Dianhydrogalactitol Overcomes Multiple Temozolomide Resistance Mechanisms in Glioblastoma.

Glioblastoma (GBM) is the most frequent and aggressive primary tumor type in the central nervous system in adults. Resistance to chemotherapy remains one of the major obstacles in GBM treatment. Identifying and overcoming the mechanisms of therapy resistance is instrumental to develop novel therapeutic approaches for patients with GBM. To determine the major drivers of temozolomide (TMZ) sensitivity, we performed shRNA screenings in GBM lines with different O6-methylguanine-DNA methyl-transferase (MGMT) status. We then evaluated dianhydrogalactitol (Val-083), a small alkylating molecule that induces interstrand DNA crosslinking, as a potential treatment to bypass TMZ-resistance mechanisms. We found that loss of mismatch repair (MMR) components and MGMT expression are mutually exclusive mechanisms driving TMZ resistance in vitro Treatment of established GBM cells and tumorsphere lines with Val-083 induces DNA damage and cell-cycle arrest in G2-M phase, independently of MGMT or MMR status, thus circumventing conventional resistance mechanisms to TMZ. Combination of TMZ and Val-083 shows a synergic cytotoxic effect in tumor cells in vitro, ex vivo, and in vivo We propose this combinatorial treatment as a potential approach for patients with GBM.

Dianhydrogalactitol synergizes with topoisomerase poisons to overcome DNA repair activity in tumor cells.

1,2:5,6-Dianhydrogalactitol (DAG) is a bi-functional DNA-targeting agent currently in phase II clinical trial for treatment of temozolomide-resistant glioblastoma (GBM). In the present study, we investigated the cytotoxic activity of DAG alone or in combination with common chemotherapy agents in GBM and prostate cancer (PCa) cells, and determined the impact of DNA repair pathways on DAG-induced cytotoxicity. We found that DAG produced replication-dependent DNA lesions decorated with RPA32, RAD51, and γH2AX foci. DAG-induced cytotoxicity was unaffected by MLH1, MSH2, and DNA-PK expression, but was enhanced by knockdown of BRCA1. Acting in S phase, DAG displayed selective synergy with topoisomerase I (camptothecin and irinotecan) and topoisomerase II (etoposide) poisons in GBM, PCa, and lung cancer cells with no synergy observed for docetaxel. Importantly, DAG combined with irinotecan treatment enhanced tumor responses and prolonged survival of tumor-bearing mice. This work provides mechanistic insight into DAG cytotoxicity in GBM and PCa cells and offers a rational for exploring combination regimens with topoisomerase I/II poisons in future clinical trials.

Dianhydrogalactitol induces replication-dependent DNA damage in tumor cells preferentially resolved by homologous recombination.

1,2:5,6-Dianhydrogalactitol (DAG) is a bifunctional DNA-targeting agent causing N7-guanine alkylation and inter-strand DNA crosslinks currently in clinical trial for treatment of glioblastoma. While preclinical studies and clinical trials have demonstrated antitumor activity of DAG in a variety of malignancies, understanding the molecular mechanisms underlying DAG-induced cytotoxicity is essential for proper clinical qualification. Using non-small cell lung cancer (NSCLC) as a model system, we show that DAG-induced cytotoxicity materializes when cells enter S phase with unrepaired N7-guanine DNA crosslinks. In S phase, DAG-mediated DNA crosslink lesions translated into replication-dependent DNA double-strand breaks (DSBs) that subsequently triggered irreversible cell cycle arrest and loss of viability. DAG-treated NSCLC cells attempt to repair the DSBs by homologous recombination (HR) and inhibition of the HR repair pathway sensitized NSCLC cells to DAG-induced DNA damage. Accordingly, our work describes a molecular mechanism behind N7-guanine crosslink-induced cytotoxicity in cancer cells and provides a rationale for using DAG analogs to treat HR-deficient tumors.

Dianhydrogalactitol, a potential multitarget agent, inhibits glioblastoma migration, invasion, and angiogenesis.

