Randomized phase III trial comparing bexarotene (L1069-49)/cisplatin/vinorelbine with cisplatin/vinorelbine in chemotherapy-naive patients with advanced or metastatic non-small-cell lung cancer: SPIRIT I

Pin1-catalyzed conformational regulation after phosphorylation: A distinct checkpoint in cell signaling and drug discovery

Protein phosphorylation is one of the most common mechanisms regulating cellular signaling pathways, and many kinases and phosphatases are proven drug targets. Upon phosphorylation, protein functions can be further regulated by the distinct isomerase Pin1 through cis-trans isomerization. Numerous protein targets and many important roles have now been elucidated for Pin1. However, no tools are available to detect or target cis and trans conformation events in cells. The development of Pin1 inhibitors and stereo- and phospho-specific antibodies has revealed that cis and trans conformations have distinct and often opposing cellular functions. Aberrant conformational changes due to the dysregulation of Pin1 can drive pathogenesis but can be effectively targeted in age-related diseases, including cancers and neurodegenerative disorders. Here, we review advances in understanding the roles of Pin1 signaling in health and disease and highlight conformational regulation as a distinct signal transduction checkpoint in disease development and treatment.

Retinoid X Receptor agonists as selective modulators of the immune system for the treatment of cancer

Upon heterodimerizing with other nuclear receptors, retinoid X receptors (RXR) act as ligand-dependent transcription factors, regulating transcription of critical signaling pathways that impact numerous hallmarks of cancer. By controlling both inflammation and immune responses, ligands that activate RXR can modulate the tumor microenvironment. Several small molecule agonists of these essential receptors have been synthesized. Historically, RXR agonists were tested for inhibition of growth in cancer cells, but more recent drug discovery programs screen new molecules for inhibition of inflammation or activation of immune cells. Bexarotene is the first successful example of an effective therapeutic that molecularly targets RXR; this drug was approved to treat cutaneous T cell lymphoma and is still used as a standard of care treatment for this disease. No additional RXR agonists have yet achieved FDA approval, but several promising novel compounds are being developed. In this review, we provide an overview of the multiple mechanisms by which RXR signaling regulates inflammation and tumor immunity. We also discuss the potential of RXR-dependent immune cell modulation for the treatment or prevention of cancer and concomitant challenges and opportunities.

Modulating retinoid-X-receptor alpha (RXRA) expression sensitizes chronic myeloid leukemia cells to imatinib in vitro and reduces disease burden in vivo

Introduction: The ligand-activated transcription factors, nuclear hormone receptors (NHRs), remain unexplored in hematological malignancies except for retinoic acid receptor alpha (RARA). Methods: Here we profiled the expression of various NHRs and their coregulators in Chronic myeloid leukemia (CML) cell lines and identified a significant differential expression pattern between inherently imatinib mesylate (IM)-sensitive and resistant cell lines. Results: Retinoid-X-receptor alpha (RXRA) was downregulated in CML cell lines inherently resistant to IM and in primary CML CD34⁺ cells. Pre-treatment with clinically relevant RXRA ligands improved sensitivity to IM in-vitro in both CML cell lines and primary CML cells. This combination effectively reduced the viability and colony-forming capacity of CML CD34⁺ cells in-vitro. In-vivo, this combination reduced leukemic burden and prolonged survival. Overexpression (OE) of RXRA inhibited proliferation and improved sensitivity to IM in-vitro. In-vivo, RXRA OE cells showed reduced engraftment of cells in the bone marrow, improved sensitivity to IM, and prolonged survival. Both RXRA OE and ligand treatment markedly reduced BCR::ABL1 downstream kinase activation, activating apoptotic cascades and improving sensitivity to IM. Importantly, RXRA OE also led to the disruption of the oxidative capacity of these cells. Conclusion: Combining IM with clinically available RXRA ligands could form an alternative treatment strategy in CML patients with suboptimal response to IM.

Photodegradation of Bexarotene and Its Implication for Cytotoxicity

A detailed understanding of the stability of an active pharmaceutical ingredient and a pharmaceutical dosage form is essential for the drug-development process and for safe and effective use of medicines. Photostability testing as an inherent part of stability studies provides valuable knowledge on degradation pathways and structures of products generated under UV irradiation. Photostability is particularly important for topically administered drugs, as they are more exposed to UV radiation. Bexarotene is a more recent third-generation retinoid approved by the U.S. Food and Drug Administration and the European Medicines Agency as a topically applied anticancer agent. The present study aimed to assess bexarotene photostability, including the presence of UV filters, which have been permitted to be used in cosmetic products in Europe and the USA. The bexarotene photostability testing was performed in ethanol solutions and in formulations applied on PMMA plates. The UPLC-MS/MS technique was used to determine the tested substance. The presence of photocatalysts such as TiO₂ or ZnO, as well as the organic UV filters avobenzone, benzophenone-3, meradimate, and homosalate, could contribute to degradation of bexarotene under UV irradiation. Four photocatalytic degradation products of bexarotene were identified for the first time. The antiproliferative properties of the degradation products of bexarotene were assessed by MTT assay on a panel of human adherent cancer cells, and concentration-dependent growth inhibition was evidenced on all tested cell lines. The cytotoxicity of the formed products after 4 h of UV irradiation was significantly higher than that of the parent compound (p < 0.05). Furthermore non-cancerous murine fibroblasts exhibited marked concentration-dependent inhibition by bexarotene, while the degradation products elicited more pronounced antiproliferative action only at the highest applied concentration.

Potential therapeutic uses of rexinoids

The discovery of nuclear receptors, particularly retinoid X receptors (RXR), and their involvement in numerous pathways related to development sparked interest in their immunomodulatory properties. Genetic models using deletion or overexpression of RXR and the subsequent development of several small molecules that are agonists or antagonists of this receptor support a promising therapeutic role for these receptors in immunology. Bexarotene was approved in 1999 for the treatment of cutaneous T cell lymphoma. Several other small molecule RXR agonists have since been synthesized with limited preclinical development, but none have yet achieved FDA approval. Cancer treatment has recently been revolutionized with the introduction of immune checkpoint inhibitors, but their success has been restricted to a minority of patients. This review showcases the emerging immunomodulatory effects of RXR and the potential of small molecules that target this receptor as therapies for cancer and other diseases. Here we describe the essential roles that RXR and partner receptors play in T cells, dendritic cells, macrophages and epithelial cells, especially within the tumor microenvironment. Most of these effects are site and cancer type dependent but skew immune cells toward an anti-inflammatory and anti-tumor effect. This beneficial effect on immune cells supports the promise of combining rexinoids with approved checkpoint blockade therapies in order to enhance efficacy of the latter and to delay or potentially eliminate drug resistance. The data compiled in this review strongly suggest that targeting RXR nuclear receptors is a promising new avenue in immunomodulation for cancer and other chronic inflammatory diseases.

