Sorafenib and radiation: a promising combination in colorectal cancer

Angiogenesis in Pancreatic Cancer: Pre-Clinical and Clinical Studies

Angiogenesis is a crucial event in tumor development and progression, occurring by different mechanisms and it is driven by pro- and anti-angiogenic molecules. Pancreatic cancer vascularization is characterized by a high microvascular density, impaired microvessel integrity and poor perfused vessels with heterogeneous distribution. In this review article, after a brief introduction on pancreatic cancer classification and on angiogenesis mechanisms involved in its progression, the pre-clinical and clinical trials conducted in pancreatic cancer treatment using anti-angiogenic inhibitors will be described. Finally, we will discuss the anti-angiogenic therapy paradox between the advantage to abolish vessel supply to block tumor growth and the disadvantage due to reduction of drug delivery at the same time. The purpose is to identify new anti-angiogenic molecules that may enhance treatment regimen.

Effect of sorafenib on cisplatin-based chemoradiation in head and neck cancer cells

Despite aggressive chemoradiation (CRT) protocols in the treatment of patients with head and neck squamous cell carcinomas (HNSCC), the outcome is still unfavorable. To improve therapy efficacy we had already successfully tested the multikinase inhibitor sorafenib in combination with irradiation (IR) in previous studies on HNSCC cell lines. In this study we investigated its effect on combined CRT treatment using cisplatin.Radio- and chemosensitivity with and without sorafenib was measured in four HNSCC cell lines and normal fibroblasts (NF) by colony formation assay. Apoptosis and cell cycle analysis were performed by flow cytometry.

In HNSCC cells, sorafenib enhanced the antiproliferative effect of cisplatin without affecting apoptosis induction and with only minor effects on cell inactivation. Sorafenib added prior to irradiation enhanced cellular radiosensitivity in three of the tested HNSCC cell lines and caused massive overall cell inactivation when combined with CRT. In contrast, sorafenib did not radiosensitize NF and reduced cisplatin-induced cell inactivation. Cell inactivation by IR and cisplatin is further increased by the addition of sorafenib in HNSCC, but not in NF cells. Therefore, sorafenib is a promising candidate to improve therapy efficacy for HNSCC.

Sorafenib Acts Synergistically in Combination with Radiotherapy without Causing Intestinal Damage in Colorectal Cancer

Aims and background

Colorectal cancer is one of the commonest cancers. Chemoradiotherapy gives better results than radiotherapy or chemotherapy in colorectal cancer. To enhance radiosensitivity of tumor cells for chemoradiotherapy, targeted therapy drugs that act as radiosensitizers can be used. In the present study, we provide a scientific rationale for the clinical application of sorafenib as a radiosensitizer in colorectal cancer, without causing significant adverse effects on normal intestinal tissue.

Methods

Three human colorectal adenocarcinoma cell lines (HCT116, HT-29, and SW480) were treated with sorafenib alone, or radiation followed by sorafenib. In vitro tests were performed using colony forming assays, cell cycle analysis, and comet assays. In addition, the effects of sorafenib and radiation therapy on the inhibition HT-29 tumor growth and survival of intestinal jejunum crypts were examined in vivo.

Results

Sorafenib increased the radiosensitivity of tumor cells in human colon adenocarcinoma cell lines (HCT116, HT-29, and SW480), as well as in HT-29 xenograft animal models. Sorafenib, in combination with ionizing radiation, induced the accumulation of tumor cells in the G2-M phase and delayed the repair of DNA damage caused by ionizing radiation. The combination of sorafenib and ionizing radiation did not enhance the apoptosis of intestinal crypt cells, compared with the use of radiation alone.

Conclusions

We provide a scientific rationale for the use of sorafenib in combination with radiotherapy in colorectal cancer.

Combined sorafenib and yttrium-90 radioembolization for the treatment of advanced hepatocellular carcinoma

BACKGROUND AND AIMS

In this pilot study, we assessed the safety and tolerability of combining sorafenib with ⁹⁰Y radioembolization for the treatment of unresectable hepatocellular carcinoma (hcc).

METHODS

The study, conducted prospectively during 2009-2012, included eligible patients with unresectable hcc and a life expectancy of at least 12 weeks. Each patient received sorafenib (400 mg twice daily) for 6-8 weeks before ⁹⁰Y treatment. Safety and tolerability were assessed.

