Understanding the benefit of metformin use in cancer treatment

Biguanides have been developed for the treatment of hyperglycemia and type 2 diabetes. Recently, metformin, the most widely prescribed biguanide, has emerged as a potential anticancer agent. Epidemiological, preclinical and clinical evidence supports the use of metformin as a cancer therapeutic. The ability of metformin to lower circulating insulin may be particularly important for the treatment of cancers known to be associated with hyperinsulinemia, such as those of the breast and colon. Moreover, metformin may exhibit direct inhibitory effects on cancer cells by inhibiting mammalian target of rapamycin (mTOR) signaling and protein synthesis. The evidence supporting a role for metformin in cancer therapy and its potential molecular mechanisms of action are discussed

Mechanistic Insight into the Reactivation of BCAII Enzyme from Denatured and Molten Globule States by Eukaryotic Ribosomes and Domain V rRNAs

In all life forms, decoding of messenger-RNA into polypeptide chain is accomplished by the ribosome. Several protein chaperones are known to bind at the exit of ribosomal tunnel to ensure proper folding of the nascent chain by inhibiting their premature folding in the densely crowded environment of the cell. However, accumulating evidence suggests that ribosome may play a chaperone role in protein folding events in vitro. Ribosome-mediated folding of denatured proteins by prokaryotic ribosomes has been studied extensively. The RNA-assisted chaperone activity of the prokaryotic ribosome has been attributed to the domain V, a span of 23S rRNA at the intersubunit side of the large subunit encompassing the Peptidyl Transferase Centre. Evidently, this functional property of ribosome is unrelated to the nascent chain protein folding at the exit of the ribosomal tunnel. Here, we seek to scrutinize whether this unique function is conserved in a primitive kinetoplastid group of eukaryotic species Leishmania donovani where the ribosome structure possesses distinct additional features and appears markedly different compared to other higher eukaryotic ribosomes. Bovine Carbonic Anhydrase II (BCAII) enzyme was considered as the model protein. Our results manifest that domain V of the large subunit rRNA of Leishmania ribosomes preserves chaperone activity suggesting that ribosome-mediated protein folding is, indeed, a conserved phenomenon. Further, we aimed to investigate the mechanism underpinning the ribosome-assisted protein reactivation process. Interestingly, the surface plasmon resonance binding analyses exhibit that rRNA guides productive folding by directly interacting with molten globule-like states of the protein. In contrast, native protein shows no notable affinity to the rRNA. Thus, our study not only confirms conserved, RNA-mediated chaperoning role of ribosome but also provides crucial insight into the mechanism of the process

In vivo quantification of photosensitizer fluorescence in the skin-fold observation chamber using dual-wavelength excitation and NIR imaging

A major challenge in biomedical optics is the accurate quantification of in vivo fluorescence images. Fluorescence imaging is often used to determine the pharmacokinetics of photosensitizers used for photodynamic therapy. Often, however, this type of imaging does not take into account differences in and changes to tissue volume and optical properties of the tissue under interrogation. To address this problem, a ratiometric quantification method was developed and applied to monitor photosensitizer meso-tetra (hydroxyphenyl) chlorin (mTHPC) pharmacokinetics in the rat skin-fold observation chamber. The method employs a combination of dual-wavelength excitation and dualwavelength detection. Excitation and detection wavelengths were selected in the NIR region. One excitation wavelength was chosen to be at the Q band of mTHPC, whereas the second excitation wavelength was close to its absorption minimum. Two fluorescence emission bands were used; one at the secondary fluorescence maximum of mTHPC centered on 720 nm, and one in a region of tissue autofluorescence. The first excitation wavelength was used to excite the mTHPC and autofluorescence and the second to excite only autofluorescence, so that this could be subtracted. Subsequently, the autofluorescence-corrected mTHPC image was divided by the autofluorescence signal to correct for variations in tissue optical properties. This correction algorithm in principle results in a linear relation between the corrected fluorescence and photosensitizer concentration. The limitations of the presented method and comparison with previously published and validated techniques are discussed

Metformin efficacy and safety for colorectal polyps: a double-blind randomized controlled trial

