Combined therapies of bone disease with bisphosphonates.

Bisphosphonates are standard treatment for cancer-induced bone disease, a common feature of many advanced malignancies. Traditionally used to inhibit bone turnover and reduce the risk of skeletal-related events, there is now increasing pre-clinical evidence that these agents may also affect tumour burden and disease progression. In particular, combining bisphosphonates with chemotherapeutic agents has been demonstrated to cause substantially increased anti-tumour effects compared to giving the single agents. Clinical studies are in progress to determine whether adding bisphosphonates to standard anti-cancer therapy results in improved outcome for patients. Here we give an overview of the key pre-clinical studies of anti-tumour effects of bisphosphonates, alone and in combination with other agents, and introduce some of the ongoing clinical trials that aim to determine the clinical relevance of bisphosphonates in combination therapy.

Discovery and evaluation of Escherichia coli nitroreductases that activate the anti-cancer prodrug CB1954.

Gene-directed enzyme prodrug therapy (GDEPT) aims to achieve highly selective tumor-cell killing through the use of tumor-tropic gene delivery vectors coupled with systemic administration of otherwise inert prodrugs. Nitroaromatic prodrugs such as CB1954 hold promise for GDEPT as they are readily reduced to potent DNA alkylating agents by bacterial nitroreductase enzymes (NTRs). Transfection with the nfsB gene from Escherichia coli can increase the sensitivity of tumor cells to CB1954 by greater than 1000-fold. However, poor catalytic efficiency limits the activation of CB1954 by NfsB at clinically relevant doses. A lack of flexible, high-throughput screening technology has hindered efforts to discover superior NTR candidates. Here we demonstrate how the SOS chromotest and complementary screening technologies can be used to evaluate novel enzymes that activate CB1954 and other bioreductive and/or genotoxic prodrugs. We identify the major E. coli NTR, NfsA, as 10-fold more efficient than NfsB in activating CB1954 as purified protein (k(cat)/K(m)) and when over-expressed in an E. coli nfsA(-)/nfsB(-) gene deleted strain. NfsA also confers sensitivity to CB1954 when expressed in HCT-116 human colon carcinoma cells, with similar efficiency to NfsB. In addition, we identify two novel E. coli NTRs, AzoR and NemA, that have not previously been characterized in the context of nitroaromatic prodrug activation.

The nitroreductase prodrug SN 28343 enhances the potency of systemically administered armed oncolytic adenovirus ONYX-411(NTR).

Conditionally replicating adenoviruses (CRAd) 'armed' with prodrug-activating genes have the potential to augment the efficacy of virotherapy. An Escherichia coli nitroreductase (NTR) gene (nfsB) was introduced into the E3B region of the systemically active CRAd ONYX-411, to produce ONYX-411(NTR), which had single agent oncolytic activity equivalent to unarmed virus in vitro and in vivo. A fluorogenic probe (SN 29884) developed to monitor NTR expression revealed robust, durable NTR expression in ONYX-411(NTR) infected neoplastic but not primary human cell lines. NTR expression occurred >24 h post-infection in parallel with fiber and was sensitive to ara-C indicating transcriptional linkage to viral replication. A novel NTR prodrug, the 3,5-dinitrobenzamide-2-bromomustard SN 27686, was shown to be more dose potent and selective than CB 1954 and provided a superior bystander effect in 3D multicellular layer cultures. Its water-soluble phosphate ester SN 28343 was substantially more active than CB 1954 against xenografts containing a minority of stable NTR-expressing cells. A single intravenous dose of ONYX-411(NTR) (10(8) PFU) to nude mice bearing large H1299 xenografts (>350 mm(3)) resulted in tumor-specific NTR expression which increased over time. Despite extensive viral spread by day 14, this conservative virus dose and schedule was unable to control such well-established tumors. However, subsequent administration of SN 28343 resulted in the majority of mice (62.5%) being tumor-free on day 120.