New advances in lung cancer chemotherapy: topotecan and the role of topoisomerase I inhibitors

Molecular docking, DFT and antimicrobial studies of Cu(II) complex as topoisomerase I inhibitor

Herein, we report the synthesis and single crystal X-ray structure of Cu(II)-picolinic acid complex, 1 as a potent topoisomerase I inhibitor. The complex 1 crystallized in the triclinic crystal system with space group P-1. Comparative in vitro binding studies of complex 1 with CT DNA and tRNA were carried out revealing an electrostatic binding mode with higher binding propensity towards tRNA. The intrinsic bonding constant value, K_b was calculated to be 4.36 × 10⁴ and 8.78 × 10⁴ M^-1 with CT DNA and tRNA respectively. DNA cleavage activity was carried out with a pBR322 plasmid DNA substrate to ascertain the cleaving ability. Furthermore, Topo-I inhibition assay of complex 1, performed via gel electrophoresis revealed a significant inhibitory effect on the enzyme catalytic activity at a minimum concentration of 15 µM. The DFT studies were carried out to provide better insight in the electronic transitions observed in the absorption spectrum of the complex 1. Molecular docking studies were carried out with DNA, RNA and Topo-I to determine the specific binding preferences at the target site and complement the spectroscopic studies. The antimicrobial potential of complex 1 was screened against E. coli, S. aureus, P. aeruginosa, B. subtilis and C. albicans; and compared with doxycycline, exhibiting an excellent maximum zone of inhibition of 28 mm against E. coli.Communicated by Ramaswamy H. Sarma.

Structure elucidation {spectroscopic, single crystal X-ray diffraction and computational DFT studies} of new tailored benzenesulfonamide derived Schiff base copper(II) intercalating complexes: Comprehensive biological profile {DNA binding, pBR322 DNA cleavage, Topo I inhibition and cytotoxic activity}

New tailored copper(II)-based intercalating complexes [Cu(L1)2] (1) and [Cu(L2)2] (2) were synthesized from Schiff base scaffold HL1 and HL2(E)-4-(2-((2-hydroxy-3-methoxybenzylidene)amino)ethyl)benzenesulfonamide and (E)-4-(2-((2-hydroxybenzylidene)amino)ethyl)benzenesulfonamide, respectively. The structure elucidation of complexes 1 and 2 was carried out by employing various spectroscopic techniques viz., FT-IR, UV-vis, ESI-MS, EPR and single X-ray crystal diffraction studies. The complexes 1 and 2 were crystallized in monoclinic P21/n and triclinic P-1 space group, respectively possessing square planar geometry around Cu(II) coordinated with N,O-donor Schiff base ligands. An analysis of Hirshfeld surfaces of complexes 1 and 2 were performed to ascertain different intra and intermolecular non-covalent interactions (H-bonding, CH⋯ πetc.) responsible for the stabilization of crystal lattices. Calculations based on Density functional theory (B3LYP/DFT), have been carried out to obtain energies of Frontier molecular orbitals. Comparative in vitro binding profile of complexes 1 and 2 with ct-DNA was evaluated employing various biophysical techniques viz., UV-vis, fluorescence, circular dichroism and cyclic voltammetry which suggested non-covalent intercalative binding mode with more avid binding propensity of complex 1 compared to complex 2. The cleavage experiments of complex 1 was performed by gel electrophoretic assay which revealed efficient cleavage mediated via oxidative pathway. Furthermore, topoisomerase I enzymatic activity of complex 1 was carried out employing gel electrophoretic assay which demonstrated significant inhibitory effects at a low concentration of 25 µM. The cytotoxic potential of complex 1 was analyzed by SRB assay on a panel of selected human cancer cell lines which revealed selective activity for MCF-7 (breast cancer) cell line with GI50 = 16.21 µg/ml.

