Phase Ib study of CP-868,596, a PDGFR inhibitor, combined with docetaxel with or without axitinib, a VEGFR inhibitor

Phase I/Ib study of crenolanib with ramucirumab and paclitaxel as second-line therapy for advanced esophagogastric adenocarcinoma

PURPOSE

Paclitaxel plus ramucirumab is a standard second-line regimen for patients with advanced gastric adenocarcinoma, but clinical benefit remains modest. One potential resistance mechanism to VEGFR2 inhibition is activation of the PDGF/PDGFR pathway, which can be blocked by the selective inhibitor crenolanib. Therefore, we performed a phase I/Ib study of crenolanib in combination with paclitaxel/ramucirumab.

METHODS

Patients with metastatic esophagogastric adenocarcinoma refractory to first-line therapy received escalating doses of crenolanib [60 mg twice daily (BID) to 100 mg three times daily (TID)] in combination with paclitaxel 80 mg/m2 intravenously on days 1, 8 and 15 and ramucirumab 8 mg/kg intravenously on days 1 and 15 of a 28-day cycle. The primary objective was to determine the maximally tolerated dose (MTD) of crenolanib. Additional patients were enrolled in the dose expansion cohort to assess 6-month progression-free survival (PFS) at the MTD.

RESULTS

We enrolled 19 patients in the dose escalation phase and 8 patients in the dose expansion phase at the MTD of crenolanib 100 mg BID. Common grade 3/4 treatment-emergent adverse events included leukopenia (19%), anemia (11%) and neutropenia (11%). In the 14 patients treated at the MTD, 6-month PFS was 43% [95% confidence interval (CI) 23-78%] and the objective response rate (ORR) was 42% (95% CI 15-72%). The trial was terminated early due to withdrawal of crenolanib by the sponsor.

CONCLUSIONS

The addition of crenolanib to paclitaxel/ramucirumab is safe and well-tolerated at a dose level up to 100 mg BID.

CLINICAL TRIAL REGISTRATION

NCT03193918. June 19, 2017.

Phase I study using crenolanib to target PDGFR kinase in children and young adults with newly diagnosed DIPG or recurrent high-grade glioma, including DIPG

Background

Platelet-derived growth factor receptor (PDGFR) signaling has been directly implicated in pediatric high-grade gliomagenesis. This study evaluated the safety and tolerability of crenolanib, a potent, selective inhibitor of PDGFR-mediated phosphorylation, in pediatric patients with high-grade glioma (HGG).

Methods

We used a rolling-6 design to study the maximum tolerated dose (MTD) of once-daily crenolanib administered during and after focal radiation therapy in children with newly diagnosed diffuse intrinsic pontine glioma (DIPG) (stratum A) or with recurrent/progressive HGG (stratum B). Pharmacokinetics were studied during the first cycle at the first dose and at steady state (day 28). Alterations in PDGFRA were assessed by Sanger or exome sequencing and interphase fluorescence in situ hybridization or single nucleotide polymorphism arrays.

Results

Fifty evaluable patients were enrolled in the 2 strata, and an MTD of 170 mg/m² was established for both. Dose-limiting toxicities were primarily liver enzyme elevations and hematologic count suppression in both strata. Crenolanib AUC_0-48h and C _MAX did not differ significantly for crushed versus whole-tablet administration. Overall, PDGFRA alterations were observed in 25% and 30% of patients in stratum A and B, respectively. Neither crenolanib therapy duration nor survival outcomes differed significantly by PDGFRA status, and overall survival of stratum A was similar to that of historical controls.

Conclusions

Children tolerate crenolanib well at doses slightly higher than the established MTD in adults, with a toxicity spectrum generally similar to that in adults. Studies evaluating intratumoral PDGFR pathway inhibition in biomarker-enriched patients are needed to evaluate further the clinical utility of crenolanib in this population.

