Modulation of the ribonucleotide reductase-antimetabolite drug interaction in cancer cell lines

Doxycycline potentiates the anti-proliferation effects of gemcitabine in pancreatic cancer cells

Gemcitabine is often recommended as a first-line treatment for patients with metastatic pancreatic cancer. However, gemcitabine resistance is a major challenge in the treatment of pancreatic ductal adenocarcinoma. Our group serendipitously identified the role of doxycycline as a potentiator of gemcitabine efficacy in pancreatic cancer cells. Doxycycline and gemcitabine co-treatment was significantly more cytotoxic to pancreatic cancer cells compared to gemcitabine alone. Interestingly, doxycycline only exerted synergistic effects when coupled with gemcitabine as opposed to other conventional chemotherapeutics including nucleoside analogs. The anti-clonogenic effects of gemcitabine on pancreatic cancer cells were also enhanced by doxycycline. According to cell cycle analyses, doxycycline prolonged gemcitabine-mediated S phase cell cycle arrest. Further, gene expression profiling analyses indicated that a small set of genes involved in cell cycle regulation were uniquely modulated by gemcitabine and doxycycline co-treatment compared to gemcitabine alone. Western blot analyses indicated that several cell cycle-related proteins, including cyclin D1, p21, and DNA damage inducible transcript 4 (DDIT4), were further modulated by doxycycline and gemcitabine co-treatment. Taken together, our findings indicate that doxycycline enhances the effects of gemcitabine on cell cycle progression, thus rendering pancreatic cancer cells more sensitive to gemcitabine. However, additional studies are required to assess the mechanisms of doxycycline and gemcitabine synergism, which might lead to novel treatment options for pancreatic cancer.

Antibiotic therapy augments the efficacy of gemcitabine-containing regimens for advanced cancer: a retrospective study

BACKGROUND

The addition of antibiotics reportedly augments the efficacy of gemcitabine (GEM) in tumor-bearing mice. However, whether this phenomenon is also observed in cancer patients remains unclear. In the present study, we aimed to assess whether antibiotics for treatment or prevention of infection augments treatment efficacies of GEM-containing regimens in patients with any type of cancer.

METHODS

Medical records of patients diagnosed with cancer histopathologically and treated with GEM-containing regimens (n=169) were retrospectively reviewed. Patients were assigned into two groups: antibiotics-untreated group (patients who were treated with GEM-containing regimens but without antibiotics) and antibiotics-treated group (patients who were treated with GEM-containing regimens plus antibiotics). Response rates, progression-free survival (PFS) time, and overall survival (OS) time were analyzed for each group.

RESULTS

The response rates of the antibiotics-untreated and antibiotics-treated groups with GEM-containing regimens were 15.1% and 27.6%, respectively. The median PFS times of the antibiotics-untreated and antibiotics-treated groups were 2.5 (95% CI: 1.86-3.73) and 4.9 (95% CI: 3.47-6.0) months, respectively. The median OS times of the antibiotics-untreated and antibiotics-treated groups were 7.53 (95% CI: 5.63-9.57) months and 13.83 (95% CI: 10.83-16.43) months, respectively.

CONCLUSION

The addition of antibiotics augments the treatment efficacies of GEM-containing regimens, and it may be a potential therapeutic option to improve treatment efficacies of GEM-containing regimens in patients with advanced cancer.

Chronic p27Kip1 Induction by Dexamethasone Causes Senescence Phenotype and Permanent Cell Cycle Blockade in Lung Adenocarcinoma Cells Over-expressing Glucocorticoid Receptor

Dexamethasone (Dex), co-administered to lung adenocarcinoma patients with pemetrexed chemotherapy, protects against pemetrexed cytotoxicity by inducing reversible G1 arrest, reflected by the effect of Dex on FLT-PET images of patient tumors. However, perioperative Dex treatment increases survival but the mechanism is unknown. In cells with glucocorticoid receptor-α (GR) expression corresponding to higher clinical tumor levels, Dex-induced growth arrest was followed by marked cell expansion, beta-galactosidase expression and Ki67 negativity, despite variable p53 and K-RAS status. Dex induced a transient early surge in p21^Cip1. However, a progressive, irreversible loss of clonogenic growth, whose time of onset was dependent on GR level and Dex dose, was independent of p21^Cip1and caused by gradual accumulation of p27^Kip1 due to transcriptional activation of p27^Kip1 by Dex. This effect was independent of canonical pathways of senescence or p27^Kip1 regulation. The in vitro observations were reflected by growth suppression and P27^Kip1 induction in GR-overexpressing tumor xenografts compared with isogenic low-GR tumors. Extended Dex treatment induces irreversible cell cycle blockade and a senescence phenotype through chronic activation of the p27^Kip1 gene in GR overexpressing lung tumor cell populations and hence could improve outcome of surgery/pemetrexed chemotherapy and sensitize tumors to immunotherapy.

