A pilot study of zoledronic acid in the treatment of patients with advanced malignant pleural mesothelioma

Introduction

Malignant pleural mesothelioma (MPM) is an aggressive tumor of serosal surfaces. Its incidence is increasing worldwide due to asbestos use.¹ MPM occurs mainly in men, aged 60–80 years, and the majority of them die due to local extension and/or respiratory failure.^1,2 Median survival of patients ranges from 12 to 19 months with combination chemotherapy. Pemetrexed plus cisplatin, the current standard chemotherapy regimen, yield a median overall survival (OS) of 12.1 months and a median time to progression of 5.7 months.³ Poor prognostic markers include: poor performance status (PS), high leukocyte count, high platelet count (>400,000/µL), nonepithelial tumor type, and male gender.⁴ Despite new chemotherapy combinations, MPM patient outcome is modest,^5–11 thus a great need for improvement exists.

Bisphosphonates are osteoporosis drugs that have been in clinical use for decades.¹² In addition to their antiresorptive effects in osteoporosis and cancer-induced osteolytic bone disease, nitrogen-containing bisphosphonates (such as zoledronic acid and risedronic acid) inhibit tumor proliferation.^12–14 Zoledronic acid effectively inhibits proliferation of mesothelioma cell lines in vitro and in vivo.¹⁵ This result is likely an outcome of mevalonate pathway inhibition,^12,16 leading to depletion of prenyl groups needed in posttranslational modification and activation of small GTPases,¹⁴ ultimately inhibiting cell growth. In addition, zoledronic acid reduces experimental malignant pleural effusions.¹⁷ It demonstrates antiangiogenic effects^18–20 and suppresses vascular endothelial growth factor (VEGF) blood levels.²¹ VEGF levels have been associated with MPM progression and poor survival^22,23 in relation to high tumor microvessel density.^22,24

Computed tomography (CT) response evaluation criteria in solid tumors (RECIST) is difficult to use in MPM due to circumferential and axial growth. Thus, MPM response to treatment is usually measured with imaging using modified RECIST assessment criteria.²⁵ MPM is 2-deoxy-2-[fluorine-18]fluoro-d-glucose (¹⁸F-FDG) positron emission tomography (PET) avid,²⁶ and ¹⁸F-FDG PET scans can be used to document early responses^27,28 and have been useful in the assessment of prognosis and staging.^29,30 Mesothelin and osteopontin are glycoproteins that are overexpressed in mesothelioma and are associated with tumor progression. Serum markers such as mesothelin and osteopontin are of interest for prognosis, tumor response, and tumor progression.^31–33 On the basis of these findings, we conducted a pilot, proof-of-concept feasibility study of zoledronic acid in the treatment of advanced MPM. We measured the levels of antiangiogenic factors (VEGF, bFGF, IL-8, and TGF-β), mesothelin, and osteopontin before and during treatment.

Patients and methods

Study design and patients

This single-arm, prospective study was conducted at the University of Alabama at Birmingham Comprehensive Cancer Center. The primary objective of this study was to evaluate the antitumor activity of zoledronic acid in subjects with unresectable, advanced MPM assessed by the modified RECIST criteria,²⁵ and/or metabolic response ¹⁸F-FDG PET assessment.³⁴ The secondary objectives were to assess duration of response, progression-free survival (PFS), OS, and safety and tolerability of zoledronic acid in MPM patients. Blood levels of VEGF, bFGF, IL-8, TGF-β, mesothelin, and osteopontin were measured to investigate the influence of zoledronic acid.

Inclusion criteria included: adult patients (age>18) with unresectable MPM who had progressed after one or more prior systemic therapies, had not received prior systemic therapy due to poor PS, and/or were unwilling to receive systemic chemotherapy. Other eligibility criteria included life expectancy of at least 2 months, measurable disease by CT or ¹⁸F-FDG PET, willing to consent to contraception (if applicable), and ability to provide consent. Exclusion criteria were brain metastasis, second cancer diagnosis, heart disease (class 3 or 4 heart failure by New York Heart failure classification), acute coronary syndrome (within 6 months), known human immunodeficiency virus or hepatitis, clinically significant arrhythmias, serious acute systemic disease, dental disease, and history of osteonecrosis of the jaw.

