Durable Growth Inhibition Research Articles

GalNAc-conjugated siRNA targeting the DNAJB1-PRKACA fusion junction in fibrolamellar hepatocellular carcinoma

Fibrolamellar hepatocellular carcinoma (FLC) is a rare liver cancer caused by a dominant recurrent fusion of the heat shock protein (DNAJB1) and the catalytic subunit of protein kinase A (PRKACA). Current therapies such as chemotherapy and radiation have limited efficacy, and new treatment options are needed urgently. We have previously shown that FLC tumors are dependent on the fusion kinase DNAJB1::PRKACA, making the oncokinase an ideal drug target. mRNA degrading modalities such as antisense oligonucleotides or small interfering RNAs (siRNAs) provide an opportunity to specifically target the fusion junction. Here, we identify a potent and specific siRNA that inhibits DNAJB1::PRKACA expression. We found expression of the asialoglycoprotein receptor in FLC to be maintained at sufficient levels to effectively deliver siRNA conjugated to the GalNAc ligand. We observe productive uptake and siRNA activity in FLC patient-derived xenografts (PDX) models invitro and invivo. Knockdown of DNAJB1::PRKACA results in durable growth inhibition of FLC PDX in vivo with no detectable toxicities. Our results suggest that this approach could be a treatment option for FLC patients.

Enhanced Ocular Anti-Aspergillus Activity of Tolnaftate Employing Novel Cosolvent-Modified Spanlastics: Formulation, Statistical Optimization, Kill Kinetics, Ex Vivo Trans-Corneal Permeation, In Vivo Histopathological and Susceptibility Study.

Tolnaftate (TOL) is a thiocarbamate fungicidal drug used topically in the form of creams and ointments. No ocular formulations of TOL are available for fungal keratitis (FK) treatment due to its poor water solubility and unique ocular barriers. Therefore, this study aimed at developing novel modified spanlastics by modulating spanlastics composition using different glycols for enhancing TOL ocular delivery. To achieve this goal, TOL basic spanlastics were prepared by ethanol injection method using a full 32 factorial design. By applying the desirability function, the optimal formula (BS6) was selected and used as a nucleus for preparing and optimizing TOL-cosolvent spanlastics according to the full 31.21 factorial design. The optimal formula (MS6) was prepared using 30% propylene glycol and showed entrapment efficiency percent (EE%) of 66.10 ± 0.57%, particle size (PS) of 231.20 ± 0.141 nm, and zeta potential (ZP) of −32.15 ± 0.07 mV. MS6 was compared to BS6 and both nanovesicles significantly increased the corneal permeation potential of TOL than drug suspension. Additionally, in vivo histopathological experiment was accomplished and confirmed the tolerability of MS6 for ocular use. The fungal susceptibility testing using Aspergillus niger confirmed that MS6 displayed more durable growth inhibition than drug suspension. Therefore, MS6 can be a promising option for enhanced TOL ocular delivery.

Synergistic activity of neratinib in combination with olaparib in uterine serous carcinoma overexpressing HER2/neu

IntroductionUterine serous carcinoma (USC) is an aggressive variant of endometrial cancer with a poor prognosis. Approximately 30% of USC overexpress HER2/neu, a recognized target for trastuzumab in advanced/recurrent HER2/neu-positive USC. We evaluated the efficacy of the pan-c-erb inhibitor neratinib and the poly (ADP-ribose)-polymerase (PARP) inhibitor olaparib as single agents and in combination against USC cell lines and xenografts. MethodsIn-vitro cell-viability assays with olaparib, neratinib, and olaparib/neratinib were assessed using flow-cytometry based assays against a panel of USC cell lines with high and low HER2/neu expression. Homologous recombination deficiency (HRD) signatures were evaluated as described by Alexandrov et al. (Nature;2020;578:94–101) while downstream signaling affected by neratinib/olaparib exposure was assessed with immunoblotting. Efficacy of single- versus dual-agent inhibition was evaluated in-vivo using two USC-xenografts with 3+ HER2/neu expression. ResultsNeratinib was more potent than olaparib in suppression of in-vitro growth of HER2/neu 3+ cell lines (ARK1: p = 0.0047; ARK2: p = 0.0428) while no difference was noted against HER2/neu 1+ tumors (ARK4). Importantly, the combination of olaparib with neratinib synergistically improved tumor suppression compared to either single-agent in vitro. USC cells exposed to olaparib upregulated HER2/neu expression, while neratinib treatment increased PARP activity (ARK1: p < 0.0001; ARK2: p < 0.0001). Single-agent neratinib transiently inhibited in vivo growth of USC xenografts harboring HER2/neu gene amplification (ARK1: p < 0.05; ARK2: p < 0.05). In contrast, the combination of the two inhibitors caused a stronger and durable growth inhibition in both USC xenografts (ARK1: p < 0.05; ARK2: p < 0.05). ConclusionThe combination of olaparib and neratinib is active and synergistic against primary HER2/neu + USC. This combination may represent a novel therapeutic option for USC patients with HER2/neu+, homologous recombination-proficient tumors resistant to chemotherapy.

