Molecular-based choice of cancer therapy: realities and expectations

Topoisomerase II-mediated DNA damage is differently repaired during the cell cycle by non-homologous end joining and homologous recombination

Topoisomerase II (Top2) is a nuclear enzyme involved in several metabolic processes of DNA. Chemotherapy agents that poison Top2 are known to induce persistent protein-mediated DNA double strand breaks (DSB). In this report, by using knock down experiments, we demonstrated that Top2α was largely responsible for the induction of γH2AX and cytotoxicity by the Top2 poisons idarubicin and etoposide in normal human cells. As DSB resulting from Top2 poisons-mediated damage may be repaired by non-homologous end joining (NHEJ) or homologous recombination (HR), we aimed to analyze both DNA repair pathways. We found that DNA-PKcs was rapidly activated in human cells, as evidenced by autophosphorylation at serine 2056, following Top2-mediated DNA damage. The chemical inhibition of DNA-PKcs by wortmannin and vanillin resulted in an increased accumulation of DNA DSB, as evaluated by the comet assay. This was supported by a hypersensitive phenotype to Top2 poisons of Ku80- and DNA-PKcs- defective Chinese hamster cell lines. We also showed that Rad51 protein levels, Rad51 foci formation and sister chromatid exchanges were increased in human cells following Top2-mediated DNA damage. In support, BRCA2- and Rad51C- defective Chinese hamster cells displayed hypersensitivity to Top2 poisons. The analysis by immunofluorescence of the DNA DSB repair response in synchronized human cell cultures revealed activation of DNA-PKcs throughout the cell cycle and Rad51 foci formation in S and late S/G2 cells. Additionally, we found an increase of DNA-PKcs-mediated residual repair events, but not Rad51 residual foci, into micronucleated and apoptotic cells. Therefore, we conclude that in human cells both NHEJ and HR are required, with cell cycle stage specificity, for the repair of Top2-mediated reversible DNA damage. Moreover, NHEJ-mediated residual repair events are more frequently associated to irreversibly damaged cells.

Small interference RNA targeting Krüppel-like factor 8 inhibits the renal carcinoma 786-0 cells growth in vitro and in vivo

PURPOSE

Krüppel-like factor 8 (KLF8) plays an important role in oncogenic transformation and is highly overexpressed in several types of human cancer. We investigated the expression of KLF8 in renal cell carcinoma (RCC) tissues and the role of small interference RNA targeting KLF8 on growth, cell cycle, and apoptosis of human renal carcinoma cell line 786-0 in vitro and in vivo.

METHODS

The expression of KLF8 protein and mRNA in human renal carcinoma samples was detected by immunochemistry and reverse transcription polymerase chain reaction (RT-PCR). The effects of small interference RNA (siRNA) targeting KLF8 on growth, invasiveness, cell cycle, and apoptosis of 786-0 cells were evaluated by MTT assay, Matrigel Invasion Assay, and flow cytometry in vitro. We also investigated effect of siRNA targeting KLF8 on growth of 786-0 cells in nude mice in vivo.

RESULTS

Immunohistochemistry and RT-PCR results showed the expression of KLF8 protein and mRNA in RCC specimens was significantly higher than that in the adjacent non-tumorous renal tissues (P < 0.001). KLF8-siRNA depressed the cellular growth and invasion of 786-0 cells in vitro. The flow cytometry results revealed that KLF8-siRNA could induce an increase in G0/G1 phase cells and induce cell apoptosis. Intratumor injection of siRNA targeting KLF8 inhibited the growth of 786-0 cells in vivo in nude mice tumor model.

CONCLUSIONS

KLF8 possibly involved in regulating the cell growth, invasion, apoptosis, and proliferation of renal carcinoma cancer cells. Blocking the KLF8 channel might be a potential therapeutic strategy for RCC.

Breast cancer therapy for BRCA1 carriers: moving towards platinum standard?