Alternative splicing in lung cancer

Lung cancer has the highest mortality rate of all cancers worldwide. Lung cancer is a very heterogeneous disease that is often diagnosed at later stages which have a poor prognosis. Aberrant alternative splicing patterns found in lung cancer contribute to important cell functions. These include changes in splicing for the BCL2L1, MDM2, MDM4, NUMB and MET genes during lung tumourigenesis, to affect pathways involved in apoptosis, cell proliferation and cellular cohesion. Global analyses of RNASeq datasets suggest there may be many more potentially influential aberrant splicing events that need to be investigated in lung cancer. Changes in expression of the splicing factors that regulate alternative splicing events have also been identified in lung cancer. Of these, changes in expression of QKI, RBM4, RBM5, RBM6, RBM10 and SRSF1 proteins regulate many of the most frequently referenced aberrant splicing events in lung cancer. The expanding list of genes known to be aberrantly spliced in lung cancer along with the altered expression of splicing factors that regulate them are providing new clues as to how lung cancer develops, and how these events can be exploited for better treatment. This article is part of a Special Issue entitled: RNA structure and splicing regulation edited by Francisco Baralle, Ravindra Singh and Stefan Stamm.

Escalating topotecan in combination with treosulfan has acceptable toxicity in advanced pediatric sarcomas

Patients with advanced pediatric sarcomas have a poor prognosis and novel combination therapies are needed to improve the response rates. Hematological and organ related toxicities have been observed when administering topotecan in combination with, e.g., high dose thiotepa. This study evaluates the toxicity of escalating doses of topotecan alone or in combination with thiotepa or treosulfan. We compared the toxicity including death of complication (DOC) of topotecan alone or in combination with thiotepa or treosulfan in advanced pediatric sarcomas (n = 12). Ten of 12 patients (0.83) suffered from advanced tumors of the Ewing family (i.e., bone or marrow metastases or relapse <24 month after diagnosis, including one neuroepithelial tumor of the kidney) and two from alveolar rhabdomyosarcoma stage IV (0.17). Median age was 15 years (range 5-28). Ratio of female to male was 1:1. Two patients received topotecan alone (1.25 mg/m(2) q 5d and 1.5 mg/m(2) q 5d), three patients received four courses of topotecan (2 mg/m(2) q d 1-5) in combination with thiotepa (100 mg/m(2) q d 1-5), and seven patients received topotecan (2 mg/m(2) q d 1-5) in combination with treosulfan (10g/m(2) q d 3-5). Overall toxicity was not different between all three groups; mean scores were 1.6, 1.8, and 1.7 according to WHO grading (Scale 0-4). Organ related toxicity ranged between 0 and 4 and was not different as well. DOC was 0/2, 1/3, and 0/7 patients respectively. Escalating therapy with topotecan in combination with treosulfan has acceptable toxicity and warrants further investigation in advanced pediatric sarcomas.

Recent Pharmacological Advances: Focus on Small-cell Lung Cancer

Small cell lung cancer (SCLC) represents approximately 15% of all lung cancers, and is the most aggressive form of lung cancer. Left untreated, the time from diagnosis to death is 2–3 months. With current treatment, expected survival is 7–20 months, depending on the stage of disease. A new drug, amrubicin, is approved in Japan for lung cancer and has demonstrated efficacy in U.S. and European phase II trials of SCLC patients with either untreated disease or relapsed refractory illness. In a phase II study of amrubicin in previously untreated patients, response rates reached 75% with a median survival time of almost 1 year. Amrubicin is a fully synthetic 9-aminoanthracycline, and an analog of doxorubicin and epirubicin. The major mechanism of action of amrubicin is inhibition of topoisomerase II. Unlike doxorubicin, however, it exhibits little or no cardiotoxicity in clinical studies and preclinical models. In preclinical rodent tumor models, it is selectively distributed to tumour tissue and is not detected in the heart when compared with doxorubicin, which is distributed equivalently to these sites. The primary metabolite of amrubicin, amrubicinol, is up to 100 times more cytotoxic in vitro than the parent compound. This review describes the mechanisms of action of amrubicin as well as clinical studies which demonstrate the potential of this drug in future SCLC treatment. The review also puts forward hypothetical considerations for the use of other drugs such as lenalidomide, an immunomodulatory drug acting on multiple signalling pathways, or histone deacetylase inhibitors, in combination with amrubicin in SCLC.

