The Molecular Origins of Lung Cancer

I had the luxury of attending the AACR-IASLC Joint Conference on Molecular Origins of Lung Cancer; Biology, Therapy and Personalized Medicine held in San Diego earlier this month. I say luxury, for as my schedule closes in on me and I sometimes find myself working 13-hour days, it can be difficult to take even a couple of days away to attend meetings. But this conference was too good to pass up (hats off to Marge Foti and all the AACR staff for all their great work).

This symposium organized by David Carbone and Roy Herbst, brought together a broad spectrum of sophisticated scientists and international investigators, as well as community members and fundraising organizations who had the opportunity to present a special session on patient advocacy.

The meeting began with a keynote address examining microRNAs and lung cancer presented by Frank Slack from Yale University. He examined the growing recognition that lung cancer arises not only from gene mutations but also from small fragments of RNA that can up- or down-regulate normal genes in abnormal ways. This was the topic of discussion for many subsequent presentations.

As an aside, many of the readers will know that I am generally underwhelmed by genomic analyses for the prediction of cancer response. The fact that normal genes can function abnormally under the control of these small RNA sequences is just one more example of the genotype–phenotype dichotomy that cannot be adequately examined on static contemporary genomic platforms.

Many presentations examined the molecular biology of lung cancer with important distinctions being drawn between adenocarcinoma and squamous cell carcinomas. While adenocarcinomas reveal a growing number of targets – EGFR, ALK, ROS, RAS, and others – all the subject of small molecule inhibitors; squamous cell carcinomas provide fewer opportunities for the use of these classes of drugs.

One of the interesting discussions was the frequent mutation of LKB1 in lung cancers. Work going back several years by John Minna, a pioneer in this field, identified changes in this metabolic regulator as a common finding in lung malignancies.

Additional presentations examined chemoprevention, molecular pathology, new mechanisms to categorize lung cancer subtypes, and a very interesting discussion of field cancerization. In a particularly interesting analysis, Ignacio Wistuba from M.D. Anderson, showed that molecular changes in the surface epithelium of the lung bronchioles recapitulated the molecular biology of the final tumor in a step-wise manner, inversely related to the distance to the tumor. That is, starting at the main bronchi, one or two mutational changes were detected. Moving closer to the site of the tumor, additional mutations were accumulated. Finally arriving at the site of the established malignancy, all of the constituent mutations associated with this particular cancer became manifest; a saltatory slide into cancer presumably associated with exposure to carcinogens.

Among the other exciting presentations were updates on redox-based approaches to cancer presented by Kenneth Tew and Garth Powis.

Jeff Engelman presented an update on a new class of agents that target the RAS pathway. This is ongoing work that he and his group have reported on over the last several years. We have been engaged in related work using an MEK/ERK inhibitor similar to the compound that Dr. Englemen reported on at this meeting. It is exciting indeed to see early clinical results with this class of compounds, for we have identified many patients who might benefit from this pathways’ inhibition. We wait with great anticipation for FDA approval of these compounds so that our patients currently being identified as candidates in the laboratory may soon receive these treatments.

Targeted Therapies — The Next Chapter

Within this blog, we have intermittently reviewed the concept of targeted therapies. To reiterate, these are classes of drugs that target specific pathways considered tumorigenic. Among the pathways initially targeted were the epidermal growth factor receptor and the closely related HER2. Shortly after the introduction of EGFr and HER2 directed therapies came the development of drugs that target another critical pathway, mTOR.

Hundreds of compounds are now under development intended to more accurately hone in on the pathways of interest in patients’ tumors. Regrettably, the medical community continues to apply old clinical trial methods to this newest era of drugs. While the selective application of drugs like: Tarceva for EGFR mutants, Herceptin for HER2 over-expressers, and Crizotinib for EML4-ALK mutants, are much more effective in patients with these gene expressions, these are a select few examples of linear thinking that bore fruit.

That is, this gene is associated with this disease state and can be treated with this drug.

Many, if not most cancers will prove to be demonstrably more complicated. Genomic trials can only succeed if we first know the gene of interest and second know that its (over) expression alone is pathogenetic for the disease entity. Even meeting these conditions is likely to result in comparatively brief partial responses due to the crosstalk, redundancy and complexity of human tumor signaling pathways — the “targets” of these new drugs.

To address these complexities, functional analytic platforms that examine outcomes, not targets, are needed. This bottom-up approach has now enabled my team to explore the activity of novel compounds. When investigators develop interesting “small molecules,” we examine the disease specificity, combinatorial potential and sequence dependence of these compounds in short-term cultures to provide meaningful insights that can then be addressed on genomic and proteomic platforms. This reduces the time required to take these new agents from bench to bedside. We cannot solve tomorrow’s questions using yesterday’s mindsets

Horizontal and Vertical Signal Pathway Inhibition

The importance of signal pathway inhibition in human tumor primary culture microspheroids.

Signal transduction pathways are important targets in cancer therapy. Small molecule inhibitors for the tyrosine kinase and serine threonine kinase pathways are already available for clinical therapy. Additionally, compounds targeting the PI3K, AKT and MEK pathways will be available in the coming years. To explore the interaction of these parallel survival pathways, we compared activity and combined these inhibitors in human tissues — the results were instructive.

Our findings include favorable interactions between EGFr tyrosine kinase inhibitors and compounds that block the PI3K pathways. The most active combinations were those that inhibited the cross-talk between pathways (horizontal inhibition) over drug combinations that targeted the same pathway at different downstream points (vertical inhibition). Similar observations have been made combining PI3k inhibitors and MEK inhibitors. One such report in PNAS (May 10, 2010) closely paralleled the work conducted in our laboratory, Rational Therapeutics, that we reported at the AACR.

Noteworthy, a series of studies utilizing these combinations, indicate that certain tumors respond to their drug exposure by undergoing autophagic death, not necrotic or apoptotic. This distinction is possible, as the Ex-Vivo Analysis of Programmed Cell Death (EVA-PCD®) platform has the capacity to measure all forms of cell death – apoptotic and non-apoptotic.

We continue these studies in numerous solid tumors to explore those diseases that will be the best candidates for these types of combination therapies. Please leave a comment below if you would like more information on these studies.