Is there a role for urokinase-type plasminogen activator inhibitors as maintenance therapy in patients with ovarian cancer?

There is abundant evidence that the urokinase-type plasminogen activator (uPA), its inhibitors PAI-1 and PAI-2 (plasminogen activator inhibitor type-1 and type-2) and its cells surface receptor (uPA-R, CD87) play a fundamental role in tumor invasion and metastasis and are of significant prognostic significance for many tumor types. We performed a systematic Med-line search on uPA, PAI, uPA-R and (epithelial) ovarian cancer (EOC). The majority of malignant EOC specimens show moderate to strong immunostating of tumor and stromal cells. Overexpression of u-PA and PAI-1 can be found in more the 75% of primary ovarian carcinomas, in most metastatic EOC samples and all examined epithelial ovarian cancer cell lines. uPA overexpression in primary specimens was significantly associated with tumor stage, grade, residual disease status after cytoreductive surgery, and poor clinical outcome. This may be explained by increased chemoresistance, a lower resectability and more aggressive tumor biology and tumor dissemination in patients with high uPA and PAI-1. Several therapeutical approaches aimed at inhibiting the uPA/uPAR functions have shown to possess anti-tumor effects in vitro and in animal models. When treating a patient with advanced ovarian cancer it may to be assumed that inhibiting the progression of established (micro) metastases may be more therapeutically relevant than trying to destroy all tumor cells which is not possible in most cases with current systemic treatment modalities. Taking into account the role of uPA and PAI in cell detachment, formation of new stroma, tumor cell reimplantation and metastasis uPA inhibition should be further investigated as maintenance treatment in patients with advanced EOC.

Pre-clinical study of 213Bi labeled PAI2 for the control of micrometastatic pancreatic cancer.

PURPOSE: The urokinase plasminogen activator (uPA) and its receptor (uPAR) are expressed by pancreatic cancer cells and can be targeted by the plasminogen activator inhibitor type 2 (PAI2). We have labeled PAI2 with (213)Bi to form the alpha conjugate (AC), and have studied its in vitro cytotoxicity and in vivo efficacy. METHODS AND MATERIALS: The expression of uPA/uPAR on pancreatic cell lines, human pancreatic cancer tissues, lymph node metastases, and mouse xenografts were detected by immunohistochemistry, confocal microscopy, and flow cytometry. Cytotoxicity was assessed by the MTS and TUNEL assay. At 2 days post-cancer cell subcutaneous inoculation, mice were injected with AC by local or systemic injection. RESULTS: uPA/uPAR is strongly expressed on pancreatic cancer cell lines and cancer tissues. The AC can target and kill cancer cells in vitro in a concentration-dependent fashion. Some 90% of TUNEL positive cells were found after incubation with 1.2 MBq/ml of AC. A single local injection of approximately 222 MBq/kg 2 days post-cell inoculation can completely inhibit tumor growth over 12 weeks, and an intraperitoneal injection of 111 MBq/kg causes significant tumor growth delay. CONCLUSIONS: (213)Bi-PAI2 can specifically target pancreatic cancer cells in vitro and inhibit tumor growth in vivo. (213)Bi-PAI2 may be a useful agent for the treatment of post-surgical pancreatic cancer patients with minimum residual disease.

In vitro and preclinical targeted alpha therapy for melanoma, breast, prostate and colorectal cancers.

Targeted alpha therapy (TAT) can inhibit the growth of micrometastases by selectively killing isolated and preangiogenic clusters of cancer cells. The alpha emitting radioisotopes Tb-149 and Bi-213 were chelated to cancer specific monoclonal antibodies to form alpha-immunoconjugates (AIC) against melanoma, leukaemia, prostate and colorectal cancer, and to the plasminogen activator inhibitor type-2 (PAI2) to form alpha-PAI2 (API) against breast and prostate cancer. These conjugates were found to be highly stable, specific and cytotoxic in vitro. Melanoma and breast cancer tumour growth was observed in nude mouse models for untreated controls and non-specific AIC/API at 2 days post-subcutaneous inoculation of cancer cells. Complete inhibition of melanoma and breast cancer growth was found for local injections of AIC and API, respectively. Intra-lesional TAT of established melanoma showed that all melanomas regressed with 100 microCi injections of AIC. These results point to the potential application of local and systemic TAT in the management of metastatic cancer.

Antigenic expression of human metastatic prostate cancer cell lines for in vitro multiple-targeted alpha-therapy with 213Bi-conjugates.

PURPOSE: Control of metastatic prostate cancer (CaP) is an elusive objective. Some 30% of patients with clinically localized CaP will develop micrometastatic disease. Defining the expression of tumor-associated antigens on CaP will enable appropriate selection of therapeutic targets. METHODS AND MATERIALS: The expression of tumor-associated antigens on CaP cell lines (PC-3, DU 145, and LNCaP-LN3) was detected by immunohistochemistry and flow cytometry. Test and control alpha-conjugates were prepared using monoclonal antibodies, an inhibitor, plasminogen activator inhibitor type 2, that binds to the cell-membrane-bound protease, urokinase plasminogen activator, and a control protein labeled with (213)Bi using standard methods. These were used singly or together against three different CaP cell lines in vitro. The cytotoxicity of the alpha-conjugates was assessed using the [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, inner salt] (MTS) assay. RESULTS: The PC-3 and DU 145 cancer cell lines expressed antigens that bind monoclonal antibodies BLCA-38 and #394 (mouse anti-human urokinase plasminogen activator B-chain) but not J591. The LNCaP-LN3 cells bound J591 but not #394 or BLCA-38. For the PC-3, DU 145, and LNCaP-LN3 cell lines, multiple-targeted alpha-therapy combining four alpha-conjugates (one-quarter doses of each) gave D(0) (37% cell survival) values of 15, 17, and 27 microCi/mL compared with those of the controls of 272, 289, and 281 microCi/mL, respectively. CONCLUSION: Metastatic prostate cancer-associated antigens recognized by multiple monoclonal antibodies are potential targets for alpha-therapy. Multiple-targeted alpha-therapy produced cytotoxicity specific to three CaP cell lines and may form the basis of treatment for micrometastatic CaP, overcoming the heterogeneity of expression of the targeted antigens.

Suppression of pulmonary metastases of rat mammary cancer by recombinant urokinase plasminogen activator inhibitor.

A pivotal point in the process of invasion and metastasis of cancer cells rests on the capability of those cells to present a proteolytic interface to the surrounding tissue matrix as well as to the lymphovascular channels supplying the tumor. The MATB rat mammary cancer cells used in this study, along with a number of cancers of epithelial cell origin, provide that proteolytic interface by cell surface-bound plasmin. Inhibition of tumor cell surface plasmin formation in this study was achieved through the addition of the urokinase plasminogen activator inhibitor (PAI-2) to the infusion of rat mammary cancer cells introduced into the pulmonary arterial circulation of female Fisher 344 rats. The results show a significant decrease in the numbers of pulmonary metastases in those rats receiving the inhibitor. This effect was demonstrable for cells delivered as a bolus as well as for those delivered slowly over a 7-day period via an osmotic pump. Delivery of the inhibitor was by osmotic pump in each instance. The evidence suggests a basis for an additional approach to control the spread of selected cancers.