A phase II/III randomized, blinded study of tozuleristide for fluorescence imaging detection during neurosurgical resection of pediatric primary central nervous system (CNS) tumors: PNOC012 (Pacific Pediatric Neuro-oncology Consortium)

TPS2575

Background: Tozuleristide (also known as BLZ-100 or Tumor Paint) is a fluorescent imaging drug designed to specifically label and accumulate in tumor tissue, thus enabling more precise surgical tumor resection intraoperatively. Tozuleristide achieves tumor targeting through the peptide portion of the molecule, a modified chlorotoxin peptide, and its imaging properties from a coupled near-infrared fluorescent dye, an indocyanine green. Tozuleristide has been studied in 4 Phase 1 studies, including a trial in pediatric brain cancer subjects. No tozuleristide SAEs or dose limiting toxicity were observed in the 97 subjects treated in the Phase 1 program at doses up to 30 mg in adults or 17.3 mg/m2 in pediatrics (Hansen S et al, WMIC 2018, P196). Eighty percent of pediatric subjects receiving tozuleristide had tumors considered fluorescence positive, including high and low grade glioma, ependymoma, and medulloblastoma. Methods: This study randomizes subjects in a 1:10 ratio to standard of care or tozuleristide arms. The primary efficacy objectives and endpoints are based on equivocal regions of tissue encountered in surgery. Prior to fluorescence assessment, the surgeon assesses the suspected nature of the tissue (more likely tumor/less likely tumor). Tissue specimens of equivocal regions are collected for blinded central pathology assessment. Sensitivity and specificity of the surgeon’s designation, fluorescence assessment, and ratios of surgeon to fluorescence assessments comprise the primary efficacy analyses. Tozuleristide is given as an IV bolus dose of 15 mg/m2 to pediatric subjects 1 to 36 hours prior to surgery. Subjects must have a MRI documented lesion consistent with a CNS tumor for which resection is planned. Measures of safety include adverse events, laboratory measures of hematology, liver and kidney function and changes in vital signs and ECGs. Pharmacokinetic blood samples are collected up to 3 hr post dose. Fluorescence imaging is assessed during surgery using an investigational “Canvas System” imaging device attached to a surgical microscope. Collected pathology specimens will also be subjected to further genetic, molecular and pathology studies, including fluorescence assessment of frozen tissue sections. SAEs and patient reported outcomes are collected for 3 months. The SMC for the study last reviewed the data for this study in July 2019 and recommended the trial continue as planned. Clinical trial information: NCT03579602 .

Granulocyte-macrophage colony-stimulating factor receptor-targeted therapy of chemotherapy- and radiation-resistant human myeloid leukemias

Contemporary therapies for acute myeloid leukemia (AML) commonly fail to cure patients because of the emergence of drug resistance. Drug resistance in AML is multifactorial but can be associated with the overexpression of transmembrane transporter molecules, including P-glycoprotein (Pgp) or the multidrug resistance-associated protein (MRP), or associated with inactivation of the p53 tumor suppressor gene, as well as overexpression of the anti-apoptotic protein bcl-2. We are investigating if novel recombinant biotherapeutics can circumvent these resistance mechanisms to effectively treat refractory AML. To target the lethal action of diphtheria toxin (DT) to high affinity granulocyte-macrophage colony-stimulating factor (GMCSF) receptors on AML blasts, we have produced a recombinant chimeric fusion toxin, DTctGMCSF. Since DTctGMCSF enters and kills its target cells by unique mechanisms (GMCSF-receptor binding and protein synthesis inhibition) and is not similar in structure to Pgp or MRP substrates, we postulated that it would be an active agent against therapy-resistant AML. DTctGMCSF was selectively cytotoxic (IC50 1-10ng/ml) to GMCSF-receptor positive AML cells expressing the Pgp- or MRP-associated multi-drug resistant phenotypes, despite high level resistance to conventional chemotherapeutic agents. DTctGMCSF also efficiently killed AML cells deficient in p53 expression, as well as radiation-resistant AML cells and mixed lineage leukemia cells expressing high levels of bcl-2. In addition, DTctGMCSF killed > 99% of primary leukemic progenitor cells from therapy-refractory AML patients under conditions that we have previously found to not adversely affect the proliferative capacity or differentiation of pluripotent normal hematopoietic progenitor cells. DTctGMCSF may prove useful in treating myeloid leukemias that are otherwise resistant to a wide range of conventional therapies.

A recombinant fusion toxin targeted to the granulocyte-macrophage colony-stimulating factor receptor

Human granulocyte-macrophage colony stimulating factor (GMCSF) and its high affinity receptor function to regulate the proliferation and differentiation of myeloid lineage hematopoietic cells, and may participate in the pathogenesis of many malignant myeloid diseases. We have used genetic engineering based on the elucidated molecular structures of human granulocyte-macrophage colony-stimulating factor and diphtheria toxin (DT) to produce a recombinant fusion toxin, DTctGMCSF, that targets diphtheria toxin to high affinity GMCSF receptors expressed on the surface of blast cells from a large fraction of patients with acute myeloid leukemia (AML). DTctGMCSF was specifically immunoreactive with antidiphtheria toxin and anti-GMCSF antiseras, and exhibited the characteristic catalytic activity of diphtheria toxin, catalyzing the in vitro ADP-ribosylation of purified elongation factor 2. The cytotoxic effects of DTctGMCSF were examined using the 3-(4,5-dimethylthiazol-2-yl)-2,5-tetrazolium (MTT) bromide assay of cell viability and in vivo assays of protein synthesis inhibition. DTctGMCSF were specifically cytotoxic to human leukemia cell lines bearing high affinity receptors for human GMCSF with IC50 of 10(-9) to 10(-11) M. It was not toxic to mammalian hematopoietic cell lines lacking human GMCSF (hGMCSF) receptors. In receptor positive cells, cytotoxicity can be specifically blocked by a large excess of hGMCSF, confirming that its cytotoxicity is mediated through the hGMCSF receptor. THough DTctGMCSF inhibited granulocyte-macrophage colony formation by committed myeloid progenitor cells (CFU-GM), it did not significantly affect erythroid burst formation by committed erythroid progenitor cells (BFU-E), or mixed granulocyte-erythroid-macrophage-megakaryocyte colony formation by pluripotent multilineage progenitor cells (CFU-GEMM). DTctGMCSF holds promise for the treatment of myeloid lineage malignancies, and is a useful reagent to study hematopoiesis.

Induction of apoptosis in multidrug-resistant and radiation-resistant acute myeloid leukemia cells by a recombinant fusion toxin directed against the human granulocyte macrophage colony-stimulating factor receptor

Multiagent chemotherapy regimens fail to cure more than one-half of the patients with acute myeloid leukemia (AML) because of the emergence of dominant multidrug-resistant subclones of leukemia cells. We have developed a recombinant diphtheria toxin-human granulocyte macrophage colony-stimulating factor chimeric fusion protein (DTctGMCSF) that specifically targets GMCSF receptor-positive AML cells. This novel biotherapeutic agent induced rapid apoptotic cell death of chemotherapy-resistant AML cell lines and primary leukemic cells from treatment-refractory AML patients. Our results suggest that DTctGMCSF may be useful in the treatment of AML patients whose leukemia has recurred and developed resistance to contemporary chemotherapy programs.