Capecitabine

Expansion of a bacterial operon during cancer treatment ameliorates drug toxicity

Dose-limiting toxicities remain a major barrier to drug development and therapy, revealing the limited predictive power of human genetics. Herein, we demonstrate the utility of a more comprehensive approach to studying drug toxicity through longitudinal study of the human gut microbiome during colorectal cancer (CRC) treatment (NCT04054908) coupled to cell culture and mouse experiments. 16S rRNA gene and metagenomic sequencing revealed significant shifts in gut microbial community structure during treatment with oral fluoropyrimidines, which was validated in an independent cohort. Gene abundance was also markedly changed by oral fluoropyrimidines, including an enrichment for the preTA operon, which is sufficient for the inactivation of active metabolite 5-fluorouracil (5-FU). Higher levels of preTA led to increased 5-FU depletion by the gut microbiota grown ex vivo. Germ-free and antibiotic-treated mice had increased fluoropyrimidine toxicity, which was rescued by colonization with the mouse gut microbiota, preTA+ E. coli, or CRC patient stool with high preTA levels. preTA abundance was negatively associated with patient toxicities. Together, these data support a causal, clinically relevant interaction between a human gut bacterial operon and the dose-limiting side effects of cancer treatment. Our approach is generalizable to other drugs, including cancer immunotherapies, and provides valuable insights into host-microbiome interactions in the context of disease.

Cutaneous Squamous Cell Carcinoma: An Updated Review

Representing the second most common skin cancer, the incidence and disease burden of cutaneous squamous cell carcinoma (cSCC) continues to increase. Surgical excision of the primary site effectively cures the majority of cSCC cases. However, an aggressive subset of cSCC persists with clinicopathological features that are indicative of higher recurrence, metastasis, and mortality risks. Acceleration of these features is driven by a combination of genetic and environmental factors. The past several years have seen remarkable progress in shaping the treatment landscape for advanced cSCC. Risk stratification and clinical management is a top priority. This review provides an overview of the current perspectives on cSCC with a focus on staging, treatment, and maintenance strategies, along with future research directions.

smProdrugs: A repository of small molecule prodrugs

In modern drug discovery and development, the prodrug approach has become a crucial strategy for enhancing the pharmacokinetic profiles of drugs. A prodrug is a chemical compound, which gets metabolized into a pharmacologically active form (drug) inside the body after its administration. In the current work, we report 'smProdrugs' (http://cheminfolab.in/databases/prodrug/), which is one of the first exclusive databases on small molecule prodrugs. It stores the structures, physicochemical properties and experimental ADMET data manually curated from literature. SmProdrugs lists 626 small molecule prodrugs and their active compounds with the above mentioned experimental data from 1808 research articles and 61 patents have been stored. The information page of each record gives the structures and properties of the prodrug and the active drug side by side which makes it easy for the user to instantly compare them. The structural modifications in the prodrug/active drugs are highlighted in a different colour for easy comparison. Experimental data has been curated from the downloaded PubMed and patent articles and were catalogued in a tabular form with more than 25 fields under sub-sections i) name and structures of the prodrugs and their active compounds, ii) mode of activation of the prodrug and enzyme/biocatalyst involved in the conversion, iii) indications/disease, iv) pharmacological target, v) experimental pharmacokinetic properties such as solubility, absorption, volume of distribution, half-life, clearance etc. and vi) information on the purpose/gain from the prodrug strategies. Considering the ever expanding utility of the prodrug approach smProdrugs will be of great use to the scientific community working on rational design of small molecule prodrugs.

Health-related quality of life with palbociclib plus endocrine therapy versus capecitabine in postmenopausal patients with hormone receptor-positive metastatic breast cancer: Patient-reported outcomes in the PEARL study

BACKGROUND

The PEARL study showed that palbociclib plus endocrine therapy (palbociclib/ET) was not superior to capecitabine in improving progression-free survival in postmenopausal patients with metastatic breast cancer resistant to aromatase inhibitors, but was better tolerated. This analysis compared patient-reported outcomes.

