Regioselective synthesis of water-soluble monophosphate derivatives of combretastatin A-1.

The natural products combretastatin A-4 (CA4) and combretastatin A-1 (CA1) are potent cancer vascular disrupting agents and inhibitors of tubulin assembly (IC₅₀ = 1-2 μM). The phosphorylated prodrugs CA4P and CA1P are undergoing human clinical trials against cancer. CA1 is unique due to its incorporation of a vicinal phenol, which has afforded the opportunity to prepare both diphosphate and regioisomeric monophosphate derivatives.

Functionalized benzophenone, thiophene, pyridine, and fluorene thiosemicarbazone derivatives as inhibitors of cathepsin L.

A series of thiosemicarbazone analogs based on the benzophenone, thiophene, pyridine, and fluorene molecular frameworks has been prepared by chemical synthesis and evaluated as small-molecule inhibitors of the cysteine proteases cathepsin L and cathepsin B. The two most potent inhibitors of cathepsin L in this series (IC(50)<135 nM) are brominated-benzophenone thiosemicarbazone analogs that are further functionalized with a phenolic moiety (2 and 6). In addition, a bromo-benzophenone thiosemicarbazone acetyl derivative (3) is also strongly inhibitory against cathepsin L (IC(50)=150.

Pharmacokinetic/pharmacodynamic modeling identifies SN30000 and SN29751 as tirapazamine analogues with improved tissue penetration and hypoxic cell killing in tumors.

Purpose: Tirapazamine (TPZ) has attractive features for targeting hypoxic cells in tumors but has limited clinical activity, in part because of poor extravascular penetration. Here, we identify improved TPZ analogues by using a spatially resolved pharmacokinetic/pharmacodynamic (SR-PKPD) model that considers tissue penetration explicitly during lead optimization.

Experimental Design: The SR-PKPD model was used to guide the progression of 281 TPZ analogues through a hierarchical screen.

Regio- and stereospecific synthesis of mono-beta-d-glucuronic acid derivatives of combretastatin A-1.

Synthetic routes have been established for the preparation of regio- and stereoisomerically pure samples of the mono-beta-d-glucuronic acid derivatives of combretastatin A-1, referred to as CA1G1 (5a) and CA1G2 (6a). Judicious choice of protecting groups for the catechol ring was required for the regiospecific introduction of the glucuronic acid moiety. The tosyl group proved advantageous in this regard.

Design, synthesis, and biological evaluation of potent thiosemicarbazone based cathepsin L inhibitors.

A small library of 36 functionalized benzophenone thiosemicarbazone analogs has been prepared by chemical synthesis and evaluated for their ability to inhibit the cysteine proteases cathepsin L and cathepsin B. Inhibitors of cathepsins L and B have the potential to limit or arrest cancer metastasis. The six most active inhibitors of cathepsin L (IC50<85 nM) in this series incorporate a meta-bromo substituent in one aryl ring along with a variety of functional groups in the second aryl ring.

Hypoxia-selective 3-alkyl 1,2,4-benzotriazine 1,4-dioxides: the influence of hydrogen bond donors on extravascular transport and antitumor activity.

Tirapazamine (TPZ) and related 1,2,4-benzotriazine 1,4 dioxides (BTOs) are selectively toxic under hypoxia, but their ability to kill hypoxic cells in tumors is generally limited by their poor extravascular transport. Here we show that removing hydrogen bond donors by replacing the 3-NH2 group of TPZ with simple alkyl groups increased their tissue diffusion coefficients as measured in multicellular layer cultures. This advantage was largely retained using solubilizing 3-alkylaminoalkyl substituents provided these were sufficiently lipophilic at pH 7.

Pharmacokinetic/pharmacodynamic model-guided identification of hypoxia-selective 1,2,4-benzotriazine 1,4-dioxides with antitumor activity: the role of extravascular transport.

Pharmacokinetic/pharmacodynamic (PK/PD) modeling has shown the antitumor activity of tirapazamine (TPZ), a bioreductive hypoxia-selective cytotoxin, to be limited by poor penetration through hypoxic tumor tissue. We have prepared a series of 1,2,4-benzotriazine 1,4-dioxide (BTO) analogues of TPZ to improve activity against hypoxic cells by increasing extravascular transport. The 6 substituents modified lipophilicity and rates of hypoxic metabolism.

