Inhibition of carboplatin-induced DNA interstrand cross-link repair by gemcitabine in patients receiving these drugs for platinum-resistant ovarian cancer

Repair of genomic interstrand crosslinks

Genomic interstrand crosslinks (ICLs) are formed by reactive species generated during normal cellular metabolism, produced by the microbiome, and employed in cancer chemotherapy. While there are multiple options for replication dependent and independent ICL repair, the crucial step for each is unhooking one DNA strand from the other. Much of our insight into mechanisms of unhooking comes from powerful model systems based on plasmids with defined ICLs introduced into cells or cell free extracts. Here we describe the properties of exogenous and endogenous ICL forming compounds and provide an historical perspective on early work on ICL repair. We discuss the modes of unhooking elucidated in the model systems, the concordance or lack thereof in drug resistant tumors, and the evolving view of DNA adducts, including ICLs, formed by metabolic aldehydes.

Comet Assay Profiling of FLASH-Induced Damage: Mechanistic Insights into the Effects of FLASH Irradiation

Numerous studies have demonstrated the normal tissue-sparing effects of ultra-high dose rate 'FLASH' irradiation in vivo, with an associated reduction in damage burden being reported in vitro. Towards this, two key radiochemical mechanisms have been proposed: radical-radical recombination (RRR) and transient oxygen depletion (TOD), with both being proposed to lead to reduced levels of induced damage. Previously, we reported that FLASH induces lower levels of DNA strand break damage in whole-blood peripheral blood lymphocytes (WB-PBL) ex vivo, but our study failed to distinguish the mechanism(s) involved. A potential outcome of RRR is the formation of crosslink damage (particularly, if any organic radicals recombine), whilst a possible outcome of TOD is a more anoxic profile of induced damage resulting from FLASH. Therefore, the aim of the current study was to profile FLASH-induced damage via the Comet assay, assessing any DNA crosslink formation as a putative marker of RRR and/or anoxic DNA damage formation as an indicative marker of TOD, to determine the extent to which either mechanism contributes to the "FLASH effect". Following FLASH irradiation, we see no evidence of any crosslink formation; however, FLASH irradiation induces a more anoxic profile of induced damage, supporting the TOD mechanism. Furthermore, treatment of WB-PBLs pre-irradiation with BSO abrogates the reduced strand break damage burden mediated by FLASH exposures. In summary, we do not see any experimental evidence to support the RRR mechanism contributing to the reduced damage burden induced by FLASH. However, the observation of a greater anoxic profile of damage following FLASH irradiation, together with the BSO abrogation of the reduced strand break damage burden mediated by FLASH, lends further support to TOD being a driver of the reduced damage burden plus a change in the damage profile mediated by FLASH.

Efficacy and toxicity of carboplatin and gemcitabine administered on day 1 and day 8 (day1&8) versus day 1-only for platinum-sensitive recurrent epithelial ovarian cancer

OBJECTIVE

To compare response rate, progression-free survival, overall survival, and toxicity of carboplatin and gemcitabine administered on day 1 and day 8 (day1&8) versus a modified day 1-only regimen in recurrent platinum-sensitive ovarian cancer.

METHODS

A retrospective single-institution cohort study was performed in women with recurrent platinum-sensitive ovarian cancer between January 2009 and December 2020 treated with carboplatin and gemcitabine on a 21-day cycle. The impact of dosing schedule on response rate, progression-free survival, overall survival, and toxicities was assessed with univariate and multivariate models.

RESULTS

Of 200 patients, 26% (n=52) completed day 1&8, 21.5% (n=43) started day 1&8 but dropped day 8, and 52.5% (n=105) received day 1-only. There were no differences in demographics. Median starting carboplatin and gemcitabine doses were area under curve (AUC) 5 and 600 mg/m² for day 1-only versus AUC4 and 750 mg/m² among day 1&8, respectively (p<0.001). A total of 43 patients (45.3%) dropped day 8 primarily due to neutropenia (51.2%) or thrombocytopenia (30.2%). The response rates were 69.3% for day 1&8-completed, 67.5% for day 1&8-dropped, and 67.6% for day 1-only (p=0.92). Median progression-free survival was 13.1, 12.1, and 12.4 months for day 1&8-completed, day 1&8-dropped, and day 1-only, respectively (p=0.29). Median overall survival was 28.2, 33.5, and 34.3 months for the above groups (p=0.42). The rate of grade 3/4 hematologic toxicity (48.9% vs 31.4%, p=0.002), dose reductions (58.9% vs 33.7%, p<0.001), blood transfusions (22.1% vs 10.5%, p=0.025), and treatment with pegfilgrastim (64.2% vs 51%, p=0.059) were higher among day 1&8 versus day 1-only, respectively.

CONCLUSIONS

There was no difference in response rate, progression-free survival, or overall survival for day 1&8 versus day 1-only, regardless of whether day 8 was dropped. Day 1&8 was associated with greater hematologic toxicity. A modified day 1-only regimen may represent an alternative to day 1&8 and warrants prospective study.

