Pharmacokinetic approach to rational therapeutic doses for human tumor-bearing nude mice

How translational modeling in oncology needs to get the mechanism just right

Translational model‐based approaches have played a role in increasing success in the development of novel anticancer treatments. However, despite this, significant translational uncertainty remains from animal models to patients. Optimization of dose and scheduling (regimen) of drugs to maximize the therapeutic utility (maximize efficacy while avoiding limiting toxicities) is still predominately driven by clinical investigations. Here, we argue that utilizing pragmatic mechanism‐based translational modeling of nonclinical data can further inform this optimization. Consequently, a prototype model is demonstrated that addresses the required fundamental mechanisms.

Targeted 1,3-dipolar cycloaddition with acrolein for cancer prodrug activation

Cytotoxic anticancer drugs used in chemotherapy are often antiproliferative agents that preferentially kill rapidly growing cancer cells. Their mechanism relies mainly on the enhanced proliferation rate of cancer cells and is not genuinely selective for cancer cells. Therefore, these drugs can also significantly affect healthy cells. Prodrug therapy provides an alternative approach using a less cytotoxic form of anticancer drug. It involves the synthesis of inactive drug derivatives which are converted to an active form inside the body and, preferably, only at the site of cancerous tissues, thereby reducing adverse drug reaction (ADR) events. Herein, we demonstrate a prodrug activation strategy by utilizing the reaction between aryl azide and endogenous acrolein. Since acrolein is generally overproduced by most cancer cells, we anticipate our strategy as a starting point for further applications in mouse models with various cancers. Furthermore, cancer drugs that have had therapeutic index challenges might be reconsidered for application by utilizing our strategy.

Opportunities for Quantitative Translational Modeling in Oncology

A 2-day meeting was held by members of the UK Quantitative Systems Pharmacology Network () in November 2018 on the topic of Translational Challenges in Oncology. Participants from a wide range of backgrounds were invited to discuss current and emerging modeling applications in nonclinical and clinical drug development, and to identify areas for improvement. This resulting perspective explores opportunities for impactful quantitative pharmacology approaches. Four key themes arose from the presentations and discussions that were held, leading to the following recommendations: Evaluate the predictivity and reproducibility of animal cancer models through precompetitive collaboration. Apply mechanism of action (MoA) based mechanistic models derived from nonclinical data to clinical trial data. Apply MoA reflective models across trial data sets to more robustly quantify the natural history of disease and response to differing interventions. Quantify more robustly the dose and concentration dependence of adverse events through mathematical modelling techniques and modified trial design.

Collagen gel droplet-embedded culture drug sensitivity testing in squamous cell carcinoma cell lines derived from human oral cancers: Optimal contact concentrations of cisplatin and fluorouracil

The collagen gel droplet-embedded culture drug sensitivity test (CD-DST) is an anticancer drug sensitivity test that uses a method of three-dimensional culture of extremely small samples, and it is suited to primary cultures of human cancer cells. It is a useful method for oral squamous cell carcinoma (OSCC), in which the cancer tissues available for testing are limited. However, since the optimal contact concentrations of anticancer drugs have yet to be established in OSCC, CD-DST for detecting drug sensitivities of OSCC is currently performed by applying the optimal contact concentrations for stomach cancer. In the present study, squamous carcinoma cell lines from human oral cancer were used to investigate the optimal contact concentrations of cisplatin (CDDP) and fluorouracil (5-FU) during CD-DST for OSCC. CD-DST was performed in 7 squamous cell carcinoma cell lines derived from human oral cancers (Ca9-22, HSC-3, HSC-4, HO-1-N-1, KON, OSC-19 and SAS) using CDDP (0.15, 0.3, 1.25, 2.5, 5.0 and 10.0 µg/ml) and 5-FU (0.4, 0.9, 1.8, 3.8, 7.5, 15.0 and 30.0 µg/ml), and the optimal contact concentrations were calculated from the clinical response rate of OSCC to single-drug treatment and the in vitro efficacy rate curve. The optimal concentrations were 0.5 µg/ml for CDDP and 0.7 µg/ml for 5-FU. The antitumor efficacy of CDDP at this optimal contact concentration in CD-DST was compared to the antitumor efficacy in the nude mouse method. The T/C values, which were calculated as the ratio of the colony volume of the treatment group and the colony volume of the control group, at the optimal contact concentration of CDDP and of the nude mouse method were almost in agreement (P<0.05) and predicted clinical efficacy, indicating that the calculated optimal contact concentration is valid. Therefore, chemotherapy for OSCC based on anticancer drug sensitivity tests offers patients a greater freedom of choice and is likely to assume a greater importance in the selection of treatment from the perspectives of function preservation and quality of life, as well as representing a treatment option for unresectable, intractable or recurrent cases.

