Category Archives: Targeted treatment

Precision medicine and AR-V7


To view this blog at my blog’s website where you can sign up to be notified and read other posts relevant to prostate cancer, click here.

Much of the news this week in prostate cancer will be generated by the annual ASCO Meeting in Chicago where VP Joe Biden will be speaking tomorrow about the moon shot. It will be hard to miss the excitement – perhaps even eclipsing (for a day or so) the ongoing circus that is our presidential politics at the moment.

In prostate cancer, there are likely to be considerable news releases regarding precision medicine, and especially AR-V7, so I thought I would explain this a bit. Precision medicine is the broad terminology that (in oncology) refers to looking at the individual patient’s tumor genetic profile. In the broadest sense, it can also refer to all of our genetic makeup that can influence, for example, how we metabolize drugs. The optimal dose for you might be different from that for me based on our inheritance of slightly different enzymes that are involved in breaking down a certain drug. In oncology, it is now possible to perform whole exome sequencing (WES) on circulating tumor cells that give a nearly complete picture of an individual’s cancer – what is driving it, and what it might be susceptible to. In metastatic prostate cancer, as you know from my previous post, the tumor cells circulating in the blood stream could be coming from a variety of places, and likely each individual cell might have slightly different genetics – creating a considerable challenge in the long run for picking out “the” drug that is best for that patient, even with this high-tech approach. Nevertheless, WES has already demonstrated exceptional ability to find targetable mutations in cancer cells, often with several different pathways of potential susceptibility in each patient. Two challenges arise: 1) the drugs that target each “driver pathway” are often frightfully expensive, and 2) which one or ones would be the best to target?

So what about AR-V7? 14 of the 214 prostate cancer abstracts (keep that in mind when you ask your doctor, “Hey doc, is there anything new out there?”) deal with this biomarker. AR-V7 stands for Androgen Receptor – Splice Varient 7. I know…”too complicated for me to understand”. Think of it this way: The AR is the energizer bunny, and testosterone is the battery. Put the battery in the bunny, and he hops into the nucleus of the cancer cell and turns on all sorts of genes (including psa) that drive the cancer cell to do bad things (divide, invade surrounding tissue, metastasize, etc.). Now suppose the bunny becomes autonomous – no need for a battery – he can hop in and do his thing whether or not testosterone is present. This means that all of the new treatments that target testosterone (abiraterone/Zytiga™, enzalutamide/Xtandi™, etc.) really won’t do much. We call this resistance. Castrate resistant prostate cancer (CRPC) used to mean “simply” tumor progressing in spite of very low levels of testosterone (achieved with drugs like leuprolide/Lupron™, goserelin/Zoladex™, etc) or T-blockers like bicalutamide/Casodex™. What we now know is that patients whose cancers are expressing the AR-V7 form of the AR will not respond well to any of these drugs. This means that it could make more sense to proceed directly to treating with chemotherapy with a drug like docetaxel/Taxotere™. Dr. Scher and colleagues at MSKI report in this weeks JAMA Oncology and at the ASCO meeting on the utility of looking for AR-V7 in circulating tumor cells to guide therapy. Screen Shot 2016-06-05 at 8.21.17 AMUsing special immunofluorescent stains, they can identify the “bunny” (shown in white on this photograph from their publication) in the nucleus of some cells in some patients, and these patients are better treated with chemotherapy than with approaches targeting the AR. The implications of this are that we may be able to use such tests to avoid the expense and wasted time of trying to use AR directed therapies in some patients. As often happens, the science is far ahead of the insurance companies however. The Hopkins group have commercialized the test and in an abstract show that it can be cost effective in populations of patients where AR-V7 is likely to be >5% prevalent. Better yet, these insights are now in clinical trial to hopefully develop new treatments for these patients such as galeterone, which may be able to degrade (“kill”) the bunny as described in this abstract from the ASCO meeting.

So YES, we are making progress, and there is a LOT that is new “out there”. Scan the abstracts for yourself – it really isn’t that hard – and kudos to the prostate cancer researchers who are moving this fight forward so quickly.

 

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Filed under General Prostate Cancer Issues, Prostate cancer therapy, Targeted treatment, Uncategorized

Olaparib for resistant prostate cancer


To view this blog at my blog’s website where you can sign up to be notified and read other posts relevant to prostate cancer, click here.

In what is the first (and hopefully one of many) example of using modern genomic methods to match treatments to the molecular defects in prostate cancer, the FDA has just granted “breakthrough designation” to olaparib, a drug made by AstraZeneca. This followed a publication in the NEJM with nearly as many authors as patients, illustrating the power of team science and international collaboration.

Cancer cells develop numerous mutations that provide them with the ability to divide, metastasize, escape immune surveillance and so forth. One of the drivers of this mutation cascade is genetic instability, in part due to the accumulation of mutations that keep the cells from correcting DNA alterations. These mutations in DNA-repair enzymes can leave the cancer susceptible to additional inhibitors of DNA repair, one of which is PARP, an enzyme found in the nucleus that detects DNA strand breaks and initiates repair. When olaparib interferes with this enzyme, cells can become so genetically unstable they die.

In the TOPARP-A trial, 50 patients who had castrate resistant prostate cancer and had progressed on second generation anti-androgen treatment and docetaxel were given olaparib. 16 of 49 evaluable patients responded, however the exciting finding was that because these patients participated in the clinical trial and allowed the investigators to biopsy their tumors, it was possible to relate response to the presence of defects in the DNA repair genes. For this subgroup, 14 of 16 responded, indicating that using the repair defects as a biomarker you could predict high response rates, while at the same time, patients without such genetic defects had a much lower response rate (2/33). There is an excellent video that illustrates the results accompanying the publication that you can find by clicking here.

Although this is terrific news for prostate cancer patients, it brings a number of challenges. Testing for genetic mutations is a growing (and somewhat expensive) process. When compared to giving patients a drug that predictably won’t work, however, it can be very cost effective. Second, when you biopsy a tumor, the results can vary depending on where you biopsy as I discussed in this previous blog. “Liquid biopsies” of circulating DNA or tumor cells may provide some help in meeting this challenge.  Third, responses to targeted therapies such as olaparib tend to be rather short-lived, as the cancer cells continue to mutate to find ways around the new agent. The hope would be that combining a targeted treatment like olaparib with an immune approach might bring more prolonged responses. Finally, we must find a way to deal with the extraordinary costs of the new oncology drugs. The actual cost of olaparib is $13,440/month according to this article in the ASCO post. I have previously opined on this issue and invite you to join the discussion by clicking here.

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Filed under General Prostate Cancer Issues, Prostate cancer therapy, Targeted treatment