Recently Byrski et al. reported the first-ever breast cancer (BC) study, which specifically selected BRCA1-carriers for the neoadjuvant treatment and used monotherapy by cisplatin instead of conventional schemes. Although the TNM staging of the recruited patients was apparently more favorable than in most of published neoadjuvant trials, the results of Byrski et al. clearly outperform any historical data. Indeed, 9 of 10 BRCA1-associated BC demonstrated complete pathological response to the cisplatin treatment, i.e. these women have good chances to be ultimately cured from the cancer disease. High sensitivity of BRCA1-related tumors to platinating agents has been discussed for years, but it took almost a decade to translate convincing laboratory findings into first clinical observations. With increasing stratification of tumor disease entities for molecular subtypes and rapidly growing armamentarium of cancer drugs, it is getting technically and ethically impossible to subject all promising treatment options to the large randomized prospective clinical trials. Therefore, alternative approaches for initial drugs evaluation are highly required, and one of the choices is to extract maximum benefit from already available collections of biological material and medical charts. For example, many thousands of BC patients around the world have already been subjected to second- or third-line therapy with platinum agents, but the association between BRCA status and response to the treatment has not been systematically evaluated in these women. While potential biases of retrospective studies are widely acknowledged, it is frequently ignored that the use of archival collections may provide preliminary answers for long-standing questions within days instead of years. However, even elegantly-designed, small-sized, hypothesis-generating retrospective studies may require multicenter efforts and somewhat cumbersome logistics, that may explain the surprising lack of historical data on the platinum-based treatment of BC in BRCA1 carriers.

EGFR mutation in kidney carcinoma confers sensitivity to gefitinib treatment: a case report

Mutations of the epidermal growth factor receptor (EGFR) gene are known to be associated with the pronounced tumor response to EGFR tyrosine kinase inhibitors (TKI). Unfortunately, these TKI-sensitizing alterations have been detected almost exclusively in lung adenocarcinomas; indeed, their occurrence in tumors of other histologic types or other organs is exceptionally rare. Here we report a case of intragenic EGFR microdeletion in renal cell carcinoma (RCC) associated with the effect of treatment by gefitinib. Patient G., 60 years old, underwent radical surgery for clear cell RCC, however local relapse and metastatic lesions in the lungs were revealed 33 months later. The patient was successfully treated by interleukin-2 (first line therapy), tamoxifen (second line), and interferon-alpha (third line). After disease progression, EGFR mutation test was performed as a compassionate attempt. It revealed "classical" 15 base pair deletion, so gefitinib was administered. This treatment led to a dramatic symptomatic response within the first week of therapy; reduction of dyspnea was so evident that it allowed the patient to return to work. Clinical examination demonstrated significant improvement with respect to pleuritis and pericarditis. The duration of tumor response, which was classified as disease stabilization, was equal to 4 months. This case report suggests that kidney tumors have to be investigated more closely with respect to the occurrence of TKI-sensitizing EGFR mutations.

Measurement of DPD and TS transcripts aimed to predict clinical benefit from fluoropyrimidines: confirmation of the trend in Russian colorectal cancer series and caution regarding the gene referees

BACKGROUND

Measurement of intratumoral expression of dihydropyrimidine dehydrogenase (DPD) and thymidylate synthase (TS) may have some value in predicting the response to fluoropyrimidine-containing therapy.

PATIENTS AND METHODS

We attempted to validate this association in a series of Russian metastatic colorectal cancer cases. While replicating already published protocols, we unexpectedly found that the use of commonly utilized gene referees, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and beta-actin, may lead to artifacts due to pseudogene-driven amplification from the genomic DNA template. We have developed a real-time PCR protocol which amplifies short PCR fragments, thus allowing efficient analysis of archival formalin-fixed paraffin-embedded tumor samples, and relies on succinate dehydrogenase (SDHA) as a gene referee, therefore avoiding amplification from genomic DNA.

RESULTS

Low content of DPD transcripts was observed in 13/20 (65%) patients with disease control (tumor response or disease stabilization) as compared to only 3/9 (33%) subjects with progressive disease (p = 0.11). Despite the low number of patients, this association reached the level of statistical significance when similar analysis was done for TS expression (11/20 (55%) vs. 1/9 (11%); p = 0.03).

CONCLUSIONS

Our data confirm that low DPD and TS expressors have higher chances of success of fluoropyrimidine-containing regimens.