Epithelial ovarian cancer: Review article

Epithelial ovarian cancer is the second commonest cause of death amongst all gynaecological cancers. Treatment is challenging because almost 75% of cases are diagnosed in advanced stages. Front line treatment with aggressive cytoreduction and adjuvant treatment decides the outcome. Despite the complete response to primary treatment majority will relapse with disease. Treatment options of recurrent disease depends on platinum free interval. Systemic therapy is the mainstay of treatment and secondary cytoreduction may be beneficial in selected patients Newer therapeutic agents are being added in the front line and recurrent setting to improve outcome.

The BRCA Gene in Epithelial Ovarian Cancer

Epithelial ovarian cancer (EOC) is still the most lethal gynecological cancer. Germline alterations in breast cancer 1 (gBRCA1) and breast cancer 2 (gBRCA2) genes have been identified in up to 18% of women diagnosed with EOC, and somatic mutations are found in an additional 7%. Testing of BRCA at the primary diagnosis of patients with EOC is recommended due to the implications in the genomic counseling of the patients and their families, as well as for the therapeutic implications. Indeed, the introduction of poly-(ADP ribose) polymerase inhibitors (PARPis) has changed the natural history of patients harboring a mutation in BRCA, and has resulted in a new era in the treatment of patients with ovarian cancer harboring a BRCA mutation.

Platinum rechallenge treatment using gemcitabine plus carboplatin with or without bevacizumab for platinum-resistant ovarian cancer

PURPOSE

Platinum-resistant ovarian cancer (PROC) is usually treated with single-agent chemotherapy. A synergistic effect of gemcitabine and platinum has been reported in PROC. We evaluated the efficacy and safety of gemcitabine and carboplatin with or without bevacizumab (GC ± B) in patients with PROC.

METHODS

From April 2014 to April 2018, patients with PROC received gemcitabine on days 1 and 8, and carboplatin on day 1, with or without bevacizumab (Bev) on day 1 every 3 weeks. The primary endpoint was objective response rate (ORR). The secondary endpoints were disease control rate (DCR), progression-free survival (PFS), overall survival (OS), and rate of adverse events.

RESULTS

In total, 215 cycles were administered to 31 patients, of whom 21 received Bev and the median number of cycle for each patient was 6 (range, 2-19). The median platinum-free interval (PFI) was 4 months. The ORR and DCR were 51.9% and 92.6%, respectively. Median PFS and OS were 7.9 months and 16.1 months, respectively. PFS and OS of patients with 3-6 months PFI were significantly longer than those with PFI < 3 months (median PFS, 9.7 vs. 5.8 months; p < 0.01; median OS, 20.0 vs. 12.1 months; p = 0.03). Grade 3 or 4 hematological toxicities observed included neutropenia (71.0%), leukopenia (54.8%), anemia (51.6%), and thrombocytopenia (25.8%). No other grade 2-4 nonhematological toxicity was observed except for hypertension in one and CBDCA hypersensitivity reaction in two.

CONCLUSION

GC ± B may be effective and safe treatment alternative for PROC, especially with PFI of 3-6 months, despite hematological toxicity.

Advanced Nanoengineering Approach for Target-Specific, Spatiotemporal, and Ratiometric Delivery of Gemcitabine-Cisplatin Combination for Improved Therapeutic Outcome in Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC) is an intractable malignancy with a dismal survival rate. Recent combination therapies have had a major impact on the improvement of PDAC prognosis. Nevertheless, clinically used combination regimens such as FOLFIRINOX and gemcitabine (Gem)/nab-paclitaxel still face major challenges due to lack of the safe and ratiometric delivery of multiple drugs. Here, a rationally designed mesoporous silica nanoparticle (MSN)-based platform is reported for the target-specific, spatiotemporal, ratiometric, and safe co-delivery of Gem and cisplatin (cisPt). It is shown that systemic administration of the nanoparticles results in synergistic therapeutic outcome in a syngeneic and clinically relevant genetically engineered PDAC mouse model that has rarely been used for the therapeutic evaluation of nanomedicine. This synergism is associated with a strategic engineering approach, in which nanoparticles provide redox-responsive controlled delivery and in situ differential release of Gem/cisPt drugs with the goal of overcoming resistance to Pt-based drugs. The platform is also rendered with additional tumor-specificity via a novel tumor-associated mucin1 (tMUC1)-specific antibody, TAB004. Overall, the platform suppresses tumor growth and eliminates the off-target toxicities of a highly toxic chemotherapy combination.

The systemic treatment of recurrent ovarian cancer revisited

Treatment approaches for relapsed ovarian cancer have evolved over the past decade from a calendar-based decision tree to a patient-oriented biologically driven algorithm. Nowadays, platinum-based chemotherapy should be offered to all patients with a reasonable chance of responding to this therapy. The treatment-free interval for platinum is only one of many factors affecting patients' eligibility for platinum re-treatment. Bevacizumab increases the response to chemotherapy irrespective of the cytotoxic regimen and can be valuable in patients with an urgent need for symptom relief (e.g. pleural effusion, ascites). For patients with recurrent high-grade ovarian cancer, which responds to platinum-based treatment, maintenance therapy with a poly(ADP-ribose) polymerase inhibitor can be offered, regardless of the BRCA mutation status. Here we review contemporary decision-making processes in the systemic treatment of relapsed ovarian cancer.

