Professor Tom Connors and the development of novel cancer therapies by the Phase I/II Clinical Trials Committee of Cancer Research UK

Polymer therapeutics at a crossroads? Finding the path for improved translation in the twenty-first century

Despite the relatively small early investment, first generation 'polymer therapeutics' have been remarkably successful with more than 25 products licenced for human use as polymeric drugs, sequestrants, conjugates, and as an imaging agent. Many exhibit both clinical and commercial success with new concepts already in clinical trials. Nevertheless after four decades of evolution, this field is arriving at an important crossroads. Over the last decade, the landscape has changed rapidly. There are an increasing number of failed clinical trials, the number of 'copy' and 'generic' products is growing (danger of ignoring the biological rationale for design and suppression of innovation), potential drawbacks of PEG are becoming more evident, and the 'nanomedicine' boom has brought danger of loss of scientific focus/hype. Grasping opportunities provided by advances in understanding of the patho-physiology and molecular basis of diseases, new polymer/conjugate synthetic and analytical methods, as well as the large database of clinical experience will surely ensure a successful future for innovative polymer therapeutics. Progress will, however, be in jeopardy if polymer safety is overlooked in respect of the specific route of administration/clinical use, poorly characterised materials/formulations are used to define biological or early clinical properties, and if clinical trial protocols fail to select patients most likely to benefit from these macromolecular therapeutics. Opportunities to improve clinical trial design for polymer-anticancer drug conjugates are discussed. This short personal perspective summarises some of the important challenges facing polymer therapeutics in R&D today, and future opportunities to improve successful translation.

Cancer Research UK Centre for Drug Development: translating 21st-century science into the cancer medicines of tomorrow

The Cancer Research UK Centre (CRUK) for Drug Development (CDD) can trace its origins back to the Cancer Research Campaign Phase I/II Committee (created in 1980) and to date has tested over 120 potential cancer medicines in early-phase clinical trials. Five drugs are now registered, providing benefit to thousands of patients with cancer as part of their routine standard of care. In recent years, the CDD has established several different business and operating models that provide it with access to the pipelines of pharmaceutical and biotechnology companies. This has enabled potential new treatments to be taken into clinical development that might have otherwise languished on companies' shelves and has increased the number of drug combinations being explored in early-phase clinical trials.

Abiraterone acetate: redefining hormone treatment for advanced prostate cancer

Prostate cancer has long since been recognised as being hormonally driven via androgen receptor signalling. Abiraterone acetate (AA) is a rationally designed CYP17 inhibitor that blocks the conversion of androgens from non-gonadal precursors effectively, thus reducing testosterone to undetectable levels. AA has recently been proved to extend survival for men with metastatic castration-resistant prostate cancer who have progressive disease after first-line chemotherapy treatment. In addition, it is currently being tested in a Phase III trial in the pre-chemotherapy setting. This paper will review the preclinical discovery and clinical development of AA and will outline the strategy of parallel translational research.

Effects of cytokine-induced macrophages on the response of tumor cells to banoxantrone (AQ4N)

Tumor-associated macrophages (TAMs) are found in many solid tumors and have often been shown to accumulate in the hypoxic regions surrounding areas of necrosis. TAMs are the major site of expression of nitric oxide synthase (NOS), a heme-containing homodimeric enzyme consisting of oxygenase and reductase domains. The latter has a high degree of sequence homology to cytochrome P450 reductase and a functional consequence of this is the ability of NOS, under hypoxic conditions, to activate the bioreductive drugs tirapazamine and RSU1069. Banoxantrone (AQ4N) is a bioreductive prodrug activated in hypoxia by an oxygen-dependent two-electron reductive process to yield the topoisomerase II inhibitor AQ4. A feature of this process is that the final product could potentially show bystander cell killing. Thus, in this study, we investigated the ability of inducible NOS (iNOS)-expressing TAMs to activate AQ4N and elicit toxicity in cocultured human tumor cells. Murine macrophages were induced to overexpress iNOS by treatment with a combination of cytokines, mixed with HT1080 and HCT116 human tumor cells, and the toxicity of AQ4N was determined under aerobic or hypoxic conditions. The aerobic toxicity of AQ4N toward tumor cells was not affected through coculturing with macrophages. However, under hypoxic conditions, the induction of iNOS activity in the macrophages was associated with an increase in AQ4N metabolism and a substantial increase in tumor cell toxicity, which was dependent on the proportion of macrophages in the culture. This study is the first demonstration of TAM-mediated prodrug activation to result in bystander killing of human tumor cells.

