Elsevier

Lung Cancer

Volume 50, Issue 1, October 2005, Pages 9-18
Lung Cancer

The retinoid X receptor agonist bexarotene (Targretin) synergistically enhances the growth inhibitory activity of cytotoxic drugs in non-small cell lung cancer cells

https://doi.org/10.1016/j.lungcan.2005.05.008Get rights and content

Summary

This study was designed to evaluate, using preclinical models of non-small cell lung cancer (NSCLC), the growth inhibitory effects of the retinoid X receptor (RXR) agonist bexarotene (LGD1069, Targretin) in combination with cytotoxic agents currently used as standard first-line therapy in advanced disease. Although single-agent bexarotene had modest growth inhibitory effects in several cell lines, efficacy was observed only in the micromolar range (>1 μM), which approximates the plasma Cmax measured in pharmacokinetic studies in patients. However, when combined with paclitaxel or vinorelbine, bexarotene produced a concentration-dependent enhancement of the growth inhibitory activities of paclitaxel and vinorelbine. Formal synergy analysis using the Calu3 cell line demonstrated that the combination of bexarotene with either cytotoxic agent produced synergistic activity (combination index, CI < 1). The in vitro observations were confirmed in vivo in a NSCLC xenograft tumor model (Calu3), where both bexarotene/paclitaxel and bexarotene/vinorelbine combinations produced significantly greater antitumor effects than the single agents. These results demonstrate that bexarotene can cooperate with widely used cytotoxic agents to decrease the growth of NSCLC tumor cells both in vitro and in vivo, and suggest the potential benefit of adding a RXR-selective agonist in combination with chemotherapy for NSCLC treatment. Furthermore, the data support the clinical observation from phase I/IIa trials suggesting that bexarotene has beneficial effects on survival when used in combination with cytotoxic agents in advanced NSCLC.

Introduction

Lung cancer is the leading cause of cancer death for both men and women [1]. The American Cancer Society estimates that in 2004 there will be about 173,770 new cases of lung cancer in the United States, and about 160,440 people will die of this disease. Non-small cell lung cancer (NSCLC) is the most common type, accounting for almost 80% of lung cancers. Unfortunately, most NSCLC patients already have advanced disease (stage IIIB/IV) at diagnosis and this is associated with a poor prognosis. Currently the major treatment modality for patients with unresectable NSCLC is chemotherapy with a platinum-based agent (e.g., cisplatin, carboplatin) in combination with a second cytotoxic agent such as paclitaxel, vinorelbine or docetaxel [2]. Although it has been demonstrated that modern two-drug combinations are more active than single agents, the benefits are still modest, and the current 5-year survival rate has not improved significantly since the implementation of these combination regimens [3]. This has motivated researchers to explore the possibility of adding a third agent to the two-drug regimens. While Phase II clinical trials of three-drug combination therapy in NSCLC have been encouraging, the 5-year survival rate has still not improved with this strategy and these regimens often come at the cost of a significant increase in toxicity [4], [5]. Recent data from clinical trials of a number of novel targeted agents administered in combination with chemotherapy unfortunately did not show significant survival benefit over chemotherapy alone [6], [7], [8]. These data emphasize that agents capable of enhancing the activity of the current treatment regimens while exhibiting better-tolerated, non-overlapping side effects are still desired.

Bexarotene (LGD1069, Targretin®) is a retinoid X receptor (RXR) selective agonist which binds and activates all three RXR isoforms (RXRα, RXRβ, and RXRγ) with equivalent affinity and potency [9]. Our previous work in solid tumor models has demonstrated that bexarotene is an efficacious chemopreventive and chemotherapeutic agent in a number of preclinical rodent models of human cancer and in the rat N-nitrosomethylurea (NMU)-induced mammary carcinoma model, where it was shown to be effective against both tamoxifen-resistant and tamoxifen-sensitive tumors [10], [11], [12]. In addition, we have recently demonstrated that the bexarotene/paclitaxel combination resulted in a synergistic growth inhibition (combination index, CI < 1) in a rat mammary tumor-derived cell line in vitro [13]. In the rat NMU-induced tumor model in vivo, the combination regimen resulted in a statistically significant decrease in total tumor burden and an increase in overall objective response without further intensifying the major side effects of paclitaxel. More recently, we have shown that bexarotene can prevent and overcome acquired paclitaxel resistance in human NSCLC cells [14].