Managing recurrent ovarian cancer in daily clinical practice: case studies and evidence review with a focus on the use of trabectedin

Following the failure of first-line platinum-based chemotherapy in ovarian cancer, options for further therapy in potentially platinum-responsive patients are: carboplatin doublets with pegylated liposomal doxorubicin, gemcitabine or paclitaxel in association with bevacizumab, followed by maintenance with bevacizumab (for nonpretreated patients); or maintenance monotherapy with a poly(ADP-ribose) polymerase inhibitor after a response. The choice of biological therapy depends on a patient’s previous treatments and priority for a symptomatic response. In cases of a rapidly growing tumor or need for symptomatic relief, the addition of bevacizumab should be considered. Patients with limited potential sensitivity to platinum, such as those with a platinum treatment-free interval of 6–12 months, may benefit from intercalation with trabectedin and pegylated liposomal doxorubicin to possibly restore platinum sensitivity.

ESMO-ESGO consensus conference recommendations on ovarian cancer: pathology and molecular biology, early and advanced stages, borderline tumours and recurrent disease

The development of guidelines is one of the core activities of the European Society for Medical Oncology (ESMO) and European Society of Gynaecologial Oncology (ESGO), as part of the mission of both societies to improve the quality of care for patients with cancer across Europe. ESMO and ESGO jointly developed clinically relevant and evidence-based recommendations in several selected areas in order to improve the quality of care for women with ovarian cancer. The ESMO-ESGO consensus conference on ovarian cancer was held on April 12-14, 2018 in Milan, Italy, and comprised a multidisciplinary panel of 40 leading experts in the management of ovarian cancer. Before the conference, the expert panel worked on five clinically relevant questions regarding ovarian cancer relating to each of the following four areas: pathology and molecular biology, early-stage and borderline tumours, advanced stage disease and recurrent disease. Relevant scientific literature, as identified using a systematic search, was reviewed in advance. During the consensus conference, the panel developed recommendations for each specific question and a consensus was reached. The recommendations presented here are thus based on the best available evidence and expert agreement. This article presents the recommendations of this ESMO-ESGO consensus conference, together with a summary of evidence supporting each recommendation.

ESMO-ESGO consensus conference recommendations on ovarian cancer: pathology and molecular biology, early and advanced stages, borderline tumours and recurrent disease†

The development of guidelines recommendations is one of the core activities of the European Society for Medical Oncology (ESMO) and European Society of Gynaecologial Oncology (ESGO), as part of the mission of both societies to improve the quality of care for patients with cancer across Europe. ESMO and ESGO jointly developed clinically relevant and evidence-based recommendations in several selected areas in order to improve the quality of care for women with ovarian cancer. The ESMO-ESGO consensus conference on ovarian cancer was held on 12-14 April 2018 in Milan, Italy, and comprised a multidisciplinary panel of 40 leading experts in the management of ovarian cancer. Before the conference, the expert panel worked on five clinically relevant questions regarding ovarian cancer relating to each of the following four areas: pathology and molecular biology, early-stage and borderline tumours, advanced stage disease and recurrent disease. Relevant scientific literature, as identified using a systematic search, was reviewed in advance. During the consensus conference, the panel developed recommendations for each specific question and a consensus was reached. The recommendations presented here are thus based on the best available evidence and expert agreement. This article presents the recommendations of this ESMO-ESGO consensus conference, together with a summary of evidence supporting each recommendation.

Insights from HuR biology point to potential improvement for second-line ovarian cancer therapy

This retrospective study aimed to investigate the role that an RNA-binding protein, HuR, plays in the response of high-grade serous ovarian tumors to chemotherapeutics. We immunohistochemically stained sections of 31 surgically-debulked chemo-naïve ovarian tumors for HuR and scored the degree of HuR cytoplasmic staining. We found no correlation between HuR intracellular localization in tumor sections and progression free survival (PFS) of these patients, 29 of whom underwent second-line gemcitabine/platin combination therapy for recurrent disease. Ribonucleoprotein immunoprecipitation (RNP-IP) analysis of ovarian cancer cells in culture showed that cytoplasmic HuR increases deoxycytidine kinase (dCK), a metabolic enzyme that activates gemcitabine. The effects of carboplatin treatment on HuR and WEE1 (a mitotic inhibitor) expression, and on cell cycle kinetics, were also examined. Treatment of ovarian cancer cells with carboplatin results in increased HuR cytoplasmic expression and elevated WEE1 expression, arresting cell cycle G2/M transition. This may explain why HuR cytoplasmic localization in chemo-naïve tumors is not predictive of therapeutic response and PFS following second-line gemcitabine/platin combination therapy. These results suggest treatment of recurrent ovarian tumors with a combination of gemcitabine, carboplatin, and a WEE1 inhibitor may be potentially advantageous as compared to current clinical practices.

From Anthramycin to Pyrrolobenzodiazepine (PBD)-Containing Antibody-Drug Conjugates (ADCs)

The pyrrolo[2,1-c][1,4]benzodiazepines (PBDs) are a family of sequence-selective DNA minor-groove binding agents that form a covalent aminal bond between their C11-position and the C2-NH2 groups of guanine bases. The first example of a PBD monomer, the natural product anthramycin, was discovered in the 1960s, and the best known PBD dimer, SJG-136 (also known as SG2000, NSC 694501 or BN2629), was synthesized in the 1990s and has recently completed Phase II clinical trials in patients with leukaemia and ovarian cancer. More recently, PBD dimer analogues are being attached to tumor-targeting antibodies to create antibody-drug conjugates (ADCs), a number of which are now in clinical trials, with many others in pre-clinical development. This Review maps the development from anthramycin to the first PBD dimers, and then to PBD-containing ADCs, and explores both structure-activity relationships (SARs) and the biology of PBDs, and the strategies for their use as payloads for ADCs.