Statistical optimization of hyaluronic acid enriched ultradeformable elastosomes for ocular delivery of voriconazole via Box-Behnken design: in vitro characterization and in vivo evaluation

Voriconazole (VCZ) is a well-known broad spectrum triazole antifungal, mainly used orally and intravenously. The study aimed to formulate VCZ into ultradeformable elastosomes for the topical treatment of ocular fungal keratitis. Different formulae were prepared using a modified ethanol injection method, employing a 33 Box-Behnken design. They were characterized by measuring their entrapment efficiency (EE%), particle size (PS), polydispersity index (PDI) and zeta potential (ZP). The optimized formula was subjected to further in vitro investigations and in vivo evaluation studies. The prepared vesicles had satisfactory EE%, PS, PDI and ZP values. The numerical optimization process suggested an optimal elastosomal formula (OE) composed of phosphatidyl choline and brij S100 at the weight ratio of 3.62: 1, 0.25%w/v hyaluronic acid and 5% (percentage from phosphatidyl choline/brij mixture) polyvinyl alcohol. It had high EE (72.6%), acceptable PS and PDI (362.4 nm and 0.25, respectively) and highly negative ZP of −41.7 mV. OE exhibited higher elasticity than conventional liposomes, with acceptable stability for three months. Transmission electron microscopy demonstrated the spherical morphology of vesicles with an external transparent coat of Hyaluronic acid. OE was expected to cause no ocular irritation or blurring in vision as reflected by pH and refractive index measurements. The histopathological study revealed the safety of OE for ocular use. The fungal susceptibility testing using Candida albicans demonstrated the superiority of OE to VCZ suspension, with greater and more durable growth inhibition. Therefore, OE can be regarded as a promising formula, achieving both safety and efficacy.

Voriconazole Ternary Micellar Systems for the Treatment of Ocular Mycosis: Statistical Optimization and InVivo Evaluation.

Voriconazole (VRC) is a broad spectrum, second generation triazole antifungal. The main use of VRC is via the oral and intravenous route. The study aimed to formulate VRC into ternary micellar systems (TMSs) for the topical treatment of ocular mycosis. TMSs were successfully prepared by water addition/solvent evaporation method, applying a 3-factor D-optimal design. The numerical optimization process suggested an optimal formula (OTMS) composed of total Pluronics to drug weight ratio of 22.89: 1, 1:1 weight ratio of Pluronic® P123 and F68, and 2% w/v of Labrasol. OTMS had high solubilization efficiency of 98.0%, small micellar size of 21.8 nm and suitable zeta potential and polydispersity index values of -9.0 mV and 0.261, respectively. OTMS exhibited acceptable stability for 3months. Transmission electron microscopy demonstrated the spherical morphology of micelles. OTMS was expected to cause no ocular irritation or blurring in vision as reflected by pH and refractive index measurements. The histopathological study revealed the safety of OTMS for ocular use. The fungal susceptibility testing using Candida albicans demonstrated the superiority of OTMS to VRC suspension, with greater and more durable growth inhibition. Therefore, ocular application of optimized VRC-loaded TMSs can be a promising treatment for ocular mycosis.

Intrinsic Resistance to MEK Inhibition through BET Protein-Mediated Kinome Reprogramming in NF1-Deficient Ovarian Cancer.

