This work presents a review of pH measurement methods and applications in cancers. Magnetic resonance spectroscopic imaging and magnetic resonance imaging measurements indicate that pH gradients of up to 1.0 pH unit can exit within 1-cm distance. Although measurement of blood pH can indicate systemic problems, it cannot pinpoint the lesion or quantitatively assess the magnitude of excursion from normal pHe. Hence, there is need to develop pHe measurement methods with high spatiotemporal resolution. The two major approaches being investigated include magnetization transfer (MT) methods and relaxation methods. pH-dependent MT effects can be observed with endogenous signals or exogenously applied chemical exchange saturation transfer (CEST) agents. While endogenous signals have the advantage of being fully noninvasive and relatively straightforward to apply, they lack a full biophysical characterization and dynamic range that might be afforded by future CEST agents. pH-dependent relaxivity also requires the injection or infusion of exogenous contrast reagents. In both MT and relaxographic approaches, the magnitude of the effect, and thus, the ability to quantify pHe, depends on a spatially and temporally varying concentration of the CR. A number of approaches have been proposed to solve this problem and once it is solved, pH imaging methods will be applicable to human clinical pathologies.

Iron oxide nanoparticles (IONPs) have emerged as a promising alternative to conventional contrast agents (CAs) for magnetic resonance imaging (MRI). They have been extensively investigated as CAs due to their high biocompatibility and excellent magnetic properties. Furthermore, the ease of functionalization of their surfaces with different types of ligands (antibodies, peptides, sugars, etc.) opens up the possibility of carrying out molecular MRI. Thus, IONPs functionalized with epithelial growth factor receptor antibodies, short peptides, like RGD, or aptamers, among others, have been proposed for the diagnosis of various types of cancer, including breast, stomach, colon, kidney, liver or brain cancer. In addition to cancer diagnosis, different types of IONPs have been developed for other applications, such as the detection of brain inflammation or the early diagnosis of thrombosis. This review addresses key aspects in the development of IONPs for MRI applications, namely, synthesis of the inorganic core, functionalization processes to make IONPs biocompatible and also to target them to specific tissues or cells, and finally in vivo studies in animal models, with special emphasis on tumor models.

Bacteria of the genera Pseudomonas and Bacillus can promote plant growth and protect plants from pathogens. However, the interactions between these plant-beneficial bacteria are understudied. Here, we explore the interaction between Bacillus subtilis 3610 and Pseudomonas chlororaphis PCL1606. We show that the extracellular matrix protects B. subtilis colonies from infiltration by P. chlororaphis. The absence of extracellular matrix results in increased fluidity and loss of structure of the B. subtilis colony. The P. chlororaphis type VI secretion system (T6SS) is activated upon contact with B. subtilis cells, and stimulates B. subtilis sporulation. Furthermore, we find that B. subtilis sporulation observed prior to direct contact with P. chlororaphis is mediated by histidine kinases KinA and KinB. Finally, we demonstrate the importance of the extracellular matrix and the T6SS in modulating the coexistence of the two species on melon plant leaves and seeds.

Previous studies using MR spectroscopy have shown that the extracellular pH (pH_e) of tumors is acidic compared to normal tissues. This has a number of important sequelae that favor the emergence of more aggressive and therapy‐resistant tumors. New MRI methods based on pH‐sensitive T₁ relaxivity are an attractive alternative to previous spectroscopic methods, as they allow improvements in spatial and temporal resolution. Recently, pH‐dependent GdDOTA‐4AmP^5‐ and a pH‐independent analog, GdDOTP^5‐, were used to image renal pH in mice. The current study has used a similar approach to image pH_e in rat gliomas. Significant differences were observed compared to the renal study. First, the relaxivity of GdDOTP^5‐ was found to be affected by the higher extracellular protein content of tumors. Second, the pixel‐by‐pixel analysis of the GdDOTP^5‐ and GdDOTA‐4AmP^5‐ pharmacokinetics showed significant dispersion, likely due to the temporal fluctuations in tumor perfusion. However, there was a robust correlation between the maximal enhancements produced by the two boluses. Therefore, to account for the local time‐courses differences, pH_e maps were calculated at the time of maximal enhancement in each pixel. Finally, the comparison of the pH_e and the time to maximal intensity maps revealed an inverse relationship between pH_e and tumor perfusion. Magn Reson Med, 2006.