Reto Ritschard

Targeting Tumor-Associated Endothelial Cells: Anti-VEGFR2 Immunoliposomes Mediate Tumor Vessel Disruption and Inhibit Tumor Growth

Purpose: Angiogenesis is a key process in tumor progression. By binding VEGF, VEGF receptor-2 (VEGFR2) is a main signaling transducer in tumor-associated angiogenesis. Accordingly, therapeutic approaches against the VEGF/VEGFR2 signaling axis have been designed. However, an efficient and specific chemotherapeutic targeting of tumor-associated endothelial cells has not yet been achieved. Experimental Design: We have employed anti-VEGFR2 antibodies covalently linked to pegylated liposomal doxorubicin (PLD) to specifically ablate tumor-associated endothelial cells in the Rip1Tag2 mouse model of insulinoma, in the MMTV-PyMT mouse model of breast cancer, and in the HT-29 human colon cancer xenograft transplantation model. Results: In each model, anti-VEGFR2–targeted immunoliposomes (ILs) loaded with doxorubicin (anti-VEGFR2-ILs-dox) were superior in therapeutic efficacy to empty liposomes, empty anti-VEGFR2-ILs, antibodies alone, and PLD. Efficacy was similar to that of the oral VEGFR1, -2, and -3 inhibitor PTK787. Detailed histopathologic and molecular analysis revealed a strong antiangiogenic effect of anti-VEGFR2-ILs-dox, and the observed antiangiogenic therapy was significantly more efficient in reducing tumor burden in well-vascularized transgenic mouse models as compared with the less-vascularized xenograft model. Conclusions: Anti-VEGFR2 ILs provide a highly efficient approach to selectively deplete VEGFR2-expressing tumor vasculature. They offer a novel and promising anticancer strategy. Clin Cancer Res; 18(2); 454–64. ©2011 AACR.

EGFR-targeted immunoliposomes derived from the monoclonal antibody EMD72000 mediate specific and efficient drug delivery to a variety of colorectal cancer cells

We hypothesized that immunoliposomes (ILs) constructed using Fab′ from the humanized anti-EGFR monoclonal antibody, EMD72000, can provide efficient intracellular drug delivery in EGFR-overexpressing colorectal tumor cells. ILs were constructed modularly with various MAb fragments, including Fab′ from EMD72000 (matuzumab) or C225 (cetuximab, Erbitux®) covalently linked to stabilized liposomes containing chemotherapeutic drugs or probes. Immunoliposome preparation was optimized, including Fab′ reduction and linkage, and evaluated for specific binding and cytotoxicity in epidermal growth factor receptor (EGFR)—overexpressing colorectal cancer cell lines in vitro. Flow cytometry showed that EGFR-targeted ILs, but not non-targeted liposomes or irrelevant ILs, were efficiently bound and internalized by a variety of EGFR-overexpressing colorectal cancer cells. Linkage of the Fab′ to a longer PEG chain (Mal-PEG3400-DSPE) resulted in an increased uptake of immunoliposomal constructs when compared to previously used materials (Mal-PEG2000-DSPE). ILs derived from EMD72000-Fab′ were used to deliver doxorubicin to EGFR-overexpressing target cells in vitro. Immunoliposomal doxorubicin was significantly more cytotoxic than the corresponding non-targeted liposomal drug in target cells, such as HCT116, while equivalent in cells lacking EGFR-overexpression, such as Colo205. We conclude that EGFR-targeted ILs derived from the humanized MAb EMD72000 provide efficient and targeted delivery of anticancer drugs in colorectal cancer cells overexpressing EGFR.

