Arvinas Stock Price Doubled Today: Why It Happened

By Amit Chowdhry ● Dec 14, 2020
  • The stock price of Arvinas Inc (NASDAQ: ARVN) doubled from $29.93 in the previous close to $60.60 as of 2:09 PM. And it hit as high as $75 per share today. This is why it happened.

The stock price of Arvinas Inc (NASDAQ: ARVN) doubled from $29.93 in the previous close to $60.60 as of 2:09 PM. And it hit as high as $75 per share today. The main trigger for why the stock price doubled is due to an announcement from the company revealing information about interim clinical data.

Arvinas — which is a clinical-stage biopharmaceutical company creating a new class of drugs based on targeted protein degradation using its PROTAC Discovery Engine — announced clinical program updates for its PROTAC protein degraders ARV-471 and ARV-110. 

For ARV-471, the interim Phase 1 data show potential for best-in-class safety and tolerability, estrogen receptor (ER) degradation superior to that previously reported for the current standard of care agent (fulvestrant), and robust efficacy signals in heavily pretreated patients with locally advanced or metastatic ER positive / HER2 negative (ER+/HER2-) breast cancer. And the efficacy signals include one Response Evaluation Criteria in Solid Tumors (RECIST) confirmed partial response (PR), two additional patients with unconfirmed PRs, and a clinical benefit rate (CBR) of 42%. 

And for ARV-110, the ongoing dose-escalation portion of the Phase 1/2 trial in men with metastatic castration-resistant prostate cancer (mCRPC) has provided additional evidence of anti-tumor activity and patient benefit, including a prostate-specific antigen reduction of more than 50% (PSA50) rate of 40% in a molecularly defined patient population. So Arvinas initiated a Phase 2 dose expansion to explore a two-pronged development strategy, including the potential for accelerated approval in molecularly defined late-line patients, and broader development in less-heavily pretreated mCRPC patients with fewer androgen receptor (AR)-independent mechanisms of tumor resistance.

Both ARV-471 and ARV-110 have been well tolerated (neither has reached a maximum tolerated dose) and the Phase 1 dose-escalation trials for both programs continue. And a Phase 1b combination trial of ARV-471 and Ibrance (palbociclib) is expected to begin in December 2020 and a Phase 2 expansion cohort for ARV-471 is scheduled to begin in the first half of 2021.

ARV-471 Clinical Update

As of the data cut-off date of November 11, 2020, 21 adult patients with locally advanced or metastatic ER+/HER2- breast cancer completed at least one treatment cycle with ARV-471 (orally, once-daily) in the Phase 1 clinical trial. And 100% of these patients were previously treated with a cyclin-dependent kinase (CDK) 4/6 inhibitor, 71% of patients received prior fulvestrant, and 23% of patients were pretreated with investigational selective estrogen receptor degraders (SERDs). Overall, patients had a median of five prior therapies.

And in metastatic breast cancer, prior treatment with CDK4/6 inhibitors predicts high tumor ER-independence, rendering ER-targeting therapies ineffective. However, one patient in the ARV-471 trial had a confirmed PR with a 51% reduction in target lesion size as assessed by RECIST. Plus 2 additional patients had unconfirmed PRs and one additional patient demonstrated stable disease with >50% target lesion shrinkage. For evaluation of CBR, 12 patients had sufficient follow-up to be included. And 5 of 12 patients (42%) achieved CBR (CBR defined as PRs + complete responses + stable disease at 6 months). And 3 of these 5 patients had previously received fulvestrant and another was treated with two investigational SERDs.

ARV-471 has been well tolerated at all dose levels as of the data cut-off date. And the most common treatment-related Grade 1-2 adverse events were nausea (24%), arthralgia (19%), fatigue (19%), and decreased appetite (14%). None of these led to discontinuation or dose reduction of ARV-471. No patients had reported treatment-related Grade 3 of 4 adverse events and no dose-limiting toxicities (DLTs) have been reported. A maximum tolerated dose (MTD) has not been reached and dose escalation continues.

The plasma exposures of ARV-471 have been dose-proportional up to and including 360 mg orally once daily and have substantially exceeded Arvinas’ predicted thresholds of efficacy based on preclinical studies. And the estimated half-life of ARV-471 is 28 hours, supporting a once-daily schedule of administration. Analysis of 5 paired tumor biopsies at doses up to 120 mg provide compelling proof of mechanism for ARV-471 — which has demonstrated ER degradation up to 90% (average of 62%) at those doses, while dose escalation continues.

And the combined profile of ARV-471, including efficacy signals in a highly refractory population, excellent tolerability profile, and high levels of ER degradation, support a potential best-in-class ER-targeting therapy.

A Phase 2 dose expansion of ARV-471 is expected to begin in the first half of 2021. And Arvinas also expects to initiate a Phase 1b cohort expansion of ARV-471 in combination with Ibrance (palbociclib) in December 2020. 

