Association between GSTP1 polymorphisms and prognosis of osteosarcoma in patients treated with chemotherapy: a meta-analysis

Abstract

Objective

The aim of this study was to evaluate the relationship between GSTP1 polymorphisms and prognosis of osteosarcoma in patients treated with chemotherapy, by performing a meta-analysis.

Methods

The studies of effects of GSTP1 gene polymorphisms on osteosarcoma survival after chemotherapy were collected. STATA (version 12.0) was used to perform data synthesis.

Results

Six studies involving 898 participants were included. A meta-analysis was performed on studies in GSTP1 313A>G(rs1695) assessing the association between tumor response and the polymorphisms in GSTP1 (AA vs AG, AA vs GG), the pooled odds ratios (ORs) were 2.06 (95% confidence interval [CI]: 1.48–2.86, P=0.628, I²=0.0%). There was significant association between the polymorphisms in GSTP1 (AA vs AG, AA vs GG) and the events that happened, the pooled ORs were 1.86 (95% CI: 1.14–3.06, P=0.034, I²=58.6%), and there was significant association between the polymorphisms in GSTP1 (AA vs AG, AA vs GG) and survival times (overall survival and progression-free survival) in osteosarcoma patients treated with chemotherapy, and the pooled ORs were 2.14 (95% CI: 1.51–3.04, P=0.675, I²=0.0%) and 2.77 (95% CI: 1.56–4.91, P=0.347, I²=9.3%), respectively. Two studies assessed the association of polymorphisms in GSTP1 I105V (IIe/IIe vs IIe/Val, IIe/IIe vs Val/Val) with overall survival in human osteosarcoma. The pooled ORs were 1.20 (95% CI: 0.64–2.27, P=0.010, I²=73.5%). The study showed an insignificant difference in overall survival for the polymorphisms in GSTP1 (IIe/IIe vs IIe/Val, IIe/IIe vs Val/Val).

Conclusion

This meta-analysis indicated that GSTP1 polymorphisms might influence osteosarcoma risk and suggests that GSTP1 polymorphisms may be an important risk factor for osteosarcoma.

Keywords:

• GSTP1
• polymorphisms
• osteosarcoma
• chemotherapy
• prognosis
• meta-analysis

Introduction

Osteosarcoma derives from primitive bone-forming mesenchymal cells, and it is the most common malignant tumor of bones and one of the leading cause of death from cancer in children and adolescents.¹ The real mechanism of developing osteosarcoma is still not well understood, but its genesis and progression may be regulated by genetic factors.² Standard treatment of osteosarcoma involves neoadjuvant therapy before definitive resection of the primary tumor, followed by multiple chemotherapeutic agents after operation.³ Nevertheless, more than 40% patients have a poor tumor response to chemotherapy, and the estimated survival is approximately 45%–55%,⁴ and the 5-year overall relapse-free survival rate is approximately 65%.⁵ According to biomarkers, individualized chemotherapy may improve the patients’ tumor response to chemotherapy and the clinical outcome. Therefore, fully understanding the role of pharmacogenetics could help establish individualized chemotherapy for patients to benefit more from chemotherapy to prolong their life. In recent years, several common gene polymorphisms, including in GSTP1, have been identified to be associated with osteosarcoma.⁶

Glutathione S-transferases (GSTs) are a family of cytosolic enzymes, which are involved in metabolizing chemotherapeutic agents and play an important role in the detoxification of various exogenous and endogenous reactive species.^7,8 Glutathione S-transferase p1 (GSTP1) belongs to the pi class and encodes a glutathione S-transferase. This gene is a polymorphic gene encoding differently active, functional GSTP1 proteins in xenobiotic metabolism.⁹ GSTP1 plays a role in susceptibility to some cancers, such as breast cancer and osteosarcoma.^6,10 The genetic polymorphisms could affect drug metabolizers and transporters, which could affect the plasma concentration of chemotherapy drugs and influence the effectiveness of chemotherapy.

Numerous studies have reported GSTP1 polymorphisms are associated with prognosis of osteosarcoma patients treated with chemotherapy, especially GSTP1 313A>G and GSTP1 I105V, but the results are inconclusive, which may be due to the limitation of the small sample size in each of published studies. Therefore, we performed a meta-analysis of the published studies to estimate the association more accurately.

