Pharmacokinetics and pharmacodynamics of long-term continuous-infusion doxorubicin

A physiologically-based pharmacokinetic model for predicting doxorubicin disposition in multiple tissue levels and quantitative toxicity assessment

Doxorubicin is a widely-used chemotherapeutic drug, however its high toxicity poses a significant challenge for its clinical use. To address this issue, a physiologically-based pharmacokinetic (PBPK) model was implemented to quantitatively assess doxorubicin toxicity at cellular scale. Due to its unique pharmacokinetic behavior (e.g. high volume of distribution and affinity to extra-plasma tissue compartments), we proposed a modified PBPK model structure and developed the model with multispecies extrapolation to compensate for the limitation of obtaining clinical tissue data. Our model predicted the disposition of doxorubicin in multiple tissues including clinical tissue data with an overall absolute average fold error (AAFE) of 2.12. The model's performance was further validated with 8 clinical datasets in combined with intracellular doxorubicin concentration with an average AAFE of 1.98. To assess the potential cellular toxicity, toxicity levels and area under curve (AUC) were defined for different dosing regimens in toxic and non-toxic scenarios. The cellular concentrations of doxorubicin in multiple organ sites associated with commonly observed adverse effects (AEs) were simulated and calculated the AUC for quantitative assessments. Our findings supported the clinical dosing regimen of 75 mg/m2 with a 21-day interval and suggest that slow infusion and separated single high doses may lower the risk of developing AEs from a cellular level, providing valuable insights for the risk assessment of doxorubicin chemotherapy. In conclusion, our work highlights the potential of PBPK modelling to provide quantitative assessments of cellular toxicity and supports the use of clinical dosing regimens to mitigate the risk of adverse effects.

Individualized chemotherapy drug dose escalation in dogs with multicentric lymphoma

BACKGROUND

This study was performed to determine the ability to escalate drug doses in a 15-week CHOP protocol in dogs with multicentric lymphoma.

HYPOTHESIS

We hypothesized that at least 50% of dogs could successfully be escalated in at least 1 drug. Secondary aims were to establish objective response rate (ORR), progression-free interval (PFI), and overall survival time (OST).

ANIMALS

Thirty dogs with newly diagnosed multicentric lymphoma were prospectively treated with a 15-week CHOP protocol.

METHODS

This was a prospective cohort study. Drug doses that did not cause dose-limiting adverse effects (AEs) were increased using a standardized escalation protocol. AEs and response were assessed using VCOG criteria. Serial blood samples were collected after the first dose of each drug for pharmacokinetic analysis.

RESULTS

Of the 23 dogs with the opportunity to dose escalate, at least 1 drug was successfully escalated in 18 (78%). Vincristine was successfully escalated to 0.8 mg/m2 or higher in 11 dogs, cyclophosphamide to 300 mg/m2 or higher in 16 dogs, and doxorubicin to 35 mg/m2 or 1.4 mg/kg or higher in 9 dogs. Three of the 23 dogs (13%) were hospitalized at least once because of drug-induced AEs. Neutropenia was the most common dose-limiting toxicosis for all drugs. Peak doxorubicin concentrations were significantly lower in dogs where doxorubicin was successfully escalated. The objective response rate was 100%. The median progression free interval was 171 days. The median overall survival time was 254 days.

CONCLUSIONS

Drugs in the CHOP protocol can often be escalated safely with manageable AEs.

Interim results of the PML-16, PML-19 protocols for primary mediastinal large B-cell lymphoma therapy

Introduction. Primary mediastinal lymphoma (PML) is an aggressive lymphoid tumor treatment success of which is determined by induction therapy. To date, none of the standard chemotherapy regimens (CT) have demonstrated an advantage in efficacy. Intensive therapy programs are associated with high toxicity.

Aim — to evaluate the efficacy and toxicity of two pilot prospective treatment protocols PML-16 and PML-19 as well as the possibility of using the analysis of freely circulating tumor DNA (ctDNA) to assess MRD in patients with PML.

Materials and methods. From January 2016 to January 2022, 34 previously untreated PML patients were included in the study; average age — 32; stage > I — in 60 %; extramediastinal lesions — in 14.7 %; bulky disease — in 73.5 % of patients. Positron emission tomography combined with computed tomography (PET-CT) was performed; ctDNA was determined to assess the completeness of remission.

Results. Eighteen patients received treatment according to the PML-16 protocol (6 courses of chemotherapy; 2 blocks of RmNHL-BFM-90 + 4 courses of R-EPOCH). After the end of therapy, all 18 patients achieved PET-negative remission. The next 16 patients received treatment according to the PML-19 protocol (4 courses of chemotherapy; 2 blocks of R-mNHL-BFM-90 + 2 courses of R-EPOCH) in combination with lenalidomide. After the end of therapy, 9 (56 %) patients achieved PET-negative remission; 7 (44 %) retained pathological activity (D4–5 points). After 3 and 6 months 15 (94 %) patients achieved normalization of metabolic activity. Considering the high frequency of false-positive results in patients with PML, a ctDNA study was performed to determine the depth of remission in 15 patients. After the end of therapy, all 15 patients had complete elimination of ctDNA. Of these, 5 (33 %) remained PET-positive at the end of treatment. During further observation, after 3–6 months, in 4 patients the level of metabolic activity decreased to physiological without the use of consolidating therapy. After the end of therapy, one patient suffered the new coronavirus infection, COVID-19. A month later, residual formation of SUVmax 14.2 remained in the mediastinum. The patient is currently under observation. With a median follow-up of 36 months (9 to 76 months) all 34 patients are in remission.

Conclusion. The effectiveness of PML-16 made it possible to abandon the consolidation therapy and refuted the idea of the need for 6 courses of CT. The combination of programs based on the application of the principle of high-dose shortpulse induction of remission (R-mNHL-BFM-90) in combination with the prolonged administration of medium doses (R-EPOCH) was crucial in achieving a successful result. The inclusion of lenalidomide in the “PML-19” program made it possible to achieve complete remission in 100 % of cases after 4 courses. The possibility of using DNA analysis to assess MRD in patients with PML was shown.

Cytotoxic mechanisms of doxorubicin at clinically relevant concentrations in breast cancer cells

Doxorubicin (DOX) is a chemotherapeutic agent frequently used for the treatment of a variety of tumor types, such as breast cancer. Despite the long history of DOX, the mechanistic details of its cytotoxic action remain controversial. Rather than one key mechanism of cytotoxic action, DOX is characterized by multiple mechanisms, such as (1) DNA intercalation and adduct formation, (2) topoisomerase II (TopII) poisoning, (3) the generation of free radicals and oxidative stress, and (4) membrane damage through altered sphingolipid metabolism. Many past reviews of DOX cytotoxicity are based on supraclinical concentrations, and several have addressed the concentration dependence of these mechanisms. In addition, most reviews lack a focus on the time dependence of these processes. We aim to update the concentration and time-dependent trends of DOX mechanisms at representative clinical concentrations. Furthermore, attention is placed on DOX behavior in breast cancer cells due to the frequent use of DOX to treat this disease. This review provides insight into the mechanistic pathway(s) of DOX at levels found within patients and establishes the magnitude of effect for each mechanism.