Design of New Therapeutic Agents Targeting FLT3 Receptor Tyrosine Kinase Using Molecular Docking and 3D-QSAR Approach

Background:

FMS-like tyrosine kinase-3 (FLT3) belongs to the class III Receptor Tyrosine Kinase (RTK) family. FLT3 is involved in normal hematopoiesis and is generally expressed in early hematopoietic progenitor cells. Mutations either with an internal tandem duplication of FMS-like tyrosine kinase-3 (FLT3-ITD) or point mutation at the activation loop leads to the Acute Myeloid Leukemia (AML), a highly heterogeneous disease. Thus, FLT3 is an important therapeutic target for AML.

Method:

In the present work, docking and 3D-QSAR techniques were performed on a series of diaminopyrimidine derivatives as FLT3 kinase antagonists.

Results:

Docking study recognized important active site residues such as Leu616, Gly617, Val624, Ala642, Phe830, Tyr693, Cys694, Cys695, Tyr696 and Gly697 that participate in the inhibition of FLT3 kinase. Receptor-based CoMFA, RF-CoMFA and CoMSIA models were developed. RFCoMFA model revealed relatively better statistical results compared to other models. Furthermore, the selected RF-CoMFA model was evaluated using various validation techniques. Contour maps of the RF-CoMFA illustrated that steric and electronegative substitutions were favored at R1 position whereas steric and electropositive substitutions were favored at R2 position to enhance the potency.

Conclusion:

Based on the designed strategy, we derived from the contour map analysis, 14 novel FLT3 inhibitors were designed and their activities were predicted. These designed inhibitors exhibited more potent activity than the most active compounds of the dataset.

Integrated Molecular Characterization of Gastrointestinal Stromal Tumors (GIST) Harboring the Rare D842V Mutation in PDGFRA Gene

Gastrointestinal stromal tumors (GIST) carrying the D842V activating mutation in the platelet-derived growth factor receptor alpha (PDGFRA) gene are a very rare subgroup of GIST (about 10%) known to be resistant to conventional tyrosine kinase inhibitors (TKIs) and to show an indolent behavior. In this study, we performed an integrated molecular characterization of D842V mutant GIST by whole-transcriptome and whole-exome sequencing coupled with protein–ligand interaction modelling to identify the molecular signature and any additional recurrent genomic event related to their clinical course. We found a very specific gene expression profile of D842V mutant tumors showing the activation of G-protein-coupled receptor (GPCR) signaling and a relative downregulation of cell cycle processes. Beyond D842V, no recurrently mutated genes were found in our cohort. Nevertheless, many private, clinically relevant alterations were found in each tumor (TP53, IDH1, FBXW7, SDH-complex). Molecular modeling of PDGFRA D842V suggests that the mutant protein binds imatinib with lower affinity with respect to wild-type structure, showing higher stability during the interaction with other type I TKIs (like crenolanib). D842V mutant GIST do not show any actionable recurrent molecular events of therapeutic significance, therefore this study supports the rationale of novel TKIs development that are currently being evaluated in clinical studies for the treatment of D842V mutant GIST.

Discovery of a Diaminopyrimidine FLT3 Inhibitor Active against Acute Myeloid Leukemia

Profiling of the kinase-binding capabilities of an aminopyrimidine analogue detected in a cellular screen of the St. Jude small-molecule collection led to the identification of a novel series of FMS-like tyrosine kinase 3 (FLT3) inhibitors. Structure-activity relationship studies led to the development of compounds exhibiting good potency against MV4-11 and MOLM13 acute myelogenous leukemia cells driven by FLT3, regardless of their FLT3 mutation status. In vitro pharmacological profiling demonstrated that compound 5e shows characteristics suitable for further preclinical development.

Targeted antiangiogenic agents in combination with cytotoxic chemotherapy in preclinical and clinical studies in sarcoma

Sarcomas are a heterogeneous group of mesenchymal malignancies. In recent years, studies have demonstrated that inhibition of angiogenic pathways or disruption of established vasculature can attenuate the growth of sarcomas. However, when used as monotherapy in the clinical setting, these targeted antiangiogenic agents have only provided modest survival benefits in some sarcoma subtypes, and have not been efficacious in others. Preclinical and early clinical data suggest that the addition of conventional chemotherapy to antiangiogenic agents may lead to more effective therapies for patients with these tumors. In the current review, the authors summarize the available evidence and possible mechanisms supporting this approach.