Effects of sequential paclitaxel-carboplatin followed by gemcitabine-based chemotherapy compared with paclitaxel-carboplatin therapy administered to patients with advanced epithelial ovarian cancer: A retrospective, STROBE-compliant study

We aimed to compare the efficacy of paclitaxel and carboplatin followed by gemcitabine-based combination chemotherapy with paclitaxel-carboplatin for treating advanced epithelial ovarian cancer in this retrospective, STROBE-compliant study. Patients' tolerance to treatment was also assessed.We retrospectively analyzed the records of 178 women who underwent initial optimal debulking surgery between January 2003 and December 2011 to treat FIGO stage IIIc epithelial ovarian cancer. Patients in arm 1 (n = 88) received 4 cycles of paclitaxel and carboplatin followed by 2 to 4 cycles of gemcitabine-based combination chemotherapy. Patients in arm 2 (n = 90) received 6 to 8 cycles of paclitaxel and carboplatin. The granulocyte-colony stimulating factor was administered prophylactically to all patients.The median follow-up for both arms was 62 months. Medianprogression-free survival (PFS) between arms 1 and 2 (28 and 19 months [P = 0.003]) as well as 5-year OS (34.1% and 18.9% [P = 0.021]) differed significantly. The neurotoxicity rate was significantly higher in arm 2 than in arm 1 (45.2% vs 27.1%, P = 0.026). There was no significant difference between study arms in hematological toxicity.The sequential regimen significantly improved PFS and 5-year OS with tolerable toxicity compared with the single regimen, and offers an alternative for treating patients with advanced epithelial ovarian cancer.

A network-pathway based module identification for predicting the prognosis of ovarian cancer patients

Background

This study aimed to screen multiple genes biomarkers based on gene expression data for predicting the survival of ovarian cancer patients.

Methods

Two microarray data of ovarian cancer samples were collected from The Cancer Genome Atlas (TCGA) database. The data in the training set were used to construct Reactome functional interactions network, which then underwent Markov clustering, supervised principal components, Cox proportional hazard model to screen significantly prognosis related modules. The distinguishing ability of each module for survival was further evaluated by the testing set. Gene Ontology (GO) functional and pathway annotations were performed to identify the roles of genes in each module for ovarian cancer.

Results

The network based approach identified two 7-gene functional interaction modules (31: DCLRE1A, EXO1, KIAA0101, KIN, PCNA, POLD3, POLD2; 35: DKK3, FABP3, IRF1, AIM2, GBP1, GBP2, IRF2) that are associated with prognosis of ovarian cancer patients. These network modules are related to DNA repair, replication, immune and cytokine mediated signaling pathways.

Conclusions

The two 7-gene expression signatures may be accurate predictors of clinical outcome in patients with ovarian cancer and has the potential to develop new therapeutic strategies for ovarian cancer patients.

Chemotherapy for Patients with BRCA1 and BRCA2-Mutated Ovarian Cancer: Same or Different?

Retrospective studies have shown an improved prognosis, higher response rates to platinum-containing regimens, and longer treatment-free intervals between relapses in patients with BRCA 1 and BRCA 2 (BRCA1/2)-mutated ovarian cancer (BMOC) compared with patients who are not carriers of this mutation. These features of BMOC are attributed to homologous-recombination repair (HR) deficiency in the absence of BRCA1/2 function, which results in an impaired ability of tumor cells to repair platinum-induced double-strand breaks (DSBs), thereby conferring increased chemosensitivity and increased sensitivity to poly(ADP-ribose) polymerase (PARP) enzyme inhibition and other DNA-damaging chemotherapeutic agents such as pegylated liposomal doxorubicin (PLD). Therefore, the chemotherapeutic approach for patients with BMOC should focus on treatment with platinum-based chemotherapy at first-line and recurrent-disease settings and measures to increase the platinum-free interval following early platinum-resistant relapse (i.e., progression-free survival of less than 6 months from last platinum-based chemotherapy) by using nonplatinum cytotoxic agents, with the aim of reintroducing platinum again at a later date. The role of first-line intraperitoneal platinum-based therapy in the specific context of BMOC also merits further analysis. Other than platinum, alternative DNA-damaging agents (including PLD and trabectedin) also may have a therapeutic role in patients with recurrent BMOC. The recent approval of olaparib for clinical use in Europe and the United States will also affect chemotherapeutic strategies for these patients. Further work to clarify the precise relationship between BRCA1/2 mutation genotype and clinical phenotype is crucial to delineating the optimal therapeutic choices in the future for patients with BMOC.

