Dinaciclib inhibits the growth of acute myeloid leukemia cells through either cell cycle-related or ERK1/STAT3/MYC pathways

Although immature differentiation and uncontrolled proliferation of hematopoietic stem cells are thought to be the primary mechanisms of acute myeloid leukemia (AML), the pathophysiology in most cases remains unclear. Dinaciclib, a selective small molecule targeting multiple cyclin-dependent kinases (CDKs), is currently being evaluated in oncological clinical trials. Despite the proven anticancer potential of dinaciclib, the differential molecular mechanisms by which it inhibits the growth of different AML cell lines remain unclear. In the current study, we treated HL-60 and KG-1 AML cell lines with dinaciclib and investigated the potential mechanisms of dinaciclib-induced AML cell growth inhibition using flow cytometry and western blotting assays. Data from HL-60 and KG-1 AML cells were validated using human primary AML cells. The results showed that the growth inhibitory effect of dinaciclib was more sensitive in HL-60 cells (IC50: 8.46 nM) than in KG-1 cells (IC50: 14.37 nM). The protein decline in Cyclin A/B and CDK1 and cell cycle arrest in the G2/M phase were more profound in HL-60 cells, corresponding to its growth inhibition. Although the growth inhibition of KG-1 cells by dinaciclib was still pronounced, the cell cycle-associated proteins were relatively insensitive. In addition to cell cycle regulation, the activation/expression of ERK1/STAT3/MYC signaling was significantly reduced by dinaciclib in KG-1 cells compared with that in HL-60 cells. Regarding the results of primary AML cells, we observed ERK1/STAT3/MYC inhibition and cell cycle regulation in different patients. These findings suggest that the cell cycle-associated and ERK1/STAT3/MYC signaling pathways might be two distinct mechanisms by which dinaciclib inhibits AML cells, which could facilitate the development of combination therapy for AML in the future.

The multi-CDK inhibitor dinaciclib reverses bromo- and extra-terminal domain (BET) inhibitor resistance in acute myeloid leukemia via inhibition of Wnt/β-catenin signaling

Acute myeloid leukemia (AML) is a highly aggressive hematologic cancer with poor survival across a broad range of molecular subtypes. Development of efficacious and well-tolerable therapies encompassing the range of mutations that can arise in AML remains an unmet need. The bromo- and extra-terminal domain (BET) family of proteins represents an attractive therapeutic target in AML due to their crucial roles in many cellular functions, regardless of any specific mutation. Many BET inhibitors (BETi) are currently in pre-clinical and early clinical development, but acquisition of resistance continues to remain an obstacle for the drug class. Novel methods to circumvent this development of resistance could be instrumental for the future use of BET inhibitors in AML, both as monotherapy and in combination. To date, many investigations into possible drug combinations of BETi with CDK inhibitors have focused on CDK9, which has a known physical and functional interaction with the BET protein BRD4. Therefore, we wished to investigate possible synergy and additive effects between inhibitors of these targets in AML. Here, we describe combination therapy with the multi-CDK inhibitor dinaciclib and the BETi PLX51107 in pre-clinical models of AML. Dinaciclib and PLX51107 demonstrate additive effects in AML cell lines, primary AML samples, and in vivo. Further, we demonstrate novel activity of dinaciclib through inhibition of the canonical/β-catenin dependent Wnt signaling pathway, a known resistance mechanism to BETi in AML. We show dinaciclib inhibits Wnt signaling at multiple levels, including downregulation of β-catenin, the Wnt co-receptor LRP6, as well as many Wnt pathway components and targets. Moreover, dinaciclib sensitivity remains unaffected in a setting of BET resistance, demonstrating similar inhibitory effects on Wnt signaling when compared to BET-sensitive cells. Ultimately, our results demonstrate rationale for combination CDKi and BETi in AML. In addition, our novel finding of Wnt signaling inhibition could have potential implications in other cancers where Wnt signaling is dysregulated and demonstrates one possible approach to circumvent development of BET resistance in AML.