Biodynamic signatures from ex vivo bone marrow aspirates are associated with chemotherapy-induced neutropenia in cancer-bearing dogs

Background

Neutropenia is the most common dose‐limiting side effect of cytotoxic chemotherapy in cancer‐bearing dogs. Biodynamic imaging (BDI) is a functional imaging technology that measures dynamic light scattering from living, three‐dimensional tissues to characterize intracellular motion within those tissues. Previous studies have associated BDI biomarkers with tumour sensitivity to chemotherapy agents in dogs with naturally occurring cancer. We hypothesized that BDI, performed ex vivo on bone marrow aspirate samples, would identify dynamic biomarkers associated with the occurrence of specific degrees of neutropenia in tumour‐bearing dogs receiving doxorubicin chemotherapy.

Materials and Methods

Bone marrow aspirates were collected from 10 dogs with naturally occurring cancers prior to initiation of doxorubicin treatment. BDI was performed on bone marrow samples treated ex vivo with doxorubicin at 0.1, 1, 10 and 100 μM along with 0.1% DMSO as a control. Dogs then were treated with doxorubicin (30 mg/m², intravenously). Peripheral blood neutrophil counts were obtained on the day of treatment and again 7 days later. Receiver operating characteristic curves identified provisional breakpoints for BDI biomarkers that correlated with specific changes in neutrophil counts between the two time points.

Results

Provisional breakpoints for several BDI biomarkers were identified, specifying dogs with the largest proportionate change in neutrophils and with neutropenia that was grade 2 or higher following doxorubicin treatment.

Conclusions

Biodynamic imaging of bone marrow aspirates may identify those dogs at greater risk for neutropenia following doxorubicin chemotherapy. This approach may be useful for pre‐emptively modifying chemotherapy dosing in dogs to avoid unacceptable side effects.

Is there scope for better individualisation of anthracycline cancer chemotherapy?

Anthracyclines are used to treat solid and haematological cancers, particularly breast cancers, lymphomas and childhood cancers. Myelosuppression and cardiotoxicity are the primary toxicities that limit treatment duration and/or intensity. Cardiotoxicity, particularly heart failure, is a leading cause of morbidity and mortality in cancer survivors. Cumulative anthracycline dose is a significant predictor of cardiotoxicity risk, suggesting a role for anthracycline pharmacokinetic variability. Population pharmacokinetic modelling in children has shown that doxorubicin clearance in the very young is significantly lower than in older children, potentially contributing to their higher risk of cardiotoxicity. A model of doxorubicin clearance based on body surface area and age offers a patient-centred dose-adjustment strategy that may replace the current disparate initial-dose selection tools, providing a rational way to compensate for pharmacokinetic variability in children aged <7 years. Population pharmacokinetic models in adults have not adequately addressed older ages, obesity, hepatic and renal dysfunction, and potential drug-drug interactions to enable clinical application. Although candidate gene and genome-wide association studies have investigated relationships between genetic variability and anthracycline pharmacokinetics or clinical outcomes, there have been few clinically significant reproducible associations. Precision-dosing of anthracyclines is currently hindered by lack of clinically useful pharmacokinetic targets and models that predict cumulative anthracycline exposures. Combined with known risk factors for cardiotoxicity, the use of advanced echocardiography and biomarkers, future validated pharmacokinetic targets and predictive models could facilitate anthracycline precision dosing that truly maximises efficacy and provides individualised early intervention with cardioprotective therapies in patients at risk of cardiotoxicity.

Interspecies prediction of pharmacokinetics and tissue distribution of doxorubicin by physiologically-based pharmacokinetic modeling

The aim of the study was to develop a physiologically-based pharmacokinetic (PBPK) model to describe and predict whole-body disposition of doxorubicin following intravenous administration. The PBPK model was established using previously published data in mice and included 10 tissue compartments: lungs, heart, brain, muscle, kidneys, pancreas, intestine, liver, spleen, adipose tissue, and plasma. Individual tissues were described by either perfusion-limited or permeability-limited models. All parameters were simultaneously estimated and the final model was able to describe murine data with good precision. The model was used for predicting doxorubicin disposition in rats, rabbits, dogs, and humans using interspecies scaling approaches and was qualified using plasma and tissue observed data. Reasonable prediction of the plasma pharmacokinetics and tissue distribution was achieved across all species. In conclusion, the PBPK model developed based on a rich dataset obtained from mice, was able to reasonably predict the disposition of doxorubicin in other preclinical species and humans. Applicability of the model for special populations, such as patients with hepatic impairment, was also demonstrated. The proposed model will be a valuable tool for optimization of exposure profiles of doxorubicin in human patients.

Doxorubicin area under the curve is an important predictor of neutropenia in dogs with naturally occurring cancers

Doxorubicin (DOX) area-under-the-curve (AUC) was calculated for 40 dogs with spontaneously occurring cancers using a previously validated limited-sampling approach. All dogs were administered a dose of 30 mg/m² by intravenous infusion and serum samples were collected at 5, 45 and 60 minutes post-infusion. DOX and its major metabolite, doxorubicinol (doxol), were quantified in serum samples using high-performance liquid chromatography tandem-mass spectrometry. Wide interpatient variability was observed in the predicted DOX AUC with a coefficient of variation of 34%. A significant relationship was found between DOX AUC and absolute white blood cell count (P = 0.003), absolute neutrophil count (ANC; P = 0.002) and surviving fraction of neutrophils (P = 0.03) approximately 1 week after dosing (nadir). No changes in other hematologic parameters (red blood cells, platelets, lymphocytes, haemoglobin) were found to correlate with DOX AUC. The absolute dose (mg) and the dose per unit body weight (mg/kg) were not significantly correlated with nadir ANC. No relationships were found between maximum serum doxol concentration and myelosuppression. Baseline ANC was also significantly correlated to nadir ANC and a model was constructed using baseline ANC and DOX AUC that significantly described the nadir ANC. These findings demonstrate the important relationship between systemic DOX exposure and degree of neutropenia in dogs, and suggest a potential for individualized, pharmacokinetically-guided DOX dosing in dogs.

Population pharmacokinetics of doxorubicin and doxorubicinol in patients diagnosed with non-Hodgkin's lymphoma

AIMS

The aims of the study were: (i) to characterize the pharmacokinetics (PK) of doxorubicin (DOX) and doxorubicinol (DOXol) in patients diagnosed with non-Hodgkin's lymphoma (NHL) using a population approach; (ii) to evaluate the influence of various covariates on the PK of DOX; and (iii) to evaluate the role of DOX and DOXol exposure in haematological toxicity.

METHODS

Population PK modelling (using NONMEM) was performed using DOX and DOXol plasma concentration-time data from 45 NHL patients treated with R-CHOP (rituximab, cyclophosphamide, doxorubicin, vincristine and prednisone). The influence of drug exposure on haematological toxicity was analysed using the Mann-Whitney-Wilcoxon test.

RESULTS

A five-compartment model, three for DOX and two for DOXol, with first-order distribution and elimination for both entities best described the data. Population estimates for parent drug (CL) and metabolite (CL_m ) clearance were 62 l h^-1 and 27 l h^-1 , respectively. The fraction metabolized to DOXol (F_m ) was estimated at 0.22. While bilirubin and aspartate aminotransferase showed an influence on the CL and CL_m , the objective function value decrease was not statistically significant. A trend towards an association between the total area under the concentration-time curve (AUC_total ), the area under the concentration-time curve for DOX (AUC) plus the area under the concentration-time curve for DOXol (AUC_m ), and the neutropenia grade (P = 0.068) and the neutrophil counts (P = 0.089) was observed, according to an exponential relationship.