This study was approved by the Institutional Review Board at the University of Alabama at Birmingham Comprehensive Cancer Center. Written informed consent was obtained from all study participants.

The study was registered with the National Clinical Trials Network, number NCT01204203.

Treatment and assessments

Study schema is presented in Figure 1. Patients were treated with intravenous (IV) infusion of zoledronic acid (Novartis Pharmaceuticals, East Hanover, NJ, USA) 4 mg IV over 15 minutes on day 1 of a 3-week cycle. Patients were evaluated for response every 2 cycles with CT scans and ¹⁸F-FDG PET scans only on cycle 2. Subjects with either stable disease or response continued treatment until disease progression and/or intolerable toxicity at which patients were taken off study. Dose adjustment was allowed per standard guidelines for zoledronic acid for decreased creatinine clearance. Subjects were monitored for toxicity using National Cancer Institute Common Terminology Criteria for Adverse Events Version 3.0 criteria. Patients who completed at least one treatment cycle were included in data analysis.

Figure 1 Study schema. Abbreviations: bFGF, basic fibroblast growth factor; CBC, complete blood count; CT, computed tomography; IL-8, interleukin 8; IV, intravenous; PET, positron emission tomography; TGF-β, transforming growth factor beta; VEGF, vascular endothelial growth factor.

Sample collection and analysis for correlative objectives

Blood samples for VEGF, bFGF, IL-8, TGF-β, mesothelin, and osteopontin were collected prior to treatment on days 1 and 8 of cycle 1 and then prior to treatment on day 1 of cycles 2, 3, and 6. Plasma samples were aliquoted and stored at −70°C. Blood levels of these biomarkers were analyzed using ELISA (enzyme-linked immunosorbent assay) kits from R&D systems (R&D Systems, Inc., Minneapolis, MN, USA) Quantikine assays, according to manufacturer’s instructions.

Statistical analysis

Responses were assessed as composite response rate which include modified RECIST objective responses and metabolic response ¹⁸F-FDG PET assessment. Data are presented as descriptive statistics. OS and PFS are presented as median, whereas VEGF, bFGF, IL-8, TGF-β, mesothelin, and osteopontin are presented as mean values.

Results

Demographics

From November 2010 to January 2015, 9 patients consented, but only 8 patients were treated. All patients were male (7 Caucasian and 1 African-American), median age of 62 years (age range 49–77), and Eastern Cooperative Oncology Group ( ECOG) PS 0–2. Three patients were never-smokers. One patient had stage 2 disease, and 7 patients had stage 4 disease. The majority of the patients (n=6) had epithelioid mesothelioma. All except 2 patients reported a history of asbestos exposure. All patients included in this study had symptomatic, active disease with measurable parameters by CT and PET scans; previously treated patients had progressive symptomatic disease after the last line of treatment. Three patients were treatment naïve, whereas others had received one or more lines of chemotherapy agents, including pemetrexed/cisplatin or carboplatin, single-agent carboplatin, pemetrexed, and cediranib.

Treatment outcomes

Median duration of follow-up was 1.3 months (0.3–21 months), median number of treatment cycles was 2 (1–28 cycles). Baseline tumor parameters and response assessment after cycle 2 of treatment are summarized in Table 1. No response was seen when patients were evaluated by modified RECIST criteria; 2 patients had the best response of stable disease, 1 response lasted 21 months. When assessed with ¹⁸F-FDG PET, 1 patient with stable disease by modified RECIST had partial response by ¹⁸F-FDG PET criteria, whereas another patient thought to have progressive disease by modified RECIST had stable disease by ¹⁸F-FDG PET criteria. Overall composite response rate was 12.5%. Clinical benefit rate (response + stable disease) was 37.5%. Median PFS was 2 months (0.5–21 months). Median OS was 7 months (0.8–28 months). The histopathological characteristics of the MPM responders include 1 epithelioid and 1 mixed histology; all 6 MPM nonresponders had epithelioid histology. No treatment-related toxicities were observed.

Table 1 Summary of baseline tumor parameters and response assessment after cycle 2 of treatment Notes: aSum of the unidimensional measurement of measurable parameters. bSum of max SUVs of tumor parameters. Abbreviations: CT, computerized tomography; 18F-FDG, 2-deoxy-2-[fluorine-18]fluoro-d-glucose; PET, positron emission tomography; SUV, standardized uptake value.

