Identifying cancer drivers and actionable mutations is critical for precision oncology. In epithelial ovarian cancer (EOC) the majority of mutations lack biological or clinical validation. We fully characterized 43 lines of Patient-Derived Xenografts (PDXs) and performed copy number analysis and whole exome sequencing of 12 lines derived from naïve, high grade EOCs. Pyrosequencing allowed quantifying mutations in the source tumours. Drug response was assayed on PDX Derived Tumour Cells (PDTCs) and in vivo on PDXs. We identified a PIK3R1W624R variant in PDXs from a high grade serous EOC. Allele frequencies of PIK3R1W624R in all the passaged PDXs and in samples of the source tumour suggested that it was truncal and thus possibly a driver mutation. After inconclusive results in silico analyses, PDTCs and PDXs allowed the showing actionability of PIK3R1W624R and addiction of PIK3R1W624R carrying cells to inhibitors of the PI3K/AKT/mTOR pathway. It is noteworthy that PIK3R1 encodes the p85α regulatory subunit of PI3K, that is very rarely mutated in EOC. The PIK3R1W624R mutation is located in the cSH2 domain of the p85α that has never been involved in oncogenesis. These data show that patient-derived models are irreplaceable in their role of unveiling unpredicted driver and actionable variants in advanced ovarian cancer.

The MET oncogene encodes a tyrosine kinase (TK) receptor. Its activation protects cells from death but also stimulates DNA damage response by triggering excess replicative stress. Transcriptomic classification of cancer cell lines based on MET expression showed that response to the PARP inhibitor (PARPi) olaparib is poorer in MET overexpressing cell lines. Accordingly, a high MET expressing lung carcinoma cell line was sensitized to PARPi by MET TK inhibition. This was not linked solely to MET overexpression: other MET overexpressing cell lines were biochemically but not functionally responsive to combined inhibition. Moreover, exogenously induced MET overexpression was unable to induce resistance to PARPi. The MET overexpressing cell line, responsive to the combined PARP and MET inhibition, carried a heterozygous mutation of the ATM gene and showed an attenuated response of ATM to PARPi. Among the downstream targets of ATM activation, NuMA was phosphorylated only in response to the combined PARP and MET inhibition. Given the role played by NuMA in mitosis, data show that the latter is affected by MET and PARP inhibition in cells with haploinsufficient ATM. This is important as ATM heterozygous mutation is frequently found in human cancer and in lung carcinomas in particular.

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Patients with advanced ovarian cancers have experienced little improvement in overall survival with standard treatments even after the incorporation of anti-angiogenic therapies. Besides anti-PARP inhibitors, matching individual critical genomic alterations with the best available drugs has not advanced as in other cancers, likely because a handful of cancer-related genes are mutated at high frequency, while many more are found mutated at much lower frequencies. This so called “mutation tail” is not only long but also mostly unexplored. We used Patient Derived Xenografts (PDXs) to identify actionable cancer genes and PDX Derived Tumor Cells (PDTCs) to accelerate the discovery of treatment options. We envisioned that the alleged weakness of PDX models, i.e. lack of human stromal and immune cells, might be instrumental to identify mutations in cancer and to test approved or experimental targeted drugs as monotherapy or in different combinations to link biomarkers to treatments. Forty-nine PDX lines from metastatic epithelial ovarian carcinomas have been propagated and fully characterized as far as histology, immunohistochemistry of epithelial and high-grade serous-specific markers and presence of TP53 and BRCA1/2 mutations. Copy number variations (CNV) analysis and Whole Exome Sequencing (WES) were carried out PDX lines derived from naïve metastatic high-grade epithelial ovarian carcinomas, which came out to be refractory/resistant to platinum drugs. We studied non-synonymous mutations with allele frequencies ≥0.1. Only mutations in cancer genes listed in databases were further analyzed. SNPdb allowed ruling out polymorphisms. SIFT and PROVEAN softwares predicted deleterious or damaging effects onto the protein sequences. DGIdb helped selecting actionable genes. We identified in one PDX line, a possibly loss-of-function mutation of the PIK3R1 gene (encoding the p85alpha regulatory subunit of PI3K) had an allele frequency=0.9 in early and late passages. Moreover, in two micro-dissected FFPE samples of the source tumor this mutation had an allele frequency nearly identical to that of the mutated TP53. Hence, PIK3R1W624R could be a trunk mutation in the PDX line and possibly in the human counterpart. Treatment options were assayed ex-vivo, on short-term cultures of PDTCs of the PIK3R1W624R PDX line. Buparlisib, a pan-class I PI3K inhibitor, showed the ability to block proliferation of PDTCs and the growth in vivo of PDXs in regression preclinical trial. These data proofed-the-concept that a PDX-based pipeline is able to unveil actionable pathways for the treatment of advanced/metastatic ovarian cancer. Citation Format: Martina Olivero, Jessica Erriquez, Maddalena Arigoni, Sonia Capellero, Concetta D'Ambrosio, Gloria Mittica, Fulvio Borella, Dionyssios Katsaros, Silvana Privitera, Enrico Berrino, Tiziana Venesio, Giorgio Valabrega, Raffaele Calogero and Maria Flavia Di Renzo. PATIENT DERIVED XENOGRAFTS (PDXS) AND PDX DERIVED TUMOR CELLS (PDTC) ALLOW THE IDENTIFICATION OF ACTIONABLE CANCER GENES AND TREATMENT OPTIONS FOR PLATINUM REFRACTORY/RESISTANT OVARIAN CARCINOMAS [abstract]. In: Proceedings of the 12th Biennial Ovarian Cancer Research Symposium; Sep 13-15, 2018; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2019;25(22 Suppl):Abstract nr GMM-023.

