Novel pyrrole carboxamide inhibitors of JAK2 as potential treatment of myeloproliferative disorders.

Compound 1, a hit from the screening of our chemical collection displaying activity against JAK2, was deconstructed for SAR analysis into three regions, which were explored. A series of compounds was synthesized leading to the identification of the potent and orally bioavailable JAK2 inhibitor 16 (NMS-P830), which showed an encouraging tumour growth inhibition in SET-2 xenograft tumour model, with evidence for JAK2 pathway suppression demonstrated by in vivo pharmacodynamic effects.

Pyrrole-3-carboxamides as potent and selective JAK2 inhibitors.

We report herein the discovery, structure guided design, synthesis and biological evaluation of a novel class of JAK2 inhibitors. Optimization of the series led to the identification of the potent and orally bioavailable JAK2 inhibitor 28 (NMS-P953). Compound 28 displayed significant tumour growth inhibition in SET-2 xenograft tumour model, with a mechanism of action confirmed in vivo by typical modulation of known biomarkers, and with a favourable pharmacokinetic and safety profile.

Phase I study of the safety, tolerability and pharmacokinetics of PHA-848125AC, a dual tropomyosin receptor kinase A and cyclin-dependent kinase inhibitor, in patients with advanced solid malignancies.

PURPOSE: This phase I trial assessed the safety, maximally tolerated dose (MTD) and pharmacokinetics of TRKA/CDK inhibitor PHA-848125AC in adult patients with advanced/metastatic solid tumors. PATIENTS AND METHODS: Patients with relapsed or refractory solid tumors, for which no standard therapy existed, were eligible. PHA-848125AC was administered orally in two schedules: daily for 7 consecutive days in 2-week cycles (i.e. 7 days on/7 days off q2wks; S1) or daily for 4 consecutive days a week for 3 weeks in 4-week cycles (i.e. 4 days on/3 days off x 3wks q4wks; S2). RESULTS: Thirty-seven patients were treated in this study, 22 in S1 and 15 in S2. The recommended phase II dose (RP2D) was 150 mg/day for either schedule. The dose-limiting toxicities (DLTs) in S1 included ataxia (Grade 2-4) and tremors (Grade 2-3). In S2, DLTs included tremors (Grade 2-3), elevated lipase (Grade 3), increased creatinine (Grade 2), and nausea and vomiting (Grade 3). These events were all reversible. In S2, out of 14 patients evaluable for efficacy, 2 patients with thymic carcinoma, showed partial response and stable disease was observed in 3 patients. Stable disease was observed in 6 out 14 patients evaluable for efficacy on S1. Drug pharmacokinetics demonstrated a half-life of approximately 33 h, and dose-proportionality with accumulation by a factor of 3 after repeated administrations. CONCLUSION: The RP2D of PHA-848125AC was 150 mg/day on both schedules. Based on the responses noted in thymic carcinoma, a phase II study for patients with that disease is currently enrolling.

Miniaturizing bromodeoxyuridine incorporation enables the usage of flow cytometry for cell cycle analysis of adherent tissue culture cells for high throughput screening.

Analysis of cell cycle progression by 5-bromo-2'-deoxyuridine (BrdU) incorporation is commonly used for evaluating the mode of action of anticancer drugs, but usually requires a high number of cells and large amounts of monoclonal antibodies. In addition, manual sample handling is not suitable for high throughput. To circumvent these limitations, we have developed a miniaturized method to measure BrdU incorporation into DNA directly in 96-wells plates. Adherent cells were grown in 96-well plates in the absence or presence of compounds of interest. After BrdU pulse labeling or pulse chase, cells were harvested, transferred to polymerase chain reaction (PCR) V-bottom plates, and fixed by adding methanol. DNA denaturation was performed directly in the plates by heat using a PCR thermocycler. BrdU incorporation was detected by indirect immunocytochemical staining, and cellular DNA was counterstained using propidium iodide. Samples were acquired by a BD FACSCalibur with BD Multiwells Auto sampler or BD HTS. We defined a dynamic range of the optimal cell number, for which cells maintained exponential growth up to 72 h. The assay was robust up to 30,000 cells per well. BrdU dot plots of cell cycle phases showed an excellent separation of cell populations, and DNA histograms showed a low coefficient of variation. Thermal denaturation was suitable for 96-well plates to detect BrdU incorporation with a good signal-to-noise ratio, and cluster analysis allowed fingerprint readouts for drug sensitivity and mechanism of action as exemplified for paclitaxel and doxorubicin. This method provided rapid high-throughput BrdU/DNA content analysis with high accuracy and reproducibility, accompanied by a reduction in reagent consumption. A critical step was identified as the standardization of DNA denaturation using a PCR thermocycler. Here,we show some applications of this method for cell cycle studies in drug discovery.

