Kamil Bojarczuk

Aminolevulinic Acid (ALA) as a Prodrug in Photodynamic Therapy of Cancer

Aminolevulinic acid (ALA) is an endogenous metabolite normally formed in the mitochondria from succinyl-CoA and glycine. Conjugation of eight ALA molecules yields protoporphyrin IX (PpIX) and finally leads to formation of heme. Conversion of PpIX to its downstream substrates requires the activity of a rate-limiting enzyme ferrochelatase. When ALA is administered externally the abundantly produced PpIX cannot be quickly converted to its final product - heme by ferrochelatase and therefore accumulates within cells. Since PpIX is a potent photosensitizer this metabolic pathway can be exploited in photodynamic therapy (PDT). This is an already approved therapeutic strategy making ALA one of the most successful prodrugs used in cancer treatment.

HDACi--going through the mechanisms.

Histone deacetylases inhibitors (HDACi) have recently emerged as potent antitumor treatment modality. They are currently tested in many phase I, II and III clinical trials as single agents as wells as in combination schemes. They have demonstrated promising antitumor activity and favorable clinical outcome. Histone deacetylases (HDACs) are involved in the process of epigenetic regulation of gene expression. Epigenetic changes are believed to be crucial for the onset and progression of cancer and have recently gained remarkable attention. Since epigenetic regulation of gene expression is a reversible process, targeting histone deacetylases provides a good rationale for anticancer therapy. The acetylation status of histones regulates the organization of chromatin and the access of transcription factors. Moreover, functions of many non-histone proteins are controlled by acetylation. The broad and complicated influences of HDACi on various molecular processes may account for the observed pleiotropic effects. In this review we summarize recent advances in the understanding of biology of HDACs and mechanism of action of their inhibitors.

Approaches to improve photodynamic therapy of cancer.

Photodynamic therapy (PDT) is a clinically approved method of tumor treatment. Its unique mechanism of action results from minimal invasiveness and high selectivity towards transformed cells. However, visible light used to excite most photosensitizers has rather limited ability to penetrate tissues resulting in insufficient destruction of deeply seated malignant cells. Therefore, novel strategies for further potentiation of the anticancer effectiveness of PDT have been developed. These include combined treatments with surgery, chemo- and radiotherapy, strategies targeting cytoprotective mechanisms induced in PDT-treated cells, as well as attempts aimed at enhancement of PDT-mediated antitumor immune response. Moreover, new photosensitizers and novel light sources are being developed. Impressive progress in nanotechnology and understanding of tumor cell biology rise hopes for further improvements in this elegant and promising method of cancer treatment.

BCR signaling inhibitors differ in their ability to overcome Mcl-1-mediated resistance of CLL B cells to ABT-199.

The Bcl-2 antagonist ABT-199 (venetoclax) has demonstrated promising clinical activity in patients with chronic lymphocytic leukemia (CLL). ABT-199 is strongly cytotoxic against unstimulated peripheral blood CLL cells in vitro but is much less effective against CLL cells that have received survival signals from the microenvironment. In particular, stimulation of CLL cells with CD40L results in substantial resistance mediated by induction of the antiapoptotic Bcl-2 family proteins Bcl-xL and Bfl-1. In this study, we investigated whether resistance to ABT-199 can be conferred by B-cell receptor (BCR) stimulation, which is another important survival signal from the leukemic microenvironment. We show that sustained BCR stimulation results in significant ABT-199 resistance, which correlates with induction of the antiapoptotic protein Mcl-1 and less consistently with downregulation of proapoptotic Bmf, Hrk, and BimEL A major role for Mcl-1 in conferring ABT-199 resistance is additionally supported by knockdown and enforced expression experiments with primary CLL cells. We further show that SYK, BTK, and phosphatidylinositol 3-kinase δ (PI3Kδ) inhibitors significantly downregulate Mcl-1, but with different efficacy. Complete Mcl-1 downregulation was consistently achieved only with SYK inhibitors R406 and GS-9973 (entospletinib), whereas the BTK inhibitor ibrutinib and the PI3Kδ inhibitor idelalisib in more than half of the cases had only a partial effect. The greater ability of SYK inhibitors to downregulate Mcl-1 correlated with their greater capacity to block BCR-mediated inactivation of GSK-3, a major negative regulator of Mcl-1. The finding that BCR signaling inhibitors differ in their ability to target Mcl-1 is relevant for the design of clinical trials combining these agents with ABT-199.