Characterization of Interstrand DNA-DNA Cross-Links Using the α-Hemolysin Protein Nanopore

Nanopore-based sensors have been studied extensively as potential tools for DNA sequencing, characterization of epigenetic modifications such as 5-methylcytosine, and detection of microRNA biomarkers. In the studies described here, the α-hemolysin protein nanopore embedded in a lipid bilayer was used for the detection and characterization of interstrand cross-links in duplex DNA. Interstrand cross-links are important lesions in medicinal chemistry and toxicology because they prevent the strand separation that is required for read-out of genetic information from DNA in cells. In addition, interstrand cross-links are used for the stabilization of duplex DNA in structural biology and materials science. Cross-linked DNA fragments produced unmistakable current signatures in the nanopore experiment. Some cross-linked substrates gave irreversible current blocks of >10 min, while others produced long current blocks (10-100 s) before the double-stranded DNA cross-link translocated through the α-hemolysin channel in a voltage-driven manner. The duration of the current block for the different cross-linked substrates examined here may be dictated by the stability of the duplex region left in the vestibule of the nanopore following partial unzipping of the cross-linked DNA. Construction of calibration curves measuring the frequency of cross-link blocking events (1/τon) as a function of cross-link concentration enabled quantitative determination of the amounts of cross-linked DNA present in samples. The unique current signatures generated by cross-linked DNA in the α-HL nanopore may enable the detection and characterization of DNA cross-links that are important in toxicology, medicine, and materials science.

A novel assay revealed that ribonucleotide reductase is functionally important for interstrand DNA crosslink repair

Cells have evolved complex biochemical pathways for DNA interstrand crosslink (ICL) removal. Despite the chemotherapeutic importance of ICL repair, there have been few attempts to identify which mechanistic DNA repair inhibitor actually inhibits ICL repair. To identify such compounds, a new and robust ICL repair assay was developed using a novel plasmid that contains synthetic ICLs between a CMV promoter region that drives transcription and a luciferase reporter gene, and an SV40 origin of replication and the large T antigen (LgT) gene that enables self-replication in mammalian cells. In a screen against compounds that are classified as inhibitors of DNA repair or synthesis, the reporter generation was exquisitely sensitive to ribonucleotide reductase (RNR) inhibitors such as gemcitabine and clofarabine, but not to inhibitors of PARP, ATR, ATM, Chk1, and others. The effect was observed also by siRNA downregulation of RNR. Moreover, the reporter generation was also particularly sensitive to 3-AP, a non-nucleoside RNR inhibitor, but not significantly sensitive to DNA replication stressors, suggesting that the involvement of RNR in ICL repair is independent of incorporation of a nucleotide RNR inhibitor into DNA to induce replication stress. The reporter generation from a modified version of the plasmid that lacks the LgT-SV40ori motif was also adversely affected by RNR inhibitors, further indicating a role for RNR in ICL repair that is independent of DNA replication. Intriguingly, unhooking of cisplatin-ICL from nuclear DNA was significantly inhibited by low doses of gemcitabine, suggesting an unidentified functional role for RNR in the process of ICL unhooking. The assay approach could identify other molecules essential for ICLR in quantitative and flexible manner.

Gallium phosphinoarylbisthiolato complexes counteract drug resistance of cancer cells

In cancer therapy the platinum-based drugs are used frequently with a good clinical outcome, but besides unwanted side effects which occur, the tumour cells subjected to treatment are prone to develop tolerance or even multidrug resistance (MDR). Metal compounds with a central atom other than platinum are efficient in targeting the chemoresistant cells, therefore the biological outcome of two recently synthesized gallium phosphinoarylbisthiolato complexes was studied, having the formula [X][Ga{PPh(2-SC6H4)2-κ(3)S,S',P}{PPh(2-SC6H4)2-κ(2)S,S'}] where [X] is either the NEt3H (1) or PPh4 (2) cation. Compounds 1 and 2 display in vitro cytotoxicity against both platinum-sensitive and platinum-resistant cell lines (A2780 and A2780cis). Morphological and ultrastructural evidence points toward their capacity to impair tumour cells survival. This behaviour is based on malignant cells capacity to selectively intake gallium, and to bind to the cellular DNA. They are able to cause massive DNA damage in treated cancer cells, focusing on 7-methylguanine and 8-oxoguanine sites and oxidizing the pyrimidine bases; this leads to early apoptosis of a significant percent of treated cells. The intrinsic and extrinsic apoptotic pathways are influenced through the modulation of gene expression following the treatment with complexes 1 and 2, which accompanies the negative regulation of P-glycoprotein 1 (Pgp-1), an important cellular ABC-type transporter from the multidrug resistance (MDR) family. The studied Ga(III) compounds demonstrated the capacity to counteract the chemoresistance mechanisms in the tumours defiant to standard drug action. Compound 2 shows a good anticancer potential and it could represent an alternative to platinum-based drugs especially in the situation of standard treatment failure.

A phase II study of gemcitabine, carboplatin and bevacizumab for the treatment of platinum-sensitive recurrent ovarian cancer

PURPOSE

The doublet gemcitabine and carboplatin is effective for the treatment of recurrent ovarian cancer, while multi-agent chemotherapy with bevacizumab may add additional benefit. This phase II study tested the efficacy and safety of a biweekly gemcitabine, carboplatin, and bevacizumab combination in patients with platinum-sensitive recurrent ovarian, peritoneal, or tubal cancer (ROC).

PATIENTS AND METHODS

Eligible patients received concurrent gemcitabine 1000 mg/m(2), carboplatin area under the curve 3, and bevacizumab 10 mg/kg administered intravenously on days 1 and 15 every 28 days for six cycles or up to 24 cycles if clinical benefit occurred. The primary end points were progression-free survival (PFS) by RECIST, and safety; the secondary end points were objective response rates and overall survival.

