A couple of articles in the latest Cancer Discovery looked at some rather promising, and perhaps a little unexpected, findings pertaining to epigenetic therapy.
What are epigenetics?
If you read up on epigenetics in the medical journals, you will come across some of the most dense and complex articles I’ve ever come across in cancer biology. That said, there are a few readable examples around such as Bird’s (2007) short insight piece in Nature.
Personally, I tend to think of epigenetics – in very simple terms – as changes in gene function that can occur without a change in the sequence of the DNA. This means that we see things such as DNA methylation (where something new is added) and gene silencing (where something important is somehow switched off or lost). A classic change in cancer that often appears in many tumour types is PTEN loss, for example.
As Rodriquez-Paredes and Esteller (2011) noted in their editorial,
“No one doubts that tumorigenesis is a consequence of not only genetic but also epigenetic alterations…
Cancer epigenomes are characterized by global changes in DNA methylation and covalent histone modification patterns.”
What types of epigenetic therapy are there?
While some readers might be vaguely familiar with DNA methylating agents and histone deacetylase inhibitors (HDAC), there are quite a few other types in preclinical development including:
- histone methyltransferase inhibitors
- histone kinase inhibitors
- sirtuin inhibitors
- microRNA-related compounds
and others, to name a few.
Currently, however, there are a couple of epigenetic therapies that have been approved (eg SAHA or vorinostat), which belongs to the histone deactelyase class of inhibitors (HDAC) indicated for CTCL, while another is the DNA methyltransferase inhibitors (eg azacitadine/Vidaza and decitabine/Dacogen), which are approved for the treatment of MDS and AML, respectively. There are also several other HDACi in development, including entinostat (Syndax), which has shown activity in breast and lung cancers (see Huang et al., 2009 as an example) and panobinostat (Novartis), which is being evaluated in both hematologic malignancies and solid tumours (prostate and melanoma).
Yet what really caught my attention in the paper by Jeurgens et al., (2011) and the accompanying editorial (see references below) was that these two therapy classes are being evaluated in combination for… lung cancer. You likely won’t find HDACs or DNA methyltransferase inhbitors in the top 30 of therapies used for lung cancer at present, but that may change sooner than you think.
Background to epigenetics in lung cancer
To put this story in context, the authors (see Brock et al., 2008) previously identified a potential gene signature for recurrence associated with stage I lung cancer after surgical resection:
“Analysis of DNA methylation in tumors and mediastinal lymph nodes from a series of patients with surgically resected stage I NSCLC defined several prognostic markers associated with rapid tumor recurrence.
Four gene targets of tumor-specific epigenetic silencing, CDKN2a, CDH13, APC, and RASSF1a, were identified as strongly associated with disease recurrence and death, both singly and in combination.
Methylation of any 2 of these 4 target genes in tumor and mediastinal lymph nodes conferred a markedly worse prognosis in patients with stage I lung cancer (P < 0.001), similar to patients with stage III disease.”
As far as I’m aware, to date the clinical data with epigenetic therapies has been reported in hematologic malignancies such as leukemia, lymphoma and MDS. This is the first time we’ve seen some meaningful data in solid tumours.
What about the latest clinical trial in lung cancer?
Jeurgens and colleagues at Johns Hopkins conducted:
“A phase I/II trial of combined epigenetic therapy with azacitidine and entinostat, inhibitors of DNA methylation and histone deacetylation, respectively, in extensively pretreated patients with recurrent metastatic non–small cell lung cancer.
This therapy is well tolerated, and objective responses were observed, including a complete response and a partial response in a patient who remains alive and without disease progression approximately 2 years after completing protocol therapy.”
The NSCLC patients (n=45) were mainly smokers or former smokers (n=40) with primarily adenocarcinoma (n=34) who had been heavily pre-treated (median of 3 prior therapies).
Median overall survival in the entire group was 6.4 months, which compared favourably with the expected 4.0 months in historical controls.
“Four of 19 patients had major objective responses to subsequent anticancer therapies given immediately after epigenetic therapy.”
These responses in a small subset of patients were fascinating – the most dramatic response was seen in one patient who experienced a complete response (CR) that lasted for 14 months. A further 10 people had stabilisation that lasted at least 12 weeks (1 for 14 months and another for 18 months).
Moreover, the four gene signature referred to earlier turned out to be potentially useful as both a prognostic and predictive biomarker:
“Demethylation of a set of 4 epigenetically silenced genes known to be associated with lung cancer was detectable in serial blood samples in these patients and was associated with improved progression-free (P = 0.034) and overall survival (P = 0.035).”