The complexity of cancer has led to single-target agents exhibiting lower-than-desired clinical efficacy. Drugs with multiple targets provide a feasible option for the treatment of complex tumors. Multitarget anti-angiogenesis agents are among the new generation of anticancer drugs and have shown favorable clinical efficacy. Dianhydrogalactitol (DAG) is a chemotherapeutic agent for chronic myeloid leukemia and lung cancer. Recently, it has been tested in phase II trials of glioblastoma treatment; however, mechanisms of DAG in glioblastoma have not been elucidated. Here we show that DAG could inhibit the migration and invasion of U251 cell line by inhibiting matrix metalloproteinase-2 (MMP2) expression. Furthermore, DAG could also inhibit tumor angiogenesis in vitro as well as in the zebrafish model. Mechanistic studies reveal that DAG inhibited both VEGFR2 and FGFR1 pathways. Our results suggest that DAG may be a potential multitarget agent that can inhibit tumor migration, invasion, and angiogenesis, and the anti-angiogenic effects may be involved in dual-suppression VEGF/VEGFR2 and FGF2/FGFR1 signal pathways.

Anticancer activity and mechanisms of diacetyldianhydrogalactitol on hepatoma QGY-7703 cells.

Diacetyldianhydrogalactitol (DADAG) is a member of the hexitols which shows a significant anticancer effect. Despite the fact that the antitumor effects of DADAG have been studied in a number of cell lines, the mechanism of its action remains unclear. Herein, we explored antitumor effects of DADAG and the possible mechanisms by which it inhibited the growth of human hepatocellular carcinoma cell QGY-7,703 and its derived xenograft tumors. Cell proliferation was evaluated with the sulforhodamine B assay in vitro. The results suggested that DADAG had mild antiproliferative activity on QGY-7,703 cells. The antitumor effect of DADAG was assessed in nude mice xenografted with QGY-7,703 cells. We found that DADAG significantly inhibited the tumor growth. Flow cytometry results indicated that the retarded cell proliferation is associated with increased G2/M cell cycle arrest. Further studies showed that the induced G2/M cell cycle arrest is, at least partially, attributed to an upregulation of cyclin B1, phospho-cell division cycle 2 (cdc2) (Thr), phospho-cdc2 (Thr), and cdc25c protein expression, and a decrease in cdc2 protein expression. Taken together, our data show that DADAG has mild proliferative effects on QGY-7,703 cells in vitro, but it significantly inhibits the growth of QGY-7,703 in a xenograft model in vivo. The modulation of several cell cycle progression regulation proteins responsible for G2/M phase transition may account for its antitumor effects.

[Apoptosis of hepatocarcinoma cell line HLE induced by the combination of wild type P53 gene and 1,2:5,6-dianhydro-3,4-diacetylgalactitol].

BACKGROUND & OBJECTIVE: P53 gene is a tumor suppressor gene,and its mutation in human tumor cells is frequently observed. Previous studies revealed that wild type p53 (wt-p53)gene can suppress proliferation ,and induce apoptosis of tumor cells. However,the enhancive effect of wt-p53 on apoptosis of tumor cells is not so obvious when it is used alone. Therefore,it is a new field for tumor research that wt-p53 gene combined with drug is used to enhance apoptosis rate of tumor cells. This study was to investigate the enhancement effect of the combination of wt-p53 and 1,2:5,6-dianhydro-3,4-diacetylgalactitol (DADAG)on apoptosis of human hepatocarcinoma cell line HLE. METHODS: HLE cells were transfected with pUHD10-3-p53 plasmid contained wt-p53 gene,and treated with DADAG. After 96-hour treatment,apoptosis was evaluated by flow cytometry and DNA electrophoresis. RESULTS: The apoptosis rates were: 1.4% in untreated group, 3.5% in pUHD10-3-transfection group, 32.6% in DADAG group, 43.4% in pUHD10-3-p53-transfection group, and 74.6% in pUHD10-3-p53-transfection plus DADAG-treatment group. DNA ladder was observed in pUHD10-3-p53-transfection plus DADAG-treatment group. CONCLUSION: Apoptosis of HLE cells could be induced by both wt-p53 gene and DADAG,and the effect was more obvious when HLE cells were treated by the combination of wt-p53 gene and DADAG.

Caspases promoted DADAG-induced apoptosis in human leukemia HL-60 cells.