B-cell receptor pathway inhibitors affect CD20 levels and impair antitumor activity of anti-CD20 monoclonal antibodies

B-cell receptor pathway inhibitors affect CD20 levels and impair antitumor activity of anti-CD20 monoclonal antibodies

Bortezomib modulates surface CD20 in B-cell malignancies and affects rituximab-mediated complement-dependent cytotoxicity

Recent observations indicate that rituximab-resistant lymphoma cells exhibit upregulation of components of the ubiquitin-proteasome system (UPS). Therefore, proteasome inhibitors including the clinically approved bortezomib might influence the levels of CD20, a rituximab target antigen. We observed that incubation of tumor cells with rituximab leads to increased levels of ubiquitinated CD20. However, inhibition of the UPS is not associated with upregulation, but rather with a counterintuitive downregulation of surface CD20 levels that increases resistance of tumor cells to rituximab-mediated cytotoxicity. Although preliminary observations indicate that CD20 might be a substrate for two proteolytic systems, the mechanisms as well as significance of these findings require further studies.Unresponsiveness to rituximab treatment develops in many patients prompting elucidation of underlying molecular pathways. It was recently observed that rituximab-resistant lymphoma cells exhibit up-regulation of components of the ubiquitin-proteasome system (UPS). Therefore, we investigated in more detail the role of this system in the regulation of CD20 levels and the influence of proteasome inhibitors on rituximab-mediated complement-dependent cytotoxicity (R-CDC). We observed that incubation of Raji cells with rituximab leads to increased levels of ubiquitinated CD20. However, inhibition of the UPS was not associated with up-regulation of surface CD20 levels, although it significantly increased its ubiquitination. Short-term (24 hours) incubation of Raji cells with 10 or 20 nM bortezomib did not change surface CD20 levels, but sensitized CD20(+) lymphoma cells to R-CDC. Prolonged (48 hours) incubation with 20 nM bortezomib, or incubation with 50 nM bortezomib for 24 hours led to a significant decrease in surface CD20 levels as well as R-CDC. These effects were partly reversed by bafilomycin A1, an inhibitor of lysosomal/autophagosomal pathway of protein degradation. These studies indicate that CD20 levels are regulated by 2 proteolytic systems and that the use of proteasome inhibitors may be associated with unexpected negative influence on R-CDC.

B-cell receptor signaling in the pathogenesis of lymphoid malignancies

B-cell receptor (BCR) signaling pathway plays a central role in B-lymphocyte development and initiation of humoral immunity. Recently, BCR signaling pathway has been shown as a major driver in the pathogenesis of B-cell malignancies. As a result, a vast array of BCR-associated kinases has emerged as rational therapeutic targets changing treatment paradigms in B cell malignancies. Based on high efficacy in early-stage clinical trials, there is rapid clinical development of inhibitors targeting BCR signaling pathway. Here, we describe the essential components of BCR signaling, their function in normal and pathogenic signaling and molecular effects of their inhibition in vitro and in vivo.

