Popular cancer drug Velcade shares common mechanism of action with AMPK activator Metformin: Connection between AMPK, aging, and HIV-1 reactivation

"Hutchinson-Gilford Progeria Syndrome" by The Cell Nucleus and Aging: Tantalizing Clues and Hopeful Promises. Scaffidi P, Gordon L, Misteli T; https://commons.wikimedia.org/wiki/File:HIV-budding-Color.jpg#/media/File:HIV-budding-Color.jpg. "HIV-budding-Color" by Photo Credit: C. Goldsmith. Content Providers: CDC/ C. Goldsmith, P. Feorino, E. L. Palmer, W. R. McManus.

Here's another post I just authored on LinkedIn with a surprising finding that a really popular injectable cancer drug called Velcade (made well over a billion dollars for J&J in 2014) and other drugs that are in Velcade's drug class (called proteasome inhibitors) actually activates the same pathway (AMPK) as does metformin derived from the Galega plant, sulforaphane derived from broccoli sprouts, the vitamin A metabolite retinoic acid, rapamycin derived from bacteria, and the Nobel Prize-winning drug Artemisinin derived from the Artemisia plant. Velcade not only reactivated the dormant HIV-1 virus but also inhibited HIV-1 infectivity and viral output in cells that were actively infected, effectively "pulling a double shift". Velcade has also been shown to be a potent AMPK activator and beneficially alter gene splicing in cancer cells. MG132, another drug that works like and is in the same drug class as Velcade, also activates AMPK, reactivated latent HIV-1, alters gene splicing, and enhanced the removal of the toxic protein progerin in cells from children with Progeria when combined with retinoic acid. Considering that AMPK is critical for T cell activation, beneficially alters gene splicing, and extends lifespan, this looks like yet another example of the interconnectedness of diseases including cancer, HIV-1, Progeria, and even normal aging itself. Man, what on earth have I unearthed????? Time will soon tell:-)

Popular cancer drug Velcade shares common mechanism of action with AMPK activator Metformin: Connection between AMPK, aging, and HIV-1 reactivation

A recent study published in the journal Retrovirology in October of 2013 provided unexpected evidence that the commonly-used cancer drug Velcade (an FDA approved drug for the treatment of multiple myelomas, leukemias, and lymphoma) as well as two other members of the proteasome inhibitor drug class (MG132 and clasto-Lactacystin β-lactone) reactivated latent HIV-1 in two primary human CD4+ T cell model systems as well as in several other in vitro model systems [1].  Strikingly, Velcade (also known as bortezomib) not only reactivated the latent virus but also inhibited HIV-1 infectivity, as evidenced by reduced viral output and virion infectivity [1].  Interestingly, Velcade has been shown to beneficially alter gene splicing in cancer, MG132 has been shown to alter gene splicing and reduce progerin production in fibroblasts derived from Hutchinson-Gilford progeria (HGPS) patients, and both Velcade and MG132 have been shown to activate AMPK in separate studies (see below).  Such evidence again suggests (see prior posts) that chemically distinct compounds, including compounds comprising the proteasome inhibitor class, share an “indirect yet common mechanism of action” of AMPK activation that is likely induced by the induction of a cellular stress response.

The proteasome is a protein complex present in all eukaryotes that functions to degrade or remove damaged proteins by adding a consecutive series of tags to these proteins (called a poly-ubiquitin chain), facilitating proteasome binding and protein degradation [2].  Inhibition of the catalytic site of the 26S proteasome, leading to the accumulation of pro-apoptotic (i.e. self-destruct) factors and subsequent cancer cell death is widely accepted as the mechanism of action by which Velcade acts [3].  However, as noted below, other mechanisms are almost undoubtedly involved.

In the Retrovirology study, the authors initially observed that when OM-10.1 cells (a clonal population of HL-60 promyelocytes) that were latently infected with a replication-competent HIV-1 strain were exposed to all three proteasome inhibitors (i.e. Velcade, MG132, and clasto-Lactacystin β-lactone (CLBL)), proteasome inhibition occurred within two hours, along with a significant increase in the induction of HIV-1 RNAs, indicative of the initiation of latent viral transcription [1].  The authors further showed, using a clonal population of HeLa cells and a human CD4+ T cell line, that all three proteasome inhibitors induced the activation of proviral gene expression in both cell lines [1]. Interestingly, all three proteasome inhibitors as well as the HDAC inhibitor vorinostat also induced viral particle production (as evidenced by a significant increase in the HIV-1 p24 antigen) in OM-10.1 cells [1].  To produce the p24 antigen, the splicing of the HIV-1 genome must be inhibited to produce long unspliced HIV-1 mRNA.  Splicing of the viral genome is reduced on latent HIV-1 reactivation through reduction of the activities of the splicing factor SRSF1 by the splicing-associated factor p32.  SRSF1 is also implicated in the faulty splicing mechanism that causes symptoms of accelerated aging in HGPS as well as in aberrant gene splicing in vascular tissues of normal humans [25].

