106. The isolation of a cancer-producing hydrocarbon from coal tar. Parts I, II, and III

Abstract

Part I . Concentration of the Active Substance. By I. HIEGER. THE first experimental production of cancer by the products of distillation of coal was achieved in 1915 by Yamagiwa and Ichikawa (Mitteil. med. Facultit, kaiser. Univ. Tokyo, 1915, 15, 295), and the first enquiry into the chemical basis of tar cancer was that of Bloch and Dreifuss (Schweiz. med. Woch., 1921, 2, 1033), who concluded from their observations that the substance responsible must be a high-boiling, neutral, non-nitrogenous compound which forms a stable picrate. The production of strongly carcinogenic tars by pyrolysis of isoprene or acetylene in a current of hydrogen (Kennaway, J . Path. Bact., 1924, 27, 233; Brit. Med. J., 1925, ii, 1) showed that the agent present in these tars must be a hydrocarbon. A large number of known constituents of fractions of coal and other tars boiling above 270" were tested in this Institute with negative results. The use of the fluorescence spectrum, first applied to this problem by Mayneord in 1927, was continued by the present author (Biochem. J., 1930, 24, 505) with observations on a specific fluorescence spectrum (bands at 4O00, 4180, 44OOA.) common to the tars and mineral oils which produce cancer of the skin either as an industrial disease or i n animal experiments.These spectra suggested an attempt to isolate the fluorescing substance, whether this were the cancer-producing factor itself or some substance which closely accompanies this factor. The results of spectrographic and biological tests have now proved to be in complete agreement. Thus the preparations derived from pitch by a variety of solvent extraction methods, the fractions separated by formation of picrates, distillation and crystallisation, and finally the hydrocarbon (1 : 2-benzpyrene) have proved carcinogenic and have given in each case the fluorescence spectrum with bands at 4000,4180,4400 A. The treatment of pitch described here has yielded fractions which are f a r superior to pitch as cancer-producing agents and at the same time possess the specific fluorescence spectrum in an enhanced degree.Hence the fluorescence test can predict the behaviour of fractions of pitch when tested on animals, although it must be pointed out that certain cancer-producing hydrocarbons prepared synthetically (e.g., 1 : 2 : 5 : 64ibenzanthracene) have fluorescence spectra different from those of active pitch fractions. EXPERIMENTAL.Two tons of a medium soft pitch (see fluorescence spectrum I) which was shown to be cancer-producing (see below) were distilled from a cast-iron retort. The distillate above 510" (thermometer in liquid) resembled the deep red glassy distillate of pitch which was found some years ago to be carcinogenic (Kennaway, Brit. Med. J., 1924, i, 564). The fraction, b.p. 500-510", resembled very soft pitch and was much more sol. in ordinary solvents than the fraction, b. p. above 510". A fraction with the same physical characteristics distilled at 475-500"(pyrometer instead of thermometer); yield, about 5% of the charge of pitch. From t...

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“…Investigators therefore turned to the repeated application of cigarette smoke and its individual components to the skin of mice, the method developed for systematic studies of carcinogens in coal tar which was associated with occupational skin cancer in man. Repeated painting of mouse skin became the method of choice for demonstrating carcinogenic activity after the Kennaway group in England had used it to show that benzo(a)pyrene (BP) was the major carcinogen of coal tar (Cook et al, 1933). The isolation of BP was preceded and followed by the chemical synthesis of other carcinogenic PAHs (Cook et al, 1937;Kennaway and Hieger, 1930), some of which were later identified as minor components of coal tar.…”

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