Co-stimulatory & Co-inhibitory

Moffitt's PV-10 presentation at the 2014 annual meeting of the Society for Immunotherapy of Cancer ("SITC") is entitled Efficacy of intralesional injection with PV-10 in combination with co-inhibitory blockade in a murine model of melanoma (see Moffitt @ SITC (September 19, 2014) on the blog's News page).

Earlier this month, one of the SITC presentation's co-authors and Moffitt assistant professor and researcher, Dr. Shari Pilon-Thomas, Ph.D., co-authored an online OncLive article entitled Immunotherapy Combined With Chemotherapy for Pancreatic Cancer: A Game Changer? (see blog post Treating Cancer). In it Dr. Pilon-Thomas and her fellow authors write:

Of note, the immune system’s involvement in cancer development and progression has sparked much interest in recent years. The model of the cancer-immunity cycle suggests an interplay of immune-suppression and immune-stimulation. In normal individuals, a state of immunosurveillance is in place. However, within the tumor microenvironment, inhibitory signals and immunosuppressive cells are present and tip the scale in favor of immune suppression. {Underlined emphasis is mine}

Continued: The idea of the cancer-immunity cycle proposes that, for a cancer immune response to be generated, the net balance between immune stimulation versus immune suppression must be tipped in favor of the former. Studies in various cancers have suggested that tumors evade the immunogenic process mostly by factors that promote immunosuppression. {Underlined emphasis is mine}

The theory of immune surveillance suggests, according to Peggs et al., "...that the immune system plays a key role in suppressing tumor growth and that the incidence of cancer would be much greater were it not for the ability of the immune system to identify and eliminate nascent tumor cells...While the immune system appears capable of eliminating or containing early tumor growth, some tumor cells escape detection and eventually cause cancer." Said another way, when thinking about the growing potential role and promise of cancer immunotherapy, "...we continually develop malignant cells every day that are consumed by the immune system to prevent tumor development, and the immunotherapy drugs seem to target the failure of immune recognition and immune response" (Dr. Peter Salgo, M.D.).

The balance between co-stimulation and co-inhibition is described by Inman et al.: "If sufficient co-stimulation is provided in the presence of adequate tumor-associated antigenic stimulation, the immune system will act against tumor antigen and, thus, destroy early tumors before they become fully established. Contrarily, if co-inhibitory signaling dominates, the immune system will be tolerized to tumor antigens, and the tumor will be permitted to grow unfettered and unmolested by the immune system. If neither co-stimulatory nor co-inhibitory signals dominate, the adaptive immune system may remain in a tenuous state of equilibrium, militating against tumor outgrowth with varying degrees of success."

So, it would seem to me, generalizing (or simplifying, perhaps too much):

• If co-stimulation > co-inhibition, the immune system can act decisively against cancer,

• If co-inhibition > co-stimulation, cancer overwhelms the immune system and renders it ineffective or useless, and

• If co-stimulation = co-inhibition (that is, some sort of equilibrium state), the immune system wages battles against cancer to varying degrees of success with potentially no ultimate resolution to the war itself.

[Daniel] Chen & Mellman (2013), authors of Oncology Meets Immunology: The Cancer-Immunity Cycle, note stimulatory and inhibitory factors at step of the cycle.

Click to enlarge. Figure 2 (above) of [Daniel] Chen et al.'s article.

The authors write:

Each step of the Cancer-Immunity Cycle requires the coordination of numerous factors, both stimulatory and inhibitory in nature. Stimulatory factors shown in green promote immunity, whereas inhibitors shown in red help keep the process in check and reduce immune activity and/or prevent autoimmunity.

[Daniel] Chen et al. then note "[t]he numerous factors that come into play in the Cancer-Immunity Cycle provide a wide range of potential therapeutic targets."

