Genetics of Carcinoid Tumors: Approaches and Progress

Ramesh Shivdasani, MD
Dana-Farber Cancer Institute
Boston, MA 02115

Carcinoid tumors of the small intestine resist conventional chemotherapy. Knowing the underlying genetic changes will inform efforts to develop new treatments, but to date specific genes are not implicated in the disease and critical molecular pathways are largely unknown. My laboratory seeks to define the genetic mutations that drive development of the disease and hence pave the way for new targeted therapies. We are using a variety of genetic approaches to mine one of the largest collections of carcinoid tumors, at the Dana-Farber Cancer Institute.

Genes that are amplified or deleted in tumors provide vital clues about underlying disease mechanisms, which differ from one tumor type to another. One approach we have taken uses single nucleotide polymorphism (SNP) arrays to analyze the genome of carcinoid tumors. This technique identifies genes that have increased or decreased copy numbers in carcinoid tumors compared with normal tissue. To help identify genetic alterations that may be involved in metastatic tumor spread, we also succeeded in some cases in conducting SNP array analysis on both primary tumors and metastases from the same patient. A novel and unexpected result of these studies was that small intestine (ileal) carcinoid tumors seem to belong to two distinct groups: those with simultaneous gain of chromosomes 4, 5, 7 and 14, and those with modest copy number imbalance. One focal region of recurrent gain on chromosome 14q mapped to the locus of the gene encoding the anti-apoptotic protein DAD1. By identifying genes that are amplified or deleted in tumors, we expect to delineate genetic events that might be important in tumor formation and serve as targets for therapy.

A second approach involves using modern techniques to analyze carcinoid tumors simultaneously for dozens of potential gene mutations, particularly those commonly present in a wide range of tumors. My lab is currently performing this analysis on a group of nearly 100 carcinoid tumors, one of the largest collections assembled to date for the purpose of molecular investigation.1

Understanding of tumor biology is considerably advanced by knowledge of the cell of tumor origin, which remains a conspicuous unknown in the case of carcinoid tumors. My laboratory therefore uses a combination of mouse genetics and cell culture techniques to study the origins of normal gastrointestinal endocrine cells and the cell of origin of carcinoid tumors. By tagging specific lineages of enteroendocrine cells in the developing gut, we hope to learn more about how carcinoid tumors arise and hence consider new strategies for tumor prevention or treatment. In particular, definition of neuroendocrine lineage hierarchies will identify molecular pathways that act to generate or maintain discrete endocrine cell lineages; such pathways may be targeted for rational therapy of carcinoid tumors.

Homeodomain transcription factors often function in differentiation of specific cell types. We used targeted gene disruption to generate mice lacking Nkx6.3, a new member of the Nkx6 subfamily. These mice develop and grow normally, with a grossly intact digestive tract, but carry many fewer gastrin-producing (G) cells in the stomach; as a result, blood levels of the hormone gastrin and acid levels in the stomach are significantly reduced. There is also a corresponding increase in somatostatin-producing (D) cells. These studies implicate Nkx6.3 as a novel and selective regulator of G- and D-cell neuroendocrine cell lineages, which are believed to derive from a common progenitor, and they set the stage for further characterization of enteroendocrine differentiation pathways.2

These studies would not be possible without the generous support and far-reaching vision of the Caring for Carcinoid Foundation. For more information please see:

1. Kulke MH, Freed E, Chiang D, Philips J, Zahrieh D, Glickman JN, Shivdasani RA.
High- resolution analysis of genetic alterations in small bowel carcinoid tumors reveals areas of recurrent amplification and loss. Genes Chrom Cancer 2008; 47:591-603.

2. Choi MY, Romer AI, Wang Y, Wu MP, Ito S, Leiter AB, Shivdasani RA. Requirement of the tissue-restricted homeodomain transcription factor Nkx6.3 in differentiation of gastrin- producing G-cells in the stomach antrum. Mol Cell Biol 2008; 28:3208-3218.

You can view these publications on the Caring for Carcinoid Foundation website at: http://www.caringforcarcinoid.org/research/researchprogress.asp