The Immune Checkpoint Inhibitor Global 4 (or 5)

In 2013 Citi equity research analyst Andrew Baum projected cancer immunotherapies "...will generate sales of up to $35 billion (a year) over the next 10 years and be used in some way in the management of up to 60 percent of all cancers" (see Immune system cancer drugs tipped to be a $35 billion market, Ben Hirschler, Reuters, May 22, 2013). The analyst and others in the investment community refer to the next generations of immune checkpoint inhibitors, anti-PD-1 and anti-PD-L1 agents, having moved past approved anti-CTLA-4 agent ipilimumab (Yervoy).

Players (2013 ranking by oncology sales) in the checkpoint inhibitor space include:

• Bristol-Myers (#9): CTLA-4 (approved ipilimumab/Yervoy), and PD-1 (approved internationally nivolumab/Opdivo),

• Merck & Co. (#8): PD-1 (approved pembrolizumab/Keytruda),

• Roche (#1): PD-L1 (investigational MPDL3280A), and

• AstraZeneca (#7): PD-L1 (investigational MEDI4736).

Farther behind, it seems, is Novartis (#3): PD-1 (potential candidates via its CoStim acquisition). It could be late for Novartis to bring a checkpoint inhibitor to market. By the time it gets its version out, Novartis should have four competitors with similarly functioning drugs.

Even before Baum made his bold claim, it was clear the FDA, researchers and industry understood the combination of checkpoint inhibitors and other agents and therapies would be the eventual approach for treating late-stage disease. As result, companies established various combination study relationships, and continue to do so.

Checkpoint inhibitor companies do this because PD-1s and PD-L1s should work more effectively in combination depending on the setting (e.g., co-inhibitory/co-stimulatory). Companies with no checkpoint inhibitors (and no robust immune system primers) do this because a combination should provide them an advantage for their treatments that would be surpassed if they did not do these partnerships at all, and potentially permit much earlier market access for their non-checkpoint inhibitor agent.

For example:

• Pfizer (#11): Merck's PD-1 + targeted therapy (crizotinib/Xalkori),  + targeted therapy  axitinib/Inlyta), and + 4-1BB co-stimulatory agent (PF-05082566), 

• Amgen (#2): Bristol-Myers's CTLA-4 + intralesional (tamilogene laherparapvec or T-Vec), and Merck's PD-1 + intralesional (T-Vec),

• Celgene (#4): Bristol-Myers' PD-1 + targeted therapy (paclitaxel/Abraxane), and

• Novartis (#3): In addition to PD-1s and CAR (chimeric antigen receptor)-T cell therapy, Bristol-Myers' PD-1 + [separately] three targeted therapies (ceritinib/Zykadia, INC280, and EGF816).

SugarCone Biotech's Paul Rennert, in his September 2014 blog post Rational Immunotherapy Combinations: How’s That Work Again?, wrote about "...the question of how to parse the potential immunotherapy combinations that may soon become available, noting that different combinations may prove differentially useful across a wide range of oncology indications." His post is very informative. It is a not-so-simple process to understand and develop the appropriate rationale for why, what and how one combines different agents and therapies, as he clearly illustrates in a cursorily-populated table:

Click to enlarge.

Rennert goes on to write (where I look past his use of vaccines to the broader issue of how to generate many more antigens in order for PD-1s and PD-L1s to be more successful in their individual efforts towards the combination):

"There are other consequences in this new landscape. Nearly every oncology vaccine company claims that as soon as they run a combo trial with an anti-PD-1 or anti-CTLA4 antibody their particular vaccine approach will perform beautifully. There are a few problems with this, notably, very few of these companies have a chance in hell of getting an anti-PD-1 antibody via collaboration, and the rest will pay heavily for the privilege. Second we have no idea of how to rationally pair vaccines with immune checkpoint exposure in order to induce optimal responses. Third, there are not enough patients to go around, a simple fact in many indications."

As recent as the company's ESMO 2014 poster Provectus highlighted the combination study aspect of its business/corporate development strategy.

Click to enlarge.