The novel rexinoid MSU-42011 is effective for the treatment of preclinical Kras-driven lung cancer

Effective drugs are needed for lung cancer, as this disease remains the leading cause of cancer-related deaths. Rexinoids are promising drug candidates for cancer therapy because of their ability to modulate genes involved in inflammation, cell proliferation or differentiation, and apoptosis through activation of the retinoid X receptor (RXR). The only currently FDA-approved rexinoid, bexarotene, is ineffective as a single agent for treating epithelial cancers and induces hypertriglyceridemia. Here, we used a previously validated screening paradigm to evaluate 23 novel rexinoids for biomarkers related to efficacy and safety. These biomarkers include suppression of inducible nitric oxide synthase (iNOS) and induction of sterol regulatory element-binding protein (SREBP). Because of its potent iNOS suppression, low SREBP induction, and activation of RXR, MSU-42011 was selected as our lead compound. We next used MSU-42011 to treat established tumors in a clinically relevant Kras-driven mouse model of lung cancer. KRAS is one of the most common driver mutations in human lung cancer and correlates with aggressive disease progression and poor patient prognosis. Ultrasound imaging was used to detect and monitor tumor development and growth over time in the lungs of the A/J mice. MSU-42011 markedly decreased the tumor number, size, and histopathology of lung tumors compared to the control and bexarotene groups. Histological sections of lung tumors in mice treated with MSU-42011 exhibited reduced cell density and fewer actively proliferating cells compared to the control and bexarotene-treated tumors. Although bexarotene significantly (p < 0.01) elevated plasma triglycerides and cholesterol, treatment with MSU-42011 did not increase these biomarkers, demonstrating a more favorable toxicity profile in vivo. The combination of MSU-42011 and carboplatin and paclitaxel reduced macrophages in the lung and increased activation markers of CD8+T cells compared to the control groups. Our results validate our screening paradigm for in vitro testing of novel rexinoids and demonstrate the potential for MSU-42011 to be developed for the treatment of KRAS-driven lung cancer.

Nuclear receptors: Lipid and hormone sensors with essential roles in the control of cancer development

Nuclear receptors (NRs) are a superfamily of ligand-activated transcription factors that act as biological sensors and use a combination of mechanisms to modulate positively and negatively gene expression in a spatial and temporal manner. The highly orchestrated biological actions of several NRs influence the proliferation, differentiation, and apoptosis of many different cell types. Synthetic ligands for several NRs have been the focus of extensive drug discovery efforts for cancer intervention. This review summarizes the roles in tumour growth and metastasis of several relevant NR family members, namely androgen receptor (AR), estrogen receptor (ER), glucocorticoid receptor (GR), thyroid hormone receptor (TR), retinoic acid receptors (RARs), retinoid X receptors (RXRs), peroxisome proliferator-activated receptors (PPARs), and liver X receptors (LXRs). These studies are key to develop improved therapeutic agents based on novel modes of action with reduced side effects and overcoming resistance.

Bexarotene normalizes chemotherapy-induced myelin decompaction and reverses cognitive and sensorimotor deficits in mice

Frequently reported neurotoxic sequelae of cancer treatment include cognitive deficits and sensorimotor abnormalities that have long-lasting negative effects on the quality of life of an increasing number of cancer survivors. The underlying mechanisms are not fully understood and there is no effective treatment. We show here that cisplatin treatment of mice not only caused cognitive dysfunction but also impaired sensorimotor function. These functional deficits are associated with reduced myelin density and complexity in the cingulate and sensorimotor cortex. At the ultrastructural level, myelin abnormalities were characterized by decompaction. We used this model to examine the effect of bexarotene, an agonist of the RXR-family of nuclear receptors. Administration of only five daily doses of bexarotene after completion of cisplatin treatment was sufficient to normalize myelin density and fiber coherency and to restore myelin compaction in cingulate and sensorimotor cortex. Functionally, bexarotene normalized performance of cisplatin-treated mice in tests for cognitive and sensorimotor function. RNAseq analysis identified the TR/RXR pathway as one of the top canonical pathways activated by administration of bexarotene to cisplatin-treated mice. Bexarotene also activated neuregulin and netrin pathways that are implicated in myelin formation/maintenance, synaptic function and axonal guidance. In conclusion, short term treatment with bexarotene is sufficient to reverse the adverse effects of cisplatin on white matter structure, cognitive function, and sensorimotor performance. These encouraging findings warrant further studies into potential clinical translation and the underlying mechanisms of bexarotene for chemobrain.

Cellular retinol binding protein 1 transfection reduces proliferation and AKT-related gene expression in H460 non-small lung cancer cells

In recent years, new treatments with novel action mechanisms have been explored for advanced non-small cell lung cancer (NSCLC). Retinoids promote cancer cell differentiation and death and their trafficking and action is mediated from specific cytoplasmic and nuclear receptors, respectively. The purpose of this study was to investigate the effect of Cellular retinol binding protein-1 (CRBP-1) transfection in H460 human NSCLC cell line, normally not expressing CRBP-1. H460 cells were transfected by using a vector pTargeT Mammalian expression system carrying the whole sequence of CRBP-1 gene. For proliferation and apoptosis studies, cells were treated with different concentrations of all-trans Retinoic Acid (atRA) and retinol. AKT-related gene expression was analyzed by using western blot and Signosis array and results analysed by one-way analysis of variance (ANOVA) or by t-student test. CRBP-1⁺ showed reduced proliferation and viability in basal condition and after atRA treatment when compared to empty-transfected H460 cells. Reduced proliferation in CRBP-1⁺ H460 cells associated to the down-regulation of pAKT/pERK/pEGFR-related genes. In particular, gene array documented the down-regulation of AKT and Stat-3-related genes, including M-Tor, Akt1, Akt2, Akt3, Foxo1, p27, Jun. Restoration of CRBP-1 expression in H460 cells reduced proliferation and viability in both basal condition and after atRA treatment, likely by down-regulating AKT-related gene level. Further studies are needed to better clarify how those CRBP-1-related intracellular pathways contribute to counteract NSCLC progression in order to suggest a potential tool to improve efficacy of retinoid anti lung cancer adjuvant therapy.

Synergistic effect of a retinoid X receptor-selective ligand bexarotene and docetaxel in prostate cancer

Purpose

To explore if bexarotene (BEX) synergistically enhances docetaxel (DTX) cytotoxicity in castration-resistant prostate cancer cell lines.

Materials and methods

MTT assay was used to measure the cytotoxic effect of DTX and BEX on castration-resistant prostate cancer (CRPC) cell proliferation and the combination index (CI) values calculated to analyze the interaction between DTX and BEX. Flow cytometry and Western blot analysis identified the underlying mechanism for the synergistic effect of BEX and DTX.

Results

When mitotic slippage happens, BEX can synergistically strengthen the anti-proliferation of DTX in a way of significantly down-regulating cyclinB1 and CDK1 expression, and then arresting cells in G2 phase.

Conclusion

Results from this study showed that BEX-induced G2 arrest and DTX-induced mitotic arrest probably contributed to the synergistic effect of BEX and DTX.

Cancer Chemoprevention: Preclinical In Vivo Alternate Dosing Strategies to Reduce Drug Toxicities

Cancer chemopreventive agents inhibit the formation of precursor lesions and/or the progression of these lesions to late stage disease. This approach to disease control has the potential to reduce the physical and financial costs of cancer in society. Several drugs that have been approved by the FDA for other diseases and have been extensively evaluated for their safety and pharmacokinetic/pharmacodynamic characteristics have the potential to be repurposed for use as cancer chemopreventive agents. These agents often mechanistically inhibit signaling molecules that play key roles in the carcinogenic process. The safety profile of agents is a primary concern when considering the administration of drugs for chemoprevention, as the drugs will be given chronically to high-risk, asymptomatic individuals. To decrease drug toxicity while retaining efficacy, several approaches are currently being explored. In this short review, we describe studies that use preclinical in vivo models to assess efficacy of alternative drug dosing strategies and routes of drug administration on chemopreventive drug efficacy. In vivo drug dosing strategies that reduce toxicity while retaining efficacy will pave the way for future cancer prevention clinical trials.

