Chemosensitization by phenothiazines in human lung cancer cells: impaired resolution of γH2AX and increased oxidative stress elicit apoptosis associated with lysosomal expansion and intense vacuolation.

Chemotherapy resistance poses severe limitations on the efficacy of anti-cancer medications. Recently, the notion of using novel combinations of 'old' drugs for new indications has garnered significant interest. The potential of using phenothiazines as chemosensitizers has been suggested earlier but so far our understanding of their molecular targets remains scant. The current study was designed to better define phenothiazine-sensitive cellular processes in relation to chemosensitivity. We found that phenothiazines shared the ability to delay γH2AX resolution in DNA-damaged human lung cancer cells. Accordingly, cells co-treated with chemotherapy and phenothiazines underwent protracted cell-cycle arrest followed by checkpoint escape that led to abnormal mitoses, secondary arrest and/or a form of apoptosis associated with increased endogenous oxidative stress and intense vacuolation. We provide evidence implicating lysosomal dysfunction as a key component of cell death in phenothiazine co-treated cells, which also exhibited more typical hallmarks of apoptosis including the activation of both caspase-dependent and -independent pathways. Finally, we demonstrated that vacuolation in phenothiazine co-treated cells could be reduced by ROS scavengers or the vacuolar ATPase inhibitor bafilomycin, leading to increased cell viability. Our data highlight the potential benefit of using phenothiazines as chemosensitizers in tumors that acquire molecular alterations rendering them insensitive to caspase-mediated apoptosis.

Effect of anticancer drugs on production of transforming growth factor and expression of p53 AND Bcl-2 proteins by MCF-7 and T47D cell lines of human breast carcinoma.

AIM: To compare the capability of methotrexate, cisplatin, doxorubicine and vincristine to induce production of the transforming growth factor beta(1) (TGF-beta(1)) in two cell lines - MCF-7 and T47D - of human breast carcinoma, as well as to study sensitivity of these cells to TGF-beta(1) and mentioned anticancer drugs. MATERIALS AND METHODS: ELISA for detection of TGF-beta content in conditioned culture media and Western-blot analysis of the proapoptotic p53 and antiapoptotic Bcl-2 proteins were applied. RESULTS: T47D cells showing higher resistance to growth inhibiting effect of TGF-beta(1) were also refractory to cisplatin. There was no difference between MCF-7 and T47D cells in their sensitivity to methotrexate and doxorubicine, although T47D cells were more sensitive to vincristine. It was found that methotrexate and vincristine did not affect TGF-beta(1) production, while doxorubicine used at a dose of 1-100 ug/ml, significantly induced TGF-beta(1) production in both cell lines. p53 expression in T47D cells was higher than in MCF-7 cells where only doxorubicin induced strongly p53 expression. It should be noted, that Bcl-2 was better expressed in MCF-7 cells, while it was almost undetectable in T47D cells. CONCLUSION: In cells of human mammary carcinoma of MCF-7 and T47D lines doxorubicine, unlike vincristine and methotrexate, in dose depending manner induces production of TGF-beta(1). TGF-beta(1) production in carcinoma cells was associated with doxorubicine-mediated p53 expression in MCF-7 cells or high basal level of p53 in T47D cells. The cells of MCF-7 line were more sensitive to growth inhibition by exogenous TGF-beta(1) and to cisplatine action than T47D cells, but there was no difference between these cell lines in sensitivity to other anticancer drugs.

Smad2 suppresses the growth of Mv1Lu cells subcutaneously inoculated in mice.

Smad2 and Smad3 are intracellular signal transduction proteins of importance in transforming growth factor-beta (TGFbeta)-mediated inhibition of epithelial cell proliferation. Inactivating mutations in the Smad2 and Smad3 genes have been found in various human malignancies. Here, we show that expression of Smad2 leads to the inhibition of growth of Mv1Lu cells inoculated with Matrigel subcutaneously (s.c.) in severe combined immunodeficient (SCID) mice. In histological appearance, the Matrigel plugs with Smad2-transfected cells showed strongly reduced cell density, proliferation and angiogenesis compared with the small tumour nodules of similar size formed by the vector- or Smad3-transfected cells. The histological appearance of vector- and Smad3-transfected cells inoculated in mice was identical. Overexpression of Smad2 and Smad3 in Mv1Lu cells led to the inhibition of cell growth in three-dimensional cultures when compared with vector-transfected cells. Overexpression of Smad2 and Smad3 also decreased the hyperphosphorylation of pRb in Smad-transfected cells. Thus, increased expression of Smad2 leads to inhibition of Mv1Lu cell proliferation and a reduction in the growth of the Smad2-expressing cells inoculated in mice.

Regulation of Smad signaling by protein kinase C.

Cross talk between transforming growth factor b(TGF-b) serine/threonine kinase receptor signaling and tyrosine kinase receptor signaling modulates cell responsiveness to polypeptide growth factors regulating cell proliferation, differentiation, and apoptosis. Here we provide a mechanism through which Smad-dependent TGF-b signaling is modulated by protein kinase C (PKC). PKC, for example, is activated downstream of tyrosine kinase receptors. We show that PKC directly phosphorylates receptor-regulated Smad proteins. This phosphorylation abrogates the ability of Smad3 to bind directly to DNA, which leads to subsequent inability to mediate transcriptional responses dependent on the direct binding of Smad3 to DNA. Interference with PKC regulation of Smad functions increased cell sensitivity to transformation by the tumor promoter phorbol 12-myristate 13-acetate (PMA). PKC-dependent phosphorylation of Smad3 was found also to be a key event in the PMA-dependent inactivation of TGF-b-stimulated cell death. Thus, PKC-dependent phosphorylation of Smad3 leads to down-regulation of the growth inhibitory and apoptotic action of TGF-b.

Cisplatin-resistant derivatives of murine L1210 leukemia cells are not susceptible to growth-inhibiting and apoptosis-inducing actions of transforming growth factor-beta1.

Murine L1210 leukemia cells possessing an increased resistance to cisplatin were found to be refractory to transforming growth factor (TGF)-beta1-induced growth inhibition, while the parental L1210 cells were strongly inhibited by this cytokine. Growth inhibition was estimated on the basis of [3H]thymidine incorporation, cell counting and colony-forming assay. Cisplatin-resistant L1210 cells were also shown to be much more resistant than the parental cells to both cisplatin- and TGF-beta1-induced apoptosis. These results suggest the existence of cross-resistance to cisplatin and TGF-beta1 in the studied leukemia cells.