Molecular targets in the discovery and development of novel antimetastatic agents: current progress and future prospects.

Tumour invasion and metastasis have been recognized as major causal factors in the morbidity and mortality among cancer patients. Many advances in the knowledge of cancer metastasis have yielded an impressive array of attractive drug targets, including enzymes, receptors and multiple signalling pathways. The present review summarizes the molecular pathogenesis of metastasis and the identification of novel molecular targets used in the discovery of antimetastatic agents. Several promising targets have been highlighted, including receptor tyrosine kinases, effector molecules involved in angiogenesis, matrix metalloproteinases (MMPs), urokinase plasminogen activator, adhesion molecules and their receptors, signalling pathways (e.g. phosphatidylinositol 3-kinase, phospholipase Cγ1, mitogen-activated protein kinases, c-Src kinase, c-Met kinases and heat shock protein. The discovery and development of potential novel therapeutics for each of the targets are also discussed in this review. Among these, the most promising agents that have shown remarkable clinical outcome are anti-angiogenic agents (e.g. bevacizumab). Newer agents, such as c-Met kinase inhibitors, are still undergoing preclinical studies and are yet to have their clinical efficacy proven. Some therapeutics, such as first-generation MMP inhibitors (MMPIs; e.g. marimastat) and more selective versions of them (e.g. prinomastat, tanomastat), have undergone clinical trials. Unfortunately, these drugs produced serious adverse effects that led to the premature termination of their development. In the future, third-generation MMPIs and inhibitors of signalling pathways and adhesion molecules could form valuable novel classes of drugs in the anticancer armamentarium to combat metastasis.

Comparison between allicin and fluconazole in Candida albicans biofilm inhibition and in suppression of HWP1 gene expression.

Candida albicans is an opportunistic human pathogen with the ability to differentiate and grow in filamentous forms and exist as biofilms. The biofilms are a barrier to treatment as they are often resistant to the antifungal drugs. In this study, we investigated the antifungal activity of allicin, an active compound of garlic on various isolates of C. albicans. The effect of allicin on biofilm production in C. albicans as compared to fluconazole, an antifungal drug, was investigated using the tetrazolium (XTT) reduction-dependent growth and crystal violet assays as well as scanning electron microscopy (SEM). Allicin-treated cells exhibited significant reduction in biofilm growth (p<0.05) compared to fluconazole-treated and also growth control cells. Moreover, observation by SEM of allicin and fluconazole-treated cells confirmed a dose-dependent membrane disruption and decreased production of organisms. Finally, the expression of selected genes involved in biofilm formation such as HWP1 was evaluated by semi-quantitative RT-PCR and relative real time RT-PCR. Allicin was shown to down-regulate the expression of HWP1.

Comparison between efficacy of allicin and fluconazole against Candida albicans in vitro and in a systemic candidiasis mouse model.

The efficacy of allicin compared with fluconazole in alleviating systemic Candida albicans infections was evaluated both in vitro and in vivo through a systemic candidiasis mouse model. Determination of in vitro minimum inhibitory concentrations (MICs) for different C. albicans isolates revealed that both allicin and fluconazole showed different MICs that ranged from 0.05 to 12.5 µg mL(-1) and 0.25 to 16 µg mL(-1) , respectively. A time-kill study showed a significant effect of allicin (P<0.01) against C. albicans, comparable to that of fluconazole. Scanning electron microscopy observation revealed that, similar to fluconazole, allicin produced structural destruction of C. albicans cell surface at low MIC and lysis or puncture at high MIC concentrations. Treatment of BALB/c mice systemically infected with C. albicans showed that although the allicin treatment (at 5 mg kg(-1) day(-1) ) was slightly less efficacious than fluconazole treatment in terms of the fungal load reduction and host survival time, it was still effective against C. albicans in terms of mean survival time, which increased from 8.4 to 15.8 days. These results demonstrate the efficacy of anticandidal effects of allicin both in vitro and in an animal model of candidiasis and affirm the potential of allicin as an adjuvant therapy to fluconazole.

Expression analysis of SIR2 and SAPs1-4 gene expression in Candida albicans treated with allicin compared to fluconazole.

One of the main factors for virulence of fungus such as Candida albicans is the ability to change its morphology from yeast to hyphae. Allicin, one of the volatile sulfur-oil compounds from freshly crushed garlic, has a variety of antifungal activities. In this study, the effect of allicin on growth and hyphae production in C. albicans as compared to fluconazole, an antifungal drug was investigated using survival time in vitro and microscopic image at different time intervals. Additionally, the expression of selected genes involved in hyphae formation and development such as SIR2 and SAP1-4 was evaluated by semi-quantitative RT-PCR and relative real time RT-PCR. Allicin was shown to down-regulate the expression of SIR2 (5.54 fold), similar to fluconazole (3.48 fold) at 2x MIC concentrations. Interestingly, allicin had no effect on SAPs1-4 expression, whereas fluconazole was able to suppress SAP4 expression. Our findings showed that allicin was effective in suppressing hyphae development of C. albicans to an extent that is sometimes equal or more than fluconazole. Moreover, allicin and fluconazole seemed to share a common anti-Candida mechanism through inhibition of SIR2 gene, while fluconazole appeared to also exert its fungistatic effect through another pathway that involved SAP4 suppression.