Bexarotene and erlotinib for aerodigestive tract cancer

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.

Drug Combinatorial Therapies for the Treatment of KRAS Mutated Lung Cancers

KRAS is the most common oncogene to be mutated in lung cancer, and therapeutics directly targeting KRAS have proven to be challenging. The mutations of KRAS are associated with poor prognosis, and resistance to both adjuvant therapy and targeted EGFR TKI. EGFR TKIs provide significant clinical benefit for patients whose tumors bear EGFR mutations. However, tumors with KRAS mutations rarely respond to the EGFR TKI therapy. Thus, combination therapy is essential for the treatment of lung cancers with KRAS mutations. EGFR TKI combined with inhibitors of MAPKs, PI3K/mTOR, HDAC, Wee1, PARP, CDK and Hsp90, even miRNAs and immunotherapy, were reviewed. Although the effects of the combination vary, the combined therapeutics are one of the best options at present to treat KRAS mutant lung 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.

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.

All-trans-retinoic acid antagonizes the Hedgehog pathway by inducing patched

Male germ cell tumors (GCTs) are a model for a curable solid tumor. GCTs can differentiate into mature teratomas. Embryonal carcinomas (ECs) represent the stem cell compartment of GCTs and are the malignant counterpart to embryonic stem (ES) cells. GCTs and EC cells are useful to investigate differentiation therapy and chemotherapy response. This study explored mechanistic interactions between all-trans-retinoic acid (RA), which induces differentiation of EC and ES cells, and the Hedgehog (Hh) pathway, a regulator of self-renewal and proliferation. RA was found to induce mRNA and protein expression of Patched 1 (Ptch1), the Hh ligand receptor and negative regulator of this pathway. PTCH1 is also a target gene of Hh signaling through Smoothened (Smo) activation. Yet, this observed RA-mediated Ptch1 induction was independent of Smo. It occurred despite co-treatment with RA and Smo inhibitors. Retinoid induction of Ptch1 also occurred in other RA-responsive cancer cell lines and in normal ES cells. Notably, this enhanced Ptch1 expression was preceded by induction of the homeobox transcription factor Meis1, a direct RA target. Direct interaction between Meis1 and Ptch1 was confirmed using chromatin immunoprecipitation assays. To establish the translational relevance of this work, Ptch1 expression was shown to be deregulated in human ECs relative to mature teratoma and the normal seminiferous tubule. Taken together, these findings reveal a previously unrecognized mechanism through which RA can inhibit the Hh pathway via Ptch1 induction. Engaging this pathway is a new way to repress the Hh pathway that can be translated into the cancer clinic.

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.

A phase I, pharmacokinetic, and pharmacodynamic study of panobinostat, an HDAC inhibitor, combined with erlotinib in patients with advanced aerodigestive tract tumors

PURPOSE

Panobinostat, a histone deacetylase (HDAC) inhibitor, enhances antiproliferative activity in non-small cell lung cancer (NSCLC) cell lines when combined with erlotinib. We evaluated this combination in patients with advanced NSCLC and head and neck cancer.

EXPERIMENTAL DESIGN

Eligible patients were enrolled in a 3+3 dose-escalation design to determine the maximum tolerated dose (MTD) of twice weekly panobinostat plus daily erlotinib at four planned dose levels (DL). Pharmacokinetics, blood, fat pad biopsies (FPB) for histone acetylation, and paired pre and posttherapy tumor biopsies for checkpoint kinase 1 (CHK1) expression were assessed.

RESULTS

Of 42 enrolled patients, 33 were evaluable for efficacy. Dose-limiting toxicities were prolonged-QTc and nausea at DL3. Adverse events included fatigue and nausea (grades 1-3), and rash and anorexia (grades 1-2). Disease control rates were 54% for NSCLC (n = 26) and 43% for head and neck cancer (n = 7). Of 7 patients with NSCLC with EGF receptor (EGFR) mutations, 3 had partial response, 3 had stable disease, and 1 progressed. For EGFR-mutant versus EGFR wild-type patients, progression-free survival (PFS) was 4.7 versus 1.9 months (P = 0.43) and overall survival was 41 (estimated) versus 5.2 months (P = 0.39). Erlotinib pharmacokinetics was not significantly affected. Correlative studies confirmed panobinostat's pharmacodynamic effect in blood, FPB, and tumor samples. Low CHK1 expression levels correlated with PFS (P = 0.006) and response (P = 0.02).

CONCLUSIONS

We determined MTD at 30 mg (panobinostat) and 100 mg (erlotinib). Further studies are needed to further explore the benefits of HDAC inhibitors in patients with EGFR-mutant NSCLC, investigate FPB as a potential surrogate source for biomarker investigations, and validate CHK1's predictive role.

Targeting epidermal growth factor receptor signaling in the treatment of head and neck cancer

In this review, key aspects of epidermal growth factor receptor (EGFR) biology and the fruitful translation of these fundamental findings into recent treatment advances in head and neck squamous cell cancer (HNSCC) are highlighted. In contrast to a number of contemporary reviews of the EGFR, many of which focus on colorectal and nonsmall cell lung cancer, this review discusses the EGFR as a validated therapeutic target in HNSCC. Recent data confirm a survival advantage for the addition of the anti-EGFR monoclonal antibody cetuximab to definitive radiation therapy in locoregionally advanced HNSCC patients, as well as palliative benefits for patients with incurable recurrent and metastatic HNSCC. Small-molecule EGFR tyrosine kinase inhibitors also show considerable promise in this disease, both alone and in combination with radiation and chemotherapy. Both classes of anti-EGFR agent are generally well tolerated, with side effects (notably skin rash) that are distinct from the toxicities of conventional chemotherapy. Ongoing clinical trials will more clearly define the role for EGFR inhibitors in all treatment phases of HNSCC.

