Evaluating drug interactions caused by cytokine release syndrome (CRS) with PBPK (Physiologically
Based Pharmacokinetic) modeling has been reported in some bispecific antibody regulatory
submissions for 10 years. However, the published regulatory reviews and sponsors'
analyses seem to disagree on the roles of PBPK modeling in regulatory decision‐making.
In this editorial, we reviewed and provided our opinions on the FDA's current practice
and sponsors' position in evaluating CRS‐mediated drug interactions. We discussed
what has been done and what is lacking in the current PBPK approach assessing the
CRS‐mediated drug interactions and proposed areas to bridge the gaps. And finally,
we call to actions to improve the current practice toward a patient‐centric clinical
pharmacology approach with more quantitative assessment and management of CRS‐mediated
drug interactions.
The manuscript by Willemin et al.
1
described the use of a PBPK approach to evaluate the effect of elevated IL‐6 following
the treatment of teclistamab on the PK of CYP enzyme (1A2, 2C9, 2C19, 3A4, 3A5) substrates.
This marks the 4th PBPK publication by CPT‐PSP of the effect of CRS as a result of
biologics‐treatment on co‐medications that are CYP substrates, after blinatumomab,
2
mosunetuzumab,
3
and glofitamab.
4
The scientific community and drug developers are using the PBPK modeling tool to study
the effect of CRS on the PK and safety of co‐administered CYP substrate drugs. However,
there seems to be a gap between the peer‐reviewed papers
1
,
2
,
3
,
4
and the regulatory evaluations
5
,
6
,
7
,
8
in terms of concluding the impact of PBPK predictions. In this editorial, we examine
the gap and share our opinions on the value, expectation, and future of PBPK modeling
in this specific area with the aim of increasing awareness, calling for enhanced predictive
performance, and ultimately, achieving patient‐centric clinical pharmacology.
Cytokine release syndrome is characterized by the rapid release of pro‐inflammatory
cytokines and immune cell activation. T cell‐engaging bispecific antibodies can cause
transient release of cytokines that may potentially suppress CYP450 enzymes. Utilizing
the PBPK modeling approach to evaluate the CRS‐mediated drug interactions in a regulatory
submission can be traced back to the first FDA‐approved T‐cell‐engaging bispecific
antibody, blinatumomab, in 2014.
5
Over the past 10 years, a few additional T‐cell‐engaging bispecific antibodies were
approved by FDA (mosunetuzumab, tebentafusp, teclistamab, epcoritamab, glofitamab,
and talquetamab). We examined the FDA's biologics license application assessment packages,
USPIs (United States Prescribing Information), and relevant PBPK publications to see
how drug interactions mediated by CRS were evaluated and reported to healthcare professionals.
Among the seven programs (blinatumomab, mosunetuzumab, tebentafusp, teclistamab, epcoritamab,
glofitamab, and talquetamab), no dedicated drug–drug interaction (DDI) study for CRS
was conducted. Except for tebentafusp, six programs include “cautious periods” when
the CRS‐mediated drug interactions may occur and ask for monitoring for toxicity of
concomitant CYP substrates where minimal changes in concentration may lead to serious
adverse reactions in Section 7 (Drug Interactions) of USPI. PBPK analyses were submitted
for five programs (blinatumomab, mosunetuzumab, teclistamab, glofitamab, and talquetamab)
to evaluate the duration and magnitude of CRS‐mediated drug interactions (Table 1).
None of the PBPK evaluations was deemed adequate by the FDA. Therefore, it appears
that the recommendation in Section 7 of USPI is based on the observed CRS period.
We also noted that the delayed onset and offset effect of IL‐6 on CYP enzymes, and
the enzyme turnover rate were considered by the FDA when recommending the “cautious
period” for talquetamab.
9
TABLE 1
Summary of drug interaction evaluation in FDA‐approved T‐cell‐engaging bispecific
antibodies with PBPK analysis.
