Baomin Tian

Production and Characterization of a Camelid Single Domain Antibody–Urease Enzyme Conjugate for the Treatment of Cancer

A novel immunoconjugate (L-DOS47) was developed and characterized as a therapeutic agent for tumors expressing CEACAM6. The single domain antibody AFAIKL2, which targets CEACAM6, was expressed in the Escherichia coli BL21 (DE3) pT7-7 system. High purity urease (HPU) was extracted and purified from Jack bean meal. AFAIKL2 was activated using N-succinimidyl [4-iodoacetyl] aminobenzoate (SIAB) as the cross-linker and then conjugated to urease. The activation and conjugation reactions were controlled by altering pH. Under these conditions, the material ratio achieved conjugation ratios of 8-11 antibodies per urease molecule, the residual free urease content was practically negligible (<2%), and high purity (>95%) L-DOS47 conjugate was produced using only ultradiafiltration to remove unreacted antibody and hydrolyzed cross-linker. L-DOS47 was characterized by a panel of analytical techniques including SEC, IEC, Western blot, ELISA, and LC-MS(E) peptide mapping. As the antibody-urease conjugate ratio increased, a higher binding signal was observed. The specificity and cytotoxicity of L-DOS47 was confirmed by screening in four cell lines (BxPC-3, A549, MCF7, and CEACAM6-transfected H23). BxPC-3, a CEACAM6-expressing cell line was found to be most susceptible to L-DOS47. L-DOS47 is being investigated as a potential therapeutic agent in human phase I clinical studies for nonsmall cell lung cancer.

Development and Characterization of a Camelid Single Domain Antibody–Urease Conjugate That Targets Vascular Endothelial Growth Factor Receptor 2

Angiogenesis is the process of new blood vessel formation and is essential for a tumor to grow beyond a certain size. Tumors secrete the pro-angiogenic factor vascular endothelial growth factor, which acts upon local endothelial cells by binding to vascular endothelial growth factor receptors (VEGFRs). In this study, we describe the development and characterization of V21-DOS47, an immunoconjugate that targets VEGFR2. V21-DOS47 is composed of a camelid single domain anti-VEGFR2 antibody (V21) and the enzyme urease. The conjugate specifically binds to VEGFR2 and urease converts endogenous urea into ammonia, which is toxic to tumor cells. Previously, we developed a similar antibody–urease conjugate, L-DOS47, which is currently in clinical trials for non-small cell lung cancer. Although V21-DOS47 was designed from parameters learned from the generation of L-DOS47, additional optimization was required to produce V21-DOS47. In this study, we describe the expression and purification of two versions of the V21 antibody: V21H1 and V21H4. Each was conjugated to urease using a different chemical cross-linker. The conjugates were characterized by a panel of analytical techniques, including SDS-PAGE, size exclusion chromatography, Western blotting, and LC-MSE peptide mapping. Binding characteristics were determined by ELISA and flow cytometry assays. To improve the stability of the conjugates at physiologic pH, the pIs of the V21 antibodies were adjusted by adding several amino acid residues to the C-terminus. For V21H4, a terminal cysteine was also added for use in the conjugation chemistry. The modified V21 antibodies were expressed in the E. coli BL21 (DE3) pT7 system. V21H1 was conjugated to urease using the heterobifunctional cross-linker succinimidyl-[(N-maleimidopropionamido)-diethyleneglycol] ester (SM(PEG)2), which targets lysine resides in the antibody. V21H4 was conjugated to urease using the homobifunctional cross-linker, 1,8-bis(maleimido)diethylene glycol (BM(PEG)2), which targets the cysteine added to the antibody C-terminus. V21H4-DOS47 was determined to be the superior conjugate as the antibody is easily produced and purified at high levels, and the conjugate can be efficiently generated and purified using methods easily transferrable for cGMP production. In addition, V21H4-DOS47 retains higher binding activity than V21H1-DOS47, as the native lysine residues are unmodified.

