Part 3. Additional studies featuring small molecule inhibitors for Chronic Lymphocytic Leukemia and other B cell lymphomas.
November 18, 2013
The American Society of Hematology Meeting will take place in New Orleans, December 7 – 10, 2013. The abstracts are available at http://www.hematology.org/Meetings/Annual-Meeting/Abstracts/5810.aspx
Lets start with other compounds targeting Btk, PI3K and related kinases in the BCR signaling cascade. In part 1 of this series we looked at Idelalisib, a PI3Kdelta (d) inhibitor, and in part 2 we reviewed Ibrutinib, a Btk inhibitor. In both of those reviews we focused on data from CLL trials, as CLL is the most common B cell malignancy.
Other Btk inhibitors are moving through the clinical development process. Abstract #1630 presents Phase 1 data for relapsing/refractory Non-Hodgkin’s Lymphoma (NHL) patients, including CLL and SLL patients. CC-292 is a covalent inhibitor of Btk developed by Avila and acquired, along with that company, by Celgene. The Phase 1 is a dose escalation/dose schedule trial, with various doses between 125 and 1000 mg given once (qd) or twice (bid) a day. The maximum tolerated dose (MTD) was not reached and AEs were as usual in these trials, with cytopenias being the most common toxicity. The patients enrolled were rrCLL/SLL with high-risk characteristics, as were outlined in Part 1. Of 83 patients enrolled, response data are shown for the 55 efficacy-evaluable patients who had at least a PR (so, 66%). These patients were treated at the highest 4 dose levels: 750 mg qd, 1000 mg qd, 375 mg bid and 500 mg bid (qd = once daily and bid = twice a day). Across these 4 dose groups the ORR = 60% and all responses were PR. Some patients showed evidence of reduction of nodal (lymph node) disease as seen by a reduction in size of the nodes. Abstract #4169 lays out the pharmacodynamic (PD) assays that will likely be used in support of further optimization of this drug’s PK/PD profile. The assays include the familiar Btk autophosphorylation and PLC-g2 phosphorylation assays. Applied to the Phase 1 trial, the PK/PD analysis shows that BID dosing is preferable for CC-292, with 94% target coverage achieved at trough over 24 hours vs 83% target coverage (+/- 17%) at trough with qd dosing. This is important data that has already been applied to further clinical trials underway.
I’m hopeful that optimized dosing will allow CC-292 to achieve higher response rates. Looking beyond lymphomas, Celgene investigators will present preclinical data showing that CC-292 given in combination with a proteosome inhibitor carfilzomib had activity in Multiple Myeloma models (Abstract #682) suggesting other therapeutic areas for the development of Btk inhibitors.
Ono Pharmaceuticals will be presenting Phase 1 clinical data for ONO-4059, a covalent BTK inhibitor (Abstract #676). The trial enrolled 16 high risk rrCLL patients for a dose escalation study (20 – 320 mg). ONO-4059 is shown to have a half-life in circulation (T1/2) of 6 hours. Remarkably, PD analyses shows Btk target coverage of 100% at 24 hours at all doses tested. AEs were typical and not dose limiting. All patients initially responded. ORR is given as 70%, and 1 of 16 patients progressed. Notably, 15/16 patients are reportedly still on treatment. A second Phase 1 study (Abstract #4397), enrolled 14 patients (mantle cell lymphoma n=7, follicular lymphoma n=3, plasmablastic DLBCL n=1, ABC-DLBCL n=1, small lymphocytic lymphoma n=1 and Waldenstrom’s macroglobulinaemia n=1) using the same dose escalation design. This is a complex and difficult group of patients. ONO-4059 induced an initial response in all patients. The ORR (all patients) = 42% and for MCL patient ORR = 50%. AEs are similar to other Btk and P13K inhibitors.
The limited available data suggest that ONO-4059 is highly potent and will be an interesting drug candidate to watch. Preclinical data show synergistic efficacy with anti-CD20 antibody Obinutuzumab/GA-101 treatment, anticipating next steps (Abstract #3069).
Gilead is bringing forward a new Syk inhibitor, now in phase 2 clinical trials. Syk is the kinase just upstream of Btk and is required for Btk activation (see the model shown in Part 1). Early Syk inhibitors from Rigel and Portola were not selective and did poorly in the clinic, as discussed previously: http://sugarconebiotech.blogspot.com/2013/04/syk-inhibitors-continue-to-struggle-in.html. Gilead’s new inhibitor GS-9973 (Abstract #1634) is presented as having 7.6 nM activity against Syk with no other kinase being inhibited below 100nM. The abstract presents early activity data, with most patients responding to therapy within 4 weeks. AEs are mild except for grade 3/4 liver transaminase elevations in a small number of patients. Gilead will give a fuller picture of this phase 2 trial at the meeting. Gilead is developing GS-9973 as a single agent and also in combination with Idelalisib – the latter trial is recruiting patients with diverse types of B cell lymphomas (NCT01796470). Here again we are seeing the development of a rational combination – targeting two key elements of the signaling cascades that support lymphoma proliferation and survival.
Certainly there appears to be room for the development of additional BTK inhibitors, as this space is hardly crowded, and it will be important for companies to control their own compounds, for use in combination studies.
