3-[(4-aminobenzoyl)amino]propanoic acid

Endpoint summary

Description of key information

From the available rat and human data, it is clear that when the body is exposed to 4-aminobenzoyl-b-alanine where it is not directly injected into the blood, e.g. oral, dermal and inhalation exposure, that significant metabolism of any 4-aminobenzoyl-b-alanine which passes into the membrane (skin/GI tract/lungs) will occur via N-acetyl transferases (NATs) converting 4-aminobenzoyl-b-alanine to NABA which is then rapidly excreted from the body via the urine (potentially via active secretion in kidneys). It can also reasonably be expected that absorption via skin would be much slower and to a lesser degree than via the oral route, allowing more time for conversion of relatively less absorbed 4-aminobenzoyl-b-alanine to NABA which would then be rapidly removed from the body as soon as reaching the systemic circulation.

The negative results obtained in the in vitro genotoxicity studies performed with 4-aminobenzoyl-b-alanine also show that there is no non-threshold mode of action for carcinogenicity.

Furthermore, exposure to 4-aminobenzoyl-b-alanine will be negligible since it used as a pharmaceutical intermediate only and hence professionals will be working under strict GMP conditions. Oral exposure to workers will not occur and inhalation and dermal exposure will be negligible based on the physico-chemical properties of 4-aminobenzoyl-b-alanine.

Therefore, based on the rapid excretion of 4-aminobenzoyl-b-alanine from the body and the lack of exposure to professionals, repeated dose toxicity is not predicted and in vivo testing is considered scientifically unjustified.

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Link to relevant study records

Reference

Reference 1

Endpoint:

short-term repeated dose toxicity: oral

Type of information:

(Q)SAR

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

results derived from a valid (Q)SAR model, but not (completely) falling into its applicability domain, with adequate and reliable documentation / justification

Justification for type of information:

1. SOFTWARE
https://lazar.in-silico.de/predict

2. MODEL (incl. version number)
Lazar model

3. SMILES OR OTHER IDENTIFIERS USED AS INPUT FOR THE MODEL
SMILES code

4. SCIENTIFIC VALIDITY OF THE (Q)SAR MODEL
- Defined endpoint: Repeat dose toxicity
- Unambiguous algorithm: Not specified
- Defined domain of applicability: The following factors affect the applicability domain of an individual prediction:
•Number of neighbours
•Similarities of neighbours
•Coherence of experimental data within neighbours
- Appropriate measures of goodness-of-fit and robustness and predictivity: An oral rat LOAEL of 68.0 mg/kg bw/day with a 95% prediction interval from 0.546 mg/kg bw/day to 8470.0 mg/kg bw/day was calculated with reference to three nearest neighbours. Regarding the relatively low similarity index of the neighbours (ca. 0.2), which does not exceed the similarity threshold of 0.5, some uncertainty remains whether β-alanine, N-(4-aminobenzoyl)- is in the applicability domain of the QSAR model.
Lazar predicted a Maximum Recommended Daily Dose (Human) of 9.68 mg/kg bw/day (95% prediction interval 0.0549 - 1710.0 mg/kg bw/day). The result was supported by experimental data on 10 nearest neighbours with similarity indices between 0.533 and 0.211. As only one neighbour showed a similarity index > 0.5 it cannot completely be excluded that the query chemical is outside the applicability domain of this model.
- Mechanistic interpretation: The following information is displayed graphically in the web interface:
•Neighbours that have been used for creating the local QSAR model, together with a graphical display of their structures, activity specific similarities, and experimental measurements
•Activating and deactivating fragments are highlighted in the query compound
•Definitions for domain specific terms can be obtained by following links in the web interface

5. APPLICABILITY DOMAIN
- Descriptor domain: Lazar identifies similar compounds in the training data (neighbours) for a given query compound, creates a local prediction model based on experimental activities of neighbours, and uses the local model to predict properties of the query compound by a regression method. The following factors affect the applicability domain of an individual prediction:
•Number of neighbours
•Similarities of neighbours
•Coherence of experimental data within neighbours
The confidence of a prediction is defined by the mean neighbour similarity.
Applicability domains are tightly integrated with the lazar framework, in that any prediction is associated with a confidence value. Cumulative plots of confidence and accuracy for the experiments for acute toxicity in fish and mutagenicity in bacteria show that the confidence value provides meaningful information, as the model accuracy decreases with decreasing confidence.
- Structural and mechanistic domains: The oral rat LOAEL was calculated with reference to three nearest neighbours. Regarding the relatively low similarity index of the neighbours (ca. 0.2), which does not exceed the similarity threshold of 0.5, some uncertainty remains whether β-alanine, N-(4-aminobenzoyl)- is in the applicability domain of the QSAR model.
prediction interval 0.0549 - 1710.0 mg/kg bw/day). The result for the Maximum Recommended Daily Dose (Human) was supported by experimental data on 10 nearest neighbours with similarity indices between 0.533 and 0.211. As only one neighbour showed a similarity index > 0.5 it cannot completely be excluded that the query chemical is outside the applicability domain of this model.
- Similarity with analogues in the training set: Not determined

6. ADEQUACY OF THE RESULT
In consideration of the basis for the prediction, the Lazar estimates of oral rat LOAEL and Maximum Recommended Daily Dose in humans are considered as reliable within the constraints of QSAR predictions.

