PARP Inhibition Sensitizes Breast Cancer Cells to Eribulin

BACKGROUND

Poly(ADP-ribose) polymerases 1 and 2 (PARP1, 2), and 3 mediate protein modifications that facilitate the recruitment of DNA repair factors to single and double strand breaks. PARP3 is unique in that it is also required for efficient mitotic progression and stabilization of the mitotic spindle. Eribulin, an anti-microtubule agent used clinically to treat breast cancer, exerts its cytotoxicity by altering microtubule dynamics resulting in cell cycle arrest and apoptosis. Herein, we hypothesize that the pan PARP inhibitor olaparib has the potential to enhance the cytotoxicity of eribulin by halting mitosis through inhibition of PARP3.

METHODS

The effect of olaparib on eribulin cytotoxicity was assessed using the Sulforhodamine (SRB) assay, with two triple negative breast cancer cell lines and an estrogen receptor positive (ER+)/human epidermal growth factor receptor 2 negative (HER2-) breast cancer cell line. Alteration by the treatments on PARP3 activity and microtubule dynamics were assessed utilizing a chemiluminescent enzymatic assay and immunofluorescence, respectively. The effect of the treatments on cell cycle progression and apoptosis induction were assessed by flow cytometry using propidium iodide and Annexin V staining, respectively.

RESULTS

Our results demonstrate that non-cytotoxic concentrations of olaparib sensitize breast cancer cells regardless of ER status. Mechanistically, our results indicate that olaparib potentiates eribulin-induced cell cycle arrest at the G2/M boundary, PARP3 inhibition and microtubule destabilizing resulting in mitotic catastrophe and apoptosis.

CONCLUSIONS

In breast cancer (regardless of ER status) settings, treatment outcomes could be improved by the incorporation of olaparib in eribulin treatment regimens.

EIF4A inhibition targets bioenergetic homeostasis in AML MOLM-14 cells in vitro and in vivo and synergizes with cytarabine and venetoclax

BACKGROUND

Acute myeloid leukemia (AML) is an aggressive hematological cancer resulting from uncontrolled proliferation of differentiation-blocked myeloid cells. Seventy percent of AML patients are currently not cured with available treatments, highlighting the need of novel therapeutic strategies. A promising target in AML is the mammalian target of rapamycin complex 1 (mTORC1). Clinical inhibition of mTORC1 is limited by its reactivation through compensatory and regulatory feedback loops. Here, we explored a strategy to curtail these drawbacks through inhibition of an important effector of the mTORC1signaling pathway, the eukaryotic initiation factor 4A (eIF4A).

METHODS

We tested the anti-leukemic effect of a potent and specific eIF4A inhibitor (eIF4Ai), CR-1-31-B, in combination with cytosine arabinoside (araC) or the BCL2 inhibitor venetoclax. We utilized the MOLM-14 human AML cell line to model chemoresistant disease both in vitro and in vivo. In eIF4Ai-treated cells, we assessed for changes in survival, apoptotic priming, de novo protein synthesis, targeted intracellular metabolite content, bioenergetic profile, mitochondrial reactive oxygen species (mtROS) and mitochondrial membrane potential (MMP).

RESULTS

eIF4Ai exhibits anti-leukemia activity in vivo while sparing non-malignant myeloid cells. In vitro, eIF4Ai synergizes with two therapeutic agents in AML, araC and venetoclax. EIF4Ai reduces mitochondrial membrane potential (MMP) and the rate of ATP synthesis from mitochondrial respiration and glycolysis. Furthermore, eIF4i enhanced apoptotic priming while reducing the expression levels of the antiapoptotic factors BCL2, BCL-XL and MCL1. Concomitantly, eIF4Ai decreases intracellular levels of specific metabolic intermediates of the tricarboxylic acid cycle (TCA cycle) and glucose metabolism, while enhancing mtROS. In vitro redox stress contributes to eIF4Ai cytotoxicity, as treatment with a ROS scavenger partially rescued the viability of eIF4A inhibition.

CONCLUSIONS

We discovered that chemoresistant MOLM-14 cells rely on eIF4A-dependent cap translation for survival in vitro and in vivo. EIF4A drives an intrinsic metabolic program sustaining bioenergetic and redox homeostasis and regulates the expression of anti-apoptotic proteins. Overall, our work suggests that eIF4A-dependent cap translation contributes to adaptive processes involved in resistance to relevant therapeutic agents in AML.

Can high Ki67 predict distant recurrence in early-stage breast cancer with low Oncotype Dx score?

e12561

Background: Ki-67 is a marker of proliferating cells. The recurrence score based on the 21-gene breast cancer assay also called Oncotype Dx provides prognostic and predictive information for recurrence in early stage breast cancer patients. We previously showed that there is a moderate correlation between Ki67 and oncotype Dx recurrence score. In this retrospective study, we aimed to examine whether high Ki67 could predict the distant recurrence in early stage breast cancer with low oncotype Dx scores ( < 25). Methods: This retrospective study included 278 consecutive cases of hormone receptor-positive, HER2 negative (T1-2 N0 M0) breast cancer who were diagnosed between 2008 and 2015 with low oncotype Dx ( < 25). Patients’ clinical outcome in terms of distant recurrence after breast surgery was determined up to December 2020 (median follow-up of 7 years). Patients were divided in to low risk (Ki67 < 15%) and high risk (Ki67 > = 15%) groups. Results: Of 278 cases with average and median age of 59 and 60 respectively, 148 (53%) were in Ki67 low risk and 130 (47%) were in Ki67 high risk group. Average and median oncotype Dx were 13.86 and 15 respectively in Ki67 low risk versus 15.23 and 16 respectively in Ki67 high risk group. 13 patients (4%) experienced distant metastasis in lung, liver, bone and skin. Of these 13 cases with average and median oncotype Dx 15.84 and 19 respectively, 12 (92%) were in the Ki67 high risk group and only 1 (8%) belonged to the low risk category. High Ki67 patients were overrepresented in group with recurrent distant metastasis compare to group without recurrent disease (Pearson Chi-Square = 51.18 with 1 degree of freedom and P = < 0.001). Conclusions: Ki67 high patients in the low risk oncotype Dx group are relapsing at a significantly higher rate suggesting that Ki67 combined with low oncotype Dx further refines the risk of distant relapse.

IND.216: a phase II study of buparlisib and associated biomarkers, raptor and p70S6K, in patients with relapsed and refractory chronic lymphocytic leukemia

Buparlisib is an orally available pan-Class I PI3K inhibitor, that is more potent than idelalisib in vitro. Its distinct toxicities include hyperglycemia, hypertension, and mood disturbance. IND216 is a single arm phase II trial of buparlisib in Relapsed/refractory (R/R) chronic lymphocytic leukemia (CLL). Fourteen patients were enrolled, 13 were evaluable for response and toxicity. Six of 13 patients had a partial response (46%) with a median duration of response of 15.5 months, all 11 patients with tumor assessment experienced tumor shrinkage. The most common adverse events (≥15%) were hyperglycemia, fatigue, anxiety, and gastrointestinal toxicities; all were < grade 3 except for fatigue. Three patients stopped therapy for alterations in mood. Lower levels of raptor were significantly associated with greater tumor shrinkage, suggesting that raptor could be a biomarker for response. This requires further validation in a larger CLL patient cohort. The clinical activity of buparlisib is comparable to other phosphatidylinositol-3-kinase inhibitors, with a different toxicity profile.Novelty and impactBuparlisib, an oral, pan PI3 kinase inhibitor, is associated with a 46% partial response rate among patients with relapse chronic lymphocytic leukemia (CLL). This is a similar clinical activity to other phosphatidylinositol-3-kinase inhibitors tested. However, buparlisib has a distinct toxicity profile, characterized by hyperglycemia, hypertension, and mood alteration. In agreement with our previous preclinical study, our results suggest that basal raptor expression in CLL correlates with clinical response to buparlisib.

