A p53 GROWTH ARREST PROTECTS FIBROBLASTS FROM ANTICANCER AGENTS

E. Siobhan McCormack, Arthur M. Bruskin, Gary V. Borzillo

OSI Pharmaceuticals Inc., 106 Charles Lindbergh Blvd., Uniondale, NY 11553-3649

Received 10/27/97 Accepted October 31, 1997

2. INTRODUCTION

Negative regulators of the cell cycle have attracted interest in strategies designed to protect normal tissues from the adverse effects of radiation and chemotherapy. An arrest of the cell cycle in G1 phase, for example, has been exploited to protect cells from subsequent exposure to drugs that target DNA synthesis or mitosis. Most experimental strategies exhibit several common features that could be considered prerequisites for achieving "chemoprotection." First, the target cell population should be growth arrested before exposure to the drug or other cellular insult. Second, the effects of the growth arrest should be reversible. Chemoprotected cells that are normally proliferating need to re-enter the cell cycle and divide at appropriate rates once chemotherapy or radiation is discontinued. Third, the chemoprotecting agent should be preferential for normal cells relative to malignant cells. In some cases, differential chemoprotection has been achieved simply by targeting the arresting agent to the desired sites (1). Recently, we and others have utilized members of the TGF-beta (TGFB) superfamily of reversible growth inhibitors to increase the viability of cells exposed to chemotherapy drugs in vitro and in vivo (1-5). Results in our laboratory with TGFB3 and cultures of CCL64 epithelial cells indicated that the TGFB3 arrest could protect cells from drugs active predominantly in S phase (cytosine beta-D-arabino-furanoside hydrochloride [Ara-c]) or M phase (taxol) of the cell cycle. In contrast, TGFB3 was ineffective against drugs such as cisplatin and doxorubicin, which act via multiple mechanisms throughout the cell cycle (5).

The observation that regulatory factors such as IL-11 (6) and the TGFBs can promote the survival of cells exposed to anticancer drugs suggests the possibility that other strategies (chemicals, genes, regulatory factors) that arrest cell growth could also be used for chemoprotection.

Alternative approaches could then be compared for efficacy on the different tissues (bone marrow, oral mucosa, intestines, gonads, hair follicles) most susceptible to the adverse effects of chemotherapy in cancer patients. In the present study, we have focused on the p53 tumor suppressor as one model system to test whether other reversible arrests of the cell cycle can be utilized to chemoprotect cells. A key aspect of the study is the use of temperature-sensitive (ts) p53 mutations (mouse 135V and human 143A) to arrest fibroblasts prior to exposure to anticancer drugs, which include mitotic inhibitors (vinblastine, taxol, etoposide), antimetabolites (Ara-c, 5-fluorouracil [5FU]), and a carboplatinum agent (cisplatin).