RESULTS

Of the 40 patients enrolled, 29 completed treatment (combined therapy). In the initial cohort, the most common cause of hcc was hepatitis C (32.5%), and most patients were staged Child A (82.5%). The 29 patients who completed the study had similar baseline characteristics. Grades 1 and 2 toxicities accounted for 77.8% of all adverse events reported. The most common toxicities reported were fatigue (19.0%), alteration in liver function (7.9%), and diarrhea (6.3%). There were 12 grade 3 and 2 grade 4 toxicity events reported. One patient died of liver failure within 30 days after treatment. During the study, the sorafenib dose was reduced in 6 patients (20.7%), and sorafenib had to be interrupted in 4 patients (13.8%) and discontinued in 4 patients (13.8%). The disease control rate was 72.4% per the modified Response Evaluation Criteria in Solid Tumors, and tumour necrosis was observed in 82.8% of patients. Overall survival in patients undergoing combined therapy was 12.4 months.

CONCLUSIONS

Preliminary results demonstrate the safety and tolerability of combining ⁹⁰Y radioembolization and sorafenib for advanced hcc. A larger prospective study is needed to determine the extent of the survival benefit.

Radiotherapy for Hepatocellular Carcinoma: New Indications and Directions for Future Study

Hepatocellular carcinoma (HCC) is a leading cause of cancer death worldwide; its incidence is increasing in the United States. Depending on disease extent and underlying liver status, patients may be treated with local, locoregional, and/or systemic therapy. Recent data indicates that radiotherapy (RT) can play a meaningful role in the management of HCC. Here, we review published experiences using RT for HCC, including the use of radiosensitizers and stereotactic RT. We discuss methods for performing preclinical studies of RT for HCC and biomarkers of response. As a part of the HCC Working Group, an informal committee of the National Cancer Institute's Radiation Research Program, we suggest how RT should be implemented in the management of HCC and identify future directions for the study of RT in HCC.

Clinical Response to Sorafenib in a Patient with Metastatic Colorectal Cancer and FLT3 Amplification

Background

A considerable number of patients with metastatic colorectal cancer progress after exhausting all approved standard therapies but maintain an adequate performance status and could be candidates for further treatment. We aim at reviewing our experience with sorafenib treatment of a patient with FLT3 mutation in refractory metastatic colorectal cancer.

Methods

Treatment with sorafenib of a patient with metastatic colorectal cancer and FLT3 translocation who had previously been heavily treated.

Results

The patient with metastatic colorectal cancer, aged 51 years, showed significant symptomatic and laboratory improvement with sorafenib treatment (400 mg twice daily).

Conclusion

The presented case illustrates how an aggressive and refractory colorectal tumor may respond well to targeted therapy.

Phase 1 pharmacogenetic and pharmacodynamic study of sorafenib with concurrent radiation therapy and gemcitabine in locally advanced unresectable pancreatic cancer

PURPOSE

To define the safety, efficacy, and pharmacogenetic and pharmacodynamic effects of sorafenib with gemcitabine-based chemoradiotherapy (CRT) in locally advanced pancreatic cancer.

METHODS AND MATERIALS

Patients received gemcitabine 1000 mg/m(2) intravenously weekly × 3 every 4 weeks per cycle for 1 cycle before CRT and continued for up to 4 cycles after CRT. Weekly gemcitabine 600 mg/m(2) intravenously was given during concurrent intensity modulated radiation therapy of 50 Gy to gross tumor volume in 25 fractions. Sorafenib was dosed orally 400 mg twice daily until progression, except during CRT when it was escalated from 200 mg to 400 mg daily, and 400 mg twice daily. The maximum tolerated dose cohort was expanded to 15 patients. Correlative studies included dynamic contrast-enhanced MRI and angiogenesis genes polymorphisms (VEGF-A and VEGF-R2 single nucleotide polymorphisms).

RESULTS

Twenty-seven patients were enrolled. No dose-limiting toxicity occurred during induction gemcitabine/sorafenib followed by concurrent CRT. The most common grade 3/4 toxicities were fatigue, hematologic, and gastrointestinal. The maximum tolerated dose was sorafenib 400 mg twice daily. The median progression-free survival and overall survival for 25 evaluable patients were 10.6 and 12.6 months, respectively. The median overall survival for patients with VEGF-A -2578 AA, -1498 CC, and -1154 AA versus alternate genotypes was 21.6 versus 14.7 months. Dynamic contrast-enhanced MRI demonstrated higher baseline K(trans) in responding patients.