The potential of retinoids for combination therapy of lung cancer: Updates and future directions

Lung cancer is the most common cancer-related death worldwide. Natural compounds have shown high biological and pharmaceutical relevance as anticancer agents. Retinoids are natural derivatives of vitamin A having many regulatory functions in the human body, including vision, cellular proliferation and differentiation, and activation of tumour suppressor genes. Retinoic acid (RA) is a highly active retinoid isoform with promising anti-lung cancer activity. The abnormal expression of retinoid receptors is associated with loss of anticancer activities and acquired resistance to RA in lung cancer. The preclinical promise has not translated to the general clinical utility of retinoids for lung cancer patients, especially those with a history of smoking. Newer retinoid nano-formulations and the combinatorial use of retinoids has been associated with lower toxicity and more favorably efficacy in both the preclinical and clinical settings. Here, we highlight epidemiological and clinical therapeutic studies involving retinoids and lung cancer. We also discuss the biological actions of retinoids in lung cancer, which include effects on cancer stem cell differentiation, angiogenesis, metastasis, and proliferative. We suggest that the use of retinoids in combination with conventional and targeted anticancer agents will broaden the utility of these potent anticancer compounds in the lung cancer clinic.

Targeting PIN1 exerts potent antitumor activity in pancreatic ductal carcinoma via inhibiting tumor metastasis

The human prolyl isomerase PIN1, best known for its association with carcinogenesis, has recently been indicated in the disease of pancreatic ductal adenocarcinoma (PDAC). However, the functions of PIN1 and the feasibility of targeting PIN1 in PDAC remain elusive. For this purpose, we examined the expression of PIN1 in cancer, related paracarcinoma and metastatic cancer tissues by immunohistochemistry and analyzed the associations with the pathogenesis of PDAC in 173 patients. The functional roles of PIN1 in PDAC were explored in vitro and in vivo using both genetic and chemical PIN1 inhibition. We showed that PIN1 was upregulated in pancreatic cancer and metastatic tissues. High PIN1 expression is significantly association with poor clinicopathological features and shorter overall survival and disease‐free survival. Further stratified analysis showed that PIN1 phenotypes refined prognostication in PDAC. Inhibition of PIN1 expression with RNA interference or with all trans retinoic acid decreased not only the growth but also the migration and invasion of PDAC cells through regulating the key molecules of multiple cancer‐driving pathways, simultaneously resulting in cell cycle arrest and mesenchymal‐epithelial transition in vitro. Furthermore, genetic and chemical PIN1 ablation showed dramatic inhibition of the tumorigenesis and metastatic spread and then reduced the tumor burden in vivo. We provided further evidence for the use of PIN1 as a promising therapeutic target in PDAC. Genetic and chemical PIN1 ablation exerted potent antitumor effects through blocking multiple cancer‐driving pathways in PDAC. More potent and specific PIN1 targeted inhibitors could be exploited to treat this aggressive cancer.

Optimized Bexarotene Aerosol Formulation Inhibits Major Subtypes of Lung Cancer in Mice

Bexarotene has shown inhibition of lung and mammary gland tumorigenesis in preclinical models and in clinical trials. The main side effects of orally administered bexarotene are hypertriglyceridemia and hypercholesterolemia. We previously demonstrated that aerosolized bexarotene administered by nasal inhalation has potent chemopreventive activity in a lung adenoma preclinical model without causing hypertriglyceridemia. To facilitate its future clinical translation, we modified the formula of the aerosolized bexarotene with a clinically relevant solvent system. This optimized aerosolized bexarotene formulation was tested against lung squamous cell carcinoma mouse model and lung adenocarcinoma mouse model and showed significant chemopreventive effect. This new formula did not cause visible signs of toxicity and did not increase plasma triglycerides or cholesterol. This aerosolized bexarotene was evenly distributed to the mouse lung parenchyma, and it modulated the microenvironment in vivo by increasing the tumor-infiltrating T cell population. RNA sequencing of the lung cancer cell lines demonstrated that multiple pathways are altered by bexarotene. For the first time, these studies demonstrate a new, clinically relevant aerosolized bexarotene formulation that exhibits preventive efficacy against the major subtypes of lung cancer. This approach could be a major advancement in lung cancer prevention for high risk populations, including former and present smokers.

Testing Novel Pyrimidinyl Rexinoids: A New Paradigm for Evaluating Rexinoids for Cancer Prevention

Rexinoids, selective ligands for retinoid X receptors (RXR), have shown promise in preventing many types of cancer. However, the limited efficacy and undesirable lipidemic side-effects of the only clinically approved rexinoid, bexarotene, drive the search for new and better rexinoids. Here we report the evaluation of novel pyrimidinyl (Py) analogues of two known chemopreventive rexinoids, bexarotene (Bex) and LG100268 (LG268) in a new paradigm. We show that these novel derivatives were more effective agents than bexarotene for preventing lung carcinogenesis induced by a carcinogen. In addition, these new analogues have an improved safety profile. PyBex caused less elevation of plasma triglyceride levels than bexarotene, while PyLG268 reduced plasma cholesterol levels and hepatomegaly compared with LG100268. Notably, this new paradigm mechanistically emphasizes the immunomodulatory and anti-inflammatory activities of rexinoids. We reveal new immunomodulatory actions of the above rexinoids, especially their ability to diminish the percentage of macrophages and myeloid-derived suppressor cells in the lung and to redirect activation of M2 macrophages. The rexinoids also potently inhibit critical inflammatory mediators including IL6, IL1β, CCL9, and nitric oxide synthase (iNOS) induced by lipopolysaccharide. Moreover, in vitro iNOS and SREBP (sterol regulatory element-binding protein) induction assays correlate with in vivo efficacy and toxicity, respectively. Our results not only report novel pyrimidine derivatives of existing rexinoids, but also describe a series of biological screening assays that will guide the synthesis of additional rexinoids. Further progress in rexinoid synthesis, potency, and safety should eventually lead to a clinically acceptable and useful new drug for patients with cancer.

The success and the challenge of all-trans retinoic acid in the treatment of cancer

All-trans retinoic acid (ATRA), an active metabolite of vitamin A, plays important roles in cell proliferation, cell differentiation, apoptosis, and embryonic development. The effects of ATRA are mediated by nuclear retinoid receptors as well as non-genomic signal pathway, such as MAPK and PKA. The great success of differentiation therapy with ATRA in acute promyelocytic leukemia (APL) not only improved the prognosis of APL but also spurred the studies of ATRA in the treatment of other tumors. Since the genetic and physiopathological simplicity of APL is not common in human malignancies, the combination of ATRA with other agents (chemotherapy, epigenetic modifiers, and arsenic trioxide, etc) had been extensively investigated in a variety of tumors. In this review, we will discuss in details about ATRA and its role in cancer treatment.

A phase I/II study of bexarotene with carboplatin and weekly paclitaxel for the treatment of patients with advanced non-small cell lung cancer

BACKGROUND

Rexinoids demonstrate anti-proliferative differentiation-inducing activity in multiple cancer types, including NSCLC. Prior studies have shown promising results when combining rexinoids with chemotherapy. This phase I/II study evaluates the tolerability and activity of a rexinoid, bexarotene, combined with weekly paclitaxel and monthly carboplatin.

METHODS

Patients with confirmed advanced stage IIIB or IV NSCLC and adequate organ function were enrolled. They were scheduled to receive carboplatin (AUC =6) and 3 doses of weekly paclitaxel (100 mg/m2) every 4 weeks. Oral bexarotene was administered daily at two doses: 300 and 400 mg/m2/day.

