A simple and highly sensitive LC-MS workflow for characterization and quantification of ADC cleavable payloads.

Antibody-drug conjugates (ADC) payloads are cleavable drugs that act as the warhead to exert an ADC's cytotoxic effects on cancer cells intracellularly. A simple and highly sensitive workflow is developed and validated for the simultaneous quantification of six ADC payloads, namely SN-38, MTX, DXd, MMAE, MMAF and Calicheamicin (CM). The workflow consists of a short and simple sample extraction using a methanol-ethanol mixture, followed by a fast liquid chromatography tandem mass spectrometry (LC-MS/MS) analysis. The results showed that well-validated linear response ranges of 0.4-100 nM for SN38, MTX and DXd, 0.04-100 nM for MMAE and MMAF, 0.4-1000 nM for CM were achieved in mouse serum. Recoveries for all six payloads at three different concentrations (low, medium and high) were more than 85%. An ultra-low sample volume of only 5 µL of serum is required due to the high sensitivity of the method. This validated method was successfully applied to a pharmacokinetic study to quantify MMAE in mouse serum samples.

mAb 84, a cytotoxic antibody that kills undifferentiated human embryonic stem cells via oncosis.

The monoclonal antibody mAb 84, which binds to podocalyxin-like protein-1 (PODXL) on human embryonic stem cells (hESCs), was previously reported to bind and kill undifferentiated cells in in vitro and in vivo assays. In this study, we investigate the mechanism responsible for mAb 84-induced hESCs cytotoxicity. Apoptosis was likely not the cause of mAb 84-mediated cell death because no elevation of caspase activities or increased DNA fragmentation was observed in hESCs following incubation with mAb 84. Instead, it was preceded by cell aggregation and damage to cell membranes, resulting in the uptake of propidium iodide, and the leakage of intracellular sodium ions. Furthermore, examination of the cell surface by scanning electron microscopy revealed the presence of pores on the cell surface of mAb 84-treated cells, which was absent from the isotype control. This mechanism of cell death resembles that described for oncosis, a form of cell death resulting from membrane damage. Additional data suggest that the binding of mAb 84 to hESCs initiates a sequence of events prior to membrane damage, consistent with oncosis. Degradation of actin-associated proteins, namely, alpha-actinin, paxillin, and talin, was observed. The perturbation of these actin-associated proteins consequently permits the aggregation of PODXL, thus leading to the formation of pores. To our knowledge, this is the first report of oncotic cell death with hESCs as a model.

Selection against undifferentiated human embryonic stem cells by a cytotoxic antibody recognizing podocalyxin-like protein-1.

Future therapeutic applications of differentiated human embryonic stem cells (hESC) carry a risk of teratoma formation by contaminating undifferentiated hESC. We generated 10 monoclonal antibodies (mAbs) against surface antigens of undifferentiated hESC, showing strong reactivity against undifferentiated, but not differentiated hESC. The mAbs did not cross react with mouse fibroblasts and showed weak to no reactivity against human embryonal carcinoma cells. Notably, one antibody (mAb 84) is cytotoxic to undifferentiated hESC and NCCIT cells in a concentration-dependent, complement-independent manner. mAb 84 induced cell death of undifferentiated, but not differentiated hESC within 30 minutes of incubation, and immunoprecipitation of the mAb-antigen complex revealed that the antigen is podocalyxin-like protein-1. Importantly, we observed absence of tumor formation when hESC and NCCIT cells were treated with mAb 84 prior to transplantation into severe combined immunodeficiency mice. Our data indicate that mAb 84 may be useful in eliminating residual hESC from differentiated cells populations for clinical applications. Disclosure of potential conflicts of interest is found at the end of this article.

Conservation of oncofetal antigens on human embryonic stem cells enables discovery of monoclonal antibodies against cancer.

Monoclonal antibodies (mAbs) are used as targeted therapies against cancers. These mAbs kill cancer cells via various mechanisms of actions. In this study, human embryonic stem cells (hESCs) was used as the immunogen to generate a panel of antibodies. From this panel of mAbs, A19 was found to bind both hESC and various cancer cell lines. The antigen target of A19 was identified as Erbb-2 and glycan analysis showed that A19 binds to a N-glycan epitope on the antigen. A19 was elucidated to internalize into cancer cells following binding to Erbb-2 and hence developed as an antibody-drug conjugate (ADC). Using ADC as the mechanism of action, A19 was able to kill cancer cells in vitro and delayed the onset of tumour formation in mice xenograft model. When compared to Herceptin, A19 binds to different isoforms of Erbb-2 and does not compete with Herceptin for the same epitope. Hence, A19 has the potential to be developed as an alternative targeted therapeutic agent for cancers expressing Erbb-2.

Targeting of embryonic annexin A2 expressed on ovarian and breast cancer by the novel monoclonal antibody 2448.

Monoclonal antibodies (mAbs) play an increasingly important role in cancer therapy. To address the wide heterogeneity of the disease, the identification of novel antigen targets and the development of mAbs against them are needed. Our lab previously generated a panel of mAbs against human embryonic stem cells (hESC) using a whole cell immunization approach in mice. These mAbs can potentially target oncofetal antigens and be repurposed for antibody or antibody drug conjugate (ADC) therapy. From this panel, the novel IgG1 2448 was found to bind surface antigens on hESC and multiple cancer cell lines. Here, we show 2448 targets a unique glycan epitope on annexin A2 (ANXA2) and can potentially monitor the Epithelial-Mesenchymal Transition (EMT) in ovarian and breast cancer. To evaluate 2448 as a potential drug, 2448 was engineered and expressed as a chimeric IgG1. Chimeric 2448 (ch2448) demonstrated efficient and specific killing when conjugated to cytotoxic payloads as an ADC. In addition, ch2448 elicited potent antibody-dependent cell-mediated cytotoxicity (ADCC) activity in vitro and in vivo. Further engineering of ch2448 to remove fucose in the Fc domain enhanced ADCC. Overall, these findings indicate that embryonic ANXA2 is an attractive target and suggest that ch2448 is a promising candidate for further therapeutic development.

