compared to healthy hepatocytes. the mechanism by which bafilomycin causes this cancer specific anti-proliferative effect is multifactorial. in addition to the induction of caspase-dependent apoptosis through the mitochondrial pathway, bafilomycin also causes increased levels of reactive oxygen species and increased expression of hif1alpha. these effects suggest that inhibition of v-atpase with bafilomycin can induce a cellular stress response, including autophagy and eventual apoptosis. these somewhat contradictory effects of v-atpase inhibition in terms of inhibition or induction of apoptosis demonstrate that bafilomycin's function is critically dependent on cellular context, and can mediate either a pro-survival or pro-death phenotype. in vivo bafilomycin reduced average tumor volume in mcf-7 and mda-mb-231 xenograft mouse models by 50% and did not show toxic effects at a dosing of 1 mg/kg. additionally, when combined with sorafenib, bafilomycin also caused tumor regression in mda-mb-231 xenograft mice. in a hepg2 orthotropic hcc xenograft model in nude mice, bafilomycin prevented tumor growth. v-atpase dysregulation is thought to play a role in resistance to cancer therapies, as aberrant acidification of the extracellular environment can protonate chemotherapeutics, preventing their entry into the cell. it is unclear if` v-atpase dysregulation is a direct cause of associated poor clinical outcome or if its dysregulation primarily effects the response to treatment. although treatment with bafilomycin and cisplatin had a synergistic effect on cancer cell cytotoxicity. anti-fungal bafilomycins have been shown to inhibit plasma membrane atpase (p-atpase) as well as the atp-binding cassette (abc) transporters. these transporters are identified as good anti-fungal targets as they render organisms unable to cope with cation stress. when cryptococcus neoformans was treated with bafilomycin, growth inhibition was observed. bafilomycin has also been used in c. neoformans in conjunction with calcineurin inhibitor fk506, displaying synergistic anti-fungal activity. anti-parasitic bafilomycin has been shown to be active against plasmodium falciparum, the causative agent of malaria. upon infection of red blood cells, p. falciparum exports a membrane network into the red blood cell cytoplasm and also inserts several of its own proteins into the host membrane, including its own v-atpase. this proton pump has a role in maintaining the intracellular ph of the infected red blood cell and facilitating the uptake of small metabolites at equilibrium. treatment of the parasitized red blood cell with bafilomycin prevents the extracellular acidification, causing a dip in intracellular ph around the malarial parasite. immunosuppressant the inflammatory myopathy inclusion body myositis (ibm) is relatively common in patients over 50 years of age and involves over activation of autophagic flux. in this condition, increased autophagy results in an increase in protein degradation and therefore an increase in the presentation of antigenic peptides in muscles. this can cause over-activation of immune cells. treatment with bafilomycin can prevent the acidification of lysosomes and therefore autophagy, decreasing the number of antigenic peptides digested and displayed to the immune system. in lupus patients, the autophagy pathway has been found to be altered in both b and t cells. particularly, more autophagic vacuoles were seen in t cells as well as increased lc3-11 staining for autophagosomes, indicating increased autophagy. increased autophagy can also be seen in naïve patient b cell subsets. bafilomycin a1 treatment lowered the differentiation of plasmablasts and decreased their survival. clearance of protein aggregates in neurodegenerative diseases neurodegenerative diseases typically display elevated levels of protein aggregates within the cell that contribute to dysfunction of neurons and eventual neuronal death. as a method of protein degradation within the cell, autophagy can traffic these protein aggregates to be degraded in the lysosome. although it is unclear the exact role continuous autophagy, or autophagic flux, plays in neuronal homeostasis and disease states, it has been shown that autophagic dysfunction can be seen in neurodegenerative diseases. bafilomycin is commonly used to study this autophagic flux in neurons, among other cell types. to do this, neurons are first put into nutrient rich conditions then into nutrient starved conditions to stimulate autophagy. bafilomycin is co-administered in the condition of nutrient stress so that while autophagy is stimulated, bafilomycin blocks its final stage of autophagosome-lysosomal fusion resulting in the accumulation of autophagosomes. levels of autophagy related proteins associated with autophagosomes, such as lc3, can then be monitored to determine the level of autophagosome formation induced by nutrient deprivation. in vitro drug interactions lysosomotropic drugs some cationic drugs, such as chloroquine and sertraline, are known as lysosomotropic drugs. these drugs are weak bases that become protonated in the acidic environment of the lysosome. this traps the otherwise non-protonated compound within the lysosome, as protonation prevents its passage back across the lipid membrane of the organelle. this phenomenon is known as ion trapping. trapping of the cationic compound also draws water into the lysosome through an osmotic effect, which can sometimes lead to vacuolization seen in in vitro cultured cells. diagram showing how protonation of weak bases like chloroquine in the acidic environment of the lysosome results in ion trapping, or accumulation of the weak base in the lysosome. bafilomycin inhibits this trapping through its action on v-atpase, which normally acidifies the lysosome. when one of these drugs is co-applied to cells with bafilomycin a1, the action of bafilomycin a1 prevents the acidification of the lysosome, therefore preventing the phenomenon of ion trapping in this compartment. as the lysosome cannot acidify, lysosomotropic drugs do not become protonated and subsequently trapped in the lysosome in the presence of bafilomycin. additionally, when cells are preloaded with lysosomotropic drugs in vitro, then treated with bafilomycin, bafilomycin acts to release the cationic compound from its accumulation in the lysosome. pretreating cells with bafilomycin before administration of a cationic drug can alter the kinetics of the cationic compound. in a rabbit contractility assay, bafilomycin was used to pre-treat isolated rabbit aorta. the lipophilic agent xylometazoline, an alpha-adrenoreceptor agonist, displayed an increased effect when administered after bafilomycin treatment. with bafilomycin, faster contraction and relaxation of the aorta was seen as bafilomycin prevented the ion trapping of xylometazoline in the lysosome. without pre-treatment with bafilomycin, the functional v-atpase causes the lysosome to become a reservoir for xylometazoline, slowing its effect on contractility. chloroquine as a lysosomotropic drug, chloroquine typically accumulates in the lysosome disrupting their degradative function, inhibiting autophagy, and inducing apoptosis through bax-dependent mechanisms. however, in cultured cerebellar granule neurons (cgns) low treatment with bafillomycin of 1 nm decreased chloroquine induced apoptosis without affecting chloroquine inhibition of autophagy. the exact mechanism of this protection is unknown, although it is hypothesized to lie downstream of autophagosome-lysosome fusion yet upstream of bax induction of apoptosis. chemotherapeutics bafilomycin has been shown to potentiate the effect of taxol in decreasing matrix metalloprotease (mmp) levels by depressing bcl-xl's mitochondrial protective role. additionally, within cisplatin resistant cells, v-atpase expression was found to be increased, and co-treatment of bafilomycin with cisplatin sensitized these cells to cisplatin-induced cytotoxicity. bafilomycin has also been shown to increase the efficacy of egfr inhibitors in anti-cancer applications.