RESULTS

Thirty-three patients were enrolled. Fourteen received 300 mg/m2/day and 19 received 400 mg/m2/day of bexarotene. Hematologic toxicity included grade 3 neutropenia in 7 patients. Hyperlipidemia was a major non-hematologic toxicity which was medically managed. The recommended phase II dose of bexarotene was 400 mg/m2/day. Response rate was 35%. Median overall survival (OS) for all patients was 8.3 months with 1-year survival of 43%. Median OS for the 300 mg/m2 dose of bexarotene was 6.6 versus 9.8 months for the 400 mg/m2 dose (HR, 0.73; Log rank P=0.37). Patients who experienced hypertriglyceridemia had a median OS of 9.8 months compared to 4.9 months for those who did not (HR, 0.69; Log rank P=0.33).

CONCLUSIONS

The 43% 1-year survival for patients receiving bexarotene with weekly paclitaxel and monthly carboplatin is encouraging. With the availability of new classes of agents for lung cancer, further evaluation of this regimen in unselected patients is not warranted. Our study confirms prior subgroup analyses showing a significant correlation between bexarotene-induced hypertriglyceridemia and survival. Further research is needed to identify molecular biomarkers to identify this subset of patients and to explore rexinoids in other combinations, especially with immunotherapy.

Pro-apoptotic signaling induced by Retinoic acid and dsRNA is under the control of Interferon Regulatory Factor-3 in breast cancer cells

Breast cancer is one of the most lethal malignancies for women. Retinoic acid (RA) and double-stranded RNA (dsRNA) are considered signaling molecules with potential anticancer activity. RA, co-administered with the dsRNA mimic polyinosinic-polycytidylic acid (poly(I:C)), synergizes to induce a TRAIL (Tumor-Necrosis-Factor Related Apoptosis-Inducing Ligand)- dependent apoptotic program in breast cancer cells. Here, we report that RA/poly(I:C) co-treatment, synergically, induce the activation of Interferon Regulatory Factor-3 (IRF3) in breast cancer cells. IRF3 activation is mediated by a member of the pathogen recognition receptors, Toll-like receptor-3 (TLR3), since its depletion abrogates IRF3 activation by RA/poly(I:C) co-treatment. Besides induction of TRAIL, apoptosis induced by RA/poly(I:C) correlates with the increased expression of pro-apoptotic TRAIL receptors, TRAIL-R1/2, and the inhibition of the antagonistic receptors TRAIL-R3/4. IRF3 plays an important role in RA/poly(I:C)-induced apoptosis since IRF3 depletion suppresses caspase-8 and caspase-3 activation, TRAIL expression upregulation and apoptosis. Interestingly, RA/poly(I:C) combination synergizes to induce a bioactive autocrine/paracrine loop of type-I Interferons (IFNs) which is ultimately responsible for TRAIL and TRAIL-R1/2 expression upregulation, while inhibition of TRAIL-R3/4 expression is type-I IFN-independent. Our results highlight the importance of IRF3 and type-I IFNs signaling for the pro-apoptotic effects induced by RA and synthetic dsRNA in breast cancer cells.

Inhibition of the prolyl isomerase Pin1 enhances the ability of sorafenib to induce cell death and inhibit tumor growth in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the sixth most common cancer, but is the second leading cause of cancer deaths, partially due to its heterogeneity and drug resistance. Sorafenib is the only medical treatment with a proven efficacy against advanced HCC, but its overall clinical efficacy is still modest. Therefore, a major challenge is how to improve its therapeutic efficacy. The unique prolyl isomerase Pin1 regulates numerous cancer-driving pathways. Notably, Pin1 is overexpressed in about 70% HBV-positive HCC patients and contributes to HCC tumorigenesis. However, the role of Pin1 in the efficacy of sorafenib against HCC is unknown. Here we found that sorafenib down-regulated Pin1 mRNA and protein expression, likely through inhibition of Pin1 transcription by the Rb/E2F pathway. Importantly, Pin1 knockdown potently enhanced the ability of sorafenib to induce cell death in HCC, which was further supported by the findings that Pin1 knockdown led to stabilization of Fbxw7 and destabilization of Mcl-1. Furthermore, all-trans retinoic acid (ATRA), a known anticancer drug that inhibits and ultimately induces degradation of active Pin1 in cancer cells, also potently sensitized HCC cells to sorafenib-induced cell death at least in part through a caspase-dependent manner. Moreover, ATRA also synergistically enhanced the ability of sorafenib to reduce Pin1 and inhibit tumor growth of HCC in mouse xenograft models. Collectively, these results not only demonstrate that Pin1 down-regulation is a key event underlying the anti-tumor effects of sorafenib, but also uncover that Pin1 inhibitors offer a novel approach to enhance the therapeutic efficacy of sorafenib against HCC.

Chemical or genetic Pin1 inhibition exerts potent anticancer activity against hepatocellular carcinoma by blocking multiple cancer-driving pathways

Hepatocellular carcinoma (HCC) is one of the most prevalent and malignant cancers with high inter- and intra-tumor heterogeneity. A central common signaling mechanism in cancer is proline-directed phosphorylation, which is further regulated by the unique proline isomerase Pin1. Pin1 is prevalently overexpressed in human cancers including ~70% of HCC, and promotes tumorigenesis by activating multiple cancer-driving pathways. However, it was challenging to evaluate the significance of targeting Pin1 in cancer treatment until the recent identification of all-trans retinoic acid (ATRA) as a Pin1 inhibitor. Here we systematically investigate functions of Pin1 and its inhibitor ATRA in the development and treatment of HCC. Pin1 knockdown potently inhibited HCC cell proliferation and tumor growth in mice. ATRA-induced Pin1 degradation inhibited the growth of HCC cells, although at a higher IC50 as compared with breast cancer cells, likely due to more active ATRA metabolism in liver cells. Indeed, inhibition of ATRA metabolism enhanced the sensitivity of HCC cells to ATRA. Moreover, slow-releasing ATRA potently and dose-dependently inhibited HCC growth in mice. Finally, chemical or genetic Pin1 ablation blocked multiple cancer-driving pathways simultaneously in HCC cells. Thus, targeting Pin1 offers a promising therapeutic approach to simultaneously stop multiple cancer-driving pathways in HCC.

A Way Forward for Cancer Chemoprevention: Think Local

As cells progress through carcinogenesis, the associated exponential expansion of genetic and molecular aberrations and resultant heterogeneity make therapeutic success increasingly unattainable. Therapeutic intervention at early stages of carcinogenesis that occurs within the primary organ and in the face of a lower burden of molecular aberrations, constitutes a basic tenet of cancer chemoprevention, and provides a situation that favors a greater degree of therapeutic efficacy compared with that of advanced cancer. A longstanding barrier to chemoprevention relates to the requirement for essentially no systemic toxicity, and the fact that when large numbers of people are treated, the emergence of systemic toxicity is almost universal. A rational means to address this in fact relates to a second basic tenet of the chemopreventive strategy: the focus of therapeutic intervention is to disrupt a process that is in essence localized to a single organ. Based upon this consideration, a strategy which is based upon local delivery of therapeutics to an at-risk organ will achieve therapeutic efficacy while avoiding systemic delivery and its associated toxicity. This article will review the rationale for undertaking such an approach, describe successful clinical achievements based on this strategy, describe ongoing efforts to expand the impact of this approach, and together will highlight the high impact that this approach has already had on the field as well as its extremely high potential for future impact. Cancer Prev Res; 10(1); 14-35. ©2016 AACR.

The isomerase PIN1 controls numerous cancer-driving pathways and is a unique drug target

Targeted drugs have changed cancer treatment but are often ineffective in the long term against solid tumours, largely because of the activation of heterogeneous oncogenic pathways. A central common signalling mechanism in many of these pathways is proline-directed phosphorylation, which is regulated by many kinases and phosphatases. The structure and function of these phosphorylated proteins are further controlled by a single proline isomerase: PIN1. PIN1 is overactivated in cancers and it promotes cancer and cancer stem cells by disrupting the balance of oncogenes and tumour suppressors. This Review discusses the roles of PIN1 in cancer and the potential of PIN1 inhibitors to restore this balance.

