Back in 2004, PubMed had the findings of a few studies that looked at PCa androgen receptor [AR] at diagnosis & in hormone refractory prostate cancer (HRPC), as CRPC was then called. At diagnosis - meaning before treatment - the AR was essentially 'wild type'.
From a 1995 paper [2]:
"We found high-level AR amplification in seven of 23 (30%) recurrent tumours, but in none of the specimens taken from the same patients prior to therapy. Our results suggest that AR amplification emerges during androgen deprivation therapy by facilitating tumour cell growth in low androgen concentrations."
And from 2004 (Mary-Ellen Taplin) [3]:
"... Hormone therapy in the form of medical or surgical castration remains the mainstay of systemic treatment in prostate cancer. Over the last 15 years with the clinical use of prostate specific antigen (PSA), there has been a shift to using hormone therapy earlier in the disease course and for longer duration. Despite initial favorable response to hormone therapy, over a period of time these tumors will develop androgen-independence that results in death. The androgen receptor (AR) is central to the initiation and growth of prostate cancer and to its response to hormone therapy. Analyses have shown that AR continues to be expressed in androgen-independent tumors and AR signaling remains intact as demonstrated by the expression of the AR regulated gene, PSA. Androgen-independent prostate cancers have demonstrated a variety of AR alterations that are either not found in hormone naïve tumors or found at lower frequency. These changes include AR amplification, AR point mutation, and changes in expression of AR co-regulatory proteins. These AR changes result in a "super AR" that can respond to lower concentrations of androgens or to a wider variety of agonistic ligands. There is also mounting evidence that AR can be activated in a ligand independent fashion by compounds such as growth factors or cytokines working independently or in combination. These growth factors working through receptor tyrosine kinase pathways may promote AR activation and growth in low androgen environments. The clinical significance of these AR alterations in the development and progression of androgen-independent prostate cancer remains to be determined. Understanding the changes in AR signaling in the evolution of androgen-independent prostate cancer will be key to the development of more effective hormone therapy."
I would have taken "there has been a shift to using hormone therapy earlier in the disease course" as a warning, since it was understood that ADT was effective only for 18-24 months for the majority of men - uncomfortable to contemplate at age 56.
When my prostatectony & salvage radiation therapy immediately failed, my doctor told me: "There are some who would say that you should ...". I was already shaking my head, and he knew that I wasn't about to start ADT. But it was common back then. Odd to begin a palliative therapy before one needs palliation, IMO.
Jumping forward to 2021 [1]:
"Although rarely mutated or amplified in treatment-naïve prostate cancer (PCa), AR signaling drives tumor growth and as a result, therapies that aim to inhibit AR signaling, called ARSIs* (AR signaling inhibitors), have been in clinical use for >70 years. Unfortunately, the clinical efficacy of ARSIs is short-lived and the majority of treated patients develop castration-resistant PCa (CRPC). Numerous molecular mechanisms have been proposed for castration resistance; however, the cellular basis for CRPC emergence has remained obscure."
* or ARAT (androgen receptor axis targeted)
deja vu
But here's a new wrinkle (for me - with the exception of stem-like tumor cells):
"One under-appreciated cellular mechanism for CRPC development is the AR heterogeneity that pre-exists in treatment-naive primary tumors, i.e., although most PCa cells express AR (i.e., AR+), there is always a population of PCa cells that express no/low AR (i.e., AR-/lo). Importantly, this AR heterogeneity becomes accentuated during ARSI treatment and highly prominent in established CRPC."
So, while we might eventually be able to prevent AR adaptations, we will still be left with this non-standard AR population that will be selected by ARSI/ARAT.
"Here, we provide a succinct summary of AR heterogeneity across the PCa continuum and discuss its impact on PCa response to treatments. While AR+ PCa cells/clones exhibit exquisite sensitivities to ARSIs, AR-/lo PCa cells/clones, which are greatly enriched in stem cell signaling pathways, display de novo resistance to ARSIs. Finally, we offer several potential combinatorial strategies, e.g., ARSIs with stem cell targeting therapeutics, to co-target both AR+ and AR-/lo PCa cells and metastatic clones."