Promising molecular mechanisms responsible for gemcitabine resistance in cancer

Gemcitabine is the first-line treatment for pancreatic ductual adenocarcinoma (PDAC) as well as acts against a wide range of other solid tumors. Patients usually have a good initial response to gemcitabine-based chemotherapy but would eventually develop resistance. To improve survival and prognosis of cancer patients, better understanding of the mechanisms responsible for gemcitabine resistance and discovery of new therapeutic strategies are in great need. Amounting evidence indicate that the developmental pathways, such as Hedgehog (Hh), Wnt and Notch, become reactivated in gemcitabine-resistant cancer cells. Thus, the strategies for targeting these pathways may sensitize cancer cells to gemcitabine treatment. In this review, we will summarize recent development in this area of research and discuss strategies to overcome gemcitabine resistance. Given the cross-talk between these three developmental signaling pathways, designing clinical trials using a cocktail of inhibitory agents targeting all these pathways may be more effective. Ultimately, our hope is that targeting these developmental pathways may be an effective way to improve the gemcitabine treatment outcome in cancer patients.

Identifying compound efficacy targets in phenotypic drug discovery

The identification of the efficacy target(s) for hits from phenotypic compound screens remains a key step to progress compounds into drug development. In addition to efficacy targets, the characterization of epistatic proteins influencing compound activity often facilitates the elucidation of the underlying mechanism of action; and, further, early determination of off-targets that cause potentially unwanted secondary phenotypes helps in assessing potential liabilities. This short review discusses the most important technologies currently available for characterizing the direct and indirect target space of bioactive compounds following phenotypic screening. We present a comprehensive strategy employing complementary approaches to balance individual technology strengths and weaknesses.

Glucocorticoid receptor status is a principal determinant of variability in the sensitivity of non-small-cell lung cancer cells to pemetrexed

INTRODUCTION

Pemetrexed is an S-phase targeted drug in front-line or maintenance therapy of advanced nonsquamous non-small-cell lung cancer (NSCLC) but methods are needed for predicting the drug response. Dexamethasone is typically administered the day before, the day of, and the day after pemetrexed. As dexamethasone strongly regulates many genes including p53 through the glucocorticoid receptor (GR), we hypothesized that dexamethasone influences tumor response to pemetrexed.

METHODS

Eight nonsquamous NSCLC cell line models with varied p53 and GRα/GRβ status were used for gene expression and cell-cycle analyses and for loss- or gain-of-function experiments.

RESULTS

In three cell lines dexamethasone profoundly, but reversibly, suppressed the fraction of S-phase cells. Dexamethasone also reversibly repressed expression of thymidylate synthase and dihydrofolate reductase, which are primary targets of pemetrexed but are also quintessential S-phase enzymes as well as the S-phase-dependent expression of thymidine kinase 1. Dexamethasone also decreased expression of the major pemetrexed transporters, the reduced folate carrier and the proton coupled folate transporter. Only cells expressing relatively high GRα showed these dexamethasone effects, regardless of p53 status. In cells expressing low GRα, the dexamethasone response was rescued by ectopic GRα. Further, depletion of p53 did not attenuate the dexamethasone effects. The presence of dexamethasone during pemetrexed treatment protected against pemetrexed cytotoxicity in only the dexamethasone responsive cells.

CONCLUSIONS

The results predict that in nonsquamous NSCLC tumors, reversible S-phase suppression by dexamethasone, possibly combined with a reduction in the drug transporters, attenuates responsiveness to pemetrexed and that GR status is a principal determinant of tumor variability of this response.

