Early treatment with metformin induces resistance against tumor growth in adult rats

Abstract

It is known that antidiabetic drug metformin, which is used worldwide, has anti-cancer effects and can be used to prevent cancer growth. We tested the hypothesis that tumor cell growth can be inhibited by early treatment with metformin. For this purpose, adult rats chronically treated with metformin in adolescence or in adulthood were inoculated with Walker 256 carcinoma cells. Adult rats that were treated with metformin during adolescence presented inhibition of tumor growth, and animals that were treated during adult life did not demonstrate any changes in tumor growth. Although we do not have data to disclose a molecular mechanism to the preventive metformin effect, we present, for the first time, results showing that cancer growth in adult life is dependent on early life intervention, thus supporting a new therapeutic prevention for cancer.

Keywords: AUC, area under the curve; HOMA-IR, homeostasis model assessment of insulin resistance; HOMA-β, homeostasis model assessment of β-cell function; LBW, body weight loss; MHC-I, major histocompatibility complex class I; NAL, nasal anal length; VEGF, vascular endothelial growth factor.; Walker 256 tumor; adolescence; antidiabetic; early treatment; metformin; prevention; tumor growth inhibition.

Figure 1.

Schematic representation of the protocols. Metformin treatment was initiated during 2 different age periods, at weaning or during adulthood. For this purpose, 21-day-old male rats were submitted to metformin gavage once a day until they reached 100 d old. Another batch of animals, at 60 d old, were submitted to metformin gavage until the reached 139 d old. Thus, both groups of rats received metformin treatment for 79 d, and the same procedure was performed with the groups that received water instead of the drug. After treatment ended, 101-day-old animals and 140-day-old animals were inoculated subcutaneously with carcinoma cells, and after 14 d of inoculation, the animals were sacrificed and subsequent protocols performed.

Figure 2.

The effect of chronic metformin treatment initiated during 2 different ages on tumor growth of rats. The bars represent the mean ± SEM of the tumor mass related to body weight that were obtained from 12 animals for each group. In the insert of figure, the bars represent the mean ± SEM of tumor mass (g). The letters over the bars represent statistically significant differences among the groups based on one-way ANOVA (P <0.0001); the treatment groups were as follows: (A) Water treatment from 21 to 100 d old, (B) Metformin treatment from 21 to 100-day-old, (C) Water treatment from 60 to 139 d old and (D) Metformin treatment from 60 to 139 d old.

Figure 3.

Percentage of Cachexia. The bars represent the mean ± SEM of% of rats that lost more than 10% of body weight, which were obtained from 12 animals for each group. The letters over the bars represent statistically significant differences among the groups based on one-way ANOVA (P < 0.0001); where: (A) Water treatment from 21 to 100-day-old, (B) Metformin treatment from 21 to 100 d old, (C) Water treatment from 60 to 139 d old and (D) Metformin treatment from 60 to 139 d old.

Figure 4.

The effect of chronic metformin treatment initiated during 2 different ages on fasting insulinemia of rats with or without inoculation with Walker 256 tumor cells. The bars represent the mean ± SEM of fasting plasma insulin levels obtained from 12 rats for group in which treatment was initiated at 21-day-old to 100 day-old (A) and the group in which treatment was initiated at 60-day-old to 139-day-old (B). The letters over the bars represent statistically significant differences among the groups based on one-way ANOVA (P < 0.0001); where: a) Animals that received water treatment from 21 to 100-day-old or from 60 to 139-day-old without tumor cells grafted and b) with tumor cells grafted; (C) Animals that received metformin treatment from 21 to 100-day-old or from 60 to 139-day-old without tumor cells grafted and (D) with tumor cells grafted. The symbols (−) and (+) indicate the absence or presence of tumor, respectively.