Prostascint (Capromab Pendetide) - Description

DESCRIPTION

ProstaScint^® (Capromab Pendetide) is the murine monoclonal antibody, 7E11-C5.3, conjugated to the linker-chelator, glycyl-tyrosyl-(N,-diethylenetriaminepentaacetic acid)-lysine hydrochloride (GYK-DTPA-HCl). The 7E11-C5.3 antibody is of the IgG1, kappa subclass (IgG1K). This antibody is directed against a glycoprotein expressed by prostate epithelium known as Prostate Specific Membrane Antigen (PSMA). The PSMA epitope recognized by monoclonal antibody (MAb) 7E11-C5.3 is located in the cytoplasmic domain. Expression of this glycoprotein has not been demonstrated on any other adenocarcinomas or transitional cell cancers tested. The antibody is produced by serum-free in vitro cultivation of cells, and purified by sequential protein isolation and chromatographic separation procedures.

Each ProstaScint^® kit consists of two vials which contain all of the non-radioactive ingredients necessary to produce a single unit dose of Indium In 111 ProstaScint^®, an immunoscintigraphic agent for administration by intravenous injection only. The ProstaScint^® vial contains 0.5 mg of capromab pendetide in 1 mL of sodium phosphate buffered saline solution adjusted to pH 6; a sterile, pyrogen-free, clear, colorless solution that may contain some translucent particles. The vial of sodium acetate buffer contains 82 mg of sodium acetate in 2 mL of Water for Injection adjusted to pH 5-7 with glacial acetic acid; it is a sterile, pyrogen-free, clear, and colorless solution. Neither solution contains a preservative. Each kit also includes one sterile 0.22 μm Millex^® GV filter, prescribing information, and two identification labels.

The sodium acetate solution must be added to the sterile, non-pyrogenic high purity Indium In 111 Chloride solution to buffer it prior to radiolabeling ProstaScint^®. The immunoscintigraphic agent Indium In 111 Capromab Pendetide (Indium In 111 ProstaScint^®) is formed after radiolabeling with Indium In 111.

Physical Characteristics of Indium In 111

Indium In 111 decays by electron capture with a physical half-life of 67.2 hours (2.8 days).¹ The energies of the photons that are useful for detection and imaging studies are listed in TABLE 1.

TABLE 1 - INDIUM IN 111 PRINCIPAL RADIATION EMISSION DATA¹

Radiation	Mean % per     Disintegration	Mean Energy (keV)
Gamma 2	90.2	171.3
Gamma 3	94	245.4

External Radiation

The exposure rate constant for 37 MBq (1 mCi) of Indium In 111 is 8.3 x 10^-4 C/kg/hr (3.21 R/hr). The first half-value thickness of lead (Pb) for Indium In 111 is 0.023 cm. A range of values for the relative attenuation of the radiation emitted by this radionuclide that results from the interposition of various thicknesses of Pb is shown in TABLE 2. For example, the use of 0.834 cm of lead will decrease the external radiation exposure by a factor of about 1,000.

TABLE 2 - INDIUM IN 111 RADIATION ATTENUATION OF LEAD SHIELDING

Shield Thickness (Pb) cm	Attenuation          Factor
0.023	0.5
0.203	10-1
0.513	10-2
0.834	10-3
1.120	10-4

These estimates of attenuation do not take into consideration the presence of longer-lived contaminants with higher energy photons, namely Indium In 114m/114.

To allow correction for physical decay of Indium In 111, the fractions that remain at selected intervals before and after the time of calibration are shown in TABLE 3.

Calibration Time

TABLE 3 - INDIUM IN 111 PHYSICAL DECAY CHART, HALF-LIFE 67.2 HOURS (2.8 DAYS)

^*

	Hours	Fraction               Remaining
	-48	1.64
	-36	1.44
	-24	1.28
	-12	1.13
	0*	1.00
	12	0.88
	24	0.78
	36	0.69
	48	0.61
	60	0.54
	72	0.48
	84	0.42
	96	0.37
	108	0.33
	120	0.29
	132	0.26
	144	0.23