Anticancer effects of metformin in experimental animal models of different types of cancer: a systematic review and meta-analysis

Association of metformin use and cancer incidence: a systematic review and meta-analysis

BACKGROUND

Metformin is among the most widely used antidiabetics medications because of its minimal toxicity, favorable safety profile, availability, and low cost. In addition to its role in diabetes management, metformin may reduce cancer risk.

METHODS

We conducted a comprehensive systematic review and meta-analysis to investigate the association between metformin use and cancer risk, with evaluation by specific cancer type when possible. Applicable studies were identified in PubMed/MEDLINE, Embase, Cochrane Library, Web of Science, and Scopus from inception through March 7, 2023, with metformin use categorized as "ever" or "yes" and a cancer diagnosis as the outcome. Article quality was evaluated using National Heart, Lung, and Blood Institute guidelines, and publication bias was evaluated using the Egger test, Begg test, and funnel plots. Pooled relative risk (RR) estimates were calculated using random-effects models, and sensitivity analysis was completed through leave-one-out cross-validation.

RESULTS

We included 166 studies with cancer incidence information in the meta-analysis. Reduced risk for overall cancer was observed in case-control studies (RR = 0.55, 95% confidence interval [CI] = 0.30 to 0.80) and prospective cohort studies (RR = 0.65, 95% CI = 0.37 to 0.93). Metformin use was associated with reduced gastrointestinal (RR = 0.79, 95% CI = 0.73 to 0.85), urologic (RR = 0.88, 95% CI = 0.78 to 0.99), and hematologic (RR = 0.87, 95% CI = 0.75 to 0.99) cancer risk. Statistically significant publication bias was observed within the studies (Egger P < .001).

CONCLUSIONS

Metformin may be associated with a decreased risk of many cancer types, but high heterogeneity and risk of publication bias limit confidence in these results. Additional studies in populations without diabetes are needed to better understand the utility of metformin in cancer prevention.

Addition of metformin for non-small cell lung cancer patients receiving antineoplastic agents

Background and purpose: Previous studies have found that metformin can inhibit tumor growth and improve outcomes for cancer patients. However, the association between the addition of metformin to the treatment regimen and survival in non-small cell lung cancer (NSCLC) patients receiving antineoplastic agents such as chemotherapy drugs, epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs), and immune checkpoint inhibitors (ICIs) remains unclear. This study aimed to evaluate the effect of metformin in NSCLC patients who received the aforementioned antineoplastic therapies.

Methods: Several electronic databases were searched for relevant studies published by 10 September 2022. The primary and secondary outcomes were overall survival (OS) and progression-free survival (PFS); eligible studies were those comparing patients with and without the addition of metformin. Hazard ratios (HRs) and 95% confidence intervals (CIs) were combined, with all statistical analyses performed using STATA 15.0.

Results: A total of 19 studies involving 6,419 participants were included, of which six were randomized controlled trials. The overall pooled results indicate that the addition of metformin improved OS (HR = 0.84, 95% CI: 0.71–0.98, p = 0.029) and PFS (HR = 0.85, 95% CI: 0.74–0.99, p = 0.039). However, subgroup analysis based on treatment type and comorbidity of diabetes mellitus demonstrated that improvements in OS and PFS were observed only in diabetic and EGFR-TKI-treated patients (OS: HR = 0.64, 95% CI: 0.45–0.90, p = 0.011; PFS: HR = 0.59, 95% CI: 0.34–1.03, p = 0.061).

Conclusion: Overall, this meta-analysis found that metformin use could improve outcomes for diabetic patients receiving EGFR-TKIs. However, no significant association between the addition of metformin and the survival of non-diabetic NSCLC patients receiving chemotherapy or ICI therapy was identified based on the current evidence.

Metformin Treatment Modulates Long Non-Coding RNA Isoforms Expression in Human Cells

Long noncoding RNAs (lncRNAs) undergo splicing and have multiple transcribed isoforms. Nevertheless, for lncRNAs, as well as for mRNA, measurements of expression are routinely performed only at the gene level. Metformin is the first-line oral therapy for type 2 diabetes mellitus and other metabolic diseases. However, its mechanism of action remains not thoroughly explained. Transcriptomic analyses using metformin in different cell types reveal that only protein-coding genes are considered. We aimed to characterize lncRNA isoforms that were differentially affected by metformin treatment on multiple human cell types (three cancer, two non-cancer) and to provide insights into the lncRNA regulation by this drug. We selected six series to perform a differential expression (DE) isoform analysis. We also inferred the biological roles for lncRNA DE isoforms using in silico tools. We found the same isoform of an lncRNA (AC016831.6-205) highly expressed in all six metformin series, which has a second exon putatively coding for a peptide with relevance to the drug action. Moreover, the other two lncRNA isoforms (ZBED5-AS1-207 and AC125807.2-201) may also behave as cis-regulatory elements to the expression of transcripts in their vicinity. Our results strongly reinforce the importance of considering DE isoforms of lncRNA for understanding metformin mechanisms at the molecular level.