This trial will evaluate the safety and tolerability of ARV-471 in combination with palbociclib and seek to identify a recommended combination dose. And Arvinas expects to begin two additional studies of ARV-471 in the second half of 2021: a combination trial of ARV-471 and another targeted therapy in 2L/3L metastatic breast cancer, and a window of opportunity study in adjuvant breast cancer. This combined data from these studies will inform Arvinas’ global development strategy and path forward toward the goal for ARV-471 to become the leading endocrine therapy in ER+/HER2- breast cancer.

ARV-110 Clinical Update

For the Phase 1 clinical trial in men with mCRPC, ARV-110 continues to show promising activity in a very late-line population with PSA reductions >50% observed at doses greater than 280 mg, the last reported cohort.

And in the dose-escalation, ARV-110 exposures have risen dose proportionally and at 420 mg oral daily dosing, exposures in nearly all patients have surpassed a threshold associated with tumor responses with ARV-110 in enzalutamide-resistant preclinical models of prostate cancer. The increases in exposure are associated with increased frequency of PSA reductions.

For the Phase 1 dose-escalation trial, 76% of patients had been treated with prior chemotherapy and 82% previously received both abiraterone and enzalutamide. And patients had a median of 5 prior lines of therapy. Multiple lines of therapy in nonmetastatic and metastatic castrate resistant prostate cancer are associated with a decreased responsiveness to AR-directed therapies and an increase in tumor heterogeneity, including in genetic mutations — which reduce the tumor’s dependence on the AR signaling axis. 

Genetic profiling of trial patient tumors has led to significant learnings about the ARV-110 Phase 1 patient population, especially regarding genetic variability. And 84% of patients in the trial have non-AR gene mutations and as such, they would not be expected to respond. Plus rates of specific AR mutations have been found to be higher than reported in publications that have characterized prevalence of AR mutations in men with mCRPC.

Despite the highly heterogeneous nature of the Phase 1 patient population, Arvinas had identified a molecularly defined late-line population with a particularly strong response to ARV-110. And 2 of 5 patients (40%) with T878 or H875 mutations in AR had PSA reductions >50%, including one patient with a confirmed PR by RECIST and tumor size reduction of 80%.

In addition, 2 of 15 patients (13%) with wild-type AR also had PSA reductions >50%, representing activity in a broader patient population. For the full group of patients with exposures above the minimum threshold Arvinas predicted to be efficacious by preclinical studies, 4 of 28 (14%) had PSA reductions >50%. These PSA50 rates are higher than would be expected from approved AR-directed therapies in such late-line patients. Specifically, PSA50 response rates from standard-of-care AR-directed therapies generally decrease to 8-15% in mCRPC patients with fewer prior therapies than the patients in the ARV-110 trial.

The dual signals of ARV-110 activity in a molecularly defined population (T878/H875) and in wild-type patients supports Arvinas’ two-pronged strategy for ARV-110 development and suggest a robust opportunity to address unmet need in patients with mCRPC. And a daily dose of 420 mg was selected as a Phase 2 expansion dose based on pharmacokinetics, safety profile, and the activity signals in both T878/H875 and wild-type patients. 

In the ARDENT Phase 2 expansion, T878/H875 patients will be enriched in a subgroup to ensure sufficient patient numbers to support the potential for accelerated approval in this population. And a separate subgroup will enrich for less-pretreated patients (i.e., no prior chemotherapy and with only one previous second-generation AR-directed therapy, such as enzalutamide or abiraterone) to ensure sufficient numbers of patients whose tumors are expected to be more AR-dependent, less genetically complex and more responsive to ARV-110.

And the ARDENT Phase 2 expansion (N = ~100) started enrolling in October 2020. And Arvinas expects to provide interim data from the trial in the second half of 2021. 

Next year, Arvinas also expects to begin at least one Phase 1b combination trial with a standard-of-care prostate cancer therapy and provide complete data from the Phase 1 dose escalation.

KEY QUOTES:

“After initiating our clinical efforts just last year, we now have what we believe are clear signals of efficacy in both of our clinical-stage development programs. The clinical benefits we’ve seen in both patient populations, including tumor shrinkage and low incidence of adverse effects, are compelling and reinforce our belief that our PROTAC protein degraders could dramatically change the lives of patients who have few or no therapeutic options.”

— John Houston, Ph.D., Chief Executive Officer at Arvinas

“Based on data to date, we believe ARV-471 is the most promising ER-targeting therapy in the clinic, showing early signs of efficacy, a favorable tolerability profile, and better ER degradation than that previously reported for fulvestrant, the current standard of care. It is exciting to see that ARV-110 continues to be active and well tolerated in what we believe is the most heavily pretreated patient population that has ever been studied with an AR-directed therapy. Our recently initiated ARDENT Phase 2 cohort expansion is specifically designed to investigate the potential of a precision medicine approach in molecularly defined, late-line patients with few available treatment options, while also fully characterizing the safety and activity of ARV-110 in earlier line patients irrespective of molecular profile, setting ARV-110 on a potential two-pronged registrational path.”

— Ron Peck, Ph.D., Chief Medical Officer at Arvinas

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