Mutation or deletion of Neurofibromin 1 (NF1), an inhibitor of RAS signaling, frequently occurs in epithelial ovarian cancer (EOC), supporting therapies that target downstream RAS effectors, such as the RAF-MEK-ERK pathway. However, no comprehensive studies have been carried out testing the efficacy of MEK inhibition in NF1-deficient EOC. Here, we performed a detailed characterization of MEK inhibition in NF1-deficient EOC cell lines using kinome profiling and RNA sequencing. Our studies showed MEK inhibitors (MEKi) were ineffective at providing durable growth inhibition in NF1-deficient cells due to kinome reprogramming. MEKi-mediated destabilization of FOSL1 resulted in induced expression of receptor tyrosine kinases (RTK) and their downstream RAF and PI3K signaling, thus overcoming MEKi therapy. MEKi synthetic enhancement screens identified BRD2 and BRD4 as integral mediators of the MEKi-induced RTK signatures. Inhibition of bromo and extra terminal (BET) proteins using BET bromodomain inhibitors blocked MEKi-induced RTK reprogramming, indicating that BRD2 and BRD4 represent promising therapeutic targets in combination with MEKi to block resistance due to kinome reprogramming in NF1-deficient EOC. IMPLICATIONS: Our findings suggest MEK inhibitors will likely not be effective as single-agent therapies in NF1-deficient EOC due to kinome reprogramming. Cotargeting BET proteins in combination with MEKis to block reprogramming at the transcriptional level may provide an epigenetic strategy to overcome MEKi resistance in NF1-deficient EOC.

Bayesian model of signal rewiring reveals mechanisms of gene dysregulation in acquired drug resistance in breast cancer.

Small molecule inhibitors, such as lapatinib, are effective against breast cancer in clinical trials, but tumor cells ultimately acquire resistance to the drug. Maintaining sensitization to drug action is essential for durable growth inhibition. Recently, adaptive reprogramming of signaling circuitry has been identified as a major cause of acquired resistance. We developed a computational framework using a Bayesian statistical approach to model signal rewiring in acquired resistance. We used the p1-model to infer potential aberrant gene-pairs with differential posterior probabilities of appearing in resistant-vs-parental networks. Results were obtained using matched gene expression profiles under resistant and parental conditions. Using two lapatinib-treated ErbB2-positive breast cancer cell-lines: SKBR3 and BT474, our method identified similar dysregulated signaling pathways including EGFR-related pathways as well as other receptor-related pathways, many of which were reported previously as compensatory pathways of EGFR-inhibition via signaling cross-talk. A manual literature survey provided strong evidence that aberrant signaling activities in dysregulated pathways are closely related to acquired resistance in EGFR tyrosine kinase inhibitors. Our approach predicted literature-supported dysregulated pathways complementary to both node-centric (SPIA, DAVID, and GATHER) and edge-centric (ESEA and PAGI) methods. Moreover, by proposing a novel pattern of aberrant signaling called V-structures, we observed that genes were dysregulated in resistant-vs-sensitive conditions when they were involved in the switch of dependencies from targeted to bypass signaling events. A literature survey of some important V-structures suggested they play a role in breast cancer metastasis and/or acquired resistance to EGFR-TKIs, where the mRNA changes of TGFBR2, LEF1 and TP53 in resistant-vs-sensitive conditions were related to the dependency switch from targeted to bypass signaling links. Our results suggest many signaling pathway structures are compromised in acquired resistance, and V-structures of aberrant signaling within/among those pathways may provide further insights into the bypass mechanism of targeted inhibition.

Abstract B62: Evaluation of scheduling for triple therapy gemcitabine/CHEK1 inhibitor/WEE1 inhibitor in pancreatic cancer models

