Pevonedistat (MLN4924), discovered by Millennium, is a small molecule inhibitor of the NEDD8-Activating Enzyme (NAE), a key component of the protein homeostasis pathway. MLN4924 is a mechanism-based inhibitor of NAE and creates a covalent NEDD8-MLN4924 adduct catalyzed by the enzyme. The NEDD8-MLN4924 adduct resembles NEDD8 adenylate, the first intermediate in the NAE reaction cycle, but cannot be further utilized in subsequent intraenzyme reactions. The stability of the NEDD8-MLN4924 adduct within the NAE active site blocks enzyme activity, thereby accounting for the potent inhibition of the NEDD8 pathway by MLN4924. This drug is in phase II clinical trial for the treatment acute myeloid leukemia, chronic myelomonocytic leukemia and myelodysplastic syndromes. In addition in phase I for treatment acute lymphoblastic leukemia. The ability of MLN4924 to cross the blood-brain barrier, its low toxicity, and clinical efficacy in other cancers suggests that this drug is an attractive treatment against glioblastomas.

Crenolanib is an orally active, highly selective, small molecule, next generation inhibitor of platelet-derived growth factor receptor (PDGFR) tyrosine kinase. Crenolanib, manufactured by Arog Pharmaceuticals in Dallas, is taken orally with chemotherapy. The compound is currently being evaluated for safety and efficacy in clinical trials for various types of cancer, including acute myeloid leukemia (AML), gastrointestinal stromal tumor (GIST), and glioma. Crenolanib is an orally bioavailable, selective small molecule inhibitor of type III tyrosine kinases with nanomolar potencies against platelet-derived growth factor receptors (PDGFR) (isoforms PDGFRα and PDGFRβ) and Fms-related tyrosine kinase 3 (FLT3). Besides PDGFR and FLT3, crenolanib does not inhibit any other known receptor tyrosine kinase (RTK) (e.g. VEGFR and FGFR) or any other serine/threonine kinase (e.g., Abl, Raf) at clinically achievable concentrations. Preclinical trials have shown Crenolanib to be active in inhibiting both wild-type and mutant FLT3. Crenolanib is cytotoxic to the FLT3/ITD-expressing leukemia cell lines Molm14 and MV411, with IC50s of 7 nM and 8 nM, respectively. In immunoblots, crenolanib inhibited phosphorylation of both the wild-type FLT3 receptor (in SEMK2 cells) and the FLT3/ITD receptor (in Molm14 cells) in culture medium with IC50s of 1-3 nM. Importantly, the IC50 of crenolanib against the D835Y mutated form of FLT3 was 8.8 nM in culture medium. Furthermore, crenolanib had cytotoxic activity against primary samples that were obtained from patients who had developed D835 mutations while receiving FLT3 TKIs. In vitro, the IC50 of crenolanib for inhibition of FLT3/ITD in plasma was found to be 34 nM, indicating a relatively low degree of plasma protein binding. From pharmacokinetic studies of crenolanib in solid tumor patients, steady state trough plasma levels of roughly 500 nM were found to be safe and tolerable, suggesting that crenolanib could potentially inhibit the target in vivo. Crenolanib has no significant activity against c-KIT, which may be an advantage in that myelosuppression can be avoided.1Furthermore, there was no evidence of QTc prolongation in patients treated with crenolanib. In summary, crenolanib offers a number of advantages over other FLT3 TKIs. Clinical trials of crenolanib in AML patients with FLT3 activating mutations are being planned.

8-chloroadenosine (8-Cl-Ado) is a ribonucleoside analog. The mechanism of its action remains poorly understood, however, it is known that the drug inhibits RNA synthesis. It has significant cytotoxic activity against lymphoid and myeloid malignant cells. The nucleoside analog 8-Cl-Ado is phosphorylated into its cytotoxic triphosphate 8-Cl-ATP. The accumulation of the cytotoxic metabolite results in a parallel decrease of the ATP cellular pools. 8-Cl-Ado gets incorporated into RNA during transcription, hindering this process. In addition, this triphosphate inhibits ATP-dependent poly(A) tail synthesis, and, as a consequence, mRNA processing is inhibited, resulting in vitro cytotoxicity in several solid and hematological malignancies. This agent is currently in clinical trials for the treatment of chronic lymphocytic leukemia and acute myeloid leukemia.

Volasertib (BI 6727), a dihydropteridinone derivative, is a small-molecule cell cycle inhibitor of polo-like kinase-1 (PLK-1). Volasertib induces G2-M arrest and induction of apoptosis in cancer cells and potently inhibits tumor growth in xenograft models. Boehringer Ingelheim is developing intravenously administered volasertib for the treatment of acute myeloid leukaemia (AML), myelodysplastic syndromes (MDS), chronic myelomonocytic leukaemia (CMML), non-small cell lung cancer, urogenital cancer, ovarian cancer and solid tumours.