Identification of a novel potent CDK inhibitor degrading cyclinK with a superb activity to reverse trastuzumab-resistance in HER2-positive breast cancer in vivo

CDK12 is overexpressed in HER2-positive breast cancers and promotes tumorigenesis and trastuzumab resistance. Thus CDK12 is a good therapeutic target for the HER2-positive breast tumors resistant to trastuzumab. We previously reported a novel purine-based CDK inhibitor with an ability to degrade cyclinK. Herein, we further explored and synthesized new derivatives, and identified a new potent pan-CDK inhibitor degrading cyclinK (32e). Compound 32e potently inhibited CDK12/cyclinK with IC50 = 3 nM, and suppressed the growth of the both trastuzumab-sensitive and trastuzumab-resistant HER2-positive breast cancer cell lines (GI50's = 9-21 nM), which is superior to a potent, clinical pan-CDK inhibitor dinaciclib. Moreover, 32e (10, 20 mg/kg, ip, twice a week) showed a dose-dependent inhibition of tumor growth and a more dramatic anti-cancer effect than dinaciclib in mouse in vivo orthotopic breast cancer model of trastuzumab-resistant HCC1954 cells. Kinome-wide inhibition profiling revealed that 32e at 1 μM exhibits a decent selectivity toward CDK-family kinases including CDK12 over other wildtype protein kinases. Quantitative global proteomic analysis of 32e-treated HCC1954 cells demonstrated that 32e also showed a decent selectivity in degrading cyclinK over other cyclins. Compound 32e could be developed as a drug for intractable trastuzumab-resistant HER2-positive breast cancers. Our current study would provide a useful insight in designing potent cyclinK degraders.

Drug combinations identified by high-throughput screening promote cell cycle transition and upregulate Smad pathways in myeloma

Drug resistance and disease progression are common in multiple myeloma (MM) patients, underscoring the need for new therapeutic combinations. A high-throughput drug screen in 47 MM cell lines and in silico Huber robust regression analysis of drug responses revealed 43 potentially synergistic combinations. We hypothesized that effective combinations would reduce MYC expression and enhance p16 activity. Six combinations cooperatively reduced MYC protein, frequently over-expressed in MM and also cooperatively increased p16 expression, frequently downregulated in MM. Synergistic reductions in viability were observed with top combinations in proteasome inhibitor-resistant and sensitive MM cell lines, while sparing fibroblasts. Three combinations significantly prolonged survival in a transplantable Ras-driven allograft model of advanced MM closely recapitulating high-risk/refractory myeloma in humans and reduced viability of ex vivo treated patient cells. Common genetic pathways similarly downregulated by these combinations promoted cell cycle transition, whereas pathways most upregulated were involved in TGFβ/SMAD signaling. These preclinical data identify potentially useful drug combinations for evaluation in drug-resistant MM and reveal potential mechanisms of combined drug sensitivity.

Structural basis of CDK3 activation by cyclin E1 and inhibition by dinaciclib

Cell cycle transitions are controlled by multiple cell cycle regulators, especially CDKs. Several CDKs, including CDK1-4 and CDK6, promote cell cycle progression directly. Among them, CDK3 is critically important because it triggers the transitions of G0 to G1 and G1 to S phase through binding to cyclin C and cyclin E1, respectively. In contrast to its highly related homologs, the molecular basis of CDK3 activation remains elusive due to the lack of structural information of CDK3, particularly in cyclin bound form. Here we report the crystal structure of CDK3 in complex with cyclin E1 at 2.25 Å resolution. CDK3 resembles CDK2 in that both adopt a similar fold and bind cyclin E1 in a similar way. The structural discrepancy between CDK3 and CDK2 may reflect their substrate specificity. Profiling a panel of CDK inhibitors reveals that dinaciclib inhibits CDK3-cyclin E1 potently and specifically. The structure of CDK3-cyclin E1 bound to dinaciclib reveals the inhibitory mechanism. The structural and biochemical results uncover the mechanism of CDK3 activation by cyclin E1 and lays a foundation for structural-based drug design.

Identification of novel piperazine-tethered phthalazines as selective CDK1 inhibitors endowed with in vitro anticancer activity toward the pancreatic cancer