Vinorelbine Delivery and Efficacy in the MDA-MB-231BR Preclinical Model of Brain Metastases of Breast Cancer

PURPOSE

To evaluate vinorelbine drug exposure and activity in brain metastases of the human MDA-MB-231BR breast cancer model using integrated imaging and analysis.

METHODS

Brain and systemic metastases were created by administration of cancer cells in female NuNu mice. After metastases developed, animals were administered vinorelbine at the maximal tolerated dose (12 mg/kg), and were evaluated thereafter for total and unbound drug pharmacokinetics, biomarker TUNEL staining, and barrier permeability to Texas red.

RESULTS

Median brain metastasis drug exposure was 4-fold greater than normal brain, yet only ~8% of non-barrier systemic metastases, which suggests restricted brain exposure. Unbound vinorelbine tissue/plasma partition coefficient, K_p,uu, equaled ~1.0 in systemic metastases, but 0.03-0.22 in brain metastases, documenting restricted equilibration. In select sub-regions of highest drug-uptake brain metastases, K_p,uu approached 1.0, indicating complete focal barrier breakdown. Most vinorelbine-treated brain metastases exhibited little or no positive early apoptosis TUNEL staining in vivo. The in vivo unbound vinorelbine IC₅₀ for TUNEL-positive staining (56 nM) was 4-fold higher than that measured in vitro (14 nM). Consistent with this finding, P-glycoprotein expression was observed to be substantially upregulated in brain metastasis cells in vivo.

CONCLUSIONS

Vinorelbine exposure at maximum tolerated dose was less than one-tenth that in systemic metastases in >70% of brain metastases, and was associated with negligible biomarker effect. In small subregions of the highest uptake brain metastases, compromise of blood-tumor barrier appeared complete. The results suggest that restricted delivery accounts for 80% of the compromise in drug efficacy for vinorelbine against this model.

Comparison of hypoxia-activated prodrug evofosfamide (TH-302) and ifosfamide in preclinical non-small cell lung cancer models

Evofosfamide (TH-302) is a hypoxia-activated prodrug of the cytotoxin bromo-isophosphoramide. In hypoxic conditions Br-IPM is released and alkylates DNA. Ifosfamide is a chloro-isophosphoramide prodrug activated by hepatic Cytochrome P450 enzymes. Both compounds are used for the treatment of cancer. Ifosfamide has been approved by the FDA while evofosfamide is currently in the late stage of clinical development. The purpose of this study is to compare efficacy and safety profile of evofosfamide and ifosfamide in preclinical non-small cell lung cancer H460 xenograft models. Immunocompetent CD-1 mice and H460 tumor-bearing immunocompromised nude mice were used to investigate the safety profile. The efficacy of evofosfamide or ifosfamide, alone, and in combination with docetaxel or sunitinib was compared in ectopic and intrapleural othortopic H460 xenograft models in animals exposed to ambient air or different oxygen concentration breathing conditions. At an equal body weight loss level, evofosfamide showed greater or comparable efficacy in both ectopic and orthotopic H460 xenograft models. Evofosfamide, but not ifosfamide, exhibited controlled oxygen concentration breathing condition-dependent antitumor activity. However, at an equal body weight loss level, ifosfamide yielded severe hematologic toxicity when compared to evofosfamide, both in monotherapy and in combination with docetaxel. At an equal hematoxicity level, evofosfamide showed superior antitumor activity. These results indicate that evofosfamide shows superior or comparable efficacy and a favorable safety profile when compared to ifosfamide in preclinical human lung carcinoma models. This finding is consistent with multiple clinical trials of evofosfamide as a single agent, or in combination therapy, which demonstrated both anti-tumor activity and safety profile without severe myelosuppression.

