Pharmacogenetics and pharmacoepigenetics of gemcitabine

Cytidine deaminase enzyme activity is a predictive biomarker in gemcitabine-treated cancer patients

BACKGROUND

Gemcitabine is a chemotherapeutic agent, widely used for the treatment of many types of cancer. Cytidine deaminase (CDA) enzyme plays an important role in the metabolism of gemcitabine. This study aimed to assess the power of serum CDA residual activity in predicting drug efficacy and toxicity in gemcitabine-treated cancer patients.

METHODS

This prospective observational study enrolled 63 patients with different types of malignancies who received gemcitabine chemotherapy between May 2019 and January 2022. Blood samples were obtained before the initiation of chemotherapy and serum CDA residual activity was determined using a modification of the Berthelot assay. The patients were followed up for at least 12 months up to 41 months. Overall survival was recorded and treatment-related toxicities were documented according to National Cancer Institute Common Terminology Criteria.

RESULTS

Kaplan-Meier analysis showed that patients with a lower than median CDA value (≤ 8.06 U/mg protein) had a significantly longer survival compared to patients with higher CDA values (> 8.06 U/mg, P ˂ 0.005). Among several potentially involved factors, a significant association between CDA activity and overall survival was observed in univariate analysis (HR = 4.219, 95% CI 1.40-12.74, P = 0.011). On the other hand, the rate of anemia was significantly higher in low-CDA patients compared to high-CDA individuals (P < 0.05).

CONCLUSION

These findings suggest that CDA activity could be a promising biomarker to predict survival and the occurrence of anemia in cancer patients treated with gemcitabine.

A polyethylene glycol-conjugate of deoxycytidine analog, DFP-14927, produces potential antitumor effects on pancreatic tumor-xenograft murine models via inducing G2/M arrest

A deoxycytidine analog is a potential agent for the treatment of several cancers, which includes poorly prognostic pancreatic cancer. We previously developed deoxycytidine analog DFP-10917, and long-term/low-dose infusions of this analog has produced antitumor effects in leukemia cancer- and ovarian cancer-xenograft models. DFP-10917 is now undergoing clinical Phase III study in the United States for the treatment of patients with relapsed or refractory acute myeloid leukemia. PEG-drug conjugation has become a promising technique to improve the pharmacokinetic and pharmacodynamic properties of anti-cancer drugs. In the present study, we synthesized a novel PEG-drug conjugate of DFP-10917, referred to hereafter as DFP-14927, using a 4-armed CTPEG system to endow the DFP-10917 drug with favorable long-circulating properties that maximize its utility and antitumor efficacy. Intravenous injection of the synthesized DFP-14927 returned encouraging antitumor effects in a Panc-1 human pancreatic tumor- and a BxPC-3 human pancreatic tumor-xenograft models. These effects were comparable to that of free DFP-10917 as well as to that of gemcitabine, which is considered a standard in the treatment of pancreatic cancer. In vitro studies revealed that DFP-14927 inhibits cell division on human pancreatic cancer cell lines via arrest of the G2/M phase in the cell cycle, which is consistent with the effects of free DFP-10917. Intravenous administration of the newly synthesized DFP-14927 has induced G2/M arrest in human pancreatic tumor-xenograft murine models, which represents an improvement in the pharmacokinetics of DFP-10917. DFP-14927 could be an alternative for patients who cannot accept prolonged or continuous infusions of DFP-10917.

Gene-Gene Interactions of Gemcitabine Metabolizing-Enzyme Genes hCNT3 and WEE1 for Preventing Severe Gemcitabine-Induced Hematological Toxicity