Metabolic rewiring beyond Warburg in chronic lymphocytic leukemia: How much do we actually know?

Chronic Lymphocytic Leukemia (CLL) is the most common adult leukemia in the western world. CLL consists of the accumulation of malignant B-cells in the blood stream and homing tissues. Although treatable, this disease is not curable, and resistance or relapse is often present. In many cancers, the study of metabolic reprograming has uncovered novel targets that are already being exploited in the clinic. However, CLL metabolism is still poorly understood. The ability of CLL lymphocytes to adapt to diverse microenvironments is accompanied by modifications in cell metabolism, revealing the challenge of targeting the CLL lymphocytes present in all different compartments. Despite this, the study of CLL metabolism led to an ongoing clinical trial using glucose uptake and mitochondrial respiration inhibitors. In contrast, glutamine and fatty acid metabolism remain to be further exploited in CLL. Here, we summarize the present knowledge of CLL metabolism, as well as the metabolic influence of Myc, ATM and p53 on CLL lymphocytes.

Ibrutinib Resistance Is Reduced by an Inhibitor of Fatty Acid Oxidation in Primary CLL Lymphocytes

Chronic Lymphocytic Leukemia (CLL) is an incurable disease, characterized by the accumulation of malignant B-lymphocytes in the blood stream (quiescent state) and homing tissues (where they can proliferate). In CLL, the targeting of B-cell receptor signaling through a Burton's tyrosine kinase inhibitor (ibrutinib) has rendered outstanding clinical results. However, complete remission is not guaranteed due to drug resistance or relapse, revealing the need for novel approaches for CLL treatment. The characterization of metabolic rewiring in proliferative cancer cells is already being applied for diagnostic and therapeutic purposes, but our knowledge of quiescent cell metabolism—relevant for CLL cells—is still fragmentary. Recently, we reported that glutamine metabolism in primary CLL cells bearing the del11q deletion is different from their del11q negative counterparts, making del11q cells especially sensitive to glutaminase and glycolysis inhibitors. In this work, we used our primary CLL lymphocyte bank and compounds interfering with central carbon metabolism to define metabolic traits associated with ibrutinib resistance. We observe a differential basal metabolite uptake linked to ibrutinib resistance, favoring glutamine uptake and catabolism. Upon ibrutinib treatment, the redox balance in ibrutinib resistant cells is shifted toward NADPH accumulation, without an increase in glutamine uptake, suggesting alternative metabolic rewiring such as the activation of fatty acid oxidation. In accordance to this idea, the curtailing of fatty acid oxidation by CPT1 inhibition (etomoxir) re-sensitized resistant cells to ibrutinib. Our results suggest that fatty acid oxidation could be explored as a target to overcome ibrutinib resistance.

PARP3 inhibitors ME0328 and olaparib potentiate vinorelbine sensitization in breast cancer cell lines

PURPOSE

PARP-3 is member of the PARP family of poly (ADP-ribose) polymerases involved in ADPribosylation. PARPs are involved in the basic mechanisms of DNA repair. PARP3, a critical player for efficient mitotic progression, is required for the stabilization of the mitotic spindle by regulation of the mitotic components, NuMA and Tankyrase 1.

METHODS

The sensitization effect of vinorelbine on PARP3 inhibition-induced cytotoxicity was assessed by the SRB assay. The contribution of programed cell death and cell cycle arrest to the sensitization effect were determined by assessing changes in Annexin V, a marker of apoptosis. Alterations in cell cycle progression were assessed by cell cycle analysis. We used immunofluorescence to assess the effect of vinorelbine and/or PARP3 inhibitors on tubulin and microtubule depolarization. The PARP3 chemiluminescent assay kit was used for PARP3 activity.

RESULTS

PARP3 inhibitors sensitize breast cancer cells to vinorelbine, a vinca alkaloid used in the treatment of metastatic breast cancer. Olaparib which was originally described as a PARP1 and 2 inhibitor has recently been shown to be a potent PARP3 inhibitor while ME0328 is a more selective PARP3 inhibitor. The combination of vinorelbine with nontoxic concentrations of ME0328 or olaparib reduces vinorelbine resistance by 10 and 17 fold, respectively, potentiating vinorelbine-induced arrest at the G2/M boundary. In addition, PARP3 inhibition potentiates vinorelbine interaction with tubulin. Furthermore, olaparib or ME0328 potentiates vinorelbine-induced PARP3 inhibition, mitotic arrest, and apoptosis.

CONCLUSION

Our results indicated this approach with PARP3 inhibitors and vinorelbine is unique and promising for breast cancer patients with metastases. This combination could significantly increase the survival of breast cancer patients with metastases.

Adaptive metabolic rewiring to chronic SFK inhibition

Src family kinases (SFK) are key regulators of cellular proliferation, differentiation, survival, motility and angiogenesis. As such, SFK inhibitors are being tested in clinical trials to prevent metastasis as an alternative to current treatment regimens for a variety of cancers including breast cancer. To contribute to the development of molecular tools improving SFK-targeted therapies, we used the SFK inhibitor dasatinib and a well characterized triple negative breast cancer cell line (BT20). Comparison of the response of BT20 cells with acquired resistance to dasatinib and its’ parental counterpart suggest that chronic exposure to SFK inhibition results in increased dependency on TGFβ signaling for proliferation, both in the absence or the presence of dasatinib. In addition, we found that acquired (but not de novo) resistance to dasatinib was reduced by non-cytotoxic concentrations compounds hindering on PI3K, mTORC1 signaling, endoplasmic reticulum stress or autophagy.

Abstract 5327: Simultaneous inhibition of ATR and PARP greatly sensitizes colon cancer cell lines to irinotecan

Enhanced DNA damage repair is one mechanism behind colon cancer drug resistance. Thus, targeting molecular components of repair pathways with specific small molecule inhibitors may improve the efficacy of chemotherapy. ABT-888 and VE-821, inhibitors of poly-ADP-ribose-polymerase (PARP) and the serine/threonine-kinase Ataxia telangiectasia related (ATR), respectively, were used to treat colon cancer cell lines in combination with the topoisomerase-I inhibitor irinotecan (SN38). Our findings show that each of these molecules at nontoxic single agent concentrations synergized with SN38 to produce a 2.2 to 3 fold reduction in the 50% inhibitory concentration (IC50) of SN38 (Table 1). When combined, nontoxic concentrations of ABT-888 and VE-821 produced a 4.5 to 27 fold reduction in the IC50 of SN38. Furthermore, the combination of all three agents was associated with maximal G2-M arrest and enhanced DNA-damage (γH2AX). The mechanism of this enhanced synergy was associated with maximal suppression of SN38 induced PARP activity in the presence of both inhibitors. Furthermore, VE-821 enhancement of SN38 induced DNA-PK phosphorylation was abrogated by ABT-888, resulting in more unrepaired DNA damage. This novel combination of DNA repair inhibitors may be useful to enhance the activity of DNA damaging chemotherapies such as irinotecan and help circumvent resistance to this drug in colon cancer.