The cyclin-dependent kinase inhibitor PHA-848125 suppresses the in vitro growth of human melanomas sensitive or resistant to temozolomide, and shows synergistic effects in combination with this triazene compound.

PHA-848125 is a novel cyclin-dependent kinase inhibitor under Phase I/II clinical investigation. In this study, we describe, for the first time, the effect of PHA-848125 on human melanoma cells in vitro. Seven melanoma cell lines with different sensitivity to temozolomide (TMZ) were exposed to PHA-848125 for 5 days and then assayed for cell growth. In all cases, including TMZ-resistant cells, PHA-848125 IC(50) values were significantly below the maximum plasma concentrations achievable in the clinic. In the most PHA-848125-sensitive cell line, the drug caused a concentration-dependent G(1) arrest. PHA-848125 also impaired phosphorylation of the retinoblastoma protein at CDK2 and CDK4 specific sites, decreased retinoblastoma protein and cyclin A levels, and increased p21(Cip1), p27(Kip1) and p53 expression. Combined treatment with fixed ratios of TMZ plus PHA-848125 was studied in three melanoma cell lines. PHA-848125 was added to the cells 48 h after TMZ and cell growth was evaluated after 3 additional days of culture. Parallel experiments were performed in the presence of O(6)-benzylguanine (BG), to prevent repair of methyl adducts at O(6)-guanine induced by TMZ. Drug combination of TMZ plus BG and PHA-848125 produced additive or synergistic effects on cell growth, depending on the cell line. In the absence of BG, the combination was still more active than the single agents in the cell line moderately sensitive to TMZ, but comparable to PHA-848125 alone in the two TMZ-resistant cell lines. When TMZ plus BG were used in combination with PHA-848125 against cultured normal melanocytes, neither synergistic nor additive antiproliferative effects were observed. Our results indicate that PHA-848125 can have a therapeutic potential in melanoma patients, alone or combined with TMZ. Moreover this agent appears to be particularly attractive on the bases of its effectiveness against TMZ-resistant melanoma cells.

Optimization of 6,6-dimethyl pyrrolo[3,4-c]pyrazoles: Identification of PHA-793887, a potent CDK inhibitor suitable for intravenous dosing.

We have recently reported CDK inhibitors based on the 6-substituted pyrrolo[3,4-c]pyrazole core structure. Improvement of inhibitory potency against multiple CDKs, antiproliferative activity against cancer cell lines and optimization of the physico-chemical properties led to the identification of highly potent compounds. Compound 31 (PHA-793887) showed good efficacy in the human ovarian A2780, colon HCT-116 and pancreatic BX-PC3 carcinoma xenograft models and was well tolerated upon daily treatments by iv administration. It was identified as a drug candidate for clinical evaluation in patients with solid tumors.

Discovery of Stereospecific PARP-1 Inhibitor Isoindolinone NMS-P515.

Poly(ADP-ribose) polymerase-1 (PARP-1) is an enzyme involved in signaling and repair of DNA single strand breaks. PARP-1 employs NAD+ to modify substrate proteins via the attachment of poly(ADP-ribose) chains. PARP-1 is a well established target in oncology, as testified by the number of marketed drugs (e.g., Lynparza, Rubraca, Zejula, and Talzenna) used for the treatment of ovarian, breast, and prostate tumors. Efforts in investigating an uncharted region of the previously identified isoindolinone carboxamide series delivered (S)-13 (NMS-P515), a potent inhibitor of PARP-1 both in biochemical (K d: 0.016 µM) and cellular (IC50: 0.027 µM) assays. Cocrystal structure allowed explaining NMS-P515 stereospecific inhibition of the target. After having ruled out potential loss of enantiopurity in vitro and in vivo, NMS-P515 was synthesized in an asymmetric fashion. NMS-P515 ADME profile and its antitumor activity in a mouse xenograft cancer model render the compound eligible for further optimization.