Abstract Sensitization of cancer cells to gemcitabine (Gem) has been shown with checkpoint kinase CHEK1 (CHK1) and WEE1 inhibitors. Our aim is to determine, using in vitro and in vivo models, the optimal regime for application of the triple combination in pancreatic cancer. First, we have investigated the dual combinations of Gem + either CHEK1 or WEE1 inhibitors in growth inhibition assays in vitro. Synergistic growth inhibition was identified using both Bliss Independence and Loewe models, in MIA PaCa-2 cells at 10 – 30 nM Gem + 300 – 1000 nM CHEK1 inhibitor MK8776; or 10 – 30 nM Gem + 30 – 100 nM WEE1 inhibitor MK1775. The synergistic concentrations were submaximal, i.e. below the single agent GI50 concentrations, which were 30 nM for Gem, 6 μM for MK8776, and 500 nM for MK1775. The Panc-1 cell line is more resistant to Gem as a single agent, but synergy was evident: in colony forming assays the dual combination of either 30 nM gem + 300 nM MK1775 or 30 nM Gem + 1 μM MK8776 inhibited colony formation by 97 +/- 1.6 % and 91 +/- 2% respectively. Single agent Gem inhibited colony formation by only 23 +/- 4 % and MK1775 or MK8776 did not inhibit colony formation at these concentrations. Next, we investigated scheduling of the Gem/CHEK1i/Wee1i triple combination, at the synergistic concentrations, with kinetic live-cell imaging assays. MIA PaCa-2 cells treated continuously with 10 nM Gem plus 1 μM MK8776 showed durable growth inhibition over 72 hours. However, if both drugs were washed off after 24 hours the Gem + CHEK1i-treated cells recovered and began to proliferate within 24 hours. Different schedules of the trio were tested, and the most durable growth inhibition (&amp;gt; 5 days) was obtained when Gem + MK8776 were washed off at 24 hours and replaced with 300 nM MK1775, whereas 300 nM MK1775 in the absence of Gem + MK8776 pretreatment did not significantly inhibit growth, compared to control. Different scheduling options were also tested in Panc-1 cells in colony forming assays, and again the most effective schedule was Gem + MK8776 for 24 hours, followed by MK1775. MIA PaCa-2 xenograft studies are now underway, initially with the dual combination, to be followed with the drug trio of simultaneous Gem + MK8776, followed by MK1775. To reduce the likelihood of toxicity, Gem doses lower than the typical “full” dose (100 mg/kg IP twice per week) were tested. We found that 25 mg/kg Gem twice in a day (8h apart), twice per week was not well tolerated even as a single agent, but both 25 and 50 mg/kg Gem once in a day, twice per week was tolerated when co-dosed with 25 mg/kg MK8776, and when this combination was followed 8 hours later by 60 mg/kg MK1775 (OG). A pharmacokinetic study revealed that plasma Gem (dFdC) concentrations were not altered by co-dosing Gem with MK8776, but intratumor dFdCTP (the active intracellular metabolite of Gem) was elevated at 1 – 8 hours after the 25 mg/kg Gem + MK8776 dose (AUC0 –last 49 +/- 7.9 hr.pmoles/mg tissue) compared to mice with 25 mg/kg Gem alone (AUC0-last 21 +/- 2.6 hr.pmoles/mg tissue). CHEK1 target inhibition was demonstrated in vivo, with abrogation of Gem-induced CHEK1 S296 autophosphorylation for at least 4h post Gem + MK8776 dosing, using Western blot analyses of tumor lysate. There was also increased γH2AX and pRPA32 S4/8 at 4 - 8 hours post-dose with Gem + MK8776 compared to Gem alone, indicating enhanced DNA damage. Pharmacodynamic and efficacy studies with the triple combination, will determine whether enhanced efficacy can be observed, when compared to full dose, single agent gemcitabine (100 mg/kg IP twice per week). Citation Format: Siang-Boon Koh, Frances M. Richards, Yann Wallez, Duncan I. Jodrell.{Authors}. Evaluation of scheduling for triple therapy gemcitabine/CHEK1 inhibitor/WEE1 inhibitor in pancreatic cancer models. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2016 May 12-15; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2016;76(24 Suppl):Abstract nr B62.

Abstract 2824: G1T38, a novel, oral, potent and selective CDK4/6 inhibitor for the treatment of Rb competent tumors