Identification of proteins from feeder conditioned medium that support human embryonic stem cells.

The maintenance of undifferentiated human embryonic stem cells (hESC) requires feeder cells, either in co-culture or feeder-free with conditioned medium (CM) from the feeders. In this study, we compared the CM of a supporting primary mouse embryonic feeder (MEF) and an isogenic but non-supporting MEF line (DeltaE-MEF) in order to gain an insight to the differential expression profile of secreted factors. Using two-dimensional electrophoresis (2-DE) and matrix-assisted laser desorption/ionization-time of flight (MALDI) tandem mass spectrometry, 13 protein identities were found to be downregulated in DeltaE-MEF compared to MEF, of which 4 were found to be soluble factors and 3 proteins were membrane-associated or related to the extracellular matrix. In addition, four other proteins were identified to be differentially expressed in MEF-CM using high pressure liquid chromatography (HPLC) and cytokine arrays. In functional experiments where CM was replaced with six of the factors identified, hESC were able to proliferate for five continuous passages whilst maintaining 68-82% and 74-98% expression of pluripotent markers, Oct-4 and Tra-1-60, respectively. Using proteomic tools, important proteins from CM that supports hESC culture have been identified, which when replaced with recombinant proteins, continue to support undifferentiated hESC growth in a feeder-free culture platform.

Selective removal of undifferentiated human embryonic stem cells using magnetic activated cell sorting followed by a cytotoxic antibody.

One of the most pertinent concerns of using differentiated cells derived from human embryonic stem cells (hESC) is the presence of residual undifferentiated hESC, because they carry a risk of teratoma formation. A new cell-cell separation approach that eliminates teratoma-forming hESC in order to ensure safer cell therapy was developed. By combining antibodies (IgMs or IgGs) for the selective removal of undifferentiated hESC using magnetic activated cell sorting (MACS) followed by selective killing of residual hESC with the unique cytotoxic antibody mAb 84, the required purity of differentiated hESC can be achieved. The applicability and robustness of this separation strategy is shown here in a case study using pools of undifferentiated hESC and human fibroblast cells at different ratios (5%-50% hESC) to reflect the different scenario of contaminating hESC in a differentiated cell population. Notably, 97.2%-99.7% of the hESC were removed after the MACS step and 99.1%-100%, after the mAb 84 treatment step, which was confirmed by double-staining flow cytometry and RT-qPCR analysis. These in vitro findings were further validated in an in vivo severe combined immunodeficiency (SCID) mouse model. Importantly, we observed the absence of teratoma formation in eight out of nine SCID mice 28 weeks postinjection of cells after the MACS step, whereas teratomas were observed in all of the controls. Thus, the combination of MACS with the unique cytotoxic antibody mAb 84 constitutes an indispensible tool for successful and safe cell therapy.

Perfusion cultures of human embryonic stem cells.

Human embryonic stem cells (hESC) are self-renewing pluripotent cells capable of differentiating into cells representative of all three embryonic germ layers. Hence, they hold great potential for regenerative medicine. However, significant cell numbers are required to fulfill their potential therapeutic applications. In this study, perfusion with supplemented conditioned media (SCM), produced by mouse embryonic fibroblasts (MEF), was adopted to improve cell densities of hESC cultures. Perfusion enhanced hESC numbers by 70% compared to static conditions, on both organ culture dish (OCD) and petri dish cultures. All cultures maintained healthy expression of the pluripotent marker, Oct-4 transcription factor. In vivo, perfused hESC formed teratomas in severe combined immunodeficiency (SCID) mice models that represent the three embryonic germ layers. When SCM was produced with lower concentrations of MEF, hESC densities and Oct-4 levels were reduced. Hence, perfusion with SCM is a potential feeding method for scale-up production of hESC.

High density cultures of embryonic stem cells.

Embryonic stem cells (ESC) have the unique ability to differentiate into a variety of tissue types. However, the realization of regenerative medicine will require the production of large quantities of ESC which subsequently have to be differentiated into the final phenotype. Thus, we sought to develop a simple and scaleable bioprocess to increase densities of ESC to achieve this goal. Using mouse embryonic stem cells (mESC) as a model, by combining automated feeding and culture of mESC on petriperm dishes, cell densities were enhanced up to 6.4 x 10(6) cells/cm2 compared to conventional petri dish culture which only reached 0.2 to 1.4 x 10(6) cells/cm2. It was found that mESC from all experiments maintained excellent viability, pluripotency, and genetic stability after growing for 6 days in petriperm cultures with automated feeding. The expression of Oct-4 transcription factor was observed in all cultures, mESC formed embryoid bodies in differentiated cultures and teratomas in SCID mice, confirming their pluripotency, and karyotype of the cultures was normal. This culture method was stable for routine passaging and a second mESC cell line was shown to perform in a similar manner on petriperm with automated feeding. This work represents an important step towards achieving high density cultures of ESC.