Overview of human primary tumorgraft models: comparisons with traditional oncology preclinical models and the clinical relevance and utility of primary tumorgrafts in basic and translational oncology research

Laboratory models that accurately replicate human tumor initiation and characteristics are integral to advancing knowledge in cancer research. However, comparative studies between commonly employed laboratory models and human tumors have demonstrated that some models have molecular and genomic alterations dissimilar to the cancer type they attempt to replicate. In contrast, several recent comparative studies suggest that because patient-derived tumors grown in mice maintain many of the important characteristics of the original tumor, they represent an important tool for the development of new cancer therapeutics. Detailed in this overview are the advantages and disadvantages of the most commonly used cancer models for mechanistic and therapeutic research, with an emphasis on the advances made in the production and use of patient-derived tumorgrafts.

Pharmacokinetic modeling of an induction regimen for in vivo combined testing of novel drugs against pediatric acute lymphoblastic leukemia xenografts

Current regimens for induction therapy of pediatric acute lymphoblastic leukemia (ALL), or for re-induction post relapse, use a combination of vincristine (VCR), a glucocorticoid, and L-asparaginase (ASP) with or without an anthracycline. With cure rates now approximately 80%, robust pre-clinical models are necessary to prioritize active new drugs for clinical trials in relapsed/refractory patients, and the ability of these models to predict synergy/antagonism with established therapy is an essential attribute. In this study, we report optimization of an induction-type regimen by combining VCR, dexamethasone (DEX) and ASP (VXL) against ALL xenograft models established from patient biopsies in immune-deficient mice. We demonstrate that the VXL combination was synergistic in vitro against leukemia cell lines as well as in vivo against ALL xenografts. In vivo, VXL treatment caused delays in progression of individual xenografts ranging from 22 to >146 days. The median progression delay of xenografts derived from long-term surviving patients was 2-fold greater than that of xenografts derived from patients who died of their disease. Pharmacokinetic analysis revealed that systemic DEX exposure in mice increased 2-fold when administered in combination with VCR and ASP, consistent with clinical findings, which may contribute to the observed synergy between the 3 drugs. Finally, as proof-of-principle we tested the in vivo efficacy of combining VXL with either the Bcl-2/Bcl-xL/Bcl-w inhibitor, ABT-737, or arsenic trioxide to provide evidence of a robust in vivo platform to prioritize new drugs for clinical trials in children with relapsed/refractory ALL.

Experimental models of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a common and deadly cancer whose pathogenesis is incompletely understood. Comparative genomic studies from human HCC samples have classified HCCs into different molecular subgroups; yet, the unifying feature of this tumor is its propensity to arise upon a background of inflammation and fibrosis. This review seeks to analyze the available experimental models in HCC research and to correlate data from human populations with them in order to consolidate our efforts to date, as it is increasingly clear that different models will be required to mimic different subclasses of the neoplasm. These models will be instrumental in the evaluation of compounds targeting specific molecular pathways in future preclinical studies.

Proliferation assay on a silicon chip applicable for tumors extirpated from mammalians

We describe a novel anticancer drug sensitivity assay on a silicon chip applicable for tumors extirpated from in vivo mammalians. Human promyelocytic leukemia (HL-60) cells were subcutaneously (s.c.) inoculated in SCID mice, then removed 31 days after the inoculation. The cells were embedded in a small volume (18 nL) of a collagen-gel matrix on a pyramid-shaped silicon microstructure for further cultivation. The respiration activity of the cells on the chip was measured by scanning electrochemical microscopy (SECM). The proliferation behavior was continuously monitored for 6 days. It seemed that the proliferation rate of the cells removed from the mice was lower than that cultured in a flask and conformed to that in mice. The effects of cisplatin (CDDP) and etoposide (VP-16) on the HL-60 cultured in vivo were in good agreement with those obtained by a conventional colorimetric assay. Our results suggest that the SECM-based assay is appropriate for biopsy specimens in a relatively short-time evaluation.