AIM: To investigate the roles of caspases in diacetyldianhydrogalactitol (DADAG)-induced apoptosis in human leukemia HL-60 cells. METHODS: Inhibition of proliferation was measured by MTT assay. DADAG-induced apoptosis in HL-60 cells was observed by electron microscopy, flow cytometry, and DNA fragmentation assay. Caspase-3 activity was determined by ApoAlert CPP32 colorimetric assay kit. The cleavage of substrates of caspases was detected by Western blot. RESULTS: DADAG exhibited potent antiproliferative activity and induced apoptosis in HL-60 cells. After treatment with DADAG 8 mg/L for 24 h, caspase-3 activity increased markedly and the cleavage of poly-(ADP-ribose) polymerase (PARP), lamin B, and DFF45 appeared. All of the apoptotic signals were suppressed by z-VAD fmk (a general inhibitor of caspase activities), whereas z-DEVD fmk, a selective inhibitor of caspase-3 activity, only induced partial reversion of the apoptotic effects. CONCLUSION: DADAG induced apoptosis in HL-60 cells by activating caspases. Caspases promoted apoptosis through the cleavage of substrates of PARP, lamin B, and DFF45.

[Apoptosis induced by diacetyldianhydrogalactitol and its mechanism in HL-60 leukemia cells].

AIM: To investigate the apoptosis induced by diacetyldianhydrogalactitol (DADAG) and its mechanism in human HL-60 leukemia cells. METHODS: Inhibition of proliferation was measured by MTT assay. DADAG-induced apoptosis in HL-60 cells was observed by electron microscopy, flow cytometry and DNA fragmentation assay. The levels of Bcl-2 family proteins were detected by Western blotting. Caspase-3 activity was determined by ApoAlert CPP32 colorimetric assay kit. RESULTS: DADAG exhibited potent antiproliferative activity and induced apoptosis in HL-60 cells. After treatment with DADAG 8 micrograms.mL-1 for various times, the Bcl-XL protein level decreased in a time-dependent manner, while the Bad protein level was upregulated. The caspase-3 activity increased markedly after treatment with DADAG for 24 h. The apoptotic signals were suppressed by z-VAD.fmk (a general inhibitor of caspases), whereas z-DEVD.fmk, a selective inhibitor of caspase-3, only induced partial reversion of the apoptotic effects. CONCLUSION: DADAG-induced apoptosis in HL-60 cells required caspase-3 activation and caspase-3 activation was related with Bcl-2 family members.

Interaction of immunosuppressive drugs in mouse experiments with special regards to bacterial translocation.

Following intraperitoneally (i.p.) applied treatment with 12.5 mg/mouse prednisolonum (PRD) no bacterial translocation (BT) was observed in mice. The PRD treatment applied in combination with lymphotropic cytostatics as dianhydrogalactitol (30 mg/kg i.p.) or chlorpromazine (75 mg/kg i.p.) both causing BT, did not increase the mice's drug sensitivity to the used agents. According to our results, PRD can be suitable for combined application with other immunosuppressive agents as it can increase immunosuppression without increase of side-effects such as those induced by bacterial translocation.

[Interaction of immunosuppressive drugs in mice with special regard to bacterial translocation]. / Immun szuppresszív gyógyszerek kölcsönhatásainak kísérletes vizsgálata különös tekintettel a bakteriális transzlokációra.

Following intraperitoneally (i.p.) applied treatment with 12.5 mg/mouse prednisolonum (PR) no bacterial translocation (BT) was observed in mice. The PR treatment applied in combination with lymphotropic cytostatics as dianhydrogalactitol (30 mg/kg i.p.) or chlorpromazine (75 mg/kg i.p.) both causing BT, did not increase the mice's drug sensitivity to the used agents. According to our results, RP can be suitable for combined application with other immunosuppressive agents as it can increase immunosuppression without increase of side-effect such as those induced by bacterial translocation.

[Effect of immunosuppressive agents and antilymphocyte serum on bacterial translocation in mice]. / Immunszupresszív szerek antilymphocyta savó kezelés hatása a bakteriális transzlokációra egerekben.

Following intraperitoneally applied treatment with 0.5 ml of ana partes diluted antilymphocyte serum (ALS) of immunosuppressive effect no bacterial translocation (BT) was observed in mice. The ALS treatment applied in combination with other immunosuppressive agents such as lymphotropic cytostatics as dianhydrogalactitol (30 mg/kg) or chlorpromazine (75 mg/kg) did not increase the mice drug sensitivity to used agents. According to our results, ALS can be suitable for combined application with other immunosuppressive agents as it can increase immunosuppression without side-effects such as those induced by bacterial translocation.

Effect of antilymphocyte serum on bacterial translocation in mice.

