Rap1/B-Raf signaling is activated in neuroendocrine tumors of the digestive tract and Raf kinase inhibition constitutes a putative therapeutic target.

OBJECTIVE: Molecular pathogenesis of digestive neuroendocrine tumors (dNETs) is largely unknown. Recently, the serine-threonine kinase B-Raf was identified as an oncogene in endocrine cancer such as thyroid carcinoma. In endocrine cells, the small G-protein Rap1 stimulates mitogen-activated protein kinase (MAPK) signaling by activating B-Raf. We examined the expression of Rap1 and B-Raf in dNETs and their contribution to MAPK signaling in neuroendocrine cell lines. In addition, we explored the effect of suppressing B-Raf kinase by the recently developed inhibitor BAY43-9006 (Sorafinib) on growth, apoptosis and MAPK activation neuroendocrine cell lines. METHODS AND RESULTS: Expression of Rap1 and B-Raf in dNETs (19 insulinomas, 15 carcinoid tumors and 10 gastrinomas) was examined by immunohistochemistry, which revealed that Rap1 and B-Raf were highly prevalent in the majority of dNETs. Overexpression of Rap1 and B-Raf activated MAPK extracellular dependent kinase (ERK) ERK-2 and ERK-dependent transcription factor Elk-1 in neuroendocrine cell lines Bon and INS-1. Suppression of B-Raf by BAY43-9006 inhibited growth and induced apoptosis in Bon and INS-1 cells. In addition, BAY43-9006 suppressed phosphorylation of MAPK ERK1/2 and its upstream kinase MEK1/2 in Bon and INS-1 cells. CONCLUSION: These results indicate that Rap1-B-Raf signaling may contribute to pathogenesis of dNETs and provides a molecular target for treatment of dNETs.

[Activity of cathepsin D in some neoplasms of the gastrointestinal tract]. / Aktywnosc katepsyny D w niektórych nowotworach przewodu pokarmowego.

In the present paper we analyzed cathepsin D activity in digestive tract cancers. Cathepsin D activity was estimated in 10% homogenates of oesophageal cancer, gastric cancer and colon cancer tissues and in the blood serum and expressed as the amount of liberated tyrosine which was assayed acc. to Folin-Ciocalteau. Mean cathepsin D activities in neoplastic tissues and normal counterparts were as follows: oesophaged cancer (218.5 mM Tyr/1/2 h vs 145.0 mM Tyr/1/2 h), gastric cancer (285.4 mM Tyr/1/2 h vs 142.3 mM Tyr/1/2 h) and colon cancer (233.7 mM Tyr/1/2 h vs 159.5 mM Tyr/1/2 h). In all examined neoplastic tissues cathepsin D activity was almost too-fold higher than in the normal counterparts. Cathepsin D activity in the sera of cancer patients was too a lesser degree higher than in the sera of normal subjects. The data indicate that estimating of cathepsin D activity in the neoplastic tissues homogenates and in the blood serum may be of diagnostic value and may constitute an information which is complementary to the analysis of other tumor markers and histopathologic examination.

Trial of sequential trimetrexate, fluorouracil, and high-dose leucovorin in previously treated patients with gastrointestinal carcinoma.

PURPOSE: Trimetrexate (TMTX) is a dihydrofolate reductase inhibitor, which, like methotrexate (MTX), has been shown to potentiate fluorouracil (FU) cytotoxicity by increasing phosphoribosylpyrophosphate (PRPP) levels. We investigated the safety and efficacy of a sequential TMTX/FU/leucovorin (LV) combination. PATIENTS AND METHODS: Forty-one patients with advanced gastrointestinal carcinoma (mostly colorectal) received variable doses of TMTX followed 24 hours later by FU/LV (500 mg/m2 of each drug). Almost all patients had received previous chemotherapy. The initial 19 patients were treated on a 3-week-on/1-week-off schedule without any significant toxicity; the remaining patients were treated for 6 consecutive weeks followed by a 2-week rest period. TMTX was escalated in 30-mg/m2 increments from 20 to 110 mg/m2 in separate patient cohorts. When the 110-mg/m2 dose of TMTX was reached, the FU dose was escalated from 500 mg/m2 to 600 mg/m2. RESULTS: The partial response (PR) rate in assessable patients with colorectal cancer (all previously treated) was 20% (seven of 35; 95% confidence interval, 7% to 33%), and with other gastrointestinal cancers was one of four patients. Median survival has not been reached with a median follow-up of 13.5 months. The maximum-tolerated dose (MTD) was 110 mg/m2 for TMTX, 500 mg/m2 for FU, and 500 mg/m2 for LV on a 6-weeks-on/2-weeks-off cycle. The principal toxicities were grade 3 or 4 diarrhea, which occurred in 17% of patients, and hypersensitivity reactions, which occurred in 26% of patients. CONCLUSION: TMTX can be administered at maximal doses in combination with FU and LV without increasing toxicity. The PR rate of 20% in advanced colorectal carcinoma patients previously treated with chemotherapy is encouraging and merits further study.