Most patients experience severe hematological toxicity during treatment with gemcitabine; thus, preventing such toxicity would improve the treatment effects and patient quality of life. We analyzed 13 polymorphisms in the transporters, metabolizing enzymes, targets, and genes involved in DNA damage and the folate pathway among 132 patients treated with gemcitabine and studied their association with the severity of the hematological toxicities. Single-locus analysis showed that the single-nucleotide polymorphisms (SNPs) RRM1 rs12806698 and rs11031918 and DCTD rs7663494 were significantly associated with severe neutropenia, hENT1 rs760370 and hCNT3 rs7867504 and rs4877831 were associated with severe leukopenia, CDA rs2072671, DCTD rs7663494, and WEE1 rs3910384 were associated with severe anemia, and MTHFR rs1801133 was associated with severe thrombocytopenia after stringent Bonferroni correction (P < .0038). The gene-gene interaction analysis identified the overall best models, including a 2-way interaction model (hCNT3 rs7867504 and dCK rs12648166) for severe leukopenia (P = .0022) and a 3-locus model (CDA rs207671, DCTD rs7663494, and WEE1 rs3910384) for severe anemia with a strong synergistic effect (P = .0001). The association with hematological toxicity was further strengthened by the results of a haplotype analysis, in which the homozygous genotype combination of rs3910384 CC, rs2072671 AA, rs12648166 GG, rs7867504 CC, and rs7663494 TT conferred high genetic susceptibility to severe thrombocytopenia. Our results suggest that the gene-gene interaction of gemcitabine metabolic pathway genes and WEE1 contributes to susceptibility to gemcitabine-induced hematological toxicity. Moreover, we propose a promising data-mining analysis approach (generalized multifactor dimensionality reduction) to detect and characterize gene-gene interactions.

Characterization of deoxyribonucleoside transport mediated by concentrative nucleoside transporters

Human concentrative nucleoside transporters (CNTs) are responsible for cellular uptake of ribonucleosides; however, although it is important to better characterize CNT-subtype specificity to understand the systemic disposition of deoxyribonucleosides (dNs) and their analogs, the involvement of CNTs in transporting dNs is not fully understood. In this study, using COS-7 cells that transiently expressed CNT1, CNT2, or CNT3, we investigated if CNTs could transport not only ribonucleosides but also dNs, i.e., 2'-deoxyadenosine (dAdo), 2'-deoxyguanosine (dGuo), and 2'-deoxycytidine (dCyd). The cellular uptake study demonstrated that dAdo and dGuo were taken up by CNT2 but not by CNT1. Although dCyd was taken up by CNT1, no significant uptake was detected in COS-7 cells expressing CNT2. Similarly, these dNs were transported by CNT3. The apparent K_m values of their uptake were as follows: CNT1, K_m ＝ 141 μM for dCyd; CNT2, K_m ＝ 62.4 μM and 54.9 μM for dAdo and dGuo, respectively; CNT3, K_m ＝ 14.7 μM and 34.4 μM for dGuo and dCyd, respectively. These results demonstrate that CNTs contribute not only to ribonucleoside transport but also to the transport of dNs. Moreover, our data indicated that CNT1 and CNT2 selectively transported pyrimidine and purine dNs, respectively, and CNT3 was shown to transport both pyrimidine and purine dNs.

Novel method for DNA methylation analysis using high-performance liquid chromatography and its clinical application

The aim of this study was to develop a new methodology that is suitable for DNA methylation diagnostics and to demonstrate its clinical applicability. We developed a new anion-exchange column for high-performance liquid chromatography (HPLC) with electrostatic and hydrophobic properties. Both cytosine and thymine, corresponding to methylated and unmethylated cytosine after bisulfite modification, respectively, are captured by electrostatic interaction and then discriminated from each other by their hydrophobic interactions. The DNA methylation levels of synthetic DNA were quantified accurately and reproducibly within 10 minutes without time-consuming pretreatment of PCR products, and the measured values were unaffected by the distribution of methylated CpG within the synthetic DNA fragments. When the DNA methylation status of the FAM150A gene, a marker of the CpG island methylator phenotype specific to clear cell renal cell carcinoma (ccRCC), was examined in 98 patients with ccRCC, bulk specimens of tumorous tissue including cancer cells showing DNA methylation of the FAM150A gene were easily identifiable by simply viewing the differentiated chromatograms, even when the cancer cell content was low. Sixteen ccRCC showing DNA methylation more frequently exhibited clinicopathological parameters reflecting tumor aggressiveness (ie, a larger diameter, higher histological grade, vascular involvement, renal vein tumor thrombi, infiltrating growth, tumor necrosis, renal pelvis invasion and higher pathological TNM stage), and had significantly lower recurrence-free and overall survival rates. These data indicate that HPLC analysis using this newly developed anion-exchange column could be a powerful tool for DNA methylation diagnostics, including prognostication of patients with cancers, in a clinical setting.