CONCLUSIONS

The PK of DOX and DOXol were well characterized by the model developed, which could be used as a helpful tool to optimize the dosage of this drug. The results suggest that the main active metabolite of DOX, DOXol, is involved in the haematological toxicity of the parent drug.

Correlation of aldo-ketoreductase (AKR) 1C3 genetic variant with doxorubicin pharmacodynamics in Asian breast cancer patients

AIMS

Aldo-ketoreductases have been implicated in the metabolism of doxorubicin. We sought to assess the influence of AKR1C3 genetic variants on doxorubicin metabolism.

METHODS

We sequenced AKR1C3 exon 5 and genotyped seven functional single nucleotide polymorphisms in CBR3, ABCB1 and SLC22A16 involved in doxorubicin pharmacology in 151 Asian breast cancer patients treated with doxorubicin-containing chemotherapy, and correlated these genotypes with doxorubicin pharmacokinetics and pharmacodynamics.

RESULTS

Two previously reported AKR1C3 intronic variants, IVS4-212 C>G and IVS4+218 G>A, were detected. The AKR1C3 IVS4-212 GG genotype was associated with significantly lower cycle 1 day 15 leucocyte (mean leucocytes 2.49 ± 1.57 × 10(9) vs. 3.85 ± 3.42 × 10(9) l(-1) , P = 0.007) and neutrophil counts (mean neutrophils 0.70 ± 1.01 × 10(9) vs. 1.56 ± 2.80 × 10(9) l(-1) , P = 0.008) and significant improvement of progression-free survival [PFS, mean PFS 49.0 (95% confidence interval 42.2-55.8) vs. 31.0 (95% confidence interval 20.7-41.2) months, P = 0.017] and overall survival [OS; mean OS 64.4 (95% confidence interval 58.3-70.5) vs. 46.3 (95% confidence interval 35.1-57.5) months, P = 0.006] compared with those carrying at least one C allele. There was no significant association between AKR1C3 IVS4-212 C>G and doxorubicin pharmacokinetics. Of the other seven single nucleotide polymorphisms genotyped, CBR3 G11A correlated with doxorubicinol area under the concentration-time curve and OS, ABCB1 G2677T/A correlated with doxorubicin clearance and platelet toxicity, while ABCB1 IVS26+59 T>G correlated with OS. The AKR1C3 IVS4-212 C<G genotype remained significantly correlated with both PFS and OS on multivariate analysis with clinical prognosticators.

CONCLUSIONS

The AKR1C3 IVS4-212 GG genotype was associated with greater haematological toxicity and longer progression-free survival and overall survival after doxorubicin-based therapy, suggesting potential interaction of this variant with doxorubicin metabolism.

The expression and actions of androgen receptor in upper urinary tract urothelial carcinoma (UUTUC) tissues and the primary cultured cells

Sex hormone receptors, androgen receptor (AR) and estrogen receptors (ERs) including both ERα and ERβ, mediate the actions of sex hormones. In this study, we aimed to evaluate sex hormone receptors expression in upper urinary tract urothelial carcinomas (UUTUCs) of ureter and renal pelvis with different tumor stages and grades as well as their possible roles in tumor progression. Immunohistochemistry was used to assay the expression of AR and ERs in the primary UUTUCs. XTT viability test was applied to evaluate cell responses for anticancer drug treatment. Wound healing assay was performed to determine cell migration abilities. AR and ERβ immunoreactivities were observed in both UUTUCs, but ERα was not detected in either UUTUCs. In UUTUC of ureter specimens, higher AR expression was found in superficial or lower grade tumors. In contrast, little difference of ERβ expression was found in superficial versus muscle-invasive tumor stages or low grades versus high grades in UUTUCs of ureter specimens. Furthermore in the primary cultured cells from UUTUC specimens, the addition of functional AR reduced cell chemosensitivity, but increased cell migration. These results provide the first data showing the expression patterns of sex hormone receptors in both renal pelvis and ureter UUTUCs. From results, we concluded that there is a positive correlation for higher AR expression found in superficial or low-grade UUTUCs of ureter and identified the functional roles of AR in UUTUC progression.

Modifications to induction therapy decrease risk of early death in infants with acute lymphoblastic leukemia treated on Children's Oncology Group P9407

BACKGROUND

Infants (<366 days of age) with acute lymphoblastic leukemia (ALL) have a poor prognosis. Most treatment failures occur within 6-9 months of diagnosis, primarily from relapse.

PROCEDURE

The Children's Oncology Group P9407 study was designed to test if early intensified treatment would improve outcome for infants with ALL. Due to a significant number of early deaths (< 90 days from enrollment), Induction therapy was amended three times. Cohorts 1 + 2 (n = 68), received identical Induction therapy except for reduced daunorubicin dose in Cohort 2. Cohort 3 (n = 141) received prednisone (40 mg/m(2)/day) instead of dexamethasone (10 mg/m(2)/day) and short infusion daunorubicin (30 minutes) instead of continuous infusion (48 hours), as well as additional supportive care measures throughout therapy.

RESULTS

Early deaths occurred in 17/68 (25%) infants in Cohorts 1 + 2 and 8/141 (5.7%) infants in Cohort 3 (P < 0.0001). Among infants ≤90 days of age at diagnosis, early death occurred in 10/17 (58.8%) in Cohorts 1 + 2 and 4/27 (14.8%) in Cohort 3 (P = 0.006). Among infants >90 days of age at diagnosis, early death occurred in 7/51 (13.7%) in Cohorts 1 + 2 and 4/114 (3.5%) in Cohort 3 (P = 0.036). Bacterial, viral, and fungal infections were more common in Cohorts 1 + 2 versus Cohort 3.

CONCLUSIONS

Early morbidity and mortality for infants with ALL were reduced by substitution of prednisone (40 mg/m(2)/day) for dexamethasone (10 mg/m(2)/day), the delivery of daunorubicin over 30 minutes instead of a continuous infusion for 48 hours, and the provision of more specific supportive care measures.

Development of a limited-sampling model for prediction of doxorubicin exposure in dogs

Understanding the relationship between drug dose and exposure (pharmacokinetics, PK) and the relationship between exposure and effect (pharmacodynamics) is an important component of pharmacology when attempting to predict clinical effects of anticancer drugs. PK studies can provide a better understanding of these relationships; however, they often involve intensive sampling over an extended period of time, resulting in increased cost and decreased compliance. Doxorubicin (DOX), one of the most widely used antineoplastic agents in veterinary cancer therapy, is characterized by large interpatient variability in overall drug exposure and the development and degree of myelosuppression following equivalent dosages. We have developed and validated a limited-sampling strategy for DOX, in which three blood samples are obtained over 1 h post-treatment, that accurately predicts patient exposure. This strategy could allow for refining of dosing variables and utilization of therapeutic drug monitoring to ensure optimized dosing.

Inverse relationship between leukaemic cell burden and plasma concentrations of daunorubicin in patients with acute myeloid leukaemia

AIMS

It has been shown that the cellular uptake and cytotoxicity of anthracyclines decrease with increasing cell density in vitro, an event termed 'the inocculum effect'. It is not known whether such an effect occurs in vivo. In this study the relationships between white blood cell (WBC) count, plasma and cellular concentrations of daunorubicin (DNR) in patients with acute myeloid leukaemia were investigated.