Antitumor activity of edotecarin in breast carcinoma models.

PURPOSE: Edotecarin (J-107088, formerly ED-749) is a potent indolocarbazole topoisomerase-I inhibitor that has the potential to treat solid tumors. The current studies evaluated the potency and antitumor activity of edotecarin, as a single agent and in combination with capecitabine or docetaxel. METHODS: Antiproliferative activity was tested in vitro in a panel of 13 mammary cell lines and antitumor efficacy was tested in vivo in various breast cancer models. RESULTS: Edotecarin inhibited cellular proliferation in breast carcinoma cell lines: 50% inhibitory concentrations ranged from 8 nmol/L in SKBR-3 cells to approximately 30 micromol/L in BT20 cells. Single dose and weekly intravenous treatments with edotecarin 30 and 150 mg/kg produced significant antitumor activity in the SKBR-3 human breast carcinoma xenograft model, with no major toxicities, compared with vehicle solvent treatment. Daily administration of edotecarin 15 mg/kg for 10 days was not well tolerated, whereas the total dose of 150 mg/kg was safe when administered in a single injection. Edotecarin 3 and 30 mg/kg given after docetaxel in the nude mouse SKBR-3 xenograft model produced tumor growth delays that were greater than those observed with either agent alone and with no toxicity as evaluated on the basis of body weight reduction (<20%). Furthermore, edotecarin 3 mg/kg in combination with capecitabine produced more than additive effects and the combination was well tolerated. However, edotecarin at a dose of 30 mg/kg in combination with capecitabine was lethal. Edotecarin also exhibited potent antitumor activity against xenografted human MX-1 cells, MMTV-v-Ha-ras oncogene-driven mouse breast tumors, and chemically induced rat mammary tumors. CONCLUSIONS: The data suggest that edotecarin may be useful as a single agent or a component of combination chemotherapy regimens for treating human breast cancer.

Antitumor efficacy of edotecarin as a single agent and in combination with chemotherapy agents in a xenograft model.

The novel indolocarbazole edotecarin (J-107088, formerly ED-749) differs from other topoisomerase I inhibitors both pharmacokinetically and pharmacodynamically. In vitro, it is more potent than camptothecins and has a variable cytotoxic activity in 31 different human cancer cell lines. Edotecarin also possesses greater than additive inhibitory effects on cell proliferation when used in combination with other agents tested in vitro against various cancer cell lines. The present in vivo studies were done to extend the in vitro findings to characterize the antitumor effects of edotecarin when used either alone or in combination with other agents (i.e., 5-fluorouracil, irinotecan, cisplatin, oxaliplatin, and SU11248) in the HCT-116 human colon cancer xenograft model. Treatment effects were based on the delay in onset of an exponential growth of tumors in drug-treated versus vehicle control-treated groups. In all studies, edotecarin was active both as a single agent and in combination with other agents. Combination therapy resulted in greater than additive effects, the extent of which depended on the specific dosage regimen. Toxicity in these experiments was minimal. Of all 359 treated mice, the six that died of toxicity were in the high-dose edotecarin/oxaliplatin group. The results suggest that edotecarin may serve as effective chemotherapy of colon cancer when used as a single agent, in combination with standard regimens and other topoisomerase inhibitors or with novel agents, such as the multitargeted tyrosine kinase inhibitor SU11248.

Entrectinib, a Pan-TRK, ROS1, and ALK Inhibitor with Activity in Multiple Molecularly Defined Cancer Indications.