Phase II trial of dose-dense chemotherapy followed by dose-intense erlotinib for patients with newly diagnosed metastatic non-small cell lung cancer

This phase II study investigated dose-intense erlotinib maintenance after dose-dense chemotherapy for patients with metastatic non-small cell lung cancer and examined two cell cycle biomarkers. Patients with newly diagnosed metastatic non-small cell lung cancer received docetaxel 75 mg/m² and cisplatin 75 mg/m² on day 1 and pegfilgrastim on day 2 every 14 days for four cycles. Patients then received erlotinib with initial doses based on smoking status. Doses were increased in 75 mg increments every two weeks depending on toxicities until each patient's maximal tolerable dose (MTD) was achieved. Cyclin D1 and D3 biomarkers were measured by immunohistochemistry. The objectives of the study were to evaluate time to progression (TTP) and overall survival (OS) for the entire population and biomarker subgroups. Forty-five patients were enrolled. Intra-patient erlotinib MTD ranged from 0 to 525 mg. Median MTD achieved in smokers was higher than in non-smokers (300 vs. 150 mg; P=0.019). TTP for the entire cohort was not significantly improved compared to historical controls. Patients with high cyclin D1 expressing tumors demonstrated improved TTP on erlotinib (8.2 vs. 4.7 months; hazard ratio, 4.1; 95% CI, 1.6–0.6; P=0.003) and improved OS (20.5 vs. 8.0 months; hazard ratio 2.8; 95% CI, 1.2–6.3; P=0.016). Intratumoral cyclin D3 expression did not impact clinical outcomes. Current smokers but not former smokers exhibit a higher erlotinib MTD. High cyclin D1 expression was associated with favorable TTP and OS.

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.

The molecular pathogenesis of head and neck squamous cell carcinoma

Squamous cell carcinoma of the head and neck (HNSCC) is a relatively common human cancer characterized by high morbidity, high mortality, and few therapeutic options outside of surgery, standard cytotoxic chemotherapy, and radiation. Although the most important risk factors are tobacco use and alcohol consumption, the disease is also linked to infection with high-risk types of human papilloma viruses (HPVs). Recent genetic analyses have yielded new insights into the molecular pathogenesis of this disease. Overall, while somatic activating mutations within classical oncogenes including PIK3CA and RAS occur in HNSCC, they are relatively uncommon. Instead genetic data point to a contribution of multiple tumor suppressor pathways, including p53, Rb/INK4/ARF, and Notch, in tumor initiation, progression, and maintenance. The increasingly refined knowledge of HNSCC genetics, combined with ever-more-sophisticated animal models and newer drug targeting strategies, should promote novel therapeutic approaches and improved disease outcomes.

Evidence for the ubiquitin protease UBP43 as an antineoplastic target

New pharmacologic targets are needed for lung cancer. One candidate pathway to target is composed of the E1-like ubiquitin-activating enzyme (UBE1L) that associates with interferon-stimulated gene 15 (ISG15), which complexes with and destabilizes cyclin D1. Ubiquitin protease 43 (UBP43/USP18) removes ISG15 from conjugated proteins. This study reports that gain of UBP43 stabilized cyclin D1, but not other D-type cyclins or cyclin E. This depended on UBP43 enzymatic activity; an enzymatically inactive UBP43 did not affect cyclin D1 stability. As expected, small interfering RNAs that reduced UBP43 expression also decreased cyclin D1 levels and increased apoptosis in a panel of lung cancer cell lines. Forced cyclin D1 expression rescued UBP43 apoptotic effects, which highlighted the importance of cyclin D1 in conferring this. Short hairpin RNA-mediated reduction of UBP43 significantly increased apoptosis and reduced murine lung cancer growth in vitro and in vivo after transplantation of these cells into syngeneic mice. These cells also exhibited increased response to all-trans-retinoic acid, interferon, or cisplatin treatments. Notably, gain of UBP43 expression antagonized these effects. Normal-malignant human lung tissue arrays were examined independently for UBP43, cyclin D1, and cyclin E immunohistochemical expression. UBP43 was significantly (P < 0.01) increased in the malignant versus normal lung. A direct relationship was found between UBP43 and cyclin D1 (but not cyclin E) expression. Differential UBP43 expression was independently detected in a normal-malignant tissue array with diverse human cancers. Taken together, these findings uncovered UBP43 as a previously unrecognized antineoplastic target.

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.

Bexarotene plus erlotinib suppress lung carcinogenesis independent of KRAS mutations in two clinical trials and transgenic models

The rexinoid bexarotene represses cyclin D1 by causing its proteasomal degradation. The epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI) erlotinib represses cyclin D1 via different mechanisms. We conducted a preclinical study and 2 clinical/translational trials (a window-of-opportunity and phase II) of bexarotene plus erlotinib. The combination repressed growth and cyclin D1 expression in cyclin-E- and KRAS/p53-driven transgenic lung cancer cells. The window-of-opportunity trial in early-stage non-small-cell lung cancer (NSCLC) patients (10 evaluable), including cases with KRAS mutations, repressed cyclin D1 (in tumor biopsies and buccal swabs) and induced necrosis and inflammatory responses. The phase II trial in heavily pretreated, advanced NSCLC patients (40 evaluable; a median of two prior relapses per patient (range, 0-5); 21% with prior EGFR-inhibitor therapy) produced three major clinical responses in patients with prolonged progression-free survival (583-, 665-, and 1,460-plus days). Median overall survival was 22 weeks. Hypertriglyceridemia was associated with an increased median overall survival (P = 0.001). Early PET (positron emission tomographic) response did not reliably predict clinical response. The combination was generally well tolerated, with toxicities similar to those of the single agents. In conclusion, bexarotene plus erlotinib was active in KRAS-driven lung cancer cells, was biologically active in early-stage mutant KRAS NSCLC, and was clinically active in advanced, chemotherapy-refractory mutant KRAS tumors in this study and previous trials. Additional lung cancer therapy or prevention trials with this oral regimen are warranted.