. 2021 Jun 9;S0304-3835(21)00289-5. doi: 10.1016/j.canlet.2021.06.006. Online ahead of print.
Androgen receptor (AR) heterogeneity in prostate cancer and therapy resistance
Anmbreen Jamroze 1 , Gurkamal Chatta 2 , Dean G Tang 3
Affiliations collapse
Affiliations
1 Department of Pharmacology & Therapeutics, Roswell Park Comprehensive Cancer Center, Buffalo, NY, 14263, USA. Electronic address: anmbreen.jamroze@roswellpark.org.
2 Department of Medicine, Roswell Park Comprehensive Cancer Center, Buffalo, NY, 14263, USA.
3 Department of Pharmacology & Therapeutics, Roswell Park Comprehensive Cancer Center, Buffalo, NY, 14263, USA; Experimental Therapeutics (ET) Graduate Program, University at Buffalo & Roswell Park Comprehensive Cancer Center, NY, 14263, USA. Electronic address: dean.tang@roswellpark.org.
PMID: 34118355 DOI: 10.1016/j.canlet.2021.06.006
Abstract
Androgen receptor (AR), a ligand-dependent nuclear transcription factor and a member of steroid hormone receptor family, plays an important role in prostate organogenesis by regulating epithelial differentiation and restricting cell proliferation. Although rarely mutated or amplified in treatment-naïve prostate cancer (PCa), AR signaling drives tumor growth and as a result, therapies that aim to inhibit AR signaling, called ARSIs (AR signaling inhibitors), have been in clinical use for >70 years. Unfortunately, the clinical efficacy of ARSIs is short-lived and the majority of treated patients develop castration-resistant PCa (CRPC). Numerous molecular mechanisms have been proposed for castration resistance; however, the cellular basis for CRPC emergence has remained obscure. One under-appreciated cellular mechanism for CRPC development is the AR heterogeneity that pre-exists in treatment-naive primary tumors, i.e., although most PCa cells express AR (i.e., AR+), there is always a population of PCa cells that express no/low AR (i.e., AR-/lo). Importantly, this AR heterogeneity becomes accentuated during ARSI treatment and highly prominent in established CRPC. Here, we provide a succinct summary of AR heterogeneity across the PCa continuum and discuss its impact on PCa response to treatments. While AR+ PCa cells/clones exhibit exquisite sensitivities to ARSIs, AR-/lo PCa cells/clones, which are greatly enriched in stem cell signaling pathways, display de novo resistance to ARSIs. Finally, we offer several potential combinatorial strategies, e.g., ARSIs with stem cell targeting therapeutics, to co-target both AR+ and AR-/lo PCa cells and metastatic clones.
Keywords: Androgen receptor; Cancer cell heterogeneity; Cancer stem cells; Castration-resistant prostate cancer; Prostate cancer; Therapy resistance.
Exactly what I am doing now. My first test cycle of 6 weeks SPT then one month off was favorable (PSA from .08 went up to just .185 on T, then came down to .123 off.) My 2nd cycle of one month High T then one month off was just completed, resulted in even lower PSA of 0.075. No ADT used during off cycles. My body likes it very much. Restoring some muscle mass and strength.
As a lay person, if I understand you correctly, this means that an ADT vacation is only (physiologically) worthwhile if testosterone returns during the vacation and thereby rensensitises the body to ADT. I don’t mean to barrage you with questions, but...
- at what point should one reasonably expect to take an ADT vacation (e.g., before or after CR, at a certain PSA level, X years after starting ADT,...)?
- what level of testosterone return would indicate that the vacation is potentially worthwhile?
- how long should you wait for return of testosterone before abandoning the vacation?
- in what percent of men is testosterone restored during an ADT vacation?
Apologies in advance for what may be dumb questions with no clear cut answers.
Basically, in the order of a year on then a year off. Or 2 years on, 2 years off.
But that only works so long as the PSA level is successfully suppressed during the on year and stays suppressed during the off year.
So the timing is really determined by listening to PSA levels.
This obviously won't work with really aggressive prostate cancer.
Tall Allen has mentioned a trial where sustained ADT was proven better than intermittent Adt, but I don't know how aggressive the cancers were.
