide dismutases to elevate reactive oxygen species (ROS) production. The increase in ROS in turn induced the expression of cell cycle inhibitor p21(WAF1). We therefore propose that ERR alpha and ERR gamma are alternative targets of troglitazone important for mediating its growth suppressive effect.

Anticancer Role of PPARgamma Agonists in Hematological Malignancies Found in the Vasculature, Marrow, and Eyes

The use of targeted cancer therapies in combination with conventional chemotherapeutic agents and/or radiation treatment has increased overall survival of cancer patients. However, longer survival is accompanied by increased incidence of comorbidities due, in part, to drug side effects and toxicities. It is well accepted that inflammation and tumorigenesis are linked. Because peroxisome proliferator-activated receptor (PPAR)-gamma agonists are potent mediators of anti-inflammatory responses, it was a logical extension to examine the role of PPARgamma agonists in the treatment and prevention of cancer. This paper has two objectives: first to highlight the potential uses for PPARgamma agonists in anticancer therapy with special emphasis on their role when used as adjuvant or combined therapy in the treatment of hematological malignancies found in the vasculature, marrow, and eyes, and second, to review the potential role PPARgamma and/or its ligands may have in modulating cancer-associated angiogenesis and tumor-stromal microenvironment crosstalk in bone marrow.

PPAR-γ agonists and their effects on IGF-I receptor signaling: Implications for cancer

It is now well established that the development and progression of a variety of human malignancies are associated with dysregulated activity of the insulin-like growth factor (IGF) system. In this regard, promising drugs have been developed to target the IGF-I receptor or its ligands. These therapies are limited by the development of insulin resistance and compensatory hyperinsulinemia, which in turn, may stimulate cancer growth. Novel therapeutic approaches are, therefore, required. Synthetic PPAR-γ agonists, such as thiazolidinediones (TZDs), are drugs universally used as antidiabetic agents in patients with type 2 diabetes. In addition of acting as insulin sensitizers, PPAR-γ agonists mediate in vitro and in vivo pleiotropic anticancer effects. At least some of these effects appear to be linked with the downregulation of the IGF system, which is induced by the cross-talk of PPAR-γ agonists with multiple components of the IGF system signaling. As hyperinsulinemia is an emerging cancer risk factor, the insulin lowering action of PPAR-γ agonists may be expected to be also beneficial to reduce cancer development and/or progression. In light of these evidences, TZDs or other PPAR-γ agonists may be exploited in those tumors "addicted" to the IGF signaling and/or in tumors occurring in hyperinsulinemic patients.