Cyclin D as a therapeutic target in cancer

Cyclin D1, and to a lesser extent the other D-type cyclins, is frequently deregulated in cancer and is a biomarker of cancer phenotype and disease progression. The ability of these cyclins to activate the cyclin-dependent kinases (CDKs) CDK4 and CDK6 is the most extensively documented mechanism for their oncogenic actions and provides an attractive therapeutic target. Is this an effective means of targeting the cyclin D oncogenes, and how might the patient subgroups that are most likely to benefit be identified?

Vitamin A and retinoid derivatives for lung cancer: a systematic review and meta analysis

BACKGROUND

Despite reported antiproliferative activity of vitamin A and its common use for cancer, there is no comprehensive synthesis of its safety and efficacy in lung cancers. To address this issue we conducted a systematic review of the safety and efficacy of vitamin A for the treatment and prevention of lung cancers.

METHODS AND FINDINGS

Two independent reviewers searched six electronic databases from inception to July 2009 for clinical, observational, and preclinical evidence pertaining to the safety and efficacy of vitamin A and related retinoids for lung cancers. 248 studies were included for full review and analysis. Five RCTs assessed treatment of lung cancers, three assessed primary prevention, and three looked at secondary prevention of lung cancers. Five surrogate studies, 26 phase I/II, 32 observational, and 67 preclinical studies were also included. 107 studies were included for interactions between vitamin A and chemo- or radiation-therapy. Although some studies demonstrated benefits, there was insufficient evidence overall to support the use of vitamin A or related retinoids for the treatment or prevention of lung cancers. Retinyl palmitate combined with beta carotene increased risk of lung cancer in smokers in the large CARET trial. Pooling of three studies pertaining to treatment and three studies on secondary prevention revealed no significant effects on response rate, second primary tumor, recurrence, 5-year survival, and mortality. There was a small improvement in event free survival associated with vitamin A compared to controls, RR 1.24 (95% CI 1.13-1.35). The synthetic rexinoid bexarotene increased survival significantly among a subset of patients in two RCTs (p<0.014, <0.087).

CONCLUSIONS

There is a lack of evidence to support the use of naturally occurring retinoids for the treatment and prevention of lung cancers. The rexinoid bexarotene may hold promise for use among a subset of patients, and deserves further study.

Cotargeting cyclin D1 starts a new chapter in lung cancer prevention and therapy

Lung cancer has limited effective therapy and no effective prevention. Cytotoxic chemotherapy has not improved when combined with the epidermal growth factor receptor (EGFR) inhibitor erlotinib (standard lung cancer therapy) or with the rexinoid bexarotene. Combining erlotinib and bexarotene, however, to cotarget cyclin D1 via the retinoid X receptor and EGFR was active preclinically in KRAS-driven lung cancer cells derived from transgenic mice and in two clinical studies in lung cancer (including wild-type EGFR tumors, with or without KRAS mutations), as reported in this issue of the journal by Dragnev and colleagues (beginning on page 818). These results, along with closely related clinical results of the BATTLE program, support the promise of this cotargeting approach for lung cancer prevention and therapy and of cyclin D1 as a predictive, personalizing marker for it.

The BATTLE trial: personalizing therapy for lung cancer

The Biomarker-integrated Approaches of Targeted Therapy for Lung Cancer Elimination (BATTLE) trial represents the first completed prospective, biopsy-mandated, biomarker-based, adaptively randomized study in 255 pretreated lung cancer patients. Following an initial equal randomization period, chemorefractory non-small cell lung cancer (NSCLC) patients were adaptively randomized to erlotinib, vandetanib, erlotinib plus bexarotene, or sorafenib, based on relevant molecular biomarkers analyzed in fresh core needle biopsy specimens. Overall results include a 46% 8-week disease control rate (primary end point), confirm prespecified hypotheses, and show an impressive benefit from sorafenib among mutant-KRAS patients. BATTLE establishes the feasibility of a new paradigm for a personalized approach to lung cancer clinical trials.

SIGNIFICANCE

The BATTLE study is the first completed prospective, adaptively randomized study in heavily pretreated NSCLC patients that mandated tumor profiling with "real-time" biopsies, taking a substantial step toward realizing personalized lung cancer therapy by integrating real-time molecular laboratory findings in delineating specific patient populations for individualized treatment.

Quantitative automated microscopy (QuAM) elucidates growth factor specific signalling in pain sensitization

Background

Dorsal root ganglia (DRG)-neurons are commonly characterized immunocytochemically. Cells are mostly grouped by the experimenter's eye as "marker-positive" and "marker-negative" according to their immunofluorescence intensity. Classification criteria remain largely undefined. Overcoming this shortfall, we established a quantitative automated microscopy (QuAM) for a defined and multiparametric analysis of adherent heterogeneous primary neurons on a single cell base.

