Targeting the Notch Pathway in Cancer

PL03-04 Chromosomal translocations that produce a truncated and activated form of the NOTCH1 receptor have been identified in rare cases of human T-cell acute lymphoblastic leukemia (T-ALL). To uncover more frequent types of NOTCH1-activating mutations, we analyzed primary T-ALL samples and identified NOTCH1 mutations within the heterodimerization domain (HD) in 27% and truncating mutations that deleted the PEST destruction box (DPEST) in 15% of childhood T-ALL blasts. Both of these regions were simultaneously mutated in the same NOTCH1 gene of 16% of cases, providing evidence for multi-hit mutagenesis affecting a single oncogene in primary T-ALL samples at diagnosis.These mutations were shown to occur within each of the multistep molecular pathways that can lead to the transformation of T-cell progenitors during development, suggesting that some form of NOTCH pathway disruption may be required as a first step in the induction of most cases of T-ALL. These findings greatly expand the role of activated NOTCH1 in the molecular pathogenesis of human T-ALL, and provide a strong rationale in for targeted therapies of this disease that interfere with NOTCH signaling, because mutationally activated forms of NOTCH1 are still dependent on enzymatic cleavage for activity. To capitalize on this opportunity, a novel Phase I clinical trial of a potent NOTCH pathway inhibitor was recently conducted at the Dana-Farber Cancer Institute to specifically target the NOTCH pathway in adults with relapsed or refractory T-ALL. These results in T-ALL suggested that the HD-N, HD-C and Pest domains of the human NOTCH 1, 2, 3 and 4 receptors might also be the target of mutational activation in other types of human cancers. This rationale is particularly compelling in tumor types for which functional data implicate NOTCH pathway activation (e.g., breast cancer, glioblastoma, CLL, pancreatic cancer, and colon cancer). However, we sequenced the HD-N, HD-C and Pest coding regions of all 4 NOTCH genes in >20 primary tumors or tumor cell lines of breast, pancreas, prostate, kidney, and lung cancers, glioblastoma, melanoma, multiple myeloma, CLL, and neuroblastoma and did not identify any activating mutations similar to the ones that we found in T ALL. Nevertheless, very low Numb levels have been documented in ~50% of human breast cancers, which should accentuate trafficking of the Notch signal from the cell surface to the nucleus, and such cases have been shown to have inhibited colony-forming potential in the presence of a NOTCH pathway inhibitor (Pece S et al, 2004). In addition, gene amplification and overexpression of the NOTCH3 receptor has been reported in a high percentage of high-risk ovarian carcinomas (Park JT et al, 2006). Accordingly, phase I/II trials of a potent NOTCH pathway inhibitor are now underway in high risk relapsed or metastatic adult solid tumors. Reference: 1. Weng AP, Ferrando AA, Lee W, Morris, IV JP, Silverman LB, Sanchez-Irizarry C, Blacklow SC, Look AT, Aster JC. Activating mutations of NOTCH1 in human T-cell acute lymphoblastic leukemia. Science 306:269-271, 2004. 2. Pece S, Serresi M, Santolini E, Capra M, Hulleman E, Galimberti V, Zuarrida S, Maisonneuve P, Viale G, Di Fiore PP. Loss of negative regulation by Numb over Notch is relevant to human breast carcinogenesis. J Cell Biol. 167:215-221, 2004. 3. Park JT, Li M, Nakayama K, Mao T-L, Davidson B, Zhang Z, Kurman RJ, Eberhart CG, Shih I-M, Wang T-L. Notch3 gene amplification in ovarian cancer. Cancer Res. 66:6312-6318, 2006.