Generic Name/Trade Name/Year Approved/Pharmacologic class
FDA Conclusions on PBPK Model Adequacy and Rationale
Description of DDI Potential in USPI
Sponsor's Publications
Cytokines Assessed in Trials
CYPs Assessed in PBPK Model
Blinatumomab/Blincyto/2014/
bispecific CD19‐directed CD3 T‐cell engager
Conclusion: Inadequate
5
Rationale: The PBPK model prediction cannot adequately address drug interaction potential
of blinatumomab, as an exposure–response relationship between plasma IL‐6 levels and
change in CYP activities in humans has not been established
The highest drug–drug interaction risk is during the first 9 days of the first cycle
and the first 2 days of the second cycle.
Modeling IL‐6 profile: An IL‐6 model with zero‐order infusion and first‐order elimination
kinetics were assumed to describe transient IL‐6 profile after dosing of biologics.
Worst‐case investigation: Both the mean IL‐6 profile, and the IL‐6 profile in patient
with the highest IL‐6 (C
max ~20,000 pg/mL) after dosing of biologics were investigated for CYP suppression
potential.
2
TNF‐α, IL‐2, IL‐6, IL‐8, IL‐10, IL‐12, IL‐4, IFN‐γ
3A4, 1A2, and 2C9
Mosunetuzumab‐axgb/Lunsumio/2022 /bispecific CD20‐directed CD3 T‐cell engager
Conclusion: Inadequate
6
Rationale: PBPK analyses are inadequate to evaluate drug interaction potential of
mosunetuzumab and duration of its effect on CYP3A substrates because exposure–response
relationships between cytokines and CYP3A activity in human have not been established.
The time course of the effects of cytokine release caused by antibody treatment on
CYP enzyme activity in non‐RA patients has not been studied. The ability of PBPK modeling
to predict the time course of the effect of IL‐6 on CYP3A activity cannot be assessed
Increased exposure of CYP450 substrates is more likely to occur after the first dose
of LUNSUMIO on Cycle 1 Day 1 and up to 14 days after the second 60 mg dose on Cycle
2 Day 1 and during and after CRS.
Modeling IL‐6 profile: i.v. infusion (a zero‐order input rate, mg/h) of different
hypothetical doses (mg) was used to model IL‐6 formation following different doses
of mosunetuzumab.
Worst‐case investigation: Assumed significant elevation of IL‐6 in gut as a result
of mosunetuzumab treatment to account for suppression of gut CYP3A in addition to
liver.
Used a virtual cancer population for DDI simulations. Used both the mean IL‐6 profile
and the profile close to the 95th percentile of the observed data (extreme IL‐6 levels
up to 12,000 pg/mL).
3
IL‐2, IL‐6, IL‐10, TNF‐α, IFN‐γ
3A
Teclistamab‐cqyv/Tecvayli /2022/bispecific B‐cell maturation antigen (BCMA)‐ directed
CD3 T‐cell engager
Conclusion: Inadequate
8
Rationale: FDA requested additional information during the review of the sponsor's
evaluation of DDI potential, including a quantitative assessment of the effects of
CRS on CYP enzyme activities. The PBPK model limitations include the lack of clinical
drug interaction data for model verification, evaluation was limited to IL‐6 effects,
and lack of sensitivity analysis on interaction parameters
The highest risk of drug–drug interaction is expected to occur from initiation of
TECVAYLI step‐up dosing schedule up to 7 days after the first treatment dose and during
and after CRS.
Modeling IL‐6 profile: i.v. infusion model with different IL‐6 doses to describe observed
data in patients.
Worst‐case investigation: Used IL‐6 profiles representing mean IL‐6 C
max and the highest IL‐6 C
max of 288 pg/mL observed in patients to simulate CYP suppression.
1
,
10
IL‐6, IL‐10, TNF‐α, IFN‐γ, and IL‐2R
1A2, 2C9, 2C19, 3A4/5
Glofitamab‐gxbm/Columvi/2023/bispecific CD20‐directed CD3 T‐cell engager
Conclusion: Inadequate
7
Rationale: The exposure – response relationship between plasma IL‐6 levels and CYP
activity has not been established in humans
Increased exposure of CYP substrates is more likely to occur after the first dose
of COLUMVI on Cycle 1 Day 8 and up to 14 days after the first 30 mg dose on Cycle
2 Day 1 and during and after CRS.
Modeling IL‐6 profile: i.v. infusion model with different IL‐6 doses was used to generate
low, medium, and high IL‐6 transient profiles after dosing of biologics and compared
with observed data.
