By generating isogenic mutants with a chromosomal in-frame deletion in either inlA or inlB, we have identified InlA and InlB as surface-bound proteins of L. monocytogenes with molecular weights of 88,000 and 65,000, respectively. These results were obtained with monoclonal antibodies raised against either protein and corroborated by N-terminal end sequencing of InlA and InlB. By immunoblot analysis, the production of both polypeptides was found to be strongly dependent on growth temperature and, particularly for InlB, on the presence of the PrfA regulator protein. Expression of InlA was not strictly dependent on the presence of the PrfA regulator protein. Transcription analysis of the inlAB locus revealed that the inlA gene was transcribed by several promoters, of which only one is PrfA dependent. This PrfA-dependent inlA promoter, which contains two base substitutions within its putative PrfA DNA-binding palindrome, is responsible for transcription of both inlA and inlB genes. A hitherto unrecognized promoter located 51 bp upstream of the GTG start codon of the inlB gene was also detected. Hence, inlA and inlB are transcribed both individually and in an operon by PrfA-dependent and-independent mechanisms. Tissue culture invasion assays employing various epithelial cell lines demonstrated that both InlA and InlB are required for invasion. In vivo studies using the mouse infection model revealed that both internalin mutants were attenuated for virulence.

The cancer cell secretome has emerged as an attractive subproteome for discovery of candidate blood-based biomarkers. To choose the best performing workflow, we assessed the performance of three first-dimension separation strategies prior to nanoLC-MS/MS analysis: (1) 1D gel electrophoresis (1DGE), (2) peptide SCX chromatography, and (3) tC2 protein reversed phase chromatography. 1DGE using 4-12% gradient gels outperformed the SCX and tC2 methods with respect to number of identified proteins (1092 vs 979 and 580, respectively), reproducibility of protein identification (80% vs 70% and 72%, respectively, assessed in biological N = 3). Reproducibility of protein quantitation based on spectral counting was similar for all 3 methods (CV: 26% vs 24% and 24%, respectively). As a proof-of-concept of secretome proteomics for blood-based biomarker discovery, the gradient 1DGE workflow was subsequently applied to identify IGF1R-signaling related proteins in the secretome of mouse embryonic fibroblasts transformed with human IGF1R (MEF/Toff/IGF1R). VEGF and osteopontin were differentially detected by LC-MS/MS and verified in secretomes by ELISA. Follow-up in serum of mice bearing MEF/Toff/IGF1R-induced tumors showed an increase of osteopontin levels paralleling tumor growth, and reduction in the serum of mice in which IGF1R expression was shut off and tumor regressed.

5015 Background: Based on results of animal experiments intermittent androgen blockade was suggested to delay progression of advanced prostate cancer to the hormone refractory stage. We conducted a prospective randomized study to compare intermittent with continuous androgen suppression. Methods: This was a multi-centre, randomised, two-arm study comparing treatment with goserelin + bicalutamide (intermittent, group A) vs. goserelin + bicalutamide (continuous, group B). The primary endpoint was time to clinical and/or biochemical progression of the disease despite androgen suppression. Secondary enpoints were survival time, patient’s quality of life (QoL) and toxicity. Patients eligibility criteria were: histologically confirmed adenocarcinoma of the prostate in clinical stage T1–4N1–3M0 or T1–4N0–3M1 (D1 oder D2). After an induction phase of 24 weeks with MAB, 335 patients whose PSA decreased under 4 ng/ml or = 90% from baseline were randomized. Results: About two-thirds of the patients of both the intermittent and the continuous therapy arm (65% versus 66%, ITT population) experienced a clinical and/or biochemical disease progression due to any reason during this study. The median time to disease progression was longer for patients randomised to the intermittent therapy arm (16.6 months) compared with patients randomised to the continuous therapy arm (11.5 months). This difference however was not statistically significant (log rank test, p=0.1758). The median time to death from any cause was 51.4 month in the intermittent arm compared and 53.8 months in the continuous therapy arm (p = 0.658). There were no differences in the incidence of patients with AEs or SAEs or in any other safety parameter between patients treated intermittently and patients treated continuously. Patients’ self-assessment of their overall health and of their sexual activity appeared to be favourable in the intermittent compared with the continuous therapy arm. 88% of all patients treated intermittently experienced more than 50% of the number of treatment days as treatment-free days. Conclusions: Intermittent therapy in D1 and D2 prostate cancer patients appears to be safe and feasible. Off treatment periods are > 40 % and attribute to patients quality of life. No significant financial relationships to disclose.