Topoisomerase I amplification in melanoma is associated with more advanced tumours and poor prognosis

In this study, we used array-comparative genomic hybridization (aCGH) and fluorescent in situ hybridization (FISH) to examine genetic aberrations in melanoma cell lines and tissues. Array-comparative genomic hybridization revealed that the most frequent genetic changes found in melanoma cell lines were amplifications on chromosomes 7p and 20q, along with disruptions on Chr 9, 10, 11, 12, 22 and Y. Validation of the results using FISH on tissue microarrays (TMAs) identified TOP1 as being amplified in melanoma tissues. TOP1 amplification was detected in a high percentage (33%) of tumours and was associated with thicker, aggressive tumours. These results show that TOP1 amplification is associated with advanced tumours and poor prognosis in melanoma. These observations open the possibility that TOP1-targeted therapeutics may be of benefit in a particular subgroup of advanced stage melanoma patients.

Mechanisms of leukemia translocations

PURPOSE OF REVIEW

This review highlights recent findings about the known DNA repair machinery, its impact on chromosomal translocation mechanisms and their relevance to leukemia in the clinic.

RECENT FINDINGS

Chromosomal translocations regulate the behavior of leukemia. They not only predict outcome but they define therapy. There is a great deal of knowledge on the products of leukemic translocations, yet little is known about the mechanism by which those translocations occur. Given the large number of DNA double-strand breaks that occur during normal progression through the cell cycle, especially from V(D)J recombination, stalled replication forks or failed decatenation, it is surprising that leukemogenic translocations do not occur more frequently. Fortunately, hematopoietic cells have sophisticated repair mechanisms to suppress such translocations. When these defenses fail leukemia becomes far more common, as seen in inherited deficiencies of DNA repair. Analyzing translocation sequences in cellular and animal models, and in human leukemias, has yielded new insights into the mechanisms of leukemogenic translocations.

SUMMARY

New data from animal models suggest a two hit origin of leukemic translocations, where there must be both a defect in DNA double-strand break repair and a subsequent failure of cell cycle arrest for leukemogenesis.

[Small cell lung cancer--state of the art and future perspectives]

Lung cancer is the leading cause of cancer-related death in Portugal. Almost 3500 Portuguese are expected to be diagnosed with lung cancer in 2006; approximately 20% will have small cell lung cancer (SCLC). At presentation, 25% to 30% of patients will have local or regional disease, classified as limited stage disease. The concurrent chemovalidation therapy is the best choice. Once daily thoracic radiation therapy to doses in the range of 50 Gy to 60 Gy would reflect an accepted standard of care in daily practice. Because of the increase toxicity associated with hyper fractionated radiation, this approach is often limited to select patients. Etoposide plus cisplatin are synergistic, well tolerated and result in equal or superior survival compared with other regimens. This is the standard regimen for concomitant therapy in limited stage and for extensive disease SCLC. Despite good chemo sensitivity and radio sensitivity, the prognosis of SCLC is very poor because of the early development of resistance and the associated high tendency to recurrence, making second line treatment of SCLC a problem of real medical relevance. Topotecan now offers an effective and well tolerated monosubstance for second line therapy of recurrent SCLC. There has been a significant increase in median survival for patients with SCLC receiving topotecan plus symptomatic therapy versus symptomatic therapy. The efficacy of this drug is comparable to the efficacy of the three-drug combination CAV. The tolerability can be improved by means of toxicity-adapted dosing. In elderly and in patients with performance status 2, topotecan is also well tolerated and has good efficacy. Initial studies into weekly administration also demonstrate good efficacy. The combination of topotecan with cranial radiotherapy is well tolerated and effective in the treatment of cerebral metastases of SCLC. New classes of agents, such as antiangiogenic agents including bevacizumab, small molecule tyrosine kinase inhibitors and thalidomide are being evaluated with chemotherapy for patients with extensive stage SCLC.

DNA topoisomerase I is a cofactor for c-Jun in the regulation of epidermal growth factor receptor expression and cancer cell proliferation

DNA topoisomerase I (Topo I) is a molecular target for the anticancer agent topotecan in the treatment of small cell lung cancer and ovarian carcinomas. However, the molecular mechanisms by which topotecan treatment inhibits cancer cell proliferation are unclear. We describe here the identification of Topo I as a novel endogenous interaction partner for transcription factor c-Jun. Reciprocal coimmunoprecipitation analysis showed that Topo I and c-Jun interact in transformed human cells in a manner that is dependent on JNK activity. c-Jun target gene epidermal growth factor receptor (EGFR) was identified as a novel gene whose expression was specifically inhibited by topotecan. Moreover, Topo I overexpression supported c-Jun-mediated reporter gene activation and both genetic and chemical inhibition of c-Jun converted cells resistant to topotecan-elicited EGFR downregulation. Topotecan-elicited suppression of proliferation was rescued by exogenously expressed EGFR. Furthermore, we demonstrate the cooperation of the JNK-c-Jun pathway, Topo I, and EGFR in the positive regulation of HT-1080 cell proliferation. Together, these results have identified transcriptional coactivator Topo I as a first endogenous cofactor for c-Jun in the regulation of cell proliferation. In addition, the results of the present study strongly suggest that inhibition of EGFR expression is a novel mechanism by which topotecan inhibits cell proliferation in cancer therapy.