Abstract The development of therapeutically effective inhibitors of the cyclin dependent kinase (CDK) family has been challenging due to a poor understanding of target and structural biology leading to the development of drugs that are toxic with limited efficacy. Recently, the first highly selective CDK4/6 inhibitor, palbociclib, was approved by the FDA for use in combination with letrozole as a first line treatment in patients with ER+/ HER2- metastatic breast cancer. While this first approved CDK4/6 inhibitor is highly efficacious, it causes severe myelosuppression during daily treatment resulting in at least a 7 day treatment holiday in every 28 day cycle to allow recovery of neutrophil counts. This leads to an increased risk of febrile neutropenia, potential tumor growth during the treatment holiday, and emergence of drug resistance. CDK4/6-induced myelosuppression is the result of on-target inhibition of hematopoietic stem and progenitor cell proliferation causing a narrow therapeutic window between tumor efficacy and neutropenia. Thus, a next generation CDK4/6 inhibitor will need to produce a potent, selective G1 arrest in Rb competent tumors while minimizing the effect on the bone marrow. With a new understanding of CDK4/6 biology, we have generated compounds with unique properties that maintain tumor efficacy while minimizing inhibition of bone marrow proliferation. Here we describe G1T38, a novel, oral, potent, and selective CDK4/6 inhibitor. Biochemical profiling demonstrates G1T38 is a competitive, nanomolar inhibitor of CDK4/6 with highly selectivity for CDK4-cyclin D1 and CDK6-cyclin D3. Kinome profiling exhibits on-target selectivity across 468 independent kinases at 100 nM, with no significant activity against other cell cycle or mitotic kinases. G1T38 elicits a precise G1 arrest profile along with loss of Rb phosphorylation in Rb competent cells with no impact in Rb deficient cells up to three orders of magnitude above the biochemical IC50. In cell proliferation assays, G1T38 exhibits a low EC50 (&amp;lt;100 nM) in Rb competent cell lines compared to &amp;gt;3 μM in Rb null cells. In vivo, daily oral treatment with G1T38 causes significant, durable growth inhibition of tumors in a HER2/neu GEMM and in MCF7 xenograft breast cancer models. G1T38 is cleared from the plasma but significantly accumulates in tumors. The level of G1T38 in the tumor correlates with significant reductions in Rb phosphorylation and tumor cell proliferation. Additionally, daily oral dosing of G1T38 in mice, rats and dogs for up to 28 days has shown a dose dependent decrease in neutrophils without severe neutropenia. These data demonstrate that the unique pharmacokinetic and pharmacodynamic properties of G1T38 allow it to be highly efficacious against tumors while having a mild effect on the bone marrow, thus making it optimal for use as a daily oral antineoplastic agent. Citation Format: Jessica A. Sorrentino, John E. Bisi, Patrick J. Roberts, Jay C. Strum. G1T38, a novel, oral, potent and selective CDK4/6 inhibitor for the treatment of Rb competent tumors. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2824.

Abstract 3497: Mechanism-based scheduling of triple therapy gemcitabine/CHK1i/WEE1i in pancreatic cancer at submaximal yet synergistic concentrations

Abstract Sensitization of cancer cells to gemcitabine has been shown with checkpoint kinase CHK1 and WEE1 inhibitors. To rationalize and optimize the concomitant use of these three agents, we first performed growth inhibition assays on MIA PaCa-2 pancreatic cancer cells using gemcitabine in combination with either CHIR-124 (CHK1 inhibitor) or MK-1775 (WEE1 inhibitor). In silico analysis with three mathematical models (Bliss Independence, Loewe and Highest Single Agent) identified synergistic growth inhibition at submaximal (i.e. &amp;lt;GI50) concentrations of the single agents (10nM gemcitabine, 20nM CHIR-124, 300nM MK-1775) in MIA PaCa-2 cells. At these concentrations of gemcitabine+CHIR-124, quantitative image-based cytometry demonstrated S-phase redistribution, with 31% of &amp;gt;8000 individual cells undergoing extensive fork collapse (compared to 0-1% with single agents) as evidenced by co-staining of yH2AX and hyper-phosphorylated RPA32. Conversely, submaximal gemcitabine+MK-1775 induced clear reduction of inhibitory CDK1 Y15 level compared to single agents. Consistent with this G2/M abrogation, in a Fucci-based CDT1/geminin-expressing MIA PaCa-2 stable cell line, gemcitabine+MK-1775 partially reversed the accumulation of the geminin-expressing (S/G2) population induced by gemcitabine alone. This was accompanied by an increase in the CDT1-expressing (G1) population, alongside aberrant mitotic cells with features of perturbed kinetochore-microtubule integrity. Based on these findings, we performed a series of long-term, kinetic live-cell imaging assays to determine the optimal scheduling for gemcitabine/CHK1i/WEE1i as a triplet at synergistic concentrations. In contrast to the widely proposed scheduling regimen, we found that delayed administration of CHK1i (at 24 hours), relative to gemcitabine, did not lead to synergy. However, concurrent administration yielded durable growth inhibition, even when the two agents were removed after 24 hours. This inhibition was further enhanced with the subsequent addition of WEE1i at 24 hours, but not continuation of a CHK1i. Together, our results illustrate differential mechanistic effects of CHK1 and WEE1 inhibitors with gemcitabine, when combined at sub-GI50 concentrations, and propose a novel triple agent schedule that will be evaluated in vivo. Citation Format: Siang-Boon Koh, Frances M. Richards, Esther Rodriguez, Scott K. Lyons, Duncan I. Jodrell. Mechanism-based scheduling of triple therapy gemcitabine/CHK1i/WEE1i in pancreatic cancer at submaximal yet synergistic concentrations. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3497. doi:10.1158/1538-7445.AM2015-3497

