Gwendlyn Kollmorgen

Sharpin Contributes to TNFα Dependent NFκB Activation and Anti-Apoptotic Signalling in Hepatocytes

TNFα stimulates both pro- and anti-apoptotic signalling in hepatocytes. Anti-apoptotic signalling depends on a cascade of ubiquitylation steps leading to NFκB activation. Using Sharpin-deficient mice, we show that the ubiquitin binding protein Sharpin interacts with Hoip, an E3 ligase which generates linear ubiquitin chains. Sharpin-deficiency sensitized hepatocytes to induction of apoptosis by TNFα even in the absence of transcriptional inhibition. TNFα induced activation of NFκB was strongly reduced in hepatocytes from Sharpin-deficient mice, due to reduced and delayed phosphorylation and degradation of IκBα. Injection of TNFα-inducing lipopolysaccharides led to strongly exacerbated liver damage and premature death in Sharpin-deficient mice. Our findings point to an essential role of Sharpin in linear ubiquitin chain formation, NFκB activation, and protection of the liver against inflammatory damaging signals.

Antibody mediated CDCP1 degradation as mode of action for cancer targeted therapy

CUB‐domain‐containing‐protein‐1 (CDCP1) is an integral membrane protein whose expression is up‐regulated in various cancer types. Although high CDCP1 expression has been correlated with poor prognosis in lung, breast, pancreas, and renal cancer, its functional role in tumor formation or progression is incompletely understood. So far it has remained unclear, whether CDCP1 is a useful target for antibody therapy of cancer and what could be a desired mode of action for a therapeutically useful antibody. To shed light on these questions, we have investigated the cellular effects of a therapeutic antibody candidate (RG7287). In focus formation assays, prolonged RG7287 treatment prevented the loss of contact inhibition caused by co‐transformation of NIH3T3 cells with CDCP1 and Src. In a xenograft study, MCF7 cells stably overexpressing CDCP1 reached the predefined tumor volume faster than the parental MCF7 cells lacking endogenous CDCP1. This tumor growth advantage was abolished by RG7287 treatment. In vitro, RG7287 induced rapid tyrosine phosphorylation of CDCP1 by Src, which was accompanied by translocation of CDCP1 to a Triton X‐100 insoluble fraction of the plasma membrane. Triggering these effects required bivalency of the antibody suggesting that it involves CDCP1 dimerization or clustering. However, this initial activation of CDCP1 was only transient and prolonged RG7287 treatment induced internalization and down‐regulation of CDCP1 in different cancer cell lines. Antibody stimulated CDCP1 degradation required Src activity and was proteasome dependent. Also in three different xenograft models with endogenous CDCP1 expression RG7287 treatment resulted in significant tumor growth inhibition concomitant with substantially reduced CDCP1 levels as judged by immunohistochemistry and Western blotting. Thus, despite transiently activating CDCP1 signaling, the RG7287 antibody has a therapeutically useful mode of action.

Characterization of a re-engineered, mesothelin-targeted Pseudomonas exotoxin fusion protein for lung cancer therapy.

Mesothelin overexpression in lung adenocarcinomas correlates with the presence of activating KRAS mutations and poor prognosis. Hence SS1P, a mesothelin‐targeted immunotoxin, could offer valuable treatment options for these patients, but its use in solid tumor therapy is hampered by high immunogenicity and non‐specific toxicity. To overcome both obstacles we developed RG7787, a de‐immunized cytotoxic fusion protein comprising a humanized SS1 Fab fragment and a truncated, B‐cell epitope silenced, 24 kD fragment of Pseudomonas exotoxin A (PE24). Reactivity of RG7787 with sera from immunotoxin‐treated patients was >1000 fold reduced. In vitro RG7787 inhibited cell viability of lung cancer cell lines with picomolar potency. The pharmacokinetic properties of RG7787 in rodents were comparable to SS1P, yet it was tolerated up to 10 fold better without causing severe vascular leak syndrome or hepatotoxicity. A pharmacokinetic/pharmacodynamic model developed based on NCI‐H596 xenograft studies showed that for RG7787 and SS1P, their in vitro and in vivo potencies closely correlate. At optimal doses of 2–3 mg/kg RG7787 is more efficacious than SS1P. Even large, well established tumors (600 mm3) underwent remission during three treatment cycles with RG7787. Also in two patient‐derived lung cancer xenograft models, Lu7336 and Lu7187, RG7787 showed anti‐tumor efficacy. In monotherapy two treatment cycles were moderately efficacious in the Lu7336 model but showed good anti‐tumor activity in the KRAS mutant Lu7187 model (26% and 80% tumor growth inhibition, respectively). Combination of RG7787 with standard chemotherapies further enhanced efficacy in both models achieving near complete eradication of Lu7187 tumors.

