Poster from Rational Therapeutics Session at 2011 AACR Meeting

As I mentioned in a previous post, on April 3, 2011, I traveled to Florida to present our most recent findings on novel compounds that target two parallel circuits in cancer cells at the American Association of Cancer Research Meeting.

Following are shots of the poster that was presented. I encourage you to leave any comments and/or questions here, as I would be pleased to respond to your inquiries.

Can PARP Inhibitors be Tested Using the EVA-PCD Assay?

Poly ADP ribose polymerase (PARP) is a nuclear enzyme associated with response to DNA damage. Following single strand DNA breaks, the enzyme attaches a backbone of ADP and ribose that serves to initiate DNA repair. Certain classes of chemotherapeutics, specifically alkylating agents, can induce injury that results in extensive poly ADP ribosylation resulting in the exhaustion of intercellular pools of NAD and ATP ultimately leading to cell death.

Although PARP inhibitors have recently entered the clinical cancer literature mostly relating to the treatment of BRCA+ and triple negative patients, neither PARP nor PARP inhibitors are new to the cancer researcher community.

Our group first became interested following a 1988 study by Distelhorst from Case Western Reserve (Distelhorst CW, Blood 1988 Oct;72(4):1305-09) that described a mechanism of cell death that correlated with our work in childhood leukemia. Previously, investigators at Scripps Clinic had described PARP’s role in response to 2CDA (Seto, S., et al. J Clin. Invest. 1985 Feb;75(2):377-83). We have studied small molecule inhibitors of PARP for many years, and more recently, we have expanded these investigations to include BSI201 (iniparib) and AZD2281 (olaparib). Both of which are undergoing clinical investigations. We will be reporting our findings with these PARP inhibitors at the 2011 ASCO meeting (Nagourney, R., et al Proceedings Amer Soc Clin Oncol. 2011).

PARP inhibitors are easily studied and provide interesting signals in the tissue studied. We see activity in BRCA+ patients and some triple negative breast cancers. We have also identified synergy with other classes of drugs. The compounds are a welcome addition to our cancer therapy armamentarium and continue to be actively studied in the EVA-PCD platform.

Of interest is the recent failure of the iniparib plus Carboplatin & gemcitabine Phase III trial to meet progression-free and overall survival goals in triple negative breast cancer patients (Zacks Investment Research on January 31, 2011). This failure may reflect the need to apply predictive methodologies to select candidates for these drugs, similar to our successful work with other classes of compounds.

Jump Starting Cancer Drug Development

The April 12 issue of PNAS (Proceedings of the National Academy of Sciences) features a lead article by investigators at NYU, Cornell and Rational Therapeutics, on the identification of three compounds that inhibit the important cell signaling pathway known as WNT.

The WNT pathway was originally described in fruit flies as a determinate of wing shape. It was subsequently shown to be an important factor in human stem cell differentiation. Thereafter, its role in cancer was described. Certain colon cancers associated with a familial syndrome have a mutation in the WNT pathway. This results in an extremely high incidence of colon cancer. We now know that lung cancers, breast cancers, leukemias and lymphomas may share this pathway.

To date, there have been no clinical therapies available to treat WNT-driven tumors. Recognizing the importance of this pathway, the investigators at NYU and Cornell used a technology known as small interfering RNA (SIRNA) to shut down the WNT signal. They then screened 14,000 know chemicals for activity that mimicked the SIRNA effect. Three compounds were identified.

When the compounds showed activity in cell-lines that were WNT addicted, the investigators at NYU provided the compounds to Rational Therapeutics where we applied the EVA-PCD technique to measure activity in human tumor samples. The results confirmed activity and showed that several colon cancers, as well as other tumor types, had favorable profiles. The compounds were not uniformly effective, indicating that they were not simply toxins. Instead, they appeared to selectively injure cells that we assume are driven by WNT-related events.