Cell LineVE-821 (μM)ABT-888 (μM)SN38 (IC50) ± SE (nM)I valueP valueLoVo13.5±1.214.5±1.90.30.020.55.8±2.00.40.030.59.4±1.00.70.0610.53.0±1.20.20.010.50.54.7±1.90.40.02HCT-1168.1±0.713.5±0.50.50.010.55.2±0.60.70.030.53.9±1.10.50.0310.50.3±0.030.10.010.50.52.1±0.40.30.01HT-2920.5±1.819.3±0.60.60.010.512.2±1.30.70.020.512.9±0.70.60.0210.53.9±0.50.30.010.50.56.1±0.20.40.01

Table 1 Colon cancer cell lines LoVo, HCT-116 and HT-29 were treated with SN38 alone or in combination with various concentrations of the ATR inhibitor VE-821 and/or the PARP inhibitor ABT-888. The IC50 values of SN38 were significantly reduced in the presence of VE-821 and/or ABT-888 for all cell lines. Drug synergy (I) values were determined, according to Berenbaum (1978), by calculating the ratio:

(IC50 SN38 with inhibitors/IC50 SN38 alone) + (inhibitor concentration used/IC50 inhibitor alone); I less than 1 = synergism, I equal to 1 = additive effect and I greater than 1 = antogonism.

Citation Format: David Davidson, Atlal Abu-Sanad, Yunzhe Wang, Fatemeh Hasheminasab, Justin Panasci, Raquel Aloyz, Lawrence Panasci. Simultaneous inhibition of ATR and PARP greatly sensitizes colon cancer cell lines to irinotecan. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5327. doi:10.1158/1538-7445.AM2015-5327

Simultaneous inhibition of ATR and PARP sensitizes colon cancer cell lines to irinotecan

Enhanced DNA damage repair is one mechanism involved in colon cancer drug resistance. Thus, targeting molecular components of repair pathways with specific small molecule inhibitors may improve the efficacy of chemotherapy. ABT-888 and VE-821, inhibitors of poly-ADP-ribose-polymerase (PARP) and the serine/threonine-kinase Ataxia telangiectasia related (ATR), respectively, were used to treat colon cancer cell lines in combination with the topoisomerase-I inhibitor irinotecan (SN38). Our findings show that each of these DNA repair inhibitors utilized alone at nontoxic single agent concentrations resulted in sensitization to SN38 producing a 1.4–3 fold reduction in the 50% inhibitory concentration (IC₅₀) of SN38 in three colon cancer cell lines. When combined together, nontoxic concentrations of ABT-888 and VE-821 produced a 4.5–27 fold reduction in the IC₅₀ of SN38 with the HCT-116 colon cancer cells demonstrating the highest sensitization as compared to LoVo and HT-29 colon cancer cells. Furthermore, the combination of all three agents was associated with maximal G₂ −M arrest and enhanced DNA-damage (γH2AX) in all three colon cancer cell lines. The mechanism of this enhanced sensitization was associated with: (a) maximal suppression of SN38 induced PARP activity in the presence of both inhibitors and (b) ABT-888 producing partial abrogation of the VE-821 enhancement of SN38 induced DNA-PK phosphorylation, resulting in more unrepaired DNA damage; these alterations were only present in the HCT-116 cells which have reduced levels of ATM. This novel combination of DNA repair inhibitors may be useful to enhance the activity of DNA damaging chemotherapies such as irinotecan and help produce sensitization to this drug in colon cancer.

A 12-gene signature to distinguish colon cancer patients with better clinical outcome following treatment with 5-fluorouracil or FOLFIRI

Currently, there is no marker in use in the clinical management of colon cancer to predict which patients will respond efficiently to 5‐fluorouracil (5‐FU), a common component of all cytotoxic therapies. Our aim was to develop and validate a multigene signature associated with clinical outcome from 5‐FU therapy and to determine if it could be used to identify patients who might respond better to alternate treatments. Using a panel of 5‐FU resistant and sensitive colon cancer cell lines, we identified 103 differentially expressed genes providing us with a 5‐FU response signature. We refined this signature using a clinically relevant DNA microarray‐based dataset of 359 formalin‐fixed and paraffin‐embedded (FFPE) colon cancer samples. We then validated the final signature in an external independent DNA microarray‐based dataset of 316 stage III FFPE samples from the PETACC‐3 (Pan‐European Trails in Alimentary Tract Cancers) clinical trial. Finally, using a drug sensitivity database of 658 cell lines, we generated a list of drugs that could sensitize 5‐FU resistant patients using our signature. We confirmed using the PETACC‐3 dataset that the overall survival of subjects responding well to 5‐FU did not improve with the addition of irinotecan (FOLFIRI; two‐sided log‐rank test p = 0.795). Conversely, patients who responded poorly to 5‐FU based on our 12‐gene signature were associated with better survival on FOLFIRI therapy (one‐sided log‐rank test p = 0.039). This new multigene signature is readily applicable to FFPE samples and provides a new tool to help manage treatment in stage III colon cancer. It also provides the first evidence that a subgroup of colon cancer patients can respond better to FOLFIRI than 5‐FU treatment alone.

Resistance to Dasatinib in primary chronic lymphocytic leukemia lymphocytes involves AMPK-mediated energetic re-programming

Chronic lymphocytic leukemia (CLL) is the most common leukemia in adults in the western world. Although promising new therapies for this incurable disease are being tested in clinical trials, the therapeutic relevance of metabolic rewiring in chronic lymphocytic leukemia (CLL) is poorly understood. The aim of this study was to identify targetable metabolic differences in primary CLL lymphocytes by the use of Dasatinib. Dasatinib is a multi-tyrosine kinase inhibitor used to treat chronic myelogenous leukemia (CML) and is being tested in clinical trials for several cancers including CLL. This drug has been shown to be beneficial to CML patients suffering from diabetes by reducing their glucose plasma levels. In keeping with this previous observation, we report that Dasatinib induced glucose use while reducing lactate production, suggesting that this tyrosine kinase inhibitor decreases aerobic glycolysis and shifts glucose use in primary CLL lymphocytes. Our results suggest that primary CLL lymphocytes (independently of traditional prognostic factors) can be stratified in two subsets by their sensitivity to Dasatinib in vitro. Increased glucose use induced by Dasatinib or by inhibition of mitochondrial respiration was not sufficient to sustain survival and ATP levels in CLL samples sensitive to Dasatinib. The two subsets of primary CLL lymphocytes are characterized as well by a differential dependency on mitochondrial respiration and the use of anabolic or catabolic processes to cope with induced metabolic/energetic stress. Differential metabolic reprogramming between subsets is supported by the contrasting effect on the survival of Dasatinib treated CLL lymphocytes with pharmacological inhibition of two master metabolic regulators (mTorc1 and AMPK) as well as induced autophagy. Alternative metabolic organization between subsets is further supported by the differential basal expression (freshly purified lymphocytes) of active AMPK, regulators of glucose metabolism and modulators of AKT signaling. The contrasting metabolic features revealed by our strategy could be used to metabolically target CLL lymphocyte subsets creating new therapeutic windows for this disease for mTORC1 or AMPK inhibitors. Indeed, we report that Metformin, a drug used to treat diabetes was selectively cytotoxic to Dasatinib sensitive samples. Ultimately, we suggest that a similar strategy could be applied to other cancer types by using Dasatinib and/or relevant tyrosine kinase inhibitors.

