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Fig. 2 | Clinical and Translational Medicine

Fig. 2

From: Analyses of repeated failures in cancer therapy for solid tumors: poor tumor-selective drug delivery, low therapeutic efficacy and unsustainable costs

Fig. 2

Schematic representation of plasma concentration of different molecular size drugs [33, 34]: a low-MW free drugs (e.g., doxorubicin, DOX) and b–e their polymer complexes. The drug concentration in plasma after i.v. injection of low-MW drugs decreases rapidly (a). Representative polymer conjugates, micelles, and the liposomal drug (DOX) complex remain in the plasma at higher levels (b–e). However (b) shows a micellar drug of non-covalently encapsulated low MW drug which burst rapidly. Thus, no therapeutic benefit due to the EPR effect as its stability is too poor; (c) a styrene-co-maleic acid (SMA)-polymer covalent conjugate having better relative stability [103, 105]; (d) a more biocompatible polymer (HPMA) of pirarubicin conjugate [34]; (e) highly stable and biocompatible liposome complex such as Doxil®, showing high concentration in plasma for long period. This stable liposome complex is a pegylated stealth liposome. However, it is too stable and thus little drug release even after reaching to the target tumor, and thus only a limited therapeutic effect. Nano-size drugs (c–e) of high biocompatibility, having long plasma half-lifer, are advantageous for tumor selective targeting because they can utilize the EPR effect [33, 34]

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