RESULTS

Overall, 45 patients were enrolled. The median PFS was 13.3 months (95% CI, 11.3 to 15.3). The objective response rate was 69%. Grade 4 hematologic toxicities included neutropenia (27%) and thrombocytopenia (2%). Grades 3 and 4 non-hematologic toxicities included fatigue (18%), pain (9%), and nausea/vomiting (4%). There were 2 episodes of cerebrovascular accidents, 2 noted DVTs, and no episodes of bowel perforation. Median OS was 36.1 months (95% CI, 26.7 to 45.5).

CONCLUSION

Biweekly gemcitabine, carboplatin, and bevacizumab were an effective regimen in recurrent ovarian cancer, with comparable toxicity to recently reported day 1 gemcitabine, carboplatin, bevacizumab, and day 8 gemcitabine. Response rate and PFS are improved from reported outcomes of the gemcitabine carboplatin doublet. The degree to which biweekly dosing may present a more rationale schedule for this triplet should be evaluated further.

Opportunities for translation: targeting DNA repair pathways in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) remains one of the poorest prognosis neoplasms. It is typified by high levels of genomic aberrations and copy-number variation, intra-tumoural heterogeneity and resistance to conventional chemotherapy. Improved therapeutic options, ideally targeted against cancer-specific biological mechanisms, are urgently needed. Although induction of DNA damage and/or modulation of DNA damage response pathways are associated with the activity of a number of conventional PDAC chemotherapies, the effectiveness of this approach in the treatment of PDAC has not been comprehensively reviewed. Here, we review chemotherapeutic agents that have shown anti-cancer activity in PDAC and whose mechanisms of action involve modulation of DNA repair pathways. In addition, we highlight novel potential targets within these pathways based on the emerging understanding of PDAC biology and their exploitation as targets in other cancers.

Gemcitabine as a molecular targeting agent that blocks the Akt cascade in platinum-resistant ovarian cancer

BACKGROUND

Gemcitabine (2', 2' -difluorodeoxycytidine) is one of many nonplatinum drugs that exhibit activity in recurrent, platinum-resistant ovarian cancer. However, the molecular mechanisms by which Gemcitabine treatment inhibits the proliferation of platinum-resistant ovarian cancer cells still remain unclear. We investigated whether Gemcitabine increases the efficacy of Cisplatin in platinum-resistant ovarian cancer models in vitro and in vivo.

METHODS

We used Cisplatin-resistant Caov-3 cells, A2780CP cells and Cisplatin-sensitive A2780 cells to examine the sensitivity of the cell viability of Cisplatin and Gemcitabine using a 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay and the sensitivity of the invasive activity of Cisplatin and Gemcitabine using an invasion assay with Matrigel. We examined the Akt kinase activity and matrix metalloproteinase 9 (MMP9) expression following Cisplatin and Gemcitabine treatment using a Western blot analysis and the mRNA expression of vascular endothelial growth factor (VEGF) using semi-quantitative RT-PCR. Moreover, we evaluated the effects of Cisplatin and Gemcitabine on the intra-abdominal dissemination of ovarian cancer in vivo.

RESULTS

Gemcitabine significantly inhibited Cisplatin-induced Akt activation in the Caov-3 and A2780CP cells, but not in the A2780 cells. In the presence of Gemcitabine, Cisplatin-induced growth inhibition and apoptosis were significantly enhanced in the Caov-3 and A2780CP cells. Co-treatment with Cisplatin and Gemcitabine almost completely inhibited invasion of both types of cells through the Matrigel; however, neither Cisplatin nor Gemcitabine alone inhibited the invasion of both types of cells. Gemcitabine inhibited not only the Cisplatin-induced activation of Akt, but also the MMP9 and mRNA expression of VEGF. Moreover, treatment with Gemcitabine increased the efficacy of Cisplatin-induced growth inhibition of the intra-abdominal dissemination and production of ascites in the athymic nude mice inoculated with Caov-3 cells.

CONCLUSIONS

We herein demonstrated that Gemcitabine inhibits the Akt kinase activity and angiogenetic activity following treatment with Cisplatin in platinum-resistant ovarian cancer cells. These results provide a rationale for using Gemcitabine in clinical regimens containing molecular targeting agents against platinum-resistant ovarian cancers.

γ-H2AX foci formation as a pharmacodynamic marker of DNA damage produced by DNA cross-linking agents: results from 2 phase I clinical trials of SJG-136 (SG2000)

PURPOSE

To evaluate γ-H2AX foci as a pharmacodynamic marker for DNA damage induced by DNA interstrand cross-linking drugs.

EXPERIMENTAL DESIGN

γ-H2AX foci formation was validated preclinically in comparison with the Comet assay, and evaluated pharmacodynamically in two phase I studies of different dosing schedules of the novel cross-linking agent SJG-136 (SG2000).