<p>Abstract</p> <p>Background</p> <p>Colorectal cancer is one of the major neoplasms and a leading cause of cancer death worldwide, and new preventive strategies are needed to lower the burden of this disease. Metformin, a biguanide, which is widely used for treating diabetes mellitus, has recently been suggestive to have a suppressive effect on tumorigenesis and cancer cell growth. In a previous study conducted in non-diabetic subjects, we showed that oral short-term low-dose metformin suppressed the development of colorectal aberrant crypt foci (ACF). ACF have been considered as a useful surrogate biomarker of CRC, although the biological significance of these lesions remains controversial. We devised a prospective randomized controlled trial to evaluate the chemopreventive effect of metformin against metachronous colorectal polyps and the safety of this drug in non-diabetic post-polypectomy patients.</p> <p>Methods/Design</p> <p>This study is a multi-center, double-blind, placebo-controlled, randomized controlled trial to be conducted in non-diabetic patients with a recent history of undergoing colorectal polypectomy. All adult patients visiting the Yokohama City University hospital or affiliated hospitals for polypectomy shall be recruited for the study. Eligible patients will then be allocated randomly into either one of two groups: the metformin group and the placebo group. Patients in the metformin group shall receive oral metformin at 250 mg per day, and those in the placebo group shall receive an oral placebo tablet. At the end of 1 year of administration of metformin/placebo, colonoscopy will be performed to evaluate the polyp formation.</p> <p>Discussion</p> <p>This is the first study proposed to explore the effect of metformin against colorectal polyp formation. Metformin activates AMPK, which inhibits the mammalian target of rapamycin (mTOR) pathway. The mTOR pathway plays an important role in the cellular protein translational machinery and cell proliferation. Patients with type 2 diabetes taking under treatment with metformin have been reported to be at a lower risk of cancer development than those not taking under treatment with metformin. We showed in a previous study that metformin suppressed the formation of human colorectal ACF. We therefore decided to conduct a study to determine whether metformin might suppress the formation of human colorectal polyps.</p> <p>Trial registration</p> <p>This trial has been registered in the University hospital Medical Information Network (UMIN) Clinical Trials Registry as <a href="http://www.clinicaltrials.gov/ct2/show/UMIN000006254">UMIN000006254</a></p

Phase I dose escalation study of telatinib (BAY 57-9352) in patients with advanced solid tumours

Telatinib (BAY 57-9352) is an orally available, small-molecule inhibitor of vascular endothelial growth factor receptors 2 and 3 (VEGFR-2/-3) and platelet-derived growth factor receptor β tyrosine kinases. In this multicentre phase I dose escalation study, 71 patients with refractory solid tumours were enroled into 14 days on/7 days off (noncontinuous dosing) or continuous dosing groups to receive telatinib two times daily (BID). Hypertension (23%) and diarrhoea (7%) were the most frequent study drug-related adverse events of CTC grade 3. The maximum-tolerated dose was not reached up to a dose of 1500 mg BID continuous dosing. Telatinib was rapidly absorbed with median tmax of 3 hours or less. Geometric mean Cmax and AUC0−12 increased in a less than dose-proportional manner and plateaued in the 900–1500 mg BID dose range. Two renal cell carcinoma patients reached a partial response. Tumour blood flow measured by contrast-enhanced magnetic resonance imaging and sVEGFR-2 plasma levels decreased with increasing AUC0−12 of telatinib. Telatinib is safe and well tolerated up to a dose of 1500 mg BID continuous dosing. Based on pharmacokinetic and pharmacodynamic criteria, 900 mg telatinib BID continuously administered was selected as the recommended phase II dose

Acquired immunologic tolerance: with particular reference to transplantation

The first unequivocally successful bone marrow cell transplantation in humans was recorded in 1968 by the University of Minnesota team of Robert A. Good (Gatti et al. Lancet 2: 1366–1369, 1968). This achievement was a direct extension of mouse models of acquired immunologic tolerance that were established 15 years earlier. In contrast, organ (i.e. kidney) transplantation was accomplished precociously in humans (in 1959) before demonstrating its feasibility in any experimental model and in the absence of a defensible immunologic rationale. Due to the striking differences between the outcomes with the two kinds of procedure, the mechanisms of organ engraftment were long thought to differ from the leukocyte chimerism-associated ones of bone marrow transplantation. This and other concepts of alloengraftment and acquired tolerance have changed over time. Current concepts and their clinical implications can be understood and discussed best from the perspective provided by the life and times of Bob Good