Structural Requirements for Cub Domain Containing Protein 1 (CDCP1) and Src Dependent Cell Transformation

Cub domain containing protein 1 (CDCP1) is strongly expressed in tumors derived from lung, colon, ovary, or kidney. It is a membrane protein that is phosphorylated and then bound by Src family kinases. Although expression and phosphorylation of CDCP1 have been investigated in many tumor cell lines, the CDCP1 features responsible for transformation have not been fully evaluated. This is in part due to the lack of an experimental system in which cellular transformation depends on expression of exogenous CDCP1 and Src. Here we use retrovirus mediated co-overexpression of c-Src and CDCP1 to induce focus formation of NIH3T3 cells. Employing different mutants of CDCP1 we show that for a full transformation capacity, the intact amino- and carboxy-termini of CDCP1 are essential. Mutation of any of the core intracellular tyrosine residues (Y734, Y743, or Y762) abolished transformation, and mutation of a palmitoylation motif (C689,690G) strongly reduced it. Src kinase binding to CDCP1 was not required since Src with a defective SH2 domain generated even more CDCP1 dependent foci whereas Src myristoylation was necessary. Taken together, the focus formation assay allowed us to define structural requirements of CDCP1/Src dependent transformation and to characterize the interaction of CDCP1 and Src.

A re-engineered immunotoxin shows promising preclinical activity in ovarian cancer

RG7787 is a re-engineered mesothelin-targeted immunotoxin with reduced immunogenicity composed of a humanized anti-mesothelin Fab fragment and a B-cell epitope silenced 24 kD fragment of Pseudomonas exotoxin A. High prevalence of mesothelin-positive cases and a large unmet medical need make ovarian cancer a promising indication for the clinical development of RG7787. However, ovarian cancer patients also frequently have elevated serum levels of the cancer antigen 125 (CA-125). In principle this could pose a problem, since the binding sites for CA-125 and RG7787 on mesothelin were reported to overlap. However, we show here that RG7787 can readily displace even excess amounts of CA-125 in different cellular assays. Moreover when tested in-vitro on a panel of 12 ovarian cancer cell lines, RG7787 had high cytotoxic activity on COV644, Caov-4, and SNU-119 cells and fully inhibited growth of EFO-21, KURAMOCHI, OVSAHO, and Caov-3 cells with potency values ranging from 1 to 86 pM. Finally, we evaluated the in-vivo efficacy of RG7787 in OvCa6668, a patient-derived ovarian cancer model with high levels of CA-125 expression. RG7787 had moderate monotherapy efficacy but in combination with standard chemotherapies (cisplatin, paclitaxel) achieved pronounced tumor regressions. In summary our data support clinical testing of RG7787 in ovarian cancer.

Abstract 5321: Preclinical validation for treatment with RG7787 in ovarian cancer

RG7787 is composed of a Fab fragment from an anti-MSLN antibody fused to a de-immunized and truncated pseudomonas endotoxin A variant. Once RG7787 is bound and internalized by MSLN positive cells, the toxin is transported to the cytosol, where it inhibits protein synthesis, eventually causing tumor cell death. Mesothelin (MSLN) is a tumor specific differentiation antigen. On normal tissue, its expression is restricted to differentiated mesothelial cells that line as single cell layer body cavities and major organs (e.g. pleura, pericardium, and peritoneum). In cancer, MSLN is highly expressed not only on mesotheliomas but also on a number of other types of solid tumors like ovarian and pancreatic cancer. In both indications patients frequently also have significant serum levels of the cancer antigen-125 (CA-125), sometimes even >1000 U/ml. MSLN has been described to bind CA-125 and this interaction has been suggested to play a role for the ability of cancer cells to metastasize e.g. to the peritoneum. The region in MSLN that is responsible for its interaction with CA-125 has been reported to overlap with the binding epitope of RG7787 potentially resulting in competition between CA-125 and RG7787 for binding to MSLN. The high percentage of MSLN positive cases as well as a clear unmet medical need makes ovarian and pancreatic cancer promising indications for clinical development of RG7787. We investigated, whether abundance of CA-125 can negatively affect ability of RG7787 to bind and be taken up by tumor cells thereby antagonizing RG7787 treatment. We found that indeed RG7787 competes with CA-125 for binding to mesothelin. However, in SPR experiments, the interaction of MSLN with CA-125 was not strong enough to block binding of the anti-MSLN Fab moiety that targets RG7787 to tumor cells. At 20°C the absolute affinity (KD) of RG7787 for human MSLN was determined to be 12.5 pM using two orthogonal “affinity in solution” methods, ELISA and SPR. In agreement with such high affinity binding, we found that adding soluble CA-125 to cell viability assays did not reduce the cytotoxic potency of RG7787. In one set of assays, ascites fluid containing a 10 fold excess of CA-125 compared to the average levels observed in sera of ovarian patients was used for competition. In another set of assays, we used a 100 fold excess of a truncated recombinant CA-125 fragment, containing the domain that interacts with MSLN. Neither the ascites fluid, nor the recombinant CA-125 fragment had any effect on the in-vitro potency of RG7787, indicating that soluble CA-125 levels in patients will not antagonize RG7787 treatment. Finally we demonstrated in cell-cell interaction assays that RG7787 can efficiently block the attachment of MSLN positive cells to OVCAR3 cells that express high levels of CA-125 on their surface. Based on these encouraging data we are currently evaluating in-vivo efficacy of RG7787 in a patient-derived ovarian cancer model. Citation Format: Gwendlyn Kollmorgen, Klara Palme, Annette Seidl, Stefan Scheiblich, Christian Clemens, Edgar Voss, Martin Kaufmann, Klaus Hirzel, Pamela Wilfert, Moritz Marcinowski, Bernd Satzinger, Frank Herting, Gerhard Niederfellner. Preclinical validation for treatment with RG7787 in ovarian cancer. [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 5321. doi:10.1158/1538-7445.AM2015-5321

