Chloroquine as a hyperthermia potentiator

Hyperthermic sensitization by the radical initiator 2,2'-azobis (2-amidinopropane) dihydrochloride (AAPH). I. In vitro studies

AAPH (2,2'-azobis-(2-amidinopropane dihydrochloride)) is a water-soluble, heat-labile azo compound which undergoes thermal decomposition to produce carbon-centred free radicals. These carbon-centred radicals might be directly cytotoxic or may react with oxygen to produce potentially cytotoxic alkoxyl and peroxyl radicals. The rate of free radical production as a result of AAPH thermal decomposition increases with increasing temperature. We have evaluated the efficacy of AAPH as a heat sensitizer for Chinese hamster V79 cells by the clonogenic assay. AAPH (50 mM) was not cytotoxic to V79 cells at 37 degrees C for exposures up to 3 h. In contrast, AAPH (50 mM) was found to markedly sensitize cells exposed to 42, 43 and 45 degrees C. For a 75 min exposure to 42 degrees C alone, cell survival was reduced to 9 x 10(-1); however, a 75 min exposure at 42 degrees C+AAPH resulted in survival of 5.5 x 10(-4). For 43 and 45.5 degrees C heating, cell survival was potentiated by AAPH at the 1% survival level by 4.1 and 1.4-fold, respectively. AAPH was also found to sensitize both hypoxic cells and thermotolerant cells. These findings would encourage in vivo evaluation of AAPH (or analogues) as a temperature-dependent heat sensitizer. AAPH represents a new class of heat sensitizers which may have use in unravelling the mechanism(s) of heat killing and may have utility in local hyperthermia treatment.

Antimelanoma activity of chloroquine, an antimalarial agent with high affinity for melanin

The antimalarial agent chloroquine is known for high affinity for melanin. This 4-aminoquinoline derivative was examined for anti-melanoma activity and uptake into melanoma cells. Chloroquine inhibited growth of cultured melanoma cells; the effect was much greater to a moderately pigmented cell line HMV-II than to a nonpigmented HMV-I. Treatment with chloroquine at a dose of 62 mg/kg i.p. for 12 days prolonged by 71% the life span of mice bearing B16 melanoma, while 24-day treatment at 31 mg/kg resulted in a 81% increase in life span. HMV-II cells showed a two-fold increase in uptake of chloroquine as compared with HMV-I cells. Chloroquine, 24 hr after administration to mice implanted s.c. with B16 melanoma, was selectively accumulated in the pigmented tissues, melanoma and eyes. Other nonpigmented tissues such as the liver, lung, and kidney showed rapid uptake (within 1 hr) and release. These results suggest that chloroquine is toxic to pigmented melanoma cells, the process being partly mediated by binding to melanin.

The effect of chloroquine and hyperthermia on murine neuroblastoma

A number of reports suggest that hyperthermia is an effective adjunctive treatment modality in management of neural crest tumors. Recent studies have demonstrated a synergistic effect of induced hyperthermia when coupled with chloroquine in an in vitro model. This study examines the effect of chloroquine and hyperthermia in an in vivo murine neuroblastoma model. Forty-seven Ajax white mice (weighing 20 to 30 g) received a subaxillary tumor burden (C-1300 murine neuroblastoma) per trochar (1.25 x 10(6) cells). The tumor was then incubated for 9 days. Mice were then divided into four groups: group 1, controls (n = 15); group 2, hyperthermia (n = 12); group 3, chloroquine (n = 10); and group 4, chloroquine with hyperthermia (n = 10). Hyperthermia was induced with 40 to 69 mW/cm2 at 2,450 MHz microwave radiation for 4 minutes to achieve a temperature of 41.5 degrees C for 10 of 14 treatment days. Chloroquine was administered intraperitoneally at a dose of 40 mg/kg body weight for 10 of 14 treatment days. Mice were weighed and tumor size was determined daily. Animals were killed on day 21 and postmortem examination was performed, with tumors graded histologically. Animal weight, tumor weight, and tumor size were similar for all groups (P greater than .05). Mortality was 6% in group 1, 25% in group 2, 50% in group 3, and 40% in group 4 (P less than .05). Rate of tumor metastases was also statistically different from controls: group 1, 0%; group 2, 60%; group 3, 90%; and group 4, 90% (P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)