PATIENTS AND METHODS

The PEARL quality of life (QoL) population comprised 537 patients, 268 randomised to palbociclib/ET (exemestane or fulvestrant) and 269 to capecitabine. Patients completed the European Organisation for Research and Treatment of Cancer QLQ-C30 and QLQ-BR23 and EQ-5D-3L questionnaires. Changes from the baseline and time to deterioration (TTD) were analysed using linear mixed-effect and stratified Cox regression models, respectively.

RESULTS

Questionnaire completion rate was high and similar between treatment arms. Significant differences were observed in the mean change in global health status (GHS)/QoL scores from the baseline to cycle 3 (2.9 for palbociclib/ET vs. -2.1 for capecitabine (95% confidence interval [CI], 1.4-8.6; P = 0.007). The median TTD in GHS/QoL was 8.3 months for palbociclib/ET versus 5.3 months for capecitabine (adjusted hazard ratio, 0.70; 95% CI, 0.55-0.89; P = 0.003). Similar improvements for palbociclib/ET were also seen for other scales as physical, role, cognitive, social functioning, fatigue, nausea/vomiting and appetite loss. No differences were observed between the treatment arms in change from the baseline in any item of the EQ-5D-L3 questionnaire as per the overall index score and visual analogue scale.

CONCLUSION

Patients receiving palbociclib/ET experienced a significant delay in deterioration of GHS/QoL and several functional and symptom scales compared with capecitabine, providing additional evidence that palbociclib/ET is better tolerated.

TRIAL REGISTRATION NUMBER

NCT02028507 (ClinTrials.gov).

EUDRACT STUDY NUMBER

2013-003170-27.

Nucleobase and Nucleoside Analogues: Resistance and Re-Sensitisation at the Level of Pharmacokinetics, Pharmacodynamics and Metabolism

Antimetabolites, in particular nucleobase and nucleoside analogues, are cytotoxic drugs that, starting from the small field of paediatric oncology, in combination with other chemotherapeutics, have revolutionised clinical oncology and transformed cancer into a curable disease. However, even though combination chemotherapy, together with radiation, surgery and immunotherapy, can nowadays cure almost all types of cancer, we still fail to achieve this for a substantial proportion of patients. The understanding of differences in metabolism, pharmacokinetics, pharmacodynamics, and tumour biology between patients that can be cured and patients that cannot, builds the scientific basis for rational therapy improvements. Here, we summarise current knowledge of how tumour-specific and patient-specific factors can dictate resistance to nucleobase/nucleoside analogues, and which strategies of re-sensitisation exist. We revisit well-established hurdles to treatment efficacy, like the blood-brain barrier and reduced deoxycytidine kinase activity, but will also discuss the role of novel resistance factors, such as SAMHD1. A comprehensive appreciation of the complex mechanisms that underpin the failure of chemotherapy will hopefully inform future strategies of personalised medicine.

Human Thymidylate Synthase Inhibitors Halting Ovarian Cancer Growth

Human thymidylate synthase (hTS) has an important role in DNA biosynthesis, thus it is essential for cell survival. TS is involved in the folate pathways, specifically in the de novo pyrimidine biosynthesis. Structure and functions are intimately correlated, account for cellular activity and, in a broader view, with in vivo mechanisms. hTS is a target for anticancer agents, some of which are clinical drugs. The understanding of the detailed mechanism of TS inhibition by currently used drugs and of the interaction with the mechanism of action of other anticancer agents can suggest new perspective of TS inhibition able to improve the anticancer effect and to overcome drug resistance. TS-targeting drugs in therapy today are inhibitors that bind at the active site and that mostly resemble the substrates. Nonsubstrate analogs offer an opportunity for allosteric binding and novel mode of inhibition in the cancer cells. This chapter illustrates the relationship among the large number of hTS actions at molecular and clinical levels, its role as a target for ovarian cancer therapy, in particular in cases of overexpression of hTS and other folate proteins such as those induced by platinum drug treatments, and address the potential combination of TS inhibitors with other suitable anticancer agents.