Experimental chemotherapy against canine mammary cancer xenograft in SCID mice and its prediction of clinical effect

The effectiveness of 6 antitumor agents has been evaluated for canine mammary gland tumor (CMG-6) serially transplanted into severe combined immunodeficiency (SCID) mice. CMG-6 diagnosed as a solid carcinoma was subcutaneously transplanted into SCID mice and six antitumor agents were intravenously given to the mice as a single injection. The effectiveness was evaluated by Treatment group/Control group percent (T/C %) and statistical significance determined by Mann-Whitney's U-test in tumor volume. The minimum effective doses (MEDs; mg/kg) of mice were as follows; cyclophosphamide (CPM) 65, doxorubicin (DXR) 6, cisplatin (CDDP) 5, vincristine (VCR) 1.6, vinblastine (VLB) more than 5.5, 5-fluorouracil (5-FU) 105. Clinical effects of the drugs were predicted based on area under the curve (AUC) of dogs given a clinical dose (AUCdog)/AUC of mice given a MED (AUCmouse) ratios from published references. The AUC ratios were as follows; CPM 2.24, DXR 0.19, CDDP 1.20, VCR 0.04, VLB <1.24 and 5-FU 1.15. Drugs indicating more than 1.0 in AUCdog/AUCmouse ratio were CPM, CDDP and 5-FU, and would be suggested as effective in the original patient with CMG-6. The combination chemotherapy using clinically equivalent doses in CDDP and CPM, which were the two highest values in AUCdog/AUCmouse ratio by single agent therapy, was performed and shown to have additional effects as compared to the responsiveness of each agent against CMG-6.

Inhibitory effects of combinations of HER-2/neu antibody and chemotherapeutic agents used for treatment of human breast cancers

Previous studies have demonstrated a synergistic interaction between rhuMAb HER2 and the cytotoxic drug cisplatin in human breast and ovarian cancer cells. To define the nature of the interaction between rhuMAb HER2 and other classes of cytotoxic drugs, we applied multiple drug effect/combination index (CI) isobologram analysis to a variety of chemotherapeutic drug/rhuMAb HER2 combinations in vitro. Synergistic interactions at clinically relevant drug concentrations were observed for rhuMAb HER2 in combination with cisplatin (CI=0.48, P=0.003), thiotepa (CI=0.67, P=0.0008), and etoposide (CI=0.54, P=0.0003). Additive cytotoxic effects were observed with rhuMAb HER2 plus doxorubicin (CI=1.16, P=0.13), paclitaxel (CI=0.91, P=0.21), methotrexate (CI=1.15, P=0.28), and vinblastine (CI=1.09, P=0.26). One drug, 5-fluorouracil, was found to be antagonistic with rhuMAb HER2 in vitro (CI=2.87, P=0.0001). In vivo drug/rhuMAb HER2 studies were conducted with HER-2/neu-transfected, MCF7 human breast cancer xenografts in athymic mice. Combinations of rhuMAb HER2 plus cyclophosphamide, doxorubicin, paclitaxel, methotrexate, etoposide, and vinblastine in vivo resulted in a significant reduction in xenograft volume compared to chemotherapy alone (P<0.05). Xenografts treated with rhuMAb HER2 plus 5-fluorouracil were not significantly different from 5-fluorouracil alone controls consistent with the subadditive effects observed with this combination in vitro. The synergistic interaction of rhuMAb HER2 with alkylating agents, platinum analogs and topoisomerase II inhibitors, as well as the additive interaction with taxanes, anthracyclines and some antimetabolites in HER-2/neu-overexpressing breast cancer cells demonstrates that these are rational combinations to test in human clinical trials.