Ganetespib (formerly called STA-9090) is a novel, injectable resorcinolic triazolone small molecule inhibitor of Hsp90, developed by Synta Pharmaceuticals. Ganetespib inhibits the growth of many tumor types in vitro and in vivo including AML, ALL, CML, NHL, neuroblastoma, Ewing sarcoma, rhabdoid cancer, rhabdomyosarcoma, melanoma, and carcinomas of the breast, lung, prostate, bladder and colon7-10,14-27. Ganetespib has being studied in multiple adult oncology indications. The 50% inhibitory concentrations (IC50) for Ganetespib against malignant mast cell lines are 10-50 times lower than that for 17-AAG, indicating that triazolone class of HSP90 inhibitors likely exhibits greater potency than geldanamycin based inhibitors. Ganetespib inhibits MG63 cell lines with IC50 of 43 nM. Ganetespib binds to the ATP-binding domain at the N-terminus of Hsp90 and serves as a potent Hsp90 inhibitor by causing degradation of multiple oncogenic Hsp90 client proteins including HER2/neu, mutated EGFR, Akt, c-Kit, IGF-1R, PDGFRα, Jak1, Jak2, STAT3, STAT5, HIF-1α, CDC2 and c-Met as well as Wilms' tumor 1. Ganetespib, at low nanomolar concentrations, potently arrests cell proliferation and induces apoptosis in a wide variety of human cancer cell lines, including many receptor tyrosine kinase inhibitor- and tanespimycin-resistant cell lines. Ganetespib exhibits potent cytotoxicity in a range of solid and hematologic tumor cell lines, including those that express mutated kinases that confer resistance to small-molecule tyrosine kinase inhibitors. Ganetespib has been studied in 5 completed Synta-sponsored clinical trials (Studies 9090-02, 9090-03, 9090-04, 9090-05, and 9090-07) and 3 completed Synta-sponsored studies in normal healthy volunteers (9090-12, 9090-13, and 9090-15). Ganetespib is currently being studied in 6 Synta-sponsored clinical trials. Studies include: one Phase 1 study, three Phase 2 studies, one Phase 2b study, and one Phase 3 study. Ganetespib is also being studied in 24 Investigator Sponsored Trials (ISTs)

Barasertib (AZD1152) is a dihydrogen phosphate prodrug of a pyrazoloquinazoline Aurora kinase inhibitor [AZD1152–hydroxyquinazoline pyrazol anilide (HQPA)] and is converted rapidly to the active AZD1152-HQPA in plasma. AstraZeneca was developing the aurora kinase inhibitor, barasertib (AZD 1152) as a therapeutic for cancer. AZD1152-HQPA is a highly potent and selective inhibitor of Aurora B (Ki, 0.36nmol/L) compared with Aurora A (Ki, 1,369nmol/L) and has a high specificity versus a panel of 50 other kinases. Consistent with inhibition of Aurora B kinase, addition of AZD1152-HQPA to tumour cells in vitro induces chromosome misalignment, prevents cell division, and consequently reduces cell viability and induces apoptosis. Barasertib (AZD1152) potently inhibited the growth of human colon, lung, and haematologic tumour xenografts (mean tumour growth inhibition range, 55% to ≥100%; P < 0.05) in immunodeficient mice. Detailed pharmacodynamic analysis in colorectal SW620 tumour-bearing athymic rats treated i.v. with Barasertib (AZD1152) revealed a temporal sequence of phenotypic events in tumours: transient suppression of histone H3 phosphorylation followed by accumulation of 4N DNA in cells (2.4-fold higher compared with controls) and then an increased proportion of polyploid cells (>4N DNA, 2.3-fold higher compared with controls). Histologic analysis showed aberrant cell division that was concurrent with an increase in apoptosis in AZD1152-treated tumours. Bone marrow analyses revealed transient myelosuppression with the drug that was fully reversible following cessation of Barasertib (AZD1152) treatment. Barasertib (AZD1152) was in phase III for the treatment of Acute myeloid leukaemia, but later these studies were discontinued.

Zosuquidar (LY-335979) is an experimental antineoplastic drug. It is is a potent modulator of P-glycoprotein-mediated multi-drug resistance with Ki of 60 nM. Zosuqidar was initially characterized by Syntex Corporation, which was acquired by Roche in 1990. Roche licensed the drug to Eli Lilly in 1997. It was granted orphan drug status by the FDA in 2006 for AML. Zosuquidar Trihydrochloride had been in phase III clinical trials by Kanisa Pharmaceuticals for the treatment of acute myeloid leukaemia. However, this research has been discontinued.

CPI-613 is a lipoate derivative synthesized to be catalytically inert but to potentially mimic lipoate catalytic intermediates. The drug is in phase II of clinical trials for the treatment of Myelodysplastic syndromes; Pancreatic cancer; Small cell lung cancer; Solid tumors; Bile duct cancer; Acute Myeloid leukemia. The mechanism of CPI-613 action can be explained by (I) inhibition of tumor cell pyruvate dehydrogenase complex (PDC) through activation of pyruvate dehydrogenase kinases leading to inactivating phosphorylation of the E1alpha-subunit of PDC; and (II) inhibition of alpha-ketoglutarate dehydrogenase.

Lestaurtinib (CEP-701, KT-5555) is an orally bio-available polyaromatic indolocarbazole alkaloid derived from K-252a. Lestaurtinib is a multi-targeted tyrosine kinase inhibitor which has been shown to potently inhibit FLT3 at nanomolar concentrations in preclinical studies, leading to its rapid development as a potential targeted agent for treatment of AML. Phase I studies have shown lestaturtinib to be an active agent particularly when used in combination with cytotoxic drugs. Currently, Phase II and Phase III studies are underway aiming to establish the future of this agent as a treatment option for patients with FLT3-ITD AML.

2-Cyano-3,12-dioxooleana-1,9-diene-28-oic acid (CDDO, also known as Bardoxolone) is a synthetic triterpenoid that displays potent anti-inflammatory and antitumorigenic activities. CDDO was in the clinical trial phase I for the treatment patients with Solid tumors and leukemia, but that studies were discontinued. It is known, that CDDO blocks the cellular synthesis of inducible nitric oxide synthase and inducible COX-2. In addition, was discovered, that CDDO disrupted intracellular redox balance and thereby induce apoptosis. Moreover, CDDO is a ligand for peroxisome proliferator-activated receptor that it induces genes regulated by Nrf2, including heme oxygenase-1 and eotaxin-1, which play a role in antioxidant response element signaling activity.