Inside the biochemical pathways of thymidylate synthase perturbed by anticancer drugs: Novel strategies to overcome cancer chemoresistance

Our current understanding of the mechanisms of action of antitumor agents and the precise mechanisms underlying drug resistance is that these two processes are directly linked. Moreover, it is often possible to delineate chemoresistance mechanisms based on the specific mechanism of action of a given anticancer drug. A more holistic approach to the chemoresistance problem suggests that entire metabolic pathways, rather than single enzyme targets may better explain and educate us about the complexity of the cellular responses upon cytotoxic drug administration. Drugs, which target thymidylate synthase and folate-dependent enzymes, represent an important therapeutic arm in the treatment of various human malignancies. However, prolonged patient treatment often provokes drug resistance phenomena that render the chemotherapeutic treatment highly ineffective. Hence, strategies to overcome drug resistance are primarily designed to achieve either enhanced intracellular drug accumulation, to avoid the upregulation of folate-dependent enzymes, and to circumvent the impairment of DNA repair enzymes which are also responsible for cross-resistance to various anticancer drugs. The current clinical practice based on drug combination therapeutic regimens represents the most effective approach to counteract drug resistance. In the current paper, we review the molecular aspects of the activity of TS-targeting drugs and describe how such mechanisms are related to the emergence of clinical drug resistance. We also discuss the current possibilities to overcome drug resistance by using a molecular mechanistic approach based on medicinal chemistry methods focusing on rational structural modifications of novel antitumor agents. This paper also focuses on the importance of the modulation of metabolic pathways upon drug administration, their analysis and the assessment of their putative roles in the networks involved using a meta-analysis approach. The present review describes the main pathways that are modulated by TS-targeting anticancer drugs starting from the description of the normal functioning of the folate metabolic pathway, through the protein modulation occurring upon drug delivery to cultured tumor cells as well as cancer patients, finally describing how the pathways are modulated by drug resistance development. The data collected are then analyzed using network/netwire connecting methods in order to provide a wider view of the pathways involved and of the importance of such information in identifying additional proteins that could serve as novel druggable targets for efficacious cancer therapy.

Epirubicin Plus Cyclophosphamide Followed by Docetaxel Versus Epirubicin Plus Docetaxel Followed by Capecitabine As Adjuvant Therapy for Node-Positive Early Breast Cancer: Results From the GEICAM/2003-10 Study

PURPOSE

Capecitabine is an active drug in metastatic breast cancer (BC). GEICAM/2003-10 is an adjuvant trial to investigate the integration of capecitabine into a regimen of epirubicin and docetaxel for node-positive early BC.

PATIENTS AND METHODS

Patients with operable node-positive BC (T1-3/N1-3) were eligible. After surgery, 1,384 patients were randomly assigned to receive epirubicin plus cyclophosphamide (EC; 90 and 600 mg/m(2), respectively, × four cycles), followed by docetaxel (100 mg/m(2) × four cycles; EC-T) or epirubicin plus docetaxel (ET; 90 and 75 mg/m(2), respectively, × four cycles), followed by capecitabine (1,250 mg/m(2) twice a day on days 1 to 14, × four cycles; ET-X); all regimens were given every 3 weeks. The primary end point was invasive disease-free survival. Secondary end points included safety (with an alopecia-specific study) and overall survival (OS).

RESULTS

After a median follow-up of 6.6 years and 297 events, 86% of patients who received EC-T and 82% of those who received ET-X were invasive disease free at 5 years (hazard ratio, 1.30; 95% CI, 1.03 to 1.64; log-rank P = .03). The OS difference between arms was not statistically significant (hazard ratio, 1.13; 95% CI, 0.82 to 1.55; log-rank P = .46). The most frequent grade 3 to 4 adverse events in the EC-T versus ET-X arms were neutropenia (19% v 10%), with 7% febrile neutropenia across arms; fatigue (13% v 11%); diarrhea (3% v 11%); hand-foot syndrome (2% v 20%); mucositis (6% v 5%); vomiting (both, 5%); and myalgia (4.5% v 1%). Incomplete scalp hair recovery was more frequent in the EC-T than ET-X arm (30% v 14%), and patients who received EC-T wore wigs significantly longer than those who received ET-X (8.35 v 6.03 months).

