Protein phosphorylation is an impo-rtant cellular regulatory mechanism as many enzymes and receptors are activated/deactivated by phosphorylation and dephosphorylation events, by means of kinases and phosph-atases. In particular, the protein kinases are responsible for cellular transduction signaling and their hyperactivity, malfunction or overexpression can be found in several diseases, mostly tumors. Therefore, it is evident that the use of kinase inhibitors can be valuable for the treatment of cancer. In this review, we discuss the mechanism of action of phosphorylation, with particular attention to the importance of phosphorylation under physiological and pathological conditions. We also discuss the possibility of using kinase inhibitors in the treatment of tumors.

/pdf/the-crucial-role-of-protein-phosphorylation-in-cell-1382fjkubf.pdf

The crucial role of protein phosphorylation in cell signaling and its use as targeted therapy (Review)

A matter of life and death.

Combination chemotherapy and nanoparticle drug delivery are two areas that have shown significant promise in cancer treatment. Combined therapy of two or more drugs promotes synergism among the different drugs against cancer cells and suppresses drug resistance through distinct mechanisms of action. Nanoparticle drug delivery, on the other hand, enhances therapeutic effectiveness and reduces side effects of the drug payloads by improving their pharmacokinetics. These two active research fields have been recently merged to further improve the efficacy of cancer therapeutics. This review article summarizes the recent efforts in developing nanoparticle platforms to concurrently deliver multiple types of drugs for combination chemotherapy. We also highlight the challenges and design specifications that need to be considered in optimizing nanoparticle-based combination chemotherapy.

Nanoparticle-assisted combination therapies for effective cancer treatment

Cells require tight regulation of the intracellular redox balance and consequently of reactive oxygen species for proper redox signaling and maintenance of metal (e.g., of iron and copper) homeostasis. In several diseases, including cancer, this balance is disturbed. Therefore, anticancer drugs targeting the redox systems, for example, glutathione and thioredoxin, have entered focus of interest. Anticancer metal complexes (platinum, gold, arsenic, ruthenium, rhodium, copper, vanadium, cobalt, manganese, gadolinium, and molybdenum) have been shown to strongly interact with or even disturb cellular redox homeostasis. In this context, especially the hypothesis of “activation by reduction” as well as the “hard and soft acids and bases” theory with respect to coordination of metal ions to cellular ligands represent important concepts to understand the molecular modes of action of anticancer metal drugs. The aim of this review is to highlight specific interactions of metal-based anticancer drugs with t...

/pdf/anticancer-activity-of-metal-complexes-involvement-of-redox-30f2s1cc98.pdf

Anticancer activity of metal complexes: involvement of redox processes.

Fabrication of gold nanoparticles for targeted therapy in pancreatic cancer

Tyrosine kinases are important mediators of the signaling cascade, determining key roles in diverse biological processes like growth, differentiation, metabolism and apoptosis in response to external and internal stimuli. Recent advances have implicated the role of tyrosine kinases in the pathophysiology of cancer. Though their activity is tightly regulated in normal cells, they may acquire transforming functions due to mutation(s), overexpression and autocrine paracrine stimulation, leading to malignancy. Constitutive oncogenic activation in cancer cells can be blocked by selective tyrosine kinase inhibitors and thus considered as a promising approach for innovative genome based therapeutics. The modes of oncogenic activation and the different approaches for tyrosine kinase inhibition, like small molecule inhibitors, monoclonal antibodies, heat shock proteins, immunoconjugates, antisense and peptide drugs are reviewed in light of the important molecules. As angiogenesis is a major event in cancer growth and proliferation, tyrosine kinase inhibitors as a target for anti-angiogenesis can be aptly applied as a new mode of cancer therapy. The review concludes with a discussion on the application of modern techniques and knowledge of the kinome as means to gear up the tyrosine kinase drug discovery process.

Tyrosine kinase - Role and significance in Cancer

This article addresses and investigates the dual incorporation of daunorubicin (DR) and 6-mercaptopurine (6-MP) in liposomes for better chemotherapy. These drugs are potential candidates for interaction due to the quinone (H acceptor) and hydroxyl (H donor) groups on DR and 6-MP, respectively. Interactions between the two drugs in solution were monitored by UV/Vis and fluorescence spectroscopy. Interaction between the two drugs inside the liposomes was evaluated by HPLC (for 6-MP) and by fluorescence spectroscopy (for daunorubicin) after phospholipase-mediated liposome lysis. Our results provide evidence for the lack of interaction between the two drugs in solution and in liposomes. The entrapment efficiencies of 6-MP in the neutral Phosphatidyl choline (PC):Cholesterol (Chol):: 2:1 and anionic PC:Chol:Cardiolipin (CL) :: 4:5:1 single and double drug liposomes were found to be 0.4% and 1.5% (on average), respectively. The entrapment efficiencies of DR in the neutral and anionic double drug liposomes were found to be 55% and 31%, respectively. The corresponding entrapment of daunorubicin in the single drug liposomes was found to be 62% on average. Our thin layer chromatography (TLC) and transmission electron microscopy (TEM) results suggest stability of lipid and liposomes, thus pointing plausible existence of double drug liposomes. Cytotoxicity experiments were performed by using both single drug and double drug liposomes. By comparing the results of phase contrast and fluorescence microscopy, it was observed that the double drug liposomes were internalized in the jurkat and Hut78 (highly resistant cell line) leukemia cells as viewed by the fluorescence of daunorubicin. The cytotoxicity was dose dependent and had shown a synergistic effect when double drug liposome was used.