The E1B19K-deleted oncolytic adenovirus mutant AdΔ19K sensitizes pancreatic cancer cells to drug-induced DNA-damage by down-regulating Claspin and Mre11

Adenovirus-mediated sensitization of cancer cells to cytotoxic drugs depends on simultaneous interactions of early viral genes with cell death and survival pathways. It is unclear what cellular factors mediate these interactions in the presence of DNA-damaging drugs. We found that adenovirus prevents Chk1-mediated checkpoint activation through inactivation of Mre11 and downregulation of the pChk1 adaptor-protein, Claspin, in cells with high levels of DNA-damage induced by the cytotoxic drugs gemcitabine and irinotecan. The mechanisms for Claspin downregulation involve decreased transcription and increased degradation, further attenuating pChk1-mediated signalling. Live cell imaging demonstrated that low doses of gemcitabine caused multiple mitotic aberrations including multipolar spindles, micro- and multi-nucleation and cytokinesis failure. A mutant virus with the anti-apoptotic E1B19K-gene deleted (AdΔ19K) further enhanced cell killing, Claspin downregulation, and potentiated drug-induced DNA damage and mitotic aberrations. Decreased Claspin expression and inactivation of Mre11 contributed to the enhanced cell killing in combination with DNA-damaging drugs. These results reveal novel mechanisms that are utilised by adenovirus to ensure completion of its life cycle in the presence of cellular DNA damage. Taken together, our findings reveal novel cellular targets that may be exploited when developing improved anti-cancer therapeutics.

Mocetinostat combined with gemcitabine for the treatment of leiomyosarcoma: Preclinical correlates

Leiomyosarcoma (LMS) is a malignant soft tissue sarcoma (STS) with a dismal prognosis following metastatic disease. Chemotherapeutic intervention has demonstrated to have modest clinical efficacy with no curative potential in LMS patients. Previously, we demonstrated pan-HDAC inhibition to have a superior effect in various complex karyotypic sarcomas. In this study, our goal is to evaluate the therapeutic efficacy of mocetinostat alone and in combination with gemcitabine in LMS. Human leiomyosarcoma (LMS) cell lines were used for in vitro and in vivo studies. Compounds tested included the class I HDAC inhibitor, mocetinostat, and nucleoside analog, gemcitabine. MTS and clonogenic assays were used to evaluate the effect of mocetinostat on LMS cell growth. Cleaved caspase 3/7 analysis was used to determine the effects of mocetinostat on apoptosis. Compusyn software was used to determine in vitro synergy studies for the combination of mocetinostat plus gemcitabine. A LMS xenograft model in SCID mice was used to test the impact of mocetinostat alone, gemcitabine alone and the combination of mocetinostat plus gemcitabine. Mocetinostat abrogated LMS cell growth and clonogenic potential, and enhanced apoptosis in LMS cell lines. The combination of mocetinostat plus gemcitabine exhibited a synergistic effect in LMS cells in vitro. Similarly, mocetinostat combined with gemcitabine resulted in superior anti-LMS effects in vivo. Mocetinostat reduced the expression of gemcitabine-resistance markers RRM1, RRM2, and increased the expression of gemcitabine-sensitivity marker, hENT1, in LMS cells. LMS are aggressive, metastatic tumors with poor prognosis where effective therapeutic interventions are wanting. Our studies demonstrate the potential utility of mocetinostat combined with gemcitabine for the treatment of LMS.

Molecular alterations contributing to pancreatic cancer chemoresistance

Pancreatic ductal adenocarcinoma (PDAC) is one of the most common causes of cancer-related death all over the world. This disease is difficult to treat and patients have an overall 5-year survival rate of less than 5%. Although two drugs, gemcitabine (GEM) and 5-fluorouracil (5-FU) have been shown to improve the survival rate of patients systematically, they do not increase general survival to a clinically acceptable degree. Lack of ideal clinical response of pancreatic cancer patients to chemotherapy is likely to be due to intrinsic and acquired chemoresistance of tumor cells. Various mechanisms of drug resistance have been investigated in pancreatic cancer, including genetic and epigenetic changes in particular genes or signaling pathways. In addition, evidence suggests that microRNAs (miRNAs) play significant roles as key regulators of gene expression in many cellular processes, including drug resistance. Understanding underlying genes and mechanisms of drug resistance in pancreatic cancer is critical to develop new effective treatments for this deadly disease. This review illustrates the genes and miRNAs involved in resistance to gemcitabine in pancreatic cancer.