Cisplatin in the modern era: The backbone of first-line chemotherapy for non-small cell lung cancer

The treatment of advanced non-small cell lung cancer (NSCLC) may be changing, but the cisplatin-based doublet remains the foundation of treatment for the majority of patients with advanced NSCLC. In this respect, changes in practice to various aspects of cisplatin use, such as administration schedules and the choice of methods and frequency of monitoring for toxicities, have contributed to an incremental improvement in patient management and experience. Chemoresistance, however, limits the clinical utility of this drug in patients with advanced NSCLC. Better understanding of the molecular mechanisms of cisplatin resistance, identification of predictive markers and the development of newer, more effective and less toxic platinum agents is required. In addition to maximising potential benefits from advances in molecular biology and associated therapeutics, modification of existing cisplatin-based treatments can still lead to improvements in patient outcomes and experiences.

Targeting truncated RXRα for cancer therapy

Retinoid X receptor-alpha (RXRα), a unique member of the nuclear receptor superfamily, is a well-established drug target, representing one of the most important targets for pharmacologic interventions and therapeutic applications for cancer. However, how RXRα regulates cancer cell growth and how RXRα modulators suppress tumorigenesis are poorly understood. Altered expression and aberrant function of RXRα are implicated in the development of cancer. Previously, several studies had demonstrated the presence of N-terminally truncated RXRα (tRXRα) proteins resulted from limited proteolysis of RXRα in tumor cells. Recently, we discovered that overexpression of tRXRα can promote tumor growth by interacting with tumor necrosis factor-alpha-induced phosphoinositide 3-kinase and NF-κB signal transduction pathways. We also identified nonsteroidal anti-inflammatory drug Sulindac and analogs as effective inhibitors of tRXRα activities via a unique binding mechanism. This review discusses the emerging roles of tRXRα and modulators in the regulation of cancer cell survival and death as well as inflammation and our recent understanding of tRXRα regulation by targeting the alternate binding sites on its surface.

Retinoids and rexinoids in cancer prevention: from laboratory to clinic

Early in the age of modern medicine the consequences of vitamin A deficiency drew attention to the fundamental link between retinoid-dependent homeostatic regulation and malignant hyperproliferative diseases. The term "retinoid" includes a handful of endogenous and a large group of synthetic derivatives of vitamin A. These multifunctional lipid-soluble compounds directly regulate target genes of specific biological functions and critical signaling pathways to orchestrate complex functions from vision to development, metabolism, and inflammation. Many of the retinoid activities on the cellular level have been well characterized and translated to the regulation of processes like differentiation and cell death, which play critical roles in the outcome of malignant transformation of tissues. In fact, retinoid-based differentiation therapy of acute promyelocytic leukemia was one of the first successful examples of molecularly targeted treatment strategies. The selectivity, high receptor binding affinity and the ability of retinoids to directly modulate gene expression programs present a distinct pharmacological opportunity for cancer treatment and prevention. However, to fully exploit their potential, the adverse effects of retinoids must be averted. In this review we provide an overview of the biology of retinoid (activated by nuclear retinoic acid receptors [RARs]) and rexinoid (engaged by nuclear retinoid X receptors [RXRs]) action concluded from a long line of preclinical studies, in relation to normal and transformed states of cells. We will also discuss the past and current uses of retinoids in the treatment of malignancies, the potential of rexinoids in the cancer prevention setting, both as single agents and in combinations.

Marked lowering of high-density lipoprotein cholesterol levels due to high dose bexarotene therapy

CONTEXT

Bexarotene is a retinoid X receptor agonist, which is currently used for the treatment of cutaneous T-cell lymphoma (CTCL). It is known to induce central hypothyroidism as well as dyslipidemia including elevation of triglycerides (TG) and low-density lipoprotein cholesterol along with slight lowering of high-density lipoprotein cholesterol (HDL-C). Marked lowering of HDL-C has never been previously reported in bexarotene-treated patients and whether it is related to hypothyroidism remains unclear.

CASE REPORT

A 49-year-old African female with a history of CTCL on treatment with bexarotene of 300 mg/d, presented with serum total cholesterol level of 249 mg/dL (6.4 mmol/L), TG level of 92 mg/dL (1.03 mmol/L), HDL-C level of 78 mg/dL (2.02 mmol/L), thyroid stimulating hormone (TSH) of 0.68 μIU/mL, and free thyroxine level of 0.5 ng/dL. Six months later, on increasing the bexarotene dose to 600 mg daily, serum TG increased to 310 mg/dL (3.5 mmol/L) and HDL-C dropped to 3 to 5 mg/dL (0.077-0.13 mmol/L), whereas the TSH was undetectable (0.01 μIU/mL). Despite adequate levothyroxine replacement to 225 μg daily resulting in free thyroxine levels up to 1.5 ng/dL, HDL-C remained extremely low of 4 to 9 mg/dL (0.103-0.233 mmol/L). Bexarotene was discontinued due to poor response of CTCL, 3 months after which her HDL-C levels returned to baseline of 80 to 90 mg/dL (2.07-2.33 mmol/L).

CONCLUSIONS

High dose bexarotene can markedly lower HDL-C levels, which normalize on discontinuation of the drug. Lowering of HDL-C with bexarotene may be due to an increase in cholesterol ester transfer protein activity and appears to be independent of central hypothyroidism.

Active Pin1 is a key target of all-trans retinoic acid in acute promyelocytic leukemia and breast cancer

A common key regulator of oncogenic signaling pathways in multiple tumor types is the unique isomerase Pin1. However, available Pin1 inhibitors lack the required specificity and potency for inhibiting Pin1 function in vivo. By using mechanism-based screening, here we find that all-trans retinoic acid (ATRA)--a therapy for acute promyelocytic leukemia (APL) that is considered the first example of targeted therapy in cancer, but whose drug target remains elusive--inhibits and degrades active Pin1 selectively in cancer cells by directly binding to the substrate phosphate- and proline-binding pockets in the Pin1 active site. ATRA-induced Pin1 ablation degrades the protein encoded by the fusion oncogene PML-RARA and treats APL in APL cell and animal models as well as in human patients. ATRA-induced Pin1 ablation also potently inhibits triple-negative breast cancer cell growth in human cells and in animal models by acting on many Pin1 substrate oncogenes and tumor suppressors. Thus, ATRA simultaneously blocks multiple Pin1-regulated cancer-driving pathways, an attractive property for treating aggressive and drug-resistant tumors.

Cardiovascular comorbidities and survival of lung cancer patients: Medicare data based analysis

OBJECTIVES

To evaluate the role of cardiovascular disease (CVD) comorbidity in survival of patients with non-small cell lung cancer (NSCLC).

MATERIALS AND METHODS

The impact of seven CVDs (at the time of NSCLC diagnosis and during subsequent follow-up) on overall survival was studied for NSCLC patients aged 65+ years using the Surveillance, Epidemiology, and End Results data linked to the U.S. Medicare data, cancer stage- and treatment-specific. Cox regression was applied to evaluate death hazard ratios of CVDs in univariable and multivariable analyses (controlling by age, TNM statuses, and 78 non-CVD comorbidities) and to investigate the effects of 128 different combinations of CVDs on patients' survival.

