What do, can and should we learn from models to evaluate potential anticancer agents?

Targeted Radionuclide Therapy in Patient-Derived Xenografts Using 177Lu-EB-RGD

Currently, most patients with non-small cell lung cancer (NSCLC) are diagnosed in advanced stages with a poor five-year survival rate. Therefore, intensive research aimed at finding novel therapeutic strategies has been ongoing; experimental models that reliably emulate NSCLC disease are greatly needed to predict responses to novel therapeutics. Therefore, we developed patient-derived xenograft (PDX) models of NSCLC, which we then used to evaluate the therapeutic efficacy of ¹⁷⁷Lu-EB-RGD, a peptide-based radiopharmaceutical with improved pharmacokinetics that targets integrin α_vβ₃ In this study, three different groups of NSCLC-PDXs were successfully established, all of which maintained the same IHC and genetic characteristics of the human primary tumor. The two NSCLC-PDX groups with intense and low expression of integrin α_vβ₃ (denoted as PDX_αvβ3+ and PDX_αvβ3-) were chosen as the experimental models to evaluate the in vivo biological behavior of ¹⁷⁷Lu-EB-RGD. In SPECT imaging and biodistribution studies, ¹⁷⁷Lu-EB-RGD showed significantly higher accumulation in PDX_αvβ3+ and PDX_αvβ3- models than its corresponding monomer ¹⁷⁷Lu-RGD. A single dose of 18.5 MBq ¹⁷⁷Lu-EB-RGD was enough to completely eradicate the tumors in PDX_αvβ3+, with no sign of tumor recurrence during the observation period. Such treatment was also efficacious in PDX_αvβ3-: a single dose of 29.6 MBq ¹⁷⁷Lu-EB-RGD led to a significant delay in tumor growth as compared with that in the control or ¹⁷⁷Lu-RGD group. The preclinical data from the use of this model suggest that ¹⁷⁷Lu-EB-RGD may be an effective treatment option for NSCLC and should be further evaluated in human trials.

BRAF(V600E) Kinase Domain Duplication Identified in Therapy-Refractory Melanoma Patient-Derived Xenografts

The therapeutic landscape of melanoma is improving rapidly. Targeted inhibitors show promising results, but drug resistance often limits durable clinical responses. There is a need for in vivo systems that allow for mechanistic drug resistance studies and (combinatorial) treatment optimization. Therefore, we established a large collection of patient-derived xenografts (PDXs), derived from BRAF^V600E, NRAS^Q61, or BRAF^WT/NRAS^WT melanoma metastases prior to treatment with BRAF inhibitor and after resistance had occurred. Taking advantage of PDXs as a limitless source, we screened tumor lysates for resistance mechanisms. We identified a BRAF^V600E protein harboring a kinase domain duplication (BRAF^V600E/DK) in ∼10% of the cases, both in PDXs and in an independent patient cohort. While BRAF^V600E/DK depletion restored sensitivity to BRAF inhibition, a pan-RAF dimerization inhibitor effectively eliminated BRAF^V600E/DK-expressing cells. These results illustrate the utility of this PDX platform and warrant clinical validation of BRAF dimerization inhibitors for this group of melanoma patients.

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Patient-derived xenograft (PDX) platform comprises 89 metastatic melanoma tumors

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Platform includes several pre-vemurafenib and vemurafenib-resistant PDXs

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Duplication of the BRAF^V600E kinase domain is identified as a resistance mechanism

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Pan-RAF dimerization inhibitor LY3009120 eliminates melanoma cells with this duplication

Drugs for solid cancer: the productivity crisis prompts a rethink

Despite remarkable progress in cancer-drug discovery, the delivery of novel, safe, and sustainably effective products to the clinic has stalled. Using Src as a model, we examine key steps in drug development. The preclinical evidence on the relationship between Src and solid cancer is in sharp contrast with the modest anticancer effect noted in conventional clinical trials. Here, we consider Src inhibitors as an example of a promising drug class directed to invasion and metastasis and identify roadblocks in translation. We question the assumption that a drug-induced tumor shrinkage in preclinical and clinical studies predicts a successful outcome. Our analysis indicates that the key areas requiring attention are related, and include preclinical models (in vitro and mouse models), meaningful clinical trial end points, and an appreciation of the role of metastasis in morbidity and mortality. Current regulations do not reflect the natural history of the disease, and may be unrelated to the key complications: local invasion, metastasis, and the development of resistance. Alignment of preclinical and clinical studies and regulations based on mechanistic trial end points and platforms may help in overcoming these roadblocks. Viewed kaleidoscopically, most elements necessary and sufficient for a novel translational paradigm are in place.