Materials and methods

Ethics statement

The study was approved by the Ethics Committee of Union Hospital, Tongji Medical College, Huazhong University of Science and Technology and conforms with the provisions of the Declaration of Helsinki.

Search strategies

We searched for non-English and English articles included in PubMed, SCI, Elsevier, and CNKI database. Search terms included the following key words: glutathione S-transferase p1, GSTP1, polymorphisms, osteosarcoma, and chemotherapy. Studies up to October 2014 were included. There was no restriction on time period, population, language, or type of study. All eligible studies were retrieved, and their bibliographies were checked for other relevant publications. The computerized search was supplemented by a manual search of the bibliographies of all retrieved articles by two independent reviewers.

Inclusion/exclusion criteria of literature

The studies were included if they satisfied the following criteria:

1. The study design was case-control;

2. They had information on the relationship between GSTP1 polymorphisms and osteosarcoma risk or clinical outcome after chemotherapy;

3. The papers provided the size of the samples, distribution of alleles, genotypes, or other informations that could help us estimate an odds ratio and 95% confidence interval.

4. The studies were excluded if one of the following existed:

5. If they were review articles and studies that contained overlapping data;

6. If they did not offer the source of cases and controls or other essential information;

7. If more than one study from the same group occurred, we only used the most recent study or the study where complete data was available.

Statistical analysis

The following information was extracted from each eligible study by two investigators independently with the standard protocol: the name of first author, year of publication, country of origin, ethnicity of the population studied, the sample size of cases and controls, genotyping methods and allele and genotype distribution in cases and controls, tumor response after chemotherapy, overall survival, progression-free survival, event-free survival, and events after chemotherapy. Different ethnicities of the population were categorized as Caucasians, Asian. To ensure the accuracy of the extracted information, two investigators checked the data extraction results and reached consensus on all of the data extracted. If different results were generated, they would check the data again and have a discussion to come to an agreement. The results were reviewed by a third investigator and any disagreement was resolved by discussion.

Risk ratio (RR) and a 95% CI were used for presenting the statistical results for dichotomous outcomes. Weighted mean difference (WMD) and a 95% CI were employed for presenting the statistical results for continuous outcomes. Mantel–Haenszel analysis was utilized for dichotomous variables, and inverse variance method was used for continuous variables.¹¹ The statistical significance was set at P<0.05.

The difference was considered to be statistically significant if a P-value was less than 0.10 and was also quantitatively assessed by using the value of I-square (I²<25%, no heterogeneity; I² between 25% and 50%, moderate heterogeneity; and I²>50%, high heterogeneity).¹² If I²<50% or P>0.10, it shows that the studies were homogeneous or slightly heterogeneous, and we used the fix effects model to combine the effect size. If I²>50% or P<0.10, indicating that the studies were moderately or highly heterogeneous, and we employed the random effects model to combine the effect size.¹³ Statistical calculations were performed by using STATA version 12.0 (StataCorp LP, College Station, TX, USA).

Results

Search results and features of studies included

The initial search was independently executed by two reviewers, and 25 articles were preliminarily selected based on the research criteria. After screening by title and abstract, in accordance with inclusion/exclusion criteria, 19 studies were excluded. After a thorough discussion between the two reviewers, six articles were found to be related to this study. The 36 articles were then subjected to a second stage of review. Finally, a total of six studies were included for the meta-analysis. The detailed steps of the literature search are shown in Figure 1. Six studies,^14–19 covering data from a total of 898 participants, were included in this review. The information about the authors, publication year, national sources, ethnicity, method, genotype, and outcome parameter of each study are listed in Table 1. There were five studies in Asians and only one study in Caucasians. The genotype distribution in the controls of all the studies included in our meta-analysis was consistent with the Hardy–Weinberg equilibrium (HWE). Information on gene and the sample size, OR estimation, and 95% CI of each study are given in Table 2.

Figure 1 Flow diagram of the steps in the literature search.