Oxygen dependence and extravascular transport of hypoxia-activated prodrugs: comparison of the dinitrobenzamide mustard PR-104A and tirapazamine.

Purpose: To compare oxygen dependence and tissue transport properties of a new hypoxia-activated prodrug, PR-104A, with tirapazamine, and to evaluate the implications for antitumor activity when combined with radiotherapy.

Methods And Materials: Oxygen dependence of cytotoxicity was measured by clonogenic assay in SiHa cell suspensions. Tissue transport parameters were determined using SiHa multicellular layers.

Oxygen dependence of the metabolic activation and cytotoxicity of tirapazamine: implications for extravascular transport and activity in tumors.

The hypoxic cytotoxin tirapazamine (TPZ) is currently in phase III clinical trial and appears to have clinical activity. One hypothesis as to why TPZ has been used more successfully in the clinic than most other bioreductive drugs is that its unusual O(2) dependence allows killing of radioresistant cells at "intermediate" O(2) concentrations. We have determined the O(2) dependence of the metabolism of TPZ to its reduction product SR 4317, and its cytotoxicity, in stirred suspensions of HT29 colon carcinoma cells while monitoring O(2) in solution with an Oxylite trade mark probe.

Selective potentiation of the hypoxic cytotoxicity of tirapazamine by its 1-N-oxide metabolite SR 4317.

Tirapazamine (TPZ), a bioreductive drug with selective toxicity for hypoxic cells in tumors, is currently in Phase III clinical trials. It has been suggested to have a dual mechanism of action, both generating DNA radicals and oxidizing these radicals to form DNA breaks; whether the second (radical oxidation) step is rate-limiting in cells is not known. In this study we exploit the DNA radical oxidizing ability of the 1-N-oxide metabolite of TPZ, SR 4317, to address this question.

HIF-1 as a target for drug development.

Sensing and responding to fluxes in oxygen tension is perhaps the single most important variable in physiology, and animal tissues have developed a number of essential mechanisms to cope with the stress of low physiological oxygen levels, or hypoxia. Among these coping mechanisms is the response mediated by the hypoxia-inducible transcription factor, or HIF-1. HIF-1 is an essential component in changing the transcriptional repertoire of tissues as oxygen levels drop, and could prove to be a very important target for drug development, as treatments evolve for diseases, such as cancer, heart disease and stroke, in which hypoxia is a central aspect.

Unsymmetrical DNA cross-linking agents: combination of the CBI and PBD pharmacophores.

A set of 10 compounds, each combining the seco-1,2,9,9a-tetrahydrocyclopropa[c]benz[e]indol-4-one (seco-CBI) and pyrrolo[2,1-c][1,4]benzodiazepine (PBD) pharmacophores, was designed and prepared. These compounds were anticipated to cross-link between N3 of adenine and N2 of guanine in the minor groove of DNA. The compounds, which differ in the chain length separating the two alkylation subunits, and the configuration of the CBI portion, showed great variation in cellular toxicity (over 4 orders of magnitude in a cell line panel) with the most potent example exhibiting IC50s in the pM range.

Marked potentiation of the antitumour activity of chemotherapeutic drugs by the antivascular agent 5,6-dimethylxanthenone-4-acetic acid (DMXAA).

Purpose: To determine whether there is a therapeutic interaction between the antivascular agent 5,6-dimethylxanthenone-4-acetic acid (DMXAA) and nine chemotherapy drugs against an early-passage mouse mammary tumour (MDAH-MCa-4), and to investigate the mechanism of any such interaction.

Methods And Results: Female C3H/HeN mice bearing intramuscular MDAH-MCa-4 tumours were injected intraperitoneally with DMXAA (80 micro mol/kg) or chemotherapy drug (at a range up to the maximum tolerated dose) alone, or coadministered. A small reduction in the dose of the chemotherapy drug was required in most cases, but the increase in antitumour effect was much greater than the increase in host toxicity (body weight loss).