Worst‐case investigation: Used the highest IL‐6 profile to simulate CYP suppression
(C
max of IL‐6 ~2000 pg/mL).
4
IL‐2, IL‐6, IL‐10, TNF‐α, IFN‐γ
1A2, 2C9, 3A4
Talquetamab‐tgvs/Talvey /2023/bispecific G protein‐coupled receptor family C group
5 member D (GPRCD5)‐directed CD3 T‐cell engager
Conclusion: Inadequate
9
Rationale: The exposure – response relationship between plasma IL‐6 levels and changes
in CYP activity in vivo has not been established in humans
Increased exposure of CYP substrates is more likely to occur from initiation of the
TALVEY step‐up dosing schedule up to 14 days after the first treatment dose and during
and after CRS.
Modeling IL‐6 profile: i.v. infusion model with different IL‐6 doses to describe observed
data in patients.
Worst‐case simulation: Predicted CYP suppression liability using IL‐6 profiles representing
observed systemic median and the highest C
max (3682 pg/mL) in patients.
11
IL‐6, IL‐10, TNF‐α, IFN‐γ, IL‐2R
1A2, 2C9, 2C19, 3A4/5
Abbreviations: C
max, maximal concentration; i.v., intravenous; IFN, interferon; IL, interleukin; IL‐1RA,
interleukin‐1 receptor antagonist; IL‐2R, interleukin‐2 receptor; TNF, tumor necrosis
factor.
On the contrary, the sponsors appear to have high confidence in their PBPK model predictions
of CRS‐mediated drug interactions.
1
,
2
,
3
,
4
The quantitative prediction results are also published on the product website to inform
the healthcare providers regarding the exposure changes of concomitantly administered
CYP substrates.
10
,
11
In our opinion, the current practice of informing Section 7 of USPI is not optimal
and not a patient‐centric clinical pharmacology approach. In the following sections,
we evaluate what has been done and what is lacking in the current PBPK analyses, and
propose approaches to improve the confidence in the PBPK modeling and simulation,
and eventually to better inform the USPI, healthcare providers, and patients on the
risk of CRS‐mediated drug interactions.
Because detailed FDA assessments were often redacted, we have to assume that the same
analyses published by the sponsors were submitted in BLA (Table 1). We found that
sponsors' analyses were generally rigorous and risk‐based. All sponsors developed
a fit‐for‐purpose PK model of IL‐6 to capture transient elevation of the cytokine
after dosing of the biologic product, combined cytokine profiles with its CYP suppression
mechanism and turnover of the CYP enzyme to predict the magnitude and duration of
DDI. For all cases, worst‐case scenarios were explored using IL‐6 profile that represented
patient(s) with the highest observed elevation following treatment of the biologics.
In some cases, the effects of CRS on CYP3A in the gut,
1
,
3
co‐medications that may suppress IL‐6,
1
and underlying disease (using virtual cancer population)
3
were evaluated.
The rationales behind FDA's inadequate conclusions include the lack of an established
exposure–response relationship between IL‐6 and CYP suppression as well as the time
course of the interaction, the focus on evaluating the effect of IL‐6 on CYP substrates
but no other cytokines (such as IL‐2, IL‐6, IL‐10, TNF‐α, IFN‐γ, etc.), and the use
of data in patients with chronic autoimmune and inflammatory diseases to validate
PBPK model for IL‐6.
5
,
6
,
7
,
8
The IL‐6 levels in those diseases are generally much lower compared with the IL‐6
levels in CRS (a few hundred vs. several thousand pg/mL reported by the sponsors
2
,
3
,
4
,
5
,
6
,
7
), while the reported in vitro EC50 of IL‐6 against CYP3A4 activity was ~200 pg/mL
in the absence of dexamethasone.