Also there is something called BAT (bipolar androgen therapy) in which testosterone is violently alternated from highly suppressed to extremely highly increased on approximately a month by month tempo.
This doesn't work for everyone, but when it does, it is very effective. It is used only when regular adt is failing.
"It is used only when regular adt is failing." Schweizer did one RCT on those castrate sensitive, and I am doing my own N=1 trial. Hard to interpret the results (my interpretation of the Schweizer trial is that he concluded BAT is safe for that cohort), but looking at the many BAT trials for those CR it seems to me more likely to help than hurt for those still castrate sensitive. And Mr. O'Shea and others seem to be succeeding with a BAT-like program while still castrate sensitive.
I am a simple traveler with APC for 2 years, sure this was growing since long time.I followed standard protocols ...scans, ADT , RT....now what...
--- What is called aggressive PC, it is very heterogeneous , depending on the health condition of each person.
Some are pretty healthy and others go thru extreme pains etc. but we are together here, sharing.
---- When in remission, what to do...wait for recurrence
Why not do something when cancer cells are in sleepy mood, in senescence.
Nothing for that except individual therapy...why not.
As Dr scholz says take supplements, if they work great otherwise stop.
-- I feel that each of us may go for supplements and lifestyle changes,
Some trust the therapy, keep their lifestyle as it is ... not many here.
Docs give no indication or guidelines on diet, exercise, mind body....supplements Why ?
Most of us follow
plant based diet, exercise, mind body activation, off label drugs, grains, nuts, herbs
with no real markers if these work or not ...a question of faith
Sometimes Faith is a big healer.
---- How long to continue ADT... again different situations, different docs, different patients ....this differs.....Role of IADT....again for whom ?
During remission what are the markers to indicate to take vacation....NOTHING
Just gut feeling and a sort of mutual relation with onco.
One thing I found interesting as marker mentioned by ONCO is to observe if PSA stays stable over long time 6 months or year...that is encouraging to try IADT.
But if PSA wiggles even in narrow range then what ?
How one knows if one is cured....
I believe that APC can be cured thru combination of standard therapy, diet, exercise supplements and mind....again belief and positive look that anything is possible . Essential is not to get trapped by analytical approach,...All these specialists imprisoned in their own limited world whereas human being is an integrated being nourished by life force.
Whole is not sum of parts but much different ...a new vibrant positive space not seen in each part.
Many thanks for forum members which show that sum of members opinion takes us to new creative healthy hopeful space ....different from limited individual look.
"Essential is not to get trapped by analytical approach,...All these specialists imprisoned in their own limited world whereas human being is an integrated being nourished by life force."
It's unwise to rely on "life force" and other undiscovered laws of physics.
Complex biological systems do not share their logic easily.
Patients have a known susceptibility to Dunning Krueger effect.
For evidence see generally Quack watch.com
So so many people led to their death by common sense treatments.
Thanks. I’m not sure what “really aggressive prostate cancer” means in this context (GS 9?). I’m marginally familiar with BAT. It doesn’t seem to be embraced by the SOC MO community, but if Nalakrats views it as potentially worthwhile, I’m open to it. Nonetheless, it seems like a real gamble for those who are not yet castrate resistant.
At this point, there are numerous papers on the subject of IADT. When I started out, the experts ridiculed IADT as clearly being inferior to continuous ADT, but many men are extremely unhappy while on continuous ADT.
Dr. Myers once said that with ADT less than a year, PSA returns very fast. He himself was miserable while on ADT for 18 months. His aim was to try to keep ADT to ~12 months before starting the off-phase, & the hope was that the 'vacation' would be substantially longer than the on-phase - because "you only get 2 or 3 cycles before" CRPC.
My problem with this is that failure is built in. 12 months of ADT gets tumors close to CRPC and testosterone recovery is too slow to reverse the adaptations.
Your questions about the "rules" for IADT have various answers. Here is a recent definition:
In time, we will see an IADT trial where T is immediately restored during the off-phase. I don't think that (injected) testosterone cypionate should be used. Transdermal T patches would be better, since treatment could be quickly halted if PSA misbehaved.
