Cancers are heterogeneous at the cell level, and the mechanisms leading to cancer heterogeneity could be clonal evolution or cancer stem cells. Cancer stem cells are resistant to most anti-cancer treatments and could be preferential targets to reverse this resistance, either targeting stemness pathways or cancer stem cell surface markers. Gold nanoparticles have emerged as innovative tools, particularly for photo-thermal therapy since they can be excited by laser to induce hyperthermia. Gold nanoparticles can be functionalized with antibodies to specifically target cancer stem cells. Preclinical studies using photo-thermal therapy have demonstrated the feasibility of targeting chemo-resistant cancer cells to reverse clinical chemoresistance. Here, we review the data linking cancer stem cells and chemoresistance and discuss the way to target them to reverse resistance. We particularly focus on the use of functionalized gold nanoparticles in the treatment of chemo-resistant metastatic cancers.

Purpose: Developing strategies to overcome resistance to sunitinib is a major challenge in human renal cell carcinoma (RCC). We hypothesized that sunitinib-induced tumor necrosis-associated hypoxia could interact with renal cancer stem cells in patients with metastatic RCC.Experimental Design: We studied tissue samples from 7 patients with primary metastatic RCC, before and after sunitinib treatment, and from six xenograft models derived from human RCC. Two xenograft models were responders to sunitinib, the four others were nonresponders. CD133/CXCR4-coexpressing cells derived from the two responder xenograft models were used for in vitro studies.Results: In the seven primary RCCs, we identified a significantly larger number of CD133/CXCR4-coexpressing cells in perinecrotic versus perivascular areas. Their numbers also significantly increased after treatment, in perinecrotic areas. We reproduced these clinical and pathologic results in all six RCC xenograft models with again a preferential perinecrotic distribution of CD133-expressing cells. Necrosis occurred at day 7 in the two responder models treated with sunitinib, whereas it occurred at day 21 in the untreated controls and in the four nonresponder models. Strikingly, when we studied the six RCC xenograft models at the time necrosis, whether spontaneous or sunitinib-induced, occurred, necrosis area correlated with stem-cell number in all 120 xenografted RCCs. When studied under experimental hypoxia, the number of CD133/CXCR4-coexpressing cells and their tumorigenic potency increased whereas their sensitivity to sunitinib decreased.Conclusions: In human RCC, sunitinib was able to generate resistance to its own therapeutic effect via induced hypoxia in perinecrotic areas where cancer stem cells were found in increased numbers.