Monoclonal antibodies used in the detection and treatment of epithelial ovarian cancer

Minimal residual disease in ovarian cancer as a target for complement-mediated mAb immunotherapy

Ovarian cancer is potentially well suited for local monoclonal antibody (mAb) immunotherapy, because it remains within the peritoneal cavity for a long period of time before giving rise to distant metastases. At the stage of minimal residual disease, the cells appear to be in a state of dormancy (G(0)) or at least have lower rates of tumour cell proliferation. They should be a promising target for immunotherapy. Here we first examined the cell-cycle expression of CD59 and decay-accelerating factor (DAF; CD55) on four different ovarian carcinoma cell lines, using simultaneous flow cytometric analysis of DNA content or the cell-cycle-specific nuclear proliferation protein Ki67 and CD59 or DAF surface expression. We found that CD59 and DAF are stably expressed throughout the cell cycle. The polyvalent approach to target-independent antigens to improve the efficiency of mAb complement (C)-mediated damages was promising, and tumour cells become sensitive to C damage, when incubated with cross-linked mAb against different tumour-associated antigens. Although, such immune complex-mediated C activation was rather ineffective in killing the cells, it could be potentiated by the addition of blocking mAb against CD59 and DAF. Our results suggest that the activities of intrinsic C regulators must be neutralized to make minimal residual disease a promising target for antibody therapy.

Radioimmunoscintigraphy in patients with ovarian cancer

The use of radiolabeled monoclonal antibodies (MoAbs) has significantly improved the ability to detect tumor antigens, thus improving in vivo tumor diagnosis and treatment. The management of ovarian carcinoma still poses a challenging medical problem. Clinical trials using radioimmunoscintigraphy or a hand-held gamma detection probe intraoperatively were performed in patients with clinical evidence of primary or recurrent ovarian cancer. Immunoscintigraphy of ovarian cancer lesions has been performed mainly with 99mTc, 111In and 123I labeled with HMFG1, HMFG2, OC-125, B72.3, H17E2, OVTL3, MoAb170, Mov18 and other MoAbs. Antibody guided imaging using radioimmunoscintigraphy has demonstrated improved targeting of ovarian cancer, resulting in a highly sensitive and specific method. However, it is not yet known which type of MoAb is the most efficient for radioimmunoscintigraphy. Since these tumors represent a potentially curable disease, radioimmunoscintigraphy could contribute mainly to accurate staging as a supplementary to conventional diagnostic methods, as well as for the localization of active disease after chemotherapy and monitoring for the presence of recurrent disease. Nevertheless, prospective studies in a large number of patients should be undertaken in order to further evaluate the diagnostic contribution of this approach.

Radioimmunoscintigraphy in patients with ovarian cancer

The targeting potential of three different monoclonal antibodies (MAbs) was assessed in patients with ovarian cancer. HMFG1, OC-125 and H17E2 labelled with 111In or 123I were evaluated prospectively for their ability to localize ovarian tumour. Forty two patients with ovarian cancer, aged 40-78 years (median = 58 years) were studied using OC-125 (n = 9), HMFG1 (n = 11) and H17E2 (n = 22). Imaging data were compared with the CT and the surgical findings. Presence of tumour was confirmed in 35/42 (83%) patients (8/9 OC-125, 10/11 HMFG1 and 17/22 H17E2) and correlated well with the conventional radiology diagnostic methods. One patient with a negative H17E2 scan and a large abdominal mass detected at laparotomy revealed a PLAP-negative tumour on immunohistochemistry. Scintigraphy revealed the presence of active disease, confirmed by laparotomy/laparoscopy in 6/8 patients considered to be in clinical remission. The sensitivity of the method was high enough and the diagnostic contribution of this approach should be further evaluated.

Complement-regulatory proteins in ovarian malignancies

Ovarian cancer has features that makes it well-suited for MAb adjuvant immunotherapy. Several of the MAbs used in clinical trials mediate cancer cell destruction by activation of complement (C). In this study, therefore, we examined the ability of ovarian-tumor cells to resist C attack. We found that the C regulators membrane cofactor protein (MCP, CD46) and protectin (CD59) were strongly expressed in the tumor cells in all 28 benign and malignant tumors examined. Decay-accelerating factor (DAF; CD55) was more heterogeneously expressed, and only 75% of the tumors exhibited a moderate amount of DAF in the tumor cells. In adenoma cells, CD59 and DAF were preferentially located apically, while in adenocarcinoma cells they were expressed also at the basolateral cell surface. The ovarian-carcinoma cell lines SK-OV-3, Caov-3, SW626 and PA-1 expressed both the 58- and the 68-kDa isoforms of MCP. DAF was present as a glycosyl-phosphatidylinositol(GPI)-anchored 70-kDa glycoprotein. The surface-expression level of DAF varied, and correlated with the vulnerability of the cells to C-mediated lysis. CD59 was expressed as a GPI-linked 19- to 25-kDa protein exhibiting multiple glycosylation variants. The surface expression of CD59 correlated with the amount of the main 1.9 + 2.1-kb CD59 mRNA transcripts. Neutralization of CD59 with an anti-CD59 MAb significantly enhanced C-mediated killing of the cell lines. Low expression of C regulators on the PA-1 teratocarcinoma cell line was associated with high sensitivity to C lysis. Thus, the expression of C regulators on malignant ovarian cells may constitute a tumor escape mechanism, and is a critical parameter to be examined when MAb therapy is being considered.