The growth factors NGF, GDNF and EGF activate the MAP-kinase Erk1/2 via receptor tyrosine kinase signalling. NGF and GDNF are established factors in regeneration and sensitization of nociceptive neurons. If also the tissue regenerating growth factor, EGF, influences nociceptors is so far unknown. We asked, if EGF can act on nociceptors, and if QuAM can elucidate differences between NGF, GDNF and EGF induced Erk1/2 activation kinetics. Finally, we evaluated, if the investigation of one signalling component allows prediction of the behavioral response to a reagent not tested on nociceptors such as EGF.

Results

We established a software-based neuron identification, described quantitatively DRG-neuron heterogeneity and correlated measured sample sizes and corresponding assay sensitivity. Analysing more than 70,000 individual neurons we defined neuronal subgroups based on differential Erk1/2 activation status in sensory neurons. Baseline activity levels varied strongly already in untreated neurons. NGF and GDNF subgroup responsiveness correlated with their subgroup specificity on IB4(+)- and IB4(-)-neurons, respectively. We confirmed expression of EGF-receptors in all sensory neurons. EGF treatment induced STAT3 translocation into the nucleus. Nevertheless, we could not detect any EGF induced Erk1/2 phosphorylation. Accordingly, intradermal injection of EGF resulted in a fundamentally different outcome than NGF/GDNF. EGF did not induce mechanical hyperalgesia, but blocked PGE₂-induced sensitization.

Conclusions

QuAM is a suitable if not necessary tool to analyze activation of endogenous signalling in heterogeneous cultures. NGF, GDNF and EGF stimulation of DRG-neurons shows differential Erk1/2 activation responses and a corresponding differential behavioral phenotype. Thus, in addition to expression-markers also signalling-activity can be taken for functional subgroup differentiation and as predictor of behavioral outcome. The anti-nociceptive function of EGF is an intriguing result in the context of tissue damage but also for understanding pain resulting from EGF-receptor block during cancer therapy.

Treatment for Barrett's oesophagus

BACKGROUND

Treatments for Barrett's oesophagus, the precursor lesion of adenocarcinoma, are available but whether these therapies effectively prevent the development of adenocarcinoma, and in some cases eradicate the Barrett's oesophagus segment, remains unclear.

OBJECTIVES

To summarise, quantify and compare the efficacy of pharmacological, surgical and endoscopic treatments for the eradication of dysplastic and non-dysplastic Barrett's oesophagus and prevention of these states from progression to adenocarcinoma.

SEARCH STRATEGY

We searched CENTRAL (The Cochrane Library 2004, issue 4), MEDLINE (1966 to June 2008) and EMBASE (1980 to June 2008).

SELECTION CRITERIA

Randomised controlled trials (RCTs) comparing medical, endoscopic or non-resectional surgical treatments for Barrett's oesophagus. The primary outcome measures were complete eradication of Barrett's and dysplasia at 12 months, and reduction in the number of patients progressing to cancer at five years or latest time point.

DATA COLLECTION AND ANALYSIS

Three authors independently extracted data and assessed the quality of the trials included in the analysis.

MAIN RESULTS

Sixteen studies, including 1074 patients, were included. The mean number of participants in the studies was small (n = 49; range 8 to 208). Most studies did not report on the primary outcomes. Medical and surgical interventions to reduce symptoms and sequelae of gastro-oesophageal reflux disease (GORD) did not induce significant eradication of Barrett's oesophagus or dysplasia. Endoscopic therapies (photodynamic therapy (PDT with aminolevulinic acid or porfimer sodium), argon plasma coagulation (APC) and radiofrequency ablation (RFA)) all induced regression of Barrett's oesophagus and dysplasia. The data for photodynamic therapy were heterogeneous with a mean eradication rate of 51% for Barrett's oesophagus and between 56% and 100% for dysplasia, depending on the treatment regimens. The variation in photodynamic therapy eradication rates for dysplasia was dependent on the drug, source and dose of light. Radiofrequency ablation resulted in eradication rates of 82% and 94% for Barrett's oesophagus and dysplasia respectively, compared to a sham treatment. Endoscopic treatments were generally well tolerated, however all were associated with some buried glands, particularly following argon plasma coagulation and photodynamic therapy, as well as photosensitivity and strictures induced by porfimer sodium based photodynamic therapy in particular.

AUTHORS' CONCLUSIONS

Despite their failure to eradicate Barrett's oesophagus, the role of medical and surgical interventions to reduce the troubling symptoms and sequelae of GORD is not questioned. Whether therapies for GORD reduce the cancer risk is not yet known. Ablative therapies have an increasing role in the management of dysplasia within Barrett's and current data would favour the use of radiofrequency ablation compared with photodynamic therapy. Radiofrequency ablation has been shown to yield significantly fewer complications than photodynamic therapy and is very efficacious at eradicating both dysplasia and Barrett's itself. However, long-term follow-up data are still needed before radiofrequency ablation can be used in routine clinical care without the need for very careful post-treatment surveillance. More clinical trial data and in particular randomised controlled trials are required to assess whether or not the cancer risk is reduced in routine clinical practice.

Bexarotene: a promising anticancer agent

Retinoids are biologically active derivatives of vitamin A, which play essential roles in embryonic or adult cell behavior modulating cell proliferation, differentiation and apoptosis. The biologic effects of retinoids are mediated by two distinct families of intracellular receptors: retinoid acid receptors (RARs)-α, -β and -γ and retinoid X receptors (RXR)-α, -β and -γ. Bexarotene is a selective RXR agonist, which exerts its effects in blocking cell cycle progression, inducing apoptosis and differentiation, preventing multidrug resistance, and inhibiting angiogenesis and metastasis, making it a promising chemopreventive agent against cancer.