Issues in experimental design and endpoint analysis in the study of experimental cytotoxic agents in vivo in breast cancer and other models

Considerable effort has been placed into the identification of new antineoplastic agents to treat breast cancer and other malignant diseases. The basic approaches, in terms of model selection, endpoints, and data analysis, have changed in the previous few decades. This article deals with many of the issues associated with designing in vivo studies to investigate the activity of experimental and established compounds and their potential interactions. Endpoints for both in situ and excision assays are described, including approaches for determining cell kill, tumor growth delay, survival, and other estimates of activity. Suggestions for approaches that may limit the number of animals also are included, as are possible alternatives for death as an experimental endpoint. Other concerns, such routes for drug administration, drug dosage, and preliminary assessments of toxicity also are addressed. Statistical considerations are only briefly discussed, since these are addressed in detail in the accompanying article by Hanfelt (Hanfelt JJ, Breast Cancer Res Treat 46:279-302, 1997). The approaches suggested within this article are presented to draw attention to many of the key issues in experimental design and are not intended to exclude other approaches.

P-glycoprotein-mediated acquired multidrug resistance of human lung cancer cells in vivo

We examined whether the increased expression of P-glycoprotein (P-gp) encoded by the human multidrug resistance gene MDR1 is related to the acquired multidrug resistance of lung cancer in vivo. We estimated the chemosensitivity of lung cancer xenografts (LC-6, adenocarcinoma; Lu-24, small-cell cancer) by calculation of relative tumour growth (T/C%, treated/control) in vivo, based on statistical significance determined by the Mann-Whitney U test (P < 0.01, one-sided). MDR1 gene expression levels were evaluated by reverse transcription-polymerase chain reaction (RT-PCR) assay. P-gp production and P-gp localisation were examined by Western blotting and by immunohistochemical analysis respectively. LC-6 and Lu-24 were initially sensitive to both vincristine (VCR, 1.6 mg kg-1: LC-6, 45%; Lu-24, 39%) and doxorubicin (DOX, 12 mg kg-1: LC-6, 26%; Lu-24, 27%) in vivo. VCR-resistant variants (LC-6R, 66% and Lu-24R, 68%) selected with VCR (0.4 mg kg-1, x 9) significantly acquired cross-resistance to DOX (LC-6R, 55% and Lu-24R, 55% respectively). RT-PCR assay showed increased levels of MDR1 expression in LC-6R and Lu-24R with stable MDR1 expression levels. P-gp expression levels were elevated, and the percentage of P-gp-positive tumour cells increased in both LC-6R and Lu-24R. These results suggest that P-gp/MDR1 overexpression is related to acquired multidrug resistance in lung cancer in vivo.

P-31 changes as a measure of therapy response in resistant and sensitive osteosarcomas implanted into nude mice

OBJECTIVE

To determine if changes in PCr/Pi and PME can be used to predict lack of tumor response to chemotherapy in a murine model of a chemotherapy-resistant human osteosarcoma.

MATERIAL AND METHODS

Cisplatin-resistant sublines were grown from high-grade cisplatin-sensitive human osteosarcoma. Surface coil localized 31P NMR spectroscopy of implanted cisplatin-resistant and sensitive osteosarcoma tumors in nude mice was performed.

RESULTS

A cisplatin-resistant subline of a sensitive human osteosarcoma was developed that was five times more resistant to cisplatin than the parent cell line. Our NMR data shows a statistically significant difference in the change in the PCr/Pi ratio after treatment between sensitive and resistant osteosarcomas at the alpha = 0.05 level. Changes in PME were seen in the sensitive tumors but were not statistically significant.

CONCLUSIONS

Changes in PCr/Pi predict lack of tumor treatment response in human osteosarcoma implanted into nude mice with a specificity of 70% and a sensitivity of 54%. Monitoring of PCr/Pi in human osteosarcoma patients may allow detection of response to chemotherapy before conventional imaging techniques.