Following intraperitoneally applied treatment with antilymphocyte serum (ALS) of immunosuppressive effect no bacterial translocation (BT) was observed in mice. The ALS treatment applied in combination with other immunosuppressive agents such as lymphotropic cytostatics as dianhydrogalactitol or chlorpromazine did not increase the mice's drug sensitivity to the used agents. According to our results, ALS can be suitable for combined application with other immunosuppressive agents as it can increase immunosuppression without side-effects such as those induced by bacterial translocation.

Dominant expression of multidrug resistance in intraspecific murine lymphoma hybrid cells.

Cultured P388/VCR mouse lymphoma cells resistant to vincristine (VCR) and to 5-bromodeoxyuridine (BUdR) and deficient in thymidine kinase (TK-) were fused with P388/DAG cells resistant to 1.2:5,6-dianhydrogalactitol (DAG), an anticancer alkylating agent, and to 6-thioguanine (6-TG) and deficient in hypoxanthine phosphoribosyl-transferase (HPRT-). The hybrid cells expressed multidrug resistance (MDR), i.e., resistance to VCR and cross-resistance to Adriamycin (ADM) and actinomycin D (Act. D), in a dominant manner. The presence of glycoprotein p170, the MDR gene product, was detected in the hybrid cells. Resistance to DAG was also expressed dominantly, whereas cross-resistance to dibromodulcitol (DBD), a chemically related anticancer drug, was slight.

The diverse modification of N-butyl-N-(4-hydroxybutyl) nitrosamine induced carcinogenesis in urinary bladder by dibromodulcitol and dianhydrodulcitol.

The effects of intravesical therapy with adriamycin, 1.6-dibromo-1.6-dideoxydulcitol (DBD) or with 1.6-dianhydrodulcitol (DAD) on bladder carcinogenesis were investigated in rats. To induce premalignant lesions in the urinary bladder female Sprague-Dawley rats received 0.05% N-butyl-N-(4-hydroxybutyl) nitrosamine (BBN) in their drinking water for 4 weeks and then post-treated intravesically with one of the antitumor drugs and examined once a week for 3 months. These antitumor drugs in healthy rats (i.e. without the pre-administration of BBN) did not cause any significant morphological changes in the urinary bladder after intravesical application once a week for 3 months. In the applied dose BBN alone induced only premalignant lesions in the urinary bladder. However, neoplastic lesions occurred in the groups treated with BBN and adriamycin (9 papillomas and 3 carcinomas in 14 animals). Similarly intravesical application of DBD after BBN administration resulted 5 carcinomas among the 11 animals. On the contrary no urinary bladder tumor was found in the animals treated with BBN and DAD. As DAD is one of the conversion products of DBD it is conceivable that the difference between DBD and DAD action may be due to the formation of other solvolytic product from DBD than DAD.

Benzamide potentiation of the cytotoxicity of bifunctional galactitol [correction of galacticol] in resistant P388 leukemia correlates with inhibition of DNA ligase II.

Benzamide (BA) enhances the cytotoxicity of 1,2:5,6-dianhydrogalactitol (DAG) in resistant P388 leukemia cell lines but not in the sensitive parent line. To examine the reason for this difference in response, we carried out an alkaline elution assay using proteinase K to study DNA interstrand cross-linking. At early time points, equal concentrations of DAG produced the same level of interstrand cross-linking (ICL) in the resistant and sensitive P388 leukemic cells, although marked differences were observed in their cytotoxicity toward the two cell lines. In the sensitive cells, neither the amount of DNA cross-linking nor the cytotoxicity changed during the observation period (38 h) in either the presence or the absence of BA. In contrast, the elution rate of the DNA of DAG-treated resistant cells increased with time and had reached the control levels by 38 h. However, when these cells were postincubated with BA for 38 h, the elution rate of DNA was much faster than that observed for the untreated resistant cells, indicating an accumulation of DNA single-strand breaks (SSB). The SSB accumulation caused by BA was associated with an inhibition of the activity of ligase II enzyme, which was stimulated when resistant cells were treated with DAG alone. The potentiating effect of BA on the resistant cells can thus be related to the inhibiting action of BA on the DNA-rejoining enzyme, ligase II. The lack of sensitization by BA of the DAG-treated parent cell line may be attributable to the absence of DNA-SSB formation, which is necessary for ligase II activation through the stimulation of poly(ADP-ribose) synthesis.