Activated ALK and ROS1 tyrosine kinases, resulting from chromosomal rearrangements, occur in a subset of non-small cell lung cancers (NSCLC) as well as other tumor types and their oncogenic relevance as actionable targets has been demonstrated by the efficacy of selective kinase inhibitors such as crizotinib, ceritinib, and alectinib. More recently, low-frequency rearrangements of TRK kinases have been described in NSCLC, colorectal carcinoma, glioblastoma, and Spitzoid melanoma. Entrectinib, whose discovery and preclinical characterization are reported herein, is a novel, potent inhibitor of ALK, ROS1, and, importantly, of TRK family kinases, which shows promise for therapy of tumors bearing oncogenic forms of these proteins. Proliferation profiling against over 200 human tumor cell lines revealed that entrectinib is exquisitely potent in vitro against lines that are dependent on the drug's pharmacologic targets. Oral administration of entrectinib to tumor-bearing mice induced regression in relevant human xenograft tumors, including the TRKA-dependent colorectal carcinoma KM12, ROS1-driven tumors, and several ALK-dependent models of different tissue origins, including a model of brain-localized lung cancer metastasis. Entrectinib is currently showing great promise in phase I/II clinical trials, including the first documented objective responses to a TRK inhibitor in colorectal carcinoma and in NSCLC. The drug is, thus, potentially suited to the therapy of several molecularly defined cancer settings, especially that of TRK-dependent tumors, for which no approved drugs are currently available. Mol Cancer Ther; 15(4); 628-39. ©2016 AACR.

3-Aminopyrazole inhibitors of CDK2/cyclin A as antitumor agents. 2. Lead optimization.

Inhibitors of cyclin-dependent kinases (CDK) such as CDK2/cyclin A-E are currently undergoing clinical trials to verify their potential as new anticancer agents. In a previous article we described the lead discovery process of a 3-aminopyrazole class of CDK2/cyclin A-E inhibitors. The endpoint of this process was PNU-292137, a compound endowed with in vivo antitumor activity in a mouse tumor xenograft model. We optimized this lead compound to improve some physicochemical properties, notably solubility and plasma protein binding. This lead optimization process brought us to the discovery of (2S)-N-(5-cyclopropyl-1H-pyrazol-3-yl)-2-[4-(2-oxo-1-pyrrolidinyl)phenyl]propanamide (PHA-533533, 13), a compound with a balanced activity vs druglike profile. Compound 13 inhibited CDK2/cyclin A with a K(i) of 31 nM, counteracting tumor cell proliferation of different cell lines with an IC(50) in the submicromolar range. Solubility was improved more than 10 times over the starting lead, while plasma protein binding was decreased from 99% to 74%. With exploitation of this globally enhanced in vitro profile, 13 was more active than PNU-292137 in vivo in the A2780 xenograft model showing a tumor growth inhibition of 70%. Proof of mechanism of action was obtained in vivo by immunohistochemical analysis of tumor slices of 13-treated vs untreated animals.

Optimization of diarylthiazole B-raf inhibitors: identification of a compound endowed with high oral antitumor activity, mitigated hERG inhibition, and low paradoxical effect.

Aberrant activation of the mitogen-activated protein kinase (MAPK)-mediated pathway components, RAF-MEK-ERK, is frequently observed in human cancers and clearly contributes to oncogenesis. As part of a project aimed at finding inhibitors of B-Raf, a key player in the MAPK cascade, we originally identified a thiazole derivative endowed with high potency and selectivity, optimal in vitro ADME properties, and good pharmacokinetic profiles in rodents, but that suffers from elevated hERG inhibitory activity. An optimization program was thus undertaken, focused mainly on the elaboration of the R(1) and R(2) groups of the scaffold. This effort ultimately led to N-(4-{2-(1-cyclopropylpiperidin-4-yl)-4-[3-(2,5-difluorobenzenesulfonylamino)-2-fluorophenyl]thiazol-5-yl}-pyridin-2-yl)acetamide (20), which maintains favorable in vitro and in vivo properties, but lacks hERG liability. Besides exhibiting potent antiproliferative activity against only cell lines bearing B-Raf V600E or V600D mutations, compound 20 also intriguingly shows a weaker "paradoxical" activation of MEK in non-mutant B-Raf cells than other known B-Raf inhibitors. It also demonstrates very good efficacy in vivo against the A375 xenograft melanoma model (tumor volume inhibition >90% at 10 mg kg(-1) ); it is therefore a suitable candidate for preclinical development.

Discovery of 2-[1-(4,4-Difluorocyclohexyl)piperidin-4-yl]-6-fluoro-3-oxo-2,3-dihydro-1H-isoindole-4-carboxamide (NMS-P118): A Potent, Orally Available, and Highly Selective PARP-1 Inhibitor for Cancer Therapy.

