Down-regulation of the Human Tumor Antigen Mucin by Gemcitabine on the Pancreatic Cancer Cell Line Capan-2

The nucleoside analogue gemcitabine displays therapeutic effects mainly against breast, ovarian and pancreatic cancer. Mucin, encoded by the gene MUC1, is a well-established tumor antigen expressed on these tumors. Knowledge of possible effects of chemotherapeutic drugs on the level of mucin epitope expression is important for the design of clinical protocols combining chemo- and immunotherapeutic approaches. In this study, we determined the influence of gemcitabine on the mucin expression of the human pancreatic carcinoma cell line Capan- 2. The cells were treated with three different concentrations (0.01 Ig/ml, 0.1 Ig/ml and 0.25 Ig/ml) of gemcitabine or were left untreated and were analyzed after 24 hours, 3 and 5 days. Flow cytometric analysis showed a dose-dependent decrease of mucin expression on the cell surface which remained over 5 days. The strongest reduction of mucin expression was detectable 24 hours after application of the drug. The down-regulation of the tumor antigen mucin by gemcitabine might weaken an immune response against mucin-expressing tumors, which are under treatment with this chemotherapeutic drug. Human pancreatic cancer is a leading cause of cancer- related death in most Western industrialized countries. It is difficult to diagnose, metastatic spread is fast and there is no effective systemic therapy available. Therefore less than 2-3% of the patients with adenocarcinoma of the pancreas live longer than 5 years after diagnosis (1, 2). However, in recent clinical trials concerning the treatment of pancreatic cancer, the chemotherapeutic drug gemcitabine displayed a promising therapeutic potency including statistically significant higher response rates, improved symptom control and prolonged survival (3-6). Gemcitabine (2',2'-difluorodeoxycytidine) is a nucleoside analogue of cytidine that is active as a single agent or in combination with cisplatin and other drugs against a wide range of solid tumors such as pancreatic, lung, breast, bladder, ovarian, head and neck cancer (7-13). The antiproliferative effect is based on its incorporation into DNA molecules with the subsequent addition of one further base to the DNA strand, a process known as "masked chain termination" (14). The halt of DNA synthesis, which is invisible to DNA repair systems, directs the cells into apoptosis. Furthermore, gemcitabine blocks cellular DNA synthesis by inhibition of the