Quantitative angiogenesis assays: Progress and problems

In cancer patients, dormant micrometastases are often asymptomatic and clinically undetectable, for months or years, until relapse. We have studied dormant lung metastases under angiogenesis suppression in mice. The metastases exhibited rapid growth when the inhibition of angiogenesis was removed. Tumour cell proliferation, as measured by bromodeoxyuridine incorporation and immunohistochemical staining proliferating cell nuclear antigen, was not significantly different in dormant and growing metastases. However, tumour cells of dormant metastases exhibited a more than threefold higher incidence of apoptosis. These data show that metastases remain dormant when tumour cell proliferation is balanced by an equivalent rate of cell death and suggest that angiogenesis inhibitors control metastatic growth by indirectly increasing apoptosis in tumour cells.

A novel, noninvasive method was developed for microvascular permeability measurements in non-malignant (mature granulation) and neoplastic (VX2 carcinoma) tissues grown in the rabbit ear chamber. Dextran of 150,000 molecular weight, tagged with fluorescein isothiocyanate (FITC), was used as a representative tracer molecule. In vivo plasma concentration of dextran was measured by photometric analysis of the plasma layer of microvessels in the ear chamber. The plasma concentration in both normal and tumor preparations rose rapidly to a steady state with a time constant of 4.06 +/- 0.2 sec, and remained relatively constant at that level for the next 2 hr (elimination time constant = 1.77 +/- 0.9 X 10(5) sec). Extravasation of macromolecules from individual microvessels into the extravascular space was measured with the same photometric technique. Interstitial diffusion coefficients and microvascular permeability coefficients were determined by fitting a one-dimensional permeability-diffusion model to the extravasation data. The diffusivity of dextran in tumor interstitium was 2.2 +/- 1.4 X 10(-8) cm2/sec (n = 6) and in granulation tissue interstitium was 6.7 +/- 4.4 X 10(-10) cm2/sec (n = 6). Microvascular permeability in tumors was 7.26 +/- 3.29 X 10(-8) cm/sec (n = 11) and in granulation tissue was 57.24 +/- 39.24 X 10(-8) cm/sec (n = 10). These results on increased permeability (8-fold; P less than 0.002) and increased diffusivity (33-fold; P less than 0.001) in tumors provide a rational basis for the use of large-molecular-weight agents in the detection and treatment of solid tumors.

Angiogenesis plays a fundamental role in human breast tumor progression. In fact, recent findings indicate that vascular density is a prognostic indicator of breast cancer disease status. Evidence is presented that the integrin alpha v beta 3 is not only a marker of human breast tumor-associated blood vessels, but that it plays a significant role in human angiogenesis and breast tumor growth. To assess the role of alpha v beta 3-dependent angiogenesis in the progression of human breast cancer, we examined a SCID mouse/human chimeric model with transplanted full thickness human skin containing alpha v beta 3-negative human breast tumor cells. This tumor induced a human angiogenic response as measured by vascular cell immunoreactivity with monoclonal antibodies LM609 and P2B1 directed to human alpha v beta 3 and CD31, respectively. Intravenous administration of LM609 either prevented tumor growth or markedly reduced tumor cell proliferation within the microenvironment of the human skin. These LM609-treated tumors not only contained significantly fewer human blood vessels but also appeared considerably less invasive than tumors in control animals. These findings demonstrate that alpha v beta 3 antagonists may provide an effective antiangiogenic approach for the treatment of human breast cancer.