A dual-functional buformin-mimicking poly(amido amine) for efficient and safe gene delivery.

Biguanides (i.e. metformin, phenformin and buformin) are antidiabetic drugs with potential antitumor effects. Herein, a polycationic polymer, N,N'-bis(cystamine)acrylamide-buformin (CBA-Bu), containing multiple biodegradable disulphide bonds and buformin-mimicking side chains was synthesised. CBA-Bu was equipped with high efficiency and safety profile for gene delivery, meanwhile exhibiting potential antitumor efficacy. As a gene vector, CBA-Bu was able to condense plasmid DNA (pDNA) into nano-sized (<200 nm), positively-charged (>30 mV) uniform polyplexes that were well resistant to heparin and DNase I. Due to the reduction responsiveness of the disulphide bonds, CBA-Bu/pDNA polyplexes could release the loaded pDNA in the presence of dithiothreitol, and induce extremely low cytotoxicity in NIH/3T3 and U87 MG cells. The transfection results showed that CBA-Bu had a cellular uptake efficiency comparable to 25 kDa PEI, while a significantly higher gene expression level. Additionally, CBA-Bu had a lower IC50 value than its non-biguanide counterpart in two cancer cell lines. Furthermore, CBA-Bu could activate AMPK and inhibit mTOR pathways in U87 MG cells, a mechanism involved in the antitumor effect of biguanides. Taken together, CBA-Bu represented an advanced gene vector combining desirable gene delivery capability with potential antitumor activity, which was promising to achieve enhanced therapeutic efficacy in antitumor gene therapy.

Buformin inhibits the stemness of erbB-2-overexpressing breast cancer cells and premalignant mammary tissues of MMTV-erbB-2 transgenic mice.

BACKGROUND: Metformin, an FDA-approved drug for the treatment of Type II diabetes, has emerged as a promising anti-cancer agent. Other biguanide analogs, including buformin and phenformin, are suggested to have similar properties. Although buformin was shown to reduce mammary tumor burden in carcinogen models, the anti-cancer effects of buformin on different breast cancer subtypes and the underlying mechanisms remain unclear. Therefore, we aimed to investigate the effects of buformin on erbB-2-overexpressing breast cancer with in vitro and in vivo models. METHODS: MTT, cell cycle, clonogenic/CFC, ALDEFLUOR, tumorsphere, and Western blot analyses were used to determine the effects of buformin on cell growth, stem cell populations, stem cell-like properties, and signaling pathways in SKBR3 and BT474 erbB-2-overexpressing breast cancer cell lines. A syngeneic tumor cell transplantation model inoculating MMTV-erbB-2 mice with 78617 mouse mammary tumor cells was used to study the effects of buformin (1.2 g buformin/kg chow) on tumor growth in vivo. MMTV-erbB-2 mice were also fed buformin for 10 weeks, followed by analysis of premalignant mammary tissues for changes in morphological development, mammary epithelial cell (MEC) populations, and signaling pathways. RESULTS: Buformin significantly inhibited SKBR3 and BT474 cell growth, and in vivo activity was demonstrated by considerable growth inhibition of syngeneic tumors derived from MMTV-erbB-2 mice. In particular, buformin suppressed stem cell populations and self-renewal in vitro, which was associated with inhibited receptor tyrosine kinase (RTK) and mTOR signaling. Consistent with in vitro data, buformin suppressed mammary morphogenesis and reduced cell proliferation in MMTV-erbB-2 mice. Importantly, buformin decreased MEC populations enriched with mammary reconstitution units (MRUs) and tumor-initiating cells (TICs) from MMTV-erbB-2 mice, as supported by impaired clonogenic and mammosphere formation in primary MECs. We further demonstrated that buformin-mediated in vivo inhibition of MEC stemness is associated with suppressed activation of mTOR, RTK, ER, and ß-catenin signaling pathways. CONCLUSIONS: Overall, our results provide evidence for buformin as an effective anti-cancer drug that selectively targets TICs, and present a novel prevention and/or treatment strategy for patients who are genetically predisposed to erbB-2-overexpressing breast cancer.

The enhancement of oxidative DNA damage by anti-diabetic metformin, buformin, and phenformin, via nitrogen-centered radicals.

Metformin (N,N-dimethylbiguanide), buformin (1-butylbiguanide), and phenformin (1-phenethylbiguanide) are anti-diabetic biguanide drugs, expected to having anti-cancer effect. The mechanism of anti-cancer effect by these drugs is not completely understood. In this study, we demonstrated that these drugs dramatically enhanced oxidative DNA damage under oxidative condition. Metformin, buformin, and phenformin enhanced generation of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) in isolated DNA reacted with hydrogen peroxide (H2O2) and Cu(II), although these drugs did not form 8-oxodG in the absence of H2O2 or Cu(II). An electron paramagnetic resonance (EPR) study, utilizing alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone and 3,3,5,5-tetramethyl-1-pyrroline-N-oxide as spin trapping agents, showed that nitrogen-centered radicals were generated from biguanides in the presence of Cu(II) and H2O2, and that these radicals were decreased by the addition of DNA. These results suggest that biguanides enhance Cu(II)/H2O2-mediated 8-oxodG generation via nitrogen-centered radical formation. The enhancing effect on oxidative DNA damage may play a role on anti-cancer activity.

Biguanide-induced mitochondrial dysfunction yields increased lactate production and cytotoxicity of aerobically-poised HepG2 cells and human hepatocytes in vitro.