RESULTS

The measurement of γ-H2AX foci in human fibroblasts and lymphocytes in vitro was more than 10-fold more sensitive than Comet assay measurement of cross-linking, with peak γ-H2AX response 24 hours after the peak of cross-linking. In lymphocytes from a phase I study (every three week schedule), γ-H2AX foci were detectable 1 hour following the end of administration, and in all patients, maximum response was observed at 24 hours. Significant levels of foci were still evident at days 8 and 15 consistent with the known persistence of the DNA damage produced by this agent. In two tumor biopsy samples, foci were detected 4 hours postinfusion with levels higher than in lymphocytes. Extensive foci formation was also observed before the third dose in cycle 1 in lymphocytes from a second phase I study (daily × 3 schedule). These foci also persisted with a significant level evident before the second cycle (day 21). An increased γ-H2AX response was observed during the second cycle consistent with a cumulative pharmacodynamic effect. No clear relationship between foci formation and administered drug dose was observed.

CONCLUSION

This is the first use of γ-H2AX as a pharmacodynamic response to a DNA cross-linking agent in a clinical trial setting.

Small-molecule inhibitors of DNA damage-repair pathways: an approach to overcome tumor resistance to alkylating anticancer drugs

A major challenge in the future development of cancer therapeutics is the identification of biological targets and pathways, and the subsequent design of molecules to combat the drug-resistant cells hiding in virtually all cancers. This therapeutic approach is justified based upon the limited advances in cancer cures over the past 30 years, despite the development of many novel chemotherapies and earlier detection, which often fail due to drug resistance. Among the various targets to overcome tumor resistance are the DNA repair systems that can reverse the cytotoxicity of many clinically used DNA-damaging agents. Some progress has already been made but much remains to be done. We explore some components of the DNA-repair process, which are involved in repair of alkylation damage of DNA, as targets for the development of novel and effective molecules designed to improve the efficacy of existing anticancer drugs.

Evidence for different mechanisms of 'unhooking' for melphalan and cisplatin-induced DNA interstrand cross-links in vitro and in clinical acquired resistant tumour samples

Background

DNA interstrand cross-links (ICLs) are critical lesions produced by several cancer chemotherapy agents including platinum drugs and nitrogen mustards. We have previously shown in haematological (multiple myeloma) and solid tumours (ovarian cancer) that clinical sensitivity to such agents can result from a defect in DNA ICL processing leading to their persistence. Conversely, enhanced repair can result in clinical acquired resistance following chemotherapy. The repair of ICLs is complex but it is assumed that the ‘unhooking’ step is common to all ICLs.

Methods

Using a modification of the single cell gel electrophoresis (Comet) assay we measured the formation and unhooking of melphalan and cisplatin-induced ICLs in cell lines and clinical samples. DNA damage response in the form of γ-H2AX foci formation and the formation of RAD51 foci as a marker of homologous recombination were also determined. Real-time PCR of 84 genes involved in DNA damage signalling pathways was also examined pre- and post-treatment.

Results

Plasma cells from multiple myeloma patients known to be clinically resistant to melphalan showed significant unhooking of melphalan-induced ICLs at 48 hours, but did not unhook cisplatin-induced ICLs. In ovarian cancer cells obtained from patients following platinum-based chemotherapy, unhooking of cisplatin-induced ICLs was observed at 48 hours, but no unhooking of melphalan-induced ICLs. In vitro, A549 cells were proficient at unhooking both melphalan and cisplatin-induced ICLs. γ-H2AX foci formation closely followed the formation of ICLs for both drugs, and rapidly declined following the peak of formation. RPMI8226 cells unhooked melphalan, but not cisplatin-induced ICLs. In these cells, although cross-links form with cisplatin, the γ-H2AX response is weak. In A549 cells, addition of 3nM gemcitabine resulted in complete inhibition of cisplatin-induced ICL unhooking but no effect on repair of melphalan ICLs. The RAD51 foci response was both drug and cell line specific. Real time PCR studies highlighted differences in the damage response to melphalan and cisplatin following equi-ICL forming doses.

Conclusions

These data suggest that the mechanisms by which melphalan and cisplatin-induced ICLs are ‘unhooked’ in vitro are distinct, and the mechanisms of clinical acquired resistance involving repair of ICLs, are drug specific.

Antiproliferative effect of novel platinum(II) and palladium(II) complexes on hepatic tumor stem cells in vitro

Novel platinum and palladium complexes with (2-isopropoxyphenyl)dicyclohexylarsine and (2-methoxyphenyl)dicyclohexylarsine ligands were synthesized and tested on different tumor cells. Adducts with general formula MX(2)L(2) (M = Pt(II), Pd(II); X = Cl or I; L = organoarsenic ligand) were fully characterized. According to the crystallographic data, in all complexes the organoarsenic ligands coordinate the metal center through the arsenic atom only, in a trans arrangement with the halogen atoms. The antiproliferative potential of complexes 1-4 was evaluated in vitro on human tumor cell lines. A markedly biological activity was observed against the chemoresistant hepatic tumor stem cell line, the normal hepatic stem cells and towards the hepatocellular carcinoma (non-stem) cells. The new compounds toxicity is selectively limited in normal liver cells, unlikeness with the oxaliplatin, which displays a more intense effect in normal cells, compared with the two tumor cell lines. The stem cells treatment with compounds 1-4 causes DNA damages; the antimitotic effect of these compounds is based on their genotoxicity and on the capacity to form crosslinks with the DNA interstrand. In the case of platinum complexes 1 and 3 this mechanism gives rise to specific lesions on DNA that induces apoptosis in stem cells, influencing their selectivity in tumor cell growth inhibition. Compounds 1, 2 and 4 display higher activity against tumor stem cells. The novel platinum complexes 1 and 3 are more efficient against tumor stem cells than oxaliplatin, and if used in combination with sorafenib-based monoclonal anticancer therapy, complexes 1, 3 and 4 have the ability to induce superior chemosensitivity relative to sorafenib than the standard platinum-based drug, making them promising candidates for prodrug development.