31P changes as a measure of therapy response in human osteosarcomas implanted into nude mice

Our objective was to determine whether changes in PME and PCr/Pi can be used to predict lack of tumor response to chemotherapy in a murine model of human osteosarcoma. A chemotherapy-sensitive human osteosarcoma cell line was implanted into the flank of 22 nude mice. Cisplatin was administered to 11 of the mice 9 days postimplantation. 31P MR spectroscopy was performed pre- and post-chemotherapy in both sets of mice. Statistically significant changes in PCr/Pi occur from post-chemotherapy in the treated mice, but not in the untreated mice during the same time. Change in PME parallels changes in tumor volume. Changes in PCr/Pi predict lack of chemotherapy treatment in human osteosarcoma implanted into nude mice with a specificity of 80% and a sensitivity of 63%. The change in PCr/Pi occurs prior to any changes in volume of the tumor [corrected].

Differential chemosensitivity of local and metastatic human gastric cancer after orthotopic transplantation of histologically intact tumor tissue in nude mice

We have established a metastatic model of human gastric cancer using orthotopic transplantation of histologically intact tissue in nude mice, and have used this model to evaluate the effects of immunochemotherapy using OK-432, 5-fluorouracil (5-FU) and mitomycin C (MMC) against SC-I-NU, a human stomach cancer line. One-quarter or one-half maximum tolerated doses (MTDs) of 5-FU or MMC resulted in a significant reduction of stomach tumor growth, while liver metastases were not reduced, possibly due to suppression of natural killer (NK)-cell activity by both drugs. On the other hand, when combined with OK-432, half MTDs of 5-FU and MMC significantly reduced liver metastases, with synergistic reduction of stomach tumor growth, possibly reflecting a rescue of NK-cell activity by treatment with OK-432. This metastatic model of human stomach cancer shows that locally growing and metastatic tumors may have different chemosensitivities, and provides the opportunity to test both with various treatment regimens.

Rhabdomyosarcoma. From the laboratory to the clinic

The prospect of identifying and developing new agents for treatment of rhabdomyosarcomas is discussed in the light of current prognosis for children with advanced stage disease. Preliminary attempts to identify tumor-specific agents using in vitro cell culture show potential promise, but as yet remain unproven. The more complex system of identifying therapeutically active agents using human tumor xenografts has demonstrated usefulness. The potential problems associated with this system are discussed.

Prediction of ACNU plasma concentration-time profiles in humans by animal scale-up

Plasma concentration-time profiles of nimustine hydrochloride, 1-[(4-amino-2-methyl-5-pyrimidinyl)methyl]-3-(2-chloroethyl)-3-nitrosour ea hydrochloride (ACNU), in the mouse, rat, rabbit, and dog were determined by high-performance liquid chromatographic analysis. The pharmacokinetic parameters for these four animal species and previously reported clinical data were analyzed for investigation of interspecies correlation. Log-log plots of body weight (W; kg) vs total plasma clearance (CLtot,p; ml/min) and steady-state distribution volume (Vd,ss; l) for the four animal species were linear, with high correlation coefficients (r 0.996 for both parameters), despite the fact that the nonrenal clearance was greater than 97% in these species. Linear regression on the plots excluding human data yielded allometric equations (CLtot,p = 50.6 W0.957; Vd, ss = 1.29 W1.03) that were extrapolated to predict ACNU pharmacokinetic parameters in humans. For both parameters, however, there were 3-fold differences between the predicted and observed parametric values. To investigate these discrepancies, we measured serum protein binding of ACNU in these animal species and in humans. The values of CLtot,p and Vd,ss were converted into those of CLutot,p and Vd,uss, which correspond to the parameters for unbound ACNU. In this case, correlation coefficients of the log-log plots excluding human data (CLutot,p = 71.7 W0.891; Vd,uss = 1.82 W0.966) were also high (r greater than or equal to 0.991). The extrapolated values vs those observed in a 70-kg human were the following: CLutot,p, 3,160 vs 2,290 ml/min; Vd,uss, 110 vs 106 l. Thus, the animal data were successfully extrapolated to yield better predictions of human pharmacokinetic parameters if the analysis was based on the unbound plasma concentration of ACNU. In addition, the predicted plasma concentration-time profile for humans also showed good agreement with the observed ones. These results suggest the importance of measuring unbound fractions of drugs for more accurate prediction of human pharmacokinetic parameters by extrapolation of animal data to the human situation.