These encouraging preclinical results with bexarotene led us to further examine its role in combination regimens with other cytotoxic agents.

The first goal of this study was to extend our observation on the combination effect of bexarotene and paclitaxel in the rat NMU-induced mammary carcinoma model to models of NSCLC and determine whether the addition of bexarotene could enhance the activity of chemotherapy agents commonly used in first-line treatment of advanced NSCLC. We evaluated combinations of bexarotene with several cytotoxic agents in a panel of 10 NSCLC cell lines that represent different histomorphologies (Table 1). In addition, we sought to extend the in vitro observations to in vivo xenograft tumor models of NSCLC. Our results show that bexarotene enhanced the growth inhibitory activity of both paclitaxel and vinorelbine. These observations were confirmed in vivo where the antitumor efficacy of the combination regimen was superior to that of the single agents.

Section snippets

Chemicals and reagents

RPMI 1640 medium, glutamine and gentamycin were obtained from Cambrex (Walkersville, MD). Fetal bovine serum was from HyClone (Logan, UT). Vinorelbine (10 mg/mL in sterile solution) and paclitaxel for injection (6 mg/mL in 1:1 (v/v) in Cremophor EL and dehydrated alcohol) were purchased through Pharmaceutical Buyers Inc. (Cedarhurst, NY). Bexarotene was synthesized at Ligand Pharmaceuticals (San Diego, CA). RXR-isoform specific binding affinity and activation data for bexarotene has been

Bexarotene monotherapy has modest growth inhibitory activity on human NSCLC cell lines

Before investigating the activity of bexarotene in combination with cytotoxic drugs, bexarotene's growth inhibitory activity as single agent was surveyed against a panel of human NSCLC cell lines. Table 1 lists the NSCLC cell lines used in this study; they represent the variety of NSCLC histomorphology typical for this disease. In general, bexarotene had modest growth inhibitory effect when used as single agent (up to 10 μM), and only in a subset of the lines tested (Fig. 1). The level of growth

Discussion

The purpose of this study was to evaluate the efficacy of combinations of bexarotene with cytotoxic chemotherapeutic drugs commonly used in the treatment of NSCLC. We examined various combinations of bexarotene and cytotoxic agents for growth inhibition, using a panel of NSCLC cell lines, and confirmed the in vitro observations in vivo, transitioning to NSCLC xenograft tumor models. Our in vitro data show that although bexarotene had little or only modest antitumor activity when used as a

Acknowledgement

The authors thank Mr. Manny R. Corpuz for conducting xenograft studies and Ms. Tracy A. Cooke for analysis of RXR expression profiles in cell lines.

References (39)

  • G. Frasci et al.

    Cisplatin, gemcitabine, and paclitaxel in locally advanced or metastatic non-small-cell lung cancer: a phase I–II study. Southern Italy Cooperative Oncology Group

    J Clin Oncol

    (1999)
  • R.S. Herbst et al.

    Gefitinib in combination with paclitaxel and carboplatin in advanced non-small-cell lung cancer: a phase III trial–INTACT 2

    J Clin Oncol

    (2004)
  • G. Giaccone et al.

    Gefitinib in combination with gemcitabine and cisplatin in advanced non-small-cell lung cancer: a phase III trial–INTACT 1

    J Clin Oncol

    (2004)
  • R. Perez-Soler

    The role of erlotinib (Tarceva, OSI 774) in the treatment of non-small cell lung cancer

    Clin Cancer Res

    (2004)
  • M.F. Boehm et al.

    Synthesis and structure-activity relationships of novel retinoid X receptor-selective retinoids

    J Med Chem

    (1994)
  • M.M. Gottardis et al.