The design and discovery of water soluble 4-substituted-2,6-dimethylfuro[2,3-d]pyrimidines as multitargeted receptor tyrosine kinase inhibitors and microtubule targeting antitumor agents

The design, synthesis and biological evaluations of fourteen 4-substituted 2,6-dimethylfuro[2,3-d]pyrimidines are reported. Four compounds (11-13, 15) inhibit vascular endothelial growth factor receptor-2 (VEGFR-2), platelet-derived growth factor receptor β (PDGFR-β), and target tubulin leading to cytotoxicity. Compound 11 has nanomolar potency, comparable to sunitinib and semaxinib, against tumor cell lines overexpressing VEGFR-2 and PDGFR-β. Further, 11 binds at the colchicine site on tubulin, depolymerizes cellular microtubules and inhibits purified tubulin assembly and overcomes both βIII-tubulin and P-glycoprotein-mediated drug resistance, and initiates mitotic arrest leading to apoptosis. In vivo, its HCl salt, 21, reduced tumor size and vascularity in xenograft and allograft murine models and was superior to docetaxel and sunitinib, without overt toxicity. Thus 21 affords potential combination chemotherapy in a single agent.

FLT3 inhibitors for acute myeloid leukemia: a review of their efficacy and mechanisms of resistance

Since the Food and Drug Administration approval of imatinib for treatment of chronic myeloid leukemia in 2001, tyrosine kinase inhibitors (TKIs) have become a mainstay in the care of many malignancies. In acute myeloid leukemia (AML), activating mutations in the FMS-like tyrosine kinase 3 (FLT3) gene result in survival and proliferation of leukemic blasts and are associated with adverse prognosis. Therefore, the FLT3 receptor is an appealing target for inhibition. Multiple small molecule TKIs are currently in development for FLT3-mutated AML, and agents are beginning to show promising efficacy. In other malignancies, the development of resistance to TKIs during the course of therapy has proven to be a challenge, and thus far, in clinical trials of FLT3 TKIs, resistance to inhibition represents a significant barrier to successful FLT3 inhibition. Understanding the mechanisms of resistance and overcoming these obstacles to target inhibition will be central to the success of these agents.

Crenolanib inhibits the drug-resistant PDGFRA D842V mutation associated with imatinib-resistant gastrointestinal stromal tumors

PURPOSE

To determine the potential of crenolanib, a potent inhibitor of PDGFRA, to treat malignancies driven by mutant PDGFRA.

EXPERIMENTAL DESIGN

The biochemical activity of crenolanib was compared with imatinib using a panel of PDGFRA-mutant kinases expressed in several different cell line models, including primary gastrointestinal stromal tumors (GIST) cells. The antiproliferative activity of crenolanib was also studied in several cell lines with PDGFRA-dependent growth.

RESULTS

Crenolanib was significantly more potent than imatinib in inhibiting the kinase activity of imatinib-resistant PDGFRA kinases (D842I, D842V, D842Y, DI842-843IM, and deletion I843). For example, crenolanib was 135-fold more potent than imatinib against D842V in our isogenic model system, with an IC(50) of approximately 10 nmol/L. The relative potency of crenolanib was further confirmed in BaF3 and primary GIST cells expressing PDGFRA D842V. In contrast, imatinib was at least 10-fold more potent than crenolanib in inhibiting the V561D mutation. For all other tested PDGFRA mutations, crenolanib and imatinib had comparable potency.

CONCLUSIONS

Crenolanib is a potent inhibitor of imatinib-resistant PDGFRA kinases associated with GIST, including the PDGFRA D842V mutation found in approximately 5% of GISTs. The spectrum of activity of crenolanib suggests that this drug is a type I inhibitor (inhibitor of activated conformation of kinase). Based in part on these results, a phase II clinical study of this agent to treat GIST with the PDGFRA D842V mutation has been initiated.

