Prevention of Cancer with Rapamycin, Theory

Prevention of Cancer by Inhibiting Aging

Cancer is an Age-Related Disease


"Common cancers such as lung, breast, prostate, colon, gastric, pancreatic, thyroid, brain and certain leukemias are age-related diseases." (1)  "Cancer incidence rises dramatically during aging in humans and animals. Cancer disproportionately strikes individuals of ages 65 and older. Median age of cancer patients at death for the major tumors range from 71-77 years. The median age for prostate cancer is 79 years. Incidence of common cancer increase sharply with age." (2) "The incidence of cancer is lowest at age 20 and then increases exponentially, doubling every eight years." (2).


Why cancer is an age-related disease

Several mTOR-dependent processes acting in concert promote cancer

1. Mutations accumulate with age. Some mutations may increase mTOR. In mice, mTOR was shown to increase activity with age.

2. Cellular aging promotes cancer.

3. Elevated mTOR increases obesity and obesity increases mTOR. 

4. Obesity, Cellular Aging and cancer are all mTOR-driven process.

5. Rapamycin may decrease cancer by (a) slowing aging, (b) preventing obesity, (c) directly affecting cancer cells. (Ref 3)







Cases of Tumor Regression in Young Animals

"In exciting experiments where cancer cells were introduced into embryonic tissues, embryonic microenviornments normalized aggressive melanoma cells toward a more benign melanocytic phenotype."

"In certain animal models, transplanted tumors preferentially grow in old animals" but regressed in young animals. "Intravenously injected tumor cells grow in lungs of old but not young animals."

It was concluded that with age the microenviornment becomes permissive to tumor growth. (Ref 2)

Latent versus clinical Cancer

"Latent cancers are microscopic lesions that are commonly diagnosed at autopsy, when a person dies from other causes. Latent cancers do not necessarily become clinical. This indicates that oncogenic mutations are not sufficient to cause clinical cancer; despite oncogenic mutations cancer cells may be latent."


"After age 50 years, both incidence and mortality rates from prostate cancer increase ar a nearly exponential rate. Autopsy study from many countries demonstrate that 15-30% of men older than 50 years have histological evidence of latent prostate cancer. The presence of latent cancer increases with age so that by age 80 approximately 60% to 70% of men have evidence of histologic carcinoma at autopsy. Yet, with similar incidence of histological cancer, clinical cancer is 10-20 times less frequent in Japan than in USA and prostate mortality is low in Japan. Thus, prevention of cancer progression (from latent to clinical) is an important target for pharmacologic intervention." (Ref  2)

Senescent Stroma may Promote Cancer

"Stroma cells affect cancer growth...Changes in the tissue milieu, such as those that accompany normal aging, may determine the ability of a genetically aberrant cell to produce a tumor."


"By altering the tissue microenviornment, senescent cells may contribute to the rise in cancer that occurs with age."..."Senescent stromal cells can stimulate neighboring premalignant or dormant cells to form tumors. Senescent cells produce enzymes, growth factors and inflammatory cytokines...Senescent fibroblast promote tumor growth."


One example, "senescent cells secrete matrix metaloproteinases (MMP), a major mediators of basement membrane degradation, tumor invasion and metastasis. Thus, senescent human fibroblasts increase the early growth of xenograft tumors via MMP secretion" [in experiments]. Rapamycin inhibits secretion MMP


TOR and Permissive Enviornment

TOR stimulates cell growth, causing cell hypertrophy. TOR activates secretion of large number of bioactive molecules. These bioactive molecules promote cancer growth. Rapamycin blocks secretion of these cancer promoting bioactive molecules. (Ref  2)


Cancer requires a genetically altered cell, which develops as result of random damage and can not be prevented. However, for that genetically altered cell to produce a clinical tumor, requires the cooperation of the local tissue microenviornment. The TOR pathway, through the creation and hyperstimulation of senescent cells promotes cancer. 


"

Rapamycin for Cancer Prevention

There are two models of cancer-prevention by rapalogs. (A) direct anticancer effect, Rapalogs suppress cancer cells, prevent cancer. (B) Indirect anticancer effect due to aging-suppression. Rapalogs suppress aging and thus prevent cancer.


Cancer treatment with Rapamycin:

"Given the universal activation of the mTOR pathway in cancer, rapalogs are used for cancer treatment." Temsirolimus, a prodrug of rapamycin (Sirolimus) is approved fro treatment of renal cancer. Rapalogs play a modest role in cancer treatment. Rapamycin at relevant concentrations are not toxic drugs: they do not kill cells but rather slow their growth. 


