Breast cancer, melanoma and glioblastoma cells undergo cell-mediated aggregation and aggregate coalescence in a transparent 3D Matrigel environment. Cells from normal tissue and non-tumorigenic cell lines do not exhibit these behaviors. Here, 266 monoclonal antibodies (mAbs) demonstrated to interact with a wide variety of membrane, secreted and matrix proteins, have been screened for their capacity to block these tumorigenic cell-specific behaviors in a 3D environment. Remarkably, only six of the 266 tested mAbs exhibited blocking activity, four targeting integrin ß-1, one targeting integrin α-3 and one targeting CD44. Colocalization of integrins ß-1 and α-3 in fixed cells and in live aggregates suggests that the integrin α-3 ß-1 dimer plays a central role in cancer cell aggregation in the 3D environment provided by Matrigel. Our results suggest that blocking by anti-integrin and anti-CD44 mAbs involves interference in cell-cell interactions.

CD44 is a transmembrane glycoprotein that binds to hyaluronic acid, plays roles in a number of cellular processes and is expressed in a variety of cell types. It is up-regulated in stem cells and cancer. Anti-CD44 monoclonal antibodies affect cell motility and aggregation, and repress tumorigenesis and metastasis. Here we describe four new anti-CD44 monoclonal antibodies originating from B cells of a mouse injected with a plasmid expressing CD44 isoform 12. The four monoclonal antibodies bind to the terminal, extracellular, conserved domain of CD44 isoforms. Based on differences in western blot patterns of cancer cell lysates, the four anti-CD44 mAbs separated into three distinct categories that include P4G9, P3D2, and P3A7, and P3G4. Spot assay analysis with peptides generated inEscherichia colisupport the conclusion that the monoclonal antibodies recognize unglycosylated sequences in the N-terminal conserved region between amino acid 21–220, and analyses with a peptide generated in human embryonic kidney 293 cells, demonstrate that these monoclonal antibodies bind to these peptides only after deglycosylation. Western blots with lysates from three cancer cell lines demonstrate that several CD44 isoforms are unglycosylated in the anti-CD44 target regions. The potential utility of the monoclonal antibodies in blocking tumorigenesis was tested by co-injection of cells of the breast cancer-derived tumorigenic cell line MDA-MB-231 with the anti-CD44 monoclonal antibody P3D2 into the mammary fat pads of mice. All five control mice injected with MDA-MB-231 cells plus anti-IgG formed palpable tumors, while only one of the six test mice injected with MDA-MB-231 cells plus P3D2 formed a tiny tumor, while the remaining five were tumor-free, indicating that the four anti-CD44 mAbs may be useful therapeutically.

322 Background: Hypoxia induced factor 1α/2α (HIFs) and vascular endothelial growth factor (VEGF) are overexpressed in ccRCC and associated with increased tumor angiogenesis, vascular instability and drug resistance. In xenografts, high dose SLM resulted in sustained down regulation of HIFs, normalization of tumor vasculature that resulted in increased drug delivery, and therapeutic synergy with anti-VEGF therapeutic. These effects were highly SLM dose, sequence, and schedule dependent. Methods: After completion of the escalating phase I (3+3) trial, the non-toxic SLM dose of 4000μg was administered orally twice daily (BID) for 14 days, followed by once daily in combination with axitinib 5 mg BID. The primary endpoint is safety and the secondary end point include overall response rate (ORR), progression free survival (PFS), and overall survival (OS). To assess the potential effects of SLM on tumor vascular function, dual energy computed tomography (DECT) was conducted at baseline, day 14 of SLM, and at 3 months of SLM + axitinib. Results: Thirty subjects are screened. Of whom 25 have efficacy data (3 subjects screen failure, 1 withdrew, 1 taken off study prior to first scan due to progression with brain lesions likely present prior to study entry). 13/25 (52%) have confirmed response (CR/PR). Two subjects had CR lasting for at least 35 and 44 months, 6 subjects achieved stable disease (SD) lasting at least 6 months accounting for disease control rate (DCR) of 76%, mPFS is 9.5 months. 5/30 patients have sarcomatoid features, all of which are evaluable for efficacy with 1 PR achieved (20%). In the 20 patients without sarcomatoid features, 12/20 achieved PR (60%). The most prevalent adverse events (AE) included fatigue, diarrhea, anorexia, nausea, hoarseness, weight loss, and hypertension. No deaths nor grade 4 toxicities observed. The blood selenium concentrations achieved in the 4000μg SLM dose cohorts are similar to those determined molecularly and therapeutically synergistic with axitinib in xenografts and are being achieved clinically without significant toxicity. DECT data demonstrated increased iodine uptake by tumor lesions, but not in normal tissues, on day 14 SLM treatment and decreased in these same lesions at 3 months of SLM/axitinib. Conclusions: Blood selenium concentrations and duration of treatment seem to be critical determinants of response. Pre and concurrent treatment with SLM enhance the ORR and PFS of axitinib, with no additional toxicity. Currently documented responses are similar across IMDC risk groups. Clinical trial information: NCT02535533 .