GDF15 is a dynamic biomarker of the integrated stress response in the central nervous system

AIM

Characterize Growth Differentiation Factor 15 (GDF15) as a secreted biomarker of the integrated stress response (ISR) within the central nervous system (CNS).

METHODS

We determined GDF15 levels utilizing in vitro and in vivo neuronal systems wherein the ISR was activated. Primarily, we used the murine model of vanishing white matter disease (VWMD), a neurological disease driven by persistent ISR in the CNS, to establish a link between levels of GDF15 in the cerebrospinal fluid (CSF) and ISR gene expression signature in the CNS. GDF15 was also determined in the CSF of VWM patients.

RESULTS

GDF15 expression was increased concomitant to ISR activation in stress-induced primary astrocytes as well as in retinal ganglion cells following optic nerve crush, while treatment with 2Bact, a specific eIF2B activator, suppressed both the ISR and GDF15. In the VWMD model, CSF GDF15 levels corresponded with the magnitude of the ISR and were reduced by 2BAct. In VWM patients, mean CSF GDF15 was elevated >20-fold as compared to healthy controls, whereas plasma GDF15 was undifferentiated.

CONCLUSIONS

These data suggest that CSF GDF15 is a dynamic marker of ISR activation in the CNS and may serve as a pharmacodynamic biomarker for ISR-modulating therapies.

Abstract 947: An antibody drug conjugate (ADC) directed to lymphocyte antigen 6 complex, locus E (LY6E) delivers targeted chemotherapy to a wide range of solid tumor malignancies

Chemotherapies are limited by a narrow therapeutic index resulting in suboptimal exposure of the tumor to the drug and acquired tumor resistance. One approach to overcome this is through Antibody Drug Conjugates (ADCs); that facilitate greater potency via target specific chemotherapy delivery. In this study, we used a bioinformatics approach to identify Lymphocyte antigen 6, locus E, (LY6E), an interferon-inducible glycosylphosphatidylinositol (GPI)-linked cell membrane protein, as a promising ADC target. Immunohistochemical analysis revealed LY6E was overexpressed in a number of tumor types, such as, breast, including triple negative breast cancer, lung, gastric, ovarian, pancreatic and head/neck carcinomas. Characterization of the endocytic pathways for LY6E revealed rapid uptake of the LY6E specific antibody into cells leading to lysosomal accumulation. Consistent with this, a LY6E specific ADC inhibited in vitro cell proliferation and produced durable tumor regression in vivo in high LY6E expressing cancers. Our results identify LY6E as a highly promising molecular ADC target for a variety of solid tumor types with current unmet medical need.

Citation Format: Jyoti Asundi, Lisa Crocker, Jarrod Tremayne, Paul Polakis, Ron Firestein. An antibody drug conjugate (ADC) directed to lymphocyte antigen 6 complex, locus E (LY6E) delivers targeted chemotherapy to a wide range of solid tumor malignancies. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 947. doi:10.1158/1538-7445.AM2015-947

An Antibody-Drug Conjugate Directed against Lymphocyte Antigen 6 Complex, Locus E (LY6E) Provides Robust Tumor Killing in a Wide Range of Solid Tumor Malignancies

PURPOSE

Chemotherapies are limited by a narrow therapeutic index resulting in suboptimal exposure of the tumor to the drug and acquired tumor resistance. One approach to overcome this is through antibody-drug conjugates (ADC) that facilitate greater potency via target-specific delivery of highly potent cytotoxic agents.

EXPERIMENTAL DESIGN

In this study, we used a bioinformatics approach to identify the lymphocyte antigen 6 complex locus E (LY6E), an IFN-inducible glycosylphosphatidylinositol (GPI)-linked cell membrane protein as a promising ADC target. We developed a monoclonal anti-LY6E antibody and characterized in situ LY6E expression in over 750 cancer specimens and normal tissues. Target-dependent anti-LY6E ADC killing was investigated both in vitro and in vivo using patient-derived xenograft models.

RESULTS

Using in silico approaches, we found that LY6E was significantly overexpressed and amplified in a wide array of different human solid tumors. IHC analysis revealed high LY6E protein expression in a number of tumor types, such as breast, lung, gastric, ovarian, pancreatic, kidney and head/neck carcinomas. Characterization of the endocytic pathways for LY6E revealed that the LY6E-specific antibody is internalized into cells leading to lysosomal accumulation. Consistent with this, a LY6E-specific ADC inhibited in vitro cell proliferation and produced durable tumor regression in vivo in clinically relevant LY6E-expressing xenograft models.

CONCLUSIONS

Our results identify LY6E as a highly promising molecular ADC target for a variety of solid tumor types with current unmet medical need.

Abstract 2924: MAPK pathway inhibition enhances the efficacy of an anti-endothelin B receptor drug conjugate by inducing target expression in melanoma

Therapies targeting the MAP kinase pathway in melanoma have produced significant clinical responses; however, duration of response is limited by acquisition of drug resistance. Rationale drug combinations may improve outcomes in this setting. We assessed the therapeutic combination of an antibody drug conjugate (ADC) targeting the Endothelin B receptor (EDNRB) with small molecule inhibitors of the MAP kinase signaling pathway in melanoma. Cell lines and tumor models containing either mutant BRAF or NRAS, or wildtype for both, were exposed to small molecule inhibitors or BRAF and MEK. Expression of EDNRB was analyzed and the therapeutic impact of combining the anti-EDNRB ADC with the BRAF and MEK inhibitors was assessed. Increased expression of EDNRB in response to inhibition of BRAF and/or MEK was observed and augmented the antitumor activity of the ADC. Enhanced target expression and ADC anti-tumor activity were realized irrespective of the response of the tumor model to the BRAF or MEK inhibitors alone and could be achieved in melanoma with mutant NRAS, BRAF or neither mutation. Cells that acquired resistance to BRAF inhibition through long-term culture retained drug-induced elevated levels of EDNRB expression. Expression of EDNRB was not enhanced in normal human melanocytes by inhibition of BRAF and the combination of the ADC with MAPK inhibitors was well tolerated in mice. The anti-EDNRB ADC combines well with BRAF and MEK inhibitors and could have therapeutic utility in the majority of human melanoma cases.

