c7E3 Fab inhibits human tumor angiogenesis in a SCID mouse human skin xenograft model

The alphavbeta3 integrin plays an important role in tumor growth and angiogenesis. Inhibition of this receptor by intact bivalent antibodies has been shown to inhibit angiogenesis and tumor growth. In this study we tested the chimeric Fab of 7E3 (c7E3 Fab), an antibody reactive with human platelet GPIIb/IIIa and alphavbeta3 to determine if it would inhibit in vivo angiogenesis and tumor growth in a SCID mouse/human skin tumor growth and angiogenesis model. c7E3 Fab inhibited human tumor angiogenesis and tumor growth. These data suggest monovalent antibody fragments devoid of antibody effector function can have efficacy in preclinical models of angiogenesis.

Abciximab pharmacodynamics are unaffected by antecedent therapy with other GPIIb/IIIa antagonists in non-human primates

BACKGROUND

Tirofiban and eptifibatide are currently approved for the medical stabilization of non-ST segment elevation acute coronary syndromes. In patients undergoing percutaneous coronary intervention (PCI) during infusion of these drugs, conversion to abciximab, which has long term proven clinical efficacy and cost-effectiveness, following PCI may be desirable. The purpose of this study was to determine if the binding or pharmacodynamics of abciximab is affected by a prior infusion of either tirofiban or eptifibatide.

METHODS

In vitro binding experiments were performed to determine if prior exposure to tirofiban or eptifibatide altered the affinity and extent of binding of abciximab to GPIIb/IIIa. For in vivo experiments, cynomolgus monkeys were pretreated with a bolus and 18 hour infusion of saline, tirofiban, or eptifibatide. At the end of the initial treatment, a bolus and 12 hr infusion of abciximab was started without delay. Inhibition of platelet aggregation, GPIIb/IIIa receptor blockade and abciximab pharmacokinetics were measured during and after both infusions.

RESULTS

Equilibrium binding of abciximab in vitro was unaffected by tirofiban or eptifibatide. The extent and duration of abciximab inhibition of ex vivo platelet aggregation, receptor blockade, and abciximab pharmacokinetics in monkeys during and after the abciximab infusion were not affected by prior infusion of the animals with tirofiban or eptifibatide.

CONCLUSIONS

In vitro and in vivo studies revealed that the molecular interaction of abciximab with the platelet GPIIb/IIIa receptor is not altered by immediate prior exposure of platelets to small molecule GPIIb/IIIa antagonists. These preclinical studies suggest that the efficacy of abciximab should not be impaired if it is initiated following termination of therapy with small molecule GPIIb/IIIa antagonists.

7E3 F(ab')2, an effective antagonist of rat alphaIIbbeta3 and alphavbeta3, blocks in vivo thrombus formation and in vitro angiogenesis

Abciximab (c7E3 Fab, ReoPro) blocks GPIIb/IIIa and alphavbeta3 and inhibits thrombotic and proliferative events only in humans and non-human primates. The bivalent F(ab')2 fragment is an effective anti-thrombotic agent in canine models. In the present study, 7E3 F(ab')2 was also found to bind to rat GPIIb/IIIa (KD = 27 +/- 4 microg/mL) and alphavbeta3 (KD = 9 +/- 8 microg/mL), to block in vitro rat platelet aggregation (IC50 = 16 +/- 6 microg/mL), and to inhibit alphavbeta3-mediated microvessel sprout formation in a rat aortic ring assay. Following administration of 7E3 F(ab')2 (4 mg/kg) to rats, platelet aggregation was completely blocked for up to 6 h and thrombus formation in response to a rat abdominal aorta double crush injury was prevented. Effective chronic dosing was achieved with 6 mg/kg daily I.P. injections. In vitro mixing experiments indicated that 7E3 F(ab')2 redistributed to unlabeled platelets in 2 h. Ex vivo, 7E3 F(ab')2 was detected on platelets for up to 4 days after a single 4-mg/kg injection. These data suggest that 7E3 F(ab')2 may be a useful agent to study the effects of GPIIb/IIIa and alphavbeta3 blockade in rat models of thrombosis and vascular disease.

Abciximab (ReoPro, chimeric 7E3 Fab) demonstrates equivalent affinity and functional blockade of glycoprotein IIb/IIIa and alpha(v)beta3 integrins

BACKGROUND

Large, randomized, and blinded clinical trials (EPIC, EPILOG, and CAPTURE) have demonstrated that abciximab (ReoPro, chimeric 7E3 Fab) markedly reduces thrombotic events associated with percutaneous transluminal coronary interventions. The marked early benefits at 30 days were sustained at 6 months and 3 years. Initially developed because of its efficacy in blocking GP IIb/IIIa (alphaIIb/beta3) receptors on platelets, abciximab also binds with equivalent affinity to alpha(v)beta3.

METHODS AND RESULTS

This study presents a detailed characterization of the alphavss3 interaction, including the ability of abciximab to (1) bind with comparable affinity to alpha(v)beta3 and GP IIb/IIIa, (2) inhibit alpha(v)beta3 and GP IIb/IIIa-mediated cell adhesion in vitro with IC50 values approximating binding KD values, and (3) redistribute between GP IIb/IIIa and alpha(v)beta3 integrins in vitro.

CONCLUSIONS

As an antagonist of not only GP IIb/IIIa but also alpha(v)beta3, abciximab may provide additional clinical benefit in preventing alpha(v)beta3-mediated effects such as thrombin generation, clot retraction, or smooth muscle cell migration and proliferation. Abciximab binds with equivalent affinity to both GP IIb/IIIa and alphavss3 and redistributes between the 2 integrin receptors in vitro. Abciximab has been previously shown to circulate on platelets for up to 2 weeks. Taken together, these findings suggest that abciximab may have the ability to inhibit both GP IIb/IIIa and alpha(v)beta3 for extended periods.