Studies on tumor induced angiogenesis

Macrophage role in the anti-prostate cancer response to one class of antiangiogenic agents

BACKGROUND

Tumor-associated macrophages (TAMs) can either promote angiogenesis (i.e., the formation of new blood vessels) in tumors by secreting tumor necrosis factor-alpha (TNF-alpha) or inhibit angiogenesis by producing granulocyte-macrophage colony-stimulating factor (GM-CSF), which in turn stimulates production of the antiangiogenic protein plasminogen activator inhibitor type 2 (PAI-2). We tested, alone or in combination, the anti-prostate cancer activity of agents that perturb macrophage function.

METHODS

By use of enzyme-linked immunosorbent assays, we measured the effects of Linomide (roquinimex), thalidomide, pentoxifylline, and genistein on TNF-alpha and GM-CSF production in vitro by virally transformed RAW 264.7 mouse macrophages and on PAI-2 production in vitro by human macrophages. The antitumor effects of these agents were tested in vivo on transplanted Dunning R-3327 MAT-Lu rat prostate cancers; TAM numbers and blood vessel densities in these cancers were determined by use of immunocytochemistry.

RESULTS

Linomide selectively inhibited mouse macrophage secretion of TNF-alpha but not of GM-CSF; however, thalidomide, pentoxifylline, and genistein inhibited the production of both cytokines. Linomide, but not thalidomide or pentoxifylline, increased production of PAI-2 by human macrophages. When administered to rats bearing MAT-Lu tumors, each of the tested agents reduced TAM numbers (Linomide, by 46%; thalidomide, by 94%; pentoxifylline, by 71%; and genistein, by 96%). However, all of the agents reduced tumor blood vessel density and tumor growth, with Linomide being the most effective (44% reduction in blood vessel density and 69% inhibition of tumor growth). None of the other agents potentiated Linomide's antitumor effect.

CONCLUSIONS

Linomide is unique among the antiangiogenic agents tested, in that it inhibits the stimulatory effects of TAMs on tumor angiogenesis without eliminating their antiangiogenic effects, and may thus prove to be more effective against prostate cancer.

The effect of pentoxifylline on spontaneous and experimental metastasis of the mouse Neuro2a neuroblastoma

Pentoxifylline (PTX) has been reported to have both direct and indirect anti-tumor effects in experimental tumor models. We studied the effect of PTX on (1) the proliferation of Neuro2a mouse neuroblastoma cells in vitro and in vivo, (2) spontaneous and experimental metastasis, (3) tumor cell membrane fluidity and (4) adhesion to a fibronectin-coated surface. PTX significantly reduced the proliferation of Neuro2a cells in vitro as determined by DNA measurement (P < 0.01) and total cell count (P < 0.02). In vivo, PTX reduced the growth of subcutaneously transplanted primary tumors in syngeneic A/J mice (P < 0.01; n = 15). All seven animals (100%) receiving intravenous tumor cells developed extensive liver metastasis. In contrast, only 1/11 (9%) of animals pre-treated with oral PTX and injected with PTX-treated cells developed liver metastases. Of five mice receiving PTX-treated cells without oral pretreatment of PTX, two out of five (40%) developed liver metastases. There was a slight, but not significant (P = 0.08) increase in both experimental and spontaneous lung metastases formation in PTX-treated animals. However, tumor nodule formation on the lung surface was inefficient. PTX also increased membrane fluidity of the Neuro2a cells and significantly decreased tumor cell adhesion to fibronectin-coated microtiter wells (P < 0.01). We conclude that PTX has a cytostatic effect on the Neuro2a mouse neuroblastoma and exerts an anti-tumor effect on liver metastases following intravenous administration of neuroblastoma cells. Whether these results are directly related to the changes in membrane properties caused by pentoxifylline remains to be established.

The role of PDGF-BB on the development of the collateral circulation after acute arterial occlusion

The survival of tissues in the presence of arterial occlusion is critically dependent on the development of collateral blood vessels. Identification of the biochemical mediators and their mechanism of action is fundamental to an understanding of the evolution of the collateral circulation. The ability of PDGF-BB to promote this was evaluated in an animal model of hind limb ischaemia. In order to obtain significant quantities of this mitogen for use in our animal model, human recombinant PDGF-BB was expressed in a Chinese Hamster Ovary (CHO) cell line. The transfected CHO cells produced 544 micrograms/l of PDGF-BB in serum free medium (SFM). The 30 kDa form of PDGF-BB was purified to homogeneity as judged by silver staining and amino-acid sequencing. Purified PDGF-BB was shown to be bioactive by a cell proliferation assay. The exogenous administration of PDGF-BB enhanced the recovery of blood flow after acute arterial occlusion. The results suggest that PDGF-BB may have therapeutic value in promoting collateral development following arterial occlusion.