6-Mercaptopurine and Daunorubicin Double Drug Liposomes—Preparation, Drug-Drug Interaction and Characterization

Dithiothreitol abrogates the effect of arsenic trioxide on normal rat liver mitochondria and human hepatocellular carcinoma cells.

Inhibition of xanthine oxidase-catalyzed conversion of xanthine to uric acid by various pyrazolopyrimidine-based inhibitors (allopurinol derivatives) was evaluated and compared with the standard inhibitor allopurinol. Three compounds out of the seven compounds used in the study were found to be reasonably good inhibitors of xanthine oxidase (XO). 4-Amino-6-mercaptopyrazolo-3,4-d-pyrimidine was found to be the most potent inhibitor of XO (IC50 = 0.600 +/- 0.009 microM). 4-Mercapto-1H-pyrazolo-3,4-d-pyrimidine (IC50 = 1.326 +/- 0.013 microM) and 4-amino-6-hydroxypyrazolo-3,4-d-pyrimidine (IC50 = 1.564 +/- 0.065 microM) also showed comparable inhibitory activity to that of allopurinol (IC50 = 0.776 +/- 0.012 microM). All three compounds showed competitive type of inhibition with comparable Ki values. Induction of the electron transfer reaction catalyzed by XO in the presence of these compounds monitored as reduction of 2,6-dichlorophenolindophenol (DCPIP) revealed that electron transfer by 4-amino-6-mercaptopyrazolo-3,4-d-pyrimidine is comparable to that obtained by allopurinol or xanthine. However, 4-mercapto-1H-pyrazolo-3,4-d-pyrimidine and 4-amino-6-hydroxypyrazolo-3,4-d-pyrimidine did not show DCPIP reduction. On the other hand, enzymatic reduction of cytochrome c in the presence of the three compounds was found to be insignificant and much less in comparison to allopurinol and xanthine. Therefore, both 4-amino-6-hydroxypyrazolo-3,4-d-pyrimidine and 4-mercapto-1H-pyrazolo-3,4-d-pyrimidine displayed the inhibitory property and also did not produce XO-mediated reactive oxygen species (ROS). Since 4-mercapto-1H-pyrazolo-3,4-d-pyrimidine was found to have some toxicity, the effect of 4-amino-6-hydroxypyrazolo-3,4-d-pyrimidine on the enzymatic formation of uric acid and ROS was investigated and it was found that this compound was inhibiting enzymatic generation of both uric acid and ROS. It can be noted that the standard inhibitor, allopurinol, inhibits uric acid formation but produces ROS.

Biochemical characterization of some pyrazolopyrimidine-based inhibitors of xanthine oxidase.

The anticancer drug, 6-mercaptopurine (6MP) is subjected to metabolic clearance through xanthine oxidase (XOD) mediated hydroxylation, producing 6-thiouric acid (6TUA), which is excreted in urine. This reduces the effective amount of drug available for therapeutic efficacy. Co-administration of allopurinol, a suicide inhibitor of XOD, which blocks the hydroxylation of 6MP inadvertently enhances the 6MP blood level, counters this reduction. However, allopurinol also blocks the hydroxylation of hypoxanthine, xanthine (released from dead cancer cells) leading to their accumulation in the body causing biochemical complications such as xanthine nephropathy. This necessitates the use of a preferential XOD inhibitor that selectively inhibits 6MP transformation, but leaves xanthine metabolism unaffected. Here, we have characterized two such unique inhibitors namely, 2-amino-6-hydroxy-8-mercaptopurine (AHMP) and 2-amino-6-purinethiol (APT) on the basis of IC50 values, residual activity in bi-substrate simulative reaction and the kinetic parameters like Km, Ki, kcat. The IC50 values of AHMP for xanthine and 6MP as substrate are 17.71 ± 0.29 μM and 0.54 ± 0.01 μM, respectively and the IC50 values of APT for xanthine and 6MP as substrates are 16.38 ± 0.21 μM and 2.57 ± 0.08 μM, respectively. The Ki values of XOD using AHMP as inhibitor with xanthine and 6MP as substrate are 5.78 ± 0.48 μM and 0.96 ± 0.01 μM, respectively. The K i values of XOD using APT as inhibitor with xanthine and 6MP as substrate are 6.61 ± 0.28 μM and 1.30 ± 0.09 μM. The corresponding Km values of XOD using xanthine and 6MP as substrate are 2.65 ± 0.02 μM and 6.01 ± 0.03 μM, respectively. The results suggest that the efficiency of substrate binding to XOD and its subsequent catalytic hydroxylation is much superior for xanthine in comparison to 6MP. In addition, the efficiency of the inhibitor binding to XOD is much more superior when 6MP is the substrate instead of xanthine. We further undertook the toxicological evaluation of these inhibitors in a single dose acute toxicity study in mice and our preliminary experimental results suggested that the inhibitors were equally non-toxic in the tested doses. We conclude that administration of either APT or AHMP along with the major anti-leukemic drug 6MP might serve as a good combination cancer chemotherapy regimen.

/pdf/preferential-inhibition-of-xanthine-oxidase-by-2-amino-6-2uosznjrze.pdf

Anup K. Mukhopadhyay

Papers

Tyrosine kinase - Role and significance in Cancer

6-Mercaptopurine and Daunorubicin Double Drug Liposomes—Preparation, Drug-Drug Interaction and Characterization

Dithiothreitol abrogates the effect of arsenic trioxide on normal rat liver mitochondria and human hepatocellular carcinoma cells.

Biochemical characterization of some pyrazolopyrimidine-based inhibitors of xanthine oxidase.

Preferential inhibition of xanthine oxidase by 2-amino-6-hydroxy-8-mercaptopurine and 2-amino-6-purine thiol