Mammary epithelial regeneration implies the existence of cellular progenitors with retained replicative capacity, prolonged lifespan and developmental potency. Evidence exists that DN-p63 isoforms preserve these features by modulating p53 activity in basal epithelia. DN-p63 mRNA levels decline at the onset of differentiation suggesting that its transcriptional regulation may contribute to the initiation of differentiation. To study transcriptional regulation of DN-p63, a 10.3 kbp fragment containing the DN-p63 promoter was isolated. We report here that DN-p63 is a positive and negative transcriptional target of p53 and DN-p63-a, respectively. Disruption of p53 activity or expression abolishes the expression of DN-p63-a. This regulation is mediated by a p53-binding element sufficient to confer these activities to a heterologous promoter. Chromatin immune-precipitation indicates that, in asynchronously growing cells, p53 occupies this element. In response to DNA damage, DN-p63-a is recruited to this element as transcription of DN-p63 declines. Disruption of DN-p63-a expression had differential effects on the transcriptional regulation of several p53-target genes. These findings indicate that p53 contributes to the preservation of basal epithelia by driving the expression of DN-p63 isoforms. These studies also suggest that in response to genotoxic stress, DN-p63-a mediates the silencing of its own promoter thereby altering the pattern of p53-target gene expression.

Monoclonal antibodies (mAb) and related molecules are being developed at a remarkable pace as new therapeutics for the treatment of diseases ranging from cancer to inflammatory disorders. However, characterization of these molecules at all stages of development and manufacturing presents tremendous challenges to existing analytical technologies because of their large size (ca. 150 kDa) and inherent heterogeneity resulting from complex glycosylation patterns and other post-translational modifications. Multidimensional liquid chromatography is emerging as a powerful platform technology that can be used to both improve analysis speed for these molecules by combining existing one-dimensional separations into a single method (e.g., Protein A affinity separation and size-exclusion chromatography) and increasing the resolving power of separations by moving from one dimension of separation to two. In the current study, we have demonstrated the ability to combine hydrophilic interaction (HILIC) and RP separations in an online comprehensive 2D separation coupled with high resolution MS detection (HILIC × RP-HRMS). We find that active solvent modulation (ASM) is critical for coupling these two separation modes, because it mitigates the otherwise serious negative impact of the acetonitrile-rich HILIC mobile phase on the second dimension RP separation. The chromatograms obtained from these HILIC × RP-HRMS separations of mAbs at the subunit level reveal the extent of glycosylation on the Fc/2 and Fd subunits in analysis times on the order of 2 h. In comparison to previous CEX × RP separations of the same molecules, we find that chromatograms from the HILIC × RP separations are richer and reveal separation of some glycoforms that coelute in the CEX × RP separations.

As research, development, and manufacturing of biosimilar protein therapeutics proliferates, there is great interest in the continued development of a portfolio of complementary analytical methods that can be used to efficiently and effectively characterize biosimilar candidate materials relative to the respective reference (i.e., originator) molecule. Liquid phase separation techniques such as liquid chromatography and capillary electrophoresis are powerful tools that can provide both qualitative and quantitative information about similarities and differences between reference and biosimilar materials, especially when coupled with mass spectrometry. However, the inherent complexity of these protein materials challenges even the most modern one-dimensional (1D) separation methods. Two-dimensional (2D) separations present a number of potential advantages over 1D methods, including increased peak capacity, 2D peak patterns that can facilitate unknown identification, and improvement in the compatibility of some separation methods with mass spectrometry. In this study, we demonstrate the use of comprehensive 2D-LC separations involving cation-exchange (CEX) and reversed-phase (RP) separations in the first and second dimensions to compare 3 reference/biosimilar pairs of monoclonal antibodies (cetuximab, trastuzumab and infliximab) that cover a range of similarity/disimilarity in a middle-up approach. The second dimension RP separations are coupled to time-of-flight mass spectrometry, which enables direct identification of features in the chromatograms obtained from mAbs digested with the IdeS enzyme, or digestion with IdeS followed by reduction with dithiothreitol. As many as 23 chemically unique mAb fragments were detected in a single sample. Our results demonstrate that these rich datasets enable facile assesment of the degree of similarity between reference and biosimilar materials.

In this paper, we describe the findings of a study aimed at assessing the detection sensitivity of comprehensive two-dimensional high-performance liquid chromatography (LCxLC) separation of a degraded active pharmaceutical ingredient (API) with UV absorption as the detection technique. Specifically, we have examined the impact of the volume and solvent composition (referred to as "interface conditions") of fractions of first-dimension column effluent transferred to the second dimension for further separation on the ability to resolve and detect low-abundance compounds. Historically, LCxLC has been perceived as being inferior to 1D-LC from the point of view of detection sensitivity. In this work, we demonstrate that LCxLC is sufficiently sensitive to be useful in the pharmaceutical context where in general impurities present at 0.05 % (relative to the API concentration) should be quantified. Moreover, we find that this level of sensitivity is only attained under certain conditions: dilution of the first column effluent with weak solvent (water in this case) prior to injection into the second-dimension column is very beneficial because it promotes focusing of the analyte band in the second column, thereby improving the detection sensitivity of the LCxLC system; and, quantitation limits are also a strong function of peak location in the second-dimension separation window, where baseline disturbances near the dead time of the second column can limit reliable detection of low-abundance compounds.

In this proof-of-concept study, rituximab, which is a reference therapeutic monoclonal antibody (mAb), was characterized through the implementation of online, selective comprehensive two-dimensional liquid chromatography (sLC×LC) coupled with mass spectrometry (MS), using a middle-up approach. In this setup, cation exchange chromatography (CEX) and reverse-phase liquid chromatography (RPLC) were used as the first and second separation dimensions, respectively. As illustrated in this work, the combination of these two chromatographic modes allows a direct assignment of the identities of CEX peaks, using data from the TOF/MS detector, because RPLC is directly compatible with MS detection, whereas CEX is not. In addition, the resolving power of CEX is often considered to be limited; therefore, this 2D approach provides an improvement in peak capacity and resolution when high-performance second-dimension separations are used, instead of simply using the second-dimension separation as a desalting step. This was particularly relevant when separating rituximab fragments of medium size (25 kDa), whereas most of the resolution was provided by CEX in the case of intact rituximab samples. The analysis of a commercial rituximab sample shows that online sLC×LC-TOF-MS can be used to rapidly characterize mAb samples, yielding the identification of numerous variants, based on the analysis of intact, partially digested, and digested/reduced mAb samples.