Effect of Lipopolysaccharide from Proteus mirabilis, alone or with Antitumor Agents, against Experimental Animal Tumors

Abstract

Antitumor effect of Lipopolysaccharide (LPS) from Proteus mirabilis RMS-203 was evaluated.
Minimal effective doses detected by the Pigment test of LPS from both wild type and heptoseless mutant against solid-type Ehrlich carcinoma was 0.005mg/kg given by either intravenous or intraperitoneal administration. Besides Ehrlich carcinoma, solid-type tumors, such as Sarcomas 180 and 37, Meningeal sarcoma MS-147, Walker carcinosarcoma 256 and Adenocarcinoma 755, were also sensitive to LPS, but several other solid-type tumors, such as Yoshida sarcoma and C3H spontaneous sarcoma, as well as all ascites form of tumors were insensitive.
Ehrlich carcinoma and Sarcomas 180 and 37 in mice were completely regressed, but other three types of tumors sensitive to LPS by the Pigment test were not cured because of regrowth of the tumors.
The blockage of blood stream into the tumor tissue after administration of LPS to the mice bearing solid-type tumors was clearly demonstrated by exclusion (‘Lock out’) or by defect in exudation (‘Lock in’) from the tumor tissues of the injected materials. Using this action of LPS, the mice bearing Meningeal sarcoma MS-147 or Walker carcinosarcoma 256 was successfully treated with combined use of LPS and a small amount of antitumor agent, such as 6-mercaptopurine or cyclophosphamide.