The Efficacy of Adjuvant Chloroquine for Glioblastoma: A Meta-Analysis of Randomized Controlled Studies

Abstract

Introduction  The efficacy of adjuvant chloroquine for glioblastoma remains controversial. We conduct a systematic review and meta-analysis to explore the influence of adjuvant chloroquine on treatment efficacy for recurrent glioblastoma.

Methods  We search PubMed, Embase, Web of science, EBSCO, and Cochrane library databases through January 2020 for randomized controlled trials (RCTs) assessing the efficacy of adjuvant chloroquine for glioblastoma. This meta-analysis is performed using the random-effect model.

Results  Three RCTs are included in the meta-analysis. Overall, compared with control group for glioblastoma, adjuvant chloroquine is associated with significantly reduced mortality (risk ratio [RR] = 0.59; 95% confidence interval [CI] = 0.47–0.72; p  < 0.00001), improved remission (RR = 11.53; 95% CI = 1.53–86.57; p  = 0.02), and prolonged survival time (Std.MD = 11.53; 95% CI = 1.53–86.57; p  = 0.02), but has no substantial effect on recurrence (RR = 0.42; 95% CI = 0.12–1.49; p  = 0.18).

Conclusion  Adjuvant chloroquine may provide additional benefits for the treatment of glioblastoma.

Introduction

Relatively few advances in therapy are obtained despite the development of the diagnosis of glioblastoma multiforme. ^{1 2 3} The prognosis of these patients still has not changed considerably. ^{4 5 6} The median survival of 14 to 16 months for glioblastoma is estimated to be 26 to 33% 2-year survival rate. ^{7 8} Stereotactic radiosurgery is regarded as one of the most sophisticated approaches, but still has failed to improve survival or quality of life. ⁹

These poor prognosis may be caused by the infiltrative nature of glioblastoma multiforme and the presence of cancer cells resistant to radiotherapy and chemotherapy. ⁴ Ionizing radiation and antineoplastic drugs are found to increase the rate of mutagenesis of malignant glial cells. ^{10 11} Antimalarial drugs such as chloroquine and quinacrine are lysosomotropic and strong deoxyribonucleic acid-intercalating agents. Chloroquine and quinacrine are antimutagenic in the cancer cells, but they have no substantial antineoplastic effect. ¹² In cultured glioma cells and in malignant glioma in rats, chloroquine has a strong potentiating effect on the antineoplastic action of carmustine and maintains the long-term susceptibility of malignant glioma cells to chemotherapy. ¹³

Current evidence is insufficient for routine clinical use of adjuvant chloroquine for glioblastoma. Recently, several studies have investigated the efficacy of adjuvant chloroquine for these patients, but the results are conflicting. ^{4 11 14} The therapeutic dose and toxic dose of chloroquine were 10 mg/kg and 20 mg/kg separately. The patients received chloroquine 150 mg/day plus standard therapy for glioblastoma generally. ^{4 11 14} This systematic review and meta-analysis of randomized controlled trails (RCTs) aim to assess the efficacy of adjuvant chloroquine for glioblastoma.

Materials and Methods

This systematic review and meta-analysis are performed based on the guidance of the Preferred Reporting Items for Systematic Reviews and Meta-Analysis statement and Cochrane Handbook for Systematic Reviews of Interventions. ^{15 16} No ethical approval and patient consent are required because all analyses are based on previous published studies.

Literature Search and Selection Criteria

We systematically search several databases including PubMed, Embase, Web of science, EBSCO, and the Cochrane library from inception to January 2020 with the following keywords: chloroquine and glioblastoma. The reference lists of retrieved studies and relevant reviews are also hand-searched and the process above is performed repeatedly to include additional eligible studies.

The inclusion criteria are presented as follows: (1) study design is RCT, (2) patients are diagnosed as glioblastoma, and (3) intervention treatments are chloroquine plus standard therapy versus standard therapy.

Data Extraction and Outcome Measures

Some baseline information is extracted from the original studies, and they include first author, number of patients, age, female, Karnofsky score, and detailed methods in two groups. Data are extracted independently by two investigators, and discrepancies are resolved by consensus. We have contacted the corresponding author to obtain the data when necessary.

The primary outcomes are mortality and remission. Secondary outcomes include survival time and recurrence.

Quality Assessment in Individual Studies

The methodological quality of each RCT is assessed by the Jadad Scale which consists of three evaluation elements: randomization (0–2 points), blinding (0–2 points), dropouts and withdrawals (0–1 points). ¹⁷ One point would be allocated to each element if they have been conducted and mentioned appropriately in the original article. The score of Jadad Scale varies from 0 to 5 points. An article with Jadad score ≤ 2 is considered to be of low quality. The study is thought to be of high quality if Jadad score ≥ 3. ¹⁸

Statistical Analysis

We assess risk ratios (RR) with 95% confidence interval (CI) for dichotomous outcomes (mortality, remission, and recurrence) and standard mean difference (Std. MD) for continuous outcomes (survival time). Heterogeneity is evaluated using the I ² statistic, and I ²  > 50% indicates significant heterogeneity. ¹⁹ The random-effect model is used for all meta-analysis. We search for potential sources of heterogeneity for significant heterogeneity. Sensitivity analysis is performed to detect the influence of a single study on the overall estimate via omitting one study in turn or performing the subgroup analysis. Owing to the limited number (<10) of included studies, publication bias is not assessed. Results are considered as statistically significant for p  < 0.05. All statistical analyses are performed using Review Manager Version 5.3 (The Cochrane Collaboration, Software Update, Oxford, UK).