METHODS

Plasma and mononuclear blood cells were isolated from peripheral blood from 40 patients with acute myeloid leukaemia at end of infusion (time 1 h), 5 and 24 h following the first DNR infusion. DNR concentrations were determined by high-pressure liquid chromatography and related to the WBC count at diagnosis. A population pharmacokinetic model was used to estimate the correlations between baseline WBC count, volume of distribution and clearance of DNR.

RESULTS

A clear but weak inverse relationship between the baseline WBC count and plasma concentrations of DNR (r(2)=0.11, P<0.05) at time 1 was found. Furthermore, a clear relationship between baseline WBC count and DNR central volume of distribution using population pharmacokinetic modelling (dOFV 4.77, P<0.05) was also noted. Analysis of plasma DNR and the metabolite daunorubicinol (DOL) concentrations in patients with a high WBC count support that the low DNR/DOL concentrations are due a distribution effect.

CONCLUSION

This study shows that the leukaemic cell burden influences the plasma concentrations of anthracyclines. Further studies are needed to explore if patients with high a WBC count may require higher doses of anthracyclines.

Drug exposure: still an excellent biomarker

Relationships between plasma drug concentrations and clinical outcome have been defined for various chemotherapeutic agents, showing that drug exposure may be a marker of toxicity, mainly hematological and gastrointestinal toxicity, as well as efficacy, expressed as tumor response and survival. Biomarkers provide information for guidance in dosing and the minimization of interindividual variation in response. Drug exposure is commonly measured with parameters such as area under the plasma concentration-time curve, steady-state plasma or serum concentrations, peak concentrations and duration above a threshold concentration. In this review, we focus on drugs where pharmacokinetic/pharmacodynamic relationships as well as systemic exposure have been associated to toxicity and/or efficacy in solid and hematological tumors, these include: carboplatin, methotrexate, busulphan, 5-fluorouracil, etoposide, anthracyclines, irinotecan, vinorelbine and docetaxel.

Genotype of human carbonyl reductase CBR3 correlates with doxorubicin disposition and toxicity

OBJECTIVES

Doxorubicin is a cytotoxic drug with potential for severe myelosuppression that is highly variable and poorly predictable.

METHODS

We correlated CBR1 and CBR3 genotypes with the pharmacokinetics and pharmacodynamics of doxorubicin in 101 Southeast Asian breast cancer patients receiving first-line doxorubicin.

RESULTS

A common CBR3 11G>A variant was associated with lower doxorubicinol area under the concentration-time curve (AUC)/doxorubicin AUC metabolite ratio (P=0.009, GG vs. AA; trend test, P=0.004), lower CBR3 expression in breast tumor tissue (P=0.001, GG vs. AA), greater tumor reduction (P=0.015, GG vs. AA), and greater percentage reduction of leukocyte and platelet counts at nadir (trend test, P < or = 0.03). Chinese and Malays had higher frequency of the CBR3 11G>A variant than Indians (P < or = 0.002). Another variant CBR3 730G>A was associated with higher doxorubicinol AUC (P=0.009, GG vs. AA) and CBR3 expression in breast tumor tissue (P=0.001, GG vs AA).

CONCLUSION

Polymorphisms in CBR3 may explain interindividual and interethnic variability of doxorubicin pharmacokinetics and pharmacodynamics.

On the synergistic effect of doxorubicin and mitomycin C against breast cancer cells

The combination of doxorubicin and mitomycin C has been shown previously to result in supra-additive tumor cell killing in vitro in both murine and human breast cancer cells and in vivo against murine breast cancer cells. Median effect analysis was used to determine the significance and degree of interaction. The origin of this synergy was sought by evaluating the contribution of membrane efflux pump modulation, formaldehyde production, reactive oxygen species, DNA cross-linking, and DNA double-strand breaks to this effect. The interaction of mitomycin C and doxorubicin in vitro was found to be a true synergy whose mechanism was efflux pump-independent. DNA cross-links were only found to increase additively with co-administration of the drugs; however, a supra-additive increase in DNA double-strand breaks was observed. The results suggest that poisoning of topoisomerase IIalpha by doxorubicin may interact with drug-induced DNA cross-links to enhance the formation of DNA double-strand breaks. This interaction, together with glutathione depletion and mitomycin C-derived formaldehyde, may be the underlying mechanism(s) of the synergy observed between mitomycin C and doxorubicin.

Phase I study of inhaled Doxorubicin for patients with metastatic tumors to the lungs

PURPOSE

To evaluate the toxicity profile of inhalational doxorubicin in patients with malignant disease in the lung.

EXPERIMENTAL DESIGN

The OncoMyst Model CDD-2a inhalation device aerosolizes compounds to particles of 2 to 3 mum and prevents exhaled aerosol from escaping into the environment. Deposition efficiency of inhaled Technetium 99m was used to predict deposition of doxorubicin and calculate dose. Treatment was repeated every 3 weeks. No more than moderate pulmonary dysfunction was permitted (forced expiratory volume in 1 s, forced vital capacity, and diffusing capacity for carbon monoxide, all >50% predicted; resting SaO(2) >90%).

RESULTS

Fifty-three patients were enrolled at 13 dose levels ranging from 0.4 to 9.4 mg/m(2). The most common histologic diagnoses were sarcoma (n = 19) and non-small cell lung cancer (n = 16). Dose-limiting toxicity (DLT) was observed at the 9.4 mg/m(2) dose level when two of four patients experienced pulmonary DLT. Of 11 patients treated at the 7.5 mg/m(2) dose level, only one showed DLT consisting of a decline in forced vital capacity of >20% from baseline. No significant systemic drug-related toxicity was observed. Several patients experienced declines in pulmonary function test variables, which were attributed to progressive disease. Observed activity included a partial response in a patient with metastatic soft tissue sarcoma previously treated with i.v. doxorubicin and ifosfamide.

CONCLUSIONS

Inhaled doxorubicin is safe up to a dose of 7.5 mg/m(2) every 3 weeks in patients with cancer who had normal to moderately impaired pulmonary function.

Dose-adjusted EPOCH plus rituximab is an effective regimen in patients with poor-prognostic untreated diffuse large B-cell lymphoma: results from a prospective observational study

This study was designed to assess the efficacy and safety of an infusional DA-EPOCH (dose-adjusted etoposide/vincristine/doxorubicin/bolus cyclophosphamide/prednisone) and rituximab (DA-EPOCH-R) regimen for patients with poor prognosis diffuse large B-cell lymphoma (DLBCL). Thirty-three patients, aged 21-76 years, with an age-adjusted International Prognostic Index (IPI) of 2 or 3, were enrolled, and 31/33 patients were evaluable for response. Consolidative radiation therapy was given to eight patients with bulky (> or =10 cm) disease at presentation. Overall, 26 patients (83.8%) achieved a complete remission (CR), four patients (12.9%) achieved a partial remission, and one patient (3.2%) died during induction. Two patients relapsed (7.6%) within 15 months. Grade 3-4 neutropenia developed in 52% of cycles and neutropenic fever in 14% of cycles (51% of patients). The estimates for event-free survival (EFS) and overall survival at 2 years were 68% and 75% respectively. The only factor related to poor EFS was the presence of three age-adjusted IPI-risk factors. We conclude that DA-EPOCH-R has clinically significant activity with a favourable toxicity profile for poor-prognostic DLBCL patients. The administration of DA-EPOCH-R as an outpatient regimen by using a single portable infusion pump may be a feasible alternative to improve the compliance and to reduce the total cost of this very effective regimen.

