The ATP-binding cassette transporters are a transport system superfamily that is one of the largest and possibly one of the oldest gene families. It is represented in all extant phyla, from prokaryotes to humans. ABC transporters belong to translocases.
The activity of these proteins, severely reduces the amount of therapeutics that penetrates the tumor cells. Roy et al. hypothesized that ABC transporter expression could correlate with survival surrogates. They assessed the expression of four commonly expressed ABC transporters in GBM samples and investigated if mRNA levels could serve as a prognostic biomarker.
Methods: Human specimens were analyzed by qPCR to assess ABCB1, ABCC1/3 and ABCG2 expression. Kaplan-Meier and multivariate analyses were then used to evaluate the correlation with overall survival (OS) and progression-free survival (PFS).
The cohort included 22 non-tumoral samples as well as 159 GBM tumor specimens. ABC transporters were significantly more expressed in GBM samples compared to non-tumoral tissue. Moreover, ABCC1 and 3 mRNA expression were significantly increased at recurrence. Statistical analyses revealed that increased expression of either ABCC1 or ABCC3 did not confer a poorer prognosis. However, increased ABCC1 mRNA levels did correlate with a significantly shorter PFS.
The expression of the four ABC transporters evaluated would not be suitable prognostic biomarkers. They believe that when estimating prognosis, the plethora of mechanisms implicated in chemoresistance should be analyzed as a multi-facetted entity rather than isolated units 1).