RESULTS

Overall, 95,167 patients with stage I (n=29,836, 31.4%), II (n=5133, 5.4%), IIIA (n=11,884, 12.5%), IIIB (n=18,020, 18.9%), and IV (n=30,294, 31.8%) NSCLC were selected. Most CVDs increased the risk of death for stages I-IIIB patients, but did not significantly impact survival of stage IV patients. The worse survival of patients was associated with comorbid heart failure, myocardial infarction, and cardiac arrhythmias that occurred during a period of follow-up: HRs up to 1.85 (p<0.001), 1.96 (p<0.05), and 1.67 (p<0.001), respectively, varying by stage and treatment. The presence of hyperlipidemia at baseline (HR down to 0.71, p<0.05) was associated with better prognosis. Having multiple co-existing CVDs significantly increased mortality for all treatments, especially for stages I and II patients treated with surgery (HRs up to 2.89, p<0.05) and stages I-IIIB patients treated with chemotherapy (HRs up to 2.59, p<0.001) and chemotherapy and radiotherapy (HRs up to 2.20, p<0.001).

CONCLUSION

CVDs impact the survival of NSCLC patients, particularly when multiple co-existing CVDs are present; the impacts vary by stage and treatment. This data should be considered in improving cancer treatment selection process for such potentially challenging patients as the elderly NSCLC patients with CVD comorbidities.

Regulation of the nongenomic actions of retinoid X receptor-α by targeting the coregulator-binding sites

Retinoid X receptor-α (RXRα), a unique member of the nuclear receptor superfamily, represents an intriguing and unusual target for pharmacologic interventions and therapeutic applications in cancer, metabolic disorders and neurodegenerative diseases. Despite the fact that the RXR-based drug Targretin (bexarotene) is currently used for treating human cutaneous T-cell lymphoma and the fact that RXRα ligands (rexinoids) show beneficial effects in the treatment of cancer and diseases, the therapeutic potential of RXRα remains unexplored. In addition to its conventional transcription regulation activity in the nucleus, RXRα can act in the cytoplasm to modulate important biological processes, such as mitochondria-dependent apoptosis, inflammation, and phosphatidylinositol 3-kinase (PI3K)/AKT-mediated cell survival. Recently, new small-molecule-binding sites on the surface of RXRα have been identified, which mediate the regulation of the nongenomic actions of RXRα by a class of small molecules derived from the nonsteroidal anti-inflammatory drug (NSAID) Sulindac. This review discusses the emerging roles of the nongenomic actions of RXRα in the RXRα signaling network, and their possible implications in cancer, metabolic and neurodegenerative disorders, as well as our current understanding of RXRα regulation by targeting alternate binding sites on its surface.

Phase I and pharmacokinetic study of bexarotene in combination with gefitinib in the third-line treatment of non-small-cell lung cancer: brief report

Gefitinib (an epidermal growth factor receptor tyrosine kinase inhibitor) and bexarotene (a rexinoid) affect similar oncogenic pathways and are both metabolized through cytochrome P450 CYP3A4. We studied the combination of bexarotene and gefitinib in the third-line treatment of advanced non-small-cell lung cancer to examine pharmacokinetic interactions and establish the maximum tolerated dose. This was a single-institution, nonrandomized, open-label, phase I clinical trial with a standard 3+3 dose escalation. Three patients were enrolled at each dose level on the basis of pharmacokinetic analysis with dose level 1 including gefitinib (Iressa) 250 mg oral daily and bexarotene (Targretin) 400 mg/m oral daily and dose level +1 including gefitinib 500 mg oral daily and bexarotene 400 mg/m oral daily. Patients received gefitinib alone for 2 weeks to allow for steady state and thereafter, bexarotene was added. In dose level 1, two of three patients had undetectable gefitinib levels at day 15 for unknown reasons. However, the peak levels on day 29 for all three patients receiving 250 mg of gefitinib with bexarotene are lower than published peak levels. Among the three patients in dose level +1, ∼40% lower gefitinib plasma concentrations were noted on day 29 compared with day 15 along with a mean 44% reduction in area under the plasma concentration-time curve from 0 to 24 h (AUC0-24). Bexarotene appears to lower the C max and AUC0-24 of gefitinib through cytochrome P450 CYP3A4. Our results have pharmacokinetic implications for ongoing trials that combine bexarotene with other small molecules in the era of personalized cancer therapy.

Headway and hurdles in the clinical development of dietary phytochemicals for cancer therapy and prevention: lessons learned from vitamin A derivatives

Accumulating epidemiologic and preclinical evidence support the pharmacologic use of a variety of dietary chemicals for the prevention and treatment of cancer. However, it will be challenging to translate these findings into routine clinical practice since phytochemicals have pleiotropic biological activities that have to be balanced for optimal efficacy without unacceptable and potentially unanticipated toxicities. Correctly matching patient populations and settings with optimal, natural product-based phytochemical therapies will require a greater understanding of the specific mechanisms underlying the efficacy, toxicity, and resistance of each agent in a variety of normal, premalignant, and malignant settings. This, in turn, necessitates continued commitment from the basic research community to guide carefully designed and informed clinical trials. The most developed class of anticancer phytochemicals consists of the derivatives of vitamin A called retinoids. Unlike other natural product chemicals currently under study, the retinoids have been extensively tested in humans. Over 30 years of clinical investigation has resulted in several disappointments, but there were some spectacular successes where certain retinoid-based protocols are now FDA-approved standard of care therapies to treat specific malignancies. Furthermore, retinoids are one of the most evaluated pharmacologic agents in the ultra-challenging setting of interventional cancer prevention. This review will summarize the development of retinoids in cancer therapy and prevention with an emphasis on currently proposed mechanisms mediating their efficacy, toxicity, and resistance.

RXRs: collegial partners

Retinoid X Receptors (RXR) were initially identified as nuclear receptors binding with stereo-selectivity the vitamin A derivative 9-cis retinoic acid, although the relevance of this molecule as endogenous activator of RXRs is still elusive. Importantly, within the nuclear receptor superfamily, RXRs occupy a peculiar place, as they are obligatory partners for a number of other nuclear receptors, thus integrating the corresponding signaling pathways. In this chapter, we describe the structural features allowing RXR to form homo- and heterodimers, and the functional consequences of this unique ability. Furthermore, we discuss the importance of studying RXR activity at a genome-wide level in order to comprehensively address the biological implications of their action that is fundamental to understand to what extent RXRs could be exploited as new therapeutic targets.

Pharmacogenetics of the nuclear hormone receptors: the missing link between environment and drug effects?

In the last decade, genetic variations in ABC/SLC transporters and phase I/II enzymes have raised pharmacogenetic markers as being predictive to the attention of researchers in the field of personalized medicine in oncology. However, it is becoming evident that the sequence variations in these genes cannot address by themselves the sharp interindividual variability in drug effects. Recently, nuclear receptors (NRs), including pregnane X receptor, constitutive androstane receptor, retinoid X receptor, farnesoid X receptor, liver X receptor, vitamin D receptor, peroxisome proliferator-activated receptors and HNF4A, have demonstrated key roles in regulating transporter and metabolic gene expression in response to xeno/endobiotics, as well as antineoplastic drugs. These findings attracted interest to the genetics of the NRs for their possible role in influencing the metabolism and pharmacological profiles of chemotherapeutics. In this review, we aim to summarize the most recent findings in the innovative field of NR pharmacogenetics and findings in how they could integrate with more traditional markers in order to improve drug treatment personalization.