The nuclear protein poly(ADP-ribose) polymerase-1 (PARP-1) has a well-established role in the signaling and repair of DNA and is a prominent target in oncology, as testified by the number of candidates in clinical testing that unselectively target both PARP-1 and its closest isoform PARP-2. The goal of our program was to find a PARP-1 selective inhibitor that would potentially mitigate toxicities arising from cross-inhibition of PARP-2. Thus, an HTS campaign on the proprietary Nerviano Medical Sciences (NMS) chemical collection, followed by SAR optimization, allowed us to discover 2-[1-(4,4-difluorocyclohexyl)piperidin-4-yl]-6-fluoro-3-oxo-2,3-dihydro-1H-isoindole-4-carboxamide (NMS-P118, 20by). NMS-P118 proved to be a potent, orally available, and highly selective PARP-1 inhibitor endowed with excellent ADME and pharmacokinetic profiles and high efficacy in vivo both as a single agent and in combination with Temozolomide in MDA-MB-436 and Capan-1 xenograft models, respectively. Cocrystal structures of 20by with both PARP-1 and PARP-2 catalytic domain proteins allowed rationalization of the observed selectivity.

Endothelial cells overexpressing basic fibroblast growth factor (FGF-2) induce vascular tumors in immunodeficient mice.

Basic fibroblast growth factor (FGF-2) is expressed in vascular endothelium during tumor neovascularization and angioproliferative diseases, including vascular tumors and Kaposi's sarcoma (KS). We have investigated the in vivo biological consequences of endothelial cell activation by endogenous FGF-2 in a mouse aortic endothelial cell line transfected with a retroviral expression vector harboring a human FGF-2 cDNA and the neomycin resistance gene. FGF-2 transfectants, named pZipbFGF2-MAE cells, caused the rapid growth of highly vascularized, non-infiltrating tumors when injected in nude mice. In contrast, lesions grew poorly when cells were injected in immunocompetent syngeneic animals. Histologically, the tumors had the appearance of hemangioendothelioma with spindled areas resembling KS and with numerous CD31+ blood vessels and lacunae. Southern blot analysis of tumor DNA, as well as disaggregation of the lesion followed by in vitro cell culture, revealed that less than 10% of the cells in the tumor mass retain FGF-2 overexpression and neomycin resistance at 6-8 weeks post-injection. Nevertheless, in vitro G418 selection allowed the isolation from the tumor of a FGF-2-overexpressing cell population showing biochemical and biological characteristics similar to those of pZipbFGF2-MAE cells, including the capacity to originate vascular lesions when re-injected in nude mice. To evaluate the effect of angiostatic compounds on the growth and vascularization of pZipbFGF2-MAE cell-induced lesions, nude mice were treated weekly (100mg/kg, i.p.) with the angiostatic sulfonated distamycin A derivative 2,2'-(carbonyl-bis-[imino-N-methyl-4,2-pyrrole carbonyl-imino-{N-methyl-4,2-pyrrole}carbonylimino])-bis-(1,5-naphthalene) disulfonic acid (PNU 153429). The results demonstrate that PNU 153429 inhibits the growth of the lesions and causes a approximately 50% decrease in CD31+ microvessel density. In conclusion, the data indicate that FGF-2-overexpressing endothelial cells cause vascular lesions in immunodeficient mice which may represent a novel model for opportunistic vascular tumors suitable for the evaluation of angiostatic compounds.

3-Aminopyrazole inhibitors of CDK2/cyclin A as antitumor agents. 1. Lead finding.

Abnormal proliferation mediated by disruption of the normal cell cycle mechanisms is a hallmark of virtually all cancer cells. Compounds targeting complexes between cyclin-dependent kinases (CDK) and cyclins, such as CDK2/cyclin A and CDK2/cyclin E, and inhibiting their kinase activity are regarded as promising antitumor agents to complement the existing therapies. From a high-throughput screening effort, we identified a new class of CDK2/cyclin A/E inhibitors. The hit-to-lead expansion of this class is described. X-ray crystallographic data of early compounds in this series, as well as in vitro testing funneled for rapidly achieving in vivo efficacy, led to a nanomolar inhibitor of CDK2/cyclin A (N-(5-cyclopropyl-1H-pyrazol-3-yl)-2-(2-naphthyl)acetamide (41), PNU-292137, IC50 = 37 nM) with in vivo antitumor activity (TGI > 50%) in a mouse xenograft model at a dose devoid of toxic effects.