Figure 3 (below) "...highlights examples of some of the therapies currently under preclinical or clinical evaluation. Key highlights include that vaccines can primarily promote cycle step 2, anti-CTLA4 can primarily promote cycle step 3, and anti-PD-L1 or anti-PD-1 antibodies can primarily promote cycle step 7. Although not developed as immunotherapies, chemotherapy, radiation therapy, and targeted therapies can primarily promote cycle step 1, and inhibitors of VEGF can potentially promote T cell infiltration into tumors—cycle step 5."

Click to enlarge. Figure 3 (above) of [Daniel] Chen et al.'s article.

In my illustration below, found on the blog's PV-10, and the Cancer Immunity Cycle, I endeavored to show Provectus' drug promoted steps 1, 2, 3 and 7. I believe, but with no confirmation of course, Moffitt has shown via primarily their murine model work (and maybe their human study) that PV-10 promotes steps 4, 5 and 6.

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I revised my table of combination study deals to reflect [as I think they are] stimulatory and inhibitory compounds is below.

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Pilon-Thomas et al. concluded (note the article discussed immunosurveillance in the context of chemotherapy, immunotherapy and pancreatic cancer):

The cancer-immunity cycle is an ideal model to envision how tumor cells evade immuno-surveillance as well as where future modalities may intervene with hopes of potentiating tumor cell death. The cancer-immunity cycle together with the immune-modulating functions of chemotherapies that are used in pancreatic cancer creates a rationale for investigating vaccine-chemotherapy combinations. 

Studies to date have suggested benefits of adding immunotherapies to standard chemotherapy regimens. Additional benefits are also suggested by the indication that immunotherapy may render improved chemosensitivity at later dates. In addition, vaccines are often well tolerated with minimal toxicities, which make them a favorable approach. The hope is that we can identify the appropriate combination of vaccine and immune-modulating chemotherapy that will eradicate the disease. There is also likely to be a role for immune checkpoint therapy with inhibitors of PD-1 and PD-L1. Such phase I single-agent studies are currently in progress for pancreatic cancer. The results of studies so far create hope that the combination of chemotherapy with immunotherapy may be a game changer in the treatment of pancreatic cancer.

PV-10 has some interesting features that cross categories. Provectus management previously had called the drug as a chemoablative immunotherapeutic agent (later revising the descriptor to "immuno-chemoablative"). Underlined portion number one, "chemoablative," described PV-10's chemotherapeutic-like feature of rapid tumor ablation and destruction mechanism of action ("MOA"). Underlined portion number two, immuno," described the drug's MOA whereby it harnessed the immune system to battle cancer locally (at the site of injection) and elsewhere around the body.

While not specifically a vaccine because PV-10 is not antigen-specific, it could be considered vaccine-like because it is minimally or not at all toxic but expresses many, many more than one antigen.

As a side note, immune checkpoint therapy in the above Moffitt comments refers to, I believe, ipilimumab, which is why anti-CTLA4 is in step 3, priming and activation, of the cancer immunity cycle (and why Bristol-Myers is exploring the combination of ipilimumab and anti-PD-1 agent nivolumab.

[Lieping] Chen et al. write, when discussion combination therapies:

Traditional chemotherapy and radiation therapy, together with depleting mAbs or treatment with small-molecule inhibitors, all directly target and kill cancer cells, leading to the destruction of the tumour stroma and the release of tumour antigens. When coupled with these direct killing mechanisms, immunomodulatory biologics promote the priming and expansion of existing tumour-specific T cells and their de novo generation, with a potential to form long-lasting and self-sustained antitumour responses. In recent years, small-molecule inhibitors targeting tumours that harbour mutated BRAF (vemurafenib (Zelboraf; Plexxikon/Roche)) or translocated BCR–ABL (imatinib (Gleevec; Novartis)) have shown high initial response rates in clinical trials165. However, the duration of the antitumour response is limited owing to acquired drug resistance. A combination of these fast-acting small-molecule inhibitors with immune co-inhibitory blockade — for example, with CTLA4-specific or PD1-specific mAbs — could promote the priming and expansion of tumour-specific CTLs against multiple tumour antigens and/or epitopes, prevent the generation of escape variants or drug-resistant mutant cancer cells and induce sustained T cell responses. {Underlined emphasis is mine.}

Circling back to beginning of this post, Moffitt's presumed presentation at SITC potentially entitled Efficacy of intralesional injection with PV-10 in combination with co-inhibitory blockade in a murine model of melanoma, the cancer center previously have described their successful pre-clinical work that combined PV-10 with systemic immunotherapies to mean, I believe, checkpoint inhibitors (e.g., ASCO 2014).