Gemcitabine: Selective cytotoxicity, induction of inflammation and effects on urothelial function

Intravesical gemcitabine has recently been introduced for the treatment of superficial bladder cancer and has a favourable efficacy and toxicity profile in comparison to mitomycin c (MMC), the most commonly used chemotherapeutic agent. The aim of this study was to assess the cytotoxic potency of gemcitabine in comparison to MMC in urothelial cell lines derived from non-malignant (UROtsa) and malignant (RT4 and T24) tissues to assess selectivity. Cells were treated with gemcitabine or mitomycin C at concentrations up to the clinical doses for 1 or 2h respectively (clinical duration). Treatment combined with hyperthermia was also examined. Cell viability, ROS formation, urothelial function (ATP, acetylcholine and PGE2 release) and secretion of inflammatory cytokines were assessed. Gemcitabine displayed a high cytotoxic selectivity for the two malignant cell lines (RT4, T24) compared to the non-malignant urothelial cells (UROtsa, proliferative and non-proliferative). In contrast, the cytotoxic effects of MMC were non-selective with equivalent potency in each of the cell lines. The cytotoxic effect of gemcitabine in the malignant cell lines was associated with an elevation in free radical formation and was significantly decreased in the presence of an equilibrative nucleoside transporter inhibitor. Transient changes in urothelial ATP and PGE₂ release were observed, with significant increase in release of interleukin-6, interleukin-8 and interleukin-1β from urothelial cells treated with gemcitabine. The selectivity of gemcitabine for malignant urothelial cells may account for the less frequent adverse urological effects with comparison to other commonly used chemotherapeutic agents.

The effects of microRNA on the absorption, distribution, metabolism and excretion of drugs

The importance of genetic factors (e.g. sequence variation) in the absorption, distribution, metabolism, excretion (ADME) and overall efficacy of therapeutic agents is well established. Our ability to identify, interpret and utilize these factors is the subject of much clinical investigation and therapeutic development. However, drug ADME and efficacy are also heavily influenced by epigenetic factors such as DNA/histone methylation and non-coding RNAs [especially microRNAs (miRNAs)]. Results from studies using tools, such as in silico miRNA target prediction, in vitro functional assays, nucleic acid profiling/sequencing and high-throughput proteomics, are rapidly expanding our knowledge of these factors and their effects on drug metabolism. Although these studies reveal a complex regulation of drug ADME, an increased understanding of the molecular interplay between the genome, epigenome and transcriptome has the potential to provide practically useful strategies to facilitate drug development, optimize therapeutic efficacy, circumvent adverse effects, yield novel diagnostics and ultimately become an integral component of personalized medicine.

A meta-analysis of gemcitabine biomarkers in patients with pancreaticobiliary cancers

OBJECTIVES

The objective of this study was to summarize all clinical studies evaluating the prognostic role of gemcitabine (GEM) metabolic genes in pancreaticobiliary (PB) cancer patients receiving GEM therapy in the neoadjuvant, adjuvant, or palliative settings.

METHODS

Meta-analyses were performed to calculate the pooled hazard ratios for each gene by each clinical outcome (overall survival [OS], disease-free survival [DFS], and progression-free survival) using a random-effects approach.

RESULTS

The search strategy identified 16 eligible studies, composed of 632 PB patients total, with moderate quality. Compared with low expression, pooled hazard ratios for OS of hENT1, dCK, RRM1, RRM2, and DPD were 0.37 (95% confidence interval [CI], 0.28-0.47), 0.40 (95% CI, 0.20-0.80), 2.21 (95% CI, 1.12-4.36), 2.13 (95% CI, 1.00-4.52), and 1.91 (95% CI, 1.16-3.17), respectively. A similar trend was observed for each of these biomarkers in DFS and progression-free survival prognostication. Subgroup analyses for hENT1 showed a comparable survival correlation in the adjuvant and palliative settings.

CONCLUSIONS

High expression of hENT1 in PB cancer patients receiving GEM-based adjuvant therapy is associated with improved OS and DFS and may be the best examined prognostic marker to date. Evidence for other biomarkers is limited by a small number of publications investigating these markers.

