Abstract P2-02-04: Li-Fraumeni syndrome in females with early onset breast cancer in a Mexican population

Background: Breast cancer in Mexican patients presents in average 10 year earlier compared to other populations. Among patients with TP53 mutations, breast cancer is the most common malignancy. In this study we aim to determine the rate of TP53 mutations among young Mexican breast cancer patients.

Methods: Breast cancer patients younger that 45 were retrospectively identified, only patients without BRCA1/2 mutations were included. Clinical records and pedigrees were reviewed. Next generation sequencing test for TP53 was performed from blood specimens. All pathogenic mutations were confirmed by Sanger sequencing and verified if were included in the IACR TP53 database.

Results: Among the 78 patients younger than 45yo evaluated and tested with next generation sequencing, we identified 5 patients with a TP53 mutation (6.4%). All were younger than 36 corresponding to a rate of 9.4% of mutations in this group of individuals (n = 53). Two, not previously described, frameshift mutations were found (c.291delC and c.273dupG) and three missense mutations (c.844C>T, c.517G>A, c.604C>T). A VUS c.672G>A that causes a silent mutation in a splicing-donor site was identified. All patients with a TP53 mutation had locally advanced disease and tumors were high grade and Her2 positive.

Conclusions: Among Mexican women younger than 45yo, the rate of TP53 mutations was higher than in other populations where it's estimated to be 1%. Among patients younger than 36 the proportion was even higher. All patients had a family history suggestive of Li-Fraumeni syndrome. The VUS found in our series needs a deeper analysis (family segregation, structure and function of the resulting protein). Our results support the international recommendation of performing molecular testing for TP53 in breast cancer patients younger than 35 years. Identification of patients with TP53 mutation has important prognostic, therapeutic and quality of life implications for the proband in addition of the risk reduction strategies and intensive surveillance recommended in their families.

Citation Format: Gallardo-Alvarado LN, Cantu-De Leon DF, Tusie-Luna T, Tusie-Luna I, Diaz-Chavez J, Herrera EM, Chavez-MacGregor M, Bargallo-Rocha E, Villarreal C, Herrera.Montalvo LA, Segura-Kato YX. Li-Fraumeni syndrome in females with early onset breast cancer in a Mexican population [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P2-02-04.

Invasive phenotype of Trypanosoma cruzi restricted to a population expressing trans-sialidase

Trypanosoma cruzi expresses a developmentally regulated trans-sialidase implicated in the pathogenesis of Chagas' disease. On inhabitation of the extracellular milieu of cultured cells by infective trypomastigotes, the enzyme is restricted to a small (20 to 30%) population of parasites. The biological significance of trans-sialidase expression on this subset, termed TS+, and not on the majority (70 to 80%) of morphologically similar trypanosomes, named TS-, is unknown. To determine the roles of the TS+ and TS- subsets in T. cruzi invasion, we prepared pure populations of TS- and TS+ trypanosomes using magnetic beads coated with a monoclonal antibody specific for the tandem repeat unit of the trans-sialidase C terminus. After removal of nonadherent TS- trypomastigotes, the TS+ trypomastigotes were isolated from the beads by specific elusion with a synthetic peptide epitope of the trans-sialidase monoclonal antibody. Confirmation of TS+ and TS- phenotypes was obtained by immunofluorescence, immunoblotting, and sialidase or sialyl transferase activity measurements. The TS+ trypanosomes were highly invasive, as they attached to, penetrated, and thrived in cultured mammalian cells much more efficiently than did unfractionated parasites. The critical role of the trans-sialidase in invasion was underscored by the observation that infection was neutralized by human antibodies to transsialidase. What's more, the TS- parasites, in sharp contrast to their TS+ counterparts, were extremely inefficient in invading epithelial cells and fibroblasts. Further, introduction of small amounts of exogenous trans-sialidase into suspensions of nonpenetrating TS- parasites converted them to a highly invasive phenotype indistinguishable from that of the TS+ population. Rescue of the invasive phenotype was specific for the T. cruzi enzyme, for it didn't happen with bacterial and viral sialidases. The in vitro results were confirmed in the murine model of Chagas' disease, as TS- trypomastigotes were relatively avirulent while TS+ trypomastigotes were more virulent than unfractionated parasites.

Mediation of Trypanosoma cruzi invasion by heparan sulfate receptors on host cells and penetrin counter-receptors on the trypanosomes

Trypanosoma cruzi attaches and invades a large variety of mammalian cells by receptor-mediated interactions, one of them involving the binding of parasite trans-sialidase to host sialyl receptors. Three proteoglycan-deficient mutants of Chinese hamster ovary (CHO) cells were used to probe the role of host heparin and heparan sulfate glycosaminoglycans (GAG) in T. cruzi invasion. All three mutants supported adhesion and infection to a much lower extent than the parental CHO cells. One of the mutants, pgsD-677, did not express heparan sulfate while containing three- to four-fold excess chondroitin sulfate, yet the cell line was a poor substrate for T. cruzi adhesion. Proteoglycan-deficient cells obtained by inhibiting GAG synthesis in parental cells with p-nitrophenyl-beta-D-xyloside, were also poor hosts for T. cruzi invasion. Furthermore, digestion of parental cells with heparinase and heparitinase, two lyases that specifically depolymerize heparin and heparan sulfate, reduced the potential of the cells to support T. cruzi adhesion and growth. Lyases that digested chondroitin sulfate and other GAGs did not affect T. cruzi invasion. These results suggest that heparin/heparan sulfate epitopes are receptors for T. cruzi invasion. The corresponding counter-receptor on T. cruzi appears to be penetrin, a heparin-binding protein that promotes trypanosome penetration into cells. Purified penetrin caused agglutination of red blood cells, and the hemagglutination was exquisitely sensitive to heparin and heparan sulfate. However, sialic acid and sialyl compounds did not inhibit penetrin-induced hemagglutination. Recombinant penetrin competitively inhibited T. cruzi invasion of proteoglycan-containing parental cells, but not of proteoglycan-deficient mutants nor of heparitinase-treated cells. Furthermore, consistent with the sugar specificity of penetrin as a hemagglutinin, recombinant penetrin competed for trypanosome invasion of a CHO cell mutant (Lec2) that expresses heparan sulfate but not sialyl residues. Given that the release of sialic acid from the proteoglycan-deficient mutants further reduced T. cruzi invasion, as did the removal of heparan sulfate from the Lec2 mutant, and given that penetrin does not bind to sialic acid with high affinity, the results indicate that the penetrin-heparan sulfate pathway for T. cruzi invasion is distinct from the trans-sialidase-sialic acid route.