The interplay of co-stimulation and co-inhibition (with the goal of more of the former than the latter), and Moffitt's use of what seems to be the broader term co-inhibitory blockade, I wonder whether their work describes the better therapeutic outcome of PV-10 and inhibitory factors of step 7 of the cancer immunity cycle above (see Figures 2 and 3 of [Daniel] Chen et al.).

Immune Surveillance

Following up on my Juxtaposition blog post, there is the potential for a melanoma combination therapy Phase 1 (or 1b)/2 trial of PV-10 and a checkpoint inhibitor, which management briefly discussed on their 2Q14 conference call.

Eric: As Pete mentioned earlier, we're also looking beyond single-agent therapy with PV-10 to address the needs of patients with more extensive disease, particularly those with visceral tumors that are not injectable. One attractive and complementary approach may be to combine PV-10 with a systemic immunotherapy, such as an immune checkpoint protein inhibitor. Immune checkpoint protein inhibitors, such as anti-CTLA4, anti-PD-1, and anti-PD-L1 agents, are an important advance in the treatment of melanoma and other cancers, another subject of intense development in our industry. 

However, while these drugs represent an important step forward, like any drug they are not perfect and they might be improved. As was clearly presented by the medical oncology community earlier this summer at ASCO, using an agent like PV-10 to prime the immune system could be synergistic in combination with such a systemic agent. 

Our patent application on this strategy was published in 2012 and we've been vigorous by pursuing this approach since. The nonclinical research we first presented at the Society for Immunotherapy of Cancer Annual Meeting in 2012, together with ongoing translational clinical research on PV-10's mechanism of action that we were sponsoring at Moffitt Cancer Center and our own Phase 2 data, provide a rationale for combination testing of PV-10. 

This development track, separate from the Phase 3 study I discussed earlier, could represent a path forward for patients with significant disease burden not amenable to intralesional injection, and is a possible candidate for co-development with one or more pharmaceutical or biotech companies. {Underlined emphasis is mine}

Eric wouldn't insert statements about this topic into his comments until and unless at least minimally substantive progress has been made towards this end. He first addressed a combination study via St. Luke’s Cancer Center and Temple University's and principal investigator Dr. Sanjiv Agarwala, M.D.'s presentation at the 10th European Association of Dermato-Oncology (EADO) congress in May ("Commencement of combination studies in Stage IV disease in second half of 2014"). The reality of a combination study/trial probably is dependent on the partnering pharmaceutical company's, the one with the checkpoint protein inhibitor to be combined with PV-10, interest in and willingness to:

• At a minimum, run and shoulder the cost of a trial, aside from Provectus's minimal expense to provide PV-10 drug product,
• At a minimum (more than likely) make a one-time payment to Provectus, such as was the case in Bristol-Meyers' collaboration with Celldex Therapeutics, and
• Forego meaningful rights of first somethings, unless the partner fully compensates Provectus for this ask.

I summarized a number of previously announced and/or conducted combination studies in my Combinations (July 24, 2014) news items under the blog's News tab.

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Although Provectus management has understood and communicated the potential for combination therapy involving PV-10 for the treatment of metastatic melanoma, noting this on the 2Q14 conference call (i.e., the Provectus-Pfizer patent application, the SITC 2012 poster presentation), they historically have not prioritized this potential regulatory pathway, and have been disinterested in and unwilling to allocate resources to conduct a typical combination study where companies share trial costs and the "non-CTLA-4/PD-1" (i.e., non-Bristol-Myers or Merck) partner conducts (sponsors) the trial.

