Finding the ‘Sweet Spot’ For Targeted Therapy In Prostate Cancer
- Emerging data suggest some molecular pathways (e.g., PI3K/AKT) may be more therapeutically relevant earlier in the prostate cancer treatment course.
- Prior failures of PI3K pathway inhibitors in mCRPC may reflect suboptimal timing rather than lack of target validity, highlighting the limitations of late-stage drug development paradigms.
- Data from the CAPItello-281 trial support earlier pathway targeting within advanced disease, demonstrating improved rPFS in mHSPC with high-level PTEN loss when capivasertib is added to standard therapy.
- The broader challenge is identifying the therapeutic “sweet spot,” Dr. Eleni Efstathiou, an oncologist at the OHSU Knight Cancer Institute, tells SurvivorNet Connect. “Some of these molecular pathways that may be giving the cancer the opportunity to grow are happening earlier in the disease spectrum … If you try to use such a drug later, you might completely miss that window of opportunity.”
With the increasing role of targeted therapies in prostate cancer care, questions have emerged about the appropriate or most effective time to target different molecular alterations. New data suggest that targeting the PI3K pathway earlier on may lead to better outcomes.
“Some of these molecular pathways that may be giving the cancer the opportunity to grow are happening earlier in the disease spectrum, and they are more important for disease growth and progression earlier in the disease spectrum,” Dr. Eleni Efstathiou, an oncologist at the OHSU Knight Cancer Institute, tells SurvivorNet Connect. “If you try to use such a drug later, you might completely miss that window of opportunity.”
This evolving understanding is beginning to reshape how clinicians think about inhibitor therapy in prostate cancer.
The PI3K Pathway
The PI3K/AKT/mTOR signaling axis has long been recognized as a central driver of prostate cancer biology, particularly in the setting of PTEN loss. When PTEN is lost through deletion, mutation, or other mechanisms, PI3K signaling becomes unrestrained, promoting tumor growth, survival, and resistance to therapy.
Despite this well-established biology, early clinical attempts to target the pathway yielded disappointing results. Trials of PI3K, AKT, and mTOR inhibitors in metastatic castration-resistant prostate cancer (mCRPC) showed limited efficacy as monotherapy and inconsistent benefit in combination strategies.
In retrospect, these results may reflect a failure of timing rather than target.
“We have always known that the PI3 kinase pathway is also a nodal pathway in the progression of prostate cancer,” says Dr. Efstathiou. “But we have failed to completely understand whether it should be targeted early in the disease or later.”
CAPItello-281: A Step Earlier
The recent CAPItello-281 trial did not evaluate PI3K pathway inhibition in early-stage disease, but rather in metastatic hormone-sensitive prostate cancer (mHSPC) — still an advanced disease state, but earlier than the castration-resistant setting.
The trial “was designed to use that drug early on when the disease is still hormone sensitive,” Dr. Efstathiou explains.
The trial effectively tested whether targeting the PI3K/AKT pathway earlier within the advanced disease continuum (before the development of castration resistance) could improve outcomes.
Patients with high-level PTEN loss (≥90% by immunohistochemistry) were randomized to standard therapy with androgen deprivation plus abiraterone, with or without the addition of capivasertib (brand name Truqap).
The study met its primary endpoint, demonstrating an improvement in radiographic progression-free survival. Importantly, this represents evidence that targeting the pathway before the onset of castration resistance may be more effective than prior approaches in heavily pretreated disease.
However, it does not establish a role for PI3K pathway inhibition outside of advanced disease, nor does it define the optimal timing beyond this setting.
The ‘Sweet Spot’ Problem In Drug Development
The broader lesson extends beyond PTEN and PI3K inhibition. It speaks to a fundamental challenge of identifying the optimal point in the disease trajectory to deploy a given therapy.
As Dr. Efstathiou notes, the standard approach of testing new drugs in late-stage disease, where the unmet need is greatest, may mean missing “that window of opportunity.”
“…If you find that sweet spot, you’re going to maximize it,” she adds.
This “sweet spot” concept is increasingly recognized across therapeutic classes. With androgen receptor pathway inhibitors, for example, the survival benefit expands dramatically when these agents are moved from late-stage to hormone-sensitive disease, highlighting the importance of earlier intervention.
Similarly, radioligand therapies, such as lutetium-PSMA (brand name Pluvicto), demonstrate efficacy across disease states, but the magnitude and nature of benefit vary depending on timing.
Earlier is not always better, but the right timing can be transformative.
The Early-Stage Hypothesis
To be clear, there is no clinical evidence today supporting the use of capivasertib in localized or early-stage prostate cancer.
There are no phase III data in that setting. There is no established role outside of advanced disease. And importantly, capivasertib is not currently FDA-approved for prostate cancer, with regulatory review still pending.
Any discussion of moving this class of drugs earlier must remain, at this point, a hypothesis. Earlier does not always mean better, but the key is discovering the moment when each pathway matters the most.
“Have we maximized the benefit? Have we found the absolute sweet spot? No. But, you want to see these incremental improvements and say, ‘Oh, it’s better to use it earlier than later,'” Dr. Efstathiou says.
The ongoing challenge, she notes, is figuring out which drugs make sense in earlier settings.