Patients with advanced ovarian cancers have experienced little improvement in overall survival with standard treatments. We used patient derived models to accelerate the discovery of treatment options. We developed a platform of Patient Derived Xenografts (PDX), by implanting and propagating patient's tumor samples collected at surgery in severely immunocompromised mice. From each PDX line we derived short term cultures of PDX Derived Tumor Cells (PDTCs). We envisioned that the weakness of PDXs and PDTCs, i.e. lack of human stromal and immune cells, might be instrumental to link tumor biomarkers to treatments. We have successfully propagated 49 PDX lines from metastatic EOC, which were fully characterized as far as histology, immunohistochemistry of epithelial and tissue specific markers and presence of TP53 and BRCA1/2 mutations. On PDTCs cultures we first assessed sensitivity to Carboplatin, currently used as first-line drug in ovarian cancer treatment. Of PDX lines derived from naïve metastatic HGS-EOC copy number variations and whole exome sequencing analyses were carried out, in order to identify putative and actionable cancer genes. Thus, on PDTCs we assayed also approved or experimental targeted drugs as monotherapy or in combinations. In one PDX line we identified a possibly loss-of-function mutation (W624R) of the PIK3R1 gene (encoding the p85alpha regulatory subunit of PI3K) with an allele frequency of 0.9, which could result in activation of the PI3K pathway. Several PI3K inhibitors were assayed on PDTCs of this PDX line harboring the PIK3R1W624R. Buparlisib (a Pan Class I PI3Ki) showed the ability to block proliferation of the PDTCs and the growth of the relevant PDXs in vivo. Altogether these data show that Patient Derived models are invaluable tools to unveil actionable pathways for the treatment of advanced/metastatic HGS-EOC. Citation Format: Concetta D'Ambrosio, Jessica Erriquez, Maddalena Arigoni, Sonia Capellero, Gloria Mittica, Eleonora Ghisoni, Fulvio Borella, Dionyssios Katsaros, Silvana Privitera, Marisa Ribotta, Elena Maldi, Giovanna Di Nardo, Enrico Berrino, Tiziana Venesio, Riccardo Ponzone, Marco Vaira, Douglas Hall, Mercedes Jimenez-Linan, Anna Paterson, Giorgio Valabrega, Raffaele Calogero, James Brenton, Mariaflavia Di Renzo, Martina Olivero. Assays of conventional chemotherapeutics and targeted drugs for ovarian cancer using patient derived models [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1677.

Patients with advanced ovarian cancers have experienced little improvement in overall survival with standard treatments even after the incorporation of anti-angiogenic therapies. Besides anti-PARP inhibitors, matching individual critical genomic alterations with the best available drugs has not advanced as in other cancers, likely because a handful of cancer-related genes are mutated at high frequency, while many more are found mutated at much lower frequencies. This so called “mutation tail” is not only long but also mostly unexplored. We used Patient Derived Xenografts (PDXs) to identify actionable cancer genes and PDX Derived Tumor Cells (PDTCs) to accelerate the discovery of treatment options. We envisioned that the alleged weakness of PDX models, i.e. lack of human stromal and immune cells, might be instrumental to identify mutations in cancer and to test approved or experimental targeted drugs as monotherapy or in different combinations to link biomarkers to treatments. Fourty-nine PDX lines from metastatic epithelial ovarian carcinomas have been propagated and fully characterized as far as histology, immunohistochemistry of epithelial and high-grade serous-specific markers and presence of TP53 and BRCA1/2 mutations. Copy number variations (CNV) analysis and Whole Exome Sequencing (WES) were carried out of 12 PDX lines derived from naïve metastatic high-grade serous epithelial ovarian carcinomas. We studied non-synonymous mutations with allele frequencies ≥0.1. Only mutations in cancer genes listed in databases were further analyzed. SNPdb allowed ruling out polymorphisms. SIFT and PROVEAN softwares predicted deleterious or damaging effects onto the protein sequences. DGIdb helped selecting actionable genes. We identified mutations in 1-4 cancer genes in 8/12 PDX lines. In one PDX line, a possibly loss-of-function mutation of the PIK3R1 gene (encoding the p85alpha regulatory subunit of PI3K) had an allele frequency=0.9 in early and late passages. Moreover, in two micro-dissected FFPE samples of the source tumor this mutation had an allele frequency nearly identical to that of the mutated TP53. Hence, PIK3R1W624R could be a trunk mutation in the PDX line and possibly in the human counterpart. Treatment options were assayed ex-vivo, on short-term cultures of PDTCs of the PIK3R1W624R PDX line. Buparlisib, a pan-class I PI3K inhibitor, showed the ability to block proliferation of PDTCs and the growth in vivo of PDXs in regression preclinical trial. These data proofed-the-concept that a PDX-based pipeline is able to unveil actionable pathways for the treatment of advanced/metastatic ovarian cancer. Citation Format: Martina Olivero, Jessica Erriquez, Maddalena Arigoni, Sonia Capellero, Concetta D'Ambrosio, Gloria Mittica, Fulvio Borella, Dionyssios Katsaros, Silvana Privitera, Enrico Berrino, Tiziana Venesio, Giorgio Valabrega, Raffaele Calogero, Maria Flavia Di Renzo. Identification of actionable cancer genes and treatment options for metastatic ovarian carcinomas using patient-derived xenografts and PDX-derived tumor cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3102.