Phase I study of paclitaxel and topotecan for the first-line treatment of extensive-stage small cell lung cancer

Extensive-stage small cell lung cancer (SCLC) is an aggressive disease with a median survival of approximately 8 months. Although current combination chemotherapy regimens provide high initial tumor response rates, they have not translated into large gains in survival. Topotecan and paclitaxel have nonoverlapping mechanisms of action and are active agents in SCLC. Additionally, these two agents demonstrate in vitro synergy in animal and human tumor models. We investigated the maximum tolerated dose of 3-day topotecan in combination with paclitaxel in previously untreated patients with extensive SCLC. Seventeen patients were enrolled in an open-label, phase I, dose-escalation study and were treated with intravenous paclitaxel 135-175 mg/m(2) over 1 hour on day 1, followed by intravenous topotecan 1.25-1.5 mg/m(2) over 30 minutes on days 1-3 of a 21-day course. Sixty-nine courses of therapy were administered with no delays due to hematologic toxicity. Prophylactic hematologic support was required for 24% of patients. The topotecan/paclitaxel combination was well tolerated, with 24%, 12%, and 6% of patients experiencing grade 3/4 neutropenia, anemia, or thrombocytopenia, respectively. Dose-limiting neutropenia was seen in three of five patients treated with topotecan 1.5 mg/m(2) and paclitaxel 175 mg/m(2). Therefore, topotecan 1.5 mg/m(2) with paclitaxel 135 mg/m(2) was determined to be the maximum tolerated dose. Of the 17 evaluable patients, 53% achieved a partial response and 18% achieved stable disease. In summary, we have identified a regimen of topotecan 1.5 mg/m(2) and paclitaxel 135 mg/m(2) that was well tolerated and active in this patient group. Additional studies of topotecan and paclitaxel at these dose levels are needed to fully elucidate the efficacy of this combination in extensive SCLC.

Topoisomerase I protein expression in primary colorectal cancer and lymph node metastases

Topoisomerase I (topo I) is an important target for the treatment of malignant disease, especially colorectal cancer. Because there is little information on the expression of topo I in colorectal tumors, this study evaluated and characterized topo I protein expression in primary colorectal cancer and lymph node metastases and studied the association between topo I protein expression and clinicopathologic data, p53 status, and proliferating cell nuclear antigen (PCNA) status. Immunohistochemistry assay was performed for topo I protein expression in 249 primary human colorectal cancer and 42 paired lymph node metastasis samples. Topo I expression was described as the percentage of cells staining positive for topo I, along with the intensity and localization of the staining. Clinicopathologic data (sex, age, Dukes' stage, differentiation grade, survival status), p53 status, and PCNA status were statistically analyzed for association with topo I protein expression. Topo I expression in paired primary lymph node metastases were studied for concordance. Topo I protein expression was detected in 127 (51%) samples, including 24.4% with >50% positive tumor cells. The majority had nuclear (70.1%) or nuclear and cytoplasmic staining (17.3%). A higher percentage of cells expressing topo I in primary colorectal cancer was significantly associated with advanced age (P =.040). Patients with rectal cancer had greater topo I expression than those with colon tumors (P =.029). No significant correlation was found between topo I protein expression and sex, Dukes' stage, differentiation grade, survival status, p53 status, and PCNA status. Concordance in topo I staining between primary and lymph node metastases was observed in 33 of 42 cases (P =.029). This suggests that the activity of topo I inhibitors will not differ across various tumor stages, pathology, and patient gender. p53 and PCNA status do not appear to influence topo I expression, and topo I has no apparent association with the acquisition of a metastatic phenotype. Topo I expression now needs to be evaluated in patients undergoing topo I-inhibitor therapy, to better define the role of this protein as a predictive marker.