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4-[3-(2-Nitro-1-imidazolyl)propylamino]-7-chloroquinoline Hydrochloride (NLCQ-1), a Novel Bioreductive Agent as Radiosensitizer In Vitro and In Vivo: Comparison With Tirapazamine

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Abstract:

The novel hypoxia-selective cytotoxin NLCQ-1, which is a weak DNA intercalator, was studied in conjunction with radiation against V79 cultured cells and EMT6 or SCCVII tumors in their syngeneic mice and compared with tirapazamine (TPZ). NLCQ-1 was a very potent and efficient radiosensitizer of hypoxic V79 cells, providing SER values of 2.27–2.56 at 20–80 μM concentration (measured at 10% survival level). Its C1.6 (concentration for an SER of 1.6 to be obtained) was 7.2 ± 0.2 μM. Its in vitro therapeutic index (ThI, defined as CT50(Air)/C1.6) varied by the exposure time from 57 (1-h exposure) to 145 (4.5-h exposure). The corresponding C1.6 value for TPZ was 16.9 μM whereas its in vitro therapeutic index was 49 (3-h exposure). A schedule-dependent synergistic interaction was observed between NLCQ-1 or TPZ and 20 Gy of radiation in both tumor models examined, by using the in vivo–in vitro assay as endpoint. Optimal synergism (>1 log) was observed in EMT6 tumors when each bioreductive drug was given between 45 and 60 min before irradiation. NLCQ-1 alone had no significant antitumor activity at 10 mg/kg (28% of its single LD50), whereas a 0.4 surviving fraction was obtained by TPZ at 30 mg/kg (38% of its single LD50). SER values of 1.52 and 1.25 were obtained with 10 mg/kg NLCQ-1 and 30 mg/kg TPZ, respectively, in EMT6 tumors. An SER value of 1.58 was obtained for both hypoxia-selective cytotoxins, at equitoxic doses, in SCCVII tumors, by using a fractionated regimen. These results suggest a possible use of NLCQ-1 or TPZ as adjuvants to radiotherapy.

Keywords: Key words: NLCQ-1; Radiosensitizers;; Tirapazamine

Document Type: Research Article

DOI: https://doi.org/10.3727/096504001108747774

Affiliations: The Radiation Medicine Institute at Evanston Northwestern Healthcare, 2650 Ridge Avenue, Evanston, IL 60201

Publication date: 2001-08-01

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