Pharmacologic inhibition of the oncogenic protein kinases using small molecules is a promising strategy to combat several human malignancies. CDK1 is an example of such a valuable target for the management of pancreatic ductal adenocarcinomas (PDAC); its overexpression in PDAC positively correlates with the size, histological grade and tumor aggressiveness. Here we report the identification of novel series of 1-piperazinyl-4-benzylphthalazine derivatives (8a-g, 10a-i and 12a-d) as promising anticancer agents with CDK1 inhibitory activity. The anti-proliferative activity of these agents was first screened on a panel of 11 cell lines representing 5 cancers (pancreas, melanoma, leukemia, colon and breast), and then confirmed on two CDK1-overexpressing PDAC cell lines (MDA-PATC53 and PL45 cells). Phthalazines 8g, 10d and 10h displayed potent activity against MDA-PATC53 (IC₅₀ = 0.51, 0.88 and 0.73 μM, respectively) and PL45 (IC₅₀ = 0.74, 1.14 and 1.00 μM, respectively) cell lines. Furthermore, compounds 8g, 10d and 10h exhibited potent and selective inhibitory activity toward CDK1 with IC₅₀ spanning in the range 36.80-44.52 nM, whereas they exerted weak inhibitory effect on CDK2, CDK5, AXL, PTK2B, FGFR, JAK1, IGF1R and BRAF kinases. Western blotting of CDK1 in MDA-PATC53 cells confirmed the ability of target phthalazines to diminish the CDK1 levels, and cell cycle analyses revealed their ability to arrest the cell cycle at G2/M phase. In conclusion, a panel of potent and selective CDK1 inhibitors were identified which can serve as lead compounds for designing further CDK1 inhibitors.

Targeting cyclin-dependent kinase 1 (CDK1) in cancer: molecular docking and dynamic simulations of potential CDK1 inhibitors

Cell cycle dysregulation is a characteristic hallmark of malignancies, which results in uncontrolled cell proliferation and eventual tumor formation. Cyclin-dependent kinase 1 (CDK1) is a member of the family of cell cycle regulatory proteins involved in cell cycle maintenance. Given that overexpression of CDK1 has been associated with cancer, CDK1 inhibitors may restore equilibrium to the skewed cell cycle system and operate as an effective therapeutic drug. This study aimed to identify and classify inhibitors having a higher affinity for CDK1 and also evaluate the expression pattern and prognostic relevance of CDK1 in a wide range of cancers. We investigated therapeutic molecules structurally similar to dinaciclib for their ability to inhibit CDK1 selectively. To assess the therapeutic potential of screened Dinaciclib analogs, we used drug likeliness analysis, molecular docking, and simulation analysis. CDK1 was found to be highly upregulated across several malignancies and is associated with poor overall and relapse-free survival. Molecular docking and dynamics evaluation identified two novel dinaciclib analogs as potent CDK1 inhibitors with high binding affinity and stability compared to dinaciclib. The results indicate that increased CDK1 expression is associated with decreased OS and RFS. Additionally, dinaciclib analogs are prospective replacements for dinaciclib since they exhibit increased binding affinity, consistent with MDS findings, and have acceptable ADMET qualities. The discovery of new compounds may pave the road for their future application in cancer prevention through basic, preclinical, and clinical research.

Synthetic lethality of cyclin-dependent kinase inhibitor Dinaciclib with VHL-deficiency allows for selective targeting of clear cell renal cell carcinoma

Clear cell renal cell carcinoma (CC-RCC) remains one of the most deadly forms of kidney cancer despite recent advancements in targeted therapeutics, including tyrosine kinase and immune checkpoint inhibitors. Unfortunately, these therapies have not been able to show better than a 16% complete response rate. In this study we evaluated a cyclin-dependent kinase inhibitor, Dinaciclib, as a potential new targeted therapeutic for CC-RCC. In vitro, Dinaciclib showed anti-proliferative and pro-apoptotic effects on CC-RCC cell lines in Cell Titer Glo, Crystal Violet, FACS-based cell cycle analysis, and TUNEL assays. Additionally, these responses were accompanied by a reduction in phospho-Rb and pro-survival MCL-1 cell signaling responses, as well as the induction of caspase 3 and PARP cleavage. In vivo, Dinaciclib efficiently inhibited primary tumor growth in an orthotopic, patient-derived xenograft-based CC-RCC mouse model. Importantly, Dinaciclib targeted both CD105⁺ cancer stem cells (CSCs) and CD105⁻ non-CSCs in vivo. Moreover, normal cell lines, as well as a CC-RCC cell line with re-expressed von-Hippel Lindau (VHL) tumor suppressor gene, were protected from Dinaciclib-induced cytotoxicity when not actively dividing, indicating an effective therapeutic window due to synthetic lethality of Dinaciclib treatment with VHL loss. Thus, Dinaciclib represents a novel potential therapeutic for CC-RCC.

Bioinformatics analysis identified CDC20 as a potential drug target for cholangiocarcinoma

BACKGROUND

Cholangiocarcinoma (CCA) is a malignancy that originates from bile duct cells. The incidence and mortality of CCA are very high especially in Southeast Asian countries. Moreover, most CCA patients have a very poor outcome. Presently, there are still no effective treatment regimens for CCA. The resistance to several standard chemotherapy drugs occurs frequently; thus, searching for a novel effective treatment for CCA is urgently needed.