Indirect "anti-aging model". 

Blagosklonny suggests that cancer could be prevented by inhibiting aging with rapamycin or "by staying young". This could be done by reversing cell senescence in stoma and thus blocking clinical cancer development. 


The reasoning is that while the effects of rapamycin are relatively modest as a monotherapy anti-cancer drug; rapamycin is a potent cancer-prevention drug in animal models and a potent anti-aging drug. 


Blagosklonny concludes that rapamycin acts to prevent cancer, not by targeting cancer cells; but rather by slowing down the aging process. ((Ref 1)


Rapamycin, Lifespan and Cancer, Mouse, normal

Harrison, 2009, Rapamycin fed late in life in genetically heterogeneous mice.

This was first study to show rapamycin extends lifespan in mice. (Ref 4).

An oral dose of rapamycin was fed to 600 days of age mice. "Based on age at 90% mortality, rapamycin led to an increase of 14% for females and 9% for males. "Disease patterns of rapamycin-treated mice did not differ from those of control mice." "This was roughly the equivalent to starting treatment in 60-year old person." The leading cause of death in both rapamycin treated and control mice was cancer. 


The conclusion was, "Rapamycin may extend lifespan by postponing death from cancer, by retarding mechanisms of aging, or both."


10 years later that is still an open question.

Miller, Harrison 2011, Rapamycin, but not Resveratrol or Simvastatin, Extends LifeSpan of Mice

This study was done by same group as 2009 study with same dose rapamycin. Only differnce was rapamycin was started at 9 months as opposed to 600 days.  


Results: For males rapamycin led to an increase of 10% in median age, ans an increase 16% in the 90th percentile age. For females, the corresponding values was 18% for median and 13% for 90th percentile ages."


                                          Males                 Females

Median                             10%                       18%

Maximum                         16%                       13%                       [9% males,  14% females, 2009 study]


93% controls, 89% rapamycin group died from cancer.  The 3 most common causes of death (70% controls, 66% rapamycin group) were lymphoma, hemangiosarcoma, lung cancer. For the 5 most causes of death (all cancer) the mean age at death is listed:


                                                                                 Age at death, days

                                                                              Control       Rapamycin

Hemangiosarcoma                                               884             890

Liver Cancer                                                          841           1006

Lung cancer                                                          755           1004

Lymphoma                                                            920              951

Breast cancer                                                       826            1142


Average age death all 5 cancers                      866                980   (13% increase)


[Using a weighted average for above 5 cancer I calculated 13% increase age at death for rapamycin treated group]


The conclusion states: "The principal cause of death of the HET3 mice is cancer, with the largest proporton of deats attributable to lymphoma, Therefore, it is possible that rapamycin may extend life span at least in part through delay or prevention of cancer."




                       


                  

Miller, Harrison, Rapamycin-mediated lifespan in mice

This 2014 study (Ref 6) was by same group as above 2 studies. The same type HET3 mice were used and treatment was begun at 9 months similar to 2011 study. What was new was they used a "standard"  dose as used in 2009 study and a dose than was 1/3 standard dose (low) and a dose 3 times the standard dose (high).

The following chart shows lifespan for the 3 groups for male and female and median increase percent lifespan and 90th percentile percent lifespan increase.


                                                              Median Increase          90th % increase

Males, Rapamycin

Low                                                                3%                               6%

Standard                                                      13%                              8%

High                                                              23%                              8%


Females, Rapamycin

Low                                                              16%                              5%

Standard                                                     21%                            11%

High                                                            26%                             11%


Abstract: "Rapamycin...increased median lifespan of genetically heterogeneous mice by 23% (males) to 26% (females) when tested at a dose threefold higher than used in our previous studies."


They concluded: "It seems likely that rapamycin-mediated increases in lifespan reflect both broad spectrum antitumor effects as well as a deceleration of aging processes more generally."..The spectrum of specific lethal illnesses, mostly neoplastic, was not altered by rapamycin."