The impact of both platinum-based chemotherapy and EGFR-TKIs on overall survival of patients with advanced non-small cell lung cancer

Both platinum-based doublet chemotherapy (PBC) and epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) prolong the survival of patients with advanced non-small cell lung cancer (NSCLC). In early studies, most patients underwent PBC as first-line treatment, but not all patients could afford EGFR-TKIs as second-line treatment. To understand the impact of PBC and EGFR-TKIs on NSCLC prognosis, we evaluated the association between the receipt of both regimens and overall survival (OS). Using MEDLINE and EMBASE, we identified prospective, randomized, controlled phase III clinical trials in advanced NSCLC that met the inclusion criteria: in general population with advanced NSCLC, the percentage of patients treated with both PBC and EGFR-TKIs was available in the trial and OS was reported. After collecting data from the selected trials, we correlated the percentage of patients treated with both PBC and EGFR-TKIs with the reported OS, using a weighted analysis. Fifteen phase III clinical trials—involving 11,456 adult patients in 32 arms—were included in the analysis, including 6 trials in Asian populations and 9 in non-Asian (predominantly Caucasian) populations. The OS was positively correlated with the percentage of patients treated with both PBC and EGFR-TKIs (r = 0.797, P < 0.001). The correlation was obvious in the trials in Asian populations (r = 0.936, P < 0.001) but was not statistically significant in the trials in predominantly Caucasian populations (r = 0.116, P = 0.588). These results suggest that treatment with PBC and EGFR-TKIs may provide a survival benefit to patients with advanced NSCLC, highlighting the importance of having both modalities available for therapy.

Hypertriglyceridemia in patients with metastatic breast cancer and treatment with capecitabine

Several reports have described hypertriglyceridemia (HTG) in cancer patients, including breast cancer patients treated with capecitabine (CAP). However, the exact range of HTG in patients with metastatic breast cancer (MBC) treated with CAP has clearly not been defined. A retrospective analysis on 54 patients with MBC treated with CAP longer than 2 months was conducted. HTG was defined as triglyceride blood level above 150 mg/dl. Baseline data included age, body mass index (BMI), tumour characteristics, treatment duration, concomitant treatment with lapatinib, diagnosis of dyslipidemia, and diabetes mellitus, as well as antihyperlipidemic therapy. Clinically significant HTG (triglycerides >300 mg/dl) was found in 4/54 (7%) of patients. Post-treatment HTG was associated only with concomitant treatment with lapatinib (P<0·01). Three of the patients had dyslipidemia before treatment with CAP, and one patient also had diabetes-mellitus. No HTG-related complications occurred. Clinically significant HTG in MBC patients treated with CAP may be associated with pre-existing risk factors, such as dyslipidemia or diabetes-mellitus.

The role of aldehyde dehydrogenase (ALDH) in cancer drug resistance

Chemotherapy in cancer patients is still not satisfactory because of drug resistance. The main mechanism of drug resistance results from the ability of cancer cells to actively expel therapeutic agents via transport proteins of the ABC family. ABCB1 and ABCG2 are the two main proteins responsible for drug resistance in cancers. Recent investigations indicate that aldehyde dehydrogenase (ALDH) can also be involved in drug resistance. Expression of the ABC transporters and ALDH enzymes is observed in normal stem cells, cancer stem cells and drug resistant cancers. Current chemotherapy regimens remove the bulk of the tumour but are usually not effective against cancer stem cells (CSCs) expressing ALDH. As a result, the number of ALDH positive drug resistant CSCs increases after chemotherapy. This indicates that therapies targeting drug resistant CSCs should be developed. A number of therapies targeting CSCs are currently under investigation. These therapies include differentiation therapy using different retinoic acids (RA) as simple agents or in combination with DNA methyltransferase inhibitors (DNMTi) and/or histone deacetylase inhibitors (HDACi). Therapies that target cancer stem cell signaling pathways are also under investigation. A number of natural compounds are effective against cancer stem cells and lead to decreasing numbers of ALDH positive cells and downregulation of the ABC proteins. Combinations of differentiation therapies or therapies targeting CSC signaling pathways with classical cytostatics seem promising. This review discusses the role of ALDH and ABC proteins in the development of drug resistance in cancer and current therapies designed to target CSCs.

Synthesis and SAR study of modulators inhibiting tRXRα-dependent AKT activation

RXRα represents an intriguing and unique target for pharmacologic interventions. We recently showed that Sulindac and a designed analog could bind to RXRα and modulate its biological activity, including inhibition of the interaction of an N-terminally truncated RXRα (tRXRα) with the p85α regulatory subunit of phosphatidylinositol-3-OH kinase (PI3K). Here we report the synthesis, testing and SAR of a series of novel analogs of Sulindac as potential modulators for inhibiting tRXRα-dependent AKT activation. A new compound 30 was identified to have improved biological activity.

Molecular pathways: current role and future directions of the retinoic acid pathway in cancer prevention and treatment

Retinoids and their naturally metabolized and synthetic products (e.g., all-trans retinoic acid, 13-cis retinoic acid, bexarotene) induce differentiation in various cell types. Retinoids exert their actions mainly through binding to the nuclear retinoic acid receptors (α, β, γ), which are transcriptional and homeostatic regulators with functions that are often compromised early in neoplastic transformation. The retinoids have been investigated extensively for their use in cancer prevention and treatment. Success has been achieved with their use in the treatment of subtypes of leukemia harboring chromosomal translocations. Promising results have been observed in the breast cancer prevention setting, where fenretinide prevention trials have provided a strong rationale for further investigation in young women at high risk for breast cancer. Ongoing phase III randomized trials investigating retinoids in combination with chemotherapy in non-small cell lung cancer aim to definitively characterize the role of retinoids in this tumor type. The limited treatment success observed to date in the prevention and treatment of solid tumors may relate to the frequent epigenetic silencing of RARβ. Robust evaluation of RARβ and downstream genes may permit optimized use of retinoids in the solid tumor arena.

Lung cancer chemoprevention: difficulties, promise and potential agents?

INTRODUCTION

In a variety of cancers there is evidence that specific regimens can prevent or significantly delay the development of cancer. Thus, for breast cancer (ER+) use of SERMs or aromatase inhibitors can substantially decrease tumor incidence. For cervical cancer, HPV vaccination will inhibit long term cancer incidence. For colon cancer, the second greatest cancer killer, administration of aspirin and other NSAIDs decreases advanced colon adenomas in Phase II trials and epidemiologic data support their ability to prevent colon cancer. To date prevention trials in the area of lung cancer have shown minimal efficacy.

AREAS COVERED

The paper examines and discusses in greater detail certain promising agents which the authors have tested either preclinically and or in early phase clinical trials. These agents include RXR agonists, EGFr inhibitors, NSAIDs and Triterpenoids. Other agents including glucocorticoids, pioglitazone and iloprost are briefly mentioned. In addition, the paper presents various types of potential Phase II lung cancer prevention trials and describes their strengths and weaknesses. The potential use of various biomarkers as endpoints in trials e.g. histopathology, non-specific biomarkers (e.g., Ki67, cyclin D expression, apoptosis) and molecular biomarkers (e.g. specific phosphorylated proteins, gene expression etc.) is presented. Finally, we examine at least one approach, the use of aerosols, which may diminish the systemic toxicity associated with certain of these agents.

EXPERT OPINION

The manuscript presents: a) a number of promising agents which appear applicable to further Phase II prevention trials; b) approaches to defining potential preventive agents as well; c) approaches which might mitigate the side effects associated with potential agents most specifically the use of aerosols. Finally, we discuss biomarker studies both preclinical and clinical which might help support potential Phase II trials. The particular appeal to the preclinical studies is that they can be followed to a tumor endpoint. We hope that this will give the reader further background and allow one to appreciate the potential and some of the hurdles associated with lung cancer chemoprevention.