Metabolically stable bradykinin B2 receptor agonists enhance transvascular drug delivery into malignant brain tumors by increasing drug half-life

<p>Abstract</p> <p>Background</p> <p>The intravenous co-infusion of labradimil, a metabolically stable bradykinin B2 receptor agonist, has been shown to temporarily enhance the transvascular delivery of small chemotherapy drugs, such as carboplatin, across the blood-brain tumor barrier. It has been thought that the primary mechanism by which labradimil does so is by acting selectively on tumor microvasculature to increase the local transvascular flow rate across the blood-brain tumor barrier. This mechanism of action does not explain why, in the clinical setting, carboplatin dosing based on patient renal function over-estimates the carboplatin dose required for target carboplatin exposure. In this study we investigated the systemic actions of labradimil, as well as other bradykinin B2 receptor agonists with a range of metabolic stabilities, in context of the local actions of the respective B2 receptor agonists on the blood-brain tumor barrier of rodent malignant gliomas.</p> <p>Methods</p> <p>Using dynamic contrast-enhanced MRI, the pharmacokinetics of gadolinium-diethyltriaminepentaacetic acid (Gd-DTPA), a small MRI contrast agent, were imaged in rodents bearing orthotopic RG-2 malignant gliomas. Baseline blood and brain tumor tissue pharmacokinetics were imaged with the 1^stbolus of Gd-DTPA over the first hour, and then re-imaged with a 2^ndbolus of Gd-DTPA over the second hour, during which normal saline or a bradykinin B2 receptor agonist was infused intravenously for 15 minutes. Changes in mean arterial blood pressure were recorded. Imaging data was analyzed using both qualitative and quantitative methods.</p> <p>Results</p> <p>The decrease in systemic blood pressure correlated with the known metabolic stability of the bradykinin B2 receptor agonist infused. Metabolically stable bradykinin B2 agonists, methionine-lysine-bradykinin and labradimil, had differential effects on the transvascular flow rate of Gd-DTPA across the blood-brain tumor barrier. Both methionine-lysine-bradykinin and labradimil increased the blood half-life of Gd-DTPA sufficiently enough to increase significantly the tumor tissue Gd-DTPA area under the time-concentration curve.</p> <p>Conclusion</p> <p>Metabolically stable bradykinin B2 receptor agonists, methionine-lysine-bradykinin and labradimil, enhance the transvascular delivery of small chemotherapy drugs across the BBTB of malignant gliomas by increasing the blood half-life of the co-infused drug. The selectivity of the increase in drug delivery into the malignant glioma tissue, but not into normal brain tissue or skeletal muscle tissue, is due to the inherent porous nature of the BBTB of malignant glioma microvasculature.</p

LKB1 and AMPK and the cancer-metabolism link - ten years after

The identification of a complex containing the tumor suppressor LKB1 as the critical upstream kinase required for the activation of AMP-activated protein kinase (AMPK) by metabolic stress was reported in an article in Journal of Biology in 2003. This finding represented the first clear link between AMPK and cancer. Here we briefly discuss how this discovery came about, and describe some of the insights, especially into the role of AMPK in cancer, that have followed from it. In September 2003, our groups published a joint paper [1] in Journal of Biology (now BMC Biology) that identified the long-sought and elusive upstream kinase acting on AMP-activated protein kinase (AMPK) as a complex containing LKB1, a known tumor suppressor. Similar findings were reported at about the same time by David Carling and Marian Carlson [2] and by Reuben Shaw and Lew Cantley [3]; at the time of writing these three papers have received between them a total of over 2,000 citations. These findings provided a direct link between a protein kinase, AMPK, which at the time was mainly associated with regulation of metabolism, and another protein kinase, LKB1, which was known from genetic studies to be a tumor suppressor. While the idea that cancer is in part a metabolic disorder (first suggested by Warburg in the 1920s [4]) is well recognized today [5], this was not the case in 2003, and our paper perhaps contributed towards its renaissance. The aim of this short review is to recall how we made the original finding, and to discuss some of the directions that these findings have taken the field in the ensuing ten years