Tools and Technologies II
Cancer is one of the leading causes of death in California. Cancer treatment and cancer patient care cost Californians tens of billions of dollars every year. Despite some improvement in the survival of cancer patient in general, certain cancers such as pancreatic and lung cancers remain highly lethal; the survival rate of pancreatic cancer patients is below 5% and lung cancer below 20% . Therefore, there is an urgent need for new treatments for these human cancers. Pre-clinic cancer models are critical for the development of new cancer therapy. Mouse models for human cancers are valuable physiological tools for studying the tumorigenesis pathways. However, due to clear cellular and physiological differences between mouse and human, mouse models often fail to recapitulate the human tumorigenesis. For example, while cancers developed in mouse are mostly lymphomas and sarcomas, the major types of human cancers are of epithelial origin. These differences also lead to the common dilemma in drug discovery that a cancer therapy works well in mouse models but poorly in human patients. Therefore, there is an increasing need for more physiologically relevant human cancer models for mechanistic studies and drug development. In particular, there is an urgent need for relevant models for some of the most lethal human cancers - pancreatic and lung cancers. Human ES cells (hESCs), which can undergo unlimited self-renewal and retain the pluripotency to differentiate into all cell types in the body, present a possible solution to model human cancers. Induced pluripotent stem cells (iPSCs), reprogrammed from somatic cells with defined factors, could be useful to model certain human diseases. However, iPSCs are not suitable to model human cancers for several reasons. For example, one of the hallmarks of human cancer is genomic instability. Therefore, iPSCs derived from human cancer cells will harbor extensive unknown genetic abnormalities that are specific for that cancer cell, excluding their use as a disease model. In addition, the common genetic abnormalities in cancer such as the p53 mutations could disrupt proper self-renewal and differentiation of pluripotent stem cells. With established expertise in sophisticated genetic manipulation of hESCs, we propose to introduce the most common causative cancer mutations found in human pancreatic and lung cancers into hESCs that can be induced in a pancreatic lineage- or lung epithelial-specific manner. By determining the tumorigenesis of primary cells derived from these genetically modified hESCs in vitro and in vivo, we aim to establish a new generation of relevant pre-clinic cancer models that can be useful for both mechanistic studies and drug development.
Statement of Benefit to California:
Cancer is the second leading cause of death in California (behind heart disease), costing California billions of dollar in cancer care and treatment each year. It is estimated that 2 out 5 Californians will be diagnosed with cancer during the lifetime. Pancreatic cancer, diagnosed in thousands of Californians each year, is the most lethal cancer with a survival rate below 5%. Lung cancer, which is one of the most common cancers among Californians, is also highly lethal with a survival rate about 20%. Therefore, despite some improvement in the overall cancer survival during the past decade, there is a critical need to develop new therapies to treat these lethal cancers such as pancreatic and lung cancers. In order to develop new cancer treatment, relevant pre-clinic cancer models are critical for providing the mechanistic insight to design novel treatment and testing the efficacy of the new treatments. The existing mouse models for cancers or mouse xenograft cancer models have many intrinsic deficiencies, leading to the common scenario that drugs work well in these models but poorly in human patients. Our proposed research is aimed to employ sophisticated genetic manipulation technology to genetically modify human ES cells to develop a new generation of physiologically relevant cancer models for human pancreatic and lung cancers. These models will become important tools for studying mechanism of cancer development and developing new treatments for these lethal human cancers.
This proposal aims to develop human pancreatic and lung carcinoma models by engineering human embryonic stem cells (hESCs) to conditionally obtain mutations commonly occurring in these cancers that can be induced or expressed in a pancreatic lineage or lung epithelial-specific manner. The applicants will create homozygous conditional knockout mutations of two key tumor suppressor genes and then will introduce additional modifications allowing for differentiated expression in lung or pancreatic progenitor cell lineages of a specific mutation and for cell selection. They propose to test the differentiated cells for their oncogenic potential in vitro and in immune-deficient animals. The applicants expect that such validated models will provide a new and necessary tool for cancer research. Although reviewers did not comment specifically on the significance of this work towards overcoming a bottleneck in stem cell research, they did view the application of human embryonic stem cells to cancer model development as quite innovative. Relatively little is understood about the developmental effects of cancer mutations in humans. However, a major concern regarding this proposal is the significance of these hESC-derived cancer cells as compared to primary tumor cells. The strategy of identifying effects of specific mutations implicated in cancer on development and cell cancer phenotypes is justified, but it is not clear how these cell lines will be comparable to or better models than current human cancer cell lines. Presumably these hESC-derived cells could be used to identify phenotypes of specific mutations in the absence of the numerous genetic and genomic instabilities that accompany the cancer. However, this advantage is balanced by the concern that the hESC-derived cells may not be an accurate model of human cancer. Thus, the perceived significance of this project is as a complement to existing cell lines and primary tumor tissue rather than eliciting a major advance in regenerative medicine. Reviewers noted that the embryonic stem cell line engineering is carefully designed as described in the Preliminary Data section and likely to be very effective. However, several major flaws in the experimental design were identified. One critical point is that the cell of origin for many pancreatic and lung cancers is not well understood. Thus, the plan to differentiate hESC into adult cell types relevant to the cancer is unlikely to be feasible. A second flaw is the lack of sufficient characterization to validate the hESC cancer model. There is no plan to compare the hESC models with human cancer cell lines and no detailed explanation of what might be done in vitro to validate these models. Finally, there is no characterization of the epithelial cells that would be produced by the hESC cancer models and what effect the proposed mutations might have on differentiation or phenotypes. The dearth of assays and plans to characterize these cancer models and the lack of comparative models reduce the likelihood that hESC based cancer models will lead to any meaningful insights. The principal investigator (PI) is contributing the appropriate 20% effort to the project and has the necessary expertise in cancer cell biology and embryonic stem cell culture. The PI has a very impressive publication and funding record. The laboratory of PI is very well equipped to conduct the proposed study and a key collaborator provides the necessary expertise in pancreatic cancer and the in vivo model of cancer. Reviewers expressed no concerns about the qualifications of the research team. Overall, while this proposal is innovative, it is not clear how the proposed cell lines will represent a better cancer model than cancer cell lines obtained from primary tumor tissue.
- This application scored below the initial scientific merit funding line, no programmatic reason to fund the application was suggested, and the GWG voted to place the application in Tier 3, Not Recommended for Funding.