CONCLUSION

Invasive disease-free survival, but not OS, was significantly superior for patients with node-positive early BC who received the adjuvant standard schedule EC-T than for those who received the experimental ET-X regimen. Toxicity profiles differed substantially across arms.

Role of ABC transporters in fluoropyrimidine-based chemotherapy response

Since over 50 years, 5-fluorouracil (5-FU) is in use as backbone of chemotherapy treatment regimens for a wide range of cancers including colon, breast, and head and neck carcinomas. However, drug resistance and severe toxicities such as mucositis, diarrhea, neutropenia, and vomiting in up to 40% of treated patients often lead to dose limitation or treatment discontinuation. Because the oral bioavailability of 5-FU is unpredictable and highly variable, 5-FU is commonly administered intravenously. To overcome medical complications and inconvenience associated with intravenous administration, the oral prodrugs capecitabine and tegafur have been developed. Both fluoropyrimidines are metabolically converted intracellularly to 5-FU, which then needs metabolic activation to exert its damaging activity on RNA and DNA. The low response rates of 10-15% of 5-FU monotherapy can be improved by combination regimens of infusional 5-FU and leucovorin together with oxaliplatin (FOLFOX) or irinotecan (FOLFIRI), thereby increasing response rates to 30-40%. The impact of metabolizing enzymes in the development of fluoropyrimidine toxicity and resistance has been studied in great detail. In addition, membrane drug transporters, which are critical determinants of intracellular drug concentrations, may play a role in occurrence of toxicity and development of resistance against fluoropyrimidine-based therapy as well. This review therefore summarizes current knowledge on the role of drug transporters with particular focus on ATP-binding cassette transporters in fluoropyrimidine-based chemotherapy response.

Lack of prognostic value of mean corpuscular volume with capecitabine therapy in metastatic breast cancer

BACKGROUND

Capecitabine is an oral fluoropyrimidine derivative which is frequently used alone or in combination regimens for the treatment of metastatic breast cancer. Although overall and progression free survivals have increased in recent years with the use of new generation drugs, predictive factors that would further improve the outcomes are needed. Previous studies have demonstrated the relation between post-treatment increase in mean corpuscular volume (MCV) and predicting therapy response as well as survival. The present study investigated the clinical impact of MCV elevation in metastatic breast cancer patients treated with capecitabine.

MATERIALS AND METHODS

The data of a total of 82 patients from three centers followed between June 2005 and June 2013 were retrospectively analyzed. The demographic data and hormone receptor status of the patients, as well as initial examination before and after treatment and data concerning progression were recorded. MCV ≥ 100 fl was considered as macrocytosis. Capecitabine was given at a dose of 2500 mg/m2 daily for 14 days every three weeks. Pre-treatment and post-treatment MCV and other parameters of complete blood count were recorded. Post-treatment initial evaluation was performed after 2 cycles of therapy.

RESULTS

The median age of the patients was 46.5 years (range 26-72 years) and 54% were premenopausal. Performance status was ECOG 0 and 1 in 81 (99%) patients. The median number of cycles for capecitabine therapy was 5 (min-max: 2-18). The median ΔMCV level (post-treatment values at sixth week - baseline) was 6.4. Whilst ΔMCV was ≥ 6.4 in 42 patients, it was <6.4 in 40 patients. Clinical benefit (complete response+partial response+stable disease) was observed in 37 (88%) of 42 patients with a median ΔMCV ≥ 6.4 and in 30 (75%) of 40 patients with ΔMCV <6.4 with no statistically significant difference (p=0.158). No significant difference was determined between the group with ΔMCV ≥ 6.4 and the group with ΔMCV <6.4 in terms of progression-free survival (11 vs 12 months) (p=0.55) and overall survival (20 months vs. 24 months) (p=0.11).

