89, 90 It also has to be considered that drug companies may choose to lower the therapeutic benefit rather than the size of the patient collective amenable to treatment. Because breakthrough achievements are unlikely to result from specific (pathway) targeted approaches in HCCs, our attention should also focus on mechanisms that are constantly needed by the tumor (that is, the tumors’ “Achilles’ heels”). These represent either necessarily required cellular functions that support learn more a protumorigenic phenotype or are
central mechanisms that allow for tumor persistence or progression. Examples of the first are the chaperone network (e.g., HSP90 and interacting factors)91 as well as all factors that support tumor cell proliferation and cell cycle progression. Tumor-associated neoangiogenesis may represent a double-edged sword: on one hand, it is an indispensable prerequisite for tumor growth; on the other hand, it is required to build up sufficient intratumoral drug concentrations. Recent results indicate that the effect of antiangiogenic approaches may depend on tumor characteristics (e.g., tumor cell biology and stroma content) that may need further attention.92 Examples
for central tumor-relevant mechanisms may provide an even more attractive basis for therapeutic concepts. Global down-regulation of miRNAs is found in most tumors this website and suggests a role for the miRNA processing machinery. There is recent evidence for a critical role of dicer and some link to the p53 family members.93, 94 It will have to be shown whether this holds true in HCC and can be modulated in an antineoplastic manner. Tumor cell aneuploidy, as present in almost all HCCs, is a condition usually not compatible with cell survival under physiological conditions; this may explain the usually higher apoptosis rate of malignant tumors, but tumor cells must also
have established mechanisms to prevail MCE and maintain all vital cell functions despite the presence of significant aneuploidy. First screens have demonstrated genes that may provide increased aneuploidy tolerance;95 the future will show whether they may represent valid and innovative drug targets. These considerations provide different challenges for drug design. Tumor cell specificity may not be achieved by addressing pathways or specific mechanisms that are more or less exclusive to tumor cells; instead, pharmacokinetics and pharmacodynamics may have to be modulated in order to favor tumor cell–associated activity or activation of the drug employing tumor preferential mechanisms.96 Predictive marker analyses do not play a role in current clinical diagnostics in HCC, but it will be necessary to include them in future clinical trials. Even if broader therapeutic approaches are tested, predictive marker analyses may well indicate response as well as primary and secondary resistance to therapy.
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