UBE1L causes lung cancer growth suppression by targeting cyclin D1

UBE1L is the E1-like ubiquitin-activating enzyme for the IFN-stimulated gene, 15-kDa protein (ISG15). The UBE1L-ISG15 pathway was proposed previously to target lung carcinogenesis by inhibiting cyclin D1 expression. This study extends prior work by reporting that UBE1L promotes a complex between ISG15 and cyclin D1 and inhibited cyclin D1 but not other G1 cyclins. Transfection of the UBE1L-ISG15 deconjugase, ubiquitin-specific protein 18 (UBP43), antagonized UBE1L-dependent inhibition of cyclin D1 and ISG15-cyclin D1 conjugation. A lysine-less cyclin D1 species was resistant to these effects. UBE1L transfection reduced cyclin D1 protein but not mRNA expression. Cycloheximide treatment augmented this cyclin D1 protein instability. UBE1L knockdown increased cyclin D1 protein. UBE1L was independently retrovirally transduced into human bronchial epithelial and lung cancer cells. This reduced cyclin D1 expression and clonal cell growth. Treatment with the retinoid X receptor agonist bexarotene induced UBE1L and reduced cyclin D1 immunoblot expression. A proof-of-principle bexarotene clinical trial was independently examined for UBE1L, ISG15, cyclin D1, and Ki-67 immunohistochemical expression profiles in pretreatment versus post-treatment tumor biopsies. Increased UBE1L with reduced cyclin D1 and Ki-67 expression occurred in human lung cancer when a therapeutic bexarotene intratumoral level was achieved. Thus, a mechanism for UBE1L-mediated growth suppression was found by UBE1L-ISG15 preferentially inhibiting cyclin D1. Molecular therapeutic implications are discussed.

The rexinoid LG100268 and the synthetic triterpenoid CDDO-methyl amide are more potent than erlotinib for prevention of mouse lung carcinogenesis

Female A/J mice injected with the carcinogen vinyl carbamate develop atypical adenomatous hyperplasias in lungs 4 weeks after injection with the carcinogen. The number and severity of tumors then increase over time, making these mice a useful model for evaluating potential chemopreventive agents. The rexinoid LG100268 (LG268), a selective ligand for the retinoid X receptor, and the methyl amide of the synthetic triterpenoid 2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oic acid (CDDO) both significantly reduced the number, size, and severity of the histopathology of lung tumors in female A/J mice when fed in diet for 14 to 20 weeks. The total tumor burden was 85% to 87% lower in mice fed LG268 and CDDO-MA than in controls, and the percentage of high-grade tumors decreased from 59% in the controls to 25% or 30% with CDDO-MA and LG268. Erlotinib, which is used to treat lung cancer patients and is an inhibitor of the epidermal growth factor receptor, was less effective in this model. Immunohistochemical staining of geminin, a marker of cell cycle progression, was higher in lung sections from control mice than in mice treated with LG268. Because rexinoids and triterpenoids signal through different biological pathways, they should be tested in combination for the prevention of lung cancer.

Synergistic inhibition of ErbB signaling by combined treatment with seliciclib and ErbB-targeting agents

PURPOSE

The aims of this study were to investigate whether the cyclin-dependent kinase inhibitor seliciclib could synergize with agents that target ErbB receptors and to elucidate the molecular mechanism of the observed synergy.

EXPERIMENTAL DESIGN

Synergy between seliciclib and ErbB receptor targeted agents was investigated in various cell lines using the Calcusyn median effect model. The molecular mechanism of the observed synergy was studied in cultured cells, and the combination of seliciclib and the epidermal growth factor receptor (EGFR) inhibitor erlotinib was evaluated in an H358 xenograft model.

RESULTS

Seliciclib synergized with the anti-HER2 antibody trastuzumab in a breast cancer cell line, which overexpresses the HER2 receptor, and with the erlotinib analogue AG1478 in non-small cell lung cancer cell lines. In the H358 non-small cell lung cancer cell line, synergy involved decreased signaling from the EGFR, with AG1478 directly inhibiting kinase activity while seliciclib decreased the levels of key components of the receptor signaling pathway, resulting in enhanced loss of phosphorylated extracellular signal-regulated kinase and cyclin D1. The combination of seliciclib and erlotinib was evaluated further in an H358 xenograft and shown to be significantly more active than either agent alone. An enhanced loss of cyclin D1 was also seen in vivo.

CONCLUSIONS

This is the first report that investigates combining seliciclib with an EGFR inhibitor. The combination decreased signaling from the EGFR in vitro and in vivo and was effective in cell lines containing either wild-type or mutant EGFR, suggesting that it may expand the range of tumors that respond to erlotinib, and therefore, such combinations are worth exploring in the clinic.

Cyclin degradation for cancer therapy and chemoprevention

Cancer is characterized by uncontrolled cell division resulting from multiple mutagenic events. Cancer chemoprevention strategies aim to inhibit or reverse these events using natural or synthetic pharmacologic agents. Ideally, this restores normal growth control mechanisms. Diverse classes of compounds have been identified with chemopreventive activity. What unites many of them is an ability to inhibit the cell cycle by specifically modulating key components. This delays division long enough for cells to respond to mutagenic damage. In some cases, damage is repaired and in others cellular damage is sufficient to trigger apoptosis. It is now known that pathways responsible for targeting G1 cyclins for proteasomal degradation can be engaged pharmacologically. Emergence of induced cyclin degradation as a target for cancer therapy and chemoprevention in pre-clinical models is discussed in this article. Evidence for cyclin D1 as a molecular pharmacologic target and biological marker for clinical response is based on experience of proof of principle trials.