CONCLUSIONS

Concurrent sorafenib with CRT had modest clinical activity with increased gastrointestinal toxicity in localized unresectable pancreatic cancer. Select VEGF-A/VEGF-R2 genotypes were associated with favorable survival.

Combined therapeutic efficacy of 188Re-liposomes and sorafenib in an experimental colorectal cancer liver metastasis model by intrasplenic injection of C26-luc murine colon cancer cells

Rhenium-188 (¹⁸⁸Re) displays abundant intermediate energy β emission and possesses a physical half-life of 16.9 h. Sorafenib is an orally available multikinase inhibitor that targets Raf kinases and vascular endothelial growth factor receptors (VEGFRs). Sorafenib has demonstrated preclinical and clinical activity against several types of tumors, such as renal cell and colorectal carcinoma. In this study, we investigated the efficacy of radiotherapeutics of ¹⁸⁸Re-liposomes combined with sorafenib in a C26-luc metastatic colorectal liver tumour mouse model. Liver metastases were established by intrasplenic injection of C26-luc murine colon cancer cells. Based on the results of the toxicity assessment, an administration dose of 80% the maximum tolerated dose was selected. ¹⁸⁸Re-liposomes were administered on day 1, when metastases of several hundred micrometers in diameter were observed. In the combination therapy group, 10 mg/kg sorafenib (co-developed and co-marketed by Bayer and Onyx Pharmaceuticals as Nexavar) was administered every other day for 1 week and the survival of mice was assessed. The tumor growth was more significantly inhibited in the ¹⁸⁸Re-liposome plus sorafenib group compared with the ¹⁸⁸Re-liposome alone, sorafenib alone and untreated normal saline groups (P=0.0000). Furthermore, ¹⁸⁸Re-liposomes combined with sorafenib achieved higher survival rates compared with the ¹⁸⁸Re-liposome alone, sorafenib alone and untreated normal saline groups (P=0.0000). These results support the use of combined radio-chemotherapy with ¹⁸⁸Re-liposomes plus sorafenib as a viable treatment option in the adjuvant setting for liver metastases of colorectal cancer.

Multicenter phase II study of sequential radioembolization-sorafenib therapy for inoperable hepatocellular carcinoma

BACKGROUND

The safety and tolerability of sequential radioembolization-sorafenib therapy is unknown. An open-label, single arm, investigator-initiated Phase II study (NCT0071279) was conducted at four Asia-Pacific centers to evaluate the safety and efficacy of sequential radioembolization-sorafenib in patients with hepatocellular carcinoma (HCC) not amenable to curative therapies.

METHODS

Sorafenib (400 mg twice-daily) was initiated 14 days post-radioembolization with yttrium-90 (90Y) resin microspheres given as a single procedure. The primary endpoints were safety and tolerability and best overall response rate (ORR) using RECIST v1.0.Secondary endpoints included: disease control rate (complete [CR] plus partial responses [PR] and stable disease [SD]) and overall survival (OS).

RESULTS

Twenty-nine patients with Barcelona Clinic Liver Cancer (BCLC) stage B (38%) or C (62%) HCC received a median of 3.0 GBq (interquartile range, 1.0) 90Y-microspheres followed by sorafenib (median dose/day, 600.0 mg; median duration, 4.1 months). Twenty eight patients experienced ≥1 toxicity; 15 (52%) grade ≥3. Best ORR was 25%, including 2 (7%) CR and 5 (18%) PR, and 15 (54%) SD. Disease control was 100% and 65% in BCLC stage B and C, respectively. Two patients (7%) had sufficient response to enable radical therapy. Median survivals for BCLC stage B and C were 20.3 and 8.6 months, respectively.

CONCLUSIONS

This study shows the potential efficacy and manageable toxicity of sequential radioembolization-sorafenib.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00712790.

Sorafenib sensitizes head and neck squamous cell carcinoma cells to ionizing radiation

BACKGROUND AND PURPOSE

There is a great need to improve the outcome of locoregionally advanced squamous cell carcinomas of the head and neck (HNSCC). Standard treatment includes a combination of surgery, radio- and chemotherapy. The addition of molecular targeting agents to conventional treatment may improve outcomes. In this study the Raf inhibitor sorafenib was used to increase the radiosensitivity of HNSCC cell lines.

MATERIAL AND METHODS

In a panel of six cell lines (A549, FaDu, UTSCC 60A, UTSCC 42A, UTSCC 42B, UTSCC 29) radiosensitivity was measured by colony formation assay and apoptosis and cell cycle analysis were performed by flow cytometry. DNA repair was analyzed by 53BP1 immunohistochemistry.