Evaluation of antitumor activity in a human breast tumor/nude mouse model with a special emphasis on treatment dose

Eight lines of human breast tumors implanted in nude mice were treated with various antitumor agents at two different doses, maximum tolerated doses (MTD) and rational doses (RD) that were pharmacokinetically equivalent to the clinical doses; the response rates to both doses were compared. With MTD, the response rates to mitomycin C and vinblastine were 100%, and those to other agents including cyclophosphamide, nimustine (a water-soluble nitrosourea), vincristine, Adriamycin (doxorubicin; Adria Laboratories, Columbus, OH), 5-fluorouracil (5-FU), and methotrexate were 30%-50%, indicating high responsiveness to the former two agents. In contrast, when the RD were used, the response rates to the majority of these agents were 25%-40%, and those to vincristine and nimustine were 13% and 0%, respectively. These results agree with the reported clinical results compared with those with MTD, suggesting the importance of the use of clinically equivalent doses in the evaluation of antitumor efficacy in a human tumor/nude mouse system.

Responsiveness of human lung cancer/nude mouse to antitumor agents in a model using clinically equivalent doses

The responses of 14 lines of human lung cancer xenografts in BALB/c-nu/nu mice to eight known antitumor agents were investigated. These xenografts consisted of four small-cell carcinomas (SCLC) and ten non-small-cell carcinomas (four large cell, three squamous cell, and three adenocarcinomas; NSCLC). The doses used in the experiments were the maximum tolerated dose (MTD) in nude mice and the "rational dose" (RD), the latter considered to be pharmacokinetically equivalent to the clinical dose. When given at MTDs, all drugs except 5-fluorouracil (5-FU) and methotrexate (MTX) were extremely effective against NSCLC as well as SCLC. The response rates of drug-sensitive SCLC to mitomycin C (MMC), ACNU, and vinblastine (VLB) were 100%, and those to Adriamycin (ADR) and vincristine (VCR) were 75%. In addition, the response rates of even drug-resistant NSCLC to MMC and VLB were 70% and 90%, respectively. In contrast, the response rates of NSCLC to RDs of the drugs were reduced to less than 40% and corresponded well to the respective clinical rates. In SCLC, a good correlation of experimental and clinical response rates was observed with four drugs [cyclophosphamide (CPM), ACNU, VLB, and 5-FU]. As a result, we emphasize that a more reasonable prediction of the clinical effectiveness of antitumor agents can be made by a protocol using clinically equivalent doses.

Responsiveness of human gastric tumors implanted in nude mice to clinically equivalent doses of various antitumor agents

To reproduce clinical effects of various antitumor agents in the human tumor/nude mouse model, we investigated the responsiveness of 11 lines of human gastric tumor xenografts to doses of the agents pharmacokinetically equivalent to the respective clinical doses, which we designated the "rational dose" (RD). We found that the response rates to mitomycin C, 3-[(4-amino-2-methyl-5-pyrimidinyl]methyl-1-[2-chloroethyl]-1- nitrosourea (ACNU), adriamycin, 5-fluorouracil were 18%, and that to vinblastine was 30%; on the other hand, those to vincristine, methotrexate, and cyclophosphamide were poor. In contrast, in our previous study using the maximum tolerated doses, response rates to mitomycin C, ACNU, and vinblastine were as high as 64-82%, and those to adriamycin and 5-fluorouracil were 18%. When these results were compared with the clinical response rates of gastric tumors, as a whole, the results with RD's exhibited much better coincidence with the clinical data in terms of relative therapeutic potency, indicating the validity of the use of clinically equivalent doses instead of maximum tolerated doses in the human tumor model.