Transporters beyond transport. Focus on "Deregulation of apoptotic volume decrease and ionic movements in multidrug-resistant tumor cells: role of chloride channels"

AqF026 may act as a cancer therapeutic agent via inducing cancer cell oncosis

Cancer is one of the leading causes of death worldwide, and metastasis is the major cause of death in cancer, therefore, treatments to attenuate metastasis are urgently needed. Cell migration is indispensable in metastatic cascade, and aquaporins (AQPs) promote cell migration by facilitating water influx at cell front (lamellipodia). In fact, AQPs overexpressed widely among many cancer types. Accordingly, previous efforts of targeting AQPs as strategies of cancer treatments were based on AQP inhibitors, yet the efficacy of AQP inhibition was limited based on recent surveys. On the contrary, whether AQP agonist has role in cancer treatments has not been explored. AqF026, an AQP1 agonist, was initially applied to a mouse model of peritoneal dialysis. Herein, we aimed to apply AqF026 to magnify the water influx into lamellipodia of migrating cancer cells so as to induce oncosis by causing overloaded cancer cell swelling in advance of metastatic cascade. Cell swelling is a characteristic of oncosis. With impairment or insufficient regulatory volume decrease (RVD), cell swelling can lead to oncosis. Cancer cells with metastatic potentials shared the same population of cancer cells with multidrug resistance (MDR) lineage, and the impairment or insufficient RVD is shown in cancer cells with MDR. Taken together, the author hypothesized that given appropriate concentration or dose of AQP1 agonist AqF026, the AqF026 may induce oncosis of cancer cells preferentially rather than normal cells by causing overloaded water influx via AQP1 and consequent irreversible cell swelling.

In vivo chlorine and sodium MRI of rat brain at 21.1 T

OBJECT

MR imaging of low-gamma nuclei at the ultrahigh magnetic field of 21.1 T provides a new opportunity for understanding a variety of biological processes. Among these, chlorine and sodium are attracting attention for their involvement in brain function and cancer development.

MATERIALS AND METHODS

MRI of (35)Cl and (23)Na were performed and relaxation times were measured in vivo in normal rat (n = 3) and in rat with glioma (n = 3) at 21.1 T. The concentrations of both nuclei were evaluated using the center-out back-projection method.

RESULTS

T 1 relaxation curve of chlorine in normal rat head was fitted by bi-exponential function (T 1a = 4.8 ms (0.7) T 1b = 24.4 ± 7 ms (0.3) and compared with sodium (T 1 = 41.4 ms). Free induction decays (FID) of chlorine and sodium in vivo were bi-exponential with similar rapidly decaying components of [Formula: see text] ms and [Formula: see text] ms, respectively. Effects of small acquisition matrix and bi-exponential FIDs were assessed for quantification of chlorine (33.2 mM) and sodium (44.4 mM) in rat brain.

CONCLUSION

The study modeled a dramatic effect of the bi-exponential decay on MRI results. The revealed increased chlorine concentration in glioma (~1.5 times) relative to a normal brain correlates with the hypothesis asserting the importance of chlorine for tumor progression.

Resistance to paclitaxel increases the sensitivity to other microenvironmental stresses in prostate cancer cells

The microenvironment is central to many aspects of cancer pathobiology and has been proposed to play a role in the development of cancer cell resistance to therapy. To examine the response to microenvironmental conditions, two paclitaxel resistant prostate cancer (PCa) cell lines (stable and reversible) and one reversible heat resistant cell line were studied. In comparison to their parental cell lines, both paclitaxel resistant cell lines (stable and reversible) were more sensitive to microenvironmental heat, potentially yielding a synergistic therapeutic opportunity. In the two phenotypic cells repopulated after acute heat or paclitaxel treatments, there was an inverse correlation between paclitaxel and heat resistance: resistance to paclitaxel imparted sensitivity to heat; resistance to heat imparted sensitivity to paclitaxel. These studies indicate that as cancer cells evolve resistance to single microenvironmental stress they may be more sensitive to others, perhaps allowing us to design new approaches for PCa therapy.

Regulation of gap junction coupling in bovine ciliary epithelium

Aqueous humor is formed by fluid transfer from the ciliary stroma sequentially across the pigmented ciliary epithelial (PE) cells, gap junctions, and nonpigmented ciliary epithelial (NPE) cells. Which connexins (Cx) contribute to PE-NPE gap junctional formation appears species specific. We tested whether small interfering RNA (siRNA) against Cx43 (siCx43) affects bovine PE-NPE communication and whether cAMP affects communication. Native bovine ciliary epithelial cells were studied by dual-cell patch clamping, Lucifer Yellow (LY) transfer, quantitative polymerase chain reaction with reverse transcription (qRT-PCR), and Western immunoblot. qRT-PCR revealed at least 100-fold greater expression for Cx43 than Cx40. siCx43 knocked down target mRNA expression by 55 +/- 7% after 24 h, compared with nontargeting control siRNA (NTC1) transfection. After 48 h, siCx43 reduced Cx43 protein expression and LY transfer. The ratio of fluorescence intensity (R(f)) in recipient to donor cell was 0.47 +/- 0.09 (n = 11) 10 min after whole cell patch formation in couplets transfected with NTC1. siCx43 decreased R(f) by approximately 60% to 0.20 +/- 0.07 (n = 13, P < 0.02). Dibutyryl-cAMP (500 microM) also reduced LY dye transfer by approximately 60%, reducing R(f) from 0.41 +/- 0.05 (n = 15) to 0.17 +/- 0.05 (n = 20) after 10 min. Junctional currents were lowered by approximately 50% (n = 6) after 10-min perfusion with 500 microM dibutyryl-cAMP (n = 6); thereafter, heptanol abolished the currents (n = 5). Preincubation with the PKA inhibitor H-89 (2 microM) prevented cAMP-triggered current reduction (n = 6). We conclude that 1) Cx43, but not Cx40, is a major functional component of bovine PE-NPE gap junctions; and 2) under certain conditions, cAMP may act through PKA to inhibit bovine PE-NPE gap junctional communication.