Optimizing targeted cancer therapy: towards clinical application of systems biology approaches

In cancer, genetic and epigenetic alterations ultimately culminate in discordant activation of signal transduction pathways driving the malignant process. Pharmacological or biological inhibition of such pathways holds significant promise with respect to devising rational therapy for cancer. Thus, technical concepts pursuing robust characterization of kinase activity in tissue samples from cancer patients have been subject of investigation. In the present review we provide a comprehensive overview of these techniques and discuss their advantages and disadvantages for systems biology approaches to identify kinase targets in oncological disease. Recent advances in the development and application of array-based peptide-substrate kinase activity screens show great promise in overcoming the discrepancy between the evaluation of aberrant cell signaling in specific malignancies or even individual patients and the currently available ensemble of highly specific targeted treatment strategies. These developments have the potential to result in a more effective selection of kinase inhibitors and thus optimize mechanism-based patient-specific therapeutic strategies. Given the results from current research on the tumor kinome, generating network views on aberrant tumor cell signaling is critical to meet this challenge.

Axitinib targeted cancer stemlike cells to enhance efficacy of chemotherapeutic drugs via inhibiting the drug transport function of ABCG2

Stemlike cells have been isolated by their ability to efflux Hoechst 33342 dye and are called the side population (SP). We evaluated the effect of axitinib on targeting cancer stemlike cells and enhancing the efficacy of chemotherapeutical agents. We found that axitinib enhanced the cytotoxicity of topotecan and mitoxantrone in SP cells sorted from human lung cancer A549 cells and increased cell apoptosis induced by chemotherapeutical agents. Moreover, axitinib particularly inhibited the function of adenosine triphosphate (ATP)-binding cassette subfamily G member 2 (ABCG2) and reversed ABCG2-mediated multidrug resistance (MDR) in vitro. However, no significant reversal effect was observed in ABCB1-, ABCC1- or lung resistance-related protein (LRP)-mediated MDR. Furthermore, in both sensitive and MDR cancer cells axitinib neither altered the expression of ABCG2 at the mRNA or protein levels nor blocked the phosphorylation of AKT and extracellular signal-regulated kinase (ERK)1/2. In nude mice bearing ABCG2-overexpressing S1-M1-80 xenografts, axitinib significantly enhanced the antitumor activity of topotecan without causing additional toxicity. Taken together, these data suggest that axitinib particularly targets cancer stemlike cells and reverses ABCG2-mediated drug resistance by inhibiting the transporter activity of ABCG2.

Gastrointestinal stromal tumors: a review of case reports, diagnosis, treatment, and future directions

Gastrointestinal stromal tumor (GIST) is a nonepithelial, mesenchymal tumor first described by Mazur and Clark in 1983. Since then, its molecular biology has been studied in great detail. Special interest in the role of tyrosine kinase in its regulation has been the target by different drug research. Mutation in c-kit exons 9, 11, 13, 17 and PDGFRA mutation in exons 12, 14, 18 are responsible for activation of gene signaling system resulting in uncontrolled phosphorylation and tissue growth. However, 5 to 15% of GISTs does not harbor these mutations, which raises additional questions in another alternate signaling pathway mutation yet to be discovered. Diagnosis of GISTs relies heavily on KIT/CD117 immunohistochemical staining, which can detect most GISTs except for a few 3% to 5% that harbors PDGFRA mutation. Newer staining against PKC theta and DOG-1 genes showed promising results but are not readily available. Clinical manifestation of GISTs is broad and highly dependent on tumor size. Surgery still remains the first-line treatment for GISTs. The advancement of molecular biology has revolutionized the availability of newer drugs, Imatinib and Sunitinib. Together with its advancement is the occurrence of Imatinib/Sunitinib drug resistance. With this, newer monoclonal antibody drugs are being developed and are undergoing clinical trials to hopefully improve survival in patients with GISTs.