Epigenetic-dependent regulation of drug transport and metabolism: an update

The pharmacokinetics of a drug are subject to large interindividual variability, which can result in lack of response or adverse drug reactions. In addition to genetic polymorphisms and drug interactions, key genes involved in the metabolism and transport of drugs are demonstrated to have epigenetic influences that can potentially affect interindividual variability in drug response. Emerging studies have focused on the importance of DNA methylation for ADME gene expression and for drug action and resistance, particularly in cancer. However, the epigenetic and ncRNA-dependent regulation of these genes, as well as the pharmacological consequences, is in need of greater attention. In the current review we provide an update of epigenetic and ncRNA-dependent regulation of ADME genes.

The antitumor activity of recombinant antitumor antiviral protein and the associated molecular mechanism in pancreatic tumor cells

BACKGROUND

Pancreatic cancer has poor prognosis and high mortality. Currently, the therapy of pancreatic cancer remains a challenge. In this study, we compared the antitumor activity of the recombinant antitumor antiviral protein (RAAP), an improved interferon, with gemcitabine, a classic chemotherapy agent used for pancreatic cancer treatment.

METHODS

The proliferation of Bx-PC3 pancreatic cancer cells was evaluated by an MTT assay. Cell cycle arrest and apoptosis were evaluated by flow cytometry and annexin V-FITC/propidium iodide double staining, respectively. The expressions of matrix metalloproteinase (MMP)-2, MMP-9, caspase-3, caspase-8, and caspase-9 genes were evaluated by reverse transcription-polymerase chain reaction and the Western blot analysis. A xenograft pancreatic cancer model was established by inoculating Bx-PC3 cells into athymic nude mice. The antitumor activity of RAAP and gemcitabine was tested in the xenograft tumor model.

RESULTS

RAAP significantly inhibited proliferation, induced cell cycle arrest, and induced apoptosis in Bx-PC3 cells in vitro and delayed tumor growth in vivo. The antitumor activity of 20 ng/mL of RAAP was a little more effective than 10 μM of gemcitabine. The antitumor activity of RAAP was associated with its role in inducing caspase-3 and caspase-8 expression as well as downregulating MMP-2 expression.

CONCLUSIONS

RAAP can effectively suppress human pancreatic cancer cell growth in vitro and in vivo. The antitumor efficacy of RAAP is similar to gemcitabine.

Synthesis and in vitro evaluation of novel lipophilic monophosphorylated gemcitabine derivatives and their nanoparticles

Gemcitabine hydrochloride (HCl) is approved for the treatment of a wide spectrum of solid tumors. However, the rapid development of resistance often makes gemcitabine less efficacious. In the present study, we synthesized several novel lipophilic monophosphorylated gemcitabine derivatives, incorporated them into solid lipid nanoparticles, and then evaluated their ability to overcome major known gemcitabine resistance mechanisms by evaluating their in vitro cytotoxicities in cancer cells that are deficient in deoxycytidine kinase (dCK), deficient in human equilibrative nucleoside transporter (hENT1), over-expressing ribonucleotide reductase M1 subunit (RRM1), or over-expressing RRM2. In dCK deficient cells, the monophosphorylated gemcitabine derivatives and their nanoparticles were up to 86-fold more cytotoxic than gemcitabine HCl. The majority of the gemcitabine derivatives and their nanoparticles were more cytotoxic than gemcitabine HCl in cells that over-expressing RRM1 or RRM2, and the gemcitabine derivatives in nanoparticles were also resistant to deamination by deoxycytidine deaminase. The gemcitabine derivatives (in nanoparticles) hold a great potential in overcoming gemcitabine resistance.

DNA methylation-independent reversion of gemcitabine resistance by hydralazine in cervical cancer cells

Background

Down regulation of genes coding for nucleoside transporters and drug metabolism responsible for uptake and metabolic activation of the nucleoside gemcitabine is related with acquired tumor resistance against this agent. Hydralazine has been shown to reverse doxorubicin resistance in a model of breast cancer. Here we wanted to investigate whether epigenetic mechanisms are responsible for acquiring resistance to gemcitabine and if hydralazine could restore gemcitabine sensitivity in cervical cancer cells.