RESULTS

Sorafenib added prior to irradiation resulted in an increased cellular radiosensitivity (DEF0.5=1.11-1.84). Radiosensitization was not caused by an enhanced rate of apoptosis or cell cycle effects. In contrast, sorafenib was shown for the first time to block the repair of DNA double-strand breaks (DSB).

CONCLUSION

Our data suggest that sorafenib may be used to overcome the radioresistance of HNSCC through the inhibition of DSB repair.

Molecularly targeted agents as radiosensitizers in cancer therapy--focus on prostate cancer

As our understanding of the molecular pathways driving tumorigenesis improves and more druggable targets are identified, we have witnessed a concomitant increase in the development and production of novel molecularly targeted agents. Radiotherapy is commonly used in the treatment of various malignancies with a prominent role in the care of prostate cancer patients, and efforts to improve the therapeutic ratio of radiation by technologic and pharmacologic means have led to important advances in cancer care. One promising approach is to combine molecularly targeted systemic agents with radiotherapy to improve tumor response rates and likelihood of durable control. This review first explores the limitations of preclinical studies as well as barriers to successful implementation of clinical trials with radiosensitizers. Special considerations related to and recommendations for the design of preclinical studies and clinical trials involving molecularly targeted agents combined with radiotherapy are provided. We then apply these concepts by reviewing a representative set of targeted therapies that show promise as radiosensitizers in the treatment of prostate cancer.

Sorafenib enhances radiation-induced apoptosis in hepatocellular carcinoma by inhibiting STAT3

PURPOSE

Hepatocellular carcinoma (HCC) is one of the most common and lethal human malignancies. Lack of efficient therapy for advanced HCC is a pressing problem worldwide. This study aimed to determine the efficacy and mechanism of combined sorafenib and radiation therapy treatment for HCC.

METHODS AND MATERIALS

HCC cell lines (PLC5, Huh-7, Sk-Hep1, and Hep3B) were treated with sorafenib, radiation, or both, and apoptosis and signal transduction were analyzed.

RESULTS

All 4 HCC cell lines showed resistance to radiation-induced apoptosis; however, this resistance could be reversed in the presence of sorafenib. Inhibition of phospho-STAT3 was found in cells treated with sorafenib or sorafenib plus radiation and subsequently reduced the expression levels of STAT3-related proteins, Mcl-1, cyclin D1, and survivin. Silencing STAT3 by RNA interference overcame apoptotic resistance to radiation in HCC cells, and the ectopic expression of STAT3 in HCC cells abolished the radiosensitizing effect of sorafenib. Moreover, sorafenib plus radiation significantly suppressed PLC5 xenograft tumor growth.

CONCLUSIONS

These results indicate that sorafenib sensitizes resistant HCC cells to radiation-induced apoptosis via downregulating phosphorylation of STAT3 in vitro and in vivo.

A phase I study of the combination of sorafenib with temozolomide and radiation therapy for the treatment of primary and recurrent high-grade gliomas

PURPOSE

Despite recent advances in the management of high-grade and recurrent gliomas, survival remains poor. Antiangiogenic therapy has been shown to be efficacious in the treatment of high-grade gliomas both in preclinical models and in clinical trials. We sought to determine the safety and maximum tolerated dose of sorafenib when combined with both radiation and temozolomide in the primary setting or radiation alone in the recurrent setting.

METHODS AND MATERIALS

This was a preclinical study and an open-label phase I dose escalation trial. Multiple glioma cell lines were analyzed for viability after treatment with radiation, temozolomide, or sorafenib or combinations of them. For patients with primary disease, sorafenib was given concurrently with temozolomide (75 mg/m(2)) and 60 Gy radiation, for 30 days after completion of radiation. For patients with recurrent disease, sorafenib was combined with a hypofractionated course of radiation (35 Gy in 10 fractions).

RESULTS

Cell viability was significantly reduced with the combination of radiation, temozolomide, and sorafenib or radiation and sorafenib. Eighteen patients (11 in the primary cohort, 7 in the recurrent cohort) were enrolled onto this trial approved by the institutional review board. All patients completed the planned course of radiation therapy. The most common toxicities were hematologic, fatigue, and rash. There were 18 grade 3 or higher toxicities. The median overall survival was 18 months for the entire population.