Doxorubicin pharmacokinetics is correlated to the effect of induction therapy in children with acute myeloid leukemia

We studied the pharmacokinetics of doxorubicin in 41 children treated for newly diagnosed acute myeloid leukemia. Doxorubicin, 75 mg/m2 body surface area, was administered by constant i.v. infusion over 8 h. Four children with Down's syndrome (DS), 1.2-2.3 years old, had a median total body clearance of 523 ml/min/m2. The median clearance in non-DS children, 0.6-1.8 years old (n = 4) and 2.5-17.7 years old (n = 33), was 446 and 538 ml/min/m2, respectively. Patients who went into complete remission (CR) after induction therapy had a significantly higher median plasma concentration of doxorubicin than those who did not, 249 compared with 180 ng/ml, respectively (P = 0.036; analysis restricted to non-DS patients). Doxorubicin plasma concentration was an independent factor for CR, both in univariate (P = 0.031) and multivariate analysis including sex, age and white blood cell count at diagnosis (P = 0.021). Patients who reached CR had a significantly lower doxorubicin clearance than those who did not, 513 and 657 ml/min/m2, respectively (P = 0.017). In conclusion, doxorubicin plasma concentration and total body clearance during up-front treatment were correlated to the effect of induction therapy. Prospective studies should be performed to confirm the concentration-effect relationship and explore the possibility of therapeutic monitoring.

Mechanistic models for myelosuppression

As myelosuppression is the dose-limiting toxicity for most chemotherapeutic drugs, modelers attempt to find relationships between drug and toxicity to optimize treatment. Mechanistic models, i.e. models based on physiology and pharmacology, are preferable over empirical models, as prior information can be utilized and as they generally are more reliable for extrapolations. To account for different dosing-regimens and possible schedule-dependent effects, the whole concentration-time profile should be used as input into the pharmacokinetic-pharmacodynamic model. It is also of importance to model the whole time course of myelosuppression to be able to predict both the degree and duration of toxicity as well as consecutive courses of therapy. A handful of (semi)-mechanistic pharmacokinetic-pharmacodynamic models with the above properties have been developed and are reviewed. Ideally, a model of myelosuppression should separate drug-specific parameters from system related parameters to be applicable across drugs and useful under different clinical settings. Introduction of mechanistic models of myelosuppression in the design and evaluation of clinical trials can guide in the decision of optimal sampling times, contribute to knowledge of optimal doses and treatment regimens at an earlier time point and identify sub-groups of patients at a high risk of myelosuppression.

Epirubicin in patients with liver dysfunction: development and evaluation of a novel dose modification scheme

This study aimed to develop an epirubicin dose modification scheme in women with breast cancer and liver dysfunction. We first identified target areas under the concentration-time curve (AUCs) of 2400 and 1600 ng/ml.h from pharmacokinetic studies in 15 women with normal liver tests. In a second group of 16 women with abnormal liver biochemistry, the relationship between raised asparate aminotransferase (AST) and epirubicin clearance was: dose=AUC (97.5-34.2xlog AST). Adaptive dosing was evaluated prospectively in a third group of 41 women with serum AST > or =2xnormal+/-raised bilirubin. The median AUCs were 2444 and 1608 ng/ml.h, close to the high and low target AUCs, respectively. Variability in AUC was lower with adaptive dosing than in a fourth group given an unadjusted dose of epirubicin (coefficient of variation=25.8, 30.0 and 46.5%, respectively; P=0.06). Epirubicin dosing based on AST is safe and may reduce pharmacokinetic variability.

Pharmacokinetics of doxorubicin in children with acute lymphoblastic leukemia: multi-institutional collaborative study

BACKGROUND

In adults, it has been shown that the pharmacokinetics of doxorubicin are highly variable, despite standardization of the dose based on body surface area (BSA). The purpose of this study was to determine the plasma concentrations of doxorubicin and its active metabolite doxorubicinol in children treated for acute lymphoblastic leukemia (ALL).

PROCEDURE

Children, 107 in number, aged 1.3-17.3 years, were studied at Day 1 of induction therapy according to the current Nordic protocol. Five infants, 3-9 months old, were also included. Plasma samples were drawn 23 hr after the start of a 24-hr infusion of doxorubicin 40 mg/m(2), and analyzed by reversed-phase liquid chromatography.

RESULTS

There was a more than 10-fold difference between patients in dose normalized plasma concentration of doxorubicin, median 62.8 ng/ml, range 22.6-334 ng/ml. The doxorubicin concentrations differed significantly between age groups (P = 0.003). Children aged 4-6 years had the highest doxorubicin concentrations, median 77.9 ng/ml, followed by 2-4-year-old children, median 64.3 ng/ml. Both younger and older children had median values of about 50 ng/ml. Patients with white blood cell (WBC) count > 50 x 10(9)/L at diagnosis had significantly lower doxorubicin concentrations, median 55.3 ng/ml, than those with WBC count < 10 x 10(9)/L, median 64.4 ng/ml (P = 0.015). There was no difference in doxorubicin concentration between boys and girls. No correlation was found between doxorubicin levels and serum aminotransferases or serum creatinine. The concentration of doxorubicinol was 13% (median value) of that of doxorubicin. Four infants, 7-9 months old, had plasma clearance between 350-431 ml/min/m(2), which is in the same range as in older children. A 3-month-old infant had a clearance of 181 ml/min/m(2).

CONCLUSIONS

The age groups who had the highest doxorubicin concentrations, (2-) 4-6-year-old children, are known to make up a large proportion of standard risk ALL cases with good prognosis. The correlation between doxorubicin plasma levels and clinical effect needs further study. The influence of age, body composition, and tumor burden on the pharmacokinetics of antineoplastic drugs should also be further explored, aiming at improvements in the current dosing regimen based on BSA.

Dose-adjusted EPOCH chemotherapy for untreated large B-cell lymphomas: a pharmacodynamic approach with high efficacy

We hypothesized that incremental improvements in the cyclophosphamide-doxorubicin-vincristine-prednisone (CHOP) chemotherapy regimen through optimization of drug selection, schedule, and pharmacokinetics would improve outcome in patients with large B-cell lymphomas. A prospective multi-institutional study of administration of etoposide, vincristine, and doxorubicin for 96 hours with bolus doses of cyclophosphamide and oral prednisone (EPOCH therapy) was done in 50 patients with previously untreated large B-cell lymphomas. The doses of etoposide, doxorubicin, and cyclophosphamide were adjusted 20% each cycle to achieve a nadir absolute neutrophil count below 0.5 x 10(9)/L. The median age of the patients was 46 years (range, 20-88 years); 24% were older than 60 years; and 44% were at high-intermediate or high risk according to International Prognostic Index (IPI) criteria. There was a complete response in 92% of patients, and at the median follow-up time of 62 months, the progression-free survival (PFS) and overall survival (OS) rates were 70% and 73%, respectively. Neither IPI risk factors nor the index itself was associated with response, PFS, or OS. Doses were escalated in 58% of cycles, and toxicity levels were tolerable. Significant inverse correlations were observed between dose intensity and age for all adjusted agents, and drug clearance of doxorubicin and free etoposide was also inversely correlated with age (r = -0.54 and P(2) =.08 and r = -0.45 and P(2) =.034, respectively). Free-etoposide clearance increased significantly during successive cycles (P(2) =.015). Lymphomas with proliferation of at least 80% had somewhat lower progression and those expressing bcl-2 had significantly higher progression (P(2) =.04). Expression of bcl-2 may discriminate the recently described activated B-like from germinal-center B-like large-cell lymphomas and provide important pathobiologic and prognostic information. Dose-adjusted EPOCH may produce more cell kill than CHOP-based regimens. Dynamic dose adjustment may overcome inadequate drug concentrations, particularly in younger patients, and compensate for increased drug clearance over time.

