Molecular characterization of Wilms' tumor from a resource‐constrained region of sub‐Saharan Africa

Abstract

Sub-Saharan African children have an increased incidence of Wilms tumor (WT) and experience alarmingly poor outcomes. Although these outcomes are largely due to inadequate therapy, we hypothesized that WT from this region exhibit features of biologic aggressiveness that may warrant broader implementation of high-risk therapeutic protocols. We evaluated 15 Kenyan WT (KWT) for features of aggressive disease (blastemal predominance, Ki67/cellular proliferation) and treatment resistance (anaplasia, p53 immunopositivity). To explore additional biologic features of KWT, we determined the mutational status of the CTNNB1/β-catenin and WT1 genes and performed immunostaining for markers of Wnt pathway activation (β-catenin) and nephronic progenitor cell self-renewal (WT1, CITED1, SIX2). We characterized the proteome of KWT using imaging mass spectrometry (IMS). Results were compared to histology and age-matched North American WT (NAWT) controls. For KWT patients, blastemal predominance was noted in 53.3% and anaplasia in 13%. We detected increased loss to follow up (p=0.028), disease relapse (p=0.044), mortality (p=0.001), and nuclear unrest (p=0.001) in KWT patients compared to controls. KWT and NAWT showed similar Ki67/cellular proliferation. We detected an increased proportion of epithelial nuclear β-catenin in KWT (p=0.013). All 15 KWT were found to harbor wild-type β-catenin, and 1 contained a WT1 nonsense mutation. WT1 was detected by immunostaining in 100% of KWT, CITED1 in 80%, and SIX2 in 80%. IMS revealed a molecular signature unique to KWT that was distinct from NAWT. African WTs appear to express markers of adverse clinical behavior and treatment resistance and may require alternative therapies or implementation of high-risk treatment protocols.

Race Disparities in Peptide Profiles of North American and Kenyan Wilms Tumor Specimens

“…To initiate discovery of the biological basis for the disparate incidences of WT between race groups, we previously conducted two pilot analyses of WT specimens originating from Tennessean and Kenyan patients, and those prior efforts suggested WT peptide profiles might indeed differ according to race group. (5, 20) In the current studies, we aimed to build on those concepts and to examine, using MALDI-TOF-IMS and subsequent LC-MS/MS, a much larger cohort of WT specimens for peptide signatures that could lead to the discovery of new race-specific targets, while incorporating molecular fingerprints of other patient and disease characteristics, as an initial means to personalize WT therapy.…”

“…Using MALDI-TOF-IMS as previously described,(20) we analyzed a single tissue section from each specimen block of the 40 black NAWT, the 40 white NAWT, and the 18 KWT specimens. Three 6 µm serial sections were cut from each specimen block, and the middle section was H&E stained.…”

“…Photomicrographs of these 98 H&E slides were marked with multiple 300µm diameter circles on histologic regions of interest (Mirax Desk, 3D Histech, Budapest, Hungary). (20) To control for peptide profiles varying according to the different WT cellular compartments, histologic regions were labeled separately as “triphasic”, “blastema”, and “stroma”. Next, corresponding tissue sections for IMS analysis were deparaffinized and subjected to heatinduced antigen retrieval, and the annotated H&E stained images were digitally registered to the unstained sections.…”

“…In a previous pilot study seeking to explain potential biological differences in WT between race groups, we observed unique peptide profiles that may discriminate specimens according to race, but the power of that study was too low to draw substantial conclusions or to identify specific mechanistic pathways. (20) These current studies were designed to build on those preliminary findings and to test the hypotheses that WT specimens express a molecular fingerprint specific to race and that these profiles might reveal candidate targets as an initial step to personalize therapy.…”

Current frontiers in clinical research application of MALDI imaging mass spectrometry

“…Thus, variances measured are considered significant if they are reproducible. In contrast, human samples can be rare or hard to collect in large numbers, especially if a specific kind of fixation (e.g., cryofixation), comprehensive clinical follow-up data (e.g., survival) or samples of uncommon diseases [15] are required. Unfortunately, these factors can add up which might lead to a shortage of available material.…”