Effects of dna-dependent protein kinase inhibition by NU7026 on dna repair and cell survival in irradiated gastric cancer cell line N87

Repair of radiation-induced dna double-strand breaks is a key mechanism in cancer cell radio-resistance. The synthesized compound NU7026 specifically inhibits dna-dependent protein kinase (dna-pk) within the non-homologous end-joining repair mechanism. Earlier studies demonstrated increased radiosensitivity in dna-pk deficient cells compared with wild-type cells. In chronic leukemia cells, NU7026 appears to enhance the cytotoxic effect of chlorambucil. The radio-modifying effects of NU7026 on cell survival, cell cycle, apoptosis, and dna double-strand break repair have yet to be studied in gastric cancer cells.

METHODS

The gastric cancer cell line N87 was treated with 0 Gy or 4 Gy in the presence of NU7026 at a dose range of 0-20 μmol/L. Clonogenic assays were used to assess cell survival after treatment. Cell-cycle distribution was analyzed using propidium iodide with fluorescence-activated cell sorting. Apoptosis was detected using annexin-V and propidium iodide with fluorescence-activated cell sorting. The γH2AX assay was used to measure dna double-strand breaks.

RESULTS

Statistically significant increases in G2/M arrest were observed in N87 cells treated with radiation and NU7026 compared with those treated with radiation alone (p = 0.0004). Combined treatment also led to an increase in apoptosis (p = 0.01). At 24 hours, the γH2AX analysis revealed more dna double-strand breaks in N87 cells treated with radiation and NU7026 than in those treated with radiation alone (p = 0.04). Clonogenic assays demonstrated declining cell survival as both the radiation and the NU7026 dose increased. The dose enhancement factor at 0.1 survival fraction was 1.28 when N87 cells were treated with 4 Gy radiation and 5 μmol/L NU7026.

CONCLUSIONS

In gastric cancer cells, NU7026 appears to enhance the cytotoxic effect of irradiation as assessed by clonogenic assays. This increased cytotoxicity might be the result of an increase in dna double-strand breaks resulting in G2/M cell arrest and possibly higher levels of apoptosis.

Telomerase contributes to fludarabine resistance in primary human leukemic lymphocytes

We report that Imetelstat, a telomerase inhibitor that binds to the RNA component of telomerase (hTR), can sensitize primary CLL lymphocytes to fludarabine in vitro. This effect was observed in lymphocytes from clinically resistant cases and with cytogenetic abnormalities associated with bad prognosis. Imetelstat mediated-sensitization to fludarabine was not associated with telomerase activity, but with the basal expression of Ku80. Since both Imetelstat and Ku80 bind hTR, we assessed 1) if Ku80 and Imetelstat alter each other's binding to hTR in vitro and 2) the effect of an oligonucleotide complementary to the Ku binding site in hTR (Ku oligo) on the survival of primary CLL lymphocytes exposed to fludarabine. We show that Imetelstat interferes with the binding of Ku70/80 (Ku) to hTR and that the Ku oligo can sensitize CLL lymphocytes to FLU. Our results suggest that Ku binding to hTR may contribute to fludarabine resistance in CLL lmphocytes. This is the first report highlighting the potentially broad effectiveness of Imetelstat in CLL, and the potential biological and clinical implications of a functional interaction between Ku and hTR in primary human cancer cells.

Abstract B13: ATR and PARP inhibition enhances topoisomerase I-dependent DNA damage in colon cancer cell lines

Introduction: The understanding of DNA repairs pathways and their interactions allowed for the development of several targeted therapies, which sensitize neoplastic cells to the effects of DNA damaging chemotherapy. Poly-ADP ribose polymerase (PARP) inhibitors can increase the cytotoxicity of several anticancer agents by inhibiting various DNA repair pathways including Rad51 related homologous recombinational repair (HRR). However, inhibition of PARP may result in compensatory activation of the ATR pathway partially limiting the sensitization of chemotherapeutic agents seen with PARP inhibitors. Recently, a specific ATR inhibitor, VE-821 has demonstrated excellent sensitization to various chemotherapeutic agents with preferential antitumor activity in tumor cells as compared to normal cells (Reaper PM et al Nature Chem Biol 7: 428-30, 2011)

Colon cancer cell lines: HCT116/Lovo (p53 wild type) and HT29 (p53 mutated) were treated with SN38, the PARP inhibitor (ABT-888) and/or the ATR inhibitor (VE821) at different concentrations. The SRB cytotoxicity assay was used to determine the IC50 of each drug separately and in combination. DNA damage caused by these agents was quantified by phosphorylated-H2AX. Cell cycle alterations and protein levels (western analysis) were determined after drug treatment.

Results: Nontoxic concentrations (0.5-1 μM) of ABT-888 or VE-821 demonstrated a two to three fold decrease in the IC50 of SN38 in the colon cancer cell lines. Significantly, the combination of both inhibitors at the same nontoxic concentrations resulted in a dramatic 4 to 25-fold decrease in the IC50 of SN38 [HCT116 (8.1 nM to 0.3 nM), HT29 (20.5 nM to 3.9 nM) and Lovo (13.5nM to 3 nM)]. Notably, the observed effect was dose-dependent. In the Lovo cell line, the combination of SN38/VE821/ABT888 increased G2/M cell cycle arrest compared to SN38/VE821, SN38/ABT888 and SN38 alone. Similarly, increased phosphorylated-H2AX and apoptosis were seen with SN38/VE821/ABT888 in the Lovo and HCT-116 cell lines. Preliminary data utilizing the annexin-5 apoptosis assay in the HCT116 cell line supports the increased cell killing by the combination of all three agents. In the HCT116 cell line, treated with the SN38/VE821/ABT888 combination as compared to cells treated with SN38 alone, increased expression of p21 along with decreased expression of phospho-Chk1 was observed.

Conclusion: The SN38/ABT888/VE821 combination resulted in maximal synergy/chemosensitivity in all colon cancer cell lines, associated with increased DNA damage and apoptosis. Our data suggests that this combination may effectively overcome colon cancer resistance to irinotecan-based chemotherapy.