Phase I/II trial of the multidrug-resistance modulator valspodar combined with cisplatin and doxorubicin in refractory ovarian cancer

PURPOSE

To determine the maximum-tolerated dose (MTD) of doxorubicin when given in combination with cisplatin and the multidrug-resistance (MDR) modulator valspodar and the remission rate induced by this combination in patients with platinum- and anthracycline-resistant ovarian cancer.

PATIENTS AND METHODS

Fifty-nine patients who had failed prior platinum- and anthracycline-based chemotherapy were enrolled. During the dose-finding phase, patients received a loading dose of valspodar (1.5 or 2 mg/kg) via 2-hour intravenous (IV) infusion on day 1 and continuous IV infusion (CIVI) of valspodar (2, 4, or 10 mg/kg/d) over 3 days. Doxorubicin (starting from 20 up to 50 mg/m(2)) and cisplatin (50 mg/m(2)) were administered via 15- to 20-minute IV infusions on day 3. During the efficacy phase, patients received at least two treatment cycles unless toxicity was unacceptable, and responding patients and those with stable disease received four to six cycles.

RESULTS

All patients completed at least one cycle of combined treatment. The MTD of doxorubicin was determined to be 35 mg/m(2) when administered with valspodar at 2 mg/kg loading dose and 10 mg/kg/d CIVI plus 50 mg/m(2) cisplatin. At these doses, valspodar blood concentrations known to reverse MDR in vitro were reached in all patients. Valspodar was well tolerated at all dose levels. Dose-limiting toxicities of the combination were primarily hematologic and included febrile neutropenia and prolonged leucopenia. The addition of valspodar to the treatment did not worsen cisplatin-related toxicity. Among 33 patients treated at the MTD for doxorubicin, one (3%) had a complete response, and four (12%) had a partial response. An additional seven patients experienced a stabilization of their previously progressive disease. The survival rates at 6 and 12 months were 59% and 19%, respectively.

CONCLUSION

Valspodar can be safely coadministered with doxorubicin and cisplatin. Although the regimen used in this trial produced renewed responses in patients with heavily pretreated, refractory ovarian cancer, the value of valspodar in reversing resistance mediated by P-glycoprotein remains to be determined.

Body surface area as a determinant of pharmacokinetics and drug dosing

Body surface area (BSA) was introduced into medical oncology in order to derive a safe starting dose for phase I studies of anticancer drugs from preclinical animal toxicology data. It is not clear however, as to why dosing by BSA was extended to the routine dosing of antineoplastic agents. Several formulas exist to estimate BSA, but the formula derived by DuBois and DuBois is the one used in adult medical oncology. This formula was derived based on data from only nine patients; subsequent attempts to validate the formula have found the DuBois formula to either over or underestimate the actual determined BSA. While cardiac output does correlate with BSA, the relationship between BSA and other physiologic measures relevant for drug metabolism and disposition, such as, renal and hepatic function, is weak or nonexistent. Further only epirubicin, etoposide, and carboplatin have been studied to determine if dosing by BSA would reduce interpatient variability, and none of these drugs were found to have significant relationships between their pharmacokinetics and BSA. Future clinical trials of new agents should not presume that dosing based on BSA reduces interpatient variability. Studies should examine the role, if any, BSA has in dosing new chemotherapeutic agents in initial phase I studies.

Pharmacokinetically guided administration of chemotherapeutic agents

The current practice for the dose calculation of most anticancer agents is based on body surface area in m2, although lower interpatient variation in pharmacokinetic parameters has been reported with pharmacokinetically guided administration. As chemotherapeutic agents have a narrow therapeutic window, pharmacokinetically guided administration may lead to less toxicity and higher efficacy than administration on the basis of body surface area. Pharmacokinetically guided administration, using parameters such as area under the plasma concentration-time curve (AUC), steady-state plasma drug concentration and drug exposure time above a certain plasma concentration, has been studied for many antineoplastic agents. Assessment of pharmacokinetic profiles allows the characterisation of relationships between pharmacokinetic parameters and efficacy and toxicity. AUC appears to be more closely correlated with pharmacodynamics than does the dose per unit of body surface area. In particular, the AUC-guided administration of carboplatin has been extensively studied, based on the close relationship between the renal clearance of the drug and glomerular filtration rate. Several formulae and limited sampling models have been derived to predict the AUC of carboplatin. The relationship between AUC and pharmacodynamics has also been studied for other anticancer agents, for example fluorouracil, topotecan, etoposide, cisplatin and busulfan, but all less extensively than for carboplatin. The pharmacokinetically guided administration of these agents needs to be investigated further before the use of alternative administration formulae can become standard clinical practice. Prospective studies of pharmacokinetically guided versus surface area-based administration should be performed to validate pharmacokinetic-pharmacodynamic relationships and to facilitate optimal dosage of anticancer agents in the clinic.

Adaptive control methods for the dose individualisation of anticancer agents

Numerous studies have found a clear relationship between systemic exposure and the toxicity or (more rarely) the efficacy of anticancer agents. Moreover, the clearance of most of these drugs differs widely between patients. These findings, combined with the narrow therapeutic index of anticancer drugs, suggest that patient outcome would be improved if doses were individualised to achieve a target systemic exposure. Bayesian maximum a posteriori probability (MAP) forecasting is an efficient and robust method for the optimisation of drug therapy, but its use for anticancer drugs is not yet extensive. The aim of this paper is to review the application of population pharmacokinetics and MAP to anticancer drugs and to evaluate whether and when MAP Bayesian estimation improves the clinical benefit of anticancer chemotherapy. For each drug, the relationships between pharmacokinetic variables [e.g. plasma concentration or the area under the concentration-time curve] and pharmacodynamic effects are described. Secondly, the methodologies employed are considered and, finally, the results are analysed in terms of predictive performance as well as, where possible, the impact on clinical end-points. Some studies were retrospective and intended only to evaluate individual pharmacokinetic parameter values using very few blood samples. Among the prospective trials, a few studied the pharmacokinetic/pharmacodynamic relationships which provided the basis for routine pharmacokinetic monitoring. Others were performed in clinical context where MAP Bayesian estimation was used to determine maximum tolerated systemic exposure (e.g. for carboplatin, topotecan, teniposide) or for pharmacokinetic monitoring (e.g. for methotrexate or platinum compounds). Indeed, its flexibility in blood sampling times makes this technique much more applicable than other limited sampling strategies. These examples demonstrate that individual dose adjustment helps manage toxicity. The performance of pharmacokinetic monitoring is linked to the methodology used at each step of its design and application. Moreover, a limitation to the use of pharmacokinetic monitoring for certain anticancer drugs has been the difficulty in obtaining pharmacokinetic or pharmacodynamic data. Recent progress in analytical methods, as well as the development of noninvasive methods (such as positron emission tomography) for evaluating the effects of chemotherapy, will help to define pharmacokinetic-pharmacodynamic relationships. Bayesian estimation is the strategy of choice for performing pharmacokinetic studies, as well as ensuring that a given patient benefits from the desired systemic exposure. Together, these methods could contribute to improving cancer chemotherapy in terms of patient outcome and survival.