New PI3K inhibitors will report data at ASH, with IPI-145 from Infinity Pharmaceuticals updating a Phase 1 trial in B cell lymphomas, including rrCLL. IPI-145 is a potent PI3Kgamma/delta inhibitor, and impacts signaling through both of these isoforms at a sub-nM KD. The Abstract #677 reveals a maximum tolerated dose of 75 mg bid and also suggests that 25 mg bid is sufficient for target coverage by PK/PD analyses. The PK/PD analysis is shown in abstract #1633. These are the data that support the dosing regimen used in the ongoing Phase 3 clinical trials. The preliminary ORR for the rrCLL patients in the Phase 1 trial (19 patients) = 53%, and it appears there were a high number of discontinuations. Importantly, AEs appear to be in line with other drugs in this class. At the meeting, Infinity will present updates data from treatment-naïve CLL patients who received IPI-145 at 25 mg bid and R/R CLL patients who received IPI-145 at 25 or 75 mg bid.
Amgen is developing AMG 319, a selective PI3Kdelta inhibitor. Results from the Phase 1 dose escalation trial are shown in Abstract #678. Doses were 25 – 400 mg qd. AEs were diverse and included colitis in some patients at the 400mg dose. Ex vivo analysis of the phosphorylation of AKT (downstream of PI3K) showed nearly 100% inhibition 24 hours after dosing at 400 mg. Clinical activity was seen in all patients at all doses, with dose dependent activity observed.
Gilead has a 2nd generation PI3Kd inhibitor in clinical development, GS-9820. In Abstract #2881 dose escalation results from the Phase 1b trial are shown for doses ranging from 50 – 400 mg bid. No MTD was observed, there was no liver toxicity and 9/12 patients showed some response to therapy.
Bayer has a very interesting presentation of phase 2 data with BAY 80-6946, a selective PI3Kalpha/delta inhibitor. This drug is given IV at 0.8 mg/kg. There are notable toxicities (neutropenia, hyperglycemia, hypertension) but the efficacy is impressive at least at this early stage of development. I calculated %ORR and %CR by B cell lymphoma type, as follows (note that the sample sizes are small):
The hypertension AE is being studied in a sub-study of the ongoing Phase 2 trial (NCT01660451).
TG Therapeutics will show early data for TGR-1202 a novel orally available PI3Kdelta inhibitor. Patients have been dosed from 50 – 400 mg qd. DLT was not observed and at the 200 mg dose about half the patients had stable disease and half had progressed. The company plans to present updated results at the meeting.
Sanofi will present phase 2 results of its pan-PI3K inhibitor SAR245409, using the MTD as defined in solid tumor studies. This drug also targets the downstream signaling proteins mTORC1 and mTORC2. Data are presented in Abstract #4170. Focusing just on the CLL patients (n=10) 5 patients have SD, PFS ~ 6 months and 5 patients have a PR, PFS ~ 16.5 months. That’s not a bad result, except that AEs are notable – all patients have cytopenias, GI complications, and hypotension. An update will be presented at the meeting. Follicular lymphoma (FL) patient data from the same trial is shown in Abstract #86. rrFL patients were given SAR245409 at 50 mg bid until disease progression (PD) or withdrawal. 36% of patients were lost to PD and 7% to AEs. 24 patients were available for evaluation, as they had responses as follows: ORR = 50%, PR = 36%, CR = 7%. For those 28 patients PFS had not been reached at 8 months.
As we can see from this Sanofi drug, moving to a pan-inhibitor and also moving further down the signaling pathways (mTORC1/2) doesn’t necessarily translate to better mono-therapeutic efficacy.
A different approach is seen with the Merck drug MK2206, an allosteric AKT inhibitor. Abstract #2882 presents a very interesting Phase 1 study. There is a 1 week “run-in” with MK2206 alone, sufficient to demonstrate a PD effect. After the first week, MK2206 is given along with bendamustine (B) and Rituxan (R). The MTD is shown to be 90 mg/week. Early results show an ORR = 89% and CR = 22% in the small Phase 1 study (n=9). These results compare favorably to BR alone (9% CR and 59% ORR) in rrCLL patients.
Other PI3K, AKT, mTOR and related drugs are in the pipeline for hematologic malignancies, and this is an area that should evolve quickly.
Next we will look at few promising pathways and drugs, coming up in Part 4.
Syk inhibitors have had a rough ride, with both Rigel and Portola running into significant issues in clinical development.
Rigel and partner Astra Zeneca released data from a Phase 2 Rheumatoid Arthritis study, summarized here:
“In the study known as OSKIRA-1, two doses of fostamatinib significantly improved the signs and symptoms of rheumatoid arthritis compared to a placebo following 24 weeks of treatment. However, fostamatinib failed to show improvements over placebo in bone erosion and joint-space narrowing as measured by X-ray.” from http://www.thestreet.com/story/11888193/1/astra-rigel-arthritis-pill-posts-mixed-trial-results.html).
Sadly thats about all you need to know about fostamatinib, especially given that earlier data have been unimpressive as we discussed in December. There is no clear role for this drug in RA given the label granted to Pfizer for their JAK inhibitor tofacitinib, approved for use as second line therapy for RA. Tofacitinib also has shown clear evidence of protection from joint damage, something fostamatinib has failed to do.
Fostamatinib is apparently moving forward in multiple oncology indications, and therein may lie its future, if it has one.
Portola’s Syk inhibitor, licensed by Biogen Idec, is in development limbo, and the clinical trial in RA was withdrawn. Whether this is due to toxicity issues, efficacy concerns, or commercial strategy is not known, as Biogen has not provided an update on this drug.
In the meantime companies continue to focus on kinases that signal downstream of Syk, notably Btk and PI3K. While PI3K inhibition may carry too much toxicity for use outside of oncology, Btk inhibitors appear to be safe enough to develop in autoimmunity and inflammation. We will continue to watch the development of small molecule inhibitors in this space, and anticipate success for novel Btk inhibitors.