CONCLUSIONS

The identification of new predictive markers in metastatic breast cancer is very important. In some recent studies, increase in MCV has been suggested as a marker in tumor response. In the present study, however, no significant difference was determined between tumor response and increase in MCV. Further studies including higher numbers of patients are needed to determine whether increase in MCV is a predictive marker or not.

DCA increases the antitumor effects of capecitabine in a mouse B16 melanoma allograft and a human non-small cell lung cancer A549 xenograft

PURPOSE

Capecitabine is one of the few chemotherapy drugs with high oral availability. Recently, sodium dichloroacetate (DCA) has shown great potential as an anticancer agent. In the present study, we assessed the anticancer effect of DCA in combination with capecitabine for cancers that modestly expressed TP.

METHODS

A mouse B16 melanoma allograft and a human non-small cell lung cancer A549 xenograft were used to assess the effect of DCA and capecitabine combined treatment. Histology and immunohistochemistry were used to detect the apoptosis and proliferation of cancer cells. Real-time PCR and Western blot were carried out to detect the expression of TP and caspases, respectively.

RESULTS

For the first time, we report that DCA increased the antitumor effects of capecitabine in a mouse B16 allograft and a human A549 xenograft by promoting apoptosis of tumor cells. DCA has little effect on the expression of TP.

CONCLUSIONS

Our finding suggests that DCA in combination with capecitabine might be potential as a new therapeutic regimen against some cancers.

Increased anticoagulant activity of warfarin used in combination with doxifluridine

PURPOSE

The purpose of this article is to report the first case of markedly increased anticoagulant activity of warfarin when used in combination with doxifluridine, given as a replacement for capecitabine.

METHODS

International normalized ratio (INR) of a 73-year-old female patient receiving warfarin was increased after starting chemotherapy using oral fluoropyrimidines (capecitabine or doxifluridine). Since the concomitant use of warfarin and the oral fluoropyrimidines was unavoidable in this case, the warfarin dosage was adjusted to keep INR within goal range (1.7-2.7). To evaluate the effects of the oral fluoropyrimidines on the anticoagulant activity of warfarin, the INR/Dose (warfarin dose in mg/day) was used.

RESULTS

To keep INR within goal range, the maintenance dosage of warfarin was reduced during the treatment with doxifluridine as well as capecitabine. It was finally reduced from 5 mg daily in the absence of oral fluoropyrimidines to 1.5 mg daily during the concomitant use of doxifluridine (600 mg daily). In contrast, the higher INR/Dose (1.03-1.66) was continued during the concomitant use of warfarin and doxifluridine compared with the INR/Dose before the start of chemotherapy (about 0.5). These results clearly indicate that the anticoagulant activity of warfarin was markedly increased by the concomitant use of doxifluridine as well as capecitabine.

CONCLUSIONS

It is important that physicians closely monitor anticoagulant activity in patients concomitantly receiving doxifluridine and warfarin, and appropriately adjust the dose of warfarin.

A Phase I dose-finding study using an innovative sequential biweekly schedule of irinotecan followed 24 hours later by capecitabine

BACKGROUND

Irinotecan and capecitabine have a broad spectrum of activity in human malignancy and are synergistic in an animal model when irinotecan precedes capecitabine.

PATIENTS AND METHODS

A Phase I design of the combination of irinotecan IV Day 1 with capecitabine on Days 2-8 every 2 weeks was evaluated in 27 adult patients with solid tumors. Two sequential schema were used: Arm A fixed the dose of irinotecan at 100 mg/m(2) and escalated capecitabine in cohorts, and arm B fixed the dose of capecitabine at 750 mg/m(2) PO BID and escalated the dosage of irinotecan.

RESULTS

Neutropenia was dose limiting with nausea and diarrhea as the most common nonhematological toxicities. Significant interpatient variation in toxicity occurred despite uniform dosing. No Grade IV toxicities were encountered. Grade III toxicity occurred in first cycle in 15 percent (3/20) patients in arm A and 29 percent (2/7) of patients in arm B. All toxicities were reversible. Repetitive dosing was feasible with prolonged disease stabilization in 8 patients.

