Association between metformin medication, genetic variation and prostate cancer risk

Drug-target Mendelian randomization revealed a significant association of genetically proxied metformin effects with increased prostate cancer risk

The association between metformin use and risk of prostate cancer remains controversial, while data from randomized trials is lacking. We aim to evaluate the association of genetically proxied metformin effects with prostate cancer risk using a drug-target Mendelian randomization (MR) approach. Summary statistics for prostate cancer were obtained from the Prostate Cancer Association Group to Investigate Cancer Associated Alterations in the Genome Consortium (79,148 cases and 61,106 controls). Cis-expression quantitative trait loci (cis-eQTL) variants in the gene targets of metformin were identified in the GTEx project and eQTLGen consortium. We also obtained male-specific genome-wide association study data for type 2 diabetes, body mass index (BMI), total testosterone, bioavailable testosterone, estradiol, and sex hormone binding globulin for mediation analysis. Inverse-variance weighted (IVW) regression, weighted median, MR-Egger regression, and MR-PRESSO were performed in the main MR analysis. Multivariable MR was used to identify potential mediators and genetic colocalization analysis was performed to assess any shared genetic basis between two traits of interest. We found that genetically proxied metformin effects (1-SD HbA1c reduction, equivalent to 6.75 mmol/mol) were associated with higher risk of prostate cancer (odds ratioIVW [ORIVW]: 1.55, 95% confidence interval, CI: 1.23-1.96, p = 3.0 × 10-3). Two metformin targets, mitochondrial complex I (ORIVW: 1.48, 95% CI: 1.07-2.03, p = 0.016) and gamma-secretase complex (ORIVW: 2.58, 95%CI :1.47-4.55, p = 0.001), showed robust associations with prostate cancer risk, and their effects were partly mediated through BMI (16.4%) and total testosterone levels (34.3%), respectively. These results were further supported by colocalization analysis that expressions of NDUFA13 and BMI, APH1A, and total testosterone may be influenced by shared genetic factors, respectively. In summary, our study indicated that genetically proxied metformin effects may be associated with an increased risk of prostate cancer. Repurposing metformin for prostate cancer prevention in general populations is not supported by our findings.

[Metformin and malignant neoplasms: a possible mechanism of antitumor action and prospects for use in practice]

Metformin is a first-line antidiabetic drug for the treatment of type 2 diabetes mellitus (DM2); its molecular target is AMP-activated protein kinase (AMPK), which is involved in many metabolic processes. Metformin not only reduces blood glucose levels and improves insulin sensitivity, but also inhibits lipolysis and reduces cardiovascular risk in patients with DM2. In recent years, it has been proven that metformin slows down the aging process, stimulates hair growth, eliminates cognitive impairment, and also has an antitumor effect. Most basic studies have shown that metformin inhibits the growth of tumor cells and promotes cellular apoptosis, while clinical studies show contradictory results. This discrepancy can be explained by the difference in the concentration of metformin between basic and clinical studies. The maximum daily dose of metformin for patients with DM2 is 2500 mg / day, and the dose used in basic research was much higher. Metformin directly activates the AMPK signaling pathway, inhibits the production of reactive oxygen species, induces the activation of mTORC1, inhibits cyclin D1, which leads to a reduction in the risk of the occurrence and development of malignant neoplasms. In addition, metformin indirectly inhibits tumor growth, proliferation, invasion and metastasis by reducing the concentration of glucose in the blood, insulin resistance, as well as by reducing inflammation and affecting the tumor microenvironment. Glycolysis plays an important role in the energy metabolism of tumors, and metformin is able to have an inhibitory effect on it. Currently, studies of the mechanism of antitumor effects of metformin are becoming more extensive and in-depth, but there are still some contradictions.

Targeting of the tumor immune microenvironment by metformin

Stimulating antitumor immunity is an attractive idea for suppressing tumors. CD4 + and CD8 + T cells as well as natural killer cells (NK) are the primary antitumor immune cells in the tumor microenvironment (TME). In contrast to these cells, regulatory T cells (Tregs), myeloid-derived suppressor cells (MDSCs), cancer-associated fibroblasts (CAFs), and tumor-associated macrophages (TAMs) release several molecules to suppress antitumor immunity and stimulate cancer cell invasion and proliferation. Adjuvant treatment with certain nontoxic agents is interesting to boost antitumor immunity. Metformin, which is known as an antidiabetes drug, can modulate both antitumor and protumor immune cells within TME. It has the ability to induce the proliferation of CD8 + T lymphocytes and NK cells. On the other hand, metformin attenuates polarization toward TAMs, CAFs, and Tregs. Metformin also may stimulate the antitumor activity of immune system cells, while it interrupts the positive cross-talk and interactions between immunosuppressive cells and cancer cells. The purpose of this review is to explain the basic mechanisms for the interactions and communications between immunosuppressive, anti-tumoral, and cancer cells within TME. Next, we discuss the modulating effects of metformin on various cells and secretions in TME.

Metformin and Malignant Tumors: Not Over the Hill

Malignant tumors are a major cause of death, and their incidence is increasing worldwide. Although the survival rate for some cancers has improved, treatments for other malignant tumors are limited, and their mortality rate continues to increase. People with type 2 diabetes have a higher risk of malignant tumors and a higher mortality rate than those without diabetes. Metformin is a commonly used hypoglycemic drug. In recent years, a growing number of studies have indicated that metformin has antitumor effects and increases the sensitivity of malignant tumors to chemotherapy. However, the effect of metformin on different tumors is currently controversial, and the mechanism of metformin's antitumor action is not fully understood. Insights into the effect of metformin on malignant tumors and the possible mechanism may contribute to the development of antitumor drugs.

Isolation and characterization of castration-resistant prostate cancer LNCaP95 clones

The androgen receptor (AR) is a validated therapeutic target for prostate cancer and has been a focus for drug development for more than six decades. Currently approved therapies that inhibit AR signaling, such as enzalutamide, rely solely on targeting the AR ligand-binding domain and, therefore, have limited efficacy on prostate cancer cells that express truncated, constitutively active AR splice variants (AR-Vs). The LNCaP95 cell line is a human prostate cancer cell line that expresses both functional full-length AR and AR-V7. LNCaP95 is a heterogeneous cell population that is resistant to enzalutamide, with its proliferation dependent on transcriptionally active AR-V7. The purpose of this study was to identify a LNCaP95 clone that would be useful for evaluating therapies for their effectiveness against enzalutamide-resistant prostate cancer cells. Seven clones from the LNCaP95 cell line were isolated and characterized using morphology, in vitro growth rate, and response to ralaniten (AR N-terminal domain inhibitor) and enzalutamide (antiandrogen). In vivo growth of the clones as subcutaneous xenografts was evaluated in castrated immunodeficient mice. All of the clones maintained the expression of full-length AR and AR-V7. Cell proliferation of the clones was insensitive to androgen and enzalutamide but importantly was inhibited by ralaniten, which is consistent with AR-Vs driving the proliferation of parental LNCaP95 cells. In castrated immunodeficient animals, the growth of subcutaneous xenografts of the D3 clone was the most reproducible compared to the parental cell line and other clones. These data support that the enzalutamide-resistant LNCaP95-D3 subline may be suitable as a xenograft tumor model for preclinical drug development with improved reproducibility.