NLCQ-1

Metastases cause most cancer-related deaths. We investigated the use of hypoxia-selective cytotoxins as adjuvants to radiotherapy in the control of metastatic tumour growth.

The NLCQ-1, RB6145 and tirapazamine were assessed against the spontaneously metastasising KHT model. Subcutaneous KHT tumours (250 mm(3)) were irradiated with 25 Gy (single fraction) to control primary growth. Equitoxic drug treatments (NLCQ-1 (10 mg kg(-1)) once daily; RB6145 (75 mg kg(-1)) and tirapazamine (13 mg kg(-1)) twice daily) were administered 3-6 days post-radiotherapy when hypoxic cells were evident in lung micrometastases. Mice were culled when 50% of controls exhibited detrimental signs of lung metastases.

In total, 95% of control mice presented with lung disease. This was significantly reduced by NLCQ-1 (33%; P=0.0002) and RB6145 (60%; P=0.02). Semi-quantitative grading of lung disease revealed a significant improvement with all treatments, with NLCQ-1 proving most efficacious (median grades: control, 4; NLCQ, 0 (P<0.0001); RB6145, 1 (P<0.001), tirapazamine, 3 (P=0.007)). Positron emission tomography (PET) was evaluated as a non-invasive means of assessing metastatic development. Primary and metastatic KHT tumours showed robust uptake of [(18)F]fluorodeoxyglucose ([(18)F]FDG). Metastatic burden discernable by [(18)F]FDG PET correlated well with macroscopic and histological lung analysis.

The hypoxia-selective cytotoxin NLCQ-1 controls metastatic disease and may be a successful adjuvant to radiotherapy in the clinical setting.

Abstract:  4‐[3‐(2‐Nitro‐1‐imidazolyl)‐propylamino]‐7‐chloroquinoline hydrochloride (NLCQ‐1), a 2‐nitroimidazole‐based hypoxia‐selective cytotoxin has been shown to target hypoxic regions of solid tumours. The present study is one of several pre‐clinical toxicology studies conducted in support of an ‘investigational new drug’ (IND) application to test this agent as an adjuvant to radio/chemotherapy for the treatment of cancer in humans. Twenty‐four dogs were each assigned to one vehicle control group or to one of three test article‐treated groups (three dogs/sex/treatment group). Intravenous (i.v.) doses of 0, 2.74, 5.48 and 10.95 mg/kg/day (54.8, 109.6 or 219 mg/m2/day) were administered on a per day × 5 days (qd × 5) schedule. NLCQ‐1 was formulated as a solution in sterile saline at 1.5 mg/ml. None of the dogs died during this 33‐day study. With few exceptions, most of the clinical signs of toxicity were noted within 2 hr following dosing in the 10.95 mg/kg/day dose group. These observations included aggressive behaviour, ataxia, tachypnea, emesis, hypoactivity, excessive salivation, tremors, and involuntary urination and defecation. Aggressive behaviour was judged to be dose‐limiting. No clinical signs of toxicity were noted during the 28‐day observation period that followed the 5‐day dose period. Findings in a functional observation battery examination were consistent with the clinical observations. No drug‐related effects were noted on the body weight or food consumption values, and no drug‐related changes were noted during ocular examinations made on these animals prior to scheduled necropsy or during examination of electrocardiogram recordings made at 15 min. and 2 hr after dosing on days 1 and 5. No definitive changes in haematology, clinical chemistry or coagulation values were noted in dogs treated with NLCQ‐1. NLCQ‐1 was detected in the plasma of treated dogs on days 1 and 5, up to 60 min. after dosing (2.74 and 5.48 mg/kg/day) and up to 8 hr after dosing (10.95 mg/kg/day). There was a dose‐related increase in maximum plasma concentration of NLCQ‐1 at 5 min. after dosing; comparable concentrations were noted on days 1 and 5. No definitive test article‐related lesions were noted during microscopic evaluation of tissues from dogs in this study, although lesions noted at the injection site and in the vascular tissue, lungs, thymus, prostate gland, muscle, adrenal cortex and tongue may have resulted from treatment with this drug. Any drug‐related toxicity noted was readily reversible and not cumulative. No sex difference was detected in the susceptibility to NLCQ‐1‐induced toxicity.