Large-scale manufacturing of GMP-compliant anti-EGFR targeted nanocarriers: Production of doxorubicin-loaded anti-EGFR-immunoliposomes for a first-in-man clinical trial

We describe the large-scale, GMP-compliant production process of doxorubicin-loaded and anti-EGFR-coated immunoliposomes (anti-EGFR-ILs-dox) used in a first-in-man, dose escalation clinical trial. 10 batches of this nanoparticle have been produced in clean room facilities. Stability data from the pre-GMP and the GMP batch indicate that the anti-EGFR-ILs-dox nanoparticle was stable for at least 18 months after release. Release criteria included visual inspection, sterility testing, as well as measurements of pH (pH 5.0-7.0), doxorubicin HCl concentration (0.45-0.55 mg/ml), endotoxin concentration (<1.21 IU/ml), leakage (<10%), particle size (Z-average of Caelyx ± 20 nm), and particle uptake (uptake absolute: >0.50 ng doxorubicin/μg protein; uptake relatively to PLD: >5 fold). All batches fulfilled the defined release criteria, indicating a high reproducibility as well as batch-to-batch uniformity of the main physico-chemical features of the nanoparticles in the setting of the large-scale GMP process. In the clinical trial, 29 patients were treated with this nanoparticle between 2007 and 2010. Pharmacokinetic data of anti-EGFR-ILs-dox collected during the clinical study revealed stability of the nanocarrier in vivo. Thus, reliable and GMP-compliant production of anti-EGFR-targeted nanoparticles for clinical application is feasible.

Simultaneous targeting of VEGF-receptors 2 and 3 with immunoliposomes enhances therapeutic efficacy

Abstract Background: Tumor progression depends on angiogenesis. Vascular endothelial growth factor (VEGF) receptors (VEGFRs) are the main signal transducers that stimulate endothelial cell migration and vessel sprouting. At present, only VEGFR2 is targeted in the clinical practice. Purpose: To develop new, anti-angiogenic nanoparticles (immunoliposomes, ILs), that redirect cytotoxic compounds to tumor-associated vascular cells. Methods: Pegylated liposomal doxorubicin (PLD) was targeted against VEGFR2- and VEGFR3-expressing cells by inserting anti-VEGFR2 and/or anti-VEGFR3 antibody fragments into the lipid bilayer membrane of PLD. These constructs were tested in vitro, and in vivo in the Rip1Tag2 mouse model of human cancer. Results: The combination treatment with anti-VEGFR2-ILs-dox and anti-VEGFR3-ILs-dox was superior to targeting only VEGFR2 cells and provides a highly efficient approach of depleting tumor-associated vasculature. This leads to tumor starvation and pronounced reduction of tumor burden. Conclusion: Nanoparticles against VEGFR2 and −3 expressing tumor-associated endothelial cells represent a promising and novel anti-cancer strategy.

Abstract 2664: PQR309: Structure-based design, synthesis and biological evaluation of a novel, selective, dual pan-PI3K/mTOR inhibitor

Phosphoinositide 3-kinase/mammalian target of rapamycin (PI3K/mTOR) signaling is key to the control of many physiological and pathophysiological processes, and promotes cancer and inflammatory disease. Therefore, targeting of PI3K and/or mTOR pathways is currently explored in numerous clinical studies. PQR309 is a novel, brain penetrant, potent and selective pan-PI3K/mTOR inhibitor with PK properties suitable for once a day oral dosing in humans. Structure activity relationship studies for PI3K and mTOR interactions are presented, including X-Ray analysis of PI3Kgamma co-crystal structures, modeling of PI3Kalpha and mTOR structures, and chemical derivatization. This led to the identification of PQR309 as a potent pan-PI3K and moderate mTOR inhibitor. PQR309 displays excellent selectivity versus PI3K-related lipid kinases (PIKKs) and protein kinases (KINOMEscan), as well as excellent selectivity versus unrelated targets (Cerep expresSProfile). PQR309 features excellent cell permeability, and was characterized as a BCS class II compound due to its limited water solubility (40 μM). Moreover, PQR309 is not a substrate for P-glycoprotein 1 (P-gp). In A2058 melanoma cells PQR309 demonstrated inhibition of protein kinase B (PKB/Akt; pS473) and ribosomal protein S6 (S6, pSer235/236) phosphorylation with IC50 values of 0.13 μM and 0.58 μM, respectively. In IGF-stimulated MCF7 breast cancer cells, PQR309 at 1 μM inhibited phosphorylation of downstream substrates of PI3K including PKB/Akt, S6, p70S6 kinase, GSK3 and Bad by 60-95%. PQR309 inhibited proliferation of all 58 cell lines of the NCI60 panel (GI50 from 50 to 3300 nM), of the NTRC Oncoline panel (44 cell lines, GI50 from 100-6700 nM) and of a lymphoma cell line panel (40 lymphoma cell lines, GI50 from 25-1740 nM). A concise 4-step synthetic process utilizing a novel protective group strategy provides a robust and scalable supply of PQR309 for clinical trials. In summary, PQR309 is a novel, potent, dual pan-PI3K/mTOR inhibitor with a balanced PI3K vs. mTOR profile, and displays excellent physico-chemical and pharmacological properties. The safety profile of PQR309 is currently addressed in Phase I clinical studies. Citation Format: Vladimir Cmiljanovic, Natasa Cmiljanovic, Romina Marone, Florent Beaufils, Xuxiao Zhang, Marketa Zvelebil, Paul Hebeisen, Marc Lang, Juergen Mestan, Anna Melone, Thomas Bohnacker, Eugenio Gaudio, Chiara Tarantelli, Francesco Bertoni, Reto Ritschard, Vincent Pretre, Andreas Wicki, Doriano Fabbro, Petra Hillmann, Roger Williams, Bernd Giese, Matthias P. Wymann. PQR309: Structure-based design, synthesis and biological evaluation of a novel, selective, dual pan-PI3K/mTOR inhibitor. [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 2664. doi:10.1158/1538-7445.AM2015-2664

