Phase I trial of CYT997, a novel cytotoxic and vascular-disrupting agent.

BACKGROUND: CYT997 is a novel microtubule inhibitor and vascular-disrupting agent with marked preclinical anti-tumour activity. METHODS: This phase I dose-escalation study assessed the safety, tolerability, pharmacokinetics and pharmacodynamics of CYT997 administered by continuous intravenous infusion over 24 h every 3 weeks to patients with advanced solid tumours. RESULTS: Thirty-one patients received CYT997 over 12 dose levels (7-358 mg m(-2)). Doses up to 202 mg m(-2) were well tolerated. Dose-limiting toxicities were observed at 269 and 358 mg m(-2), consisting of grade 3 prolonged corrected QT interval in two patients and grade 3 hypoxia and grade 4 dyspnea in one patient. All toxicities were reversible. The pharmacokinetics of CYT997 were linear over the entire dose range. Dynamic contrast-enhanced magnetic resonance imaging scans showed significant changes in tumour K(trans) values consistent with vascular disruption in 7 out of 11 evaluable patients treated at CYT997 doses of >or=65 mg m(-2). Moreover, plasma levels of von Willebrand factor and caspase-cleaved cytokeratin-18 increased post-treatment at higher dose levels. Among 22 patients evaluable for response, 18 achieved stable disease for >2 cycles. CONCLUSIONS: CYT997 was well tolerated at doses that were associated with pharmacodynamic evidence of vascular disruption in tumours.

Small-molecule Bcl-2 inhibitors sensitise tumour cells to immune-mediated destruction.

The cytotoxic effects of anticancer immune cells are mediated by perforin/granzyme-B, Fas ligand and tumour necrosis factor-related apoptosis-inducing ligand (TRAIL), and therefore depend on intact apoptotic responses in target tumour cells. As killing by all three of these mechanisms is blocked by the frequently overexpressed antiapoptotic oncoprotein Bcl-2, we hypothesised that coexposure to a Bcl-2 inhibitor might enhance anticancer immune responses. We evaluated this in U937 lymphoma cells, and A02 melanoma cells, which both show strong Bcl-2 expression. Valpha24(+) Vbeta11(+) natural killer T (NKT) cells expanded from peripheral blood of normal donors (n=3) were coincubated with PKH26-labelled U937 cells, and cytotoxicity was determined by flow cytometry after annexin-V-FITC and 7-AAD staining. In all cases, addition of the HA14-1 small-molecule Bcl-2 inhibitor to the cocultures significantly increased apoptosis in the target U937 cells. Using a similar assay, killing of A02 cells by the cytotoxic T-lymphocyte clone 1H3 was shown to be amplified by coexposure to the potent small-molecule Bcl-2 inhibitor ABT-737. Experiments with immune effectors preincubated with concanamycin-A suggested that sensitisation to perforin/granzyme-B may underlie enhanced target-cell killing observed in the presence of Bcl-2 inhibitors. We conclude that immune destruction of malignant cells can be amplified by molecular interventions that overcome Bcl-2-mediated resistance to apoptosis.

HA14-1 selectively induces apoptosis in Bcl-2-overexpressing leukemia/lymphoma cells, and enhances cytarabine-induced cell death.

The Bcl-2 oncoprotein is commonly overexpressed in hematological malignancy, where it promotes the survival of neoplastic cells. Recently, a small molecule (HA14-1) was reported to bind the surface pocket of Bcl-2 that mediates antiapoptotic interactions, triggering apoptosis in a Bcl-2-transfected cell line. We investigated the activity of this compound in a panel of malignant hematopoietic cell lines. Consistent with its proposed role as a Bcl-2 inhibitor, HA14-1 was most cytotoxic in lines expressing high levels of Bcl-2. In addition, at lower concentrations (5-12.5 muM), the compound predominantly triggered apoptosis. However, at concentrations two-fold higher than this and above, increasing primary necrosis was observed, suggesting the onset of interactions supplementary to Bcl-2 inhibition. In experiments on primary cells, 25 muM HA14-1 induced extensive apoptosis in acute leukemic blasts, but also suppressed normal hematopoietic colony formation to <50% of baseline. Importantly, low-concentration HA14-1 (5 muM) was nontoxic to normal colony-forming cells, whereas it enhanced the cytotoxicity of the antileukemia drug cytarabine in Bcl-2-positive lymphoblastic leukemia cells. In conclusion, our results indicate that HA14-1 at low concentration selectively triggers apoptosis in malignant hematopoietic cells that overexpress Bcl-2. Agents of this class may have particular utility in combination with cytotoxic chemotherapy drugs.

Characterization of the Epha1 receptor tyrosine kinase: expression in epithelial tissues.