Results

Literature Search, Study Characteristics, and Quality Assessment

Fig. 1 shows the detail flowchart of the search and selection results. One-hundred forty-five potentially relevant articles are identified initially. Finally, three RCTs are included in the meta-analysis. ^{4 11 14}

Fig. 1.

Flow diagram of study searching and selection process.

The baseline characteristics of three included RCTs are shown in Table 1 . These studies are published between 2003 and 2011, and the total sample size is 144. Among the included RCTs, chloroquine is administered at the dose of 150 mg daily, and the follow-up time ranges from 5 to 59 months.

Table 1. Characteristics of included studies.

Number	Authors	Chloroquine group					Control group						Jadad scores
		Number	Age	Female ( n )	Karnofsky score	Methods	Number	Age	Female ( n )	Karnofsky score	Methods	Follow-up
1	Cheng 2011	48	47.3 ± 2.6	–	–	Chloroquine 150 mg/d plus standard therapy	48	47.3 ± 2.6	–	–	Standard therapy	24–50 mo	3
2	Sotelo et al 2006 4	15	40.8 ± 11.8	6	81.3 ± 9.9	Oral chloroquine at 150 mg/d for 12 mo plus standard therapy	15	46.1 ± 12.7	7	82.7 ± 11.6	Standard therapy	5–59 mo	4
3	Briceño et al 2003 11	9	33.6 ± 10.2	3	86.7 ± 13.2	150-mg dose of chloroquine daily plus standard therapy	9	36 ± 10.1	4	88.9 ± 6	Standard therapy	24–50 mo	4

Three studies report mortality, ^{4 11 14} two studies report remission, ^{11 14} two studies report survival time, ^{4 11} and two studies report recurrence. ^{11 14} Jadad scores of the three included studies vary from 3 to 4, and all three studies have high-quality based on the quality assessment.

Primary Outcomes: Mortality and Recurrence

The random-effect model is used for the analysis of primary outcomes. The results find that compared with control group for glioblastoma, adjuvant chloroquine is associated with significantly reduced mortality (RR = 0.59; 95% CI = 0.47–0.72; p  < 0.00001) with no heterogeneity among the studies ( I ²  = 0%, heterogeneity p  = 0.53, Fig. 2 ) and improved remission (RR = 11.53; 95% CI = 1.53–86.57; p  = 0.02) with no heterogeneity among the studies ( I ²  = 0%, heterogeneity p  = 0.43, Fig. 3 ).

Fig. 2.

Forest plot for the meta-analysis of mortality. CI, confidence interval; IV, intravenous.

Fig. 3.

Forest plot for the meta-analysis of remission. CI, confidence interval; IV, intravenous.

Sensitivity Analysis

There is no heterogeneity for objective response, and thus we do not perform sensitivity analysis by omitting one study in each turn to detect the source of heterogeneity.

Secondary Outcomes

In comparison with control group for glioblastoma, adjuvant chloroquine can substantially prolong survival time (Std.MD = 11.53; 95% CI = 1.53–86.57; p  = 0.02; Fig. 4 ), but demonstrate no substantial impact on recurrence (RR = 0.42; 95% CI = 0.12–1.49; p  = 0.18; Fig. 5 ).

Fig. 4.

Forest plot for the meta-analysis of survival time. CI, confidence interval; IV, intravenous.

Fig. 5.

Forest plot for the meta-analysis of recurrence. CI, confidence interval; IV, intravenous.

Discussion

Despite the advances in maximal safe surgical resection, radiotherapy with concurrent chemotherapy, glioblastoma still has poor prognosis. ^{20 21 22} Median survival after aggressive treatment combining surgery, radiotherapy, and chemotherapy was ∼1 year. ^{23 24} In patients with tumor progression, combinational therapies result in the objective response rate of 6%, 6-month progression free survival of 15%, and median overall survival of 6 months. ^{25 26}

The addition of chloroquine to the conventional therapeutic approach for glioblastoma multiforme shows the potential in increasing mid-term survival, ⁴ which may be more effective than other recently with novel chemotherapeutic agents. ⁷ Our meta-analysis suggests that adjuvant chloroquine can substantially reduce the mortality and improve remission, survival time for glioblastoma, but shows no obvious influence on the recurrence. Chloroquine is not a cytotoxic substance, and has no relevant antineoplastic effect. The effect adjunct chloroquine on therapy may rely on the enhancement of cytotoxicity induced by conventional treatments or the prevention of mutagenicity in neoplastic cells, which maintains the susceptibility to radiotherapy and chemotherapy.

Additional intracellular actions of chloroquine may increase the susceptibility of malignant glioma cells to standard therapy. Some neoplastic drugs have extended permanence inside cancer cells because of elevation of endosomal and lysosomal pH, which increase and maintains the concentration of lipophilic antineoplastic drugs (e.g., carmustine). ^{27 28} Chloroquine is able to prevent and delay the outward cell transport of antineoplastic drugs like vincristine. This conspicuous effect can effectively reverse multidrug resistance of cancer cells. ^{4 29} Regarding the adverse events, hematologic results were found to be similar between chloroquine-treated patients and control patients. One trial reported that mean values of leukocytes and platelets were lower in chloroquine-treated group than those in control group at the 8 months after the beginning of treatment, but they became comparable after another 1 month. ⁴ Chloroquine is not cytotoxic and safe for patients.

Several limitations exist here. First, our analysis is based on only three RCTs, and more RCTs with large sample size should be conducted to explore this issue. Next, different combination treatment and patients population may have some influence on the pooling results. Finally, some unpublished and missing data may lead to some bias to the pooled effect.

Conclusion

Adjuvant chloroquine may increase the efficacy of standard therapy for glioblastoma.