Abstract 2667: RG7287, a novel humanized anti-CDCP1 antibody with superior preclinical in vivo efficacy in combination with Paclitaxel

CUB domain-containing protein 1 (CDCP1) is a transmembrane glycoprotein and a substrate of Src family kinase (SFK). It has been shown to be upregulated and significantly contributing to a number of different cancers, including colon, lung, breast, kidney, and pancreas cancer. High expression of CDCP1 has been shown to correlate with poor prognosis. CDCP1 is involved in the regulation of anoikis resistance, cell migration and invasion. We have recently described RG7287, a humanized glycoengineered therapeutic anti-CDCP1 antibody with a dual mode of action. (1) downregulation of the receptor from the cell surface, and (2) engaging immune effector functions such as antibody-dependent cellular cytotoxicity (ADCC). Upon ligation of RG7287 to CDCP1 an initial phosphorylation of CDCP1 occurs, this transient activation results in the down-regulation of CDCP1. RG7287 prohibits the transformation potential of CDCP1 and Src in focus formation assays. In vivo, RG7287 increased the survival time of mice bearing tumors of MCF7 cells stably expressing CDCP1 compared to untreated CDCP1 overexpressing MCF7 tumors. Treatment of three different xenograft models with RG7287 inhibited tumor growth. In this study we looked at the possibility of eradicating the tumors by combining RG7287 with paclitaxel. Combining the cytostatic with RG7287 increases tumor growth inhibition compared to RG7287 alone in one xenograft model. In another model the combination of RG7287 with paclitaxel leads to tumor stasis. These results indicate a potential combination therapy for RG7287. We also tested whether RG7287 inhibits metastasis in vivo. Using a metastasis model we could show convincing inhibition of metastasis. Citation Format: Gwendlyn Kollmorgen, Alexander Lifke, Adam Nopora, Frieder Bauss, Gerhard Niederfellner, Birgit Bossenmaier. RG7287, a novel humanized anti-CDCP1 antibody with superior preclinical in vivo efficacy in combination with Paclitaxel. [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 2667. doi:10.1158/1538-7445.AM2014-2667

Abstract 4510: RG7787 - a novel de-immunized PE based fusion protein for therapy of mesothelin-positive solid tumors

Attaching toxic payloads to antibodies has recently been established as a breakthrough in cancer therapy. Most of the currently developed antibody drug conjugate programs represent targeted chemotherapy with microtubule polymerization inhibiting drugs and hence share resistance mechanisms and side effects with classical chemotherapeutics like Taxol. Inhibition of protein synthesis by Pseudomonas Exotoxin (PE) is a more powerful mode of action that interferes with all hallmarks of cancer cells, not just with proliferation. However, its clinical use has been limited by immunogenicity as shown for SS1P, a mesothelin targeted immunotoxin. We have developed a novel de-immunized PE fusion protein (RG7787) for treatment of mesothelin-positive tumors. In order to de-immunize PE, point mutations have been introduced into domain III and the entire domain II has been deleted reducing the size of the effector moiety to approximately 24 kD. PE24 fusions with a disulfide-stabilized Fv fragment have previously been shown to be much better tolerated in rodents, but this could, at least in part, also be attributed to a much reduced serum half-life and exposure. In order to also de-immunize the targeting moiety of RG7787 and restore PK parameters similar to those of SS1P, we substituted the mouse dsFv moiety by a humanized Fab fragment. We show that RG7787 has indeed similar PK properties to SS1P in mouse and cyno. Cell viability assays show that RG7787 has similar cytotoxic potency as SS1P on different cell lines. In-vivo equipotency to SS1P in different xenograft models has been achieved at ∼3 fold higher doses indicating that tumor penetration of SS1P might be slightly better. However, RG7787 is up to tenfold better tolerated in rodents and cynomolgus monkeys, indicating that the therapeutic window is improved. RG7787 achieves potent tumor growth inhibition and even tumor regressions in several xenograft models. We also observed clearly synergistic efficacy with Taxol treatment in different tumor models making this a promising combination for clinical trials. Citation Format: Gerhard Niederfellner, Frieder Bauss, Sabine Imhof-Jung, Friederike Hesse, Sven Kronenberg, Roland Staak, Martin Lechmann, Ben Krippendorff, Wolfgang Richter, Rita Mateus, Gwendlyn Kollmorgen, Ulli Brinkmann, Masanori Onda, Ira Pastan, Klaus Bosslet. RG7787 - a novel de-immunized PE based fusion protein for therapy of mesothelin-positive solid tumors. [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 4510. doi:10.1158/1538-7445.AM2014-4510