The Eph family of receptor tyrosine kinases plays a crucial role during development and is implicated in oncogenesis. Using a partial cDNA clone of an Eph-related kinase (Esk) we isolated the complete coding region of a gene which we show to be murine EphA1 by both structural and functional criteria. The chromosomal localization is shown to be syntenic to hEphA1 and the genomic organization also shows distinct features found in the hEphA1 gene. Functionally, in keeping with findings for the human homologue, both soluble recombinant and "native" mEphA1 show preferential binding to ephrin A1. However, we also observed significant binding to other A-type ligands as has been observed for other Eph receptors. We analysed the expression of mEphA1 mRNA by in situ hybridization on tissue sections. mEphA1 was expressed in epithelial elements of skin, adult thymus, kidney and adrenal cortex. Taken together with previous Northern blotting data these results suggest that mEphA1 is expressed widely in differentiated epithelial cells.

Matched-pair analysis of peripheral blood stem cells compared to marrow for allogeneic transplantation.

We performed a case-control analysis of 42 patients with advanced leukemia or MDS comparing peripheral blood stem cell (PBSC) with marrow grafts (BMT) from HLA-matched sibling donors. PBSC were mobilized with G-CSF (7.5 microg/kg/day) and yielded a median of 6.7 x 10(6) CD34+ cells/kg (range, 1.6-15.0) and 2.7 x 10(8) CD3+ cells/kg (range, 1.1-7.1) vs marrow grafts with a median of 2.0 x 10(8) nucleated cells/kg (range, 1.8-2.2). Recovery was significantly faster after PBSCT compared to BMT, with a median of 17 (range, 12-26) vs 26 (range, 16-36) days, respectively, to neutrophils >0.5 x 10(9)/l (P < 0.01), and 22 (range, 12->60) vs 42 (range, 18->60) days, for platelet recovery (P < 0.01). Transplantation of >/=7 x 10(6) CD34+ cells/kg accelerated recovery to >20 x 10(9) l platelets; median 17 days (range, 12-19) vs 23 days (range, 17-36) for those receiving <7 x 10(6)/kg (P = 0.01). PBSC and marrow recipients had similar risks of grades II-IV or III-IV acute GVHD or extensive chronic GVHD (all P > 0.3). At 1 year after PBSCT and BMT, the risk of relapse was 41% and 32%, respectively (P = 0.47), and the probability of survival was 46% and 48%, respectively (P = 0.70). HLA-matched sibling PBSCT resulted in faster neutrophil and platelet engraftment compared to BMT, with no subsequent differences in acute or chronic GVHD, relapse or survival. A minimum of 7 x 10(6) CD34+ cells/kg in PBSC grafts may be required for very rapid platelet engraftment. Bone Marrow Transplantation (2000) 26, 723-728.

Fas ligand is highly expressed in acute leukemia and during the transformation of chronic myeloid leukemia to blast crisis.

Fas ligand (FasL) induces apoptosis in susceptible Fas-bearing cells and is critically involved in regulating T-cell immune responses. It is highly expressed in several human malignancies, and a role in the suppression of antitumor immune responses has been suggested. We evaluated FasL expression in leukemia and normal hematopoietic cells. By Western blotting, all acute leukemic cell lines (n = 9) and primary samples of acute leukemic marrow (n = 4) revealed high levels of FasL. In contrast, much weaker signals were observed in samples of normal marrow (n = 5), and either weak or intermediate expression was seen in chronic myeloid leukemia (CML) in chronic phase (n = 7). Additional leukemic samples were examined by immunohistochemistry. Staining for FasL was negative in 7 of 9 cases of chronic-phase CML, whereas all cases of CML in blast crisis (n = 6), acute lymphoblastic leukemia (n = 6), and acute myeloid leukemia (n = 11) stained strongly in 60 to 100% of nucleated cells. FasL+ leukemic cell lines did not trigger Fas-mediated apoptosis in either Jurkat cells or activated human T lymphocytes, possibly related to the intracellular location of the ligand. Western analysis of normal marrow subpopulations revealed that most FasL in marrow mononuclear cells was expressed by CD7+ lymphocytes. FasL also was strongly expressed in CD34+ hematopoietic progenitor cells from both normal and chronic-phase CML marrow, suggesting a correlation with primitive maturation stage. In summary, high levels of FasL expression were associated with aggressive biologic behavior in leukemia, including transformation of CML to blast crisis. This could potentially represent a response to loss of proapoptotic Fas signaling, which is known to occur in acute leukemic blasts.

Embryonic stem cells express multiple Eph-subfamily receptor tyrosine kinases.