Randomized international phase III trial of ERCC1 and RRM1 expression-based chemotherapy versus gemcitabine/carboplatin in advanced non-small-cell lung cancer

PURPOSE

We assessed whether chemotherapy selection based on in situ ERCC1 and RRM1 protein levels would improve survival in patients with advanced non-small-cell lung cancer (NSCLC).

PATIENTS AND METHODS

Eligible patients were randomly assigned 2:1 to the trial's experimental arm, which consisted of gemcitabine/carboplatin if RRM1 and ERCC1 were low, docetaxel/carboplatin if RRM1 was high and ERCC1 was low, gemcitabine/docetaxel if RRM1 was low and ERCC1 was high, and docetaxel/vinorelbine if both were high. In the control arm, patients received gemcitabine/carboplatin. The trial was powered for a 32% improvement in 6-month progression-free survival (PFS).

RESULTS

Of 331 patients registered, 275 were eligible. The median number of cycles given was four in both arms. A tumor rebiopsy specifically for expression analysis was required in 17% of patients. The median time from informed consent to expression analysis was 11 days. We found no statistically significant differences between the experimental arm and the control arm in PFS (6.1 months v 6.9 months) or overall survival (11.0 months v 11.3 months). A subset analysis revealed that patients with low levels for both proteins who received the same treatment in both treatment arms had a statistically better PFS (P = .02) in the control arm (8.1 months) compared with the experimental arm (5.0 months).

CONCLUSION

This demonstrates that protein expression analysis for therapeutic decision making is feasible in newly diagnosed patients with advanced-stage NSCLC. A tumor rebiopsy is safe, required in 17%, and acceptable to 89% (47 of 53) of patients.

A kinome screen identifies checkpoint kinase 1 (CHK1) as a sensitizer for RRM1-dependent gemcitabine efficacy

Gemcitabine is among the most efficacious and widely used antimetabolite agents. Its molecular targets are ribonucleotide reductase M1 (RRM1) and elongating DNA. Acquired and de novo resistance as a result of RRM1 overexpression are major obstacles to therapeutic efficacy. We deployed a synthetic lethality screen to investigate if knockdown of 87 selected protein kinases by siRNA could overcome RRM1-dependent gemcitabine resistance in high and low RRM1-expressing model systems. The models included genetically RRM1-modified lung and breast cancer cell lines, cell lines with gemcitabine-induced RRM1 overexpression, and a series of naturally gemcitabine-resistant cell lines. Lead molecular targets were validated by determination of differential gemcitabine activity using cell lines with and without target knock down, and by assessing synergistic activity between gemcitabine and an inhibitor of the lead target. CHK1 was identified has the kinase with the most significant and robust interaction, and it was validated using AZD7762, a small-molecule ATP-competitive inhibitor of CHK1 activation. Synergism between CHK1 inhibition and RRM1-dependent gemcitabine efficacy was observed in cells with high RRM1 levels, while antagonism was observed in cells with low RRM1 levels. In addition, four cell lines with natural gemcitabine resistance demonstrated improved gemcitabine efficacy after CHK1 inhibition. In tumor specimens from 187 patients with non-small-cell lung cancer, total CHK1 and RRM1 in situ protein levels were significantly (p = 0.003) and inversely correlated. We conclude that inhibition of CHK1 may have its greatest clinical utility in malignancies where gemcitabine resistance is a result of elevated RRM1 levels. We also conclude that CHK1 inhibition in tumors with low RRM1 levels may be detrimental to gemcitabine efficacy.

Depletion of HDAC6 enhances cisplatin-induced DNA damage and apoptosis in non-small cell lung cancer cells

Histone deacetylase inhibitors (HDACi) are promising therapeutic agents which are currently used in combination with chemotherapeutic agents in clinical trials for cancer treatment including non-small cell lung cancer (NSCLC). However, the mechanisms underlying their anti-tumor activities remain elusive. Previous studies showed that inhibition of HDAC6 induces DNA damage and sensitizes transformed cells to anti-tumor agents such as etoposide and doxorubicin. Here, we showed that depletion of HDAC6 in two NSCLC cell lines, H292 and A549, sensitized cells to cisplatin, one of the first-line chemotherapeutic agents used to treat NSCLC. We suggested that depletion of HDAC6 increased cisplatin-induced cytotoxicity was due to the enhancement of apoptosis via activating ATR/Chk1 pathway. Furthermore, we showed that HDAC6 protein levels were positively correlated with cisplatin IC(50) in 15 NSCLC cell lines. Lastly, depletion of HDAC6 in H292 xenografts rendered decreased tumor weight and volume and exhibited increased basal apoptosis compared with the controls in a xenograft mouse model. In summary, our findings suggest that HDAC6 is positively associated with cisplatin resistance in NSCLC and reveal HDAC6 as a potential novel therapeutic target for platinum refractory NSCLC.