Citation Format: Atlal Abu-Sanad, David Davidson, Yunzhe Wang, John Pollard, Raquel Aloyz, Lawrence Panasci. ATR and PARP inhibition enhances topoisomerase I-dependent DNA damage in colon cancer cell lines. [abstract]. In: Proceedings of the AACR Precision Medicine Series: Synthetic Lethal Approaches to Cancer Vulnerabilities; May 17-20, 2013; Bellevue, WA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(5 Suppl):Abstract nr B13.

The PARP inhibitor ABT-888 synergizes irinotecan treatment of colon cancer cell lines

Poly [ADP-ribose] polymerase-1 (PARP-1) localizes rapidly to sites of DNA damage and has been associated with various repair mechanisms including base excision repair (BER) and homologous recombination/non-homologous end joining (HRR/NHEJ). PARP-1 acts by adding poly-ADP ribose side chains to target proteins (PARylation) altering molecular interactions and functions. Recently small molecule inhibitors of PARP-1 have been shown to have significant clinical potential and third generation PARP inhibitors are currently being investigated in clinical trials. These drugs alone or in combination with radio/chemotherapy have resulted in meaningful patient responses and an increase in survival in metastatic breast cancer cases bearing BRCA-deficient or triple negative tumors and BRCA-deficient ovarian cancer patients. ABT-888, a potent PARP-1 inhibitor, sensitizes many cancer cells in-vitro and in-vivo to temozolomide. As such, we hypothesized that colon cancers would be sensitized to the DNA damaging chemotherapeutic agents, oxaliplatin and irinotecan, by ABT-888. Using colon cancer cell lines significant synergy was observed between ABT-888 and irinotecan at concentrations of ABT-888 as low as 0.125 μM. The level of synergy observed correlated with the degree of PARP1 inhibition as measured biochemically in cell lysates. ABT-888 at concentrations of 0.5-4 μM resulted in synergy with oxaliplatin. Furthermore, 24 h post treatment combinations of ABT-888/irinotecan generally resulted in increased G2/M cell cycle arrest and increased levels of DNA damage, followed by increased levels of apoptosis 48 h post treatment. In conclusion this study suggests that ABT-888 may be a clinically effective adjuvant to current colon cancer therapies that include the use of irinotecan and/or oxaliplatin.

Small Molecules, Inhibitors of DNA-PK, Targeting DNA Repair, and Beyond

Many current chemotherapies function by damaging genomic DNA in rapidly dividing cells ultimately leading to cell death. This therapeutic approach differentially targets cancer cells that generally display rapid cell division compared to normal tissue cells. However, although these treatments are initially effective in arresting tumor growth and reducing tumor burden, resistance and disease progression eventually occur. A major mechanism underlying this resistance is increased levels of cellular DNA repair. Most cells have complex mechanisms in place to repair DNA damage that occurs due to environmental exposures or normal metabolic processes. These systems, initially overwhelmed when faced with chemotherapy induced DNA damage, become more efficient under constant selective pressure and as a result chemotherapies become less effective. Thus, inhibiting DNA repair pathways using target specific small molecule inhibitors may overcome cellular resistance to DNA damaging chemotherapies. Non-homologous end joining a major mechanism for the repair of double-strand breaks (DSB) in DNA is regulated in part by the serine/threonine kinase, DNA dependent protein kinase (DNA-PK). The DNA-PK holoenzyme acts as a scaffold protein tethering broken DNA ends and recruiting other repair molecules. It also has enzymatic activity that may be involved in DNA damage signaling. Because of its’ central role in repair of DSBs, DNA-PK has been the focus of a number of small molecule studies. In these studies specific DNA-PK inhibitors have shown efficacy in synergizing chemotherapies in vitro. However, compounds currently known to specifically inhibit DNA-PK are limited by poor pharmacokinetics: these compounds have poor solubility and have high metabolic lability in vivo leading to short serum half-lives. Future improvement in DNA-PK inhibition will likely be achieved by designing new molecules based on the recently reported crystallographic structure of DNA-PK. Computer based drug design will not only assist in identifying novel functional moieties to replace the metabolically labile morpholino group but will also facilitate the design of molecules to target the DNA-PKcs/Ku80 interface or one of the autophosphorylation sites.

Heterozygous mutations in the PALB2 hereditary breast cancer predisposition gene impact on the three-dimensional nuclear organization of patient-derived cell lines

PALB2/FANCN is a BRCA1- and BRCA2-interacting Fanconi Anemia (FA) protein crucial for key BRCA2 genome caretaker functions. Heterozygous germline mutations in PALB2 predispose to breast cancer and biallelic mutations cause FA. FA proteins play a critical role in the telomere maintenance pathway, with telomeric shortening observed in FA cells. Less is known about telomere maintenance in the heterozygous state. Here, we investigate the roles of PALB2 heterozygous mutations in genomic instability, an important carcinogenesis precursor. Patient-derived lymphoblastoid (LCL) and fibroblast (FCL) cell lines with monoallelic truncating PALB2 mutations were investigated using a combination of molecular imaging techniques including centromeric FISH, telomeric Q-FISH and spectral karyotyping (SKY). Mitomycin C and Cisplatin sensitivity was assayed via cellular metabolism of WST-1. The PALB2 c.229delT FCL showed increases in telomere counts associated with increased mean intensity compared with two wild-type FCLs generated from first-degree relatives (P =1.04E-10 and P =9.68E-15) and it showed evidence of chromosomal rearrangements. Significant differences in centromere distribution were observed in one of three PALB2 heterozygous FCLs analyzed when compared with PALB2 wild-type, BRCA1 and BRCA2 heterozygous FCLs. No significant consistently increased sensitivity to Mitomycin C or Cisplatin was observed in LCLs. Our results are suggestive of an altered centromere distribution profile and a telomere instability phenotype. Together, these may indicate critical nuclear organization defects associated with the predisposition to transformation and early stage development of PALB2-related cancers.

The phosphatidylinositol-3 kinase I inhibitor BKM120 induces cell death in B-chronic lymphocytic leukemia cells in vitro

BKM120, a pan class I PI3K inhibitor, was cytotoxic in the majority of primary B-chronic lymphocytic leukemia (CLL) lymphocytes, including samples from patients who have a high-risk for poor response to treatment (patient with del11 and del17) at clinically obtainable concentrations. The PI3Kδ inhibitor Cal-101 is cytotoxic in B-CLL lymphocytes in vitro and is active in the treatment of CLL in vivo. Interestingly, we demonstrated that BKM120 is 3.6 fold more toxic than Cal-101 in malignant B-CLL lymphocytes in vitro. BKM120 cytotoxicity correlated with the basal expression of proteins involved in the PI3K/Akt pathway. A protein signature of PI3K pathway proteins predicts the response to BKM120 treatment. In the primary B-CLL lymphocytes tested in vitro, BKM120 decreased the phosphorylation status of molecular biomarkers used as indicators of PI3K pathway inhibition in vivo. Also, BKM120 induced apoptosis in primary B-CLL cells culture in the presence and absence of stromal cell support. Our findings suggest that BKM120 should be tested clinically in CLL.