METHODS

In this study, comprehensive bioinformatics analyses for identification of novel target genes for CCA therapy based on three microarray gene expression profiles (GSE26566, GSE32225 and GSE76297) from the Gene Expression Omnibus (GEO) database were performed. Based on differentially expressed genes (DEGs), gene ontology and pathway enrichment analyses were performed. Protein-protein interactions (PPI) and hub gene identifications were analyzed using STRING and Cytoscape software. Then, the expression of candidate genes from bioinformatics analysis was measured in CCA cell lines using real time PCR. Finally, the anti-tumor activity of specific inhibitor against candidate genes were investigated in CCA cell lines cultured under 2-dimensional and 3-dimensional cell culture models.

RESULTS

The three microarray datasets exhibited an intersection consisting of 226 DEGs (124 up-regulated and 102 down-regulated genes) in CCA. DEGs were significantly enriched in cell cycle, hemostasis and metabolism pathways according to Reactome pathway analysis. In addition, 20 potential hub genes in CCA were identified using the protein-protein interaction (PPI) network and sub-PPI network analysis. Subsequently, CDC20 was identified as a potential novel targeted drug for CCA based on a drug prioritizing program. In addition, the anti-tumor activity of a potential CDC20 inhibitor, namely dinaciclib, was investigated in CCA cell lines. Dinaciclib demonstrated huge anti-tumor activity better than gemcitabine, the standard chemotherapeutic drug for CCA.

CONCLUSION

Using integrated bioinformatics analysis, CDC20 was identified as a novel candidate therapeutic target for CCA.

MYC Upregulation Confers Resistance to Everolimus and Establishes Vulnerability to Cyclin-Dependent Kinase Inhibitors in Pancreatic Neuroendocrine Neoplasm Cells

INTRODUCTION

Dysregulation of the mechanistic target of rapamycin complex 1 (mTORC1)-dependent pathways in pancreatic neuroendocrine neoplasms (PanNENs) underlies the introduction of the mTORC1 inhibitor everolimus as treatment of advanced progressive PanNENs. Although everolimus significantly increases progression-free survival, most patients acquire secondary resistance to the drug. This study aimed at identifying mechanisms involved in acquisition of resistance to everolimus.

METHODS

BON-1 and everolimus-resistant (ER) BON-1 cells were used as in vitro system of sensitivity and acquired resistance. Transcriptome changes occurring in BON-1 and ER-BON-1 were investigated by RNA sequencing and validated by quantitative PCR analysis. RNA extracted from patients' biopsies was used to validate MYC upregulation. Drug screening and functional assays were performed using ER-BON-1 cells. Cell cycle progression was evaluated by FACS analysis.

RESULTS

Our results show that MYC overexpression is a key event in the development of secondary resistance to everolimus in PanNEN cell lines and in metastatic lesions from neuroendocrine neoplasm patients. MYC knockdown restored ER-BON-1 sensitivity to everolimus. Pharmacological inhibition of MYC mediated by the cyclin-dependent kinase inhibitor dinaciclib strongly reduced viability of ER-BON-1. Dinaciclib synergized with everolimus and inhibited ER-BON-1 cell cycle progression.

DISCUSSION

Our findings suggest that MYC upregulation drives the development of secondary resistance to everolimus in PanNENs and that its inhibition is an exploitable vulnerability. Indeed, our results indicate that combined treatments with cyclin-dependent kinase and mTOR inhibitors may counteract secondary resistance to everolimus in PanNENs and may pave the ground for new therapeutic regimens for these tumors.

Accumulated cytotoxicity of CDK inhibitor dinaciclib with first-line chemotherapy drugs in salivary adenoid cystic carcinoma cells

