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Alcatraz San FranciscoIn yesterday’s post on novel targets in advanced prostate cancer, we looked at a potential new concept that is emerging and being evaluated in clinical trials.

Today, we continue that approach with a look at another novel – and quite different target – as well as ways of repurposing old drugs to help potentially overcome the drug resistance seen with newer therapies for this disease.

Warning: the concepts discussed here may well take you by surprise, although they are based on rational and logical evidence from recent scientific research.

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Background

Dr Nima Sharifi, Cleveland Clinic

Dr Nima Sharifi, Cleveland Clinic

Dr Nima Sharifi (Cleveland Clinic) gave an intriguing talk at the ASCO Genitourinary symposium recently (#GU16), where he explored new ways of targeting and old target i.e. the androgen receptor with abiraterone.

He noted that 2015 was a landmark year for prostate cancer in terms of genetic characterisation of the disease with a key publication in Cell from several groups including Levi Garraway, Charles Sawyers and Arul Chinnaiyan’s labs via the Stand Up to Cancer research program.

It’s a well written and easy to read paper that I highly recommend reading (see Robinson et al., 2015 in the References below).

In addition, the TCGA work is summarised for those interested in Cell via the TCGA portal for prostate cancer (Link) based on integrated profiling of 333 primary prostate adenocarcinoma samples (the separate Cell paper is also included in the References below). For the geeky scientists here, you can also access and query the raw data they collated at the NCI (Link) and the full TCGA datasets for numerous cancers (most were updated in December 2015) can also be found here (Link).

Overall, the SU2C effort is particularly impressive on several fronts and the massive collaboration effort involved sought to determine the genetic factors at play in mCRPC:

“A multi-institutional integrative clinical sequencing analysis reveals that the majority of affected individuals with metastatic castration-resistant prostate cancer (mCRPC) harbor clinically actionable molecular alterations, highlighting the need for genetic counseling to inform precision medicine in affected individuals with advanced prostate cancer.”

The group identified the following key pathways involved in mCRPC, which may lead to more refined clinical work in the near future to optimise and improve the therapy options available for patients with this disease:

Source: Robinson et al., (2015)

Source: Robinson et al., (2015)

One thing that I really hope to see going forward is more focused and rational clinical trials in advanced prostate cancer, where different subsets such as those identified by the SU2C project are tackled with more logical combinations rather than treating everyone the same.  This is a highly heterogeneous cancer, after all.

For example, we saw in yesterday’s post on DNA repair how trials are already starting or planned – some are allcomer trials (why oh why?!) and some are more specific including only patients with mismatch repair that the PARP inhibitors are supposed to target (a much better approach in our view).

It drives me crazy when, even in 2016, we see companies treating a targeted therapy in an untargeted fashion and expect to see positive results from such a diluted approach!

So what do we have in store today?  At the recent ASCO Genitourinary symposium (#GU16), there were a number of intriguing talks that we will continue to highlight for the rest of this week.

After a look at what’s new in PARP inhibition, we now turn our focus and attention to the androgen receptor (AR) and abiraterone acetate (Zytiga), in particular.  This drug was first approved by the FDA in 2010 for CRPC patients who had received prior chemotherapy (docetaxel) and then subsequently in the pre-chemotherapy setting. Both Zytiga and enzalutamide (Xtandi) compete with each other in both of these settings.  One particular challenge is that the therapies work well as single agents but the effect lessens over time as resistance sets in.

A fresh look at abiraterone and steroidogenesis

In this particular talk, Dr Sharifi focused specifically on the androgen receptor (AR) where we have two drugs now approved – enzalutamide, which binds to the AR directly and abiraterone, which impacts steroidogenesis downstream.

The key question being addressed here was that we know abiraterone targets steroidogenesis, but does a bidirectional effect occur i.e. can steroidogenesis come back and regulate abiraterone? If so, is this also a potential mechanism of resistance and how can we improve the clinical situation for patients?

The majority of this work is also covered in recent publications by Li et al., (2015) and Sharifi (2015) see References.

What happens when we give abiraterone to mice and men?

First off, Sharifi described abiraterone and androgens as ‘kissing cousins’ with a shared metabolism, which I found quite amusing. Essentially, the abiraterone is converted to D4A, a metabolite. This occurs consistently in both species, although the concentrations are more variable in humans.

Is D4A inert and doesn’t do much or is it clinically relevant?

To answer this question, they looked at the essential steps in the androgen pathway in CRPC and looked at the impact on DHT synthesis. In two out of three cases, they found that D4A was a more potent inhibitor than abiraterone, while the other was equivalent.

Does D4A bind to the AR?

Both abiraterone and D4A have a common 3-Keto element in their structure, similarly to testosterone. Does this impact AR binding capacity?