Anisimov, Blagosklonny, 2011 Rapamycin increases lifespan and inhibits tumorigenesis in female mice

This study involved used female 129/Sv mice that have a normal lifespan and normal cancer incidence. Rapamycin was started from the age of 2 months and administered 3 times a week for 2 weeks followed by 2 week break for 2 year study. "we found rapamycin significantly increased lifespan and delayed spontaneous cancer." {ref 7]


They state in introduction:

Rapamycin is a clinically approved drug"...Rapamycin could be used for extension of healthy lifespan and prevention of age-related disease by slowing down the aging process. This may become one of the major breakthroughs in medicine since the discovery of antibiotics."


Results

11 control mice "survived until 800 day ( 35.5%) compared with 19 (54.3% in the rapamycin treated group," 8 mice exposed to rapamycin survived the age of death of the last mouse in control group (22.9%).

Rapamycin increased median lifespan by 10.1% as well as maximum lifespan by 9.3%. 

they calculated that from day 435 (day of appearance first tumor detection); the risk of death in the rapamycin treated mice was 2.5 times lower and rate of aging 1.4 times lower.


There were 23 tumor-bearing mice in control group with 27 tumors compared to  10 tumor bearing mice in rapamycin group with 11 tumors.


Abstract

"Rapamycin decreased aging rate, increased lifespan and delayed spontaneous cancer 22.9%.

L

H

D

C

Rapamycin, Mouse studies in Cancer prone mice

Rapamycin studies in HER-2/neu Cancer prone mice

These are two studies using transgenic cancer prone mice by Anisimov group in St. Petersburg, Russia and Blagosklonny group in Buffalo, NY. 


The HER gene is associated with breast cancer in humans. A transgenic model was created in mice with the human HER gene. "In this model, mammary carcinoma in female mice overexpressing the oncogene HER2; cancer advances very fast with average lifespan of about 9 months" and first cancer appearing about 7 months. (ref 8).  


Two studies were done. In the 2010 study (Ref 8) the mice were treated with a dose of rapamycin in dose of 1.5 mg/kg 3 times a week by subcutaneous injection. The injection was given 3 times a week for 2 weeks followed by 2 week interval. The injections were started at 2 months of age. In the 2014 study (ref 9) the same mice were used. The mice were given 1/3 the dose, 0.45 mg/kg. The same schedule of 3 subcutaneous injection a week for 2 weeks followed by 2 week break. In this 2nd study using the 1/3 dose, treatment was started at 2 months, 4 months and at 5 months in 3 groups of mice. 


Abstract:

"Rapamycin dramatically delayed tumor onset as well as decreasing the number of tumors per animal and tumor size. We sugest that, by slowing down organismal aging, rapamycin delay cancer"


                                         Effect of Rapamycin on  Lifespan 

                                                       Control                Rapamycin

Median lifespan                            288                        327  (+13.6%)

Mean lifespan last 10%               356                        395 (+11%)

Aging rate                                     3.02                       1.67 (--1.8 times)



                                                Effect of Rapamycin on Breast Cancers

                                                                                                       Control           Rapamycin

Mean latency first cancer days                                                  202                     240 (+16.5%)

Total number breast cancers                                                     233                     126

Tumors per tumor-bearing mouse                                            8.3                       5.5  (-33.7%)

Mean time of death of metastases-bearing mice                   301                      357  (18.8%)


Discussion

"Here we show for the first timethat rapamyin prolongs lifespan and decreases rate of aging in cancer-prone mice. Noteworthy, rapamycin failed to increase lifespan when given to mice with already established tumors, even through it decelerated tumor growth (data not shown). This suggests that rapamycin decreases tumorigenesis by slowing aging rather than increases lifespan by decelerating cancer."


"There are several lines of evidence supporting the indirect mecahnism of action of rapamycin on tumorigenesis."

(a) "Rapamycin inhibited cancer growth in micemore profoundly than in cell culture."

(b). "Rapamycin extends lifespan in a heterogeneous group of mice, whicch di fromvarous diseases not necessarily related to cancer."


"In fact, rapamycin delays other age-related diseasessuch as atherosclerosis, metabolic disorders and neurodegeneration, organ fibrosis, age-related macular degeneration, and osteoarthritis. Taken together, thesedata support the notion that rapamycin decelerates age-related diseases by slowing down organismal aging."


Conclusion

"Importantly, as we demonstated here, rapamycin extends maximal lifespaneven when administered intermittently (two consecutive weeks followed by a two-week break)...We suggest that slowing down the aging process by intermittent administration of rapamycin would be beneficial for humans with high risk of cancer. "


Results 2014 study (ref 9)

In this study used 1/3 dose of prior study. 