Abstract A74: CAR-T cells harboring camelid single domain antibody as targeting agent to CEACAM6 antigen in pancreatic cancer

Carcinoembryonic Antigen Related Cell Adhesion Molecule 6 (CEACAM6) is overexpressed in many types of human cancers such as breast, pancreatic, colorectal, and non-small-cell lung adenocarcinoma, and is an independent predictor of overall survival and disease free survival. Targeting this molecule by antibodies has slowed tumor progression in certain animal models. 2A3 is a camelid single domain antibody isolated from a whole cancer cell immunized llama library. The antibody binds specifically to the CEACAM6 antigen with high affinity (5nM as measured by SPR) and inhibits the proliferation of CEACAM6-expressing cancer cells in vitro. In this study, Chimeric-Antigen Receptor (CAR) T cells were engineered to target human CEACAM6 antigen by transducing the 2A3 antibody sequence to generate a modified chimeric CD28 signaling domain fused to chimeric CD3-zeta. Transduction efficiency and expression of 2A3 antibody were verified by flow cytometry. Co-incubation of CEACAM6-specific CAR-T (CEACAM6-CAR-T) cells with the CEACAM6-expressing pancreatic cell line BxPC-3 resulted in augmented cytotoxicity and cytokines (IL-2 and IFN-γ) release, suggesting potential anti-cancer activity of the CAR-T cells. Data from real-time cell analysis showed a significant increase in BxPC-3 cell cytotoxicity by CEACAM6-CAR-T cells, as compared to native T cells. However, CEACAM6-CAR-T cells showed much lower cytotoxic activity on negative control cell lines. The efficacy of CEACAM6-CAR-T cells in xenograft model was examined in vivo. BxPC-3 cells were inoculated subcutaneously into the hind flank of CIEA NOG mice. Three groups of mice then received intravenous injection of either PBS, native T cells, or CEACAM6-CAR-T cells, respectively, at day 1, 8, and 15. The data demonstrated very high efficacy of CEACAM6-CAR-T cells against the pancreatic cancer xenograft. CEACAM6-CAR-T cells significantly decreased the growth of the BxPC-3 xenograft as compared to that of native T cells (p-value=0.00025) and PBS (p-value=7.91x106). No toxic effect was observed based on body weight measurement. The results strongly support that CEACAM6-CAR-T cells can be used as an effective immunotherapy agent against CEACAM6-expressing cancers, and that camelid single domain antibodies can be easily adopted for CAR-T type therapies. Citation Format: Wah Yau Wong, Jamshid Tanha, Lakshmi Krishnan, Baomin Tian, Praveen Kumar, Kim Gaspar, Steve Demas, Sven Rohmann, Heman Chao. CAR-T cells harboring camelid single domain antibody as targeting agent to CEACAM6 antigen in pancreatic cancer. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2016 Oct 20-23; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2017;5(3 Suppl):Abstract nr A74.

Abstract 3770: CAR-T cell harboring a camelid single domain antibody as a targeting agent to kill tumors expressing VEGFR2

