Novel Tubulin Antagonist Pretubulysin Displays Antivascular Properties In Vitro and In Vivo

Abstract

Objective-Pretubulysin (PT) is a novel, synthetically accessible myxobacterial compound that acts as a tubulindepolymerizing agent and inhibits cancer cell growth in vitro and in vivo. Moreover, PT was found to attenuate tumor angiogenesis. Here, we hypothesized that PT could exert antivascular activities on existing tumor vessels. Approach and Results-We aimed to characterize the antivascular effects of PT and to elucidate the underlying mechanisms in endothelial cells. In vitro, PT rapidly induced endothelial hyperpermeability and a concentration-dependent disassembly of established endothelial tubes on Matrigel and in an ex vivo aortic ring model. It disrupted endothelial cell junctions and triggered F-actin stress fiber formation and cell contraction by the RhoA/Rho-associated protein kinase pathway without causing cell death. In vivo, using a hamster dorsal skinfold chamber preparation, PT significantly decreased blood flow and vessel diameter in hamster A-Mel-3 amelanotic melanoma tumors but not in the neighboring healthy tissue. In a second tumor model using mice with subcutaneous murine B16 melanoma tumors, a single dose of PT (10 mg/kg) caused a shut down of tumor blood flow and a strong central tumor cell necrosis within 24 hours. Repeated PT administration significantly decelerates tumor growth and seems to be well tolerated. Conclusions-In

Combined antitumoral effects of pretubulysin and methotrexate

“…With regard to drug-induced apoptotic events in L1210 or KB cells, treatment with PT or MTX alone resulted in a steady increase of apoptotic cells which is in accordance with previous work. 6,10,34,37 Yet, apoptosis could not be further enhanced by combining both agents.…”

“…Moreover, it displays remarkable antitumoral potency in the subnanomolar region . PT not only leads to reduced tumor cell growth of different cell lines and inhibits cancer cell migration in vitro, it also shows great potential in vivo: PT inhibits tumor growth and metastasis and also significantly reduces angiogenesis …”

“…6,7 Moreover, it displays remarkable antitumoral potency in the subnanomolar region. 6,8 PT not only leads to reduced tumor cell growth of different cell lines 6 and inhibits cancer cell migration in vitro, 8 it also shows great potential in vivo: PT inhibits tumor growth 6,[8][9][10][11] and metastasis 6,12 and also significantly reduces angiogenesis. 8,10 Antifolates, which belong to the class of antimetabolites, were among the first chemotherapeutic drugs to be investigated for the cure of metastatic cancer.…”

A Straightforward Approach towards Cyclic Photoactivatable Tubulysin Derivatives

“…We are particularly interested in pretubulysin, a biosynthetic precursor of the tubulysins (Figure 2), which inhibits the growth of a wide range of tumor cells in the low nanomolar range. [19] Like the tubulysins, pretubulysin interacts with the microtubuli skeleton, [20] suppressing angiogenesis, [21] and is therefore an excellent candidate for the development of antitumor drugs. [22] Structure-activity relationship (SAR) studies indicate that pretubulysin-derived esters are 3-6 times less active than pretubulysin, while amides are even less active (10-20fold) depending on the derivative.…”

Pretubulysin derived probes as novel tools for monitoring the microtubule network via activity-based protein profiling and fluorescence microscopy

“…4b). Interestingly, the same phenotype has been reported for pretubulysin previously [38][39][40] but so far the direct binding to tubulin could not be directly confirmed. Here we demonstrate by co-staining with the tubulin directed antibody as well as the fluorescent probe that pretubulysin derivative 4 binds to monomeric tubulin which appear as little spots in the image ( Fig.…”