    Chemoprevention of mammary carcinoma by LGD1069 (Targretin): an RXR-selective ligand

    Cancer Res

    (1996)
  • E.D. Bischoff et al.

    Effect of the retinoid X receptor-selective ligand LGD1069 on mammary carcinoma after tamoxifen failure

    J Natl Cancer Inst

    (1999)
  • E.D. Bischoff et al.

    Beyond tamoxifen: the retinoid X receptor-selective ligand LGD1069 (TARGRETIN) causes complete regression of mammary carcinoma

    Cancer Res

    (1998)
  • W-C. Yen et al.

    Synergistic effect of a retinoid X receptor-selective ligand bexarotene (LGD1069, Targretin) and paclitaxel (Taxol) in mammary carcinoma

    Breast Cancer Res Treat

    (2004)
  • Cited by (34)

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

      2021, Seminars in Cancer Biology
      Citation Excerpt :

      The synthetic RXRα ligand bexarotene (also known as targretin) is used currently for treating refractory cutaneous T cell lymphoma (CTCL) [156] (Table 1). Bexarotene acted synergistically with standard first-line cytotoxic chemotherapy [157] and overcame the acquired resistance to paclitaxel in non-small cell lung cancer (NSCLC) [158]. Interestingly, bexarotene also appeared to increase the survival of a segment of NSCLC patients developing high-grade hypertriglyceridemia [159,160].

    • VHL enhances 9-cis-retinoic acid treatment by down-regulating retinoid X receptor α in renal cell carcinomas

      2020, Biochemical and Biophysical Research Communications
      Citation Excerpt :

      The results of the present study demonstrated that the antitumor growth effect of 9-cis-RA was more prominent in the VHL-proficient RCC cells, which exhibit lower expression of RXRα. It was reported that this RXR agonist also exerts a prominent effect on non-small-cell lung cancer [23], in which reduced levels of the RXRα protein have been observed [24]. These results suggest that low expression of RXRα may be more beneficial for RXRα agonists to exert their antitumor effects.

    • Nanoformulation of dual bexarotene-tailed phospholipid conjugate with high drug loading

      2017, European Journal of Pharmaceutical Sciences
      Citation Excerpt :

      Bexarotene has been clinically used in the treatment of cutaneous T-cell lymphoma (Abbott et al., 2009; Mehta et al., 2012). It is also extremely effective in inhibiting non-small cell lung cancer (Yen et al., 2004b; Hermann et al., 2005) and promisingly useful in suppressing breast and prostate cancer (Wu et al., 2002; Li et al., 2008; Chen et al., 2014). However, bexarotene has a poor solubility with a maximum about 10 μM in aqueous solution.

    • Bexarotene nanocrystal - Oral and parenteral formulation development, characterization and pharmacokinetic evaluation

      2014, European Journal of Pharmaceutics and Biopharmaceutics
      Citation Excerpt :

      Current chemotherapeutic agents target a specific pathway to ultimately shrink the tumor size, such as alkylating agents, mustards, anti-metabolites, spindle poisons, and DNA binders and cutters, However, they often fail to eradicate tumors or prevent their recurrence. Bexarotene (Fig. 1A) is a retinoid X receptor (RXR) selective agonist which binds and activates all three RXR isoforms (RXRα, RXRβ, and RXRγ) with equivalent affinity and potency [4]. It exhibits anti-tumor activities by inhibiting cell growth, inducing differentiation and promoting apoptosis in a variety of tumor cell lines [5].

    • Gene and doxorubicin co-delivery system for targeting therapy of glioma

      2012, Biomaterials
      Citation Excerpt :

      The potential synergy of the combination of DOX and pORF-hTRAIL towards U87 MG cells was evaluated by the CI analysis. In the CI analysis, values of CI < 1, =1 and >1 indicate synergy, additivity, and antagonism, respectively [31]. This combination treatment resulted in a synergistic growth inhibition (CI < 1) in U87 MG cells.

    View all citing articles on Scopus
    1

    TWH and WCY contributed equally to this work and share first authorship.

    View full text