Thanks for your thoughtful reply. “In time, we will see an IADT trial where T is immediately restored during the off-phase.” Is that BAT? If so, does that mean that there have been no ‘legitimate’ BAT trials to date? My husband can reluctantly deal with the increasing physical side effects of ADT (Eligard + Zytiga), but the cognitive side effects are becoming a problem, especially since he’s still working.
I have been using testosterone for 16 years, but only recently tried the BAT protocol as defined by Sam Denmeade, which I had to modify because the 28-day cycle doesn't work for me (400mg testosterone cypionate takes a long time to clear, in my experience.)
In the pre-BAT days, I used ADT for 3 months followed by testosterone for 3 months. My PSA would climb to ~35 and then get knocked down to ~1, and the QoL was very good. Not everyone's idea of IADT, & I never thought of it that way.
For a while, Howard Scher at Sloan-Kettering played around with something he called "Rapid Androgen Cycling".
In my versions, I limited ADT to a maximum of 3 months, since I felt that any adaptation might be reversible with short-term ADT.
I was not attracted to BAT initially, because I viewed it as continuous ADT with periodic boosts of T. I was looking for extended periods of high-normal T.
cesces, above, says BAT is "... intended for use to reset things after you have become castrate resistant." One might get that impression because Denmeade's focus has been CRPC. Men with CRPC are in great need of options, and I suspect that it is far easier to get accrual for CRPC studies. However, the BATMAN study used hormone-sensitive [HS] men:
"BAT demonstrated preliminary efficacy in men with HS PC following 6-month of ADT. BAT may improve QoL in men treated with ADT."
A key part of Denmeade's BAT has become the use of supraphysiological levels of T (~2,000 ng/dL - twice high-normal) to induce double-strand breaks. In the past, my use of T (mostly transdermal) aimed for ~1,000 ng/dL.
I see Denmeade's BAT as one of a number of possible protocols that use T to reverse adaptations. Ideally, men beginning ADT would be put on one of the protocols. Some fine-tuning might be required depending on the individual. The ultimate aim would be to extend the use of AR-axis treatments indefinitely.
Thanks for sharing your experience, Patrick. Seems like the highs and lows of BAT would be hard to deal with mentally and physically, but it certainly does look intriguing. It’s reassuring that one of the leading BAT investigators is within driving distance (we live in Fairfax), should we choose to pursue this option.
Very interesting Patrick, but the abstract alone is a bit of a tease in that it does not reveal the combination treatments referred to. Have you been able to locate a free full text of it?
Hello there! I can always assist in getting papers! I get them online from a Swedish hospital through my work. This is something that goes out to anyone here on HU. Happy to help!
Thank you TB. We are looking for the full text of this article, of which Patrick posted the abstract only. Thank you. :
. 2021 Jun 9;S0304-3835(21)00289-5. doi: 10.1016/j.canlet.2021.06.006. Online ahead of print.
Androgen receptor (AR) heterogeneity in prostate cancer and therapy resistance
Anmbreen Jamroze 1 , Gurkamal Chatta 2 , Dean G Tang 3
Affiliations collapse
Affiliations
1 Department of Pharmacology & Therapeutics, Roswell Park Comprehensive Cancer Center, Buffalo, NY, 14263, USA. Electronic address: anmbreen.jamroze@roswellpark.org.
2 Department of Medicine, Roswell Park Comprehensive Cancer Center, Buffalo, NY, 14263, USA.
3 Department of Pharmacology & Therapeutics, Roswell Park Comprehensive Cancer Center, Buffalo, NY, 14263, USA; Experimental Therapeutics (ET) Graduate Program, University at Buffalo & Roswell Park Comprehensive Cancer Center, NY, 14263, USA. Electronic address: dean.tang@roswellpark.org.
IMO, the most interesting thing in the full text - from a practical perspective - is mention of Venetoclax:
"... recent results have led to an ongoing phase Ib/II clinical trial of treating
Enza-naïve metastatic PCa patients with a combination of Enza and Venetoclax, the FDA-approved BCL-2 inhibitor (NCT03751436). Notably, BCL-2 has recently been reported to be a potential therapeutic target in AR-/lo NEPC and small-cell carcinoma. RNA-seq data, collected from AR-active PCa (ARPC), small-cell neuroendocrine PCa (SCNPC) and two NEPC, were cross-compared to identify conserved druggable targets. This analysis revealed BCL-2 as highly upregulated in SCNPC compared to ARPC, and treatment with the BCL-2 inhibitor Navitoclax reduced SCNPC PDX tumor growth in vivo."