12
The limitation that the time course of the CRS‐mediated inhibition effect on CYP enzymes
has not been studied (clinically) in the non‐rheumatoid arthritis patients and the
PBPK modeling may not capture the time course of recovery from the suppression effect,
is a valid point. However, the transient nature of CRS and the number of CYP enzymes
likely affected by elevated cytokines indeed make it difficult to design and conduct
dedicated clinical studies to address CRS‐mediated drug interactions.
We believe that PBPK offers a useful alternative to the dedicated drug interaction
studies, and the ultimate goal of PBPK modeling is to better inform the clinical use,
such as removing the cautious languages if no true concerns or providing guidance
on dosage adjustment when there is a real concern on drug interaction. To achieve
this goal, the clinical pharmacology community should realize that the current practice
of informing CRS‐mediated drug interaction risks is neither optimal nor patient‐centric.
We wish to see one break the pattern of applying a PBPK modeling that the agency continuously
considers inadequate, yet the drug interaction risk being‐based primarily on the CRS
period without the context of CYP suppression potency in Section 7 of USPI. We also
acknowledge that some additional work is needed and propose addressing the following
scientific gaps.
Higher cytokine levels: The transient cytokine levels in CRS are generally higher
than those observed in patients with chronic immune and infectious diseases, and could
be higher than in vitro EC50 values.
12
The PBPK model was generally validated against drug interaction data obtained at lower
cytokine concentrations. Evidence on the effect of cytokines at higher concentrations
on CYP enzymes might be needed given that the in vivo EC50 values have not been estimated.
The effect of other cytokines on the CYP enzyme activities: The in vivo data supporting
a direct effect of IL‐2, IL‐8, IL‐10, IL‐17, TNF‐α, or IFN‐γ are inconclusive.
12
The decision on which cytokine(s) to focus on and which CYPs to evaluate therefore
should continue to be based on pharmacology principles. Analysis of CYP suppression
by elevated IL‐6 can help guide the decision on other cytokines/CYPs.
The patient populations beyond the differences in cytokine levels: Different patient
populations may have disease‐specific baseline cytokine levels,which can change upon
therapeutic interventions. This should be considered in a PBPK analysis.
Additional in vivo data might be needed to address the knowledge gaps. A recent PBPK
publication evaluated the impact of elevated IL‐6 on CYP3A substrates in patients
with COVID‐19 predicted DDI liability under the highest observed IL‐6 concentration
of 4462 pg/mL, which might provide an additional dataset for model validation.
13
Ideally, a dedicated drug interaction study could be conducted with appropriate design
and data collection for relevant model validation. This can be considered as an one‐time
investment to evaluate future (and confirm the past) CRS‐mediated drug interactions.
Recognizing the challenge of conducting dedicated clinical studies to fully address
transient nature of CRS and the number of CYPs affected, one can establish real‐world
evidence detecting potential adverse effects related to elevated exposure of co‐medications
as a result of much higher cytokine levels during CRS . Considering the number of
T‐cell‐engaging bispecific antibodies in development, and the common pathway of the
postulated drug interaction through CRS, it might be worthwhile for both the sponsors
and regulators to collaborate on addressing these knowledge gaps and enhancing the
predictability of PBPK.
To summarize, we commented on the current practice of how CRS‐mediated drug interaction
risk is being communicated by both the Agency and the sponsors. We expressed our opinion
that the current practice is not optimal, not patient‐centric, and lacks quantitative
evaluation. We reviewed what has been done and what is lacking in the current PBPK
modeling to evaluate the CRS‐mediated drug interactions. We identified a few gaps
and discussed the approaches to achieve the goal of using PBPK to better inform the
clinical use of concomitant medications in CRS events. We hope that soon, there will
be a breakthrough in utilizing the quantitative approach to inform patients and healthcare
providers about CRS‐mediated drug interaction risks.
FUNDING INFORMATION
No funding was received for this work.
CONFLICT OF INTEREST STATEMENT
The authors declared no competing interests for this work.
DISCLAIMER
The views expressed in this editorial are those of the authors and do not represent
the opinions of their employers.