In tests, they found that D4A binds to the AR receptor as least as well as enzalutamide and also blocks PSA expression in the same fashion. These data suggest that D4A is an antagonist, not an agonist.

Is their any evidence that this translates into anti-tumour efficacy?

In CRPC xenograft experiments, the researchers found that D4A has more potent anti-tumour activity than abiraterone or enzalutamide, based on the PFS in mice. This may not translate to clinical benefit in humans, but it should at least be worth exploring based on the findings of these models.

Sharifi also mentioned some unpublished work where they noticed that the D4A A/B rings also look like the testosterone structure. Interestingly, this is the substrate for 5α-reductase… so they asked the critical question: can the D4A metabolites be 5α-reduced and 5Ɓ-reduced? Note 5Ɓ-reductase serves to inactivate steroids via a different function.

The answer to both 5α-Abi and 5Ɓ-Abi was yes, they can be reduced.

In addition, Sharifi highlighted the chemical molecules and conformation – 5α-Abi retains a similar plane and conformation structrure as a steroid (i.e. a lookalike), whereas 5Ɓ-Abi is different and has a 90 degree bend at one end, which leads to steroid inactivation.

What happens when you expose prostate cancer cell lines (LNCaPr) to D4A?

They found that within 2 days, D4A was almost depleted because it was converted to the 5α-Abi metabolite.

What are the effects of 5α-Abi on enzymes required for DHT synthesis?

Essentially, they found that 5α-Abi < D4A, i.e. a weaker inhibitor.

What about downstream of metabolism?

Recall that 5α-Abi has the same A/B rings as DHT. They also found that 5α-Abi binds to AR, so does it cause agonist or antagonist effects? It turned out to be an agonist, which would explain the weaker inhibitory effects described above. In mouse xenograft models, this was alos confirmed by a much shorter PFS, which you would expect with an agonist.

What about the good and the bad effects?

By now, we can see that D4A can reduced to both good (5α-Abi) and bad (5Ɓ-Abi) metabolites. This leads to the next question: can we block the bad effects and enhance the good effects? Part of the answer to this lies in data from a phase 2 clinical trial that Dr Mary Ellen Taplin (DFCI) is running in mCRPC (Link).

Here, they are comparing the impact of adding a 5α-reductase inhibitor, dutasteride, to abiraterone plus prednisone versus abi plus steroid alone.

Remember that 5α-reductase inhibitors such as dutasteride and finasteride are old drugs originally approved by the FDA in the early 2000’s for symptomatic benign prostatic hyperplasia (BPH) in men with an enlarged prostate, so prostate cancer experts are well versed with these agents. The standard dose for dutasteride for BPH is 0.5mg/day, although this trial used a much higher dose, 3.5mg/day as an anti-cancer therapy.

The schematic for the trial is as follows – note that by exploring the doublet first then adding in the dutasteride, each patient acts as their own control, which may reduce intra-patient variability:

Phase 2 trial schematic

Phase 2 trial schematic

What did they find?

1) The Good: D4A concentrations nearly doubled when you add dutasteride
2) The Bad: 5α-Abi had a profound (90%) drop when dutasteride was added*
3) The Ugly: 5Ɓ-Abi had no real change in any of the 3 metabolites

*They saw a similar and highly consistent depletion with the other two 5α-Abi metabolites as well.

This preliminary research suggests that when a 5α-reductase inhibitor is added to abiraterone plus prednisone, it blocks the bad effects and enhances the good effects, exactly as we might expect or hope to see.

This is a very nice proof of principle in a small study that such a combination might be useful in mCRPC. What we do need to see now are outcomes data in a larger randomised controlled trial before attempting a more definitive conclusion.

Here are Dr Sharifi conclusions from their work, which I don’t disagree with:

Source: Dr Sharifi at ASCO GU 2016

Source: Dr Sharifi at ASCO GU 2016

Conclusions and Additional Commentary:

“Prostate cancer resistance to castration occurs because tumours acquire the metabolic capability of converting precursor steroids to 5α-dihydrotestosterone (DHT), promoting signalling by the androgen receptor and the development of castration-resistant prostate cancer.”

What this work suggests is that in the short term, there may be some clinical utility in combining a 5α-reductase inhibitor such as dutasteride with a CYP17A1 inhibitor such as abiraterone plus a steroid (prednisone), in order to reduce resistance to therapy and prolong outcomes for men with advanced prostate cancer.

In addition, the authors suggest a novel approach to next generation development of new AR agents targeting steroidogenesis:

“We propose that direct treatment with D4A would be more clinically effective than abiraterone treatment.”