The beauty of this study represents the introduction of a new paradigm of drug development. Following the elegant and highly sophisticated high throughput method employed by investigators at NYU and Cornell, these compounds were put to the very practical test of human relevance. The identification of activity in human tissues at concentrations similar to those associated with other classes of drugs, suggest that these novel compounds may have promise with these heretofore-untreatable cancers. This highly productive collaboration could prove a new model for the development of effective new therapies.

American Association of Cancer Research (AACR) Meeting 2011

The Sunday, April 3, 2011, experimental and molecular therapeutics session at the AACR 102nd annual meeting included our presentation on signal transduction inhibitors. Using MEK/ERK and PI3K-MTOR inhibitors we explored the activities, synergies and possible clinical utilities of these novel compounds.

The findings were instructive. First, we saw a good signal for both compounds utilizing the Ex-vivo Analysis of Programmed Cell Death (EVA-PCD) platform. Second, we 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 our expectation. After all, many melanomas carry mutations in the BRAF gene, and BRAF signals downstream to MEK/ERK. By blocking MEK/ERK, it appeared that we blocked a pathway fundamental to melanoma progression. Indeed, MEK/ERK inhibitors are currently under investigation for melanoma.

For PI3K inhibitors, the highest activity was observed in uterine cancers. This is interest, because uterine carcinomas are often associated with a mutation in the PTEN gene. PTEN is a phosphatase tumor suppressor that functions to block activation of the PI3K pathway. Thus, mutations in the tumor suppressor unleash PI3K signaling, driving tumors to grow and metastasize. Blocking PI3K provided a strong signal, indicating that this approach may be very active in tumors associated with these oncogenic events.

The third point of interest in our report was, perhaps, its most important. Specifically, that we can explore those diseases where MEK-ERK, PI3K and mTOR signaling are less established targets. Cancers of the lung, ovary, colon or breast all manifested profiles of interest. When we combined both pathway inhibitors in a process we call horizontal inhibition, renal cell carcinoma popped up as the best target. These results, though exploratory, suggest a superior approach for drug development, allowing us to identify important leads much faster than the clinical trial process.

What’s the Best Treatment for Metastatic Colorectal Cancer?

The answer is: nobody knows.

We have previously described a patient with a small bowel cancer for whom a treatment regimen contrary to the most widely used triplet was recommended. While it is arguable that small bowel adenocarcinoma is rare enough that no one really has a favorite regimen, colorectal management has become somewhat rigidly focused on FOLFOX. Yet, this popular combination may not be right for every patient with colon cancer.

We know, for example, that FOLFOX combined with Avastin provided no advantage in the adjuvant setting. We also know that the random addition of Erbitux to FOLFOX similarly failed to provide an advantage. As the modes of action differ between drugs, it is not surprising that subsets of colon cancer patients may do better with Irinotecan based therapies. Indeed, clinical trials combining the new monoclonal antibodies with Irinotecan have proven quite favorable, including the 2007 BOND-2 trial reported by investigators at Memorial Sloan Kettering in New York.

With this in mind, patients who present with both untreated colon cancer and a favorable profile for Irinotecan based combinations always interest us. One such patient presented to our attention in the last few weeks. This patient, in his mid 30s, was found to have inoperable, widely metastatic disease with extensive liver involvement. Confirmatory biopsies provided tissue for analysis and revealed no evidence of mismatch repair.

The results of the EVA-PCD platform were interesting on many levels. First, the EGFr active drugs provided a uniquely favorable profile, as did the down-stream inhibition of the MEK-ERK inhibitor we studied. These findings strongly suggested that the patient was RAS wild type (i.e. non-mutated). It is known that RAS mutation confers resistance to the EGFr active drugs. By inference, his sensitivity to the EGFr active drugs was prima facie evidence of RAS wild type, a finding that was confirmed later by molecular analysis. There was also a favorable profile for VEGF active drugs. Most favorable of all was the combination of Irinotecan with inhibitors of both VEGF and EGFr. This was the regimen that we selected.

We wait with interest the results of the therapy, as re-staging for response will be conducted in the coming months.