More importantly, however, the authors demonstrated that both Velcade and MG132 significantly induced HIV-1 proviral gene expression in two latent HIV-1 primary human CD4+ T cell models that mimic central and effector memory T cells (two memory T cell subsets that are known reservoirs for latent HIV-1) [1].  Also, Velcade and MG132 did not activate uninfected primary human resting CD4+ T cells, indicating that both proteasome inhibitors selectively activate only CD4+ memory T cells that are latently infected with HIV-1 [1].

Perhaps most startling, however, was the finding that Velcade was able to significantly reduce viral output in activated primary human CD4+ T cells isolated from PBMCs from healthy donors, as evidenced by a 30% increase in HIV-1 p24 antigen in untreated cells compared to Velcade-treated cells [1].  Velcade was also able to decrease the infectivity of viruses produced from infected CD4+ T cells, with viruses from Velcade-treated cells only able to infect one forth the number of HeLaT4 cells compared to viruses collected from untreated primary CD4+ T cells [1]. Hence, Velcade appears to able to selectively reactivate latent HIV-1 without activating uninfected resting CD4+ T cells, but inhibit HIV-1 infectivity and viral output in productively infected cells.

This seemingly perplexing, multi-pronged antiviral mechanism demonstrated by Velcade and other proteasome inhibitors can be explained by the activation of AMPK.  T cell activation (and thus latent HIV-1 reactivation) is critically dependent on the activation of AMPK and both Velcade and MG132 have been independently shown to activate AMPK, possibly via a stress-induced signal generated by the accumulation of ubiquitinated and damaged proteins [4-6].  Indeed, both PMA and ionomycin, a combination positive control for numerous latent HIV-1 reactivation studies, have been shown to activate AMPK and AMPK activation is essential to mount an effective immune response to viral and bacterial challenges [7-11].  Also, vorinostat, an HDAC inhibitor used in the Retrovirology study as a positive control to gauge latent HIV-1 reactivation, also activates AMPK, and bryostatin (PKC activator) and JQ1 (BET bromodomain inhibitor) each have been shown to both activate AMPK and potently induce latent HIV-1 reactivation without global T cell activation in independent studies [12-15].

Furthermore, low dose proteasome inhibition using MG132 has recently been shown to alter gene splicing and induce a protective antioxidative defense response dependent on the transcription factor Nrf2, a master regulator of the cellular antioxidant response [16,17].  Interestingly, AMPK activation has recently been shown to beneficially alter gene splicing in cells derived from patients with the genetic disorder myotonic dystrophy type I (DM1) and metformin (an AMPK activator) has been shown to beneficially alter gene splicing in normal humans and increase the expression of Nrf2 [18,19].  Also, both Velcade and vorinostat have been shown to alter gene splicing in human hepatoma HepG2 and Huh6 cells by altering the splicing of the Bcl-X transcript, thus preferentially increasing the levels of Bcl-xS (the short pro-apoptotic isoform) compared to Bcl-xL (the pro-survival isoform) [20].

Proteasome inhibition has also been shown to play a role in HGPS, a disease characterized by faulty alternative gene splicing leading to an accelerated aging phenotype. Interestingly, MG132, either alone or in combination with the vitamin A metabolite all-trans retinoic acid, led to a decrease in progerin levels in HGPS cells via a proteasome inhibitor-mediated induction of autophagy, implicating both autophagic and proteasomal pathways in progerin reduction [21].  Indeed, both rapamycin (derived from bacteria) and sulforaphane (from broccoli sprouts) have each been shown to activate AMPK in vivo and induce the autophagic degradation of progerin (toxic protein product that causes accelerated aging) in HGPS fibroblasts [21-24].

Cumulatively, the foregoing studies provide convincing evidence that activation of AMPK by chemically distinct compounds (as indicated in the figure below), including the proteasome inhibitors Velcade and MG132, represents an “indirect yet common mechanism of action” that links pathological diseases states associated with gene splicing, viral latency and replication, and likely many others.

https://www.linkedin.com/pulse/popular-cancer-drug-velcade-shares-common-mechanism-action-finley?trk=prof-post

References:

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