Oncolytic adenoviruses: A thorny path to glioma cure.

Glioblastoma Multiforme (GBM) is a rapidly progressing brain tumor. Despite the relatively low percentage of cancer patients with glioma diagnoses, recent statistics indicate that the number of glioma patients may have increased over the past decade. Current therapeutic options for glioma patients include tumor resection, chemotherapy, and concomitant radiation therapy with an average survival of approximately 16 months. The rapid progression of gliomas has spurred the development of novel treatment options, such as cancer gene therapy and oncolytic virotherapy. Preclinical testing of oncolytic adenoviruses using glioma models revealed both positive and negative sides of the virotherapy approach. Here we present a detailed overview of the glioma virotherapy field and discuss auxiliary therapeutic strategies with the potential for augmenting clinical efficacy of GBM virotherapy treatment.

Studies of some mechanisms of drug resistance in chronic myeloid leukemia (CML).

CML is the myeloproliferative disorder connected with the specific chromosome translocation (9;22) and occurrence of the fusion gene/protein BCR-ABL. BCR-ABL protein is believed to inhibit apoptosis and to cause drug resistance. We investigated the correlation of two different forms of BCR-ABL mRNA in 94 pts with their overall survival. It was found that b2a2 (but not b2a3) mRNA expression correlates with longer survival of patients treated with chemotherapy. We did not find an influence of different types of BCR/ABL mRNA on the survival of pts treated with interferon-alpha. FAS/APO-1 antigen was expressed by the cells of 34% of the pts in CML blast crisis (BC) and directly correlated with the the expression of CD34, CD13 and CD14 differentiation antigens. FAS/APO-1 non-expression correlated with higher rate of remissions in BC. We investigated P-glyco-protein (Pgp) expression and functional activity in 40 BC CML pts. 2-fold shorter survival was found in the pts with Pgp expression. Pgp expression strongly correlated with CD13 antigen. Consecutive studies of pts in BC CML show that Pgp expressing cells often do not multiply in the course of BC CML. We postulate that Pgp may be regarded as differentiation marker of the cells and the unfavorable prognostic factor in BC CML.

Distinct effects of various p53 mutants on differentiation and viability of human K562 leukemia cells.

Mutations of the p53 tumor suppressor are often observed in various human tumors, including blast crisis of chronic myelogenous leukemia (CML). The pattern of p53 mutations in CML shows some peculiarities compared with majority of other malignancies. In particular, the substitutions at codon 273, one of the most common p53 alterations in various tumors, are not characteristic of CML. To test whether the distinctions in the pattern of p53 mutations are connected with some peculiarities of the biological effects of different mutant proteins in leukemic cells, we obtained and analyzed a panel of human K562 cell sublines expressing various exogenous p53; human Pro156, His175, His194, Trp248, and His273, or murine temperature-sensitive (ts) Val135 that has properties of mutant protein at 37 degrees C, but shows activities of the wild-type (wt) p53 at 32 degrees C. We have found that expression of wt-p53 enhanced the dependence of cells on growth/survival factors. Incubation of sparse (< 10(5) cells per/ml) K562/Val135 cultures at 32 degrees C caused apoptosis. In media conditioned by cells of different origin (K562, colorectal carcinoma LIM1215, Rat1 fibroblasts) the p53-dependent apoptosis was inhibited. Under such conditions the expression of ts-wt-p53 was accompanied by dramatic increase in the number of cells producing specific markers of erythroid differentiation-GlycPhA and Ag-Eb. Unlike to the wt-p53, the majority of tumor-derived mutant p53 (Pro156, His175, His194) increased cell survival in low serum and decreased the number of cells expressing Glyc-PhA, CD9, CD15, and CD71 differentiation antigens. On the other hand, expression of His273-p53 caused significant augmentation in the number of CD9-positive cells and enhanced the dependence on growth/survival factors that are present in serum or conditioned media. The data obtained allow to suggest that an unusual pattern of p53 mutations in CML reflects some peculiarities of biological effects of certain mutant proteins on differentiation and viability of leukemic cells.

Studies of P-glycoprotein in chronic myelogenous leukaemia patients: expression, activity and correlations with CD34 antigen.

Over-expression of the P-glycoprotein (Pgp), transmembrane drug efflux pump, has been shown to cause multidrug resistance of tumour cells (MDR). To investigate the clinical significance of Pgp expression for chronic myeloid leukaemia (CML) diagnosis and monitoring we have studied 38 CML patients in various phases of the disease (chronic phase, CP; accelerated phase, AP; blast crisis, BC). Anti-Pgp monoclonal antibody UIC2 and FACScan analysis were used. Pgp functional activity was investigated by evaluation of verapamil influence upon rhodamine 123 efflux from the cells. Correlations between Pgp and CD34 expression were investigated. In CP, Pgp-expressing cells were found in 2/14 patients; in one of them Pgp proved to be non-functional. There were few Pgp-expressing cells in AP cases. The group of BC patients consisted of cases resistant to chemotherapy. This gave us the opportunity to consider whether drug resistance of BC CML patients is preferentially connected with Pgp-mediated MDR. 11/22 BC patients had 20% or more of Pgp-expressing blasts in the peripheral blood. In all four Pgp+ BC cases studied for Pgp activity this protein was functional. Only 4/22 BC patients demonstrated large (40% or more) fractions of Pgp+ blasts. Moreover, sequential studies of 11 BC CML patients during treatment revealed an increase in the number of Pgp-expressing cells in only two cases. This suggests that Pgp+ cells did not often accumulate in BC CML patients due to chemotherapy and are the cause of drug resistance in only a few cases. A positive correlation between Pgp and CD34 expression was found (r = 0.69; P = 0.0004). 3/22 BC CML patients had large fractions of both Pgp+ and CD34+ blasts in their peripheral blood. The BC CML patients with this immunophenotype of blast cells may represent a subtype of BC CML resistant to treatment due to Pgp overexpression.