Abstract B24: De novo and acquired resistance to first-line standard therapy in colorectal cancer: from cell lines to metastatic tumors

Introduction: Personalized medicine (PM) is a concept that has raised high expectations amongst scientists, clinicians, and patients. An emerging approach is to examine tumor biopsy material for genomic changes that are known targets of currently available therapeutic agents, with the assumption that a clinical benefit will be observed if the target is inhibited. While striking anecdotal reports are predictable from this approach, the clinical impact of these agents is limited by the inevitable development of therapeutic resistance. Our focus is on the design of parallel research programs using both in vitro and in vivo strategies, in an effort to delay or inhibit resistance. We present here preliminary data for a signature of resistance to standard first-line treatment - fluorouracil, folinic acid, oxaliplatin and bevacizumab (FOLFOX/B) using cell line models of resistance to this regimen. In parallel, we are conducting a prospective study to identify biomarkers of clinical resistance to first-line therapy in patients with metastatic colorectal cancer (CRC) (NCT00984048).

Methods: Ten established CRC cell lines were treated with FOLFOX/B and categorized as resistant or sensitive based on IC50 values. In parallel, patients who consented to an initial biopsy and one at disease progression following an initial response were identified as intrinsically resistant or as having acquired resistance during treatment. CRC cell lines that were initially sensitive were rendered resistant to mimic the acquired resistance in patients, by serial passages with gradual increases in concentration of the combination regimen. We compared microarray data from three sensitive and three resistant cell lines.

Results: We found a different expression pattern from microarray data comparing sensitive and resistant cell lines, thereby indicating a potential signature of resistance to FOLFOX/B. Interestingly, we found that the Src family kinase Lyn was overexpressed in resistant cells lines. Treating cells with non-cytotoxic concentration of dasatinib, a dual Src family kinase and Abl inhibitor, sensitized both the parental sensitive cells and the cells with acquired resistance to FOLFOX/B, thereby suggesting that combination treatment with dasatinib may be effective in delaying or inhibiting resistance. We have thus far collected needle core biopsies from liver metastases from forty patients who agreed to partake in this multi-center trial. Eligible patients have confirmed metastatic CRC, measurable disease, and consent to three needle-core biopsies (NCBs) of a non-resectable liver metastasis before treatment and at resistance, as well as serial blood collection throughout the study. Using standard operating procedures developed for this trial, we were able to both preserve morphology and obtain high-quality genomic material from biopsy tissue. We will determine if the resistance signature and overexpression of Lyn observed in the resistant CRC cell lines are similarly demonstrated in patients that were intrinsically resistant to FOLFOX/B.

Conclusions: We have designed parallel in vitro and in vivo experiments to study resistance to standard first-line treatment for mCRC. These studies provide insight on metastatic signatures of resistance and suggest combination therapies to delay or inhibit therapeutic resistance in patients.

Abstract 5534: Building the organization framework for biopsy-driven translational research: The Quebec Clinical Research Organization in Cancer (Q-CROC) experience

Introduction: The success of personalized medicine in oncology relies on translational research efforts to identify biomarkers that will influence clinical management. The discovery and validation of biomarkers is a concerted effort requiring an organizational framework that is often underestimated. The Quebec Clinical Research Organization in Cancer (Q-CROC) consortium is a multi-disciplinary and multi-institutional group of scientists and clinicians devoted to integrating and enhancing translational and clinical research capacity in Quebec. We describe here the organizational framework driving a multicenter, prospective study to identify biomarkers of clinical resistance to first-line therapy in metastatic colorectal cancer (NCT00984048, Q-CROC-01). Results: The Q-CROC consortium has put in place an organizational infrastructure to support the activities and operations of its translational projects. We identified and addressed several critical issues during the course of the Q-CROC-01 translational project that were also common to our subsequent biomarker-driven trial in lymphoma (Q-CROC-02, NCT01238692) and breast cancer (Q-CROC-03, NCT01276899). Examples of these issues include: (i) feasibility and burden of tissue collection at participating sites, (ii) limiting pre-analytical variability in blood and tissue specimens for functional downstream applications, (iii) verification of tumor content on biopsy specimens, (iv) tracking sample flow, (v) integration of clinical data with discovery platforms, and (vi) engaging participation throughout all steps of the project. In part to address the above issues, we established five operational Cores: clinical, biobank, biospecimen processing, bioanalytical and bioinformatic. A further challenge was the integration between these Cores, who for the most part operated in silos. We observed that a critical element to unify all components of the consortium was a scientific project management team, consisting of dedicated individuals regularly interacting with each Core to ensure that objectives were aligned and deliverables were met. This academic framework for translational research may be comparable to that of multicenter clinical trials undertaken by industry, but some challenges, including financial and time constraints, data sharing and IP agreements, and engagement of its members, may be more palpable in the academic setting. Conclusion: Infrastructure science is underestimated and under-reported in translational cancer research and is crucial to the success of any large-scale biomarker discovery effort. Our experience with three multi-institutional biomarker-driven trials is that progress hinges upon the availability of an infrastructure that is not only the sum of its parts but that provides a concrete link between each component.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5534. doi:1538-7445.AM2012-5534

Trastuzumab and vinorelbine in early stages of HER2-positive breast cancer

The combination of vinorelbine and trastuzumab (VH) is highly active and well tolerated in patients with metastatic HER2+ breast cancer. We assessed the efficacy and tolerability of VH as an alternative adjuvant treatment for patients with localized breast cancer refusing or ineligible for standard adjuvant trastuzumab-based chemotherapy. Twenty-eight patients with stage I-III breast cancer were treated only with VH as preoperative or postoperative chemotherapy. Fourteen patients received VH as adjuvant treatment for pT1a-b pN0 or eR+ pT1c pN0 cancers. VH was well tolerated, the only grade 3-4 toxicity being neutropenia with 2 cases of febrile neutropenia. At a median follow-up of 39 months, no breast cancer relapses were documented; moreover, overall and disease-free survival was 96.4%. In summary, our results indicate that VH is effective and well tolerated. VH should be prospectively tested as adjuvant treatment for pN0 pT1a-b breast cancer patients for which no standard treatment is well defined.

Magnetotactic bacteria penetration into multicellular tumor spheroids for targeted therapy

Preliminary experiments showed that MC-1 magnetotactic bacteria (MTB) could be used for the delivery of therapeutic agents to tumoral lesions. Each bacterium can provide a significant thrust propulsion force generated by two flagella bundles exceeding 4pN. Furthermore, a chain of single-domain magnetosomes embedded in the cell allows computer directional control and tracking using a magnetic resonance imaging (MRI) system. Although these embedded functionalities suggest that MTB when under the influence of an external computer could be considered as biological microrobots with the potential of targeting tumors, little is known about their level of penetration in tumoral tissues. In this paper, in vitro experiments were performed to assess the capability of these bacteria to penetrate tumor tissue for the delivery of therapeutic agents. Multicellular tumor spheroids were used since they reproduce many properties of solid tumors. The results show the ability of these MTB when submitted to a directional magnetic field to penetrate inside a 3D multicellular tumor spheroid through openings present in the tissue.