If the clinical results from Dr Taplin’s triplet vs. doublet combination trial are encouraging then don’t be surprised to see a company with a prostate cancer franchise doing a deal with a small company developing anti-D4A inhibitors in the near future since the affinity of D4A for androgen receptors was significantly greater than that of abiraterone, similar to that of enzalutamide, and greater than that of bicalutamide.

As far as I know, the phase 2 study analysis was due to complete in December 2015, so an abstract may have been submitted to ASCO for the 2016 annual meeting (the deadline is this month).  That’s probably the next likely milestone for a comprehensive readout and presentation of the full data.

References

ResearchBlogging.orgRobinson, D., Van Allen, E., Wu, Y., Schultz, N., Lonigro, R., Mosquera, J., Montgomery, B., Taplin, M., Pritchard, C., Attard, G., Beltran, H., Abida, W., Bradley, R., Vinson, J., Cao, X., Vats, P., Kunju, L., Hussain, M., Feng, F., Tomlins, S., Cooney, K., Smith, D., Brennan, C., Siddiqui, J., Mehra, R., Chen, Y., Rathkopf, D., Morris, M., Solomon, S., Durack, J., Reuter, V., Gopalan, A., Gao, J., Loda, M., Lis, R., Bowden, M., Balk, S., Gaviola, G., Sougnez, C., Gupta, M., Yu, E., Mostaghel, E., Cheng, H., Mulcahy, H., True, L., Plymate, S., Dvinge, H., Ferraldeschi, R., Flohr, P., Miranda, S., Zafeiriou, Z., Tunariu, N., Mateo, J., Perez-Lopez, R., Demichelis, F., Robinson, B., Sboner, A., Schiffman, M., Nanus, D., Tagawa, S., Sigaras, A., Eng, K., Elemento, O., Sboner, A., Heath, E., Scher, H., Pienta, K., Kantoff, P., de Bono, J., Rubin, M., Nelson, P., Garraway, L., Sawyers, C., & Chinnaiyan, A. (2015). Integrative Clinical Genomics of Advanced Prostate Cancer Cell, 162 (2) DOI: 10.1016/j.cell.2015.06.053

Cancer Genome Atlas Research Network. Electronic address: schultz@cbio.mskcc.org, & Cancer Genome Atlas Research Network (2015). The Molecular Taxonomy of Primary Prostate Cancer. Cell, 163 (4), 1011–25 PMID: 26544944

Li Z, Bishop AC, Alyamani M, Garcia JA, Dreicer R, Bunch D, Liu J, Upadhyay SK, Auchus RJ, & Sharifi N (2015). Conversion of abiraterone to D4A drives anti-tumour activity in prostate cancer. Nature, 523 (7560), 347–51 PMID: 26030522

Sharifi N (2015). Prostate cancer: CYP17A1 inhibitor failure-lessons for future drug development. Nature reviews. Urology, 12 (5), 245–6 PMID: 25823374

Sharifi N (2015). Steroid sidestep: evading androgen ablation by abiraterone. Clinical cancer research : an official journal of the American Association for Cancer Research, 21 (6), 1240–2 PMID: 25432158

SGEN Booth ASH15

Seattle Genetics ASH 2015 Exhibit – photo with permission

San Francisco – Seattle Genetics are presenting later today at the JP Morgan Healthcare conference (2.30pm PST) and we’ll be covering this as part of our daily rolling blog.

As blog subscribers already know, one of the presentations that caught our attention at ASH 2015 was the updated phase 1 data for Seattle Genetics latest ADC, denintuzumab mafodotin (SGN-CD19A) in B-cell malignancies, including diffuse large B-Cell lymphoma (DLBCL).

Unlike with brentuximab vedotin, where one of the main side effects seen is peripheral neuropathy, with 19A, as it’s commonly known, there is ocular toxicity. Will this toxicity bring the house of cards down for Seattle Genetics?

I spoke to President and CEO Clay Siegall, PhD about this, the company’s corporate strategy moving forwards in 2016 and how checkpoint inhibitors may impact classical Hodgkin’s Lymphoma (cHL).

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We’ve had a couple of requests come in for a revival of the old conference series… ‘Gems from the poster halls’ because quite a few folks are interested in the up and coming data from small to medium biotechs.

SABCS San Antonio CrowdA bunch of my Post Doc chums in this field were at the San Antonio Breast Cancer Symposium (SABCS) meeting and gleefully highlighted mobbed posters or areas where they thought the data looked potentially interesting.

From these, we selected a few for review in today’s look at the nuggets that can be gleaned from cool and intriguing trials or preclinical research that may influence future trials.

Companies covered in this article include Seattle Genetics, Jounce, Immunomedics, Syndax and MedImmune.

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Today the immunotherapy and related data flooding out of the annual meeting of the San Antonio Breast Cancer Symposium (SABCS) is pretty exciting!