Eph and its homologues form the largest subfamily of receptor tyrosine kinases. Normal expression patterns of this subfamily indicate roles in differentiation and development, whereas their overexpression has been linked to oncogenesis. This study investigated the potential role of Eph-related molecules during very early embryonic development by examining their expression in embryonic stem (ES) cells and embryoid bodies differentiated from ES cells in vitro. By use of a strategy based on reverse transcriptase-mediated PCR, nine clones containing Eph-subfamily sequence were isolated from ES cells. Of these, eight were almost identical to one of four previously identified molecules (Sek, Nuk, Eck, and Mek4). However, one clone contained sequence from a novel Eph-subfamily member, which was termed embryonic stem-cell kinase or Esk. Northern analysis showed expression of Esk in ES cells, embryoid bodies, day 12 mouse embryos, and some tissues of the adult animal. Levels of expression were similar in ES cells and embryoid bodies. By comparison, Mek4 showed no significant transcription in the ES cell cultures by Northern analysis, whereas Eck displayed stronger signals in ES cells than in the embryoid bodies. These results suggest that Eph-subfamily molecules may play roles during the earliest phases of embryogenesis. Furthermore, the relative importance of different members of this subfamily appears to change as development proceeds.

Phase II study of glycosylated recombinant human granulocyte colony-stimulating factor after HLA-identical sibling bone marrow transplantation.

BACKGROUND: The lengthy period of neutropenia which follows allogeneic bone marrow transplantation (BMT) results in significant morbidity and some mortality. Recombinant human granulocyte colony-stimulating factor (rhuG-CSF) effectively reduces neutropenia and morbidity when given after autologous BMT, but has not been adequately investigated in allografts. AIMS: To assess the tolerability, safety and efficacy of rhuG-CSF after allogeneic BMT. METHODS: rhuG-CSF was administered to 13 adult patients with haematological malignancies after HLA-identical sibling BMT. Five micrograms/kg of rhuG-CSF was given daily by subcutaneous bolus injection, commencing four hours after marrow infusion and continuing until the neutrophil count was > or = 1.0 x 10(9)/L on three consecutive days. Graft-versus-host disease (GVHD) prophylaxis was cyclosporin and short-course methotrexate (days 1, 3, 6 and 11). Prophylactic intravenous (IV) antibiotics were administered from the onset of neutropenia. The control group consisted of patients with comparable diagnoses, transplanted before and after the current study using identical supportive care and GVHD prophylaxis policies. RESULTS: Although time to recovery of the neutrophil count to > 0.1 x 10(9)/L was similar, the rhuG-CSF-treated patients experienced accelerated recovery to > 0.5 x 10(9)/L, which occurred at a median of 15 days (range 11-21) after marrow infusion in study patients compared to 18.5 days (range 14-41) in the controls (p = 0.04). No significant differences were detected in any of the indices of transplant-related morbidity examined, including the number of days of fever, the incidence of culture-positive infections, the usage of antibiotics, the requirement for parenteral nutrition and IV morphine, the maximum severity of mucositis and GVHD, and the day of discharge. CONCLUSION: Within the context of this study, rhuG-CSF had limited impact on the clinical outcome of HLA-identical sibling BMT.

Combined chemotherapy and granulocyte colony-stimulating factor (G-CSF) mobilise large numbers of peripheral blood progenitor cells in pretreated patients.

The aim of this study was to examine the effect of G-CSF given after salvage chemotherapy on the mobilisation of peripheral blood progenitor cells (PBPC) in pretreated patients. Seven patients with relapsed or refractory non-Hodgkin's lymphoma (NHL) were treated with methotrexate, cyclophosphamide, cytarabine, etoposide and dexamethasone. G-CSF was given at a dose of 3.8-7.2 micrograms/kg (1-2 ampoules) daily by subcutaneous injection from the onset of neutropenia (< 1.0 x 10(9)/L). A median of 3 leukaphereses was performed when the white cell count was recovering. The median number of granulocyte-macrophage colony-forming cells (GM-CFC) collected was 99 x 10(4)/kg per leucapheresis (range 19-800) or 260 x 10(4)/kg in total per patient (110-1800). Six patients underwent myeloablative chemotherapy with PBPC rescue. No autologous bone marrow or growth factors post-PBPC infusion were administered. The median duration of severe neutropenia (< 0.5 x 10(9)/L) was 8.5 days (range 5-10) and to recovery of neutrophils post-PBPC infusion was 11.5 days (10-15). Severe thrombocytopenia (< 20 x 10(9)/L) was present for 4 days (range 1-5) and the median number of days post-infusion to platelet-transfusion independence was 9 (6-12). In conclusion, G-CSF combined with chemotherapy mobilised large numbers of PBPC for subsequent autotransplantation in pretreated patients with NHL. A single leukapheresis procedure may be sufficient following this protocol.