Mechanism of cell death resulting from DNA interstrand cross-linking in mammalian cells

DNA interstrand cross-links (ICLs) are critical cytotoxic lesions produced by cancer chemotherapeutic agents such as the nitrogen mustards and platinum drugs; however, the exact mechanism of ICL-induced cell death is unclear. Here, we show a novel mechanism of p53-independent apoptotic cell death involving prolonged cell-cycle (G₂) arrest, ICL repair involving HR, transient mitosis, incomplete cytokinesis, and gross chromosomal abnormalities resulting from ICLs in mammalian cells. This characteristic ‘giant' cell death, observed by using time-lapse video microscopy, was reduced in ICL repair ERCC1- and XRCC3-deficient cells. Collectively, the results illustrate the coordination of ICL-induced cellular responses, including cell-cycle arrest, DNA damage repair, and cell death.

Mechanism of action: the unique pattern of bendamustine-induced cytotoxicity

Bendamustine has demonstrated substantial efficacy in the treatment of hematologic malignancies and continues to distinguish itself from other alkylating agents with regard to its activity in tumor cells. The mechanistic and clinical differences associated with bendamustine may be directly related to its unique structural features. Although the precise mechanisms of action are still poorly understood, bendamustine is associated with extensive and durable DNA damage. The increased potency of bendamustine may be due to secondary mechanisms such as inhibition of mitotic checkpoints, inefficient DNA repair, and initiation of p53-dependent DNA-damage stress response, all of which lead to mitotic catastrophe and apoptosis. It has also been hypothesized that the presence of a benzimidazole ring in addition to the nitrogen mustard group may influence the way bendamustine interacts with DNA and/or confer antimetabolite properties. Further elucidation of the mechanisms of action for bendamustine and the signaling pathways involved in the response to bendamustine-induced DNA damage is essential to maximize its therapeutic potential, identify biomarkers for response, and understand the potential for synergy with other agents involved in DNA damage and inhibition of DNA repair. This review will discuss the current understanding and hypotheses regarding bendamustine mechanisms of action and suggest future investigations that would shed light on the many unanswered questions.

Adjuvant carboplatin and gemcitabine combination chemotherapy postamputation in canine appendicular osteosarcoma

BACKGROUND

Appendicular osteosarcoma (OSA), the most common bone tumor in dogs, is typically treated by amputation and adjuvant chemotherapy. Despite numerous efforts, the median survival time (MST) for dogs receiving a platinum compound, doxorubicin, or a combination of these remains at 8-12 months. Evidence from studies in mice suggests that gemcitabine has activity against OSA in vivo. Our preliminary work demonstrated that the addition of low-dosage (10 mM) gemcitabine to carboplatin resulted in synergistic inhibition of OSA cell viability in vitro.

OBJECTIVE

The purpose of the following study was to determine whether the addition of low-dosage (2 mg/kg) gemcitabine to carboplatin chemotherapy in dogs with OSA after amputation would improve MST over carboplatin monotherapy.

ANIMALS

Fifty dogs with histologically confirmed appendicular OSA.

METHODS

Dogs were treated prospectively with amputation and up to 4 dosages of carboplatin and gemcitabine in combination every 3 weeks.

RESULTS

The chemotherapeutic regimen was well tolerated with only 5 episodes of grade 3 or 4 hematologic toxicity. The median disease-free interval (DFI) was 203 days and the MST was 279 for all dogs in this study. The 1- and 2-year survival rates were 29.5 and 11.3%, respectively. Dogs with proximal humeral OSA had a shorter median DFI (P = .04) compared with dogs with OSA in other locations.

CONCLUSIONS AND CLINICAL IMPORTANCE

These results are comparable to those reported for carboplatin monotherapy indicating that the addition of gemcitabine to carboplatin in dogs with appendicular OSA does not appear to improve outcome.

The development of pyrrolobenzodiazepines as antitumour agents

INTRODUCTION

DNA interacting agents play a major role in cancer chemotherapy, either as single agents, in combination drug regimens, or as components of novel targeted therapies. The search for more selective and efficacious drugs that can deliver critical DNA damage with minimal side effects continues.

AREAS COVERED

The development of the pyrrolobenzodiazepines (PBDs) from their discovery as natural products in the 1960s, through synthetic PBD monomers, PBD hybrids and conjugates, and PBD dimers is described. The latter molecules are capable of forming sequence selective, non-distorting and potently cytotoxic DNA interstrand cross-links in the minor groove of DNA. In particular, the development of PBD dimer SJG-136 (SG2000), currently in Phase II clinical trials, is presented. Potential future cancer therapeutic applications of PBDs, including their use as components of targeting strategies, are also discussed.

EXPERT OPINION

The culmination of over four decades of study on structure-activity relationships of PBDs has led to a detailed understanding of how to introduce structural modification to enhance biological activity and potency. The challenge for the next phase in the development of the PBDs is to harness this activity and potency in a new generation of cancer therapeutics.