Wiki: "Venetoclax attaches to a protein called Bcl-2. This protein is present in high amounts in {chronic lymphocytic leukemia} cancer cells, where it helps the cells survive for longer in the body and makes them resistant to cancer medicines. By attaching to Bcl-2 and blocking its actions, venetoclax causes the death of cancer cells and thereby slows down progression of the disease."
Bcl-2 is hardly a new concern in PCa - there are over 2,000 PCa hits on PubMed - but it's exciting that there is now an approved inhibitor, albeit not for PCa.
Yes that section is very interesting indeed. Also ABT-199 and Navitoclax. Learning much about AR signaling and variations and CSCs from this in castrate resistance and neoendocrine differentiation. A new word too: “stemness”.
5.3 BCL-2
BCL-2 is a well-studied pro-survival BCL-2 family member that has been implicated in facilitating castration resistance (reviewed in [36]). Our early studies indicated that in (PSA-/lo)AR-/lo PCa cells, BCL- 2 is preferentially associated with the bivalent (i.e., H3K4me3 and H3K27me3) chromatin occupancy [37]. In the LNCaP AD → AI progression model, castration slightly upregulated BCL-2 in the ADT- resistant tumors and ADT/Enza led to further substantially increased BCL-2 [36]. Thus, combination of Enza and the BCL-2 antagonist, ABT-199, inhibited the emergence of Enza-resistant AR+/hi CRPC by 75%, and ABT-199 alone also inhibited the growth of AR-/lo LAPC9 AI tumors [36]. Significantly, BCL-2, but not BCL-xL and MCL-1, is exclusively upregulated in PCa patients who have been treated with
neoadjuvant ADT [36]. These recent results [36] have led to an ongoing phase Ib/II clinical trial of treating Enza-naïve metastatic PCa patients with a combination of Enza and Venetoclax, the FDA-approved BCL-2 inhibitor (NCT03751436). Notably, BCL-2 has recently been reported to be a potential therapeutic target in AR-/lo NEPC and small-cell carcinoma [72]. RNA-seq data, collected from AR-active PCa (ARPC), small-cell neuroendocrine PCa (SCNPC) and two NEPC, were cross-compared to identify conserved druggable targets. This analysis revealed BCL-2 as highly upregulated in SCNPC compared to ARPC, and treatment with the BCL-2 inhibitor Navitoclax reduced SCNPC PDX tumor growth in vivo
As I wrote to Patrick:Hello there! I can always assist in getting papers! I get them online from a Swedish hospital through my work. This is something that goes out to anyone here on HU. Happy to help!
I did 6 months of ADT (estrogen-based) followed by 19 months and counting of SPT (400 mg cypionate weekly). PSA is 0.039
If I was given the opportunity to redo things I would have waited longer before starting ADT. My PSA was <0.01. I would have at least waited until my PSA was detectable. Then I could have seen the decrease in PSA and the velocity. I would have switched to SPT when 3 consecutive PSA readings were <0.01.
There aren't too many docs doing BAT. If I may, could I ask who you used to supervise this treatment?
By the way, if you want a second opinion on this type of treatment (why not), Sartor at Tulane is good person to go to. I believe he does a fair amount of this type of treatment.
I was my own doctor. After I was diagnosed I fully expected that the SOC doctor system would take care of me as best as possible.
But right away two nationally renowned doctors at Mayo wanted me to take Lupron, followed quickly by radiation with chemo to come later. They didn't budge from the Lupron diagnosis despite my explaining my family history of mental issues, arthritis on my mom's side, and my own osteopenia which was on the verge of osteoarthritis. I asked about using estrogen. I was told by these doctors that estrogen wouldn't lower my testosterone to castrate levels. So I went to 3 others. It was the same story and one even said that it wouldn't do a thing to testosterone levels since they were different substances. At that point, I realized that my high school biology teacher knew more about hormones than any of these doctors (lest anyone think otherwise, I was very nice and very sincere in my questions and never lectured them on biology).