Targeting the epidermal growth factor receptor in high-grade astrocytomas

OPINION STATEMENT

High-grade astrocytomas, including glioblastoma multiforme (GBM) and anaplastic astrocytoma (AA), are the most common and aggressive primary malignant brain tumors in adults. Despite improvements in survival with the addition of temozolomide to radiation in the adjuvant setting, the prognosis of patients affected by these tumors remains relatively poor. One approach to improve outcomes in these patients is to target the epidermal growth factor receptor (EGFR). EGFR-targeted therapy is a rational approach since EGFR overexpression and mutant EGFRvIII expression occur in approximately 50% of patients with GBM. Unfortunately, monotherapy with anti-EGFR agents in malignant gliomas has not provided the dramatic results sometimes seen with other targeted therapies, such as imatinib in chronic myelogenous leukemia. Anti-EGFR agents currently being studied in malignant gliomas include the tyrosine kinase inhibitors (TKI), monoclonal antibodies (MAb), and anti-EGFR vaccines. Of all these agents, the tyrosine kinase inhibitors-which include erlotinib and gefitinib-have been the most extensively tested in clinical trials. Retrospective analyses have highlighted co-expression of EGFRvIII and wild-type PTEN (phosphatase and tensin homologue deleted in chromosome 10) as a significant predictor of EGFR TKI response in patients with GBM. As the EGFR signaling pathway is exceptionally complex, newer approaches targeting multiple points in the pathway are being developed to improve treatment efficacy.

Screening for ligands of human retinoid X receptor-alpha using ultrafiltration mass spectrometry

Retinoid X receptors (RXRs) function as ligand-activated transcription factors and are obligatory components of a large number of nuclear receptor heterodimers. RXRs help regulate diverse physiological responses including the cancer prevention responses of cell proliferation, inflammation, cell differentiation, and apoptosis. Since RXRs represent important targets for cancer chemoprevention, an ultrafiltration mass spectrometry-based assay was developed to facilitate the discovery of potential chemoprevention agents that bind to human RXRalpha. Natural and synthetic ligands for RXRalpha including 9-cis-retinoic acid, docosahexaenoic acid, and LG100268 could be detected and identified in DMSO (dimethyl sulfoxide) or even complex matrixes such as extracts of marine bacteria. Specific binding of ligands to RXRalpha was demonstrated through competitive binding using ultrafiltration LC-MS/MS (liquid chromatography-tandem mass spectrometry), and ligands could be ranked in order of affinity for RXRalpha. Therefore, ultrafiltration LC-MS/MS is suitable for the screening of complex mixtures such as natural product extracts for the discovery of new ligands to RXRalpha.

Uncovering novel targets for cancer chemoprevention

Tobacco carcinogen treatment of immortalized human bronchial epithelial (HBE) cells has uncovered novel targets for cancer chemoprevention. Experiments were conducted with HBE cells and independent treatments with tobacco carcinogens along with the chemopreventive agent all-trans-retinoic acid (RA). That work highlighted D-type and E-type cyclins as novel molecular pharmacologic targets of several chemopreventive agents. G1 cyclins are often aberrantly expressed in bronchial preneoplasia and lung cancers. This implicated these species as targets for clinical cancer chemoprevention. Retinoid regulation mechanisms of D-type cyclins in lung cancer chemoprevention have been comprehensively explored. Retinoid chemoprevention has been mechanistically linked to proteasomal degradation of cyclin D1 and cyclin D3. Threonine 286 mutation stabilized cyclin D1, implicating phosphorylation in this retinoid chemoprevention. Studies with a phospho-specific anti-cyclin D1 antibody confirmed this hypothesis. Glycogen synthase kinase (GSK) inhibitors established a role for this kinase in the retinoid regulation of cyclin D1, but not cyclin D3. Involvement of D-type cyclins in this chemoprevention was shown using small interfering RNAs (siRNAs). Gene profiling experiments highlighted the E1-like ubiquitin-activating enzyme (UBE1L) in the retinoid regulation of cyclin D1. Proof of principle trials have translated these studies into the clinic and established that chemopreventive agents can target D-type cyclins. These findings have been built upon with a targeted combination regimen that cooperatively affects D-type cyclins. Taken together, these preclinical and clinical findings strongly implicate these cyclins as novel molecular pharmacological targets for cancer chemoprevention.

Triterpenoids and rexinoids as multifunctional agents for the prevention and treatment of cancer

Synthetic oleanane triterpenoids and rexinoids are two new classes of multifunctional drugs. They are neither conventional cytotoxic agents, nor are they monofunctional drugs that uniquely target single steps in signal transduction pathways. Synthetic oleanane triterpenoids have profound effects on inflammation and the redox state of cells and tissues, as well as being potent anti-proliferative and pro-apoptotic agents. Rexinoids are ligands for the nuclear receptor transcription factors known as retinoid X receptors. Both classes of agents can prevent and treat cancer in experimental animals. These drugs have unique molecular and cellular mechanisms of action and might prove to be synergistic with standard anti-cancer treatments.

A pharmacogenomic study of docetaxel and gemcitabine for the initial treatment of advanced non-small cell lung cancer

BACKGROUND

Pharmacogenomic profiling is an attractive strategy for individualizing chemotherapy. Several genetic polymorphisms predict the survival of patients with non-small cell lung cancer treated with platinum-based chemotherapy. This phase II clinical trial was performed using a non-platinum-based chemotherapy doublet. The impact of previously identified polymorphisms on clinical outcomes was assessed.