Table 1 Characteristics of included studies in this meta-analysis

References	Country/ethnicity	Study design	Method	Sample size	Patient			Outcome parameter	HWE
313A.G(rs1695)					AA	AG	GG
Li et al^Citation14	People’s Republic of China/Asian	CCS	PCR–RFLP	162	68	63	31	TR, events, OS	Yes
Windsor et al^Citation15	United Kingdom/Caucasian	CCS	PCR–RFLP	58	25	23	2	TR, PFS	Yes
Liu et al^Citation16	People’s Republic of China/Asian	CCS	PCR–RFLP	186	76	72	38	TR, events, PFS, OS	Yes
Teng et al^Citation17	People’s Republic of China/Asian	CCS	PCR–RFLP	146	57	57	32	TR, events, OS	Yes
I105V					IIe/IIe	IIe/Val	Val/Val
Yang et al^Citation18	People’s Republic of China/Asian	CCS	PCR–RFLP	187	54	26	17	TR, OS	Yes
Zhang et al^Citation19	People’s Republic of China/Asian	CCS	TaqMan	159	93	40	26	Events, EFS, OS	Yes

Abbreviations: HWE, Hardy–Weinberg equilibrium; CCS, case-control study; PCR–RFLP, polymerase chain reaction-restriction fragment length polymorphism; TR, tumor response; OS, overall survival; PFS, progression-free survival; EFS, event-free survival.

Table 2 Patients and characteristics of the trials included in the meta-analysis

References	Genotypes	Tumor response	Event	Overall survival	Progression-free survival
		OR (95% CI)	OR (95% CI)	OR (95% CI)	OR (95% CI)
Li et al^Citation14	AA vs AG	1.67 (0.78–3.57)	1.84 (0.85–4.16)	1.84 (0.85–4.16)	NA
	Aa vs GG	3.33 (1.26–8.99)	3.86 (1.41–10.2)	3.86 (1.41–10.20)	NA
Windsor et al^Citation15	AA vs AG	7.80 (1.60–37.50)	NA	NA	3.10 (0.60–16.40)
	AA vs GG	1.60 (0.06–42.70)	NA	NA	10.00 (0.90–116.00)
Liu et al^Citation16	AA vs AG	1.53 (0.80–2.94)	1.81 (0.94–3.48)	1.58 (0.74–3.40)	1.81 (0.90–3.67)
	AA vs GG	2.11 (0.76–5.87)	4.29 (1.82–10.10)	2.80 (1.14–6.85)	4.29 (1.70–11.28)
Teng et al^Citation17	AA vs AG	1.74 (0.78–3.76)	0.83 (0.42–1.62)	1.61 (0.72–3.69)	NA
	AA vs GG	2.73 (1.07–7.81)	1.26 (0.58–2.72)	2.73 (1.05–7.45)	NA
Yang et al^Citation18	IIe/IIe vs IIe/Val	1.17 (0.57–2.43)	NA	0.85 (0.51–1.42)	NA
	IIe/IIe vs Val/Val	1.60 (0.84–4.15)	NA	0.53 (0.24–1.16)	NA
Zhang et al^Citation19	IIe/IIe vs IIe/Val	NA	NA	1.93 (0.98–3.45)	NA
	IIe/IIe vs Val/Val	NA	NA	2.35 (1.13–4.85)	NA

Abbreviations: OR, odds ratio; CI, confidence interval; NA, not available.

Result of meta-analysis

A meta-analysis was performed on studies relating to GSTP1 313A>G(rs1695) to assess the association between tumor response in osteosarcoma patients treated with chemotherapy and the polymorphisms in GSTP1 (AA vs AG, AA vs GG). The pooled ORs were 2.06 (95% CI: 1.48–2.86, P=0.628, I²=0.0%) (Figure 2). There was significant association between the polymorphisms in GSTP1 (AA vs AG, AA vs GG) and the events that happen in osteosarcoma patients treated with chemotherapy, and the pooled ORs were 1.86 (95% CI: 1.14–3.06, P=0.034, I²=58.6%) (Figure 3). There was significant association between the polymorphisms in GSTP1 (AA vs AG, AA vs GG) and survival times (overall survival and progression-free survival) in osteosarcoma patients treated with chemotherapy, the pooled ORs were 2.14 (95% CI: 1.51–3.04, P=0.675, I²=0.0%) and 2.77(95% CI: 1.56–4.91, P=0.347, I²=9.3%), respectively (Figures 4 and 5).

Figure 2 Association between GSTP1 313A>G(rs1695) polymorphism and tumor response in osteosarcoma patients treated with chemotherapy.