Adenoid cystic carcinoma (ACC) is one of the most common salivary gland malignant tumors. Its treatment failure is partly due to the limitations of chemotherapeutic agents and their adverse effects. The objective of this study was to determine the potential additive anti-cancer effect of a novel CDK inhibitor dinaciclib with first-line chemotherapy drugs in ACC. Protein expression of phosphorylated CDK2 (p-CDK2) in paraffin-embedded tissue specimens of ACC from 17 patients was investigated by immunohistochemistry (IHC). Cell Counting Kit (CCK-8), clone formation assay, and flow cytometry were used to test the proliferation and apoptosis of ACC-2 cells treated with dinaciclib with or without other first-line chemotherapy drugs. Protein expression was also determined by Western blot. Interestingly, we discovered that p-CDK2 protein was expressed in both cytoplasmic and nucleus in salivary ACC tissues, which was higher than that in normal salivary tissues, indicating that agents targeting CDK2 may be potential therapeutic strategies against this type of tumor. As expected, CDK inhibitor dinaciclib significantly induced ACC-2 cells apoptosis. Moreover, it sensitized cells to the chemotherapeutic agents such as cisplatin, pemetrexed, and etoposide (VP-16), and this effect by dinaciclib may induce cell cycle arrest via abrogating CDK2 activity. Therefore, combinational therapy of CDK inhibitor dinaciclib with first-line chemotherapy drugs may be a promising strategy in the treatment of salivary ACC.

High-throughput screening identifies candidate drugs for the treatment of recurrent respiratory papillomatosis

Recurrent respiratory papillomatosis (RRP) is a benign neoplasm of the larynx caused mainly by human papillomavirus type 6 or 11 and its standard treatment involves repeated surgical debulking of the laryngeal tumors. However, significant morbidity and occasional mortality due to multiple recurrences occur. Conditional reprogramming (CR) was used to establish a HPV-6 positive culture from an RRP patient, named GUMC-403. High-throughput screening was performed at the National Center for Advanced Technology (NCATS) to identify potential drugs to treat this rare but morbid disease. GUMC-403 cells were screened against the NPC library of >2800 approved drugs and the MIPE library of >1900 investigational drugs to identify new uses for FDA-approved drugs or drugs that have undergone significant research and development. From the two libraries, we identified a total of 13 drugs that induced significant cytotoxicity in RRP cells at IC50 values that were clinically achievable. We validated the efficacy of the drugs in vitro using CR 2D and 3D models and further refined our list of drugs to panobinostat, dinaciclib and forskolin as potential therapies for RRP patients.

Anti-tumor effect of CDK inhibitors on CDKN2A-defective squamous cell lung cancer cells

BACKGROUND

Squamous cell lung cancer (SqCLC) is a distinct histologic subtype of non-small cell lung cancer (NSCLC). Although the discovery of driver mutations and their targeted drugs has remarkably improved the treatment outcomes for lung adenocarcinoma, currently no such molecular target is clinically available for SqCLC. The CDKN2A locus at 9p21 encodes two alternatively spliced proteins, p16^INK4a (p16) and p14^ARF (p14), which function as cell cycle inhibitors. The Cancer Genome Atlas (TCGA) project revealed that CDKN2A is inactivated in 72% of SqCLC cases. In addition, it was found that CDKN2A mutations are significantly more common in SqCLC than in adenocarcinoma. Down-regulation of p16 and p14 by CDKN2A gene inactivation leads to activation of cyclin-dependent kinases (CDKs), thereby permitting constitutive phosphorylation of Rb and subsequent cell cycle progression. Here, we hypothesized that CDK inhibition may serve as an attractive strategy for the treatment of CDKN2A-defective SqCLC.

METHODS

We investigated whether the CDK inhibitors flavopiridol and dinaciclib may exhibit antitumor activity in CDKN2A-defective SqCLC cells compared to control cells. The cytotoxic effect of the CDK inhibitors was evaluated using cell viability assays, and the induction of apoptosis was assessed using TUNEL assays and Western blot analyses. Finally, anti-tumor effects of the CDK inhibitors on xenografted cells were investigated in vivo.

RESULTS

We found that flavopiridol and dinaciclib induced cytotoxicity by enhancing apoptosis in CDKN2A-defective SqCLC cells, and that epithelial to mesenchymal transition (EMT) decreased and autophagy increased during this process. In addition, we found that autophagy had a cytoprotective role.

CONCLUSION

Our data suggest a potential role of CDK inhibitors in managing CDKN2A-defective SqCLC.

The emerging roles of CDK12 in tumorigenesis

Cyclin-dependent kinases (CDKs) are key regulators of both cell cycle progression and transcription. Since dysregulation of CDKs is a frequently occurring event driving tumorigenesis, CDKs have been tested extensively as targets for cancer therapy. Cyclin-dependent kinase 12 (CDK12) is a transcription-associated kinase which participates in various cellular processes, including DNA damage response, development and cellular differentiation, as well as splicing and pre-mRNA processing. CDK12 mutations and amplification have been recently reported in different types of malignancies, including loss-of-function mutations in high-grade serous ovarian carcinomas, and that has led to assumption that CDK12 is a tumor suppressor. On the contrary, CDK12 overexpression in other tumors suggests the possibility that CDK12 has oncogenic properties, similarly to other transcription-associated kinases. In this review, we discuss current knowledge concerning the role of CDK12 in ovarian and breast tumorigenesis and the potential for chemical inhibitors of CDK12 in future cancer treatment.

