Combined biodifferentiating and antiangiogenic oral metronomic therapy is feasible and effective in relapsed solid tumors in children: single-center pilot study

BACKGROUND

To outline an outpatient-based treatment for children with relapsed solid tumors, who already have been extensively pretreated, we defined a 4-drug protocol named COMBAT (combined oral maintenance biodifferentiating and antiangiogenic therapy). Using this protocol, we performed a pilot study to determine its feasibility in children with relapsed and/or high-risk pediatric solid tumors.

PATIENTS AND METHODS

22 children received the COMBAT protocol. Treatment consisted of daily celecoxib administration along with daily 13-cisretinoic acid (2 weeks on / 2 weeks off) and cycles of metronomic temozolomide (90 mg/m2 for 42 days) and low-dose etoposide (21 days). The treatment was scheduled for a period of 1 year.

RESULTS

9 of the 14 patients assessable for response demonstrated evidence of treatment benefit manifested as prolonged disease stabilization or response. The protocol medication was well tolerated with very good compliance. Only minimal side effects where observed which responded to dose modification or local therapy.

CONCLUSIONS

The COMBAT regimen is well tolerated by patients with intensive prior therapy including myeloablative regimens. Favorable responses observed in this cohort of patients support the further exploration of this and/or similar strategies in the treatment of pediatric solid tumors.

Differentiation of HL-60 myeloid leukemia cells induced by all-trans retinoic acid is enhanced in combination with caffeic acid

We investigated a possible enhancement of all-trans retinoic acid (ATRA)-induced differentiation of HL-60 human myeloid leukemia cells by caffeic acid (CA), a widely distributed plant phenolic compound. Our results showed that CA, in the concentration of 13 or 52 micro M, had no or minimal influence on cell differentiation, whereas the differentiating activity of ATRA was potentiated by CA treatment. We proved, using flow cytometric detection of the CD66b surface molecule, a synergistic effect of CA: at day 10, 18.3% of CD66b-positive cells were detected after treatment with ATRA only, and 33% when CA and ATRA were combined together. NBT-assay confirmed that this additive effect of CA on ATRA-induced differentiation. Proliferating activity as assessed by MTT-assay was generally not affected by CA at given concentrations. However, cell proliferation was significantly reduced by 52 micro M CA at 96-h intervals. This effect was markedly enhanced when CA, at both concentrations, and ATRA were combined. The possibility to enhance the differentiation potential of ATRA by CA may improve outcomes in the therapy of acute promyelocytic leukemia.

Specific cytoskeleton changes during apoptosis accompanying induced differentiation of HL-60 myeloid leukemia cells

Changes in actin filaments and microtubules were studied in the human myeloid leukemia HL-60 cell line during the process of apoptotic cell death accompanying induced differentiation. These cytoskeleton changes were assessed during a 6-day cultivation in the presence of 10(-6) M all-trans retinoic acid (ATRA), a specific inductor of both differentiation into granulocytes and apoptosis, or during a 18-day cultivation in the presence of 1.6 nM phorbol myristylacetate (PMA), which induces differentiation into macrophages. The processes were studied at the morphological level by fluorescence microscopy and, quantitatively, by flow cytometry. The results showed that the actin cytoskeleton underwent specific structural changes during the apoptotic process, but microtubules were not actively involved. In the initial stages of apoptosis, a fine meshwork of actin filaments turned into actin granules that, in the final stages, were transformed into a network of long actin fibres distributed throughout the cytoplasm. These actin structures were considered to play an active role in two main morphological events of apoptosis - formation of blebs and final cell disintegration into apoptotic bodies. In addition, high proportion of cells with apoptotic nuclei and completely destroyed actin structures were found in the differentiating ATRA-treated cell population. Flow cytometric measurement of cytoskeletal proteins content confirmed all these observed changes. Alterations and rearrangements of both cytoskeletal structures are common for the apoptotic cell death of HL-60 cells and they are independent on the course of differentiation.

Effect of retinoic acid on the actin cytoskeleton in HL-60 cells

The cytoskeleton, in addition to its structural and kinetic functions, is also involved in modulating signal transfer in cell proliferation, differentiation and death. In some myeloid leukemic cell lines, the process of cell differentiation accompanied by apoptosis, can be induced by all-trans retinoic acid (ATRA). In this report, we describe the morphological changes in actin cytoskeleton, taking place during apoptosis in cells of the human leukemic HL-60 cell line. By using fluorescent microscopy, the morphology of microfilaments and the proportion of apoptotic cells in the cell populations untreated or treated with 10(-6) M ATRA were detected. Interphase HL-60 cells showed aggregations of short, thick microfilament bundles in the region between the plasma membrane and the nucleus. In comparison with both interphase and mitotic cells, the cells with apoptotic nuclear fragmentation showed a different organisation of the actin cytoskeleton. The following types of F-actin structures were observed: (i) Cells with a high number of large dots/patches of F-actin under the plasma membrane. These dots might be localised only in the part of the cell or occurred under the whole plasma membrane. This arrangement was often associated with a diffuse signal for F-actin. (ii) Cells with 3D-network of F-actin fibres through the cytoplasm between remnants of the cell nucleus. This 3D-structure probably played an important active role in the process of apoptotic bodies formation. (iii) Cells without any detectable signal for F-actin or cells with only a very low F-actin signal. Both of these showed typical apoptotic collapse of chromatin. It is concluded that the actin cytoskeleton is a dynamic structure actively involved in the executive phase of the process of apoptosis. It is suggested that the rearrangement of the microfilament network and its subsequent degradation are necessary for the main morphological changes of apoptotic cells, i.e., plasma membrane blebbing and apoptotic bodies formation.