The effect of a DNA repair gene on cellular invasiveness: XRCC3 over-expression in breast cancer cells

Over-expression of DNA repair genes has been associated with resistance to radiation and DNA-damage induced by chemotherapeutic agents such as cisplatin. More recently, based on the analysis of genome expression profiling, it was proposed that over-expression of DNA repair genes enhances the invasive behaviour of tumour cells. In this study we present experimental evidence utilizing functional assays to test this hypothesis. We assessed the effect of the DNA repair proteins known as X-ray complementing protein 3 (XRCC3) and RAD51, to the invasive behavior of the MCF-7 luminal epithelial-like and BT20 basal-like triple negative human breast cancer cell lines. We report that stable or transient over-expression of XRCC3 but not RAD51 increased invasiveness in both cell lines in vitro. Moreover, XRCC3 over-expressing MCF-7 cells also showed a higher tumorigenesis in vivo and this phenotype was associated with increased activity of the metalloproteinase MMP-9 and the expression of known modulators of cell-cell adhesion and metastasis such as CD44, ID-1, DDR1 and TFF1. Our results suggest that in addition to its' role in facilitating repair of DNA damage, XRCC3 affects invasiveness of breast cancer cell lines and the expression of genes associated with cell adhesion and invasion.

Irinotecan and DNA-PKcs inhibitors synergize in killing of colon cancer cells

This study sought to measure the degree of synergy induced by specific small molecule inhibitors of DNA-PK [NU7026 and IC486241 (ICC)], a major component of the non-homologous end-joining (NHEJ) pathway, with SN38 or oxaliplatin. Synergy between the DNA damaging drugs and the DNA-PK inhibitors was assessed using the sulforhodamine-B assay (SRB). Effects of drug combinations on cell cycle and DNA-PK activity were determined using flow cytometry and western blot analysis. DNA damage was assessed via comet assay and quantification of γH2AX. The role of homologous recombination repair (HRR) was determined by nuclear Rad51 protein levels and a GFP reporter recombination assay. Significant reductions in the IC(50) values of SN38 were observed at 5 and 10 μM of DNA-PK inhibitors. Moreover, at 1-2 μM (attainable concentrations with ICC in mice) these DNA-PKcs inhibitors demonstrated synergistic reductions in the IC(50) of SN38. Flow cytometric data indicated that SN38 and SN38 in combination with DNA-PKcs inhibitors showed dramatic G2/M arrest at 24 h. Furthermore, reduced phosphorylation of DNA-PKcs and increased DNA damage were observed at this time point with SN38 in combination with DNA-PKcs inhibitors as compared to cells treated with SN38 alone. SN38 alone and in the presence of ICC increased nuclear Rad51 protein levels. Furthermore, inhibition of DNA-PKcs increased HRR suggesting that NHEJ is a negative regulator of HRR. These data indicate that small molecule inhibitors of DNA-PKcs dramatically enhance the efficacy of SN38 in colon cancer cell lines.

Vav-1 expression correlates with NFκB activation and CD40-mediated cell death in diffuse large B-cell lymphoma cell lines

Diffuse large B-cell lymphoma (DLBCL) is an aggressive malignancy with a variable response to therapy. We have previously shown that DLBCL cell lines differ in their susceptibility to CD40-mediated cell death, and that resistance to CD40-targeted antibodies correlated with increased expression of markers of immature B-cell and absence of Vav-1 mRNA. We used gene expression profiling to investigate the mechanism of CD40 resistance in these cell lines, and found that resistance correlated with lack of Vav-1 and inability to activate NFκB upon CD40 ligation. Analysis of tissue microarrays of 213 DLBCL cases revealed that Vav-1 expression correlated with a higher proliferative index and the presence of the post-germinal centre marker Irf-4. Our results suggest that Vav-1 expression may be associated with activated B-cell DLBCL origin and higher proliferative activity, and indicate Vav-1 as a potential marker to identify tumours likely to respond to CD40-targeted therapies.

p53 and autophagy contribute to dasatinib resistance in primary CLL lymphocytes

B-cell chronic lymphocytic leukemia (CLL) is the most common leukemia in adults and there is no cure for the disease. Although dasatinib is cytotoxic to primary CLL lymphocytes in vitro, the drug has been shown to be active in a small percent of CLL patients. Our previous results suggest that dasatinib targets del17 CLL lymphocytes which are the CLL patients with the worst prognosis. Here we present mechanistic evidence that dasatinib induces endoplasmic reticulum stress and autophagy in CLL lymphocytes. Furthermore we provide evidence suggesting that autophagy mediates resistance to the drugs, process that is modulated by p53.

Abstract LB-100: Optimal modulation of DNA repair in CLL therapy

Resistance to chlorambucil (CLB) in chronic lymphocytic leukemia (CLL) can occur as a consequence of increased DNA repair including c-abl stimulated Rad-51 related homologous recombinational repair (HRR) and DNA-PK related nonhomologous endjoining (NHEJ).

Recent reports suggest that the nonreceptor tyrosine kinase c-abl plays an important role in CLL. In particular, we have previously demonstrated that imatinib inhibition of c-abl or NU7026 inhibition of DNA-PK in CLL lymphocytes results in sensitization to CLB in most samples. Here we report that nilotinib, a superpotent (20-30 fold greater than niltinib) inhibitor of c-abl is more efficacious than imatinib in sensitizing CLL lymphocytes to CLB in the majority of the CLL lymphocyte samples associated with a greater nilotinib related inhibition of c-abl autophosporylation, increased apoptosis and decreased repair of CLB-induced DNA damage (increased activated H2AX).

Furthermore, in CLL samples in which c-abl was inhibited by either inhibitor, there was an increased activation of DNA-PK. Utilizing NU7026, a specific inhibitor of DNA-PK, with nilotinib or imatinib resulted in further sensitization to CLB but there was a greater sensitization to CLB with nilotinib than imatinib. These results suggest: (1) a more potent inhibition of c-abl is more efficacious in sensitizing CLL lymphocytes to CLB, (2) inhibition of c-abl results in a compensatory increase in DNA-PK and (3) inhibiting both DNA repair systems optimally sensitizes CLL lymphocytes to CLB, an effect which is most pronounced with the more potent c-abl inhibitor, nilotinib.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-100.

Trastuzumab and vinorelbine (TV) in early stages of breast cancer

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Background: HER-2+ breast cancers (BCs) have a higher relapse rate, even for early stages of disease. The combination of trastuzumab and vinorelbine (TV) displays a high degree of synergism both preclinically and in metastatic BC patients that typically tolerate TV remarkably well. Occasionally, patients refuse standard treatment with chemotherapy and trastuzumab because of toxic side effects. In our institution, some of these patients accepted to receive treatment with TV. Methods: We retrospectively collected data on patients with stage I-III BCs, treated with TV as the only chemotherapy regimen. Most patients received TV on a weekly basis (one week off for V every 3–4 weeks) for ∼6 months, followed by 6 more months of T only. Results: Between May 2003 and June 2008, 23 patients were started on weekly TV. Median age was 66. Five patients received TV as preoperative treatment for BCs with the following clinical stages: IIB (1); IIIA (1); IIIB (3). The other 18 patients were pathologically staged as: stage I (11); IIA (5); IIIB (2). All cancers were HER2+; 65% of patients also received hormonal treatment for ER/PR+ disease. 3 patients had been previously treated for BC, and received TV as “adjuvant” treatment after a local relapse. Only one of these patients had previously received chemotherapy, while none had received prior T. No pathological complete response was found at surgery after preoperative TV. TV was very well tolerated, with one patient developing febrile neutropenia, 4 patients grade 3–4 uncomplicated neutropenia, and no other grade 3–4 events. During therapy, 5 patients had an asymptomatic 10–20% drop in the LVEF (Grade 1). Follow-up MUGA scans at 1 year after TV so far failed to show any significant abnormality. At an average follow-up of 26 months, one patient died for non-BC related causes, and all the other 22 patients are disease-free. Conclusions: TV is safe and very well tolerated, with no significant cardiac toxicity in our patient population. Preliminary follow-up data suggest that TV may be an acceptable alternative (neo-)adjuvant therapy for patients refusing “toxic” chemotherapy. Further studies prospectively testing TV as adjuvant treatment should be considered for patients with stage 1A BC, for which no standard treatment is clearly defined.