Citation Format: Jyoti Asundi, Paul Polakis, Jennifer A. Lacap, Michelle Nannini. MAPK pathway inhibition enhances the efficacy of an anti-endothelin B receptor drug conjugate by inducing target expression in melanoma. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2924. doi:10.1158/1538-7445.AM2014-2924

Abstract B192: Pharmacokinetic characterization of anti-ETBR antibody drug conjugate in preclinical species

Purpose. Anti-ETBR-MC-vc-PAB-MMAE (anti-ETBR-vc-E) is an antibody-drug conjugate (ADC) targeting the Endothelin B receptor. It comprises the humanized IgG1 anti-ETBR monoclonal antibody and a potent anti-mitotic agent, monomethyl auristatin E (MMAE), linked through MC-VC-PAB linker. Anti-ETBR antibody and its conjugate cross-react with mouse, rat, cynomolgus monkey and human, which provides an opportunity to compare and evaluate the impact of normal tissue expression on ADC disposition in preclinical species.

Methods. Anti-ETBR-vc-E was administered intravenously in mice (0.5 and 5 mg/kg), rats (0.5 and 5 mg/kg), and cynomolgus monkeys (0.3 and 1 mg/kg). The samples were assayed for total antibody and conjugated antibody concentrations in mice and rats while total antibody and antibody-conjugated MMAE concentrations were determined in monkeys. Concentration-time data were used to estimate the pharmacokinetic parameters.

Results. The pharmacokinetic behavior of the ADC was characterized by monitoring and comparing total antibody, conjugated antibody, and antibody-conjugated MMAE disposition. The clearances for all three analytes were dose-independent after intravenous administration in mice, rats, or cynomolgus monkeys over the dose range studied. Conjugated antibody and antibody-conjugated MMAE clearances were approximately 2-fold higher than total antibody clearance. Clearance of total antibody in rat was approximately 2-fold higher than in mouse and monkey, with values of 19.4, 7.91, and 8.99 mL/day/kg, respectively. Half-life ranged from 8 to 10 days and volume of distribution ranged from 37 to 40 mL/kg.

Conclusions. The pharmacokinetics of anti-ETBR-vc-E total antibody was dose proportional in rodents and monkey suggesting that the presence of cross-reactive antigen in the preclinical species had no impact on clearance. All three species showed a relatively higher deconjugation clearance compared to total antibody clearance.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr B192.

Differential fluorescence induction analysis of Streptococcus pneumoniae identifies genes involved in pathogenesis

Differential fluorescence induction (DFI) technology was used to identify promoters of Streptococcus pneumoniae induced under various in vitro and in vivo conditions. A promoter-trap library using green fluorescent protein as the reporter was constructed in S. pneumoniae, and the entire library was screened for clones exhibiting increased gfp expression under the chosen conditions. The in vitro conditions used were chosen to mimic aspects of the in vivo environment encountered by the pathogen once it enters a host: changes in temperature, osmolarity, oxygen, and iron concentration, as well as blood. In addition, the library was used to infect animals in three different models, and clones induced in these environments were identified. Several promoters were identified in multiple screens, and genes whose promoters were induced twofold or greater under the inducing condition were mutated to assess their roles in virulence. A total of 25 genes were mutated, and the effects of the mutations were assessed in at least two different infection models. Over 50% of these mutants were attenuated in at least one infection model. We show that DFI is a useful tool for identifying bacterial virulence factors as well as a means of elucidating the microenvironment encountered by pathogens upon infection.

Ribozyme-mediated suppression of the G protein gamma7 subunit suggests a role in hormone regulation of adenylylcyclase activity

Human HEK 293 cells present a simple and tractable system to directly test the hypothesis that the G protein gamma subunits contribute to the specificity of receptor signaling pathways in vivo. To begin to elucidate the functions of the individual gamma subunits in these cells, a ribozyme strategy was used to specifically inactivate the mRNA encoding the gamma7 subunit. A phosphorothioated DNA-RNA chimeric hammerhead ribozyme was constructed and analyzed for specificity toward the targeted gamma7 subunit. In vitro cleavage analysis of this ribozyme revealed a highly efficient cleavage activity directed exclusively toward the gamma7 RNA transcript. In particular, this ribozyme did not result in cleavage of the gamma12 RNA transcript, which is 75% identical to the gamma7 RNA transcript. Using a transient transfection assay, in vivo analysis of this ribozyme showed a specific reduction in both the mRNA and protein expression of the gamma7 subunit in HEK 293 cells. Coincident with this loss in gamma7 subunit, there was a specific reduction in the protein expression of the beta1 subunit, suggesting that the beta1 and gamma7 subunits may functionally interact to form a betagamma dimer in vivo. Functional analysis of the consequences of ribozyme-mediated suppression of the gamma7 subunit expression indicated that it was associated with significant attenuation of isoproterenol-, but not prostaglandin E1-, stimulated adenylylcyclase activity. Suppression of the gamma7 subunit expression had no effect on carbachol- and ATP-mediated stimulation of phosphatidylinositol turnover. Taken together, these results not only indicate the feasibility of using the ribozyme technology to determine the roles of individual gamma subunits in receptor-G protein-effector pathways in vivo, but they point to a specific role of the gamma7 subunit in the regulation of adenylylcyclase activity in response to isoproterenol.