Eight-hour infusion versus bolus injection of doxorubicin in the EAP regimen in patients with advanced gastric cancer: a prospective randomised trial

BACKGROUND

Doxorubicin (40 mg/m2/cycle), etoposide (360 mg/m2/cycle) and cisplatin (80 mg/m2/cycle) comprise an efficient regimen in patients with advanced gastric cancer (AGC). However, its excessive hematological toxicity led doctors to avoid using the combination. Doxorubicin is the main cause of myelotoxicity in the EAP regimen. The aim of this study was to compare an eight-hour infusion of doxorubicin (arm A) with intravenous injection of doxorubicin (arm B) in the EAP regimen with respect to toxicity, objective responses, time to progression (TTP) and survival in patients with AGC.

PATIENTS AND METHODS

One-hundred twenty chemotherapy-naïve patients with measurable AGC were randomised between September 1994 and August 1998. Sixty patients in arm A and sixty patients in arm B were considered as fully evaluable. The arms were well balanced for age, sex distribution, previous therapy, histological grade and performance status. One-hundred eighty cycles were applied in arm A (median 2) and 201 in arm B (median 4).

RESULTS

No difference was detected (P = 0.28) in the response rate of arm A 20% (CR 3; PR 9; 95% CI: 10-30) and B 28% (CR 3; PR 14; 95% CI: 17-40). But there was a significant difference in PD (P = 0.005) between arm A (51%) and arm B (36%). TTP (P = 0.01) and survival (P = 0.02) analyses detected an advantage for arm B vs. arm A. Grades 3-4 toxicity were as follows (arms A%/B%): anemia 8/10, leukopenia 24/26, thrombocytopenia 6/16 (significance, P = 0.05), nausea/vomiting 5/8, diarrhea 6/2, mucositis 8/5. Apart from the trombocytopenia, there was no significant difference in toxicity grades 3-4 between the two arms. Four treatment-related deaths occurred, two in each arm.

CONCLUSIONS

Bolus injection of doxorubicin is superior to eight-hour doxorubicin infusion in the EAP regimen in terms of survival, TTP and PD without being significantly more toxic.

What is the effect of adjusting epirubicin doses for body surface area?

Doses of cytotoxic drugs are routinely adjusted according to body surface area. We have evaluated this practice in 32 women with advanced breast cancer treated with single-agent epirubicin 12.5-120 mg m(-2). Epirubicin and its metabolites were measured by high-performance liquid chromatography (HPLC). Unadjusted plasma clearance was calculated from dose in mg, and adjusted clearance from dose in mg m(-2). Unadjusted clearance did not correlate with surface area, height, weight, per cent ideal body weight or body mass index. There was no difference in the coefficient of variation (CV) of adjusted and unadjusted clearance (39.4% and 37.7% respectively). The AUC that would have resulted from giving an unadjusted dose was calculated. This predicted AUC was accurate, unbiased and had the same CV as the actual AUC. Similarly, in 11 patients an analysis of actual and predicted neutropenia confirmed that unadjusted dosing would have had no significant effect on the pattern of myelosuppression. Normalization of epirubicin dosage according to surface area appears not to reduce either pharmacokinetic or pharmacodynamic variability.

Use of body surface area to calculate chemotherapeutic drug dose in dogs: II. Limitations imposed by pharmacokinetic factors

Anticancer drug dosages that specify the maximum dose and minimum dosing interval that are tolerated in a population of dogs are commonly recommended. Because the differences between the effective and toxic doses of most cancer chemotherapeutics is slight, it is important to achieve therapeutic concentrations in tumor tissues at the same time that concentrations in nontarget tissues are minimized. In order to determine the dosage regimen that will most likely accomplish these goals, similar drug concentrations must be achieved in all patients dosed according to a specific regimen. Dosing based on body surface area (BSA) is generally used in an effort to normalize drug concentrations. This is because it is well recognized that measures of many physiologic parameters that are responsible for drug disposition, including renal function and energy expenditure, can be normalized by use of BSA. However, there is substantial evidence that drug disposition is not always proportional to BSA. Differences in distribution, metabolism, and excretion pathways may preclude dose extrapolation among species or among individuals within a species based on BSA. Moreover, genetic differences in drug metabolism are well recognized in humans and in laboratory animals, and it is likely that similar differences exist among breeds of dogs. A review of the pharmacokinetic disposition of several cancer chemotherapeutics suggests that studies are needed to determine the most effective method to achieve equivalent anticancer drug concentrations in diverse veterinary patients.

Pharmacokinetics of anticancer agents in patients with impaired liver function

This report reviews published information on the clinical pharmacokinetics of antitumour agents in patients with liver dysfunction, associated with primary liver disease or liver metastases. Information was available for anthracyclines and their related compounds, antimetabolites, cyclophosphamide, vinca alkaloids, taxanes and epipodophyllotoxins. Changes in the pharmacokinetic profile or metabolism in patients with mild or severe hepatobiliary dysfunction are described and the relationships between serum levels, parameters employed for measuring hepatic function and toxic or therapeutic effects are examined. Current knowledge of the pharmacokinetics of antineoplastic agents in liver disease is far from complete, mostly obtained in small numbers of non-homogeneous patients often presenting only moderate liver dysfunction, and empirical guidelines for dose assessment are still largely applied in clinical practice. Because of the complex pathophysiological mechanisms of liver insufficiency in cancer patients, there is still doubt whether endogenous markers are useful. Although caution in treating cancer patients with liver insufficiency is compulsory, for most compounds there seems no need to recommend dose reductions for moderate impairment. However, for the tubulin acting agents, vincristine, vinblastine and possibly for paclitaxel and docetaxel, there is strong evidence that dose adjustment is mandatory in order to avoid excessive neutropenia and neurotoxicity.

Benefits of pharmacological knowledge in the design and monitoring of cancer chemotherapy

Prescribing chemotherapy is a difficult task, because of drug resistance, which prevents all tumors to respond to a given protocol and because of drug toxicity, which is generally unavoidable but which must be limited to acceptable levels. The therapeutic window of anticancer drugs is very narrow and clinicians have to try to optimize the individual doses and schedules of the drugs to be administered. They can rely upon simple anthropometric features, such as body weight or surface area; they can also take into account the physiological status of the patient: age, liver and kidney function, genetic characteristics of drug metabolism, etc. The best way for dose adaptation lies in the establishment of pharmacokinetic/pharmacodynamic relationships, i.e., between the behavior of a drug in the body and its efficacy and toxicity. When it is established that the optimal effect of a drug is related to a given parameter, such as the area under the curve plotting plasma concentration vs. time (AUC), it becomes possible to administer the drug with the dose allowing to obtain the target parameter value. Individual dose adaptation can be achieved thanks to the study of the pharmacokinetics of a test dose preceding that of the therapeutic dose, or by the measure of drug plasma levels, either at steady state during a protracted infusion, or from cycle to cycle during repetitive protocols. Population analysis now allows the adaptation of anticancer drug dosing from a minimum knowledge of individual pharmacokinetic features, together with other characteristics of the patients such as age, gender or physiological functions.

