Antitumor effects of abrin and ricin used singly and in combination with cisplatin

Abrin, ricin, and cisplatin produced significant increases in survival times of mice inoculated with 10(6) Ehrlich ascites carcinoma or L1210 leukemia cells 24 hours prior to treatment. Combinations of abrin or ricin with cisplatin produced markedly synergistic action in prolonging survival times of mice bearing cell line A of L1210 leukemia. For example, a dosage of 1.33 micrograms per kg abrin produced a 40 percent increased length of survival (ILS) and 2.5 mg per kg of cisplatin produced a 45 percent ILS while a combination of the two agents resulted in a 229 percent ILS and produced 60-day survivors or "cures" in 20 percent of the mice treated. Similar combinations of abrin or ricin with cisplatin also produced significant additive or synergistic increases in survival times of mice bearing cell line B of L1210 leukemia or Ehrlich ascites carcinoma. Aged solutions of abrin and ricin appeared to be less toxic, but have similar antitumor effect alone or in combination with cisplatin, than freshly prepared solutions.