NMS-E973, a novel synthetic inhibitor of Hsp90 with activity against multiple models of drug resistance to targeted agents, including intracranial metastases.

PURPOSE: Recent developments of second generation Hsp90 inhibitors suggested a potential for development of this class of molecules also in tumors that have become resistant to molecular targeted agents. Disease progression is often due to brain metastases, sometimes related to insufficient drug concentrations within the brain. Our objective was to identify and characterize a novel inhibitor of Hsp90 able to cross the blood-brain barrier (BBB). EXPERIMENTAL DESIGN: Here is described a detailed biochemical and crystallographic characterization of NMS-E973. Mechanism-based anticancer activity was described in cell models, including models of resistance to kinase inhibitors. Pharmacokinetics properties were followed in plasma, tumor, liver, and brain. In vivo activity and pharmacodynamics, as well as the pharmacokinetic/pharmacodynamic relationships, were evaluated in xenografts, including an intracranially implanted melanoma model. RESULTS: NMS-E973, representative of a novel isoxazole-derived class of Hsp90 inhibitors, binds Hsp90α with subnanomolar affinity and high selectivity towards kinases, as well as other ATPases. It possesses potent antiproliferative activity against tumor cell lines and a favorable pharmacokinetic profile, with selective retention in tumor tissue and ability to cross the BBB. NMS-E973 induces tumor shrinkage in different human tumor xenografts, and is highly active in models of resistance to kinase inhibitors. Moreover, consistent with its brain penetration, NMS-E973 is active also in an intracranially implanted melanoma model. CONCLUSIONS: Overall, the efficacy profile of NMS-E973 suggests a potential for development in different clinical settings, including tumors that have become resistant to molecular targeted agents, particularly in cases of tumors which reside beyond the BBB.

Down-regulation of the PTTG1 proto-oncogene contributes to the melanoma suppressive effects of the cyclin-dependent kinase inhibitor PHA-848125.

We previously demonstrated that PHA-848125, a cyclin-dependent kinase inhibitor presently under Phase II clinical investigation, impairs melanoma cell growth. In this study, gene expression profiling showed that PHA-848125 significantly modulated the expression of 128 genes, predominantly involved in cell cycle control, in the highly drug-sensitive GL-Mel (p53 wild-type) melanoma cells. Up-regulation of 4 selected genes (PDCD4, SESN2, DDIT4, DEPDC6), and down-regulation of 6 selected genes (PTTG1, CDC25A, AURKA, AURKB, PLK1, BIRC5) was confirmed at protein levels. The same protein analysis performed in PHA-848125-treated M10 melanoma cells - p53 mutated and less sensitive to the drug than GL-Mel cells - revealed no DEPDC6 expression and no changes of PTTG1, PDCD4 and BIRC5 levels. Upon PHA-848125 treatment, a marked PTTG1 down-modulation was also observed in A375 cells (p53 wild-type) but not in CN-Mel cells (p53 mutated). PTTG1 silencing significantly inhibited melanoma cell proliferation and induced senescence, with effects less pronounced in p53 mutated cells. PTTG1 silencing increased PHA-848125 sensitivity of p53 mutated cells but not that of A375 or GL-Mel cells. Accordingly, in M10 but not in A375 cells a higher level of senescence was detected in PHA-848125-treated/PTTG1-silenced cells with respect to PHA-848125-treated controls. In A375 and GL-Mel cells, TP53 silencing attenuated PHA-848125-induced down-modulation of PTTG1 and decreased cell sensitivity to the drug. These findings indicate that PHA-848125-induced down-regulation of PTTG1 depends, at least in part, on p53 function and contributes to the antiproliferative activity of the drug. Our study provides further molecular insight into the antitumor mechanism of PHA-848125.

Therapeutic efficacy of the pan-cdk inhibitor PHA-793887 in vitro and in vivo in engraftment and high-burden leukemia models.