Methodology/Principal Findings

The cervical cancer cell line CaLo cell line was cultured in the presence of increasing concentrations of gemcitabine. Down-regulation of hENT1 & dCK genes was observed in the resistant cells (CaLoGR) which was not associated with promoter methylation. Treatment with hydralazine reversed gemcitabine resistance and led to hENT1 and dCK gene reactivation in a DNA promoter methylation-independent manner. No changes in HDAC total activity nor in H3 and H4 acetylation at these promoters were observed. ChIP analysis showed H3K9m2 at hENT1 and dCK gene promoters which correlated with hyper-expression of G9A histone methyltransferase at RNA and protein level in the resistant cells. Hydralazine inhibited G9A methyltransferase activity in vitro and depletion of the G9A gene by iRNA restored gemcitabine sensitivity.

Conclusions/Significance

Our results demonstrate that acquired gemcitabine resistance is associated with DNA promoter methylation-independent hENT1 and dCK gene down-regulation and hyper-expression of G9A methyltransferase. Hydralazine reverts gemcitabine resistance in cervical cancer cells via inhibition of G9A histone methyltransferase.

Genomics and pharmacogenomics of pancreatic adenocarcinoma

The last decade has brought significant advances in the development of molecularly targeted therapies for treatment of a variety of human malignancies. In contrast to other solid tumors, however, the impact of novel therapeutic strategies on clinical outcomes in patients with pancreas adenocarcinoma (PAC) has been limited to date. Gemcitabine was established as a standard of care for treatment of advanced PAC in 1997 based on an observed improvement in clinical benefit as adjudicated principally by pain scores and analgesic consumption, and demonstration of an overall survival (OS) benefit in a randomized comparison with 5-fluorouracil (5-FU). Since then, multiple agents targeting oncogenic signaling pathways and mediators of angiogenesis have failed to improve outcomes in phase III clinical trials when compared with gemcitabine monotherapy. An exception to this is the anti-epidermal growth factor receptor therapy erlotinib, which yielded a survival benefit in patients with advanced disease in combination with gemcitabine compared with gemcitabine alone, although this was a marginal incremental improvement for which the clinical significant has been heavily debated. More recently, the most significant therapeutic advance in PAC has come from the combination of several cytotoxic agents; infusional 5-FU, irinotecan and oxaliplatin. This combination chemotherapy regimen, known as FOLFIRINOX, improved survival in patients with an excellent functional status and stage IV disease by 4.3 months compared with gemcitabine alone. This improvement in survival did come at the cost expectedly of a significant increase in toxicities, including gastrointestinal and hematologic particularly. Other gemcitabine-based combination chemotherapy regimens including gemcitabine and platinum analogs and gemcitabine and capecitabine have consistently shown an increased response rate but no OS benefit in individual trials; albeit pooled and meta-analyses have indicated a survival benefit in good performance status patient for both these cytotoxic combinations. Accordingly, the 5-year survival for patients with PAC remains <5%, with an annual disease-specific mortality which approaches the incidence. The challenge remains therefore, to develop more effective systemic therapies against this challenging malignancy. Recent progress toward understanding the genetic events in the development of PAC, in combination with advances in the field of pharmacogenomics offer hope that we may build on achievements to-date to develop more effective therapeutic strategies for PAC in years to come.

Pharmacokinetic evaluation of gemcitabine hydrochloride for the treatment of cervical cancer

INTRODUCTION

Cervical cancer is the third most prevalent cancer in females worldwide. When advanced, the disease requires primary radiation concurrent with chemotherapy. However, chemotherapy alone is the standard treatment for recurrent/persistent/metastatic disease.

AREAS COVERED

Areas covered in this review include the treatment of advanced cervical cancer with gemcitabine as radiosensitizer, either alone or in combination with cisplatin. The use of gemcitabine for recurrent/persistent/metastatic cervical cancer is also reviewed.

EXPERT OPINION

Statistically significantly better survival rates are achieved with cisplatin doublets against cisplatin alone, in the management of recurrent/persistent/metastatic cervical cancer. The choice of the cisplatin doublet with paclitaxel, vinorelbine, gemcitabine and topotecan arms should be based on physician preference, pre-existing morbidity and patient-related factors. In advanced disease, a recently reported Phase III trial establishes the novel regimen of concurrent gemcitabine plus cisplatin and external radiation, followed by brachytherapy and two adjuvant 21-day cycles of gemcitabine plus cisplatin, as significantly improving survival outcomes when compared with the current standard of care. The increased acute toxicity of this regimen is clear; however, this should not deter its incorporation into clinical practice, in that the toxicity is predictable and manageable; nevertheless, the occurrence of late toxicity and survival at longer follow-up time are reasonable concerns in this regimen.