After 5 months of estrogen ADT (it worked very well to reduce testosterone), I decided that a few months with T was worth 30 years of life with zero T. I started researching options and found some references to SPT. A month later I took the plunge.
My MO is surprised at how well I am doing. I told her about the SPT a year ago and she's 100% on board with what I'm doing simply because of the results. I went to compassionate oncology for 6 months or so but I didn't feel that they added any value. So I cut out that expense.
I certainly wouldn't mind someone who was skilled in SPT commenting on my program.
RSH1 wrote >>> " ... If I was given the opportunity to redo things.... "
Always hits me that 20/20 hindsight(???) can still result in no telling how differently (for better or worse) things could have been if that alternate path was to have been taken.
I had immediate CASTRATION followed with my GL10 right half being cryoablated and a 7 month hiatus with the remaining GL6/7 in left half ablated plus the immuno injection THEN 1 month later began the biweekly Cypionate 200mg/ml @ 1ml injections with current "T" level @ 1,600ng/dL post injection and lately @ 1,000ng/dL 2 weeks following. Three years after 1st cryo a GL6/7 return in left remaining prostate tissue treated with right clear and currently back to another wait and see time frame. Plant/fish diet with some supplements, daily 1,700mg Metformin + Dutasteride and 100+ mile bicycle rides for exercise. All began in March 2015 and if I kick the bucket tomorrow it's been a good ride and I would not do things any differently.
I am willing to take risks if I feel that the risk/reward ratio is good. I'm very pleased with how things have gone but I'm not a "bird in hand" type of person.
I’m confused. These papers were written over 15 years ago and there’s been no follow thru to test the hypothesis ? This is only a hypothesis correct? Is there any clinical or other evidence that shows starting ADT later in the disease is better?if do, how late? We do know that combining ADT with secondary drugs like Zytega earlier, extends life. And most studies show no major difference between Continuous and intermittent adt. But there’s gotta be more to consider delaying right?
Patrick: I am recognizing that I do not understand how the ARlo/AR- PCCells maintain their own androgen signaling to remain viable. Is it that their ARs are intercellular or intranuclear, present internally but not expressed on the cell surface membranes? Or is it alternate
signaling or some growth factors completely independent of ARs?
Also you mention tumor stem-like cellular
pathways. Do you have a reference article that I could learn about these? Thank you. Paul
The subject of "stem-like" cells crept in after I was diagnosed, & for quite a while many doubted there was such a thing because no-one seemed to know how to find them. The term "stem-like" in PCa studies goes back to 2015, but you need more recent papers to explore the guts. It's now hard to keep up.
My simplistic understanding way back was that AR-axis treatments forced cells to morph into forms where the AR was severely down-regulated. These cells retained the ability to generate AR, but, essentially, they had retreated into 'stemness'. ADT could not touch them.
I remember an ancient rat study. The prostate of a castrated rat fades away to nothing. But not quite nothing, since T restoration causes the prostate to grow back to normal size. Prostatic stem cells survive castration. I don't know anything more than that. How do they survive/divide?
But so-called PCa stem-cells are not true stem cells - which is why I prefer "stem-like". Some prefer 'progenitor' or 'progenitor-like'. You will get a a ton of PubMed hits:
<prostate cancer "stem cells"> ... 2,080
<prostate cancer "stem-like"> ... 297
<prostate cancer "progenitor"> ... 400
An important(?) paper from MD Anderson (2006) [1]:
"Highly purified CD44+ prostate cancer cells from xenograft human tumors are enriched in tumorigenic and metastatic progenitor cells"
identified CD44 as one of the markers for stem-like cells.
Using an invaluable tool - the online PCa ouija board - I have selected one study [2]. Here is the Discussion section: (AI = androgen-independent; TM = 'Triple Marker' = ALDHhiCD44+α2β1+)
"Two principal mechanisms, i.e., intrinsic and acquired, underlie the resistance of cancer cells to both general and targeted anticancer therapeutics (40). Intrinsic resistance implies that prior to treatments, therapy-insensitive cells preexist in the tumor and become selected and enriched during treatment, whereas acquired resistance is caused by treatment-induced gene mutations and other adaptive responses. Both mechanisms of therapy resistance have been reported in clinical tumors (40–42). Here, we provide a prototypical example for a population of cancer cells that can mediate intrinsic therapy resistance.
