An in vitro enzymatic assay to measure transcription inhibition by gallium(III) and H3 5,10,15-tris(pentafluorophenyl)corroles.

Chemotherapy often involves broad-spectrum cytotoxic agents with many side effects and limited targeting. Corroles are a class of tetrapyrrolic macrocycles that exhibit differential cytostatic and cytotoxic properties in specific cell lines, depending on the identities of the chelated metal and functional groups. The unique behavior of functionalized corroles towards specific cell lines introduces the possibility of targeted chemotherapy. Many anticancer drugs are evaluated by their ability to inhibit RNA transcription. Here we present a step-by-step protocol for RNA transcription in the presence of known and potential inhibitors. The evaluation of the RNA products of the transcription reaction by gel electrophoresis and UV-Vis spectroscopy provides information on inhibitive properties of potential anticancer drug candidates and, with modifications to the assay, more about their mechanism of action. Little is known about the molecular mechanism of action of corrole cytotoxicity. In this experiment, we consider two corrole compounds: gallium(III) 5,10,15-(tris)pentafluorophenylcorrole (Ga(tpfc)) and freebase analogue 5,10,15-(tris)pentafluorophenylcorrole (tpfc). An RNA transcription assay was used to examine the inhibitive properties of the corroles. Five transcription reactions were prepared: DNA treated with Actinomycin D, triptolide, Ga(tpfc), tpfc at a [complex]:[template DNA base] ratio of 0.01, respectively, and an untreated control. The transcription reactions were analyzed after 4 hr using agarose gel electrophoresis and UV-Vis spectroscopy. There is clear inhibition by Ga(tpfc), Actinomycin D, and triptolide. This RNA transcription assay can be modified to provide more mechanistic detail by varying the concentrations of the anticancer complex, DNA, or polymerase enzyme, or by incubating the DNA or polymerase with the complexes prior to RNA transcription; these modifications would differentiate between an inhibition mechanism involving the DNA or the enzyme. Adding the complex after RNA transcription can be used to test whether the complexes degrade or hydrolyze the RNA. This assay can also be used to study additional anticancer candidates.

Lymphoepithelial carcinoma: a case of a rare parotid gland tumor.

A 29-year-old woman presented from another hospital with a 10-month history of an enlarging left-sided facial mass. Computed tomographic scan revealed a mass in the superficial lobe of the left parotid gland with left-sided cervical lymphadenopathy. The patient received a total left parotidectomy and a selective neck dissection. Histopathologic slides revealed lymphoepithelial carcinoma (LEC) that stained positive for cytokeratin, as well as Epstein-Barr virus (EBV). An LEC of the parotid is a rare salivary gland tumor accounting for less than 1% of all salivary gland tumors. As reaffirmed in our case, LEC is more common in women, occurs primarily in the parotid gland, and has an ethnic predilection. Histologic analysis reveals an infiltrative, poorly differentiated tumor nestled in a lymphoid stroma, with near 100% positivity for EBV in endemic areas. Complete resection of this poorly differentiated carcinoma followed by postoperative radiation is essential for local control.