An evaluation of hepatic extraction and clearance of doxorubicin

A swine model was developed to study quantitatively the pharmacokinetics of hepatic extraction and clearance of doxorubicin (DOX). Systemic and hepatic artery infusions of DOX (0.5-9 mg kg-1) were administered to 34 pigs. Pharmacokinetic analysis was simplified by use of a double-balloon catheter in the inferior vena cava to collect hepatic venous effluent. During hepatic artery infusion only, DOX in hepatic venous blood was extracted using activated carbon filters to prevent drug recirculation. Hepatic extraction and clearance of DOX were independent of dose and route of administration. Extraction ratios varied from 0.75 to 0.91 during hepatic artery infusion and from 0.50 to 0.72 during systemic infusion. Clearance results were analogous. After cessation of drug infusions, hepatic extraction and clearance of DOX was negative, suggesting that the liver serves as a drug reservoir during DOX infusion and subsequently is a net source of unmetabolised drug. Liver extraction and clearance of DOX in pigs are substantial. During either systemic or hepatic artery infusion of DOX, the liver serves as a drug reservoir. Subsequent mobilisation of this hepatic pool of DOX may cause prolonged systemic exposure to drug.

Iododoxorubicin in advanced breast cancer: a phase II evaluation of clinical activity, pharmacology and quality of life

Iododoxorubicin 80 mg m-2 i.v. was given 3 weekly for a maximum of six cycles as first-line chemotherapy to 14 evaluable women with metastatic breast cancer. The response rate was 14% (95% confidence intervals 4-40%); median time to progression was 3.5 months (range 0.7 to > 9.3) and median survival was 10.2 months (range 2.3 to > 20.4). Neutropenia was the main toxicity but was not associated with severe sepsis. Two patients had a significant (> 10%) but asymptomatic fall in cardiac ejection fraction; other toxicities were mild. Plasma pharmacokinetics was studied during the first cycle of treatment. Iododoxorubicin was extensively metabolised to iododoxorubicinol. Neutropenia and thrombocytopenia were both significantly correlated with the area under the concentration-time curve (AUC) for iododoxorubicin and the total AUC for iododoxorubicin and iododoxorubicinol. Quality of life (QOL), evaluated by self-report questionnaire and interview, showed little evidence of benefit in terms of physical symptom relief, level of activity, psychological symptoms or global evaluation of QOL during treatment. Iododoxorubicin is subjectively less toxic than standard anthracyclines, but at the dose and schedule used has limited activity in metastatic breast cancer, possibly because iododoxorubicinol is not clinically active.

Individual dose adaptation of anticancer drugs

The dose of anticancer drugs is currently adjusted to the patient body surface area, although patients have different abilities to clear anticancer drugs. The dose adjustment to physiological functions permits major toxic accidents to be avoided. The adjustment to tumour drug content is considered, but for ethical or technical reasons, it cannot be used routinely The best criterion for the dose adjustment seems to be drug plasma concentration. The relationship between plasma concentration and efficacy may not be excellent, since it depends on the presence of resistant cells and on the blood flow through the tumour. A relationship between plasma concentration and/or the area under the curve (AUC) with toxicity has been reported with all major anticancer drugs. Different methods of dose adjustment to the drug plasma concentration are reported. In conclusion, dose adjustment to the drug plasma concentration or to the AUC can improve the chemotherapy efficacy, while reducing toxicity.

Quantitation of cell-associated doxorubicin by high-performance liquid chromatography after enzymatic desequestration

A method for measuring cellular concentrations of the anthracycline doxorubicin was developed. The assay involves cell lysis and protein degradation by detergent and proteinase K treatment followed by DNA hydrolysis using DNase I. Prior to high-performance liquid chromatography, samples are deproteinized by the addition of ZnSO4 and methanol. The assay is linear with respect to both the cellular drug content and the number of cells assayed over the ranges tested, and drug recovery is close to 100%. The method has a limit of detection of 50 fmol injected doxorubicin. Within run and between-day coefficients of variation have consistently been found to be in the 5% and 10% range, respectively, in different cell lines exposed to doxorubicin in vitro. The method has been evaluated in analyses of doxorubicin levels in mononuclear blood cells of patients. The assay offers several advantages over commonly used organic extraction techniques and may improve cellular drug monitoring during anthracycline therapy in patients.

Multidrug resistance in cancer chemotherapy

Resistance to chemotherapy is the single most important reason for treatment failure in cancer patients. Over the past 15 years, we have gained significant insight into one of the mechanisms responsible for this process: multidrug resistance (MDR). Far from being a phenomenon limited to the laboratory, multidrug resistance has been identified in a wide variety of newly diagnosed and recurrent human tumors. A number of compounds can block p-glycoprotein and overcome MDR in vitro and in vivo. Current strategies to block MDR are discussed in this review. Future research in this area will focus on the identification of more selective and potent MDR reversing agents and the development of entirely new approaches to overcoming multidrug resistance such as monoclonal antibodies, immunotoxins, and gene therapy.

Can pharmacokinetic and pharmacodynamic studies improve cancer chemotherapy?

BACKGROUND

The exploitation of pharmacokinetic-pharmacodynamic relationships is worthwhile for drugs where there is difficulty or delay in obtaining clinical evidence of therapeutic or toxic effects, where there is a clear relationship between the pharmacokinetics and pharmacodynamics, and where the drug has a small therapeutic index. These criteria are amply met by cytotoxic anticancer agents. In particular, an extensive literature for all classes of cancer chemotherapeutics shows that the correlation between pharmacokinetic parameters (peak concentration, area under the plasma concentration-time curve, clearance or steady-state levels) and toxicity is in many cases better than the relationship between dose and toxicity. Adaptive dosing: Prospective studies of dose adaptation on the basis of pharmacokinetic or pharmacodynamic information, with or without feedback control, have shown that pharmacologically guided dosing is feasible. Adaptive dosing results in reduced pharmacokinetic variability and more consistent toxicity. Currently, there are insufficient prospective studies to allow conclusions concerning the efficacy of such a dosing system.

Protracted drug infusions in cancer treatment: an appraisal of 5-fluorouracil, doxorubicin, and platinums

The feasibility to deliver chemotherapeutic agents by protracted i.v. infusion has greatly increased in the recent past. Indwelling ports, longer lasting central venous catheters requiring less than daily maintenance 'flushing', surgical expertise in placement, use in analgesia and nutrition, and 'smart' pump technology have all contributed to their increasing popularity. Justification for use of infusions in cancer chemotherapy has been slow in appearing with few studies proceeding to the comparative stage. This review will focus on three drugs in common use in cancer treatment, with the purpose of appraising the role of such infusions in cancer therapeutics and of deriving some lessons that might be applicable to other drugs or to drug development in general. For fluorouracil and doxorubicin the rationale and clinical findings favoring further development of infusion regimens is particularly strong. In the case of platinum compounds, some toxicologic advantages have emerged, but other measures designed to protect against the toxicities of cisplatin compete with infusion regimens in this regard. The therapeutic potential for this form of drug delivery, therefore, appears still confined to a subset of patients. Stronger rationales for the use of protracted infusions may be forthcoming from pharmacodynamic findings as in the case of etoposide, combined modality therapy with radiation for FU and cisplatin, biochemical modulation for FU, and reversal of multidrug resistance and its modulation for doxorubicin. While awaiting research into these areas of clinical and pre-clinical investigations, the role of infusion appears most evident in the cardiotoxicity protection of anthracyclines, and in further efficacy exploration (through dose or modulation) of FU. Both mechanistic and pharmacologic considerations could also provide additional stimulus for development of new formulations such as long circulating liposomes, and drugs more suitable for oral administration.