"As early as 1981, Isaacs and Coffey, working on the rat Dunning R-3327-H prostate adenocarcinoma (H-tumor) model, performed a fluctuation analysis to show that the H-tumor relapse after ADT was due to continuous proliferative growth of preexisting AI prostate cancer cells after castration (43). Exactly what cell population in this model that became selected during castration was uncharacterized (43). In 1999, Craft and colleagues, by performing a similar fluctuation analysis, provided evidence in the LAPC9 model that ADT selected and clonally expanded the preexistent AI cells, resulting in outgrowth of CRPC (44). Nevertheless, which cell population in LAPC9 mediated the CRPC emergence was unclear. Here, we demonstrate that the TM+ cell population in the LAPC9 model can function as both a cell-of-origin for CRPC emergence and the tumor-propagating population for the established CRPC.
"LAPC9 is a well-known prostate cancer xenograft expressing PSA and wild-type AR, which our laboratory has been using for the past 10 years to study PCSCs (6, 7, 16, 19, 36). Our earlier work has shown that CD44+ prostate cancer cells in several xenograft models, including LAPC9, are highly enriched in PCSCs (6). Follow-up work demonstrates that the CD44+α2β1+ LAPC9 cells are even more tumorigenic than CD44+ cells (7). The current project emanated from our recent observations that the PSA−/lo cell population, which preexists in the AD tumors but becomes enriched in AI tumors, can regenerate larger tumors than PSA+ cells in fully castrated hosts (16). This study provided the first evidence for a population of preexisting human prostate cancer cells that preferentially generate AI tumors (16). Nonetheless, both PSA−/lo and PSA+ LAPC9 cells regenerated AI tumors with similar incidences (16), suggesting that only a subset of the PSA−/lo cells is actually mediating the AI regeneration. Indeed, microarray analysis led to the identification of the TM+ subset that was greatly enriched in AI tumor-regenerating activities (16).
"By establishing serially passaged AI tumors and by focusing on the LAPC9 system, we have made many important and novel findings. First, the TM+ cells in AD tumors possess long-term tumor-propagating activities in androgen-proficient hosts. Second, the TM+ cells purified from the LAPC9 AD tumors can preferentially initiate xenograft tumors in fully castrated hosts, suggesting that this population can preferentially function as the cell-of-origin for AI prostate cancer. Third, the TM+ cells gradually become enriched in serially transplanted AI tumors in vivo. Fourth, the TM+ LAPC9 cells purified from the AI tumors can serially propagate the xenograft tumors in androgen-ablated hosts compared with either TM− or TM-depleted cells, suggesting that the TM+ LAPC9 cells can also function as robust CRPC-propagating cells. Fifth, the phenotypic markers used to define TM+ cells are functionally important for the TM+ cell activities. Finally, the TM+ LAPC9 cells seem to possess a unique miRNA expression profile. To our knowledge, the (serial) tumor transplantation studies presented here (Fig. 2; Table 1) represent the most comprehensive effort to define a population of human prostate cancer cells that function as the cell-of-origin as well as the tumor-propagating cells for CRPC.