Translational pharmacokinetic-pharmacodynamic modeling from nonclinical to clinical development: a case study of anticancer drug, crizotinib

Attrition risk related to efficacy is still a major reason why new chemical entities fail in clinical trials despite recently increased understanding of translational pharmacology. Pharmacokinetic-pharmacodynamic (PKPD) analysis is key to translating in vivo drug potency from nonclinical models to patients by providing a quantitative assessment of in vivo drug potency with mechanistic insight of drug action. The pharmaceutical industry is clearly moving toward more mechanistic and quantitative PKPD modeling to have a deeper understanding of translational pharmacology. This paper summarizes an anticancer drug case study describing the translational PKPD modeling of crizotinib, an orally available, potent small molecule inhibitor of multiple tyrosine kinases including anaplastic lymphoma kinase (ALK) and mesenchymal-epithelial transition factor (MET), from nonclinical to clinical development. Overall, the PKPD relationships among crizotinib systemic exposure, ALK or MET inhibition, and tumor growth inhibition (TGI) in human tumor xenograft models were well characterized in a quantitative manner using mathematical modeling: the results suggest that 50% ALK inhibition is required for >50% TGI whereas >90% MET inhibition is required for >50% TGI. Furthermore, >75% ALK inhibition and >95% MET inhibition in patient tumors were projected by PKPD modeling during the clinically recommended dosing regimen, twice daily doses of crizotinib 250 mg (500 mg/day). These simulation results of crizotinib-mediated ALK and MET inhibition appeared consistent with the currently reported clinical responses. In summary, the present paper presents an anticancer drug example to demonstrate that quantitative PKPD modeling can be used for predictive translational pharmacology from nonclinical to clinical development.

Patient-derived xenografts of non small cell lung cancer: resurgence of an old model for investigation of modern concepts of tailored therapy and cancer stem cells

Current chemotherapy regimens have unsatisfactory results in most advanced solid tumors. It is therefore imperative to devise novel therapeutic strategies and to optimize selection of patients, identifying early those who could benefit from available treatments. Mouse models are the most valuable tool for preclinical evaluation of novel therapeutic strategies in cancer and, among them, patient-derived xenografts models (PDX) have made a recent comeback in popularity. These models, obtained by direct implants of tissue fragments in immunocompromised mice, have great potential in drug development studies because they faithfully reproduce the patient's original tumor for both immunohistochemical markers and genetic alterations as well as in terms of response to common therapeutics They also maintain the original tumor heterogeneity, allowing studies of specific cellular subpopulations, including their modulation after drug treatment. Moreover PDXs maintain at least some aspects of the human microenvironment for weeks with the complete substitution with murine stroma occurring only after 2-3 passages in mouse and represent therefore a promising model for studies of tumor-microenvironment interaction. This review summarizes our present knowledge on mouse preclinical cancer models, with a particular attention on patient-derived xenografts of non small cell lung cancer and their relevance for preclinical and biological studies.

Pharmacokinetic/pharmacodynamic modeling of crizotinib for anaplastic lymphoma kinase inhibition and antitumor efficacy in human tumor xenograft mouse models

Crizotinib [Xalkori; PF02341066; (R)-3-[1-(2,6-dichloro-3-fluoro-phenyl)-ethoxy]-5-(1-piperidin-4-yl-1H-pyrazol-4-yl)-pyridin-2-ylamine] is an orally available dual inhibitor of anaplastic lymphoma kinase (ALK) and hepatocyte growth factor receptor. The objectives of the present studies were to characterize: 1) the pharmacokinetic/pharmacodynamic relationship of crizotinib plasma concentrations to the inhibition of ALK phosphorylation in tumors, and 2) the relationship of ALK inhibition to antitumor efficacy in human tumor xenograft models. Crizotinib was orally administered to athymic nu/nu mice implanted with H3122 non-small-cell lung carcinomas or severe combined immunodeficient/beige mice implanted with Karpas299 anaplastic large-cell lymphomas. Plasma concentration-time courses of crizotinib were adequately described by a one-compartment pharmacokinetic model. A pharmacodynamic link model reasonably fit the time courses of ALK inhibition in both H3122 and Karpas299 models with EC(50) values of 233 and 666 ng/ml, respectively. A tumor growth inhibition model also reasonably fit the time course of individual tumor growth curves with EC(50) values of 255 and 875 ng/ml, respectively. Thus, the EC(50) for ALK inhibition approximately corresponded to the EC(50) for tumor growth inhibition in both xenograft models, suggesting that >50% ALK inhibition would be required for significant antitumor efficacy (>50%). Furthermore, based on the observed clinical pharmacokinetic data coupled with the pharmacodynamic parameters obtained from the present nonclinical xenograft mouse model, >70% ALK inhibition was projected in patients with non-small-cell lung cancer who were administered the clinically recommended dosage of crizotinib, twice-daily doses of 250 mg (500 mg/day). The result suggests that crizotinib could sufficiently inhibit ALK phosphorylation for significant antitumor efficacy in patients.

