Development of halofantrine resistance and determination of cross-resistance patterns in Plasmodium falciparum

Abstract

Intermittent exposure to halofantrine (HF) of both chloroquine-susceptible (T9.96) and chloroquine-resistant (K1) isolates of Plasmodium falciparum in vitro resulted in a rapid reduction in susceptibility to HF. After 6 months, the 50%o inhibitory concentration (IC..) (14,19,22,23) or the exposure of cultures to mutagenic agents followed by drug pressure to select for resistant mutants (1,16,17). However, the relevance of resistance mechanisms developed as a result of mutagenesis to resistance mechanisms developed in the field (presumably as a result of drug pressure) is very unclear. In general, it has proven difficult to induce resistance to the aminoquinolines and related schizontocides in vitro. Brockelman et al. (4) produced a mefloquine-tolerant line of P. falciparum by exposing cultures to the drug for 48-h periods separated by several cycles of culturing in non-drug-treated medium, but the stability of resistance was not assessed in that study. * Corresponding author.In the present study, we compared the ability of two different methods used to select resistance to the 9-phenanthrenemethanol halofantrine (HF) {1,3-dichloro-a-[2-(dibutylamino)ethyl] -6 -(trifluoromethyl) -9 -phenanthrenemethanol} in chloroquine-susceptible and chloroquine-resistant isolates of P. falciparum (i.e., intermittent versus continuous drug pressure). The cross-resistance patterns of the resulting resistant isolates were also evaluated. MATERIALS AND METHODSParasites and cultures. Chloroquine-resistant isolate K, (29)

In vitro susceptibility of African isolates of Plasmodium falciparum from Gabon to pyronaridine.

“…32 However, other studies showed that the acquisition of reduced halofantrine susceptibility was accompanied by similar shifts in sensitivity to quinine, mefloquine, and other antimalarial agents containing the methanolic function, but increased susceptibility to chloroquine. This suggests that the methanolic functional group is essential for activity or is of importance in the resistance mechanism, 33 resistance to halofantrine, quinine, and mefloquine is related to reduced drug accumulation within the parasite, and that this can be achieved without overexpression of Pgh 1. 34 Pyronaridine contains a methanolic functional group.…”

Defining the role of PfCRT in Plasmodium falciparum chloroquine resistance

“…It has been known for some time that CQR culture‐adapted field isolates are often hypersensitive to the anti‐influenza drug amantadine (Evans and Havlik, 1993) and to the phenanthrene methanol, halofantrine (Nateghpour et al ., 1993). Using a stepwise selection protocol, CQR lines were selected for increasing levels of resistance to either amantadine or halofantrine.…”

Evidence for a Central Role for PfCRT in Conferring Plasmodium falciparum Resistance to Diverse Antimalarial Agents

“…Sequencing of the K1HF pfcrt cDNA revealed three polymorphisms: a codon 152 threonine to alanine substitution (T152A), S163R, and a codon 275 proline to leucine substitution (P275L). Thus the same mutation (S163R) was selected, accompanied by the same phenotypic change, in independent experiments that used two structurally unrelated drugs, both of which display inverse crossresistance with CQ (Oduola et al, 1988;Nateghpour et al, 1993;Havlik, 1993,1994;Ritchie et al, 1996).…”

“…This employed the intermittent drug exposure method described in (Nateghpour et al, 1993). Briefly, the parent CQ-resistant isolate K1H6/2 was exposed to AM or HF at the predetermined IC 50 concentration until the parasitemia fell to less than 40% of control values (parasite lines cultured in the absence of drug).…”