Qualifier:

no guideline followed

Principles of method if other than guideline:

- Software tool used including version: https://lazar.in-silico.de/predict
- Model(s) used: Lazar model
- Model description: see field 'Justification for type of information'
- Justification of QSAR prediction: see field 'Justification for type of information'

GLP compliance:

no

Dose descriptor:

LOAEL

Effect level:

68 other: mg/kg bw/day

Basis for effect level:

other: QSAR prediction

Dose descriptor:

other: Maximum Recommended Daily Dose (Human)

Effect level:

9.68 other: mg/kg bw/day

Basis for effect level:

other: QSAR prediction

Critical effects observed:

not specified

Conclusions:

An oral rat LOAEL of 68.0 mg/kg bw/day was calculated with reference to three nearest neighbours by the Lazar model. Lazar also predicted a Maximum Recommended Daily Dose (Human) of 9.68 mg/kg bw/day.

Reference 2

Endpoint:

short-term repeated dose toxicity: oral

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

other:

Justification for type of information:

JUSTIFICATION FOR DATA WAIVING
In accordance with Annex XI, section 1 of Regulation No. 1907/2006, in vivo testing on 4-aminobenzoyl-b-alanine does not appear scientifically necessary for the following reasons:

TOXICOLOGICAL ARGUMENT
In the event that any 4-Aminobenzoyl-b-alanine (here-on in referred to as ABA) comes into contact with skin and manages to penetrate the outer layer, or in the event that any respirable particles are inhaled, ABA will be rapidly converted to its N-acetylated metabolite (NABA) via N-acetylation in the skin or lungs. Based on the oral bioavailability of ABA (approx. 14%, see separate IUCLID summary on oral TK), it is predicted that any dermal absorption would be relatively low, so loading of the N-acetylation pathway would not be high and therefore extensive (and possibly complete) metabolism to the NABA is likely to occur which would then be rapidly excreted from the body via urine (see IUCLID TK endpoint oral rat). Similarly, for the inhalation route, N-acetylation is expected to occur, followed by rapid excretion of NABA.

The following key points have been taken from publically available documents:

“Sufficient information has been provided - by the sponsor supporting balsalazide disodium approval - to the FDA to support their claim that the acetylation of ABA is not genetically controlled” (Clinical Pharmacology and BioPharmaceutical Reviews)

This means that variation between genotypes for acetylation in human individuals (i.e. fast/slow acetylators) will not affect the rate of conversion of ABA to its N-acetylated metabolite (NABA).

Center for Drug Evaluation and Research (application number 20-610); pharmacology review states:

Absorption of ABA in rat: following a single oral dose of 14C-ABA in rat, maximum plasma levels of ABA and NABA were reached after 15 minutes.
Metabolism of ABA in rat: Within 15 minutes of oral dosing, the ratio of NABA to ABA was 3.4:1 (approx. 80% conversion of ABA to NABA). Clearly in a very short time after exposure, metabolism of ABA to the N-acetylated metabolite occurs very quickly in rat.
Excretion of ABA in rat: most of the radioactivity in the urine was associated with NABA following oral dose, whereas the majority of radioactivity in urine after i.v. dose was associated with ABA (approx. 80% of dose). Plasma radioactivity declined quickly and was below the limit of detection within 24 hr of oral dosing.

This is clearly indicative that ABA undergoes rapid metabolism to its N-acetylated metabolite when it passes through the GI tract and liver but not when it bypasses this route by entering directly into the bloodstream (i.e. intravenous).

This is an important point, as it suggests the potential for similarly rapid N-acetylation of ABA if it enters the skin after any dermal exposure or lung membranes after any inhalation exposure, since the N-acetyl transferase (NATs) enzymes that convert ABA to NABA in the liver and GI tract also exist in significant amounts in human skin and lungs (references for NATs in human skin: https://www.ncbi.nlm.nih.gov/pubmed/2078351; http://jpet.aspetjournals.org/content/292/1/150https://www.researchgate.net/publication/258921883_N-acetylation_of_three_aromatic_amine_hair_dye_precursor_molecules_eliminates_their_genotoxic_potential and https://link.springer.com/article/10.1007/s00204-017-1954-5. Reference for NATs in human lung: https://www.sciencedirect.com/science/article/pii/S0041008X09000817).