CONCLUSIONS

The suggested Phase II dose of this combination and schedule is irinotecan 100 mg/m(2) and capecitabine 1000 mg/m(2) BID. Some patients tolerated a capecitabine dose as high as 1250 mg/m(2) BID.

In Vitro Optimization of Non-Small Cell Lung Cancer Activity with Troxacitabine,l-1,3-Dioxolane-cytidine, Prodrugs

l-1,3-Dioxolane-cytidine, a potent anticancer agent against leukemia, has limited efficacy against solid tumors, perhaps due to its hydrophilicity. Herein, a library of prodrugs were synthesized to optimize in vitro antitumor activity against non-small cell lung cancer. N4-Substituted fatty acid amide prodrugs of 10-16 carbon chain length demonstrated significantly improved antitumor activity over l-1,3-dioxolane-cytidine. These in vitro results suggest that the in vivo therapeutic efficacy of l-1,3-dioxolane-cytidine against solid tumors may be improved with prodrug strategies.

Identification of potentially useful combinations of epidermal growth factor receptor tyrosine kinase antagonists with conventional cytotoxic agents using median effect analysis

Targeted therapy for breast carcinoma has achieved a major advance with the use of trastuzumab in Her2/neu-positive tumors. The epidermal growth factor receptor superfamily thus becomes an attractive target for therapeutic agents. As the epidermal growth factor receptor tyrosine kinase family has a conformational binding site, which allows small molecules to interfere with its function, we have explored the effects of a dual kinase (epidermal growth factor receptor-1 and epidermal growth factor receptor-2) inhibitor (GW282974X) with a variety of cytotoxic agents looking for synergistic effects in vitro. Using a median effect model in four breast cancer cell lines in vitro, cytotoxic agents commonly used in treatment of human malignant disease were combined with trastuzumab or one of two epidermal growth factor receptor tyrosine kinase inhibitors in a 72-h culture and then analyzed for cytotoxic effect by 3-[26]-2,5-diphenyl-tetrazolium bromide assay. Combination index values within one standard deviation of unity were considered additive, less than unity as synergistic and more than unity as antagonistic. Synergistic results were confirmed by curve shift analysis and by an enzyme-linked immunosorbent assay measuring apoptosis by cytoplasmic histone-associated DNA fragments. Quantitative real-time polymerase chain reaction analysis was used to measure the expression of three of the critical enzymes in 5'-deoxy-5-fluorouridine metabolism and activity: thymidine phosphorylase, dihydropyrimidine dehydrogenase and thymidine synthase. 5'-Deoxy-5-fluorouridine with GW282974X demonstrated global synergy, both in high and low expressing epidermal growth factor receptor breast cancer cell lines. These results were confirmed by apoptosis assay and cell counts. RNA quantification following treatment with the dual kinase inhibitor suggested reduction in thymidine synthase levels to be a potential mechanism of synergy. The triplet of trastuzumab, GW282974X and 5'-deoxy-5-fluorouridine, and the triplet of GW282974X, epirubicin and 5'-deoxy-5-fluorouridine were highly synergistic in low expression cells (MCF7/wt) and high expression cells (MCF7/adr). These experiments suggest further studies of the dual kinase inhibitor with selected cytotoxics such as 5'-deoxy-5-fluorouridine are warranted.

Antitumor activity of novel N-sulfonylpyrimidine derivatives on the growth of anaplastic mammary carcinoma in vivo

PURPOSE

The purpose of this study was to investigate in vivo antitumor activity of newly synthesized N-sulfonylpyrimidine derivatives 1-(p-toluenesulfonyl)cytosine (4H), 1-(p-toluenesulfonyl)cytosine hydrochloride (4HxHCl) and zinc(II) complex of 1-(p-toluenesulfonyl)cytosine (4K).