[The effect of 3,4-disuccinyldianhydrogalactitol, N-nitrosourea and their combination on DNA synthesis in normal and mouse P388 tumor cells]. / Vliianie 3,4-disuktsinildiangidrogalaktitola, N-nitrozomochevin i ikh kombinatsii na sintez DNK v normal'nykh i opukholevykh kletkakh myshei s leikozom P388.

The rates of incorporation of 2-14C-thymidine into DNA of leukemia P388, bone marrow, gastrointestinal mucosa and spleen cells at various time after administration of 3,4-disuccinyldianhydrogalactitol (DisuDAG), 1-methyl-1-nitrosourea (MNU), 1-(2-hydroxyethyl)-3-(2-chloroethyl)-3-nitrosourea (HECNU) and their combinations at different doses to mice with leukemia P388 (solid form) were studied. DisuDAG (80 mg/kg) induced the deep and the stable inhibition in DNA synthesis of leukemia P388, bone marrow and spleen cells. The combination of DisuDAG and HECNU at small doses induced the deep and the stable suppression of DNA synthesis in tumor cells, however DNA synthesis in normal dividing cells was shown to recover more rapidly than in leukemia P388 cells. Administration of the combination of DisuDAG with MNU to tumor-bearing mice induced more stable inhibition of DNA synthesis in tumor cells in comparison with MNU and DisuDAG. In vivo inhibition of DNA synthesis in leukemia P388 cells with DisuDAG and HECNU was not due to damage in pool of precursors (TCA soluble fraction).

Dominance of resistance to the alkylating agent 1,2:5,6-dianhydrogalactitol in P388 mouse lymphoma hybrid cells.

Cultured P388/S mouse lymphoma cells resistant to 5-bromodeoxyuridine (BUdR) and deficient in thymidine kinase (TK-) were fused with P388/DAG cells resistant to 1,2:5,6-dianhydrogalactitol (DAG), an anticancer alkylating agent, and to 6-thioguanine (6-TG) and deficient in hypoxanthine phosphoribosyl-transferase (HPRT-). Sensitivity to DAG in the hybrid line was very close to that in the P388/DAG line, which means that resistance to DAG was inherited in a quasi-dominant manner. Hybrid cells showed cross-resistance, similar to that of the DAG-resistant line, to two other hexitols, dibromodulcitol (DBD) and disuccinyldianhydrogalactitol (DisuDAG).

Bacterial translocation in dianhydrodulcitol-treated mice.

Escherichia, Proteus, Klebsiella and Streptococcus strains were isolated from mesenteric lymph nodes, spleens and livers of conventional mice treated with dianhydrodulcitol (DAD), indicating that intestinal bacteria had appeared in organs usually containing no bacteria. The frequency of bacterial translocation showed direct relation to the dose of the drug and appeared simultaneously with the spleen atrophy caused by DAD.

Development and some characteristics of a P388 leukemia strain resistant to 1, 2:5, 6-dianhydrogalactitol.

Repeated intraperitoneal treatment of standard P388 mouse leukemia with dianhydrogalactitol (DAG) resulted in the development of a P388/DAG experimental mouse tumor which was resistant to the drug. Resistance was stable without DAG treatment throughout 80 passages. P388/DAG shows cross-resistance to alkylating agents such as nitrogen-mustard, cyclophosphamide and diacetyl-DAG but not to selected antimetabolites and tubulin binders and exhibits reduced sensitivity to nitrosoureas. Resistance to DAG could not be overcome by the administration of maximally tolerated dose of DAG to tumor bearing mice. The resistant tumor is one chromosome short and shows a 13-fold increase of cells possessing a submetacentric marker chromosome.

Inhibitory and stimulatory effects of dianhydrogalactitol, an alkylating cytostatic agent on the humoral immune response.

The effect of an alkylating agent, dianhydrogalactitol (DAG), on the humoral immune response of C57B1 mice immunized with sheep erythrocytes was studied. Different inhibitory or stimulatory effects could be achieved by varying the time and the dose of drug administration. DAG in a dose of 1.5 mg/kg given either before or after immunization induced enhanced immune responses. Higher doses (greater than 5 mg/kg) administered in the inductive phase had a marked suppressive effect while treatments at this dosage preceding immunization resulted in a stimulation. The functionally distinct cell populations acting in the immune response to sheep red blood cells are postulated to have different sensitivity to the drug.