Kenneth P. Olive

Mutant p53 Gain of Function in Two Mouse Models of Li-Fraumeni Syndrome

The p53 tumor suppressor gene is commonly altered in human tumors, predominantly through missense mutations that result in accumulation of mutant p53 protein. These mutations may confer dominant-negative or gain-of-function properties to p53. To ascertain the physiological effects of p53 point mutation, the structural mutant p53R172H and the contact mutant p53R270H (codons 175 and 273 in humans) were engineered into the endogenous p53 locus in mice. p53R270H/+ and p53R172H/+ mice are models of Li-Fraumeni Syndrome; they developed allele-specific tumor spectra distinct from p53+/- mice. In addition, p53R270H/- and p53R172H/- mice developed novel tumors compared to p53-/- mice, including a variety of carcinomas and more frequent endothelial tumors. Dominant effects that varied by allele and function were observed in primary cells derived from p53R270H/+ and p53R172H/+ mice. These results demonstrate that point mutant p53 alleles expressed under physiological control have enhanced oncogenic potential beyond the simple loss of p53 function.

The differential effects of mutant p53 alleles on advanced murine lung cancer.

We report a direct comparison of the differential effects of individual p53 mutations on lung tumor growth and progression, and the creation of a murine model of spontaneous advanced lung adenocarcinoma that closely recapitulates several aspects of advanced human pulmonary adenocarcinoma. We generated compound conditional knock-in mice with mutations in K-ras combined with one of three p53 alleles: a contact mutant, a structural mutant, or a null allele. p53 loss strongly promoted the progression of K-ras-induced lung adenocarcinomas, yielding a mouse model that is strikingly reminiscent of advanced human lung adenocarcinoma. The influence of p53 loss on malignant progression was observed as early as 6 weeks after tumor initiation. Furthermore, we found that the contact mutant p53R270H, but not the structural mutant p53R172H, acted in a partially dominant-negative fashion to promote K-ras-initiated lung adenocarcinomas. However, for both mutants, loss-of-heterozygosity occurred uniformly in advanced tumors, highlighting a residual tumor-suppressive function conferred by the remaining wild-type allele of p53. Finally, a subset of mice also developed sinonasal adenocarcinomas. In contrast to the lung tumors, expression of the point-mutant p53 alleles strongly promoted the development of sinonasal adenocarcinomas compared with simple loss-of-function, suggesting a tissue-specific gain-of-function.

The Use of Targeted Mouse Models for Preclinical Testing of Novel Cancer Therapeutics

The use of genetically engineered cancer-prone mice as relevant surrogates for patients during the development of pertinent clinical applications is an unproven expectation that awaits direct demonstration. Despite the generally disappointing findings using tumor xenografts and certain early transgenic cancer models to predict therapeutic efficacy in patients, the dramatic progress of mouse models in recent years engenders optimism that the newest generation of mouse models will provide a higher standard of predictive utility in the process of drug development.

Mice Expressing a Mammary Gland–Specific R270H Mutation in the p53 Tumor Suppressor Gene Mimic Human Breast Cancer Development

The tumor suppressor gene p53 has an apparent role in breast tumor development in humans, as approximately 30% of sporadic tumors acquire p53 mutations and Li-Fraumeni syndrome patients carrying germ line p53 mutations frequently develop breast tumors at early age. In the present study, conditional expression of a targeted mutation is used to analyze the role of the human R273H tumor-associated hotspot mutation in p53 in mammary gland tumorigenesis. Heterozygous p53(R270H/+)WAPCre mice (with mammary gland-specific expression of the p53.R270H mutation, equivalent to human R273H, at physiologic levels) develop mammary tumors at high frequency, indicating that the R270H mutation predisposes for mammary gland tumor development and acts in a dominant-negative manner in early stages of tumorigenesis. Spontaneous tumor development in these mice is further accelerated by 7,12-dimethylbenz(a)anthracene (DMBA) treatment at young age. The majority of spontaneous and DMBA-induced carcinomas and sarcomas from p53(R270H/+)WAPCre mice is estrogen receptor alpha positive, and expression profiles of genes also implicated in human breast cancer appear similarly altered. As such, p53(R270H/+)WAPCre mice provide a well-suited model system to study the role of p53 in breast tumorigenesis and the responsiveness of mammary gland tumors to chemotherapeutics.

Heterozygosity for Hypoxia Inducible Factor 1α decreases the incidence of thymic lymphomas in a p53 mutant mouse model

Hypoxia inducible factors (HIF) are critical mediators of the cellular response to decreased oxygen tension and are overexpressed in a number of tumors. Although HIF1alpha and HIF2alpha share a high degree of sequence homology, recent work has shown that the two alpha subunits can have contrasting and tissue-specific effects on tumor growth. To directly compare the role of each HIFalpha subunit in spontaneous tumorigenesis, we bred a mouse model of expanded HIF2alpha expression and Hif1alpha(+/-) mice to homozygotes for the R270H mutation in p53. Here, we report that p53(R270H/R270H) mice, which have not been previously described, develop a unique tumor spectrum relative to p53(R270H/-) mice, including a high incidence of thymic lymphomas. Heterozygosity for Hif1alpha significantly reduced the incidence of thymic lymphomas observed in this model. Moreover, reduced Hif1alpha levels correlated with decreased stabilization of activated Notch1 and expression of the Notch target genes, Dtx1 and Nrarp. These observations uncover a novel role for HIF1alpha in Notch pathway activation during T-cell lymphomagenesis.

K-Ras-driven pancreatic cancer mouse model for anticancer inhibitor analyses.

Genetically engineered mouse (GEM) models of cancer have progressively improved in technical sophistication and accurately recapitulating the cognate human condition and have had a measurable impact upon our knowledge of tumorigenesis. However, the application of such models toward the development of innovative therapeutic and diagnostic approaches has lagged behind. Our laboratory has established accurate mouse models of early and advanced ductal pancreatic cancer by conditionally expressing mutant K-ras and Trp53 alleles from their endogenous promoters in pancreatic progenitor cells. These K-Ras-dependent preclinical models provide valuable information on the cell types and pathways involved in the development of pancreatic cancer. Furthermore, they can be used to investigate the molecular, cellular, pharmacokinetic, and radiological characteristics of drug response to classical chemotherapeutics and to targeted agents. This chapter reviews the methods used to explore issues of drug delivery, imaging, and preclinical trial design in our GEM models for pancreatic cancer. We hypothesize that results of our preclinical studies will inform the design of clinical trials for pancreatic cancer patients.