How can grafted breast cancer models be optimized?

Breast cancer is the most frequent spontaneous malignancy diagnosed in women and is characterized by a broad histological diversity. Progression of the disease has a metastasizing trend and can be resistant to hormonal and chemotherapy. Animal models have provided some understanding of these features and have allowed new treatments to be proposed. However, these models need to be revised because they have some limitations in predicting the clinical efficacy of new therapies. In this review, we discuss the biological criteria to be taken into account for a realistic animal model of breast cancer graft (tumor implantation site, animal immune status, histological diversity, modern imaging). We emphasize the need for more stringent monitoring criteria, and suggest adopting the human RECIST (Response Evaluation Criteria in Solid Tumors) criteria to evaluate treatments in animal models.

Genetically engineered mouse models of diffuse gliomas

Over the last decade, genetically engineered mouse models have been extensively used to dissect the genetic requirements for neoplastic initiation and progression of diffuse gliomas. While these models faithfully recapitulate the histopathological features of human gliomas, comparative genomic analyses are increasingly being utilized to comprehensively assess their fidelity to recently identified molecular subtypes of these tumors. Future progress with these models will rely on incorporating insights not only from oncogenomics studies of cancer, but also from the developmental neuroscience and stem cell biology fields to design accurate and experimentally tractable models for use in translational cancer research, particularly for experimental therapeutics studies of molecularly defined subtypes of gliomas.

Leukemia-free survival as a surrogate end point for overall survival in the evaluation of maintenance therapy for patients with acute myeloid leukemia in complete remission

BACKGROUND

In trials designed to evaluate new therapies for hematologic malignancies, end points such as leukemia-free survival are often used as surrogates for overall survival in acute leukemia. We aimed to assess whether leukemia-free survival is an acceptable statistical surrogate for overall survival when applied to remission maintenance therapy for acute myeloid leukemia.

DESIGN AND METHODS

Data were analyzed from a randomized Phase III trial of remission maintenance immunotherapy with histamine dihydrochloride plus low-dose interleukin-2 versus no treatment in adults with acute myeloid leukemia. A two-stage surrogate validation model was applied in which correlations between Kaplan-Meier estimates of leukemia-free survival and overall survival, and between log hazard ratios reflecting treatment effects were analyzed. Country of patient enrollment was the unit of analysis.

RESULTS

Kaplan-Meier estimates of overall survival at 36, 48, and 60 months and leukemia-free survival at 24 months were reasonably correlated (R(2) ranging from 0.44 to 0.84) both for the overall (n=320) and first complete remission (n=261) populations. The effects of histamine dihydrochloride/interleukin-2 on log hazard ratios for leukemia-free survival and overall survival were well correlated (R(2)=0.88-0.93).

CONCLUSIONS

The significant correlations between overall survival and the surrogate end point (leukemia-free survival) and between the effect of histamine dihydrochloride/interleukin-2 on leukemia-free survival and overall survival satisfy the two-stage surrogate validation model.

Assessment of the consistency and robustness of results from a multicenter trial of remission maintenance therapy for acute myeloid leukemia

Background

Data from a randomized multinational phase 3 trial of 320 adults with acute myeloid leukemia (AML) demonstrated that maintenance therapy with 3-week cycles of histamine dihydrochloride plus low-dose interleukin-2 (HDC/IL-2) for up to 18 months significantly improved leukemia-free survival (LFS) but lacked power to detect an overall survival (OS) difference.

Purpose

To assess the consistency of treatment benefit across patient subsets and the robustness of data with respect to trial centers and endpoints.

Methods

Forest plots were constructed with hazard ratios (HRs) of HDC/IL-2 treatment effects versus no treatment (control) for prospectively defined patient subsets. Inconsistency coefficients (I²) and interaction tests (X²) were used to detect any differences in benefit among subsets. Robustness of results to the elimination of individual study centers was performed using "leave-one-center-out" analyses. Associations between treatment effects on the endpoints were evaluated using weighted linear regression between HRs for LFS and OS estimated within countries.

Results

The benefit of HDC/IL-2 over controls was statistically consistent across all subsets defined by baseline prognostic variables. I² and P-values of X² ranged from 0.00 to 0.51 and 0.14 to 0.91, respectively. Treatment effects were statistically significant in 14 of 28 subsets analyzed. The "leave-one-center-out" analysis confirmed that no single center dominated (P-values ranged from 0.004 to 0.020 [mean 0.009]). The HRs representing the HDC/IL-2 effects on LFS and OS were strongly correlated at the country level (R² = 0.84).