CONCLUSIONS

Sorafenib can be safely combined with radiation and temozolomide in patients with high-grade glioma and with radiation alone in patients with recurrent glioma. The recommended phase II dose of sorafenib is 200 mg twice daily when combined with temozolomide and radiation and 400 mg with radiation alone. To our knowledge, this is the first publication of concurrent sorafenib with radiation monotherapy or combined with radiation and temozolomide.

Novel antineoplastics targeting genetic changes in colorectal cancer

Cytotoxic chemotherapy remains the mainstay of the medical -management of colorectal cancer (CRC). Research over the last two decades has led to a molecular understanding of the oncogenic mechanisms involved in CRC and has contributed to the rational development of antineoplastics that target these mechanisms. During carcinogenesis, genetic changes often occur in molecules that play key functional roles in cancer such as cell proliferation, angiogenesis, apoptosis, cell death and immune-mediated destruction of cancer cells. Here, we review novel antineoplastics that are approved or in development for CRC that target molecules associated with genetic aberrations in CRC. Some of these targeted antineoplastics have proven effective against other solid tumors and hold promise in treating CRC whereas others are now routinely used in combination with cytotoxic agents. This article reviews antineoplastics that target genetic changes in CRC, their antitumor mechanisms, and their stage of development.

Sorafenib potentiates irradiation effect in hepatocellular carcinoma in vitro and in vivo

The multikinase-inhibition action of sorafenib provides strong rationales for its combination use with radiotherapy. We investigated the in vitro and in vivo effect of sorafenib combined with irradiation on hepatocellular carcinoma (HCC). Sorafenib enhanced radiosensitivity of human HCC cell lines in a schedule-dependent manner. Sorafenib selectively inhibited radiation-induced activation of vascular endothelial growth factor receptor-2 (VEGFR2) and downstream extracellular signal-regulated kinase (ERK) pathway, induced DNA damage and suppressed DNA repair capacity, decreased radiation-activated NF-κB and increased radiation-induced apoptosis. In xenograft experiments, combination treatment produced marked tumor growth delay in both concurrent and sequential schedules. These results suggest that sorafenib could potentiate irradiation effect in HCC, which warrants further investigation for its potential clinical applications.

Sorafenib modulates the radio sensitivity of hepatocellular carcinoma cells in vitro in a schedule-dependent manner

BACKGROUND

Hepatocellular carcinoma (HCC) has a high incidence and mortality. Radiotherapy and sorafenib have proven effective for HCC. Here, we investigated whether sorafenib modulated the response of HCC cells to irradiation in vitro, effect of timing of sorafenib, and the underlying mechanisms.

METHODS

Cell viability of the HCC cell lines, SMMC-7721 and Bel-7402, was examined by the 3-(4,5-dimethylthiazol-2-yl)-5(3-carboxymethoxyphenyl)-2(4-sulfophenyl)-2 H-terazolium (MTT) assays. Clonogenic growth assays of SMMC-7721 and Bel-7402 were determined by colony formation assays. DNA damage was assessed by monitoring γ-HAX foci in irradiated cells with immunofluorescence microscopy, and cell cycle distribution changes were examined by flow cytometry. Effects of sorafenib (15 μM) added 30 min prior to radiation (pre-irradiation sorafenib) of SMMC-7721 and BEL-7402 or 24 h post-irradiation (post-irradiation sorafenib) on irradiated SMMC-7721 and BEL-7402 cells were compared to those of radiation alone or no treatment.

RESULTS

The effect of sorafenib was dependent on its time of addition in relationship to irradiation of cells. Pre-irradiation sorafenib did not significantly affect the viability of SMMC-7221 and BEL-7402 cells compared with irradiation treatment alone. In contrast, post-irradiation sorafenib increased the sensitivity of irradiated SMMC-7221 and BEL-7402 cells significantly in a time-dependent manner. Pre-irradiation sorafenib significantly increased the surviving fraction of SMMC-7221 and BEL-7402 cells in clonogenic assays whereas post-irradiation sorafenib significantly reduced the surviving fractions of SMMC-7221 and BEL-7402 cells. SMMC-7721 cells treated with sorafenib 30 min before irradiation had significantly fewer cells with γ-H2AX foci (23.8 ± 2.9%) than SMMC-7721 cells receiving radiation alone (59.9 ± 2.4; P < 0.001). Similarly, BEL-7402 cells receiving sorafenib prior to irradiation had significantly fewer cells with γ-H2AX foci (46.4 ± 3.8%) than those receiving radiation alone (25.0 ± 3.0%; P < 0.001). In addition, irradiation (6 Gy) caused a significant increase in the percentage of both SMMC-7721 and BEL-7402 cells in G2/M at 12 to 16 h post irradiation, which was markedly delayed by pre-irradiation sorafenib.