OBJECTIVE: The aim of the work was to determine and characterize, in vitro and in vivo, the therapeutic activity of PHA-793887, a new potent pan-cdk inhibitor, in the context of hematopoietic neoplasms. MATERIALS AND METHODS: Thirteen leukemic cell lines bearing different cytogenetic abnormalities and normal hematopoietic cells were used in cytotoxicity and colony assays. The drug activity at the molecular level was analyzed by Western blotting. PHA-793887 was also tested in vivo in several leukemia xenograft models. RESULTS: PHA-793887 was cytotoxic for leukemic cell lines in vitro, with IC(50) ranging from 0.3 to 7 microM (mean: 2.9 microM), regardless of any specific chromosomal aberration. At these doses, the drug was not cytotoxic for normal unstimulated peripheral blood mononuclear cells or CD34(+) hematopoietic stem cells. Interestingly, in colony assays PHA-793887 showed very high activity against leukemia cell lines, with an IC(50) <0.1 microM (mean: 0.08 microM), indicating that it has efficient and prolonged antiproliferative activity. PHA-793887 induced cell-cycle arrest, inhibited Rb and nucleophosmin phosphorylation, and modulated cyclin E and cdc6 expression at low doses (0.2-1 microM) and induced apoptosis at the highest dose (5 microM). It was also effective in vivo in both subcutaneous xenograft and primary leukemic disseminated models that better mimic naturally occurring human disease. Interestingly, in one disseminated model derived from a relapsed Philadelphia-positive acute lymphoid leukemia patient, PHA-793887 showed strong therapeutic activity also when treatment was started after establishment of high disease burden. CONCLUSIONS: We conclude that PHA-793887 has promising therapeutic activity against acute leukemias in vitro and in vivo.

Efficacy of PHA-848125, a cyclin-dependent kinase inhibitor, on the K-Ras(G12D)LA2 lung adenocarcinoma transgenic mouse model: evaluation by multimodality imaging.

K-ras is the most frequently mutated oncogene in non-small cell lung cancer (NSCLC), the most common form of lung cancer. Recent studies indicate that NSCLC patients with mutant K-ras do not respond to epidermal growth factor receptor inhibitors. In the attempt to find alternative therapeutic regimes for such patients, we tested PHA-848125, an oral pan cyclin-dependent kinase inhibitor currently under evaluation in phase II clinical trial, on a transgenic mouse model, K-Ras(G12D)LA2, which develops pulmonary cancerous lesions reminiscent of human lung adenocarcinomas. We used magnetic resonance imaging and positron emission tomography to follow longitudinally disease progression and evaluate therapeutic efficacy in this model. Treatment of K-Ras(G12D)LA2 mice with 40 mg/kg twice daily for 10 days with PHA-848125 induced a significant tumor growth inhibition at the end of treatment (P < 0.005) and this was accompanied by a reduction in the cell membrane turnover, as seen by 11C-Choline-positron emission tomography (P < 0.05). Magnetic resonance imaging data were validated versus histology and the mechanism of action of the compound was verified by immunohistochemistry, using cyclin-dependent kinase-related biomarkers phospho-Retinoblastoma and cyclin A. In this study, multimodality imaging was successfully used for the preclinical assessment of PHA-848125 therapeutic efficacy on a lung adenocarcinoma mouse model. This compound induced a volumetric and metabolic anticancer effect and could represent a valid therapeutic approach for NSCLC patients with mutant K-ras.

Transcriptional analysis of an E2F gene signature as a biomarker of activity of the cyclin-dependent kinase inhibitor PHA-793887 in tumor and skin biopsies from a phase I clinical study.

A transcriptional signature of the pan-cyclin-dependent kinase (Cdk) inhibitor PHA-793887 was evaluated as a potential pharmacodynamic and/or response biomarker in tumor and skin biopsies from patients treated in a phase I clinical study. We first analyzed the expression of a number of known E2F-dependent genes that were predicted to be modulated after Cdk2 and Cdk4 inhibition in xenograft tumor and skin samples of mice treated with the compound. This panel of 58 selected genes was then analyzed in biopsies from seven patients treated with PHA-793887 in a phase I dose escalation clinical trial in solid tumors. Quantitative real-time PCR or microarray analyses were done in paired skin and tumor biopsies obtained at baseline and at cycle 1. Analysis by quantitative real-time PCR of the signature in skin biopsies of patients treated at three different doses showed significant transcriptional downregulation with a dose-response correlation. These data show that PHA-793887 modulates genes involved in cell cycle regulation and proliferation in a clinical setting. The observed changes are consistent with its mechanism of action and correlate with target modulation in skin and with clinical benefit in tumors.