Conjugates made by coupling diazotized arsanilic acid with one or another of a variety of proteins regularly brought about the complete regression of established 6C3HED lymphomas in living mice without perceptibly harming the latter, while untreated control animals regularly died with lymphomatosis. Histologic studies made plain that the lymphoma cells promptly die in mice treated with the arsenic-azoproteins, while those in untreated control animals continue to proliferate. Various inorganic and organic arsenicals (including arsanilic acid and 4-arsonophenyldiazotate) were essentially devoid of effect on the lymphoma cells in vivo, and this proved true as well of the proteins employed (serum albumins and globulins procured from several species, casein, and ovalbumin). Mixtures of arsanilic acid and the several proteins, various sulfur-azoproteins, and a number of other substances—viz., amethopterin, chlorambucil, 6-mercaptopurine, 8-azaguanine, azaserine, 6-azauracil, 5-fluorouracil, thioTEPA, and DON, each given in maximal tolerated amounts—also failed to influence notably the course of established 6C3HED lymphomas in vivo.

Although readily overcoming Lymphoma E9514 cells growing in the subcutaneous tissues of susceptible mice, the arsenic-azoproteins had little or no effect once these cells had reached the livers and spleens of susceptible hosts. Furthermore the arsenic-azoproteins had little or no effect in vivo on the cells of Lymphoma AKRL1, L1210, and L4946.

The findings were considered in relationship to the respective susceptibilities of several types of lymphoma cells to other anti-lymphoma agents—notably guinea pig serum, immune serums prepared in rabbits with mouse lymphoma cells as antigens, and a variety of chemical compounds. Taken together, the observations provide proof that lymphoma cells of various types, although resembling one another quite closely in growth characteristics following transplantation in susceptible hosts, and in morphology as disclosed by ordinary microscopy, differ notably in susceptibility to the effects of the several anti-lymphoma agents.

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