PQR309 Is a Novel Dual PI3K/mTOR Inhibitor with Preclinical Antitumor Activity in Lymphomas as a Single Agent and in Combination Therapy

Purpose: Activation of the PI3K/mTOR signaling pathway is recurrent in different lymphoma types, and pharmacologic inhibition of the PI3K/mTOR pathway has shown activity in lymphoma patients. Here, we extensively characterized the in vitro and in vivo activity and the mechanism of action of PQR309 (bimiralisib), a novel oral selective dual PI3K/mTOR inhibitor under clinical evaluation, in preclinical lymphoma models. Experimental Design: This study included preclinical in vitro activity screening on a large panel of cell lines, both as single agent and in combination, validation experiments on in vivo models and primary cells, proteomics and gene-expression profiling, and comparison with other signaling inhibitors. Results: PQR309 had in vitro antilymphoma activity as single agent and in combination with venetoclax, panobinostat, ibrutinib, lenalidomide, ARV-825, marizomib, and rituximab. Sensitivity to PQR309 was associated with specific baseline gene-expression features, such as high expression of transcripts coding for the BCR pathway. Combining proteomics and RNA profiling, we identified the different contribution of PQR309-induced protein phosphorylation and gene expression changes to the drug mechanism of action. Gene-expression signatures induced by PQR309 and by other signaling inhibitors largely overlapped. PQR309 showed activity in cells with primary or secondary resistance to idelalisib. Conclusions: On the basis of these results, PQR309 appeared as a novel and promising compound that is worth developing in the lymphoma setting. Clin Cancer Res; 24(1); 120–9. ©2017 AACR.

mTORC1/autophagy-regulated MerTK in mutant BRAFV600 melanoma with acquired resistance to BRAF inhibition.

BRAF inhibitors (BRAFi) and the combination therapy of BRAF and MEK inhibitors (MEKi) were recently approved for therapy of metastatic melanomas harbouring the oncogenic BRAFV600 mutation. Although these therapies have shown pronounced therapeutic efficacy, the limited durability of the response indicates an acquired drug resistance that still remains mechanistically poorly understood at the molecular level. We conducted transcriptome gene profiling in BRAFi-treated melanoma cells and identified that Mer tyrosine kinase (MerTK) is specifically upregulated. MerTK overexpression was demonstrated not only in melanomas resistant to BRAFi monotherapy (5 out of 10 samples from melanoma patients) but also in melanoma resistant to BRAFi+MEKi (1 out of 3), although MEKi alone does not affect MerTK. Mechanistically, BRAFi-induced activation of Zeb2 stimulates MerTK in BRAFV600 melanoma through mTORC1-triggered activation of autophagy. Co-targeting MerTK and BRAFV600 significantly reduced tumour burden in xenografted mice, which was pheno-copied by co-inhibition of autophagy and mutant BRAFV600.BRAF inhibitors (BRAFi) and the combination therapy of BRAF and MEK inhibitors (MEKi) were recently approved for therapy of metastatic melanomas harbouring the oncogenic BRAFV600 mutation. Although these therapies have shown pronounced therapeutic efficacy, the limited durability of the response indicates an acquired drug resistance that still remains mechanistically poorly understood at the molecular level. We conducted transcriptome gene profiling in BRAFi-treated melanoma cells and identified that Mer tyrosine kinase (MerTK) is specifically upregulated. MerTK overexpression was demonstrated not only in melanomas resistant to BRAFi monotherapy (5 out of 10 samples from melanoma patients) but also in melanoma resistant to BRAFi+MEKi (1 out of 3), although MEKi alone does not affect MerTK. Mechanistically, BRAFi-induced activation of Zeb2 stimulates MerTK in BRAFV600 melanoma through mTORC1-triggered activation of autophagy. Co-targeting MerTK and BRAFV600 significantly reduced tumour burden in xenografted mice, which was pheno-copied by co-inhibition of autophagy and mutant BRAFV600.