Modulation of the immune system is showing tremendous promise in the treatment of malignancies. In addition to checkpoint inhibitors that re-activate T cells present in the tumor microenvironment, exogenously transduced chimeric antigen receptor (CAR) T cells are providing excellent responses in clinical trials for the treatment of leukemias. In this study, we describe CAR-T cells that target VEGFR2-expressing tumors. Angiogenesis is the process of new blood vessel formation and is essential for a tumor to grow beyond a certain size. Tumors secrete the pro-angiogenic factor vascular endothelial growth factor (VEGF), which acts upon local endothelial cells by binding to vascular endothelial growth factor receptors (VEGFR). As VEGFR2 is also expressed by a variety of tumors, we investigated the utility of anti-VEGFR2 CAR-T cells as a method to treat VEGFR2-expressing tumors. Camelid antibodies are small (14 kD) single chain antibodies. To generate a camelid antibody targeting the extracellular domain of VEGFR2, a llama was immunized with recombinant VEGFR2/Fc. A phage display library was generated and screened to identify an antibody with high binding affinity to VEGFR2. The selected antibody was expressed in the E. coli. BL21 (DE3) pT7 system. The purified antibody was characterized by SEC, LC-MS peptide mapping and ELISA. CAR-T cells were engineered to express the camelid anti-VEGFR2 antibody in combination with the CD28 and 4-1BB costimulatory molecules and the CD3 zeta chain. Tumor cells were screened for expression of VEGFR2, and the HL-60 acute promyelocytic leukemia, ZR-75-30 breast ductal carcinoma and NCI-H23 non-small cell lung adenocarcinoma were identified. Co-incubation of anti-VEGFR2 CAR-T cells with the VEGFR-2-expressing cell lines resulted in dose-dependent target cell toxicity as measured by LDH release. In addition, T cell activity was confirmed, as high levels of IL-2 and IFN-γ were detected in the cell culture media. These results suggest that anti-VEGFR2 CAR-T may be useful in directly targeting VEGFR2-expressing tumors. We previously showed the utility of camelid antibodies in CAR-T constructs as anti-CEACAM6 CAR-T cells show both in vitro and in vitro efficacy against the pancreatic tumor Bx-PC3. The use of the a camelid V21 antibody to target VEGFR2-expressing tumors provides hope that camelid single domain antibodies can be developed for CAR-T therapies. Citation Format: Heman Chao, Baomin Tian, Marni Uger, Wah Wong. CAR-T cell harboring a camelid single domain antibody as a targeting agent to kill tumors expressing VEGFR2 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3770. doi:10.1158/1538-7445.AM2017-3770

Abstract A144: Urease-mediated alkalization of tumor microenvironment and its effects on T cell proliferation, cytokine release, and PD-1/PD-L1 interactions

The acidic tumor microenvironment is key for cancer progression by promoting invasiveness and metastatic behaviors of cancer cells. In addition, it protects cancer cells from immunotherapy by suppressing proliferation and cytotoxic activities of local immune cells. It has been reported that treatment with bicarbonate or other bases to neutralize the tumor microenvironment could improve immunotherapy responses. In this study, the novel immunoconjugate L-DOS47, which is in Phase I/II testing for non-small cell lung cancer, was used to augment the extracellular pH of acidified culture media that mimics the tumor microenvironment in vitro and its effects on the human T lymphoblastoid cell line Jurkat Clone E6-1 were examined. L-DOS47 is prepared by conjugation of a camelid single domain antibody specific for the human CEACAM6 antigen to Jack bean urease. The immunoconjugate specifically targets and delivers the urease enzyme to CEACAM6-expressing cancer cells where it induces cytotoxicity by converting urea into ammonia, raising pH in situ. Jurkat cells are susceptible to lactate-induced acidity. Cell growth inhibition was observed in media supplemented with ≥6mM lactate and a corresponding pH of ≤6.7. However, the growth inhibitory effects of lactate could be reversed in the presence of 1 μg/mL L-DOS47 and 2-4mM urea. In addition, cytokine release in phytohemagglutinin (PHA) and phorbol 12-myristate 13-acetate (PMA) stimulated Jurkat cells was also inhibited by the acidic medium, which again could be partially restored by inclusion of L-DOS47/urea. To study the interactions of programmed cell death protein 1 (PD-1) on Jurkat cells with its ligand PD-L1, the human cancer cell lines MDA-MB231 and BxPC-3 were stimulated with Interferon gamma (IFNγ) to express PD-L1 on the cell surface. The IFNγ-stimulated cell lines were found to inhibit IL-2 production in co-incubated Jurkat cells by as much as 40% compared to non-stimulated cells. Interestingly, addition of L-DOS47/urea to the culture medium could partially restore cytokine production in these cells, suggesting a potential role of L-DOS47 in the process of PD-1/PD-L1 interactions. Based on our studies, the results have demonstrated that L-DOS47 exerts its cytotoxic effects on targeted cancer cells in both direct and indirect ways. The immunoconjugate not only generates cytotoxic levels of ammonia in situ but also raises the pH of the tumor microenvironment to promote proliferation and cytotoxic activities of local immune cells. Citation Format: Wah Yau Wong, Baomin Tian, Praveen Kumar, Kim Gaspar, Steve Demas, Sven Rohmann, Heman L. Chao. Urease-mediated alkalization of tumor microenvironment and its effects on T cell proliferation, cytokine release, and PD-1/PD-L1 interactions [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr A144.

