Abstract
BackgroundOvarian carcinoma is highly dependent on the ubiquitin proteasome system (UPS), but its clinical response to treatment with the proteasome inhibitor bortezomib has been disappointing. This has driven exploration of alternate approaches to target the UPS in ovarian cancer. Recently, proteasome inhibitors targeting the 19S regulatory particle-associated RPN13 protein have been described, such as RA190. RPN13, which is encoded by ADRM1, facilitates the recognition by the proteasome of its polyubiquinated substrates. Inhibition of RPN13 produces a rapid, toxic accumulation of polyubiquitinated proteins in ovarian and other cancer cells, triggering apoptosis.Here, we sought to determine if RPN13 is available as a target in precursors of ovarian/fallopian tube cancer as well as all advanced cases, and the impact of increased ADRM1 gene copy number on sensitivity of ovarian cancer to RA190.MethodsADRM1 mRNA was quantified by RNAscope in situ hybridization and RPN13 protein detected by immunohistochemistry in high grade serous carcinoma (HGSC) of the ovary and serous tubal intraepithelial carcinoma (STIC). Amplification of ADRM1 and sensitivity to RA190 were determined in ovarian cancer cell lines.ResultsHere, we demonstrate that expression of ADRM1mRNA is significantly elevated in STIC and HGSC as compared to normal fallopian tube epithelium. ADRM1 mRNA and RPN13 were ubiquitously and robustly expressed in ovarian carcinoma tissue and cell lines. No correlation was found between ADRM1 amplification and sensitivity of ovarian cancer cell lines to RA190, but all were susceptible.ConclusionsRPN13 can potentially be targeted by RA190 in both in situ and metastatic ovarian carcinoma. Ovarian cancer cell lines are sensitive to RA190 regardless of whether the ADRM1 gene is amplified.
Highlights
Ovarian carcinoma is highly dependent on the ubiquitin proteasome system (UPS), but its clinical response to treatment with the proteasome inhibitor bortezomib has been disappointing
Validation of a highly sensitive and specific Chromogenic In Situ Hybridization (CISH) assay for ADRM1 transcript levels To develop a sensitive ADRM1 mRNA CISH assay, we used a custom hybridization probe for the RNAscope® 2.0 assay from Advanced Cell Diagnostics (ACD) that is designed for detection at the single transcript level
Elevated ADRM1 mRNA expression in matched serous tubal intraepithelial carcinoma (STIC) and high grade serous carcinomas (HGSC) Formalin-fixed, paraffin embedded blocks of 11 ovarian cancer cases were selected by three gynecologic pathologists who independently assessed the presence of STIC and HGSC carcinoma using H&E, ki-67, and p53 staining to probe morphology, proliferation and, − surrogate of TP53 muational status, respectively
Summary
Ovarian carcinoma is highly dependent on the ubiquitin proteasome system (UPS), but its clinical response to treatment with the proteasome inhibitor bortezomib has been disappointing. This has driven exploration of alternate approaches to target the UPS in ovarian cancer. Treatment with bortezomib slowed the growth of ES-2 ovarian carcinoma xenograft, alone it did not cure the mice [12] Despite this promise, early studies with bortezomib in patients with ovarian cancer or other solid tumors have demonstrated minimal clinical benefit. Despite bortezomib’s efficacy against multiple myeloma, its toxicity, and limited activity in solid tumors has driven development of inhibitors of the ubiquitin-proteasome system (UPS) with alternative mechanisms to treat ovarian cancer
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