Proline cis-trans conformational isomerization is a mechanism that affects different types of protein functions and behaviors. Using analytical characterization, structural analysis, and molecular dynamics simulations, we studied the causes of an aberrant two-peak size-exclusion chromatography profile observed for a trispecific anti-HIV antibody. We found that proline isomerization in the tyrosine-proline-proline (YPP) motif in the heavy chain complementarity-determining region (CDR)3 domain of one of the antibody arms (10e8v4) was a component of this profile. The pH effect on the conformational equilibrium that led to these two populations was presumably caused by a histidine residue (H147) in the light chain that is in direct contact with the YPP motif. Finally, we demonstrated that, due to chemical equilibrium between the cis and trans proline conformers, the antigen-binding potency of the trispecific anti-HIV antibody was not significantly affected in spite of a potential structural clash of 10e8v4 YP trans P trans conformers with the membrane-proximal ectodomain region epitope in the GP41 antigen. Altogether, these results reveal at mechanistic and molecular levels the effect of proline isomerization in the CDR on the antibody binding and analytical profiles, and support further development of the trispecific anti-HIV antibody.
Clofibrate is a peroxisome proliferator known to induce liver tumours in rats. A proteomics study was conducted to provide new insights into the molecular mechanisms of clofibrate-induced non-genotoxic hepatocarcinogenesis. Rats were treated with 250 mg/kg day clofibrate orally and sacrificed after 7 days. Proteins extracted from the liver were analysed by 2-DE using DIGE technology. The protein identification performed by MS showed that clofibrate induced up-regulation of 77 proteins and down-regulation of 27 proteins. The highest expression ratios corresponded to proteins involved in a series of biochemical pathways such as lipid metabolism, fatty acid metabolism, amino acid metabolism, protein metabolism, citric acid cycle, xenobiotic detoxification and oxidative stress. Proteins implicated in cell proliferation and apoptosis, such as prohibitin, 10-formyl tetrahydrofolate dehydrogenase, senescence marker protein-30, pyridoxine 5'-phosphate oxidase and vimentin, were also identified as being regulated. These results provide leads for further investigations into the molecular mechanisms of liver tumours induced by clofibrate. In addition, MS results showed that a series of regulated proteins were detected as several spots corresponding to different pI and/or M(r). Differential effects on those variants could result from specific PTM and could be a specific molecular signature of the clofibrate-induced protein expression modulation in rat liver.
INTRODUCTIONGemcitabine is a chemotherapeutic agent frequently used by for the treatment of several malignancies both in the adjuvant and metastatic setting. Although myelosuppression is the most adverse event of this therapy, gemcitabine might induce severe pulmonary toxicities. We describe a case of pulmonary veno-occlusive disease (PVOD) related to gemcitabine.CASE PRESENTATIONThe patient was an 83-year-old man with a metastatic pancreatic cancer who was treated by gemcitabine as first-line therapy. He was in good health and received no other chemotherapy. A dose of 1000 mg/m2 of gemcitabine was administered over a 30-minute intravenous infusion on days 1, 8, and 15 of a 28-day cycle. After a period of 6 months, a complete response was observed. Nevertheless, the patient developed a severe dyspnea, with arterial hypoxemia and very low lung diffusion for carbon monoxide. A CT scan showed diffuse ground glass opacities with septal lines, bilateral pleural effusion, and lymph node enlargement. On echocardiography, there was a suspicion of pulmonary hypertension with elevated systolic pulmonary artery pressure and normal left ventricular pressures. Right heart catheterization confirmed pulmonary hypertension and normal pulmonary artery occlusion pressure. Diagnosis of PVOD was made, and a gemcitabine-induced toxicity was suspected. A symptomatic treatment was started. At last follow-up, patient was in functional class I with near-normal of CT scan, arterial blood gases, and echocardiography. A gemcitabine-induced PVOD is the more likely diagnosis.
Levels of host cell proteins (HCPs) in purification intermediates and drug substances (DS) of monoclonal antibodies (mAbs) must be carefully monitored for the production of safe and efficacious biotherapeutics. During the development of mAb1, an immunoglobulin G1 product, unexpected results generated with HCP Enzyme-Linked Immunosorbent Assay (ELISA) kit triggered an investigation which led to the identification of a copurifying HCP called N-(4)-(β-acetylglucosaminyl)-Lasparaginase (AGA, EC3.5.1.26) by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The risk assessment performed indicated a low immunogenicity risk for the copurifying HCP and an ad hoc stability study demonstrated no mAb glycan cleavage and thus no impact on product quality. Fractionation studies performed on polishing steps revealed that AGA was coeluted with the mAb. Very interestingly, the native digestion protocol implemented to go deeper in the MS-HCP profiling was found to be incompatible with correct AGA detection in last purification intermediate and DS, further suggesting a hitchhiking behavior of AGA. In silico surface characterization of AGA also supports this hypothesis. Finally, the combined support of HCP ELISA results and MS allowed process optimization and removal of this copurifying HCP.
Multispecific antibodies,
which target multiple antigens at once,
are emerging as promising therapeutic entities to offer more effective
treatment than conventional monoclonal antibodies (mAbs). However,
these highly complex mAb formats pose significant analytical challenges.
We report here on the characterization of a trispecific antibody (tsAb),
which presents two isomeric forms clearly separated and identified
with size exclusion chromatography coupled to native mass spectrometry
(SEC-nMS). Previous studies showed that these isomers might originate
from a proline
cis
/
trans
isomerization
in one Fab subunit of the tsAb. We combined several innovative ion
mobility (IM)-based approaches to confirm the isomeric nature of the
two species and to gain new insights into the conformational landscape
of both isomers. Preliminary SEC-nIM-MS measurements performed on
a low IM resolution instrument provided the first hints of the coexistence
of different conformers, while complementary collision-induced unfolding
(CIU) experiments evidenced distinct gas-phase unfolding behaviors
upon activation for the two isomers. As subtle conformational differences
remained poorly resolved on our early generation IM platform, we performed
high-resolution cyclic IM (cIM-MS) to unambiguously conclude on the
coexistence of two conformers. The
cis
/
trans
equilibrium was further tackled by exploiting the IM
n
slicing capabilities of the cIM-MS instrument. Altogether, our results
clearly illustrate the benefits of combining state-of-the-art nMS
and IM-MS approaches to address challenging issues encountered in
biopharma. As engineered antibody constructs become increasingly sophisticated,
CIU and cIM-MS methodologies undoubtedly have the potential to integrate
the drug development analytical toolbox to achieve in-depth conformational
characterization of these products.
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