Ovarian Tumor Cells

Ovarian tumor cells, primarily associated with ovarian cancer, present a complex challenge in oncology due to their diverse histological types and biological behaviors. Ovarian cancer remains one of the leading causes of cancer-related deaths among women globally. The majority of ovarian tumors are classified as epithelial tumors, which arise from the ovarian surface epithelium.

Molecular Biology of Ovarian Tumor Cells

• Genetic alterations. The molecular characterization of ovarian tumor cells has revealed numerous genetic mutations that drive tumorigenesis. The most notable are mutations in the BRCA1 and BRCA2 genes, which significantly increase the risk of developing ovarian and breast cancers. Studies indicate that about 15-20% of high-grade serous ovarian cancers (HGSC) harbor mutations in these genes.
• Tumor microenvironment. Ovarian tumor cells interact with surrounding stromal cells, immune cells, and extracellular matrix components, leading to changes that facilitate tumor growth and metastasis. For example, fibroblasts in the stromal tissue can secrete growth factors such as transforming growth factor-beta (TGF-β) which promotes epithelial-to-mesenchymal transition (EMT). This process contributes to the increased invasiveness of tumor cells.
• Molecular pathways. Key signaling pathways involved in ovarian tumor biology include the PI3K/Akt and MAPK pathways. Dysregulation of these pathways enhances cell proliferation and survival. Research has shown that in about 70% of ovarian tumors, there are alterations in the PI3K pathway, which often correlates with poor prognosis.

Model Systems for Research

Ovarian tumor cells are used to create model systems that mimic the behavior of tumors in the body. Cultured cells that grow indefinitely and are used for experiments that require a large number of cells. Tumor cells are implanted into immunodeficient mice to study tumor growth, metastasis, and response to treatments in a more physiological context. Three-dimensional cultures recapitulate the architecture of the tumor and are useful for studying tumor-stroma interactions and drug response.

Genetic and Epigenetic Studies

Mesothelioma cell lines and animal models derived from these cells are essential in the preclinical phase of drug discovery. These models allow researchers to test the efficacy and toxicity of new drugs or combinations of drugs. This process helps to prioritize the most promising candidates for further development and clinical trials.

Immunotherapy Research

Ovarian tumor cells play a role in the development of immunotherapies, which harness the immune system to fight cancer. This includes creating vaccines that stimulate an immune response against specific antigens present in ovarian tumor cells. Additionally, identifying and targeting molecules on tumor cells that interact with immune cells to inhibit the body's immune response.

Functional Role of FZD7 in Ovarian Cancer Cells

Platinum-tolerant cells and tumors were enriched in ALDH(+) cells, formed more spheroids, and expressed increased levels of stemness-related transcription factors compared to parental cells. Additionally, platinum-tolerant cells and tumors exhibited expression of the Wnt receptor Frizzled 7 (FZD7). Knockdown of FZD7 improved platinum sensitivity, decreased spheroid formation, and delayed tumor initiation.

To further examine the functions of FZD7, the receptor was knocked down (KD) by stable transduction of shRNA or was transiently overexpressed. Decreased FZD7 mRNA expression was confirmed by Q-RT-PCR in SKOV3 and OVCAR5 cells transduced with two shRNA sequences targeting the receptor (Fig. 1A-B). FZD7 KD decreased spheroid formation (Fig. 1A-B) and expression of stemness-associated TFs (Fig. 1C). In vitro serial limited dilution assay showed that receptor KD decreased stem cell frequency, as calculated by the ELDA software in FZD7 KD vs. control cells, (p = 0.034). Likewise, FZD7 KD in Pt-T SKOV3_CDDP cells decreased sphere formation. Stable FZD7 KD in primary Pt-R tumor cells caused decreased expression levels of the stemness-associated gene ALDH1A1 (Fig. 1D-E). Conversely, transient overexpression of FZD7 (Fig. 1E-F) promoted the proliferation of SKOV3 and OVCAR5 cells as spheres (Fig. 1G) and increased the expression of stemness-associated TFs. FZD7 KD decreased IC50 to cisplatin by 2-fold (SKOV3, Fig. 1H; SKOV3_CDDP, Fig. 1I); while the receptor's overexpression increased Pt resistance (Fig. 1J).

To test the effects of FZD7 on tumor growth, a subcutaneous (s.c.) xenograft model was used. FZD7 KD in OVCAR5 cells delayed tumor initiation (sh-control 9.8±4 days. vs. sh-FZD7 25.3±4.9 days, Fig. 1K, p < 0.0001) and decreased tumor size and tumor weight (0.80±0.41 g vs. 0.14±0.15 g, p = 0.04, n = 4/group). FZD7 KD in xenografts was confirmed by IHC. ALDH (+) cells (16.5±6.5% vs. 5.9±1.8%, p= 0.05; Fig. 1L, n = 3) and spheroid forming ability (Fig. 1M, p = 0.02) were decreased in cells dissociated from FZD7 KD vs. control xenografts. Further, to test the effects of FZD7 KD on tumor initiation, an in vivo serial limited dilution assay was carried out by using 2,500; 5,000; and 10,000 FZD7 KD and control cells. FZD7 KD significantly inhibited TIC (Figure 4N) and reduced stem cell frequency, as calculated by the ELDA software (Fig. 1O). Combined, these results support that FZD7 is linked to stemness and chemo-resistance.

Fig. 1 FZD7 regulates stemness characteristics. (Wang Y, et al, 2020)

Knock-Down of RFC3 Alleviated the Viability and Proliferation of OVCAR-3 Cells

Ovarian carcinoma is one of the most common and lethal malignancies in the world. Replication factor C (RFC) plays an important role in DNA replication, DNA damage repair, and checkpoint control during cell cycle progression in all eukaryotes. The effect of RFC3 knocking down ovarian tumor cells was sought to explore. To this end, the viability and proliferation of RFC3 knocking down OVCAR-3 cells were examined, respectively. Briefly, RFC3 knocking-down OVCAR-3 and NC cells at different time points (Day 1, Day 2, and Day 3, respectively) were examined by MTS assays. The knock-down of RFC3 decreased cell viability compared to NC (Fig. 2A). Moreover, the cell growth was also examined by digesting cells at different time points into a single-cell suspension and counting the living cells. As shown in Fig. 2B, the knockdown of RFC3 notably decreased the number of living cells. Taken together, these results indicated that the knockdown of RFC3 was detrimental to the viability and proliferation of ovarian cancer cells.

Fig. 2 Knock-down of RFC3 alleviated cell viability and proliferation in OVCAR-3 cells. A. MTS assays showed that knock-down of RFC3 suppressed cell viability in ovarian cancer cells. B. The effect of RFC3-interfering on ovarian cancer cell proliferation, and cell proliferation were evaluated via cell growth curve assays. (Shen H, et al., 2015)