As a class, the biguanides induce lactic acidosis, a hallmark of mitochondrial impairment. To assess potential mitochondrial impairment, we evaluated the effects of metformin, buformin and phenformin on: 1) viability of HepG2 cells grown in galactose, 2) respiration by isolated mitochondria, 3) metabolic poise of HepG2 and primary human hepatocytes, 4) activities of immunocaptured respiratory complexes, and 5) mitochondrial membrane potential and redox status in primary human hepatocytes. Phenformin was the most cytotoxic of the three with buformin showing moderate toxicity, and metformin toxicity only at mM concentrations. Importantly, HepG2 cells grown in galactose are markedly more susceptible to biguanide toxicity compared to cells grown in glucose, indicating mitochondrial toxicity as a primary mode of action. The same rank order of potency was observed for isolated mitochondrial respiration where preincubation (40 min) exacerbated respiratory impairment, and was required to reveal inhibition by metformin, suggesting intramitochondrial bio-accumulation. Metabolic profiling of intact cells corroborated respiratory inhibition, but also revealed compensatory increases in lactate production from accelerated glycolysis. High (mM) concentrations of the drugs were needed to inhibit immunocaptured respiratory complexes, supporting the contention that bioaccumulation is involved. The same rank order was found when monitoring mitochondrial membrane potential, ROS production, and glutathione levels in primary human hepatocytes. In toto, these data indicate that biguanide-induced lactic acidosis can be attributed to acceleration of glycolysis in response to mitochondrial impairment. Indeed, the desired clinical outcome, viz., decreased blood glucose, could be due to increased glucose uptake and glycolytic flux in response to drug-induced mitochondrial dysfunction.

The inhibition of the transplacental blastomogenic effect of nitrosomethylurea by postnatal administration of buformin to rats.

N-Nitrosomethylurea (NMU) (20 mg/kg) was i.p. administered to rats on the 21st day of pregnancy. A decrease of glucose utilisation in the oral glucose tolerance test was found in 3 month old female progeny of NMU-treated rats. The serum insulin level did not differ from control, but serum cholesterol level was higher in offspring of NMU-treated rats. The ability of diethylstilboestrol to inhibit compensatory ovarian hypertrophy was decreased in female hemicastrated 3 month old rats whose mothers were treated with NMU. Postnatal administration of the antidiabetic drug buformin decreased the malignant neurogenic tumor incidence 3.5 times (to rats transplacentally treated with NMU).

[The effect of oral butyl-biguanide on oral glucose tolerance and renal glucose reabsorption in normal human subjects in vivo (author's transl)]. / Die Wirkung oral verabreichten Butyl-Biguanids auf die orale Glucosetoleranz und renale Glucoseresorption (TmG) beim gesunden Menschen in vivo.

1. Oral glucose tolerance in 11 normal subjects was significantly improved after peroral administration of 150 mg of butyl-biguanide. 2. On the other hand maxiumum capacity of renal glucose reabsorption (TmG) and lowest glomerular glucose filtration rate at which glucosuria was recorded (F min) remained uninfluenced after 150 mg of butyl-biguanide in 7 normal subjects. 3. These results are compatible with the hypothesis that the oral administration of therapeutic doses of biguanides yields concentrations at the luminal face of the intestine which inhibit glucose resorption. Plasma concentrations following oral intake of the same dose of biguanide are too low to exert any inhibiting action on renal glucose reabsorption as demonstrated by the present in vivo studies. 4. Urinary flow rate and inulin clearance remained unaltered after butyl-biguanide in these normal subjects.

[Distribution and excretion of 14c-butylbiguanide in man (author's transl)]. / Verteilung und Ausscheidung von 14C-Butylbiguanid beim Menschen.

Seven patients suffering from maturity on-set diabetes mellitus were given orally 100 mg of 14C-labelled butylbiguanide, specific activity 1.40 or 1.23 muCi/mg, resp. Three days before oral administration, two of the patients had received an i.v. injection of 50 mg butylbiguanide labelled with 120 muCi 14C. The radioactivity in the blood of the patients was followed up during the first 12-h period after administration of the drug. For determination of the radioactivity in the urine aliquots of three 24-h portions were measured. Furthermore, the radioactivity was checked of each individual sample of faeces for the first 72 h after administration. The radioactivity in the exhaled air was also measured. By comparison of the excretion after i.v. and oral application an absorption efficiency of 90% to 92% was calculated. Butylbiguanide is almost exclusively and fast excreted via the kidney. 86.5% of the i.v. administered material was eliminated within 24 h and 88.1% within 3 d in the urine of a person without kidney disease. Elimination through faeces was negligible, 0.2% in a person without kidney disease and 0.7% in a patient with renal insufficiency. The data obtained from the exhaled air show that there is only a negligible break-down of butylbiguanide, if any, to CO2 in man.

[Concentration of 14C-1-butylbiguanide in plasma of diabetic patients and its elimination after administration of a new Galenical formulation (author's transl)]. / Plasmakonznetration und Elimination von 14C-1-Butyl-biguanid-HCl bei Diabetikern nach Einnahme der Substanz in einer neuen Zubereitung

The time course of 1-butylbiguanide concentration in plasma and the urinary and fecal elimination of the substance were measured in six female elimination of the substance were measured in six female diabetic patients after oral administration of 100 mg of 14C-1-butylibiguanide hydrochloride as Sindiatil. The mean maximum plasma concentration was 37 mug/100 ml and was reached after about 2 1/2 h. At least semi-maximum plasma concentrations (greater than or equal 18 mug/100 ml) were maintained between the 1st and 8th h after administration. Within 24 h 64% of the administered dose were eliminated (36% via the kidneys, 28% with the faeces). After 3 days a total of 80% had been eliminated, one-half each in urine and faeces, respectively. The average time taken for 50% of maximum renal elimination, and thus of the absorbed quantity, to be excreted was 7.2 h.