Preclinical studies of targeted α therapy for breast cancer using 213Bi-labelled-plasminogen activator inhibitor type 2

Abstract

The control of micrometastatic breast cancer remains problematic. To this end, we are developing a new adjuvant therapy based on 213 Bi-PAI2, in which an a-emitting nuclide ( 213 Bi) is chelated to the plasminogen activator inhibitor-2 (PAI2). PAI2 targets the cellsurface receptor bound urokinase plasminogen activator (uPA), which is involved with the metastatic spread of cancer cells. We have successfully labelled and tested recombinant human PAI2 with the a radioisotope 213 Bi to produce 213 Bi-PAI2, which is highly cytotoxic towards breast cancer cell lines. In this study, the 2-day postinoculation model, using MDA-MB-231 breast cancer cells, was shown to be representative of micrometastatic disease. Our in vivo efficacy experiments show that a single local injection of 213 Bi-PAI2 can completely inhibit the growth of tumour at 2 days postcell inoculation, and a single systemic (i.p.) administration at 2 days causes tumour growth inhibition in a dose-dependent manner. The specific role of uPA as the target for 213 Bi-PAI2 therapy was determined by PAI2 pretreatment blocking studies. In vivo toxicity studies in nude mice indicate that up to 100 mCi of 213 Bi-PAI2 is well tolerated. Thus, 213 Bi-PAI2 is successful in targeting isolated breast cancer cells and preangiogenic cell clusters. These results indicate the promising potential of 213 Bi-PAI2 as a novel therapeutic agent for micrometastatic breast cancer.

Preclinical evaluation of 213Bi-labeled plasminogen activator inhibitor type 2 in an orthotopic murine xenogenic model of human breast carcinoma

“…16). a-PAI-2 was shown to specifically kill uPA-expressing tumor cells in vitro in a dose-dependent manner (16,17) and to be efficacious in preliminary studies using mouse models of human tumors (17,18). Radio-iodinated PAI-2 has also been shown to localize in human colorectal uPA-expressing tumor xenografts in nude mouse models (19), thus providing proofof-principle data for the uPA-targeting capability of PAI-2.…”

“…At this stage, the animals were euthanized (overdose of inhaled CO 2 ) and the internal organs were macroscopically examined for signs of toxicity. Because previous studies found no toxicity associated with the targeting agent PAI-2 (7,17,18) and biodistribution of the radiolabeled compound to major organs was limited to the kidneys and liver (19), histologic assessments were restricted to these organs and one lymphoid organ, the spleen. Blood smears were taken and blood was also collected into K3 EDTA and Z serum gel minicollect tubes (Greiner Bio-one) for hematology and serum blood biochemistry to complete the toxicologic assessment.…”

Preclinical studies of bismuth-213 labeled plasminogen activator inhibitor type 2 (PAI2) in a prostate cancer nude mouse xenograft model

“…The procedure for uPA staining is published elsewhere. 25,26 Pharmacokinetics. ARC Swiss nude mice were injected with 213 Bi-PAI2 chelated with CHX-A˝ and cDTPA in different activities (range 1.18-11.84 MBq).…”

“…[23][24][25][26] In this paper we investigate the growth of the tumor xenograft model by observing the tumor capillary development using CD31 staining at different stages of tumor growth. The in vivo organ uptake and pharmacokinetics/biodistribution for 213 Bi-PAI2 in mice using two chelators (cyclic dianhydride of DTPA and a DTPA derivative CHX-A˝) is also reported.…”

“…Further, we have used PAI2 as a vector for TAT of breast and prostate cancer. [23][24][25][26] Administration of specific 213 Bi-labeled monoclonal antibodies inhibits the growth of melanoma 27 and prostate cancer 26 xenografts in nude mice.…”