MATERIALS AND METHODS

In order to do that we have used mouse anaplastic mammary carcinoma (AMCa). Tumor cells (10(6)) in a volume of 0.02 ml were transplanted into the thigh of the right hind leg of CBA mice. All compounds were dissolved in distilled water immediately before injecting to animals.

RESULTS

Antitumor effect of these compounds depends on drug doses and time interval between tumor transplantation and drug application. Further the efficacy of these compounds depends on number of drug injections, i. e. whether drug was given in single or in multiple doses. Multiple doses of 400 mg/kg of 1-(p-toluenesulfonyl)cytosine (4H) showed good antitumor effect when applied on day 1, 3, 5, 7 and 9 after tumor transplantation. Still good but slightly lower antitumor effect was also achieved when that compound was given in a single dose (1,200 mg/kg) on day 1 after tumor transplantation. The longest period of tumor growth time was obtained after application of 1-(p-toluenesulfonyl)cytosine hydrochloride (4HxHCl) given as a single dose (300 mg/kg) on day 1 or on day 6 after tumor implantation. However, antitumor effect of zinc(II) complex of 1-(p-toluenesulfonyl)cytosine (4K) was very strong when 300 mg/kg was given on day 1 or day 6, while this effect was slightly lower when drug (200 mg/kg/inj) was given on day 1, 3, 5, 7 and 9 or on day 6, 8, 10, 12 and 14.

CONCLUSION

In this work it has been found that N-1-sulfonylcytosine derivatives have strong antitumor activity against mouse mammary carcinoma which is a good reason for further research of these compounds both in experimental and preclinical studies.

Enzyme-catalyzed activation of anticancer prodrugs

The rationale fo the development of prodrugs relies upon delivery of higher concentrations of a drug to target cells compared to administration of the drug itself. In the last decades, numerous prodrugs that are enzymatically activated into anti-cancer agents have been developed. This review describes the most important enzymes involved in prodrug activation notably with respect to tissue distribution, up-regulation in tumor cells and turnover rates. The following endogenous enzymes are discussed: aldehyde oxidase, amino acid oxidase, cytochrome P450 reductase, DT-diaphorase, cytochrome P450, tyrosinase, thymidylate synthase, thymidine phosphorylase, glutathione S-transferase, deoxycytidine kinase, carboxylesterase, alkaline phosphatase, beta-glucuronidase and cysteine conjugate beta-lyase. In relation to each of these enzymes, several prodrugs are discussed regarding organ- or tumor-selective activation of clinically relevant prodrugs of 5-fluorouracil, axazaphosphorines (cyclophosphamide, ifosfamide, and trofosfamide), paclitaxel, etoposide, anthracyclines (doxorubicin, daunorubicin, epirubicin), mercaptopurine, thioguanine, cisplatin, melphalan, and other important prodrugs such as menadione, mitomycin C, tirapazamine, 5-(aziridin-1-yl)-2,4-dinitrobenzamide, ganciclovir, irinotecan, dacarbazine, and amifostine. In addition to endogenous enzymes, a number of nonendogenous enzymes, used in antibody-, gene-, and virus-directed enzyme prodrug therapies, are described. It is concluded that the development of prodrugs has been relatively successful; however, all prodrugs lack a complete selectivity. Therefore, more work is needed to explore the differences between tumor and nontumor cells and to develop optimal substrates in terms of substrate affinity and enzyme turnover rates fo prodrug-activating enzymes resulting in more rapid and selective cleavage of the prodrug inside the tumor cells.