Abstract 3634: Selective targeting of tumor-associated angiogenic tip and stalk cells with immunoliposomes (ILs) directed against VEGFR-2 and VEGFR-3 expressing cells

Proceedings: AACR 102nd Annual Meeting 2011‐‐ Apr 2‐6, 2011; Orlando, FL Angiogenesis is a key process in tumor progression. Angiogenic sprouting involves specification of subpopulations of endothelial cells into tip cells that respond to vascular endothelial growth factor (VEGF) guidance cues, and stalk cells that proliferate to form the vascular network. While angiogenic stalk cells mainly express VEGFR-2, the tip cells express VEGFR-3. Up to now, therapeutic approaches have mainly been aimed against VEGFR-2 activity. Bevacizumab, a monoclonal antibody against VEGF-A, has been used with some success in different treatment regimens of metastatic bowel and breast cancer. However, it remains unclear to which extend VEGFR-2 expressing stalk and VEGFR-3 expressing tip cells contribute to tumor-associated angiogenesis in vivo. While anti-VEGF-A antibodies inhibit angiogenesis by blocking VEGFR-2 expressing stalk cells, they do not interfere with VEGFR-3 signalling. Until recently, it was not possible to directly target different populations of endothelial cells involved in neoangiogenesis. This has changed since new technologies based on liposomes allow for the transport of pharmacological compounds to selected cells in vivo. In our lab we have established a method of transportation based on immunoliposomes (ILs), i.e., liposomes coated with antibodies directed against cell surface antigens. DC101 anti-mouse VEGFR-2 and AFL4 anti-mouse VEGFR-3 antibodies were utilized to target liposomes to VEGFR-2 or -3 expressing endothelial cells in vivo. Using this technology, we are able to selectively deplete VEGFR-2 or VEGFR-3 expressing cells from the angiogenic endothelial cell pool and thereby study the functional role of these cell populations. In this study we have investigated doxorubicin-containing ILs coated with anti-VEGFR-2 or anti-VEGFR-3 antibodies in two transgenic mouse models (the Rip1Tag2 model of human insulinoma and the MMTV-PyMT model of human breast cancer) and one xenograft model (the human colon cancer cell line HT29 in nude mice). In all three models, doxorubicin-containing ILs against VEGFR-2- or VEGFR-3-positive cells were effective in suppressing tumor growth. Both were more powerful than untargeted liposomes containing the same dose of doxorubicin. Combined anti-VEGFR-2 and -3 therapy was significantly more potent than targeting anti-VEGFR-2 expressing endothelial cells alone. In the Rip1Tag2 model, tumor burden after 2 weeks of therapy was 14.4 ± 7.9 mm3 (mean ± standard deviation) in the empty liposome group, 5.4 ± 4.7 mm3 in the untargeted liposomal doxorubicin group, 2.1 ± 2.5 mm3 in the anti-VEGFR-2 ILs group, 1.1 ± 1.5 mm3 in the anti-VEGFR-3 ILs and 0.3 ± 0.4 mm3 in the combined anti-VEGFR-2 and -3 ILs group. Thus, delivery of cytotoxic drugs to different angiogenic tumor-associated cells is feasible and may be more promising than focusing on a single entity of endothelial cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3634. doi:10.1158/1538-7445.AM2011-3634