Richard J. Sharpe

Growth inhibition of murine melanoma and human colon carcinoma by recombinant human platelet factor 4

Although it is well established that angiogenesis is essential to tumor development, no human protein with high specificity and efficacy for prevention of angiogenesis has been characterized. In a previous study, we demonstrated that recombinant platelet factor 4 (rPF 4) inhibited angiogenesis in the chicken chorioallantoic membrane. In the present study, we have extended that finding to the use of recombinant human platelet factor 4 (rHuPF 4) to inhibit solid tumor growth in the mouse. rHuPF 4 effectively suppressed the growth of the B16-F10 murine melanoma in syngeneic C57BL/6J hosts and prevented the growth of primary tumors of both B16-F10 murine melanoma and HCT 116 human colon carcinoma in semisyngeneic CByB6F1/J female athymic nude mice. These two transformed cell lines were completely insensitive to rHuPF 4 in vitro at levels (50 micrograms/mL) that extensively inhibit normal endothelial cell proliferation. The migration of human endothelial cells was also inhibited at these concentrations of rHuPF 4, suggesting a second mechanism by which rHuPF 4 may modulate capillary development. The observed antitumor effects of rHuPF 4 might be due to the inhibition of angiogenesis. This finding could have implications for the development of novel therapeutic approaches to angiogenic diseases. Alternative, and possibly concurrent, mechanisms of the rHuPF 4 antitumor effect include lymphokine-activated killer cell activation and the induction of other cytokines.

Development of angiogenesis inhibitors for clinical applications

Angiogenesis, the development of new blood vessels, is associated with many life-threatening pathologies. The neovascularization of tumors for example, allows a blood supply to deliver the required nutrients for tumor development. Inappropriate blood vessel growth also contributes to the pathology of other diseases such as atherosclerosis and arthritis. The process of angiogenesis is beginning to be better understood, and as Ted Maione and Richard Sharpe explain, this understanding has led to the identification of several lead compounds that inhibit this process. At present all of these candidate drugs exhibit severe host toxicity, but more selective angiogenesis inhibitors might be expected to be extremely useful therapeutic agents.

Buspirone Inhibits Contact Hypersensitivity in the Mouse

We have observed that 8-4-[4-2-pyrimidyl)-1-piperazinyl]butyl]-8-azaspiro [4.5]decane-7.9-dione, an agent commonly known as buspirone HCl, possesses immunosuppressive activity when administered either topically or systemically, as assessed in a mouse model of contact hypersensitivity. Topical or systemic administration of buspirone significantly reduced the tissue swelling and leukocyte infiltration associated with the elicitation phase of contact hypersensitivity. Buspirone is a safe, widely used drug which has a history of use in humans throughout the world. These data demonstrate a previously unknown pharmacologic activity of buspirone.

Induction of local inflammation by recombinant human platelet factor 4 in the mouse

Platelet factor 4 (PF-4) has been shown to be chemotactic for neutrophils and monocytes in vitro. To assess whether these observations have in vivo relevance, we tested the ability of recombinant human PF-4 (rPF-4) to induce acute and chronic dermal inflammation in the mouse. When injected as a single dose intradermally, rPF-4 induced an acute inflammatory response that peaked at 6 to 12 hr and which resolved by 36 hr. Injection of an equivalent amount of cytochrome c, buffer alone, or an amino-terminal PF-4 peptide failed to elicit a significant inflammatory response; however, the carboxy-terminal PF-4 peptide retained proinflammatory properties. The inflammatory infiltrate induced by a single injection of either rPF-4 or the 41 amino acid carboxy-terminal peptide was composed of neutrophils and smaller numbers of mononuclear cells. Repeated injection of rPF-4 resulted in nearly equal numbers of neutrophils and mononuclear cells. Moreover, marked dermal fibrosis developed after only 5 days of daily injection of rPF-4. Although relatively high concentrations of rPF-4 were required to elicit an inflammatory response, these concentrations may be locally attainable during platelet aggregation. Our findings thus support the hypothesis that PF-4 may contribute to the development of inflammatory responses at sites of platelet aggregation.