Advances in drug design with RXR modulators

INTRODUCTION

Retinoid X receptors (subtypes RXRα or NR2B1, RXRβ or NR2B2 and RXRγ or NR2B3, which originate from three distinct genes) are promiscuous partners with heterodimeric associations to other members of the Nuclear Receptor (NR) superfamily. Some of the heterodimers are "permissive" and transcriptionally active in the presence of either an RXR ligand ("rexinoid") or a NR partner ligand, whereas others are "non-permissive" and unresponsive to rexinoids alone. In rodent models, rexinoids and partner agonists (mainly PPARγ, LXR, FXR) produce beneficial effects on insulin sensitization, diabetes and obesity, but secondary effects have also been noted, such as a raise in tryglyceride levels, supression of the thyroid hormone axis and induction of hepatomegaly.

AREAS COVERED

The authors review recent advances in rexinoid design, including further optimization of known scaffolds, and the discovery of novel RXR modulators by virtual ligand screening or from bioactive natural products. The understanding of rexinoid functions in permissive and non-permissive heterodimers is firmly based on structural knowledge. By strenghtening or disrupting the interaction surface with coregulators rexinoids exert agonist or (partial) antagonist activities. The activity state of the heterodimer can also be fine-tuned by the cellular context and the nature of coregulators.

EXPERT OPINION

The synthetic chemistry toolbox has provided a panel of agonists, partial (ant)agonists and/or heterodimer-selective rexinoids starting from existing, naturally occurring or serendipitously discovered scaffolds. These compounds have an unexplored therapeutic potential that might overcome some of the current limitations of rexinoids in therapy, such as hypertriglyceridemia.

Smoking history as a predictive factor of treatment response in advanced non-small-cell lung cancer: a systematic review

Recent trials in patients with advanced non-small-cell lung cancer (NSCLC) suggest that nonsmokers may benefit more from epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI) therapy than will smokers. The aim of this systematic review was to assess smoking history as a predictive factor for treatment outcomes in patients with NSCLC. Relevant published literature was identified through systematic searches of databases (MEDLINE, EMBASE, Cochrane Library), oncology and thoracic journals, and abstracts from major oncology conferences using prespecified criteria. Articles reporting treatment outcomes (overall survival [OS], progression-free survival [PFS], and/or response rate) in smoking history subgroups from randomized controlled trials of targeted therapy and/or chemotherapy were reviewed. Data from 30 trials (32 articles, 4 abstracts) were included. Of these, 23 trials tested first-line therapy. Treatment arms included EGFR TKIs (13 trials), EGFR monoclonal antibodies (2 trials), non-EGFR targeted treatments (9 trials), chemotherapy (27 trials), and placebo or best supportive care only (3 trials). Smoking history definitions and analyses of its effect on treatment outcomes varied widely. Only 11 trials reported testing for a treatment-by-smoking history interaction. The available evidence supports but does not confirm smoking history as a predictive factor for the response to TKIs, particularly in previously treated patients. The evidence does not support smoking history as a predictor of response to non-EGFR-targeted therapies or chemotherapy. Smoking history and its effect on treatment response are inadequately reported. More rigorous collection, analysis, and reporting may clarify whether smoking history is a predictor of treatment response in advanced NSCLC.

The BATTLE to personalize lung cancer prevention through reverse migration

Agents can enter clinical development for cancer prevention either initially or after previous development for a different indication, such as arthritis, with both approaches consuming many years of development before an agent is fully evaluated for cancer prevention. We propose the following, third approach: reverse migration, that is, importing agents, targets, and study designs to personalize interventions and concepts developed in advanced cancer to the setting of cancer prevention. Importing these "ready-made" features from therapy will allow reverse migration to streamline preventive agent development. We recently reported the Biomarker-integrated Approaches of Targeted Therapy for Lung Cancer Elimination (BATTLE) trial of personalized lung cancer therapy and now propose the reverse migration development of personalized lung cancer prevention based on the BATTLE model.

The effect of bexarotene on atorvastatin pharmacokinetics: results from a phase I trial of bexarotene plus chemotherapy in patients with advanced non-small cell lung cancer

PURPOSE

Bexarotene (Targretin(®) capsules) is a retinoid-X-receptor agonist and an inducer of CYP3A4-mediated metabolism. This phase I trial evaluated the pharmacokinetic (PK) and drug-drug interactions of bexarotene with chemotherapy and a lipid-lowering agent (atorvastatin or fenofibrate). This trial was run in parallel with phase III trials of the combinations to determine whether repeated doses of bexarotene capsules affect the pharmacokinetics (PK) of the chemotherapeutic or the lipid-lowering agents.

METHODS

Patients (n = 48) with advanced non-small cell lung cancer were treated with repetitive cycles of either paclitaxel/carboplatin or cisplatin/vinorelbine chemotherapy, bexarotene (400 mg/m(2)/day) administered continuously starting on day 4 of chemotherapy, and a lipid-lowering drug, either atorvastatin or fenofibrate, starting at least 5 days before chemotherapy due to hypertriglyceridemia induced by bexarotene. Extensive plasma sampling to characterize the PK profiles of the lipid-lowering drugs, relevant chemotherapy agents was performed on day 1 (without bexarotene) and during chemotherapy cycles 2 or 3 (with bexarotene).

RESULTS

Here, we report the drug-drug interactions between the lipid-lowering agents and bexarotene. Mean atorvastatin clearance and dose-corrected AUC values were reduced by nearly 50% with the addition of concomitant bexarotene. As fenofibrate was less effective at controlling hypertriglyceridemia, too few patients received this agent to make any meaningful conclusions about drug-drug interactions.

CONCLUSIONS

A drug-drug interaction was seen in this trial with bexarotene co-administration leading to a significant reduction in the AUC of atorvastatin. The likely mechanism for this interaction is through induction of CYP3A4 by bexarotene given the role of this enzyme in the metabolism of atorvastatin. Knowledge of this interaction is important for optimizing lipid management with atorvastatin for patients receiving bexarotene.

A phase I pharmacokinetic study of bexarotene with paclitaxel and carboplatin in patients with advanced non-small cell lung cancer (NSCLC)

PURPOSE

Preclinical data suggest that the synthetic retinoid bexarotene may be an effective chemopreventive agent and that it may act synergistically in combination with platinum-based chemotherapy. The primary objective of this study was to determine whether repeated doses of bexarotene capsules affect pharmacokinetic parameters of paclitaxel or carboplatin in patients with advanced non-small cell lung cancer.

METHODS

Patients received treatment with paclitaxel (200 mg/m(2)) and carboplatin to provide a target AUC of 6 mg min/mL (day 1) every 3 weeks. Continuous oral bexarotene therapy (400 mg/m(2)/day) was initiated on Day 4, and patients started lipid-lowering therapy prior to beginning chemotherapy. Blood sampling to characterize the pharmacokinetic profiles of the chemotherapeutic agents with or without bexarotene was performed during cycle 1 (without concomitant bexarotene) and during cycle 2 (with concomitant bexarotene).

RESULTS

An analysis of drug concentration data from 16 patients indicated that bexarotene did not affect the pharmacokinetics of paclitaxel, free carboplatin, or total carboplatin concentrations. However, both maximal plasma concentrations and total exposure of bexarotene increased by 80% in the presence of paclitaxel-carboplatin by an, as of yet, unexplained mechanism. The toxicities observed resembled those of either the chemotherapy regimen or bexarotene alone, and there was no evidence for an enhancement of any drug-related toxicity with the combined treatment.

CONCLUSIONS

The administration of bexarotene, paclitaxel, and carboplatin is feasible and safe; however, the increased bexarotene plasma concentrations and exposure warrant further investigation if this combination is to be utilized clinically.