Data was presented on a number of drugs including pembrolizumab, avelumab and atezolizumab, which put together with some recent publications, highlights some potentially exciting opportunities in this fast moving space.

Here, we explore the potential for checkpoint therapy combinations in TNBC, HER2 and even the ER+ subsets.  There’s a lot of new findings to take in and contemplate here.

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In the last of our American Society of Hematology (ASH) 2015 annual meeting previews, we take a broad look at a host of intriguing abstracts in a variety of different topics that haven’t been covered in the rest of the series.

We also take a look a drug that has had a chequered history in the past, namely venetoclax, from the folks at AbbVie and Genentech. Is this a dud destined for dog drug heaven, or will it make a roaring comeback, breathing fresh life into hematologic malignancies such as chronic and acute leukemias, lymphomas and even multiple myeloma?

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Aggressive lymphoma… the very phrase is enough to send chills down your spine!

ASH Annual MeetingIn the past, much of the focus at previous American Society of Hematology (ASH) meetings in this area has focused on the myriad of chemotherapy regimens and dose/schedule optimisations that followed in trying to boost patient outcomes.

This year, I’m pleased to say that things have quite a different flavour with numerous new therapeutics and promising combinations in development.

Some of these are inevitably hypothesis testing, while others will be up-levelling to large randomised controlled multi-centre trials.

As part of our ongoing preview series, we take a look at the different categories to watch out for beyond chemotherapy.  These include monoclonal antibodies, antibody drug conjugates, targeted therapies and yes, even immunotherapies.

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This year has been an unprecedented Grand Cru year for the field of multiple myeloma, with no less than four drugs approved by the FDA to date… the fourth one just this morning while writing this preview!

  • Panobinostat (Farydak) in relapsed/refractory disease in combination with bortexomib plus dexamethsone after at least 2 prior therapies.
  • Daratumumab (Darzalex) received accelerated approval based on phase 2 data and is human CD38-directed monoclonal antibody that is indicated for the treatment of patients who have received at least three prior lines of therapy.
  • Ixazomib (Ninlaro) is the first oral proteasome inhibitor and is approved in combination with lenalidomide plus dexamethasone, in people who have received at least one prior treatment.
  • Elotuzumab (Empliciti) is a monoclonal antibody against CS–1/SLAMF7 approved today in combination with lenalidomide plus dexamethasone after 1–3 lines of prior therapy.

There are also many promising new agents in development and quite a few that may well not make it to market as a result of newer, better tolerated agents coming through.

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Biomarkers are a hotly debated topic at the moment within the cancer immunotherapy field.

At the recent Society for Immunotherapy of Cancer annual meeting (SITC 2015), there was even a debate with industry representatives arguing the “pros” and “cons.” Daniel Chen, MD PhD from Genentech (pictured right) argued “pro” and Steven Averbuch MD (pictured left) from BMS argued “con.”

SITC 2015 Biomarker Debate

The challenging question for anyone at the moment is if your Parent, Spouse or Best Friend were PD-L1 negative, would you still want them to receive a PD-1/PD-L1 checkpoint inhibitor (presuming it was indicated for the disease) and have a chance of a response, even if their PD-L1 negativity would suggest only a slim chance of responding?

AT SITC 2015 we spoke with an industry expert who offered insights into a leading company’s biomarker strategy and what the future may look like in 5-7 years time.

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ASH 2014 cHL PembroOne of the hotly debated topics at the 2014 American Society of Hematology (ASH) annual meeting was the arrival of checkpoint data in classical Hodgkin’s lymphoma (cHL), with initial data presented on 20-30 patients with relapsed or refractory cHL who received either nivolumab (BMS) or pembrolizumab (Merck) in open label, single agent trials.

Updated phase I data is expected to be presented at the 2015 ASH annual meeting in Orlando (Dec 5-8) (Twitter #ASH15)

At the recent ESMO symposium on Immuno-Oncology in Lausanne (Twitter #Immuno15) – great hashtag, there was an excellent overview of checkpoint blockade in lymphomas. What did this tell us about progress in this disease and where are things going?

ESMO-Symposium-on-Immuno-Oncology-2015-banner

The ESMO IO meeting set the scene for what we can expect at ASH this year?

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Oncology R&D is tough and there are many more failures than successes, despite the FDA approving more than they’ve rejected over the last two years. That’s quite unusual in my experience.

Dr Mario SznolAs Dr Mario Sznol (Yale) told us at SITC recently, sometimes these things are sometimes more whimsical. He was referring to different types of modalities that can be used in conjunction with cancer immunotherapies, but the sentiment is also highly relevant to the FLT3 AML space.

The critical questions we need to think here about are:

  1. What’s different about the various approaches?
  2. What can we learn from the FLT3 experiences to date that give us clues about the changing landscape in AML?

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