Lysosomotropism depends on glucose: a chloroquine resistance mechanism

Abstract

There has been long-standing interest in targeting pro-survival autophagy as a combinational cancer therapeutic strategy. Clinical trials are in progress testing chloroquine (CQ) or its derivatives in combination with chemo- or radiotherapy for solid and haematological cancers. Although CQ has shown efficacy in preclinical models, its mechanism of action remains equivocal. Here, we tested how effectively CQ sensitises metastatic breast cancer cells to further stress conditions such as ionising irradiation, doxorubicin, PI3K-Akt inhibition and serum withdrawal. Contrary to the conventional model, the cytotoxic effects of CQ were found to be autophagy-independent, as genetic targeting of ATG7 or the ULK1/2 complex could not sensitise cells, like CQ, to serum depletion. Interestingly, although CQ combined with serum starvation was robustly cytotoxic, further glucose starvation under these conditions led to a full rescue of cell viability. Inhibition of hexokinase using 2-deoxyglucose (2DG) similarly led to CQ resistance. As this form of cell death did not resemble classical caspase-dependent apoptosis, we hypothesised that CQ-mediated cytotoxicity was primarily via a lysosome-dependent mechanism. Indeed, CQ treatment led to marked lysosomal swelling and recruitment of Galectin3 to sites of membrane damage. Strikingly, glucose starvation or 2DG prevented CQ from inducing lysosomal damage and subsequent cell death. Importantly, we found that the related compound, amodiaquine, was more potent than CQ for cell killing and not susceptible to interference from glucose starvation. Taken together, our data indicate that CQ effectively targets the lysosome to sensitise towards cell death but is prone to a glucose-dependent resistance mechanism, thus providing rationale for the related compound amodiaquine (currently used in humans) as a better therapeutic option for cancer.

The antimalarial drug amodiaquine stabilizes p53 through ribosome biogenesis stress, independently of its autophagy-inhibitory activity

“…AQ is more cytotoxic against cancer cells than CQ [18,44], albeit AQ displays similar or lower autophagy/lysosome inhibition [18,44]. Unlike for AQ, the CQ-induced cell death depends on glucose [44]. These differences suggest that the unique impact of AQ on rDNA transcription may explain its higher cytotoxicity.…”

Crucial role of the pentose phosphate pathway in malignant tumors (Review)

“…This axis may therefore represent a potential therapeutic target for treatment of metastatic breast cancer (88). It has been reported that inhibition of hexokinase using 2-deoxyglucose induces chloroquine-resistance in breast cancer (89). In addition, metformin stimulates the glycolytic flux caused by starvation by interfering with HK2 activity (90).…”

Inhibition of the ULK1 protein complex suppresses Staphylococcus-induced autophagy and cell death

“…For Gal-3 puncta tests, HeLa cells plated on glass coverslips were transfected with pEGFP-hGal3 (Addgene: 73080) (45) using Lipofectamine 2000 according to standard protocols, as we have previously reported (42). After 24 hours of transfection, cells were used for experiments.…”

“…Members of the Galectin family of beta-galactoside-binding proteins have served as useful tools to detect damage of endomembranes such as lysosomes. (42)(43)(44)(45). Galectin-8 plays a critical role as receptor for targeting damaged SCV to the xenophagy pathway (46).…”

“…Indeed, wildtype virulent Staphylococcus aureus strains appeared to extensively escape from their lysosomeassociated replicative niche into the cytoplasm, but agr-mutant or CC8 strains showed lower levels of this behaviour. We had previously used Gal-3 as a cellular probe to detect lysosome membrane damage following treatment with the cancer chemotherapeutic (and anti-malarial) compound chloroquine (42). A related protein Gal-8 has been shown to detect membrane damage to mount xenophagy for the restriction of Salmonella infection (46).…”