METHODS

Patients with advanced non-small cell lung cancer who had not received previous chemotherapy were treated with docetaxel 40 mg/m2 on days 1 and 8 and gemcitabine 800 mg/m2 days 1 and 8 every 21 days until disease progression or unacceptable toxicity. A pretreatment blood sample was obtained, and genomic DNA was analyzed for polymorphisms in DNA repair and metabolic genes.

RESULTS

Forty-nine patients were enrolled and evaluated for response and survival. The overall radiographic response rate was 38%, and the median survival was 8.6 months. Nonhematologic toxicity was generally mild. Two treatment related deaths occurred: one due to neutropenic sepsis during the first cycle and one due to pulmonary edema after 12 cycles of treatment. Polymorphisms in XPD, XRCC1, and XRCC3 did not significantly predict survival, but trends similar to those reported for platinum-based chemotherapy were observed. The wild-type XPD genotype was associated with prolonged survival and a significantly higher risk of grade 4 neutropenia (p = 0.02).

CONCLUSION

This regimen of docetaxel and gemcitabine is well tolerated and active for the treatment of advanced non-small cell lung cancer. The impact of XPD polymorphisms on hematologic toxicity is similar to what has been reported for platinum-based chemotherapy.

Novel targeted therapies for non-small cell lung cancer

Targeted therapies will advance the treatment of NSCLC as we improve our understanding of the underlying biology of NSCLC and enhance our ability to clinically target the optimal therapy to an individual's cancer. Ongoing translational research including tissue arrays, genomic, and proteomic studies will help to identify clinically useful biomarkers that will allow further classification of NSCLC and may allow accurate prediction of response to specific chemotherapeutic regimens. Advances in targeted therapy in NSCLC are already yielding exciting results, and promises to become an increasingly important adjunct to surgical management of NSCLC.

A Proof-of-Principle Clinical Trial of Bexarotene in Patients with Non–Small Cell Lung Cancer

PURPOSE

Bexarotene is a rexinoid (selective retinoid X receptor agonist) that affects proliferation, differentiation, and apoptosis in preclinical studies. The relationship between bexarotene levels and biomarker changes in tumor tissues has not been previously studied.

EXPERIMENTAL DESIGN

BEAS-2B human bronchial epithelial (HBE) cells, retinoid-resistant BEAS-2B-R1 cells, A427, H226, and H358 lung cancer cells were treated with bexarotene. Proliferation and biomarker expression were assessed. In a proof-of-principle clinical trial, bexarotene tumor tissue levels and intratumoral pharmacodynamic effects were assessed in patients with stages I to II non-small cell lung cancer. Bexarotene (300 mg/m(2)/day) was administered p.o. for 7 to 9 days before resection.

RESULTS

Bexarotene-induced dosage-dependent repression of growth, cyclin D1, cyclin D3, total epidermal growth factor receptor (EGFR), and phospho-EGFR expression in BEAS-2B, BEAS-2B-R1, A427, and H358, but not H226 cells. Twelve patients were enrolled, and 10 were evaluable. Bexarotene treatment was well tolerated. There was nonlinear correlation between plasma and tumor bexarotene concentrations (r(2) = 0.77). Biomarker changes in tumors were observed: repression of cyclin D1, total EGFR and proliferation in one case; repression of cyclin D3, total and phospho-EGFR in another. The cases with multiple biomarker changes had high tumor bexarotene (107-159 ng/g). A single biomarker change was detected in one case with low tumor bexarotene.

CONCLUSION

Bexarotene represses proliferation and biomarker expression in responsive, but not resistant HBE and lung cancer cells. Similar biomarker changes occur in lung tumors when therapeutic intratumoral bexarotene levels are achieved. This proof-of-principle trial approach is useful to uncover pharmacodynamic mechanisms in vivo and relate these to intratumoral pharmacokinetic effects.

International Union of Pharmacology. LXIII. Retinoid X receptors

The physiological effects of retinoic acids (RAs) are mediated by members of two families of nuclear receptors, the retinoic acid receptors (RARs) and the retinoid X receptors (RXRs), which are encoded by three distinct human genes, RXRalpha, RXRbeta, and RXRgamma. RARs bind both all-trans- and 9-cis-RA, whereas only the 9-cis-RA stereoisomer binds to RXRs. As RXR/RAR heterodimers, these receptors control the transcription of RA target genes through binding to RA-response elements. This review is focused on the structure, mode of action, ligands, expression, and pharmacology of RXRs. Given their role as common partners to many other members of the nuclear receptor superfamily, these receptors have been the subject of intense scrutiny. Moreover, and despite numerous studies since their initial discovery, RXRs remain enigmatic nuclear receptors, and there is still no consensus regarding their role. Indeed, multiple questions about the actual biological role of RXRs and the existence of an endogenous ligand have still to be answered.

Uncovering residues that regulate cyclin D1 proteasomal degradation

Cyclin D1 regulates G1 cell-cycle progression and is aberrantly expressed in carcinogenesis. Proteasomal degradation of cyclin D1 was highlighted as a cancer chemopreventive mechanism. To understand this mechanism better, residues responsible for degradation and ubiquitination of cyclin D1 were investigated. Eighteen lysines in cyclin D1 had single, double or multiple mutations engineered before transfection into BEAS-2B human bronchial epithelial (HBE) cells to evaluate stabilities after all-trans-retinoic acid (RA) or cycloheximide treatments. Specific mutations stabilized cyclin D1, including substitutions of lysines surrounding the cyclin box domain that inhibited RA-mediated degradation and extended the cyclin D1 half-life. Mutation of all cyclin D1 lysines blocked polyubiquitination. N-terminus (but not C-terminus) modification stabilized cyclin D1. Ubiquitination-resistant mutants preferentially localized cyclin D1 to the nucleus, directly implicating subcellular localization in regulating cyclin D1 degradation. Taken together, these findings uncover specific residues conferring ubiquitination of cyclin D1. These provide a mechanistic basis for proteasomal degradation of cyclin D1.

