Are nitrosamines the connecting link or one of the connecting links between the concepts of phototoxicity and photocarcinogenicity due to the intake of a contaminated medication according to the 2019/ 2023 FDA list?

This carcinogens do not need actually to be added even in small amounts - testing for them doesn’t help to
Minimise significantly cancer risk !
Elimination has to be the rule and the complete elimination with completely new production cycles !
Each and every explanation why nitrosamines has to be taken even in small
Limits - seems to be wrong for me!
Carcinogenesis is a multi step process and nitrosamines are one of the most probable part of its generation and activation independent of the intake is via water , drugs , food, air etc.

Clinicopathological findings in different papers all over the world are more than convincing for this carcinogenic/ genotoxic relationship !

The growing skin and other cancer incidence within the world globalisation progress is more than indicative that somebody is on the wrong way , espeywhen fighting against cancer

Specifically for nitrosamines and their by regulators and scientists reviewed key mechanism of concern: The Thresher studies showed that the sensitivity for nitrosamines is 93%, showing good correlation between the Ames test result and the carcinogenicity of the nitrosamine. As such, the Ames test as described in the OECD 471 guideline can be used as an indicator of the carcinogenic potential of a nitrosamine, and can be an element to an overall assessment of the potency of a nitrosamine. To derisk mutagenicity/carcinogenicity, it is typically not the only element in the weight of evidence, and todays regulator guidances remain conservative from a precautionary perspective on what the EAT can support limit-wise.

In addition to this, the photo-activation mechanism linked to NMOR has been shown to be inducable in the Ames test when using irradiation to activate NMOR, this is the key concept of the paper you have shared. So what works to induce the NMOR mechanism should also be helpful to show if the same is possible on other substrates or not and can help to show that the current literature is correct in identifying alpha-hydroxylation related photo-induced effects (especially when not alpha-hydroxylatable substrates are evaluated) and further help to establish a possible link between +S9 Ames + and -S9/photo-induced Ames +. This is truly a stress test, making abstraction if in vivo photo-induction is relevant based on the ADME and exposure route of the specific NDSRI.

Overall, there seems to be agreement in the scientific community that even if it could be (in general terms) a false positive, a positive in the Ames test should be endorsed from a precautionary principle.

In case you would only like to rely on in vivo carcinogenicity data or in vivo mutagenicity data in combination with newer data on the correlation between in vivo mutagenicity and in vivo carcinogenicity for nitrosamines:
Then I find it strange your papers focus on the CPCA for the nitrosamine AI. CPCA is a model designed for regulatory decision making on nitrosamine AIs (built on small nitrosamine data), building in a high degree of precaution to compensate for scientific uncertainty and does minimize the risk for unacceptable intakes, but does not claim to accurately predict NDSRI AIs (which can be an important element for correlation building with clinical observations). During SOT 2024 FDA scientists have also presented new data to support this.

For example your reporting on “Nitroso-sertaline is as toxic as NDMA/NNK” is not precise (which is not problematic for supplying safe medicines, but might be problematic for correlation building with clinical observations): it being treated by the model CPCA in the NDMA/NNK box does not prove the real AI is as low as the one of NDMA/NNK. The EMA reported EAT negativity on nitroso-sertraline stresses this further (cf. shift from 100 ng/day to 1500 ng/day guided acceptable intake in EU). If you would not support this test because the EAT protocol does not involve photo-activation: if you don’t agree that photo-activation is another route to similar activity and that building protective strategies around alpha-hydroxylation risks is not sufficient, it is strange your papers refer to CPCA AIs as well, as these are built on this mechanistic consideration.

Correlation building/bias risk for NDSRIs is probably influenced by the lack of studying the real AI (based on literature review or going further than only the FDA list and also looking to HC, TGA, EMA lists) and the lack of knowledge of contamination levels. Abstraction of this probably requires big studies like the one on ranitidine (allowing to approach general causality in a multifactorial context). And just like the discussion on mutagenicity and carcinogenicity correlation, there might be further discussion on the correlation between photo-induced mechanisms and enzymatic mechanisms. From an environmental exposure scenario it is easy to assume photo-induction though, but in vivo there is also the systemic availability element.

Again, CPCA is a model and not a primary source of nitrosamine acceptable intakes.

Full elimination of exposure of humans to nitrosamines is an ideal scenario you propose but probably not realistic, giving the multitude on exposure routes and the fact that they can also be formed endogenously. (See for example also the recent review of EFSA for nitrosamines via food and the work the EMA has commissioned on studying endogenous nitrosation). So it does remain all about the dose and evaluating the acceptable daily intake and building in scientifically sound protective factors around that intake.

On the urge for elimination:
Where further efforts are done usually this is called “ALARP”, going as low as reasonably/technically possible. Today we can measure ppb levels of nitrosamines, but not ppt or ppq levels, so proving “endless elimination” is not possible (and thus not formalisable in guidance) even if such a production process exists, the question what is the acceptable intake cannot be avoided. Again, I believe in toxicology it is all about the dose and determining the safe dose.
A fair balance has to be struck between protecting the patient and realising access to medicines (risk/benefit). When asking something that cannot be measured (and is not needed to be measured that low from a safety perspective), the access to medicines might be unnecessarily threatened by making getting authorisation for the medicine impossible. Surely diagnostic limitations based on the state-of-the-art are not strange to clinical practice as well and recognisible.

Investigating the principles of the LCR under ICH M7 and the design of CPCA or nitrosamine guidance will probably offer some more perspective as well.
For some background see also: Review of NDSRIs in Pharmaceutical Drugs -Pub

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:slight_smile: 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!:slight_smile:
It’s really a very professional explanation which fits also for dermatologists !:slight_smile:
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…:slight_smile:

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:

  1. directly carcinogenic / genotoxic
  2. mutagenic and subsequently carcinogenic
  3. 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 ?!:slight_smile:

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 :microbe: 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 :petri_dish: 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:

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

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