A tissue reconstitution model to study cancer cell-intrinsic and -extrinsic factors in mammary tumourigenesis.

The contribution of cancer cell-intrinsic and -extrinsic factors to metastatic breast cancer is still poorly understood, hampering development of novel therapeutic strategies that decrease breast cancer mortality. Cre/loxP-based conditional mouse models of breast cancer present unique opportunities to study sporadic tumour formation and progression in a controlled setting. Unfortunately, the generation of mouse strains carrying multiple mutant alleles needed for such studies is very time-consuming. Moreover, conditional mouse tumour models do not permit independent manipulation of tumour cell-intrinsic and -extrinsic factors. Although the latter can be achieved by cleared fat-pad transplantation of mouse mammary epithelial cells (MMECs) from tumour suppressor gene (TSG) knockouts into wild-type or mutant recipients, this procedure is not possible for mutations that cause embryonic lethality or preclude mammary gland development. Here we show that cleared fat-pad transplantations with MMECs isolated from K14cre;Cdh1(F/F); Trp53(F/F) mice expressing Cre recombinase under control of the cytokeratin-14 promoter and carrying conditional null alleles for p53 and E-cadherin (Cdh1) first resulted in the formation of phenotypically normal mammary glands, followed by the development of invasive metastatic mammary tumours. Tumour formation in the recipients mimicked tumour latency, spectrum, morphology, immunophenotype, and metastatic characteristics of the original mammary tumour model. This transplantation system, which can be expanded to other conditional TSG knockouts, permits independent genetic analysis of stromal factors and testing of additional cancer cell-intrinsic mutations that would otherwise be embryonic lethal or require intensive breeding.