Note: Weights are from random effects analysis.
Abbreviations: OR, odds ratio; CI, confidence interval.

Figure 3 Association between GSTP1 313A>G(rs1695) polymorphism and events that occur in osteosarcoma patients treated with chemotherapy.

Note: Weights are from random effects analysis.
Abbreviations: OR, odds ratio; CI, confidence interval.

Figure 4 Association between GSTP1 313A>G(rs1695) polymorphism and overall survival in osteosarcoma patients treated with chemotherapy.

Note: Weights are from random effects analysis.
Abbreviations: OR, odds ratio; CI, confidence interval.

Figure 5 Association between GSTP1 313A>G(rs1695) polymorphism and progression-free survival in osteosarcoma patients treated with chemotherapy.

Note: Weights are from random effects analysis.
Abbreviations: OR, odds ratio; CI, confidence interval.

Two studies assessed the association of polymorphisms in GSTP1 I105V (IIe/IIe vs IIe/Val, IIe/IIe vs Val/Val) with overall survival in human osteosarcoma. The pooled ORs were 1.20 (95% CI: 0.64–2.27, P=0.010, I²=73.5%) (Figure 6). The study showed an insignificant difference in overall survival for the polymorphisms in GSTP1 (IIe/IIe vs IIe/Val, IIe/IIe vs Val/Val).

Figure 6 Association between GSTP1 I105V polymorphism and overall survival in osteosarcoma patients treated with chemotherapy.

Note: Weights are from random effects analysis.
Abbreviations: OR, odds ratio; CI, confidence interval.

Publication bias

We did not draw funnel plots to demonstrate publication bias, because the number of studies included was comparatively small.

Discussion

The GST gene is a target gene which can regulate human metabolism, the immune and endocrine systems, and has a close relationship with the occurrence of osteosarcoma. It has been confirmed that different GST genes have different conversion efficiencies and enantioselectivities for various toxins which may lead to cancer.^8,20 GSTP1 is the most important member of GST family, which takes part in the detoxification of electrophilic compounds by glutathione conjugation.²¹ GSTP1 polymorphism links to enzymatic activity, and the polymorphism may confer susceptibility to cancers. A number of studies have focused on GSTP1 polymorphism and the risk of various kinds of cancers, including osteosarcoma, ovarian carcinoma, prostate cancer, and bladder cancer,^6,8,22,23 but the polymorphism was not considered to be linked with susceptibility to the chemotherapy of osteosarcoma patients. This study was performed to investigate the association between GSTP1 polymorphism and chemotherapy of osteosarcoma.

To the best of our knowledge, our study is the first meta-analysis assessing the association between GSTP1 polymorphism and chemotherapy of osteosarcoma. In this study, an obvious association among tumor response, events, and survival times was found in GSTP1 313A>G(rs1695) under the recessive model, but there was no obvious association between survival times and chemotherapy of osteosarcoma in GSTP1 I105V. We concluded that the GSTP1 313A>G(rs1695) polymorphism may be associated with chemotherapy of osteosarcoma. Although we use this comprehensive analysis to demonstrate the association between GSTP1 polymorphism and chemotherapy of osteosarcoma, some limitations still exist. On the one hand, not all of the studies used controls that were population-based, and some risk factors such as age, family history, and environmental factors were unadjusted estimates, which may cause confounding bias. And on the other hand, the number of studies and the number of samples included in this meta-analysis were relatively small. Therefore, we need additional studies with larger sample size and providing more detailed information to assess the effect of GSTP1 313A>G(rs1695) and I105V polymorphism on osteosarcoma with chemotherapy. In spite of the above shortcomings, our study still had the advantage that a meta-analysis of the association of GSTP1 polymorphism on chemotherapy of osteosarcoma is statistically more powerful than any single study, and we found that I105V gene polymorphism did not show an obvious association with chemotherapy of osteosarcoma. Whether GSTP1 polymorphism can be used as an indicator of the risk of osteosarcoma in patients and as a prognostic marker in osteosarcoma patients undergoing chemotherapy warrants further study.

Acknowledgments

This research was supported by the National Natural Science Foundation of China (grant number 81372004).

Disclosure

The authors report no conflicts of interest in this work.