Nongenotoxic p53 Activation Protects Cells against S-Phase–Specific Chemotherapy

Dominique Kranz,Matthias Dobbelstein

doi:10.1158/0008-5472.can-06-1527

Dominique Kranz, Matthias Dobbelstein

Open Access

https://doi.org/10.1158/0008-5472.can-06-1527

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Abstract

Mutations in the tumor suppressor gene TP53 represent the most frequent genetic difference between tumor cells and normal cells. Here, we have attempted to turn this difference into an advantage for normal cells during therapy. Using the Mdm2 antagonist nutlin-3, we first activated p53 in U2OS and HCT116 cells to induce cell cycle arrest. These arrested cells were found to be resistant to subsequent transient treatment with the nucleoside analogue gemcitabine, as revealed by clonogenic assays following drug removal. In contrast, isogenic cells lacking functional p53 continued to enter S phase regardless of nutlin-3 pretreatment and remained highly susceptible to gemcitabine-mediated cytotoxicity. The sequential treatment with nutlin-3 alone, followed by transient exposure to nutlin-3 plus gemcitabine, efficiently compromised the clonogenicity of tumor cells with deletions or mutations of p53 but largely spared the proliferation of nontransformed human keratinocytes. Nutlin-3 pretreatment also conferred protection of p53-proficient cells against cytosine arabinoside but not against doxorubicin or cisplatin. We propose that the cell cycle arrest function of p53 can be used to convert p53 from a killer to a protector of cells, with the potential to reduce unwanted side effects of chemotherapy.

Highlights

The most frequent known genetic difference between normal and cancerous cells consists of mutations within the tumor suppressor gene TP53, resulting in malfunction of its product, p53 (1)
Blocking unwanted side effects on nontumor cells through Mdm[2] inhibition would presumably increase the tolerated dose of nucleoside analogues, it will be important to determine whether an increase in gemcitabine or Ara-C dose would lead to improved treatment efficacy toward tumor cells
We consider this study as a proof of principle that supports the general feasibility of chemoprotection by p53-mediated cell cycle arrest, only representing a first step toward possible clinical applications

Summary

Introduction

The most frequent known genetic difference between normal and cancerous cells consists of mutations within the tumor suppressor gene TP53, resulting in malfunction of its product, p53 (1). It would be highly desirable to use wild-type (WT) p53 as a positive discriminator, allowing the protection of normal cells but not tumor cells in the course of cancer therapy. Such a concept seems counterintuitive at first glance because p53 is activated by genotoxic drugs, capable of inducing apoptosis, and widely regarded as a mediator of chemotherapy-induced cell death. It should be noted that chemotherapy can be effective despite tumor-associated p53 mutations, p53 does not cause apoptosis in normal cells (2). We propose here that this cell cycle arrest function can be used for the protection of normal cells because many available chemothera-

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