"Is the TM+ cell population unique to the LAPC9 model? At least in one other model, i.e., PC3, which is all PSA−, the TM+ cells exhibit significantly higher tumor-regenerating activity than the corresponding TM− cells in castrated animals. It is interesting that several other AI cell lines examined, including PPC-1, Du145, and 22Rv1, all contain significant percentages of TM+ cells, which, we believe, may also possess high AI tumor-regenerating capacities compared with the corresponding TM− cells. In several other xenograft models, including LNCaP and HPCa101, the fraction of TM+ cells in the AD tumors is small, which, nevertheless, also increases in the AI tumors, although the significance of the TM+ cell fraction in these models remains to be determined. Of significance, however, we have detected the TM+ cells in more than a dozen of untreated HPCA samples. The relative abundance of TM+ cells in primary HPCA samples vary widely, but freshly purified TM+ HPCA cells manifested significantly higher colony-forming abilities than the corresponding TM− cells in castrated culture conditions. Intriguingly, the ALDHhiCD44+ double-positive cells isolated from two HPCA samples also display significant castration-resistant CSC properties. Taken together, our studies in multiple culture/xenograft models and primary HPCA samples suggest that (i) the TM+ prostate cancer cell population seems to be widely present, (ii) the TM+ cells in some tumor systems, exemplified by LAPC9 and PC3, possess great tumor-initiating and tumor-propagating activities in androgen-deficient hosts, (iii) the TM+ HPCA cells in primary tumors also possess great survival advantages and colony-forming capabilities under androgen-deficient culture conditions, and (iv) in some HPCa samples, the ALDHhiCD44+ double-positive cells may behave similarly to the TM+ cells.
"What are the TM+ cells? qRT-PCR–based phenotyping suggests that the TM+ LAPC9 cells in both AD and AI tumors are basal-like, preferentially expressing CK5, CK14, and CD44 mRNAs and less differentiated expressing lower levels of PSA and CD26 mRNAs. This would be consistent with the fact that this subpopulation of the cells was initially uncovered from the PSA−/lo prostate cancer cell population (16). This is also consistent with our current observations that the AI cell lines, such as PPC-1, PC3, and Du145, all of which are PSA−/lo, have significantly higher percentages of the TM+ cells than the AD LAPC9, LAPC4, and LNCaP tumors, in which the majority of cells are PSA+. It should be noted, though, that cell populations that can mediate and propagate CRPC may not necessarily be all basal-like. For instance, in the BM18 xenograft model, cells that mediate CRPC prominently express luminal markers CK18 and NKX3.1 (14).
"What confers the TM+ prostate cancer cells the ‘hardy’ properties to readily regenerate and propagate the AI tumors? Part of the answer seems to reside with the three defining phenotypic markers, i.e., CD44, integrin α2, and ALDH1A1, whose knockdown all diminished the tumor-regenerating activities of the TM+ cells in castrated conditions. This is not surprising considering that the CD44 and integrin α2 function as important adhesion and signaling molecules and that ALDH1A1, and perhaps ALDH7A1, may further extend cell survival by detoxification (e.g., eliminating ROS). Another reason is that the TM+ prostate cancer cells preferentially express genes associated with (cancer) stem cells and castration, illustrated by molecules such as Reg IV, SOX9, UBE2C, and TGFBR-1. Knocking down RegIV and SOX9 in the TM+ LAPC9 cells partially inhibits tumor regeneration in androgen-deficient hosts, implicating their causal functions in TM+ cells. Finally, the TM+ cells express a unique profile of miRNAs. Using miR-499-5P as an example, which is overexpressed in the TM+ cells compared with the TM-depleted cells, we show that this miRNA is also conferring on the TM+ LAPC9 cells castration-resistant properties. Other microRNAs uncovered in this screening may also likely be involved in modulating the biologic properties of the TM+ prostate cancer cells. Collectively, the results make it clear that multiple molecules and mechanisms likely come together to endow the TM+ prostate cancer cells unique capabilities to function as both the cell of origin and tumor-propagating cells for CRPC.
"Our recent work has illustrated that the PSA−/lo prostate cancer cell population represents a therapeutic target in treating CRPC (16, 19). The current work further pinpoints the TM+ subset within the PSA−/lo population as the driving force of CRPC emergence and propagation. Ongoing work from our laboratory is focusing on devising strategies to target the highly tumorigenic TM+ cell population and on elucidating the potential relationship between TM+ cells and several other populations of prostate cancer cells, e.g., CD166+ (23) and N-Cadherin+ (24), that may also be able to propagate castration-resistant tumors."
OK. Some degree of clarity about markers defining PC tumor stem cells. Those capable of initiating new colonies and metastasis. That is the term used in radiation oncology. That successful treatment requires killing every tumor stem cell. In this latest article they are referring to PSA lo/- expressing cells rather than AR lo/- makes more sense since CR requires some of the no several known or unknown mechanisms for AR up regulation to grow in androgen deprived environment.
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