No significant financial relationships to disclose.

Dasatinib sensitizes primary chronic lymphocytic leukaemia lymphocytes to chlorambucil and fludarabine in vitro

The dual c-abl/Src kinase inhibitor, dasatinib, utilized to treat chronic myeloid leukaemia (CML) when used at clinically attainable sublethal concentrations, synergistically sensitized primary chronic lymphocytic leukaemia (CLL) lymphocytes to chlorambucil and fludarabine. In contrast, dasatinib alone demonstrated toxicity to CLL lymphocytes at concentrations that are generally not clinically attainable. Dasatinib resistance and poorer dasatinib-mediated sensitization to chlorambucil and fludarabine was associated with higher expression of c-abl protein levels. In contrast, chlorambucil and fludarabine resistance correlated with basal p53 protein levels. Moreover, Western blot analysis after in vitro treatment of primary CLL lymphocytes with dasatinib, chlorambucil and/or fludarabine, showed that dasatinib: (i) inhibited c-abl function (e.g. downregulation of c-abl protein levels and decreased the phosphorylation of a c-abl downstream target, Dok2), (ii) decreased chlorambucil/fludarabine induced accumulation of p53 protein levels, (iii) altered the response to chlorambucil/fludarabine induced DNA-damage as evidenced by an increase in chlorambucil/fludarabine-induced H2AX phosphorylation, and (iv) accentuated the c-abl downregulation induced by chlorambucil/fludarabine. Our results suggest that dasatinib in combination with chlorambucil or fludarabine may improve the therapy of CLL.

Identification and characterization of novel SNPs in CHEK2 in Ashkenazi Jewish men with prostate cancer

Checkpoint kinase 2 (CHEK2) is a protein involved in arresting cell cycle in response to DNA damage. To investigate whether it plays an important role in the development of prostate cancer (PRCA) in the Ashkenazi Jewish (AJ) population, we sequenced CHEK2 in 75 AJ individuals with prostate, breast, or no cancer (n=25 each). We identified seven coding SNPs (five are novel) that changed the amino-acid sequence, resulting in R3W, E394F, Y424H, S428F, D438Y, P509S, and P509L. We determined the frequency of each variant in 76 AJ families collected by members of the International Consortium for Prostate Cancer Genetics (ICPCG) where >or=2 men were affected by PRCA. Only one variant, Y424H in exon 11, was identified in more than two families. Exon 11 was then screened in nine additional AJ ICPCG families (a total of 85 families). The Y424H variant occurred in nine affected cases from four different families; however, it did not completely segregate with the disease. We performed bioinformatics analysis, which showed that Y424H is a non-conservative missense substitution that falls at a position that is invariant in vertebrate CHEK2 orthologs. Both SIFT and Align-GVGD predict that Y424H is a loss of function mutation. However, the frequency of Y424H was not significantly different between unselected AJ cases from Montreal/Memorial Sloan Kettering Cancer Centre (MSKCC) and AJ controls from Israel/MSKCC (OR 1.18, 95%CI: 0.34-4.61, p=.99). Moreover, functional assays using Saccharomyces cerevisiae revealed that the Y424H substitution did not alter function of CHEK2 protein. Although we cannot rule out a subtle influence of the CHEK2 variants on PRCA risk, these results suggest that germline CHEK2 mutations have a minor role in, if any, PRCA susceptibility in AJ men.

XRCC3 depletion induces spontaneous DNA breaks and p53-dependent cell death

In vertebrate cells, Xrcc3 initiates the repair of exogenous induced-DNA breaks during S and G(2)/M phases of the cell cycle by homologous recombination. However, much less is known of the role of Xrcc3 in the response to spontaneous DNA breaks. Using a siRNA approach, we show that depletion of XRCC3 inhibits the proliferation of MCF7 breast cancer cells. This inhibition of replication coincides with the accumulation of DNA breaks, as shown by the comet assay. Cell cycle specific analysis of gammaH2AX expression shows that S and G2/M phase cells express the highest fraction of gammaH2AX positive cells. This is consistent with replication-dependent accumulation of DNA breaks and deficient homologous recombination. While the induction of gammaH2AX is followed by cell death in parental cells, a p53 knockdown derivative becomes more resistant to XRCC3 depletion-induced death without changes in the levels of gammaH2AX. These results show that XRCC3 is required for the proliferation of MCF7 cells, and that decrease in its expression leads to the accumulation of DNA breaks and the induction of p53-dependent cell death.

Chlorambucil cytotoxicity in malignant B lymphocytes is synergistically increased by 2-(morpholin-4-yl)-benzo[h]chomen-4-one (NU7026)-mediated inhibition of DNA double-strand break repair via inhibition of DNA-dependent protein kinase

Chlorambucil (CLB) treatment is used in chronic lymphocytic leukemia (CLL) but resistance to CLB develops in association with accelerated repair of CLB-induced DNA damage. Phosphorylated histone H2AX (gammaH2AX) is located at DNA double-strand break (DSB) sites; furthermore, it recruits and retains damage-responsive proteins. This damage can be repaired by nonhomologous DNA end-joining (NHEJ) and/or homologous recombinational repair (HR) pathways. A key component of NHEJ is the DNA-dependent protein kinase (DNA-PK) complex. Increased DNA-PK activity is associated with resistance to CLB in CLL. We used the specific DNA-PK inhibitor 2-(morpholin-4-yl)-benzo[h]chomen-4-one (NU7026) to sensitize CLL cells to chlorambucil. Our results indicate that in a CLL cell line (I83) and in primary CLL-lymphocytes, chlorambucil plus NU7026 has synergistic cytotoxic activity at nontoxic doses of NU7026. CLB treatment results in G(2)/M phase arrest, and NU7026 increases this CLB-induced G(2)/M arrest. Moreover, a kinetic time course demonstrates that CLB-induced DNA-PK activity was inhibited by NU7026, providing direct evidence of the ability of NU7026 to inhibit DNA-PK function. DSBs, visualized as gammaH2AX, were enhanced 24 to 48 h after CLB and further increased by CLB plus NU7026, suggesting that the synergy of the combination is mediated by NU7026 inhibition of DNA-PK with subsequent inhibition of DSB repair.