No abstract

The expression of all virulence factors in Listeria monocytogenes characterized to date is controlled by the virulence regulator protein, PrfA. To identify further PrfA-regulated proteins, we examined supernatants of L. monocytogenes EGD harboring additional copies of the PrfA regulator for the presence of novel proteins. This led to the identification and biochemical purification of a hitherto uncharacterized PrfA-dependent 30-kDa protein (A. Lingnau, T. Chakraborty, K. Niebuhr, E. Domann, and J. Wehland, Infect. Immun. 64:1002-1006, 1996). Oligonucleotide primers derived from internal peptide sequences of this protein allowed the cloning and determination of the entire sequence of the respective gene. The protein comprised 297 amino acids with strong overall homology to the internalins, InlA and InlB, particularly in the region harboring the leucine-rich repeats. The gene has been designated irpA for internalin-related protein A gene. Transcriptional studies revealed that the gene was monocistronic and, like the inlA and inlB genes, was transcribed by PrfA-dependent and PrfA-independent mechanisms. Monoclonal antibodies raised against IrpA indicated that it was produced by L. monocytogenes but not by the nonpathogenic species Listeria innocua. To examine the role of IrpA in pathogenesis, we constructed an isogenic in-frame deletion mutant that removed all but 116 amino acids of the IrpA protein. This mutant was neither defective for invasion into many tissue culture cell lines nor did it demonstrate reduced intracellular survival. However, in vivo studies using the mouse infection model revealed that the irpA mutant showed reduced virulence compared to the parental strain. These results suggest a role for IrpA during disseminated infection by L. monocytogenes.

Monoclonal antibodies were generated against a 30-kDa protein fraction derived from culture supernatants of a Listeria monocytogenes strain complemented with additional copies of the prfA regulator gene. Several of the antibodies reacted specifically with a hitherto unidentified, secreted 30-kDa polypeptide. By immunoblot analysis, the expression of this 30-kDa polypeptide was found to be dependent on the presence of the PrfA regulator protein. Microsequencing of peptides derived from the partially purified 30-kDa protein revealed homologies to the InlA and InlB polypeptides of L. monocytogenes, which are required for the internalization of the bacteria into nonphagocytic cell lines. This prompted us to term the 30-kDa polypeptide internalinrelated protein (Irp). Irp-specific monoclonal antibodies cross-reacted with a 24-kDa polypeptide present in culture supernatants of Listeria ivanovii, indicating the existence of an Irp-related protein in this pathogenic Listeria species.

Higher order DR5 clustering can induce tumor cell death, however therapeutic compounds targeting DR5 have achieved limited clinical efficacy. We describe HexaBody-DR5/DR5, an equimolar mixture of two DR5-specific IgG1 antibodies with an Fc-domain mutation that augments antibody hexamerization after cell surface target binding. The two antibodies do not compete for binding to DR5 as demonstrated using binding competition studies, and binding to distinct epitopes in the DR5 extracellular domain was confirmed by crystallography. The unique combination of dual epitope targeting and increased IgG hexamerization resulted in potent DR5 agonist activity by inducing efficient DR5 outside-in signaling and caspase-mediated cell death. Preclinical studies in vitro and in vivo demonstrated that maximal DR5 agonist activity could be achieved independent of Fcγ receptor-mediated antibody crosslinking. Most optimal agonism was observed in the presence of complement complex C1, although without inducing complement-dependent cytotoxicity. It is hypothesized that C1 may stabilize IgG hexamers that are formed after binding of HexaBody-DR5/DR5 to DR5 on the plasma membrane, thereby strengthening DR5 clustering and subsequent outside-in signaling. We observed potent antitumor activity in vitro and in vivo in large panels of patient-derived xenograft models representing various solid cancers. The results of our preclinical studies provided the basis for an ongoing clinical trial exploring the activity of HexaBody-DR5/DR5 (GEN1029) in patients with malignant solid tumors.

Although immune checkpoint blockade (ICB) has shown remarkable clinical benefit in a subset of patients with melanoma and lung cancer, most patients experience no durable benefit. The receptor tyrosine kinase AXL is commonly implicated in therapy resistance and may serve as a marker for therapy-refractory tumors, for example in melanoma, as we previously demonstrated. Here, we show that enapotamab vedotin (EnaV), an antibody–drug conjugate targeting AXL, effectively targets tumors that display insensitivity to immunotherapy or tumor-specific T cells in several melanoma and lung cancer models. In addition to its direct tumor cell killing activity, EnaV treatment induced an inflammatory response and immunogenic cell death in tumor cells and promoted the induction of a memory-like phenotype in cytotoxic T cells. Combining EnaV with tumor-specific T cells proved superior to either treatment alone in models of melanoma and lung cancer and induced ICB benefit in models otherwise insensitive to anti–PD-1 treatment. Our findings indicate that targeting AXL-expressing, immunotherapy-resistant tumors with EnaV causes an immune-stimulating tumor microenvironment and enhances sensitivity to ICB, warranting further investigation of this treatment combination. Significance: These findings show that targeting AXL-positive tumor fractions with an antibody–drug conjugate enhances antitumor immunity in several humanized tumor models of melanoma and lung cancer.