Differential Effects of Trp53 Alterations in Murine Colorectal Cancer

BACKGROUND

Colorectal cancer (CRC) development is a multi-step process resulting in the accumulation of genetic alterations. Despite its high incidence, there are currently no mouse models that accurately recapitulate this process and mimic sporadic CRC. We aimed to develop and characterize a genetically engineered mouse model (GEMM) of Apc/Kras/Trp53 mutant CRC, the most frequent genetic subtype of CRC.

METHODS

Tumors were induced in mice with conditional mutations or knockouts in Apc, Kras, and Trp53 by a segmental adeno-cre viral infection, monitored via colonoscopy and characterized on multiple levels via immunohistochemistry and next-generation sequencing.

RESULTS

The model accurately recapitulates human colorectal carcinogenesis clinically, histologically and genetically. The Trp53 R172H hotspot mutation leads to significantly increased metastatic capacity. The effects of Trp53 alterations, as well as the response to treatment of this model, are similar to human CRC. Exome sequencing revealed spontaneous protein-modifying alterations in multiple CRC-related genes and oncogenic pathways, resulting in a genetic landscape resembling human CRC.

CONCLUSIONS

This model realistically mimics human CRC in many aspects, allows new insights into the role of TP53 in CRC, enables highly predictive preclinical studies and demonstrates the value of GEMMs in current translational cancer research and drug development.

A Genetically Engineered Mouse Model of Sporadic Colorectal Cancer

Despite the advantages of easy applicability and cost-effectiveness, colorectal cancer mouse models based on tumor cell injection have severe limitations and do not accurately simulate tumor biology and tumor cell dissemination. Genetically engineered mouse models have been introduced to overcome these limitations; however, such models are technically demanding, especially in large organs such as the colon in which only a single tumor is desired. As a result, an immunocompetent, genetically engineered mouse model of colorectal cancer was developed which develops highly uniform tumors and can be used for tumor biology studies as well as therapeutic trials. Tumor development is initiated by surgical, segmental infection of the distal colon with adeno-cre virus in compound conditionally mutant mice. The tumors can be easily detected and monitored via colonoscopy. We here describe the surgical technique of segmental adeno-cre infection of the colon, the surveillance of the tumor via high-resolution colonoscopy and present the resulting colorectal tumors.

Abstract 4263: Establishment and initial characterization of human hepatocellular carcinoma organoid culture

Background:

Hepatocellular carcinoma (HCC) is the 3rd most leading cause of cancer death in the world. Despite extensive research, HCC has a strikingly bad prognosis due to the limited therapeutic options: Other than surgical resection, there is no curative treatment. No cytotoxic agent has shown efficacy so far, and the only currently approved systemic agent, sorafenib, is only used in a palliative context.

This dilemma is due to the therapy-resistant biology as well as its variable pathogenesis and biological diversity, which requires excellent preclinical models to allow differential and innovative studies.

Innovative 3D culture methods such as organoid culture have been increasingly implemented in routine in vitro research for many tumor entities. However, due to its distinct biology, organoid culture of HCC has been a challenge. We here describe the initial establishment and characterization of HCC organoid culture.

Materials/Methods:

Surgical HCC tissue specimens were obtained in the operating rooms of the University Hospital Dresden; biopsy specimens were obtained via CT-/ultrasound-guided biopsy of HCC lesions. All samples were processed according to a novel protocol and cultured in Matrigel supplemented with a highly specialized culture medium. Organoids were propagated, passaged and frozen at regular intervals. Proliferation was measured using a modified WST proliferation assay protocol. Next-generation sequencing (NGS) was performed on corresponding triplets of healthy tissue, tumor tissue and organoid samples using the TruSight One Sequencing Panel (Illumina) on an Illumina MiSeq Sequencer. Histology was performed on formalin-fixed and paraffin-embedded organoids using standard protocols.

Results:

We were able to establish a method to culture HCC samples as organoids in vitro. Proliferation assays revealed distinct differences in organoid growth of HCCs from different patients and correlated well with both clinical behavior and histological grading of the tumors. Amplicon sequencing (targeting 4,813 cancer-associated genes) of corresponding sets of tumor specimens and HCC organoids demonstrated the HCC origin of the organoids and their genetic and genomic stability in culture. Treatment of HCC organoids with sorafenib showed the expected reduction in proliferation and viability. Interestingly, treatment of the HCC organoids with hepatocyte growth factor (HGF) resulted in a marked reduction in proliferation as opposed to healthy liver organoids, which had increased proliferation activity upon stimulation with HGF. Histology of the HCC organoids showed distinct features of HCC and corresponded well with the corresponding HCC tissue samples.

Conclusion:

We successfully established a protocol reliably allowing 3D organoid culture of HCC. The organoids faithfully recapitulate the biology of the corresponding tumor and can be used for multiple purposes including in vitro therapeutic testing.

Citation Format: Sebastian Schölch, Lahiri K. Nanduri, Daniel Kühn, Jürgen Weitz, Moritz Koch, Nuh N. Rahbari. Establishment and initial characterization of human hepatocellular carcinoma organoid culture. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4263.

Validation of microarray-based resequencing of 93 worldwide mitochondrial genomes

The human mitochondrial genome consists of a multicopy, circular dsDNA molecule of 16,569 base pairs. It encodes for 13 proteins, two ribosomal genes, and 22 tRNAs that are essential in the generation of cellular ATP by oxidative phosphorylation in eukaryotic cells. Germline mutations in mitochondrial DNA (mtDNA) are an important cause of maternally inherited diseases, while somatic mtDNA mutations may play important roles in aging and cancer. mtDNA polymorphisms are also widely used in population and forensic genetics. Therefore, methods that allow the rapid, inexpensive and accurate sequencing of mtDNA are of great interest. One such method is the Affymetrix GeneChip Human Mitochondrial Resequencing Array 2.0 (MitoChip v.2.0) (Santa Clara, CA). A direct comparison of 93 worldwide mitochondrial genomes sequenced by both the MitoChip and dideoxy terminator sequencing revealed an average call rate of 99.48% and an accuracy of > or =99.98% for the MitoChip. The good performance was achieved by using in-house software for the automated analysis of additional probes on the array that cover the most common haplotypes in the hypervariable regions (HVR). Failure to call a base was associated mostly with the presence of either a run of > or =4 C bases or a sequence variant within 12 bases up- or downstream of that base. A major drawback of the MitoChip is its inability to detect insertions/deletions and its low sensitivity and specificity in the detection of heteroplasmy. However, the vast majority of haplogroup defining polymorphism in the mtDNA phylogeny could be called unambiguously and more rapidly than with conventional sequencing.