In contrast to dose of 1.5 mg/kg  as intermittent dose, 0.45 mg/kg produced modest results compared to robust results of higher dose. There was life extension in some groups and cancer delay in other groups; but results were mixed.


The conclusion was "cancer was modestly prevented by low-dose administration of rapamycin."


This study shows that for best results need an adequate dose of rapamycin. 

 

Rapamycin studies in p53 deficiency Cancer prone mice

The p53 germline mutations exists in humans as a rare disorder that makes patients highly prone to cancer at a very young age. The condition is called Li-Fraumeni syndrome and is analogous to p53+/- mice. Carriers have 50% incidence of cancer at the age of 40 and 90% at the age of 60."


Introduction (Ref 10)

"The mTORpathway playsa crucial role in the geroconversion from cell cycle arrest to senescence (geroconversion). Rapamycin suppresses or decelerates geroconversion, maintaining quiescence instead."

"p53 is a tumor suppressor. p53 can inhibit mTOR. While causing cell cycle arrest, p53 can suppress geroconversion, thus preventing a senescent phenotype in the arrested cells. Therefore, it is not surprising that p53 inhibits hyper-secretory phenotype, a hallmark of senescence whereas p53-deficiency results in pro-inflammatory phenotype." (Ref 10)


" Noteworthy, the activity of p53 decreases with aging. Lack of one p53 allele (p53+/-) accelerates carcinogenesis and shortens lifespan. Here we show experimental evidence supporting this hypothesis."


[Note: lack of p53 will result in geroconversion and senescent cells which will promote aging and cancer.]



D

A

Promote current deals

R

S

H

H

C

Prevention of Lung Cancer with Rapamycin in Mouse

Cancer Statistics

"A total of 1,400,000 new cancer cases and 565,000 deaths from cancer were expected in the United States in 2006. When deaths are aggregated by age, cancer has surpassed heart disease as the leading cause of death for those younger than 85."

Lung cancer is the leading cause of cancer death in both men and women. Prostate and breast are most frequently diagnosed cancer in men and women, respectively. Colorectal cancer is the third most common cancer.



Lung Cancer

"The death toll from lung cancer in the United States is the highest of all cancer, estimated to kill more than 170,000 Americans in 2006." Presently, there are over 90,000,000 current or former smokers in the United States at permanent increased risk for the development of lung cancer. Moreover, tobacco use accounts for 30% of overall cancer mortality." (Ref 5)


The major tobacco-specific carcinogen is NNK, which is metabolite of nicotine. NNK rapidly stimulate activation of Akt and mTOR in primary human bronchial and small airway epithelial cells. The Akt/mTOR pathway is an important mediator in the formation of tobacco-carcinogen-induced lung tumors. (Ref 5).


In this study by Granville in 2007 (Ref 5) they exposed mice to NNK to induce lung tumors. They gave mice rapamycin to determine effect of rapamycin on tumor development.

Rapamycin Mouse Tobacco Carcinogen Study

Experimental design: 

A/J mice were given 3 doses of NNK by injection once a week for 3 weeks. On 4th week began treatment with rapamycin every other day (3 injections a week)  for 12 weeks of rapamycin 1.5 mg/kg. At 16 weeks mice were sacrificed and examined for lung tumors. 


Results: Rapamycin decreased the number of NNK-induced tumors by 90%. Mice that received NNK without rapamycin had an average of 20.8 tumors per mouse, whereas those treated with rapamycin developed an average of 2.2 tumors per mouse. In addition to reducing number, tumors arising in presence of rapamycin were 74% smaller. Rapamycin decreased number of hyperplastic lesions by 45% (not tumors) and decreased number of actual tumors (adenomas) by 82%. Rapamycin treated tumors had lower rate of proliferation. This showed that even when lesions developed with rapamycin, they were smaller and less aggressive compared with mice without rapamycin treatment.


Conclusion: "Pharmacologically relevant doses of rapamycin...when given before tumor development , profoundly reduces lung tumor multiplicity, size and phenotypic progression. These studies show that mTOR plays a critical role in the development of tobacco carcionogen-induced lung tumorigensis.


Note that half-life rapamycin in mice is 6.4 hours, thus once every 48 hours is intermittent treatment, once every 7.5 half lives. (Once every 7.5 half lives would be equivalent to a human dose schedule of rapamycin once every 20 days.)

Significance

This study suggests that intermittent rapamycin could be used in those persons at high risk for lung cancer.