Correlative studies result

Higher baseline levels of VEGF and osteopontin were observed in nonresponders (Table 2). Decreasing levels of mesothelin and osteopontin were seen in patients with response or stable disease. Zoledronic acid initially led to increase in VEGF levels in all patients with subsequent decrease. Increasing VEGF levels was seen in patients with progressive disease. No association with disease burden or progression was seen with IL-8, bFGF, or TGF-β.

Table 2 Correlative analysis of VEGF, mesothelin, and osteopontin blood levels during treatment with zoledronic acid Notes: aNormal range =31–86 pg/mL. bNormal range =9.6–40.6 ng/mL. cNormal range =0.3–20 ng/mL. Abbreviation: VEGF, vascular endothelial growth factor.

Discussion

This pilot feasibility study assessed whether bisphosphonates could have a role in the treatment of mesothelioma due to their antiangiogenic properties. Our findings suggest that zoledronic acid has single-agent activity in MPM treatment. Angiogenesis is a complex process, difficult to target due to multiple VEGF-dependent and VEGF-independent pathways.^35,36 Multiple antiangiogenic agents have been previously used for the treatment of MPM; however, responses have been modest with bevacizumab having the most evidence.^37–47 A recent publication reporting the combination of bevacizumab with pemetrexed and cisplatin showed increased PFS and OS.⁴¹ Zoledronic acid can mitigate angiogenesis at subcellular level by mevalonate pathway inhibition and is beneficial in antitumor therapy.^{14,15,48–50} In our study, clinical benefit in at least 2 patients was observed without toxicity, which makes this drug an attractive agent for combination with chemotherapy or other antiangiogenic agents for future trials. Lower VEGF levels were associated with favorable responses similar to previous results.^41,42,51 However, an interesting finding was the initial increase and then decrease in VEGF levels with zoledronic therapy in responder patients (Table 2). It has been shown that maximal tolerated chemotherapy increases the expression of VEGF and other proangiogenic growth factors in a rebound response to treatment. It is possible that similar initial rebound effect can be seen with zolendronic acid in responders; and more profound effect in nonresponders, indicative of an adaptive (evasive) mechanism of resistance.⁵²

IL-8 and bFGF, which have been shown to enhance neovascularization and promote tumor growth,⁵³ did not correlate with zoledronic acid therapy. Serum mesothelin levels are elevated in MPM, but is not used as a biomarker for diagnosis due to low sensitivity.^31,54,55 It has been shown to correlate with prognosis^56–58 and has been a target for MPM immunotherapy.^59,60 Our study reports that mesothelin and osteopontin levels decline in patients who have favorable therapy response and potentially may represent promising biomarkers of this disease.

In our patient population, as well as in the SEER Cancer Statistics, the incidence of mesothelioma is much more common in men than in women.⁶¹ This prevalence is reflected in the demographic data of our study. Previous studies have shown women diagnosed with mesothelioma typically have more favorable outcomes and a statistically better chance of survival than males.⁶¹

Conclusion

Our pilot study suggests modest activity of zoledronic acid as a single agent in the treatment of mesothelioma and warrants further investigation in combination with other agents.

Acknowledgments

This work was supported by the UAB Comprehensive Cancer Center Core Grant-CA13148 and Novartis. The funding sources provided financial resources and had no involvement in the study design, collection/analysis/interpretation of data, report writing, or in the decision to submit the article for publication. The authors greatly appreciate the participation of the study patients. The authors would like to thank the Clinic Research team and Tasha Renee Smith PhD, MPH who assisted with manuscript preparation.

Disclosure

Dr Robert reports grants from UAB Comprehensive Cancer Center Core Grant-CA13148 and Novartis during the conduct of the study. He reports grants from TRACON, Stemcentrx, Inc., Pfizer, AstraZeneca, Boehringer Ingelheim, Sanofi, EMD Serono, Clovis Oncology, Threshold Pharmaceuticals, Mirati Therapeutics, and Novartis and personal fees from Merck and Boehringer Ingelheim outside the submitted work. The other authors report no conflicts of interest in this work.

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