Interactions of Nucleoside Analogs, Caffeine, and Nicotine with Human Concentrative Nucleoside Transporters 1 and 2 Stably Produced in a Transport-Defective Human Cell Line

Pharmacologically important drugs were examined as potential inhibitors or permeants of human concentrative nucleoside transporters 1 (hCNT1)- and 2 (hCNT2)-producing stable transfectants by assessing their abilities to inhibit uridine transport. hCNT1 exhibited high affinities for uridine analogs (5-fluorouridine, 2'-deoxyuridine, 5-fluoro-2'-deoxyuridine, and 5-fluoro-5'-deoxyuridine) with K(i) values of 22 to 33 microM, whereas hCNT2 exhibited moderate affinities for 5-fluoro-2'-deoxyuridine, high affinities for 2'-deoxyuridine and 5-fluorouridine, and low affinity for 5-fluoro-5'-deoxyuridine. The uridine analogs were transported at 2-fold higher rates (at 10 microM) by hCNT1 than by hCNT2. Enantiomeric configuration and the 3'-hydroxyl group of the ribose ring were important determinants for interaction with hCNTs, whereas the 2'-hydroxyl group was less important. Both transporters bound N(6)-(p-aminobenzyl)adenosine with affinities similar to those of adenosine (K(i) = 28-39 microM). Other adenosine receptor ligands, including caffeine, bound better to hCNT1 than to hCNT2 (K(i) = 46 versus 103 microM, respectively), whereas 2-chloroadenosine bound better to hCNT2 than to hCNT1 (K(i) = 37 and 101 microM, respectively). There was a greater than 3-fold difference in binding affinities between hCNT1 and hCNT2 for nicotine (K(i) = 63 versus 227 microM). However, direct measurements of nicotine and caffeine uptake rates (10 microM) failed to demonstrate mediated uptake by either transporter. Although hCNT1 bound several adenosine analogs relatively well, it did not transport 2-chloro-2'-deoxyadenosine (cladribine) or 2-fluoro-9-beta-d-arabinofuranosyladenine (fludarabine), whereas hCNT2 transported both, albeit with low activities. The results indicated that although hCNT1 and hCNT2 possess some overlap in transport of several uridine and adenosine analogs, they also exhibit distinct differences in capacity to interact with some adenosine receptor ligands, adenosine-based drugs, and nicotine.

Neurologic complications of cancer therapy

Neurologic complications of chemotherapy are relatively common. The diagnosis of chemotherapy-associated neurotoxicity remains a clinical one, and is largely based on the exclusion of other possible causes. The goal of this review is to describe the neurotoxicity associated with established chemothrerapeutic agents and with some of the newer biologic agents, monoclonal antibodies and targeted molecular therapies used in the treatment of cancer.

Prognostic value of tumoral thymidylate synthase and p53 in metastatic colorectal cancer patients receiving fluorouracil-based chemotherapy: phenotypic and genotypic analyses

PURPOSE

The aim of this multicenter prospective study was to evaluate the role of intratumoral parameters related to fluorouracil (FU) sensitivity in 103 metastatic colorectal cancer patients receiving FU-folinic acid.

PATIENTS AND METHODS

Liver metastatic biopsy specimens were obtained for all patients and primary tumor biopsy specimens for 54 patients. Thymidylate synthase (TS), folylpolyglutamate synthetase, and dihydropyrimidine dehydrogenase were measured by radioenzymatic assays; TS promoter polymorphism (2R/2R v 2R/3R v 3R/3R) was determined by polymerase chain reaction; and p53 protein and mutations were analyzed by immunoluminometric assay and denaturing gradient gel electrophoresis, respectively.

RESULTS

p53 mutations were observed in 56.7% of metastases. TS activity was significantly higher in 2R/3R tumors as compared with 2R/2R or 3R/3R. TS activity in metastasis was the only parameter linked to clinical responsiveness (responders exhibited the lower TS, P =.047). Univariate Cox analyses demonstrated that TS activity in primary tumor (the greater the TS, the poorer the survival; P =.040), TS promoter polymorphism in primary tumor (risk of death of 2R/3R v 2R/2R, 2.68; P =.035), and p53 stop mutation in metastasis (risk of death of stop mutations v wild type, 3.14; P =.018) were the only significant biologic predictors of specific survival. Stepwise analysis did not discriminate between TS activity and TS polymorphism.

CONCLUSION

Present results confirm the value of tumoral TS activity for predicting FU responsiveness, point out the importance of detailed p53 mutation analysis for predicting survival, and suggest that TS genotype in primary tumor carries a prognostic value similar to that of TS activity.