The value proposition/rationale (but not necessarily the specific medical and scientific rationale and sequencing) for combining PV-10 with a checkpoint inhibitor seems straightforward:

• Immune checkpoint inhibitors have been and will be combined with intralesional agents. Thus far, Bristol-Myers & CTLA-4/ipilimumab/Yervoy and Amgen's T-Vec, Merck & PD-1/pembrolizumab/Keytruda and T-Vec. As expected, the combination of ipilimumab and T-Vec produced responses rates higher than the individual treatments themselves (ASCO 2014). That is, Response_A+B > Response_B > Response_A (A = ipilimumab, B = T-Vec).

• The combination produced notable immunologic signaling. This also was reported from the CTLA-4/ipilimumab and T-Vec combination study at ASCO 2014. The greater the immunologic signaling, the greater [one would imagine] the response and interaction of the immune system to fight and hopefully beat cancer. That is, perhaps, Signaling_A+B > Signaling_B > Signaling_A. The poster presented at ASCO of this work only conveyed the immunologic signaling of the combination.

• PV-10 kills tumors far better than T-Vec. PV-10 produce higher complete responses than T-Vec. The medical community has understood for a while the more antigens produced and presented as a result of tumor destruction (antigenization) the more likely the potential of a greater immune response by the body.

If T-Vec works, PV-10 should work better. But, how much better?

Dr. Agarwala noted in his October 12th presentation at the III Eurasian Melanoma and Skin Cancers Forum that intralesional therapies (PV-10 and T-Vec, since Allovectin-7 failed its metastatic melanoma Phase 3 trial) would form the backbone of combination therapies.

Click to enlarge.

The challenge for Big Pharma, perhaps for some of them more than others, is the lack of "hard data" about PV-10's strong immunologic properties. Presumably Moffitt Cancer Center's presentation on November 8th -- Coinhibition and Costimulation: Targets and Strategies session, Efficacy of Intralesional Injection with PV-10 in Combination with Co-Inhibitory Blockade in a Murine Model of Melanoma poster -- will provide it.

What makes Provectus think they can overcome Rennert's obstacles above?

First, does Provectus have a chance of collaborating with a PD-1 and/or PD-L1 owner? I think the company has a good chance, but the cost or benefit of doing so has yet to be determined (i.e., the details, considerations and concessions of a contractual relationship, and not so much the trial design itself). Obviously, the more a checkpoint inhibitor owner wants to combine with PV-10, the better for Provectus.

I think it's reasonable to believe the Global 5 are aware of PV-10's potential, and its possibilities in combination with immune checkpoint inhibitors. Due diligence begins with getting to know the compound, the available data and practitioners knowledgeable in its use, and then learning more about its combination potential. In regards to the former (i.e., getting to know PV-10), a Merck researcher purportedly attended Moffitt's Dr. Vernon Sondak's June 27th PV-10 presentation at the 4th European Post-Chicago Melanoma/Skin Cancer Meeting specifically to hear/learn more about the drug (a European-based Provectus shareholder routinely attends PV-10 data presentations at European medical conferences). Roche seems to be aware of PV-10, but questions the lack of "hard data" about the compound's immunologic signaling.

Second, how would Big Pharma and Provectus rationally pair immune checkpoint blockade with PV-10? Moffitt's upcoming SITC work presumably should begin to describe how to rationally pair, and dose and sequence PV-10 and a checkpoint inhibitor. It seems the immune system primer & activator/cancer antigen releaser should be given first, followed by the checkpoint inhibitor. In the ipilimumab + T-Vec trial noted above, the investigators sequenced the drugs in that way:

T-VEC was given intralesionally at week 1, week 4, and then every other week. Ipilimumab was given every third week starting at week 6. Treatment continued until dose limiting toxicity, intolerance, all injectable tumors disappeared or disease progression.

I think Rennert's larger question is the whys of rationally pairing drugs, before getting around to the hows. I liken it to understanding what step or steps of the cancer immunity cycle each drug partner in a combination promotes.

Third, are there enough patients to go around? According to Provectus there are sufficient patients available because investigators have asked to use PV-10 in combination with other agents in studies when they are established. This too remains to be seen.

Speaking of Dr. Agarwala, he probably will make a similar presentation to the one he made in Suzdal, Russia at the 2014 Society for Melanoma Research Congress in Zurich, Switzerland (a satellite symposium sponsored by Amgen and entitled Oncolytic immunotherapy – engaging the immune system to target melanoma).