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(1933) established that polynuclear aromatic hydrocarbons (PAHs) were carcinogenic components of pitch. ... Although less is known about their health effects than about those of PAHs, it is clear that some nitro-PAHs are potent mutagens and carcinogens.(1)

Benzene and polynuclear hydrocarbons containing more than two benzene rings fused together are toxic and said to possess cancer producing (carcinogenic) property. Such polynuclear hydrocarbons are formed on incomplete combustion of organic materials like tobacco, coal and petroleum.(2)

From the two sources cited above, I keep seeing that polybenzenoid compounds like 1,2-benzanthracene, 3-methylcholanthrene and 1,2- benzpyrene are mentioned to be carcinogens.

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In general, why are polynuclear compounds carcinogenic? I google searched on this topic and all I could find is their effects and concentrations in various substances.

My questions are:

  1. Why are they carcinogenic

  2. Is there a reason for a given organic compound to be carcinogenic?

References

  1. Potential Carcinogenic Effects of Polynuclear Aromatic Hydrocarbons and Nitroaromatics in Mobile Source Emissions, STEPHEN S.HECHT(link)
  2. pg403, NCERT Class XI part 2(pdf link)
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  • $\begingroup$ Search the term intercalation of DNA by polyaromatics. Not all organic compounds are carcinogens. Our whole body has thousands of organic compounds. $\endgroup$
    – AChem
    Jan 3, 2020 at 4:59
  • $\begingroup$ i meant for a given organic compound $\endgroup$
    – Haha Hahaha
    Jan 3, 2020 at 5:00
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    $\begingroup$ There is no way to predict beforehand. Experiment decides it. One can make guesses from known classes of compounds by extrapolation. For example, if PAHs are bad, aromatic amines are also powerful carcinogens. $\endgroup$
    – AChem
    Jan 3, 2020 at 5:05
  • $\begingroup$ See chemistry.stackexchange.com/questions/125402/… $\endgroup$
    – Aniruddha Deb
    Jan 3, 2020 at 5:22
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    $\begingroup$ @Haha HaHaHa Reality is often very unsatisfactory. That does not make an answer, pointing to such reality, unsatisfactory as well. $\endgroup$
    – Poutnik
    Jan 3, 2020 at 5:49

1 Answer 1

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Why are they carcinogenic?

From my point of view as a medicinal chemist, polycyclic aromatic hydrocarbons compounds tend to be metabolized by specific cytochrome P450 (CYP 450) isoforms to form highly electrophilic species, which are highly reactive and can react with the DNA of the cell and damage it. Specifically, they can react with the nucleophilic nitrogen in the DNA bases such as adenine.

Is there a reason for a given organic compound to be carcinogenic?

Mechanism for carcinogenicity can vary, in general, any compound damaging or altering the DNA can be carcinogenic. For example, highly reactive electrophiles (such as formaldehyde).

Reference

  1. https://socratic.org/questions/how-do-polycyclic-aromatic-hydrocarbons-cause-cancer
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