RXR: From Partnership to Leadership in Metabolic Regulations

Vitamin A signaling occurs through nuclear receptors recognizing diverse forms of retinoic acid (RA). The retinoic acid receptors (RARs) bind all-trans RA and its 9-cis isomer (9-cis RA). They convey most of the activity of RA, particularly during embryogenesis. The second subset of receptors, the rexinoid receptors (RXRs), binds 9-cis RA only. However, RXRs are obligatory DNA-binding partners for a number of nuclear receptors, broadening the spectrum of their biological activity to the corresponding nuclear receptor-signaling pathways. The present chapter more particularly focuses on RXR-containing transcriptional complexes for which RXR is not only a structural component necessary for DNA binding but also acts as a ligand-activated partner. After positioning RXR among the nuclear receptor superfamily in the first part, we will give an overview of three major signaling pathways involved in metabolism, which are sensitive to RXR activation: LXR:RXR, FXR:RXR, and PPAR:RXR. The third and last part is focused on RXR signaling and its potential role in metabolic regulation. Indeed, while the nature of the endogenous ligand for RXR is still in question, as we will discuss herein, a better understanding of RXR activities is necessary to envisage the potential therapeutic applications of synthetic RXR ligands.

Phase II Trial of Bexarotene Capsules in Patients With Advanced Non–Small-Cell Lung Cancer After Failure of Two or More Previous Therapies

Purpose

To evaluate the effect of bexarotene on survival in patients with relapsed non–small-cell lung cancer (NSCLC).

Patients and Methods

Patients with stage IIIB NSCLC with pleural effusion or stage IV NSCLC, who had Eastern Cooperative Oncology Group performance status 0 to 2, and were previously treated with ≥ two different regimens that must have included a platinum and a taxane, received oral bexarotene 400 mg/m2/d plus concomitant levothyroxine and a lipid-lowering agent. Primary efficacy end point was survival.

Results

For the 146 assessable patients treated with bexarotene, median age was 66 years (range, 34 to 87 years), 51% were men, and the median number of prior regimens was three (range, one to seven). The overall median survival was 5 months (95% CI, 4 to 7 months) and the 1-year survival was 23% (95% CI, 16% to 31%). Survival was significantly longer in patients with bexarotene-induced hypertriglyceridemia and/or skin rash. In 26 patients who had both adverse effects, the median and 1-year survival rates were 12 months (95% CI, 8 to 15 months) and 48%, respectively. In 40 patients who had neither adverse effect, median and 1-year survival rates were 2 months (95% CI, 2 to 5 months) and 15%, respectively (P = .0002). Twenty patients (14%) discontinued therapy because of bexarotene-related toxicity. For the remaining patients, adverse reactions to bexarotene were generally mild to moderate.

Conclusion

In the intent-to-treat population, bexarotene given as third or subsequent line of therapy for relapsed NSCLC did not achieve the intended median survival of 6 months. Survival may have been extended in patients who developed bexarotene-induced hypertriglyceremia and/or skin rash. It is important to confirm these observations in a randomized controlled trial.

Second- and third-line treatments in non-small cell lung cancer

Slow but steady progress has been made in the treatment of advanced non-small cell lung cancer. For first-line therapy, multiple chemotherapy combination therapies can extend survival and improve quality of life. And recently, for the first time ever, a noncytotoxic agent, the antivascular endothelial growth factor antibody bevacizumab, has been shown to improve survival when added to chemotherapy. Striking improvements have also been made in second-line treatment. In August 2004, only one agent was US Food and Drug Administration (FDA) approved in this setting, docetaxel, but by the beginning of 2005, two more were available, pemetrexed and erlotinib. All three of these drugs can significantly benefit patients, with 1-year survival in excess of 30%. Choosing between the three agents can be challenging, and this review focuses on the toxicity differences and predictors of response that can help guide this decision. Docetaxel and pemetrexed, both traditional intravenous cytotoxins, are excellent options for patients who have shown some response to first-line chemotherapy, but at this time, no other means exist to determine likelihood of response. When choosing between the two, pemetrexed causes significantly less neutropenia than does docetaxel, at least on the standard every-3-week regimen. With erlotinib, an oral epidermal growth factor receptor (EGFR) inhibitor, there are factors that can predict for response, including little or no smoking history, and adenocarcinoma histology. Therefore, patients who fit these characteristics are good candidates for second-line erlotinib. However, the relationship between response to erlotinib and improved survival remains unclear, and several laboratory analyses that may help further, such as evaluation of EGFR gene copy number, are still under development. Although erlotinib is the only FDA-approved option currently available for third-line therapy, many patients with good performance status may benefit from third-line therapy and beyond. In addition to the approved second-line options, other single-agent chemotherapies to consider for treatment beyond second-line are gemcitabine, irinotecan, and oral topotecan. Many new drugs, including bevacizumab, ZD6474 (AstraZeneca, Wilmington, DE), sorafenib, cetuximab, paclitaxel poliglumex, epothilones, and others, alone or in combination with traditional agents, are currently undergoing investigation and hold great promise.