slight_smile: lot of thanks again for the kind explanations!
I have understood the most of them , but will share several issues shortly after finishing something at the hospital!
It’s really a very professional explanation which fits also for dermatologists !
Thanks for that, dear colleague!
Regarding the first passage I agree , but not completely! It /Anes test/ has been used to detect mutagenic potential in bacteria!
Mutagenic action is not always equivalent of carcinogenic one !
This is more than clear !!!
From that point of view we have to share the opinion that carcinogenicity may result without induction of mutations!
Genotoxic effects also!
Nitrosamines are per definitions genotoxic chemical carcinogens!
Some of them might be, but must not be mutagenic one!
Others are non carcinogenic!
Ames test seems to probably not the best way…
The problem is that we can have false negative results in the Ames test especially when we the substances have directly and only carcinogenic action !
The systemic availability of nitrosamines and the the exposition to
Environmental nitrosamines statement:
I agree that this is possible and has to be calculated , of course!
But if and when we prove the photo induction of the most available nitrosamines in drugs / their Phototoxicity and carcinogenicity : this doesn’t change the position that their external intake has to be minimalised or completely eliminated ?!
My opinion is that CPCA test was /when I am
Not wrong/ a model for carcinogenicity prove in rodents and has more significance than Ames test which used bacteria as evaluating model!
Ames test is mutagenicity test and CPCA is for me more relevant as carcinogenicity test in rodents !
Mutagenicity does not prove that the substance is a carcinogen!
Not all carcinogens are mutagens also…
My understanding was till now that nitrosamines might be:
- directly carcinogenic / genotoxic
- mutagenic and subsequently carcinogenic
- non carcinogenic and nonmutagenic
What’s your opinion about that statements ?
CPCA is a model for
Carcinogenicity for
Eycaryotes or test in rodents for example!
Ames test is mutagenicity test I procaryotes / bacteria and its significance to humans has to be sometimes very questionable if we want to be objective , of course ?!
It’s not obligatory that’s some positive mutagens in Ames test are. It obligatory dangerous for humans !!!
Other , possibly dangerous for humans carcinogens does not obligatory show a positive mutagenic test or Ames test!
Carcinogenesis is a complex process as known already! Multistep process …each mutation within the time of making the risk for phenotypic expression more and more possible within time…, in humans !
Photo-induced genotoxicity, as phototoxicity is too broad and the related API to the NDSRI can be photosensitive as well.
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How do you plan to prove carcinogenicity of NDSRIs without accepting Ames testing (and the correlation between nitrosamine carcinogenicity and Ames test result) or the proposed option of in vivo mutagenicity data in combination with newer data on the correlation between in vivo mutagenicity and in vivo carcinogenicity for nitrosamines? 2 year rodent carcinogenicity studies with different dose groups (and probably including a stress group with UV exposure focus) are not evident.
While CPCA is a general model, Ames test data is typically component-specific and therefore can be superior to CPCA although being designed around a different end point, especially considering the known correlation between nitrosamine carcinogenicity (rodent TD50 data) and nitrosamine Ames test calls, whereas in a WoE approach metabolisation data and QSAR considerations can be used as well to support the negative Ames. In addition to this, the size of the Ames test data set compared to the TD50 data set also has to be considered. There are several NDSRIs for which with different in vitro and in vivo follow-up genotoxicity studies it was shown that the Ames test was more predictive than the CPCA.
For NDSRIs, CPCA is a mere model, it does not have underlying carcinogenicity data on the NDSRI studied but predicts the potency category of the NDSRI based on structural features and the data available on nitrosamines with such structural features (typically small nitrosamines). Things like molecular weight, 3D structural-conformational elements are not considered.
At the same time CPCA is applied around precaution. You will probably agree that the TSNA NNK is well described. Depending on the AI calculation method used the available rodent carcinogenicity data (Rivenson 1988) can be extrapolated to 100-182 ng/day. Regulators prefer to use 100 ng/day and design CPCA category 2 around this. However, if you do the CPCA exercise on NNK, a category 1 - 18-26.5 ng/day is obtained. (Similarly you can check the EMA limit list for examples of structures with known TD50 rodent carcinogenicity data and check the correlation between CPCA and the AI from the TD50 data: e.g. N-nitroso-diphenylamine: 78000 ng/day (but CPCA would mean category 5 - 1500 ng/day)).
If somebody would now write a paper and use CPCA as secondary source for the AI of NNK instead of the primary source (Rivenson 1988 or other real data on NNK) without understanding the degree of conservativeness in CPCA this can be problematic, especially if the purpose is identifying correlations between acceptable intake and clinical observations and comparing different molecules (whereas CPCA is not equally inaccurate for all molecules as can be seen from the NNK to nitrosodiphenylamine CPCA-based AI to TD50-based AI (based on calculation methodologies established in guidance) comparison.
And again if you believe a risk exists for nitrosamines that are direct but not indirect acting mutagens and for direct mutagenicity mechanisms being other than alpha-hydroxylation (replacing the enzyme by a photo-induced route), then CPCA is not the source for you. As CPCA scores structural features in the NDSRI based on their predicted effect on alpha-hydroxylation (activating/de-activating), the structure-activity relation might be different if you are coming from a completely different mechanistic angle (and if this were to be the reason for not accepting the available and growing insights on the correlation between nitrosamine genotoxicity and carcinogenicity).