Limitations

Small sample sizes in some of the subsets analyzed.

Conclusions

These analyses confirm the consistency and robustness of the HDC/IL-2 effect as compared with no treatment. LFS may be an acceptable surrogate for OS in future AML trials. Analyses of consistency and robustness may aid interpretation of data from multicenter trials, especially in populations with rare diseases, when the size of randomized clinical trials is limited.

Trial Registration

ClinicalTrials.gov: NCT00003991

Impact of metronomic UFT/cyclophosphamide chemotherapy and antiangiogenic drug assessed in a new preclinical model of locally advanced orthotopic hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is an intrinsically chemotherapy refractory malignancy. Development of effective therapeutic regimens would be facilitated by improved preclinical HCC models. Currently, most models consist of subcutaneous human tumor transplants in immunodeficient mice; however, these do not reproduce the extensive liver disease associated with HCC or metastasize. To address this deficiency, we developed an orthotopic model. Human HCC cells were transfected with the gene encoding secretable beta-subunit human choriogonadotropin (beta-hCG), which was used as a surrogate marker of tumor burden. The HCC cells were implanted into the left liver lobe of severe combined immunodeficient (SCID) mice, after which the efficacy of different therapies was evaluated on established, but liver-confined human Hep3B cell line HCC. Treatments included sorafenib or metronomic chemotherapy using cyclophosphamide (CTX), UFT, an oral 5-fluorouracil prodrug, or doxorubicin either alone or in various combinations, with or without an antiangiogenic agent, DC101, an anti-vascular endothelial growth factor receptor-2 antibody. Sorafenib inhibited tumor growth in a dose-dependent manner but caused severe weight loss in SCID mice, thus necessitating use of DC101 in subsequent experiments. Although less toxicity was observed using either single or doublet metronomic chemotherapy without any added antiangiogenic agent, none, provided survival benefit. In contrast, significantly improved overall survival was observed using various combinations of metronomic chemotherapy regimens such as UFT + CTX with DC101. In conclusion, using this model of liver-confined but advanced HCC suggests that the efficacy of a targeted antiangiogenic drug or metronomic chemotherapy can be mutually enhanced by concurrent combination treatment.

Models for prevention and treatment of cancer: problems vs promises

Current estimates from the American Cancer Society and from the International Union Against Cancer indicate that 12 million cases of cancer were diagnosed last year, with 7 million deaths worldwide; these numbers are expected to double by 2030 (27 million cases with 17 million deaths). Despite tremendous technological developments in all areas, and President Richard Nixon's initiative in the 1974 "War against Cancer", the US cancer incidence is the highest in the world and the cancer death rate has not significantly changed in the last 50 years (193.9 per 100,000 in 1950 vs 193.4 per 100,000 in 2002). Extensive research during the same time, however, has revealed that cancer is a preventable disease that requires major changes in life style; with one third of all cancers assigned to Tobacco, one third to diet, and remaining one third to the environment. Approximately 20 billion dollars are spent annually to find a cure for cancer. We propose that our inability to find a cure to cancer lies in the models used. Whether cell culture or animal studies, no model has yet been found that can reproduce the pathogenesis of the disease in the laboratory. Mono-targeted therapies, till know in most cases, have done a little to make a difference in cancer treatment. Similarly, molecular signatures/predictors of the diagnosis of the disease and response are also lacking. This review discusses the pros and cons of current cancer models based on cancer genetics, cell culture, animal models, cancer biomarkers/signature, cancer stem cells, cancer cell signaling, targeted therapies, therapeutic targets, clinical trials, cancer prevention, personalized medicine, and off-label uses to find a cure for cancer and demonstrates an urgent need for "out of the box" approaches.

Antitumor efficacy testing in rodents

The preclinical research and human clinical trials necessary for developing anticancer therapeutics are costly. One contributor to these costs is preclinical rodent efficacy studies, which, in addition to the costs associated with conducting them, often guide the selection of agents for clinical development. If inappropriate or inaccurate recommendations are made on the basis of these preclinical studies, then additional costs are incurred. In this commentary, I discuss the issues associated with preclinical rodent efficacy studies. These include the identification of proper preclinical efficacy models, the selection of appropriate experimental endpoints, and the correct statistical evaluation of the resulting data. I also describe important experimental design considerations, such as selecting the drug vehicle, optimizing the therapeutic treatment plan, properly powering the experiment by defining appropriate numbers of replicates in each treatment arm, and proper randomization. Improved preclinical selection criteria can aid in reducing unnecessary human studies, thus reducing the overall costs of anticancer drug development.