CONCLUSIONS

Sorafenib combined with irradiation exerted a schedule-dependent effect in HCC cells in vitro, which has significant implications for the combined use of sorafenib and radiotherapy for HCC patients.

Tumor reoxygenation following administration of Mitogen-Activated Protein Kinase inhibitors: a rationale for combination with radiation therapy

BACKGROUND AND PURPOSE

The relevance of Mitogen Activated Protein Kinase (MAPK) inhibitors as co-treatments for radiation therapy is investigated, with special focus on a potential link between the MAPK pathway and tumor hypoxia, which is a critical determinant for response to therapy.

MATERIALS AND METHODS

The effects of two MAPK inhibitors, Sorafenib and PD0325901, were monitored daily using in vivo EPR (Electron Paramagnetic Resonance) oximetry in FSaII and TLT tumor models in order to identify a window of reoxygenation, during which tumor blood flow, oxygen consumption and radiation sensitivity were assessed.

RESULTS

Reoxygenation was shown after two days of treatments with Sorafenib or PD0325901 in two tumor models, which was further successfully exploited with Sorafenib for improving the radiation response of FSaII tumors by a factor of 1.5. The increase in tumor oxygenation was shown to be the result of two major factors: (i) an increase in blood flow for Sorafenib, that might be linked to its anti-angiogenic effect (vascular normalization), and (ii) a decrease in oxygen consumption for Sorafenib and PD0325901, due to an alteration of the mitochondrial activity.

CONCLUSION

We evidenced tumor reoxygenation in vivo following MAPK inhibition and suggest a rationale for the combination of radiation therapy with Sorafenib.

Sorafenib sensitizes human colorectal carcinoma to radiation via suppression of NF-κB expression in vitro and in vivo

Over-expression of transcription factor nuclear factor-κB (NF-κB) in the residual tumor after the treatment is often observed at the later period of cancer radiotherapy, results in tumor radioresistance and poor treatment outcome. In this study, we combined sorafenib, a multikinase inhibitor, with ionizing radiation to evaluate the therapeutic effect, and to elucidate the possible mechanism responsible for the radiosensitization of sorafenib on a human HT29/tk-luc colorectal carcinoma in vitro and in vivo. Clonogenic survival and cell cycle analysis were used to evaluate the cytotoxicity of sorafenib in vitro. The combination effect and the role of NF-κB in therapeutic efficacy with respects in apoptosis and tumor cell invasion were studied with HT29/tk-luc tumor-bearing animal model. The expression of NF-κB and its downstream-related proteins were assayed with electrophoretic mobility shift assay (EMSA) and Western blot. Sorafenib combined with radiation shows the synergistic cytotoxicity on HT29/tk-luc cells and increased tumor cell apoptosis. Both EMSA and Western blot show that the NF-κB activity induced by radiation is significantly suppressed by sorafenib. Combination of sorafenib and radiation shows the maximum tumor growth inhibition as compared to that of sorafenib alone or radiation alone in vivo (P<0.001). In conclusion, the effect of sorafenib combined with radiation for the treatment of human colorectal carcinoma is synergistic. The mechanism of synergism is through the inhibition of radiation-induced NF-κB expression and its regulated downstream gene products.

Targeting DNA damage and repair: embracing the pharmacological era for successful cancer therapy

DNA is under constant assault from genotoxic agents which creates different kinds of DNA damage. The precise replication of the genome and the continuous surveillance of its integrity are critical for survival and the avoidance of carcinogenesis. Cells have evolved an arsenal of repair pathways and cell cycle checkpoints to detect and repair DNA damage. When repair fails, typically cell cycle progression is halted and apoptosis is initiated. Here, we review the different sources and types of DNA damage including DNA replication stress and oxidative stress, the repair pathways that cells utilize to repair damaged DNA, and discuss their biological significance, especially with reference to cancer induction and cancer therapy. We also describe the main methodologies currently used for the detection of DNA damage with their strengths and limitations. We conclude with an outline as to how this information can be used to identify novel pharmacological targets for DNA repair pathways or enhancers of DNA damage to develop improved treatment strategies that will benefit cancer patients.