Prenyltransferases Regulate CD20 Protein Levels and Influence Anti-CD20 Monoclonal Antibody-mediated Activation of Complement-dependent Cytotoxicity

Background: The influence of farnesyltransferase inhibitors (FTIs) on CD20 levels is unknown. Results: FTIs increase CD20 expression and improve rituximab-mediated activation of complement-dependent cytotoxicity. Conclusion: FTIs sensitize tumor cells to anti-CD20 mAbs. Significance: The combination of FTIs with anti-CD20 mAbs seems to be a reasonable therapeutic approach worth to be tested in patients with B-cell tumors. Anti-CD20 monoclonal antibodies (mAbs) are successfully used in the management of non-Hodgkin lymphomas and chronic lymphocytic leukemia. We have reported previously that statins induce conformational changes in CD20 molecules and impair rituximab-mediated complement-dependent cytotoxicity. Here we investigated in more detail the influence of farnesyltransferase inhibitors (FTIs) on CD20 expression and antitumor activity of anti-CD20 mAbs. Among all FTIs studied, L-744,832 had the most significant influence on CD20 levels. It significantly increased rituximab-mediated complement-dependent cytotoxicity against primary tumor cells isolated from patients with non-Hodgkin lymphomas or chronic lymphocytic leukemia and increased CD20 expression in the majority of primary lymphoma/leukemia cells. Incubation of Raji cells with L-744,832 led to up-regulation of CD20 at mRNA and protein levels. Chromatin immunoprecipitation assay revealed that inhibition of farnesyltransferase activity was associated with increased binding of PU.1 and Oct-2 to the CD20 promoter sequences. These studies indicate that CD20 expression can be modulated by FTIs. The combination of FTIs with anti-CD20 mAbs is a promising therapeutic approach, and its efficacy should be examined in patients with B-cell tumors.

Inhibitors of SRC kinases impair antitumor activity of anti-CD20 monoclonal antibodies

Clinical trials with SRC family kinases (SFKs) inhibitors used alone or in a combination with anti-CD20 monoclonal antibodies (mAbs) are currently underway in the treatment of B-cell tumors. However, molecular interactions between these therapeutics have not been studied so far. A transcriptional profiling of tumor cells incubated with SFKs inhibitors revealed strong downregulation of MS4A1 gene encoding CD20 antigen. In a panel of primary and established B-cell tumors we observed that SFKs inhibitors strongly affect CD20 expression at the transcriptional level, leading to inhibition of anti-CD20 mAbs binding and increased resistance of tumor cells to complement-dependent cytotoxicity. Activation of the AKT signaling pathway significantly protected cells from dasatinib-triggered CD20 downregulation. Additionally, SFKs inhibitors suppressed antibody-dependent cell-mediated cytotoxicity by direct inhibition of natural killer cells. Abrogation of antitumor activity of rituximab was also observed in vivo in a mouse model. Noteworthy, the effects of SFKs inhibitors on NK cell function are largely reversible. The results of our studies indicate that development of optimal combinations of novel treatment modalities with anti-CD20 mAbs should be preceded by detailed preclinical evaluation of their effects on target cells.

The Mutual Interactions between Mesenchymal Stem Cells and Myoblasts in an Autologous Co-Culture Model

Both myoblasts and mesenchymal stem cells (MSC) take part in the muscle tissue regeneration and have been used as experimental cellular therapy in muscular disorders treatment. It is possible that co-transplantation approach could improve the efficacy of this treatment. However, the relations between those two cell types are not clearly defined. The aim of this study was to determine the reciprocal interactions between myoblasts and MSC in vitro in terms of the features important for the muscle regeneration process. Primary caprine muscle-derived cells (MDC) and bone marrow-derived MSC were analysed in autologous settings. We found that MSC contribute to myotubes formation by fusion with MDC when co-cultured directly, but do not acquire myogenic phenotype if exposed to MDC-derived soluble factors only. Experiments with exposure to hydrogen peroxide showed that MSC are significantly more resistant to oxidative stress than MDC, but a direct co-culture with MSC does not diminish the cytotoxic effect of H2O2 on MDC. Cell migration assay demonstrated that MSC possess significantly greater migration ability than MDC which is further enhanced by MDC-derived soluble factors, whereas the opposite effect was not found. MSC-derived soluble factors significantly enhanced the proliferation of MDC, whereas MDC inhibited the division rate of MSC. To conclude, presented results suggest that myogenic precursors and MSC support each other during muscle regeneration and therefore myoblasts-MSC co-transplantation could be an attractive approach in the treatment of muscular disorders.