Validation of tumour models for use in anticancer nanomedicine evaluation: the EPR effect and cathepsin B-mediated drug release rate

Abstract

PurposeIntravenously (i.v.) administered nanomedicines have the potential for tumour targeting due to the enhanced permeability and retention (EPR) effect, but in vivo tumour models are rarely calibrated with respect to functional vascular permeability and/or mechanisms controlling intratumoural drug release. Here the effect of tumour type and tumour size on EPR-mediated tumour localisation and cathepsin B-mediated drug release was studied.MethodsEvans Blue (10 mg/kg) and an N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer–doxorubicin (Dox) conjugate (FCE28068) (5 mg/kg Dox-equiv) were used as probes and tumour levels (and Dox release) measured at 1 h after i.v. administration in a panel of murine and human xenograft tumours.ResultsEvans Blue and FCE28068 displayed similar tumour levels in the range of 2–18 % dose/g at 1 h for B16F10 and L1210. Approximately half of the tumour models evaluated exhibited tumour size-dependent accumulation of FCE28068; smaller tumours had the highest accumulation. Administration of free Dox (5 mg/kg) produced tumour levels of <2.5 % dose/g independent of tumour size. Whereas the degree of EPR-mediated targeting showed ~12-fold difference across the tumour models evaluated, Dox release from FCE28068 at 1 h displayed ~200-fold variation.ConclusionsMarked heterogeneity was seen in terms of EPR effect and Dox release rate, underlining the need to carefully calibrate tumour models used to benchmark nanomedicines against known relevant standard agents and for optimal development of strategies for late pre-clinical and clinical development.Electronic supplementary materialThe online version of this article (doi:10.1007/s00280-013-2209-7) contains supplementary material, which is available to authorized users.

Impact of the Enhanced Permeability and Retention (EPR) Effect and Cathepsins Levels on the Activity of Polymer-Drug Conjugates

“…Breast and ovarian cancer also showed high clinical responses to PDCs, which correlated well with high levels of cathepsins observed in these tumour types, and with reports indicating the presence of the EPR effect. This finding is in line with other studies [13,14] and in agreement with that concluded by others (e.g., [13]). Moreover, our study also suggests that careful patient selection, in the form of pre-screening for enzyme content and the EPR effect, would be a rational approach for the further development and clinical application of PDCs.…”

“…This observation also correlates with a recent study on validation of the tumour models for EPR activity, where high drug accumulation has been reported for both large and small lung tumours, and a low drug accumulation has been reported for the large breast tumours [13]. Disparities observed across the various studies are might be due to the heterogeneity within and between the tumour types (size and histological differences) and the diversity of the nanopharmaceutical characteristics [14].…”

“…A few studies involved the comparison between the free drug accumulation and the nano particle accumulation in which case the results were expressed in terms of degree of their accumulation. Some studies have indicated that the extent of the EPR effect is also dependent on the tumour sizes [3,13,94] but due to the lack of information on the tumour sizes in most of the studies, this factor was not considered in our evaluation.…”

“…With regards to expression of the various activating enzymes, again the situation is heterogeneous and unclear. It is well known that enzymes that have been exploited for activation of PDCs, such as cathepsin B, are expressed in tumour tissues [2,13,[15][16][17]. However, it has been recently noted that various factors, such as hormone levels, can affect the abundance of such enzymes.…”

“…Recent studies have considered different in vivo tumour models and these have reported that both the size and tumour type can affect the magnitude of the EPR effect [12,13]. A discussion group constituted by world experts of the EPR effect has looked at the heterogeneity of such a phenomenon and has identified its key influencing factors, mainly: (a) the nature of the vascular bed and stroma, including the presence or absence of lymphatics; (b) tumour size, type and location; and (c) patient characteristics such as age, gender, body composition, and treatment [10,13,14]. With regards to expression of the various activating enzymes, again the situation is heterogeneous and unclear.…”