Probably and surely there is some
Lack of science in this laboratory tests in my mind…, so that I have to ask:
Carcinogenicity in Vivo and mutagenicity in vivo could be done or
Performed ?! Not only with Ames test or am I wrong ?
Rodents carcinogenicity studies with different dose groups - has this been performed ? Please , share the data when possible ? Which Nitrosamines and NDSRIs have been tested ? Are there official data about that ? Share, please this data and results when possible…
Carcinogenesis is a multi step
Process ! Even u have exclude the directly driven carcinogenicity / or not pehenotypic mutagenicity of one or two NDSRIs / Nitrosamines, we all have to know that genetic mutations and aberrations could become
Manifest clinically/
Phenotypic after long period of time !
Here the permanent intake of different carcinogens within the time plays surely a role: The polycontamination of the polymedication with NDSRIS is exactly this… a complex disease 
with unpredictable end results !
However the clinical correlations are more than indicative in that relation!
Negative in vivo mutagenicity has been obtained and published by HC, EMA and/or TGA for:
- N-nitroso-N-desmethylazithromycin
- N-nitroso-azaerythromycin
- N-nitroso-calcium folinate
- N-nitroso hydrochlorothiazide
- N-nitroso quinapril
- (S)-2-(((2’-(1H-tetrazol-5-yl)-[1,1′-biphenyl]-4-yl)methyl)(nitroso)amino)-3-methylbutanoic acid
Historic rodent carcinogenicity data is available in LCDB/CPDB and literature, for new NDSRIs in vivo mutagenicity is more common.
About the clinical correlation:
Do you have such a correlation identified where the dataset is of a considerable size and a control group was used, cf. ranitidine study example shared?
I think if real data on presence and mutagenicity/carcinogenicity of the NDSRI is not available as two important data gaps, control group and sample size are even more important to avoid bias.
A scenario of permanent intake of different carcinogens in case of daily use medicines can only play if the two NDSRIs are present and both carcinogens and mutagens, not all NDSRIs are equally potent. In fact, more and more recent literature studies bring to the attention that quite some NDSRIs are not. So a literature review and guidance review (broader than FDA guidance) on the NDSRIs you are publishing on would probably be welcome prior to publication.
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Yes! It’s difficult !
I do not have the control groups…
But there is and could be always a scientific explanation why we have not to exclude this carcinogens…
I will reread it again later! It’s more difficult as supposed by me…
And what about in vivo carcinogenicity ?
Clinico - correlations are indicative moreover for in vivo carcinogenicity in humans ?!
Yes ! I believe that the mechanisms of direct carcinogenicity might be others?
Why not?
Directly genotoxic or via mutations and aberrations in RAS Oncognes or the genome regulator p53?
Is this possible?
I recognize the value of all arguments shared, dear colleague and I am really thankful for that …
My strong points are the clinical arguments and some
Basic statements and postulated concerning the carcinogenesis …
The scientific 
world
Must value and appreciate exactly this critical thinking and different view points …
This has its merit and significance …
A relevant paper may be “the photostability of Terbinafine under UVA Irradiation: The effect of UV absorbers” Photochemistry and Photobiology, 2019, 95: 911-923. Firstly this paper does indeed show the formation of nitrosamines during irradiation, however, as shown, the concerns expressed must remember that most topical formulations contain UV quenchers which will certainly reduce the effect of irradiation.
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I think that regarding terbinafine we have some very interesting data which have to be taken under considertaion. Evaluations from Australia regarding the drug/ Australia Helath ministry/ regulatory units have shown that this is till now probably one of the mostly contaminated druf. The daily acceptable dose seems to be lower in comparison to that of valsartan nad colleagues- please, take a look on page 11, sending the link now:
https://www.tga.gov.au/how-we-regulate/monitoring-safety-and-shortages/industry-information-about-specific-safety-alerts-recalls-and-shortages/nitrosamine-impurities-medicines/appendix-1-established-acceptable-intake-nitrosamines-medicines
This is not correct, this paper is about a series of photodegradation products of terbinafine that don’t include nitrosamines, whereas this paper doesn’t discuss anything on nitrosamines.
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Its not a paper, its an official document of nitrosamine impurities in terbinafine!
There are scarce data of phototoxic action of nitrosamines but this data are available already…it could be from interest, thats all
Some new papers regarding the skin cancer development and progression after intake of potentially nitrosamine contaminated drugs!
Polimedication within the context of polimorbidity must be clarified as soon as possible!
The role of the Nitrosogenesis as cofactor for skin cancer development and progression has to be clarified…
From 2016 till today I have checked all data for skin cancer patients and over 96 % of them has taken potentially nitrosamine contaminated drugs!
Polymedication and contamination should be not overlooked because of the overlapping influence of. Different carcinogens / mutagens on the human genome and human DNA!
Form one side this could cause mutations/ or genotoxic action , from other side this could
Eliminate the role
Of p53 as genome regulator!
Reparations of the nitrosamine generated genetic instability fails and cancer develops!
We have no single data about that simultaneous influence of ndsris/ nitrosamines on human DNA!
We do not postulate that the nitrosamine contamination is the main problem, but that it is a substantial cofactor!
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