Development of Novel Informative Preclinical Animal Models - CAPR Infrastructure

Division Of Basic Sciences - Nci

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Abstract

We have developed and characterized multiple GEM, GEM-derived allograft (GDA), and since recently patient-derived (PDX) murine models for diverse cancer indications for subsequent applications towards preclinical biomarker and therapeutic development. In addition, responding to growing preclinical needs and supporting collaborative activities initiated by CCR clinical investigators, CAPR specialists also recently embarked on a mission to establish several patient-derived xenograft models (PDX), to be employed for therapeutic discovery in oligo-proliferative lung cancer cases. On the path of building a state-of-art portfolio of predictive preclinical cancer models, CAPR major recent accomplishments include: 1. CAPR scientists established and characterized a novel genetic model for non-gestational choriocarcinoma (NGCO) - an unmet need rare clinical malignancy generally with poor prognosis. GEM mouse model for choriocarcinoma features inducible alterations in Brca2, Trp53, and pRb loci and develop with high penetrance (47%) the NGCO malignancy characterized by cellular features such as high presence of cytotrophoblasts and syncytiotrophoblasts, as well as expression of chorionic gonadotropin biomarker. This novel model for NGCO malignancy will provide an informative preclinical platform for mechanistic disease evaluation, establishing disease endpoints, developing imaging and other diagnostic options, as well as evaluating novel treatment strategies towards improving clinical outcomes in patients suffering from choriocarcinoma. 2. In collaboration with Dr. Alewine's lab, CAPR prepared an allelic series of models expressing human isoform of MSLN either in thyroid organ by conventional transgenesis, or in an endogenous mouse MSLN genomic locus by conventional knock-in and CRISPR/Cas9 technologies. The former model has been subsequently employed as pre-tolerized to human MSLN protein recipient animals engrafted orthotopically with PDAC cells engineered by viral transduction to express human mesothelin; whereas the latter allele has been successfully intercrossed onto the KPC background to derive KPC animals expressing human MSLN in place of its murine counterpart, in all cells normally producing MSLN, as well as in pancreatic tumors. Both types of animal models have been used in recently completed preclinical testing of iTox formulation, alone or in combination with checkpoint inhibitors CTLA-4 and PD-1, to discover the deleterious impact of PDAC desmoplastic stroma on accessibility of iTox protein in tumor tissues. Some of our findings have been recently published. 3. In collaboration with Dr. Sheue-yann Cheng, we have established and characterized a new Tpo-CreERT2 allele that has been shown to selectively express an inducible isoform of Cre recombinase in thyroid gland. This strain is currently used to assemble a genetic model for medullary thyroid carcinoma, using as oncogenic drivers conditional p53 missense mutation alleles generated at CAPR that has been also shared with Dr. Cheng. By employing different breeding schemes to incorporate distinct oncogenic drivers in the ultimate thyroid cancer models, we aim at developing murine models for both papillary and anaplastic types of thyroid malignancy. 4. We have modeled breast cancer development in the mouse by directly inducing Brca1 or Brca2 loss, inhibition of proteins of the Rb family (pRb, p107 and p130), and Trp53 loss or mutation (R172H) in the adult mammary ductal epithelium without pre-selecting the cellular subtype. The most frequently used Cre transgenes in mouse models for breast cancer are driven by various mammary tissue-specific promoters that direct genetic aberrations into a specific cell type. Although these mammary specific Cre transgenes are widely used, they do not allow for temporal control of the Cre expression, often resulting in induction of genetic events before onset of adulthood. Moreover, many of the Cre transgenes are expressed also in other tissues besides mammary gland. We have developed models with different allele combinations that cooperate to produce hormone receptor (HR) positive or negative mammary tumors of the luminal or basal subtype, respectively. Mice with Brca1 and Trp53 loss develop basal HR-negative mammary tumors, and mice with inhibition of Rb and Trp53 loss or the combination of Rb, Trp53 and Brca1 aberrations develop luminal ductal carcinoma that is positive for ER, PR and Her2 expression, but endocrine resistant. We completed molecular characterization of key pathways and analyzed drug sensitivities in vitro. We found that endocrine-resistant models exhibit upregulation of PI3K signaling and sensitivity to pathway inhibition, presenting a platform for evaluation of targeted combinations to improve chemotherapeutic response in patients. Moreover, the induction of genetic events in adult mice bypassed dependence on promoters that may express very early in mouse mammary development in progenitor cells. Therefore, these models are ideal for evaluation of cancer prevention strategies, especially those targeted towards Brca1 mutation carriers. 5. CAPR preclinical and model development scientists are assisting Dr. Laurie Krug of HIV and AIDS Malignancy Branch to establish PDX models from clinical Kaposi sarcoma samples as a valuable resource to understand the biology of Kaposi sarcomas and provide experimental platform for evaluating drug formulations effective against this type of malignancy frequently affecting population of patients suffering from AIDS or other immunologic deficiency syndromes.