From the review of study number 20060: A comparative tolerability and pharmacokinetic study of balsalazide sodium (Colazide®), Sulfasalazine (Salazopyrin®) and Mesalazine (Asacol®) following a single oral dose.

The conclusion of the review of this study in relation to ABA was that, although it was detected in plasma, it appeared to be excreted only as its N-acetylated metabolite in urine in normal, healthy male human volunteers. The ratio of the relative maximum plasma concentrations of NABA to ABA was 4.3:1, which interestingly is similar to the ratio found in the rat TK data. The plasma AUClast of ABA was 81 ng*hr/ml compared to 1422 ng*hr/ml for NABA again providing an idea of the high conversion of ABA to the metabolite which is easily excreted via urine, thus limiting the potential for accumulation to toxic levels in the body.

From the review of study number 20061: The tolerability and pharmacokinetics of single and repeated oral doses of balsalazide disodium (Colazide®)

The review of this study stated that all human volunteers had readily quantifiable concentrations of NABA in the urine and renal clearance values exceeded normal creatinine clearance values which may indicate active secretion of this metabolite.
The review also stated that the sponsor to the study admitted that the total amount in urine and clearance values should be considered as supporting data since there was no guarantee that urine collections were complete and accurately timed.
However, the rapid metabolism of orally dosed ABA to NABA and its rapid excretion via urine is consistent with Study 20060, Study GLY01/93 and with the rat TK data.

From review of study number GLY01/93 title: Pharmacokinetic study of balsalazide disodium in Patients with Ulcerative Colitis receiving long-term maintenance treatment.

Review of this study states that the mean clearance value for NABA exceeded normal creatinine clearance values which as for Study 20061, is suggestive of active secretion of this metabolite via kidneys. The data showed that the patients in this study retained a high capacity to clear the acetylated metabolite of ABA in the kidneys, thus minimising the systemic exposure to the carrier portion (i.e. ABA) of balsalazide, via its metabolite NABA.

Overall, from rat and more importantly human data, it is clear that when the body is exposed to ABA where it is not directly injected into the blood, e.g. oral, dermal and inhalation exposure, that significant metabolism of any ABA which passes into the membrane (skin/GI tract/lungs) will occur via N-acetyl transferases (NATs) converting ABA to NABA which is then rapidly excreted from the body via the urine (potentially via active secretion in kidneys). It can also reasonably be expected that absorption via skin would be much slower and to a lesser degree than via oral, allowing more time for conversion of relatively less absorbed ABA to NABA which would then be rapidly removed from the body as soon as reaching the systemic circulation.

An additional argument relates to the relative thickness of the rat skin and human skin. Human skin is thicker than rat skin, and most likely will have an N-acetylation capacity exceeding that of rats, due to higher NAT levels (and more types of NAT in humans) and longer transit time. Therefore, it is considered that non-human models for dermal exposure may not actually be suitable for producing reliable data for reproductive toxicity of ABA. Hence, any vertebrate testing would be considered scientifically unnecessary and not in the interests of animal welfare.

EXPOSURE-BASED ARGUMENT
In the case of the Annex VIII studies for which this waiver applies, relevant exposure would only be for dermal and inhalation routes, as only professionals are handling the substance. Furthermore, it should be noted that professionals would be working under strict GMP conditions, as they are using the ABA as a chemical reagent to manufacture balsalazide acid (which is subsequently used to make an API) and in this case there is a strict requirement to protect the pre-API from human contamination, meaning that appropriate PPE would be worn. It can therefore be concluded that the potential for exposure of ABA to the skin or lungs of professional workers would in reality be negligible.

Given the argumentations detailed above and in the interest of animal welfare, it is therefore considered scientifically unnecessary to perform a 28-day repeated dose oral toxicty test on ABA.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

LOAEL

68 mg/kg bw/day

Study duration:

chronic

Species:

other: QSAR

Repeated dose toxicity: inhalation - systemic effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: inhalation - local effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: dermal - systemic effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: dermal - local effects

Endpoint conclusion

Endpoint conclusion:

no study available

Mode of Action Analysis / Human Relevance Framework

No information available

Justification for classification or non-classification

Although repeated dose toxicity studies on 4-aminobenzoyl-b-alanine are unavailable, it can be predicted based on available toxicokinetic information that 4-aminobenzoyl-b-alanine does not require classification for repeated dose toxicity.