Abstract 2851: Development of an alkalizing antibody-enzyme conjugate for NSCLC treatment that is in Phase I clinical testing.

Many solid human tumors generate an acidic and hypoxic microenvironment as a result of altered metabolic pathways and aberrant tumor vasculature. In certain tumors, the chronic exposure to acidic extracellular conditions has been reported to promote invasiveness and metastatic behaviour. In addition, the lower pH may promote resistance to weakly basic chemotherapeutic agents by altering their partitioning coefficient between the extracellular and intracellular compartments. L-DOS47, an immunoconjugate cancer therapeutic, has been developed to target this unique tumor microenvironment. L-DOS47 is a conjugate of a lung adenocarcinoma specific single domain antibody and a urease enzyme. The antibody serves as a targeting agent to deliver the enzyme to the affected site while the urease enzyme coverts urea, an abundant metabolite, into ammonia and generates a local pH increase. The combined effect of ammonia toxicity and pH increase is cytotoxic to cancer cells as shown both in culture and in xenograft models. In vitro experiments showed that L-DOS47 also dramatically potentiated the cytotoxicity of a number of chemotherapeutics. Imaging studies using A549 xenografts and labelled L-DOS47 applied intravenously showed that the drug molecule preferentially accumulated and persisted at the tumor site. L-DOS47 has been studied in a number of tissue-cross reactivity studies to identify suitable animal species for toxicological studies. Cryosections of normal human, cynomolgus monkey, Sprague-Dawley rat, and CD-1 mouse tissues were compared. L-DOS47 produced specific staining to control material (BxPC-3 cells) and those tissues that are known to express CEACAM6 - an antigen for L-DOS47. Both cytoplasmic and membrane bound staining were observed. Results of these studies suggest that the primate and both rodent species are suitable for animal toxicological studies. Pivotal GLP compliant animal toxicological studies in cynomologus monkey and rat together with several non-GLP pilot animal studies were done. In the primate GLP study, L-DOS47 (0, 17, 26, and 35 μg/kg) was administered by IV infusion on Days 1, 8, 15 and 22, followed by a 28-day recovery period. Main study animals were sacrificed on Day 25 and recovery animals on Day 50. Standard toxicology parameters were evaluated. In addition, toxicokinetics, cytokine stimulation and immunogenicity were also evaluated. A separate cardiovascular safety pharmacology study was also conducted. No treatment related clinical signs were observed for the animals treated with 17 or 26μg/kg of L-DOS47. Adverse signs were observed in some but not all of the high dose (35 μg/kg) treated animals. Based on adverse clinical signs observed at 35μg/kg, the NOAEL was determined to be 26 μg/kg/day in this study. Currently L-DOS47 is approved for phase I/II studies in Europe and the U.S.A. Patient enrollment has begun in Poland and first patient has been dosed. Citation Format: Heman Chao, Baomin Tian, Kim Gaspar, John Docherty, Wah Wong. Development of an alkalizing antibody-enzyme conjugate for NSCLC treatment that is in Phase I clinical testing. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2851. doi:10.1158/1538-7445.AM2013-2851