Silencing of ribonucleotide reductase subunit M1 potentiates the antitumor activity of gemcitabine in resistant cancer cells

Gemcitabine is a deoxycytidine analog used for the treatment of a wide range of solid tumors. Its efficacy is however often reduced due to the development of resistance. Ribonucleotide reductase M1 subunit (RRM1) is a key determinant of gemcitabine resistance, and tumor cells that overexpress RRM1 are resistant to the cytotoxicity of gemcitabine. In the present study, we showed that RRM1-specific small interfering RNA (siRNA), when complexed with polyethylenimine, effectively downregulated the expression of RRM1 protein in mouse tumor cells that overexpress RRM1, both in vitro and in vivo. More importantly, systemic administration of the RRM1-specific siRNA significantly inhibited the growth of RRM1-overexpressing tumors in mice and sensitized the tumors to gemcitabine treatment. These findings suggest that silencing RRM1 expression using siRNA could potentially be an effective strategy to overcome gemcitabine resistance.

Pemetrexed induces both intrinsic and extrinsic apoptosis through ataxia telangiectasia mutated/p53-dependent and -independent signaling pathways

Pemetrexed, a new-generation antifolate, has demonstrated promising single-agent activity in front- and second-line treatments of non-small cell lung cancer. However, the molecular mechanism of pemetrexed-mediated antitumor activity remains unclear. The current study shows that pemetrexed induced DNA damage and caspase-2, -3, -8, and -9 activation in A549 cells and that treatment with caspase inhibitors significantly abolished cell death, suggesting a caspase-dependent apoptotic mechanism. The molecular events of pemetrexed-mediated apoptosis was associated with the activation of ataxia telangiectasia mutated (ATM)/p53-dependent and -independent signaling pathways, which promoted intrinsic and extrinsic apoptosis by upregulating Bax, PUMA, Fas, DR4, and DR5 and activating the caspase signaling cascade. Supplementation with dTTP allowed normal S-phase progression and rescued apoptotic death in response to pemetrexed. Overall, our findings reveal that the decrease of thymidylate synthase and the increase of Bax, PUMA, Fas, DR4, and DR5 genes may serve as biomarkers for predicting responsiveness to pemetrexed.

Biomarkers of DNA repair and related pathways: significance in non-small cell lung cancer

PURPOSE OF REVIEW

To review selected biomarkers of DNA repair and related pathways as they relate to the management of patients with non-small cell lung cancer (NSCLC), emphasizing the role of individualized, chemotherapy for advanced disease, and discussing potential applications in early disease.

RECENT FINDINGS

The activity of molecular-targeted agents in NSCLC patients whose tumor possesses relevant biomarkers [such as epidermal growth factor receptor (EGFR) activating mutations and ALK translocations] has made personalized therapy possible. In addition, preclinical and clinical studies have shown that histopathological and biomolecular factors can correlate with clinical outcome in patients with NSCLC treated with chemotherapy. As a result, tumor histology is now routinely considered in selecting chemotherapy for NSCLC patients, such as pemetrexed for nonsquamous histology. Molecular tumor and host factors, including genes involved in DNA-repair and synthesis, are potentially even more relevant as predictive biomarkers of tumor response to chemotherapy. However, individual molecular markers and gene signatures need further validation and standardization, before routine use in the clinic can be recommended.

SUMMARY

In the era of molecular-targeted agents, individualized therapy based on molecular biomarkers has become a reality in the treatment of patients with advanced NSCLC. Further studies are needed to optimize current treatment algorithms with regard to biomarkers for chemotherapy benefit, to refine molecular markers, and to translate these findings to early stage NSCLC.