One patient who did particularly well on the combination therapy was subsequently re-challenged with chemotherapy and had such a good response that the nodules in his lungs reduced significantly. After being diagnosed in December 2006 with stage IV NSCLC, he was still alive and well to tell his astonishing and heartwarming story on the press conference five years later.
Overall, the authors rightly concluded that:
“This study demonstrates that combined epigenetic therapy with low-dose azacitidine and entinostat results in objective, durable responses in patients with solid tumors and defines a blood-based biomarker that correlates with clinical benefit.”
While these results are very exciting, they are also preliminary and will need to be validated in larger scale clinical trials along with the blood biomarkers for clinical response. They do offer a very strong proof of concept for the combination of epigenetic therapy with a DNA methyltransferase inhibitor and an HDAC inhibitor with clear activity in a subset of patients.
What do these results mean in practice?
Personally, I thought these results were absolutely fascinating and offer us a glimpse into the future where we can utilise epigenetic therapies to:
- Effectively repair damaged DNA in tumours
- Offer low dose therapies with fewer side effects that give a respite from chemotherapy, while doing more good than harm
- Enable sensitization of subsequent therapies to improve outcomes
- Predict which patients are most likely to respond to epigenetic therapies, while sparing those unlikely to from any systemic side effects
To get a good clinical perspective of what these results mean, I spoke with Dr Jeff Engelman, Director, Center for Thoracic Cancers at Mass General in Boston. He described the data as ‘impressive':
“I don’t think this is going to impact the practicing oncologist today, but from a scientific stand point, from an oncology development stand point, from a future stand point, it is I think impressive to many of us, to me.
Seeing that epigenetics could have a dramatic effect even on a subset of lung cancers, we’ve never seen epigenetic modulators have such an effect on solid tumors, so it really opens the door that this may be another type of therapy that we will be able to employ for the right patients. A totally different type of approach.”
He also went on to put the story in a broader context, which I thought was very helpful:
“It is somewhat analogous to the first trials with EGFR inhibitors where had we treated 40 patients with those we would have seen a few great responses.”
“With EGFR, it was given to tons of patients, and there was a subset that responded, and it took a couple of years to find out why. Then all of sudden, boom everything makes sense and we go forward. This feels more like that, we have seen some great responses and now need to figure out why.”
Clearly, the gene signature identified by Brock et al., (2008) in stage I patients needs to be validated in a broader population of patients in clinical trials, but at least it offers a starting point to try and determine which patients with lung cancer might respond to epigenetic therapy. I think Engelman is correct here; once we determine the right biomarkers of response and how often they occur, then patients with lung cancer can be screened and appropriate therapy offered, whether that be EGFR therapy, ALK therapy, or something completely different such as treatment with epigenetic drugs.
The amazing thing is how much progress is being made of late in lung cancer and that’s very good news indeed. I look forward to hearing more about this story and also the other slices or targets as they are identified and the story evolves further.
Bird, A. (2007). Perceptions of epigenetics Nature, 447 (7143), 396-398 DOI: 10.1038/nature05913
Brock, M., Hooker, C., Ota-Machida, E., Han, Y., Guo, M., Ames, S., Glöckner, S., Piantadosi, S., Gabrielson, E., Pridham, G., Pelosky, K., Belinsky, S., Yang, S., Baylin, S., & Herman, J. (2008). DNA Methylation Markers and Early Recurrence in Stage I Lung Cancer New England Journal of Medicine, 358 (11), 1118-1128 DOI: 10.1056/NEJMoa0706550
Huang, X., Gao, L., Wang, S., Lee, C., Ordentlich, P., & Liu, B. (2009). HDAC Inhibitor SNDX-275 Induces Apoptosis in erbB2-Overexpressing Breast Cancer Cells via Down-regulation of erbB3 Expression Cancer Research, 69 (21), 8403-8411 DOI: 10.1158/0008-5472.CAN-09-2146
Juergens, R., Wrangle, J., Vendetti, F., Murphy, S., Zhao, M., Coleman, B., Sebree, R., Rodgers, K., Hooker, C., Franco, N., Lee, B., Tsai, S., Delgado, I., Rudek, M., Belinsky, S., Herman, J., Baylin, S., Brock, M., & Rudin, C. (2011). Combination Epigenetic Therapy Has Efficacy in Patients with Refractory Advanced Non-Small Cell Lung Cancer Cancer Discovery DOI: 10.1158/2159-8290.CD-11-0214
Rodriguez-Paredes, M., & Esteller, M. (2011). A Combined Epigenetic Therapy Equals the Efficacy of Conventional Chemotherapy in Refractory Advanced Non-Small Cell Lung Cancer Cancer Discovery DOI: 10.1158/2159-8290.CD-11-0271