PARP Inhibitors for Melanoma

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Some cell-based assay labs have explored the biology of PARP inhibitors, alone and in combination, in actual human tumor primary culture microspeheroids (microclusters), in breast, ovarian and other cancers. In these investigations, the lab applies the functional profiling platform to understand how PARP inhibitors enhance the effects of drugs and drug combinations. As seen with PARP inhibitors, mutations work with other proteins. Genes do not operate alone within the cell but in an intricate network of interactions.

The Sunday, April 3, 2011, experimental and molecular therapeutics poster session at the American Association for Cancer Research (AACR) 102nd annual meeting included Dr. Robert Nagourney's Rational Therapeutics presentation on signal transduction inhibitors. Using MEK/ERK and PI3K-MTOR inhibitors he explored the activities, synergies and possible clinical utilities of these novel compounds.

The results of functional analysis with the mTOR/P13K and MEK/ERK inhibitors, BEZ235 and AZD6244, alone and in combination in human tumor primary culture microspheroids (microclusters): Exploration of horizontal pathway targeting. While the profiles of each drug alone are of interest, the profiles of the drugs in combination are better still.

The phenomenon of cross-talk defines an escape mechanism whereby cancer cells blocked from one passage, find a second. When clinical therapists have the capacity to block more than one pathway, the cancer cell is trapped and often dies. This is what has been observed with these duel inhibitor combinations. What is interesting is the fact that the activities cut across tumor types. Melanomas, colon cancers and lung cancers seem to have similar propensities to drive along these paths. Once again, we find that cancer biology is non-linear.

Moreover, cancers share pathways across tumor types, pathways that might not intuitively seem related. This is the beauty of cell-based functional profiling platform. It allows the exploration of drugs and combinations that most oncologists wouldn’t think of. It is these counterintuitive explorations that will likely lead to meaningful advances.

The findings were instructive. First, it saw a good signal for both compounds utilizing the Ex-vivo Analysis of Programmed Cell Death (EVA-PCD) platform (functional profiling). Second, it saw disease-specific activity for both compounds. For the MEK/ERK inhibitor, melanoma appeared to be a favored clinical target. This is highly consistent with expectations. After all, many melanomas carry mutations in the BRAF gene, and BRAF signals downstream to MEK/ERK. By blocking MEK/ERK, it appeared that his lab blocked a pathway fundamental to melanoma progression. Indeed, MEK/ERK inhibitors are currently under investigation for melanoma.

Functional profiling measures biological signals rather than DNA indicators, which plays an important role in cancer drug selection and is demonstrably greater and more compelling data currently generated from DNA analyses. The results of their investigation support the clinical relevance of targeting the MEK/ERK and PI3K/mTOR pathways and more importantly, suggest "dual" pathway inhibition (horizontal) to be a productive strategy for further clinical development. Disease specific profiles and sequence dependence are explored and reported.

PARP is a very active enzyme involved in the repair of single-strand breaks in DNA or modified bases. It binds to DNA damage and adds multiple sugar molecules to the DNA that act as a beacon to recruit other components of DNA repair.

Emerging work on assays (PARP levels correlating with response to PARP inhibitors) have shown pretty good response with PARP inhibitors as single agents and some results combining the PARP inhbitors with mustard alkylators, platins and drug combinations to optimize PARP inhibitor combinations. These results, though exploratory, suggest a superior approach for drug development, allowing the lab to identify important leads much faster than the clinical trial process.

Source: Robert A. Nagourney, Paula Bernard, Federico Francisco, Ryan Wexler, Steve Evans, Rational Therapeutics, Long Beach, CA. Proceedings of AACR - Volume 52 - April 2011.

American Association of Cancer Research (AACR) Meeting 2011

http://robertanagourney.wordpress.com/2011/04/28/poster-from-rational-therapeutics-session-at-2011-aacr-meeting/