Isolation and identification of rhizoxin analogs from Pseudomonas fluorescens Pf-5 by using a genomic mining strategy

The products synthesized from a hybrid polyketide synthase/nonribosomal peptide synthetase gene cluster in the genome of Pseudomonas fluorescens Pf-5 were identified using a genomics-guided strategy involving insertional mutagenesis and subsequent metabolite profiling. Five analogs of rhizoxin, a 16-member macrolide with antifungal, phytotoxic, and antitumor activities, were produced by Pf-5, but not by a mutant with an insertion in the gene cluster. The five rhizoxin analogs, one of which had not been described previously, were differentially toxic to two agriculturally important plant pathogens, Botrytis cinerea and Phytophthora ramorum. The rhizoxin analogs also caused swelling of rice roots, a symptom characteristic of rhizoxin itself, but were less toxic to pea and cucumber roots. Of the rhizoxin analogs produced by Pf-5, the predominant compound, WF-1360 F, and the newly described compound 22Z-WF-1360 F were most toxic against the two plant pathogens and three plant species. These rhizoxin analogs were tested against a panel of human cancer lines, and they exhibited potent but nonselective cytotoxicity. This study highlights the value of the genomic sequence of the soil bacterium P. fluorescens Pf-5 in providing leads for the discovery of novel metabolites with significant biological properties.

Minimally invasive pharmacokinetic and pharmacodynamic technologies in hypothesis-testing clinical trials of innovative therapies

Clinical trials of new cancer drugs should ideally include measurements of parameters such as molecular target expression, pharmacokinetic (PK) behavior, and pharmacodynamic (PD) endpoints that can be linked to measures of clinical effect. Appropriate PK/PD biomarkers facilitate proof-of-concept demonstrations for target modulation; enhance the rational selection of an optimal drug dose and schedule; aid decision-making, such as whether to continue or close a drug development project; and may explain or predict clinical outcomes. In addition, measurement of PK/PD biomarkers can minimize uncertainty associated with predicting drug safety and efficacy, reduce the high levels of drug attrition during development, accelerate drug approval, and decrease the overall costs of drug development. However, there are many challenges in the development and implementation of biomarkers that probably explain their disappointingly low implementation in phase I trials. The Pharmacodynamic/Pharmacokinetic Technologies Advisory committee of Cancer Research UK has found that submissions for phase I trials of new cancer drugs in the United Kingdom often lack detailed information about PK and/or PD endpoints, which leads to suboptimal information being obtained in those trials or to delays in starting the trials while PK/PD methods are developed and validated. Minimally invasive PK/PD technologies have logistic and ethical advantages over more invasive technologies. Here we review these technologies, emphasizing magnetic resonance spectroscopy and positron emission tomography, which provide detailed functional and metabolic information. Assays that measure effects of drugs on important biologic pathways and processes are likely to be more cost-effective than those that measure specific molecular targets. Development, validation, and implementation of minimally invasive PK/PD methods are encouraged.

Antineoplastic agents. 509: synthesis of fluorcombstatin phosphate and related 3-halostilbenes(1)

The present SAR study of combretastatin A-3 (3a) focused on replacement of the 3-hydroxyl group by a series of halogens. That approach with Z-stilbenes resulted in greatly enhanced (>10-100-fold) cancer cell growth inhibition against a panel of human cancer cell lines and the murine P388 lymphocytic leukemia cell line. Synthesis of the 3-fluoro-Z-stilbene designated fluorcombstatin (11a) and its potassium 3'-O-phosphate derivative (16c) by the route 7 --> 8a --> 11a --> 14 --> 16c illustrates the general synthetic pathway. The 3'-O-phosphoric acid ester (15) of 3-bromo-Z-stilbene 13a was also converted to representative cation salts to evaluate the potential for improved aqueous solubility, and the potassium salt (16 mg/mL in water) proved most useful. The fluoro (11a), chloro (12a), and bromo (13a) halocombstatins were nearly equivalent to combretastatin A-4 (1a) as inhibitors of tubulin polymerization and of the binding of colchicine to tubulin. The tubulin binding in cell-free systems was also retained in human umbilical vein endothelial cells. All three halocombstatins retained the powerful human cancer cell line inhibitory activity of combretastatin A-4 (1a) and proved superior to combretastatin A-3 (3a). In addition, the halocombstatins targeted Gram-positive bacteria and Cryptococcus neoformans.

The assessment of antiangiogenic and antivascular therapies in early-stage clinical trials using magnetic resonance imaging: issues and recommendations

Vascular and angiogenic processes provide an important target for novel cancer therapeutics. Dynamic contrast-enhanced magnetic resonance imaging is being used increasingly to noninvasively monitor the action of these therapeutics in early-stage clinical trials. This publication reports the outcome of a workshop that considered the methodology and design of magnetic resonance studies, recommending how this new tool might best be used.

The Cancer Research UK experience of pre-clinical toxicology studies to support early clinical trials with novel cancer therapies

Pre-clinical toxicology studies in rodents and Phase I clinical trial data are summarised for 14 novel anticancer therapies. With only one exception, an antifolate antimetabolite, rodent toxicology predicted a safe Phase I trial starting dose and the majority of the dose limiting toxicities, in particular haematological toxicity. For targeted agents with well-defined pharmacodynamic markers, illustrated in the current study by 3 anti-endocrine drugs and one resistance modifier, the definition of a maximum tolerated dose can be avoided. Together with earlier data, the current study confirms that pre-clinical toxicology studies in a non-rodent species are not routinely needed for the safe conduct of early clinical trials with new cancer chemotherapies.