The microtubule-depolymerizing agent ansamitocin P3 programs dendritic cells toward enhanced anti-tumor immunity.

In addition to direct tumor cell cytotoxicity, chemotherapy can mediate tumor reduction through immune modulation of the tumor microenvironment to promote anti-tumor immunity. Mature dendritic cells (DCs) play key roles in priming robust immune responses in tumor-bearing hosts. Here, we screened a panel of 21 anticancer agents with defined molecular targets for their ability to induce direct maturation of DCs. We identified ansamitocin P3, a microtubule-depolymerizing agent, as a potent inducer of phenotypic and functional maturation of DCs. Exposure of both murine spleen-derived and human monocyte-derived DCs to ansamitocin P3 triggered up-regulation of maturation markers and production of pro-inflammatory cytokines, resulting in an enhanced T cell stimulatory capacity. Local administration of ansamitocin P3 induced maturation of skin Langerhans cells in vivo and promoted antigen uptake and extensive homing of tumor-resident DCs to tumor-draining lymph nodes. When used as an adjuvant in a specific vaccination approach, ansamitocin P3 dramatically increased activation of antigen-specific T cells. Finally, we demonstrate that ansamitocin P3, due to its immunomodulatory properties, acts in synergy with antibody-mediated blockade of the T cell inhibitory receptors PD-1 and CTLA-4. The combination treatment was most effective and induced durable growth inhibition of established tumors. Mechanistically, we observed a reduced regulatory T cell frequency and improved T cell effector function at the tumor site. Taken together, our study unravels an immune-based anti-tumor mechanism exploited by microtubule-depolymerizing agents, including ansamitocin P3, and paves the way for future clinical trials combining this class of agents with immunotherapy.

Abstract LB-122: LY2835219, a selective inhibitor of CDK4 and CDK6, inhibits growth in preclinical models of human cancer.

Abstract Cell growth is regulated by the activity of certain cyclin-dependent kinases (CDKs), including CDK4 and CDK6 (hereafter CDK4/6), which specifically regulate cell cycle progression through the G1 restriction point. These CDKs act with the D-type cyclins to phosphorylate and inactivate the retinoblastoma (Rb) tumor suppressor protein, which in turn enables cell cycle progression from G1 to S phase. LY2835219 is a selective inhibitor of CDK4/6 with IC50 of 2 and 10 nM for CDK4 and CDK6, respectively. The current study evaluates the activity of LY2835219 in preclinical models of human cancer including non-small cell lung cancer (NSCLC), melanoma, mantle cell lymphoma (MCL), and ovarian cancer. A secondary focus of this study is to identify potential predictive biomarkers for response to LY2835219 in NSCLC, melanoma, and other cancers. For NSCLC, increased sensitivity to LY2835219 is associated both in vitro and in vivo with KRAS mutations. For established melanoma cell lines, similar levels of in vitro sensitivity are observed in different genetic subtypes. Accordingly, LY2835219 shows single-agent activity in the A375 melanoma xenograft model with daily oral dosing at 45 or 90 mg/kg. For MCL, durable growth inhibition of subcutaneously implanted xenografts is achieved with daily oral dosing at 50mg/kg. Finally, in an intra-peritoneal model that recapitulates clinical features of human ovarian cancer, LY2835219 not only inhibits tumor growth but also increases survival. These studies suggest that LY2835219 may have potential therapeutic application in the treatment of human cancers with specific molecular alterations. Citation Format: Jack A. Dempsey, Edward M. Chan, Teresa F. Burke, Richard P. Beckmann. LY2835219, a selective inhibitor of CDK4 and CDK6, inhibits growth in preclinical models of human cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr LB-122. doi:10.1158/1538-7445.AM2013-LB-122