Michael Anglesio

Representing approximately 5% of all epithelial ovarian cancers, low-grade serous ovarian carcinoma (LGSC) is a rare histotype with unique genetic, molecular, and pathological features. LGSC patients are often detected at an advanced stage and respond poorly to platinum-based chemotherapy. Therefore, targeted therapies focused on exploiting oncogenic dependencies have homed in on the RAS/RAF/MEK/ERK (MAPK) signaling pathway, due to frequent activating MAPK mutations in LGSC tumours. Trials using MEK inhibitors (MEKi) have seen a modest increase in patient response, however, no cellular markers that distinguish MEKi response have been identified. This research aimed to discover and target protein markers of MEKi response by analyzing the global proteome of in-vitro cell lines previously established from patient samples through mass spectrometric analyses. 95 proteins were identified as being significantly differentially expressed between four MEKi sensitive and three MEKi resistant LGSC cell lines. Nine of these proteins were selected for further analysis, with the differentially protein expression of five markers being successfully validated. One of these confirmed markers, EGFR (a common driver of oncogenesis), was selected for paired inhibition with MEK using a combination of small molecule inhibitors specific for MEK and EGFR to induce cellular apoptosis in MEKi resistant LGSC lines. Four de novo and three acquired MEKi resistant LGSC cell lines were treated with a combination of erlotinib (EGFRi) and either selumetinib or trametinib (MEKi’s). Cellular response was analyzed by live-cell imaging, cell proliferation, and viability assays. A linear mixed effects model and drug synergism analysis was implemented to evaluate the efficacy of MEKi and EGFRi in combination. In the four de novo resistant LGSC lines, the drug combination induced complete cell death in two lines and demonstrated a degree of drug synergism in another. In the acquired MEKi resistance setting however, none of the cell lines responded to dual EGFR and MEK inhibition. Therefore, the combined inhibition of EGFR and MEK may represent a potential therapy for overcoming de novo MEKi resistance in LGSC, but not as a strategy for combatting acquired MEKi resistance.

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Introduction: Endometriosis is a chronic, inflammatory gynecological disease characterized by the ectopic growth of endometrial-like tissue. Previous studies have established endometriosis as the precursor to clear cell and endometrioid ovarian carcinomas. The presence of somatic driver mutations in endometriosis is believed to represent early events in transformation, however our group has recently described the presence of such mutations in nearly one-quarter of cases of deep infiltrating endometriosis (DE) – a form of endometriosis that rarely progresses to malignancy. These mutations may play a fundamental role in the pathogenesis of endometriosis outside of the context of cancer, however it is unclear whether they occur in other forms of endometriosis or the eutopic endometrium – the likely tissue of origin for endometriosis. The purpose of my study is to: 1) analyze and compare the mutational profiles of DE and incisional (iatrogenic; IE) endometriosis and 2) characterize somatic cancer-drivers that exist in the eutopic endometrium and determine whether the presence of such mutations reflect the aging of this tissue.Methods: I macrodissected endometriosis tissue from women with IE or DE. Extracted DNA was analyzed by targeted sequencing and mutations were orthogonally validated by droplet digital PCR. PTEN and ARID1A immunohistochemistry was also performed for each specimen. Using the same protocol, I also analyzed hysterectomy and endometrial biopsy specimens obtained from cancer-free women.Results: Overall, we detected the presence of somatic alterations in 27.5% and 36.1% of IE and DE cases respectively. These events affected canonical components of RAS/MAPK or PI3K-Akt signaling pathways. Furthermore, over 50% of cancer-free women also harboured similar somatic alterations in their eutopic endometrial tissue. The presence of somatic cancer-drivers in the eutopic endometrium are likely regional and are correlated with age (p = 0.048).Conclusions: My findings are consistent with a uterine origin of endometriosis. Somatic cancer-driver alterations are commonly found in both endometriosis and the eutopic endometrium of cancer-free women and may reflect the accumulation of DNA damage over time. These somatic alterations alone are insufficient for malignant transformation and should be interpreted with caution in the early diagnosis of gynecologic malignancies given their common occurrence in cancer-free women.

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