There is no certainty a trial comes together, but it would appear Provectus is engaged in the kind of basic or fundamental conversations, data sharing and expectation setting necessary to contemplate a combination study and develop the associated relationship between the parties involved.

The consensus of melanoma key opinion leaders appears to be that “[t]he future lies in combinational approaches with drugs from the new melanoma landscape” (e.g., intralesional therapies, BRAF inhibitors, ipilimumab, anti-PD-1 antibodies). Moffitt Cancer Center's pre-clinical work combining PV-10 with other approved and investigational immunotherapeutic agents more than likely would be, and would have to be, the driving force behind any clinical combination study focused on metastatic melanoma patients with visceral disease (i.e., Stage IV M1b-c). The cancer center already has alluded to the completion and results of this pre-clinical work, which should form the rationale for a future clinical trial or trials, at ASCO 2014 by concluding "IL PV-10 may be rationally combined with systemic immunotherapy for the treatment of metastatic melanoma," and again at the 4th European Post-Chicago Melanoma & Skin Cancer Meeting 2014 by concluding "[p]reclinical data suggest PV-10 would be a good candidate to evaluate in conjunction with available systemic therapies and new agents in development."

I previously wrote about historical pre-clinical and some clinical work on PV-10 in combination with other treatments (systemic chemotherapy [pre-clinical], systemic immunotherapy [pre-clinical], radiotherapy [clinical]) in my "IL PV-10 may be rationally combined with systemic immunotherapy for the treatment of metastatic melanoma" blog post.

A potential clinical trial combining PV-10 with a checkpoint inhibitor should be viewed in the context of other clinical trials and studies Provectus expects  hopes to commence in 2014 and/or 2015:

• Melanoma, PV-10: Phase 3 trial, locally advanced unresectable/unresected cutaneous melanoma, 2H2014,

• Dermatology, PH-10: Phase 1 trial, mechanism of action/feasibility study, 2H2014 (my estimate),

• Liver cancer, PV-10: Phase 2/3 trial, locally advanced, unresectable/unresected liver cancer (my speculation of the trial title), 1H2015 (my estimate); the trial also should include liver tumors caused by primary non-liver cancers (i.e., cancers metastatic to the liver), and

• Melanoma, PV-10: Phase 1 (or 1b)/2 trial, metastatic melanoma, 1H2015 (my estimate, if a deal is consummated in 4Q14); with a trial population similar to that of the ipilimumab+talimogene laherparepvec of mostly Stage IV M1b-c patients

I do not believe a deal between Provectus and a pharmaceutical company (and its checkpoint inhibitor), the first step towards an eventual clinical trial, would be consummated until Moffitt's preclinical combination study data is more broadly communicated. Meaning, neither Bristol-Myers nor Merck, for example, would even contemplate acceding to Provectus deal expectations until and unless Moffitt substantiates their above mentioned conclusions with very compelling data (i.e., together PV-10 makes your drug much better than your drug alone).

I think the venue for the cancer center's communication will be the 29th Annual Meeting of the Society of Immunotherapy for Cancer, November 6-9, 2014. Provectus first addressed combination treatment at the 2012 annual SITC meeting concluding the co-administration of PV-10 immuno-chemoablation with other systemic therapy could yield potent synergy in uninjected tumors.

But, more than just the pre-clinical drug combination study results, I also am very interested in other aspects of Moffitt's work, and Dr. Jeffrey Weber, M.D., Ph.D.'s comprehensive views on the utility and use of PV-10.

First, what is the basis for Weber's comment "PV-10 might offer the perfect way to prime the immune system?" Dr. Weber has said (paraphrasing) the utility of a primer is simply its ability to synergize with the immune agent in question in terms of clinical effect when given prior to the second agent. Moffitt data showing the strength of the systemic responses PV-10 can stimulate (i.e., efficacy of PV-10 plus a checkpoint inhibitor >> efficacy of the checkpoint inhibitor alone) should make this/his point.

