Determination of the Dissociation Constants of Urocanic Acid Isomers in Aqueous Solutions

cis-Urocanic acid as a potential nickel(ii) binding molecule in the human skin

cis-Urocanic acid, a component of human skin, is an efficient ligand for allergenic Ni²⁺ ions, forming high spin complexes.

Antitumor effects of cis-urocanic acid on experimental urothelial cell carcinoma of the bladder

PURPOSE

We determined the effect of protodynamic therapy against bladder cancer cells in vitro and in vivo. We investigated cis-urocanic acid in rat bladder cancer cell cultures and in an orthotopic rat urothelial carcinoma model to assess its safety and antiproliferative activity.

MATERIALS AND METHODS

The rat bladder cancer cell line AY-27 was exposed to cis-urocanic acid (BioCis Pharma, Turku, Finland) at pH 6.5 or 7.4 for 2 hours. Cell viability was measured by colorimetric assay at 24 and 48 hours. For in vivo experiments AY-27 cells were instilled into the acid treated bladder of 17 rats. After 4, 7 and 10 days 14 rats were treated intravesically with cis-urocanic acid 6% (weight per volume) or vehicle. Rats were sacrificed on day 12 and the bladders were dissected. Immunohistochemical staining was done to assess apoptosis (caspase-3) and cell proliferation (Ki-67) in vivo.

RESULTS

Cis-urocanic acid caused dose dependent, pH dependent inhibition of AY-27 cell proliferation, showing the protodynamic action at concentrations of 0.5% and 1%. At higher cis-urocanic acid doses complete cell death was observed. All tumors detected in animals treated with vehicle were muscle invasive (stage T2 or greater) but only 43% of tumors were muscle invasive in the cis-urocanic acid treated group (p=0.049). There was no difference in the percent of apoptotic or proliferating tumor cells between treatment groups. No signs of toxicity were observed.

CONCLUSIONS

Cis-urocanic acid showed direct antiproliferative activity against rat bladder cancer cells in vitro and antitumor effects in vivo. It may have therapeutic potential as an intravesical agent for nonmuscle invasive bladder cancer.

Molecular targets for the protodynamic action of cis-urocanic acid in human bladder carcinoma cells

BACKGROUND

cis-urocanic acid (cis-UCA) is an endogenous amino acid metabolite capable of transporting protons from the mildly acidic extracellular medium into the cell cytosol. The resulting intracellular acidification suppresses many cellular activities. The current study was aimed at characterizing the molecular mechanisms underlying cis-UCA-mediated cytotoxicity in cultured cancer cells.

METHODS

5367 bladder carcinoma cells were left untreated or treated with cis-UCA. Cell death was assessed by measuring caspase-3 activity, mitochondrial membrane polarization, formation and release of cytoplasmic histone-associated DNA fragments, and cellular permeabilization. Cell viability and metabolic activity were monitored by colorimetric assays. Nuclear labelling was used to quantify the effects of cis-UCA on cell cycle. The activity of the ERK and JNK signalling pathways was studied by immunoblotting with specific antibodies. Phosphatase activity in cis-UCA-treated cells was determined by assay kits measuring absorbance resulting from the dephosphorylation of an artificial substrate. All statistical analyses were performed using the two-way Student's t-test (p < 0.05).

RESULTS

Here we report that treatment of the 5637 human bladder carcinoma cells with 2% cis-UCA induces both apoptotic and necrotic cell death. In addition, metabolic activity of the 5637 cells is rapidly impaired, and the cells arrest in cell cycle in response to cis-UCA. Importantly, we show that cis-UCA promotes the ERK and JNK signalling pathways by efficiently inhibiting the activity of serine/threonine and tyrosine phosphatases.

CONCLUSIONS

Our studies elucidate how cis-UCA modulates several cellular processes, thereby inhibiting the proliferation and survival of bladder carcinoma cells. These anti-cancer effects make cis-UCA a potential candidate for the treatment of non-muscle invasive bladder carcinoma.

Protodynamic intracellular acidification by cis-urocanic acid promotes apoptosis of melanoma cells in vitro and in vivo

The extracellular tumor microenvironment is acidified, whereas the intracellular pH of tumor and stromal cells is neutral. cis-Urocanic acid (cis-UCA), an endogenous compound of the skin, can acidify the cytosol by transporting protons into the cells. This phenomenon, termed the protodynamic concept, was studied here in human cancer cells. cis-UCA dose-dependently reduced the number of viable human melanoma, cervical carcinoma, and fibrosarcoma cells at weakly acidic extracellular pH. The intracellular pH decreased by up to 0.5 pH units in a concentration-dependent manner with 0.3-30  m cis-UCA at extracellular pH 6.5 but not at pH 7.4. Under the same conditions, 30  mM cis-UCA induced annexin-V binding and activation of caspase-3 in A2058 melanoma cells as signs of apoptotic cell death. Finally, growth of human melanoma xenografts in SCID mice was suppressed by 60% following intratumoral injection of cis-UCA. Accordingly, the percentage of tumor necrosis and active caspase-3-immunopositive cells increased, whereas proliferation activity decreased. These results identify cis-UCA as an anticancer agent inhibiting melanoma growth by immediate intracellular acidification followed by apoptotic cell death in vivo.