Efficacy of Re-188-labelled sulphur colloid on prolongation of survival time in melanoma-bearing animals

In this study, the effectiveness of a ¹⁸⁸Re labeled sulfur colloid with two particle size ranges was used to evalucate the effectiveness of this agent on melanoma tumors in mice in terms of animal lifespan. Methods: Two separate group of animals were used for investigating biodistribution and survival time. A total of 188 B16F10-melanoma-bearing BDF₁ mice were injected intraperitoneally with 3.7 MBq (0.1 mCi)/2mL of radiolabeled sulfur colloid ten days after intraperitoneal inoculation of 5 × 10⁵ B16F10 melanoma cells/2ml. For group 1, 30 mice were sacrificed at 1, 4, 24, 48 and 72 hours for biodistribution studies. In group 2, 158 mice were divided into 9 groups (n = 16∼18/groups)each receiving respectively tumor alone, tumor with normal saline, cold colloid or hot colloid with 16, 23, 31, 46, 62, or 124 MBq activity. Each of these colloid groups was further divided into two groups, one receiving smaller particle sizes (<3 μm:80.4 ± 7.2%, colloid 1) and the other receiving larger particle sizes (<3 μm:12.3 ± 1.0%, colloid 2). The animals were checked daily until death and their survival recorded. Results: Colloid 2 showed higher accumulation in almost all tissues, the highest accumulation organ was tumor (∼40%), then spleen (∼20%), stomach (∼15%), diaphragm (∼3%), and liver (∼2%). There was a significant increase in survival time with increasing amount of the larger-particle-size colloid. Administered levels of 16-31 MBq/mouse were most efficacious and with higher amounts the survival times decreased significantly below that of the controls. There was a significant difference in the dose-response curves for the two preparations. Protection factors (1/Relative-risk) of nearly 5 were achieved using the larger colloid size, and nearly 30 using the smaller colloid size. An amount of 16-31 MBq of the colloid 2 was the optimal activity in these studies. On the one hand, the survival data agreed well with the biodistribution data, where higher accumulation was found in tumor with colloid 2. Conclusion: Rhenium-188 offers on-site availability, medium half-life, higher beta-particle energy of 2.12 MeV for therapy and emission of 155 keV gamma photon suitable for imaging. The present study demonstrated that ¹⁸⁸Re-sulfur colloid is an effective agent in controlling tumor cells in the abdominal cavity in animals.