Second, what is PV-10's role and participation in each step of the cancer immunity cycle (Chen & Mellman, 2013)? Under the blog's PV-10, and the Cancer Immunity Cycle tab I illustrate PV-10's involvement in steps 1 (release of cancer cell antigens), 2 (cancer antigen presentation), 3 (priming and activation) and 7 (killing of cancer cells). And although Dr. Weber has said (paraphrasing) one should prioritize which steps are the most important (presumably in order to determine how to utilize what agents in combination and why; for example, impacting on endothelial cells have been less promising as a therapeutic than many of the other steps), I'd like to understand Moffitt's view on PV-10's involvement in steps 4 (trafficking of T cells to tumors), 5 (infiltration of T cells into tumors) and 6 (recognition of cancer cells by T cells).

And third, what are Weber's thoughts about PV-10 in the context of or in regards to immune surveillance? Immune surveillance theory is:

The concept that the immune system protects the host against cancer was first posited by Ehrlich in 1909 (1) and modified in the 1950s by Burnet and Thomas (2, 3), who proposed that it was instrumental in eliminating precancerous or cancerous cells, through a “surveillance” function. However, the concept fell out of favor when studies in the 1980s indicated that tumors failed to develop more rapidly in nude mice (which lack T cells and B cells, but not NK cells) than in wild-type mice. It was resurrected in the 1990s, when a body of evidence emerged indicating that immunodeficient mice were at greater risk for spontaneous tumor development (4). These studies led to further refinement of the theory, now referred to as “cancer immunoediting,” encompassing three phases: elimination, equilibrium, and escape. (J Clin Invest. 2007;117(5):1130–1136. doi:10.1172/JCI32136)

In a February article of The American Journal of Managed Care, Weber said:

"Well, the Holy Grail of cancer immunology is to create a cancer vaccine. Provenge was the first and only cancer vaccine that was ever approved. But that is truly the mantra, that is, the immune system is the ultimate way to perform targeted therapy. So immunotherapy is targeted therapy, and its hallmark is memory." {Underlined emphasis is mine} 

And: "There are certainly data to suggest that this idea of immune surveillance is indeed valid. On the other hand, people on immunosuppressants don’t always present with 30 different types of solid tumors. Transplant patients often develop squamous skin cancers, especially virally related squamous skin cancers. So there are data to suggest that we always have immune surveillance to prevent cancer from developing." 

And: "You can divide immunotherapies into 4 or 5 categories: these include chemicals like cytokines; antibodies…cells, which are not really well developed; vaccines, which is always the Holy Grail to try to vaccinate someone against his or her own cancer. You’ve got 1 approved vaccine. One of the antibodies, which are the most exciting and promising, is approved. That’s ipilimumab, the anti-CTLA4 antibody. In terms of the cytokines, in 1996 and 1998 IL-2, interleukin-2, was approved for kidney cancer and for melanoma. The cell therapy is immature, and you will hear a lot more about the antibodies coming up in the next couple of years." {Underlined emphasis is mine} 

Recall that Moffitt said, following their initial murine model work, that:

"These murine studies confirm that PV-10 chemoablation results in both a direct effect on injected lesions as well as a systemic response that leads to regression of uninjected subcutaneous and lung lesions. Intralesional PV-10 treatment leads to the induction of tumor-specific immunity." (AACR 2013) {Underlined emphasis is mine} 

And that Provectus concluded at SITC 2012, by virtue of murine model work:

Chemoablation with PV-10 results in the induction of tumor-specific immunity. Immunodeficient mice exhibited no anti-tumor effect on re-challenge. Adoptive transfer of immunity only occurred following chemoablation in donor mice. Tumor-specific, long-term immunity and adoptive transfer implicate immune cell mediation. This immuno-chemoablative response to PV-10 is tantamount to “in situ vaccination.” (SITC 2012) {Underlined emphasis is mine}