Dinaciclib, a cyclin-dependent kinase inhibitor, is a substrate of human ABCB1 and ABCG2 and an inhibitor of human ABCC1 in vitro. Biochem Pharmacol. 2015;98:465-472. [PMID: 26300056 DOI: 10.1016/j.bcp.2015.08.099]

Dinaciclib is a novel cyclin-dependent kinase inhibitor (CDKI) with significant activity against various cancers in vitro and in vivo. ABC efflux transporters play an important role in drug disposition and are responsible for multidrug resistance in cancer cells. Inhibitors and substrates of these transporters may participate in pharmacokinetic drug-drug interactions (DDIs) that alter drug disposition during pharmacotherapy. To assess such risks associated with dinaciclib we evaluated its possible effects on efflux activities of ABCB1, ABCC1 and ABCG2 transporters in vitro. Monolayer transport, XTT cell proliferation, ATPase and intracellular accumulation assays were employed. Here, we show that the transport ratio of dinaciclib was far higher across monolayers of MDCKII-ABCB1 and MDCKII-ABCG2 cells than across MDCKII parental cell layers, demonstrating that dinaciclib is a substrate of ABCB1 and ABCG2. In addition, overexpression of ABCB1, ABCG2 and ABCC1 conferred resistance to dinaciclib in MDCKII cells. In ATPase assays, dinaciclib decreased stimulated ATPase activity of ABCB1, ABCG2 and ABCC1, confirming it has interactive potential toward all three transporters. Moreover, dinaciclib significantly inhibited ABCC1-mediated efflux of daunorubicin (EC50=18 μM). The inhibition of ABCC1 further led to a synergistic effect of dinaciclib in both MDCKII-ABCC1 and human cancer T47D cells, when applied in combination with anticancer drugs. Taken together, our results suggest that ABC transporters can substantially affect dinaciclib transport across cellular membranes, leading to DDIs. The DDIs of dinaciclib with ABCC1 substrate chemotherapeutics might be exploited in novel cancer therapies.

Randomized phase 2 study of the cyclin-dependent kinase inhibitor dinaciclib (MK-7965) versus erlotinib in patients with non-small cell lung cancer

OBJECTIVES

Dinaciclib (MK-7965, formerly SCH 727965), a novel, small-molecule inhibitor of cyclin-dependent kinases, has been shown to induce apoptosis in preclinical studies of human tumor cell lines, including non-small cell lung cancer (NSCLC) cells. Erlotinib, an epidermal growth factor receptor inhibitor, is approved for the treatment of advanced NSCLC as second- or third-line therapy. This phase 2, randomized, multicenter, open-label study compared dinaciclib with erlotinib in patients with previously treated NSCLC.

MATERIALS AND METHODS

The study was comprised of 2 parts: in part 1, patients were randomized to either intravenous (IV) dinaciclib (50 mg/m2) or oral erlotinib (150 mg) using an adaptive Bayesian design that adjusted the randomization ratio in favor of the more active arm, and in part 2, patients who had progressed on erlotinib were permitted to cross over to receive dinaciclib at the same dosage as in part 1. Patients were followed until disease progression or death, initiation of nonstudy cancer treatment, discontinuation, or withdrawal of consent. The primary efficacy end point was time-to-progression (TTP) in part 1 and objective response rate (ORR) in part 2.

RESULTS

Based on Kaplan-Meier estimates, the median TTP was 1.49 months (95% confidence interval [CI]: 1.31, 2.63) following initial treatment with dinaciclib, compared with 1.58 months (95% CI: 1.38, 2.83) with erlotinib. No objective responses were observed following initial treatment with dinaciclib. Common severe (grade 3 or 4) drug-related adverse effects included neutropenia, leukopenia, vomiting, and diarrhea.

CONCLUSIONS

Dinaciclib, administered IV, was well tolerated at the 50 mg/m2 dose, but does not have activity as monotherapy in previously treated NSCLC. Evaluation of dinaciclib in combination with other agents for other indications including breast cancer and multiple myeloma is in progress.